Updated on 2022/12/08

写真a

 
SHIMOJIMA, Atsushi
 
Scopus Paper Info  
Paper Count: 0  Citation Count: 0  h-index: 23

Citation count denotes the number of citations in papers published for a particular year.

Affiliation
Faculty of Science and Engineering, School of Advanced Science and Engineering
Job title
Professor

Concurrent Post

  • Faculty of Science and Engineering   Graduate School of Advanced Science and Engineering

Research Institute

  • 2020
    -
    2022

    理工学術院総合研究所   兼任研究員

Education

  •  
    -
    2002

    Waseda University  

  •  
    -
    1995

    Waseda University   School of Science and Engineering  

Degree

  • 早稲田大学   博士(工学)

Research Experience

  • 2017.04
    -
    Now

    Waseda University   Faculty of Science and Engineering

  • 2013.04
    -
    2017.03

    Waseda University   Faculty of Science and Engineering

  • 2008.04
    -
    2013.03

    The University of Tokyo   The Graduate School of Engineering, Department of Chemical System Engineering

  • 2007.04
    -
    2008.03

    The University of Tokyo   The Graduate School of Engineering, Department of Chemical System Engineering

  • 2006.07
    -
    2007.03

    The University of Tokyo   The Graduate School of Engineering, Department of Chemical System Engineering

  • 2005.04
    -
    2006.07

    科学技術振興機構 (JST) CREST研究員

  • 2002.04
    -
    2005.03

    日本学術振興会特別研究員 (PD)

  • 2004.04
    -
    2005.02

    University of California, Santa Barbara,

  • 2000.01
    -
    2002.03

    日本学術振興会特別研究員 (DC)

  • 1997.04
    -
    1999.02

    昭和電工(株)

▼display all

Professional Memberships

  •  
     
     

    日本MRS

  •  
     
     

    高分子学会

  •  
     
     

    化学工学会

  •  
     
     

    International Sol-Gel Society

  •  
     
     

    American Chemical Society

  •  
     
     

    ゼオライト学会

  •  
     
     

    日本ゾルゲル学会

  •  
     
     

    日本セラミックス協会

  •  
     
     

    日本化学会

▼display all

 

Research Areas

  • Synthetic organic chemistry

  • Inorganic compounds and inorganic materials chemistry

  • Inorganic/coordination chemistry

Research Interests

  • 自己修復材料

  • 多孔体材料

  • 無機-有機ナノ複合体

  • ゾルゲル法

  • 無機合成化学

Papers

  • Fluoride Ion-Encapsulated Germoxane Cages Modified with Organosiloxane Chains as Anionic Components of Ionic Liquids

    Taiki Hayashi, Nanako Murase, Naoto Sato, Koki Fujino, Natsuhiko Sugimura, Hiroaki Wada, Kazuyuki Kuroda, Atsushi Shimojima

    Organometallics   41 ( 11 ) 1454 - 1463  2022.06

    DOI

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  • Anisotropic Crystal Growth of Layered Nickel Hydroxide along the Stacking Direction Using Amine Ligands

    Keisuke Muramatsu, Mina Jimba, Yumiko Yamada, Hiroaki Wada, Atsushi Shimojima, Kazuyuki Kuroda

    Inorganic Chemistry   61 ( 22 ) 8490 - 8497  2022.06

    DOI

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  • Self-Healing Lamellar Silsesquioxane Thin Films

    Satoshi Kodama, Yoshiaki Miyamoto, Shun Itoh, Takashi Miyata, Hiroaki Wada, Kazuyuki Kuroda, Atsushi Shimojima

    ACS Applied Polymer Materials   3 ( 8 ) 4118 - 4126  2021.08

    DOI

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    3
    Citation
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  • Hydrolysis of Methoxylated Nickel Hydroxide Leading to Single-Layer Ni(OH)<inf>2</inf>Nanosheets

    Keisuke Muramatsu, Yoshiyuki Kuroda, Hiroaki Wada, Atsushi Shimojima, Kazuyuki Kuroda

    Inorganic Chemistry   60 ( 10 ) 7094 - 7100  2021.05

     View Summary

    Various methods for the preparation of inorganic nanosheets have been established and they have contributed to the substantial development of the research on diverse two-dimensional materials. Covalent surface modification of layered metal hydroxides with alkoxy groups is known to effectively weaken the interactions between layers, although the modified ligands are irreversibly immobilized. This study proposes the use of methanol as a removable surface modifier forming monodentate alkoxy bonds to prepare nickel hydroxide nanosheets through hydrolysis. Methoxylated layered nickel hydroxide, consisting of randomly stacked nano-sized nickel hydroxide sheets (10-20 nm in size) having Ni-OCH3 groups on its surface, was synthesized in a powder form through the precipitation reaction of a nickel salt in methanol at room temperature. After dispersing the aggregated methoxylated nickel hydroxide in water, single-layer nickel hydroxide nanosheets with a thickness of 1.2 nm and a lateral size of 460 nm at maximum, which is larger than the size of original methoxylated nickel hydroxide were found in the suspension. The time-course experiments during hydrolysis suggested that two-dimensional crystal growth of exfoliated nickel hydroxide sheets proceeded, resulting in the formation of the nanosheets. Moreover, single-layer and nano-sized cobalt hydroxide was prepared through a similar manner. This work demonstrates that two-dimensional alkoxides consisting of polymeric M-O-M bonds are useful precursors for the design of metal-hydroxide-based nanomaterials.

    DOI PubMed

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    1
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  • Preparation of Colloidal Monodisperse Hollow Organosiloxane-Based Nanoparticles with a Double Mesoporous Shell

    Tenkai Watanabe, Eisuke Yamamoto, Hiroaki Wada, Atsushi Shimojima, Kazuyuki Kuroda

    BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN   94 ( 5 ) 1602 - 1608  2021.05

     View Summary

    Hollow siloxane-based nanoparticles (HSNs) have attracted significant attention because of many potential applications. The interior and exterior properties of HSNs can be varied by forming double shells with different compositions, which leads to new functionalities. In this study, we prepared colloidal monodisperse HSNs (smaller than 50nm in diameter) with a double mesoporous shell by the stepwise addition of two different bridged organoalkoxysilanes [(EtO)(3)Si-C2H4-Si(OEt)(3) (BTEE1) and (EtO)(3)Si-C2H2-Si(OEt)(3) (BTEE2)] to a dispersion of colloidal silica nanoparticles (ca. 20nm in diameter) in the presence of surfactants. The hollow structure was formed by dissolution-redeposition of the silica core during the formation of an organosiloxane shell. Upon addition of BTEE1 in the first step, core-shell structure was formed. Subsequent addition of BTEE2 led to the formation of mesoporous HSNs composed of an inner shell containing ethylene (-CH2-CH2-) groups and an outer shell containing ethenylene (-CH=CH-) groups. Suppression of the diffusion of the second organosilane species into the inner region of HSNs was critical for the formation of the double shell. The ethenylene groups in the outer shell allowed for chemical modification by thiol-ene reaction while maintaining the hollow inner space of the HSNs, which will lead to the application of HSNs in various fields.

    DOI

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    1
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  • Formation of Closed Pores in Mesoporous Silica Nanoparticles by Hydrothermal Treatment

    Eisuke Yamamoto, Lulu Cheng, Tenkai Watanabe, Seiya Mori, Atsushi Shimojima, Hiroaki Wada, Kazuyuki Kuroda

    BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN   94 ( 5 ) 1625 - 1630  2021.05

     View Summary

    Mesoporous silica nanoparticles (MSNs) with closed pores have significant potential for applications such as lowdielectric-constant materials and bio-imaging owing to their controlled accessibility. In this study, we successfully prepared MSNs with closed pores by a simple hydrothermal treatment in ethanol. The mesostructure changed from open to closed mesopores through hydrothermal treatment. This simple method enabled the preparation of closed pores with encapsulated guest species.

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  • Preparation of Ordered Nanoporous Indium Tin Oxides with Large Crystallites and Individual Control over Their Thermal and Electrical Conductivities

    Yumi Saito, Takamichi Matsuno, Quansheng Guo, Takao Mori, Makoto Kashiwagi, Atsushi Shimojima, Hiroaki Wada, Kazuyuki Kuroda

    ACS Applied Materials & Interfaces   13 ( 13 ) 15373 - 15382  2021.04

    DOI

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    3
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  • Direct bottom-up synthesis of size-controlled monodispersed single-layer magnesium hydroxide nanosheets modified with tripodal ligands

    Keisuke Muramatsu, Yuya Kamiusuki, Yoshiyuki Kuroda, Hiroaki Wada, Atsushi Shimojima, Kazuyuki Kuroda

    Dalton Transactions   50 ( 9 ) 3121 - 3126  2021.03

     View Summary

    Conventional top-down methods for preparing inorganic nanosheets possess fundamental challenges of morphological control. Herein, the direct synthesis of organically modified single-layer magnesium hydroxide nanosheets with narrow size distribution was achieved by thein situmodification of magnesium hydroxide with a tripodal ligand, tris(hydroxymethyl)aminomethane.

    DOI PubMed

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    3
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  • Synthesis of Cristobalite Containing Ordered Interstitial Mesopores using Crystallization of Silica Colloidal Crystals

    Takamichi Matsuno, Takamichi Nakaya, Yoshiyuki Kuroda, Hiroaki Wada, Atsushi Shimojima, Kazuyuki Kuroda

    Chemistry – An Asian Journal   16 ( 3 ) 207 - 214  2021.02

    DOI

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    1
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    (Scopus)
  • Preparation of Sub-50 nm Colloidal Monodispersed Hollow Siloxane-Based Nanoparticles with Controlled Shell Structures

    Tenkai Watanabe, Eisuke Yamamoto, Saki Uchida, Lulu Cheng, Hiroaki Wada, Atsushi Shimojima, Kazuyuki Kuroda

    LANGMUIR   36 ( 46 ) 13833 - 13842  2020.11

     View Summary

    Hollow siloxane-based nanoparticles (HSNs) have attracted significant attention because of their promising unique properties for various applications. For advanced applications, especially in catalysis, drug delivery systems, and smart coatings, high dispersibility and monodispersity of HSNs with precisely controlled shell structures are important. In this study, we established a simple method for preparing colloidal HSNs with a uniform particle size below 50 nm by the reaction of colloidal silica nanoparticles with bridged organoalkoxysilane [1,2-bis(triethoxysilyl)ethylene: (EtO)(3)Si-C2H2 Si(OEt)(3), BTEE] in the presence of a cationic surfactant. Upon the formation of organosiloxane shells by hydrolysis and polycondensation of BTEE, the core silica nanoparticles were spontaneously dissolved, and a part of the silicate species was incorporated into the organosiloxane shells. The size of the colloidal silica nanoparticles, the amount of BTEE added, and the pH of the reaction mixture greatly affected the formation of HSNs. Importantly, colloidal HSNs having micropores and mesopores in the shells were successfully prepared using silica nanoparticles (20, 30, and 40 nm in diameter) at pH values of 9 and 11, respectively. These HSNs are potentially important for applications in drug delivery systems and catalysis.

    DOI

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    2
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  • Selective Covalent Modification of Layered Double Hydroxide Nanoparticles with Tripodal Ligands on Outer and Interlayer Surfaces

    Keisuke Muramatsu, Shiori Hayashi, Yoshiyuki Kuroda, Yuya Oka, Hiroaki Wada, Atsushi Shimojima, Kazuyuki Kuroda

    Inorganic Chemistry   59 ( 9 ) 6110 - 6119  2020.05

     View Summary

    Layered double hydroxides (LDHs) have occupied an important place in the fields of catalysts, electrocatalysts, and fillers, and their applicability can be greatly enhanced by interlayer organic modifications. In contrast to general organic modification based on noncovalent modification using ionic organic species, this study has clarified in situ interlayer covalent modification of LDH nanoparticles (LDHNPs) with the tripodal ligand tris(hydroxymethyl)aminomethane (Tris-NH2). Interlayer-modified CoAl LDHNPs were obtained by a one-pot hydrothermal treatment of an aqueous solution containing metal salts and Tris-NH2 at 180 °C for 24 h. Tris-NH2 was covalently bonded on the interlayer surface of LDHNPs. Interlayer-modified NiAl LDHNPs were also similarly synthesized. Some comparative experiments under different conditions indicate that the important parameters for interlayer modification are the number of bonding sites per a modifier, the electronegativity of a constituent divalent metal element, and the concentration of a modifier; this is because these parameters affect the hydrolytic stability of alkoxy-metal bonds between a modifier and a layer of LDHNPs. The synthesis of interlayer-modified MgAl LDHNPs was achieved by adjusting these parameters. This achievement will enable new potential applications because modification of only the outer surface has been achieved until now. Interlayer-modified LDHNPs possessing CO32- in the interlayer space were delaminated into monolayers under ultrasonication in water. The proposed method provides a rational approach for interlayer modification and facile delamination of LDHNPs.

    DOI PubMed

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    3
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  • Mesoporous Silica Nanoparticles with Dispersibility in Organic Solvents and Their Versatile Surface Modification

    Eisuke Yamamoto, Atsushi Shimojima, Hiroaki Wada, Kazuyuki Kuroda

    LANGMUIR   36 ( 20 ) 5571 - 5578  2020.05

     View Summary

    Recently, colloidal mesoporous silica nanoparticles (MSNs) have attracted keen interest in scientific and technological fields. A significant issue regarding the effective use of colloidal MSNs is their dispersibility in various solvents, which is essential for their applications through surface modification. However, the dispersion media for colloidal MSNs have been extremely limited. Here, we report a new method for obtaining stable colloidal MSNs dispersed in various organic solvents through a gradual solvent exchange of colloidal MSNs from acidic water to an organic solvent by dialysis. This allows the colloidal MSNs to be dispersed as primary nanoparticles in organic solvents such as 1-butanol, 1-dodecanol, and tetrahydrofuran (THF), which are capable of hydrogen bonding with surface silanol groups. In addition, MSNs dispersed in THF can be modified with chlorosilanes while maintaining colloidal stability. Various organosilyl groups, such as trimethylsilyl and dimethylsilyl groups, can be densely grafted on the surfaces of MSNs. After trimethylsilylation, MSNs become dispersible even in a nonpolar and hydrophobic solvent like octane through the solvent exchange due to the preferential evaporation of THF. This method will offer a versatile approach to functionalizing colloidal MSNs toward a wide range of applications.

    DOI

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    10
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  • Inorganic–Organic Hybrid Photomechanical Crystals Consisting of Diarylethenes and Cage Siloxanes

    Kajiya Ryota, Sakakibara Seiya, Ikawa Hanako, Higashiguchi Kenji, Matsuda Kenji, Wada Hiroaki, Kazuyuki Kuroda, Shimojima Atsushi

      in press  2019.12  [Refereed]

  • Tracking Rearrangement of Atomic Configurations During the Conversion from FAU Zeolite to CHA Zeolite

    Muraoka Koki, Sada Yuki, Shimojima Atsushi, Chaikittisilp Watcharop, Okubo Tatsuya

    Chemical Science   10 ( 37 ) 8533 - 8540  2019.10  [Refereed]

     View Summary

    In order to realize designed synthesis, understanding the formation mechanism of zeolites at an atomic level has long been aspired, but remains challenging due to the fact that the knowledge of atomic configurations of the species formed during the process is limited. We focus on a synthesis system that crystallizes CHA zeolite from FAU zeolite as the sole source of tetrahedral atoms of Si and Al, so that end-to-end characterization can be conducted. Solid-state Si MAS NMR is followed by high-throughput computational modeling to understand how atomic configurations changed during the interzeolite conversion. This reveals that the structural motif commonly found in FAU and CHA is not preserved during the conversion; rather, there is a specific rearrangement of silicates and aluminates within the motif. The atomic configuration of CHA seems to be influenced by that of the starting FAU, considering that CHA synthesized without using FAU results in a random Al distribution. A Metropolis Monte-Carlo simulation combined with a lattice minimization technique reveals that CHA derived from FAU has energetically favorable, biased atomic locations, which could be a result of the atomic configurations of the starting FAU. These results suggest that by choosing the appropriate reactant, Al placement could be designed to enhance the targeted properties of zeolites for catalysis and adsorption. 29

    DOI

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    30
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  • Preparation of CO2-adsorbable amine-functionalized polysilsesquioxanes containing cross-linked structures without using surfactants and strong acid or base catalysts

    Sainohira Yusaku, Fujino Koki, Shimojima Atsushi, Kuroda Kazuyuki, Kaneko Yoshiro

      91 ( 3 ) 505 - 513  2019.09  [Refereed]

  • Bioinspired Approach to Silica Nanoparticle Synthesis Using Amine-Containing Block Copoly(vinyl ethers): Realizing Controlled Anisotropy

    Sugawara-Narutaki Ayae, Tsuboike Sachio, Oda Yukari, Shimojima Atsushi, Landenberger Kira, Okubo Tatsuya, Aoshima Sadahito

    LANGMUIR   35 ( 33 ) 10846 - 10854  2019.08  [Refereed]

     View Summary

    Core-shell polymer-silica hybrid nanoparticles smaller than 50 nm in diameter were formed in the presence of micelles of poly(2-aminoethyl vinyl ether-block-isobutyl vinyl ether) (poly(AEVE(m)-b-IBVEn)) through the hydrolysis and polycondensation of alkoxysilane in aqueous solution at a mild pH and temperature. The size of the nanoparticles as well as the number and size of the core parts were effectively controlled by varying the molecular weight of the copolymers. The polymers could be removed by calcination to give hollow silica nanoparticles with Brunauer-Emmett-Teller surface areas of more than 500 m(2) g(-1). Among these, silica nanoparticles formed with poly(AEVE(115)-b-IBVE40) displayed an anisotropy of single openings in the shell. The use of an alternative copolymer, poly(AEVE-b-2-naphthoxyethyl vinyl ether) (poly(AEVE(113)-b-beta NpOVE40)), yielded core-shell nanoparticles with less pronounced anisotropy. These results showed that the degree of anisotropy could be controlled by the rigidity of micelles; the micelle of poly(AEVE(115)-b-IBVE40) was more deformable during silica deposition than that of poly(AEVE(113)-b-beta NpOVE40) in which aromatic interactions were possible. This bioinspired, environmentally friendly approach will enable large-scale production of anisotropic silica nanomaterials, opening up applications in the field of nanomedicine, optical materials, and self-assembly.

    DOI

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    4
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  • Formation of silicate nanoscrolls through solvothermal treatment of layered octosilicate intercalated with organoammonium ions

    Asakura Yusuke, Sugihara Megumi, Hirohashi Takeru, Torimoto Aya, Matsumoto Takuya, Koike Masakazu, Kuroda Yoshiyuki, Wada Hiroaki, Shimojima Atsushi, Kazuyuki Kuroda

      11 ( 27 ) 12924 - 12931  2019.07  [Refereed]

  • Synthesis of organosilyl-functionalized cage-type germanoxane containing fluoride ion

    Sato Naoto, Hayashi Taiki, Tochigi Kazuma, Wada Hirodaki, Shimojima Atsushi, Kuroda Kazuyuki

      25 ( 33 ) 7860 - 7865  2019.02  [Refereed]

  • Synthesis of Polycyclic and Cage Siloxanes by Hydrolysis and Intramolecular Condensation of Alkoxysilylated Cyclosiloxanes

    Sugiyama Tomoaki, Shiba Hiroya, Yoshikawa Masashi, Wada Hiroaki, Shimojima Atsushi, Kuroda Kazuyuki

      25 ( 11 ) 2764 - 2772  2019.02  [Refereed]

  • Fabrication of Uniaxially Aligned Silica Nanogrooves with Sub-5 nm Periodicity on Centimeter-Scale Si Substrate Using Poly(dimethylsiloxane) Stamp

    Hirota Keiya, Hara Shintaro, Wada Hiroaki, Shimojima Atsushi, Kuroda Kazuyuki

      13 ( 3 ) 2795 - 2803  2019.01  [Refereed]

  • Preparation of ordered mesoporous Au using double gyroid mesoporous silica KIT‐6 via a seed-mediated growth process

    Shimasaki Yuta, Kitahara Masaki, Shoji Miho, Shimojima Atsushi, Wada Hiroaki, Kuroda Kazuyuki

      13 ( 24 ) 3935 - 3941  2018.12  [Refereed]

  • Preparation of Siloxane‐based Microporous Crystal from Hydrogen Bonded Molecular Crystal of Cage Siloxane

    Sato Naoto, Kuroda Yoshiyuki, Wada Hiroaki, Shimojima Atsushi, Kuroda Kazuyuki

      24   17033 - 17038  2018.11  [Refereed]

  • Precise size control of layered double hydroxide nanoparticles through reconstruction using tripodal ligands

    Kuroda Yoshiyuki, Oka Yuya, Yasuda Tadao, Koichi Tatsuyuki, Muramatsu Keisuke, Wada Hiroaki, Shimojima Atsushi, Kuroda Kazuyuki

    DALTON TRANSACTIONS   47 ( 37 ) 12884 - 12892  2018.10  [Refereed]

     View Summary

    Precise size control of layered double hydroxide nanoparticles (LDHNPs) is crucial for their applications in anion exchange, catalysis, and drug delivery systems. Here, we report the synthesis of LDHNPs through a reconstruction method, using tripodal ligands (e.g., tris(hydroxymethyl)aminomethane; THAM). We found that the mechanism of reconstruction at least includes a dissolution-recrystallization process rather than topotactic transformation. THAM is immobilized on the surface of recrystallized LDHNPs with tridentate linkages, suppressing their crystal growth especially in lateral directions. The particle size of the LDHNPs is precisely controlled by the concentration of THAM regardless of the synthetic routes, such as coprecipitation and reconstruction. It is suggested that the particle size is controlled on the basis of Ostwald ripening which is governed by the equilibrium of the surface modification reaction.

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    18
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  • Synthesis of Zeolitic Macrocycles Using Site-Selective Condensation of Regioselectively Difunctionalized Cubic Siloxanes

    Saito Shohei, Wada Hiroaki, Shimojima Atsushi, Kuroda Kazuyuki

    INORGANIC CHEMISTRY   57   14686 - 14691  2018.10  [Refereed]

    DOI

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    8
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  • Self-assembly of Cyclohexasiloxanes Possessing Alkoxysilyl Groups and Long Alkyl Chains

    Yoshikawa Masashi, Ikawa Hanako, Wada Hiroaki, Shimojima Atsushi, Kuroda Kazuyuki

    CHEMISTRY LETTERS   47 ( 9 ) 1203 - 1206  2018.09  [Refereed]

    DOI

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    6
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  • Formation of Silica-Organic Hybrid Nanoparticles by Cross-linking of Ultra-small Silica Nanoparticles

    Sakamoto Shigeru, Fujino Koki, Shimojima Atsushi, Kuroda Kazuyuki

    CHEMISTRY LETTERS   47 ( 8 ) 1018 - 1021  2018.08  [Refereed]

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  • Thermoplastic polydimethylsiloxane with l-phenylalanine-based hydrogen-bond networks

    Shunsuke Tazawa, Atsushi Shimojima, Tomoki Maeda, Atsushi Hotta

    Journal of Applied Polymer Science   135 ( 24 ) 45419  2018.06  [Refereed]

     View Summary

    Thermoplastic polydimethylsiloxane (PDMS) containing l-phenylalanine was synthesized by the liquid-phase synthesis method with an Fmoc-protected amino acid and by the condensation polymerization. In order to investigate the mechanical and the thermoplastic properties of the PDMS with l-phenylalanine, the tensile testing and the dynamic mechanical analysis (DMA) were conducted. From the results of the tensile testing, it was found that the stress at break of the PDMS with l-phenylalanine nearly became seven times higher than that of the PDMS without l-phenylalanine. The DMA results revealed that the PDMS could maintain its storage modulus for three heating cycles, while the melting temperature was also kept at ∼120 °C. Moreover, the mechanical property was analyzed through two remolding cycles, and it was found that the PDMS could almost maintain its mechanical property after the heat remolding. Finally, it was found that the PDMS also possessed some self-healing property, where the Young's modulus of the cut PDMS could maintain at least 70% of its original Young's modulus after contact and self-healing. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45419.

