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gas sensors, biosensors, and field transistors (Yang and He 2011; Longano et al.
2012; Harikumar and Aravind 2016; Prabhu et al. 2017). The synthesis control of
copper oxide micro- and nanostructures is responsible for the development of new
applications and the improvement of the existing ones, once one can tailor their
morphological, chemical, and physical properties. Currently, copper oxide nanoparticles can be obtained in distinct shapes and sizes, including nanorods, nanowires,
nanotubes, nanoplatelets, nanodendrites, and nanoflowers (Vijaya Kumar et al.
2001; Cao et al. 2003; Narayanan and El-Sayed 2003; Li et al. 2004; Li et al. 2005;
Song et al. 2007).
Copper nanomaterials can be obtained by distinct chemical, physical, and biological methods, yielding nanoparticles with different morphologies, sizes, and
chemical and physical properties (Zhang et al. 2014). The synthesis methods include
metal vapor synthesis (MVS), exploding wire method, vacuum vapor deposition,
sonochemical reduction, thermal reduction, chemical reduction, biosynthesis, laser
irradiation, microemulsion techniques, sol–gel technique, thermal oxidation method
among many others (Song et al. 2007; Naika et al. 2015; Suárez-Cerda et al. 2017).
Next we briefly describe some of the methods.
Metal vapor synthesis (MVS): it consists of the sublimation and posterior recondensation of a metal under a high vacuum, aiming at combining its atoms or
small particles with ligands, preparing metal complexes. Normally, a reactor is used
to evaporate the metal, and the resulting vapor then collides with a cold wall containing the organic ligand. This method allows the production of small and homogeneous metal nanoparticles without using reactants during the nanoparticle production
(Barbaro et al. 2015).
Exploding wire method: in this method, nanopowder is produced by electric
explosion of metallic wire in an inert gas. The process starts with the application of
a rising current to the metallic wire, in which high heat generated makes the wire to
vaporize and create an electric arc, which is the responsible of the explosion. The
average particle size, its properties, and chemical composition can be determined
using different parameters, such as the voltage of the capacitor used to generate the
current, which leads to a wide variety of products (Tarasov et al. 2002).
Vacuum vapor decomposition (VDD): this method is usually employed for producing copper nanorods and nanowires, under very low pressure or vacuum conditions, where copper vapor is generated and then re-deposited on a specific target/
substrate. VDD was proposed by Liu and Bando (2003), where they used a tiny
cooper ring inside a dry pumping station with a low pressure to generate the vapor
and a molybdenum grid as the substrate. The diameter of the copper nanorods
formed varied from 50 to 100 nm.
Sonochemical reduction: Vijaya Kumar et al. (2001) showed that it is possible to
synthesize amorphous Cu and nanocrystalline Cu 2 O using an ultrasonic horn
(Ti-horn, 20 kHz, 100 W cm
−2
) and aniline as a solvent. With the methodology proposed, the authors have obtained Cu particles from 4 to 10 nm and Cu 2 O particles
from 5 to 13 nm, with a suitable distribution within the polyaniline matrix.
Chemical reduction: this method is perhaps the most popular synthesis method
for obtaining Cu nanoparticles (Suárez-Cerda et al. 2017), due to the easy control of
F. F. Pereira et al.
gas sensors, biosensors, and field transistors (Yang and He 2011; Longano et al.
2012; Harikumar and Aravind 2016; Prabhu et al. 2017). The synthesis control of
copper oxide micro- and nanostructures is responsible for the development of new
applications and the improvement of the existing ones, once one can tailor their
morphological, chemical, and physical properties. Currently, copper oxide nanoparticles can be obtained in distinct shapes and sizes, including nanorods, nanowires,
nanotubes, nanoplatelets, nanodendrites, and nanoflowers (Vijaya Kumar et al.
2001; Cao et al. 2003; Narayanan and El-Sayed 2003; Li et al. 2004; Li et al. 2005;
Song et al. 2007).
Copper nanomaterials can be obtained by distinct chemical, physical, and biological methods, yielding nanoparticles with different morphologies, sizes, and
chemical and physical properties (Zhang et al. 2014). The synthesis methods include
metal vapor synthesis (MVS), exploding wire method, vacuum vapor deposition,
sonochemical reduction, thermal reduction, chemical reduction, biosynthesis, laser
irradiation, microemulsion techniques, sol–gel technique, thermal oxidation method
among many others (Song et al. 2007; Naika et al. 2015; Suárez-Cerda et al. 2017).
Next we briefly describe some of the methods.
Metal vapor synthesis (MVS): it consists of the sublimation and posterior recondensation of a metal under a high vacuum, aiming at combining its atoms or
small particles with ligands, preparing metal complexes. Normally, a reactor is used
to evaporate the metal, and the resulting vapor then collides with a cold wall containing the organic ligand. This method allows the production of small and homogeneous metal nanoparticles without using reactants during the nanoparticle production
(Barbaro et al. 2015).
Exploding wire method: in this method, nanopowder is produced by electric
explosion of metallic wire in an inert gas. The process starts with the application of
a rising current to the metallic wire, in which high heat generated makes the wire to
vaporize and create an electric arc, which is the responsible of the explosion. The
average particle size, its properties, and chemical composition can be determined
using different parameters, such as the voltage of the capacitor used to generate the
current, which leads to a wide variety of products (Tarasov et al. 2002).
Vacuum vapor decomposition (VDD): this method is usually employed for producing copper nanorods and nanowires, under very low pressure or vacuum conditions, where copper vapor is generated and then re-deposited on a specific target/
substrate. VDD was proposed by Liu and Bando (2003), where they used a tiny
cooper ring inside a dry pumping station with a low pressure to generate the vapor
and a molybdenum grid as the substrate. The diameter of the copper nanorods
formed varied from 50 to 100 nm.
Sonochemical reduction: Vijaya Kumar et al. (2001) showed that it is possible to
synthesize amorphous Cu and nanocrystalline Cu 2 O using an ultrasonic horn
(Ti-horn, 20 kHz, 100 W cm
−2
) and aniline as a solvent. With the methodology proposed, the authors have obtained Cu particles from 4 to 10 nm and Cu 2 O particles
from 5 to 13 nm, with a suitable distribution within the polyaniline matrix.
Chemical reduction: this method is perhaps the most popular synthesis method
for obtaining Cu nanoparticles (Suárez-Cerda et al. 2017), due to the easy control of
F. F. Pereira et al.