Dendrimer-mediated formation of cobalt nanoparticles via ultraviolet irradiation

Poly(amidoamine) (PAMAM) dendrimers are three-dimensional macromolecules that have unique physical properties and chemical functionalities. In recent years, researchers have used PAMAM dendrimers to synthesize metal nanoparticles in aqueous solutions. PAMAM dendrimers can provide ligands (e.g., tertiary amines and amides) for coordinating metal ions and can serve as a suitable template for producing well-defined nanoparticles. A common method for preparing dendrimer-mediated nanoparticles involves chemical reduction of metal ions, usually with NaBH4, in the presence of dendrimers. Unfortunately, much attention on coordination and reduction has been focused mainly on a limited number of metals, particularly Cu, Ag, Au, and Pt.;Other alternative methods have been reported using photochemical reduction on metal ions in the presence of dendrimers; however, details about the photoreduction process remain uncertain. The goals of this research are to investigate the coordination of cobalt(II) with poly(amidoamine) and poly(propylene imine) dendrimers, and study the photoreduction of cobalt(II) using ultraviolet (UV) irradiation and hydroxyl-terminated PAMAM dendrimers. Our efforts for examining cobalt nanoparticles are significant and applicable in magnetic information storage devices.;In this dissertation, the results indicated the formation of cobalt nanoparticles using hydroxyl-terminated fourth-generation PAMAM dendrimers and UV irradiation in aqueous solutions. After 60 h of irradiation, the solution color changed from faint pink to a yellow-brownish tint. The absorption spectrum provided additional evidence of particle formation with an increasingly rising absorption towards shorter wavelengths. Transmission electron microscopy confirmed the presence of rod-like shaped cobalt nanoparticles and the particles averaged a length of approximately 40 nm. Alternating gradient magnetometry results revealed that the dendrimer-mediated cobalt nanoparticles exhibited magnetic behavior.