    DOI

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    12
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  • EFFECT OF INTERCALATED AMIDE MOLECULES ON INTERLAYER CONDENSATION OF LAYERED SILICATE RUB-15

    Masakazu Koike, Yusuke Asakura, Yoshiyuki Kuroda, Hiroaki Wada, Atsushi Shimojima, Kazuyuki Kuroda

    Clay Science   22 ( 1 ) 1 - 11  2018.03  [Refereed]

    DOI

  • Formation of Concentric Silica Nanogrooves Guided by the Curved Surface of Silica Particles

    Shintaro Hara, Keiya Hirota, Yuka Tabe, Hiroaki Wada, Atsushi Shimojima, Kazuyuki Kuroda

    Langmuir   34 ( 4 ) 1733 - 1741  2018.01  [Refereed]

     View Summary

    The flexible control of nanopatterns by a bottom-up process at the nanometer scale is essential for nanofabrication with a finer pitch. We have previously reported that for the fabrication of linear nanopatterns with sub-5 nm periodicity on Si substrates the outermost surfaces of assembled micelles facing the substrates can be replicated with soluble silicate species generated from the Si substrates under basic conditions. In this study, concentrically arranged nanogrooves with a sub-5 nm periodicity were prepared on Si substrates by replicating the outermost surfaces of bent micelles guided by silica particles. The Si substrates, where silica particles and surfactants films were deposited, were exposed to an NH3-water vapor mixture. During the vapor treatment, cylindrical micelles became arranged in concentric patterns centered on the silica particles, and their outermost surfaces facing the substrates were replicated by soluble silicate species on the Si substrates. The thinness of the surfactant film on the substrate is crucial for the formation of concentric silica nanogrooves because the out-of-plane orientations of the micelles are suppressed at the interface. Surprisingly, the domains of the concentric silica nanogrooves spread to much larger areas than the maximum cross-sectional areas of the particles, and the size of the domains increased linearly with the radii of the particles. The extension of concentric nanogrooves is discussed on the basis of the orientational elastic energies of the micelles around one silica particle. This study of the formation of bent nanogrooves guided by the outlines of readily deposited nanoscale objects provides a new nanostructure-guiding process.

    DOI

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    3
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  • Formation of Single-Digit Nanometer Scale Silica Nanoparticles by Evaporation-Induced Self-Assembly

    Shigeru Sakamoto, Masashi Yoshikawa, Kota Ozawa, Yoshiyuki Kuroda, Atsushi Shimojima, Kazuyuki Kuroda

    Langmuir   34 ( 4 ) 1711 - 1717  2018.01  [Refereed]

     View Summary

    There are emerging demands for single-digit nanoscale particles in multidisciplinary fields, such as nanomedicine, optics, catalysis, and sensors, to create new functional materials. Here, we report a novel route to prepare silica nanoparticles less than 3 nm in size via the evaporation-induced self-assembly of silicate species and quaternary trialkylmethylammonium surfactants, which usually form reverse micelles. The solvent evaporation induces a local concentration increase and simultaneous polycondensation of silicate species within the hydrophilic region of the surfactant mesophases. Extremely small silica nanoparticles in the silica-surfactant mesostructures can be stably dispersed in organic solvents by destroying the mesostructure, which is in clear contrast to the preparation of silica nanoparticles using the conventional reverse micelle method. The surface chemical modification of the formed silica nanoparticles is easily performed by trimethylsilylation. The particle size is adjustable by changing the ratio of the surfactants to the silica source because the hydrophobic/hydrophilic ratio determines the curvature and diameter of the resulting spherical silica-surfactant domains in the mesostructure. The versatility of this method is demonstrated by the fabrication of very small titania nanoparticles. These findings will increase the designability of oxide nanoparticles at the single-digit nanoscale because conventional methods based on the generation and growth of nuclei in a solution cannot produce such nanoparticles with highly regulated sizes.

    DOI

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    7
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  • Transformation of Mesostructured Silica Nanoparticles into Colloidal Hollow Nanoparticles in the Presence of a Bridged-Organosiloxane Shell

    Eisuke Yamamoto, Saki Uchida, Atsushi Shimojima, Hiroaki Wada, Kazuyuki Kuroda

    Chemistry of Materials   30 ( 2 ) 540 - 548  2018.01  [Refereed]

     View Summary

    Hollow siloxane-based nanoparticles (HSNs) have attracted significant attention because of their unique properties and applications. Recently, it was discovered that the simple covering of silica nanoparticles with an organosiloxane shell leads to the spontaneous formation of HSNs
    however, the detailed mechanism of their formation has not yet been established. In this study, colloidal 30 nm HSNs were prepared by adding organically bridged alkoxysilane to an aqueous dispersion of mesostructured silica-surfactant composite nanoparticles, and the temporal changes of the morphology and chemical state of the nanoparticles were monitored to elucidate the formation mechanism. Core silica was dissolved after the formation of the core-shell structured nanoparticles, and almost all the dissolved silicate species were incorporated in the organosiloxane shell, changing the shell thickness. Two conditions were essential for silica dissolution induced by covering with organosiloxane: (i) presence of a sufficient amount of uncondensed Si-OH groups in the organosiloxane shell, and (ii) elevated temperature and pH for the promotion of the hydrolysis of silica. These findings will enable the fabrication of various HSNs through organosiloxane-induced silica dissolution and redeposition.

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    18
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  • In situ synthesis of magnesium hydroxides modified with tripodal ligands in an organic medium

    Keisuke Muramatsu, Yoshiyuki Kuroda, Hiroaki Wada, Atsushi Shimojima, Kazuyuki Kuroda

    Dalton Transactions   47 ( 9 ) 3074 - 3083  2018  [Refereed]

     View Summary

    Layered magnesium hydroxides modified organically with tris(hydroxymethyl)aminomethane (Tris-NH2) were directly synthesized from magnesium chloride dissolved in a polar organic solvent, like dimethyl sulfoxide (DMSO), containing a small amount of water. Tris-NH2 acted as a base for precipitating magnesium hydroxides as well as an organic modifier. In contrast to the case of an aqueous solution, the use of organic solvents substantially increased the degree of modification of layered magnesium hydroxides with Tris-NH2 owing to the formation of bidentate Mg-O-C linkages by Tris-NH2 in addition to its tridentate bonding mode. Bidentate linkages, hydrolyzed readily in water, are stable in the organic media. Pentaerythritol (Tris-CH2OH), trimethylolethane (Tris-CH3), and trimethylolpropane (Tris-C2H5) were also successfully used for the synthesis of organically-modified layered magnesium hydroxides by the addition of tetrabutylammonium hydroxide as a base with DMSO as the solvent. The synthesis of hybrid magnesium hydroxides in organic solvents is expected to expand the chemistry of organically modified layered metal hydroxides with various metallic species and a wide variety of organic functional groups.

    DOI PubMed

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  • Polymerization of cyclododecasiloxanes with Si-H and Si-OEt side groups by the piers-Rubinsztajn reaction

    Masashi Yoshikawa, Hiroya Shiba, Hiroaki Wada, Atsushi Shimojima, Kazuyuki Kuroda

    Bulletin of the Chemical Society of Japan   91 ( 5 ) 747 - 753  2018  [Refereed]

     View Summary

    Two types of cyclododecasiloxanes possessing SiH and SiOEt side groups were polymerized by the Piers-Rubinsztajn (P-R) reaction. Cyclododecasiloxane possessing both methyl and ethoxydimethylsilyl side groups (Cyclo12-Me-Si- Me2(OEt)) was synthesized by ethoxylation of cyclododecasiloxane possessing both methyl and dimethylsilyl side groups (Cyclo12-Me-SiHMe2). Cyclo12-Me-SiMe2(OEt) and Cyclo12-Me-SiHMe2 were polymerized by the P-R reaction, using B(C6F5)3 as a catalyst. The original cyclic structures were retained after the reaction without cleavage of the SiOSi bonds. Dimethylsilane elimination between two side SiHMe2 groups and the consecutive siloxane-bond formation occurred concomitantly during the main P-R reaction. The effectiveness of the P-R reaction between oligosiloxanes toward preparation of polyorganosiloxanes with well-defined architectures has been demonstrated.

    DOI

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    14
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  • Protecting and Leaving Functions of Trimethylsilyl Groups in Trimethylsilylated Silicates for the Synthesis of Alkoxysiloxane Oligomers

    Masashi Yoshikawa, Yasuhiro Tamura, Ryutaro Wakabayashi, Misa Tamai, Atsushi Shimojima, Kazuyuki Kuroda

    ANGEWANDTE CHEMIE-INTERNATIONAL EDITION   56 ( 45 ) 13990 - 13994  2017.11  [Refereed]

     View Summary

    The concept of protecting groups and leaving groups in organic synthesis was applied to the synthesis of siloxane-based molecules. Alkoxy-functionalized siloxane oligomers composed of SiO4, RSiO3, or R2SiO2 units were chosen as targets (R: functional groups, such as Me and Ph). Herein we describe a novel synthesis of alkoxysiloxane oligomers based on the substitution reaction of trimethylsilyl (TMS) groups with alkoxysilyl groups. Oligosiloxanes possessing TMS groups were reacted with alkoxychlorosilane in the presence of BiCl3 as a catalyst. TMS groups were substituted with alkoxysilyl groups, leading to the synthesis of alkoxysiloxane oligomers. Siloxane oligomers composed of RSiO3 and R2SiO2 units were synthesized more efficiently than those composed of SiO4 units, suggesting that the steric hindrance around the TMS groups of the oligosiloxanes makes a difference in the degree of substitution. This reaction uses TMS groups as both protecting and leaving groups for SiOH/SiO- groups.

    DOI

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    16
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  • Organic-Free Synthesis of a Highly Siliceous Faujasite Zeolite with Spatially Biased Q(4)(nAl) Si Speciation

    Matthew D. Oleksiak, Koki Muraoka, Ming-Feng Hsieh, Marlon T. Conato, Atsushi Shimojima, Tatsuya Okubo, Watcharop Chaikittisilp, Jeffrey D. Rimer

    ANGEWANDTE CHEMIE-INTERNATIONAL EDITION   56 ( 43 ) 13366 - 13371  2017.10  [Refereed]

     View Summary

    We report the most siliceous FAU-type zeolite, HOU-3, prepared via a one-step organic-free synthesis route. Computational studies indicate that it is thermodynamically feasible to synthesize FAU with SAR=2-7, though kinetic factors seemingly impose a more restricted upper limit for HOU-3 (SAR approximate to 3). Our findings suggest that a slow rate of crystallization and/or low concentration of Na+ ions in HOU-3 growth mixtures facilitate Si incorporation into the framework. Interestingly, Q(4)(nAl) Si speciation measured by solid-state NMR can only be modeled with a few combinations of Al positioning at tetrahedral sites in the crystal unit cell, indicating the distribution of Si(-O-Si)(4-n)(-O-Al)(n) species is spatially biased as opposed to being random. Achieving higher SAR is desirable for improved zeolite (hydro)thermal stability and enhanced catalytic performance, which we demonstrate in benchmark tests that show HOU-3 is superior to commercial zeolite Y.

    DOI

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    43
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    (Scopus)
  • Spontaneous Crack Healing in Nanostructured Silica-Based Thin Films

    Shun Itoh, Satoshi Kodama, Maho Kobayashi, Shintaro Hara, Hiroaki Wada, Kazuyuki Kuroda, Atsushi Shimojima

    ACS NANO   11 ( 10 ) 10289 - 10294  2017.10  [Refereed]

     View Summary

    Self-healing materials that can spontaneously repair damage under mild conditions are desirable in many applications. Significant progress has recently been made in the design of polymer materials capable of healing cracks at the molecular scale using reversible bonds; however, such a self-healing mechanism has rarely been applied to rigid inorganic materials. Here, we demonstrate the self-healing ability of lamellar silica-based thin films formed by self assembly of silica precursors and quaternary ammonium type surfactants. Specifically, spontaneous healing of cracks (typically less than 1.5 mu m in width) was achieved under humid conditions even at room temperature. The randomly oriented lamellar structure with thin silica layers is suggested to play an essential role in crack closure and the reformation of siloxane networks on the fracture surface. These findings will lead to the creation of smart self-healing silica-based materials based on reversible siloxane bonds.

    DOI

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    14
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  • Nanospace-Mediated Self-Organization of Nanoparticles in Flexible Porous Polymer Templates

    Yoshiyuki Kuroda, Itaru Muto, Atsushi Shimojima, Hiroaki Wada, Kazuyuki Kuroda

    LANGMUIR   33 ( 36 ) 9137 - 9143  2017.09  [Refereed]

     View Summary

    Self-organization is a fundamental process for the construction of complex hierarchically ordered nanostructures, which are widespread in biological systems. However, precise control of size, shape, and surface properties is required for self-organization of nanoparticles. Here, we demonstrate a novel self-organization phenomenon mediated by flexible nanospaces in templates. Inorganic nanoparticles (e.g., silica, zirconia, and titania) are deposited in porous polymer thin films with randomly distributed pores on the surface, leaving a partially filled nanospace in each pore. Heating at temperatures beyond the glass transition temperature of the template leads to self-organization of the inorganic nanoparticles into one-dimensional chainlike networks. The self-organization is mediated by the deformation and fusion of the residual nanospaces, and it can be rationally controlled by sequential heat treatments. These results show that a nanospace, defined by the nonexistence of matter, interacts indirectly with matter and can be used as a component of self-organization systems.

    DOI

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    5
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  • Topotactic conversion of layered silicate RUB-15 to silica sodalite through interlayer condensation in N-methylformamide

    Masakazu Koike, Yusuke Asakura, Megumi Sugihara, Yoshiyuki Kuroda, Hidehiro Tsuzura, Hiroaki Wada, Atsushi Shimojima, Kazuyuki Kuroda

    DALTON TRANSACTIONS   46 ( 31 ) 10232 - 10239  2017.08  [Refereed]

     View Summary

    Silica sodalite was obtained using topotactic conversion of layered silicate RUB-15 through stepwise processes that consisted of the control of stacking sequence of the layers, interlayer condensation by refluxing, and elimination of intercalated guest species. The interlayer condensation of RUB-15, in which acetic acid was pre-intercalated between the layers to control the stacking sequence, afforded a sodalite framework containing organic guest species by refluxing in N-methylformamide (NMF). The pre-intercalated acetic acid molecules were largely replaced with NMF. This formation process of silica sodalite containing large amounts of intercalated organic guest species is in clear contrast to the previously reported process that used direct calcination of an intercalation compound of layered RUB-15 accommodating acetic acid between the layers. Calcination of the condensed product provided sodalite with fewer defects than the directly calcined product, thus indicating the advantage of the stepwise process. The method reported here is useful for the preparation of pure silica sodalite with relatively low defects and plate-like morphology.

    DOI

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    8
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  • Role of Cubic Siloxane Cages in Mesostructure Formation and Photoisomerization of Azobenzene-Siloxane Hybrid

    Sufang Guo, Jun Sasaki, Shiho Tsujiuchi, Shintaro Hara, Hiroaki Wada, Kazuyuki Kuroda, Atsushi Shimojima

    CHEMISTRY LETTERS   46 ( 8 ) 1237 - 1239  2017.08  [Refereed]

     View Summary

    A mesostructured siloxane-based hybrid film is formed by the self-assembly of cubic, double-four-ring (D4R) siloxanes mono-functionalized with azobenzene. The azobenzene groups in the film exhibit reversible and a high degree of trans-cis isomerization upon UV-vis irradiation. The bulky D4R cages play an important role in both the formation of cylindrical assemblies and the improvement of the photoisomerization behavior as compared with conventional azobenzene-siloxane hybrid materials.

    DOI

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    11
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  • Synthesis of a Single-Crystalline Macroporous Layered Silicate from a Macroporous UTL-Type Zeolite and Its Accelerated Intercalation

    Yusuke Asakura, Naoki Kawaura, Yoshiyuki Kuroda, Masakazu Koike, Hiroaki Wada, Atsushi Shimojima, Kazuyuki Kuroda

    CHEMISTRY-A EUROPEAN JOURNAL   23 ( 46 ) 11022 - 11029  2017.08  [Refereed]

     View Summary

    A single-crystalline macroporous layered silicate was obtained for the first time. Firstly, UTL-type zeolite with macropores was prepared hydrothermally under the presence of acetylene black as a macropore template and the subsequent calcination to remove the template. Double four-membered ring (d4r) units in the UTL framework were selectively dissolved to yield a layered silicate with macropores. Intercalation of tetrabutylammonium ions into the macroporous layered silicate is accelerated if compared with that into the same silicate without macropores, indicating the effectiveness of macropores due to easy diffusion. The layered silicate with macropores was converted into PCR-type zeolite with macropores, a hierarchically micro- and macroporous material, through interlayer condensation.

    DOI

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    3
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  • Preparation of Mesoporous Basic Oxides through Assembly of Monodispersed Mg-Al Layered Double Hydroxide Nanoparticles

    Yuya Oka, Yoshiyuki Kuroda, Takamichi Matsuno, Keigo Kamata, Hiroaki Wada, Atsushi Shimojima, Kazuyuki Kuroda

    CHEMISTRY-A EUROPEAN JOURNAL   23 ( 39 ) 9362 - 9368  2017.07  [Refereed]

     View Summary

    Mesoporous basic Mg-Al mixed metal oxides (MMOs) with a high surface area and large pore size have been prepared through the assembly of monodispersed layered double hydroxide nanoparticles (LDHNPs) with block copolymer templates. The particle sizes of the LDHNPs were mainly controlled by varying the concentration of tris(hydroxymethyl) aminomethane (THAM), which was used as a surface stabilizing agent. LDHNPs and micelles of a block copolymer (Pluronic F127) were assembled to form a composite. The composites were calcined to transform them into mesoporous MMOs and to remove the templates. The Brunauer-Emmett-Teller surface areas, mesopore sizes, and pore volumes increased as a result of using the templates. Moreover, the pore sizes of the mesoporous MMOs could be controlled by using LDHNPs of different sizes. The mesoporous MMOs prepared from the LDHNPs showed much higher catalytic activity than a conventional MMO catalyst for the Knovenagel condensation of ethyl cyanoacetate with benzaldehyde. The mesoporous MMO catalyst prepared using the smallest LDHNPs, about 12 nm in size, showed the highest activity. Therefore, the use of monodispersed LDHNPs and templates is effective for preparing highly active mesoporous solid base catalysts.

    DOI

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    24
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  • Thickness control of 3-dimensional mesoporous silica ultrathin films by wet-etching

    Maho Kobayashi, Kyoka Susuki, Tomohiro Otani, Shinpei Enomoto, Haruo Otsuji, Yoshiyuki Kuroda, Hiroaki Wada, Atsushi Shimojima, Takayuki Homma, Kazuyuki Kuroda

    NANOSCALE   9 ( 24 ) 8321 - 8329  2017.06  [Refereed]

     View Summary

    The thickness of 3-dimensional (3D) mesoporous silica ultrathin films was controlled at a single-nano-meter scale by wet-etching. A drop casting method with an aqueous etchant of ammonium fluoride was effective in etching the surfaces of films in the direction perpendicular to their substrates. The decrease in the film thickness depends on the interface tension of etching solutions. The wettability of thin films also influences the etching. CoPt nanodots were electrodeposited within ultrathin silica films on Ru substrates to form CoPt nanodot patterns.

    DOI

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    11
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  • Pore Clogging of Colloidal Mesoporous Silica Nanoparticles for Encapsulating Guest Species

    Eisuke Yamamoto, Kouya Nagata, Kenta Onishi, Chihiro Urata, Atsushi Shimojima, Hiroaki Wada, Shinji Takeoka, Kazuyuki Kuroda

    BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN   90 ( 6 ) 706 - 708  2017.06  [Refereed]

     View Summary

    Colloidal mesoporous silica nanoparticles (CMS) are useful as carriers for imaging probes because of their unique features. A simple method for the pore clogging of CMS has been proved by the addition of tetraethoxysilane under weakly basic conditions. The pore clogging of CMS is useful for encapsulation of thermoresponsive dyes.

    DOI

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    5
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  • Two-Stage Crystallization of Meso-and Macroporous MFI and MEL Zeolites Using Tributylamine-Derived Diquaternary Ammonium Cations as Organic Structure-Directing Agents

    Sye Hoe Keoh, Watcharop Chaikittisilp, Akira Endo, Atsushi Shimojima, Tatsuya Okubo

    BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN   90 ( 5 ) 586 - 594  2017.05  [Refereed]

     View Summary

    Meso- and/or macroporous zeolites have received particular attention because the presence of secondary meso- and/or macropores, in addition to the intrinsic micropores of zeolites, can provide additional cavities at a nanometer-length scale and shorten molecular diffusion path lengths. Here, synthesis of meso- and macroporous MFI and MEL aluminosilicate zeolites via a two-stage crystallization method using diquaternary ammonium cations (N ,N ,N ,N',N',N'-hexabutylheptanediammonium, Bu-6-diquat-7) as an organic structure-directing agent (OSDA) is described. In this two-stage process, both low- and high-temperature stages were found to be crucial for the formation of zeolites. By carefully varying the amount of sodium hydroxide in the reactants, both MFI and MEL zeolites can be obtained with the same OSDA. It was revealed that Bu-6-diquat-7 was more selective to the formation of MFI and MEL zeolites than its monoquaternary counterpart (i.e., tetrabutylammonium) under the present synthesis conditions. Interestingly, the synthesis time of the first (low temperature) stage highly influenced the particle sizes of the resulting zeolites; zeolites with smaller sizes were obtained when the synthesis time was prolonged. Gas physisorption analyses and scanning transmission electron microscopy observation suggested that the obtained zeolites possessed ink-bottle-like pores consisting of meso- and macroporous internal cavities with very narrow pore necks.

    DOI

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    3
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  • Formation of Nanogrooves with Sub-5 nm Periodicity Using Local Silicification at the Interspace between a Si Substrate and Lyotropic Liquid Crystals

    Shintaro Hara, Hiroaki Wada, Atsushi Shimojima, Kazuyuki Kuroda

    ACS NANO   11 ( 5 ) 5160 - 5166  2017.05  [Refereed]

     View Summary

    Bottom-up fabrication of nanopatterns with single nanometer-scale periodicity is quite challenging. In this study, we have focused on the use of the outermost convex surfaces of lyotropic liquid crystals (LLCs) as a template. Periodically arrayed single nanometer-scale nano grooves consisting of silica are successfully formed on a Si substrate covered with LLCs composed of cylindrical micelles of cetyltrimethylammonium chloride. Soluble silicate species are generated from the Si substrate by a treatment with an NH3-water vapor mixture, infilling the interspaces between the Si substrate and the LLCs. The cross section of the nanogrooves has a symmetrical sawtooth-like profile with a periodicity of 4.7 nm, and the depth of each nanogroove is around 2 nm. Uniaxial alignment of the nanogrooves can be achieved using micrometer-scale grooves fabricated by a focused ion beam technique. Although formed nanogrooves contain defects, such as bends and discontinuities, this successful concept provides a novel fabrication method of arrayed concave patterns with sub-5 nm periodicity on the surfaces of Si substrates.

    DOI

  • Direct Synthesis of Highly Designable Hybrid Metal Hydroxide Nanosheets by Using Tripodal Ligands as One-Size-Fits-All Modifiers

    Yoshiyuki Kuroda, Tatsuyuki Koichi, Keisuke Muramatsu, Kazuya Yamaguchi, Noritaka Mizuno, Atsushi Shimojima, Hiroaki Wada, Kazuyuki Kuroda

    CHEMISTRY-A EUROPEAN JOURNAL   23 ( 21 ) 5023 - 5032  2017.04  [Refereed]

     View Summary

    Brucite-type layered metal hydroxides are prepared from diverse metallic elements and have outstanding functions; however, their poor intercalation ability significantly limits their chemical designability and the use of their potentially ultrahigh surface areas and unique properties as two-dimensional nanosheets. Here, we demonstrate that tripodal ligands (RC(CH2OH)(3), R=NH2, CH2OH, or NHC2H4SO3H) are useful as one-size-fits-all modifiers for the direct synthesis of hybrid metal hydroxide nanosheets with various constituent metallic elements (M=Mg, Mn, Fe, Co, Ni, or Cu) and surface functional groups. The hybrid nanosheets are formed directly from solution phases, and they are stacked into a turbostratic layered structure. The ligands form tridentate Mg-O-C bonds with brucite layers. The hybrid brucite intercalates various molecules and is exfoliated into nanosheets at room temperature, although the non-modified material does not intercalate any molecules. Consequently, both the constituent metallic elements and surface functional groups are freely designed by the direct synthesis.

    DOI

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    21
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  • Construction of siloxane-based porous materials by using cage-Type element blocks

    Naoto Sato, Hiroaki Wada, Atsushi Shimojima, Kazuyuki Kuroda

    Funtai Oyobi Fummatsu Yakin/Journal of the Japan Society of Powder and Powder Metallurgy   64 ( 3 ) 126 - 129  2017.03  [Refereed]

     View Summary

    Construction of nanoarchitectures using cage siloxane oligomers as element blocks is of much interest because of its excellent potential for creating novel porous materials. In this review, our recent work on the fabrication of siloxane-based nanostructures from cage siloxanes is presented. The arrangement of cage siloxanes units is controlled by various methods, including amphiphilic self-Assembly and hydrogen bonding of silanol groups, toward the preparation of well-defined porous siloxane-based materials.

