Water-selective permeation in hybrid membrane incorporating multi-functional hollow ZIF-8 nanospheres

Abstract

Incorporating metal-organic frameworks (MOFs) into polymer to fabricate hybrid membranes is an effective approach of breaking the trade-off between permeability and selectivity. In this study, hollow zeolitic imidazolate framework-8 (HZIF-8) nanospheres were prepared and blended into sodium alginate (SA) matrix to fabricate water-selective hybrid membrane, which intensify the diffusion process of water molecules dramatically owing to their well-designed hierarchical structures. The micropores on HZIF-8 nanosphere shell have a molecular sieving effect, which enhances diffusion selectivity of water molecules. The hollow structure of HZIF-8 nanospheres ensures the rapid diffusion of water molecules, thus elevating the permeation flux and separation factor simultaneously. Besides, the intervention effects of HZIF-8 nanospheres on the SA chain packing also contribute to the enhancement of permeation flux and separation factor by rendering the membrane more free volume cavities and suitable free volume cavity size for ethanol/water separation. When utilized to separate 90 wt% ethanol aqueous solution at 76 °C, the hybrid membrane containing 6 wt% HZIF-8 displays the highest separation performance with permeation flux of 2485 g/m2 h and separation factor of 1884, much superior to those for pure SA membrane and the hybrid membranes incorporating zeolitic imidazolate framework-8 (ZIF-8) nanocrystals. Desirable long-term stability of the hybrid membranes was also acquired.