Investigation of the mechanism for the controlled periodic illumination effect in TiO2 photocatalysis

The photocatalytic oxidation of formate ion at illuminated TiO2 particles w as investigated in an annular slurry reactor and in a rotating disk reactor that utilized TiO2 particulate films. Rates of CO2 formation were determin ed during continuous and periodic illumination over a range of oxygen and f ormate ion concentrations. These investigations indicated that the periodic illumination effects reported for this reaction, and for other photocataly tic oxidations, resulted from intraparticle diffusion in flocculated partic les, mass transport of oxygen to the catalyst surface, slow or weak adsorpt ion of formate ion, or a combination of these processes.