Janus ZIF-8/P(AN-MA) hybrid microfiltration membrane with selected wettability for highly efficient separation of water/oil emulsions

The separation of oil-in-water and water-in-oil emulsions with high efficiency and environmental friendly remains a challenge in the past decade. This work describes a new method to improve the trade-off of the poly(acrylonitrile-co-methyl acrylate) (P(AN-MA))-based membrane for water/oil separation. P(AN-MA) microfiltration (MF) membrane was fabricated via thermally induced phase separation (TIPS) method in this study. Then, some of the –CN groups and –COOCH3 groups were converted to –COOH groups via hydrolyzing. Finally, the selected wettability was attained by grafting PEI on one side while ZIF-8 was anchored to the other side via self-assembly and in-situ interfacial reaction methods. The ZIF-8/P(AN-MA) hybrid MF membranes are superoleophobic underwater on the PEI side while super-hydrophobic under oil on the ZIF-8 side, which can efficiently and accurately separate oil-in-water and water-in-oil emulsions at a low pressure (0.01 MPa). The separation fluxes of the PEI side were as high as 3053 L/m2 h and 1035 L/m2 h respectively, for the surfactant-free mixtures and surfactant-stabilized emulsions. For water-in-oil emulsions, the fluxes were up to 2316 L/m2 and 878 L/m2 h on the ZIF-8 side, respectively. The separation efficiency of all the mixtures and emulsions was higher than 97.5 %. Moreover, the Janus membranes showed excellent anti-oil-fouling and anti-water-fouling properties on the two sides of the membranes, as well as remarkable durability during the 10 cycles in oil/water separation. Hence, Janus ZIF-8/P(AN-MA) hybrid MF membranes show potential application prospects in oil/water separation.