    DOI CiNii

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  • Direct Observation of the Outermost Surfaces of Mesoporous Silica Thin Films by High Resolution Ultralow Voltage Scanning Electron Microscopy

    Maho Kobayashi, Ktoka Susuki, Haruo Otsuji, Yusuke Sakuda, Shunsuke Asahina, Naoki Kikuchi, Toshiyuki Kanazawa, Yoshiyuki Kuroda, Hiroaki Wada, Atsushi Shimojima, Kazuyuki Kuroda

    LANGMUIR   33 ( 9 ) 2148 - 2156  2017.03  [Refereed]

     View Summary

    The properties of the outermost surfaces of mesoporous silica thin films are critical in determining their functions. Obtaining information on the presence or absence of silica layers on the film surfaces and on the degree of mesopore opening is essential for applications of surface mesopores. In this study, the outermost surfaces of mesoporous silica thin films with 3-dimensional orthorhombic and 2-dimensional hexagonal structures were observed using ultralow voltage high resolution scanning electron microscopy (HR-SEM) with decelerating optics. SEM images of the surfaces before and after etching with NH4F were taken at various landing voltages. Comparing the images taken under different conditions indicated that the outermost surfaces of the nonetched mesoporous silica thin films are coated with a thin layer of silica. The images taken at an ultralow landing voltage (i.e., 80 V) showed that the presence or absence of surface silica layers depends on whether the film was etched with an aqueous solution of NH4F. The mesostructures of both the etched and nonetched films were visible in images taken at a conventional landing voltage (2 kV); hence, the ultralow landing voltage was more suitable for analyzing the outermost surfaces. The SEM observations provided detailed information about the surfaces of mesoporous silica thin films, such as the degree of pore opening and their homogeneities. AFM images of nonetched 2-dimensional hexagonal mesoporous silica thin films show that the shape of the silica layer on the surface of the films reflects the curvature of the top surface of the cylindrical mesochannels. SEM images taken at various landing voltages are discussed, with respect to the electron penetration range at each voltage. This study increases our understanding of the surfaces of mesoporous silica thin films, which may lead to potential applications utilizing the periodically arranged mesopores on these surfaces.

    DOI

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    7
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  • Fabrication of colloidal crystals composed of pore-expanded mesoporous silica nanoparticles prepared by a controlled growth method

    Eisuke Yamamoto, Seiya Mori, Atsushi Shimojima, Hiroaki Wada, Kazuyuki Kuroda

    NANOSCALE   9 ( 7 ) 2464 - 2470  2017.02  [Refereed]

     View Summary

    Colloidal crystals composed of mesoporous silica nanoparticles (MSNs) are expected to have various applications because of their unique hierarchical structures and tunable functions. The expansion of the mesopore size is important for introducing guest species which cannot be accommodated by using conventional colloidal crystals of MSNs; however, the preparation of MSNs with a controllable pore size, suitable for the fabrication of colloidal crystals, still remains a challenge. In this study, we fabricated colloidal crystals composed of pore-expanded MSNs using a sophisticated particle growth method to control the pore size of colloidal MSNs while retaining their monodispersity high enough to form colloidal crystals. By adding triisopropylbenzene (TIPB) only during the growth process with the stepwise addition of tetrapropoxysilane (TPOS), the particle size can be tuned from 60 nm to 100 nm, while the pore size can be tuned from 3 nm to ten plus several nm which is the largest size among the previous MSNs capable of forming colloidal crystals. These novel colloidal crystals should contribute to the expansion of nanomaterials science.

    DOI

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    25
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  • Precise Synthesis of Mesoporous Silica Nanoparticles

    Yamamoto Eisuke, Shimojima Atsushi, Kuroda Kazuyuki

    Journal of the Japanese Association for Crystal Growth   44 ( 2 ) 82 - 87  2017

     View Summary

    <p>  Mesoporous silica nanoparticles have attracted great attention because of their potential applications as catalysts, drug/gene delivery carriers, and optical materials because of high surface area, large pore volume, transparency, biocompatibility, and high cell uptake efficiency. This review reports general preparation and applications of mesoporous silica nanoparticles, and our recent efforts on the preparation of well-dispersed mesoporous silica nanoparticles with precisely controlled particle size, pore size, functionality, and morphology.</p>

    DOI CiNii

  • Synthesis of a 12-membered cyclic siloxane possessing alkoxysilyl groups as a nanobuilding block and its use for preparation of gas permeable membranes

    Masashi Yoshikawa, Hiroya Shiba, Masakoto Kanezashi, Hiroaki Wada, Atsushi Shimojima, Toshinori Tsuru, Kazuyuki Kuroda

    RSC ADVANCES   7 ( 77 ) 48683 - 48691  2017  [Refereed]

     View Summary

    A 12-membered cyclic siloxane possessing alkoxysilyl groups was synthesized as a nanobuilding block for siloxane-based materials by the alkoxysilylation of organometallasiloxane containing a 12-membered ring with Si-Me and Si-O- groups as the side groups. The cyclic structure was retained not only in the hydrolysis and condensation reactions (sol-gel process) of the alkoxysilyl groups but also in the xerogel and membrane preparation processes. The degree of condensation of the xerogel derived from the 12-membered ring siloxane was higher than that derived from alkoxysilane monomers, indicating that the alkoxysilylated cyclic oligosiloxane is useful for controlling siloxane networks. A membrane composed of the cyclic siloxane was prepared by coating the hydrolyzed solution onto a porous alumina tube for evaluating the gas permeation properties. The membrane showed a molecular sieving effect for H-2/SF6.

    DOI

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    12
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  • Factors Governing the Formation of Hierarchically and Sequentially Intergrown MFI Zeolites by Using Simple Diquaternary Ammonium Structure-Directing Agents

    Sye Hoe Keoh, Watcharop Chaikittisilp, Koki Muraoka, Rino R. Mukti, Atsushi Shimojima, Prashant Kumar, Michael Tsapatsis, Tatsuya Okubo

    CHEMISTRY OF MATERIALS   28 ( 24 ) 8997 - 9007  2016.12  [Refereed]

     View Summary

    Zeolites with hierarchical structures are of particular interest because such structures can improve molecular diffusion, particularly that of bulky molecules. N,N,N,N',N',N'-Hexapropylpentanediammonium cations (Pr-6-diquat-5), a simple diquaternary ammonium organic structure directing agent (OSDA), can direct the formation of hierarchically and sequentially intergrown MFI zeolites without employing any mesoporogens. In this paper, the effects of OSDAs having structures similar to Pr-6-diquat-5 but different lengths of alkyl spacers and/or different substituting groups on the phase selectivity and morphology of the resulting zeolites are presented. It was revealed that the number of carbon atoms between two charged nitrogens in the OSDAs significantly affected the intergrowth and morphology of the crystals formed. In addition, the propyl-substituted OSDAs were found to be very selective to the formation of MFI zeolite, whereas the butyl-substituted OSDAs were not. For Pr-6-diquat-5, the condition for the formation of hierarchically and sequentially intergrown MFI zeolites was somewhat narrow with the optimized molar composition of 1 SiO2:0.2 Pr-6-diquat-5:0.375-0.500 KOH:200 H2O:4 EtOH. Defect lines observed on the obtained zeolite crystals by a transmission electron microscope were considered to be connectors for such intergrowths. The unique intergrowth formed by Pr-6-diquat-5 was surmised to be due to the unusual fitting of Pr-6-diquat-5 inside the channels of MFI zeolite, which was explained by comparing molecular dimensions and stabilization energies of each OSDA.

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    35
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  • Selective Formation of Alkoxychlorosilanes and Organotrialkoxysilane with Four Different Substituents by Intermolecular Exchange Reaction

    Yuma Komata, Masashi Yoshikawa, Yasuhiro Tamura, Hiroaki Wada, Atsushi Shimojima, Kazuyuki Kuroda

    Chemistry-An Asian Journal   11 ( 22 ) 3225 - 3233  2016.11  [Refereed]

     View Summary

    Alkoxychlorosilanes are scientifically and industrially important toward preparing silicone and silica as well as preparation of siloxane-based nanomaterials by stepwise reactions of Si-OR (R = alkyl) and Si-Cl groups. Intermolecular exchange of alkoxy and chloro groups between alkoxysilanes and chlorosilanes (functional group exchange reaction) provides an efficient and environmentally benign route to alkoxychlorosilanes. BiCl3 as a Lewis acid catalyst can promote the functional group exchange reactions more efficiently than conventional acid catalysts. Higher reactivity has been observed for chlorosilanes with smaller numbers of Si-CH3 groups and for alkoxysilanes with larger numbers of Si-CH3 groups. The reaction mechanism is proposed and selective syntheses of alkoxychlorosilanes are demonstrated. These findings also enable us to synthesize an organotrialkoxysilane with four different substituents.

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    5
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  • Use of Mesoporous Silica Modified with Titanium Oxide as a Template for Preparation of Mesoporous Carbon Incorporating TiO2 Nanocrystals

    Masaki Kitahara, Kohei Suzuki, Saori Kubara, Yuta Shimasaki, Atsushi Shimojima, Hiroaki Wada, Kazuyuki Kuroda

    BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN   89 ( 10 ) 1207 - 1211  2016.10  [Refereed]

     View Summary

    Mesoporous silica modified with titanium oxide is shown to be useful as a template for the preparation of mesoporous carbon incorporating TiO2 nanocrystals. The nanocomposite was prepared by deposition of carbon within the mesoporous silica template modified with titanium oxide, and subsequent template removal with NaOH (aq). The high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) image of the prepared nanocomposite clearly showed that small TiO2 nanocrystals embedded on mesoporous carbon were formed. The Si-O-Ti bonds between mesoporous silica and titanium oxide layers are effective to suppress the migration of the Ti species, resulting in the formation of the TiO2 nanocrystals.

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    6
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    (Scopus)
  • Cover Picture: Cubic Siloxanes with Both Si−H and Si−OtBu Groups for Site-Selective Siloxane Bond Formation (Chem. Eur. J. 39/2016)

    Shohei Saito, Nao Yamasue, Hiroaki Wada, Atsushi Shimojima, Kazuyuki Kuroda

    Chemistry - A European Journal   22   13733  2016.09  [Refereed]

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  • Cubic Siloxanes with Both Si-H and Si-OtBu Groups for Site-Selective Siloxane Bond Formation

    Shohei Saito, Nao Yamasue, Hiroaki Wada, Atsushi Shimojima, Kazuyuki Kuroda

    CHEMISTRY-A EUROPEAN JOURNAL   22 ( 39 ) 13857 - 13864  2016.09  [Refereed]

     View Summary

    Cage-type siloxanes have attracted increasing attention as building blocks for silica-based nanomaterials as their corners can be modified with various functional groups. Cubic octasiloxanes incorporating both Si-H and Si-OtBu groups [(tBuO)(n)H8-nSi8O12; n=1, 2 or 7] have been synthesized by the reaction of octa(hydridosilsesquioxane) (H8Si8O12) and tert-butyl alcohol in the presence of a Et2NOH catalyst. The Si-H and Si-OtBu groups are useful for site-selective formation of Si-O-Si linkages without cage structure deterioration. The Si-H group can be selectively hydrolyzed to form a Si-OH group in the presence of Et2NOH, enabling the formation of the monosilanol compound (tBuO)(7)(HO)Si8O12. The Si-OH group can be used for either intermolecular condensation to form a dimeric cage compound or silylation to introduce new reaction sites. Additionally, the alkoxy groups of (tBuO)(7)HSi8O12 can be treated with organochlorosilanes in the presence of a BiCl3 catalyst to form Si-O-Si linkages, while the Si-H group remains intact. These results indicate that such bifunctional cage siloxanes allow for stepwise Si-O-Si bond formation to design new siloxane-based nanomaterials.

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    13
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  • A photoresponsive azobenzene-bridged cubic silsesquioxane network

    Sufang Guo, Tatsuya Okubo, Kazuyuki Kuroda, Atsushi Shimojima

    JOURNAL OF SOL-GEL SCIENCE AND TECHNOLOGY   79 ( 2 ) 262 - 269  2016.08  [Refereed]

     View Summary

    An azobenzene (AZO)-bridged cubic silsesquioxane network exhibiting reversible photoisomerization behavior in nonpolar solvents has been prepared via hydrosilylation reaction between 4,4'-diallyloxy-azobenzene and octahydridosilsesquioxane (H8Si8O12; H-POSS). Approximately 70 % of the corner Si-H groups of H-POSS are reacted to form a three-dimensional gel network while maintaining the cubic siloxane structure. The dried gel has a high thermal stability, which is attributed to the highly cross-linked cubic silsesquioxane network where AZOs are covalently incorporated in the main chain. The gel exhibits reversible swelling behavior in nonpolar solvents during wetting-drying cycles. In toluene, a large extent of reversible trans-cis isomerization of the AZO moiety is observed. These results are promising for the design of a new class of photoresponsive materials applicable in host-guest chemistry.
    [GRAPHICS]

    DOI

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    10
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  • A Single-Crystalline Mesoporous Quartz Superlattice

    Takamichi Matsuno, Yoshiyuki Kuroda, Masaki Kitahara, Atsushi Shimojima, Hiroaki Wada, Kazuyuki Kuroda

    ANGEWANDTE CHEMIE-INTERNATIONAL EDITION   55 ( 20 ) 6008 - 6012  2016.05  [Refereed]

     View Summary

    There has been significant interest in the crystallization of nanostructured silica into -quartz because of its physicochemical properties. We demonstrate a single-crystalline mesoporous quartz superlattice, a silica polymorph with unprecedentedly ordered hierarchical structures on both the several tens of nanometers scale and the atomic one. The mesoporous quartz superlattice consists of periodically arranged -quartz nanospheres whose crystalline axes are mostly oriented in an assembly. The superlattice is prepared by thermal crystallization of amorphous silica nanospheres constituting a colloidal crystal. We found that the deposition of a strong flux of Li+ only on the surface of silica nanospheres is effective for crystallization.

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    10
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  • Usefulness of Mesoporous Silica as a Template for the Preparation of Bundles of Bi Nanowires with Precisely Controlled Diameter Below 10nm

    Masaki Kitahara, Hasbuna Kamila, Atsushi Shimojima, Hiroaki Wada, Takao Mori, Ichiro Terasaki, Kazuyuki Kuroda

    CHEMISTRY-AN ASIAN JOURNAL   11 ( 6 ) 900 - 905  2016.03  [Refereed]

     View Summary

    The reduction of the diameter of Bi nanowires below 10nm has been an important target because of the theoretical prediction with regard to significant enhancement in thermoelectric performance by size reduction. In this study, we have demonstrated the usefulness of mesoporous silica with tunable pore size as a template for the preparation of thin Bi nanowires with diameters below 10nm. Bi was deposited within the templates through a liquid phase deposition using hexane and 1,1,3,3-tetramethyldisiloxane as a solvent and reducing agent, respectively. Bundles of thin Bi nanowires with non-crystalline frameworks were successfully obtained after the template removal. The diameter was precisely controlled between about 6nm and 9nm. The judicious choices of mesoporous silica and deposition conditions are critical for the successful preparation. The reliable formation of such thin Bi nanowires reported here opens up exciting new possibilities.

    DOI

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    6
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    (Scopus)
  • Surfactant-free synthesis of hollow mesoporous organosilica nanoparticles with controllable particle sizes and diversified organic moieties

    Natsume Koike, Watcharop Chaikittisilp, Atsushi Shimojima, Tatsuya Okubo

    RSC ADVANCES   6 ( 93 ) 90435 - 90445  2016  [Refereed]

     View Summary

    Fine control over particle sizes and organic moieties of hollow organosilica nanoparticles is of importance towards practical applications of functional colloids in, for example, catalysis, drug delivery, and coating. Here, we report the versatile synthesis of hollow mesoporous organosilica nanoparticles with controllable particle sizes and diversified organic moieties using silica nanoparticles (SNs) as sacrificial, hard templates, which are removed by dissolution under alkali conditions. The resulting organosilica nanoparticles possessed size-tunable hollow interiors that can be accessed through mesoporous shells. The diameters of such hollow organosilica nanoparticles were easily controlled by altering the diameters of the SN templates, ranging from 12 to 170 nm. Organic moieties in the mesoporous shells can be diversified by changing the organosilica sources, (EtO)(3)Si-R-Si(OEt)(3), where R = methylene, ethylene, and phenylene groups. In addition, it was revealed that there are minimum surface areas of the SN templates in the dispersions required to achieve the monodisperse silica/organosilica core/shell nanoparticles without homogeneous nucleation of organosilica nanoparticles. The nitrogen and argon adsorption-desorption isotherms of the resulting hollow organosilica nanoparticles showed type H5 hysteresis loops, which are derived from the mixed pore system of cage-like pores (hollow spaces) and open pores (interparticular voids between hollow organosilica nanoparticles). Hysteresis scanning measurements and NLDFT pore size distributions revealed the pore structures of the resulting hollow organosilica nanoparticles.

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    11
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  • Nanoparticle Vesicles with Controllable Surface Topographies through Block Copolymer-Mediated Self-Assembly of Silica Nanospheres

    Shujun Zhou, Ayae Sugawara-Narutaki, Sachio Tsuboike, Junzheng Wang, Atsushi Shimojima, Tatsuya Okubo

    LANGMUIR   31 ( 48 ) 13214 - 13220  2015.12  [Refereed]

     View Summary

    Silica nanoparticle vesicles (NPVs) with encapsulating capability and surface permeability are highly attractive in nanocatalysis, biosensing, and drug delivery systems. Herein, we report the facile fabrication of silica NPVs composed of a monolayer of silica nanospheres (SNSs, ca. 15 nm in diameter) through the block copolymer-mediated self-assembly of SNSs. The silica NPVs gain different surface topographies, such as raspberry- and brain coral-like topographies, under controlled heat treatment conditions. The vesicular assembly of SNSs is successful with a series of poly(propylene oxide)-poly(ethylene oxide)-poly(propylene oxide) block copolymers, and the size of NPVs can be tuned by changing their molecular weight. The polymer is easily extracted from the NPVs with their colloidal dispersibility and structural integrity intact. The polymer-free silica NPVs further serve as a reaction vessel and host for functional materials such as tin oxide nanoparticles.

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    14
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  • Photoinduced Bending of Self-Assembled Azobenzene Siloxane Hybrid

    Sufang Guo, Kimihiro Matsukawa, Takashi Miyata, Tatsuya Okubo, Kazuyuki Kuroda, Atsushi Shimojima

    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY   137 ( 49 ) 15434 - 15440  2015.12  [Refereed]

     View Summary

    A novel azobenzene siloxane hybrid material displaying photoinduced macroscopic motions has been prepared by one-step organosilane self-assembly. Two types of alkoxysilane precursors with either pendant or bridging azobenzene groups were synthesized via thiol-ene click reactions. Hybrid films with well-ordered lamellar structures were obtained by hydrolysis and polycondensation of these precursors. The film with solely pendant azobenzene groups showed reversible and rapid d-spacing variation upon UV-vis irradiation, which was induced by the trans-cis isomerization of azobenzene moieties. The flexible, free-standing film obtained by co-condensation of two types of precursors showed reversible bending unbending motions upon UV-vis irradiation. The partial cross-linking between the siloxane layers by bridging azobenzene groups was crucial for photoinduced distortion of the film. This film possesses high elastic modulus, good thermal stability, and shows large amplitude of photoinduced bending unbending over a wide temperature range. This is the first report on photoinduced macroscopic motions of azobenzene-containing siloxane-based materials. These materials possess great potential for applications in smart devices and energy conversion systems.

    DOI

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    90
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  • The Critical Effect of Niobium Doping on the Formation of Mesostructured TiO2: Single-Crystalline Ordered Mesoporous Nb-TiO2 and Plate-like Nb-TiO2 with Ordered Mesoscale Dimples

    Masaki Kitahara, Yuta Shimasaki, Takamichi Matsuno, Yoshiyuki Kuroda, Atsushi Shimojima, Hiroaki Wada, Kazuyuki Kuroda

    CHEMISTRY-A EUROPEAN JOURNAL   21 ( 37 ) 13073 - 13079  2015.09  [Refereed]

     View Summary

    Highly ordered mesoporous niobium-doped TiO2 with a single-crystalline framework was prepared by using silica colloidal crystals with ca. 30nm in diameter as templates. The preparation of colloidal crystals composed of uniform silica nanoparticles is a key to obtain highly ordered mesoporous Nb-doped TiO2. The XPS measurements of Nb-doped TiO2 showed the presence of Nb5+ and correspondingly Ti3+. With the increase in the amount of doped Nb, the crystalline phase of the product was converted from rutile into anatase, and the lattice spacings of both rutile and anatase phases increased. Surprisingly, the increase in the amount of Nb led to the formation of plate-like TiO2 with dimpled surfaces on one side, which was directly replicated from the surfaces of the colloidal silica crystals.

    DOI

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    12
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  • Interlayer Condensation of Protonated Layered Silicate Magadiite through Refluxing in N-Methylformamide

    Yusuke Asakura, Nami Hosaka, Shimon Osada, Taichi Terasawa, Atsushi Shimojima, Kazuyuki Kuroda

    BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN   88 ( 9 ) 1241 - 1249  2015.09  [Refereed]

     View Summary

    Interlayer-condensed materials of protonated layered silicate (magadiite) are synthesized by refluxing in N-methylformamide (NMF) and the subsequent calcination. The obtained materials possess 2-3 times higher surface areas than calcined protonated magadiite, depending on the time of refluxing. NMF molecules in the interlayer spaces are converted to organic substances with higher thermal stability during the refluxing, which is useful for the control of the stacking sequence of silicate layers and for the following interlayer condensation to increase the microporosity. The microporosity of the material obtained by the treatment of protonated magadiite with NMF at r.t. and the subsequent calcination is similar to that of simply calcined protonated magadiite, indicating that the retention of thermally stable substances in the interlayer is critical for the increase in the pore volume and surface area of the derivative from magadiite. The method reported here will stimulate re-estimation of a large number of known layered silicate organic intercalation compounds as possible candidates for the preparation of porous silica by interlayer condensation.

    DOI

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    6
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    (Scopus)
  • Critical Effect of Nb-doping on the Formation of Mesostructured TiO2 Using Silica Colloidal Crystals: Highly Ordered Mesoporous Nb-Doped TiO2 with Single Crystalline Framework and Plate-like Nb-Doped TiO2 with Ordered Meso

    Masaki Kitahara, Yuta Shimasaki, Takamichi Matsuno, Yoshiyuki Kuroda, Atsushi Shimojima, Hiroaki Wada, Kazuyuki Kuroda

    Chemistry A European Journal   21 ( 37 ) 13073-13079  2015.07  [Refereed]

    DOI PubMed

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    12
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  • Preparation of core-shell mesoporous silica nanoparticles with bimodal pore structures by regrowth method

    Hirotaka Ishii, Takaaki Ikuno, Atsushi Shimojima, Tatsuya Okubo

    JOURNAL OF COLLOID AND INTERFACE SCIENCE   448   57 - 64  2015.06  [Refereed]

     View Summary

    Core-shell structured mesoporous silica nanoparticles (MSNs) with different pore characteristics in the cores and shells have been prepared by the regrowth method. Adding a silica source to a dispersion of presynthesized silica-surfactant composite nanoparticles with two-dimensional hexagonal mesostructures results in regrowth in preference to generation of new particles. Core-shell MSNs with bimodal porosities are easily obtained by adding a pore-expanding agent, 1,3,5-trimethylbenzene, in either the core or shell formation step. Detailed characterization of the core-shell MSNs reveals that the shells consist of disordered arrangements of relatively large or small pores and that the pore sizes in the cores change when the shells formed. Core-shell MSNs will be useful for controlling the release rates of the encapsulated guest molecules and for protecting internal pores from being plugged by other species. (C) 2015 Elsevier Inc. All rights reserved.

    DOI

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    19
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  • Si Substrate as a SiO2 Source for the Preparation of Mesoporous SiO2-TiO2 Thin Films

    Shintaro Hara, Hirokatsu Miyata, Masahiko Takahashi, Atsushi Shimojima, Kazuyuki Kuroda

    CHEMISTRY LETTERS   44 ( 3 ) 372 - 374  2015.03  [Refereed]

     View Summary

    A Si substrate has been proved to be used as a SiO2 source for the preparation of mesoporous silica-titania thin films with cylindrical mesochannels. Exposing mesostructured titania-surfactant thin films to aqueous NH3 vapor reinforces the pore walls with uniformly distributed silicate species, which retain the mesostructure after calcination.

    DOI

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    1
    Citation
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  • Ring assembly of silica nanospheres mediated by amphiphilic block copolymers with oxyethylene moieties

    Shujun Zhou, Yukari Oda, Atsushi Shimojima, Tatsuya Okubo, Sadahito Aoshima, Ayae Sugawara-Narutaki

    POLYMER JOURNAL   47 ( 2 ) 128 - 135  2015.02  [Refereed]

     View Summary

    Silica nanospheres (SNSs) of ca. 15 nm in diameter assemble into nanoring structures with the aid of amphiphilic block copolymers containing the oxyethylene side chains poly[(2-ethoxyethyl vinyl ether)-block-(2-methoxyethyl vinyl ether)] [poly(EOVE-b-MOVE)]. Cryo-transmission electron microscope observation confirms that the ring assembly of SNSs occurs in the liquid phase. The SNSs favorably assemble into ring-like nanostructures in the presence of 1-2 wt% EOVE100-b-MOVE310 at pH similar to 7.8 and 45 degrees C. Irregular aggregates of SNSs form at 60 degrees C, most likely because of the hydrophobic collapse of the thermoresponsive block copolymer. A series of poly(EOVE-b-MOVE) with varying block lengths successfully induce the ring assembly of SNSs, whereas a random copolymer fails, indicating that the polymer's molecular structure critically affects the assembly mode of SNSs. Interestingly, SNSs of a larger size (ca. 30 nm) assemble one-dimensionally into chain-like nanostructures in the presence of EOVE100-b-MOVE310.

