1. Introduction
Co
3O
4 nanomaterials is one of the important nanoparticles that can provide valuable insights into the development of sensors for analytical chemistry. Recently, these nanoparticles have attracted a lot of interest because of their wide range of uses in sensors, energy storage, catalysis, environmental remediation, and among other areas. The chemical name for the inorganic compound Co
3O
4 is cobalt (II, III) oxide or Tri-cobalt-tetraoxide. It is one of the two well-defined cobalt oxides when mixed with cobalt oxide (CoO), Due to its mixed valence of Co(II) and Co(III), some cobalt atoms have a charge of +2, while others have a charge of +3. This can be shown by writing the formula as (CoO•Co₃O₄). Cobalt oxide has a 6.11gr/cm
3 density and melts at 895C
o, these particles are magnetic materials with a white tone. likewise, they have positive charge carriers considering they are P-type semiconductors [
28]. The energy required to excite electrons from the valence band to the conduction band is known as the band gap and they have two of them. Abu-Zied et al. (2020) showcased the utility of Co
3O
4 nanoparticles as an efficient sensor for hydroquinone (HQ), describing its role in analytical chemistry applications for detecting chemical species. A major aspect of these applications is the synthesis of Co₃O₄ nanoparticles, and The solution combustion allows for the synthesis of a wide range of nanoscale materials, including metals, metal oxides, alloys, and sulfides. especially this approach has been proven to be a suitable and more effective way for obtaining these nanomaterials with specific properties [37, 28, 20]. Co
3O
4 nanoparticles synthesized by solution combustion approach, provide unique prospects for a variety of applications. due to the unique properties and many proses of these nanoparticles recently many scientists and researchers had focused to study Co
3O
4 nanoparticles in a wide range of fields, many researches and articles published as shown in (
Figure 1).
Solution combustion synthesis can be classified according to the chemical composition of fuel, oxidizer, and solvent, different types of organic fuels or their mixtures are typically dissolved in a solvent with cobalt nitrate hydrates [
37]. The solution combustion method involves the exothermic reaction between cobalt cantaining precusor and a fuel, the kinetics of a reaction, describes the rate at which the system moves to equilibrium, is important from a practical point of view, and defines the characteristic temperature and synthesis processing time, which in turn controls the formation of the products with desired properties. Solution combustion synthesis of Co
3O
4 nanoparticles has proven to be a robust method, offering tailored properties for diverse applications, ranging from energy storage to environmental remediation [
37]. Numerous studies from different countries and universities as shown in (
Figure 2) have explored the potential of Co
3O
4 nanoparticles synthesized via the solution combustion method across diverse fields. The aim of this review is to present a thorough overview of the synthesis of Co
3O
4 nanoparticles using the solution combustion method, exploring their properties, components, synthesis process, applications, characterization methods and a comprehencive comparison of the previous work releated to Co
3O
4 nanoparticles performance and production. Many investigations have studied the synthesis of Co
3O
4 nanoparticles using solution combustion, examining crucial factors, such as the ratio of fuel to oxide, precursor materials, and reaction conditions. For instance, Michalska et al. (2021) demonstrated the application of nanometer-scale Co
3O
4 as an anode material for Li-ion batteries, showcasing its promise in energy storage applications. Acedera et al. (2020) investigated the use of porous Co
3O
4 nanoparticles as electrocatalysts for the oxygen evolution reaction (OER) in an alkaline medium, highlighting their potential in renewable energy technologies and emphasizing the vital role of these nano materials in energy conversion technologies. Kumar et al. (2021) investigated how the structural and physical properties of nanocrystalline Co
3O
4 were affected by the fuel-to-oxidizer ratio. Murayama et al. (2019) investigated two methods for low-temperature synthesis; the solution combustion method and the metal-organic framework-decomposition approach, recognizing the features of Co
3O
4 nanoparticles is essential in customizing their abilities for certain uses. Singhal et al. (2016), concentrated on the electrochemical characteristics of Co
3O
4 and its quick, one-pot production in several electrolytes. Deng et al. (2014) focused on Co
3O
4 nanoparticles as supercapacitor electrode materials. Co
3O
4 nanoparticles produced by the solution combustion process have a wide range of uses.
