A Small-Crystallite Metal–Organic Framework for Efficient CO2 Capture from Flue Gas

Pressure swing adsorption (PSA) is a promising technology for low-energy CO2 capture from flue gas, but its development is hindered by the lack of advanced adsorbents. Aluminum formate (ALF) shows satisfactory CO2 adsorption capacity but suffers from slow adsorption kinetics. Herein, we present a citric acid modification strategy to synthesize SNALF—an ultramicroporous ALF with small crystallite size and abundant defect sites—using nano-sized boehmite as the aluminum source. SNALF-3-90 achieved a CO2 adsorption capacity of 2.45 mmol/g within 3 min. In PSA testing with simulated flue gas (11 vol.% CO2, 82.5 vol.% N2, 6.5 vol.% O2), the CO2 concentration was enriched from 11% to over 42% with 90.13% recovery and productivity of 0.80 NL/min. DFT calculations reveal that the ligand-defective SNALF surface enables strong exothermic adsorption, confirming that the introduced defects act as active centers for CO2 capture. This work demonstrates that defect engineering combined with crystallite size reduction significantly enhances the CO2 adsorption kinetics of ALF, making it viable for large-scale PSA-based flue gas capture.