Synthesis Of Hyperbranched Polyamidoamine Grafted On Silica-gel And Its Adsorption Properties

Hyperbranched Polyamidoamine (hb-PAMAM) is perfect dendrimer, which have attracted considerable attention due to their remarkable properties such as three-dimensional branched nature, spherical structure and cavernous interior. It possess amide, tertiary, and primary amine groups arranged in regular "branched upon branched" patterns, which are displayed in geometrically progressive numbers as a function of generation. Thus, PAMAM dendrimers can serve as high capacity nanoscale containers for toxic metal ions.In this thesis, hyperbranched polyamidoamine (hb-PAMAM) were synthesized by polycondensation of AB2 type monomers. The effects of various conditions on the coordination reaction between hb-PAMAM and Co2+, Cu2+, and Ni2+ was then investigated via spectrophotometric method. The results indicate that as the mass ratio of CoCl2, CuSO4 and NiSO4 to hb-PAMAM increase, a red-shift of the maximum absorption wavelength were observed, while a new absorption peak was observed for Co2+/hb-PAMAM. When the pH value decreased from 9.02 to 3.00, the maximum absorption wavelength occurred red-shift distinctly and the the intensity of the absorption spectrum of the complex also decreased, while a new absorption peak was observed for Co+/hb-PAMAM and it shifted to longer wavelength. The absorption intensity of the complex was enhanced with increase of the reaction temperature. The speed of coordination reaction is fast, which had completed in one hour at room temperature in the experimental concentration range.A hyperbranched polyamidoamine resin grafted on silica(SiO2-hb-PAMAM) was prepared via a one-pot polycondensation of N,N-diaminoethyl-3-amino methyl propionate on the surface of silica-gel, which was modified with amino group containing silane coupling agent and hence could initiated the polycondensation. The resulting product was characterized by FT-IR, XRD, N2 sorption experiments and TG. Then, its adsorption properties, including static adsorption capacity, adsorption kinetics, adsorption thermodynamics and dynamic adsorption for Cu2+, Ag+, Hg2+ and Au3+ ions in water were investigated. The results show that this resin exhibited excellent chelating capacity for selected metal ions. The adsorption kinetics followed G. E. Boyd equation, that is, controlled by liquid film diffusion. In addition, the apparent activation energy of the adsorption process for Cu2+, Ag+, Hg2+ and Au3+ ions were 15.850 kJ.mol-1,0.269 kJ.mol-1,5.862 kJ.mol-1 and 5.641 kJ.mol-1, respectively, suggesting that the adsorption is very easy. While the adsorption thermodynamics corresponded with Langmuir model, namely, belonged to monolayer adsorption. The thermodynamic parameters were calculated and then revealed that the adsorption process was an endothermic process, indicating that increasing temperature was beneficial to the adsorption. The decrease of free energy and the increase of entropy is the impetus of adsorption.The dynamic adsorption experiments indicate that SiO2-hb-PAMAM also exhibited excellent chelating capacity for Cu2+, Ag+, Hg2+ and Au3+ ions, showing that the adsorption process was following liquid film diffusion mechanism. Acid concentrtation and pH value have an important effect on sorption properties. When the solution of 5% thiourea in HCl or HNO3 was employed as the desorption medium, the resin can be regenerated.