An overview of improving photocatalytic activity of MnO2 via the Z-scheme approach for environmental and energy applications

Rapid industrialization has triggered the proliferation of dyes and antibiotics in the water system in recent decades. Due to advantages like low cost, high catalytic efficiency, and the ability to exist in multiple valences, MnO2 as a photocatalyst has attracted more and more attention. This review covers recent progress on MnO2-based composites for photocatalytic properties obtained via the Z-scheme charge carrier mechanism. Firstly, the electronic, photoelectric, and crystallographic properties of MnO2 are highlighted, and the fabrication of heterojunctions by suitable band alignments following the Z-scheme electron transfer pathway. This article presents recent advances in MnO2-based nanomaterials, focusing on improving photocatalytic activity via the Z-scheme mechanism. Then a detailed discussion on various electron transfer pathways in MnO2-based composites offered a broader view by providing several characterization techniques to testify to the route of the Z-scheme mechanism. This review also provided a systematic summary of their applications in environmental (dye, antibiotics degradation) and energy (water splitting, CO2 reduction) applications. Although many efforts have been made, significant improvements are still required for photocatalysis. This work presents future perspectives for improving the efficacy of photocatalysts, followed by a conclusion.