Peroxymonosulfate Activation by Fe–Co–O-Codoped Graphite Carbon Nitride for Degradation of Sulfamethoxazole

Graphite carbon nitride (g-C₃N₄) has a stable structure but poor catalytic capability for activating peroxymonosulfate (PMS). In this study, the codoping of g-C₃N₄ with bimetallic oxides (iron and cobalt) and oxygen was investigated to enhance its catalytic capability. The results showed that iron, cobalt, and oxygen codoped g-C₃N₄ (Fe-Co-O-g-C₃N₄) was successfully prepared, which was capable of completely degrading sulfamethoxazole (SMX) (0.04 mM) within 30 min, with a reaction rate of 0.085 min^-1, indicating the superior catalytic activity of Fe-Co-O-g-C₃N₄. The mineralization efficiency of SMX was 22.1%. Sulfate radicals and singlet oxygen were detected during the process of PMS activation. However, the role that singlet oxygen played in degrading SMX was not obvious. Surface-bound reactive species and sulfate radicals were responsible for SMX degradation, in which sulfate radicals contributed to 46.6% of SMX degradation. The superior catalytic activity was due to the synergistic effect of metal oxides and O-g-C₃N₄, in which O-g-C₃N₄ could act as a carrier and an activator as well as an electron mediator to promote the conversion of Fe(III) to Fe(II) and Co(III) to Co(II). Four main steps of SMX degradation were proposed, including direct oxidation of SMX, bond fission of N-C, bond fission of N-S, and bond fission of S-C. The effect of the pH, temperature, PMS concentration, chloridion, bicarbonate, and humic acids on SMX degradation was investigated. Cycling experiments demonstrated the good stability of Fe-Co-O-g-C₃N₄. This study first reported the preparation of bimetallic oxide and oxygen codoped g-C₃N₄, which was an effective PMS activator for degradation of toxic organic pollutants.