Green synthesis of magnetic EDTA- And/or DTPA-cross-linked chitosan adsorbents for highly efficient removal of metals

The present paper describes a green and economic approach to explore EDTA/DTPA-functionalized magnetic chitosan as adsorbents for the removal of aqueous metal ions, such as Cd(II), Pb(II), Co(II), and Ni(II). EDTA and DTPA play roles not only as cross-linkers but also as functional groups in chelating metal ions. The morphology, structure, and property of the magnetic adsorbents were characterized by SEM, TEM, XRD, EDS, FT-IR, TGA, and VSM techniques. Their adsorption properties for the removal of metal ions by varying experimental conditions were also investigated. The kinetic results revealed that the transportation of adsorbates from the bulk phase to the exterior surface of adsorbents was the rate-controlling step. The obtained maximum adsorption capacities of magnetic adsorbents for the metal ions ranged from 0.878 to 1.561 mmol g^-1. Bi-Langmuir and Sips isotherm models fitting well to the experimental data revealed the surface heterogeneity of the adsorbents. More significantly, the resulting EDTA-/DTPA-cross-linked magnetic chitosan adsorbents had selectivity to Cu, Pb, Zn, Fe, and Ni from a practical industrial effluent. Furthermore, their good reusability and convenient magnetic separation makes them viable alternatives for real wastewater treatment.