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/m(2) h and 1035 L/m(2) h respectively, for the surfactant-free mixtures and surfactant-stabilized emulsions. For water-in-oil emulsions, the fluxes were up to 2316 L/m(2) and 878 L/m(2) 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.

Automated summary

This study describes a new method to improve the water/oil separation performance of P(AN-MA) membranes by fabricating ZIF-8/P(AN-MA) hybrid membranes with superoleophobic and superhydrophobic properties. These membranes can efficiently and accurately separate oil-in-water and water-in-oil emulsions at a low pressure, and exhibit excellent anti-oil-fouling and anti-water-fouling properties.