Performance optimization of Co/Zn-ZIF-8/PDMS mixed-matrix membranes based on tubular ceramic carriers for ethanol recovery <i>via</i> pervaporation

In the present investigation, highly hydrophobic Zn-ZIF-8 nanoparticle-filled polydimethylsiloxane (PDMS)-based mixed-matrix membranes (MMMs) were prepared from tubular ceramic carriers to meet the requirements of industrial applications, which were better than ZIF-67/PDMS (Co-ZIF-8/PDMS) MMMs in overall performance for ethanol recovery from aqueous solutions. Their separation factor for pervaporation was greatly enhanced compared with the pristine PDMS membrane; however, the flux reduction was slightly larger (flux-separation factor trade-off effect). Furthermore, Co₅₀Zn₅₀-ZIF-8/PDMS MMM was prepared through the substitution of Zn with Co in the Zn-ZIF-8 framework filler. Zn-ZIF-8 and Co₅₀Zn₅₀-ZIF-8 nanoparticles were studied using various characterizations, and the morphology and properties of the resulting MMMs were investigated. Owing to the relatively small agglomerations and enhancement of the pore volume of bimetallic Co₅₀Zn₅₀-ZIF-8 nanoparticles, the separation factor of Co₅₀Zn₅₀-ZIF-8/PDMS MMM was mostly similar to that of the Zn-ZIF-8/PDMS MMM, and the total flux was elevated, achieving the optimization of membrane properties. The best pervaporation performance of the Co₅₀Zn₅₀-ZIF-8/PDMS MMM was obtained in a 5 wt% ethanol aqueous solution at 60 °C with a total flux of 1.37 kg m^-2 h^-1, a corresponding separation factor of 10.5, and a pervaporation separation index (PSI) of 13.02 kg m^-2 h^-1. Overall, the relevant experimental results preliminarily demonstrated the potential application of Co₅₀Zn₅₀-ZIF-8/PDMS MMM in the separation of low-concentration ethanol aqueous solutions.