[Show abstract][Hide abstract] ABSTRACT: The framework hydrophobicity and flexibility of ZIF-8 are investigated by a detailed adsorption and diffusion study of a series of probe molecules including ethanol, 1-butanol, water, hexane isomers, xylene isomers, and 1,2,4-trimethylbenzene. The prospects for using ZIF-8 in biofuel recovery and hydrocarbon separations are discussed in terms of adsorption or kinetic selectivities. ZIF-8 shows extremely low water vapor uptakes and is especially suitable for vapor phase butanol-based biofuel recovery. The extraordinary framework flexibility of ZIF-8 is demonstrated by the adsorption of hydrocarbon molecules that are much larger than its nominal pore size, such as m-xylene, o-xylene and 1,2,4-trimethylbenzene. The calculation of corrected diffusion coefficients reveals an interesting spectrum of promising kinetic hydrocarbon separations by ZIF-8. These findings confirm that a molecular sieving effect tends to occur in the sorbate molecular size range of 4–6 Å rather than around the nominal ZIF-8 pore size of 3.4 Å, due to its surprising framework flexibility.
[Show abstract][Hide abstract] ABSTRACT: By modifying the synthesis route, we have synthesized ZIF-90 nanoparticles with an average particle size of 55 nm and embedded them into P84 polymeric membranes with excellent dispersion for the dehydration of isopropanol (IPA)/water mixture via pervaporation. The effects of ZIF-90 loading as well as feed temperature on pervaporation performance of the mixed matrix membranes (MMMs) were systematically investigated. The flux of MMMs increases with increasing ZIF-90 loading due to the enhanced fractional free volume, while the separation factor of water/IPA can be maintained at 5432 when the ZIF-90 loading is less than 20 wt%, but reduced to 385 when the ZIF-90 loading is 30 wt%. Interestingly, the application of sulfonated polyethersulfone (SPES) as a primer to ZIF-90 nanoparticles before fabricating MMMs consisting of 30 wt% ZIF-90 recovers the separation factor without sacrificing the flux. The best MMM showed the separation performance with a flux of 109 g m−2 h−1 and a separation factor of 5668 at 60 °C. This encouraging performance suggests a promising future of ZIF-90/P84 composite membranes for the dehydration of IPA via pervaporation process.
Journal of Membrane Science 01/2014; 453:155–167. · 4.09 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The ability to obtain a maximum loading of inorganic nanoparticles while maintaining uniform dispersion in the polymer is the key to the fabrication of mixed-matrix membranes with high pervaporation performance in bioalcohol recovery from aqueous solution. Herein, we report the simultaneous spray self-assembly of a zeolitic imidazolate framework (ZIF)–polymer suspension and a cross-linker/catalyst solution as a method for the fabrication of a well-dispersed ZIF-8–PDMS nanohybrid membrane with an extremely high loading. The ZIF-8–PDMS membrane showed excellent biobutanol-permselective pervaporation performance. When the ZIF-8 loading was increased to 40 wt %, the total flux and separation factor could reach 4846.2 g m−2 h−1 and 81.6, respectively, in the recovery of n-butanol from 1.0 wt % aqueous solution (80 °C). This new method is expected to have serious implications for the preparation of defect-free mixed-matrix membranes for many applications.
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