Development of highly-efficient ZIF-8@PDMS/PVDF nanofibrous composite membrane for phenol removal in aqueous-aqueous membrane extractive process

A highly-efficient zeolitic imidazolate framework-8 (ZIF-8) embedded polydimethylsiloxane (PDMS) mixed matrix membrane (MMM) supported by a polyvinylidene fluoride (PVDF) nanofibrous substrate was developed for phenol removal in an aqueous-aqueous membrane extractive process. Homogeneous nano-scaled dispersion of ZIF-8 in the PDMS matrix was achieved by direct incorporation without intermediate drying process, where the interaction of the randomly-moved nanofillers could be prevented, leading to evenly dispersed ZIF-8 nanofillers and defect-free ZIF-8@PDMS/PVDF nanofibrous composite membranes. The newly-developed ZIF-8@PDMS/PVDF membrane exhibited an exceptionally high overall mass-transfer coefficient, k0 of 35.7 ± 1.1 × 10−7 m/s, doubling that of the pristine membrane in the membrane extractive process. The high performance was maintained for over 360 h without loss of salt rejection. These results could be attributed to the organophilic-assisted “bi-mode” transporting mechanism of ZIF-8 nanofillers in PDMS matrix, namely: (1) the solution-diffusion transport mode; (2) the pore-flow transport mode, where the synergistic effects are expected to significantly improve the phenol transfer efficiency through the membranes. Overall, the results achieved in this work demonstrate promising potential of highly-efficient ZIF-8@PDMS/PVDF nanofibrous composite membranes used for aqueous-aqueous membrane extractive processes for organic-containing wastewater treatments.