Elucidating structure-activity relationships in CdS/ZnO heterojunctions for synergistic adsorption-photocatalysis of uranium (VI) removal

Abstract

Efficient removal of uranium(VI) from radioactive wastewater is of critical importance for sustainable utilization of uranium resources and environmental protection against uranium contamination. In this work, we report a dual–function heterojunction of CdS/ZnO for visible light-driven photocatalysis assisted with adsorption, where CdS/ZnO-140 not only accelerates reaction kinetics but also enhances overall U(VI) removal efficiency by confining adsorbed U(VI) near catalytic sites. Furthermore, CdS/ZnO composites were prepared via a facile hydrothermal method, and the effects of hydrothermal temperature on U(VI) removal performance under visible light were systematically investigated. Compared with the pristine CdS and ZnO nanoparticles, the CdS/ZnO heterojunctions exhibit higher removal performances, attributed to the introduction of ZnO component that significantly improves both adsorption capacity and spatial separation efficiency of photo-generated electron-hole pairs. More importantly, different key factors including band gap, energy level, crystallinity, specific surface area, adsorption kinetics and radical generation amount were taken into account for structure–performance investigation of U(VI) photocatalytic removal. Notably, the CdS/ZnO-140 composite exhibits superior U(VI) removal efficiency, outperforming counterparts synthesized at 100 °C and 180 °C. The investigations reveal that the enhanced U(VI) removal activity of CdS/ZnO-140 could be correlated with the efficient charge separation and migration, carrier dynamics, and surface active sites. By elucidating the role of hydrothermal temperature in tuning carrier dynamics and surface reactivity, we provide insights for designing heterojunction photocatalysts with tailored adsorption and redox functionalities.