Preparation and application of stability enhanced magnetic nanoparticles for rapid removal of Cr(VI)

A stable magnetic nanoparticle with a shell core structure of γ-Fe2O3@Fe3O4 was developed. Water soluble Polyethylenimine (PEI) was grafted to the nanoparticle to prepare a positive charged adsorbent, which was characterized by XRD, FTIR and SEM. The adsorbent was able to effectively remove anionic Cr(VI) in the pH range of 2–3 due to the large amount of protonated imine groups on its surface, and could be magnetically separated from liquid quickly. Adsorption equilibrium was reached within 30 min and independent of initial Cr(VI) concentration. The Cr(VI) maximum sorption capacity at a temperature range of 35–15 °C was obtained using the Langmuir adsorption isotherm. The calculated thermodynamic parameters (ΔG, ΔH, and ΔS) indicated that adsorption of Cr(VI) was spontaneous and exothermic in nature. Competition from coexisting ions (K+, Na+, Ca2+, Cu2+, Cl−, and NO3−) was found insignificant. The adsorbent had satisfying acid–alkali stability and could be regenerated by 0.02 mol L−1 NaOH solution. The results suggested the potential application of the PEI-modified magnetic nanoparticles in selective removal of Cr(VI) from wastewater.

► Stability enhanced magnetic nanoparticles with a shell core structure of γ-Fe2O3@Fe3O4 were prepared.
► The nanoparticles were modified with PEI to develop a surface positive-charged adsorbent.
► Adsorption of anionic Cr(VI) was rapid and selective, well fitted to Langmuir isotherm and pseudo-second-order kinetic model.
► Thermodynamic evaluation revealed that the adsorption process was spontaneous and exothermic in nature.