Determining the Charge‐Transfer Direction in a p–n Heterojunction BiOCl/g‐C3N4 Photocatalyst by Ultrafast Spectroscopy

Abstract

AbstractType‐II heterostructures composed of p‐type BiOCl and n‐type g‐C3N4 have received much attention because of their high efficiencies of charge separation in photocatalysis. However, some ambiguity exists regarding the transfer direction of photogenerated charge carriers in the BiOCl(p)/g‐C3N4(n) system. Although it seems to have not posed an issue in terms of organic photodegradation applications, misinterpretation of the charge‐transfer direction and hence misjudgment of the redox sites in the hybrid system would be a serious problem for other photocatalytic reactions, especially for half reactions, in which the determination of the redox sites is crucial. To solve this problem, we carefully interrogated this topical heterojunction system formed between p‐type BiOCl and n‐type g‐C3N4 by means of ultrafast transient absorption spectroscopy. Our experimental results reveal that the photogenerated electrons are transferred, on a time scale of a few picoseconds, from the conduction band of BiOCl to that of g‐C3N4 and not in the opposite direction. This work enables us to eliminate the ambiguity in using two opposing mechanistic scenarios to describe the p–n heterojunction based photocatalysis mechanism, thereby providing instructive information for the rational design of photocatalytic nanosystems.