Thesis (M.Eng.)--Chulalongkorn University, 2551

The practical elimination of phenylurea herbicides from water by photocatalytic reaction was studied using zinc oxide as photocatalyst and by choosing diuron, linuron, and isoproturon as representatives for the herbicides. The catalytic activities were investigated, based on the rate of phenylurea herbicides disappearance. In particular, comparison was made on their initial activities. Under identical conditions, it was found that the extent of the degradation of the phenylurea herbicide was obviously affected by amount of photocatalyst, initial phenylurea herbicide concentration, pH of the solution, and temperature. The photocatalytic reaction on the surface of zinc oxide can completely degrade the phenylurea herbicide existing in the solution. Chemical structure and stability of the phenylurea herbicide affect the rate of degradation. The higher activity or the less stability of isoproturon gives higher rate of degradation than that of diuron and linuron. Several degradation intermediates are generated by reactions of hydroxyl radical attacking to several sites of phenylurea structure, during the photocatalytic process