2. Cobalt oxide (Co3O4) nanoparticles

#### 2.1 Synthesis procedure

There are different methods to synthesize Co3O4 nanoparticles, which, among others, are chemical coprecipitation, mechanochemical reaction, thermal decomposition and oxidation route, and long-time calcining method. Manigandan et al. [11] used thermal decomposition method for the synthesis of Co3O4 nanoparticles by dispersing 0.01 M cobalt chloride in 500 mL distilled water and 10% of glycerol. The suspension was stirred for 20 min by a magnetic stirrer at a temperature of 50°C; after that the dissolved ammonium hydroxide solution (50 mL) was added slowly to control the agglomeration. The obtained cobalt hydroxide is calcined in air for 3 h at a temperature of 450°C yielding the Co3O4 nanoparticles. The TEM image of the synthesized Co3O4 nanoparticles is shown in Figure 1. Salavati-Niasari et al. [13] prepared Co3O4 nanoparticles from a solid organometallic molecular precursor of N,N<sup>0</sup> -bis(salicylaldehyde)-1,2-phenylenediamino cobalt(II); Co(salophen) estimated the magnetic behavior of the Co3O4 nanoparticles. In another study, Salavati-Niasari et al. [14] used thermal deposition method for the preparation of

The Cobalt Oxide-Based Composite Nanomaterial Synthesis and Its Biomedical and Engineering… DOI: http://dx.doi.org/10.5772/intechopen.88272

Co3O4 nanoparticles by using benzene dicarboxylate complexes, especially phthalate ones, as precursors and characterized using Fourier transform infrared and X-ray photoelectron spectroscopy and observed temperature-dependent

Figure 1. TEM image of synthesized Co3O4 nanoparticles [12].

widely for applications in solid-state sensors, electrochromic devices, and heterogeneous catalysts as well as lithium batteries and also medical applications [1–5]. There are several methods to synthesize the Co3O4 nanoparticles, which include the Co3O4 nanowires [6], the surfactant-templated approach for fabricating Co3O4 nanoboxes [7], the mechanochemical reaction method for the synthesis of Co3O4 nanoparticles [8], the thermal decomposition and oxidation route for the growth of

Some of the reports dealing with the synthesis of Co3O4 nanoparticles and their potential use are succinctly reviewed below. Manigandan et al. [11] used the thermal decomposition method. Mariano et al. [12] synthesized Co3O4 nanoparticles and prepared ethylene glycol-based nanofluids. Salavati-Niasari et al. [13] prepared Co3O4 nanoparticles from solid organometallic molecular precursors. Salavati-Niasari et al. [14] used another method by considering benzene dicarboxylate complexes, in particular phthalate ones, as precursors. Alrehaily et al. [15] synthesized Co3O4 nanoparticles by gamma irradiation. All the above researchers synthesized the Co3O4 nanoparticles for engineering applications. Cavallo et al. [16] studied the cytotoxicity of Co3O4 nanoparticles in human alveolar (A549) and bronchial (BEAS-2B) cells. Alarifi et al. [17] investigated the toxicity of Co3O4 nanoparticles in HepG2 cells. Based on these studies, pure Co3O4 nanoparticles

Cobalt-based compounds also offer interesting advantages in various applications; typical cobalt-based compounds are grapheme oxide/cobalt oxide, nanodiamond-cobalt oxide, zeolite Y/cobalt oxide, and carbon nanotubes/cobalt oxide. Syam Sundar et al. [18] synthesized GO/Co3O4 hybrid nanoparticles and studied their thermal properties. Syam Sundar et al. [19] also synthesized ND-Co3O4 nanoparticles and investigated their thermal properties and toxicity. Shi et al. [20] prepared different concentrations of Co3O4/GO, studied their catalyst activity, and observed the highest catalytic activity when the Co3O4 mass loading was about 50% in the catalyst. Xiang et al. [21] synthesized rGO/Co3O4, which was used as the pseudocapacitor electrode in the 2 M KOH aqueous electrolyte solution. This book chapter emphasizes on the various synthesis methods for cobalt oxide and engineering and medical applications of this material. In addition, synthesis, characterization, and engineering and medical applications of cobalt oxide-based

