Superwetting PVDF membrane prepared by in situ extraction of metal ions for highly efficient oil/water mixture and emulsion separation

Wettability and roughness modification of membrane surface are crucial for its utilization in the separation of oil/water mixture and emulsion. However, traditional modification method for membrane had the drawbacks of high cost, complex preparation and low flux. In this study, for the first time, based on tannic acid (TA), Cu2+ and ethylenediaminetetraacetic acid disodium salt (EDTA-2Na), a novel, facile, and cost-effective interface engineering method for significantly enhancing the flux and separation efficiency of polyvinylidene fluoride (PVDF) microfiltration membrane for oil/water mixture and emulsion was developed via in situ extraction of metal ions. TA and Cu2+ could form TA-Cu2+ complex which could deposit on the surface of PVDF microfiltration membrane, and then Cu2+ was extracted by EDTA-2Na, which not only enhanced the surface roughness and wettability of the membrane, but also reserved the porous structure of the matrix membrane. The resulted membrane possessed superhydrophilicity and underwater superoleophobicity, which showed high membrane fluxes of 8841.94 Lm(-2) h(-1) bar(-1) and 1440 Lm(-2) h(-1) bar(-1) for oil/water mixtures and emulsified oil respectively, and the separation efficiency of TA/EDTA-2Na/PVDF could reach 99.99%. Moreover, the membrane still exhibited excellent stability after long soaking treatment in NaCl solution for 48 h. Thus, in this study, a new strategy for membrane surface modification was developed, which had considerable promise for real application of oily wastewater treatment.