Abstract
The use of magnetic nanoparticles (MNPs) as adsorbent/separation agents for the removal of heavy metal-based compounds from aqueous environments has received much attention in the last few years. However, in most cases, the designed particles present large dimensions (at least several tens of nm) in order to provide them with high magnetic energy and the capability to be collected with a magnet, thus decreasing their surface-to-volume ratio and displaying a non-superparamagnetic behavior which leads to their irreversible aggregation and avoid their use in repetitive adsorption cycles.
Here, we report the preparation of 8.50 nm iron oxide-based MNPs with high specific surface areas where large adsorption of heavy metals can efficiently take place. Through an exhaustive control over the synthetic procedures, we obtained MNPs with high magnetizations despite their reduced dimensions (ca. 80 emu.g(-1)) and superparamagnetic behavior, enabling their efficient separation with a single magnet whilst avoiding irreversible aggregation. After incubation of MNPs in heavy metal aqueous solutions for 24 h, extremely high adsorption values up to ca. 400 mg of arsenic oxide and 500 mg of mercury oxide per gram of MNPs were measured. The pH of the pollutant solutions has a great influence over the biore-mediation capability of the MNPs, being the largest adsorption extents at pH 10.0 and 5.5 for arsenic and mercury oxides, respectively. Moreover, the efficiency of desorption protocols and the subsequent reusability of the MNPs for at least four bioremediation cycles was also evaluated. The adsorption data were modeled following a Langmuir-type behavior, while kinetics experiments demonstrated that pollutant ions are adsorbed onto MNPs surfaces through chemisorption processes. (C) 2021 Elsevier B.V. All rights reserved.