本文要点：
为了使CO2与环氧化物的环加成成为可行的非氧化还原CO2固定途径，开发活性、稳定、选择性、无金属、可快速分离且成本有效的催化剂至关重要。
为此，通过在sp2-c连接的COF─CN的氰基上的氰基三聚反应，使用两种氰基单体和固有微孔性的聚合物(PIM-1)合成了三种新型催化剂。其中，粉末催化剂(COF─CN─COOH，COF─CN─NH2)具有酸性氢键给体(─COOH，─NH2)和碱性中心(三嗪环)，由于其可定制的氢键位点、高CO2亲和力和稳定性，在CO2环加成反应中表现出优异的催化性能。
值得注意的是，COF─CN─COOH实现了99.9%的催化产率和超过99%的选择性。20%COF─CN@sPIM-1膜催化剂由COF─CN和PIM-1共价连接而成，表现出良好的界面相容性，易于回收，同时保持了优异的催化活性。
此外，密度泛函理论(DFT)对氢键促进机理的研究表明，氢键给体(HBDs)可以显著降低活化能。因此，本工作引入了一种新的三聚反应策略，利用sp2-c连接的COF上的氰基作为反应位点，建立了独特的酸碱协同催化体系，并为开发可快速分离同时表现出高活性和稳定性的膜催化体系奠定了基础。
Figure 1. a) Synthetic strategy for preparing COF─CN─COOH, COF─CN─NH2, and COF─CN@sPIM-1. The inset shows a photograph of the COFs. b,c) Structural models of COF─CN─COOH and COF─CN─NH2 (C atoms: gray; Basic site (triazine ring): blue; Acidic site (─COOH, ─OH): red. d) Conceptual illustration of the covalent-linking strategy for the compatibility reinforcement in the MMM fabrication from COF─CN and PIM-1.
Figure 2. a) XRD patterns. b) IR spectra. COF─CN (black), COF─CN─COOH (pink), COF─CN─NH2 (orange), sPIM-1 (green), 20%COF─CN/PIM-1 (cyan), 20%COF─CN@sPIM-1 (blue), 30%COF─CN/PIM-1 (purple-red), 30%COF─CN@sPIM-1 (purple). c) XPS spectra of N 1s orbitals for COF─CN (top), COF─CN─COOH (middle), and COF─CN─NH2 (bottom). d) 13C CPMAS solid-state NMR spectra of COF─CN (top), COF─CN─COOH (middle), and COF─CN─NH2 (bottom).
Figure 3. SEM images of a) COF─CN, b) COF─CN─COOH, c) COF─CN─NH2. d) Photos of PIM-1 CHCl3 solution, COF─CN and PIM-1 solution, free-standing 20%COF─CN/PIM-1, and 20%COF─CN@sPIM-1 membranes. e) EDS of 20%COF─CN@sPIM-1 membrane. Top-view SEM images of f,g) 20%COF─CN@sPIM-1, h) 30%COF─CN@sPIM-1. i) Cross-sectional SEM images of 20%COF─CN@sPIM-1. 3D AFM image of j) 20%COF─CN@sPIM-1, k) 30%COF─CN@sPIM-1 with roughness parameters.
Figure 4. a) N2 sorption isotherms at 77 K of COF─CN, COF─CN─COOH, and COF─CN─NH2. CO2 sorption isotherms at b) 273 K, c) 298 K. d) The corresponding CO2 isosteric heats of adsorption (Qst) data using Clausius-Clapeyron equation.
Figure 5. a) Catalytic performance. b) Recyclability of COF─CN─COOH, COF─CN─NH2, and 20%COF─CN@sPIM-1 membrane for five cycles.
Figure 6. a) Proposed mechanism for CO2 cycloaddition with epichlorohydrin. b) Energy profile for the reaction with different catalysts via DFT calculation. (IM: intermediates, TS: transition states, P: product) c) DFT-optimized geometric structures of the reaction determining step (RDS) in cycloaddition reaction. The red, gray, white, blue, green, and brown balls represent O, C, H, N, Cl and Br atoms, respectively.
https://doi.org/10.1002/adfm.202422116
