Impact of Zirconium doping on structural, optical, morphological and anti-bacterial properties of Chromium ferrites

The 21st century has been called the golden age for researchers because of the widespread use of nanotechnology in the fields of pharmacy, agriculture, medicine, and biological science [1][2]. In addition to nanoparticles of metal oxides and metals, ferrite nanoparticles have gain a lot of attention due to their high paramagnetic properties and surface-to-volume ratio, that are completely different from their counterparts in quantity [3]. As magnetic particles nano-sized ferrites are not replaced by some other magnetic particles due to their large range of technical applications and they are stable and inexpensive than the others [4].

Spinel ferrite nanoparticles are of great interest in elemental science because of their surface, magnetic, and electrical properties [5]. Nanoparticles of ferrites are enormously famous for their vast applications as gas sensors, MRI, biomedical field, catalytic activity, etc. [6–9]. Properties of ferrites are highly affected by metallic ion distribution between crystallographic crystal lattices [4].

Chromium belongs to the group of stubborn metals that contains metals with higher melting points than platinum, which is 1772°C. It is the twenty-fourth most rich element in the earth's crust and is used for different applications; especially chromates have been used in printing for so long in photochemical reproduction [10] [11]. It has many advantages, i.e., high thermal stability, low toxicity, and low cost [12–14], so it can be used for the degradation of methyl orange and methylene blue dyes [15,16].

In between various elements, zirconium is a very important one because of its wide distinctive properties that can be used for different type of applications. Doping of zirconium in different metals can be produce different structural defects, such as oxygen vacancies and interstitial defects [17].

In current research work, chromium is a host and used as a heterogeneous catalyst [14] and zirconium, as a dopant, can be used as a dielectric material [18], a high-performance ceramic material [19] and a catalyst support [15,16]. The doping of zirconium in chromium ferrite enhances and stabilizes the structure of chromium at very high temperatures [20]; so, the particular tapping of electrons is held on Zr⁴⁺ in contrast with Cr³⁺ [21]. Hence, the insertion of another element like Zr helps to enhance the separation rate of photo-induced holes and electrons, enlarge the surface area of the host, and increase thermal stability.

Hydrothermal synthesis is mainly a solution-reaction-based methodology that has noteworthy benefits over others. In this technique, the development of nano-materials can occur in an extensive temperature range from very high temperature to room temperature. To regulate the morphology of the material to be made, either high-pressure or low-pressure circumstances can be used contingent on vapor pressure of the key configuration in the reaction. Nanomaterials that have high vapor pressures can be formed by the hydrothermal synthesis method with the least loss of materials and are not steady at elevated temperatures. The configurations of nano-materials to be synthesized can be efficiently controlled in hydrothermal synthesis through liquid-phase or multiphase chemical reactions [22].

Different authors have been studied the zirconium doping on different metals, such as S. Kavitha studied the effect of zirconium doping on different properties of cobalt ferrite nanoparticles [23], Desta et al. studied the properties of zirconium-doped TiO₂ [24], Khan et al. studied the zirconium doping on cerium oxide for the degradation of dyes [17] and Zahir Muhammad et al. studied the zirconium-doped chromium Nano composites for the degradation of organic dyes [25].

Till now, different methods like ball milling, sonication, co-precipitation, solid-state reactions, and flame pyrolysis [26,27] have been seen in the literature for the preparation and synthesis of different nanoparticles and nano-composites. To the best of our information, no prior literature has stated a correlation between zirconium doping levels and the simultaneous modulation of optical band gap and antifungal activity in chromium ferrites. The results were carried out by different techniques, such as X-ray diffraction, UV-visible, Fourier transform infrared spectroscopy, and SEM. 

Experimentation:

Zirconium doped chromium ferrite nanoparticles Cr_(1-x)Zr_(x)Fe₂O₄ with different concentrations (x= 0, 0.05, 0.15, 0.5) were synthesized by hydrothermal methods. 0.5 moles of each nitrate were weighed, and their solution was prepared with 20 ml distilled water. The prepared solution was then put on magnetic stirring at room temperature for half an hour to make a fine solution of them. A 20 ml solution of sodium hydroxide (NaOH) was added in the solution to maintain its pH, and it was stirred for 30 more minutes. After preparing the required solution, put it in the Teflon autoclave system. Place the autoclave system into an oven at 180℃ for 12 hours. After 12 hours the system was removed from the oven and left to cool inside the furnace for 4 hours. After cooling, the solution is transferred into a beaker, and to homogenize the particles, it is placed in the ultrasonic bath for 30 minutes at room temperature. After that, the solution is centrifuged at 3000 rpm for 15 minutes. After that the nanoparticles were washed with distilled water several times until their pH maintained at 7, and then they were filtered. The filtered particles were collected in a petri dish and dried in an oven at 100℃ for 2 hrs. Similarly, three more samples are prepared by different concentrations of chemicals and then characterize them by different techniques.

