Heterogeneous and homogeneous wastewater treatment — Comparison between photodegradation with TiO2 and the photo-fenton reaction

The oxidative destruction of phenol, cyclohexanol (CyOH), and 4-nitroaniline (4-NA) in aqueous solution by the photo-Fenton reaction and TiO2/UV-A is described and compared. The decomposition mechanisms were investigated by studying the intermediate products by HPLC and a photodiode array. The degradation of 4-NA was monitored by GC/MS to trace the decomposition products (nitrobenzene, p-benzoquinone, hydroquinone and resorcine). During the photochemical degradation of 4-NA nitrate ions were detected by an ion selective electrode. The degradation rates with the photo-Fenton reaction had the following order: Phenol > 4-NA >> CyOH, in contrast to the order CyOH > Phenol > 4-NA obtained with TiO2/UV-A. The same intermediate decomposition products were obtained for each substrate by both methods.