Simple synthesis and chelation capacity of N-(2-sulfoethyl)chitosan, a taurine derivative

This study presents a simple and effective synthesis method of N-(2-sulfoethyl)chitosan (NSE-chitosan) via a reaction between sodium 2-bromoethanesulfonate and chitosan that allows polymer transformation without using additional reagents and organic solvents. The chemical structure of the obtained NSE-chitosan was characterized by FT-IR and 1H NMR spectroscopies. Thermogravimetric study of NSE-chitosan coupled with FT-IR analysis has shown stability of the polymer up to 200 °C, which almost does not change with the increase of degree of substitution (DS). The sorption of transition and alkaline earth metal ions from multicomponent solutions on NSE-chitosan was investigated. The synthesized sorbents showed the selective recovery of silver(I) and copper(II) ions from ammonium acetate buffer solution. The increase of DS enhanced the selectivity to silver(I) ions sorption in comparison with copper(II) ions. Selectivity coefficients KAg/Cu increase from 1.3 to 10.9 with DS increasing up to 0.7 (ammonium acetate buffer solution, pH 6.5). Sorption isotherms of transition metal ions on NSE-chitosan with DS = 0.5 have been fitted using Langmuir, Freundlich, and Redlich-Peterson models. The maximum sorption capacities of sorbent in ammonium acetate buffer solution at pH 6.0 were 1.72 mmol/g for Cu(II), 1.23 mmol/g for Ag(I) and below 0.5 mmol/g for Co(II), Zn(II), Cd(II), Pb(II), Mn(II) and Ni(II) ions.