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.