Enhanced photocatalytic performance of Zn_XCd_1−XS series under visible light: an experimental and theoretical study

Abstract With different Zn 2+ /Cd 2+ ratios, Zn x Cd 1−x S (x = 0.1–0.9) were prepared by a hydrothermal method. The structural and optical properties of them were analyzed via XRD, SEM, XPS, BET, UV–Vis DRS and PL characterization tests. The results from the degradation of methylene blue (MB), rhodamine B (RhB) and tetracycline (TC) under visible light showed that the photocatalytic performance of Zn x Cd 1−x S (x = 0.1–0.9) series were superior to that of pure ZnS and CdS, and Zn 0.6 Cd 0.4 S was the best one. The photocatalytic processes were tested in different water sources, and the data implied that the degradation efficiency of dyes and TC by Zn 0.6 Cd 0.4 S in sea water, lake water, and tap water differed a little to the cases in deionized water. The degradation ratio of MB, RhB and TC could reach 98.90%, 98.99% and 91.95% by Zn 0.6 Cd 0.4 S. The photocatalytic mechanism was further revealed by active species capture experiments and theoretical calculations. The results indicated that the introduction of Cd 2+ led to a decreased band gap and an enhanced response to visible light. The photogenerated electron–hole pair separation efficiency was increased, and the electrons jumped to the conduction band to react on the catalyst surface for the degradation. The effect of the solution pH was studied as well and revealed that a natural pH was preferred. All the data indicated that Zn 0.6 Cd 0.4 S exhibited excellent photocatalytic performance and good stability which could be a promising candidate for the degradation of organic pollutants.