Investigation of storage environments on aminopolymer stabilization within UiO-67(Zr) for CO2 capture

Abstract

Aminopolymers, poly(ethylene imine) (PEI) and poly(propylene imine) (PPI), are supported within nanoporous UiO-67(Zr) and evaluated for CO₂ capture from simulated flue gas (10% CO₂) and air (400 ppm CO₂). N₂ physisorption and Fourier-transform infrared spectroscopy indicate that PEI and PPI are physisorbed in UiO-67(Zr) voids but not tethered to metal nodes or carboxylate backbones. Mass-normalized CO₂ capacity increases with repeated CO₂ uptake-regeneration cycles for 30–50 wt% PPI, suggesting CO₂ diffusion limitations at these higher loadings. 20 wt% PPI/UiO-67(Zr) and 20 wt% PEI/UiO-67(Zr) exposed to ambient air for 7 days demonstrate higher oxidative degradation in PEI than PPI, though PEI oxidation is reduced when stabilized within UiO-67(Zr) relative to when unconfined. Exposure of composites to liquid storage environments of varying polarity, hydrogen-bonding capability, and size indicate that 20 wt% PPI/UiO-67(Zr) amine efficiencies are minimally affected by solvent-induced aminopolymer conformational changes. Conversely, 20 wt% PEI/UiO-67(Zr) is more sensitive to surrounding solvent environments, exhibiting the greatest amine efficiency in methanol and the lowest in acetone due to solvent-induced aminopolymer swelling and reaction, respectively. Overall, this work provides insight into CO₂ capture efficacies and chemical stabilities of composite PEI and PPI materials under various storage environments to inform future adsorbent and system design.