Simple fabrication of Z-scheme MgIn2S4/Bi2WO6 hierarchical heterostructures for enhancing photocatalytic reduction of Cr(vi)

Abstract

Direct Z-scheme MgIn₂S₄/Bi₂WO₆ hierarchical heterostructures were simply fabricated via immobilising MgIn₂S₄ nanoflakes onto the surface of Bi₂WO₆ hierarchical nanosheet-like structures towards photocatalytic reduction of Cr(VI). The analyses of the energy band structure, UPS tests and DMPO-ESR spin-trap experiments confirm that the intimate MgIn₂S₄/Bi₂WO₆ heterointerface allows an efficient Z-scheme interfacial charge migration route between MgIn₂S₄ and Bi₂WO₆, leading to higher redox ability of photoexcited carriers, and thus favours the separation of photoexcited carriers, proved by the results of PL spectroscopy, photoluminescence decay traces, transient photocurrent densities and EIS. In addition, the MgIn₂S₄/Bi₂WO₆ heterostructures also exhibit obviously enhanced ultraviolet-visible-light absorption according to UV-vis DRS analysis, and can generate more electron–hole pairs under UV-visible light illumination, effectively improving the photocatalytic activity. Therefore, because of their synergistic effects, all the MgIn₂S₄/Bi₂WO₆ hierarchical heterostructures show distinctly improved photoreduction activities for Cr(VI), compared with pure Bi₂WO₆. The optimal hybrid (MIS/BWO-0.35) displays nearly 100% Cr(VI) reduction into Cr(III) after 40 min of simulated sunlight illumination, which is better than the majority of the reported Bi₂WO₆ and other semiconductor photocatalysts before. Its reaction rate constant for the photoreduction of Cr(VI) (0.1063 min⁻¹) is about 4.5 times higher than that of the pristine Bi₂WO₆ (0.0237 min⁻¹). This work provides a valid approach for developing efficient Z-scheme photocatalytic materials in removing Cr(VI).