Preparation And Application Of Polyvinylidene Fluoride Membrane Modified By SGO And PDA

PVDF is a well-behaved membrane material widely used in the preparation of microfiltration and ultrafiltration membranes due to outstanding chemical stability.However,due to the extremely low hydrophobicity of polyvinylidene fluoride,Oil and other hydrophobic substances in the process of easy to produce adsorption pollution,the membrane flux decreased rapidly,reducing the life of the membrane.In this paper,two methods of hydrophilic modification of PVDF were studied by using hydrophilic sulfonated graphene(SGO)blends and polymerized perfluorosulfonic acid(PFSA)modified PVDF hollow fiber ultrafiltration membranes.The use of dopamine self-polymerization reaction to form a strong adhesion performance of the poly dopamine(PDA)layer,the hydrophilic functional molecules into the surface of the material effectively improve the hydrophilicity of PVDF membrane surface.The main results of the study are as follows:Sulfonated grapheneoxide(SGO)nanohybrids were synthesized and employed to modify polyvinylidene fluoride(PVDF)hollow fiber ultrafiltration membranes accompanied with perfluorosulfonic acid(PFSA).Due to the synergism effects of PFSA and SGO,the SGO-blended PVDF membranes exhibit high permeability,anti-fouling performances and improved chemical resistance.SGO addition leads to thinner skin and porous sublayer of the membranes.The pure water permeability firstly increases from 87.8 to 174.2 L?m-2?bar-1?h-1 by adding 0.5 wt% SGO nanohybrids in dopes,and then slightly decreases to 156.2 L?m-2?bar-1?h-1 for M1.0 with the further increase of SGO content.After five fouling-cleaning cycles,SGO-modified PVDF membranes show less flux decline and more stable solute rejection than the unmodified one,which demonstrate that the SGO nanosheets act as a chlorine barrier for the PVDF membranes,resulting in an outstanding anti-fouling ability and an effective suppression of the membrane degradation under frequent oxidative cleaning.Secondly,in this study,PVDF ultrathin flat microfiltration membranes with different surface structures were prepared under different gel bath conditions.Then,PDA was coated on the surface of two kinds of basement membranes by self-polymerization reaction to form a PDA layer with strong adhesion properties.Finally,the poly-dopamine-based catechol groups can be subjected to the secondary reaction properties,further grafting of polyethyleneimine(PEI)with stronger hydrophilicity,and more hydrophilic functional molecules(amino)to introduce into the surface of the modified membrane,which effectively improve the hydrophilicity of the surface of PVDF membrane.Finally,different kinds of emulsified oil solution were used as the treatment object to study the antifouling performance of the modified membranes and the processing capacity of the emulsified oil.Finally,on the basis of the previous study,the co-deposition of PDA and nano-Si O2 on the surface of PVDF membranes were proposed.In this research,two kinds of nano-Si O2 were synthesized,one was smaller in particle size and better in water solubility and the other was modified by silane coupling agent.The hydrophilicity and pore size of the PVDF microfiltration membranes were investigated in detail.The results show that the PDA can be used as a binder to modified the nano-Si O2 on the membrane surfaces,but the smaller particle size of nano-Si O2 bring about decreasing of membrane pore size,further leading to decreased membrane permeability.The larger particle size of nano-Si O2 is more likely to be deposited on the membrane surface,and in the absence of clogging the membrane micro pores,in the condition that the hydrophilicity and permeation flux increases.