Iron and sulfur co-doped graphite carbon nitride (FeOy/S-g-C3N4) for activating peroxymonosulfate to enhance sulfamethoxazole degradation

In this study, the iron and sulfur co-doped graphite carbon nitride (FeOy/S-g-C3N4) was easily prepared by one-step pyrolysis using thiourea and ferric chloride hexahydrate as precursors and applied to activate peroxymonosulfate (PMS) for the degradation of sulfamethoxazole (SMX). The characterization results showed that iron existed as Fe2O3 and Fe3O4. Partial nitrogen atoms in the frame of g-C3N4 were substituted by sulfur atoms. FeOy/S-g-C3N4 can effectively activate PMS to produce sulfate radicals, hydroxyl radicals and singlet oxygen contributing to the SMX degradation. According to the density functional theory (DFT) calculation, the co-doping of iron and sulfur altered the charge density and its distribution of g-C3N4 surface, which enhanced the PMS activation. The effect of initial concentrations of SMX and PMS, pH, temperature and inorganic ion concentrations on SMX degradation was investigated. 0.8 mM of PMS could degrade up to 10 mg/L of SMX. The initial pH had no obvious effect on the SMX degradation. Higher temperature accelerated the SMX degradation, and the activation energy was calculated to be 43.7 kJ/mol. The effect of inorganic ions was dependent on their initial concentration. Based on the comparison of XPS spectrum before and after reaction, the decreased catalytic activity of FeOy/S-g-C3N4 after five cycle reuse was due to the breakdown of surface functional groups. Seven intermediate products were identified, and the possible degradation pathway was proposed. This study could provide a facile and cost-effective method to synthesize the efficient activator of PMS, and a mechanistic insight into PMS activation by FeOy/S-g-C3N4 for the degradation of emerging pollutants in water and wastewater.