Fabrication and photocatalytic properties of a novel Z-scheme heterojunction ZIF-67/SnS2

Designing and preparing Z-type heterojunction photocatalysts is of great significance for improving photocatalytic performance. In this work, the Z-scheme heterojunction photocatalyst ZIF-67/SnS2 was successfully fabricated by a facile in-situ growth method. The crystal structure, morphology, surface element composition and valence state, and light absorption characteristics of the photocatalyst were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectroscopy, ultraviolet-visible (UV-Vis) spectroscopy, and X-ray photoelectron spectroscopy (XPS). The photocatalytic property was assessed by the photocatalytic degradation of tetracycline (TC). The transfer mechanism of photo-generated electrons and holes at the interface of the heterojunction was discussed. The formation of the Z-Scheme heterojunction enhances the absorption ability of ZIF-67/SnS2 to visible light, promotes the transfer of photogenerated charges, and inhibits the recombination of the photogenerated electron-hole pairs, while preserving the conductivity of ZIF-67 with higher conduction band (CB) potential. The strong reducing ability of the electrons in the conduction band produces superoxide radicals which are the major active species in the reaction system, and the photogenerated holes also participate in the photocatalytic reaction. Compared to ZIF-67 and SnS2, ZIF-67/SnS2 has significantly boosted photocatalytic activity. Among the prepared composites, ZIF-67/SnS2 with a mass ratio of SnS2 of 15% had the best photocatalytic activity, and the photodegradation efficiency of TC reaches 84% after 2 hours of visible light irradiation. The photocatalytic reaction rate constant for the composite ZIF-67/SnS2 is 0.0109 min-1, which was 5.7 and 4.2 times as large as that for ZIF-67 and SnS2, respectively.