Synthesis and growth dynamics study of silver nanoparticles
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Date
2009
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Abstract
The concept of shape-controlled synthesis of metal nanoparticles is investigated by considering the growth mechanism of metal nanoparticles. This thesis is divided into four chapters, chapter one presents a general introduction about various physiochemical aspects of nanornaterials. The different characteristic properties of nanomaterials, their chemically synthesized protocols, characterization techniques, and their applications are discussed in brief. Based on these reviews, the context scope and objective of the present work are outlined.
Chapter two deals with the theory of kinetically growth of nanoparticles. The basic optical properties of metal nanoparticles as well as the structural evolution of nanoparticles are also mentioned in this chapter
In Chapter three the synthesis of silver nanoparticles with varying morphologies using different synthetic routes are described in detail. Silver nanowires were synthesized by an aqueous route using dimethyl formamide (DMF) as the reducing agent in the presence of poly (iV-vinylpyrrolidone) (PVP) without the addition of seeds. The products were characterized by UV-visible spectroscopy and transmission electron microscopy (TEM). This work was followed by a profound dig-out, to try and comprehend the mechanism for reduction and the kinetics of the reduction of silver nitrate to silver nanoparticles. It was established that in the alkaline medium the reduction of AgNC>3 is enhanced, which resulted to the formation of rod-like silver nanoparticles which were confirmed by TEM and UV-visible spectroscopy.
Silver nanodendrites, with an elongated central backbone and distinguished branches were synthesized by die reduction of silver nitrate with formamide using polyvinyl pyrrolidone (PVP) as the surfactant. The drastic evolution of the dendritic nanostructures was due to the variation of the concentration of the reactants. At low PVP concentration isotropic silver nanoparticles are visible in the transmission electron microscopy (TEM) images. The morphological evolution is confirmed by the optical measurements. The growth mechanism for the nanodendrites is discussed in some detail.
The use of single molecular precursors is a common route to synthesize nanostructured materials. There have been relatively few reports for the use of sophisticated precursors to synthesize metal nanoparticles at high temperatures. The N-(Diisoproppylthiophosphoryl) thiourea complexes of silver were synthesised using a previously reported literature method. The complexes were then used as single molecule precursors for the synthesis of hexadecylamine (HDA) and tri-octylphosphine oxide (TOPO) capped silver nanoparticles. The absorption spectra of the HDA and TOPO-capped silver nanoparticles exhibit surface plasmon resonance (SPR) absorption in 400-420 nm regions.
In chapter four, the morphological evolution of silver nanoparticles prompted the development of a Density Function Theory (DFT) model to understand the adsorption of Pyrrolidinone on the surface of silver and gold nanoparticles. The interaction between PVP and the metal atoms on the surface of silver and gold nanoparticles, was studied using Surface Enhanced Raman Spectroscopy (SERS) and modeled using
Density Function Theory (DFT). The SERS analysis was carried out on pyrrolidinone and N-methyl pyrrolidinone in silver and gold colloids, whereas the assignments of bands in the pyrrolidinone molecules were performed by density function theory (DFT) quantum chemical calculations.
Description
A thesis presented in fulfillment of the requirement for the award of the degree of
Doctor of Philosophy in the Department of Chemistry at the University of Zululand, South Africa, 2009.
Keywords
Nanoparticles, Nanornaterials