O and S co-doping induced N-vacancy in graphitic carbon nitride towards photocatalytic peroxymonosulfate activation for sulfamethoxazole degradation

Doping-induced vacancy engineering of graphitic carbon nitride (GCN) is beneficial for bandgap modulation, efficient electronic excitation, and facilitated charge carrier migration. In this study, synthesis of oxygen and sulphur co-doped induced N vacancies (OSGCN) by the hydrothermal method was performed to activate peroxymonosulfate (PMS) for sulfamethoxazole (SMX) antibiotic degradation and H2 production. The results from experimental and DFT simulation studies validate the synergistic effects of co-dopants and N-vacancies, i.e., bandgap lowering, electron-hole pairs separation, and high solar energy utilization. The substitution of sp2 N atom by O and S co-dopants causes strong delocalization of HOMO-LUMO distribution, enhancing carrier mobility, increasing reactive sites, and facilitating charge-carrier separation. Remarkably, OSGCN/PMS photocatalytic system achieved 99.4% SMX degradation efficiency and a high H2 generation rate of 548.23 μ mol g-1 h-1 within 60 min and 36 h, respectively under visible light irradiations. The SMX degradation kinetics was pseudo-first-order with retained recycling efficiency up to 4 catalytic cycles. The results of EPR and chemical scavenging experiments revealed the redox action of reactive oxidative species, wherein 1O2 was the dominant reactive species in SMX degradation. The identification of formed intermediates and the SMX stepwise degradation pathway was investigated via LC-MS analysis and DFT studies, respectively. The results from this work anticipated deepening the understanding of PMS activation by substitutional co-doping favoring N-vacancy formation in GCN lattice for improved photocatalytic activity.