    DOI

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    8
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  • Dendritic Silica Nanoparticles Synthesized by a Block Copolymer-Directed Seed-Regrowth Approach

    Junzheng Wang, Ayae Sugawara-Narutaki, Atsushi Shimojima, Minoru Osada, Renzhi Ma, Tatsuya Okubo

    LANGMUIR   31 ( 5 ) 1610 - 1614  2015.02  [Refereed]

     View Summary

    A facile seed regrowth method is presented for the preparation of a new type of colloidal dendritic silica nanoparticles (DSNPs) with unique Konpeito-like morphology and high surface area (similar to 400 m(2) g(-1)). Growth of silica nanoprotrusions on the surfaces of colloidal silica nanoparticles proceeds by hydrolysis and polycondensation of tetraethoxysilane (TEOS) in the presence of a PEO-PPO-PEO-type block copolymer (Pluronic F127) under controlled pH conditions. The polymers adsorbed on the seed surface play a crucial role in the formation of DSNPs. DSNPs with controllable size (28-85 nm) and narrow size distributions can be obtained by using monodisperse silica nanoparticles with various sizes as seeds. The surface morphology of DSNPs is tunable by changing the concentration of TEOS. Additionally, novel dendritic silica nanochains are prepared using one-dimensionally assembled silica nanoparticles as the seeds.

    DOI

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    8
    Citation
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  • Synthesis of colloidal Janus nanoparticles by asymmetric capping of mesoporous silica with phenylsilsesquioxane

    Hiroto Ujiie, Atsushi Shimojima, Kazuyuki Kuroda

    CHEMICAL COMMUNICATIONS   51 ( 15 ) 3211 - 3214  2015  [Refereed]

     View Summary

    Colloidal mesoporous silica nanoparticles asymmetrically capped with non-porous phenylsilsesquioxane have been prepared by adding phenyltriethoxysilane to an aqueous dispersion of mesostructured silica-surfactant composite nanoparticles. The integration of colloidal stability, mesoporosity and the Janus structure is quite promising for materials design applicable in various fields, including catalysis, biomedicine and coatings.

    DOI

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    25
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  • Regular assembly of cage siloxanes by hydrogen bonding of dimethylsilanol groups

    Naoto Sato, Yoshiyuki Kuroda, Takuya Abe, Hiroaki Wada, Atsushi Shimojima, Kazuyuki Kuroda

    CHEMICAL COMMUNICATIONS   51 ( 55 ) 11034 - 11037  2015  [Refereed]

     View Summary

    A new class of ordered silica-based materials has been prepared by hydrogen bond-directed assembly of cage siloxanes modified with dimethylsilanol groups, providing a soft-chemical approach to crystalline silica materials with molecularly designed architectures.

    DOI

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    30
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  • Molecularly Designed Nanoparticles by Dispersion of Self-Assembled Organosiloxane-Based Mesophases

    Shigeru Sakamoto, Yasuhiro Tamura, Hideo Hata, Yasuhiro Sakamoto, Atsushi Shimojima, Kazuyuki Kuroda

    ANGEWANDTE CHEMIE-INTERNATIONAL EDITION   53 ( 35 ) 9173 - 9177  2014.08  [Refereed]

     View Summary

    The design of siloxane-based nanoparticles is important for many applications. Here we show a novel approach to form core-shell silica nanoparticles of a few nanometers in size through the principle of "dispersion of ordered mesostructures into single nanocomponents". Self-assembled siloxane-organic hybrids derived from amphiphilic alkyl-oligosiloxanes were postsynthetically dispersed in organic solvent to yield uniform nanoparticles consisting of dense lipophilic shells and hydrophilic siloxane cores. In situ encapsulation of fluorescent dyes into the nanoparticles demonstrated their ability to function as nanocarriers.

    DOI

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    5
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  • Amino Acid-assisted One-dimensional Assembly of Semiconducting Metal Oxide Nanoparticles in Aqueous Alcohol Media

    Junzheng Wang, Hiroki Yabe, Atsushi Shimojima, Takashi Sekiguchi, Ayae Sugawara-Narutaki, Tatsuya Okubo

    CHEMISTRY LETTERS   43 ( 6 ) 934 - 935  2014.06  [Refereed]

     View Summary

    A facile approach to prepare the nanochains of semiconducting metal oxide (SnO2, CeO2, and TiO2) nanoparticles is presented. The addition of amino acid and alcohol to the corresponding sols adjusts the interparticle interactions, leading to their one-dimensional assembly.

    DOI

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    3
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  • Utilization of Alkoxysilyl Groups for the Creation of Structurally Controlled Siloxane-Based Nanomaterials

    Kazuyuki Kuroda, Atsushi Shimojima, Kazufumi Kawahara, Ryutaro Wakabayashi, Yasuhiro Tamura, Yusuke Asakura, Masaki Kitahara

    CHEMISTRY OF MATERIALS   26 ( 1 ) 211 - 220  2014.01  [Refereed]

     View Summary

    Silica-based materials have found many applications in various fields. Alkoxysilanes have been most widely used as precursors. Fine structural control of silica-based materials has become increasingly important for tuning their properties and for developing new functions. In this perspective, utilization of alkoxysilyl groups has been reviewed from the viewpoint of designing siloxane-based nanomaterials. Alkoxy groups have generally been used only as eliminating groups in the sol-gel processing; however, recent research has shown that they are useful for molecular assembly, for generating pores, for linking nanobuiliding blocks, and for selective synthesis of new oligosiloxane compounds.

    DOI

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    81
    Citation
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  • Azobenzene-siloxane hybrids with lamellar structures from bridge-type alkoxysilyl precursors

    Sufang Guo, Watcharop Chaikittisilp, Tatsuya Okubo, Atsushi Shimojima

    RSC ADVANCES   4 ( 48 ) 25319 - 25325  2014  [Refereed]

     View Summary

    Lamellar azobenzene-siloxane hybrids were prepared by controlled hydrolysis and polycondensation of three types of precursors, where azobenzene is sandwiched by mono-, di- and triethoxysilyl groups using propylene linkers. All precursors underwent reversible and fast trans-cis isomerization upon UV/Vis irradiation in dilute solution. Upon hydrolysis of the triethoxysilylated precursor in a homogeneous solution under acidic conditions, precipitation occurred by self-assembly of hydrolyzed monomers into a lamellar structure. Although di- and mono-ethoxysilylated precursors produced less ordered products under identical conditions, highly ordered lamellar films were obtainable either by evaporation induced self-assembly of the hydrolyzed monomers or by solid-state reactions of precursor films. The degree of trans-cis isomerization of azobenzene moieties in the hybrid films was enhanced by decreasing the cross-linking degree of siloxane networks using precursors with less condensable alkoxy groups.

    DOI

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    13
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  • Synthesis of string-bean-like anisotropic titania nanoparticles with basic amino acids

    Junzheng Wang, John K. Katahara, Akihito Kumamoto, Tetsuya Tohei, Ayae Sugawara-Narutaki, Atsushi Shimojima, Tatsuya Okubo

    RSC ADVANCES   4 ( 18 ) 9233 - 9235  2014  [Refereed]

     View Summary

    An "assembly-aggregation-peptization" approach is reported for the preparation of colloidal dispersions of string-bean-like anisotropic titania nanoparticles using arginine. These titania nanoparticles have a single-crystalline anatase structure and possess high surface area, which is advantageous for potential functional materials.

    DOI

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    6
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  • Facile Synthesis of Hydroxy-Modified MOF-5 for Improving the Adsorption Capacity of Hydrogen by Lithium Doping

    Masaru Kubo, Hayato Hagi, Atsushi Shimojima, Tatsuya Okubo

    CHEMISTRY-AN ASIAN JOURNAL   8 ( 11 ) 2801 - 2806  2013.11  [Refereed]

     View Summary

    A facile synthesis of partially hydroxy-modified MOF-5 and its improved H-2-adsorption capacity by lithium doping are reported. The reaction of Zn(NO3)(2)6H(2)O with a mixture of terephthalic acid (H2BDC) and 2-hydroxyterephthalic acid (H2BDC-OH) in DMF gave hydroxy-modified MOF-5 (MOF-5-OH-x), in which the molar fraction (x) of BDC-OH2- was up to 0.54 of the whole ligand. The MOF-5-OH-x frameworks had high BET surface areas (about 3300m(2)g(-1)), which were comparable to that of MOF-5. We suggest that the MOF-5-OH-x frameworks are formed by the secondary growth of BDC2--rich MOF-5 seed crystals, which are nucleated during the early stage of the reaction. Subsequent Li doping into MOF-5-OH-x results in increased H-2 uptake at 77K and 0.1MPa from 1.23 to 1.39wt.% and an increased isosteric heat of H-2 adsorption from 5.1-4.2kJmol(-1) to 5.5-4.4kJmol(-1).

    DOI

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    12
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  • Effect of Base Molecules on One-dimensional Assembly of Silica Nanospheres Mediated by a Block Copolymer

    Shujun Zhou, Junzheng Wang, Sugawara-Narutaki Ayae, Atsushi Shimojima, Tatsuya Okubo

    CHEMISTRY LETTERS   42 ( 5 ) 481 - 482  2013.05  [Refereed]

     View Summary

    Silica nanospheres (SNSs) synthesized with different base catalysts assemble into one-dimensional (1D) chain-like nanostructures at proper pH levels in the presence of the block copolymer F127. The addition of basic amino acids or the removal of base catalysts by dialysis influences the pH of 1D assembly. The base molecules affect assembly by modifying the electrostatic repulsion among the SNSs; however, they are not indispensable for this 1D assembly phenomenon.

    DOI

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    3
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  • Formation of hierarchically organized zeolites by sequential intergrowth

    Watcharop Chaikittisilp, Yuki Suzuki, Rino R. Mukti, Tatsuya Suzuki, Keisuke Sugita, Keiji Itabashi, Atsushi Shimojima, Tatsuya Okubo

    Angewandte Chemie - International Edition   52 ( 12 ) 3355 - 3359  2013.03  [Refereed]

     View Summary

    Make intergrowth, not war! Hierarchically organized MFI zeolites with micro-, meso-, and macroporosity (see scheme) in one structure were made by sequential intergrowth by using a simple organic structure-directing agent (OSDA) without meso- or macroporogens. The use of an OSDA that imperfectly fits the zeolite framework generated very thin zeolite plates with 90° rotational intergrowth. © 2013 WILEY-VCH Verlag GmbH &amp
    Co. KGaA, Weinheim.

    DOI

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    116
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  • Facile Synthesis of Well-dispersed Hollow Mesoporous Silica Nanoparticles Using Iron Oxide Nanoparticles as Template

    Takaaki Ikuno, Atsuro Nomura, Kenta Iyoki, Ayae Sugawara-Narutaki, Tatsuya Okubo, Atsushi Shimojima

    CHEMISTRY LETTERS   42 ( 3 ) 316 - 317  2013.03  [Refereed]

     View Summary

    A facile approach is demonstrated for the preparation of hollow mesoporous silica nanoparticles with large pore volume and high dispersibility. Core shell nanoparticles consisting of iron oxide (alpha-Fe2O3) core and mesostructured silica surfactant composite shell are treated with hexamethyldisiloxane under acidic conditions to achieve capping of silanol groups and removal of both surfactants and the Fe2O3 cores in a single step.

    DOI

  • Hierarchical porous silica via solid-phase hydrolysis/polycondensation of cubic siloxane-based molecular units

    Kenta Iyoki, Ayae Sugawara-Narutaki, Atsushi Shimojima, Tatsuya Okubo

    Journal of Materials Chemistry A   1 ( 3 ) 671 - 676  2013.01  [Refereed]

     View Summary

    Hierarchical micro-mesoporous silica has been synthesized by solid-phase conversion of molecular crystals of an alkoxy derivative of a cubic siloxane unit (Si&lt
    inf&gt
    8&lt
    /inf&gt
    O&lt
    inf&gt
    12&lt
    /inf&gt
    ) as a molecular building unit. Seven methoxy groups and one adamantoxy group are introduced in a cage by the reaction of octa(hydridosilsesquioxane) (H&lt
    inf&gt
    8&lt
    /inf&gt
    Si&lt
    inf&gt
    8&lt
    /inf&gt
    O&lt
    inf&gt
    12&lt
    /inf&gt
    ) with the corresponding alcohols, which are then eliminated in a step-by-step manner. First, the methoxy groups are hydrolyzed by simply dispersing the precursor powder in an acidic aqueous solution. The formation of Si-O-Si linkages between the cages while retaining the bulky adamantoxy groups is confirmed by solid-state NMR. At this stage, broad mesopores (ca. 2 to 7 nm) are formed, as confirmed by nitrogen adsorption-desorption. The adamantoxy groups are then removed by calcination to generate relatively narrow micropores (∼1 nm in diameter). Various control experiments performed suggest that the stepwise solid-phase reaction of bifunctional building blocks is crucial to the formation of such micro-mesoporous silica, providing a new pathway to nanoporous materials with controlled architectures. © 2013 The Royal Society of Chemistry.

    DOI

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  • A new synthesis of well-dispersed, core-shell Ag@SiO2 mesoporous nanoparticles using amino acids and sugars

    Philippe Saint-Cricq, Junzheng Wang, Ayae Sugawara-Narutaki, Atsushi Shimojima, Tatsuya Okubo

    JOURNAL OF MATERIALS CHEMISTRY B   1 ( 19 ) 2451 - 2454  2013  [Refereed]

     View Summary

    Mesoporous silica-coated silver nanoparticles (Ag@MSN) were prepared by a two step synthesis in an environment friendly way. Arginine and glucose were used as a catalyst for the formation of silica and as a reducing agent for silver ions, respectively, in the presence of a cationic surfactant. Ag@MSNs having single Ag nanoparticles as cores were obtained with good selectivity. They showed excellent dispersibility in ethanol, forming a uniform coating on a glass substrate. Their antibacterial activity against E. coli was demonstrated.

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  • Synthesis of ordered photoresponsive azobenzene-siloxane hybrids by self-assembly

    Sufang Guo, Ayae Sugawara-Narutaki, Tatsuya Okubo, Atsushi Shimojima

    JOURNAL OF MATERIALS CHEMISTRY C   1 ( 42 ) 6989 - 6995  2013  [Refereed]

     View Summary

    In this study, photoresponsive azobenzene-siloxane hybrids with lamellar structures were prepared by self-assembly using two types of alkoxysilane precursors, 4-[3-(triethoxysilyl) propoxy] azobenzene (P1) and 4-[3( diethoxymethylsilyl) propoxy] azobenzene (P2). The films H1 and H2 were prepared by spin-coating hydrolyzed solutions of P1 and P2, respectively, on a glass substrate followed by heating to induce polycondensation. X-ray diffraction patterns revealed that H1 and H2 have lamellar structures with different d-spacings (3.20 nm and 2.37 nm, respectively), suggesting that the arrangements of the azobenzene moieties are different. These samples show slight but reversible changes in the d-spacings under photo-irradiation. Under UV irradiation, H1 shows a slight decrease in d-spacing, while H2 shows a slight increase. Such changes were caused by trans-cis isomerization of a part of the azobenzene moieties in the films, as confirmed by UV-vis absorption spectroscopy. These processes were reversible, with the d-spacings recovering their original values under visible light irradiation. Furthermore, P1 and P2 were co-hydrolyzed and polycondensed with tetraethoxysilane to give lamellar films (H1' and H2') showing a higher degree of trans-cis photoisomerization of the azobenzene moieties. Both H1' and H2' show increase in the d-spacings after soaking in various organic solvents. Possible structural models have been proposed to explain these photoresponsive properties of the azobenzene-siloxane nanohybrids, which will find potential applications as smart sensors and adsorbents in future.

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  • Diol-Linked Microporous Networks of Cubic Siloxane Cages

    Yuko Wada, Kenta Iyoki, Ayae Sugawara-Narutaki, Tatsuya Okubo, Atsushi Shimojima

    CHEMISTRY-A EUROPEAN JOURNAL   19 ( 5 ) 1700 - 1705  2013.01  [Refereed]

     View Summary

    A new class of inorganicorganic hybrid porous materials has been synthesized by a reaction between octa(hydridosilsesquioxane) (H8Si8O12), which has a double-four-ring (D4R) structure, and various diols, such as 1,3-propanediol (PD), 1,4-cyclohexanediol (CHD), and 1,3-adamantanediol (AD). Solid-state 29Si magic-angle-spinning NMR spectroscopic analysis confirmed that most of the corner Si-H groups reacted with diols to form Si-O-C bonds with retention of the D4R cage. Nitrogen adsorptiondesorption studies showed that the products are microporous solids with high BET surface areas (up to approximate to 580 m2g-1 for CHD- and AD-linked products). If n-alkanediols are used as linkers, the surface area becomes smaller as the number of carbon atoms is increased. The thermal and hydrolytic stability of the products strongly depend on the type of diol linkers. The highest stabilities are found for the AD-linked products, which are thermally stable up to around 400 degrees C and remain intact even after being soaked in water for 1 day. In contrast, the PD-linked product is easily hydrolyzed in water to give microporous silica. These results offer a new route toward a series of silica-based porous materials with unique structures and properties.

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  • Synthesis of monodisperse organosilica nanoparticles with hollow interiors and porous shells using silica nanospheres as templates

    Natsume Koike, Takaaki Ikuno, Tatsuya Okubo, Atsushi Shimojima

    CHEMICAL COMMUNICATIONS   49 ( 44 ) 4998 - 5000  2013  [Refereed]

     View Summary

    A versatile method for the formation of monodisperse, bridged silsesquioxane nanoparticles with hollow interiors and porous shells has been developed using silica nanospheres as templates. Tunable size and shell thickness, as well as high surface areas and large pore volumes of the hollow particles, allow for practical application of these nanoparticles in many fields.

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  • Biphasic synthesis of colloidal mesoporous silica nanoparticles using primary amine catalysts

    Junzheng Wang, Ayae Sugawara-Narutaki, Atsushi Shimojima, Tatsuya Okubo

    JOURNAL OF COLLOID AND INTERFACE SCIENCE   385   41 - 47  2012.11  [Refereed]

     View Summary

    A new type of colloidal mesoporous silica nanoparticles (MSNs) is synthesized in liquid-liquid biphasic systems consisting of tetraethoxysilane (TEOS) and water in the presence of primary amines and cationic surfactants (cetyltrimethylammonium chloride, CTAC) under controlled pH conditions (pH 11.1-11.5). The obtained MSNs are characterized by scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), X-ray diffraction (XRD), and nitrogen adsorption-desorption. The results show that the colloidal MSNs with an average diameter in the range of 28-54 nm and a size polydispersity below ca. 15% have been obtained. Importantly, each MSN is composed of a number of tiny primary silica nanoparticles (PSNPs) forming 3D connected pore structure. The pore size of the MSNs can be tuned from 2.5 to 3.0 nm by changing the pH of catalyst stock solution, and larger pore sizes (3.1-4.5 nm) can be achieved by using pore swelling agent. The Brunauer-Emmett-Teller (BET) surface areas and total pore volumes vary from 550 to 750 m(2) g(-1) and from 1.2 to 1.7 cm(3) g(-1), respectively. Compared with conventional MCM-41-type MSNs, our new MSNs show outstanding colloidal and hydrothermal stabilities. They are colloidally stable at room temperature over 1 year, and their mesostructure was retained even after hydrothermal treatment at 120 degrees C for 24 h. Finally, based on the analysis of the morphology and structure of MSNs, a formation scheme based on the cooperative self-assembly of PSNPs and surfactant molecules is proposed. (c) 2012 Elsevier Inc. All rights reserved.

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  • OSDA-free synthesis of MTW-type zeolite from sodium aluminosilicate gels with zeolite beta seeds

    Yoshihiro Kamimura, Kenta Iyoki, Shanmugam Palani Elangovan, Keiji Itabashi, Atsushi Shimojima, Tatsuya Okubo

    MICROPOROUS AND MESOPOROUS MATERIALS   163   282 - 290  2012.11  [Refereed]

     View Summary

    Seed-assisted methods have provided a new route for the organic structure-directing agent (OSDA)-free synthesis of industrially valuable zeolites. In the present study, we have reported the discovery of the OSDA-free synthesis of ZSM-12 (MTW-type zeolite) by adding calcined zeolite beta seed crystals to the OSDA-free Na-aluminosilicate gel. Various parameters in this synthesis have been comprehensively investigated. Characterization by XRD, FE-SEM, ICP-AES, and Al-27 MAS NMR showed that the obtained MTW products without impurity (SiO2/Al2O3 = 31.8-46.4) possessed high crystallinity and a well-defined rod-like morphology. Adsorption-desorption isotherm of water and NH3-TPD profiles of MTW product showed enough adsorption capacity for water and ammonia molecules, respectively. Moreover, considering the crystallization behavior of seeded and non-seeded Na-aluminosilicate gels, the following key factors were found for inducing the crystallization of MTW by zeolite beta seeds under the hydrothermal condition: the structural similarity between seeds and target zeolite, and the initial gel compositions that provide specific aluminosilicate precursors for the crystallization of MTW prior to the spontaneous nucleation of other zeolite. This methodology provides a promising approach toward designed syntheses of valuable zeolites under environmentally benign conditions. (C) 2012 Elsevier Inc. All rights reserved.

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  • A surfactant-based, regularly arrayed nanostructure gel matrix for migration of small molecules

    Masaru Kato, Yusuke Suwanai, Atsushi Shimojima, Tomofumi Santa

    ELECTROPHORESIS   33 ( 22 ) 3339 - 3342  2012.11  [Refereed]

     View Summary

    The preparation of nanometer-scale pores, or nanopores, has become easy because of the progress in nanotechnology. Surfactants are promising materials for the preparation of nanostructures containing nanopores, because surfactants form many different phase structures, including cubic, micellar, and lamellar structures. We prepared a gel matrix with a cubic structure from a commercially available surfactant, polyoxyethylene(50) lauryl ether (C12EO50, Adekatol LA-50). This gel matrix had regularly arrayed nanopores between the packed spherical micelles. We used the gel to separate biomolecules by means of slab gel electrophoresis. The gel was applicable to migration of amino acids and peptides; however, larger molecules, such as proteins and single-walled carbon nanotubes, did not migrate through the gel. We concluded that the pore size was too small for the penetration of large molecules, and that only small molecules could penetrate the gel matrix. The migration mechanism of small molecules was similar to that observed in conventional gel electrophoresis. We concluded that the gel matrix prepared from surfactant is a promising matrix for migration and purification of small molecules. We also expect that the gel can be used as a nanoscale filter to trap large molecules, allowing only small molecules to pass.

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  • One-Dimensional Assembly of Silica Nanospheres: Effects of Nonionic Block Copolymers

    Shujun Zhou, Takeshi Sakamoto, Junzheng Wang, Ayae Sugawara-Narutaki, Atsushi Shimojima, Tatsuya Okubo

    LANGMUIR   28 ( 37 ) 13181 - 13188  2012.09  [Refereed]

     View Summary

    The effects of polymers on the one-dimensional assembly of silica nanospheres (SNSs) in the liquid phase are systematically investigated using nonionic poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) (abbreviated as PEO-PPO-PEO) triblock copolymers with varying hydrophilic-lipophilic balance (HLB) values. Scanning electron microscopy is employed for morphological observations of the polymer-mediated assemblies of SNSs on the basis of which the optimal pH for ID assembly (pH(1D)) is determined. To clarify the polymers' effects on the ID assembly of SNSs, the relationships between pHID and polymers' HLB values, the numbers of hydrophilic EO and hydrophobic PO units, and the relative ratio of N-PO/N-EO are examined. Zeta potential measurements are conducted to investigate the electrostatic repulsion among the SNSs in the presence of block copolymers. It is found that the relative hydrophilicity of the block copolymers greatly affects the balance of interactions in the ID assembly of SNSs. Block copolymers with large HLB values promote the ID assembly of SNSs under near-neutral pH conditions, whereas the block copolymers with small HLB values promote ID assembly under basic pH conditions. Therefore, the ID assembly of SNSs is achieved over an extensive pH range (7.5-9.5) through the employment of block copolymers of different hydrophilic and hydrophobic block lengths.

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  • Antibacterial Activity of Silver-Loaded "Green Zeolites"

    Philippe Saint-Cricq, Yoshihiro Kamimura, Keiji Itabashi, Ayae Sugawara-Narutaki, Atsushi Shimojima, Tatsuya Okubo

    EUROPEAN JOURNAL OF INORGANIC CHEMISTRY   ( 21 ) 3398 - 3402  2012.07  [Refereed]

     View Summary

    Green Zeolites were prepared, without the use of organic structure-directing agents (OSDAs), by the seed-assisted method and were loaded with silver by a simple ion-exchange procedure. The silver-loaded zeolites were characterized by XRD, transmission electron microscopy and inductively coupled plasma atomic emission spectroscopy, which reveals that the ion-exchange procedure does not affect the structure of the zeolites and the presence of silver cations inside the aluminosilicate matrix. Two types of zeolites presenting different pore arrangements were studied: the beta-type with three-dimensionally interconnected pores and the MTW-type with one-dimensionally interconnected pores. Their activity against E. coli was studied and compared with a commercial zeolite. The influence of the arrangement of the pore channels and the amount of silver loaded were studied. Comparison with the commercial product shows that a smaller amount of silver inside the zeolite is necessary to achieve a similar antibacterial performance within one hour.

