Constructing in-situ grown ZIF-90/PI MMMs via self-anchoring of metal ions with polymer backbone for efficient CO₂ separation

ZIF-90 is in-situ grown in benzimidazole-containing polyimide (DB55) via Zn 2+ anchoring for CO₂ separation. • In-situ growth gives uniform filler dispersion and strong interfacial adhesion via Zn 2+ -benzimidazole coordination. • The in-situ grown membrane shows 2.5-fold higher CO₂ permeability than blended MMMs. The intrinsic permeability-selectivity trade-off and CO₂-induced plasticization, exacerbated under high-feed pressure and elevated operating temperatures, severely restrict the application of polyimide membranes in CO₂ capture processes. In this work, a benzimidazole-containing polyimide (DB55) was employed as an anchoring platform for Zn 2+ ions to carry out the confined in-situ growth of ZIF-90 crystals directly within the polymer chains. The coordination bonds between Zn 2+ and the benzimidazole groups of DB55, as evidenced by FTIR and XRD, effectively suppress polymer chain mobility and filler agglomeration, facilitating rapid gas transport. The optimized ZIF-90/dB55–2 membrane exhibits a CO₂ permeability of 269.57 Barrer with CO₂/N₂ and CO₂/CH₄ selectivities of 42.04 and 40.08, respectively, surpassing the 2008 Robeson upper bound for CO₂/CH₄ separation. Compared with physically blended membranes, the optimized in-situ grown membranes show a clear advantage in permeability (approximately 4.4-fold over pristine DB55) along with improved solvent resistance, while the physically blended membranes exhibit slightly higher selectivity due to the partial conversion of Zn 2+ into ZIF-90 during in-situ growth. Temperature-dependent tests reveal that the incorporation of ZIF-90 reduces the activation energies for CO₂, N₂, and CH₄ permeation, and that the ZIF-90/dB55–2 membrane exhibits a smaller decline in CO₂/CH₄ selectivity with increasing temperature than the pristine DB55 membrane. Pressure-dependent tests up to 3.0 MPa further reveal that the MMMs retain stable performance with a smaller loss in CO₂/CH₄ selectivity (6.9%) than the neat polymer (10.0%), indicating enhanced plasticization resistance. This work offers a promising approach to simultaneously improve permeability, selectivity, and operational stability in polyimide-based membranes via in-situ MOF growth within a suitably designed polymer matrix.