Heavy metals [chromium (VI) and lead (II)] removal from water using mesoporous magnetite (Fe3O4) nanospheres

• Hollow Fe3O4 nanospheres were made by one-pot, template-free solvothermal method.
• Magnetite nanospheres were employed to remove heavy metal ions for the first time.
• Magnetic nanosphere Langmuir adsorption capacities were 19 (Pb2+) and 9 mg/g (Cr6+).
• Pb2+ and Cr6+ adsorption mechanisms were intensively proposed.
• Magnetic separation allows process flexibility during adsorbent recovery and reuse.

Magnetite nanospheres with hollow interiors were synthesized using a simple, one-pot, and template free solvothermal method with ferric chloride as the iron precursor. The composition, surface properties and morphology were studied using X-ray powder diffraction (XRD), energy dispersive X-ray fluorescence (EDXRF), Fourier transform infrared spectroscopy (FTIR), surface area analysis, point of zero charge (pHpzc), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and magnetic moment determination. These mesoporous nanospheres have a SBET = 11.3 m2/g and a high saturation magnetization of 77.5 emu/g. These magnetite nanospheres successfully remediated Cr6+ and Pb2+ from water. The optimum pHs for Cr6+ and Pb2+ adsorption were 4.0 and 5.0, respectively. Adsorption was carried out at 25, 35 and 45 °C. The sorption data were fitted using Freundlich, Langmuir, Redlich–Peterson, Sips, Koble–Corrigan, Radke and Prausnitz and Toth adsorption models. The pseudo-second order model better fitted the kinetics data. The Langmuir adsorption capacities of magnetic nanospheres were ∼9 and ∼19 mg/g for Cr6+ and Pb2+, respectively. Magnetic collection of these magnetite nanospheres can be used to isolate and regenerate the used adsorbent.

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