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  • A Working Hypothesis for Broadening Framework Types of Zeolites in Seed-Assisted Synthesis without Organic Structure-Directing Agent

    Keiji Itabashi, Yoshihiro Kamimura, Kenta Iyoki, Atsushi Shimojima, Tatsuya Okubo

    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY   134 ( 28 ) 11542 - 11549  2012.07  [Refereed]

     View Summary

    Recent research has demonstrated a new synthesis route to useful zeolites such as beta, RUB-13, and ZSM-12 via seed-assisted, organic structure-directing agent (OSDA)-free synthesis, although it had been believed that these zeolites could be essentially synthesized with OSDAs. These zeolites are obtained by adding seeds to the gels that otherwise yield other zeolites; however, the underlying crystallization mechanism has not been fully understood yet. Without any strategy, it is unavoidable to employ a trial-and-error procedure for broadening zeolite types by using this synthesis method. In this study, the effect of zeolite seeds with different framework structures is investigated to understand the crystallization mechanism of zeolites obtained by the seed-assisted, OSDA-free synthesis method. It has been found that the key factor in the successful synthesis of zeolites in the absence of OSDA is the common composite building unit contained both in the seeds and in the zeolite obtained from the gel after heating without seeds. A new working hypothesis for broadening zeolite types by the seed-assisted synthesis without OSDA is proposed on the basis of the findings of the common composite building units in zeolites. This hypothesis enables us to design the synthesis condition of target zeolites. The validity of the hypothesis is experimentally tested and verified by synthesizing several zeolites including ECR-18 in K-aluminosilicate system.

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  • Effect of Lithium Doping into MIL-53(Al) through Thermal Decomposition of Anion Species on Hydrogen Adsorption

    Masaru Kubo, Atsushi Shimojima, Tatsuya Okubo

    JOURNAL OF PHYSICAL CHEMISTRY C   116 ( 18 ) 10260 - 10265  2012.05  [Refereed]

     View Summary

    Lithium-doped MIL-53(Al) (Li-MIL-53(Al)) is prepared by impregnating MIL-53(Al) with an ethanol solution of LiNO3, followed by heat treatment in vacuum. The nitrate anion is thermally decomposed and removed in the form of NO and N2O at 573 K. This temperature is much lower than the decomposition temperature of bulk LiNO3, which can be attributed to the smaller size of LiNO3 in the pores as well as to the high charge density of aluminum in the MIL-53(Al) skeleton. The doped amount can be varied by changing the concentration of the LiNO3 solution. The lithium doping enhances the hydrogen uptake from 1.66 to 1.84 wt % at 77 K and 1 atm when the doped amount is Li/Al = 0.036. This enhancement suggests that one lithium cation can adsorb two hydrogen molecules. However, the isosteric heat of hydrogen adsorption is not enhanced, possibly due to the interaction of the doped lithium cations with carboxyl groups, as suggested by C-13 CP/MAS NMR Electron-withdrawing oxygen atoms of the carboxyl group should weaken the affinity of the doped lithium cation to hydrogen molecules. Thus, the lithium cations only act as the additional adsorption sites with an affinity to hydrogen molecules similar to that of the internal surface of MIL-53(Al). Similarly, other alkaline/alkaline earth metal cations, such as Na2+, Me2+, and Ca2+, can also be doped into MIL-53(Al), resulting in the increase in the hydrogen uptakes to 1.76, 1.76, and 1.69 wt % for Na+, Mg2+, and Ca2+, respectively.

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  • Chain-like nanostructures from anisotropic self-assembly of semiconducting metal oxide nanoparticles with a block copolymer

    Junzheng Wang, Suminto Winardi, Ayae Sugawara-Narutaki, Akihito Kumamoto, Tetsuya Tohei, Atsushi Shimojima, Tatsuya Okubo

    CHEMICAL COMMUNICATIONS   48 ( 90 ) 11115 - 11117  2012  [Refereed]

     View Summary

    A facile method is reported for the preparation of chain-like nanostructures by anisotropic self-assembly of TiO2 and SnO2 nanoparticles with the aid of a block copolymer in an aqueous medium. Well-defined crystallographic orientations between neighbouring nanoparticles are observed in TiO2 nanochains, which is important for tailoring the grain boundaries and thus enhancing charge transport.

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  • Effect of organic groups on hydrogen adsorption properties of periodic mesoporous organosilicas

    Masaru Kubo, Keisuke Ishiyama, Atsushi Shimojima, Tatsuya Okubo

    MICROPOROUS AND MESOPOROUS MATERIALS   147 ( 1 ) 194 - 199  2012.01  [Refereed]

     View Summary

    We investigate the hydrogen adsorption properties of periodic mesoporous organosilicas (PMOs) and focus, in particular, on how these properties are affected by diverse organic groups embedded in the walls. PMOs with pi electrons on the pore surface adsorb more hydrogen molecules per unit area and have a higher isosteric heat of hydrogen adsorption (Q(st)). The number of adsorbed hydrogen molecules per unit area correlates well with the density of organic groups on the pore surface. We attribute the high Q(st) to the high polarizability of organic groups with pi electrons, which enhances the dispersion force. The molecular order of organic groups affects the adsorption-site affinity to hydrogen molecules as well as the location of adsorption sites. For phenylene-bridged PMOs with crystal-like pore walls, Q(st) decreases rapidly with increasing hydrogen loading, which indicates two types of adsorption sites with different affinities to hydrogen molecules: one is an exposed CH bond and the other is a siloxane bond. However, Q(st), for phenylene-bridged PMOs with amorphous pore walls exhibits a moderate slope, which might be caused by the random order of organic groups; this results in several types of adsorption sites with various affinities. (C) 2011 Elsevier Inc. All rights reserved.

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  • Porous Siloxane-Organic Hybrid with Ultrahigh Surface Area through Simultaneous Polymerization-Destruction of Functionalized Cubic Siloxane Cages

    Watcharop Chaikittisilp, Masaru Kubo, Takahiko Moteki, Ayae Sugawara-Narutaki, Atsushi Shimojima, Tatsuya Okubo

    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY   133 ( 35 ) 13832 - 13835  2011.09  [Refereed]

     View Summary

    A novel hierarchically porous, hyper-cross-linked siloxane organic hybrid (PSN-5) has been synthesized by Friedel-Crafts self-condensation of benzyl chloride-terminated double-four-ring cubic siloxane cages as a singular molecular precursor. Simultaneous polymerization of the organic functional groups and destruction of the siloxane cages during synthesis yielded PSN-5, which has an ultrahigh BET surface area (similar to 2500 m(2) g(-1)) and large pore volume (similar to 3.3 cm(3) g(-1)) that to our knowledge are the highest values reported for siloxane-based materials. PSN-5 also shows a high H(2) uptake of 1.25 wt % at 77 K and 760 Torr.

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  • Role of Acidic Pretreatment of Layered Silicate RUB-15 in Its Topotactic Conversion into Pure Silica Sodalite

    Takahiko Moteki, Watcharop Chaikittisilp, Yasuhiro Sakamoto, Atsushi Shimojima, Tatsuya Okubo

    CHEMISTRY OF MATERIALS   23 ( 15 ) 3564 - 3570  2011.08  [Refereed]

     View Summary

    Topotactic conversion of crystalline layered silicates into zeolite provides an opportunity to create new chemical compositions, framework types, and macroscopic morphologies that are difficult to achieve by conventional hydrothermal synthesis. We have recently reported the successful synthesis of pure silica sodalite with a unique sheet-like morphology from layered silicate RUB-1S occluding interlayer TMA(+) cations. Pretreatment of RUB-15 with acetic acid was found to be crucial for topotactic dehydration-condensation between the silicate layers upon heating. In this study, a homologous series of carboxylic acids of varying concentrations is examined for their capability to generate an ordered intermediate state, and important factors for topotactic conversion are determined. Both length of the alkyl chains and concentration of the carboxylic acids strongly affected the crystallinity of the products, and well-crystallized sodalite was obtained using either acetic or propionic acid. Transmission electron microscopy showed that the sodalite with sheet-like morphology has the thickness of several hundred nanometers in which the (110) plane is oriented parallel to the surface. Two key factors elucidated for successful conversion are (i) proton-exchange of interlayer TMA(+) cations to shorten the interlayer distance and to form Si-OH groups and (ii) intercalation of carboxylic acid molecules between the layers to maintain the well-ordered layered structure prior to calcination.

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  • Extension of size of monodisperse silica nanospheres and their well-ordered assembly

    Ryota Watanabe, Toshiyuki Yokoi, Erina Kobayashi, Yuki Otsuka, Atsushi Shimojima, Tatsuya Okubo, Takashi Tatsumi

    JOURNAL OF COLLOID AND INTERFACE SCIENCE   360 ( 1 ) 1 - 7  2011.08  [Refereed]

     View Summary

    A liquid-phase method for preparing uniform-sized silica nanospheres (SNSs) 12 nm in size and their three-dimensionally ordered arrangement upon solvent evaporation have recently been pioneered by us. Here we report the successful control of the sphere sizes in the wide range from 14 to 550 nm by the seed regrowth method. In this method, the dispersion of SNSs 14 nm in size as seeds was prepared in the emulsion system containing Si(OEt)(4) (TEOS), water and arginine under weakly basic conditions (pH 9-10). An appropriate portion of this dispersion is added to the solution containing water, ethanol and arginine, and then TEOS is added. The additional TEOS introduced into the regrowth system contributed only to the resumed growth of the seeds, not to the formation of new silica particles. The size of interparticle pores was finely tuned by changing the size of the spheres. The preparation of three-dimensionally ordered porous carbons by using the colloidal array of silica nanospheres as a template is also reported. (C) 2010 Elsevier Inc. All rights reserved.

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  • Two-Phase Synthesis of Monodisperse Silica Nanospheres with Amines or Ammonia Catalyst and Their Controlled Self-Assembly

    Junzheng Wang, Ayae Sugawara-Narutaki, Masashi Fukao, Toshiyuki Yokoi, Atsushi Shimojima, Tatsuya Okubo

    ACS APPLIED MATERIALS & INTERFACES   3 ( 5 ) 1538 - 1544  2011.05  [Refereed]

     View Summary

    A significant progress has recently been made in the synthesis of monodisperse silica nanoparticles less than 30 nm in diameter by using basic amino acids (e.g., lysine) as a base catalyst for hydrolysis of silicon alkoxide. Alternatively, a more versatile and economical amino acid-free method has been developed to synthesize uniform silica nanospheres (SNSs) with low polydispersity (&lt;12%) in liquid-liquid biphasic systems containing tetraethoxysilane (TEOS), water, and primary amine (or ammonia) under precisely controlled pH conditions (pH 10.8-11.4). The diameter of the SNSs determined from scanning electron microscopy (SEM) can be tuned from similar to 12 to similar to 36 nm by simply changing the initial pH of the aqueous phase in the reaction mixtures. Furthermore, the as-synthesized sol was taken as the starting material for studying the influences of the type of base catalysts on the solvent evaporation-induced three-dimensional (3D) self-assembly of SNSs. X-ray diffraction (XRD) and nitrogen adsorption-desorption are used to characterize the degree of packing of the resulting 3D arrays. The assembled SNSs with large interparticle mesopores with the diameter of ca. 8.1 nm and low packing fraction of ca. 66.1% are observed upon solvent evaporation of as-synthesized sol in the presence of primary amine. This indicates that SNSs are loosely packed, compared with the packing fraction of 74% for a face-centered cubic array of ideal hard spheres. In contrast, with the aid of an organic buffer or lysine as additives, the assembly of SNSs having smaller mesopores (ca. 3.9 nm) and higher packing fraction of 70.5-71.5% are achieved. It is suggested that the chemical additives with the ability to maintain relatively strong repulsive interaction until the final stage of evaporation play a vital role in the fabrication of well-ordered SNSs arrays.

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  • A combined top-down and bottom-up approach to fabricate silica films with bimodal porosity

    Kazuya Ijichi, Ayumu Fukuoka, Atsushi Shimojima, Masakazu Sugiyama, Tatsuya Okubo

    MATERIALS LETTERS   65 ( 5 ) 828 - 831  2011.03  [Refereed]

     View Summary

    We report a method to fabricate silica films with bimodal porosity based on the surfactant-directed self-assembly process followed by post-treatment with reactive ion etching (RIE). By RIE of a surfactant-templated mesoporous silica film with a 3D hexagonal structure, vertically-etched pores with the size of several tens of nanometers and the depth of ca. 60 nm are generated, while the original caged mesopores (ca. 5 nm in size) are still retained in the unetched parts of the film. Pre-treatment of the mesoporous silica film by wet-etching to expose the pores on the surface, followed by sputter deposition of a Pt layer for partial masking, is crucial for the anisotropic etching of the film. Such a combined top-down and bottom up approach offers an opportunity to fabricate silica films with hierarchical pore architectures. (C) 2010 Published by Elsevier B.V.

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  • Synthesis of silicalite-1 using a disiloxane-based structure-directing agent

    Hirotaka Ishii, Keiji Itabashi, Tatsuya Okubo, Atsushi Shimojima

    MICROPOROUS AND MESOPOROUS MATERIALS   139 ( 1-3 ) 158 - 163  2011.03  [Refereed]

     View Summary

    A cationic organosiloxane compound where two tetrapropylammonium (TPA) cations are bridged by a tetramethyldisiloxane unit (MSi-TPA) has been used as a structure-directing agent (SDA) for the synthesis of a pure silica MFI-type zeolite, silicalite-1, with a unique microstructure and particle morphology. The hydrothermal treatment of the mixture of tetraethoxysilane as a silica source, MSi-TPAOH, and water yields solid products that are identified as silicalite-1 by X-ray diffraction and solid-state (29)Si MAS NMR. Solid-state (29)Si and (13)C CP/MAS NMR and elemental analyses confirm that MSi-TPA is covalently incorporated in the MFI framework via cleavage of the disiloxane linkage. Compared with conventional silicalite-1 prepared with TPA cations, the amount of defect sites is higher, which can be attributed to the attachment of the organosilyl groups to the framework by Si-O-Si bonds. Scanning electron microscopic (SEM) observation shows spherical particle morphology that is quite different from the typical coffin-shaped crystals obtained with TPA. Importantly, MFI is not formed when triethoxysilyl- and diethoxysilyl-TPAs, instead of MSi-TPA, are used as SDAs under similar conditions, suggesting that the possible number of Si-O-Si linkages formed by SDAs greatly affects the crystallization process of MFI zeolite. (c) 2010 Elsevier Inc. All rights reserved.

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  • Synthesis of mesostructured silica from monoalkyl-substituted double five-ring units

    Atsushi Shimojima, Hideki Kuge, Kazuyuki Kuroda

    JOURNAL OF SOL-GEL SCIENCE AND TECHNOLOGY   57 ( 3 ) 263 - 268  2011.03  [Refereed]

     View Summary

    A mesostructured silica-based material was synthesized by self-assembly of a novel amphiphilic molecule consisting of a well-defined siloxane head with a double five-ring (D5R) structure and a hydrophobic alkyl tail. A precursor functionalized with ethoxy groups, C(22)H(45)Si(10)O(15)(OEt)(9) (1), was hydrolyzed under an acidic condition with the retention of the D5R units, leading to the formation of two-dimensional (2D) hexagonal phase by evaporation-induced self-assembly of amphiphilic hydrolyzed molecules. Solid-state (29)Si MAS NMR analysis of the resulting hybrid solid confirmed that the D5R units were cross-linked to form siloxane networks. Calcination of this hybrid solid gave mesoporous silica with high BET surface area (740 m(2) g(-1)). These results expand the design possibility of silica-based materials at both molecular- and meso-scales, leading to the bottom up synthesis of hierarchically ordered materials.

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  • Hierarchically porous ZSM-5 synthesized by nonionic- and cationic-templating routes and their catalytic activity in liquid-phase esterification

    Mukti R.R, Kamimura Y, Chaikittisilp W, Hirahara H, Shimojima A, Ogura M, Cheralathan K.K, Elangovan S.P, Itabashi K, Okubo T

    ITB Journal of Science   43 A ( 1 ) 59 - 72  2011.02  [Refereed]

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  • Investigation on specific adsorption of hydrogen on lithium-doped mesoporous silica

    Masaru Kubo, Hiroshi Ushiyama, Atsushi Shimojima, Tatsuya Okubo

    ADSORPTION-JOURNAL OF THE INTERNATIONAL ADSORPTION SOCIETY   17 ( 1 ) 211 - 218  2011.02  [Refereed]

     View Summary

    This paper reports the synthesis, structure, and hydrogen adsorption property of Li-doped mesoporous silica (MPS) with a 2D hexagonal structure. The Li-doping is achieved by impregnation of the cylindrical mesopores with an ethanol solution of lithium chloride followed by heat treatment. Detailed characterization by solid-state NMR, TG-MS, and FT-IR suggests that, during the heat treatment, lithium chloride reacts with surface ethoxy groups (a parts per thousand Si-OEt) to form a parts per thousand SiOLi groups, while ethyl chloride is released into the gas phase. The hydrogen uptake at 77 K and 1 atm increases from 0.68 wt% for the undoped MPS to 0.81 wt% for Li-doped MPS (Li-MPS). The isosteric heat of adsorption is 4.8 kJ mol(-1), which is consistent with the quantum chemistry calculation result (5.12 kJ mol(-1)). The specific hydrogen adsorption on Li-MPS would be explained by the frontier orbital interaction between HOMO of hydrogen molecules and LUMO of a parts per thousand SiOLi. These findings provide an important insight into the development of hydrogen storage materials with specific adsorption sites.

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  • Synthesis of Ordered Porous Graphitic-C3N4 and Regularly Arranged Ta3N5 Nanoparticles by Using Self-Assembled Silica Nanospheres as a Primary Template

    Yuki Fukasawa, Kazuhiro Takanabe, Atsushi Shimojima, Markus Antonietti, Kazunari Domen, Tatsuya Okubo

    CHEMISTRY-AN ASIAN JOURNAL   6 ( 1 ) 103 - 109  2011.01  [Refereed]

     View Summary

    Uniform-sized silica nanospheres (SNSs) assembled into close-packed structures were used as a primary template for ordered porous graphitic carbon nitride (g-C3N4), which was subsequently used as a hard template to generate regularly arranged Ta3N5 nanoparticles of well-controlled size. Inverse opal g-C3N4 structures with the uniform pore size of 20-80 nm were synthesized by polymerization of cyanamide and subsequent dissolution of the SNSs with an aqueous HF solution. Back-filling of the C3N4 pores with tantalum precursors, followed by nitridation in an NH3 flow gave regularly arranged, crystalline Ta3N5 nanoparticles that are connected with each other. The surface areas of the Ta3N5 samples were as high as 60 m(2) g(-1), and their particle size was tunable from 20 to 80 nm, which reflects the pore size of g-C3N4. Polycrystalline hollow nanoparticles of Ta3N5 were also obtained by infiltration of a reduced amount of the tantalum source into the g-C3N4 template. An improved photocatalytic activity for H-2 evolution on the assembly of the Ta3N5 nanoparticles under visible-light irradiation was attained as compared with that on a conventional Ta3N5 bulk material with low surface area.

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    101
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  • Crystallization Behavior of Zeolite Beta in OSDA-Free, Seed-Assisted Synthesis

    Yoshihiro Kamimura, Shinya Tanahashi, Keiji Itabashi, Ayae Sugawara, Toru Wakihara, Atsushi Shimojima, Tatsuya Okubo

    JOURNAL OF PHYSICAL CHEMISTRY C   115 ( 3 ) 744 - 750  2011.01  [Refereed]

     View Summary

    Recent reports on the organic structure-directing agent (OSDA)-free synthesis of some zeolites with the aid of seed crystals have opened a new way to the robust and environmentally friendly production of industrially valuable zeolites. However, the details on the crystallization behavior as well as the role of the seeds have not been fully clarified yet. In this study, the crystallization process of zeolite beta in the OSDA-free, seed-embedded Na+-aluminosilicate gel system, which never yields beta in the absence of the seeds, is investigated in detail. The XRD and TEM studies of the solid aluminosilicate products in the course of the hydrothermal treatment suggest that the crystallization of zeolite beta proceeds on the outer surface of amorphous aluminosilicates. The Raman spectroscopy, solid-state Al-27 and Na-23 MAS NMR and high-energy XRD analyses of seeded and nonseeded amorphous materials just before crystallization reveal that the beta seeds induce no major changes in their structures, implying that the nucleation of beta does not occur directly from the amorphous phase. The intermediate addition of the seeds after prehydrothermal treatment of a nonseeded gel enhances the crystallization rate and results in the increased number of beta crystals with smaller size. It is elucidated that, during the hydrothermal treatment, the beta seeds embedded in the gel provide crystal growth surface after they are exposed and/or released to the liquid phase by partial dissolution of the amorphous aluminosilicates. These findings provide a promising approach to the designed syntheses of valuable zeolites in the completely OSDA-free system.

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  • Preparation of Anisotropic Silica Nanoparticles via Controlled Assembly of Presynthesized Spherical Seeds

    Junzheng Wang, Ayae Sugawara, Atsushi Shimojima, Tatsuya Okubo

    LANGMUIR   26 ( 23 ) 18491 - 18498  2010.12  [Refereed]

     View Summary

    A facile solution process for the preparation of anisotropic silica nanoparticles (ASNPs) is presented. ASNPs are prepared via controlled self-assembly of spherical silica seeds (22 nm) in alcohol-water mixed media, followed by their in situ fixation and overgrowth with tetraethoxysilane (TEOS). Ethanol and L-arginine (Arg) are used to modify the dielectric constant and ionic strength of the reaction media, by which seed assembly is controlled through the adjustment of electrostatic in:eraction. Ethanol and Arg also serve as a cosolvent and a catalyst for hydrolysis and condensation of TEOS, respectively, which enables us to produce ASNPs in a simple one-pot process. In addition to ASNPs with wormlike structures, different kinds of NPs (bimodal spherical NPs, monodisperse spherical NPs, and spherical aggregates) have also been obtained by changing the concentrations of ethanol and Arg. The length, thickness, or both of ASNPs are controlled systematically by varying the concentrations of Arg, seed NPs, and TEOS. Other alcoholic cosolvents, such as methanol, 1-propanol, 2-propanol, and t-butanol, are also effective to give ASNPs when the dielectric constant of the alcohol-water mixed media is properly adjusted, showing the versatility of the present method.

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    21
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  • Effect of organic additives on the formation of alkylsiloxane mesophases

    Atsushi Shimojima, Mikako Sakurai, Kazuyuki Kuroda, Tatsuya Okubo

    JOURNAL OF COLLOID AND INTERFACE SCIENCE   350 ( 1 ) 155 - 160  2010.10  [Refereed]

     View Summary

    The effects of organic additives (1,3,5-trialkylbenzenes, n-alkanes, and n-alkyl alcohols) on the formation of hybrid siloxane organic mesophases from alkoxylated precursors (C(n)H(2n+1)Si(OSi(OMe)(3))(3), 1Cn, n = 6, 10, and 16) have been investigated. These precursors become amphiphilic upon hydrolysis of the alkoxy groups, thus forming two-dimensional (2D) hexagonal phase (n = 6 and 10) and lamellar phase (n = 16) by evaporation-induced self-assembly followed by polycondensation. The addition of 1,3,5-trialkylbenzenes or n-alkanes to the 1C10 system leads to swollen 2D hexagonal phases, thereby achieving pore-size expansion of the calcined samples from 2.0 nm up to 3.8 nm in diameter. The effect of these organic additives depends largely on the alkyl chain length of 1Cn; the 2D hexagonal structure (n = 6) undergoes structural disordering, while the lamellar structure (n = 16) remains unchanged. On the other hand, the addition of alkyl alcohols to the 1C10 system causes a drastic change in the mesostructure from 2D hexagonal to lamellar, which can be attributed to possible interactions between alcohol molecules and silanol groups of hydrolyzed 1C10. These results provide a facile approach to the fine structural control of nanohybrid materials assembled from single siloxane-based molecules. (C) 2010 Elsevier Inc. All rights reserved.

