Ca(II) imprinted chitosan microspheres: An effective and green adsorbent for the removal of Cu(II), Cd(II) and Pb(II) from aqueous solutions

• Ca(II)–CS was first synthesized as an effective and green absorbent for heavy metal removal.
• Ca(II) ions were valid for tuning the crosslinking degree of chitosan by a weak NH2–Ca(II) complexation.
• Ca(II)–CS presented a fast adsorption kinetics and universal practicability for Pb(II), Cu(II), and Cd(II).
• Ca(II)–CS microspheres have uniform size and morphology fit for the use in packed column.

Ca(II)–CS microspheres with uniform size and morphology were first synthesized as a green and effective absorbent for the treatment of hazardous wastewater containing heavy metal ions. The adsorption capacities for Pb(II), Cd(II) and Cu(II) reached 47.1 mg, 49.9 mg and 41.5 mg per gram of Ca(II)–CS microsphere within 30 min, respectively. The pseudo-first-order equation and Langmuir isotherm model are fit to describe the adsorption kinetics and equilibrium separately. The orders of ΔG°, ΔH° and ΔS° for three metal ions adsorption were in accordance with the theoretical analysis. TGA, FTIR and XPS measurements verified that Ca(II) ions played a role in tuning crosslinking degree by a weak complexation of NH2–Ca(II), and only amino groups were well-recognized as active sites for metal ions adsorption. An insight can be gained into the use of Ca(II)–CS microspheres for various heavy metal ions treatment in packed column.