ISSN: 2456–5474 RNI No.  UPBIL/2016/68367 VOL.- IX , ISSUE- I February  - 2024
Innovation The Research Concept

Structural Modification of Zinc Ferrite Nanoparticles by Glycerol Influence
Paper Id :  18703   Submission Date :  14/02/2024   Acceptance Date :  19/02/2024   Publication Date :  23/02/2024
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DOI:10.5281/zenodo.10800285
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Subhash Chander
Associate Professor
Department Of Physics
S.S. Jain Subodh P.G. College
Jaipur,Rajasthan, India
Abstract

The current study provides for the evidence of the role of glycerol as a stabilizing and structure directing agent for the synthesis of stable zinc ferrite nanoparticles by means of a modified coprecipitation method. We report on the structural modifications obtained by the improved synthesis methodology in which the products are synthesized by the oxidation of glycerol that act on the zinc ferrite (ZnFe2O4) crystals. Glycerol inclusion has specific effects on the morphology of synthesized ZnFe2O4 nanoparticles that are reflected on comparison with other ZnFe2O4 nanoparticles obtained by the traditional and other novel methods.
Keywords Ferrites, Nanoparticles, X-ray diffraction (XRD), Morphology, Glycerol.
Introduction
Ferrites are found in various crystalline materials and have received increased attention in fundamental research due to their electrical, magnetic, optical and catalytic properties, finding applications in a variety of industrial sectors [1-3]. Among the spinel system, zinc ferrite (ZnFe2O4) is found to be one of the most extensively studied. It possesses an AB2O4 structure with tetrahedral A site occupied by Zn2+ ions and octahedral B site with Fe3+ ions in a face-centered cubic unit cell [4]. This ceramic presents high electromagnetic performance [1-5] great chemical stability and good catalytic activity. Such properties are strongly influenced by particle size, agglomeration and morphology which can be controlled in the synthesis process. The correlation between synthesis parameters and resulting physical properties provides insights on the activity and stability of these spinel ferrites. Therefore, several studies have been performed using a variety of wet chemistry techniques, such as sol-gel [6,7], hydrothermal, polymeric precursor method, sol-gel auto-combustion [8,9], polyol and coprecipitation [10, 11].
Aim of study

The objective of this paper is to study the Structural Modification of Zinc Ferrite Nanoparticles by Glycerol Influence.
Review of Literature

Coprecipitation is one of the most widely used methods for the synthesis of ferrite nanomaterials [12, 13]. This method consists of mixing aqueous solutions of metal salts at certain molar ratios in highly basic solutions, either at room temperature or at elevated temperature. The nanoparticles morphology and size depend on the type of salt used, ionic strength, pH and other reaction parameters such as stirring rate, dropping speed of basic solution, etc. However, the main challenge in this approach lies on the control of particles aggregation, once strong dipole-dipole magnetic interactions lead to a wide distribution in crystal sizes and coalescence effects caused by the thermal treatment can significantly affect the material efficiency. In principle, surfactant/polymer or ionic groups have been used to increase the stability and dispersion of nanoparticles, preventing the agglomeration and coalescence phenomena [14-16]. In this context, glycerol has been reported as an excellent chelating agent, once the ability of alcohol adsorption to prevent excessive growth and hydrophilic hydroxyl groups on the surface of the produced nanoparticles gives greater stability and avoid aggregation. Furthermore, glycerol is an organic compound widely used in single-component reactions such as oxidation and hydrogenolysis due to the susceptibility of three hydroxyl groups in the glycerol molecule [17].

In this work, we investigated an alternative coprecipitation route using glycerol for the production of zinc ferrites. In this route, we explore the chelating capacity of the glycerol, combined with its oxidation and the generated products so that structural and morphological aspects of the zinc ferrites nanoparticles are achieved. The structural and morphological characteristics of the nanoparticles were evaluated by means of different techniques such as X-ray diffraction (XRD). The obtained results demonstrate that zinc ferrite crystals synthesized in the presence of glycerol are initially bigger than those synthesized in absence of it, but according to the oxidation process they tend to decrease giving rise to intermediate phases. Interestingly, these samples grow again during further stages and become structurally better organized, compared to the series of samples produced in absence of glycerol.
Methodology

