Preparing of CuCo 2 O 4 compound by Sol-gel method and studying its structural properties

The CuCo2O4 compound has been prepared by the Sol-gel method starting with cobalt sulfate CoSO4.7H2O and copper nitrate, using Pectin as a stabilizer. The samples have been annealed at different temperatures (400-1000°C) to produce CuCo2O4. Thermo-gravimetric analysis (TGA), Fourier transform infrared spectroscopy (FT-IR), Scanning Electron Microscope (SEM) and X-ray diffraction (XRD) techniques have been used to characterize the compositional properties of the prepared compound. The optimum temperature for synthesis is found at 600°C. According to X-ray diffraction patterns, CuCo2O4 spinel has a face-centered cubic crystal (FCC) and belonged to the Fd3m space group. The lattice constants, unit cell volume, and number of formulas have been calculated. Their values are 8.044 Å, 520.49 Å3, and 8, respectively. It is found that the grain size of the compound is 17.4nm. The experimental results for d corresponded to the reference card values with an accuracy of 99.5% as a minimum. The theoretical and experimental density of the prepared compound have been calculated and the results are approximately identical. The differential thermal analysis curves showed five thermal effects, the most important of which are the exo-thermal peak at 390°C and end-thermal peak at 740°C, which indicate to start forming and decomposition of Cu respectively. The IR spectroscopy encouraged our results during the bonding vibrations of Co-O,


Introduction
Spinel is an important family of mixed metal oxides, the standard chemical formula for spinel is AB2O4, where A and B are cations that occupy tetrahedral and octahedral sites, respectively.B is a trivalent atom whereas A is often a divalent atom.Only oneeighth of the tetrahedral sites and one-half of the octahedral sites are occupied by the cations 1 .Cobaltbased spinels MCo2O4 (M = Ni, Cu, Zn, Mg, Mn, Cd, etc.) are an intriguing class of oxide ceramics with significant technological uses; they have been used extensively in fields like chemical sensors [2][3][4] , electrode material 5,6 , electrocatalysts 7 , supercapacitor 8 and other related fields.Common methods for producing cobaltite include solid-state reactions 9 , coprecipitation 10 , hydrothermal 11,12 , combustion 13,14 , microwave 15,16 and sol-gel processes [17][18][19][20] .When the material is synthesized utilizing a solution-based technique, the drawbacks of solid-state methods, such as inhomogeneity, lack of stoichiometry control, high temperature, and poor surface area, are improved.Due to its benefit of creating pure and ultrafine powders at low temperatures, the sol-gel process is a practical and alluring method for manufacturing cobaltite spinels.

Abstract
The CuCo2O4 compound has been prepared by the Sol-gel method starting with cobalt sulfate CoSO4.7H2O and copper nitrate, using Pectin as a stabilizer.The samples have been annealed at different temperatures (400-1000°C) to produce CuCo2O4.Thermo-gravimetric analysis (TGA), Fourier transform infrared spectroscopy (FT-IR), Scanning Electron Microscope (SEM) and X-ray diffraction (XRD) techniques have been used to characterize the compositional properties of the prepared compound.The optimum temperature for synthesis is found at 600°C.According to X-ray diffraction patterns, CuCo2O4 spinel has a face-centered cubic crystal (FCC) and belonged to the Fd3m space group.The lattice constants, unit cell volume, and number of formulas have been calculated.Their values are 8.044 Å, 520.49Å3, and 8, respectively.It is found that the grain size of the compound is 17.4nm.The experimental results for d corresponded to the reference card values with an accuracy of 99.5% as a minimum.The theoretical and experimental density of the prepared compound have been calculated and the results are approximately identical.The differential thermal analysis curves showed five thermal effects, the most important of which are the exo-thermal peak at 390°C and end-thermal peak at 740°C, which indicate to start forming and decomposition of Cu respectively.The IR spectroscopy encouraged our results during the bonding vibrations of Co-O, Cu-O.https://doi.org/10.21123/bsj.2024.9200P-ISSN: 2078-8665 -E-ISSN: 2411-7986 Baghdad Science Journal One of the most efficient and interesting transition metal oxides is copper cobaltite CuCo2O4 which has a spinel structure.It has been extensively researched because of its applications in supercapacitors and gas sensors properties [21][22][23] .In the present investigation, CuCo2O4 nanocrystals are made using the sol-gel method.Thermogravimetric analysis (TGA), X-ray diffraction (XRD), and Fourier transform infrared (FTIR) spectroscopy have all been used in characterization studies.The novelty in the research lies in utilization an organic compound (Pectin) as a stabilizer in the process of copper cobaltite preparation from mineral salts.The crystal structure of the as-prepared CuCo2O4 is shown in Fig. 1.It is obvious to see that cobalt and copper atoms are distributed over the centers of the stacked octahedra and tetrahedra, while the oxygen atoms are distributed over the corners of the octahedra and tetraherdra.

