In situ construction of a 2D/2D heterostructured ZnIn2S4/Bi2MoO6Z-scheme system for boosting the photoreduction activity of Cr(vi)

Abstract

The direct 2D/2D Z-scheme heterostructures of ZnIn₂S₄/Bi₂MoO₆ were rationally constructed by growing ZnIn₂S₄ ultrathin nanoflakes on the surface of Bi₂MoO₆ nanosheets, in situ, towards photocatalytic Cr(VI) reduction. After the tight contact of the ZnIn₂S₄ nanoflakes and the Bi₂MoO₆ nanosheets, internal built-in electric fields (IBEFs) with the direction from ZnIn₂S₄ to Bi₂MoO₆ are formed at the ZnIn₂S₄/Bi₂MoO₆ interface due to the electron (e⁻) transfer from ZnIn₂S₄ to Bi₂MoO₆ based on the XPS results. The IBEFs and the staggered alignment of band edges at the heterointerface favor the separation and migration of photoinduced carriers through the Z-scheme route, which is demonstrated according to the results of DMPO-ESR spin-trap experiments. The elegant Z-scheme system with a ZnIn₂S₄/Bi₂MoO₆ heterostructure effectively accelerates the spatial separation and migration of photoinduced e⁻ and holes (h⁺), and then results in the stronger redox ability of charge carriers. Furthermore, the combination of ZnIn₂S₄ with Bi₂MoO₆ helps to extend the visible-light absorption range, so as to promote light harvesting, which also contributes to the enhanced photoreduction activity of Cr(VI). Therefore, the as-prepared ZnIn₂S₄/Bi₂MoO₆ heterostructures show obviously enhanced photocatalytic activity for Cr(VI) reduction as compared with pure Bi₂MoO₆ under visible light (λ ≥ 420 nm) irradiation. The optimized ZnIn₂S₄/Bi₂MoO₆ photocatalyst (ZIS/BMO-0.6) exhibits almost close to 100% of Cr(VI) reduction after 60 min of irradiation, which is higher than the majority of previously reported Bi₂MoO₆ and other semiconductor-based catalysts. Its reaction rate constant for photocatalytic reduction of Cr(VI) (0.0491 min⁻¹) is more than one order of magnitude higher than that of pure Bi₂MoO₆ (0.00479 min⁻¹). This work makes a contribution to constructing high-efficiency photocatalytic materials for environmental pollution remediation applications.