Recent Developments of Advanced Ti³⁺-Self-Doped TiO₂ for Efficient Visible-Light-Driven Photocatalysis

Research into the development of efficient semiconductor photocatalytic materials is a promising approach to solving environmental and energy problems worldwide. Among these materials, TiO₂ photocatalysts are one of the most commonly used due to their efficient photoactivity, high stability, low cost and environmental friendliness. However, since the UV content of sunlight is less than 5%, the development of visible light-activated TiO₂-based photocatalysts is essential to increase the solar energy efficiency. Here, we review recent works on advanced visible light-activated Ti³⁺-self-doped TiO₂ (Ti³⁺–TiO₂) photocatalysts with improved electronic band structures for efficient charge separation. We analyze the different methods used to produce Ti³⁺–TiO₂ photocatalysts, where Ti³⁺ with a high oxygen defect density can be used for energy production from visible light. We categorize advanced modifications in electronic states of Ti³⁺–TiO₂ by improving their photocatalytic activity. Ti³⁺–TiO₂ photocatalysts with large charge separation and low recombination of photogenerated electrons and holes can be practically applied for energy conversion and advanced oxidation processes in natural environments and deserve significant attention.