3.1 Metal Oxides/Sulfides
43
3.1.3.4 Coprecipitation Method
There are three primary mechanisms of coprecipitation: occlusion, adsorption, and
inclusion. Impurities can be adsorbed via weak bonding to the surface of the precipitate, and impurities physically trapped in the crystal lead to occlusions as the crystal
grows.
Ma et al. reported the growth mechanism of Ag/Fe 3 O 4 core–shell nanowires. They
synthesized 1D Ag/Fe 3 O 4 core–shell hetero-nanowires by an effective and facile
coprecipitation method (Ma et al. 2015). The Ag nanowires acted as a nucleation site
for the growth of ferriferous oxide in aqueous solution. Controlling factors affecting
the morphology and size of the core–shell nanowires included poly(vinylpyrrolidone)
(PVP) concentration, FeCl 3 /FeCl 2 concentration, time, and reaction temperature. The
results show that the thickness of the Fe 3 O 4 shell could be tuned from 6 to 76 nm and
that the morphology could be varied between nanorods and nanospheres. First and
foremost, nucleation points were added to the surface of the Ag nanowires by the C=O
moieties of PVP. The accumulation of Fe
2+ and Fe
3+ on the Ag nanowire surface was
promoted by an in situ oxidation reaction between FeCl 3 /FeCl 2 and the Ag nanowire
solution. Additionally, the Ag nanowire surface attached to the nucleus of the Fe 3 O 4
nanoparticles. Finally, the Fe 3 O 4 nanoparticles grew from the Ag nanowire surface.
Higher temperature or higher FeCl 3 /FeCl 2 concentration resulted in faster growth
or nucleation. Lower temperature and lower concentration led to slower growth or
nucleation, causing the formation of Fe 3 O 4 nanospheres. Moreover, the Ag-Fe 3 O 4
core–shell nanowires exhibited good ferromagnetic and electrical properties at room
temperature.
3.1.4 Other Methods
3.1.4.1 Top-Down Routine
1D nanostructures could provide prospects for enhancing the mechanical, electrical,
and thermal properties of a broad range of composites and functional materials,
nonetheless their synthesis processes are typically expensive and elaborate. Consequently, top-down method has been successfully designed. The method could transform the bulk materials into 1D nanowires under ambient conditions without external
stimuli or catalysts (Danni et al. 2017). Figure 3.2i shows the schematic representation of the nanowire formation. The formation process of Al ethoxide nanowires
could be seen in Fig. 3.2c–h. The nanowires have been fabricated via minimization of strain energy at the boundary of a chemical. Experimental results show the
transformation of multimicrometer-sized particles of magnesium or aluminum alloys
into alkoxide nanowires of tunable dimensions, which are converted into 1D oxide
nanowires upon heating in air. Particularly, the aluminum oxide nanowires could be
43
3.1.3.4 Coprecipitation Method
There are three primary mechanisms of coprecipitation: occlusion, adsorption, and
inclusion. Impurities can be adsorbed via weak bonding to the surface of the precipitate, and impurities physically trapped in the crystal lead to occlusions as the crystal
grows.
Ma et al. reported the growth mechanism of Ag/Fe 3 O 4 core–shell nanowires. They
synthesized 1D Ag/Fe 3 O 4 core–shell hetero-nanowires by an effective and facile
coprecipitation method (Ma et al. 2015). The Ag nanowires acted as a nucleation site
for the growth of ferriferous oxide in aqueous solution. Controlling factors affecting
the morphology and size of the core–shell nanowires included poly(vinylpyrrolidone)
(PVP) concentration, FeCl 3 /FeCl 2 concentration, time, and reaction temperature. The
results show that the thickness of the Fe 3 O 4 shell could be tuned from 6 to 76 nm and
that the morphology could be varied between nanorods and nanospheres. First and
foremost, nucleation points were added to the surface of the Ag nanowires by the C=O
moieties of PVP. The accumulation of Fe
2+ and Fe
3+ on the Ag nanowire surface was
promoted by an in situ oxidation reaction between FeCl 3 /FeCl 2 and the Ag nanowire
solution. Additionally, the Ag nanowire surface attached to the nucleus of the Fe 3 O 4
nanoparticles. Finally, the Fe 3 O 4 nanoparticles grew from the Ag nanowire surface.
Higher temperature or higher FeCl 3 /FeCl 2 concentration resulted in faster growth
or nucleation. Lower temperature and lower concentration led to slower growth or
nucleation, causing the formation of Fe 3 O 4 nanospheres. Moreover, the Ag-Fe 3 O 4
core–shell nanowires exhibited good ferromagnetic and electrical properties at room
temperature.
3.1.4 Other Methods
3.1.4.1 Top-Down Routine
1D nanostructures could provide prospects for enhancing the mechanical, electrical,
and thermal properties of a broad range of composites and functional materials,
nonetheless their synthesis processes are typically expensive and elaborate. Consequently, top-down method has been successfully designed. The method could transform the bulk materials into 1D nanowires under ambient conditions without external
stimuli or catalysts (Danni et al. 2017). Figure 3.2i shows the schematic representation of the nanowire formation. The formation process of Al ethoxide nanowires
could be seen in Fig. 3.2c–h. The nanowires have been fabricated via minimization of strain energy at the boundary of a chemical. Experimental results show the
transformation of multimicrometer-sized particles of magnesium or aluminum alloys
into alkoxide nanowires of tunable dimensions, which are converted into 1D oxide
nanowires upon heating in air. Particularly, the aluminum oxide nanowires could be