Ammoniated Covalent Organic Frameworks for Water-Lean Carbon Capture

Amine-based carbon dioxide (CO₂) capture materials are traditionally constrained by a 2:1 amine-to-CO₂ stoichiometry, limiting working capacity and increasing regeneration costs. While water can promote a 1:1 stoichiometry through bicarbonate formation, it also accelerates amine degradation and increases the thermal energy demand. Here, we report a water-lean carbon capture (WLCC) strategy using microporous covalent organic frameworks (COFs), NUS-44 and NUS-45, functionalized with primary amines via postsynthetic Mannich grafting. Specifically, NUS-44 chemisorbs CO₂ via carbamic acid formation in the absence of water, as confirmed by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and ¹³C/¹⁵N-labeled solid-state nuclear magnetic resonance (ssNMR). Crucially, the carbamic acid species are stabilized by intrapore hydrogen bonding, allowing them to persist under dry conditions and enabling each amine to bind one CO₂ molecule directly and efficiently─thus overcoming the conventional 2:1 amine-to-CO₂ limitation. NUS-44 exhibits high CO₂ uptakes at ultralow pressures (0.3 and 30 mmHg), maintains performance in both dry and humid environments, and can be fully regenerated at only 80 °C. Energy analysis based on sensible heat calculations further revealed a 20.6-27.8% reduction in the regeneration heat requirement for NUS-44 compared with the water-containing system, underscoring the intrinsic energy advantage of the WLCC process. These findings establish hydrogen-bond-stabilized carbamic acid as a new chemisorption motif in porous frameworks and position NUS-44 and NUS-45 as a low-energy, moisture-independent sorbent for next-generation carbon capture from dilute CO₂ streams.