A Novel Strategy to Enhance the Performance of CO₂ Adsorption Separation: Grafting Hyper-cross-linked Polyimide onto Composites of UiO-66-NH₂ and GO

Graphene oxide (GO) is widely used to improve the pore structure, dispersion capacity, adsorption selectivity, resistance to acids and bases, and thermal stability of metal–organic frameworks (MOFs). However, it remains a daunting challenge to enhance selectivity simply by modifying the pore surface polarity and producing a suitable pore structure for CO2 molecules through a combination of GO with MOFs. Herein, we demonstrate a novel porous hyper-cross-linked polyimide–UiO–graphene composite adsorbent for CO2 capture via in situ chemical knitting and condensation reactions. Specifically, a network of polyimides rich in carbonyl and nitrogen atoms with amino terminations was synthesized via the reaction of 4,4′-oxydiphthalic anhydride (ODPA) and 2,4,6-trimethyl-1,3-phenylenediamine (DAM). The product plays a crucial role in the separation of CO2 from N2. As expected, the resulting composite (PI-UiO/GO-1) exhibited a 3-fold higher CO2 capacity (8.24 vs 2.8 mmol·g–1 at 298 K and 30 bar), 4.2 times higher CO2/N2 selectivity (64.71 vs 15.43), and significantly improved acid–base resistance stability compared with those values of pristine UiO-66-NH2. Furthermore, breakthrough experiments verified that the porous composites can effectively separate CO2 from simulated fuel gas (CO2/N2 = 15/85 vol %) with great potential in industrial applications. More importantly, this strategy can be extended to prepare other MOF-based composites. This clearly advances the development of MOF–polymer materials for gas capture.