1. Introduction

Magnetic nanoparticles (NPs) are attracting increased researchers' interest due to their potential wide use in many engineering and medical applications. The most commonly used magnetic materials are Fe2O3, Fe3O4, Ni, Co, CoO, and Co3O4. However, among all these magnetic materials, cobalt oxide (Co3O4) nanoparticles are being preferred due to their good magnetic properties. Pure cobalt is not stable at room temperature as it can be converted to oxides like CoO, Co2O3, and Co3O4; Co3O4 is the most stable phase. It is a P-type semiconductor, and it has high Young's modulus, which varies between 116 and 160 GPa. Co3O4 exhibits a normal spinel crystal structure with occupation of tetrahedral sites by Co2+ and octahedral sites by Co3+. Its magnetic moment arises due to Co2+ ions largely because of spins, with a small contribution from spin-orbit coupling. Co3O4 has excellent properties such as gas-sensing, catalytic, and electrochemical properties, and it has been studied

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

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

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

Figure 1.

Figure 2.

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

TEM image of synthesized Co3O4 nanoparticles [12].

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

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 are toxic.

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 composite materials are also reviewed.
