Polyethyleneimine-Modified UiO-66-NH₂(Zr) Metal–Organic Frameworks: Preparation and Enhanced CO₂ Selective Adsorption

UiO-66-NH₂, a zirconium-based functional metal-organic framework (MOF), was postsynthetically modified via Schiff base reaction between aldehyde groups in glutaraldehyde and amino groups in UiO-66-NH₂ and CO₂-preabsorbed polyethyleneimine (PEI). The resulting PEI-modified MOFs, abbreviated as PEIC@UiO, were characterized with ¹H NMR, Fourier transform infrared, powder X-ray diffraction, Brunauer-Emmett-Teller, scanning electron microscopy, and thermogravimetric analysis and evaluated as CO₂ adsorbents. In comparison with pristine UiO-66-NH₂, the PEIC@UiO adsorbents have reduced specific surface area (7-150 m²/g) but maintained the same crystal structure. Particularly, the PEIC96@UiO adsorbent exhibited significantly improved CO₂/N₂ adsorption selectivity (48 vs 25) and higher CO₂ adsorption capacity (3.2 vs 2.7 mmol/g). The adsorbent also displayed moderate desorption energy (68 kJ/mol CO₂), superior moisture endurance, and recyclability, which are very desirable for practical applications.