Adsorption of Pb(Ⅱ) from aqueous solution by silica-gel supported hyperbranched polyamidoamine dendrimers

摘要

The adsorption properties of silica-gel supported hyperbranched polyamidoamine dendrimers (SiO_2-G0-SiO_2-G4.0) have been investigated by batch method. The effect of pH of the solution, contact time, initial Pb(Ⅱ) ion concentration, temperature and coexisting metal ions have been demonstrated. The results indicated that the optimum pH value was 5. Adsorption kinetics was found to follow the pseudo-second-order model and controlled by film diffusion. The adsorption isotherms were fitted by Langmuir, Freundlich and Dubinin-Radushkevich (D-R) isotherm models. Langmuir isotherm model was found to be more suitable to describe the equilibrium data, suggesting the uptake of Pb(Ⅱ) ions by monolayer adsorption. From D-R isotherm model, the calculated mean free energy ￡ demonstrated the adsorption processes occurred by chemical ion-exchange mechanism. FTIR analysis revealed that amine groups were mainly responsible for the adsorption of Pb(Ⅱ) by amino-terminated adsorbents, while C=0 of ester groups also participated in the adsorption process of ester-terminated ones. The adsorbents can selectively adsorb Pb(Ⅱ) from binary ion systems in the presence of Mn(Ⅱ), Cu(Ⅱ), Co(Ⅱ), and Ni(Ⅱ). Based on the results, it is concluded that SiO_2-G0-SiO_2-G4.0 had great potential for the removal of Pb(Ⅱ) from aqueous solution.