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Abstract
供体-受体共价有机框架（D-A COFs）因其可调带隙而被视为光催化水分离的理想材料。然而，快速电荷重组和较低的光稳定性阻碍了它们的效率。在此作者提出了一种供体结构工程策略，以提高 D-A COFs 的光催化活性，从而解决这些问题。作者制备了两种具有不同供体的苯并噻二唑基 D-A COF（DHU-COF-BB 和 DHU-COF-BP），用于光催化 H2 进化反应（HER）。作为对比，还设计并合成了不含苯并噻二唑分子的 DHU-COF-TB。令人印象深刻的是，在可见光（≥420 nm）照射下，DHU-COF-BB 的光催化 H2 产率达到 12.80 mmol g-1 h-1，分别是 DHU-COF-BP （6.47 mmol g-1 h-1）和 DHU-COF-TB （4.06 mmol g-1 h-1）的近 2.0 倍和 3.1 倍。此外，在 420 纳米波长下，DHU-COF-BB 的表观量子效率（AQE）高达 5.04%。光催化和电化学测量结果表明，DHU-COF-BB 氢演化活性的增强可归因于供体中引入了适当的苯分子，从而提高了电荷分离效率，抑制了电子-空穴重组。密度泛函理论（DFT）计算显示，在 DHU-COF-BB 上，三苯胺和苯并噻二唑单元是 HER 的主要活性位点。这项工作为通过供体结构工程策略研究 D-A COF 的光催化制氢活性提供了新的视角。
Highlights
1. 设计了两种含苯并噻二唑的供体-受体共价有机框架材料(DHU-COF-BB和DHU-COF-BP),并与不含苯并噻二唑的DHU-COF-TB进行比较。
2. DHU-COF-BB在可见光照射下(≥420 nm)的氢气产生速率高达12.80 mmol g-1 h-1,相比DHU-COF-BP和DHU-COF-TB分别提高了2.0倍和3.1倍。
3. DHU-COF-BB的量子效率可达5.04%(420 nm),光催化和电化学测试表明这是因为苯环结构的引入提高了电荷分离效率,抑制了电子-空穴复合。
4. 密度泛函理论计算表明三苯胺和苯并噻二唑单元是DHU-COF-BB上主要的活性位点。
results
Fig.1 (A) Synthetic routes and (B) photoexcited carrier separation ability of the three donor‒acceptor covalent organic frameworks (D‒A COFs).
Fig.2 Experimental and simulated powder X-ray diffraction (PXRD) patterns of (A) DHU-COF-BB, (B) DHU-COF-BP, and (C) DHU-COF-TB. AA stacking mode of (D) DHU-COF-BB, (E) DHU-COF-BP, and (F) DHU-COF-TB.
Fig.3 (A) Fourier-transform infrared (FT-IR) spectra and (B) solid-state 13C CP/MAS nuclear magnetic resonance (NMR) spectra of three donor‒acceptor covalent organic frameworks (D‒A COFs). (C) Scanning electron microscopy (SEM) image of DHU-COF-BB. (D) Transmission electron microscopy (TEM) image of DHU-COF-BB. High-resolution TEM (HR-TEM) images of (E) DHU-COF-BB and (F) DHU-COF-BP. Nitrogen sorption isotherms measured at 77 K for (G) DHU-COF-BB, (H) DHU-COF-BP, and (I) DHU-COF-TB.
Fig.4 (A) Ultraviolet‒visible (UV‒vis) diffuse reflectance absorption spectra (DRS) and (B) Tauc plots of three donor‒acceptor covalent organic frameworks (D‒A COFs). (C) Mott‒Schottky (M‒S) plots for DHU-COF-BB. (D) Experimental energy levels of three D‒A COFs.
Fig.5 (A) Photocatalytic H2 evolution performances of three donor‒acceptor covalent organic frameworks (D‒A COFs) at visible light illumination (λ > 420 nm). (B) Wavelength-dependent apparent quantum efficiency (AQE) of photocatalytic water splitting by DHU-COF-BB photocatalyst. (C) Time-dependent hydrogen evolution curves of DHU-COF-BB with different Pt loading amounts under the visible light irradiation. (D) Recyclability of DHU-COF-BB for H2 generation over 25 h.
Fig.6 (A) Transient photocurrents responses, (B) electrochemical impedance spectroscopy (EIS) Nyquist plots, (C) steady-state photoluminescence (PL) spectra (λex = 420 nm), and (D) time-resolved fluorescence emission decay spectra of three donor‒acceptor covalent organic frameworks (D‒A COFs). (E) The calculated hydrogen adsorption free energy at active site of DHU-COF-BB. (F) Electrostatic potential (ESP) of the DHU-COF-BB model at N2 and C6 sites.
Details
Constructing benzothiadiazole-based donor‒acceptor covalent organic frameworks for efficient photocatalytic H2 evolution
原文链接：
https://doi.org/10.1002/agt2.669
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