Studies On Hydrophilic Modification And Oil-water Separation Performance Of Electrospinning PVDF Composite Membranes

The rapid progress of the chemical industry and the development of industrialization have brought huge challenges to the ecosystem.The wanton discharge of wastewater containing organic pollutants and heavy metal pollutants has seriously threatened the health of human beings,as well as the survival and reproduction of animals and plants.Among them,daily production and life,crude oil extraction,oil transportation,etc.generated a large quantity of hard-to-treat oily wastewater,especially the emulsified oil that contains surfactant ingredients that forms a stable interface.Therefore,membrane separation technology with high separation performance,low energy requirements and flexible operability stands out among numbers of oil-water separation technologies.However,in large-scale applications,separation membranes have problems such as membrane compaction or the adsorption of pollutants,resulting in reduced of flux separation efficiency.For this reason,many studies have devoted themselves to constructing superhydrophilic surfaces,which is,showing superoleophobic properties underwater.The boundary layer between the hydrophilic membrane and the aqueous solution has hydrogen-bonding force,which preferentially adsorbs water molecules to form a continuous water film to isolate the attraction between the composite membrane and the oil droplets,so as to achieve separation and antifouling effect.Water can continuously pass through the membrane,while oil droplets are retained.On the basis of above research,this topic aims to the fabrication of functional PVDF electrospinning membrane,which has been modified by blending and surface coating modification,giving it hydrophilic and antifouling ability,and developing superhydrophilic-underwater superoleophobic property.First,a simple one-step electrospinning method was used to prepare polyvinylidene fluoride(PVDF),polyvinylpyrrolidone(PVP)and titanium dioxide(TiO₂)nanoparticles blended nanofiber membranes.It is found that the presence of PVP provides certain strength for the PVDF nanofiber membrane,and the pores formed by the dissolution of PVP are conducive to the loading of TiO₂ NPs,which improves the wettability of the composite membrane.The introduction of these three components makes the porous nanofiber membrane have a hierarchical rough structure,which is hydrophilic in the air and oleophobic under the water.The membrane can show excellent separation efficiency(up to 98.4%)for different emulsions without applying any external force,and has good antifouling performance.After multiple cycles,the flux recovery rate is 95.68%,and the total pollution rate is 15.18%,which will be a simple and promising method to prepare reusable and functional separation membranes.In order to give the separation membrane multi-functionality,realize the effective separation of emulsified oil and soluble inorganic salt,while keeping the PVDF nanofiber membrane stable under strong acid and alkali conditions.We used the coordination network between tannic acid(TA)and Fe³⁺to conduct surface hydrophilic modification of PVDF-PVP blend nanofiber membrane by filtration assisted deposition of GO/TiO₂ on the membrane surface in semi-ordered accumulation.TiO₂ is inserted into GO nanosheets to expand the interlayer spacing and prevent film compaction.TA and Fe³⁺enhance the interlayer force through covalent bonds,cation-?and coordination bonds,and endow the coating with stability.The coating of the composite membrane can maintain its integrity even after being soaked in extreme conditions(strong acid and alkali)for 1 month.The results show that the underwater oil contact angle of the composite membrane is 152.5°.In addition,compared with the same type of oil-water separation membrane,the membrane has a higher flux(243.11 L/h·m~2·bar)and oil(>98%)/salt(>47%)rejection rate,and can still be maintained after 30 min ultrasonic treatment.This work provides an ingenious and flexible method for constructing a stable graphene oxide modified hydrophilic membrane.