Adsorption of lead (II) on SBA-15 mesoporous molecular sieve functionalized with –NH2 groups

Abstract SBA-15 substrate functionalized with –NH 2 groups were tested in adsorptive elimination of lead (II) from aqueous solutions. The NH 2 /SBA-15 adsorbents were prepared by grafting of synthesized SBA-15 substrate with different concentrations of 3-aminopropyltriethoxysilane (APTES) in order to determine the optimum amine group concentration. The largest adsorption capacity showed sorbent prepared using tetraethyl orthosilicate (TEOS)/APTES molar ratio of 3.3. All sorbents were characterized by N 2 adsorption–desorption isotherms, powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA–DTG) and X-ray photoelectron spectroscopy (XPS). Regardless of the concentration of amine groups, all synthesized NH 2 /SBA-15 samples showed higher adsorption capacity for Pb (II) ions than pure SBA-15 material. For the optimized sorbent formulation, experimental data showed that the maximum Pb (II) adsorption occurred in the range of pH 5–6 with adsorption maximum of 93%. The characterization of sorbents after Pb(II) adsorption by UV–vis and XPS spectroscopes point out to a mechanism of lead adsorption through van der Waals electrostatic interaction between Pb(II) ions and –NH 2 groups located on the sorbent surface. The mechanism of lead adsorption through the ionic exchange of Pb(II) ions with surface Si–NH 3 + groups, as determined by XPS, is precluded because they acts repulsively with approaching lead ions.