*3.1.2 Sol–gel method*

The sol–gel method [70, 71] is a promising approach used for the preparation of ferrite nanomaterials. Sol is a colloidal suspension of solid particles of ions in a solvent and gel is a semi-rigid mass that forms when the solvent from the sol starts evaporating and the particles left behind join together. The resultant is in the form of colloidal powder or films. This method is appreciable due to the controlled microstructure. The final particles formed are of uniform and small size. Also, this technique of synthesis is economical and it is achievable at low temperature. The temperature conductivity was observed to be higher than pure ZnCu ferrite. There was a declination in the dielectric constant with an increase in nickel concentration. This method is advantageous because it is less time-consuming. The prepared ferrite consists of a pure cubic spinel structure.

## *3.1.3 Combustion method*

The combustion process is an effective and low-cost method to synthesize nanomaterials. This process is simple, versatile, and fast for nanomaterial preparation. The salient feature of this method is, it requires less time and energy during the synthesis. The nanoparticles produced are pure and homogeneous. Researchers synthesized ZnCu ferrites by using this method [72, 73]. Copper nitrate [Cu(NO3)2.6H2O], zinc nitrate [Zn(NO3)2.6H2O], iron nitrate [Fe(NO3)3.9H2O] were taken in appropriate proportions and urea [CO(NH2)2] was used as a reducing agent in this process. A solution is formed by adding these materials in deionized water and heated at 480°C in air. Then, it is ignited within 5 s with a flame temperature of ~1600°C. The combustion technique is doping with other elements to decrease the lattice parameter, which reflects the fact that the ions of dopants get trapped at the grain limits. They hinder the development of grain and may cause an increase in strain on the grains that leads to a decrease in lattice parameters. The fuel chosen has a very vital impact on the ZnCu ferrites prepared. The fuels that are preferred in this method are urea and glycine, by which uniform nano ferrites with controlled stoichiometry are obtained.

### **3.2 Spectroscopic characterization**

The characterizations of ZnCu ferrites are studied with an X-ray diffractometer, scanning electron microscopy [74–76]. The magnetic properties of the ferrites are studied by vibrating sample magnetometer (VSM), magnetization hysteresis (M − H) loops [77], and electron spin resonance (ESR) hysteresis loop measurements. The X-ray investigation is carried with an X-ray diffractometer with CuKα radiation (λ = 1.5405 Å). Many techniques are used to determine the shape, size, and morphology of magnetic nanoparticles such as XRD, SEM, TEM, HRTEM (High-resolution transmission electron microscopy), and FESEM (Field emission scanning electron microscopy). By using HRTEM we can get information about shape, size, crystallinity, and lattice spacing. XRD is used to determine the size by using the Scherrer equation. However, SEM is effective because the size of very small magnetic nanoparticles is determined.

#### **3.3 XRD analysis**

The crystalline structure of the Zinc copper ferrite as prepared and annealed at 500°C and 600°C are shown in **Figure 1**. All the diffraction peaks can be registered to the standard Zinc copper ferrite with the cubic spinel structure and the reflection peaks match adequately with standard data (JCPDS 82–1042). This indicates the synthesized nanoparticles have an Fd3m space group and indicating a high degree of purity. The average crystallite sizes, D, are calculated from the (311) peaks through Scherrer's formula around 32 nm. It is observed that the sample Zn1-x CuxFe2O4 crystallized in cubic structure and the lattice parameter is found to be 8.355 Å, which is less than the values reported for bulk compounds [78]. The crystallite size of ferrite nanoparticles is in the range of 2.3–11.8 nm and the average crystallite size and lattice constant were found to be 6.52 nm and 8.443 Å

*The Presented Study of Zn-Cu Ferrites for Their Application in "Photocatalytic Activities" DOI: http://dx.doi.org/10.5772/intechopen.99535*