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  • Microporous Hybrid Polymer with a Certain Crystallinity Built from Functionalized Cubic Siloxane Cages as a Singular Building Unit

    Watcharop Chaikittisilp, Ayae Sugawara, Atsushi Shimojima, Tatsuya Okubo

    CHEMISTRY OF MATERIALS   22 ( 17 ) 4841 - 4843  2010.09  [Refereed]

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  • Synthesis of MTW-type Zeolites in the Absence of Organic Structure-directing Agent

    Kenta Iyoki, Yoshihiro Kamimura, Keiji Itabashi, Atsushi Shimojima, Tatsuya Okubo

    CHEMISTRY LETTERS   39 ( 7 ) 730 - 731  2010.07  [Refereed]

     View Summary

    The synthesis of MTW-type aluminosilicate zeolites in the absence of organic structure-directing agents (OSDAs) was successfully attained by the addition of calcined ZSM-12 seeds to (Li, Na)-aluminosilicate gels. In this system, Li cation plays a crucial role in the growth of the MTW crystals.

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  • Formation of Reactive Microporous Networks from Alkoxyvinylsilylated Siloxane Cages

    Yoshiaki Hagiwara, Atsushi Shimojima, Kazuyuki Kuroda

    BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN   83 ( 4 ) 424 - 430  2010.04  [Refereed]

     View Summary

    A bifunctional siloxane cage, where double four-membered ring (D4R) silicate was capped with alkoxyvinylsilyl groups, was synthesized as a novel building block for the formation of inorganic-organic microporous solids in order to show its usefulness for synthesizing silica-based nanomaterials with unique structures and properties. The nanobuilding blocks were connected to each other either by hydrolysis and condensation of alkoxysilyl groups to form Si-O-Si linkages or by hydrosilylation of vinyl groups with hydrogen-terminated D4R (H8Si8O12), which was used as a linking agent, to form Si-CH2CH2-Si linkages. Xerogel obtained by hydrosilylation showed a significant increase in the surface area upon removal of alkoxy groups by post treatment. The molecular design of bifunctionally-silylated D4R units provides a new approach to the formation of microporous networks with uniform distribution of reactive groups that allow post-modification.

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    17
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  • Synthesis and characterization of aluminium containing CIT-1 and their structure-property relationship to hydrocarbon trap performance

    Thomas Mathew, S. P. Elangovan, Toshiyuki Yokoi, Takashi Tatsumi, Masaru Ogura, Yoshihiro Kubota, Atsushi Shimojima, Tatsuya Okubo

    MICROPOROUS AND MESOPOROUS MATERIALS   129 ( 1-2 ) 126 - 135  2010.04  [Refereed]

     View Summary

    The present work focuses on the synthesis of Al-CIT-1 by various post-modification procedures of B-CIT-1 and their structure-property relation to hydrocarbon trap performance. Al substitution in B-CIT-1 was carried out by three different post-modification procedures, viz., direct exchange (Al-CIT-1_DEX), insertion (Al-CIT-1_INS), and impregnation (Al-CIT-1_IMP), and characterized in detail by various physico-chemical techniques such as XRD, N(2) adsorption, SEM, NH(3)-TPD, XPS, and solid state (27)Al and (29)Si MAS NMR. The Al-CIT-1 samples were tested for their adsorption-desorption characteristics of toluene, and 2,2,4-trimethylpentane (2,2,4-TMP) to understand the Al distribution in CIT-1 as well as the efficacy of these materials as hydrocarbon traps. The Al distribution in Al-CIT-1 plays a critical role in the adsorption-desorption characteristics of toluene and 2,2,4-TMP. Al-CIT-1 with high relative proportion of framework Al and less extraframework Al (Al-CIT-1_DEX) showed maximum toluene and 2,2,4-TMP adsorption capacity. The presence of finely distributed extraframework Al(2)O(3) species in Al-CIT-1_INS modify the pores and causes a slow release of toluene during desorption. Al-CIT-1_IMP with less Al content and acidity showed the lowest toluene desorption temperature. Large amount of surface Al species hinder a relatively bulky molecule 2,2,4-TMP to access the available active sites of tetrahedral Al and the associated Bronsted sites in the zeolite, and as a result, Al-CIT-1_INS showed hardly any adsorption towards 2,2,4-TMP. Thus, by varying the post-modification method and treatment condition, it is possible to tune the performance of Al incorporated CIT-1 as a useful material for hydrocarbon trap. (C) 2009 Elsevier Inc. All rights reserved.

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    13
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  • Tri(quaternary ammonium) Surfactant with a Benzene Core as a Novel Template for Synthesis of Ordered Porous Silica

    Yuki Fukasawa, Ayae Sugawara, Hirotomo Hirahara, Atsushi Shimojima, Tatsuya Okubo

    CHEMISTRY LETTERS   39 ( 3 ) 236 - 237  2010.03  [Refereed]

     View Summary

    A novel rigid-core surfactant where three trimethylammonium heads are attached to a benzene core via flexible hydrocarbon chains was examined as a template for synthesizing ordered porous silica. A well-ordered 2D hexagonal silica structure with relatively small pores was generated owing to the formation of the stable mesophase where the surfactants were stacked to form cylindrical assemblies.

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  • Direct Hydrothermal Synthesis of Hierarchically Porous Siliceous Zeolite by Using Alkoxysilylated Nonionic Surfactant

    Rino R. Mukti, Hirotomo Hirahara, Ayae Sugawara, Atsushi Shimojima, Tatsuya Okubo

    LANGMUIR   26 ( 4 ) 2731 - 2735  2010.02  [Refereed]

     View Summary

    A hierarchically porous siliceous MFI zeolite (silicalite-1) with narrow mesoporosity has been hydrothermally synthesized by using trialkoxysilylated alkyl poly(oxyethylene ether) as mesopore-directing agent, A mesostructured silica-surfactant composite was formed at the early stage of the reaction, and zeolite crystallization proceeded during Subsequent hydrothermal treatment. The scanning electron microscopy (SEM) and transmission electron microscopy, (TEM) observations of the crystallized products showed that micro-and mesopores were hierarchically assembled ill unique particle morphology with rugged surfaces. Solid-state (29)Si and (13)C NMR revealed that the covalent bonds between the zeolite framework and mesopore-directing agent were present in the products before calcination. The use of nonsilylated alkyl poly(oxyethylene ether) or a silylated alkytrimethyl-ammonium-type cationic surfactant for the synthesis of silicalite-1 resulted in a mixture of mesoporous silica and zeolite as the final product, which Suggests that the covalent interaction and nonelectrostatic charge matching interaction favor the formation of hierarchically mesoporous siliceous zeolite. This alkoxysilylated nonionic surfactant can also be extended to synthesize aluminosilicate MFI zeolite (ZSM-5).

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  • 種結晶により誘起される有機構造規定剤を用いない*BEA 型ゼオライトの結晶化機構

    棚橋 紳也, 上村 佳大, 板橋 慶治, 下嶋 敦, 大久保 達也

    化学工学会 研究発表講演要旨集   2010   638 - 638  2010

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  • 種結晶添加・有機構造規定剤無添加による種々のゼオライトの合成

    上村 佳大, 板橋 慶治, 下嶋 敦, 大久保 達也

    化学工学会 研究発表講演要旨集   2010   637 - 637  2010

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  • メソポーラス有機シリカにおける有機基の水素吸着特性

    石山 啓介, 久保 優, 下嶋 敦, 大久保 達也

    化学工学会 研究発表講演要旨集   2010   228 - 228  2010

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  • 有機構造規定剤を用いないMTW型ゼオライトの合成と特性

    伊與木 健太, 上村 佳大, 板橋 慶治, 下嶋 敦, 大久保 達也

    化学工学会 研究発表講演要旨集   2010   230 - 230  2010

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  • Mesoporous Silica Nanoparticles with Remarkable Stability and Dispersibility for Antireflective Coatings

    Yasuto Hoshikawa, Hiroki Yabe, Atsuro Nomura, Takeyuki Yamaki, Atsushi Shimojima, Tatsuya Okubo

    CHEMISTRY OF MATERIALS   22 ( 1 ) 12 - 14  2010.01  [Refereed]

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  • Hybrid Porous Materials with High Surface Area Derived from Bromophenylethenyl-Functionalized Cubic Siloxane-Based Building Units

    Watcharop Chaikittisilp, Ayae Sugawara, Atsushi Shimojima, Tatsuya Okubo

    CHEMISTRY-A EUROPEAN JOURNAL   16 ( 20 ) 6006 - 6014  2010  [Refereed]

     View Summary

    Sonogashira cross-coupling of bromophenylethenyl-terminated cubic, double four-ring, siloxane cages with di-/triethynyl compounds results in microporous poly(ethynylene aryleneethenylene silsesquioxane) networks, simply termed as polyorganosiloxane networks (PSNs). In comparison with porous organic polymers reported previously, these PSNs show relatively high surface area and comparable thermal stability. Their apparent BET specific surface areas vary in the range of 850-1040 m(2) g(-1) depending on the length and the connectable sites of the ethynyl compounds. Analyses of pore size distribution revealed bimodal micropores with relatively narrow distribution. The degree of cross-linking affects the degree of cleavage of the siloxane bonds, and this suggests that partial cleavage of the siloxane cages is mainly a result of cage distortion. Hydrogen adsorption was performed to evaluate potential of the PSNs as hydrogen storage media. Uptakes of up to 1.19 wt% at 77 K and 760 Torr and initial isosteric heats of adsorption as high as 8.0 kJ mol(-1) were observed. These materials have been obtained by a combination of structural, synthetic organic, and materials chemistry, which can exploited to synthesize porous hybrid materials with specifically designed structures and functions.

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  • Critical Factors in the Seed-Assisted Synthesis of Zeolite Beta and "Green Beta" from OSDA-Free Na+-Aluminosilicate Gels

    Yoshihiro Kamimura, Watcharop Chaikittisilp, Keiji Itabashi, Atsushi Shimojima, Tatsuya Okubo

    CHEMISTRY-AN ASIAN JOURNAL   5 ( 10 ) 2182 - 2191  2010  [Refereed]

     View Summary

    Organic structure-directing agent (OSDA)-free synthesis of zeolite beta is a subject of both scientific and industrial interest. Herein, we report a comprehensive investigation into the effects of various parameters on the seed-assisted crystallization of zeolite beta in the absence of OSDA. The crystallization behavior of "OSDA-free beta" is strongly governed by the chemical composition of the starting Na+-aluminosilicate gel as well as by the Si/Al ratios of the calcined beta seed crystals, which are prepared using tetraethylammonium hydroxide (TEAOH). Furthermore, OSDA-free beta seed crystals can be used to form zeolite beta, termed "green beta". XRD, scanning electron microscopy, inductively coupled plasma atomic emission spectroscopy, and Al-27 magic angle spinning NMR analyses showed that the OSDA-free beta and green beta were of high purity and crystallinity. The nitrogen adsorption-desorption of OSDA-free beta and green beta revealed higher surface areas and larger volumes in the micropore region than those of the beta seeds synthesized with OSDA after calcination. These results provide a robust and reliable process for the environmentally friendly production of high-quality zeolite beta in a completely OSDA-free Na+-aluminosilicate system.

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    158
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  • Alignment Control of Self-Assembled Organosiloxane Films Derived from Alkyloligosiloxane Amphiphiles

    Jenny Du, Madoka Fukushima, Shigeru Sakamoto, Mikako Sakurai, Takashi Suzuki, Atsushi Shimojima, Hirokatsu Miyata, Cathleen M. Crudden, Kazuyuki Kuroda

    LANGMUIR   25 ( 23 ) 13614 - 13618  2009.12  [Refereed]

     View Summary

    Transparent and continuous organosiloxane Films with macroscopically oriented mesostructures were prepared by dip-coating a substrate, on which a rubbing-treated polyimide film is formed, with hydrolyzed solutions of oligosiloxane precursors (C(n)H(2n+1)Si(OSi(OMe(3))(3)), The structure of the films depends on the alkyl chain length of the precursors such that films with two-dimensional (2D) hexagonal and lamellar structures are obtained when n = 10 and 16, respectively. In the 2D hexagonal film, the cylindrical organic moieties are aligned perpendicular to the rubbing direction in the plane of the film over the whole film thickness. Oil the other hand, the lamellar film changes its orientation with increased distance from the substrate surface. While the orientation of the lamellae at the surface of the film is parallel to the film-air interface, they are perpendicularly aligned in the vicinity of the substrate with the layer normal parallel to the rubbing direction. The observed unique orientation of the mesostructures is attributed to the anisotropic hydrophobic interactions between the alkyl chains of the hydrolyzed oligosiloxane molecules and the polymer chains of the polyimide layer oriented by the rubbing treatment.

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  • One-Dimensional Assembly of Silica Nanospheres Mediated by Block Copolymer in Liquid Phase

    Masashi Fukao, Ayae Sugawara, Atsushi Shimojima, Wei Fan, Manickam Adhimoolam Arunagirinathan, Michael Tsapatsis, Tatsuya Okubo

    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY   131 ( 45 ) 16344 - +  2009.11  [Refereed]

     View Summary

    Colloidal silica spheres and their assembly processes are encountered in nature and numerous technological applications. We report here a novel and facile method to prepare highly anisotropic one-dimensional (1D) arrays of silica nanospheres (SNSs) in the liquid phase. Uniform-sized SNSs ca. 15 nm in size assemble into a 1 D chain-like structure in the presence of a commercially available block copolymer. The 1 D assembly in the liquid phase is evident from Cryo-TEM observations and time-dependent turbidity measurement of the suspension. The mode of the assembly has been systematically controlled by the concentration of the block copolymer, pH of the suspension, and the concentration of a salt added to the system. These resutls suggest the importance of the balance between electrostatic repulsion and block copolymer-mediated attractive interaction that are operative between particles in the formation of 1D array.

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    41
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  • Structural Control of Phenylene-bridged Periodic Mesoporous Organosilica with Organic Additives

    Ayumu Fukuoka, Yasuto Hoshikawa, Atsushi Shimojima, Tatsuya Okubo

    CHEMISTRY LETTERS   38 ( 11 ) 1026 - 1027  2009.11  [Refereed]

     View Summary

    The effects of organic additives on the structure of phenylene-bridged periodic mesoporous organosilica have been investigated. The mesostructure and pore size were controlled by adding organic additives, such as 1,3,5-triisopropylbenzene and benzyl alcohol under acidic or basic conditions.

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    3
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  • Control of Silica-Alkyltrimethylammonium Bromide Mesophases with 1,3,5-Trialkylbenzenes under Acidic Conditions

    Ayumu Fukuoka, Izumi Kikkawa, Yukichi Sasaki, Atsushi Shimojima, Tatsuya Okubo

    LANGMUIR   25 ( 18 ) 10992 - 10997  2009.09  [Refereed]

     View Summary

    This article reports the structural variation of SBA-type mesostructured silica formed from a mixture of tetraethyl orthosilicate (TEOS), alkyltrimethylammonium bromides, and 1,3,5-trialkylbenzenes under acidic conditions. Swollen 2D hexagonal mesophases were formed from the silica source and hexadecyltrimethylammonium bromide (C16TAB) with varying amounts of trimethylbenzene (TMB) and triethylbenzene (TEB), whereas drastic Structural changes were observed with triisopropylbenzene (TIPB). Characterization by X-ray diffraction and transmission electron microscopy observation revealed that the mesophase wits changed from hexagonal p6mm to cubic Pm (3) over barn to cubic Fm (3) over barm with increasing amounts of TIPB. Thus, the addition of TIPB leads to the preferential formation of spherical micelles rather than the swelling of rodlike micelles. When tetradecyltrimethylammonium bomide (C14TAB) wits used, similar structural changes were triggered by smaller amounts of TIPB; however, almost no structural change wits observed when octadecyltrimethylammonium bromide (C18TAB) was used. These findings provide a better understanding of the roles of 1,3,5-trialkylbenzenes in the structural control of silica-alkyltrimethylammonium mesophases.

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  • Preparation of silica/carbon composites with uniform and well-ordered mesopores by esterification method

    Toshiyuki Yokoi, Shizuka Seo, Naotaka Chino, Atsushi Shimojima, Tatsuya Okubo

    MICROPOROUS AND MESOPOROUS MATERIALS   124 ( 1-3 ) 123 - 130  2009.08  [Refereed]

     View Summary

    Silica/carbon composites with uniform and well-ordered mesopores were prepared by the newly developed esterification method, which is based on esterification of furfuryl alcohol (FA) with silanol groups on the pore walls of SBA-15-type mesoporous silica via Si-O-C linkages, followed by carbonization of the modified surface at elevated temperatures. As a reference, a typical impregnation method was employed for preparing the silica/carbon composites with various carbon contents. Thus obtained two kinds of composites were comparatively characterized by XRD, nitrogen-, water- and benzene-adsorptions, high-resolution SEM and so on. The water adsorption measurements revealed that the composites prepared by the esterification method were more hydrophobic than those by the impregnation method. The benzene adsorption measurements revealed that the total amount adsorbed on the composite prepared by the esterification method was greater than that prepared by the impregnation method. These results suggest that the carbon introduced by the esterification method would be more homogeneously distributed on the wall of the mesopores. (C) 2009 Elsevier Inc. All rights reserved.

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    18
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  • Mechanism of Formation of Uniform-Sized Silica Nanospheres Catalyzed by Basic Amino Acids

    Toshiyuki Yokoi, Junji Wakabayashi, Yuki Otsuka, Wei Fan, Marie Iwama, Ryota Watanabe, Kenji Aramaki, Atsushi Shimojima, Takashi Tatsumi, Tatsuya Okubo

    CHEMISTRY OF MATERIALS   21 ( 15 ) 3719 - 3729  2009.08  [Refereed]

     View Summary

    A liquid-phase method for preparing uniform-sized silica nanospheres (SNSs) 12 nm in size and their three-dimensionally ordered arrangement upon solvent evaporation have recently been pioneered by us. The SNSs are formed in the emulsion system containing Si(OEt)(4) (TEOS), water, and basic amino acids under weakly basic conditions (pH 9-10). Here, We report the formation mechanism of the SNSs the reasons for the uniform size and the ordered arrangement are described in detail. The formation process is monitored by FE-SEM, SAXS, and liquid-state NMR. The FE-SEM observations reveal that silica nanoparticles ca. 4 rim in size arc formed in the water phase at the early stage (similar to 0.5 h) of the reaction. The SAXS measurements suggest that the number density of the particles remains unchanged when they are gradually grown. Liquid-state (1)H NMR analyses suggest that TEOS are slowly hydrolyzed at the oil-water interface to continuously supply silicate species into the water phase. The silicate species are immediately consumed for the growth of the parent particles without forming new particles. The size of the SNSs can be tuned from 8 to 35 nm by varying the synthesis conditions and/or the amount of TEOS. The zeta potential and pH of the dispersion of SNSs throughout the solvent evaporation process are almost constant approximately at -40 mV and 9-10, respectively, the SNSs have been well-dispersed until the final stage of the evaporation process. The critical roles of basic amino acids in the formation and regular arrangement of SNSs are discussed based oil the experimental results.

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  • Formation of Two- and Three-Dimensional Hybrid Mesostructures from Branched Siloxane Molecules

    Shigeru Sakamoto, Atsushi Shimojima, Keiichi Miyasaka, Juanfang Ruan, Osamu Terasaki, Kazuyuki Kuroda

    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY   131 ( 28 ) 9634 - 9635  2009.07  [Refereed]

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  • 界面制御による球状シリカナノ粒子の一次元配列

    深尾 将士, 菅原 彩絵, 下嶋 敦, 大久保 達也

    化学工学会 研究発表講演要旨集   2009   369 - 369  2009

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  • 非イオン性界面活性剤のシリル誘導体を用いたMFI型ゼオライトのメソ多孔体化

    下嶋 敦, Mukti Rino, 平原 悠智, 菅原 彩絵, 大久保 達也

    化学工学会 研究発表講演要旨集   2009   322 - 322  2009

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  • メソポーラスシリカナノ粒子の有機修飾による分散安定性の制御

    干川 康人, 下嶋 敦, 野村 篤朗, 大久保 達也

    化学工学会 研究発表講演要旨集   2009   295 - 295  2009

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  • リチウム修飾したシリカ多孔体表面での特異的水素吸着挙動の解明

    久保 優, 牛山 浩, 下嶋 敦, 大久保 達也

    化学工学会 研究発表講演要旨集   2009   511 - 511  2009

    DOI CiNii

  • Silica Sodalite without Occluded Organic Matters by Topotactic Conversion of Lamellar Precursor

    Takahiko Moteki, Watcharop Chaikittisilp, Atsushi Shimojima, Tatsuya Okubo

    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY   130 ( 47 ) 15780 - +  2008.11  [Refereed]

     View Summary

    Novel pure silica sodalite with hollow sodalite-cages has been synthesized for the first time by topotactic conversion of layered silicate (RUB-15) precursor. This success has been achieved by stepwise syntheses from silicate monomers, through clusters and layers, to microporous crystals. The pretreatment of layered silicate with small carboxylic acids before conversion is a crucial step. The obtained sodalite possesses accessible micropores, as confirmed by physical adsorption of hydrogen molecules. This plate-like silica sodalite would be very promising as fillers in mixed-matrix membranes for hydrogen separation

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    92
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  • Self-Assembly of Amphiphilic Alkyloligosiloxanes within Cylindrically and Spherically Confined Spaces

    Mikako Sakurai, Atsushi Shimojima, Yusuke Yamauchi, Kazuyuki Kuroda

    LANGMUIR   24 ( 22 ) 13121 - 13126  2008.11  [Refereed]

     View Summary

    The self-assembly of amphiphilic alkyloligosiloxane molecules within cylindrically and spherically confined spaces has been investigated. Hydrolyzed solutions of the precursors consisting of an alkylsiloxane core and three branching trimethoxysilyl groups (CnH2n+1Si(OSi(OMe)(3))(3), n = 10 and 16) were impregnated into the cylindrical pores of porous anodic alumina membranes (PAAMs), leading to the formation of rod- and tubelike hybrids. A two-dimensional (2D) hexagonal mesostructure with a circular orientation and a lamellar mesostructure with a multitubular orientation were confirmed for n = 10 and 16, respectively. The pore diameters of PAAMs ranging from 30 to 400 nm did not significantly affect the mesostructures of the hybrids. The self-assembly in the spherical droplets was also performed by spray-drying of the hydrolyzed solutions. At high temperature, vesicular lamellar mesostructures were formed, independent of the alkyl chain length of the precursors (n = 10 or 16). Spherical hybrids with a core-shell structure (a 2D hexagonal core and a lamellar shell) were also prepared by lowering the drying temperature in the case of it = 10. These are the first findings on the confined assembly of single siloxane-based amphiphiles that will lead to the fabrication of novel hierarchically ordered hybrid materials having Si-C covalent bonds at the interfaces.

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    11
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  • Controlled synthesis of nanostructured silica-based materials from designed alkoxysilanes

    Atsushi Shimojima, Kazuyuki Kuroda

    JOURNAL OF SOL-GEL SCIENCE AND TECHNOLOGY   46 ( 3 ) 307 - 311  2008.06  [Refereed]

     View Summary

    Recent progress in the synthesis of nanostructured silica-based materials through the self-assembly process using well-designed alkoxysilane precursors is presented. Alkoxysilanes with covalently attached hydrophobic organic tails become amphiphilic when hydrolyzed to form silanol groups, leading to the formation of various mesostructures upon evaporation of solvents. The precursors having large oligosiloxane heads are particularly important because of their ability to form cylindrical assemblies, providing a direct pathway to ordered porous silica by removal of the organic groups. Our recent research includes (i) templated-synthesis of hierarchically ordered structures and (ii) design of molecules having chemically cleavable bonds to generate pores without calcination.

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    16
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  • Microwave-induced synthesis of highly dispersed gold nanoparticles within the pore channels of mesoporous silica

    Jinlou Gu, Wei Fan, Atsushi Shimojima, Tatsuya Okubo

    JOURNAL OF SOLID STATE CHEMISTRY   181 ( 4 ) 957 - 963  2008.04  [Refereed]

     View Summary

    Highly dispersed gold nanoparticles have been incorporated into the pore channels of SBA-15 mesoporous silica through a newly developed strategy assisted by microwave radiation (MR). The sizes of gold are effectively controlled attributed to the rapid and homogeneous nucleation, simultaneous propagation and termination of gold precursor by MR. Diol moieties with high dielectric and dielectric loss constants, and hence a high microwave activation, were firstly introduced to the pore channels of SBA-15 by a simple addition reaction between amino group and glycidiol and subsequently served as the reduction centers for gold nanoparticles. Extraction of the entrapped gold from the nanocomposite resulted in milligram quantities of gold nanoparticles with low dispersity. The successful assembly process of diol groups and formation of gold nanoparticles were monitored and tracked by solid-state NMR and UV-vis measurements. Characterization by small angle X-ray diffraction (XRD) and transmission electron microscopy (TEM) indicated that the incorporation of gold nanoparticles would not breakup the structural integrity and long-range periodicity of SBA-15. The gold nanoparticles had a narrow size distribution with diameters in the size range of 5-10 nm through TEM observation. The average particles size is 7.9nm via calculation by the Scherrer formula and TEM measurements. Nitrogen adsorption and desorption isotherms gave further evidence that the employed method was efficient and gold nanoparticles were successfully incorporated into the pore channels of SBA-15. (c) 2008 Elsevier Inc. All rights reserved.

