Competitive role of structural properties of titania-silica mixed oxides and a mechanistic study of the photocatalytic degradation of phenol

TiO2-SiO2 mixed oxide materials were hydrothermally synthesized and the photocatalytic degradation of phenol under UV-irradiation was evaluated. We also demonstrated that varying the co-solvent, modulates the structural properties of the materials. In particular, the use of non-polar co-solvents such as toluene seemed to increase the crystallinity, surface area, and pore diameter while the crystallite size of titania seemed to change little. A comprehensive characterization using surface and bulk techniques evidenced the role of porosities, crystallinity, and Ti-O-Si linkages of the mixed oxides as significant factors that contribute to the degradation of phenol. The TiO2-SiO2 mixed oxide material prepared using only ethanol as the solvent showed 24% degradation of phenol after 120 mm of irradiation whereas other mixed oxide materials degraded phenol more efficiently (57% to 100%) in the same duration of time. The higher photocatalytic activities of the mixed oxide materials prepared using non-polar solvents is attributed to a combination of factors that include higher Apparent Surface Coverages of Ti-O-Si heterolinkages, larger pore sizes, and most importantly higher crystallinities of the titania phase. Larger pore sizes enabled better transport of reactant molecules and products to and from the active sites (Ti-O-Si heterolinkages) and the higher crystallinities of the titania phase helped in minimizing the electron-hole recombination in these photocatalysts, and thus resulted in high degradation efficiencies. (C) 2013 Elsevier B.V. All rights reserved.