Superparamagnetic Spinel-Ferrite Nano-Adsorbents Adapted for Hg, Dy, Tb Removal/Recycling: Synthesis, Characterization, and Assessment of Toxicity.

In the present work, superparamagnetic adsorbents based on 3-aminopropyltrimethoxy silane (APTMS)-coated maghemite (γFeO@SiO-NH) and cobalt ferrite (CoFeO@SiO-NH) nanoparticles were prepared and characterized using transmission-electron microscopy (TEM/HRTEM/EDXS), Fourier-transform infrared spectroscopy (FTIR), specific surface-area measurements (BET), zeta potential (ζ) measurements, thermogravimetric analysis (TGA), and magnetometry (VSM). The adsorption of Dy, Tb, and Hg ions onto adsorbent surfaces in model salt solutions was tested. The adsorption was evaluated in terms of adsorption efficiency (%), adsorption capacity (mg/g), and desorption efficiency (%) based on the results of inductively coupled plasma optical emission spectrometry (ICP-OES). Both adsorbents, γFeO@SiO-NH and CoFeO@SiO-NH, showed high adsorption efficiency toward Dy, Tb, and Hg ions, ranging from 83% to 98%, while the adsorption capacity reached the following values of Dy, Tb, and Hg, in descending order: Tb (4.7 mg/g) > Dy (4.0 mg/g) > Hg (2.1 mg/g) for γFeO@SiO-NH; and Tb (6.2 mg/g) > Dy (4.7 mg/g) > Hg (1.2 mg/g) for CoFeO@SiO-NH. The results of the desorption with 100% of the desorbed Dy, Tb, and Hg ions in an acidic medium indicated the reusability of both adsorbents. A cytotoxicity assessment of the adsorbents on human-skeletal-muscle derived cells (SKMDCs), human fibroblasts, murine macrophage cells (RAW264.7), and human-umbilical-vein endothelial cells (HUVECs) was conducted. The survival, mortality, and hatching percentages of zebrafish embryos were monitored. All the nanoparticles showed no toxicity in the zebrafish embryos until 96 hpf, even at a high concentration of 500 mg/L.