180
Dry Methods
Solid-state synthesis: this synthesis method consists of the use of the precursors that
are first milled and then calcinated at a high temperature (typically above 700 °C),
leading to the formation of a well-crystallized structure (Monmaturapoj and
Yatongchai 2010; Qi et al. 2017). The precursors can be, for example, CaCO 3
and CaHPO 4 .
Molten salt synthesis: it employs a molten salt for preparing complex oxides
from their constituent materials as oxides and carbonates. This method allows synthesizing hydroxyapatite nanoparticles with high thermal stability but having the
inconvenience of employing high temperatures (>800 °C) (Taş 2004; Sadat-Shojai
et al. 2013; Qi et al. 2017).
7.2.5 Silver Nanoparticles
There are several methods available for synthesizing silver nanoparticles (Silva
et al. 2017a), which can be divided into chemical, physical, and biological methods
(Silva et al. 2017a; Ahmed et al. 2017) Tran et al. 2013), which employ bottom-up
and top-down approaches (Tolaymat et al. 2010; Abou El-Nour et al. 2010; Silva
et al. 2017a; Ahmed et al. 2017). Bottom-up approaches are those based on chemical methods that make silver nanoparticles from silver atoms (Tolaymat et al. 2010).
On the other hand, top-down approaches are mainly physical methods that employ
mechanical forces to downgrade macroscopic silver to the nanoscale size (Ju-Nam
and Lead 2008). More details on some of the synthesis methods are given below.
Chemical approach: this is the most common method used for obtaining silver
nanoparticles (Sharma et al. 2009; Tolaymat et al. 2010). Chemical silver nanoparticles can be synthesized by basic elements/ingredients, including metal salt precursors, solvents, reductants, and stabilizing agents (Tolaymat et al. 2010; Tran et al.
2013). In this method, ionic silver is reduced and then precipitated to form the
nanoparticles (Rai et al. 2009; Tran et al. 2013). Silver nitrate is the most used salt
precursor (Tolaymat et al. 2010), owing to the chemical stability and low cost, followed by silver acetate, silver perchlorate, silver sulfate, and others of low use.
Water is used as solvent in about 80% of the synthesis processes, followed by ethanol, dimethylformamide (DMF), EG, toluene, and others of less importance
(Tolaymat et al. 2010). Reductants are important for providing free electrons to
reduce silver ions and form nanoparticles (Tolaymat et al. 2010). The most used
reductant agents are borohydride and citrate, and others such as ascorbate and elemental hydrogen (Tolaymat et al. 2010; Abou El-Nour et al. 2010; Becaro et al.
2015; Ahmed et al. 2017, Trans et al. 2013). Stabilizing agents are used to prevent
particles from aggregation and to yield nanoparticle of uniform size. The most used
stabilizing agents for silver nanoparticle synthesis are citrate, PVP, amines, amide,
and others (Tolaymat et al. 2010).
F. F. Pereira et al.
Dry Methods
Solid-state synthesis: this synthesis method consists of the use of the precursors that
are first milled and then calcinated at a high temperature (typically above 700 °C),
leading to the formation of a well-crystallized structure (Monmaturapoj and
Yatongchai 2010; Qi et al. 2017). The precursors can be, for example, CaCO 3
and CaHPO 4 .
Molten salt synthesis: it employs a molten salt for preparing complex oxides
from their constituent materials as oxides and carbonates. This method allows synthesizing hydroxyapatite nanoparticles with high thermal stability but having the
inconvenience of employing high temperatures (>800 °C) (Taş 2004; Sadat-Shojai
et al. 2013; Qi et al. 2017).
7.2.5 Silver Nanoparticles
There are several methods available for synthesizing silver nanoparticles (Silva
et al. 2017a), which can be divided into chemical, physical, and biological methods
(Silva et al. 2017a; Ahmed et al. 2017) Tran et al. 2013), which employ bottom-up
and top-down approaches (Tolaymat et al. 2010; Abou El-Nour et al. 2010; Silva
et al. 2017a; Ahmed et al. 2017). Bottom-up approaches are those based on chemical methods that make silver nanoparticles from silver atoms (Tolaymat et al. 2010).
On the other hand, top-down approaches are mainly physical methods that employ
mechanical forces to downgrade macroscopic silver to the nanoscale size (Ju-Nam
and Lead 2008). More details on some of the synthesis methods are given below.
Chemical approach: this is the most common method used for obtaining silver
nanoparticles (Sharma et al. 2009; Tolaymat et al. 2010). Chemical silver nanoparticles can be synthesized by basic elements/ingredients, including metal salt precursors, solvents, reductants, and stabilizing agents (Tolaymat et al. 2010; Tran et al.
2013). In this method, ionic silver is reduced and then precipitated to form the
nanoparticles (Rai et al. 2009; Tran et al. 2013). Silver nitrate is the most used salt
precursor (Tolaymat et al. 2010), owing to the chemical stability and low cost, followed by silver acetate, silver perchlorate, silver sulfate, and others of low use.
Water is used as solvent in about 80% of the synthesis processes, followed by ethanol, dimethylformamide (DMF), EG, toluene, and others of less importance
(Tolaymat et al. 2010). Reductants are important for providing free electrons to
reduce silver ions and form nanoparticles (Tolaymat et al. 2010). The most used
reductant agents are borohydride and citrate, and others such as ascorbate and elemental hydrogen (Tolaymat et al. 2010; Abou El-Nour et al. 2010; Becaro et al.
2015; Ahmed et al. 2017, Trans et al. 2013). Stabilizing agents are used to prevent
particles from aggregation and to yield nanoparticle of uniform size. The most used
stabilizing agents for silver nanoparticle synthesis are citrate, PVP, amines, amide,
and others (Tolaymat et al. 2010).
F. F. Pereira et al.