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The use of titania-silica in photocatalytic process has been proposed as an alternative to the conventional TiO 2 catalysts. Mesoporous materials have been of great interest as catalysts because of their unique textural and structural properties. Mesoporous TiO 2 , SiO 2 nanoparticles and TiO 2 /SiO 2 nanocomposites were successfully synthesized by sol-gel method using titanium (IV) isopropoxide, tetra-ethylorthosilicate as starting materials. The synthesized samples are characterized by X-ray diffraction, UV-Vis spectroscopy, Fourier transform infrared spectroscopy, Brunauett-Emmett-Teller and field-dependent photoconductivity. The UV-Vis spectrum of as-synthesized samples shows similar absorption in the visible range. The crystallite size of the as-synthesized samples was calculated by Scherrer's formula. The BET surface area for TiO 2 /SiO 2 nanocomposite is found to be 303 m 2 /g and pore size distribution has average pore diameter about 10 nm. It also confirms the absence of macropores and the presence of micro and mesopores. The field-dependent photoconductivity of TiO 2 /SiO 2 nanocomposite shows nearly 300 folds more than that of TiO 2 nanoparticle for a field of 800 V/cm.

The SiO 2 -Fe 3 O 4 core-shell nanostructures were synthesized by sol-gel chemistry. The morphological features of the nanostructures were examined by field emission scanning electron microscopy which revealed the core-shell nature of the nanoparticles. X-ray diffraction studies evidenced the formation of SiO 2 -Fe 3 O 4 core-shell nanostructures with high degree of homogeneity. The elemental composition of the SiO 2 -Fe 3 O 4 core-shell nanostructures was determined by energy-dispersive X-ray spectroscopy analysis. Fourier transform infrared spectroscopy showed the Si-O-Fe stretching vibrations. On analysis of the optical properties with UV-Vis spectra and Tauc's plot, it was found that the band gap of SiO 2 -Fe 3 O 4 core-shell nanostructures diminished to 1.5 eV. Investigation of the electrical properties of the core-shell nanostructures using field-dependent conductivity measurements presented a significant increase in photoconductivity as compared to those of its single components, thereby rendering them as promising candidates for application as photoelectrodes in dye-sensitized solar cells.

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