Covalent Organic Frameworks with Deep Eutectic Linkages for Low-Concentration Carbon Capture

Adsorbents with low regeneration temperatures and high oxidation resistance are highly desirable for cost-effective carbon capture. While amine-based technologies demonstrate efficient CO₂ capture capabilities at low concentrations, their inherent susceptibility to degradation under aerobic conditions significantly increases operational costs in carbon capture processes. Herein, we report the conversion of the imidazole linkage into a deep eutectic linkage (DEL) through embedding a strong superbase─1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD)─in imidazole-based covalent organic frameworks (COFs), capable of CO₂ chelation at low concentrations with low regeneration temperature (60 °C) and high oxidation resistance. The successful conversion of the imidazole COF (Im-COF) to DEL COF (Im-TBD) is demonstrated through X-ray photoelectron spectroscopy (XPS), zeta potential tests, and ¹³C and ¹⁵N solid-state nuclear magnetic resonance (ssNMR) characterizations. Im-TBD exhibits a dramatic enhancement in CO₂ affinity, achieving an exceptionally high CO₂/N₂ selectivity of 1711 under direct air capture conditions (DAC, 0.3 mmHg CO₂) and 230 under carbon capture from the flue gas of natural gas combined-cycle power plants (NGCC, 30 mmHg CO₂). More excitingly, Im-TBD can be readily regenerated at 60 °C under dry open air (V_O2/V_N2 = 21/79) and maintains stable performance over 20 consecutive cycles. Energy analysis based on sensible heat calculations further revealed a 72-96% reduction in the regeneration heat requirement for Im-TBD compared with the water-containing system. CO₂ chelation mechanisms in Im-TBD are further proven through ¹³CO₂-dosed ssNMR, in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and thermodynamic calculations. Our strategy establishes a foundation for the development of next-generation nonamine adsorbents for carbon capture.