Mechanochemical preparation of ternary polyethyleneimine modified magnetic illite/smectite nanocomposite for removal of Cr(VI) in aqueous solution

A ternary nanocomposite integrating polyethyleneimine (PEI), magnetite (Fe3O4) nanoparticles, and illite/ smectite clay nanoflakes (denoted as PEI-MI/S) was prepared via a mechanochemical route in a high-energy density stirred bead mill. The ternary PEI-MI/S nanocomposite was determined by X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetry, scanning electron microscopy, transmission electron microscopy, vibrating sample magnetometry and X-ray photoelectron spectroscopy, respectively. The results show that ternary PEI-MI/S nanocomposite can be prepared in the presence of intense grinding, which can graft a more amount of PEI rather than that prepared in the absence of grinding. The compressive and shear stresses in intense grinding can disperse Fe3O4 nanoparticles and exfoliate/destruct I/S clay nanoflakes. Also, the mechanochemical effect facilitates the hydrogen bond and electrostatic interaction between PEI and magnetic I/S, and the crosslink reaction between PEI and glutaraldehyde in grinding, resulting in a more grafting amount of PEI. Ternary PEI-MI/S nanocomposite was applied for the removal of hexavalent chromium (Cr(VI)) anions in aqueous solution. The effect of parameters (i.e., pH value, adsorption time, temperature, and initial concentration of Cr(VI) anions) on the adsorption performance was investigated. It is indicated that the adsorption of Cr(VI) anions onto PEI-MI/S nanocomposite be related to the adsorption/reduction process. Ternary magnetic PEI-MI/S nanocomposite with a saturated magnetization (Ms) of 14.7 emu/g facilitates the magnetic separation and reusability. The regenerated ternary PEI-MI/S nanocomposite can maintain 71.43% of initial activity for adsorption of Cr(VI) anions after 6 cycles.