Research On The Structure And Application Performance Of PVDF Membrane Based On Coagulation Bath Double Diffusio

In order to enhance the hydrophilicity of polyvinylidene fluoride(PVDF)membrane and enhance the anti-pollution performance of the membrane,as well as to solve the problem that conventional ultrafiltration membranes are difficult to remove small-molecule organic contaminants.In this study,a polymer/non-solvent co-induced phase separation method was proposed to successfully prepare hydrophilic modified PVDF ultrafiltration membranes,and the effect of coagulation bath temperature on the membrane structure and performance was investigated.The hydroxypropyl-β-cyclodextrin(HP-β-CD)was also modified onto the modified PVDF membrane by chemical grafting to functionalize it,and its adsorption performance was investigated.Firstly,we investigated the effects of high polymer concentration coagulation bath temperature on the phase separation process,membrane structures and performances of modified PVDF ultrafiltration membrane.We found that as the temperature of the of the coagulation bath increased,the phase separation process changed from delayed to instantaneous,the membrane surface changed from porous to dense,and the macroporous structure and sponge-like pore structure appeared on the cross-section.At the same time,the pure water flux of the modified membenae decreased from 229.3L/(m~2·h)to 2.08 L/(m~2·h),the protein rejection rate increased from 83.87%to 100%,and the surface water contact angle increased from 63°to 90°.And found by protein filtration experiments that increasing the coagulation bath temperature is not conducive to improving the fouling resistance of the hydrophilicity modified PVDF ultrafiltration membran.Then,the hydrophilic modified PVDF ultrafiltration membrane was used as the base membrane and grafted with HP-β-CD to make it adsorbent,and the effect of grafting conditions on the membrane was investigated.The results showed that when the concentration of sodium hydroxide in the system was incerased,the membrane morphology structure was damaged,the pure water flux increased from 104.14 L/(m~2·h)to 210.19 L/(m~2·h),and the protein rejection rate would decrease from 91.2%to 83%.Meanwhlie,with the increase of Na OH concentration,reaction time and temperature,the mechanical properties of the grafted HP-β-CD membrane all decreased to some extent compared with the original membrane.In addition,an increase in the amount of cross-linker epichlorohydrin(EPI)caused the membrane to become dense,resulting in a decrease in the pure water flux decreased from 104.14 L/(m~2·h)to 28.66 L/(m~2·h)and an increase in the protein rejection rate from 86.15%to 92.83%,as well as an increase in the membrane strength and a decrease in elongation at break.The optimum grafting reaction conditions were found by phenolphthalein adsorption experiments,with a Na OH concentration of 0.05 mol/L,a reaction temperature of 50°C,a reaction time of8 h,and EPI amount of 2%of the solution volume ratio.In order to further investigate the ability of PVDF ultrafiltration membrane with adsorption function to remove different structured small molecule organic pollutants from wastewater.We used bisphenol A and 2-naphthol as target adsorption molecules and found that the adsorption of bisphenol A and 2-naphthol was in accordance with the Langmuir isothermal adsorption model and the pseudo-secondary kinetic equation.In the separation experiments,the removal rates of bisphenol A and 2-naphthol by PVDF ultrafiltration membrane with adsorption function were 53.81%and 64.5%,respectively,while its retention rate of protein was 90%.In addition,it was found that after 10 adsorption-desorption cycles,the adsorption regeneration rate of the membrane was 44%for bisphenol A adsorption and 61%for 2-naphthol adsorption.