2D/2D covalent organic framework/CdS Z-scheme heterojunction for enhanced photocatalytic H2 evolution: Insights into interfacial charge transfer mechanism. (20th February 2023)

• Record Type: Journal Article
• Authors: Gao, Ruiqi; Bai, Junxian; Shen, Rongchen; Hao, Lei; Huang, Can; Wang, Lei; Liang, Guijie; Zhang, Peng; Li, Xin
• Is Part Of: Journal of materials science & technology. Volume 137(2023)
• Page Start: 223
• Page End: 231
• Publication Date: 2023-02-20
• Subjects: Femtosecond transient absorption -- Photocatalytic hydrogen evolution -- Covalent organic frameworks (COFs) -- Direct Z-scheme heterojunction -- CdS; COFs Covalent organic frameworks -- MOFs metal-organic frameworks -- TAP 2, 4, 6-tris(4-aminophenyl)-1, 3, 5-triazine -- Tp 1, 3, 5-triformylphloroglucinol -- EIS electrochemical impedance spectra -- fs-TAS femtosecond transient absorption spectroscopy -- UPS ultraviolet photoelectron spectroscopy -- XPS X-ray photoelectron spectroscopy -- ESR Electron spin resonance -- IEF internal electric field -- PXRD powder X-ray diffraction -- FT-IR Fourier Transform Infrared -- BET Brunauer-Emmett-Teller -- SEM scanning electron microscope -- HRTEM high-resolution transmission electron microscopy -- HER hydrogen evolution reaction -- AQY apparent quantum yield -- PL photoluminescence -- RHE reversible hydrogen electrode -- Efb flat band potential -- PIA photoinduced excited-state absorption -- VB valence band -- GSB ground-state bleach -- ECB conduction band potential -- Eg bandgap; Metals -- Periodicals; Materials science -- Periodicals; Materials science; Metals; Periodicals; 620.1105
• DOI: 10.1016/j.jmst.2022.09.001
• Languages: English
• ISSNs: 1005-0302

Abstract

Highlights: The 2D/2D COF/CdS Z-scheme heterojunction was first reported. The Z-scheme charge transfer pathways were first identified by Femtosecond transient absorption. The excellent photocatalytic hydrogen evolution was achieved. The improved charge separation and hydrogen-evolution kinetics were confirmed. Abstract: Covalent organic frameworks (COFs) with high crystallinity and flexible designability have been considered as promising candidates for photocatalytic hydrogen evolution. However, the existence of unpropitious exciton effects in COFs leads to poor charge separation, and thus results in low photocatalytic efficiency. 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 normalized 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 photocorrosion of CdS. Additionally, ultraviolet photoelectron spectroscopy (UPS), in-situ X-ray photoelectron spectroscopy (XPS), transient photovoltage measurements, and electron spin resonance (ESR) spectroscopy 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.