A novel Z-scheme CoWO4/RGO/g-C3N4 photocatalyst for efficient visible-light-induced removal of organic pollutants

A ternary CoWO 4 /RGO/g-C 3 N 4 photocatalyst was synthesized via a facile hydrothermal method for visible-light-driven degradation of the azo dye Direct Blue 71 (DB 71). Structural, morphological, and optical characterizations (XRD, FT-IR, SEM, EDS, UV–Vis DRS, and PL) confirmed the uniform incorporation of CoWO 4 and reduced graphene oxide (RGO) into the g-C 3 N 4 framework, resulting in enhanced visible-light absorption and suppressed charge recombination through an RGO-mediated Type-II heterojunction. The optimized 0.1CoWO 4 /RGO/g-C 3 N 4 composite achieved 97% degradation and 73% TOC removal within 40 min, following pseudo-first-order kinetics (k = 0.08546 min -1 ). Behnajady–Modirshahla–Ghanbary (BMG) modeling yielded b = 0.79875 min -1 and m = 1.265, confirming high oxidative capacity. Photocatalytic activity was optimal under acidic to neutral pH and moderate catalyst dosage, with •OH and h + identified as the dominant reactive species. The catalyst maintained 89% efficiency after six cycles and achieved 54–74% TOC removal in real urban surface waters from Hanoi. A preliminary techno-economic analysis estimated a production cost of 15–40 USD·kg -1 , underscoring its scalability and economic viability for sustainable wastewater treatment. • CoWO 4 /RGO/g-C 3 N 4 achieves 97% DB71 removal and 73% TOC reduction in 40 min. • Hydroxyl radicals and photogenerated holes dominate the degradation process. • RGO bridge enhances charge transfer and visible-light utilization efficiency. • Catalyst maintains 89% activity after six cycles with negligible metal leaching. • Photocatalyst particles show scalable potential for wastewater purification