Figure 1: Schematic diagram for the preparation of Cr_(1-x)Zr_(x)Fe₂O₄

Results and Discussion:

Structure and Phase Analysis:

XRD patterns of zirconium-doped chromium ferrite nanoparticles Cr_(1-x)Zr_(x)Fe₂O₄ where (x = 0, 0.05, 0.15, 0.5) are synthesized by the hydrothermal process as shown in Figure 1. The main reflections of the planes are (220), (400), (422), (511) and (311), which show the presence of a cubic-spinel phase with Fd3m group symmetry. XRD spectra matches with typical data (JCPDS card-no o6–0523), and the creation of chromium ferrite NPs is confirmed with JADE software. The most intense peak (311) is observed at 35.8°, which is the characteristic peak of spinel ferrites.

a

b

Fig. 2. (a) Diffraction patterns of Cr_(1-x)Zr_(x)Fe₂O₄ (x=0, 0.05, 0.15, and 0.5) nanocomposites. (b). Magnified view of peak (311).

The Debye-Scherrer formula is used to calculate the crystalline size and is given by [28]:

Where ‘k’ is the Scherrer constant, ‘λ’ is the wavelength of the X-ray radiation, β is the peak FWHM (full width at half maxima in radians), and ‘θ’ is the position of the XRD peak.

The crystallite size is observed to increase with increasing value of ‘x’ as seen in Figure 3. This increase in particle size is due to zirconium atoms substituting the chromium atoms in sites having smaller radii than that of dopant atoms. When large-sized atoms inhabit the small-sized atom voids, there is an extension in lattice arrangement due to which the size of nanoparticles increases [29]. The shifting of the peak in the magnified image in Figure 2b towards the lower 2θ value is also verification of increasing grain size with the addition of zirconium content [30].

Figure 3. Variation of crystalline size and lattice parameter with Zr concentration.

The strain induced in powders because of distortion and crystal imperfection is determined using the formula [31]:

ε=β_hkl/4tanθ                        --------3

The Williamson-Hall plot method is the simplified integral breadth method, which discriminates between strain-induced and size-induced peak expansion by studying the peak width as a function of h2θ. To measure crystalline size with the W-H method, the following equation is used [32]:

β_hklcosθ=Kλ/D + 4εsinθ                      --------------------------4

The above equation is in the form of a straight line, and this plot method 4sinθ is plotted against the x-axis and β_hklcosθ is schemed against the y-axis, shown in Figure  4 (a-d). From a linear fit to the data, the crystallite size is assessed from the y-intercept, and strain is obtained from the slope of the graph. The positive slope value for (x=0.5) signifies the tensile strain, while the negative value shows the compressive strain. The crystallite size calculated by the W-H plot is smaller than that calculated by the Debye-Scherrer formula due to the compressive and tensile strain induced in the lattice.

Figure  4 (a-d). W-H plots of Cr_(1-x)Zr_(x)Fe₂O₄.

Halder-Wagner is the alternative equation that comprises the integral breadth (β*) of the reciprocal lattice point and the lattice plane spacing (d*) of the reciprocal cell. This process is very useful to determine lattice strain and size altogether for the chromium nano ferrites with different zirconium concentrations. The H-W relation for particle size measurement is given below [32]:

β/(d)² = kβ^*/[D(d^*)²] + 2ε²   5

Where,

β^*= βcosθ/λ

d^*= 2sinθ/λ

So the equation will be in the form of [32]:

βcosθ/(sinθ)² = (kλ/D)[βcosθ/(sin²θ)] + 16ε²  (6)

In this method, the plot is made between (β*)/(tanθ)² on the y-axis and (β*)/(tanθsinθ) on the x-axis. By linear fit to data, the slope gives the crystalline size, and the intercept provides the strain values.

It can be observed from Table 1 that the crystallite size calculated by all three methods follows the same increasing trend with increasing Zr concentration.

a	b
c	d

Figure 5 (a-d): H-W plots of Cr_(1-x)Zr_(x)Fe₂O₄ with different concentrations.

