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 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 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. (C) 2012 Published by Elsevier Inc.