Implications of Defect Density and Polymer Interactions for CO 2 Capture on Amine-Functionalized MIL-101(Cr).

Rising anthropogenic carbon emissions have dire environmental consequences, necessitating remediative approaches, which includes use of solid sorbents. Here, aminopolymers (poly(ethylene imine) (PEI) and poly(propylene imine) (PPI)) are supported within solid mesoporous MIL-101(Cr) to examine effects of support defect density on aminopolymer-MOF interactions for CO 2 uptake and stability during uptake-regeneration cycles. Using simulated flue gas (10 % CO 2 in He), MIL-101(Cr)-ρ high (higher defect density) shows 33 % higher uptake capacity per gram adsorbent than MIL-101(Cr)-ρ low (lower defect density) at 308 K, consistent with increased availability of undercoordinated Cr adsorption sites at missing linker defects. Increasing aminopolymer weight loadings (10-50 wt.%) within MIL-101(Cr)-ρ low and MIL-101(Cr)-ρ high increases amine efficiencies and CO 2 uptake capacities relative to bare MOFs, though both incur CO 2 diffusion limitations through confined, viscous polymer phases at higher (40-50 wt.%) loadings. Benchmarked against SBA-15, lower polymer packing densities (PPI>PEI), weaker and less abundant van der Waals interactions between aminopolymers and pore walls, and open framework topology increase amine efficiencies. Interactions between amines and Cr defect sites incur amine efficiency losses but grant higher thermal and oxidative stability during uptake-regeneration cycling. Finally, >25 % higher CO 2 uptake capacities are achieved for aminopolymer/MIL-101(Cr)-ρ high under humid conditions, demonstrating promise for realistic applications.