Preparation of ternary amino-functionalized magnetic nano-sized illite-smectite clay for adsorption of Pb(II) ions in aqueous solution

Ternary amino-functionalized magnetic illite-smectite (AMNI/S) nanocomposites were prepared via integrating two-dimensional illite-smectite nanoflakes (NI/S), magnetite nanoparticles (Fe₃O₄), and 3-aminopropyltriethoxysilane (APTES). The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and vibrating sample magnetometry (VSM). The results show that Fe₃O₄ nanoparticles can be well dispersed on NI/S flakes and the hydrolyzed APTES molecules can simultaneously bond to the hydroxyl groups of Fe₃O₄ and NI/S. Due to the synergetic effect, magnetic NI/S composite can graft more amount of APTES molecules rather than Fe₃O₄ nanoparticles or NI/S alone. When the mass ratio of NI/S:Fe₃O₄ is 1:1, the saturation magnetization of AMNI/S-1 is 17.4 emu/g, facilitating the efficient magnetic separation in aqueous solution. Also, AMNI/S-1 shows a maximal adsorption amount of Pb(II) ions of 227.8 mg/g calculated by the Langmuir model. The effects of initial concentration of Pb(II) ions, pH value, adsorption time, and temperature on the adsorption amount of Pb(II) ions were investigated. The adsorption kinetic models and isotherm models were applied to analyze the adsorption of Pb(II) ions, respectively. The thermodynamic analysis reveals that the adsorption of Pb(II) onto AMNI/S-1 is spontaneous and endothermic in nature. The mechanism for the adsorption of Pb(II) ions onto AMNI/S-1 is due to the surface complexation of Fe₃O₄ and NI/S, and the chelation of amine groups (–NH₂). AMNI/S-1 can be efficiently reused and the regenerated AMNI/S-1 remains 82.91% of initial adsorption capacity after 6-cycle adsorption/desorption process. Thus, ternary AMNI/S-1 could be used as a prospective effective adsorbent.