Studies on the effects of copper salts on the separation performance of chitosan membranes

The effects of copper salts on the pervaporation performance of chitosan membranes for water/ethanol mixtures were studied. The results show that the selectivity to water can be improved by addition of Cu2+ in the feed, and that CuSO4, was more effective than CuCl2,. The reason for the marked increase in selectivity and the difference in performance between the copper salts is explained as follows. With CuSO4, the multivalent metal ion forms a complex with four -NH2, ligands of the chitosan molecules and the new conformation is simultaneously immobilized by the ionic crosslinking with SO42. This is different from the Cu2+ of CuCl2, which mainly coordinates with -OH in the C-6 position of chitosan, and Cl- cannot crosslink the complexes. Therefore, chitosan membranes have a stronger absorption capability for the Cu2+ of CuSO4, than for Cu2+ from CuCl2. In addition, ion crosslinking formed by CuSO4 more strongly decreases the permeation of ethanol. Studies of the effects of acid on pervaporation performance of the Cu2+-treated chitosan membrane show that separation properties of the membrane change with addition of acid to the feed. This is attributed to Cu2+ being eluted from the chitosan membrane followed by the reaction of acid molecules with the -NH, functional groups of the chitosan membrane. (C) 2000 Society of Chemical Industry.