Enhancing the catalytic activity of g-C3N4 through Me doping (Me = Cu, Co and Fe) for selective sulfathiazole degradation via redox-based advanced oxidation process

In this study, Me-doped g-C3N4 (Me = Cu, Co and Fe) catalysts with various % w/w of Me dopant are prepared by a versatile calcination protocol for catalytic redox-based advanced oxidation process. The characterization study using FESEM, EDX, TEM, XRD, TGA, XPS, FTIR and BET indicates that all the Me-doped g-C3N4 consist of irregular morphology with at least 1.4–1.9 times higher surface area than that of pristine g-C3N4. The catalysts were used to generate SO4− from peroxymonosulfate (PMS) for selective sulfathiazole (STZ) degradation. The results show that the catalytic activities of the Me-doped g-C3N4 are in the following order: Co-doped g-C3N4 (0.59% w/w Co, Co–g–4) > Fe–doped g-C3N4 ≫ Cu-doped g-C3N4 ∼ pristine g-C3N4. The excessive Me doping have a negative effect on catalytic performance due to the undesired SO4− scavenging by surface defects (–CN) and excess Me. The STZ degradation were highly influenced by the pH, catalyst loading and Oxone® dosage. The predominant reactive radical is identified to be SO4− which contributes to >82% of total STZ degradation. The LC/MS/MS system was used to confirm the selectivity of SO4− for STZ degradation. The main STZ degradation pathway is also proposed. The performance of Co–g–4/PMS system for STZ removal in the treated drinking water (TW) and secondary wastewater effluent (SE) was investigated. It is found that, despite having poorer performance compared with the DI water due to the presence of various water matrix species particularly the dissolved organic matter, the selectivity of SO4− for STZ in SE and TW is evidenced. Overall, the Co-g-4/PMS system shows promising performance and excellent stability for selective catalytic degradation of sulfonamide antibiotics in water.