Structural Properties of Magnetic-Cored Dendrimers Affect Adsorption of Organic and Inorganic Contaminants

Abstract

In this dissertation, structural characteristics of magnetic cored dendrimer (MCD) and their effects on the adsorption of organic and inorganic contaminants were studied to expand the applicability of MCD in environmental field. The main objectives of this research were: i) to investigate physicochemical characteristics of MCD varied with the core size, MCD generation growth, and MCD functionalization and ii) to demonstrate the effectiveness of MCD on organic inorganic contaminants. In Chapter 2, amine functionalized magnetite (Fe3O4-NH2) of two different size were synthesized and compared as environmental adsorbents. The 10 nm and 250 nm sizes of Fe3O4-NH2 were synthesized co-precipitation (C-Fe3O4-NH2) and solvothermal (S-Fe3O4-NH2) methods, respectively. The S-Fe3O4-NH2 exhibited magnetic saturation value of 61.54 emu/g which was higher than that of C- Fe3O4-NH2 (47.81 emu/g). However, both could be separated from an aqueous solution using an external magnet. The surface area and the pore volume of C-Fe3O4-NH2 was larger than that S-Fe3O4-NH2, but stronger aggregation was observed in C-Fe3O4-NH2. The C-Fe3O4-NH2 exhibited agglomeration of 187.9 nm when dispersed water, while S-Fe3O4-NH2, showed little agglomeration of particles at 239.2 nm. Batch adsorption of lead was performed and the maximum lead adsorption on C- Fe3O4-NH2 (74.48 mg/g) was higher than that of S-Fe3O4-NH2 (54.54 mg/g). The smaller core size of C-Fe3O4-NH2 showed stronger aggregation than larger core size of S-Fe3O4-NH2, but this aggregation did not affect the adsorption performance of C-Fe3O4-NH2 as an environmental adsorbent. In Chapter 3, the number of amine end groups in generation 0 (G0) to 3 (G3) MCDs were investigated experimentally and their binding effect with lead (Pb (II)) ion were studied. The estimated number of end groups in G0-, G1-, G2-, and G3-MCDs were 258, 490, 758, and 1142, respectively. The less growth rate of end groups in higher generation of MCDs was due to unreacted end groups during the synthesis. The distance of the groups in each generation MCD tended to decrease as G0-MCD (1.29 nm) to G3-MCD (0.76 nm) as the MCD generation grew. Adsorption of Pb (II) ion onto MCD increased as generation increased exhibiting the highest adsorption on G2-MCD (298.09 mg/g). However, the decreased adsorption occurred in G3-MCD because of less space in limited volume leading. The most Pb (II) ion adsorption per end group exhibited in the G0-MCD and G1, G2, and G3-MCD followed in order. This was because Pb (II) ions were difficult to access due to the end groups close to each other. Therefore, the numbers and formation of end groups in MCD directly affect to Pb (II) ion adsorption. Additionally, the Pb (II) ion adsorption under the coexistence of organic and inorganic compounds and Pb (II) ion with a low ionic radius showed the highest adsorption efficiency. The G1-MCD with combination of alkaline pretreatment applied as a secondary system for wastewater and revealed a high removal rate of heavy metals. The MCD can be utilized for wastewater treatment. In Chapter 4, MCD was functionalized with organic acids by amide condensation between amine groups and carboxyl groups in MCD and organic acid, respectively. A citric acid (CA), a succinic acid (SA), and a vanillic acid (VA) were terminalized onto MCD. Adsorption potential of the composites was assessed by monitoring methylene blue (MB), ciprofloxacin (CIP), and norfloxacin (NOR) removal from contaminated solution. The highest MB adsorption occurred at pH 11, and CIP and NOR showed the highest adsorption performance at pH 7. This was because cationic MB, CIP and bound with anionic carboxyl and hydroxyl groups in MCD composite. The CA-MCD exhibited best adsorption performance on MB (216.30 mg/g), CIP (29.44 mg/g), and NOR (17.58 mg/g) due to higher number of functional moieties per CA-MCD branch. Regeneration of CA-, SA-, and VA-MCDs displayed good reusability over 90% removal efficiency in three cycles. Similarly, CIP and NOR reuse experiments showed high reusability. Antibacterial test was also performed and the CA-, and VA-MCDs were non-toxic to gram positive and negative bacteria. Therefore, the MCD through terminal group modification is biocompatible and can be applied to various organic contaminants adsorption. This study demonstrated that agglomeration of MCD particles does not affect to the adsorption whereas affected by end groups in MCD. Furthermore, MCD can be applied to both organic and inorganic contaminants through functionalization. The understanding of structural characteristics of magnetic dendrimers by composition conducted in this study are expected to expand their applicability of various contaminants.