Dependence of Catalyst Surface in Photocatalytic Degradation of Phenyl Urea Herbicides

Photocatalytic degradations of various contaminants using in-house synthesized catalysts have been generally reported, but the degradation intermediates formed are normally inconsistent. This issue is particularly important for the degradation of toxic compounds which may form intermediates with increased toxicity. This work resolves this issue by systematically investigating adsorption and photocatalytic degradation of diuron, linuron, and 3,4-dichloroaniline (DCA) on two forms of zinc oxide (ZnO), i.e., conventional particles with zinc- and oxygen-terminated polar surfaces, and nanorods with mixed-terminated non-polar surfaces. Experimental results indicate that both rate of degradation and degradation pathway depend upon the adsorption configuration of the compound undergoing the degradation onto the surface of the catalyst. The adsorption configuration is surface dependent. On polar surfaces, both aliphatic and aromatic sides of diuron and linuron molecules adsorb on the surface, allowing the attack of hydroxyl radicals on both ends. On the other hand, on non-polar surface, only the aliphatic chain adsorbs onto the surface, resulting in the hydroxyl radicals attack only on the aliphatic side. The structure of the catalyst is therefore a crucial factor determining the dominant degradation pathway.