To emphasize the adaptability of these nanoparticles in energy storage devices, it is essential to understand the structure of Co3O4 nanoparticles in order to maximize their effectiveness, by concentrating on morphological characteristics. Keneshbekova et al. (2023) explored the Morphological features of Co3O4 nanoparticles obtained by the solution combustion method, providing valuable insights into their structural characteristics and the finer points of particle creation. Beyond energy storage and electrocatalysis, Co3O4 nanoparticles have found applications in environmental remediation. El-Shafie et al. (2022) investigated the synthesis and application of Co3O4-impregnated biochar for the removal of pharmaceutical contaminants, highlighting its potential in water treatment. Farhadi et al. (2016) characterized cobalt oxide nanoparticles prepared via the thermal decomposition of a complex and explored their photocatalytic activity, showcasing their multifunctional applications. Jahani et al. (2020) investigated the impact of Co3O4 nanoparticles on Brassica napus L., and focused on ion leakage, total phenol, antioxidant enzyme activities, and cobalt accumulation. Furthermore, research by Pagar et al. (2019) described how Co3O4 nanoparticles impacted plants and investigated Co3O4 nanoparticles that were biosynthesized using plant extracts, respectively.
Our work includes a comparison of previous investigations on the synthesis of Co3O4 nanoparticles using the solution combustion method, examining their properties, synthesis processes, applications, and characterization. A comprehensive understanding of the developments and possible future directions in the field of Co3O4 nanoparticles can be obtained by examining these publications.
2. Synthesis of Co3O4 Nanoparticles by Solution Combustion Method
The solution combustion method is a widely employed technique for synthesizing Co
3O
4 nanoparticles due to its simplicity and scalability. Initial precursors are solid powders of different oxidizers (typically metal nitrites) and fuels (e.g., glycine, citric acid, and urea). These powders have high solubility in solvents (e.g., water). The reactive solution is the oxidizer and fuel dissolved in a desired ratio in a solvent [
34]. Synthesized nanoparticles by solution combustion method have highly magnetic characteristics and are useful for different bio-applications [
15]. Using cobalt nitrate as an initial precursor results in the formation of nanoscale Co
3O
4 particles [28, 20].
For sure preparation of precursors, weighed a calculated amount of cobalt nitrate hexahydrate (Co(NO
3)
2·6H
2O) in different ratios, φ (0.5, 1.0 and 1.5) based on the desired Co
3O
4 nanoparticle size to Synthesize the Co
3O
4 nanoparticles by the solution combustion method [21, 82]. Dissolved the oxidizor in deionized water to form a clear solution. When the precursor is prepared then in fuel Addition term, a calculated amount of the fuel to the cobalt nitrate solution is added. The solution vigorously Stired to ensure complete dissolution of the fuel and the crucible containing precursor solution placed on a hotplate for placing the solution combustion,. When the resulting gel precursor is heated within a temperature range of 300 to 900
oC for 1-2h in air. The exothermic reaction results in the formation of Co
3O
4 nanoparticles [
21]. Once the combustion reaction is complete, quenched the reaction by adding ethanol to the hot solution. Collected the precipitated Co
3O
4 nanoparticles by centrifugation or filtration. Washed the obtained nanoparticles with ethanol and deionized water to remove residual reactants. Then dried the collected nanoparticles at a moderate temperature. Optionally, anneal the dried nanoparticles to enhance crystallinity and structural stability [
21]. The combustion reaction involves decomposition of precursors, fuel oxidation, combustion reaction and cobalt oxide formation steps, such as Cobalt nitrate hexahydrate decomposes upon heating to produce cobalt oxide species (2). The citric acid fuel acts as a reducing agent and gets oxidized (3). The generated carbo monoxide (CO) from the fuel reacts with the oxygen released during the decomposition of cobalt nitrate, resulting in the combustion of the fuel (4). The high-temperature environment facilitates the formation of Co
3O
4 nanoparticles (5).
