Visible-light-driven Z-scheme Zn3In2S6/AgBr photocatalyst for boosting simultaneous Cr (VI) reduction and metronidazole oxidation: Kinetics, degradation pathways and mechanism

It is urgently needed to develop high-performance materials that can synchronously remove heavy metals and organic pollutants. Herein, the visible-light responsive Zn3In2S6/AgBr composites were prepared for concurrent removals of metronidazole (MNZ) and Cr (VI). In the Cr (VI)-MNZ coexisting system, the removals of MNZ and Cr (VI) using the optimized Zn3In2S6/AgBr-15 photocatalyst reached 98.2% and 94.8% within 2 h, respectively; higher than those using counterparts. The radical species trapping and electron spin resonance (ESR) results demonstrated that ·OH was the most dominated species for MNZ oxidation, and photo-generated electrons were responsible for Cr (VI) reduction. Besides, slight competition for ·O2- during the simultaneous MNZ degradation and Cr (VI) reduction occurred. Energy band structure analysis, ESR and the outstanding photocatalytic performance for MNZ and Cr (VI) removals demonstrated that the Zn3In2S6/AgBr-15 was a Z-scheme photocatalyst, which promoted photo-induced carrier's separation. Possible MNZ degradation pathways and mechanism over the Z-scheme Zn3In2S6/AgBr were also proposed based on the identified intermediates. This study could inspire new ideas for design of efficient Z-scheme photocatalysts for wastewater treatment.