Light-induced oxidation of phenol over ZnO powder

The photo-oxidation of phenol in aqueous suspensions of ZnO was studied under different experimental conditions. It was observed that the yield of phenol decomposition decreases with increasing initial phenol concentration, decreasing oxygen concentration in solution and increasing pH. The amount of hydrogen peroxide formed during irradiation decreases with increasing phenol concentration over the range 10 -4 - 10 -2 M. On the other hand, ZnO shows a certain degree of instability. After 60 min of irradiation of a 10 -3 M phenol solution containing 8 g l -1 of ZnO in suspension. 0.24% of the initial ZnO was photodecomposed. From the results of the present work it can be concluded that in diluted solutions phenol is oxidized preferentially by homogeneous reaction with OH{radical dot} radicals, while for concentrated solutions the oxidation can proceed by reaction with photogenerated holes. © 1988.