Principles, mechanism, and identification of S‐scheme heterojunction for photocatalysis: A critical review

Semiconductor photocatalysis has been extensively used in the degradation of pollutants and the production of hydrogen fuel. The main drawback in the application of semiconductor photocatalysis is the rapid recombination of charge carriers. Several strategies have been applied to improve charge carrier separation to preserve them for imparting in photocatalytic reactions. Among the modifications that are made in the photocatalytic systems, the construction of different types of heterostructures, including type II, Z‐scheme, p–n junction, and Schottky junction, has received great attention. Recently, emerging S‐scheme heterojunctions have been shown to be able to preserve powerful charge carriers for photocatalytic reactions, which is not the case in other heterostructures. In this review, principles and mechanisms of charge transfer in S‐scheme heterostructures are discussed, and important semiconductors that have been used in the construction of this type of heterojunctions are reviewed. Methods for identification of S‐scheme heterojunction, challenges, and prospects have been addressed. An S‐scheme heterojunction consists of oxidation photocatalyst and reduction photocatalyst with staggered band structures. An S‐scheme heterojunction resembles a type II heterojunction, but the route of charge transfer differs from that of type II heterostructure. In S‐scheme photocatalytic heterostructures, the powerful photogenerated electrons in the conduction band of reduction photocatalyst and the photogenerated holes in the valence band of oxidation photocatalyst are preserved, and weak electrons and holes are recombined. The powerful photogenerated charge carriers can impart in the photocatalytic reactions.