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 (MnO2) under the assistance of heat for sulfamethoxazole (SMX) degradation. Effects of some key reaction parameters such as PDS concentration, MnO2 dosage, initial pH and temperature were evaluated. The MnO2/heat/PDS synergistic system presented high performance on SMX degradation compared to the MnO2/PDS and heat/PDS systems. The degree of synergistic effect between MnO2 and heat in the MnO2/heat/PDS system was calculated and it was 88.62%. Both SO4 center dot-and center dot OH rather than 1O2 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 MnO2/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, MnO2 could keep its excellent catalytic performance even after four consecutive oxidation cycles. Therefore, this paper advances the understanding of the synergy of MnO2 with heat for enhanced PDS activation.