Poly(ionic liquid)-Grafted MOF Gels: A Co-catalyst-free Platform for High-Efficiency CO2 Cycloaddition.

Abstract

Poly(ionic liquid)-grafted UiO-66-NH2 gels are developed as a high-performance and co-catalyst-free platform for efficient CO2 capture and chemical fixation under mild conditions. To address the mass transfer limitations and high energy barriers typical of purely microporous powder materials, a series of hierarchically porous metal-organic framework (MOF)-poly(ionic liquid) hybrid gels (HP-MOF-PILs) were engineered within a structurally adaptive UiO-66-NH2 gel matrix by integrating covalent anchoring with subsequent radical polymerization. Structural characterization reveals that the hybrid catalyst maintains the structural integrity of the MOF gel framework while successfully preserving the well-defined, highly interconnected mesoporous network inherent to the gel skeleton. Although the intensive grafting of PIL segments leads to a reduction in intrinsic microporosity, the gel-derived open mesopores significantly alleviate mass transfer resistance, preventing the active-site burial and heavy aggregation common in bulk polymers or packed powders, thereby ensuring high accessibility to the catalytic centers. The hybrid catalyst achieves over 99% cyclochloroallyl carbonate yield under 0.1 MPa CO2 without any co-catalyst. The high catalytic efficiency stems from a multi-site cooperative effect, wherein coordinatively unsaturated Zr4+ Lewis acid centers assisted by structural Zr-OH groups on the MOF nodes electrophilically activate epoxide C-O bonds, while grafted PIL segments supply hydrogen-bonding donors and nucleophilic Br- anions for rapid ring-opening. Furthermore, owing to the macrostructural stability and resilient coordination network of the gel matrix, the catalyst exhibits excellent durability over six consecutive cycles. This work provides a promising strategy for designing integrated gel-based composite catalysts with self-supporting pore architectures for sustainable carbon utilization.