Experimental Details

(a) Synthesis

All chemicals used, FeCl3·6H2O, ZnCl2, NaOH and glycerol were of analytical grade, purchased from Sigma-Aldrich and used as received. Two series of zinc ferrite samples have been prepared by coprecipitation methods. The first series consists of the modified coprecipitation method, in which the samples were prepared with glycerol as structure directing and stabilizing agent. The samples prepared include intermediates that were characterized so that the role played by glycerol could be studied. For the preparation of these samples a mixed aqueous solution was prepared by dissolving 3.3637 g of FeCl3·6H2O and 0.8481 g of ZnCl2 in 3 mL of distilled water. Glycerol was added to this solution (4 mL), under vigorous stirring, and then 10 mL of 4.97 mol L-1 NaOH (precipitating agent) was added dropwise. An aliquot of the formed suspension was centrifuged and the separated solid named as Z1-gly (stage 1). The main suspension was transferred to an alumina tube and heated to 150 ºC for 15 h, under static conditions. An aliquot of the resulting material was separated, centrifuged and the solid named as Z2-gly (stage 2). The suspension was then heated at 350 ºC for 1 h under rotation in air atmosphere (90 mL min-1). Again, an aliquot was separated, and named as Z3-gly (stage 3). The remaining material was heated at 600 ºC, under the same atmosphere and rotation conditions of the previous sample. The obtained material was named as Z4-gly (stage 4). All these samples were washed with distilled water, centrifuged at 6000 rpm and dried at 100 ºC for 8 h.

The second series consists of zinc ferrite nanoparticles synthesized by means of the traditional coprecipitation method. In this case, the synthesis procedures were similar to the above described method, but without using glycerol. The correspondent obtained samples were named as Z1-Ø, Z2-Ø, Z3-Ø and Z4-Ø.

Characterization

XRD experiments were performed using an X-ray powder diffractometer X’pert MPD (Panalytical) operated at 35 kV and 30 mA. The high-resolution diffraction is obtained with a hybrid monochromator for incidence beam, which consists of mirror and Ge monochromator producing a parallel and highly monochromatic beam, respectively. The XRD measurements were performed from 10º to 90º with counting time of 150 s. Structure refinement and quantitative analysis of the obtained nanoparticles were carried out by the Rietveld method. The crystallographic data of zinc ferrite (ZnFe2O4), dihydrate zinc oxalate (ZnC2O4×2H2O) and zinc oxide (ZnO) were imported from the inorganic crystal structure database [18]. These results were used to calculate the average crystallite size of the samples through Scherrer equation [19], D = (kλ) / (βcosθ), where k is the shape coefficient, θ is the Bragg angle and β is the full-width at half maximum (FWHM) of the diffraction peaks, which was corrected for instrumental broadening.
Result and Discussion

X-ray diffraction (XRD)

Figure 1 and 2 show the results for the two series of samples prepared according to the modified and the traditional methods, respectively. In addition, Rietveld refinement results and quantitative analyses of all obtained nanoparticles are presented in Figures Z1, Z2,. By using both methods, the diffraction patterns obtained for the samples at the stage 1 (Figures 1b and 2b) show the presence of only a zinc ferrite crystalline phase. The insets of Figures 1 and 2 show the diffraction peaks with amplified intensity, which provide an easier visualization. Moreover, the sample produced in presence of glycerol presents FWHM lower than for the sample obtained via traditional route, which indicates that there is difference in the crystallite sizes depending on the method used. In fact, the average particles size calculated by Scherrer equation is 5 nm for the sample Z1-gly and 2 nm for the sample Z1-Ø. The bigger crystal size observed for the sample Z1-gly can be considered a direct result of the variation in the precursor salts solubility in the presence of glycerol, due to the hydrogen bonding between hydroxyl groups of glycerol and the ions in the solution [20]. Despite this, both samples (Z1-gly and Z1-Ø) are composed of crystalline materials with very small dimensions. In principle, this reduced crystal sizes are associated with basicity and the ionic strength of the precipitation medium, i.e., the higher the pH the smaller the crystal size [21, 22].


Figure 1 XRD patterns of the samples obtained by the modified method: (a) standards for zinc ferrite peaks; (b) Z1-gly; (c) Z2-gly; (d) Z3-gly (with the highlighted peaks referring to zinc oxide phase) and (e) Z4-gly. The inset shows (a) standards for zinc oxide peaks and, in a magnified scale, (b) Z1-gly and (c) Z2-gly (with the highlighted peaks referring to zinc oxalate phase).


