Synthesis of ethylenediamine modified chitosan and evaluation for removal of divalent metal ions

Selective modification of chitosan has been achieved by incorporating ethylene-1,2-diamine molecule in a regioselective manner using N-phthaloylchitosan and chloro-6-deoxy N-phthaloylchitosan as precursors. The present modification results in additional nitrogen centres which function as potential binding sites during adsorption of metal ions. The derivative ethylene-1,2-diamine-6-deoxy-chitosan and its pthaloylated precursor have been evaluated for divalent metal ion removal. The former is found to have higher capacity for adsorption due to the presence of additional NH2 group. The samples exhibited highest affinity for Cu and least for Zn. About 80% of the adsorbed metal ions could be stripped in a solution of pH 1.2. The interaction between acidic metal centres and basic nitrogen centres on surface of the adsorbent appears to govern adsorption. Intrachain and interchain co-ordinate bonding involving NH and NH2 groups is proposed to be the mechanism of formation of metal–adsorbent complex. The adsorption process is described by Langmuir model.