Stabilizing Covalent Organic Frameworks through Hydrogen Bonding Bridges for Polyamine Entanglement toward Carbon Capture from Point-Source Emissions

Incorporating polyamine into covalent organic frameworks (COFs) is a promising strategy for developing carbon capture adsorbents with fast mass transfer, in which avoiding crystallinity and porosity loss of COFs becomes essential. Herein, we propose a hydrogen bonding (HB) bridge strategy to stabilize the crystallinity and porosity of a two-dimensional (2D) mesoporous COF with sp² linkage (termed NUS-43) during in situ free radical polymerization. Specifically, HB bridges between 4-vinylbenzylamine hydrochloride (VBAH) and the vinylpyridine moieties of NUS-43 suppress interlayer shifting, while the sp²-linked framework serves as a robust scaffold for introducing polyamine functionalities into the COF pores. This stabilization is confirmed through powder X-ray diffraction (PXRD), solid-state UV-vis spectroscopy, differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) spectroscopy, solid-state nuclear magnetic resonance (ssNMR) spectroscopy, and density functional theory (DFT) calculations. The universality of the HB strategy is demonstrated by substituting VBAH with (4-vinylphenyl)ethylamine hydrochloride (VEAH). Deprotonated NUS-43-VBA/VEA COFs exhibit good CO₂ capture performance under simulated natural gas combined cycle (NGCC) conditions, with CO₂ uptakes of 0.5/0.2 mmol g^-1 and 0.6/0.38 mmol g^-1 under dry and humid environments at 25 °C, respectively, as validated through diverse sorption techniques. More importantly, the CO₂ adsorption and oxidative amine degradation mechanisms in NUS-43-VBA are further characterized by FTIR and ¹³C/¹⁵N ssNMR spectroscopy. This work not only underscores the critical role of the HB bridge in maintaining crystallinity and porosity of 2D COFs during polyamine incorporation but also offers new insights into the oxidation mechanism of amines during carbon capture.