Photocatalytic bleaching of p-nitrosodimethylaniline in TiO2 aqueous suspensions: A kinetic treatment involving some primary events photoinduced on the particle surface

The photocatalytic bleaching of p-nitrosodimethylaniline (P) has been investigated in aqueous suspensions of TiO2. It was found that both charge carriers (hole and electron) were reactive to P to result in a bleaching. The roles of O-2, and several hole scavengers (HCOO-, EDTA, I-) have also been examined. A reaction mechanism has been proposed with consideration of several primary processes photoinduced on TiO, surface. The results of the kinetic analysis fit fairly well to those of the experiments. The rate constant (k(p)(h)) of the reaction between P and the adsorbed hydroxyl radical was estimated to be in the order 10(10) M-1 s(-1), which is in good agreement with that obtained from the homogeneous reaction of P with free OH radicals, Of particular interest is the pH dependence of the photobleaching rate. Around both pK(a) of P and pH(ZPC) of TiO2, the photobleaching of P was steeply enhanced. This can be reasonably attributed to the mutual interaction (repulsion versus attraction) between P and TiO2 particles in different pH ranges.