Engineering CAU-10-H in the preparation of mixed matrix membranes for gas separation

Abstract

Metal-organic frameworks (MOFs) are highly compatible with polymers and can be used to create mixed matrix membranes (MMMs) for gas separation. Herein, we engineered the particle size as well as the number of missing linkers in CAU-10-H MOFs via either applying the plasma treatment (CAU-10-H_Plasma) or varying the water/N,N-dimethylformamide (H2O/DMF) co-solvent ratios (CAU-10-H_Micro and CAU-10-H_Nano). The CAU-10-H_Nano showed the largest number of missing linkers, but the lowest adsorption uptake of CO2 and CH4 albeit the largest BET surface area. In contrast, both CAU-10-H_Plasma and CAU-10-H_Micro exhibited relatively high adsorption uptakes of CO2 and CH4. In addition, all the MMMs fabricated using 6FDA-mPDA:DABA (3:2) exhibited a good interaction between Al2+ metal ions of CAU-10-H and carboxylic groups of 6FDA-mPDA:DABA (3:2). Importantly, the 6FDA-mPDA:DABA (3:2)/CAU-10-H_Plasma (75/25 w/w) MMM exhibited more attractive selectivities of CO2/CH4 and H2/CH4 (e.g., 68 and 184, respectively) compared to those of the other two MMMs under single-gas conditions. It also showed the highest CO2/CH4 selectivity of 67 under equimolar CO2/CH4 mixed-gas conditions. As CAU-10-H_Plasma possessed the lowest quantity of defective sites among the three CAU-10-H samples, our results suggest that suppressing defective sites in MOFs could be an effective approach for enhancing the CO2 separation efficiency.