Highly stable and covalently functionalized magnetic nanoparticles by polyethyleneimine for Cr(VI) adsorption in aqueous solution

In the present work, highly stable magnetic nanoparticles covalently functionalized by polyethyleneimine (PEI), denoted as PEI-MNPs, were prepared based on the glutaraldehyde crosslinking reaction between the aldehyde moiety in glutaraldehyde and the amine groups in both PEI and Fe3O4 magnetic nanoparticles (MNPs), and showed strong adsorption affinity to Cr(VI). The successful modification by PEI was confirmed by a series of measurements, such as TEM, XRD, FT-IR, TGA, et al. The time-dependent adsorption experiments indicated that the adsorption of Cr(VI) onto PEI-MNPs finished within 10 min and the adsorption process could be described by the pseudo-second-order kinetics model. The studies on the adsorption of Cr(VI) revealed that the Langmuir adsorption isotherm with the adsorption capacity of 175.76 mg g (1) at 318 K fit the adsorption data. The calculated thermodynamic parameters (Delta G, Delta H, and Delta S) indicated that adsorption of Cr(VI) on PEI-MNPs was spontaneous and exothermic. Furthermore, the stability testing demonstrated that the used adsorbents could be regenerated effectively with 0.5 mol L-1 NaOH solution and no significant loss of adsorption capacity were observed after a run of 20 adsorption-desorption cycles, showing their high stability in extremely acidic and alkaline solution. Most importantly, the obtained PEI-MNPs composite can effectively and selectively absorb Cr(VI) from complex industrial wastewater, indicating that PEI-MNPs could be used as a promising adsorbent for removal of Cr(VI) from real wastewater with high efficiency.