Photodegradation of isoproturon on titanium dioxide and zinc oxide

Abstract

Photocatalytic degradation of isoproturon (N,N-dimethyl-N-[4-(1- methylethyl) phenyl] urea), which is one of phenylurea herbicides often found contaminating ground and surface waters, was investigated by using commercial titanium dioxide, commercial zinc oxide and synthesized zinc oxide as photocatalysts. The synthesized zinc oxide was synthesized by sol-gel method. In the process, 10-ppm of isoproturon in aqueous solution was conducted in a batch photo-reactor with 6 UV-A lamps. The solution was periodically sampled to monitor the concentration of isoproturon by using high performance liquid chromatography (HPLC). The decrease of total organic carbon (TOC) as a result of mineralization of isoproturon was also observed. In addition, identification degradation intermediates was detected through liquid chromatography with mass spectroscopy (LC-MS/MS). Studies of adsorption isotherms were used to describe the adsorption of isoproturon on surface of the photocatalysts. It was found that adsorption behavior of isoproturon on titanium dioxide and zinc oxide are different. Comparing between commercial titanium dioxide and commercial zinc oxide, the degradation performance on the commercial zinc oxide is much higher than that on the commercial titanium dioxide, although commercial zinc oxide has much lower surface area while the difference of photocatalytic efficiency of commercial and synthesized zinc oxide are different may come from the different of isoproturon adsorption on catalyst which may result from the rearrangement of Zn+ and O- on surface are different. Moreover, intermediates formed by the reaction on different photocatalysts and various pH of solution are also different.