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, 13 C NMR, and 29 Si 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 ∼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 dichloroand trichlorosilanes were used for silylation. This leads to a new method for constructing novel organosilicate nanomaterials utilizing layered silicates.
b S Supporting Information N anosized metal oxide semiconductors have been actively studied for the past few decades, especially for their potential applications for photocatalytic reactions, photobreaching of toxic compounds, artificial photosynthesis, and photovoltaics. 1À5 Among all metal oxide semiconductors, TiO 2 is one of the most important materials because of the abundance of titanium as a natural resource, corrosion resistivity, transparency in the visible region, and nontoxicity. The kinetically favorable anatase crystalline phase is the most widely studied due to its ease of preparation, stability of the crystal up to ∼600°C, and advantages for catalytic and electronic properties. The anatase crystal of TiO 2 has a few fundamental low-index facet systems, such as {101}, {001}, {100}, {110}, and {103}. 2 Typical anatase crystal of TiO 2 , including naturally grown crystals, consists of mostly the {101} facet due to the much greater stability of this surface than other surfaces due to its lower surface energy. Therefore the characteristics of TiO 2 nanoparticles, in most cases, have been supposed to be attributed to the {101} facet, regradless of whether it is mentioned in the literature, since it had been extremely difficult to selectively synthesize other unstable surfaces, such as the (001) surface. 2,6 Recently, however, Lu et al. proposed a novel synthesis to selectively increase the fraction of {001} facet and thus introduced a new area of study, the chemically reactive (001) surface, into the widely studied TiO 2 nanoparticles. 7 The proposed novel process is composed of the addition of a relatively large amount of hydrofluoric acid (HF) for hydrothermal growth of TiO 2 . Although a few groups also reported the follow-up work of {001} facet-dominating TiO 2 preparation, most groups used the same procedure using HF. 8À11 The role of HF in TiO 2 synthesis was also suggested to be that the fluorine-termination of TiO 2 surface stabilizes the (001) surface more than the other facets and results in a larger fraction of intrinsically unstable (001) surface; the result of the first-principle calculations also supported this explanation. 7 The typical fraction of {001} facet in reports varies from 40 to 80%, usually determined by the characteristic bipyramidal structure of particles revealing the trapezoidal (101) and rectangular (001) surfaces observed by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). 7À12 Since the surface energy of the {001} facet is higher than that of the {101} facet, recent reports indicated a few characteristic features of the {001} facet, a site-selective reaction, enhancement of reactivity, adsorption of molecules, and water dissociation with {001} facetdominating TiO 2 nanoparticles 13À15 for application to photocatalytic reactions 10,11 and photovoltaics. 12,16 Additionally, a few theoretical investigations based on first-principle calculations also reported the characteristic reactivity of the {001} facet. 17,18 Nevertheless, detailed analysi...
A novel methodology for constructing molecularly ordered silica nanostructures with two-dimensional (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 [ROSiCl(3), 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 degrees 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.
Dialkoxydichlorosilanes ((RO)2SiCl2, R = alkyl) react almost completely with interlayer silanol groups in a layered silicate octosilicate to create a new crystalline silicate structure consisting of new five-membered rings arranged regularly on both sides of the silicate layers. The introduction of dialkoxysilyl groups to the interlamellar region of layered silicates with regular reaction sites provides a new methodology for the design and construction of novel crystalline silicate frameworks by a soft chemical route.
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