Polyethylenimine-Grafted Nanoporous Zr-Based Organic Frameworks for Enhanced CO ₂ Adsorption

Metal–organic frameworks (MOFs) have attracted attention for carbon dioxide (CO2) capture due to their large surface area and easily regulated pores. However, their application still suffers from a low CO2 adsorption capacity and short lifespan under humid environments. We herein report on a promising strategy in which polyethylenimine (PEI) is postsynthetically grafted onto Zr-based organic frameworks (UiO-66-NH2) ligands to develop the nanoporous UiO-66-NH-acetyl (Ac)-PEI for CO2 adsorption. UiO-66-NH-Ac-PEI had a high specific surface area of 728.27 m2/g, with the particle size concentrated between 20 and 55 nm. Benefiting from the chemistry and environment created within the pores, UiO-66-NH-Ac-PEI exhibited a high CO2 adsorption capacity of 2.26 mmol/g at 298 K, and 1 bar, and an excellent CO2/N2 selectivity of 42. Breakthrough experiments demonstrated that nanoporous UiO-66-NH-Ac-PEI can efficiently separate CO2 from N2 under high-humidity conditions. The CO2 adsorption mechanisms are thoroughly analyzed by density functional theory calculations, which demonstrate that the aminated pores have an excellent affinity for CO2; thus, it is preferentially adsorbed by the MOFs. This study significantly advances the strategy of designing nanoporous Zr-MOF by grafting amine moieties onto its backbone ligands, thereby enabling strong binding with CO2 in humid environments.