Effect of heat treatment time in oxygen atmosphere on the stabilization of magnetite NPs: synthesis, characterization, and magnetic response

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The use of this agent allowed for the complete crystallization of pure magnetite phase at 200°C, without atmosphere control during the thermal treatment for crystallization. Different thermal treatment times (4, 8, 16, 24, and 48 hours) and their effects on the structure, microstructure, and magnetic properties of the nanoparticles were evaluated. The results showed that the magnetite phase remained stable and pure up to 8 hours of thermal treatment in an air atmosphere, with nanoparticles exhibiting a crystallite size of 30 nm and saturation magnetization of 57 emu/g. After 16 hours, the presence of a magnetite/hematite heterostructure was observed, with approximately 22.5% hematite (α-Fe 2 O 3 ). The presence of hematite increased with the thermal treatment time, reaching 25.4% at 48 hours, and the saturation magnetization decreased with the reduction of magnetite phase in the nanoparticles. Additionally, the NPs dispersion in different liquid media (isopropyl alcohol, distilled water, and ethylene glycol) was verify to evaluated suspension stability and total magnetic collection time, aiming for potential applications as a magnetic fluid. Nanoparticles Magnetite Fe3O4 sol-gel heterostructure thermal treatment Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Highlights - Pure NPs magnetite by sol-gel method at 200°C, without atmosphere control during the thermal treatment for crystallization. - NPs magnetite phase remained stable and pure up to 8 hours of thermal treatment in 200°C in air atmosphere. - After 16 hours and 48 hours, the presence of a magnetite/hematite heterostructure was observed, with approximately 22.5% and 25,4% hematite (α-Fe 2 O 3 ), respectively. - NPs dispersion in different liquid media (isopropyl alcohol, distilled water, and ethylene glycol) showed potential applications as a magnetic fluid. Introduction Magnetite (Fe 3 O 4 ) nanoparticles (NPs) have shown promise in various fields such as electronics, biomedicine, transportation, drug delivery, cell separation, localized magnetic hyperthermia therapy, tissue repair, ferrofluids, catalysis, and magnetic devices [ 1 ]. These applications benefit from the unique properties of this material, which is non-toxic, biocompatible, and exhibits the highest magnetic response among all natural minerals. Magnetite have an inverse spinel crystal structure with the formula B[AB]O 4 , where Fe 3+ ions occupy half of the tetrahedral sites (A) and Fe 2+ and Fe 3+ ions occupy half of the octahedral sites (B), resulting in significant ferrimagnetic behavior [ 2 – 4 ]. When the size of magnetite particles decreases to values below 30 nm, they exhibit superparamagnetic behavior [ 3 , 5 ], along with increased reactivity due to enhanced surface area and high dispersion in polar solvents of medium to high viscosity, which favors their efficiency in biomedical and catalytic applications with partial/total magnetic recovery [ 2 ]. However, magnetite (Fe 3 O 4 ) is not the most stable phase of iron oxide and can transform into other phases such as maghemite (γ-Fe 2 O 3 ) and hematite (α-Fe 2 O 3 ) under ambient conditions and temperatures above 300°C [ 6 ]. Therefore, the synthesis of magnetite, especially on a nanoscale, requires careful control of synthesis parameters and the use of inert or reducing atmospheres during the thermal treatment for crystallization in order to delay the transformation to more stable phases and ensure the complete crystallization of nanoparticles [ 7 ]. In the literature, chemical synthesis methods that ensure reduced control over particle size and morphology, such as controlled precipitation [ 8 ], co-precipitation [ 9 ], hydrothermal and solvothermal methods [ 10 , 11 ], combustion [ 12 , 13 ], and sol-gel [ 7 , 14 – 16 ], have been utilized in recent years to obtain stable magnetite at temperatures below 350°C. Generally, in these methods involving thermal decomposition for crystallization, all thermal treatments must be conducted under controlled atmosphere conditions as mentioned earlier and discussed by Niculescu et al. [ 1 ] in the 2022 review on magnetite nanoparticle synthesis. Manikandan et al. [ 12 ], in the synthesis of magnetite using microwave-assisted combustion method (2.45 GHz 850 W) and conventional heating (500°C, 2 h, 5°C/min), observed that the nitrogen-rich atmosphere self-generated during the combustion process between the oxidizing reagent (Fe(NO 3 ) 3 ·9H 2 O) and urea (CO(NH 2 ) 2 ) as a fuel, favored the formation of pure magnetite phase in both heating methods, with microwave being energetically less costly. Similarly, Aali et al. [ 13 ], in obtaining pure magnetite by the combustion method evaluating the use