Use of 7-amine-4-azahepthylsilica and 10-amine-4-azadecylsilica xerogels as adsorbent for Pb(II): Kinetic and equilibrium study

Two silica based hybrid materials containing the chelating Si–O–(CH2)3–NH–R–NH2 group, where R is –(CH2)3– or –(CH2)6– designed as AAH Si and AAD Si, respectively, were obtained with almost similar organic content, by using the sol–gel method under the same experimental conditions. The adsorbent materials were characterized by FTIR spectroscopy and N2 adsorption–desorption isotherms. The adsorbent materials were employed for Pb(II) uptaking using batch adsorption procedure. Kinetic studies were carried-out, and showed that the metal uptake followed better the pseudo-second order kinetic model. The pseudo-second order constant rate obtained by using a 20.0 mg l−1 Pb(II) were 0.0117 and 0.0252 g mg−1 min−1 for AAH Si and AAD Si, respectively. Equilibrium adsorption isotherms were obtained. The values were fitted to non-linear Langmuir, Freundlich, Sips and Redlich–Peterson isotherm models. With exception of Freundlich isotherm, all the models were suitably fitted. The maximum adsorption capacity for Pb(II) using AAH Si and AAD Si were 36.64 and 30.27 mg g−1, respectively. The higher adsorption capacity for AAH Si could be attributed mainly to the larger pore diameter and pore volume and higher surface area.