Rational construction of S-scheme ZnIn2S4/g-C3N4 heterojunction for effective sacrificial agent-free uranium photocatalysis in air

Abstract

Photocatalysis holds promise for extracting uranium from aqueous solution. Nevertheless, conventional approaches generally rely on sacrificial agents and anaerobic conditions to maintain photocatalytic efficiency, which increases costs and causes secondary pollution. Herein, we introduce the design and synthesis of an S-scheme ZnIn2S4/g-C3N4 (ZISCN) heterojunction photocatalyst for the efficient removal of uranium via in-situ generating ZnIn2S4 on g-C3N4. Photoelectric characterization and theoretical calculation indicate that ZISCN boosts the absorption of visible light and promotes the effective separation and migration of charge carriers by forming an internal electric field (IEF) at the S-scheme heterojunction interface. This configuration integrates the strong reducing electrons of g-C3N4 and the potent oxidation holes of ZnIn2S4. Consequently, the as-synthesized ZISCN can efficiently remove uranium under an air atmosphere without the need for sacrificial agents and anaerobic conditions. The achieved U(VI) removal rate of 94.8 % surpasses that of ZnIn2S4 and g-C3N4 individually. Moreover, the photocatalytic extraction of U(VI) by ZISCN photocatalyst demonstrated excellent stability and anti-interference performance. After five cycles, the U(VI) removal rate remained above 85 %. Mechanism studies reveal that when electrons are generated by light in the ZISCN systems, they can reduce O2, leading to the formation of reactive species ·O2/H2O2. These species subsequently interact with U(VI), resulting in the precipitation of (UO2)O2·2H2O on the surface of ZISCN. This research provides valuable insights for the design of heterojunction photocatalysts for efficient, sacrificial agent-free uranium removal in ambient air environments.