of different fuels (glycine, urea, and citric acid), determined that glycine (C 2 H 5 NO 2 ) was the only fuel that provided a sufficiently reducing atmosphere rich in H 2 and CO 2 to ensure the stability of pure magnetite after the combustion process. On the other hand, Wan et al. [ 17 ] reported the use of ethylene glycol in the preparation of monodispersed nanometric magnetite mesocrystals by the solvothermal method at 200°C in the presence of NaOH, where they found that the formed Fe(OH) 2 hydroxide is balanced by the intercalation of the ethylene glycol anion, allowing the formation of primary magnetite particles ordered in spherical superstructures/mesocrystals. Similarly, Cótica et al. [ 18 ] reported the synthesis of magnetite NPs by the thermal decomposition method using an ethylene glycol and ferric nitrate precursor solution, using temperatures of 300°C and 500°C in an argon atmosphere, the authors reported the stabilization of the phase even up to 500°C with particle sizes of 20 nm and saturation magnetization values of 67 emu/g close to those of bulk magnetite (92 emu/g). In the other hand, there are few reports in the literature on the use of ethyleneglycol as a chelating agent during sol-gel synthesis. Takai et al. [ 15 ] synthesized magnetite nanoparticles via the sol-gel method using ethylene glycol, FeCl 2 , and FeCl 3 as precursors. The authors employed thermal treatment temperatures of 200°C, 300°C, and 400°C under vacuum, obtaining crystallites with sizes ranging approximately between 2 and 25 nm. However, at temperatures of 300°C and 400°C, the authors observed the formation of secondary phases of maghemite and hematite alongside the magnetite phase. Polla et al. [ 16 ], using iron nitrate as a precursor for obtaining magnetite NPs for water treatment, also conducted thermal treatments at temperatures of 200°C, 300°C, and 400°C without atmosphere control, resulting in pure magnetite phase formation at the first two temperatures. Thus, the use of ethyleneglycol as a solvent in both solvothermal and sol-gel methods is highly promising for the production of magnetite nanoparticles. Thus, in this work, magnetite nanoparticles were synthesized by the sol-gel method using ethylene glycol as a chelating agent. Thermal treatments for decomposition/crystallization were conducted without atmosphere control, and different treatment times were evaluated to analyze their effects on the structural, microstructural, and magnetic behaviors of the nanoparticles. Experimental The magnetite nanoparticles (NPs) were obtained through a modified sol-gel method, using ethylene glycol (C 2 H 6 O 2 , Synth, 99%) as a chelating agent. Initially, ethylene glycol and iron nitrate (Fe 3 (NO 3 ) 3 ·9H 2 O, Merck, 99%) were mixed under constant stirring. Subsequently, the temperature was raised to 80°C and maintained for 1 hour with continuous stirring, resulting in the orange-colored solution transitioning into a dark brown gel. The gel was completely dehydrated at 100°C to obtain the xerogel. Thermal analysis was conducted using differential scanning calorimetry and thermogravimetric analysis (DSC/TG - NETZSCH STA 409 C/CD) with a heating rate of 5°C/min to examine the behavior of the xerogel with increasing temperature. Following this, the xerogel was subjected to thermal treatments ranging from 170°C to 250°C to determine the most suitable magnetite crystallization temperature. Since these temperatures are below the decomposition temperature of the organic phase, the material underwent chemical washing with a 3.0 M acetic acid solution to ensure complete removal of residual organic phase. Once the optimal magnetite crystallization temperature was determined (200°C), the xerogel was thermally treated in a furnace (EDG 3000) at this temperature for varying hold times: 4, 8, 16, 24, and 48 hours. All NPs obtained under different conditions underwent chemical washing with 3.0 M acetic acid (CH 3 COOH). The structural analysis of all NPs was performed using a Bruker AXS diffractometer with CuKα radiation as the source. Approximate magnetite concentrations for each condition were estimated from the diffractograms using the intensity equation (Eq. 1 ). $$\%Magnetite Phase= \frac{{I}_{311 \left(Magnetite\right)}}{{I}_{311 \left(Magnetite\right)+{I}_{104 \left(Hematite\right) }}}$$ 1 where I 311 and I 104 correspond to the maximum intensity value of the main peak of magnetite (311) located at 2θ = 35.6 and hematite (104) located at 2θ = 33.2, respectively. The crystallite sizes (L) were calculated using the Scherrer equation (Eq. 2 ) $$L= \frac{K\lambda }{\text{cos}\theta \beta }$$ 2 where K is the dimensionless size factor, typically close to unity (K ~ 0.9), λ is the wavelength, in this case, 0.15418 nm, β is the full width at half maximum, and θ is the value corresponding to the peak of highest intensity. The microstructural