181
Physical approach: this method involves mechanical approaches such as grinding, milling, and thermal/laser ablation (Ahmed et al. 2016) to produce the nanoparticles. Other physical methods include thermal decomposition and
evaporation–condensation with tube furnace at atmospheric pressure. However, the
latter has a number of disadvantages, such as the room necessary for the equipment,
energy consumption, and temperature stability (Abou El-Nour et al. 2010).
Biological and green syntheses: more recently, biological and green syntheses
(Ahmed et al. 2016; Tran et al. 2013) of silver nanoparticles have gained some
popularity (Silva et al. 2017a). Silver nanoparticles obtained by biological synthesis
are those produced by living organisms (Tran et al. 2013), such as bacteria (e.g.,
Bacillus sp and Lactobacillus), fungi, yeasts, or algae (Kaler et al. 2010).
Plant extracts such as Cassia angustifolia and Daucus carota (Kaler et al. 2010;
Tran et al. 2013) have been studied, and many authors consider that such synthesis
is environmental friendly due to the high rate of metal ion reduction (Ramya and
Subapriya 2012) Tran et al. 2013). However, contaminants and restrictions on replying results can be considered as a limitation (Kumar and Yadav 2009; Kumar et al.
2010; Kumar and Yadav 2012; Silva et al. 2017b).
7.2.6 Zinc Oxide Nanoparticles
Mechanochemical processing (MCP) and physical vapor synthesis (PVS) are two
widely used methods employed for obtaining zinc oxide nanoparticles (Espitia et al.
2012), but other synthetic methods can be considered, such as precipitation, thermal
decomposition, and hydrothermal synthesis. MCP combines physical and chemical
methods, where the particles are reduced mechanically and chemically during milling. It is a simple and low-cost method and does not involve organic solvents, being
less harmful to environment (Lu et al. 2008; Espitia et al. 2012). Physical vapor
synthesis (PVS) consists of the application of plasma arc energy under high temperature on contact with a solid precursor, requiring high energy to produce the
reactions (Moezzi et al. 2012; Espitia et al. 2012). Chemical methods that are also
employed for obtaining zinc oxide nanoparticles include microemulsion, Sol–gel
method, precipitation, chemical reduction, hydrothermal method, solvothermal
method, and chemical vapor deposition. More recently, biological methods have
become an important methodology for obtaining zinc oxide nanoparticles (Dobrucka
and Długaszewska 2016; Ahmed et al. 2017). However, biological methods involve
a number of steps, as the selection of the organisms is more adapted to this function
and appropriate conditions, which hinders industrial applications.
7 Toxicity of Engineered Nanostructures in Aquatic Environments
Physical approach: this method involves mechanical approaches such as grinding, milling, and thermal/laser ablation (Ahmed et al. 2016) to produce the nanoparticles. Other physical methods include thermal decomposition and
evaporation–condensation with tube furnace at atmospheric pressure. However, the
latter has a number of disadvantages, such as the room necessary for the equipment,
energy consumption, and temperature stability (Abou El-Nour et al. 2010).
Biological and green syntheses: more recently, biological and green syntheses
(Ahmed et al. 2016; Tran et al. 2013) of silver nanoparticles have gained some
popularity (Silva et al. 2017a). Silver nanoparticles obtained by biological synthesis
are those produced by living organisms (Tran et al. 2013), such as bacteria (e.g.,
Bacillus sp and Lactobacillus), fungi, yeasts, or algae (Kaler et al. 2010).
Plant extracts such as Cassia angustifolia and Daucus carota (Kaler et al. 2010;
Tran et al. 2013) have been studied, and many authors consider that such synthesis
is environmental friendly due to the high rate of metal ion reduction (Ramya and
Subapriya 2012) Tran et al. 2013). However, contaminants and restrictions on replying results can be considered as a limitation (Kumar and Yadav 2009; Kumar et al.
2010; Kumar and Yadav 2012; Silva et al. 2017b).
7.2.6 Zinc Oxide Nanoparticles
Mechanochemical processing (MCP) and physical vapor synthesis (PVS) are two
widely used methods employed for obtaining zinc oxide nanoparticles (Espitia et al.
2012), but other synthetic methods can be considered, such as precipitation, thermal
decomposition, and hydrothermal synthesis. MCP combines physical and chemical
methods, where the particles are reduced mechanically and chemically during milling. It is a simple and low-cost method and does not involve organic solvents, being
less harmful to environment (Lu et al. 2008; Espitia et al. 2012). Physical vapor
synthesis (PVS) consists of the application of plasma arc energy under high temperature on contact with a solid precursor, requiring high energy to produce the
reactions (Moezzi et al. 2012; Espitia et al. 2012). Chemical methods that are also
employed for obtaining zinc oxide nanoparticles include microemulsion, Sol–gel
method, precipitation, chemical reduction, hydrothermal method, solvothermal
method, and chemical vapor deposition. More recently, biological methods have
become an important methodology for obtaining zinc oxide nanoparticles (Dobrucka
and Długaszewska 2016; Ahmed et al. 2017). However, biological methods involve
a number of steps, as the selection of the organisms is more adapted to this function
and appropriate conditions, which hinders industrial applications.
7 Toxicity of Engineered Nanostructures in Aquatic Environments