Preparation Of Monovalent Selective Anion Exchange Membrane By Electrochemical Deposition Modification Method

In recent years,with the ion exchange membrane maturation applied to the electrodialysis separation process,the development of ion exchange membrane with high monovalent selective separation performance research is focused by people in today's world.However,after the separation of the concentrated liquid,it is generally difficult to handle and direct to use,which requires the resulting concentrated solution can be separated from the different ions.The monovalent selective ion exchange membrane material,with its unique structure and property,can separate the monovalent ions from the mixture solution with both the divalent and monovalent ions directly.Thus,it has great potential of application in practical industrial production.The commercial ion exchange membrane has been able to achieve selective separation of anions and cations,but,how to solve the current commercial ion exchange membrane with the monovalent separation and stability is the key to further improve its application.The content of this paper is based on the electro-chemical deposition modification method to realize the using of electrochemical method of a variety of ways to improve the monovalent selective anion exchange membrane and overcome the instability of the modified layer,susceptible to organic pollution characteristics and self-accumulation agglomeration which caused by the high resistance of the membrane surface.The main research contents are as follows:1.Mimicking the cell membrane: bio-inspired simultaneous functions with monovalent anion selectivity and antifouling properties of anion exchange membrane.A new bio-inspired method was applied in this study to simultaneously improve the monovalent anion selectivity and antifouling properties of anion exchange membranes(AEMs).Three-layer architecture was developed by deposition of polydopamine(PDA)and electro-deposition of N-O-sulfonic acid benzyl chitosan(NSBC).The innermost and outermost layers were PDA with different deposition time.The middle layer was prepared by NSBC.Fourier transform infrared spectroscopy and scanning electron microscopy confirmed that PDA and NSBC were successfully modified on the surfaces of AEMs.The contact angle of the membranes indicated an improved hydrophilicity of the modified membranes.A series of electrodialysis experiments in which Cl-/SO42-separation was studied,demonstrating the monovalent anion selectivity of the samples.The Cl-/SO42-permselectivity of the modified membranes can reach up to 2.20,higher than that of the commercial membrane(only 0.78)during 90 minutes in electrodialysis(ED).The increase value of the resistance of the membranes was also measured to evaluate the antifouling properties.Sodium dodecyl benzene sulfonate(SDBS)was used as the fouling material in the ED process and the membrane area resistance of modified membrane increase value of was only 0.08 ?cm2 30 minutes later.2.An anion exchange membrane modified by alternate electro-deposition layers with enhanced monovalent selectivity.A novel anion exchange membrane(AEM)is developed through poly(sodium 4-styrene sulfonate)(PSS)and hydroxypropyltrimethyl ammonium chloride chitosan(HACC)alternate electro-deposition to enhance the monovalent selectivity.Compared to the commercial original AEM,coating of the(PSS/HACC)N alternate electro-deposition multilayer on the membrane surface dramatically enhance the selectivity of anions.In addition,the permselectivity for monovalent anions of the membranes was investigated by electrodialysis experiments.For comparison,the corresponding Cl-/SO42-were chosen and the average values of permselectivity and separation efficiency of commercial AEM are 0.66 and-0.19 respectively.As result of alternate electro-deposition of PSS/HACC layers,the permselectivity raised up to 2.90 and the separation efficiency also increased up to 0.28 for nine PSS/HACC bilayers needed.Under the optimal fabricating conditions,the area resistance of membrane arrived at 4.52 ?·cm2 with nine PSS/HACC bilayers.Meanwhile,the polarization current-voltage curves and ?-potential of membranes were also tested to characterize the electrochemical behavior of the modified membrane.The high selectivities of these membranes may enable electrodialysis applications in separation of monovalent and divalent anions.3.Construct monovalent anions selectivity separation layers by electric pulse technology.Advanced filtration membranes with monovalent separation must be developed to meet rising worldwide demand.Here we report an anion exchange membrane with excellent monovalent anions selectivity and modification layers stability was fabricated by electric pulse deposition method,coating the hydroxypropyltrimethyl ammonium chloride chitosan and N-O-sulfonic acid benzyl chitosan layers assembly.