Synergistic effect of persulfate and g-C3N4 under simulated solar light irradiation: Implication for the degradation of sulfamethoxazole

A method combining g-C3N4 and potassium peroxydisulfate (PDS) under simulated sunlight was put forward to effectively degrade sulfamethoxazole (SMX). The SMX removal efficiency was substantially improved compared with the processes involving only g-C3N4 or PDS. The kinetic constants for the g-C3N4, PDS and g-C3N4/PDS systems were 0.0023, 0.0239 and 0.068 min-1, respectively. The g-C3N4/PDS process reached an SMX removal rate of 98.4 % after 60 min of simulated sunlight; in addition, the proposed system showed desirable efficiency for SMX degradation in two different actual water samples as well. The reaction mechanism was illustrated by trapping experiments, which showed that g-C3N4 can promote S2O82- to transfer SO4-, S2O82- favored the generation of O2-, and O2-, SO4- and holes (h+) were the main oxidative species for the SMX degradation in the combined reaction process under simulated sunlight. Then, to further explore this mechanism, the intermediates generated during the combined reaction process were analyzed by LC/MS and possible degradation pathways were proposed. The result showed that the breaking of the SN and C-S bonds, the hydroxylation of the benzene ring and the oxidation of the amino group were identified as the main pathways in the SMX degradation process by the g-C3N4/PDS system under simulated sunlight.