| With the increasing of environment problem and the demand of energy,people are seeking ways to use new technology to cope with the pollution in industry and develop renewable clean energy.The ion exchange membrane technology has draw much attention since 1950s.It has achieve great success and is widely used in chemical engineering,pharmaceutical industry and energy storage.As an effective method for ion separation,diffusion dialysis with ion exchange membrane is a common way for the recovery of industrial waste.Diffusion dialysis membrane is the core component,of which good chemical stability is often required for the acid working environment.Generally the diffusion dialysis membranes are dense membranes with only one kind of polymer or modified dense membranes.The thickness is high,thus resulting in hindering of ion transport in the membrane and poor ion permeability and selectivity.In order to improve the stability of diffusion dialysis membrane,researchers have also attempted to fabricate membranes consisting of multi-polymers.Membranes prepared by multicomponents are heterogeneous and facing the problem of poor compatibility between mixed polymers.Here we prepared semi-interpenetrating network poly(QVBC-DVB)/PVDF anion exchange membrane by radical polymerization reaction.The distinctive semi-interpenetrating network made the membrane semi-homogeneous,leading improved compatibility between mixed polymers,and brought dense and compact structure which are beneficial to mechanical stability and chemical stability.The prepared semi-interpenetrating network poly(QVBC-DVB)/PVDF membrane still facing the problem of thickness with the 80?m dense structure,which are common for dense diffusion dialysis membranes.Inspired by the asymmetric membranes consisting of thin dense active layer and thick porous supporting layer,we modified the poly(QVBC-DVB)/PVDF into asymmetric membrane with controllable dense middle layer and porous surface layers in both sides.To achieve this we apply electric field to poly(QVBC-DVB)/PVDF base membrane.The electric field would drive the charged semi-interpenetrating network emigrate from the membrane matrix to the surrounding solution,leaving spongy pores on the surface of the membrane.Further research found that this asymmetric morphology can be tuned by changing the time and current density of applied electric field.When the base membrane was placed in the electric field of 50mA/cm2 for 72h,the dense layer was 46.8?m,which is almost half of the thickness of base membrane.When the base membrane was placed in the electric field of 100mA/cm2 for 48h,the dense layer was 56.8?m,while further increasing the time would make the dense layer disappear,that is to say,the membrane became a porous membrane.We investigated basic properties of the asymmetric membranes and their diffusion dialysis performance.The IEC decreases with the time increase when the applied current density is 100 mA/cm2.This is in accord with the trend of dense layer thickness.After 96h the IEC decreased to 0.15 mmol/g,which was much smaller than that of the base membrane(1.16 mmol/g).48h of applied electric field would reduce the thickness of dense layer and maintain high IEC(0.0928 mmol/g)at the same time.We were surprised to find that the water uptake increased with the decrease of IEC.It can be deduced that the spongy pores helped to retain water despite the IEC decreased.Diffusion dialysis performance was carried out with HCl/FeCl2 system.The membrane with current density of 50 mA/cm2 for 48 h shows the best separation factor(s)and proton permeability(UH+),which are 198 and 12.12×10 3 m/h,respectively.Generally speaking,semi-interpenetrating network poly(QVBC-DVB)/PVDF membrane was prepared by radical polymerization reaction,and electric field was employed to reduce the thickness of dense layer.Diffusion dialysis test proved that this method could reduce the ion transfer hindrance and maintain chemical stability,thus proving new way for the improvement of diffusion dialysis performance. |
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