Removal of metal ions from water using nanohydrogel tragacanth gum-g-polyamidoxime: Isotherm and kinetic study

A new biosorbent was prepared by grafting polyacrylonitrile onto iranian tragacanth gum (ITG), a naturally and abundantly available polysaccharide, and subsequent amidoximation in the presence of hydroxylamine hydrochloride. This nanohydrogel with amidoxime functional groups [C(NH2)NOH], named polyamidoxime-g-tragacanth (ITG-g-PAO), was characterized and used for the removal of metal ions from aqueous solution. The effect of pH, agitation time, concentration of adsorbate and amount of adsorbent on the extent of adsorption was investigated. The experimental data were analyzed by four isotherms and kinetics equations, and the results were fitted well with the Temkin isotherm and pseudo-second-order model. The maximum adsorption capacities (Qm) of ITG-g-PAO as obtained from Langmuir adsorption isotherm were found to be 100.0, 76.92, 71.42 and 66.67 (mg g−1) for the adsorption of metal ions in order of Co(II) > Zn(II) > Cr(III) > Cd(II). The experimental results demonstrate that the above selective order of adsorption capacity is due to formation of stable chelating ring between the bidentate amidoxime ligand and metal ion.