Abstract

Structural control of siloxane-based materials at multiple length scales is important for various applications. In this study, we report the controlled assembly of cage oligosiloxane building blocks by both intermolecular hydrogen bonding and hydrophobic interactions. A cage siloxane molecule modified with seven dimethylsilanol groups and an octadecyldimethylsilyl group was synthesized by stepwise silylation of double-four-ring (D4R) cage octasilicate anions. This molecule self-assembled to form a molecularly and mesoscopically ordered structure by solvent evaporation. Furthermore, the silanol groups in the assembled solids were cross-linked by silylation with dichlorodimethylsilane. This approach will allow for the creation of various hierarchically ordered siloxane-based materials by molecular design.

Graphical Abstract

Isolated dimethyltin species were successfully grafted to the regularly arranged silanol groups of crystalline layered silicate.

Highly ordered mesoporous N-doped TiO₂ with large crystallites was prepared by hard-templating method, followed by calcination with urea. The thermal conductivity was lowered by the nanosized pore walls and the ordered pore wall surfaces.

Cage siloxanes modified with diisopropylsilanol groups were synthesized and crystallized into a layered structure containing 1,3,5-trimethylbenzene molecules in the interlayer voids, which indicates that the organic groups attached to the silanol groups have an important role in the assembling behavior of cage siloxanes.

Siloxane-based nanoporous materials have a wide range of applications. In this study, a double-four-ring cage siloxane modified with dimethylsilanol groups at eight vertices was cross-linked via reaction with titanium(IV) tetraethoxide to construct a three-dimensional network with SiOTi bonds, producing a nanoporous material. The product exhibited catalytic activity for the liquid-phase oxidation of cyclohexene with relatively high selectivity. This building block approach opens a new route to nanoporous materials composed of fully inorganic SiOSi and SiOTi linkages.

Interlayer silylation of layered sodium octosilicate (Na-Oct) with various organoalkoxysilanes was conducted using hexadecyltrimethylammonium ion-exchanged layered octosilicate (C16TMA-Oct) as an intermediate in the presence or absence of tetrabutylammonium fluoride (TBAF). The degree of silylation was increased by adding TBAF. It is suggested that F− ions perform a nucleophilic attack on the alkoxysilanes, which promotes the silylation reaction. C16TMA-Oct was silylated with octyltriethoxysilane (C8TES) or 3-mercaptopropyltriethoxysilane (MPTES) to compare the reactivity of the two organoalkoxysilanes in the presence or absence of TBAF. A higher degree of silylation of C16TMA-Oct was observed with MPTES, suggesting the higher accessibility of this silylating agent into the interlayer polar region of C16TMA-Oct. Overall TBAF appears as a relevant catalyst for the covalent interlayer surface modification of layered silicates with organic functional groups.

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.

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.

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.

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.

<p>Tetraalkylammonium cations of cage germanoxanes encapsulating a fluoride ion inside the cage were exchanged with other tetraalkylammonium cations in both discrete and cross-linked states.</p>

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.

Nanoporous materials with anionic pentacoordinate organosilicon frameworks were prepared using organoalkoxysilanes, tris-catechol linkers (2,3,6,7,10,11-hexahydroxytriphenylene, HHTP), and primary diamines as a cation source. The products have both microporous and mesoporous frameworks with some crystallinity. Design of novel catalysts, adsorbents, and ionexchangers based on the charged frameworks and various organic substituents will be expected.

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.

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.

A new class of inorganicorganic hybrid photomechanical material has been created by mono-substitution of polyhedral oligomeric silsesquioxane (POSS) with an azobenzene group via amide bond formation. This compound formed needle-like molecular crystals showing reversible photoinduced bending motions. This finding provides a new design concept of photomechanical materials for various applications.

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

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.

Siloxane-based nanomaterials have a wide variety of applications, such as catalysis, adsorption, coatings, optics, and nanomedicine. The use of siloxane-based building blocks with well-defined structures and compositions is a promising approach for designing siloxane-based nanomaterials. This chapter summarizes the recent progress that has been made in both the molecular design of silane/siloxane precursors and their controlled assembly.

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.

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.

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.

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.

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.

In this chapter, preparation, structures, and photoresponsive properties of various azobenzene-siloxane hybrid nanomaterials based on the design of element blocks are described. Hydrolysis and polycondensation reactions accompanied by self-assembly of different types of azobenzene-functionalized alkoxysilane precursors yield hybrids with ordered mesostructures. Lamellar films show reversible dspacing changes and macroscopic bending-unbending motion by partial trans-cis photoisomerization of the azobenzene groups. Further, incorporation of a cage oligosiloxane into the precursor leads to the formation of cylindrical assemblies, in which efficient photoisomerization of azobenzene is achieved. These findings will contribute to the creation of novel photoresponsive materials.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

<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>

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.

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.

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.

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.

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.

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.
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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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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).

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

This presentation describes a facile solution process for the preparation of anisotropic silica nanoparticles (ASNPs). ASNPs are prepared via one-dimensional 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 silica seed assembly is controlled through the adjustment of electrostatic interaction. Ethanol and Arg also serve as cosolvent and 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.

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.

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.

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.

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.

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.

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.

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.

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.

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).

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.

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.

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.

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.

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.

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.

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.

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.

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

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.