MnInS nanosheets growing on rods-like β-MnO via covalent bonds as high-performance photocatalyst for boosting Cr(VI) photocatalytic reduction under visible light irradiation: Behavior and mechanism study.

It is an urgent and onerous task to develop catalysts for photocatalytic reduction of Cr(VI) in wastewater under wide pH range. In this work, a novel hierarchical Z-scheme MnO/MnInS (MISO) heterojunction photocatalyst with MnInS nanosheets growing on the surface of β-MnO nanorods is constructed for efficient photocatalytic reduction of Cr(VI). The optimized 2.0-MISO photocatalyst exhibits the almost 100% reduction efficiency in the pH range of 2.1-5.6 under visible light irradiation, and the apparent rate constant is 0.05814 min, which is 29.96 and 3.27 times higher than the pure β-MnO and MnInS, respectively. A efficient photocatalytic reduction of Cr(VI) to Cr(III) species on 2.0-MISO photocatalyst in actual industry wastewater (286.7 mg/L) up to 99.8% is achieved. Under natural light, the 2.0-MISO photocatalyst also shows rapid reduction of Cr(VI) species. The photocorrosion of MnInS was significantly hindered by the construction of heterojunction. And the O and e species are the main active species during the Cr(VI) photoreduction process. The connection mode between MnInS and β-MnO is verified by DFT calculations and a possible photocatalytic mechanism is also proposed.