Enhanced photocatalytic performance of ZnIn2S4/g-C3N4/WO3 ternary dual S-Scheme heterojunctions for polymer wastewater purification

Defect engineering and dual electric fields can direct interfacial charge migration and separation while supplying the driving force for photogenerated carriers, thus serving as an effective strategy to accelerate photocatalysis. Here, a ZnIn2S4/g-C3N4/WO3 (denoted as ZIS/CN/WO3) dual S-Scheme heterojunction was synthesized via a simple hydrothermal method and subsequent thermal treatment, with sulfur vacancies in ZIS used to modulate the internal electric field and drive carrier migration. Meanwhile, the photocatalytic performance of ZIS/CN/WO3 was evaluated through the degradation of methyl orange (MO), the reduction of Cr(VI), and the degradation of sulfonated phenolic–formaldehyde resin (SMP). The MO degradation rate of ZIS/CN/WO3 (0.058 min-1) was 4.46, 9.67, 14.5, and 2.15 times higher than those of pure ZIS (0.013 min-1), CN (0.006 min-1), WO3 (0.004 min-1), and ZIS/CN (0.027 min-1), respectively. Similarly, the Cr(VI) reduction rate (0.051 min-1) exceeded ZIS (0.022 min-1), CN (0.009 min-1), WO3 (0.004 min-1), and ZIS/CN (0.030 min-1) by 2.32, 5.67, 12.75, and 1.70 times. Notably, the chemical oxygen demand (COD) after SMP degradation by ZIS/CN/WO3 (0.313 h-1) was 1.86, 2.78, 7.45, and 1.24 times higher than that of ZIS (0.168 h-1), CN (0.113 h-1), WO3 (0.042 h-1), and ZIS/CN (0.252 h-1), respectively. In addition, the band-gap analysis, internal electric fields, and surface potential mapping indicate that the enhanced activity of ZIS/CN/WO3 stems from an S-Scheme heterojunction with sulfur vacancies and dual electric fields. This study provides insights into the application of dual S-Scheme heterojunctions for wastewater treatment in abandoned drilling fluids.