Design of S-Scheme CuInS₂/CeO₂ Heterojunction for Enhanced Photocatalytic Degradation of Pharmaceuticals in Wastewater

The release of common medications and illegal drugs into the environment could be potentially harmful to the ecosystem and hamper the behavior and growth of plants and animals. These pollutants gain access to water through sewage and factory discharges and have been found to exceed safety limits in water bodies. Therefore, there is an urgent need for improved wastewater purification systems. In this study, semiconductor-based heterojunction photocatalyst CuInS₂/CeO₂, synthesized through a facile solvothermal process, was explored for the photocatalytic degradation of ciprofloxacin, commonly used antibiotics. Studies on the electronic properties of the heterojunction revealed interfacial characteristics that were suitable for enhanced charge carrier separation and transport and a potential S-scheme charge transfer mechanism. The heterojunction achieved ∼90% efficiency for the degradation of CIP compared to 60% and 12% reported for CeO₂ and CuInS₂, respectively. This shows an improvement in the activity, which results from the improved charge carrier properties of the heterojunction. Further investigation of the charge transfer mechanism through radical scavenging experiments identified ^•OH, O2^•-, and h⁺ as active species contributing to the catalyst's efficacy. Based on X-ray photoelectron spectroscopy analysis, a proposed S-scheme charge transfer mechanism was suggested for the CuInS₂/CeO₂ heterojunction. The findings indicate the potential of the CuInS₂/CeO₂ heterojunction as a promising photocatalyst for treating waste effluents from the pharmaceutical industry.