Free-standing ZIF-71/PDMS nanocomposite membranes for the recovery of ethanol and 1-butanol from water through pervaporation

Free-standing zeolitic imidazolate framework-71 (ZIF-71)/polydimethylsiloxane (PDMS) nanocomposite membranes with 0, 5, 25 and 40 wt% ZIF-71 loadings were prepared and the pervaporation separation performance for ethanol and 1-butanol from water was measured. ZIF-71 was stable in water for seven days (both at room temperature and 60 °C); the crystal structure and morphology remained the same. ZIF-71/PDMS composite membranes were formed through addition cure and condensation cure methods. The addition cure method is not compatible with ZIF-71 resulting in membranes with poor mechanical properties, while the condensation cure method results in membranes with good mechanical properties. With the condensation cure PDMS synthesis method, the 40 wt% ZIF-71 nanocomposite membranes achieved a maximum ethanol/water selectivity of 0.81±0.04 (separation factor of 12.5±0.3 for 2 wt% ethanol feed) and maximum 1-butnaol/water selectivity of 5.64±0.15 (separation factor of 69.9±1.8 for 2 wt% 1-butanol feed). The mechanical properties of membranes were quantified with tensile testing. The Young's modulus increased considerably with increasing ZIF-71 loadings, indicating increased stiffness of PDMS membranes with addition of ZIF-71 particles. The fracture strain deceased with the introduction of ZIF-71 particles, suggesting decreased ductility. This is the first report of free-standing ZIF-71/PDMS mixed matrix membranes (MMMs) and the highest ethanol/water selectivity reported for ZIF-71/PDMS MMMs (free-standing or supported).