TiO2-based S-scheme photocatalyst

Solar-driven photocatalysis with oxide semiconductors shows great potential in solving growing energy and environmental crises. TiO2, as the most popular photocatalyst, has attracted wide attention owing to its stability, nontoxicity, cheapness, etc. Monocomponent TiO2 suffers from the fast recombination of photogenerated charge carriers and thereby shows poor photocatalytic efficiency. TiO2-based type-II photocatalysts achieve charge separation but weaken the redox ability of as-separated charge carriers. TiO2-based S-scheme heterojunctions composed of oxidation and reduction photocatalysts present a solution to the dilemma faced by traditional type-II photocatalysts. In such S-scheme heterojunctions, the useless photogenerated charge carriers are recombined and eliminated, while the useful electrons and holes are reserved for surface redox. The S-scheme pathway facilitates charge separation and meanwhile maintains strong redox capability of survived charge carriers. In this chapter, the phase structure, preparation methods, and band structure of TiO2 photocatalysts are first described. The advantages and disadvantages of typical TiO2-based heterojunction photocatalysts are also summarized. The design principle and photocatalytic mechanism of TiO2-based S-scheme heterojunctions, as well as the driving force for the S-scheme charge transfer and separation pathway, are specially elucidated in detail. Moreover, the applications of TiO2-based S-scheme heterojunctions in the field of H2 production, CO2 reduction, pollutant degradation, etc. are also reviewed. Finally, the challenges and perspectives of S-scheme heterojunctions are underlined, which would deepen a systematic understanding of the design and fabrication of more efficient TiO2-based photocatalysts in the future.