Post‐Synthetic Covalent Grafting of Amines to NH2‐MOF for Post‐Combustion Carbon Capture

Abstract Herein, a post‐synthetic modification strategy is used to covalently graft polyamines, including ethylenediamine (ED), diethylenetriamine (DETA), tris(2‐aminoethyl)amine (TAEA), and polyethyleneimine (PEI) to the amino‐ligand inside of a Cr‐MOF, NH 2 ‐Cr‐BDC, for post‐combustion carbon capture applications. X‐ray absorption spectroscopy (XAS), X‐ray photoelectron spectroscopy (XPS), and ion chromatography (IC) reveal that ≈45% of the MOF ligands are grafted with polyamines. Next, assessment of CO 2 uptake, CO 2 /N 2 selectivity, isosteric heats of CO 2 adsorption, separation performance during humid CO 2 /N 2 (15/85) breakthrough experiments, and cyclability, reveals an enhanced performance for the polyamine‐containing composites and the following performance trend: NH 2 ‐Cr‐BDC<ED<DETA<TAEA<PEI. The best‐performing materials, including the TAEA and PEI‐grafted MOFs, offer CO 2 uptakes of 1.0 and 1.55 mmol g −1 , respectively, at 0.15 bar and 313 K. Further, these composites also offer a high CO 2 capacity after 200 temperature swing adsorption/desorption (TSA) cycles in simulated humid flue gas. Last, after soaking the composites in water, there is no loss of CO 2 capacity; on the contrary, when the same MOF is impregnated with polyamines using traditional approaches, there is ≈85% CO 2 capacity loss after soaking. Thus, this covalent grafting strategy successfully immobilizes amines in MOF pores preventing leaching and hence can be an effective strategy to extend the adsorbent lifetime.