UV light-assisted persulfate activation by Cu0-Cu2O for the degradation of sulfamerazine

Sulfate radicals-based advanced oxidation process (SRAOP) has received increasing attention in the wastewater treatment area because sulfate radicals have high redox potential. The key for SRAOP is to develop high efficient catalysts that can effectively and stably activate persulfate (PS) to produce sulfate radicals. Cu2O is a good activator of PS and photo-catalyst. However, its catalytic activity is relatively low because of the poor stability and the recombination of electron and holes. In theory, Cu-0 can reduce Cu2+ to form Cu+, which can decrease the recombination of electron and holes from the Cu2O by the formation of heterojunction. In this study, (CuCu2O)-Cu-0 was synthesized by a simple ball-milling method. The as-prepared Cu-0-Cu2O was characterized and used to activate PS for sulfamerazine (SMZ) degradation by means of UV illumination. In the Cu-0-Cu2O/PS/UV system, the removals of 100% SMZ and 30% TOC within 30 min were achieved, respectively, and the removal efficiency of SMZ decreased by only 12.2% after 5 cycles. The high efficiency and good catalytic stability of Cu-0-Cu2O for the activation of PS were due to that Cu-0 and photo-induced electron of Cu2O promoted the conversion of Cu2+ to Cu+. Quenching experiments demonstrated that the hydroxyl radicals and sulfate radicals contributed to SMZ degradation. However, the concentrations and fractions of radicals was affected by the initial pH of solution. Nine intermediate products were identified, and the degradation pathways were proposed, including the fission of sulfur and nitrogen bond, the oxidation of methyl group and the hydroxylation of benzene ring. The effects of initial pH, PS concentration, Cu-0-Cu2O dosage and SMZ initial concentration on the degradation of SMZ were investigated. This study provided an effective catalyst that could simultaneously activate PS and utilize UV to form photo-induced electron, which could enhance the degradation and mineralization of organic pollutants.