Anionic polypeptide poly(γ-glutamic acid)-functionalized magnetic Fe3O4-GO-(o-MWCNTs) hybrid nanocomposite for high-efficiency removal of Cd(II), Cu(II) and Ni(II) heavy metal ions

Abstract

A novel hybrid adsorbent, anionic polypeptide poly(γ-glutamic acid)—(γ-PGA) functionalized magnetic Fe3O4-GO-(o-MWCNTs) hybrid nanocomposite was successfully prepared via a simple one-pot reaction. The as-prepared γ-PGA-Fe3O4-GO-(o-MWCNTs) composites were characterized via SEM, TEM, FTIR, XRD, TGA, AFM, zeta potential analysis and magnetic properties analysis. The results indicate that the addition of o-MWCNTs solves the serious aggregation problem of GO and thus makes the GO exposed more grafted sites bonded to large amount of γ-PGA molecule chains. The prepared γ-PGA-Fe3O4-GO-(o-MWCNTs) composites not only have a higher specific surface area to offer abundant surface adsorption sites, but also can be separated more easily from solution systems. Furthermore, the adsorption tests of the γ-PGA-Fe3O4-GO-(o-MWCNTs) were analyzed in Cd(II), Cu(II) and Ni(II) solutions at various pH values, contact time, and initial concentrations of ions. This work indicates that the hybrid adsorbent can be the suitable absorbent materials for various types of heavy metal ions pollution removal and exhibit higher adsorbing capacities in the pH range of 2–10. Its maximum removal capacity calculated by Langmuir model under the optimal conditions toward Cd(II), Cu(II) and Ni(II) is 625.00, 574.71 and 384.62 mg/g, respectively. The adsorption process was well described by the pseudo-second-order kinetics model and the Langmuir isotherm model, respectively. The adsorption mechanism may involve characteristic coordination bonding and electrostatic attraction between γ-PGA-Fe3O4-GO-(o-MWCNTs) and metal ions. Additionally, anionic polypeptide γ-PGA-Fe3O4-GO-(o-MWCNTs) composite can be easily regenerated and recycled at least for three adsorption–desorption recycles. The unique characteristics render the composite highly promising as an advanced adsorbent material for the removal of heavy metal ions.