Tannin-inspired superhydrophilic and underwater superoleophobic polypropylene membrane for effective oil/water emulsions separation

In this work, a novel two-pot coating process that facilely transform polypropylene (PP) microfiltration membrane hydrophobicity into superhydrophilicity and underwater superoleophobicity was reported. Tannic acid (TA) and ferric ions (Fe III ) were selected as organic ligand and inorganic cross-linker, respectively. Compared with the membrane modified by the one-pot method, the two-pot treated substrate has uniformly distributed coatings, better wettability, higher water permeability (7092   L   m −2   h −1   bar −1 , which is 4.5 times higher than that of the one-pot modified membrane), and excellent oil/water emulsions separation performance. This treatment only took about 15   min and the underwater superoleophobicity was well maintained even after rigorous long-term washing operation. More importantly, both the remaining solutions of TA and Fe III could be recycled and reused easily in the next two-pot coating process. Such a rapid, green, and cost-effective modification method highlights its potential for practical application in oil/water emulsions separation.