There are different methods to synthesize Co3O4 nanoparticles, which, among others, are chemical coprecipitation, mechanochemical reaction, thermal decomposition and oxidation route, and long-time calcining method. Manigandan et al. [11] used thermal decomposition method for the synthesis of Co3O4 nanoparticles by dispersing 0.01 M cobalt chloride in 500 mL distilled water and 10% of glycerol. The suspension was stirred for 20 min by a magnetic stirrer at a temperature of 50°C; after that the dissolved ammonium hydroxide solution (50 mL) was added slowly to control the agglomeration. The obtained cobalt hydroxide is calcined in air for 3 h at a temperature of 450°C yielding the Co3O4 nanoparticles. The TEM image of the synthesized Co3O4 nanoparticles is shown in Figure 1. Salavati-Niasari et al. [13] prepared Co3O4 nanoparticles from a solid organometallic molecular precursor of


Co3O4 nanorods [9], and the Co3O4 nanowalls [10].

Cobalt Compounds and Applications

composite materials are also reviewed.

2.1 Synthesis procedure

N,N<sup>0</sup>

32

2. Cobalt oxide (Co3O4) nanoparticles

are toxic.

Figure 2. Co3O4 nanofluids: (a) thermal conductivity and (b) viscosity [12].

magnetization curve in zero-field-cooled, where Co3O4 nanoparticles exhibit weak ferromagnetism. Alrehaily et al. [15] synthesized Co3O4 nanoparticles by gamma irradiation of 0.2–0.3 mM of CoSO4 solutions. Syam Sundar et al. [18] used chemical coprecipitation method for the synthesis of Co3O4 nanoparticles, and they estimated their thermal properties at different particle volume concentrations and temperatures.

2.2 Thermal properties

DOI: http://dx.doi.org/10.5772/intechopen.88272

2.3 Toxicity

Figure 5.

35

HepG2 cells [17].

Co3O4 nanofluids have a potential use in several mechanical engineering applications; in particular, as replacement of low thermal conductivity fluids such as water and ethylene glycol, as a consequence, the thermal properties of nanofluids are of great interest. Mariano et al. [12] prepared Co3O4 nanofluids by dispersing cobalt(II, III) oxide nanopowder in ethylene glycol and determined experimentally their thermal conductivity and viscosity. The thermal conductivity and viscosity of Co3O4/EG nanofluids are shown in Figure 2a and b; it is noticed that the increase of particle volume concentration ð Þ ϕ yields increased values of thermal conductivity and viscosity. They observed thermal conductivity enhancement for 5.7% volume

The Cobalt Oxide-Based Composite Nanomaterial Synthesis and Its Biomedical and Engineering…

concentration of Co3O4/EG nanofluids is 27% at temperature of 323.15 K

of Co3O4/EG nanofluids is 40% at a temperature of 303.15 K (Figure 2b).

(Figure 2a); similarly, the viscosity enhancement for 5.7% volume concentration

Knowledge about the toxicity of Co3O4 nanoparticles is very important consid-

ering their eventual use in medical applications. Cavallo et al. [16] studied the cytotoxicity of Co3O4 nanoparticles in human alveolar (A549) and bronchial

Co3O4 nanoparticle toxicity in HepG2 cells: representative microphotographs showing Co3O4 NP- and Co2+-induced ROS generation in HepG2 cells. Images were snapped with Nikon phase contrast with a fluorescence microscope. (A) Control, (B) 15 μg/mL of Co2+, (C) 15 μg/mL of Co3O4NPs, and (D) percentage change in ROS generation after 24 and 48 h of exposure to various concentrations of Co3O4NPs and Co2+ in

#### Figure 3.

Co3O4 nanoparticle toxicity in A549 cells: hydrodynamic size distributions of Co3O4 nanoparticles in RPMI 1640 medium with 10% fetal bovine serum (FBS) at t = 0 and after a 24-h exposure without and with A549 cells. In the right panels, the relative Co3O4 NP suspensions used for DLS measurements, showing NP sedimentation after a 24-h exposure in the medium without cells [16].

#### Figure 4.

Co3O4 nanoparticle toxicity in BEAS-2B cells: hydrodynamic size distribution of Co3O4 nanoparticles in BEGM medium at t = 0 and after a 24-h exposure without and with BEAS-2B cells [16].

The Cobalt Oxide-Based Composite Nanomaterial Synthesis and Its Biomedical and Engineering… DOI: http://dx.doi.org/10.5772/intechopen.88272
