本文要点：
近年来共价有机框架(COFs)的快速发展已经牢固地将它们确立为一类新的分子精确和高度可调的多孔材料。然而，与其他多孔材料(如沸石和金属有机框架)相比，将分级多孔性成功整合到COFs中在很大程度上仍未被探索。挑战在于确定合适的合成方法来引入次生孔隙，而不损害COFs的内在结构孔隙度。
在本研究中，作者实现了一种模板诱导的合成方法来促进多孔COFs的构建。这种新方法利用市售氧化锌纳米粒子作为硬模板，能够增加一系列β-酮烯胺连接的COF以及亚胺基COF的总孔体积，同时保持其表面积。
除了透射电子显微镜和气体吸附分析，小角X射线散射和脉冲场梯度核磁共振技术被用于研究客体分子在hCOFs中的分级孔隙率和扩散率。
这项研究表明，hCOFs的分级多孔性质显著降低了扩散限制，从而同时提高了吸附容量、扩散性和催化性能。
Figure 1. a) Synthesis scheme of template-induced approach toward hierarchical porosity in ??-ketoenamine COFs. b) XRPD patterns and c) FTIR-ATR spectra of the pristine and the hierarchical COF vs. the zinc oxide loaded version.
Figure 2. TEM analysis of a) ZnO@TpBz with dense regions attributed to ZnO NP as shown by FFT in the inset and b) hTpBz with absence of the dark ZnO particles and secondary textural pores at the brighter spots exemplified by red dotted circles. Size estimation of ZnO NPs (ZnO@TpBz, ≈18 nm) and the induced mesopores (hTpBz, ≈17 nm) was performed via an image analysis software (ImageJ 1.54e).
Figure 3. a) SAXS profiles of the (h)TpBz system in double-logarithmic representation, with the TpBz (blue), ZnO@TpBz (yellow), hTpBz (red), and the ZnO NP suspension (gray). SAXS profiles of b) TpBz and c) hTpBz and the residual curves (turquoise) resulting from subtracting the power law description of the low q (0.017 – 0.15 Å−1) scattering from experimental data.
Figure 4. N2 adsorption isotherms of non-hierarchically and hierarchically porous a) TpBz, b) TpTPD, and c) TpQPD systems.
Figure 5. a) PFG-NMR spin-echo attenuation for MeCN loaded TpBz and hTpBz. Lines represent fits with a bi-exponential model. b) Faradaic efficiencies (FE) of the CoTPP loaded (h)TpBz COFs at different potentials.
https://doi.org/10.1002/adma.202415882
