Yuzhong Niu

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

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 E 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 CO 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.

Synthesis of silica gel supported salicylaldehyde modified PAMAM dendrimers for the effective removal of Hg(II) from aqueous solution.

A series of silica gel supported salicylaldehyde modified PAMAM dendrimers (SiO2-G0-SA ∼ SiO2-G2.0-SA) were synthesized and their structures were characterized by FTIR, XRD, SEM, TGA, and porous structure analysis. The feasibility of these adsorbents for the removal of Hg(II) from aqueous solution was first described and the adsorption mechanism was proposed. The adsorption was found to depend on solution pH, the generation number of salicylaldehyde modified PAMAM dendrimers, contact time, temperature, and initial concentration. Results showed that the optimal pH was about 6 and the adsorption capacity increased with the increasing of generation number. Density functional theory (DFT) method was used to investigate the coordination geometries and the chelating mechanism. Adsorption kinetics was found to follow the pseudo-second-order model with film diffusion process as rate controlling step. Adsorption isotherms revealed that adsorption capacities increased with the increasing of temperature. Langmuir, Freundlich and Dubinin-Radushkevich (D-R) isotherm models were employed to analyze the equilibrium data. The adsorption can be well described by Langmuir isotherm model and took place by chemical mechanism. The thermodynamics properties indicated the adsorption processes were spontaneous and endothermic nature. The maximum adsorption capacity of SiO2-G0-SA, SiO2-G1.0-SA, and SiO2-G2.0-SA were 0.91, 1.52, and 1.81 mmol g(-1), respectively. The considerable higher adsorption capacity compared with other adsorbents indicates SiO2-G0-SA ∼ SiO2-G2.0-SA are favorable and useful for the uptake of Hg (II), and can be potentially used as promising adsorbents for the effective removal of Hg(II) from aqueous solution.