Study On Preparation And Properties Of TiO₂/PVDF-g-PEGMA/PVDF Membranes

Polyvinylidene fluoride?PVDF?has become one of the popular membrane materials due to its excellent processability,chemical resistance,wear resistance,thermal stability and outstanding mechanical strength.It is widely used in the field of drinking water and wastewater treatment.But PVDF is extremely hydrophobic due to its low surface energy.This makes the PVDF membrane not only require higher membrane pressure during the application process,but also causes some hydrophobic pollutants to adsorb on the membrane surface to cause serious membrane fouling.Moreover,the surface structure of the pure PVDF membrane is relatively dense and the porosity is low,which makes the water flux extremely unsatisfactory.Therefore,the membrane's anti-pollution ability is enhanced by improving the hydrophilicity of the membrane surface,and increasing the flux of the membrane is a research focus of PVDF membrane modification technology.In this study,an amphiphilic polymer PVDF-g-PEGMA,which can significantly improve membrane hydrophilicity and pure water flux,was selected as an additive for the blend membrane.First select the ethanol solution as a non-solvent coagulation bath.The effect of the content of ethanol in the coagulation bath on the surface composition,pore size,membrane permeation,retention and anti-pollution ability of PVDF-g-PEGMA/PVDF membrane was studied.Then,anatase-type nano-TiO₂ particles were selected as additional blending additives to prepare TiO₂/PVDF-g-PEGMA/PVDF membrane.The effects of nano-TiO₂ content on membrane structure,membrane pore size,filtration performance and anti-pollution ability were studied.Finally,the oil-water mixed emulsion was tested by the prepared TiO₂/PVDF-g-PEGMA/PVDF membrane.Explore the performance and industrial potential of the modified membrane prepared in this study in oil-water separation.Through the above experiments,the main conclusions of this study are as follows:?1?The low specific gravity ethanol solution as a coagulation bath contributes to the surface transition of PVDF-g-PEGMA during membrane formation.I Iowever,when the ethanol content is too high in the coagulation bath,the PVDF-g-PEGMA enrichment rate with a hydrophilic group on the surface of the membrane is lowered.As the ethanol content in the coagulation bath increases,the hydrophilicity of the membrane surface decreases to some extent.PVDF-g-PEGMA as a blending additive tends to form PVDF crystal molecules inside the membrane to form ? crystal molecules.When ethanol is mixed into the coagulation bath,the polar ? crystal form molecules in the PVDF membrane are less as the ethanol content increases,and the non-polar ? crystal form molecules increase.By measuring the surface morphology of the membrane,it is show that the average pore size and porosity of the membrane increase with the increase of ethanol content in the coagulation bath,and the surface roughness of the membrane is also increased.Changing the ethanol content in the ethanol coagulation bath can easily change the pore size and distribution of the membrane,thereby improving the permeability of the PVDF-g-PEGMA/P VDF modified membrane.At low membrane pressure?10 psi?,the membrane water flux formed in the pure water coagulation bath is 1844.65 L/?m2 h?.And the mean pure water fluxes of the membranes formed in the coagulation baths of 10%,20%,and 30%ethanol mass fractions were 2774.61,4391.88,and 5142.35 L/?m2·h?,respectively.Although increasing the ethanol content in the coagulation bath increases the pore size of the membrane to increase the pure water flux,excessive pore size may result in poor membrane retention performance and increase irreversible contamination of the membrane such that the pure water flux recovery rate is low.The membrane sodium alginate?S A?retention rate formed by the 30%ethanol content coagulation bath was only 54.46%,and the pure water flux recovery rate after washing was only 56.85%.Considering the best performance of the membrane formed by the 10%ethanol coagulation bath,the pure water flux is 2774.61 L/?m2 h?,the BSA adsorption amount is 32.3?g/cm2,the S A rejection rate is 86.44%.And the pure water flux recovery rate was 78.81%.?2?TiO₂ particles did not segregate to the surface of TiO₂/PVDF-g-PEGMA/PVDF membrane after phase inversion process.However,the increase of TiO₂,content leads to a decrease in the enrichment of PVDF-g-PEGMA on the membrane surface.The characterization of the internal crystal form and elements of the membrane confirmed the presence of nano-TiO₂ in the film,indicating that the TiO₂ particles stayed in the PVDF network support layer after membrane formation.The results of the surface morphology of the membrane showed that the content of TiO₂ had little effect on the pore structure and surface morphology of the membrane.PVDF-g-PEGMA was still the decisive factor for membrane pores and surface morphology.As the TiO₂ content increases,the hydrophilic properties of the membrane surface will decrease to some extent.The content of TiO₂ has no obvious effect on the pure water flux of the membrane.At a transmembrane pressure of 10 psi?0.07 Mpa?,the membrane fluxes from TiO₂ dosages from 0%to 3.5%were 1727.04,1689.20,1771.97 and 1819.61 L/?m2·h?,respectively.However,because the TiO₂ particles are dispersed in the polymer skeleton,it can play a supporting role,which can increase the pressure resistance of the membrane and delay the decrease of the pure water flux caused by the compaction of the membrane.At the same time,according to the test results of flux recovery after sodium alginate?SA?filtration,it can be seen that the addition of an appropriate amount of TiO₂ can significantly improve the recovery rate of pure water flux after membrane cleaning,and reduce the irreversible pollution of the membrane.Ti0 2/PVDF-g-PEGMA/PVDF membranes produce oxidative hydroxyl radicals under UV light,giving the membrane the potential to self-clean membrane surface contamination.When the dosage of nano-TiO₂ was 2.5%,the adsorption amount of bovine serum albumin?BSA?was 40.7?g/cm2,and the pure water flux of TiO₂/PVDF-g-PEGMA/PVDF membrane was 1771.97 L/?m2 h?,the sodium alginate?SA?rejection rate was 92.06%,and the pure water flux recovery rate after washing was 89.58%,showing excellent overall performance.?3?Through the filtration experiment of the oil-water mixed emulsion,it can be concluded that:Under the condition of ultraviolet light irradiation,the TiO₂/PVDF-g-PEGMA/PVDF membrane can maintain a high oil-water separation flux under the condition that the retention capacity remains basically unchanged.And compared with the absence of ultraviolet light,the recovery rate of pure water flux after membrane cleaning under ultraviolet light irradiation is significantly improved.In the modified membrane with different nano-TiO₂ content,when the specific gravity of TiO₂ reaches 2.5%.Under ultraviolet light irradiation the average pure water flux reaches 1732.8 1 L/?m2·h?,and the attenuation rate is 43.64%after the separation of oil and water for 1 h,the rejection rate is 86.27%and has as high as 80.38%of pure water flux recovery rate after cleaning,the overall performance is the best.It showing a good industrial application potential of oil-water separation.