Unlocking Water as Docking Sites in Covalent Organic Frameworks for Enhanced Physisorptive Carbon Capture under Wet Conditions

Abstract The physisorptive CO2 capture process frequently faces the challenge of competing with moisture adsorption. Incorporating strong nucleophiles into porous materials can circumvent this issue by forming bicarbonate in the presence of moisture. However, the moisture-enhanced carbon capture (MECC) in physisorptive systems is still rarely reported. Herein, we present a physisorptive MECC capable of operating at a wide range of relative humidity (RH), employing newly developed covalent organic frameworks (COFs) with Brønsted-acidic squaramide as linkage. Specifically, the squaramide linkage and a specific pore size jointly disrupt hydrogen bonds (HBs) in water molecules, thereby converting them into effective docking sites for CO2 adsorption within the amphiphilic pores. Comprehensive column breakthrough experiments highlight a substantial enhancement in CO2 uptake capacity in the squaramide-linked COFs in the presence of moisture (up to 75% RH) compared to dry conditions. The distinctive adsorption mechanism is further interpreted through in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), solid-state 1H magic angle spinning nuclear magnetic resonance (ss 1H MAS NMR), dielectric analysis, and sorption simulation, demonstrating that the water around the squaramide linkage could play a crucial role in enhancing CO2 adsorption in the presence of moisture. This work provides new insight into converting water as an additional sorption site and a strategy for addressing the influence of moisture in physisorptive carbon capture processes.