Gas phase photocatalytic removal of toluene effluents on sulfated titania

Photocatalytic removal of toluene in the gas phase was carried out over UV-illuminated sulfated titania materials in a cylinder-like continuous reactor. A series of SO42−-TiO2 samples was obtained from the addition of H2SO4 on an amorphous titanium hydroxide gel synthesized according to a classical sol-gel procedure. The wide variety of materials led to varying photocatalytic behaviors depending strongly on the experimental synthesis parameters, having a determinant influence on the surface specific area, the crystallinity of the material, the crystallographic nature of TiO2, and the sulfate surface content. Optimization of the experimental parameters, such as the molarity of the sulfation solution, varying in the range 0.25-5 M leading to surface sulfate coverage of 2.5-14 wt%, and the calcination temperature ranging from 400 to 800 °C, promoted enhanced photocatalytic performance toward toluene removal as compared with commercially available P25 TiO2 and sulfate-free sol-gel TiO2. The most efficient photocatalyst was obtained for a near-monolayer sulfate coverage corresponding to the presence of both TiO2 and well-dispersed SO42− with optimized contact between SO42− and TiO2 domains. Furthermore, a positive role of sulfates is attributed both to an electron transfer from titanium to sulfates, leading to a positive charge trap effect, and to better desorption of electron-rich sp2-bound carbon aromatic poisons, thus limiting deactivation.