analysis of the NPs treated at different hold times was performed using a scanning electron microscope (SEM) FEI Quanta 650F, and transmission electron microscopy (TEM) in a Tecnai LaB6 - ASTAR. The resulting micrographs were analyzed using Image J software to determine the average NP size. The estimation was conducted by measuring 200 particles to ensure reliable statistics. Frequency histograms were adjusted using a LogNormal function to estimate both the average size and size distribution of the NPs. Nitrogen adsorption measurements using the BET technique for surface area analysis were carried out on a Micromeritics Gemini-2370, and the equivalent spherical diameter (D BET ) was estimated using the relationship described by Eq. 3 . $${D}_{BET}= \frac{6}{{S}_{BET} x {\rho }_{th}}$$ 3 where SBET is the surface area measured by the BET test and ρth is the theoretical density, which in this case is 5.216 g/cm 3 , as per PDF #75-1609. The dispersion of the NPs in liquid media (isopropyl alcohol, distilled water, and ethylene glycol) was performed via ultrasonication for 5 minutes at room temperature. The total collection time of the dispersed NPs in the three liquids when subjected to an external magnetic field was measured, as well as the stability time of the dispersion without the presence of an external magnetic field. Finally, for the analysis of the magnetic behavior of the samples, magnetization measurements as a function of magnetic field were carried out using a Magnetic Property Measurement System (MPMS®3) combined with a dc SQUID sensor (Quantum Design®), with a maximum field of 80 kOe, at room temperature. Results and Discussion In the thermal analyses TG-DTG/DSC in Fig. 1 , it's possible to verify that the xerogel lost a total of 75% of mass, a typical behavior in the decomposition of polymeric resins. Initially, an endothermic peak was observed at approximately 74°C, corresponding to the elimination of residual water in the sample, followed by the decomposition and oxidation of the organic phase, which occurs in two distinct stages, marked by abrupt changes in the slope of the TG curve, with clear peaks indicated by the maxima of the DTG at 150°C and 340°C. It can be observed that the width of the peak at 340°C in the DTG is relatively narrow, indicating that the evolution of decomposition/oxidation of the organic phase at this temperature is relatively rapid, initiating the crystallization process, unlike the first peak (150°C) where the decomposition and oxidation of the organic phase are slower, possibly associated with the breakage of complex polymeric chains. Through DSC analysis, the maximum exothermic peak at 330°C and the endothermic peak at 350°C, accompanied by a mass loss of approximately 15%, possibly associated with the transformation of the crystalline phase from magnetite (Fe 3 O 4 ) to hematite (α-Fe 2 O 3 ) (the more stable polymorphic phase of iron oxide), followed by the complete decomposition of the xerogel, above 350°C, no thermal events or significant changes in mass loss were observed, indicating that the system is stable. From the analysis of TG-DSC/DSC results, it was found that the thermal treatment temperature where the synthesized magnetite phase possibly retained by sol-gel is between 147°C and 330°C. Therefore, thermal treatments were carried out between 150°C and 300°C for 4 hours without atmosphere control, in order to evaluate the onset of magnetite crystallization. In Fig. 2 , the X-ray diffractograms of the xerogel thermally treated at 150°C, 200°C, and 300°C for 4 hours are presented. The thermal treatment at 150°C revealed little crystallization of the sample, indicating that there was no onset of magnetite phase crystallization at this temperature, corroborating the TG-DTG/DSC analysis in Fig. 1 , where the first exothermic peak is solely associated with the decomposition of the organic phase with a 60% mass loss. With the temperature increase to 200°C, it is possible to observe the presence of all diffraction peaks related to magnetite, namely (220), (311), (222), (400), (422), (511), and (440) according to crystallographic card PDF 75–449, indicating that the onset of magnetite crystallization occurs shortly after the elimination of the organic phase and these are not concomitant events. The peak widths suggest the presence of magnetite nanoparticles. At 300°C, the formation of magnetite phase was also observed, with approximately 25% presence of hematite phase (PDF 85–599), confirming the TG-DTG/DSC analysis in Fig. 1 regarding the temperature range between 300 and 350°C where the complete phase transformation from magnetite (Fe 3 O 4 ) to hematite phase (α-Fe 2 O 3 ) would take place. Thus, 200°C was defined as the minimum temperature for the crystallization and stabilization of magnetite without atmosphere control. One parameter taken into consideration