The values calculated with different methods of different parameters are listed in the table (1).

Table 1: Crystalline size and strain calculated by different plot methods.

The lattice parameter of nanocrystalline material obtained from XRD data is determined by the following formula [33]:

a = λ√(h² + k² + l²) / 2sinθ  ----------(7)

Where ‘hkl’ are the Miller indices and “a” is the lattice parameter.

It is observed from Figure 5 that the lattice parameter increases as the zirconium concentration increases. The increasing trend may be attributed to the fact that the addition of larger zirconium ions may cause the movement of some smaller chromium ions from the tetrahedral site to the octahedral site [34].

The x-ray density of the prepared samples can be expressed as [35].

ρ_x = 8M / Na³  -------------------(8)

Where ‘M’ is the molar mass of the product, ‘n’ is Avogadro’s number (6.022×10²³), 'a' is the lattice constant, and ‘8’ is the number of unit cells in a spinel lattice [36]. X-ray density (ρ_x) depends on the lattice constant and molecular weight. With the increase in Zn content, a constant increase in lattice and a parallel decrease in the X-ray density are observed (Table 2). 

The change in lattice constant is more significant than the molecular weight; therefore, the trend of x-ray density is showing an inverse relation with the lattice constant.

Table 2: Different structural parameters calculated from XRD data.

Hopping length (Figure 6) at A site (L_A) and B site (L_B) are calculated by following formulas (eq. 8, 9) [37].

L_A = a√3/4                        ----------9

L_B = a√2/4)                     ---------10

It is noted that hopping lengths L_A and L_B increase with the increase in the zirconium content. The increases in hopping length of the sample from x=0 to x=0.5 indicate that a large quantity of force is essential for the charge carriers to travel from one cationic site to the other cationic site. The obtained results show the same increasing trend as that of the lattice constant ‘a.' This increasing trend can be described by the enlargement of the unit cell, which is produced by a greater ionic radius of the dopant element.

Figure 6: Variation of hopping length with Zr concentration.

The relation used to determine the polaron radius is as follows [38].

γ_p= 1/2[³√π/6N']     ------- 11

From table 3 it is observed that the polaron radius is increasing with the Zr concentration. An increase in polaron radius means a large quantity of energy is necessary for charge carriers to move from one cationic site to the other [39]. In ferrites, the charge carriers are restricted in the d-shell; this restriction may be due to the creation of polarons. A minor polaron defect is formed when a carrier gets stuck at sites as a consequence of movement of adjacent ions or atoms.

Dislocation line density can be expressed as [40].

δ= 1/(D² )     --------------------12

Dislocation density is given in the table. 2 shows that it decreases as the Zr concentration increases, showing the opposite trend as that of the crystallite size.

The average ionic radii (r_A and r_B) corresponding to tetrahedral and octahedral sites are obtained by the following formula [41].

r_A = a√3)u-0.25) - R_o     -------------------------13a

r_B = a (5/8 - u) - R_o          -------------------------13b

Here 'R_o' is the radius of oxygen (1.26Å), ‘u’ is the oxygen parameter, and ‘a’ is the lattice constant. It is seen from Table 3. that ionic radii show the same increasing trend as that of the lattice constant.

Table 3: Different structural parameters calculated from XRD data.

The least space between oxygen ions and A-site cations is known as tetrahedral bond length R_A, and the smallest distance between oxygen ions and B-site cations is known as octahedral bond length R_B. The relations used to determine the bond length corresponding to tetrahedral and octahedral sites are given below [41]:

R_A=a√3(δ+1/8)                 ---------- (14a)

R_B=a(3δ+1/16-δ/2)             ------ (14b)

Where,

δ=U_system-U_ideal

In this equation:

U_ideal = 0.250 and U_system = u₁ + U_system =u₁+u₂

It can be seen in Table 3 that the bond length of the A site, R_A, is greater than that of the B site, R_B, but both lengths show an increasing trend with Zr content. This may be because of the increasing lattice parameter due to the replacement of chromium ions by bigger-sized zirconium ions.

The tolerance factor for spinel ferrites can be calculated by the following formula [42].

T=1/√3(r_A+R_o)/(r_B+R_o)+1/√2(R_o/(r_A+R_o)) ---15

It is clear from Table 3 that the values of the tolerance factor are closer to 1, which is the ideal value of a single-phase spinel structure with very small or no impurity.

