Amine-Functionalized Defective MOFs for Direct Air Capture by Postsynthetic Modification

Amine-functionalized defective metal-organic frameworks (DM) showed promise for direct air capture (DAC) of CO₂ under ambient conditions. In this work, chromium-based DM was functionalized via a two-step postsynthetic modification with ethylenediamine (EDA), tris(2-aminoethyl)amine (TAEA), and polyethylene-polyamines (PEPA). Characterization by Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), powder X-ray diffraction (PXRD), and scanning electron microscopy (SEM) confirmed successful synthesis and structural integrity. Among the samples, 1:1-PEPA-DM exhibited the best performance, with a CO₂ adsorption capacity of 1.26 mmol/g, a regeneration energy of 75.1 kJ/mol, and only 26.62% capacity loss after 12 cycles in ambient air. In contrast, 1:1-TAEA-DM showed a high regeneration energy (158.61 kJ/mol) and a 95.17% capacity loss. Physically impregnating PEPA resulted in a lower capacity (0.94 mmol/g) and a loss of 76.32% after 12 cycles. These results highlight covalent PEPA grafting as a promising strategy for developing durable DAC sorbents.