Divalent heavy metals adsorption onto different types of EDTA-modified mesoporous materials: Effectiveness and complexation rate

• Ordered mesoporous KIT-6, SBA-15 and SBA-16 were synthesized and modified.
• The structural characteristics affected the EDTA loading on each adsorbent.
• KIT-6 and SBA-15 were efficient in divalent metals removing from water.
• Adsorption rate was controlled by the exchange velocity (k_w) of each metallic ion.

The removal of heavy metals from contaminated water was investigated using three types of ordered mesoporous silica (KIT-6, SBA-15 and SBA-16). The materials were functionalized with 3-aminopropyltrimethoxy-silane and ethylenediaminetetraacetic acid (EDTA) via two steps post grafting methods. Then the modified adsorbents were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), nitrogen (N2) adsorption-desorption analysis, Fourier transform infrared spectroscopy (FT-IR), and thermogravimetric analysis. The ordering of the supports was not affected after modification. KIT-6 and SBA-15 were found to be more efficient than SBA-16 due to their structural characteristics. The adsorption experiments were then conducted under different experimental conditions, such as pH, contact time and initial metals concentrations. The kinetic adsorption data obtained for the divalent metals followed the pseudo-second-order model indicating chmisorption. The exchange velocity (k_w) of each metallic ion is the main factor controlling both the adsorption rate and the selectivity which were higher for Cu2+ and Pb2+ than for Ni2+ and Cd2+. The maximum adsorption capacities were calculated by Langmuir model and were highly dependent on the amount of immobilized EDTA.

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