3D crystal structures of the prepared samples made with the Diamond software are shown in Figure 7.

Figure 7 (a-d): Crystal structures of Cr₁₋ₓZrₓFe₂O₄ (x=0, 0.05, 0.15, 0.5).

Fourier Transform Infrared Spectroscopy (FTIR):

The FTIR peaks of Cr₁₋ₓZrₓFe₂O₄ (x = 0, 0.05, 0.15, 0.5) were recognized in the range of 400–4000 cm⁻¹ and showed the characteristic peaks of the obtained nanoparticles (Figure 8). As we know, the FTIR spectra of spinel ferrites exhibit two active bands in the range of 450–900 cm⁻¹ [43]. In this study, two bands are observed in the ranges of 400–500 cm⁻¹ and 800–900 cm⁻¹, corresponding to metal–oxygen (Fe–O and Cr–O) bonds [44]. These peaks, which are lower than 1000 cm⁻¹, are the result of interatomic vibrations [45]. The band between 1350 and 1450 cm⁻¹ is attributed to deformation vibrations of M–O–M [46]. The band in the range of 1570–1720 cm⁻¹ represents the bending and stretching vibrations of absorbed water [47]. It is noted from the graph that there is no typical absorption band in the region of 2800–2900 cm⁻¹, representing the stretching modes of surfactant hydrocarbon chains [48]. The band between 3100 and 3250 cm⁻¹ is due to the C–C functional group. As the Zr content increases, it can be seen that the FTIR bands slightly shift towards lower frequencies, which may be due to the substitution of Zr⁴⁺, with a higher ionic radius, for Cr³⁺, with a lower ionic radius. This change in band location is mostly caused by the change in the size of the unit cell.

Figure 8: FTIR spectra of Cr_(1-x)Zr_(x)Fe₂O₄ (x= 0, 0.05, 0.1, 0.15) nanoparticles.

The relations used to compute the force constants k₁ for the octahedral site and k₂ for the tetrahedral site are as follows [49]:

k₁ = 7.62 × M₁ × ν₁² × 10⁻⁷ N/m  ---16

k₂ = 10.62 × M₂ × ν₂² × 10⁻⁷ N/m  ---(17)

where M₁ and M₂ are the weights of the molecules, ν₁ is the central frequency at the tetrahedral site, and ν₂ is the central frequency at the octahedral site. The calculated values of k₁ and k₂ are recorded in Table 4.

The relation between the force constants (k₁ and k₂) and hopping lengths (Lₐ and Lᵦ) is shown in Figure 9(a, b).

It is clear from the graph that Lₐ and Lᵦ are increasing, while k₁ and k₂ are showing decreasing behavior. This trend may be due to the larger ionic radius of the dopant atom than that of the host atom, which leads to the increased distance between magnetic ions, causing a reduction in the repulsive forces and, therefore, the electrostatic energy and consequently reducing the wavenumbers, which leads to a decrease in the force constants.

(a)

(b)

Figure 9 (a, b): Trends of hopping lengths and force constant.

Table 4. IR bands, force constant, and hopping lengths of Cr₁₋ₓZrₓFe₂O₄.

Ultraviolet-Visible spectroscopy (UV-visible):

The optical absorbance spectrum of Cr₁₋ₓZrₓFe₂O₄ (x=0, 0.05, 0.15, 0.5) nano ferrites is observed using a UV-vis spectrometer in the range of 200-800 nm, and absorbance peaks are observed at 339 nm and 380 nm, as shown in the Figure 10.

The band gap energy is determined from the relation among optical band gap, absorbance coefficient, and energy hν. The relation is as follows [50]:

αhν = A(hν − E_g)ⁿ      -------18

Where A is the constant that is independent of hν, α is the absorption coefficient, E_g is the band gap energy, ν is the transition n frequency, and n is 2 for direct band gap and 1/2 for indirect band gap.

The band gap energy is determined by plotting the graph between (αhν²) and E_g by extrapolation of the linear part of the graph. As observed from Figure 10 (a), it is detected that the band gap energy (Eg) is decreasing as the concentration of Zr is increasing in the compound. The substantial decrease in band gap from 2.65 to 1.44 eV with enhancement of Zr content may be credited to many factors.

