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.
Keywords: Competitive adsorption; Desorption; Ethylene-1,2-diamine-6-deoxychitosan; Langmuir adsorption; Metal ion removal.
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