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    39
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  • Alkoxysilylated-derivatives of double-four-ring silicate as novel building blocks of silica-based materials

    Yoshiaki Hagiwara, Atsushi Shimojima, Kazuyuki Kuroda

    CHEMISTRY OF MATERIALS   20 ( 3 ) 1147 - 1153  2008.02  [Refereed]

     View Summary

    Novel oligomeric alkoxysilanes consisting of double-four-ring (D4R) units functionalized with mono-, di-, and trialkoxysilyl groups (designated as 1, 2, and 3, respectively) were designed as nanobuilding blocks for synthesizing silica-based nanomaterials. Hydrolysis and polycondensation of these oligomers were performed under acidic conditions. The gelation occurred much faster than monomeric, dimeric, and cubic octameric alkoxysilanes, which should depend on both molecular size and siloxane structures. Structural analyses of the xerogels derived from 1-3 strongly suggested that the D4R units are at least partly retained in their frameworks. The number of alkoxy groups had a large effect on their porosities: the xerogel derived from 2 was a microporous solid with the BET surface area of 600 m(2) g(-1), whereas 1- and 3-derived xerogels had very low BET surface areas. Furthermore, mesostructured silica films were successfully synthesized froth 2 and 3 by using amphiphilic triblock copolymer surfactant as a structure-directing agent. Such an approach will lead to the construction of molecularly designed siloxane networks.

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    69
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  • Design of nanohybrid and nanoporous materials through self-assembly of organosilane molecules

    Atsushi Shimojima

    JOURNAL OF THE CERAMIC SOCIETY OF JAPAN   116 ( 1350 ) 278 - 283  2008.02  [Refereed]

     View Summary

    Structural control of silica-based materials prepared by sol-gel chemistry is important from both fundamental and practical viewpoints. This paper reviews our work on the synthesis of ordered siloxane-based nanomaterials by self-assembly of organosilane-based precursors. Lamellar siloxane-organic hybrids with various structures, macroscopic morphologies, and properties have been prepared from long-chain alkyltrialkoxysilanes or organoalkoxysilane-tetraalkoxysilane mixtures by self-assembly during hydrolysis and polycondensation. Furthermore, the molecular design of novel alkylsiloxane precursors having a large oligosiloxane head led to the formation of hybrid mesostructures consisting of cylindrical assemblies that gave ordered microporous or mesoporous silica by calcination. These results open a new self-assembly route to the design of ordered nanoporous materials as well as nanohybrid materials without the use of any templates or structure-directing agents.

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    8
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  • 2種の構造規定剤の混合によるシリカライト-1の粒子形態制御

    鈴木 優貴, Chaikittisilp Watcharop, 板橋 慶治, 下嶋 敦, 大久保 達也

    化学工学会 研究発表講演要旨集   2008   766 - 766  2008

    DOI CiNii

  • ブロックコポリマーを用いた球状シリカナノ粒子の1次元配列制御

    深尾 将士, 下嶋 敦, 大久保 達也

    化学工学会 研究発表講演要旨集   2008   626 - 626  2008

    DOI CiNii

  • エチレングリコールを用いて合成されたメソポーラスシリカナノ粒子の生成機構

    野村 篤朗, 顧 金楼, 下嶋 敦, 大久保 達也

    化学工学会 研究発表講演要旨集   2008   594 - 594  2008

    DOI CiNii

  • Stable silanetriols that contain tert-alkoxy groups: Versatile precursors of siloxane-based nanomaterials

    Jumpei Suzuki, Atsushi Shimojima, Yasuhiro Fujimoto, Kazuyuki Kuroda

    CHEMISTRY-A EUROPEAN JOURNAL   14 ( 3 ) 973 - 980  2008  [Refereed]

     View Summary

    Novel tert-alkoxysilanetriols (ROSi(OH)(3), R=adamantyl and 3-ethyl-3-pentyl) have been prepared from the corresponding tert-alkoxytrichlorosilanes and successfully used as molecular building blocks to produce ordered siloxane-based nanomaterials. Controlled hydrolysis of the alkoxytrichlorosilanes led to the formation of crystalline powders of alkoxysilanetriols that were stable under ambient conditions. Solid-state polycondensation of the alkoxysilanetriols occurred upon heating, which led to the formation of ordered silica-organic nanocomposites with laminated morphologies. On the other hand, silylation of the tert-alkoxysilanetriols with chlorotrimethoxysilane enabled us to synthesize well-defined oligomeric alkoxysilanes (ROSi[OSi(OMe)(3)](3)). Hydrolysis and polycondensation of these oligomers followed by acid treatment gave microporous silica with narrow pore size distributions. Thus, tert-alkoxy groups serve not only as protecting groups of siloxane species to regulate hydrolysis and polycondensation, but also as templates to generate micropores thereby providing unique synthetic pathways for the design of ordered silica-based materials.

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    28
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  • Oligomeric alkoxysilanes with cagelike hybrids as cores: Designed precursors of nanohybrid materials

    Hideki Kuge, Yoshiaki Hagiwara, Atsushi Shimojima, Kazuyuki Kuroda

    CHEMISTRY-AN ASIAN JOURNAL   3 ( 3 ) 600 - 606  2008  [Refereed]

     View Summary

    Well-defined alkoxysilane oligomers containing a cagelike carbosiloxane core were synthesized and used as novel building blocks for the formation of siloxane-based hybrid networks. These oligomers were synthesized from the cagelike trimer derived from bis(triethoxysilyl)methane by silylation with mono-, di-, and triethoxy-chlorosilanes ((EtO)(n)Me3-n,SiCl, n=1, 2, and 3). Hybrid xerogels were prepared by hydrolysis and polycondensation of these oligomers under acidic conditions. The structures of the products varied depending on the number of alkoxy groups (n). When n=2 and 3, microporous xerogels (BET surface areas of 820 and 510 m(2) g(-1), respectively) were obtained, whereas a nonporous xerogel was obtained when n=1. Si-29 NMR spectroscopic analysis suggested that partial rearrangement of the siloxane networks, which accompanied the cleavage of the Si-O-Si linkages, occurred during the polycondensation processes. By using an amphiphilic triblock copolymer surfactant as a structure-directing agent, hybrid thin films with a 2D hexagonal mesostructure were obtained when n = 2 and 3. These results provide important insight into the rational synthesis of molecularly designed hybrid materials by sol-gel chemistry.

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    13
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  • Stepwise silylation of double-four-ring (D4R) silicate into a novel spherical siloxane with a defined architecture

    Kazufumi Kawahara, Yoshiaki Hagiwara, Atsushi Shimojima, Kazuyuki Kuroda

    JOURNAL OF MATERIALS CHEMISTRY   18 ( 27 ) 3193 - 3195  2008  [Refereed]

     View Summary

    Trimethylsilylation of a triethoxysilylated derivative of double-four-ring ( D4R) silicate led to the formation of a novel crystalline spherical siloxane molecule containing a cubic D4R core, which proves that this bottom-up process provides a new pathway to prepare silica nanoparticles with well defined size, structure, morphology, and functionality.

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    15
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  • Self-Assembly of Alkyl-Substituted Cubic Siloxane Cages into Ordered Hybrid Materials

    Atsushi Shimojima, Ryota Goto, Norimasa Atsumi, Kazuyuki Kuroda

    CHEMISTRY-A EUROPEAN JOURNAL   14 ( 28 ) 8500 - 8506  2008  [Refereed]

     View Summary

    Siloxane-organic hybrids with well-ordered mesostructures were synthesized through the self-assembly of novel amphiphilic molecules that consist of cubic siloxane heads and hydrophobic alkyl tails. The monoalkyl precursors functionalized with ethoxy groups (C(n)H(2n+1)Si(8)O(12)(OEt)(7), 1 Cn, n=16, 18, and 20) were hydrolyzed under acidic conditions with the retention of the siloxane cages, leading to the formation of two-dimensional hexagonal phases by evaporation-induced self-assembly processes. Analysis of the solid-state (29)Si MAS NMR spectra of these hybrid mesostructures confirmed that the cubic siloxane units were crosslinked to form siloxane networks. Calcination of these hybrids gave mesoporous silica, the pore diameter of which varied depending on the alkyl-chain length. We also found that the precursors that had two alkyl chains formed lamellar phases, thus confirming that the number of alkyl chains per cage had a strong influence on the mesostructures. These results expand the design possibility of novel nanohybrid and nanoporous materials through the self-assembly of well-defined oligosiloxane-based precursors.

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    58
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  • A hybrid mesoporous material with uniform distribution of carboxy groups assembled from a cubic siloxane-based precursor

    Ryota Goto, Atsushi Shimojima, Hideki Kugea, Kazuyuki Kuroda

    CHEMICAL COMMUNICATIONS   ( 46 ) 6152 - 6154  2008  [Refereed]

     View Summary

    A novel hybrid mesoporous material functionalized with carboxy groups was synthesized by self-assembly of a novel building block consisting of a cubic siloxane unit and a long organic chain with an ester bond and the following hydrolysis of ester bonds, representing a promising approach to designing hybrid structures at both molecular and mesoscopic scales.

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    35
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  • Organic-inorganic mesoporous nanocarriers, integrated with biogenic ligands

    Jinlou Gu, Wei Fan, Atsushi Shimojima, Tatsuya Okubo

    SMALL   3 ( 10 ) 1740 - 1744  2007.10  [Refereed]

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    112
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  • Preparation of mesostructured siloxane-organic hybrid films with ordered macropores by templated self-assembly

    Mikako Sakurai, Atsushi Shimojima, Masaru Heishi, Kazuyuki Kuroda

    LANGMUIR   23 ( 21 ) 10788 - 10792  2007.10  [Refereed]

     View Summary

    Novel hierarchically ordered siloxane-based hybrid films with well-defined macropores and mesostructured pore walls have been prepared by the self-assembly process using oligomeric siloxane precursors bearing alkyl chains (CnH2n+1Si(OSi(OMe)(3))(3)) in the presence of polystyrene opal films as a template. Either a two-dimensional (2D) hexagonal structure or a lamellar structure was formed depending on the alkyl chain length of the precursors (n = 10 and 16, respectively). In both of the films, the mesostructures were oriented along the spherical surface of the template and were retained after removal of the template. Calcination of the 2D hexagonal hybrid produced ordered porous silica with both macro- and microporosities. The lamellar hybrid film exhibited a unique property of accommodating alkyl alcohols with an expansion of the interlayer spacings. These results provide a new concept for designing hierarchical hybrid materials that are potentially applicable as adsorbents, catalysts, sensors, and photonic crystals.

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  • Structure and properties of multilayered siloxane-organic hybrid films prepared using long-chain organotrialkoxysilanes containing C=C double bonds

    Atsushi Shimojima, Chia-Wen Wu, Kazuyuki Kuroda

    JOURNAL OF MATERIALS CHEMISTRY   17 ( 7 ) 658 - 663  2007  [Refereed]

     View Summary

    Oriented multilayered films composed of alternating siloxane layers and organic layers were prepared from mixtures of tetramethoxysilane [Si(OMe)(4)] and unsaturated organotrimethoxysilane [RSi(OMe)(3), where R is CH2=CH(CH2)(8-) or CH2=CH(CH2)(2)CH=CH(CH2)(4)-], and the structures and macroscopic properties of the films were studied. Hydrolysis and partial condensation of the precursors led to the formation of amphiphilic organosiloxane species which self-assemble into lamellar phases. Polymerization of the organic phase occurred by UV irradiation, as evidenced by substantial decreases of the IR absorption bands due to -CH=CH2 or -CH=CH- groups. The hardness of the films was remarkably increased by the irradiation, due to the covalent linking of adjacent siloxane layers by organic polymerization. The films after organic polymerization had a much higher resistance to an alkaline solution, which enabled the patterning of the films on the micrometer length scale. These results provide an important insight into the structure-property relationships of nanostructured hybrid materials prepared by sol-gel chemistry.

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    36
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  • Sol-gel synthesis of a nanostructured hybrid material from an organosiloxane oligomer with a terminal phenyl group

    Atsushi Shimojima, Norimasa Atsumi, Noritaka Umeda, Yasuhiro Fujimoto, Kazuyuki Kuroda

    JOURNAL OF THE CERAMIC SOCIETY OF JAPAN   114 ( 1334 ) 819 - 822  2006.10  [Refereed]

     View Summary

    A novel ordered siloxane-organic hybrid material has been prepared by hydrolysis and polycondensation of a well-defined alkoxysilane precursor consisting of a tetrasiloxane unit and a 4-phenylbutyl group (1). Evaporation-induced self-assembly during hydrolysis and polycondensation of 1 led to the formation of a two-dimensional (2D) hexagonal mesostructure, which was revealed by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Solid-state C-13 CP/MAS NMR and Si-29 MAS NMR confirmed that the product consisted of 4-phenylbutyl groups and siloxane networks, both of which are linked via Si-C bonds. These results will allow us to produce functional hybrid materials by chemical modification of phenyl groups, and also by incorporating other organic groups. Furthermore, calcination of this hybrid to remove organic groups led to the creation of an ordered microporous silica with the Brunaucr-Emmett-Teller (BET) surface area of 570 m(2) g(-1) and the average pore diameter of 1.2 nm.

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    2
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  • Sol-gel synthesis of a nanostructured hybrid material from an organosiloxane oligomer with a terminal phenyl group

    Atsushi Shimojima, Norimasa Atsumi, Noritaka Umeda, Yasuhiro Fujimoto, Kazuyuki Kuroda

    Journal of the Ceramic Society of Japan   114 ( 1334 ) 819 - 822  2006.01  [Refereed]

     View Summary

    A novel ordered siloxane-organic hybrid material has been prepared by hydrolysis and polycondensation of a well-defined alkoxysilane precursor consisting of a tetrasiloxane unit and a 4-phenylbutyl group (1). Evaporation-induced self-assembly during hydrolysis and polycondensation of 1 led to the formation of a two-dimensional (2D) hexagonal mesostructure, which was revealed by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Solid-state13C CP/MAS NMR and29Si MAS NMR confirmed that the product consisted of 4-phenylbutyl groups and siloxane networks, both of which are linked via Si-C bonds. These results will allow us to produce functional hybrid materials by chemical modification of phenyl groups, and also by incorporating other organic groups. Furthermore, calcination of this hybrid to remove organic groups led to the creation of an ordered microporous silica with the Brunauer-Emmett-Teller (BET) surface area of 570 m2g-1and the average pore diameter of 1.2 nm.

    DOI CiNii

    Scopus

    2
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  • Designed synthesis of nanostructured siloxane-organic hybrids from amphiphilic silicon-based precursors

    A Shimojima, K Kuroda

    CHEMICAL RECORD   6 ( 2 ) 53 - 63  2006  [Refereed]

     View Summary

    This paper reports on recent progress in the synthesis of nanostructured siloxane-organic hybrids based on the self-assembly of amphiphilic silicon-based precursors. A variety of ordered hybrid materials have been obtained by molecular design of the precursors. Alkoxysilanes and chlorosilanes with covalently attached hydrophobic organic tails are hydrolyzed to form amphiphilic molecules containing silanol groups, leading to the formation of layered (lamellar) structures. Transparent and oriented thin films of lamellar hybrids were prepared by the reaction in the presence of tetraalkoxysilane. In addition, the design of molecules having alkyl chains and large oligosiloxane heads led to the formation of mesophases consisting of cylindrical assemblies, providing a direct pathway to ordered porous silica. The synthesis, structural features, and formation processes of these hybrid mesostructures are discussed. (C) 2006 The Japan Chemical journal Forum and Wiley Periodicals, Inc.

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    149
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  • Surfactant-free synthesis of lamellar and wormhole-like silica mesostructures by using 1-alkynyltrimethoxysilanes

    Y Fujimoto, A Shimojima, K Kuroda

    JOURNAL OF MATERIALS CHEMISTRY   16 ( 10 ) 986 - 994  2006  [Refereed]

     View Summary

    Silica-based nanomaterials with lamellar and wormhole-like mesostructures were prepared via self-assembly processes using 1-alkynyltrimethoxysilanes (CH3(CH2)(n-3)C CSi(OCH3)(3); 1Cn, n = 10, 16) containing a C-C triple bond adjacent to the silicon atom. Hydrolysis and polycondensation of 1C10 afforded a viscous paste, whereas 1C16 formed a lamellar hybrid consisting of siloxane layers and bilayers of alkynyl groups. Wormhole-like mesostructures were formed by co-hydrolysis and polycondensation of 1Cn and tetramethoxysilane ( TMOS) followed by evaporation of solvents at room temperature for n = 10 and at 50 degrees C for n = 16. Removal of alkynyl groups from the wormhole-like mesostructures either by chemical treatment using fluoride ions or by calcination afforded mesoporous silica with three-dimensional pore-connectivity. This procedure affords one of the synthetic pathways to prepare mesoporous silica without surfactants as templates. The N-2 adsorption data revealed that the chemically treated products had larger pore diameters and pore volumes than those of the calcined products. The pore diameter and the pore wall thickness were controlled by changing the alkynyl chain length and the TMOS/1Cn molar ratio, respectively. Furthermore, transparent thin films of a wormhole-like mesostructure could be prepared from a 1C10-TMOS or 1C10-1C16-TMOS system, although only a lamellar thin film was obtained from a 1C16-TMOS system.

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    15
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  • Self-assembly of designed oligomeric siloxanes with alkyl chains into silica-based hybrid mesostructures

    A Shimojima, Z Liu, T Ohsuna, O Terasaki, K Kuroda

    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY   127 ( 40 ) 14108 - 14116  2005.10  [Refereed]

     View Summary

    A novel self-assembly route to ordered silica-organic hybrids using well-defined siloxane oligomers with alkoxy functionality and covalently attached alkyl chains has been investigated. Various hybrid mesostructures were obtained by hydrolysis and polycondensation without the use of any structure-directing agents, The oligomers 1(Cn), having an alkylsilane core and three branched trimethoxysilyl groups, formed highly ordered lamellar phases when n = 14-18, while those with shorter alkyl chains formed cylindrical assemblies, slightly distorted two-dimensional (2D) hexagonal structures (n = 6-10), and a novel 2D monoclinic structure (n = 12). Furthermore, the mixtures of 1(Cn) with different chain lengths yielded well-ordered 2D hexagonal phases, possibly due to the better packing of the precursors. The hybrids consisting of cylindrical assemblies were converted to ordered porous silica with tunable pore sizes upon calcination to remove organic groups. The liquid-state Si-29 NMR analysis of the hydrolysis and polycondensation processes of l(Cn) revealed a unique intramolecular reaction yielding primarily the oligomer with a tetrasiloxane ring which is a new class of amphiphilic molecule having both self-assembling ability and high cross-linking ability. We also found that the mesostructure (lamellar or 2D hexagonal) was strictly controlled by varying the number of siloxane units per alkyl chain. These results provide a deeper understanding of the present self-assembly process that is strongly governed by the molecular packing of oligosiloxane precursors.

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    107
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  • Interlayer esterification of layered silicic acid-alcohol nanostructured materials, derived from alkoxytrichlorosilane

    Y Fujimoto, A Shimojima, K Kuroda

    LANGMUIR   21 ( 16 ) 7513 - 7517  2005.08  [Refereed]

     View Summary

    Layered silicic acid-organic nanohybrid materials consisting of long-chain alkoxy groups attached to thin silica layers have been prepared via esterification of a layered silicic acid-alcohol nanostructured material derived from hexadecoxytrichlorosilane (C(16)H(33)OSiCl(3)). The esterification reaction was performed by heating the layered composite. The detailed characterization of the product heated at 80 degrees C revealed that the interlayer alcohol molecules partly (similar to 50%) reacted with the interlayer surface silanol groups to form alkoxy groups. Unreacted alcohol molecules were removed by tetrahydrofuran (THF) treatment to form a novel alkoxylated layered silica material. This product retains its structure up to 120 degrees C and has a higher stability in organic solvents if compared with the layered silicic acid-alcohol nanocomposite before esterification, whose structure collapsed over 100 degrees C. Furthermore, various alcohols can be adsorbed into the esterified nanohybrid with the expansion of the interlayer spacing.

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    11
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  • Molecular manipulation of two- and three-dimensional silica nanostructures by alkoxysilylation of a layered silicate octosilicate and subsequent hydrolysis of alkoxy groups

    D Mochizuki, A Shimojima, T Imagawa, K Kuroda

    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY   127 ( 19 ) 7183 - 7191  2005.05  [Refereed]

     View Summary

    A novel methodology for constructing molecularly ordered silica nanostructures with twodimensional (2-D) and three-dimensional (3-D) networks has been developed by using a stepwise process involving silylation of a layered silicate octosilicate with alkoxytrichlorosilanes [ROSiCl3, R = alkyl] and subsequent reaction within the interlayer spaces. Alkoxytrichlorosilanes react almost completely with octosilicate, bridging two closest Si-OH (or -O-) sites on the silicate layers, to form new five-membered rings. The unreacted functional groups, Si-Cl and Si-OR, are readily hydrolyzed by the posttreatment with a water/dimethyl sulfoxide (DMSO) or water/acetone mixture, leading to the formation of two types of silicate structures. The treatment with a water/DMSO mixture produced a unique crystalline 2-D silicate framework with geminal silanol groups, whereas a water/acetone mixture induced hydrolysis and subsequent condensation between adjacent layers to form a new 3-D silicate framework. The 2-D structure is retained by the presence of DMSO molecules within the swelled interlayer spaces and is transformed to a 3-D silicate upon desorption of DMSO. The structural modeling suggests that both of the 3-D silicates contain new cagelike frameworks where solvent molecules are trapped even at high temperature (up to 380 &DEG; C, in the case of acetone). Both 2-D and 3-D silica structures are quite different from known layered silicates and zeolite-like materials, indicating the potential of the present approach for precise design of various silicate structures at the molecular level.

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  • Layered assembly of alkoxy-substituted bis(trichlorosilanes) containing various organic bridges via hydrolysis of Si-Cl groups

    Y Fujimoto, M Heishi, A Shimojima, K Kuroda

    JOURNAL OF MATERIALS CHEMISTRY   15 ( 48 ) 5151 - 5157  2005  [Refereed]

     View Summary

    Monoalkoxy derivatives of bis(trichlorosilanes) containing methylene, ethylene, and phenylene bridges (Cl3Si-R'-SiCl2OC16H33, R' = -CH2-, -C2H4-, -C6H4-) were synthesized and self-assembly of the amphiphilic hydrolyzed species ((HO)(3)Si - R' - Si(OH)(2)OC16H33) was investigated. Hydrolysis of all Si - Cl groups was confirmed by liquid-state Si-29 and C-13 NMR while the alkoxy groups were retained. The self-assembly was induced either by casting the hydrolyzed solutions on glass substrates or by cooling. The structures of the products were characterized by X-ray diffraction (XRD), electron microscopies (TEM and SEM), and solid-state Si-29 and C-13 NMR. The products obtained from methylene- and ethylene-bridged monomers have lamellar structures consisting of bridged polysilsesquioxane layers and all-trans hexadecanol layers, which means that alkoxy groups were cleaved during polycondensation. The large difference in the d values of these hybrids (5.84 nm and 3.40 nm) suggests the variation in the arrangement of hexadecanol molecules within the layers. In contrast, the phenylene-bridged monomer afforded a lamellar solid (d = 55.14 nm) consisting of monomeric species, where both silanol groups and alkoxy groups mostly remain intact. This is attributed to the relatively stronger interaction and hydrogen-bonding networks between hydrolyzed species.

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    (Scopus)
  • Selective formation of siloxane-based hybrid cages with methylene groups in the frameworks

    A Shimojima, K Kuroda

    CHEMICAL COMMUNICATIONS   23 ( 23 ) 2672 - 2673  2004  [Refereed]

     View Summary

    A new class of cage-like oligomers were selectively formed by hydrolysis and polycondensation of a methylene-bridged bistrialkoxysilane precursor in the presence of tetramethylammonium hydroxide, which led to the creation of novel silica-based hybrid materials.

    DOI

    Scopus

    13
    Citation
    (Scopus)
  • Formation of layered silica-alcohol nanostructured materials from alkoxytrichlorosilanes

    Y Fujimoto, A Shimojima, K Kuroda

    CHEMISTRY OF MATERIALS   15 ( 25 ) 4768 - 4774  2003.12  [Refereed]

     View Summary

    Novel layered silica-organic nanostructured materials were prepared by hydrolysis and condensation of alkoxytrichlorosilanes (n-CnH2n+1OSiCl3, n = 12, 14, 16, 18, and 20) as single precursors. The formation relies on the self-assembly of alkoxysilanetriols (n-CnH2n+1OSi-(OH)(3)) generated by the preferential hydrolysis of Si-Cl groups in the precursors. The products exhibited the XRD patterns indicative of layered structures whose d spacings varied in the range of 3.95 to 6.13 nm depending on the alkyl chain lengths. The SEM images of the products showed well-defined platelike morphologies on micrometer length scales, reflecting the layered structures of the products. Further structural characterization by solid-state Si-29 and C-13 NMR and FTIR revealed that the layered structures consisted of bimolecular layers of long-chain alcohols and thin silica layers. Condensation of alkoxysilanetriols proceeded in the solid state to form silica networks, being accompanied by the cleavage of the alkoxy groups. The present results provide a new approach for the construction of silica-based nanostructured materials with well-regulated organic arrays and silica networks.

