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

Abstract

Type‐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.

2D Bismuthene Metal Electron Mediator Engineering Super Interfacial Charge Transfer for Efficient Photocatalytic Reduction of Carbon Dioxide

“…BiOCl − and C 3 N 4 − are two outstanding layered materials with the appropriate band alignment for constructing a 2D Z-scheme photocatalytic system. , C 3 N 4 possesses a narrow band gap of 2.7 eV, located in the visible light region, which is complementary to the poor light absorption range that BiOCl possesses with the wide band gap of 3.4 eV . The combination of these two materials as a Z-scheme highly improved the solar-energy utilization efficiency and photocatalytic performances by inserting the third counterpart as the electron mediator, for instance, g-C 3 N 4 /Au/BiOCl, BiOCl/RGO/protonated g-C 3 N 4 , g-C 3 N 4 /CDs/BiOCl, and Bi@BiOCl core–shell/g-C 3 N 4 .…”

Exciton‐Mediated Energy Transfer in Heterojunction Enables Infrared Light Photocatalysis

“…The selective depositions of Pt and MnO 2 on CN and BP components would be related to the strong interfacial couplings in the system. That is, these interfacial couplings would lead to Fermi level equilibration during the formation of heterojunction (Supporting Information, Figure S12), which would be responsible for the directional transfer of charge carriers (which are generated by exciton dissociation) [41] . Moreover, given that excitonic effects dominate the photoexcitation processes of BP (Supporting Information, Figure S7), the transfer of excitons towards CN is the premise of achieving promoted photocatalytic activity under infrared light irradiation.…”

“…That is,t hese interfacial couplings would lead to Fermi level equilibration during the formation of heterojunction (Supporting Information, Figure S12), which would be responsible for the directional transfer of charge carriers (which are generated by exciton dissociation). [41] Moreover,g iven that excitonic effects dominate the photoexcitation processes of BP (Supporting Information, Figure S7), the transfer of excitons towards CN is the premise of achieving promoted photocatalytic activity under infrared light irradiation. Combining the results of photoluminescence and ESR measurements,acomplete understanding of the photoexcitation processes in BP/CN could be described as Figure 5c.I nd etail, under light irradiation, the BP nonradiatively transfer energy to CN by exciton interactions.A fter that, the indirect stimulated excitons in CN could be partial dissociated into electrons and holes at the interface of the heterojunction, accompanying with hole injection to BP and electron accumulation in CN.…”

Graphitic carbon nitride, a saturable absorber material for the visible waveband

“…7(b), it can be known that g-C 3 N 4 -2 possesses a large saturable loss (36%) and a small non-saturable loss (4%). The other favorable characteristics includes short recovery time (4 ps) [48] and high laser damage threshold (>8 MW • cm −2 for mid-infrared solid-state laser Q-switching) [19].…”