Photocatalyzed Transformation of Nitrobenzene on TiO2 and ZnO

The degradation of nitrobenzene on irradiated semiconductor oxides (TiO2 and ZnO) has been investigated. The results suggest that the degradation pathways of nitrobenzene in aerated aqueous solution in the presence of TiO2 involve mainly the formation of the three nitrophenol isomers in comparable abundance, followed by further hydroxylation and ring cleavage. Complete mineralization has been assessed and nitrate and ammonium ions finally detected in a ratio of about 6:1. Intermediate formation of nitrite ions and traces of phenol has been observed; although formation of ammonium ions is suggestive of reductive pathways, nitrosobenzene and aniline were detected at very low concentration. Degradation of the three nitrophenols was also performed under similar experimental conditions to get information on the further reaction pathways. Photocatalytic degradation of nitrobenzene on ZnO was slower than on TiO2 and showed some differences in product distribution, especially for nitrophenols, where 3-nitrophenol is the predominant isomer. Degradation on Al2O3 has also been investigated for comparison