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

Abstract

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-NH_2. 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.