Primarily, the doping of Zr with larger ionic radii in host (chromium) with smaller ionic radii causes lattice expansion as verified by increased lattice parameter values. Consequently, the band structures are amended by narrowing the band gap between the valence and conduction bands, which makes the samples conductive. Moreover, the incorporation of Zr produces structural defects like dislocations and vacancies, which create local energy states within the band gap that lead to the observed decrease in band gap [51].

Furthermore, the enhancement in crystallite size with the addition of Zr results in reducing the quantum confinement effect, hence narrowing the band. It is recognized that the band gap and the particle size possess an opposite relation; the samples with higher crystallite size will possess a lesser band gap and vice versa. Actually there are an unlimited amount of atoms when the crystallite size increases, which leads to increasing the overlying energy states or orbitals, which causes the breadth of the band to increase, and so the band gap energy is reduced [52].

Figure 10(a,b): (a) Band gap of Cr₁₋ₓZrₓFe₂O₄: (b) absorbance peaks of samples with Zr concentrations.

4.4. Scanning Electron Microscopy (SEM):

Scanning electron microscopy technique is used to examine the surface morphology and microstructure of all the synthesized samples of Cr₁₋ₓZrₓFe₂O₄ (x = 0, 0.05, 0.15, 0.5). The morphology of synthesized Cr₁₋ₓZrₓFe₂O₄ nanoparticles is shown in Figure 11 (a-h). ImageJ software was employed on the SEM images to estimate the grain size and to confirm the statistical reliability. The 20-50 grains from various regions are randomly selected within the micrographs from a specifically picked concentration of zirconium. The grain boundaries were identified on the basis of dissimilarity, and a comparable circular diameter was selected to calculate average grain size.

The obtained average grain sizes are 0.644×10³ nm, 1.14×10³ nm, 1.90×10³ nm, and 3.27×10³ nm, respectively, measured with ImageJ software. It is observed from the figures that primary-nano crystals are mostly cubic-shaped, highly homogenous, and well dispersed. The nanocrystals and their boundaries with zero Zr concentration are well defined. With increasing Zr content, the particle size of the crystals is increasing, and their shape and boundaries are starting to disappear. It is clear in the images that the bonds are breaking with the Zr concentration confirming the formation of nanoparticles. The mixture of crystalline nanoparticles and grain agglomerates is shown at a high concentration of zirconium. The crystallite size observed from XRD reveals the size of consistently diffracting domains, which signify the crystalline regions contained by a particle that are mostly smaller. In contrast, the grain size observed from the SEM micrograph includes the whole grains or visible particles, which can comprise several crystallites accumulated together; as a result, the grains are usually larger than the crystallites. This dissimilarity highlights that XRD provides more information about the inner crystalline coherence, whereas the exterior morphological features are visualized by SEM.

a	b
c	d
e	f
g	h

Fig. 10 (a-h). SEM images of Cr₁₋ₓZrₓFe₂O₄ with (a) x = 0 (b) x = 0.05 (c) x = 0.15 (d) x = 0.5 and their associated grain size distribution graph.

Biological Activity:

It is seen from Figure 11 that on LBA (Luria Bertani Agar) media, prepared samples of zirconium-doped chromium nanoparticles were inoculated. After incubation for 24 hours at 25°C, fungal growth was clearly visible. The fungal colonies were purified by the streaking method in separate plates. Zirconium-doped chromium nanoparticles were synthesized, and their antifungal activity was estimated against gram-negative and gram-positive strains. The prepared nanoparticles from 2g sample and four-gram sample are used against Alternaria solani (A), Alternaria alternata (B), Fusarium solani (C), Fusarium oxysporium (D), and Penicillium spp. (E) to check inhibition zones. The diffusion approach was applied well.

Alternaria solani is a fungal pathogen that produces a disease in tomatoes and potatoes called early blight [53]. 

Alternaria alternata causes black spot in many fruits and vegetables around the world. It is a latent fungus that develops during the cold storage of fruits [54]. The predominant hosts for Fusarium solani are potato, pea, bean, and members of the cucurbit family such as melon, cucumber, and pumpkin. Some strains may cause infections in humans [55]. Fusarium oxysporium is mostly found in water.

