Controlled Covalent Functionalization of ZIF-90 for Selective CO(2) Capture & Separation

Mixed Matrix Membranes (MMM) with enhanced selectivity and permeability are preferred for gas separations. The porous metal-organic frameworks (MOFs) materials incorporated in them play a crucial part in improving the performance of MMM. In this study, Zeolitic imidazolate frameworks (ZIF-90) are selected to fabricate Polyetherimide (PEI) MMMs owing to their lucrative structural and chemical properties. This work reports new controlled post-synthetic modifications of ZIF-90 (50-PSM-ZIF-90) with ethanolamine to control the diffusion and uptake of CO(2). Physical and chemical properties of ZIF-90, such as stability and presence of aldehyde functionality in the imidazolate linker, allow for easy modulation of the ZIF-90 pores and window size to tune the gas transport properties across ZIF-90-based membranes. Effects of these materials were investigated on the performance of MMMs and compared with pure PEI membranes. Performance of the MMMs was evaluated in terms of permeability of different gases and selective separation of CO(2) and H(2) gas. Results presented that the permeability of all membranes was in the following order, i.e., P(H(2)) > P(CO(2)) > P(O(2)) > P(CH(4)) > P(C(2)H(6)) > P(C(3)H(8)) > P(N(2)), demonstrating that kinetic gas diffusion is the predominant gas transport mode in these membranes. Among all the membranes, permeability of pure PEI membrane was highest for all gases due to the uniform porous morphology. The pure PEI membrane showed highest permeability of H(2), which is 486.5 Barrer, followed by 49 Barrer for O(2), 29 Barrer for N(2), 142 Barrer for CO(2), 41 Barrer for CH(4), 40 Barrer for C(2)H(6) and 39.6 Barrer for C(3)H(8). Results also confirm the superiority of controlled PSM-ZIF-90-PEI membrane over the pure PEI and ZIF-90-PEI membranes in CO(2) and H(2) separation performance. The 50-PSM-ZIF-90 PEI membrane exhibited a 20% increase in CO(2) separation from methane and a 26% increase over nitrogen compared to the ZIF-90-PEI membrane. The 50-PSM-ZIF-90 PEI membrane showed 15% more H(2)/O(2) separation and 9% more H(2)/CH(4) separation than ZIF-90 PEI membrane. Overall, this study represents the role of controlled PSM in enhancing the property of new materials like ZIF and its application in MMMs fabrication to develop a promising approach for the CO(2) capture and separation.