Syntheses And Adsorption Properties Of Silica-gel Supported Dendrimer-like Polyamidoamine Polymer

Polyamidoamine (PAMAM) is one of the novel dendritic polymers which was successfully synthesized in recently decades. It is an ideal candidate for metal ions adsorption because of its well-defined structure, hollow cavities deep within the branching structure and high density of functional groups. Great attenation had been paid to PAMAM dendrimer due to its great potential appalication in many fields.In this thesis, a series of ester- and amino-terminated dendrimer-like PAMAM grafted silica-gel was prepared with a divergent method by repeating two processes: (1) Michael addition of methyl acrylate (MA) to surface amino groups; (2) amidation of the resulting esters with ethylenediamine (EDA) fromγ-aminopropyl silica gel core. Their structures were characterized by FTIR, XRD, TG, porous analysis and SEM. Au³⁺, Pd²⁺, Pt⁴⁺, Ag⁺, Cu²⁺, Zn²⁺ and Hg²⁺ were chosen as representative to investigate the static and dynamic adsorption properties of the dendrimer-like PAMAM. The relationship between adsorption capacities and acid concentrtation, pH value was also evaluated. Some conclusions can be drawn as follows:1. Ester- and amino-terminated dendrimer-like highly branched PAMAM polymers were successfully grafted on the surface of silica gel via a divergent method. The percentage of grafting of dendrimer-like PAMAM polymer on the surface of silica-gel increased with increase of the number of generations of the grafted PAMAM dendrimer, but the observed grafting at every generation was much smaller than that of the theoretical value because of steric hindrance and inter- and intra-groups crosslinking.2. The monitoring by FTIR indicated it needed at least 5, 7, 8, and 9 days for SiO₂-G0.5, SiO₂-G1.5, SiO₂-G2.5 and SiO₂-G3.5 to be converted into SiO₂-G0, SiO₂-G1.0, SiO₂-G2.0,SiO₂-G3.0 and SiO₂-G4.0, respectively at 25℃.3. The BET surface area, BJH desorption average pore diameter and BJH desorption cumulative volume of pores for the products decrease after the series of grafting reactions.4. Static adsorption showed that both ester- and amino-terminated dendrimer-like PAMAM grafted silica-gel exhibited better adsorption capabilities for Au³⁺ and Pd²⁺ than for base metal ions Cu²⁺, Zn²⁺, Hg²⁺ and noble metal ions Pt⁴⁺ and Ag⁺. Also, one conclusion can be drawn form the investigation, that is, a high percentage of grafting of polymer onto the surface of silica-gel did not mean a high adsorption capacity. 5. Dynamic adsorption shows that the adsorption mechanism for Au³⁺, Pd²⁺, Pt⁴⁺, Cu²⁺, Hg²⁺ are all belongs to the Film Diffusion Control mechanism, except the dynamic adsorption of ester-terminated dendrimer-like PAMAM grafted silica-gel for Ag⁺.6. Acid concentrtation and pH value have an important effect on sorption properties. For Pd²⁺, the optimum acid concentrtation is 2mol/L. As for Ag⁺ and Cu²⁺, most of the products exhibite highest sorption capacities when pH value is 4, except the sorption for Cu²⁺ of the amino-terminated products.