Novel MOF-capped halloysite nanotubes/PDMS mixed matrix membranes for enhanced n-butanol permselective pervaporation

With the help of density functional theory calculations, a unique MOF-capped nanotube architecture was initially conceived in this study based on the solution-diffusion mechanism. Then, the novel ZIF-8-capped halloysite nanotubes (ZHNTs) were prepared and incorporated in the polydimethylsiloxane (PDMS) bulk to achieve the mixed matrix membranes (MMMs) for n-butanol permselective pervaporation. The remarkable characteristic of this membrane was that the HNT lumen (∼25 nm) in ZHNTs provided the exquisite diffusion highway for the penetrants that were first selected through the capping ZIF-8 layer. Simultaneously, the close connection of ZIF-8 layer on external surface of ZHNTs created the relatively continuous pathways for molecular permeation. As expected, the embedding ZHNTs significantly improved the separation performances of the membranes. Impressively, the as-obtained membrane acquired a high separation factor of 61.3 (58.7% higher than that of PDMS control membrane) with a comparable flux of 683 g m^-2 h^-1 (2.43-fold as much as that of PDMS control membrane) at 40 °C in the separation of 1 wt% n-butanol aqueous solution. Moreover, the presence of ZHNTs conferred excellent interfacial compatibility, mechanical properties, and good long-term stability on the resultant membranes. This study may shed light on the rational design of high-performance MMMs for biofuels recovery from fermentation broths.