Preparation And Characterization Of SnO₂-SiO₂Nanocomposites Via The Non-Hydrolytic Sol-Gel Route

As an important functional semi-conductor material, SnO2is extensively studied for its applications in gas sensing, catalysis, electrochemistry and optoelectronic devices. For many of these applications, high surface areas, which are inherent in small particle sizes, are important prerequisites. If improved nanotechnology is combined with SnO2materials, dramatic performance and application can be achieved. At present, the research on nano-Sn02mainly includes the control over morphology, doping and coating of the material and assembly of building units.Non-hydrolytic sol-gel (NHSG) processes offer the possibility of better controlling the reaction pathways on the atomic level, enabling the synthesis of nanostructure complex oxides with controlled particle morphologies, high crystallinity and high specific surface area. The NHSG process is easy to operate owing to its moderate reaction condition and the lower requirement for reactivity of the precursors.SnO2-SiO2nanocomposites have been prepared by the non-hydrolytic sol-gel method, using stannic chloride and tetraethoxysilane as precursors. Firstly, the effects of the related reaction conditions on the properties of the materials have been studied; secondly, catalytic performances of these materials have been examined for the polymerization of tetrahydrofuran (THF) and oxidation of CO. On this basis, the structures and texture properties of the materials have been characterized by FT-IR, XRD, N2-physisorption, TEM and UV-Vis. The main results and conclusions are as follows:1. The material post-treated by acetone outperforms the material obtained by direct drying on the specific surface area. The BET surface area of the former is286.3m2/g.2. The SnO2-SiO2xerogels prepared by the NHSG rout contain only tetra-coordinated Sn atoms, however after calcination, the materials contain tetra-coordinated and hexa-coordinated Sn atoms. It is shown that Sn atoms have been incorporated into the framework of SiO2with the formation of Si-O-Sn linkages.3. On the condition of direct drying, the increase of the pore volume and specific surface area with Sn content (i. e., the Lewis acid concentrations) can be ascribed to the increase of the condensation rate leading to gels with higher degree of crosslinking, able to withstand the high capillary pressures imposed on the gel network during the drying process.4. The non-hydrolytic sol-gel route has been used in the solvent-free synthesis of binary inorganic oxides based on silicon and tin. Lamellar mesoporous SnO2-SiO2nanocomposites are obtained after calcination at300℃. Tin species in the materials are highly dispersed within mesoporous siliceous matrices.5. These NHSG xerogels show excellent catalytic performances in the polymerization of tetrahydrofuran, and the yield of the polymer is up to31%.