A review of rare earth oxides-based photocatalysts: Design strategies and mechanisms

Photocatalysis has gained increasing interest due to its potential to overcome global energy and environmental challenges. Rare earth oxides (R2O3) are identified as efficient photocatalytic materials on account of their tunable bandgaps, reversible oxidation states, venerable redox potentials, unique optoelectronic properties, effective stability, and non-toxicity. However, the advancement of efficient R2O3 photocatalysts has also encountered some serious issues such as low surface area, quick photo-activated electron-hole recombination loss, and poor visible light absorption efficiency during photocatalytic reaction. Herein, we focus on recent advances in R2O3-based photocatalysts for pollutants removal, CO2 reduction and H2 generation. Firstly, the crystal structures and basic properties of R2O3 materials have been introduced. Besides, to tackle the serious photocarrier recombination, constrained visible light response, inadequate durability, and lack of reactive sites of R2O3, different design strategies are discussed. These strategies include doping, morphology control (microstructure regulation, hierarchical/hollow/core-shell/mesoporous structures), anchored co-catalysts, vacancy creation, heterojunction construction (type-II/Z-scheme/S-scheme), surface sensitization, and nanocarbon loading are discussed. In addition, the mechanistic insights associated with these design strategies for improved efficiency of R2O3-based photocatalytic systems are also reviewed and discussed. Finally, the present challenges and perspectives of R2O3 photocatalysts are given to emphasize the magnificent future and noteworthy status of R2O3 semiconductors for photocatalytic applications.