Photodegradation of commercial dye, CI Reactive Blue 160 using ZnO nanopowder: Degradation pathway and identification of intermediates by GC/MS

The ZnO-mediated photocatalysis process has been successfully applied to degradation of commercial dye, CI Reactive Blue 160 (RB 160). Eleven reaction intermediates were separated, identified and characterized by the GC–MS techniques, giving insight into mechanistic details of the ZnO-mediated catalysis process under UV irradiation and the pathways of degradation process. The degradation process take place through competitive reactions such as destruction of chromophoric group, hydroxylation of the aromatic ring, substitution on aromatic ring, desulphonation, decarboxylation and further ring opening to give aliphatic compounds. Smaller aliphatic compounds formed during the process were identified by IC, while the triazine group and naphthalene group containing compounds remains intact even after decolorization for a prolonged time due to high resistance to oxidation. The probable degradation pathways were proposed and discussed.

► ZnO is efficient photocatalyst for decolorization of Reactive Blue 160 (RB 160).
► Degree of decolorization is higher than degree of mineralization.
► Several smaller organic intermediates formed were analyzed through GC analysis.
► Eleven intermediates formed during 30 min of reaction are subsequently degraded with time.
► A detailed reaction mechanism established will help in better understanding of the photocatalytic process.