Synthesis of magnetite derivatives nanoparticles and their application for the removal of chromium (VI) from aqueous solutions

Nowadays there is a continuously increasing worldwide concern for the development of efficient wastewaters treatment technologies. Among the heavy metal ions, chromium holds a distinct position due to its high toxic nature to biological systems. This study aims to assess magnetite derivatives nanoparticles for the removal of Cr(VI) species. Crystalline magnetite-rich (Magn) and pure maghemite (Magh) nanoparticles were produced by the polyol method and by subsequent heat treatment of Magn, respectively. The XRD analysis confirmed the formation of nanosized single phase cubic spinels with a cell parameter of 8.3710(2) angstrom for Magn and 8.3401(2) angstrom for Magh, consistent with those of a magnetite-rich ferrite and maghemite, respectively. TEM analysis showed that the two nanoferrites possessed comparable mean particle size of 15 nm. Magn and Magh showed superparamagnetic behavior at room temperature and reasonable saturation magnetizations at 300 K of 69 and 67 emu.g(-1), respectively. The Curie temperature of both nanoferrites exceeded 350 degrees C allowing the materials to work in severe conditions. Room temperature, batch adsorption experiments of Cr(VI) onto maghemite nanoparticles were carried out at pH 2.0. Adsorption efficiency increased rapidly was the increase of the nanoparticles dose. For a 20 mg.L-1 Cr(VI) solution a 100% removal was found with similar to 3 g.L-1 dose. Additionally, for a given dose (4.0 g.L-1) the adsorption rate measured as a function of time for different Cr(VI) concentrations was very rapid; similar to 90% of removable Cr(VI) species was achieved within 10 min. The high rate of Cr(VI) uptake takes advantages of the high active surface chemistry of the nanoparticles. The adsorption of Cr(VI) onto Magh nanoparticles followed a pseudo-second order kinetics indicating a chemisorption process. Further, the Langmuir isotherm model was found to best describe the equilibrium data with a maximum adsorption capacity of 12.5 mg.g(-1) for an adsorbent dosage of 4.0 g.L-1. (C) 2017 Elsevier Inc. All rights reserved.