Adsorption of metal cations by water-soluble N-alkylated disaccharide chitosan derivatives

In the present study, the metal-adsorption ability of various water-soluble chitosan derivatives prepared by N-alkylation of chitosan with maltose, cellobiose, or lactose and with various degrees of substitution (DS) was first determined and compared with the native chitosan. The effects of the pH and reaction time on the metal-adsorption ability and the selective metal adsorption of the disaccharide chitosan derivatives with a DS of 30-40% were further examined. Results revealed that the metal-adsorption ability of chitosan was enhanced after N-alkylation with the disaccharides tested and with certain DS values. All the N-alkylated disaccharide derivatives and the native chitosan exhibited the highest adsorption for Pb2+ and the lowest adsorption ability for Mg2+ among all the metal ions that were tested. The DS with disaccharide affects the metal-adsorption ability of the tested chitosan derivatives. In general, the adsorption ability of these chitosan derivatives for Cu2+, Pb2+, Fe2+, and Mg2+ decreased whereas the adsorption ability for Ca2+, Ni2+, Zn2+, and Cd2+ increased upon in creasing the DS. Further study with disaccharide chitosan derivatives with 30-40% DS also revealed that the adsorption of Zn2+ and Pb2+ by these chitosan derivatives was a fairly rapid process. The Zn2+ and Pb2+ adsorption ability of these derivatives generally increased as the pH increased. These disaccharide chitosan derivatives also displayed the best selective adsorption for Pb2+ in mixed solutions with Zn2+, Ni2+, and Cd2+. (c) 2005 Wiley Periodicals, Inc.