A new core-shell heterojunction MIL-53(Fe)@ZnIn2S4 for boosted photocatalytic degradation of tetracycline and reduction of Cr (VI) under visible irradiation

Abstract

Tetracycline (TC) and hexavalent chromium (Cr(VI)) in the environment pose potential threats to ecosystems and human health, and have attracted widespread attention in recent years. Photocatalysis has been proven to be an ideal technology for removing TC and Cr(VI) in water. Herein, a new core–shell type II heterojunction MIL-53(Fe)@ZnIn₂S₄ was synthesized by using low-temperature oil bath method to effectively remove TC and Cr (VI) in aqueous solutions. MIL-53(Fe)@ZnIn₂S₄ was characterized by SEM, XPS, XRD, and FT-IR. The photocatalytic activity and stability of the composite were evaluated via photocatalytic experiments, and the mechanisms of TC degradation and Cr (VI) reduction were also explored. The results indicate that the specific surface area of MIL-53(Fe)@ZnIn₂S₄ is significantly higher than that of MIL-53(Fe) and ZnIn₂S₄ due to the core–shell structure being formed. The heterojunction interface and core–shell structure synergistically promote the transfer and separation of photogenerated electrons and holes at the interface between MIL-53(Fe) and ZnIn₂S₄. MIL-53(Fe)@ZnIn₂S₄ appears excellent photocatalytic activity and stability towards both TC and Cr (VI). The composite MZ20 with a mass ratio of 2:10 between MIL-53 (Fe) and ZnIn₂S₄ exhibits the best photocatalytic activity. The photocatalytic degradation efficiency of MZ20 to TC reach 92 % within 120 min, and the photocatalytic reduction efficiency to Cr (VI) reach 99 % within 30 min. The boosted photocatalytic activity is owing to the construction of type II heterojunction with core–shell structure, which effectively suppresses the recombination of photogenerated electron-hole pairs. This work aims at providing a new strategy for the construction of visible light responding photocatalysts for the remediation of chromium and tetracycline contaminated environments.