Computational Calculation and Experimental Binding of Heavy Metals and Dyes to Magnetic Cored Dendrimers

Abstract

In this dissertation, binding of magnetic cored dendrimer (MD) and the organic/inorganic compound was studied to extend the applicability of the MD to wastewater treatment field. The main objectives of this research were: i) investigate the specific binding configuration and interpret the different affinity of heavy metal ions onto MD using computational calculation, and ii) enhance the binding efficiency of an organic compound by modifying the terminal group of MD with carboxymethyl chitosan (CC). In Chapter 2, the adsorption experiment was carried out to investigate the binding capacity of MD with Pb (II), Cu (II), Zn (II), and Cr (VI), respectively. To demonstrate the different binding preference, density functional theory (DFT) was used. The maximal adsorption capacity of amine functionalized MD (G1-NH2- MD) for four heavy metal ions followed the sequence of Pb (II) > Cr (VI) > Zn (II) > Cu (II). The optimal configurations of the G1-NH2-MD and heavy metal ions were proposed by the DFT calculation using the pseudo-potential code SIESTA model. The affinity of metal ions for MD was interpreted through the computational result which is mainly determined by the ionic radius and coordination number of the ions. The computational result indicates that the lead (II) ions stably bind to the terminal site of G1-NH2- MD due to its relatively large ionic radius. The enthalpy of the lead (II) ion onto G1-NH2- MD shows strong affinity compare to Cu (II), Zn (II), and Cr (IV) with the stable configuration. Also, the experimental result and calculated value revealed a consensus. The result provides important information about the behavior of G1-NH2- MD and metal ions in an aqueous phase and enables to extend the applicability in wastewater treatment field. In Chapter 3, the terminal site of MD is modified with CC to enhance the binding capacity since chitosan has a high content of sorptive moiety. The carboxymethyl chitosan modified magnetic cored dendrimer (CCMD) was synthesized in a three-step method. I immobilized the chitosan derivative onto MD so that the CCMD can be magnetically separated after the adsorption process with the magnetic core. To adopt the chitosan onto MD, chitosan was modified with carboxyl groups and it was successfully cross-linked with the amine terminated MD. Also, an excessive number of carboxylic group enhance the ability of binding to cationic compounds. The CCMD exhibited different adsorption levels of anionic methyl orange (MO) and cationic methylene blue (MB) at various pH values. The optimal adsorption pH values were 3 and 11 for MO and MB, respectively. The dye-loaded MD was regenerated with 5 times repeated experiment. In comparison to another adsorbent, the CCMD in this study exhibited a higher adsorption per unit mass of chitosan and better reusability. From these results, it can be expected that CCMD can efficiently treat various types of cationic and anionic contaminants as well as dye compounds.