Accelerated TiO2 photocatalytic degradation of Acid Orange 7 under visible light mediated by peroxymonosulfate

Abstract In this study, a system involving visible light TiO 2 photocatalysis (Vis/TiO 2 ) coupled with SO 4 - -based advanced oxidation technologies (AOTs) through the addition of the oxidant peroxymonosulfate (PMS, HSO 5 - ) has been developed to oxidize the target pollutant Acid Orange 7 (AO7) in aqueous solutions. There existed a remarkable synergistic effect in the combined Vis/TiO 2 /PMS system, and the performance of this combined system was better than that of a system to which persulfate (PS, S 2 O 8 2 - ) or hydrogen peroxide (H 2 O 2 ) was added. The influence of humic acids (HAs) and inorganic anions ( H 2 PO 4 - and HCO 3 - ) on the degradation rates in the Vis/TiO 2 /PMS system was also investigated. The obtained results revealed that HAs had a positive effect on the AO7 degradation efficiency in the Vis/TiO 2 /PMS system. When added to the Vis/TiO 2 system, PMS can abrogate the adverse interference of anions in this system, such that the Vis/TiO 2 /PMS system exhibits much better degradation rates. The primary degradation intermediates of AO7 identified by GC/MS were phthalic acid, 2,4,6-trichlorophenol, coumarin and two chlorinated aromatic compounds (7-chloro-2-naphthalenol and 2,4-dichloro-1-naphthalenol). A possible pathway was proposed based on the analysis of the degradation products.