Recent advances in constructing heterojunctions of binary semiconductor photocatalysts for visible light responsive CO2 reduction to energy efficient fuels: A review

Photocatalysis of carbon dioxide by the assistance of solar energy has been one of the most promising approaches to reduce CO2 to renewable fuel. Several methods are pertained to enhance the photocatalytic activity for stimulating CO2 reduction to selective fuels. Even though many researchers have been exploring methods of assembling a suitable semiconductor, practical constraints such as charge carrier recombination and low light utilization limit the photocatalytic activity. In this review, recent advancement in semiconductors and their characteristics toward the photoreduction of CO2 has been comprehensively discussed. The major semiconductors that are discussed and analyzed based on their limitations in this review are TiO2, BiVO4, CdS, g-C3N4, ZnO, and MoS2-based composites. Initially, the fundamentals of heterogeneous photocatalysis such as the possible molecular pathways, product selectivity, and thermodynamics have been deliberated. Advancement in semiconductors in relation to quantum dots, heterojunction, and sacrificial reagent has been systematically analyzed. Doping and co-doping of semiconductors have proven to reduce the band gap notably and its outstanding electronic band position for the visible light photocatalysis has been identified. Furthermore, the developments of cocatalysts such as noble metals and nonmetals to stimulate photocatalysts performance in view of CO2 reduction to value-added products have been disclosed. Specific developments in binary semiconductors through Z-scheme, S-scheme, and ternary heterojunction for charge separation and their characterization has been thoroughly deliberated. In addition, the role of doping, structural defects, as well as sensitization in enhancing the light harvesting abilities of the photocatalyst has been discoursed. The developments in photocatalytic reactors with their characteristics and limitations are also assiduously discussed. Finally, conclusions and future directions for photocatalysis of carbon dioxide toward renewable fuel production have been suggested.