Enhancing the Photocatalytic Activity of TiO2 Catalysts

To address energy and environmental problems, innumerable titanium dioxide (TiO2)-based photocatalysts have been reported over the last four decades. TiO2 has attracted immense interest because it is low-cost, abundant, and photoresponsive. Sunlight-driven fuel production is one of the ideal photocatalytic approaches in terms of economics and the environment. However, performance issues with TiO2 photocatalysts remain, including insufficient charge separation due to the rapid recombination of photogenerated charge carriers, and poor utilization of light, because of the material's wide bandgap. To be economically efficient, TiO2 photocatalysts responsive to visible light are essential. Many researchers have investigated effective modification methods for this purpose. Numerous studies have focused on enhancing photocatalytic activity by modifying TiO2. Methods include combining TiO2 with noble metals, incorporating metals or nonmetals, and introducing vacancies by chemical and physical methods. In addition, many studies have also been conducted to comprehensively determine the underlying reaction mechanisms, and thus guide future research directions. This Review aims to understand the basic principles of photolysis, to summarize recent research trends, to envision future research directions, and to help the development of a new type of TiO2-based photocatalysts for enhanced solar energy conversion efficiency.