Durable Sulfur-Doped g-C3N4 Catalysts with High Performance for Rapid Rhodamine B Degradation in Organic Wastewater

To overcome the inherent limitations of graphitic carbon nitride (g-C3N4), specifically the rapid recombination of photogenerated electron–hole pairs and its confined light absorption range, a sulfur-doped g-C3N4 (S-g-C3N4) photocatalyst was developed in this work. The photocatalytic performance and its catalytic mechanism for rhodamine B (RhB) degradation were systematically investigated. Material characterization and performance tests revealed that S doping can narrow the band gap of g-C3N4 and effectively enhance the separation and transport efficiency of charge carriers. The as-prepared catalyst demonstrated excellent activity under simulated sunlight, achieving nearly complete degradation of 10 mg/L RhB within 15 min. Moreover, it exhibited robust stability across a pH range of 6 to 11 and in the presence of coexisting anions (Cl−, NO3−, CO32−), with negligible activity loss after five consecutive cycles. Radical trapping experiments verified that ∙OH radicals served as the primary active species, with h+ playing a secondary role in the degradation process. This work provides practical guidance for designing durable g-C3N4-based photocatalysts with high performance for organic wastewater treatment.