Dual surface defects induced efficient interfacial electron transfer in S-scheme hollow ZnO@ZnS heterojunction for uranium (VI) removal

Abstract

Photocatalytic reduction is a promising way to remove radioactive uranium U(VI) in wastewater. Herein, an S-scheme ZnO@ZnS heterojunction with hollow structure and dual-vacancies of Zn and S (ZnV, SV) is developed. The hollow confined space enhances light trapping ability through multiple light scattering and reflection, while the existence of vacancies extends light absorption, further enhancing the utilization of solar spectrum. Furthermore, the density function theory (DFT) calculations demonstrate that co-sharing of metal atoms at the interface and the ZnV and SV dual-vacancies induce enhanced internal electric field (IEF), leading to facilitated S-scheme charge transfer, thereby resulting in improved retention of redox potential and suppressed carrier recombination dynamics. ZnO@ZnS shows a highest U(VI) removal rate of 96.48% along with a highest U enrichment of 514.33 mg/g, which is 3.6 and 2.7-folds enhanced compared to pristine ZnO and ZnS, respectively. Through various quenching experiments, a potential new mechanism for the catalytic reduction of U(VI) is proposed. Our findings reveal the involvement of h+ in the reaction, highlighting its significant catalytic role in the reduction process. Moreover, ZnO@ZnS performs excellent U(VI) extraction ability in open-air conditions without any sacrificial agents, revealing the great significance for practical applications.