Dendrimer Enhanced Ultrafiltration. 1. Recovery of Cu(II) from Aqueous Solutions Using PAMAM Dendrimers with Ethylene Diamine Core and Terminal NH_2 Groups

This article discusses the feasibility of using dendrimer enhanced ultrafiltration (DEUF) to recover Cu(II) from aqueous solutions. Building upon the results of fundamental investigations of Cu(II) binding to PAMAM dendrimers with ethylenediamine (EDA) core and terminal NH_2 groups, we combine (i) dead-end ultrafiltration (UF) experiments with (ii) atomic force microscopy (AFM) characterization of membrane fouling to assess the feasibility of using DEUF to recover Cu(II) from aqueous solutions. On a mass basis, the Cu(II) binding capacities of the EDA core PAMAM dendrimers are much larger and more sensitive to solution pH than those of linear polymers with amine groups. The dendrimer−Cu(II) complexes can be efficiently separated from aqueous solutions by ultrafiltration. The metal ion laden dendrimers can be regenerated by decreasing the solution pH to 4.0; thus enabling the recovery of the bound Cu(II) ions and recycling of the dendrimers. The UF measurements and AFM characterization studies show that EDA core PAMAM dendrimers with terminal NH_2 groups have very low tendency to foul the commercially available regenerated cellulose (RC) membranes evaluated in this study. The overall results of these experiments suggest that DEUF is a promising process for recovering metal ions such as Cu(II) from aqueous solutions

Dendritic Chelating Agents. 1. Cu(II) Binding to Ethylene Diamine Core Poly(amidoamine) Dendrimers in Aqueous Solutions

This paper describes an investigation of the uptake of Cu(II) by poly(amidoamine) (PAMAM) dendrimers with an ethylenediamine (EDA) core in aqueous solutions. We use bench scale measurements of proton and metal ion binding to assess the effects of (i) metal ion−dendrimer loading, (ii) dendrimer generation/terminal group chemistry, and (iii) solution pH on the extent of binding of Cu(II) in aqueous solutions of EDA core PAMAM dendrimers with primary amine, succinamic acid, glycidol, and acetamide terminal groups. We employ extended X-ray absorption fine structure (EXAFS) spectroscopy to probe the structures of Cu(II) complexes with Gx-NH_2 EDA core PAMAM dendrimers in aqueous solutions at pH 7.0. The overall results of the proton and metal ion binding measurements suggest that the uptake of Cu(II) by EDA core PAMAM dendrimers involves both the dendrimer tertiary amine and terminal groups. However, the extents of protonation of these groups control the ability of the dendrimers to bind Cu(II). Analysis of the EXAFS spectra suggests that Cu(II) forms octahedral complexes involving the tertiary amine groups of Gx-NH_2 EDA core PAMAM dendrimers at pH 7.0. The central Cu(II) metal ion of each of these complexes appears to be coordinated to 2−4 dendrimer tertiary amine groups located in the equatorial plane and 2 axial water molecules. Finally, we combine the results of our experiments with literature data to formulate and evaluate a phenomenological model of Cu(II) uptake by Gx-NH_2 PAMAM dendrimers in aqueous solutions. At low metal ion−dendrimer loadings, the model provides a good fit of the measured extent of binding of Cu(II) in aqueous solutions of G4-NH_2 and G5-NH_2 PAMAM dendrimers at pH 7.0