Selectivity　for　monovalent　ions　is　a　very　important　feature　of　ion　exchange　membranes　in　view　of　a　further　expansion　of　the　scope　of　electrodialysis　(ED).　An　efficient　one-step　chemical　process　to　graft　a　thin　polyaniline　(PANI)　layer　on　the　surface　and　pores　of　an　ultrafiltration　(UF)　membrane　is　reported.　The　existence　of　a　PANI　layer　on　such　modified　UF　membrane　was　confirmed　by　Fourier　transform　infrared　spectroscopy　and　scanning　electron　microscopy　images.　These　membranes　were　extensively　characterized　by　studying　their　properties　such　as　water　uptake,　ion-exchange　capacity,　contact　angle,　and　performance　in　diffusion　dialysis.　ED　experiments　were　conducted　by　comparing　desalting　of　sodium　chloride　and　magnesium　chloride　solutions.　During　the　desalting　procedure,　the　driving　force　has　two　contributions,　the　electrical　field　and　the　salinity-gradient.　Initially,　transport　of　ions　by　the　electrical　field　is　dominant,　while　at　the　end　of　the　experiment,　diffusion　dialysis　by　the　salinity　gradient　plays　a　larger　role　in　ion　transport.　The　presence　of　PANI　can　hinder　Mg2+　transport　from　the　concentrate　to　the　diluate　compartment　because　of　the　electrostatic　effect,　while　there　is　no　obvious　effect　on　Na+　ions.　The　ability　of　such　a　surface　modification　layer　to　improve　the　membrane　selectivity　for　Na+/Mg2+　was　confirmed　by　means　of　ED　in　a　mixed　solution.　The　flux　of　Na+　was　slightly　increased　to　13.21　x　10(-8)　mol/L/min　while　the　flux　of　Mg2+　was　reduced　to　3.32　x　10(-8)　mol/L/min,　so　that　the　permselectivity　is　almost　doubled.　The　protonation　reaction　of　the　PANI　layer　creates　positive　charges,　thus　leading　to　an　electrical　repulsion　barrier,　which　may　reduce　the　penetration　of　divalent　cations　with　respect　to　monovalent　ions.　Polyacrylonitrile-based　UF　membranes　with　different　molecular　cutoff　was　used　to　determine　the　influence　of　the　permselectivity.　Results　showed　that　the　membrane　permselectivity　of　smaller　molecular　cutoff　UF　membranes　is　higher.　It　can　be　concluded　that　this　method　is　suitable　for　preparing　membranes　based　on　UF　membranes　for　efficient　separation　of　monovalent　ions　by　electro-driven　separation　techniques.　(C)　2017　Wiley　Periodicals,　Inc.