EXAFS and XANES studies of silica-titania sol-gel films

Abstract

Abstract.A series of SiO2-TiO2 sol-gel films with and without heat treatment were analyzed by EXAFS and XANES spectroscopies. Both techniques indicate that essentially all Ti 4+ ions remain four-fold coordinated, with a Ti--O bond distance between 1.82-1.85/~. In the glassy films produced by heat treatment at 900~ a gradual phase separation may occur at the nanoscale, as the TiO2 concentration of the films increases.

Distribution Effect of the Second Phase in Disperse Silica/X Oxides (X = Al2O3, TiO2, GeO2) on Their Surface Properties

“…Mixed oxides such as X/SiO 2 are widely used as catalysts, fillers, adsorbents, etc., and their properties depend strongly not only on the nature of the X phase but also on its distribution in the silica matrix. − Variations in the structure of mixed oxides caused by the methods of X/SiO 2 synthesis (pyrogenic, sol−gel, chemical vapor deposition (CVD), etc.) lead to materials having different characteristics (e.g., content of surface active sites, particle size distribution, topology, etc.)…”

“…lead to materials having different characteristics (e.g., content of surface active sites, particle size distribution, topology, etc.) without C X alteration. , Of X/SiO 2 oxides, alumina/silica (AS) and titania/silica (TS) are the most used oxides. − Fumed X/SiO 2 oxides are produced via hydrolysis of SiCl 4 and MCl n (e.g., M = Ti, Al, etc.) in an oxygen−hydrogen flame at T above 1300 K. 3i, Their primary particles (10−30 nm) possess a complex structure as obtained at high temperature with its great gradient; e.g., for TS, they consist of crystalline titania (rutile and anatase) and amorphous silica. 3i,, These primary particles form branched stable aggregates (0.2−0.5 μm; fractal dimension about 2.5 and apparent density about 30% of the specific density) via the ⋮M−O−M⋮ bridges caused by particle sticking and fusing at high temperatures .…”

Interfacial Reactions between Lithium and Grain Boundaries from Anatase TiO2–TUD-1 Electrodes in Lithium-Ion Batteries with Enhanced Capacity Retention

“…15,34−38 Previous reports using (near-edge) the X-ray absorption fine structure (NEXAFS and EXAFS) on silica-titania sol−gel films have demonstrated the predominant presence of tetracoordinated Ti 4+ ions. 37,39,40 After Figure 1 confirmed the formation of TiO 2 in the anatase form, the energy-dispersive X-ray spectroscopy (EDS) analysis (Figure 4) revealed that the sample consisted of 81 wt % of TiO 2 , which corresponds to a 3.1 Ti/Si molar ratio. This elemental analysis is consistent with the retention of the initial Ti/Si molar ratio.…”

“…Fourier transform infrared (FTIR) was used to confirm the formation of Si–O–Si linkages and to study the incorporation of both titania and silica, as this represents an established technique for the detection of Si–O–Ti 4+ bridges. ,− Previous reports using (near-edge) the X-ray absorption fine structure (NEXAFS and EXAFS) on silica-titania sol–gel films have demonstrated the predominant presence of tetra-coordinated Ti 4+ ions. ,, Figure shows the main vibrational modes for silica TUD-1 at 1061, 788, and 451 cm –1 , which can be attributed to the symmetric and antisymmetric Si–O–Si stretching vibration as well as the Si–O–Si bending mode, respectively. The spectrum for the samples containing Ti­(IV) also contains an additional absorption at 934 cm –1 , corresponding to the Si–O stretching vibration mode in Si–O–Ti bonds.…”

Sol–gel based optically active phenolphthalein encapsulated nanomatrices for sensing application

“…Additionally, the presence of surfactant into matrix sols helps to improve the homogeneity, but also gives the smooth surface texture because it lowers the surface tension of the hydroxylic surface of the glass to be coated and causes good adhesion between the sol and the substrate. It also helps to get the materials of high porosity and of low refractive index, which gives better catalytic and sensing performance [16,17]. Furthermore, in silicatitania (ST) hybrid matrix, heteroatoms (silica and titania) can broaden the potential of interesting characteristics.…”