Fig. 11 : In vitro antifungal activity of zirconium-doped chromium nanoparticles against Alternaria solani (A), Alternaria alternata (B), Fusarium solani (C), Fusarium oxysporium (D), Penicillium spp (E)

The inhibition zone of Alternaria solani strain with zirconium-doped chromium nanoparticles of the 2 g sample is 1.0 cm or 10 mm. The inhibition zone of Alternaria alternata strain with zirconium-doped chromium nanoparticles of the 2 g sample is 1.5 cm or 15 mm. The inhibition zone of Fusarium solani strain with zirconium-doped chromium nanoparticles of 2g sample is 1.75 cm or 17.5 mm. The inhibition zone of Fusarium oxysporium strain with zirconium-doped chromium nanoparticles of the 2 g sample is 1.0 cm or 10 mm. The inhibition zone of Penicillium spp strain with zirconium-doped chromium nanoparticles of the 2 g sample is 1.5 cm or 15 mm.

References:

1. Langer R. Biomaterials in drug delivery and tissue engineering: one laboratory’s experience. Acc Chem Res. 2000;33(2):94–101.

2. Goodarz Naseri M, Saion EB, Abbastabar Ahangar H, Shaari AH, Hashim M. Simple Synthesis and Characterization of Cobalt Ferrite Nanoparticles by a Thermal Treatment Method. J Nanomater. 2010 Dec 23;2010:e907686.

3. Kefeni KK, Mamba BB, Msagati TA. Application of spinel ferrite nanoparticles in water and wastewater treatment: a review. Sep Purif Technol. 2017;188:399–422.

4. Raghasudha M, Ravinder D, Veerasomaiah P. Magnetic properties of Cr-substituted Co-ferrite nanoparticles synthesized by citrate-gel autocombustion method. J Nanostructure Chem. 2013;3(1):1–6.

5. Nair DS, Kurian M. Chromium-zinc ferrite nanocomposites for the catalytic abatement of toxic environmental pollutants under ambient conditions. J Hazard Mater. 2018;344:925–41.

6. Deraz NM. Glycine-assisted fabrication of nanocrystalline cobalt ferrite system. J Anal Appl Pyrolysis. 2010;88(2):103–9.

7. Jacintho GV, Brolo AG, Corio P, Suarez PA, Rubim JC. Structural investigation of MFe2O4 (M= Fe, Co) magnetic fluids. J Phys Chem C. 2009;113(18):7684–91.

8. Monaji VR, Indla S, Rayaprol S, Sowmya S, Srinivas A, Das D. Temperature dependent magnetic properties of Co1+ xTxFe2- 2xO4 (T= Zr, Ti). J Alloys Compd. 2017;700:92–7.

9. Kurian M, Nair DS. Manganese zinc ferrite nanoparticles as efficient catalysts for wet peroxide oxidation of organic aqueous wastes. J Chem Sci. 2015;127(3):537–46.

10. Lunk HJ. Discovery, properties and applications of chromium and its compounds. ChemTexts. 2015;1(1):1–17.

11. Anger G, Halstenberg J, Hochgeschwender K, Scherhag C, Korallus U, Knopf H, et al. Chromium compounds. Ullmanns Encycl Ind Chem. 2005;7.

12. Verma V, Ahmad S, Dar A, Kotnala R. An Inexpensive Route to Synthesize High-Purity CrO2 for EMI Shielding in X-Band Frequencies. Tc. 2012;1:2.

13. Zhang Z, Cheng M, Lu Z, Yu Z, Liu S, Liang R, et al. Magnetic properties and thermal stability of Ti-doped CrO2 films. J Magn Magn Mater. 2018;451:572–6.

14. Chamberland BL. The chemical and physical properties of CrO2 and tetravalent chromium oxide derivatives. Crit Rev Solid State Mater Sci. 1977;7(1):1–31.

15. Larbi T, Amara MA, Ouni B, Amlouk M. Enhanced photocatalytic degradation of methylene blue dye under UV-sunlight irradiation by cesium doped chromium oxide thin films. Mater Res Bull. 2017;95:152–62.

16. Ireland CP, Palgrave RG, Bennett SC, Smith AWJ, Clark JH, Darwent JR, et al. Visible light photocatalysis by metal-to-metal charge transfer for degradation of methyl orange. J Mater Chem A. 2016;4(32):12479–86.

17. Khan M, Khan W, Naziruddin Khan M, Alhazaa AN. Enhanced visible light-driven photocatalytic performance of Zr doped CeO2 nanoparticles. J Mater Sci Mater Electron. 2019;30(9):8291–300.

18. Huang S, Wu X, Niu J, Qin S. Structural, magnetic and electronic properties of CrO 2 at multimegabar pressures. RSC Adv. 2018;8(43):24561–70.