Michalska et al. (2021) successfully utilized this method to produce Co
3O
4 anode materials for Li-ion batteries, emphasizing the nanoscale precision achieved through this approach. As shown in (
Figure 3), Powder X-ray diffraction (XRD) and Raman spectroscopy (RS) are used to characterize the structural properties of the Co
3O
4 nanoparticles. First, the Co
3O
4 nanoparticles have been found to have a crystalline nature by XRD pattern. For the observation of their surface morphology and particle size scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used. it may be concluded that the cobalt oxide consists of particles measuring 12-60 nm, with an average size of about 36 nm and loose arrangement featuring several empty spaces from the SEM and TEM imaging results [
28].
Solution combustion synthesis is best method to produce high quality Co
3O
4 nanoparticles that have great electrochemical activity used as the electrodes in lithium-ion battery. Obtained Co
3O
4 nanoparticles has specific capacity of 1060 mAhg
-1 (which is achieved in 100 cycles on the current density 100 mAg
-1) as shown in (
Figure 4 a, b). Besides, they exhibit impressive cyclability at the respective present densities between 50 and 5kmA g
-1 [
28].
In Afrooze et al. (2024) investigation the electrical tests revealed that the capacitance of the Co
3O
4 nanoparticles was 603 Fg
-1 (1 mVs
-1), and the cyclic stability of Co
3O
4 nanoparticles evaluated 97.6 % at 10 mVs
-1 scan rate for 5000 cycles. Electrochemical characteristics of cobalt oxide (Co
3O
4) nanoparticles could provide high-performance and longer-lasting Li-ion batteries [
16]. It can reversibly store eight lithium ions according to the following conversion reaction (1). The number of studies that have been revealed that they are excellent electrocatalysts [
6] as they are abundant, cheap, sensitive to the environment, and in some cases equal activity exactly like the noble metal-based catalyst. They have significant influences or can say critical effects of calcination temperature, pH, and fuel-to-oxidizer ratio on the morphology, phase composition, crystalline structure and OER function of the synthesized nanoparticles [
2]. Co
3O
4 nanoparticles prepared with an optimized amount of precursor (i.e., when the ratio of cobalt nitrate and ascorbic acid is 1:1) have increased activity towards oxygen evolution reaction. Maurya et al. (2023) employed a synthesis of Co
3O
4 nanoparticles involving the introduction of a copper interlayer to tune the reactivity of Co
3O
4 towards the OER. The controlled synthesis procedure aimed at enhancing the electrochemical performance of Co
3O
4 in oxygen evolution. The samples with lower/higher amounts of precursors described the detriment in activity with copper interlayer. This effect is due to the presence of Co
+3 at the surface. The solution combustion synthesis approach has several advantages, including its low cost and the use of a less toxic reducing component. Furthermore, compared to the produced nanoparticles exceeding earlier reported, Co
3O
4 nanostructures tested as anode coating materials in terms of electrochemical efficiency, exhibit better electrochemical performance [
28].
Synthesized Co
3O
4 nanoparticles include a porous structure with a high specific surface area and a spinel-type crystal structure with a cubic shape. It also has a foam-like shape with pores that are micro- and nano-sized, that exhibit several beneficial characteristics for electrocatalytic applications. Due to their specific surface area, crystallinity, and porosity these nanoparticles have exceptional catalytic activity for the oxygen evolution reaction [2, 6]. Vennela et al. (2019) has been studied the crystallite size of the Co
3O
4 nanoparticles. The lattice parameters of Co
3O
4 are calculated to be in good agreement with the theoretical value for spinel Co
3O
4 nanoparticles, indicating the stability of the crystal structure [
2]. Additionally, high-resolution transmission electron microscopy (HRTEM) images show well-resolved lattice fringes, confirming the crystallinity of Co
3O
4 nanoparticles. The catalytic performance is attributed to factors, such as the specific surface area, crystallinity and porosity of the nanoparticles [
43].
Figure 5.
Procedure of the Co3O4 nanoparticles synthesis by SCS.
Figure 5.
Procedure of the Co3O4 nanoparticles synthesis by SCS.
