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.