PVDF microfiltration membranes modified with AgNPs/tannic acid for efficient separation of oil and water emulsions

Treatment of oil/water mixture, especially oil/water emulsions, is of great significance in the protection of both the environment and living creatures. Herein, in this work, we reported a two-step strategy to enhance the hydrophilicity and underwater oleophobicity of PVDF microfiltration membranes using tannic acid (TA, a nature plant polyphenol) and AgNO3 solutions. After coating by Ag nanoparticles (AgNPs)/TA (0.4 mg/ml Ag+, 0.2 mg/ml TA), the PVDF membrane exhibited high hydrophilicity for a short immersion time (10.35 s) of a water droplet (V=5 µl, initial WCA=19°), underwater superoleophobicity (UOCA=161°) and antifouling property and thus, high-efficiency oil/ water emulsions (SDS/kerosene/water emulsion) separation could be realized. Compared with Fe/TA-PVDF (0.4 mg/ml Fe2+, 0.2 mg/ml TA, initial WCA=21° and UOCA=156°) and Cu/TA-PVDF (0.4 mg/ml Cu2+, 0.2 mg/ml TA, initial WCA=31° and UOCA=147°), the AgNPs/TA-PVDF in our work possessed best hydrophilicity and underwater superoleophobicity. In addition, the AgNPs/TA-PVDF could maintain its hydrophilicity, underwater superoleophobicity and mechanical property after rinsing tests and scratch resistance tests.