was the fact that, according to the thermal analyses in Fig. 1 , at 200°C, the organic phase of the xerogel was not completely oxidized and decomposed, with 15% of organic material remaining. To overcome this situation, the material treated thermally at 200°C was subjected to a chemical washing step using acetic acid (CH 3 COOH) at a concentration of 0.3 M. Figure 3 presents a comparison of the diffractograms, with and without chemical washing of the NPs obtained at 200°C. It is possible to observe that the diffraction peaks became more evident after chemical washing, revealing that the 0.3 M acetic acid used favored the elimination of residual organic phase at 200°C. Similar to Manami et al. [ 19 ], who reported the use of chemical washing to promote the precipitation of iron oxyhydroxide. Meanwhile, Ali et al. [ 20 ], to promote magnetite synthesis, prepared a nanoemulsion containing iron sources and sodium hydroxide, and finally, chemical washing with ethanol was carried out to exhibit superparamagnetic behavior with magnetization values. Once the minimum crystallization temperature and parameters for eliminating residual organic phase were defined, different holding times were proposed: 4, 8, 16, 24, and 48 hours at 200°C, aiming to evaluate the effect of the thermal treatment time under uncontrolled atmosphere conditions on the structural, microstructural, and physical properties of magnetite. The XRD analysis of the NPs subjected to different thermal treatment times presented in Fig. 4 (left) indicates the maintenance of the complete integrity of the magnetite phase for up to 8 hours of holding time at 200°C without atmosphere control. Above 16 hours, the formation of some traces of hematite phase (α-Fe 2 O 3 ) (PDF 85–599) can be observed, as evidenced by the presence of the peak at 2θ = 33.1 corresponding to the crystallographic plane (104), present at a concentration of approximately 22.5% (Eq. 1 ). It is possible to observe a slight increase in the concentration of hematite phase with increasing holding time, reaching concentrations of 24.0% and 25.4% in the treatments of 24 and 48 hours, respectively, as listed in Table 1 . It's noticeable the narrowing of all crystallographic peaks with increasing holding time, suggesting the enlargement of NP sizes, as observed in the analysis in Fig. 4 (right), which zooms in on the peak of highest intensity, corresponding to the crystallographic plane (311) adjusted using a Lorentz-type function. This indicates a smaller full width at half maximum (FWHM), and consequently, larger Scherrer crystallite size, as can be observed by calculating the crystallite size using the Scherrer equation (Eq. 2 ), as presented in Table 1 . Xu et al. [ 7 ] also observed this effect for sol-gel synthesized magnetite using iron nitrate and ethylene glycol as precursors. The authors noted that with the increase in thermal treatment temperature in the range between 200°C and 400°C, the full width at half maximum decreases and the reflection peaks become narrower, indicating larger crystallite sizes and better crystallinity of the phase. Table 1 Percentage values of hematite phase, crystallite size according to Scherrer euqation, average particle size from SEM and TEM micrographs . Holding time (hours) % Magnetite Phase * Crystallite size (nm) SEM average particle size (nm) ** TEM average particle size (nm) *** 4 100 25 35 ± 3 18 ± 0,1 8 100 30 39 ± 5 16 77.5 32 43 ± 4 32 ± 0,5 24 76.0 43 49 ± 3 - 48 74.6 52 54 ± 4 46 ± 1,1 *Calculated according to Eq. 1 , ** Based on SEM micrographs analysis, LogNormal fitting, *** Based on TEM micrographs analysis, LogNormal fitting. From the microstructural analysis presented in the SEM micrographs in Fig. 5 , it is possible to observe a high agglomeration degree, inherent to the synthesis method. Soft, easily pulverizable clusters with a heterogeneous size distribution are observed. It was also noted that at all evaluated holding times, the nanoscale size of the particles was retained, but there is evident nanoparticle growth with increasing holding time. It's possible to identify that the clusters consist of equiaxial primary particles with sizes between 35 ± 3 nm at 4 hours of holding time and 54 ± 4 nm at 48 hours, as presented in Table 1 and depicted in the size vs. time curve in Fig. 5 (f). Furthermore, it was noticeable that with longer holding times, the particles acquired a more spherical shape due to the higher energy expended in the process, assuming the thermodynamically more stable form, as verified by Cotica et al. [ 18 ]. The crystallite size was in line with the calculated average particle size inferred from SEM micrographs analysis. In this case, the same trend of larger average particle sizes with increasing holding time of the thermal treatment was observed. From the microstructural analysis using transmission electron microscopy (TEM) in Fig. 6 , the nanoscale nature of the particles is highlighted. With a holding time of 4 hours, as shown in Table 1 , the estimated average size of primary particles was 18 ± 0.1 nm, while with longer holding times, the estimated size of primary particles tripled in size, with an estimated value of 46 ± 1.1 nm, as shown in the histograms of distribution measurements in dark-field micrographs in Fig. 6 (bottom). The SAED inset in the bright-field micrographs of 4 and 16 hours shows a characteristic pattern of continuous rings typical of nanocrystalline systems, while at 48 hours, a polycrystalline pattern composed of regular spots associated with larger crystals is observed, corroborating the difference in particle size with increasing holding time. From the BET analysis, it is possible to observe the trend of decreasing surface area with increasing holding time, while the values of equivalent spherical diameter calculated using Eq. 2 were close to those obtained by TEM analysis. This result indicates the high dispersion of magnetite NPs obtained under all evaluated holding time conditions. Shaker et al. [ 21 ] studied the synthesis of magnetite with ethylene glycol at different thermal treatment temperatures ranging from 200 to 400°C, where an average particle size in the range of 30 to 90 nm was observed. Temperatures above 400°C failed to retain the magnetite phase, resulting in the formation of hematite phase. On the other hand, Nkurikiyimfura et al. [ 22 ] investigated the synthesis of magnetite by co-precipitation-reduction, where the average particle diameter was around 11 nm, exhibiting superparamagnetic behavior as expected. Table 2 Surface area and equivalent spherical diameter of the NPs obtained at different holding times. Holding time (hours) Surface area (BET) (m 2 /g) Equivalent spherical diameter (nm) * 4 106.4 11.0 8 114.6 10.0 16 105.0 11.0 24 104.1 11.0 48 67.2 17.0 * Eq. 3 The magnetite NPs obtained at 200°C for 8 and 48 hours were dispersed in isopropyl alcohol, distilled water, and ethylene glycol via ultrasonication for 5 minutes at room temperature. All resulting suspensions responded to an external magnetic field, as shown in the photographs of Fig. 7 . From the assays, it was possible to observe the high dispersion of both samples (8 and 48 h) in the three liquid media evaluated, indicating their reduced particle size, an important characteristic, especially for suspensions in water, specifically for biomedical applications, where a high dispersion of magnetite NPs in body fluids is required. In the case of the magnetic fluid used in cancer therapy, which requires high dispersion and suspension stability for a certain period, in order to improve heating efficiency to ensure the elimination of tumor cells. The total collection of NPs obtained in 8 hours when subjected to an external magnetic field occurred at times of 5, 15, and 120 minutes in alcohol, water, and ethylene glycol media, respectively. For the NPs obtained in 48 hours, which exhibit 25.4% hematite phase (α-Fe 2 O 3 ), according to XRD analysis (Fig. 4 ), as expected, the total collection times were doubled, being 15, 30, and 240 minutes in alcohol, water, and ethylene glycol media, respectively. These results indicate the good magnetic behavior of the obtained NPs. The stability of the suspensions was observed through the precipitation of the samples over a period of 2 days, as shown in Fig. 8 . These results indicate that the synthesized NPs offer a long suspension stability characteristic both in water and in ethylene glycol, an important feature for applications where prolonged dispersion is required, such as in magnetic fluids used in cancer therapy as mentioned earlier. In Fig. 9 , the magnetization curves (emu/g) as a function of the applied magnetic field (Oe) of the hematite NPs obtained at different holding times are presented. The magnetization curves revealed the superparamagnetic behavior of all NPs, which was expected for materials with particle sizes below 50 nm. As reported by several authors, superparamagnetic behavior is common in magnetite nanoparticles [ 7 , 19 , 25 , 26 ]. Table 3 presents the values of saturation magnetization, remanent magnetization, and coercive field of the magnetite NPs subjected to different thermal treatment times (4–48 hours), resulting in different initial particle sizes ranging from 30 nm to 50 nm. It is possible to observe an increase in saturation magnetization when the sample is subjected to holding times of 8 hours, possibly due to the increased crystallinity of the magnetite phase. On the other hand, for holding times above 16 hours, there is a gradual decrease in saturation magnetization, associated with the presence of hematite phase in the sample, corroborating the XRD results presented in Fig. 4 . Table 3 Magnetization properties NPs Holding time (hours) Inital