The influence of dispersed phases on polyamide/ZIF-8 nanofiltration membranes for dye removal from water

To investigate the influence of different dispersed phases on polyamide (PA)/ZIF-8 membrane properties, three different fabrication methods for dispersing ZIF-8 nanoparticles were developed to prepare the PA/ZIF-8(A) membranes (in aqueous phases), PA/ZIF-8(O) membranes (in organic phases), and PA/ZIF-8(B) membrane (in both the aqueous and organic phases), respectively. These PA/ZIF-8 membranes were characterized in detail by XRD, DLS, XPS, FTIR, SEM, AFM, and contact angle measurements, the results showed that the structure properties of the PA/ZIF-8 membranes were significantly dependent on the dispersed phases and ZIF-8 concentrations. The nanofiltration performance of the PA/ZIF-8 membranes was investigated for application in removing dye (Congo red) from water. For the PA/ZIF-8(A) and PA/ZIF-8(O) membranes, the flux and rejection were both improved at 0.05-0.15% (w/v) ZIF-8 concentration in a single phase and the PA/ZIF-8(O) membranes exhibited slightly higher fluxes than the PA/ZIF-8(A) membranes due to the better dispersion of hydrophobic ZIF-8 in organic phases. The PA/ZIF-8(B) membrane prepared by 0.10% (w/v) ZIF-8 concentration in both the aqueous and organic phases showed the best membrane performance among all prepared PA/ZIF-8 membranes: the flux significantly increased to two times that of the pure PA membrane, and the rejection was nearly 100%. Compared with the PA/ZIF-8(A) and PA/ZIF-8(O) membranes, the improvement on membrane performance of the PA/ZIF-8(B) membrane was achieved by a combination of the high ZIF-8 loading, good ZIF-8 distribution, and fewer ZIF-8 aggregates in the PA/ZIF-8 selective layer. The influence of different dispersed phases on PA/ZIF-8 membrane properties was investigated, and the PA/ZIF-8(B) membrane (ZIF-8 dispersed in both the aqueous and organic phases) exhibited the best performance for dye removal by nanofiltration.