Polyamine-co-2, 6-diaminopyridine covalently bonded on chitosan for the adsorptive removal of Hg(II) ions from aqueous solution

In the present study, 2, 6-diaminopyridine (PD) and polyamine compounds (ethylenediamine (EDA), triethylenetetramine (TETA), and tetraethylenepentamine (TEPA)) were used to modify chitosan (CS). The obtained derivatives (PD-CS, PD-EDA-CS, PD-TETA-CS, and PD-TEPA-CS) were identified and employed as adsorbents in batch experiments for the removal of Hg(II) from aqueous solutions. The results confirmed that successful modification improves the Hg(II) adsorption significantly compared to pristine CS. The adsorbed amounts of Hg(II) increased gradually and reached maxima at pH values above 4.0 for all derivatives. The Hg(II) adsorption equilibrium state was achieved within 12 h, with the process driven by a pseudo-second-order kinetic model. The Langmuir model effectively interpreted the Hg(II) adsorption isotherms; the maximum adsorption capacities for Hg(II) ions at 295 K were 172.7, 303.6, 276.0, and 230.6 mg/g for PD-CS, PD-EDA-CS, PD-TETA-CS, and PD-TEPA-CS, respectively. High temperature and low ionic strength favored Hg(II) adsorption. The Hg(II)-loaded CS derivative was easily regenerated and showed acceptable reusability. The further FT-IR and XPS analyses indicate that the Hg(II) adsorption is governed by a process combining electrostatic attraction and a coordination reaction. The CS derivatives produced from polyamine-co-2, 6-diaminopyridine covalently bonded onto CS are promising adsorbents for the adsorptive removal of Hg(II) from an aqueous solution.