Photodegradation of linuron on titania and zinc oxide

Abstract

Degradation of linuron (N-(3, 4-dichlorophenyl)-N’-methoxy-N’-methylurea), which is a harmful phenylurea herbicide commonly found as residue in water, was conducted via heterogeneous photocatalysis on commercial and synthesized titanium dioxide (TiO₂) and commercial and synthesized zinc oxide (ZnO). Nanoparticles of the photocatalysts were synthesized via the sol-gel method. The photocatalytic degradation of 10-ppm linuron aqueous solution was conducted in a batch photo-reactor. Concentration of linuron was periodically monitored using high performance liquid chromatography (HPLC) with 254-nm UV detector. The decrease of total organic carbon as a result of mineralization of linuron was also observed during the degradation process. It was found that zinc oxide shows higher performance in degradation and mineralization of linuron than titanium dioxide, regardless of much lower surface area. The degradation of linuron on zinc oxide was about 93% within 6 hours, while that achieved on titanium dioxide was only 55%. Unlike previous studies that focused on the disappearance of the pollutant, this work also investigated intermediate compounds formed during the reaction. Several intermediates were detected during the course of the degradation. Attempts were made to identify the intermediate products through analyses using liquid chromatography with mass spectrometry (LC-MS). Comparison of the intermediates formed, when different photocatalysts and difference pH were used, revealed intermediates that were observed from both catalysts as well as intermediates that were specific to one particular catalyst.