2D/2D covalent organic framework/CdS Z-scheme heterojunction for enhanced photocatalytic H 2 evolution: Insights into interfacial charge transfer mechanism

Covalent organic frameworks (COFs) with high crystallinity and flexible designability have been consid-ered as promising candidates for photocatalytic hydrogen evolution. However, the existence of unpropi-tious exciton effects in COFs leads to poor charge separation, and thus results in low photocatalytic effi-ciency. Herein, to improve the photoelectron migration efficiency, we designed a 2D/2D organic/inorganic direct Z-scheme COF-based heterojunction (TpTAP/CdS), by the in-situ growing of CdS nanosheets on the COF copolymerized via 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (TAP) and 1,3,5-triformylphloroglucinol (Tp). The femtosecond transient absorption (fs-TA) decay kinetics of TpTAP-COF and TpTAP/CdS further reveal the processes of shallow electron trapping and the recombination of the free photogenerated electron-hole pairs. In particular, the transient absorption traces for TpTAP-COF and TpTAP/CdS normal-ized to the photoinduced absorption peak can effectively verify the Z-scheme charge transfer between TpTAP-COF and CdS, which could enhance the charge mobility and separation, thus reducing the pho-tocorrosion of CdS. Additionally, ultraviolet photoelectron spectroscopy (UPS), in-situ X-ray photoelec-tron spectroscopy (XPS), transient photovoltage measurements, and electron spin resonance (ESR) spec-troscopy further confirm the establishment of the internal electric field (IEF). This work demonstrates the important role of COFs in the construction of 2D/2D organic/inorganic direct Z-scheme heterojunctions and offers a new avenue to explain the criticality of dynamics of the photogenerated carriers for the construction of Z-scheme heterojunctions.(c) 2022 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.