On the modification of photocatalysts for improving visible light and UV degradation of gas-phase toluene over TiO2

The photocatalytic behavior of different TiO₂-based photocatalysts was reported for gas-phase toluene removal under both UV and visible light illumination, and compared to that of commercial P25 (Degussa) TiO₂. Promotion by sulfates and the use of nanosized anatase TiO₂ were reported to strongly increase the toluene removal efficiency under UV illumination. Nanosized-anatase was prepared by a protecting group sol–gel synthesis using hexamethyldisilazane as crystallite growth inhibitor. Sulfates played a double positive role, with photogenerated electrons transfer effects limiting charge recombination and as repulsive species for strongly adsorbed aromatic intermediates that act as poisons. The decrease in particle size obtained on nanosized anatase TiO₂ (5 nm) yielded a considerable enhancement in the toluene removal efficiency. Pure high surface area rutile has been synthesized at low temperature by a polyethylenglycol-containing sol–gel method for visible light activation purposes. A two-way semiconductor coupling phenomenon, consisting of a reciprocal electron/hole transfer between two visible light-activated oxides, rutile TiO₂ and WO₃, was proposed to explain the large gain in efficiency when adding low amounts of WO₃ to rutile TiO₂.