Efficient removal of lead ions from water by magnetic nanosorbents based on manganese ferrite nanoparticles capped with thin layers of modified biopolymers

[Display omitted] •Nanosorbents with high magnetization were synthesized for Pb (II) removal.•Nanosorbents were capped with thin layers of modified biopolymers.•Thin layers of biopolymers were sufficient to improve Pb (II) removal.•Cheap raw materials were utilized for nanoparticle functionalization.•Nanosorbents can be recovered magnetically for reuse in Pb (II) removal. In this study we report findings on the elaboration of magnetic nanosorbents based on manganese ferrite nanoparticles (MNPs) capped with carboxymethylated biopolymers (starch or cellulose) for water remediation purposes. The functionalization was optimized through the analysis of pH-dependent speciation profiles of MNPs/biopolymers, and samples were characterized using X ray powder diffraction, atomic force microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, nitrogen adsorption–desorption surface analysis and magnetization measurements. Nanosorbents have all been shown to remove Pb (II) efficiently from aqueous solution (∼100%, after 30 min of contact) in spite of the presence of very tiny layers of biopolymers (the maximal amount of organic layer adsorbed on the MNP surface was only about 4.0% in mass and biopolymer coating thickness was estimated < 1 nm). This low biopolymer content was sufficient to increase the affinity of nanosorbents for Pb (II), preserving high magnetization of material (∼65 emu/g). Equilibrium adsorption isotherms for Pb (II) adsorption on biopolymer-modified MNPs indicated that more heterogeneous surfaces were formed after capping MNPs with biopolymers, corroborating the hypothesis that upon surface functionalization, affinity for Pb (II) adsorption by the magnetic adsorbents was enhanced. Adsorption was more effective at pH = 5.5, and the contact time required to reach equilibrium was relatively short (∼30 min), following a pseudo-second-order model, with adsorption capacities of (34 to 46 mg g−1), calculated from Sips model. Regeneration studies revealed that the nanosorbents can be recovered for reuse, indicating their use as a powerful tool for Pb (II) removal from contaminated water.