3.1 Metal Oxides/Sulfides
41
arrays were optimized to control the density and length. The longest α-MoO 3 nanorod
length of 600 nm was achieved by sintering at 673 K for 15 min using a molar ratio of
citric acid to Mo of 1.5:0.5 and dimethylacetamide as the solvent. Furthermore, the
experiment also demonstrated that factors influencing the phase change and growth
of the MoO 3 nanorods are correlated to the dissociation of the citric acid/Mo metal
compound in the sol–gel precursor liquor.
3.1.3.2 Hydrothermal/Solvothermal Methods
The hydrothermal/solvothermal route describes a synthetic strategy that relies on
the solubility of the metallic oxide material under high pressure and temperature to synthesize 1D crystalline substances (And and Mao
† 2007). This synthetic
method is usually implemented in autoclaves. A supercritical fluid is formed under
elevated pressure and temperature, which increases the solubility of the solid precursors and leads to the precipitation of 1D nanostructures from the excess inorganic
precursor. Hydrothermal processes are efficient for the development of high-quality
1D nanocrystals with high orientation and few defects, and we will describe these
methods in greater detail in the following sections. Many nanostructures have been
prepared by hydrothermal methods, including MnO 2 , (Dai et al. 2014; Wang and
Li 2002; Kim et al. 2014) Na 2 V 6 O 16 · 3H 2 O, (Jiaguo Yu et al. 2004) Ag 2 V 4 O 11 ,
(Sauvage et al. 2010; Shaoyan et al. 2010) VO 2 , (Kyung-Hoon et al. 2013; Niu et al.
2014; Ni et al. 2011) Ag 4 V 2 O 6 , (Erin et al. 2005; Albrecht et al. 2015) WO 3 , (Gao
et al. 2013), etc.
The one-step fabrication of hybrid nanostructures with high conductance and
surface area remains a challenge (Li et al. 2014). Based on the theoretical Kirkendall effect, Ag/MnO x nanotubes were produced by the solvothermal reaction
between KMnO 4 and Ag nanowire templates. The electrochemical performance and
morphology of the Ag/MnO x composite material were tuned by changing the pH
level. Tubular MnO x nanosheets with Ag nanoparticles were formed in a comparatively acidic environment (pH = 0.76), whereas ultrafine Ag nanoparticles entrapped
in amorphous manganese dioxide nanotubes were prepared in neutral solution (pH
= 7.00) (Fig. 3.2a). Various volume-dependent experiments demonstrated that the
Kirkendall effect was involved in the production of these morphologies (Fig. 3.2b).
Additionally, the tubular Ag/MnO x hierarchical nanostructures showed high electrochemical performance and maintained 80% of their initial capacity after 1000 cycles
at 1 A g
−1 . Most importantly, this synthetic mechanism may provide feasible design
guidelines for the preparation of other hierarchical 1D nanocomposites.
3.1.3.3 Microwave-Assisted Method
The microwave-assisted method provides heating during the synthetic process and
could reduce the reaction time for inorganic and organic materials through control
of the reaction kinetics (Cundy and Cox 2003; Bilecka and Niederberger 2010).
41
arrays were optimized to control the density and length. The longest α-MoO 3 nanorod
length of 600 nm was achieved by sintering at 673 K for 15 min using a molar ratio of
citric acid to Mo of 1.5:0.5 and dimethylacetamide as the solvent. Furthermore, the
experiment also demonstrated that factors influencing the phase change and growth
of the MoO 3 nanorods are correlated to the dissociation of the citric acid/Mo metal
compound in the sol–gel precursor liquor.
3.1.3.2 Hydrothermal/Solvothermal Methods
The hydrothermal/solvothermal route describes a synthetic strategy that relies on
the solubility of the metallic oxide material under high pressure and temperature to synthesize 1D crystalline substances (And and Mao
† 2007). This synthetic
method is usually implemented in autoclaves. A supercritical fluid is formed under
elevated pressure and temperature, which increases the solubility of the solid precursors and leads to the precipitation of 1D nanostructures from the excess inorganic
precursor. Hydrothermal processes are efficient for the development of high-quality
1D nanocrystals with high orientation and few defects, and we will describe these
methods in greater detail in the following sections. Many nanostructures have been
prepared by hydrothermal methods, including MnO 2 , (Dai et al. 2014; Wang and
Li 2002; Kim et al. 2014) Na 2 V 6 O 16 · 3H 2 O, (Jiaguo Yu et al. 2004) Ag 2 V 4 O 11 ,
(Sauvage et al. 2010; Shaoyan et al. 2010) VO 2 , (Kyung-Hoon et al. 2013; Niu et al.
2014; Ni et al. 2011) Ag 4 V 2 O 6 , (Erin et al. 2005; Albrecht et al. 2015) WO 3 , (Gao
et al. 2013), etc.
The one-step fabrication of hybrid nanostructures with high conductance and
surface area remains a challenge (Li et al. 2014). Based on the theoretical Kirkendall effect, Ag/MnO x nanotubes were produced by the solvothermal reaction
between KMnO 4 and Ag nanowire templates. The electrochemical performance and
morphology of the Ag/MnO x composite material were tuned by changing the pH
level. Tubular MnO x nanosheets with Ag nanoparticles were formed in a comparatively acidic environment (pH = 0.76), whereas ultrafine Ag nanoparticles entrapped
in amorphous manganese dioxide nanotubes were prepared in neutral solution (pH
= 7.00) (Fig. 3.2a). Various volume-dependent experiments demonstrated that the
Kirkendall effect was involved in the production of these morphologies (Fig. 3.2b).
Additionally, the tubular Ag/MnO x hierarchical nanostructures showed high electrochemical performance and maintained 80% of their initial capacity after 1000 cycles
at 1 A g
−1 . Most importantly, this synthetic mechanism may provide feasible design
guidelines for the preparation of other hierarchical 1D nanocomposites.
3.1.3.3 Microwave-Assisted Method
The microwave-assisted method provides heating during the synthetic process and
could reduce the reaction time for inorganic and organic materials through control
of the reaction kinetics (Cundy and Cox 2003; Bilecka and Niederberger 2010).