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Covalent triazine-based frameworks with cobalt-loading for visible light-driven photocatalytic water oxidation
Summary:
The authors from the University of Liverpool and Zhejiang Normal University developed a bipyridine-based covalent triazine framework (Bpy-CTF) with cobalt-loading, achieving high activity for visible light-driven photocatalytic water oxidation.
Background:
1. To address the challenge of efficient solar-driven photocatalytic water splitting for green hydrogen production, previous researchers have explored various organic semiconductor photocatalysts, including carbon nitrides and covalent triazine-based frameworks (CTFs), achieving certain success. However, there are still issues such as relatively low oxygen evolution rates and insufficient charge separation in some cases.
2. The authors in this study proposed an innovative approach by incorporating bipyridine units into the CTF structure and post-synthetic cobalt coordination, obtaining significantly enhanced photocatalytic oxygen evolution performance.
Research Content:
1. Synthesis:
The authors synthesized Bpy-CTF and B-CTF using a modified condensation method with aldehyde and amidine monomers. Cobalt was loaded onto the frameworks by refluxing in tetrahydrofuran containing Co(NO₃)₂·6H₂O.
2. Characterizations:
1) BET surface areas of Bpy-CTF and B-CTF were 675 and 612 m² g⁻¹, respectively, with pore size distributions indicating microporous structures.
2) SEM/TEM tests show the particle size of Bpy-CTF and B-CTF mostly in the range of 0.5–2 μm and 0.5–1 μm, respectively.
3) UV-vis light absorption spectra showed absorption onsets at 575 nm for Bpy-CTF and 610 nm for B-CTF, with band gaps of 2.21 eV and 2.07 eV, respectively. Photoluminescence and TCSPC measurements indicated that cobalt coordination in Bpy-CTF led to quenched emission and shorter excited-state lifetime, suggesting enhanced charge separation.
3. Application:
The material was tested in sacrificial photocatalytic oxygen evolution under visible light irradiation (λ ≥ 420 nm). Bpy-CTF–Co-3 achieved an oxygen evolution rate of 322 μmol g⁻¹ h⁻¹, comparable to state-of-the-art polymer photocatalysts. The apparent quantum efficiency (AQE) of Bpy-CTF–Co-3 was 0.56% at 420 nm.
4. Mechanism:
Transient absorption spectroscopy analysis showed that cobalt coordination in Bpy-CTF promoted the formation of charge-separated species with higher yield and longer lifetime compared to Bpy-CTF without cobalt, thus enhancing water oxidation activity.
Outlook:
This research expands the diversity of organic photocatalysts for visible light-driven water oxidation, highlighting the potential of structural engineering and post-synthetic metalation to improve photocatalytic performance. It provides valuable insights for designing efficient polymer photocatalysts for sustainable hydrogen production and overall water splitting applications.
Covalent triazine-based frameworks with cobalt-loading for visible light-driven photocatalytic water oxidation
Authors: Hongmei Chen, Adrian M. Gardner, Guoan Lin, Wei Zhao, Mounib Bahri, Nigel D. Browning, Reiner Sebastian Sprick, Xiaobo Li, Xiaoxiang Xu, Andrew I. Cooper
DOI: 10.1039/d2cy00773h
Link: https://doi.org/10.1039/d2cy00773h
