Novel magnetically separable anhydride-functionalized Fe(3)O(4)@SiO(2)@PEI-NTDA nanoparticles as effective adsorbents: synthesis, stability and recyclable adsorption performance for heavy metal ions

In this paper, a novel adsorbent, Fe(3)O(4)@SiO(2)@PEI-NTDA, was first prepared by the immobilization of an amine and anhydride onto magnetic Fe(3)O(4)@SiO(2) nanoparticles with polyethylenimine (PEI) and 1,4,5,8-naphthalenetetracarboxylic-dianhydride (NTDA) for the removal of heavy metal ions from aqueous solutions. The structure of Fe(3)O(4)@SiO(2)@PEI-NTDA was systematically investigated; the results confirmed that amine and anhydride groups were successfully covalently grafted onto the surface of Fe(3)O(4)@SiO(2), which showed a homogenous core–shell structure with three layers of about 300 nm diameter (Fe(3)O(4) core: 200 nm, nSiO(2) layer: 20 nm, and PEI-NTDA layer: 20 nm). The adsorption performance of Fe(3)O(4)@SiO(2)@PEI-NTDA NPs was evaluated for single Pb(2+) and coexisting Cd(2+), Ni(2+), Cu(2+), and Zn(2+) ions in an aqueous solution in a batch system. The amine and anhydride groups may have a synergistic effect on Pb(2+) removal through electrostatic interactions and chelation; Fe(3)O(4)@SiO(2)@PEI-NTDA NPs exhibited preferable removal of Pb(2+) with maximum adsorption capacity of 285.3 mg g(−1) for Pb(2+) at a solution pH of 6.0, adsorbent dosage of 0.5 g L(−1), initial Pb(2+) concentration of 200 mg L(−1) and contact time of 3 h. The adsorption mechanism conformed well to the Langmuir isotherm model, and the adsorption kinetic data were found to fit the pseudo-second order model. Fe(3)O(4)@SiO(2)@PEI-NTDA NPs could be recovered easily from their dispersion by an external magnetic field and demonstrated good recyclability and reusability for at least 6 cycles with a high adsorption capacity above 204.5 mg g(−1). The magnetic adsorbents showed high stability with a weight loss below 0.65% in the acid leaching treatment by 2 M HCl solution for 144 h. This study indicates that Fe(3)O(4)@SiO(2)@PEI-NTDA NPs are new promising adsorbents for the effective removal of Pb(2+) in wastewater treatment.