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

In this study, a system involving visible light TiO2 photocatalysis (Vis/TiO2) coupled with SO4--based advanced oxidation technologies (AOTs) through the addition of the oxidant peroxymonosulfate (PMS, HSO5-) 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/TiO2/PMS system, and the performance of this combined system was better than that of a system to which persulfate (PS, S2O82-) or hydrogen peroxide (H2O2) was added. The influence of humic acids (HAs) and inorganic anions (H2PO4- and HCO3-) on the degradation rates in the Vis/TiO2/PMS system was also investigated. The obtained results revealed that HAs had a positive effect on the AO7 degradation efficiency in the Vis/TiO2/PMS system. When added to the Vis/TiO2 system, PMS can abrogate the adverse interference of anions in this system, such that the Vis/TiO2/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.

► An efficient process of Vis/TiO2 accelerated by PMS (Vis/TiO2/PMS) for dye removal is built. ► The synergistic effects of dye-sensitization and SO4--based AOTs were investigated. ► The effects of anions and humic acids on the Vis/TiO2/PMS system were investigated. ► Major active species of system is ·OH and SO4·- and possible pathway was proposed.