Adsorption of Cu2+ and Zn2+ on SBA-15 mesoporous silica functionalized with triethylenetetramine chelating agent

Abstract

Mesoporous silica particles, based on SBA-15 matrix, were functionalized with triethylenetetramine (TETA), and characterized by transmission electron microscopy (TEM), small angle X-ray scattering (SAXS), and N2-adsorption/desorption isotherms (surface area and pore size distribution). The functionalization of SBA-15 with TETA to obtain SBA-TETA was confirmed by Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). SBA-TETA functional material was used for the adsorption of Cu2+ and Zn2+ metal ions from aqueous solutions at pH 4 and T = 298 K. The adsorption kinetics was faster for Zn2+ with respect to Cu2+ ions, and could be described by the pseudo-second order model indicating the chemisorption of the metal ions as the rate-determining step of the adsorption process. Adsorption isotherms at 298 K were carried out, and the experimental data analyzed with Freundlich, Temkin, and Langmuir models. Among the isotherm models, Langmuir gave the best fitting of the experimental data, allowing to quantify the maximal adsorbable amount of Cu2+ (23.9 mg g−1) and Zn2+ (13.6 mg g−1) by SBA-TETA. Moreover, the Langmuir constant, KL, was used to calculate the thermodynamic adsorption constant Ko and the associated ΔGo, namely –21.7 kJ mol−1 and –28.4 kJ mol−1 for Cu2+ and Zn2+ adsorption processes, respectively. These values are better than those reported in similar works, likely due to the superior performance of TETA chelating agent respect to conventional alkyl-amino ligands once grafted on SBA-15 surface.