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.