19. Ding Y, Yuan C, Wang Z, Liu S, Shi J, Xiong R, et al. Improving thermostability of CrO2 thin films by doping with Sn. Appl Phys Lett. 2014;105(9):092401.

20. Koirala R, Gunugunuri KR, Pratsinis SE, Smirniotis PG. Effect of zirconia doping on the structure and stability of CaO-based sorbents for CO2 capture during extended operating cycles. J Phys Chem C. 2011;115(50):24804–12.

21. Jung KT, Bell AT. An in situ infrared study of dimethyl carbonate synthesis from carbon dioxide and methanol over zirconia. J Catal. 2001;204(2):339–47.

22. Gan YX, Jayatissa AH, Yu Z, Chen X, Li M. Hydrothermal synthesis of nanomaterials. Vol. 2020, Journal of Nanomaterials. Hindawi; 2020.

23. Kavitha S, Kurian M. Effect of zirconium doping in the microstructure, magnetic and dielectric properties of cobalt ferrite nanoparticles. J Alloys Compd. 2019;799:147–59.

24. Meshesha DS, Matangi RC, Tirukkovalluri SR, Bojja S. Synthesis, characterization and visible light photocatalytic activity of Mg2+ and Zr4+ co-doped TiO2 nanomaterial for degradation of methylene blue. J Asian Ceram Soc. 2017;5(2):136–43.

25. Muhammad Z, Ali F, Sajjad M, Ali N, Bilal M, Shaik MR, et al. Zirconium-doped chromium IV oxide nanocomposites: synthesis, characterization, and photocatalysis towards the degradation of organic dyes. Catalysts. 2021;11(1):117.

26. Tseng TK, Lin YS, Chen YJ, Chu H. A review of photocatalysts prepared by sol-gel method for VOCs removal. Int J Mol Sci. 2010;11(6):2336–61.

27. Somraksa W, Suwanboon S, Amornpitoksuk P, Randorn C. Physical and photocatalytic properties of CeO 2/ZnO/ZnAl 2 O 4 ternary nanocomposite prepared by Co-precipitation method. Mater Res. 2020;23.

28. Holzwarth U, Gibson N. The Scherrer equation versus the’Debye-Scherrer equation’. Nat Nanotechnol. 2011;6(9):534–534.

29. Majid F, Wahid I, Ata S, Bibi I, Ali MD, Malik A, et al. Cationic distribution of nickel doped NixCoX-1Fe2O4 nanparticles prepared by hydrothermal approach: Effect of doping on dielectric properties. Mater Chem Phys. 2021;264:124451.

30. Utomo J, Agustina AK, Suharyadi E, Kato T, Iwata S. Effect of Co concentration on crystal structures and magnetic properties of Ni1-xCoxFe2O4 nanoparticles synthesized by co-precipitation method. Integr Ferroelectr. 2018;187(1):194–202.

31. Prabhu Y, Rao KV, Kumar VSS, Kumari BS. X-ray analysis of Fe doped ZnO nanoparticles by Williamson-Hall and size-strain plot methods. Int J Eng Adv Technol. 2013;2:268–74.

32. Parashar J, Saxena VK, Bhatnagar D, Sharma KB. Dielectric behaviour of Zn substituted Cu nano-ferrites. J Magn Magn Mater. 2015;394:105–10.

33. Hamedoun M, Benyoussef A, Bousmina M. Magnetic properties and phase diagram of ZnxNi1- xFe2O4: high-temperature series expansions. J Magn Magn Mater. 2010;322(21):3227–35.

34. Nasrin S, Hoque SM, Chowdhury FUZ, Hossen MM. Influence of Zn substitution on the structural and magnetic properties of Co1-xZnxFe2O4 nano-ferrites. IOSR J Appl Phys. 2014;6:58–65.

35. Farea AMM, Kumar S, Batoo KM, Yousef A, Lee CG. Structure and electrical properties of Co0. 5CdxFe2. 5- xO4 ferrites. J Alloys Compd. 2008;464(1–2):361–9.

36. Gul IH, Ahmed W, Maqsood A. Electrical and magnetic characterization of nanocrystalline Ni–Zn ferrite synthesis by co-precipitation route. J Magn Magn Mater. 2008;320(3–4):270–5.

37. Jasrotia R, Kumar G, Batoo KM, Adil SF, Khan M, Sharma R, et al. Synthesis and characterization of Mg-Ag-Mn nano-ferrites for electromagnet applications. Phys B Condens Matter. 2019;569:1–7.

