Synergistic piezo-photocatalytic reduction of U(VI) by Zn0.7Cd0.3S solid solution homojunction

Photocatalysis has been applied to the reduction of U(VI), but how to improve the separation of photogenerated carriers, realize photocatalysis without sacrificial agents, and still have a certain catalytic activity in the absence of light are still problems that need to be solved. In this paper, a series of ZnxCd1-xS (0 ≤ x ≤ 1) solid solutions with different Zn/Cd molar ratios are synthesized for piezo-photocatalytic reduction of U(VI) under air atmosphere and without the addition of sacrificial agent. Under combined visible light and ultrasound irradiation, the homojunction with bicrystalline structure, i.e., wurtzite (WZ) and zinc-blende (ZB) formed from Zn0.7Cd0.3S solid solution, provides effective space charge separation and exhibits a prominently synergetic piezo-photocatalytic U(VI) removal rate of 99.3 % for 15 min, which is 34.2 times higher than that of ultrasound alone (2.9 % in 15 min) and 1.2 times greater than that of light alone (80.7 % in 15 min). Meanwhile, the charge transfer in Zn0.7Cd0.3S homojunction was revealed in this study through DFT calculations and a mechanism for the piezo-photocatalytic synergistic reduction of U(VI) was proposed. This work promises to provide a new coupled catalytic reaction design strategy for the efficient reduction of U(VI).