Khe, Cheng Seong
(2013)
Role And Correlation Of Synthesis, Size And Morphology
To The Magnetic Properties Of Cobalt And Cobalt/Gold
Bimetallic Hierarchical Nanostructures.
PhD thesis, Universiti Sains Malaysia.
Abstract
Cobalt is a ferromagnetic material while cobalt-gold bimetallic particles are
expected to have modulated magnetic properties. Besides, gold nanostructure is also
a good plasmonic material. However, cobalt is susceptible to oxidation in aqueous
environment. The oxidised layer can harm the magnetic properties. Therefore, in
order to avoid oxidation of cobalt, this work was devoted to the synthesis of cobalt
and cobalt-gold bimetallic hierarchical particles using polyol method cum galvanic
replacement reaction. A number of synthesis conditions were experimented in order
to investigate their impacts on the morphologies of the cobalt particles produced. The
parameters studied including reaction time, sodium hydroxide, concentration of
cobalt salt, reaction temperature, reducing agent and surfactants. Various
morphologies were successfully prepared such as hierarchical microspheres,
hierarchical polyhedral shape, hierarchical raspberry like, truncated hexagonal
bipyramid, flower-like, elongated and quasi cubic-like particles. All of these
hierarchical cobalt particles exhibited their own unique magnetic properties. Sample
prepared from 1mmol cobalt chloride, 2 mmol of sodium hydroxide, 5 mmol of
hydrazine hydrate and 3.0% (w/v) of sodium dodecyl sulfate has a mixture of quasi
cubic and elongated particles. It has the highest coercivity of about 290 Oe. Cobaltgold
bimetallic hierarchical particles were prepared by galvanic replacement reaction
where cobalt acted as sacrificial template. Bimetallic particles with hollow
hierarchical structure and arbitrary shapes were produced under different synthesis
conditions.
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