One-step modification of PVDF membrane with tannin-inspired highly hydrophilic and underwater superoleophobic coating for effective oil-in-water emulsion separation

Herein, hydrophobic PVDF membranes were facilely transformed into highly hydrophilic and underwater superoleophobic ones via one-step dip-coating in tannic acid (TA)/sodium periodate (NaIO4)-mixed solution. The employment of NaIO4 could not only facilitate TA oxidation and deposition, but also introduce abundant hydrophilic carboxyl groups on membrane surface. Consequently, compared with the pristine PVDF membrane, the modified membrane showed much higher hydmphilicity and underwater oleophobicity with water contact angle decreasing from 121 degrees to 32 degrees, oil contact angle increasing from 116 degrees to 162 degrees and a tilt angle of just 2 degrees. In contrast to the two-step modification (deposition of TA followed by post-oxidation by NaIO4), our approach endowed the membrane with dramatically improved permeability (>2400 LMH/bar) and oil rejection (>98%) when dealing with different types of oil-in-water emulsions. Additionally, the membrane displayed excellent antifouling performance with flux recovery ratios of above 95% and favorable reusability after 5-cycle filtration tests. Moreover, the membrane possessed a stable TA coating even being subjected to harsh pH solutions or sonication. This work provides a simple, robust and cost-effective strategy for membrane modification.

Automated summary

The study successfully transformed hydrophobic PVDF membranes into highly hydrophilic and underwater superoleophobic ones through one-step dip-coating in a TA/NaIO4-mixed solution. The modified membrane showed enhanced permeability and oil rejection, excellent antifouling performance, and stability under harsh conditions, providing a simple, robust, and cost-effective strategy for membrane modification.