Materials and Methods
Cobalt sulfate CoSO4.7H2O(97% purity), copper nitrate Cu(NO3)2.5H2O(99% purity), Sodium hydroxide, Pectin, and distilled water.All chemicals used during the process of synthesis were purchased from Sigma-Aldrich, they were of analytical grade, and were used as received without any further purification.The CuCo2O4 compound was synthesized by Sol-gel method, and appropriate amounts of starting materials (5.7959g) CoSO4.7H2O and 2.4404g Cu(NO3)2.5H2Owere separately dissolved in 100ml distilled water.Then, they were mixed for 30 min.Next, (2.4g) NaOH was dissolved in (100ml) distilled water and added to the mixed solution.(0.05g) of Pectin was added to the solution at room temperature under constant magnetic stirring for another 30 min.The resulting mixture solution was constantly stirred at 80°C for 1h until the gel was formed.After that, the gel was heated at 110°C until the formation of a powder.Subsequently, the as-prepared precursor was calcined at range of temperature (400-1000) °C for 6 h to obtain the CuCo2O4 oxide.The weights of the starting materials used to form the CuCo2O4 system were calculated by the following reactions: Using a Differential Scanning Calorimeter (Shimadzu TG/DTA) with a ramp from 0 to 900°C at a heating rate of 30°C per min while nitrogen gas flowed, thermogravimetry differential thermal analysis (TG/DTA) was investigated.X-ray powder diffraction (XRD, Philips-PW-1840) with a Co-K radiation source λ=1.7889A o and a scanning rate of 0.02° s −1 in a 2θ range from 20 to 85° was used to carry out the structural characterization.ICCD standards were used in the analysis of the data.Using KBr pellet-based samples, an FTIR investigation was carried out using (Jascoo -FTIR) in the range of 4000 to 400 cm −1 , and the morphology of the obtained spinel oxides was explored using a Qaunta 200 scanning electron microscope (SEM).

X-ray diffraction (XRD) analysis
The XRD technique is a very useful tool to determine the phase, crystallinity and, purity of the samples prepared under various conditions 25 .Fig. 3 illustrates the XRD patterns of CuCo2O4 which have been synthesized by the sol-gel method and annealed at different temperatures for 6 hours.

Figure 3. XRD patterns of the CuCo2O4 following calcination at various temperatures.
It has been found that the compound started formation at 400°C, and by increasing the temperature from 400 to 600°C, the XRD peak intensity of CuCo2O4 spinel increases stepwise.
Meanwhile, the particle size of CuCo2O4 increases with the sintering temperature and an obvious grain growth occurs mainly at 600°C.All diffraction peaks at 600°C are attributed to the CuCo2O4 compound, and no peaks are related to copper oxide or cobalt oxide.The observed peaks at 2θ= (41.7, 57.5, 69.1, 73.1 and 78.9) above 600°C correspond with a second phase CuO (JCPDS No: 05-0661) this indicates that spinel started dissociation above this temperature.The previous discussion suggests that 600°C is the ideal temperature for the synthesis CuCo2O4 compound where the peaks intensities are higher than those observed when calcining at 400°C and 500°C.All diffraction peaks observed at 600°C indicate the characteristic peak of the cubic CuCo2O4, with the spinel structure (ICCD No: 00-001-1155) and space group Fd3m.The face-cantered cubic spinel structure can be precisely indexed to the diffraction peaks.Fig. 4 shows the XRD pattern of CuCo2O4 compound that calcined at 600°C with (hkl) index.Eq. 1 gives the relation between lattice parameters and the d-spacing for the cubic system 26 : Table 1 shows the diffraction angles, inter-planar distances, and Muller indexes that are calculated from the XRD pattern.The basic unit cell volume has been calculated using the relation: V =a 3 .The flask density method (picknometer) has been used to measure the experimental density ρt of the prepared material 27 .Depending on the material's density, the number of formulas in a single crystalline cell Z is calculated by Eq. 2 28 : Where M molecular weight of the material, Na Avogadro number, and V basic unit cell volume (cm) 3 , it is found that:  = .  .  = 8.00338 ≈ 8 Using the rounding method, it is found that Z = 8, and therefore the general formula for the content of the basic unit cell can be written as follows: Cu8Co16O32.The broadening of diffraction lines may signify the nanoscale character of the component crystallites; Eq. 3 refers to Scherrer equation [29][30][31] : D is the grain size, K is a constant equal to 0.9 λ is the wavelength of the X-ray, θ is the Bragg's diffraction angle (43.25, 45.48, 52.81, 65.9, 70.43, 77.70) and β is the full width at half maximum of the peak in radians.
Confirmed that the average crystal grain size is 17.4 nm, the obtained results are presented in Table 2. Scanning Electron Microscope SEM Fig. 5 shows SEM image of the CuCo2O4 synthesized by sol-gel and calcined at 600°C.The images exhibit some heterogeneity in the distribution of the particles on surface.The shape of the microparticles is spherical.

Conclusion
Spinel nanopowders can be produced using the solgel technique.It is incredibly easy, cheap, and produces materials with good characteristics at the nanoscale.Sol-gel technique has been used to successfully create the pure CuCo2O4 nanopowders using Pectine as a stabilizer, which shows a spinel phase structure.CuCo2O4 spinel's XRD peak intensity rises stepwise as the sintering temperature rises from 400 to 600°C.Meanwhile, CuCo2O4 particle size grows as the sintering temperature rises, with a clear grain growth occurring mostly at 600°C.It is built in a cubic shape.CuCo2O4 crystals calcined at 600°C had a size of around 17.4nm.

Figure 1 .
Figure 1.The unit cell of spinel structure of CuCo2O4.24

Fig. 2 Figure 2 .
Fig. 2 depicts the CuCo2O4 TG-DTA curve.The weight loss has been gradual and nearly totaled 90% of the overall precursor mass.The first loss of weight

Figure 5 .
Figure 5. SEM image of CuCo2O4 calcined at 600℃ .Fourier Transform Infrared SpectroscopyCuCo2O4 FT-IR spectrum is depicted in Fig.6.The metal-oxygen stretching frequencies are ascribed to FT-IR spectra in the 400-1000 cm −1 range 32 .Cu-O and Co-O such metal-oxygen stretching and bending vibrations can be attributed to two strong peaks with respective centers at 665.32 and 577.58 cm−1 33  .The OH stretching and bending modes of adsorbed water molecules are shown by the bands at 3436.6 and 1626.66 cm −1 , respectively34 .