Insight into the visible light activation of sulfite by Fe/g-C3N4 with rich N vacancies for pollutant removal and sterilization: A novel approach for enhanced generation of oxysulfur radical

• VIS/sulfite/Fe/g-C 3 N 4 (N 2 ) system shows promise in contaminant removal and sterilization. • The introduction of sulfite enhances the formation of SO 4 •− and • O 2 – . • The presence of NVs accelerates Fe 3+ /Fe 2+ redox cycle. • Fe/g-C 3 N 4-x with rich NVs exhibits stronger interaction towards HSO 3 − . • A mechanism of synergy between Fe, NVs, and g-C 3 N 4 in sulfite activation is proposed. A novel Fe-modified g-C 3 N 4 with rich N vacancies (NVs) under N 2 calcination was developed to active sulfite for the efficient removal of contaminants and bacterial inactivation under visible light (VIS). The degradation rates of VIS/sulfite/Fe/g-C 3 N 4 (N 2 ) for acetaminophen (ACT) were 10.94, 4.88, and 2.85 times higher than those of VIS/Fe/g-C 3 N 4 (N 2 ), VIS/sulfite/g-C 3 N 4 (N 2 ), and VIS/sulfite/Fe/g-C 3 N 4 (CO 2 ), respectively. Escherichia coli (E. coli) with an initial concentration of 2.5 × 10 8 CFU/mL decreased by 6.1 and 8.4 log CFU/mL within 60 min and 80 min of inactivation, respectively. The activation of sulfite led to the generation of oxysulfur radicals, and the consumption of hole (h + ) by sulfite inhibited its recombination with electron (e − ), promoting the formation of superoxide radical ( • O 2 – ). The synergistic effect of Fe, NVs, and g-C 3 N 4 in VIS/sulfite/Fe/g-C 3 N 4 (N 2 ) system promoted the generation of oxysulfur radicals. Density functional theory (DFT) calculations indicated that NVs facilitated charge transfer from Fe to g-C 3 N 4 substrate, accelerating the Fe 3+ /Fe 2+ and oxysulfur radical cycles. Fe/g-C 3 N 4 with rich NVs exhibited lower adsorption binding energy, faster charge transfer, and longer S-O bond length than pristine Fe/g-C 3 N 4 during sulfite adsorption. This work unraveled the synergistic mechanism of Fe, NVs, and g-C 3 N 4 , which provides new insights into heterogeneous photocatalysts on sulfite activation for water treatment.