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

SBA-15 substrate functionalized with –NH2 groups were tested in adsorptive elimination of lead (II) from aqueous solutions. The NH2/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 N2 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 NH2/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 –NH2 groups located on the sorbent surface. The mechanism of lead adsorption through the ionic exchange of Pb(II) ions with surface Si–NH3+ groups, as determined by XPS, is precluded because they acts repulsively with approaching lead ions.

Mechanism of Pb(II) ions adsorption on the SBA15-NH2 sorbent’s surface.Figure optionsDownload as PowerPoint slideHighlights
► Mesoporous SBA-15 silica modified with –NH2 functional group is effective sorbent for Pb(II) ions.
► The maximum of Pb(II) ions adsorption (93.0%) occurs at pH 5–6.
► The mechanism of Pb(II) adsorption is through electrostatic of Pb(II) ions interaction with –NH2 groups.