Synthesis, characterization and adsorption studies of several heavy metal ions on amino-functionalized silica nano hollow sphere and silica gel

Amino functionalized silica gel (NH2-SG) and amino functionalized silica nano hollow sphere (NH2-SNHS) with rather monodispers shape and size were prepared and characterized by X-ray differaction, scanning electron microscopy (SEM), FT-IR, thermogravimetery, and N-2 adsorption-desorption techniques. The synthesized nano particles were employed as a Cd2+, Ni2+, and Pb2+ adsorbent from aqueous solutions at room temperature. Adsorption performances of three different adsorbents prepared by functionalization of commercial silica gel (NH2-SG), silica nano hollow sphere (NH2-SNHS), and a non functionalized silica nano hollow sphere (SNHS) have been compared. Heavy metal adsorption process has been thoroughly studied from both kinetic and equilibrium points of view for all adsorbents. The adsorption isotherms were analyzed using the seven different isotherm models and correlation coefficients were determined for each isotherm. It was found that the Langmuir-Freundlich (Sips) isotherm showed better correlation with the experimental data than other isotherms. The adsorption kinetics was tested for the pseudo-first order, pseudo-second order and Elovich kinetic models at different experimental conditions. The kinetic data show that the process is very fast and the reactions follow pseudo-second-order kinetic models for amino functionalized adsorbents. Also, the maximum adsorption values for Cd2+, Ni2+, and Pb2+ under the experimental conditions were determined for all adsorbents. (C) 2011 Elsevier B.V. All rights reserved.