**Figure 1.** *XRD patterns of zinc copper ferrite nanostructures as prepared, annealed at 500°C, and 600°C.*

respectively. Thomas Abo Atia et al. [79] studied the effect of sintering temperature and observed that the average crystallite size was found to increase with an increase in sintering temperature i.e. from 35 nm to 45 nm. Shwetambaram et al. [80]. Crystallite size was calculated and found to be of 7.74, 10.80, 11.58, 12 nm for x = 0.00, 0.25, 0.50, 0.75 respectively. Anuj Jain et al. [81] observed that the crystallite size of the composite ferrites increases on increasing the Cu concentration. This is due to the decrement in the densities of nucleation centers in the doped samples which result in the formation of larger crystallite size. S B Kale et al. [82]. The value of crystallite size was 24.17 nm indicates the nanocrystalline nature of the prepared samples. A. Subha et al. [83] observed from grain size calculated using Scherrer's formula applied to the most intense peak shows similar grain size was 30 nm. A. Tony Dhiwahara et al. [84] have indicated in the XRD patterns, the linear change in peak width was reflected in a linear decrease in crystallite size from 19.37 to 15.21 nm with an increase in Zn content in the host sublattice of CuFe2O4. This is mainly because of the replacement of smaller Cu2+ ions (0.72 Å) by larger Zn2+ ions (0.74 Å) [85, 86]. In addition, as the ionic radius of Zn2+ is larger than the ionic radius of Cu2+, the Zn2+ substitution leads to a larger expansion of the lattice. Consequently, the lattice parameter increases more when compared to the Cu2+ substitution in the synthesized particles. Since ionic radius of Fe2+ (0.74 Å) ion is larger than Fe3+ ion (0.64 Å), the lattice constant increases [87]. Nonmagnetic transition metal ions Zn2+ and Cu2+ ion prefer octahedral sites whereas Fe3+ ions prefer both tetrahedral and octahedral sites. The characteristics peaks correlate with the ferrite particles and show the phase group Fd3m and spinel structure having a single phase. Hence, it is concluded that the ZnCu ferrites have a single-phase spinel cubic structure with an Fd3m phase group. However, some deviation in the structure can be observed because of doping.

#### **3.4 Morphological structure**

Various techniques such as TEM, and SEM, etc. are used to investigate the morphological structure of the ferrite nanoparticles. TEM is preferred because of its resolution. From the typical SEM analysis, morphological characteristics of Zinc copper ferrite nanoparticles annealed at 600°C are shown in **Figure 2(a)**. They show the formation of multigrain agglomerations consisting of fine crystallites with irregular shapes and sizes. Ferrite powders possessed a coarse structure with crystalline microstructure with an average grain size homogeneous is about 50 μm obtained from SEM images. This is larger than the size of nanocrystals calculated using the XRD measurements, which helps to understand that the grains are formed by aggregation of several nanocrystals. The samples are irregular shapes and sizes, and the cohesion of grains is due to the magnetic attraction. A drastic difference in microstructure of the annealed at 600°C products indicated that the substitution of metal ions like Zn, and Cu on the surface of this microstructure.

EDX analysis confirms the stoichiometric proportion of Zinc copper ferrite nanoparticles annealed at 600°C and also the percentage proportion of the constituent elements is shown in **Figure 2(b)**. The elemental weight proportion percentage is presented in the tables of weight and atomic percentage proportions, the constituent elemental proportion, and the ratios are in agreement with the expected elemental proportion and the oxygen (O) and iron (Fe) being with the highest peaks in all of the samples [88]. Typical EDX analysis reveals the existence of elements of Zn, Cu, Fe, and O. As portrayed in **Figure 3(a)**, HRTEM micrographs also confirm the particle size of ZnCu ferrite nanoparticles annealed at 600°C. The average crystallite size is around 8.38 nm. HRTEM analysis reveals that the particles are nearly spherical. The average crystallite size estimated from the HRTEM image falls in line with the observed values from powder XRD results. From **Figure 3(b)**, the HRTEM image of individual Zinc copper ferrite nanocrystal indicates that the interplanar distance is 0.26. In the SAED (**Figure 3(c)**) image of annealed at 600°C Zinc copper ferrite nanoparticles, the diffraction rings coincide with standards powder XRD diffraction data that confirms good crystallinity. The observed crystallographic d values of 2.52 Å correspond to the lattice space of the (311) plane of the Zinc copper ferrite system. The observed crystallographic d values agree well with those obtained from powder XRD analysis.

**Figure 2.** *Images of zinc copper ferrite nanostructures annealed at 600⁰C (a) SEM (b) EDX analysis.*

*The Presented Study of Zn-Cu Ferrites for Their Application in "Photocatalytic Activities" DOI: http://dx.doi.org/10.5772/intechopen.99535*

**Figure 3.** *Image of zinc copper ferrites nanostructures annealed at 600⁰C, (a) HRTEM (b) inter.*