Particle size (nm) Saturation magnetization (emu/g) Remanent magnetization (emu/g) Coercitive field (kOe) 4 35 13 0.82 22.5 x10 − 3 8 39 57 0.90 6.1x10 − 3 16 43 5 0.31 13.95 x10 − 3 24 49 30 0.42 25.35 x10 − 3 48 54 13 0.085 25.14 x10 − 3 Conclusions The sol-gel synthesis using ethylene glycol was effective in forming and stabilizing the magnetite (Fe 3 O 4 ) phase at 200°C without the use of controlled atmosphere. Up to 8 hours of thermal treatment, 100% integrity of the pure phase was maintained, while above 16 hours, the presence of 22.5% hematite phase (α-Fe 2 O 3 ) was observed, reaching up to 25.4% of this phase after 48 hours of thermal treatment. The estimated average particle sizes of the NPs varied from approximately 20 nm for 4 hours of treatment to approximately 50 nm for 48 hours of treatment where the magnetite/hematite heterostructures were presente. The magnetite NPs exhibited high dispersion for both samples (8 and 48 h) in the three evaluated liquid media (ethyl alcohol, water, and ethylene glycol), indicating their reduced particle size and remaining dispersed for a long period of time, 24–48 hours in water and ethylene glycol. The total collection of NPs obtained in 8 hours when subjected to an external magnetic field occurred within 5, 15, and 120 minutes in alcohol, water, and ethylene glycol media, respectively. For the NPs obtained in 48 hours, the total collection times were doubled, with these samples containing 25.4% hematite phase. All NPs exhibited superparamagnetic behavior due to their particle sizes being below 50 nm. The maximum saturation magnetization value obtained was 57 emu/g in the 8-hour treatment sample, which still maintained stable pure magnetite. Above 16 hours of thermal treatment, there was a gradual decrease in saturation magnetization associated with the presence of hematite phase, as expected. Declarations Acknowledgments The authors would like to thank the Structural Characterization Laboratory (LCE/DEMa/UFSCar) for the general facilities, the Hydrogen in Metals Laboratory (LHM/CPqMaE/UFSCar) for the DSC/TG results, Prof. Dr. Adilson de Oliveira and Leonardo Dalla Costa from the Superconductivity and Magnetism Group (GSM/DF/UFSCar) and the Interdisciplinary Laboratory of Electrochemistry and Ceramics, Department of Chemistry, Federal University of São Carlos (LIEC/DQ/UFSCar) for the magnetic measurements, and the funding agencies CAPES (PNPD20131474 – 33001014004P9), CNPq (Proc. 431304/2016-5), and FAPESP (Proc. 2017/2509-0) for the scholarships and general support. This work was supported by the Coordination for the Improvement of Higher Education Personnel (CAPES) - Financing Code 001. References Adelina-Gabriela Niculescu, CristinaChircov, Alexandru Mihai Grumezescu. 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De Souza Brito, Synthesis and characterization of Fe3O4 nanoparticles with perspectives in biomedical applications, Mater. Res. 17 (2014) 542–549. https://doi.org/10.1590/S1516-14392014005000050 A. Ali, H. Zafar, M. Zia, I. ul Haq, A.R. Phull, J.S. Ali, A. Hussain, Synthesis, characterization, applications, and challenges of iron oxide nanoparticles, Nanotechnol. Sci. Appl. 2016:9 (2016) 49–67. S. Shaker, S. Zafarian, C.S. Chakra, K.V. Rao, PREPARATION AND CHARACTERIZATION OF MAGNETITE NANOPARTICLES BY SOL-GEL METHOD FOR WATER TREATMENT, Int. J. Innov. Res. Sci. Eng. Technol. 2 (2013). www.ijirset.com Innocent Nkurikiyimfura, Yanmin Wang, Bonfils Safari, Emmanuel Nshingabigwi, Temperature-dependent magnetic properties of magnetite nanoparticles synthesized via coprecipitation method, Journal of Alloys and Compounds, 846, 2020, 156344, https://doi.org/10.1016/j.jallcom.2020.156344 L. Vekas, D. Bica, M.V. Avdeev, Vékás, Ladislau et al. “Magnetic nanoparticles and concentrated magnetic nanofluids： Synthesis, properties and some applications.” China Particuology 5 (2007): 43-49. Z. Li, M. Kawashita, N. Araki, M. Mistumori, M. Hiraoka, Effect of Particle Size of Magnetite Nanoparticles on Heat Generating Ability under Alternating Magnetic Field. Bioceramics Development and Applications 1 (2011), 4 pages https://doi.org/10.4303/bda/D110128 K.N. Koo, A.F. Ismail, M.H.D. Othman, M.A. Rahman, T.Z. Sheng, Preparation and characterization of superparamagnetic magnetite (Fe 3 O 4 ) nanoparticles: A short review, Malaysian J. Fundam. Appl. Sci. 15 (2019) 23–31. https://doi.org/10.1007/s11595-017-1555-4 C.A.M. Iglesias, J.C.R. de Araújo, J. Xavier, R.L. Anders, J.M. de Araújo, R.B. da Silva, J.M. Soares, E.L. Brito, L. Streck, J.L.C. Fonseca, C.C. Plá Cid, M. Gamino, E.F. Silva, C. Chesman, M.A. Correa, S.N. de Medeiros, F. Bohn, Magnetic nanoparticles hyperthermia in a non-adiabatic and radiating process, Sci. Rep. 11 (2021) 1–13. https://doi.org/10.1038/s41598-021-91334-9 Additional Declarations No competing interests reported. Supplementary Files floatimage1.jpeg