Synthesis of Co
3O
4 nanoparticles by solution combustion method can be done in different conditions as shown in (
Table 1). For instance, control over the average particle size range was achieved by tuning the reaction ignition temperature between 300
oC and 800
oC. Transmission electron microscopy (TEM) studies revealed an increase in the size range from 5–8 nm to 200–400 nm for Co
3O
4 nanoparticles synthesized at 300
oC and 800
oC, respectively. Magnetic susceptibility measurements revealed a dominant antiferromagnetic (AFM) ordering and the temperature decreases with a decreasing average particle size range from (200–400 nm) to (5–18 nm) [
32]. In a further low-temperature oxidation (190−240°C) step, very small Co
3O
4 particle size (2.3−7.4 nm) could be achieved for high loadings of Co
3O
4 (up to 59%) in the carbon network [
46], the pyrolysis and oxidation temperature increase led to an increase of nanoparticle size, porosity and electronic conductivity. both the crystallite size and the lattice parameter nanocrystalline Co
3O
4 increase with increasing the molar ratio of fuel(F)/oxidizer(O) as well as the calcination temperature [
27]. At high temperature the combustion of cobalt nitrate hexahydrate (Co(NO
3)
2·6H
2O) with citric acid (C
6H
8O
7) fuel leads to the formation of nanometer-scale Co
3O
4 particles, which are proposed as an anode material for Li-ion batteries [
28]. In solution combustion synthesis the change of the molar ratio of F/O, calcination temperature effects on the production of composite’s components, size morphology and specific surface area of the obtained Co
3O
4 nanoparticles [27, 45]. In alkaline medium, the combustion synthesis is performed using cobalt nitrate hexahydrate and citric acid, the reaction takes place in an alkaline medium [2, 44], such as the solution combustion method results in the formation of porous Co
3O
4 nanoparticles, designed for use as oxygen evolution reaction (OER) electrocatalysts in alkaline environments. Synthesis and application of cobalt oxide-impregnated olive stones biochar for the removal of rifampicin and tigecycline with multivariate controlled performance [12, 13].
Brunauer Emmett Teller (BET ) is performed to evaluate the specific surface area and porosity of Co
3O
4 nanoparticles [
2]. According to the (
Table 2), synthesis methods, raw materials and temperature are effectiveness on the porosity and specific surface area of the obtained nanocatalyst. In Acedera et al. (2020) investigation mentioned the Synthesis of foam-like Co
3O
4 nanoparticles through SCS that process parameters, such as fuel type and fuel-to-oxidizer ratio, have been correlated with the resulting morphological, structural, optical, and capacitive properties of Co
3O
4. On the other hand, utilizing ethylene di amine tetra acetic acid (EDTA) as fuel produced Co
3O
4 with BET surface area of 23 m
2g
-1 [
2].
TGA is employed to study the thermal stability and composition changes of Co
3O
4, [
12] Two samples were examined in El-Shafie et al. (2022) investigation using the TGA. As shown in (
Figure 7) the results reveal that both samples are thermally stable in the (100–450
oC) temperature for OSBC and Co-OSBC The weight loss between (50-100
oC) was (7.09%-9.69%), it may be ascribed to free water vaporization. Otherwise, a loss of 31.06% and 38.02% was observed for OSBC and Co-OSBC between (550–800
oC), which might be attributed to the loss of carbonization of polymeric material or other organic content [
12].
Co
3O
4 gives best performance for Electrochemical Characterization that can be used Cyclic Voltammetry (CV) and Galvanostatic Charge-Discharge (GCD), Used to evaluate the electrochemical properties, such as capacitance and charge-discharge behavior, for supercapacitor applications [10, 16]. Deng et al. (2014) investigation in agreement with the CV results, the GCD data determined that specific capacitances of sample-I, -II, -III and -IV were 73.1 F·g
−1, 179.7 F·g
−1, 141.6 F·g
−1 and 130.5 F·g
−1 at a current density of 0.2 Ag
−1, respectively. As shown in (
Figure 8) both measurements indicated that sample II showed the best capacitor performance among samples.