    DOI

    Scopus

    49
    Citation
    (Scopus)
  • Synthesis of multilayered silica-based hybrid films from difunctional organosilanes by co-hydrolysis and polycondensation with tetraalkoxysilane

    N Umeda, A Shimojima, K Kuroda

    JOURNAL OF ORGANOMETALLIC CHEMISTRY   686 ( 1-2 ) 223 - 227  2003.11  [Refereed]

     View Summary

    Decylethyldimethoxysilane (C10EtDMS) and didecyldimethoxysilane (2C10DMS) were used to prepare thin films of silica-based hybrids by co-hydrolysis and polycondensation with tetramethoxysilane (TMOS) followed by spin-coating. The length of the second alkyl chains (Et or n-decyl) had large effects on the formation of ordered hybrid films. In the case of C10EtDMS, transparent films of well-ordered lamellar hybrids were formed with various TMOS/C10EtDMS ratios by controlling the degree of polycondensation in the precursor solutions. In contrast, no ordered hybrids were obtained in the case of 2C10DMS under the same conditions, due to the larger steric hindrance of the longer second alkyl chain in the co-condensation. Increases of both TMOS/2C10DMS and HCl/Si ratios in the starting solutions promoted polycondensation and lead to the formation of ordered hybrid films. (C) 2003 Elsevier B.V. All rights reserved.

    DOI

    Scopus

    8
    Citation
    (Scopus)
  • Direct formation of mesostructured silica-based hybrids from novel siloxane oligomers with long alkyl chains

    A Shimojima, K Kuroda

    ANGEWANDTE CHEMIE-INTERNATIONAL EDITION   42 ( 34 ) 4057 - 4060  2003  [Refereed]

    DOI

    Scopus

    109
    Citation
    (Scopus)
  • Formation of a new crystalline silicate structure by grafting dialkoxysilyl groups on layered octosilicate

    D Mochizuki, A Shimojima, K Kuroda

    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY   124 ( 41 ) 12082 - 12083  2002.10  [Refereed]

    DOI

    Scopus

    56
    Citation
    (Scopus)
  • Structural control of multilayered inorganic-organic hybrids derived from mixtures of alkyltriethoxysilane and tetraethoxysilane

    A Shimojima, K Kuroda

    LANGMUIR   18 ( 4 ) 1144 - 1149  2002.02  [Refereed]

     View Summary

    Multilayered inorganic-organic hybrids were prepared by cohydrolysis and polycondensation of alkyltriethoxysilanes (CnTES, n = 8-18) and tetraethoxysilane (TEOS). Thin films were deposited from homogeneous solutions containing the oligomeric species by dip-coating. Self-assembly of co-condensed oligomers into lamellar structures depended essentially on the alkyl chain length of CnTES and the temperature of the solutions. By controlling the solution temperature during the dip-coating process, transparent and highly ordered films were formed from the mixtures of TEOS and CnTES with various alkyl chain lengths. The resulting hybrid materials were structurally different from those derived from CnTES alone and exhibited various interlayer structures depending on the alkyl chain length, which is due to the differences in the arrangements and conformations of the chains.

    DOI

  • Nanoworld in Inorganic-Organic Nanocomposites

    SHIMOJIMA Atsushi, KURODA Kazuyuki

    Inorganic Materials   8 ( 295 ) 580 - 585  2001.11

    DOI CiNii

  • Synthesis of silylated derivatives of a layered polysilicate kanemite with mono-, di-, and trichloro(alkyl)silanes

    A Shimojima, D Mochizuki, K Kuroda

    CHEMISTRY OF MATERIALS   13 ( 10 ) 3603 - 3609  2001.10  [Refereed]

     View Summary

    Interlayer modification of a layered polysilicate kanemite was performed by silylation with mono-, di-, and trichloro(alkyl)silanes. The introduction of silyl groups into the interlayer region was confirmed by XRD, IR, C-13 NMR, and Si-29 NMR. The layered structures of the silylated products were confirmed by swelling behavior upon adsorption of n-alkyl alcohols. The amounts of attached alkylsilyl groups varied with the number of functional groups as well as the alkyl chain length in the silylating agents. The products modified with alkyltrichlorosilanes exhibited various interlayer structures due to the different arrangements and/or conformations of the alkyl chains, depending on the chain lengths. The BET surface areas were relatively large (up to similar to 480 m(2) g(-1)) when short-chain alkyltrichlorosilanes were used, and decreased substantially to nonporous structures with increasing chain length. In addition to the inherent six-membered rings in the single layered silicate sheets of kanemite, new five- and six-membered rings were formed onto the silicate frameworks when dichloro- and trichlorosilanes were used for silylation. This leads to a new method for constructing novel organosilicate nanomaterials utilizing layered silicates.

    DOI

    Scopus

    94
    Citation
    (Scopus)
  • Synthesis of layered inorganic-organic nanocomposite films from mono-, di-, and trimethoxy(alkyl)silane-tetramethoxysilane systems

    A Shimojima, N Umeda, K Kuroda

    CHEMISTRY OF MATERIALS   13 ( 10 ) 3610 - 3616  2001.10  [Refereed]

     View Summary

    Transparent thin films of layered inorganic- organic nanocomposites were prepared by the sol-gel reactions of alkyldimethylmethoxysilane, alkylmethyldimethoxysilane, and alkyltrimethoxysilane in the presence of tetramethoxysilane followed by spin-coating. The macroscopic homogeneity and the nanostructural ordering of the films were strongly affected by the degree of polycondensation in the precursor solutions. The formation of siloxane networks containing organosiloxane units was confirmed by Si-29 MAS NMR, suggesting that the structure of the inorganic-organic interface can be designed at a molecular level by the functionalities in the alkylmethoxysilanes used. On the other hand, the 29Si NMR spectra of the precursor solutions showed that the monomeric species almost disappeared and that co-condensed oligomers were formed at the initial stages of the reactions. In the cases of mono- and dimethoxysilanes, the ability to form ordered structures depends largely on the co-condensation with tetramethoxysilane in the precursor solutions.

    DOI

    Scopus

    104
    Citation
    (Scopus)
  • Novel layered silica/organic polymer hybrid films with the interface linked by Si-C bonds

    A Shimojima, K Kuroda

    CHEMISTRY LETTERS   11 ( 11 ) 1310 - 1311  2000.11  [Refereed]

     View Summary

    Inorganic-organic hybrids films composed of alternating layers of siloxane network and organic polymer assemblies linked by Si-C bonds have been prepared via co-hydrolysis and polycondensation of alkenyltriethoxysilane-tetraethoxysilane mixtures followed by organic polymerization, providing a new methodology for the design and construction of inorganic-organic nanostructured materials.

    DOI

    Scopus

    21
    Citation
    (Scopus)
  • Synthesis of oriented inorganic-organic nanocomposite films from alkyltrialkoxysilane-tetraalkoxysilane mixtures

    A Shimojima, Y Sugahara, K Kuroda

    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY   120 ( 18 ) 4528 - 4529  1998.05  [Refereed]

    DOI

    Scopus

    82
    Citation
    (Scopus)
  • Inorganic-Organic Layered Materials Derived via the Hydrolysis and Polycondensation of Trialkoxy(alkyl)silanes

    Atsushi Shimojima, Yoshiyuki Sugahara, Kazuyuki Kuroda

    Bulletin of the Chemical Society of Japan   70 ( 11 ) 2847 - 2853  1997  [Refereed]

     View Summary

    Triethoxy(alkyl)silanes containing 12-18 carbon atoms in the alkyl groups were hydrolyzed and polycondensed to form ordered structured materials. The XRD pattern of each condensed product showed sharp diffraction peaks with higher orders. The basal spacings approximately corresponded to twice the extended molecular length of the alkyl groups, and increased linearly as a function of the alkyl chain length. The SEM images of the products exhibited a platy morphology, and the 29Si CP/MAS NMR spectra revealed the formation of siloxane bonds with various silicon sites from T1 to T3 environments. All of these results indicated the formation of highly-organized inorganic-organic layered materials.

    DOI

    Scopus

    141
    Citation
    (Scopus)

▼display all

Misc

  • Preparation of an ordered nanoporous silicone-based material using silica colloidal crystals as a hard template

    Naho Muramoto, Takamichi Matsuno, Hiroaki Wada, Kazuyuki Kuroda, Atsushi Shimojima

    Chemistry Letters   50 ( 5 ) 1038 - 1040  2021.05

    Book review, literature introduction, etc.  

     View Summary

    An ordered nanoporous silicone-based material with an inverse opal structure consisting of interconnected spherical pores was prepared by the thiol-ene reaction of linear and cyclic organosiloxanes within the interstitial voids of silica colloidal crystals, followed by removal of the silica template under basic conditions. The silicone-based framework is promising for the design of nanoporous materials with unique properties and functions.

    DOI

  • メソ多孔体薄膜研究の最近の展開 (特集 次代を切り拓く"ゼオライト"の最新技術をさぐる)

    原 慎太郎, 下嶋 敦, 黒田 一幸

    工業材料   65 ( 3 ) 54 - 57  2017.03

    CiNii

  • Precision synthesis of polymers tailored towards directed formation and arrangement of silica nanomaterials

    Kira B. Landenberger, Yu Shinke, Yukari Oda, Arihiro Kanazawa, Shokyoku Kanaoka, Sadahito Aoshima, Sachio Tsuboike, Shujun Zhou, Ayae Sugawara-Narutaki, Tatsuya Okubo, Atsushi Shimojima

    ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY   248  2014.08

    Research paper, summary (international conference)  

  • New View on Synthesis of Ordered Porous Silica

    YOKOI Toshiyuki, SHIMOJIMA Atsushi, TATSUMI Takashi, OKUBO Tatsuya

    Ceramics Japan   45 ( 10 ) 823 - 829  2010.10

    CiNii

  • Introduction to Nanospace Materials and the Recent Topics

    SHIMOJIMA Atsushi, OKUBO Tatsuya

    The Pigments,Paints and Printing Inks   83 ( 6 ) 276 - 281  2010.06

     View Summary

    ナノ空間材料とは,ナノレベルの規則的細孔,高比表面積,大細孔容量などの特徴を有し,幅広い応用が期待されるナノテクノロジーの基幹材料の一つである。さまざまな組成・構造のナノ空間材料が知られているが,本稿では,シリカ(SiO&lt;sub&gt;2&lt;/sub&gt;)系ナノ空間材料であるメソポーラスシリカ,ゼオライト,球状シリカナノ粒子集合体を取り上げ,それらの基礎と最近の話題を紹介する。

    DOI CiNii

  • 板状中空シリカソーダライト合成における酸処理の構造への影響

    茂木 堯彦, Chaikittisilp Watcharop, 下嶋 敦, 大久保 達也

    化学工学会 研究発表講演要旨集   2010 ( 0 ) 245 - 245  2010

    DOI CiNii

  • Synthesis of mesoporous silica nanoparticles with high dispersibility for optical application

    ゼオライト   27 ( 3 ) 103 - 110  2010  [Refereed]  [Invited]

    Article, review, commentary, editorial, etc. (scientific journal)  

    CiNii

  • 東京大学大学院工学系研究科化学システム工学専攻大久保・下嶋研究室

    大久保 達也, 下嶋 敦, 菅原 彩絵, 干川 康人

    化学工学 = Chemical engineering   73 ( 7 ) 350 - 350  2009.07

    CiNii

  • 有機修飾メソポーラスシリカナノ粒子の複合薄膜化及び反射防止機能の検証

    矢部 裕城, 山木 健之, 干川 康人, 下嶋 敦, 大久保 達也

    化学工学会 研究発表講演要旨集   2009 ( 0 ) 449 - 449  2009

    DOI CiNii

  • 水-エチレングリコール混合溶媒を用いた新規球状メソポーラスシリカナノ粒子の合成

    大久保 達也, 顧 金楼, 下嶋 敦

    化学工学会 研究発表講演要旨集   2008 ( 0 ) 646 - 646  2008

    DOI CiNii

  • 層状シリケートを前駆体とした中空SOD型ゼオライトのトポタクティック合成

    茂木 堯彦, Chaikittisilp Watcharop, 下嶋 敦, 大久保 達也

    化学工学会 研究発表講演要旨集   2008 ( 0 ) 657 - 657  2008

    DOI CiNii

  • Synthesis and application of well-ordered silica nanospheres assisted by basic amino acids

    YOKOI Toshiyuki, WAKABAYASHI Junji, OTSUKA Yuki, FAN Wei, IWAMA Marie, SHIMOJIMA Atsushi, WATANABE Ryota, ARAMAKI Kenji, OKUBO Tatsuya, TATSUMI Takashi

    触媒 = Catalysts & Catalysis   49 ( 6 ) 492 - 494  2007.09

    CiNii

  • COLL 297-Organic-inorganic mesoporous nanocarriers integrated with biogenic ligands

    Jinlou Gu, Tatsuya Okubo, Wei Fan, Atsushi Shimojima

    ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY   234  2007.08

    Research paper, summary (international conference)  

  • 塩基性アミノ酸存在下におけるシリカナノ粒子生成挙動の観察

    若林 隼二, 岩間 真理絵, 横井 俊之, 範 偉, 下嶋 敦, 荒牧 賢治, 辰巳 敬, 大久保 達也

    化学工学会 研究発表講演要旨集   2007 ( 0 ) 135 - 136  2007

    CiNii

  • Formation of ordered silica-organic hybrids by self-assembly of hydrolyzed organoalkoxysilanes with long organic chains

    Kazuyuki Kuroda, Atsushi Shimojima

    Materials Research Society Symposium - Proceedings   707   61 - 72  2002.12

     View Summary

    Various layered hybrid films prepared from organoalkoxysilanes with long organic chains, based on the self-assembly of the hydrolyzed species, are reviewed. Morphological control of transparent and oriented films was achieved by cohydrolysis and polycondensation with tetraalkoxysilanes, followed by dip- or spin-coating. In addition to alkytrialkoxysilanes, alkyldimethylmonoalkoxy- and alkylmethyldialkoxy-silanes were also used as the structural units, implying that the inorganic-organic interface can be designed at a molecular level. In these cases, co-condensation in the precursor solution plays an essential role in the formation of homogeneous and ordered films. Alkenyltriethoxysilanes with terminal C=C bonds were also employed to prepare layered hybrid films. Interlayer chains were polymerized upon UV irradiation, and the resulting films exhibited a significant increase in the hardness if compared with the films before polymerization. Hybrid films thus obtained are a new class of materials and of great interest for a wide range of materials chemistry.

  • Formation of ordered silica-organic hybrids by self-assembly of hydrolyzed organoalkoxysilanes with long organic chains

    Kazuyuki Kuroda, Atsushi Shimojima

    Materials Research Society Symposium - Proceedings   703   71 - 82  2002.01

     View Summary

    Various layered hybrid films prepared from organoalkoxysilanes with long organic chains, based on the self-assembly of the hydrolyzed species, are reviewed. Morphological control of transparent and oriented films was achieved by cohydrolysis and polycondensation with tetraalkoxysilanes, followed by dip- or spin-coating. In addition to alkyltrialkoxysilanes, alkyldimethylmonoalkoxy- and alkylmethyldialkoxy-silanes were also used as the structural units, implying that the inorganic-organic interface can be designed at a molecular level. In these cases, co-condensation in the precursor solution plays an essential role in the formation of homogeneous and ordered films. Alkenyltriethoxysilanes with terminal C=C bonds were also employed to prepare layered hybrid films. Interlayer chains were polymerized upon UV irradiation, and the resulting films exhibited a significant increase in the hardness if compared with the films before polymerization. Hybrid films thus obtained are a new class of materials and of great interest for a wide range of materials chemistry.

▼display all

Awards

  • 日本セラミックス協会 進歩賞

    2006  

Research Projects

  • 新規ナノハイブリッド材料、多孔体材料の創製

Specific Research

  • ミクロ-メソ構造制御に基づくシロキサン系自己修復材料の創製

    2019   岸 雅史

     View Summary

    外部から受けた損傷を自発的に修復する能力を有する材料が近年注目されている。本研究では、Si-O-Si骨格の分子レベルの制御に基づき、シロキサン系自己修復材料の設計を行った。二重のトリシロキサン環構造を有するカゴ型シロキサンオリゴマーをビルディングブロックとして用い、ポリジメチルシロキサンで分子間を架橋することによって3次元的なシロキサンネットワークを形成した。この材料は、高温多湿条件下でクラックを自己修復する能力を有することが確認された。クラック破断面のカゴ型ユニットが開裂することによってSi-OH基が生成し、脱水縮合によって修復が起こったと推定された。

  • 精密な構造制御に基づくシリカ系自己修復材料の創製

    2018  

     View Summary

     自己修復機能材料は、長寿命、メンテナンスフリー、高信頼性などの観点から注目されている。最近我々は、シロキサン(Si-O-Si)骨格からなるシリカ層とカチオン性界面活性剤の二分子層が交互に積層したラメラ薄膜が、高湿条件下で膨潤し、微小なクラックを修復する能力を有することを報告した。本研究では、シロキサン骨格中に有機成分を分子レベルで組み込むことで薄膜の柔軟性を向上させ、それによるクラック修復能力の向上について検討した。シリカ層中にSi-C2H4-Si基を導入することで、従来のラメラ薄膜では修復できない比較的大きなクラックが、比較的低湿度(70% RH)でも修復可能であることが明らかとなった。

  • 有機シロキサン系フォトメカニカル結晶の創製

    2018  

     View Summary

    光エネルギーを機械的な運動に変換可能なフォトメカニカル材料は、光駆動アクチュエータをはじめとした幅広い応用が期待されている。本研究では、光応答性分子であるジアリールエテンにカゴ型のオリゴシロキサン化合物を修飾することで、新しい無機-有機ハイブリッド型のフォトメカニカル結晶を創出した。得られた結晶にUV光を照射すると、部分的な光異性化反応が進行し、光源と反対側に湾曲した。湾曲した結晶に対して引き続き可視光を照射すると元の分子構造と形状に戻ったことから、可逆的な屈曲挙動が確認された。この結晶は、カゴ型オリゴシロキサンを導入する前のジアリールエテン結晶と比較して、高い耐熱性を示した。

  • 大環状シロキサンを用いた光応答性材料の創製

    2017   黒田一幸

     View Summary

    本研究課題では、新しい光応答性無機有機ハイブリッド材料の創出を目的として、環状のSi-O-Si骨格を有するシロキサン化合物とアゾベンゼンのナノハイブリッド材料を合成した。メチルトリエトキシシラン(MeSi(OEt)3)を原料として得られる酸素12員環からなるシロキサン-金属錯体をジメチルクロロシラン(Me2Si(H)Cl)でシリル化することで、官能基として12個のSi-H基を有する環状シロキサン誘導体を得た。さらに、片側あるいは両側にアリル基を有するアゾベンゼン誘導体を用い、ヒドロシリル化反応により、それぞれアゾベンゼンが環状シロキサンにグラフトされたハイブリッド材料、アゾベンゼンが環状シロキサンを分子間架橋したハイブリッド材料の合成に成功した。

  • 有機構造規定剤の表面固定化に基づくセオライトのナノスケール形態制御

    2015   黒田一幸

     View Summary

    本研究では、ゼオライト結晶の配向、厚さ、サイズの制御を目指し、二つの四級アンモニウムイオンを有する有機構造規定剤(OSDA)を基板上に固定化する手法について検討した。新規OSDAとしてハロゲン化アルキル基を有する OSDAを合成した後、架橋アミノ基を有する有機修飾アルコキシシランと反応させ、基板上に薄膜として塗布することで、OSDAの固定化に成功した。得られた薄膜は高い水熱安定性を有することから、ゼオライト形成の基板として有用であると考えられた。

  • シロキサン系ビルディングブロックライブラリーの構築へ向けたシリル基置換反応の開拓

    2015   黒田一幸

     View Summary

    本研究ではアルコキシシロキサンオリゴマーの新規合成手法の開発を目的とし、トリメチルシリル(TMS)基とアルコキシシリル基の交換反応について検討した。塩化ビスマス触媒下、ヘキサメチルジシロキサン(HMDS)もしくはテトラキス(トリメチルシロキシ)シラン(QM4)とクロロジメトキシメチルシランを反応させた。NMR分析により、HMDSの場合は、2個のTMS基がジメトキシメチルシリル基に置換された分子を、また、QM4の場合も 2, 3, 4個のTMS基が置換された分子の生成を確認した。以上より、TMS基を有するシロキサンオリゴマーからアルコキシシロキサンオリゴマーを得る新規ルートを開拓した。

  • 自己組織化によるシリカ-ペプチドナノ組織体の創製

    2013  

     View Summary

    本研究課題では、生体分子であるアミノ酸やペプチドがSi-C結合を介してケイ素アルコキシドと連結した分子を設計し、その自己組織化・重合により新しいハイブリッド材料を創出することを目的としている。今回は、規則的な細孔を有するメソ多孔体をターゲットとした。シリカメソ多孔体を有機修飾することによって多様な機能を付与することができるが、特に、アミノ酸やペプチドによる細孔内修飾によって生体分子の吸着、キラル分離、酵素類似反応などへの応用が期待できる。本研究では、アミノ酸にトリアルコキシシリル(-Si(OR)3)基が連結された新規アルコキシシランを合成し、界面活性剤を鋳型として用いたアミノ酸修飾メソポーラスシリカの直接合成について検討した。各種アミノ酸(グリシン (Gly)、アラニン (Ala)、フェニルアラニン (Phe)など)のエチルエステルと3-イソシアネートプロピルトリエトキシシランとの反応により、尿素結合を介してトリエトキシシリル(TES)基が結合したTES-アミノ酸を合成した。TES-Glyについては、-COOH末端にもTES基を結合させた(TES-Gly-TES)。これらの分子をテトラエトキシシラン(Si(OEt)4)と様々なモル比(x : (1-x), x = 0-0.8)で混合し、カチオン性のアルキルトリメチルアンモニウムあるいは非イオン性界面活性剤の存在下、加水分解・縮重合させることによってメソ複合体を合成し、溶媒抽出によって界面活性剤の除去を行った。TES-アミノ酸はいずれも無色透明の油状物質であったが、TES-Gly-TESは結晶性の固体であった。各分子の1H,13C,29Si NMR測定により、アミノ酸部位とTES基、さらに尿素結合に帰属されるシグナルが観測された。TES-Gly, TES-Ala, TES-Pheの添加量をx = 0.2として得られたメソ構造体は、XRD、TEMにより2Dヘキサゴナル構造をもつことがわかった。窒素吸着測定の結果、x = 0の場合と比較して細孔径が減少したものの、メソ孔を有することが確認された。IRスペクトルからは、シロキサン骨格による吸収ピークのほかに、アミノ酸由来のピークが観測され、xの増加にともなってその強度が増加した。以上の結果から、細孔表面がアミノ酸で修飾されたメソポーラスシリカの合成が確認できた。一方、TES-Gly-TESを用いた場合も同様に多孔体が得られたが、この場合、アミノ酸部位はシリカ骨格内に組み込まれていると予想された。

  • 生体に学ぶシリカ系自己修復材料の創製

    2013  

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    自己修復材料は外部応力によって生じた損傷を自発的に修復する能力を有する材料であり、幅広い分野での応用が期待されている。生体系には様々な自己修復機能が存在するが、ある種の生体高分子は可逆的な水素結合を積極的に利用して高次構造の損傷を修復することが知られている。このような水素結合の可逆性を利用したポリマーの設計は最近非常に注目されており、熱可逆性高分子ゲルなどユニークな物性を持つ材料が報告されつつある。本研究では、従来の有機ポリマー系自己修復材料よりも高い安定性、優れた力学特性、そして高い修復能を有する新しい無機-有機ハイブリッド型の自己修復材料の設計を目的としている。低ガラス転移点、耐熱性、透明性、生体適合性などの特長を有する無機高分子であるポリジメチルシロキサン(PDMS)を用い、水素結合性有機基で修飾すると同時に、剛直な無機フィラーでありかつ架橋点としても働くケージ状シロキサンオリゴマーにグラフトすることによって、水素結合性の星形ポリマーの合成について検討した。ケージ状シロキサンオリゴマーは、テトラメチルアンモニウムイオン存在下でのケイ素アルコキシド(Si(OEt)4)の加水分解・重縮合反応によって得られるケイ酸8量体をジメチルクロロシランでシリル化した後、Si-H基をSi-Cl基に変換することで合成した。次に、環状トリシロキサンのアニオンリビング重合により分子量の制御されたPDMSを合成し、停止剤として上記のSi-Cl修飾型のシロキサンオリゴマーを添加することによって、シロキサンユニットあたり4~5本のPDMSがグラフトされたポリマーが形成されたことをNMR等で確認した。さらに、あらかじめPDMSの一部のメチル基をビニル基に置換し、それらを基点に水素結合性の有機基であるウレイドピリミジノンで修飾することによって、水素結合性ポリマーの合成に成功した。今後、ポリマーの構造と物性の相関について検討を行う予定である。

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