The synthesis and characterization of gold nanoparticles in water-soluble polymers A
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Date
2010
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Abstract
Nanomaterials with critical dimensions at the nanoscale currently attract considerable
attention as they show distinct chemical and physical properties that are dependent on
their size and shape. A number of techniques have been used to synthesize metal
nanoparticles. This thesis presents modified methods for the synthesis of gold
nanoparticles, CdSe and Au-CdSe hybrid nanoparticles, capped with water soluble
polymers.
Chapter one reviews some basic concepts of nanostructured materials. The electronic
structure and properties of gold nanoparticles are discussed. The general synthetic routes
of gold nanoparticles are also reviewed with special emphasis on their preparation in
water soluble polymers. A few applications of nano-gold including electronics, catalysis
and biomedical applications are presented. Finally the characterization techniques used in
this study are discussed.
Chapter two describes the synthesis of gold nanoparticles from various chemical
reduction techniques. These techniques have yielded a combination of both spherical and
anisotropic shaped nanoparticles. Different reducing agents, such as sodium borohydride,
presence of sodium hydroxide, ascorbic acid, sodium citrate, tri-sodium citrate and
hydrogen peroxide have been used in the reduction of Au3+ ions to Au0. Water soluble
polymers such as poly vinylpyrrolidone (PVP), poly vinyl alcohol (PVA) and organic
ligands tri-n-octylphosphine oxide (TOPO) and octadecylamine (ODA) were used as
capping agents for the gold nanoparticles. Seed-mediated and two-phase techniques were
also employed to yield anisotropic nanorods of gold. Different structure-directing agents
and phase-transfer agents were used in the formation of anisotropic nanoparticles. The
optical properties of the gold nanoparticles were studied by UV/Vis spectroscopy. The
structure and morphology of the as prepared particles was determined using powder X-ray diffraction (XRD) and electron microscopy, respectively. In Chapter three the anisotropic gold nanoparticles synthesized by a UV-irradiation
technique through the interaction of HAuCl4 and a stabilizing agent, poly (vinyl
pyrrolidone) (PVP) are presented. The effect of irradiation time on the size and shape of
gold nanoparticles was investigated by UV-Visible spectroscopy and Transmission
Electron Microscopy (TEM). The other effects that were varied include; capping agent,
polymer concentration, precursor concentration, lamp wavelength, solvent, and lastly the
presence of citric acid in other reactions. The absorption spectra of all samples show a
broad band with the characteristic surface plasmon resonance (SPR) peak visible at
around 530 nm. The presence of an additional low intensity absorption peak at a longer
wavelength suggests the presence of non-spherical nanoparticles. The TEM
measurements show evidence of particle shapes such as spheres, hexagons, decahedrons
and truncated triangles as the reaction time was varied.
Chapter four describes the synthesis of CdSe semiconductor nanoparticles at room
temperature in the presence of PVP as the capping agent. Different cadmium sources
were used and the mole ratios of the starting materials were varied in order to obtain
monodispersed CdSe nanoparticles. L-cysteine and PVP-capped Au-CdSe hybrid
nanostructures were synthesized at room temperature. The UV-Vis of these hybrid
materials showed gold absorption features for the PVP-capped Au-CdSe while for
cysteine capped hybrid particles very little features were observed on the spectrum. The
denser spherical gold particles are distinctly visible in the TEM images. The high
resolution TEM clearly showed the lattice fringes that confirm the crystallinity of the
PVP capped Au-CdSe hybrid nanoparticles.
Description
A thesis submitted to the University of Zululand
for the Degree of Doctor of Philosophy in the
Department of Chemistry,
Faculty of Science and Agriculture, 2010.
Keywords
Nanomaterials, Nanostructured materials