Development of Z-scheme bimetallic tungstate-supported nitrogen deficient g-C3N4 heterojunction for the treatment of refractory pharmaceutical pollutants

Abstract

Nitrogen-deficient graphitic carbon nitride (ND-GCN) was fabricated using a simple liquid-phase polycondensation process, and the nitrogen deficiencies in GCN were verified by XPS and EDS. To develop a Z-scheme-based bimetallic tungstate (BMT) supported ND-GCN photocatalyst, wet chemical approach and polycondensation method are utilized. The physicochemical properties are characterized, and the data indicate that well-matched band structures between BMT and ND-GCN make it easier to establish a Z-scheme charge transfer route. The photocatalytic efficiency of the fabricated photocatalyst is compared using pharmaceutical effluent followed by model organic pollutants, such as azithromycin (AZI) and tetracycline (TC). The CoZnWO₄/ND-GCN composite material demonstrates the best degradation performance towards AZI (98.64%) and TC (98.17%) within 75 min, and towards pharmaceutical effluent (97.84%) within 90 min, whereas the NiCoWO₄/ND-GCN shows the following degradation performance: AZI (91.19%), TC (96.31%) and pharmaceutical effluent (95.16%). The quality of the treated pharmaceutical effluent was improved using CoZnWO₄/ND-GCN catalyst, as indicated by the reduction in chemical oxygen demand (COD) of 80.07%, and the total organic carbon (TOC) of 76.8%. A detailed examination of the mechanism demonstrates that the hydroxyl (˙OH) and superoxide (˙O₂⁻) radicals are responsible for photocatalytic degradation. The findings of this study offer a novel approach to developing a powerful photocatalyst for the mineralization of challenging organic compounds in water.