ACS Catal：D-A型三苯胺-COF--有效电荷迁移和增强氧活化

本文要点：

1. 电子给体(D)和电子受体(A)之间的高能级差和电荷转移过程中的低能量损失是构建高效D–A型共价有机骨架(COF)光催化剂的先决条件。然而，构建块的空间结构特征不可避免地导致在构建过程中D-A COF骨架的扭曲，从而阻止有效的电荷迁移。

2. 在本文中，以高能级三苯胺(TPA)作为模型电子给体，三(3-甲酰基联苯)胺(NDC)和三(4-甲酰基联苯)胺(NBC)的甲酰基位置异构体与受体1，3，5-三(4-氨基苯基)三嗪(TTA)反应，产生用于光催化CO2还原和苄胺偶联反应的D-A COFs。

3. 结构研究证明，在TTA-COFs中，甲酰基位置异构使TPA单臂的二面角从51.09°减小到2.12°，层间距从3.89°减小到3.55 Å，激子结合能从97.25 meV减小到85.86 meV。

4. 这种具有受限三叶草状通道的“近平坦”TTA-NDC结构显著加快了层内和层间电荷迁移效率，并提高了CO2吸附和氧活化能力(O2–浓度为48.01 μm ol L–1，3 h)。

5. 在原始的COF光催化剂中，TTA-NDC表现出最高的苄胺耦合效率，周转频率值为518.4 h–1，其光催化CO2还原的电子消耗率达到1632.2 μmol g–1h–1，比TTA-NBC高3.85倍，远远超过大多数COF光催化剂。

6. 同时，质子化的H-TTA-NDC由于质子传导率(σ= 1.07×10–2 S·cm–1)的提高，表现出高的CO2还原为CH4的产率(310.1 μmol·g–1·H–1)和选择性(85.1%)。

7. 此外，系统地研究了TTA-NDC的耐久性、稳定性和可能的光催化机理。

Scheme 1. (a) LUMO Energy Levels of Electron Donors. (b) Structural Characteristics and Electron Migration Behavior of TPA-Based D–A COF. (c) Synthetic Routes and the Microstructures (Enlarged Regions) of TTA-NDC and TTA-NBC

Figure 2. UV–vis DRS (a), UPS spectra (b) and energy band structures (c) of TTA-NDC and TTA-NBC. (d) Catalytic traces of the photooxidative benzylamine coupling performed by TTA-NDC and TTA-NBC, and TTA-NDC filtered after 0.5 h (black line) under the optimal conditions. (e) N-benzylbenzaldimine generation rate under various reaction conditions toward TTA-NDC. (f) Cyclic stability tests of TTA-NDC for benzylamine coupling reaction. (g) Catalytic efficiency assessment of TTA-NDC and TTA-NBC for benzylamines coupling reactions with various substrates [TOF = the moles of N-benzylbenzaldimine/(moles of photocatalyst) × (reaction time)].

Figure 3. (a) LUMO energy level differences for the two types of building blocks of D–A COFs. (b) ESP maps of TTA-NDC (top) and TTA-NBC (bottom) on the 0.001 e–/bohr iso-electron-surface. (c) Nyquist plots of TTA-NDC and TTA-NBC. (d,e) Interlayer interactions render graphs of TTA-NDC and TTA-NBC based on Becke surface. (f) Transient photocurrent responses of TTA-NDC and TTA-NBC. (g,h) Temperature-dependent PL spectra of TTA-NDC and TTA-NBC.

Figure 4. (a) EPR spectra for the O2•– detection in the presence of different photocatalysts in the dark or under light irradiation. (b) EPR spectra for the Cα radical detection in the presence of different photocatalysts in the dark or under light irradiation. (c) Time-dependent curves of O2•– concentration for TTA-NDC and TTA-NBC. (d,e) Hole–electron isosurfaces and the heat maps of hole–electron populations on the fragments of O2@TTA-NDC* and O2@TTA-NBC* at the first excited singlet (S1) state (olive and cyan isosurfaces demonstrate the population of electrons and holes, respectively).

Figure 5. (a) CO2 adsorption isotherms of TTA-COFs at 298 K. (b) Time-dependent CO2 photoreduction performances of TTA-COFs. (c) Comparison of the average CO and CH4 production rate and selectivity of TTA-COFs after 1 h of irradiation. (d) Electron consumption rate (Rele) and CH4 selectivity (SCH4) of TTA-COFs. (e) Comparison of the photocatalytic CO2RR performance of the H-TTA-NDC with the catalytic systems reported.

Figure 6. PL spectra (a) and TRPL decay spectra (b) of TTA-NDC and TTA-NBC. (c,d) HOMO and LUMO orbital distributions of the fragments of TTA-NDC and TTA-NBC based on DFT simulation.

Figure 7. (a) Schematic illustration of protonation of TTA-COFs. (b) 1H ssNMR spectra of TTA-NDC and H-TTA-NDC. Inset: the enlarged area marked by dashed rectangle. (c) XANES at C K-edge region for TTA-NDC and H-TTA-NDC. Arrhenius plots (d), Nyquist plots at 160 °C (e), and CO2-TPD curves (f) for TTA-NDC, TTA-NBC, H-TTA-NDC, and H-TTA-NBC. (g) Potential energy surface scanning for CO reduction by H-TTA-NDC. (h) In situ DRIFTS spectra of H-TTA-NDC containing CO2 and H2O under subsequent light irradiation.

https://doi.org/10.1021/acscatal.4c06754