Determination of sorption and diffusion for ethanol through superhydrophobic ZIF/PDMS mixed matrix membrane

Abstract The hydrophobicity-hydrophilicity properties of the surface play decisive roles in the resultant separation performance of the membrane, especially the hydrophobicity of mixed matrix membranes (MMMs) for pervaporation recovery of various organic systems from aqueous solution. Herein, superhydrophobic Zeolitic Imidazolate Framework-90 (S-ZIF-90) was employed as filler to incorporate into Polydimethylsiloxane (PDMS) to prepare superhydrophobic S-ZIF-90/PDMS MMMs for ethanol permselective pervaporation. The chemical structures and superhydrophobicity properties of the surface of S-ZIF-90 and S-ZIF-90/PDMS MMMs were demonstrated by various characterization techniques. The results showed that S-ZIF-90 particles and S-ZIF-90/PDMS composite membranes were successfully prepared and S-ZIF-90/PDMS MMMs have higher hydrophobicity property as compared to ZIF-90/PDMS MMMs or pure PDMS. Therefore, S-ZIF-90/PDMS MMMs showed more excellent separation performance than ZIF-90/PDMS MMMs or pure PDMS. In particular, S-ZIF-90/PDMS MMMs with 15 wt% S-ZIF-90 loading have a total flux of 1064 g/(m2 h) with a maximum separation factor of 14.9 at 40 °C for 5 wt% dilute ethanol solution. The diffusion coefficients, permeation coefficients, adsorption heat (△HS) and adsorption entropy (△S) of ethanol and water were also calculated by sorption tests, which might provide a method to further determinate the mass transfer mechanism of MMMs in pervaporation process.