Study On The Hydrophilic Modification And Properties Of Pvdf Membranes Based On Mussel Inspired Dopamine

Recently,membrane separation technology has developed rapidly owing to its high separation efficiency and relatively low energy consumption.Polyvinylidene fluoride(PVDF)membrane has been widely used for wastewater treatment due to its excellent chemical resistance,thermal stability and mechanical strength.However,the inherent strong hydrophobicity of PVDF membrane will result in two disadvantages when treating wastewater.On the one hand,the hydrophobicity will lead to low water flux.On the other hand,the hydrophobic PVDF is easily contaminated by protein and oil,resulting in a sharp decline in serviceability.Endowing the PVDF membrane with hydrophilicity is an effective strategy to solve these problems.Herein,three kinds of hydrophilic modification strategies based on the self-polymerization of dopamine are proposed and utilized to overcome the inherent hydrophobicity of PVDF membranes.The composition,formation mechnisim,wettability,and stability of the coatings decorated on PVDF membrane are investigated.Moreover,the effects of different coatings on the comprehensive performance of PVDF membranes are also studied in detail.Hydrophilic Ti O2 were decorated on the surface of PVDF ultrafiltraion membrane via self-polymerization of dopamine and subsequent hydrolysis of ammonium fluotitanate.The formation of polydopamine and Ti O2 on the membrane surface was confirmed by the attenuated total reflection fou rier transform infrared spectroscopy(ATR-FTIR)and X-ray photoelectron spectroscopy(XPS).Scanning electron microscopy(SEM)and atomic force microscopy(AFM)were used to investigate the morphologies of pristine and modified membranes.The polydopamine(p DA)layer coated on PVDF membranes could act as bio-glue and assist Ti O2 to tightly and homogeneously bind onto PVDF surface,so that the hydrophilicity of the modified membranes was significantly improved.By adjusting the hydrolysis time of ammonium fluotitanate,the hydrophilicity and water permeation properties could be controlled.And under the optimized conditions,the water flux and BSA rejection of modified PVDF ultrafiltraion membrane were as high as 227.86 L m-2 h-1 bar-1 and 92%,respectively.Static and dynamic BSA adsorption experiments indicated that the membrane decorated with Ti O2 film had much better anti-fouling performance,which could be further confirmed by the high flux recovery ratio(>90%).Moreover,the formed Ti O2 coating on the PVDF membrane was stable enough to resist drastic rinsing,which was due to the formation of the coordination bond(C–O…Ti)between Ti O2 and p DA.Besides,this strategy could be also applied to PVDF microfiltration(MF)membrane,which can render the membrane high hydrophilicity and underwater superoleophobicity.The modified PVDF microfiltration membrane had high water fulx(7600 L m-2 h-1)at 1 bar,and can effectively separate the oil-in-water emulsion.Inspired by the above mentioned two-step strategy,a one-step hydrophilic modification method was proposed according to the simultaneous polymerization of mussel inspired dopamine and hydrolysis of commercial tetraethoxysilane(TEOS)in alkalescent solution.Hydrophilic coatings could be coated on the PVDF membranes,and the hydrophilicity could be adjusted by changing the concentration of TEOS and reaction duration.SEM images indicated that the coating was uniform.ATR-FTIR analysis showd the coating was composed of Si O2 and p DA.EDX mapping revealed the homogeneous distribution of Si O2 and pDA.The TEM images of hybrid nanoparticles before and after etching disclosed the distribution of Si O2 and p DA under different reaction conditons.The formation mechanism of the hybrid coating was proposed based on the above results and the UV spectrum of mixture solution,and optimized conditions were applied to transform hydrophobic PVDF MF membrane into high hydrophilic and underwater superoleophobic membrane.The modified PVDF MF membrane had ultrahigh water flux(8606 L m-2 h-1 bar-1),which was 34 times higher than that of pristine membrane,and could effectively separate oil-in-water emulsion at atmospheric pressure.Besdies,the hybrid coatings endowed the MF membrane with excellent antifouling performance.Most importantly,the decorated hybrid coatings were extremely stable and can withstand rigorous washing and cryogenic bending.The third hydrphilic modification strategy was extended from the second strategy.The ?-(2,3-epoxypropoxy)propytrimethoxysilane(KH-560),one kind of commercially available silane coupling agent,was used with dopamin for one-step modificaiotn of PVDF membranes.The simultaneous polymerization of dopamine and hydrolysis of KH-560 could form hybrid and hydrophilc coatings on the surfaces of different PVDF membranes.The PVDF UF membranes coated with hybrid coatings were highly hydrophilic.When the concentration of KH-560 was 9 mg m L-1,the water flux and BSA rejection of modified PVDF UF membrane were 185 L m-2 h-1 bar-1 and 90%,respectively.Besides,the BSA adsorption of the modified membrane was as low as 12 ?g cm-2,indicating the desirable anti-fouling performance.Notably,compared with the previous two strategies,the third strategy could endow the modified membrane with excellent dry storage ability.The strategy could also render PVDF MF membrane superhydrophilicity and underwater superoleophobicity,and the modified MF membrane had ultrahigh water flux as high as 6500 L m-2 h-1 bar-1.Such MF membrane could be deployed for separating oily water under atmospheric conditions with superior antifouling ability.The hybrid coatings also had excellent stability.These developed strategies for hydrophilic modification of PVDF membrane could pave the way for separation membranes to be used in harsh water environmental remediation and greatly stimulate the rapid development of mussel inspired surface engineering.