Facile hydrophilic modification of PVDF membrane with Ag/EGCG decorated micro/nanostructural surface for efficient oil-in-water emulsion separation

[Display omitted] •PVDF membrane was facilely modified via coating of EGCG and Ag+.•High membrane hydrophilicity and underwater superoleophobicity were achieved.•The membrane exhibited desired performance while treating oily emulsions.•The membrane possessed satisfactory antifouling property and stability. Wettability of porous materials is crucial for the separation of emulsified oil/water mixtures. Herein, high hydrophobicity of polyvinylidene fluoride (PVDF) membrane has been facilely transformed to high hydrophilicity and underwater superoleophobicity via single-step coating of plant-derived epigallocatechin gallate (EGCG) and silver ion (Ag+) in aqueous solution. EGCG can chelate with Ag+ and in-situ reduced it into Ag nanoparticle, meanwhile Ag/EGCG composite was adhered on membrane surface due to the high surface binding affinity of EGCG. The hydrophilic EGCG and formed micro/nanostructure together improved membrane hydrophilicity and oleophobicity. The optimally Ag/EGCG modified PVDF membrane possesses high permeate flux (e.g. 735 L/(m2h) for diesel-in-water emulsion, while it is zero for pristine PVDF membrane) under a low operation pressure of 0.5 bar and high oil rejections in the treatment of surfactant-stabilized oil-in-water emulsions consisting of micro/nano scale droplets. In addition, the membrane exhibits excellent antifouling property with a flux recovery ratio of 98.1% and satisfactory reusability in a 5-cycle test. Moreover, the membrane possessed desired stability during long-term rinsing test and Ag leaching test. This work would offer new insights into surface hydrophilic manipulation of porous membrane towards practical oil emulsion purification.