38. Bosman AJ, Van Daal HJ. Small-polaron versus band conduction in some transition-metal oxides. Adv Phys. 1970;19(77):1–117.

39. Amin N, Hasan MSU, Majeed Z, Latif Z, un Nabi MA, Mahmood K, et al. Structural, electrical, optical and dielectric properties of yttrium substituted cadmium ferrites prepared by Co-Precipitation method. Ceram Int. 2020;46(13):20798–809.

40. Stokes AR, Wilson AJC. The diffraction of X rays by distorted crystal aggregates - I. Proc Phys Soc. 1944 May;56(3):174–81.

41. Nasrin S, Chowdhury FUZ, Hoque SM. Study of hyperthermia temperature of manganese-substituted cobalt nano ferrites prepared by chemical co-precipitation method for biomedical application. J Magn Magn Mater. 2019;479:126–34.

42. Arshad MI, Arshad S, Mahmood K, Ali A, Amin N, Isa M, et al. Impact of Mg doping on structural, spectral and dielectric properties of Cd–Cu nano ferrites prepared via sol-gel auto combustion method. Phys B Condens Matter. 2020;599:412496.

43. Padmapriya G, Manikandan A, Krishnasamy V, Jaganathan SK, Antony SA. Spinel NixZn1- xFe2O4 (0.0≤ x≤ 1.0) nano-photocatalysts: synthesis, characterization and photocatalytic degradation of methylene blue dye. J Mol Struct. 2016;1119:39–47.

44. Silambarasu A, Manikandan A, Balakrishnan K. Room-temperature superparamagnetism and enhanced photocatalytic activity of magnetically reusable spinel ZnFe2O4 nanocatalysts. J Supercond Nov Magn. 2017;30(9):2631–40.

45. Farzaneh F, Najafi M. Synthesis and characterization of Cr2O3 nanoparticles with triethanolamine in water under microwave irradiation. 2011;

46. Neppolian B, Wang Q, Yamashita H, Choi H. Synthesis and characterization of ZrO2–TiO2 binary oxide semiconductor nanoparticles: application and interparticle electron transfer process. Appl Catal Gen. 2007;333(2):264–71.

47. Mahmoud HR. Highly dispersed Cr2O3–ZrO2 binary oxide nanomaterials as novel catalysts for ethanol conversion. J Mol Catal Chem. 2014;392:216–22.

48. Pandey G, Dixit S, Shrivastava AK. Role of additives; sodium dodecyl sulphate and manganese chloride on morphology of Zn1- xMnxO nanoparticles and their photoluminescence properties. Mater Chem Phys. 2014;147(3):423–32.

49. Pradeep A, Priyadharsini P, Chandrasekaran G. Sol–gel route of synthesis of nanoparticles of MgFe2O4 and XRD, FTIR and VSM study. J Magn Magn Mater. 2008;320(21):2774–9.

50. Singh A, Chauhan P. Structural, electrical and optical properties of Mn0. 2Co0. 8Fe2O4 nano ferrites. Mater Today Proc. 2021;46:6264–9.

51. Anjum S, Rafique MS, Khaleeq-ur-Rahman M, Siraj K, Usman A, Hussain SI, et al. Investigation of induced parallel magnetic anisotropy at low deposition temperature in Ba-hexaferrites thin films. J Magn Magn Mater. 2012;324(5):711–6.

52. Zeeshan T, Anjum S, Waseem S, Riaz M, Zia R. Structural, optical, magnetic and (Y–K) angle studies of CdxCo1-xCr0. 5Fe1. 5O4 ferrite. Ceram Int. 2020;46(3):3935–43.

53. Olanya OM, Honeycutt CW, Larkin RP, Griffin TS, He Z, Halloran JM. The effect of cropping systems and irrigation management on development of potato early blight. J Gen Plant Pathol. 2009;75(4):267–75.

54. Fullerton RA. Brown spot of passionfruit on Niue Island caused by Alternaria alternata. N Z J Agric Res. 1982;25(3):421–3.

55. Aoki T, O’Donnell K, Homma Y, Lattanzi AR. Sudden-death syndrome of soybean is caused by two morphologically and phylogenetically distinct species within the Fusarium solani species complex—F. virguliforme in North America and F. tucumaniae in South America. Mycologia. 2003;95(4):660–84.