Boosted Cr(VI) clean up over magnetically recoverable NiS/γ-Fe2O3/C type-II heterostructure derived from bimetal (Fe/Ni)-organic framework under visible light

Abstract

Cr(VI), as a toxic species derived from processes such as electroplating, is harmful to humans, plants, animals, and microorganisms. Thus, it is required to remove and recycle Cr(VI) for chromium resource keeping and prevent toxicity issues. Here, a novel magnetically recoverable NiS/γ-Fe2O3/C type-II heterojunction was successfully prepared via one-pot calcination of MIL-101(Fe/Ni) nanoflakes as a propitiatory template in the presence of Na2S precursor. In this calcination process, the Ni/Fe in MIL-101 acts as a metallic source for simultaneous construction of NiS nanoparticles on the γ-Fe2O3 surface by an in-situ solid-state reaction and organic ligand in MIL-101 acts as an in-situ carbon source to form a C matrix for encapsulation of NiS/γ-Fe2O3 nanoparticles. NiS/γ-Fe2O3/C type-II heterojunction can adequately harvest visible light, boost the interfacial separation and quench the recombination of photogenerated charge transfer agents, proceeding significant photoreduction of Cr(VI). The proposed system exhibits a superior photocatalytic reduction activity of Cr(VI) with an efficiency of 83.85% and a DF value of 0.776 at optimum values of 20 mg/L of Cr(VI), 0.003 g NiS/γ-Fe2O3/C type II heterojunction and 35 min irradiation time. A scavenging experiment confirmed that holes and •OH radicals could be entirely trapped by tartaric acid and a photocatalytic mechanism based on the other electrochemical, optical, and physicochemical characterizations was proposed. These findings give a new approach and insight to synthesize high-performance type-II heterojunction-based photocatalysts for promising future applications.