Use of layer-by-layer assembled ultrathin membranes of dicopper-[18]azacrown-N6 complex and polyvinylsulfate for water desalination under nanofiltration conditions

A first study is presented on the use of ultrathin multilayered membranes of the dicopper complex of 18-azacrown-N6 (hexacyclen, 1,4,7,10,13,16-hexaazaoctadecane, aza6) and polyvinylsulfate (PVS) for desalination of aqueous electrolyte solutions under nanofiltration conditions. The membranes were prepared upon alternating electrostatic lbl-assembly of aza6 and PVS on porous polymer supports and subsequent treatment with copper acetate. The pressure-driven transport of a mixed aqueous solution of sodium chloride and sodium sulphate in 1:1 molar ratio (conc.: 10 mM each) was investigated. Total flux and anion content in the permeate were determined, the latter by using HPLC. The total flux of a membrane consisting of 60 layer pairs aza6/PVS was 0.85 L m−2 h−1, the rejection of chloride and sulphate ions were 45.7 and 91.9% (operating pressure: 25 bar). Effects of a variation of the number of deposited layers and the operating pressure on total flux and salt rejection were also investigated.