Photocatalytic oxidation of deposited sulfur and gaseous sulfur dioxide by TiO2 films

Thick (4 μm) films of anatase titania are used to photocatalyze the removal of deposited films of amorphous sulfur, 2.8 μm, thick and under moderate illumination conditions (I = 5.6 mW cm-2) on the open bench the process is complete within 8 or 18 h using UVC or UVA light, respectively. Using UVA light, 96% of the product of the photocatalytic removal of the film of sulfur is sulfur dioxide, SO2. The photonic efficiency of this process is 0.16%, which is much higher (>15 times) than that of the removal of soot by the same films, under similar experimental conditions. In contrast to the open bench work, in a closed system the photocatalytic activity of a titania film toward the removal of sulfur decreased with repeated use, due to the accumulation of sulfuric acid on its surface generated by the subsequent photocatalytic oxidation of the initial product, SO2. The H2SO4-inactivated films are regenerated by soaking in water. The problems of using titania films to remove SO2 from a gaseous environment are discussed briefly.