Rational design of S‒scheme Cd_0.5Zn_0.5S/CeO₂ heterojunction for enhanced photooxidation of antibiotics and photoreduction of Cr(VI)

Current photocatalysts endowed with oxidation and reduction capabilities for pharmaceuticals and heavy metals removal face numerous challenges, such as a lack of sufficient reactive sites, poor electron-hole separation, and limited oxidation and reduction capabilities. In this study, we aimed to overcome these limitations by employing a simple solvothermal method to fabricate a novel S-scheme heterojunction, Cd_0.5Zn_0.5S/CeO₂. The optimal Cd₀.₅Zn₀.₅S/CeO₂ heterojunction achieved a maximum ciprofloxacin degradation efficiency of 86 % within 30 min, showing a remarkable improvement of 2.4 and 4.6 times compared to pristine Cd₀.₅Zn₀.₅S and CeO₂, respectively. The heterojunction also demonstrated a remarkable 100 % photoreduction efficiency of Cr(VI) within 30 min, which is double the photodegradation performance of the individual materials. The combination of Cd₀.₅Zn₀.₅S with CeO₂ to form the Cd₀.₅Zn₀.₅S/CeO₂ S-scheme heterojunction effectively enhanced spatial photo-carrier separation and optimized the photo-redox capability, resulting in a substantial improvement in photocatalytic performance and stability. Through radical trapping experiments, the primary reactive species responsible for CIP degradation were identified as h⁺, OH^•, and ^•O₂⁻. Additionally, e⁻ was determined to be the key species responsible for the photoreduction of Cr(VI). Based on these findings, we proposed a plausible photocatalytic reaction pathway for the simultaneous elimination of both CIP and Cr(VI). This study underscores the significant potential of the Cd_0.5Zn_0.5S/CeO₂ S-scheme heterojunction for advanced wastewater treatment applications, highlighting its innovative approach and superior performance.