Graphical Abstract Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4178101","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":284833096,"identity":"3d84da3b-dcfd-4451-b7d9-1fd93d9f782f","order_by":0,"name":"Claudia Patricia Fernandez Perdomo","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABCUlEQVRIiWNgGAWjYDACdiDmMYCwJYBYjoH5AJiTgFMLM5oWYwa2BGK0MCC0JDYQ0sLfzPxM4k2BHYM5e+/DGx9zbNI3HGN/+OHnHoY88wbsWiQOs5lJzjFIZrDsOW5sOXNbWu6GYzzGkj3PGIplDmDXYsDMYCbNAyQNbqSxSfNuO5y74X4PGwPPAYbEGTgcZsDM/g2opZ7B4P4zsJZ0g2Pszxj/4NXCA7LlMNAWNrCWBINjDGbM+GyROMxTbDnH4DiPZU8aM8gvhjOBfpGWOSBRLIErxNrbN95486dazpz9GOONj9ts5PmAIfbxzQGbPFxaYAAWmwjrCWgAeYqwklEwCkbBKBipAADNw1Bd1gAM5QAAAABJRU5ErkJggg==","orcid":"","institution":"Federal University of São Carlos","correspondingAuthor":true,"prefix":"","firstName":"Claudia","middleName":"Patricia Fernandez","lastName":"Perdomo","suffix":""},{"id":284833097,"identity":"5779213a-b131-4c02-8a71-b69e9996107f","order_by":1,"name":"Ana Laura Caseiro","email":"","orcid":"","institution":"Federal University of São Carlos","correspondingAuthor":false,"prefix":"","firstName":"Ana","middleName":"Laura","lastName":"Caseiro","suffix":""},{"id":284833098,"identity":"fef43c20-3016-4037-84f8-7104a04dcca9","order_by":2,"name":"Marina Magro Togashi","email":"","orcid":"","institution":"Federal University of São Carlos","correspondingAuthor":false,"prefix":"","firstName":"Marina","middleName":"Magro","lastName":"Togashi","suffix":""},{"id":284833099,"identity":"645e547d-2765-490a-9ce2-a7a2f058977e","order_by":3,"name":"Ruth H.G.A. Kiminami","email":"","orcid":"","institution":"Federal University of São Carlos","correspondingAuthor":false,"prefix":"","firstName":"Ruth","middleName":"H.G.A.","lastName":"Kiminami","suffix":""}],"badges":[],"createdAt":"2024-03-27 19:52:15","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4178101/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4178101/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":53853636,"identity":"4a6d0d69-3c0a-4a3a-83c8-6a6b9d68c1e3","added_by":"auto","created_at":"2024-04-01 10:39:50","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":157877,"visible":true,"origin":"","legend":"\u003cp\u003eTG-DTG/DSC curve of the magnetite xerogel obtained in the sol-gel synthesis with ethylene glycol.\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-4178101/v1/ebae44c0ce056818962a6df1.png"},{"id":53853640,"identity":"aae8d9ce-ffe6-44f3-9966-c8d8766fa8d5","added_by":"auto","created_at":"2024-04-01 10:39:51","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":179051,"visible":true,"origin":"","legend":"\u003cp\u003eX-ray diffractograms of samples thermally treated at 150°C, 200°C, and 300°C for 4 hours without atmosphere control.\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-4178101/v1/d76950f5ba69a3e48bc54fbd.png"},{"id":53853637,"identity":"6505f267-d52d-4840-b085-037816e9dfe8","added_by":"auto","created_at":"2024-04-01 10:39:51","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":34567,"visible":true,"origin":"","legend":"\u003cp\u003eX-ray diffractograms of samples thermally treated at 200°C for 4 hours, with and without chemical washing with CH\u003csub\u003e3\u003c/sub\u003eCOOH - 0.3 M.\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-4178101/v1/bc402b7bfcf8e3ce893c5afd.png"},{"id":53853632,"identity":"c3fb423b-b196-4a6a-a79d-a70b5a5b566e","added_by":"auto","created_at":"2024-04-01 10:39:50","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":394441,"visible":true,"origin":"","legend":"\u003cp\u003eX-ray diffractograms of samples thermally treated at 200°C with different holding times: 4, 8, 16, 24, and 48 hours (left) and zoom on the peak of highest intensity corresponding to the (311) plane Lorentzian fit (right).\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-4178101/v1/790aee7be857d5e2ec0bc198.png"},{"id":53853633,"identity":"17a60891-a55c-4b2c-a6dc-3a8b52e30274","added_by":"auto","created_at":"2024-04-01 10:39:50","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":2236358,"visible":true,"origin":"","legend":"\u003cp\u003eSee image above for figure legend\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-4178101/v1/4b5cd45bcc3fcf23a4cc06ec.png"},{"id":53853634,"identity":"80919ab3-0842-4498-898c-afae5bdfc1c9","added_by":"auto","created_at":"2024-04-01 10:39:50","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":3453006,"visible":true,"origin":"","legend":"\u003cp\u003eSee image above for figure legend\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-4178101/v1/023b011ea461b0f5b1a59cda.png"},{"id":53854261,"identity":"cc5fa277-19e1-4630-af47-98acb36eb4e7","added_by":"auto","created_at":"2024-04-01 10:47:51","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":57798,"visible":true,"origin":"","legend":"\u003cp\u003ePhotographs of magnetite NPs synthesized in 200 ⁰ C with 8 and 48 hours of holding times, dispersed in isopropyl alcohol, distilled water, and ethylene glycol, after ultrasonication (left) and under the application of an external magnetic field (right).