Tunable Pervaporation Performance of Modified MIL-53(Al)-NH2/Poly(vinyl Alcohol) Mixed Matrix Membranes

Most of the mixed matrix membranes (MMMs) display the trade-off effect between flux and selectivity in pervaporation, and a strategy for breaking the effect has not been identified. In this paper, MIL-53(Al)-NH2 nanocrystals were modified with formic acid, valeric anhydride and heptanoic anhydride, and then incorporated into poly(vinyl alcohol) (PVA) membranes for use in the pervaporation of 92.5 wt% ethanol. The MMMs properties (hydrophilicity, swelling degree) and pervaporation performance were successfully adjusted. With the increased hydrophobic constants of surface substitutes, the ethanol permeance rises while the water permeance and the selectivity drops. The pervaporation performances can be tuned from trade-off to anti-trade off through surface modification of MOFs. The synergistic effect of MOFs and polymer matrix is crucial in breaking the trade-off effects. Compared with the pristine PVA membranes, the optimal MIL-53-NHCOH/PVA MMMs (4 wt% loading) display an 206% increase in water permeance, and an 200% increase in selectivity, and the optimal MIL-53-NHCOC4H9/PVA MMMs (7.5 wt% loading) display a 340 % increase in water permeance, and a 170 % increase in selectivity, demonstrating their great potential in ethanol dehydration.