(579e) In Situ Growth of ZIFs in Polybenzimidazole to Achieve Superior H2/CO2 Separation Performance

Polybenzimidazole (PBI) with a strong size-sieving ability and excellent thermal stability is a leading membrane material for H₂/CO₂ separation at elevated temperatures. For example, commercial m-PBI exhibited H₂ permeability of 9.0 Barrer and H₂/CO₂ selectivity of 14 at 100 ^oC. Incorporating porous fillers in polymers to form mixed matrix materials (MMMs) is an effective way to improve their performance. However, most porous fillers have lower H₂/CO₂ selectivity than PBI, leading to higher H₂ permeability but lower H₂/CO₂ selectivity in the MMMs. In this study, we demonstrate that ZIF nanoparticles (NPs) can be grown in-situ and grafted onto the PBI chains with excellent interfacial compatibility, which cross-links the polymer and increases simultaneously H₂ permeability and H₂/CO₂ selectivity. Specifically, the precursors of 2-methyimdazole (2-MI) and Zn(NO₃)₂•6H₂O for ZIF-8 are added to PBI/dimethylformamide solutions. The 2-MI and Zn²⁺ ions form ZIF-8 NPs, increasing gas permeability. Moreover, the imidazole rings on the PBI chains react with 2-MI and Zn²⁺ to form ZIF-7/8 structures, which cross-link PBI chains and enhance their size-sieving ability. The structures of MMMs were thoroughly characterized using FTIR, WXRD, TGA, and SEM. The ZIF-8 NPs have sizes of 0.7 - 1 μm, and ZIF-7/8 structures distribute evenly in the films. For example, an MMM containing 9.3 wt% ZIF-7/8 structures and 5.6 wt% ZIF-8 NPs exhibits H₂ permeability of 12 Barrer and H₂/CO₂ selectivity of 29 at 100 ^oC, surpassing the Robeson upper bound. Moreover, this MMM shows stable H₂/CO₂ separation performance (H₂ permeability of 11 Barrer and H₂/CO₂ selectivity of 21) when challenged with simulated syngas at 100 ^oC, indicating the great potential for practical application. This work presents a highly effective approach to prepare MMMs with great interfacial compatibility, high free volume, and strong size-sieving ability.