Enhanced and selective adsorption of copper(II) ions on surface carboxymethylated chitosan hydrogel beads

In this paper, chitosan hydrogel beads (CS) have been modified by etherization reaction with the etherification agent of chloroacetic acid. The surface carboxymethylated chitosan beads (CMC) provide not only enhanced but also improved selective adsorption for copper(II) (Cu(II)) ions from lead (Pb(II)) and magnesium (Mg(II)) ions in aqueous solutions. The fundamental Cu(II) ions adsorption behaviors of CMC, including the effect of pH, temperature, adsorption equilibrium, and kinetics, were investigated. The adsorption isotherms of CMC closely follow Langmuir model and the adsorption kinetics are well described by the pseudo-second order equation, which indicate that the adsorption behaviors are a monolayer chemical adsorption. X-ray photoelectron spectroscopy (XPS) investigations further reveal that the carboxyl groups are facile to form bidentate carboxylates with metal ions. Furthermore, the adsorbent could be easily regenerated at lower pH and reused almost without any loss of adsorption capacity. Moreover, the Cu(II) ions loaded CMC are stable enough at higher pHs, and suitable to be applied as a new adsorbent for phosphate adsorption, of which the maximal uptakes is around 58.0 mgP g−1 achieved at pH about 5.0.

► Preparation of surface carboxymethylated chitosan hydrogel beads (CMC).
► CMC showed enhanced and selective adsorption of Cu(II) ions.
► The fundamental adsorption behaviors of CMC have been studied.
► The Cu(II)-loaded adsorbents were used for secondary adsorption for the removal of phosphate.