Surface Hydrophilic Modification Of Polyvinylidene Fluoride Porous Membrane Based On Polyphenols Tannin

Polyvinylidene fluoride(PVDF)with its excellent properties has been widely used to prepare microfiltration,ultrafiltration,nanofiltration and reverse osmosis membranes for water treatment,however,its strong hydrophobicity makes it easily fouled and poor permeability in the water treatment process which immensely decrease its water treatment efficiency and service life,so it is significantly important to improve the hydrophilicity.Herein,low-cost and environmental tara tannin-based coating was facilely constructed on the surface of the PVDF membrane via a simple dip-coating method.Due to the existence of abundant catechol and pyrogallol functional group,tannin-based coating can tightly coat on the PVDF membrane surface which can effectively improve the surface properties.In one work,tara tannin was used as sole coating material to modify PVDF membrane via a simple dip-coating method.The extracted tannin from tara powder was measured by nuclear magnetic resonance(~1H-NMR).An oxidation induced aggregation mechanism was detected in the tannin solution through the use of ultraviolet spectrophotometer(UV-Vis).The morphology and chemical composition of the tannin coated PVDF membrane were characterized via field-emission scanning electron microscopy(FESEM),X-ray photoelectron spectroscopy(XPS)and attenuated total reflectance fourier transform infrared spectroscopy(ATR-FTIR),which demonstrated that the tannin coating successfully coated on the PVDF membrane surface.After coating with the tannin coating,hydrophilicity and filtration performance of PVDF membrane are both greatly enhanced comparing with pristine membrane,and the modified membranes also obtain a good emulsion separation performance and excellent antifouling property.Moreover,these membranes possess outstanding durability that is disclosed by a long-term rinsing experiment.In the other work,a tannin-based hybrid coating was coated on PVDF membrane surface through one step co-deposition of tannin and silane coupling agent(KH550and KH590).The morphology and chemical composition of modified membrane surface were measured by field-emission scanning electron microscopy(FESEM),atomic force microscope(AFM),X-ray photoelectron spectroscopy(XPS)and attenuated total reflectance fourier transform infrared spectroscopy(ATR-FTIR).It is found that a micro-nanostructure was formed on the membrane surface due to the adding of silane coupling agent,and the micro-nanostructure can adjust through changing categories and adding content of silane coupling agent.After coating with the hybrid coating,the modified membranes exhibit excellent hydrophilic and underwater superoleophobic property.The underwater superoleophobicity endows the membrane with a superior antifouling property and high oil/water separation efficiency.Meanwhile,the long-term rinsing experiment also indicated that the modified membranes have outstanding durability.