Degradation of sulfamethoxazole by MnO2/heat-activated persulfate: Kinetics, synergistic effect and reaction mechanism

Contaminants destruction via advanced oxidation processes using catalyst and heat for peroxydisulfate (PDS) activation have been proven to be a feasible method in environmental remediation. Nevertheless, the synergistic activation of PDS by Mn-based catalysts and heat was barely reported in early investigations. In this study, we focused on a systematic investigation of PDS activation over manganese dioxide (MnO 2 ) under the assistance of heat for sulfamethoxazole (SMX) degradation. Effects of some key reaction parameters such as PDS concentration, MnO 2 dosage, initial pH and temperature were evaluated. The MnO 2 /heat/PDS synergistic system presented high performance on SMX degradation compared to the MnO 2 /PDS and heat/PDS systems. The degree of synergistic effect between MnO 2 and heat in the MnO 2 /heat/PDS system was calculated and it was 88.62%. Both SO 4 •− and • OH rather than 1 O 2 were detected to be responsible for SMX oxidation. Based on identified oxidation products by the liquid chromatography-quadrupole/time-of-flight mass spectrometry, the transformation pathways of SMX in MnO 2 /heat/PDS system followed mainly four major pathways (a) cleavage of S-N bond; (b) hydroxylation for benzene ring; and (c) dehydrogenation of the amino group. Moreover, MnO 2 could keep its excellent catalytic performance even after four consecutive oxidation cycles. Therefore, this paper advances the understanding of the synergy of MnO 2 with heat for enhanced PDS activation.