Novel layered BiO2-x: Applications, developments and challenges in photocatalysis

With the widespread application of photocatalytic technology in the field of environmental remediation and clean energy generation, the development of highly efficient photocatalysts is necessary. Recently, a new type of bismuth oxide, BiO2-x photocatalysts have been extensively exploited for organic pollutant decomposition, CO2 reduction, NO removal and water decomposition due to its mixed valent (Bi3+ and Bi5+), layered structure, abundant oxygen vacancies, and narrow bandgap. However, single BiO2-x displayed high photo-generated charge recombination rates, resulting in inferior photocatalytic performance. In this review, the critical strategies to enhance photocatalytic performance of BiO2-x has been systematically summarized, such as oxygen vacancies introduction, metallic or nonmetallic doping, co-catalysts deposition, and heterojunctions construction (type I, type II, Z-scheme, and double heterojunctions). Finally, a short perspective on the challenges and future aspects of BiO2-x-based photocatalysts in this field are presented. It is expected that this work can provide useful guideline for designing of highly catalytic activity BiO2-x-based photocatalysts for the application in environmental remediation and renewable energy generation.