Covalently bridged oxygen-vacancy-rich BiOCl/g-C3N4 S-scheme heterojunction for oxygen-resistant wet Fe(II)EDTA denitrification

Wet Fe(II)EDTA complexation is a promising technology for NO removal, but its practical application is severely hindered by O 2 -induced oxidation of Fe(II)EDTA and inefficient regeneration of Fe(II)EDTA–NO. Herein, an oxygen-vacancy-rich BiOCl/g-C 3 N 4 S-scheme heterojunction with interfacial Bi–O–C covalent bonds was constructed for oxygen-resistant photocatalytic–complexation denitrification. Structural characterizations and density functional theory calculations confirmed that Bi–O–C bonds served as atomic-level charge-transfer channels, strengthening interfacial coupling and promoting directional S-scheme charge separation. This configuration preserved strongly reductive electrons on g-C 3 N 4 for the reduction of Fe( III )EDTA and Fe(II)EDTA–NO, while retaining oxidative holes on BiOCl. Meanwhile, oxygen vacancies on BiOCl acted as preferential O 2 adsorption and activation sites, converting O 2 into ·O 2 − and thereby transforming O 2 from a competitive oxidant into an electron-buffering species that suppresses BiOCl photocorrosion and regulates interfacial redox cycling. The optimized 20BCN–Fe( II )EDTA system achieved an average NO removal efficiency of 88.92% under 14% O 2 and maintained above 80.02% efficiency after 30 cycles. Product analysis revealed a reduction-dominated NO conversion pathway, with NH 4 + and N 2 as the major reduced nitrogen products, a total reduced-product selectivity of 91.9%, and a nitrogen recovery of 94.4%. Kinetic analysis confirmed that NO absorption proceeded in a fast reaction regime enhanced by interfacial redox reactions. This work provides an atomic-level strategy for designing oxygen-resistant photocatalytic systems for wet denitrification under realistic flue-gas conditions.