Design principles and mechanistic strategies of CuBi2O4-based S-scheme catalytic systems for environmental photocatalysis

Abstract

S-scheme heterojunctions have developed into a highly effective methodology for photocatalysis, due to their ability to improve charge dissociation while sustaining a substantial redox potential. Among semiconductors that can be activated with visible light, copper bismuthate (CuBi2O4) is particularly appealing due to its narrow band gap, visible light absorption, and suitable band alignment. Yet, its photocatalytic activity is limited by low charge mobility and fast recombination of photoinduced carriers, which justifies its integration into S-scheme heterojunctions. For this, the review aims to explore the photoactive CuBi2O4, S-scheme heterojunctions, focusing on their structural and electronic properties while unravelling their charge transfer processes for the first time, and advanced mechanisms of charged S-scheme operation. Notably, these include the use of density functional theory to predict electronic band alignment and charge carrier dynamics for advanced in-situ XPS, electromagnetic resonance to track reactive radical species and to electrochemical analysis for separation, redox equilibrium and photocatalytic efficiency, and charge evaluation. This collection of characterization attempts an understanding of the mechanistic photocatalytic pathway. This review also discusses the shift in designs from conventional to dual and triple S-scheme architectures, recent efforts on photocatalytic degradation of wastewater pollutants (dyes, antibiotics, and others) and addresses numerous other important aspects such as mechanistic depth, stability, scalability, and photocatalytic activity. Finally, new pathways are suggested that aim to strengthen CuBi2O4-based S-scheme photocatalysts for photocatalytic environmental remediation.