The rate performance of Co
3O
4 has been investigated by recording GCD curves at different current densities at the potential range between (0-0.35 v), the results are shown in (
Figure 10, c). The nonlinearity in the discharge curves shows the pseudo capacitance behavior of Co
3O
4, which corresponds well with the CV test as shown in (
Figure 10 a, b), for sample II-350. At the current densities between 0.2-4 Ag
−1, the specific capacitances of sample-II-350 Co
3O
4 electrode ranged from 362.8 - 285.7 Fg
−1 (
Figure 10, d). It is also found that even at a high current density of 4 Ag
−1, nearly 78.7% of the initial capacitance value remains, demonstrating excellent rate performance of the sample-II-350 Co
3O
4 electrode as shown in (
Figure 9).
These comprehensive characterization processes integrate various analytical techniques, provided a thorough understanding of the structural, morphological, chemical, and functional properties of Co3O4 nanoparticles synthesized through the solution combustion method.
3. Application
Cobalt oxide nanoparticles have a wide range of applications, such as a few examples of these nanoparticles are applications in biomedical science (antibacterial, antifungal, antiviral, antileishmanial, medications, anticancer, and drug delivery), gas sensors, solar specific absorbing materials, anode materials in lithium-ion batteries, energy storage, pigments and dyes, electromagnetic field-emitting materials, capacitors, diverse catalysis, magneto-resistive devices, and electronic lightweight films [42, 5, 16]. These applications underscore the versatility and significance of Co
3O
4 nanoparticles in various scientific and technological fields. Such as, Co
3O
4 nanoparticles exhibit promising capabilities in environmental remediation. Their application in wastewater treatment and pollutant removal displays their potential for addressing environmental challenges [31, 8]. Co
3O
4 nanoparticles exhibit sensitivity to various analyst, making them suitable for sensor applications. Integration of Co
3O
4 nanoparticles into sensor devices enhances detection capabilities in environmental monitoring and healthcare fields. Also exhibiting magnetic properties make them suitable for applications in magnetic resonance imaging, allow to enhance the contrast and diagnostic capabilities of MRI techniques [
31]. Because of their distinctive properties like Co
3O
4 is a p-type antiferromagnetic semiconductor with a direct optical band gap that is between (1.48-2.19 eV). Cobalt, [
9] and cobalt oxide (Co
3O
4) nanoparticles have attracted the most attention in many areas as shown in (
Figure 11), are abounding in nature. Only Co
3O
4 and CoO are stable, with having highest stability, Catalytic and Photocatalytic properties. Farhadi et al. (2016) investigated the photocatalytic activity of cobalt oxide nanoparticles produced by the thermal decomposition of a complex, exhibiting potential uses in catalysis. Also, Zhao et al. (2021) used laser-induced graphene to incorporate with Co
3O
4 nanoparticles for a flexible and highly sensitive enzyme-free glucose biosensor, highlighting their versatility in sensing applications.
According to the recently publications Co
3O
4 nanoparticles shows better performance in batteries as shown in (
Table 3). Mahmood et al. (2022) investigated Co
3O
4 nanoparticles as anodes in Li-ion batteries, these particles has a higher capacity about 890 mAg
-1 than graphite 370 Ag
-1. One of the usage problems of Co
3O
4 as an anode is large volume changes during repeated lithiation and delithiation processes. To solve this problem various nanostructures, such as nanoring, mesoporous, 3D nanofiber, and nanofilms of Co
3O
4 have been prepared and studied extensively. Mesoporous Co
3O
4 networks were synthesized via thermal decomposition and showed a maximum capacity of 587 mAhg
-1 after 500 cycles.
There are many kinds of catalysts for CO combustion especially, when include metal oxides, metal oxide’s compounds, and a variety of supported noble metal catalysts. To decrease the production CO and remove it from H2-rich syngas specially, to make it more ideal when applied to fuel cells the catalytic combustion of CO at low temperature is the most effective way for elimination of CO toxic gas. In Wang, X et al. (2023) investigation, it has proven that Among all the oxides studied Co3O4 is the best catalyst support, both the catalytic activity and stability of Au@CuxO/ Co3O4 are high. The Au content in the catalysts is only 0.11 wt% and the 90% CO conversion temperature is 132 oC. CO can even combust on Au@CuxO/ Co3O4 at room temperature with 51% conversion and without loss after a 72 h reaction. Furthermore, Anele et al. (2022) discussed recent trends in the environmental remediation of bacteria in waste water using Co3O4 nanoparticles.