Insight into heterogeneous Fenton-sonophotocatalytic degradation of nitrobenzene using metal oxychlorides

Heterogeneous Fenton degradation of nitrobenzene (NB, 20 ppm) was investigated at room temperature and pH = 7 using 0.1 g L-1 of FeOCI (I), CuOCI (II), ZnOCI (III) and BiOCI (IV) metal oxychlorides catalysts in presence of ultrasonic (US, 20 kHz), ultraviolet (UV, 6 W, lambda = 254 nm) and UV/US double irradiation with H2O2 (5 mM) as an oxidant. The results showed that the order of the investigated systems with regard to their degradation performance was US/UV > UV > US, with I > II > IV > III but with mineralization extents of 46%, 41%, 35% and 33%, respectively under dual irradiation for 60 min. The synergistic effect correlates with the values of band gap of used oxychlorides and plays a vital role in enhancing the degradation performance of the dual system through generated reactive radicals (center dot OH & O-2(center dot-)) besides photo-born holes (h(+)) and electrons (e(-)). Experiments conducted in presence of different scavengers indicated that (center dot OH) and (h) play a major and more important role than that of (O-2(center dot-)) in the degradation process. Scavenging the generated electrons indicated that they act as degradation inhibitors. Band gap values dictated the variable activities shown by different metal oxychlorides.