Direct Z-scheme α-MnO2@MnIn2S4 hierarchical photocatalysts with atomically defined junctions for improved photocatalytic activities

The use of semiconductor photocatalysts to generate electrons with efficient reducing capability for organic photoreduction synthesis and the removal of harmful substances has become a hotspot in the field of green chemistry research. In this work, alpha-MnO2 nanocubes and alpha-MnO2@MnIn2S4 hybrid photocatalysts with a core-shell structure were synthesized successively by a two-step method. XRD and XPS verified the coexistence of the two substances (alpha-MnO2 and MnIn2S4) in hybrid systems. According to the SEM and TEM characterization, it is clearly seen that MnIn2S4 nanosheets grow on alpha-MnO2 nanocubes to form a hierarchical structure. Furthermore, HRTEM showed that the interface contact between alpha-MnO2 and MnIn2S4 resulted in an atomically defined junction. The photocatalytic performance of the composite catalyst was evaluated by reducing 4-nitroaniline to 4-phenylenediamine and Cr(vi) to Cr(iii), respectively. The results show that the catalytic activity of the composite material is effectively improved compared to that of the single components. The Z-scheme electron transport mechanism was proved by ultraviolet-visible diffuse reflectance spectroscopy, valence band XPS, energy band structure calculation and active species detection experiments. The constructed Z-scheme hierarchical alpha-MnO2@MnIn2S4 system with an atomically defined junction can improve the redox performance of semiconductors for organic synthesis and environmental remediation.