Figure 2 XRD patterns of the samples obtained by the traditional method: (a) standards for zinc ferrite peaks; (b) Z1-Ø; (c) Z2-Ø; (d) Z3-Ø and (e) Z4-Ø. The inset shows (a) standards for zinc oxide peaks and, in a magnified scale, (b) Z1-Ø and (c) Z2-Ø. 

For the sample Z2-gly (Figure 1c) two phases were identified, namely, zinc ferrite and dihydrate zinc oxalate. The average crystal size obtained by Scherrer equation to zinc ferrite is 2 nm and for dihydrate zinc oxalate is 10 nm. It should be noted that ferrites can act as catalyst in the glycerol oxidation reactions [23, 24]. This oxidation reactions could potentially produce compounds such as glyceraldehyde and dihydroxyacetone (simultaneous and/or subsequent), which by further oxidation can be converted to some oxidized products as glyceric, tartronic, formic, glycolic and oxalic acid [23-25]. The presence of dihydrate zinc oxalate at the end of stage 2 indicates the occurrence of this process. The oxalate salt observed would result from the dissolution reaction of the zinc ferrite by the oxalic acid formed in situ. From this perspective, a decrease in the average crystal size observed for the zinc ferrite phase (compared to the sample Z1-gly) becomes clear. On the other hand, when sample Z2-Ø (Figure 2c) is compared with the previous one (Z1-Ø), no difference in size is observed, revealing that the thermal treatment applied was not able to cause perceptive changes in the crystalline structure.

As shown in Figure 1d, two crystalline phases were identified for the sample Z3-gly: zinc ferrite and zinc oxide, and their average crystal sizes were found to be 13 and 9 nm, respectively. On the other hand, without the addition of glycerol (Z3-Ø), zinc oxide formation did not occur and only zinc ferrite phase (crystal size of 10 nm) was identified. According to the XRD data analysis, the zinc ferrite structure observed in both Z3-gly and Z3-Ø samples presented similar characteristics. However, the growth of zinc ferrite nanoparticles in the sample Z3-gly was accompanied by a thermal degradation event of the dihydrate zinc-oxalic phase, i.e, water and CO2 were released from this salt during the heating process, resulting in the zinc oxide phase. Note that the calculated quantity of zinc oxide phase in the sample differs from what is expected due to the degradation which means that some zinc atoms might have been incorporated into the zinc ferrite structure.

The samples obtained at the end of stage 4 present XRD patterns of pure zinc ferrite nanoparticles with average crystal size of 46 nm for the sample Z4-gly (Figure 1e) and 20 nm for the sample Z4-Ø (Figure 2e). These different sizes essentially highlight the role of glycerol as well as its derivatives in the overall crystallization process. For the modified method, the larger size of the precipitated crystal in the stage 1 implies in a small number of nucleated crystals. In stage 2, this number of nucleated crystals is further reduced. The acid attack not only reduced the average size of the produced crystals, but also decreased the total amount, which means that a complete dissolution event might have occurred in smaller crystals. On the other hand, during the traditional method of co-precipitation, the amount of crystals remains unchanged during the similar stages. Those variations lead to different average size of zinc ferrite nanoparticles at the final stage (Z4).
Conclusion

This study has provided evidence of the role of glycerol as a stabilizing and structure directing agent for zinc ferrite nanoparticles synthesis by means of a modified coprecipitation method. Herein, we reported the modifications observed for the modified method in which the products generated by glycerol oxidation act on the zinc ferrite crystals synthesis process. The glycerol influence over the morphology of the zinc ferrite materials synthesized can be clearly observed when the crystals obtained from the different methods, the traditional and the modified ones, are compared.

The results of characterization carried out by the different techniques used in this work are consistent with a mechanism centered in partial dissolution and subsequent recrystallization of zinc ferrite mediated by glycerol and other compounds generated from it, which also act towards formation of intermediate phases and encapsulation of the formed crystals. The samples obtained by the coprecipitation modified method using glycerol showed better structural organization. Therefore, the modification of the coprecipitation method with glycerol induces to important improvements of physical properties of zinc ferrite nanoparticles produced, evidencing the potential of this method in the synthesis of ferrites.
Acknowledgement The authors acknowledge Professor K. B. Sharma for invaluable discussions for providing the equipment and technical support for the experiments involving XRD.
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