Emerging tandem S-scheme heterojunction photocatalysts

Photocatalysis is a green approach to store solar energy in the form of chemical energy or utilize it for water treatment or organic transformation reactions. However, despite the great effort devoted by the research community for several decades in the field, no breakthrough was made. The photocatalysis reaction happens on the surface of a semiconductor (photocatalyst) when it is irradiated with photo-energy that is greater than or equal to its bandgap. Ideal photocatalysts should have visible light harvesting capability, insignificant electron-hole recombination rate, sufficient redox potential to derive the catalytic reaction, abundant active sites, and the capability to adsorb the reactants and desorb the reaction products. However, a pristine semiconductor is unable to satisfy these criteria. Tandem heterojunctions have been recently introduced to utilize the synergy among cocatalyst, core@shell, and heterojunction strategies to fulfill these criteria. Extensive focused research still needs to be carried out on the design and engineering of tandem photocatalytic systems and their catalytic applications. This review article uniquely investigates state-of-the-art and challenges of tandem heterojunctions and their photocatalytic applications and gives advice on how this newly emerging and exciting research direction can be further advanced and optimized.