A Ship-in-a-Bottle Strategy: Crosslinking Amines and Epoxides inside MOF Pores for Enhanced CO₂ Capture Performance

This study introduces a "ship-in-a-bottle" technique to impregnate porous supports with amines via a straightforward in situ polymerization process. Specifically, alkylamines-tris(2-aminoethyl)amine (TAEA) and tetraethylene pentamine (TEPA)-are crosslinked with epoxides-trimethylolpropane triglycidyl ether (TMPTE) and 1,3-butadiene diepoxide (BDE)-within the pores of the metal-organic framework (MOF) Cr-BDC (also MIL-101(Cr), where BDC = 1,4-benzenedicarboxylate), producing four distinct MOF-polymer composites. These composites are subsequently evaluated for their efficacy in postcombustion carbon capture, examining metrics such as CO₂ capacity, CO₂/N₂ selectivity, isosteric heat of CO₂ adsorption, kinetic breakthrough times, and cyclability. Among the composites, Cr-BDC-TAEA-BDE (branched-linear) demonstrates the most promising results, achieving a CO₂ capacity of 2.2 mmol g^-1 at 0.15 bar and 313 K, a CO₂/N₂ selectivity of 301, and an isosteric heat of CO₂ adsorption of -110 kJ mol^-1. This composite also exhibits superior breakthrough performance, with N₂/CO₂ separation times of 103 and 143 min per gram under dry and humid conditions, respectively. Furthermore, the four MOF-polymer composites are subjected to up to 100 temperature swing adsorption/desorption cycles (at 313 and 393 K, respectively), revealing minimal amine leaching or degradation over time. Notably, the composites also show significantly enhanced cyclability compared to Cr-BDC impregnated with amines without epoxide crosslinking agents; this indicates that crosslinking inhibits amine leaching.