In situ synthesis of CdS/ZnS composite nanoparticles from ZIF-8 for visible light disposal of Cr(VI)

Zeolitic Imidazolate Framework (ZIF-8) micropolyhedra were employed as a raw material for the synthesis of fine cadmium sulfide/zinc sulfide (CdS/ZnS) composite nanoparticle. The structure and optical properties of the composite nanoparticle were investigated and the results suggested that the introduction of cadmium nitrate tetrahydrate led to the decomposition of ZIF-8 polyhedra. The CdS/ZnS composite nanoparticle was selected as catalyst for the photo-reduction of Cr(VI) ion under visible light. The catalytic data indicated that the fine CdS/ZnS composite nanoparticle displayed an excellent performance and good reusability for the reduction of Cr(VI). In addition, the influence of the dosage of the catalyst, the concentration of Cr(VI) as well as the pH on the catalytic activity was investigated. Finally, the catalytic reaction mechanism was studied to illustrate the possible reaction process by adding the radical scavengers in the reaction solution and Electron Spin-resonance Spectroscopy. It was suggested that the advantage of the fine composite nanoparticles facilitated the exposure to Cr(VI) ions and prevent the aggregation of CdS nanoparticles in the composite structure. Besides, the presence of ZnS in the composite could well prevent the combination of the electrons and holes generated from CdS.