\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-4178101/v1/201800df2367e1bc999b2248.png"},{"id":53853635,"identity":"2fa65a28-df69-4352-a5a2-4d6b0e96aeda","added_by":"auto","created_at":"2024-04-01 10:39:50","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":248396,"visible":true,"origin":"","legend":"\u003cp\u003ePhotographs of magnetite NPs synthesized with a holding time of 8 hours, dispersed in isopropyl alcohol, distilled water, and ethylene glycol, after ultrasonication (a), 1 day/24 hours (b), and 2 days/48 hours (c)\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-4178101/v1/5fc763b59aa56671f43f2d0c.png"},{"id":53854264,"identity":"20a78367-27d0-41c0-a896-56f37e8aa740","added_by":"auto","created_at":"2024-04-01 10:47:51","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":146240,"visible":true,"origin":"","legend":"\u003cp\u003eApplied magnetic field versus magnetization curves of sol-gel synthesized magnetite.\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-4178101/v1/be8a174527a90b64ddb641a8.png"},{"id":68029372,"identity":"a3444387-0f09-41e4-8a3a-1b4992c2c261","added_by":"auto","created_at":"2024-11-01 14:17:05","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":9301005,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4178101/v1/4247cef5-f8e7-4f74-a112-7e510ba43288.pdf"},{"id":53853641,"identity":"f9be91bd-66e2-4020-9d31-d8feee795c85","added_by":"auto","created_at":"2024-04-01 10:39:51","extension":"jpeg","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":477668,"visible":true,"origin":"","legend":"\u003cp\u003eGraphical Abstract\u003c/p\u003e","description":"","filename":"floatimage1.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-4178101/v1/f0863c5d675c9024c14b3d8a.jpeg"}],"financialInterests":"No competing interests reported.","formattedTitle":"Effect of heat treatment time in oxygen atmosphere on the stabilization of magnetite NPs: synthesis, characterization, and magnetic response","fulltext":[{"header":"Highlights","content":"\u003cp\u003e- Pure NPs magnetite by sol-gel method at 200\u0026deg;C, without atmosphere control during the thermal treatment for crystallization.\u003c/p\u003e\n\u003cp\u003e- NPs magnetite phase remained stable and pure up to 8 hours of thermal treatment in 200\u0026deg;C in air atmosphere.\u003c/p\u003e\n\u003cp\u003e- After 16 hours and 48 hours, the presence of a magnetite/hematite heterostructure was observed, with approximately 22.5% and 25,4% hematite (\u0026alpha;-Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e), respectively.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;- NPs dispersion in different liquid media (isopropyl alcohol, distilled water, and ethylene glycol) showed potential applications as a magnetic fluid.\u003c/p\u003e"},{"header":"Introduction","content":"\u003cp\u003eMagnetite (Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e) nanoparticles (NPs) have shown promise in various fields such as electronics, biomedicine, transportation, drug delivery, cell separation, localized magnetic hyperthermia therapy, tissue repair, ferrofluids, catalysis, and magnetic devices [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. These applications benefit from the unique properties of this material, which is non-toxic, biocompatible, and exhibits the highest magnetic response among all natural minerals.\u003c/p\u003e \u003cp\u003eMagnetite have an inverse spinel crystal structure with the formula B[AB]O\u003csub\u003e4\u003c/sub\u003e, where Fe\u003csup\u003e3+\u003c/sup\u003e ions occupy half of the tetrahedral sites (A) and Fe\u003csup\u003e2+\u003c/sup\u003e and Fe\u003csup\u003e3+\u003c/sup\u003e ions occupy half of the octahedral sites (B), resulting in significant ferrimagnetic behavior [\u003cspan additionalcitationids=\"CR3\" citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. When the size of magnetite particles decreases to values below 30 nm, they exhibit superparamagnetic behavior [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e], along with increased reactivity due to enhanced surface area and high dispersion in polar solvents of medium to high viscosity, which favors their efficiency in biomedical and catalytic applications with partial/total magnetic recovery [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eHowever, magnetite (Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e) is not the most stable phase of iron oxide and can transform into other phases such as maghemite (γ-Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e) and hematite (α-Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e) under ambient conditions and temperatures above 300\u0026deg;C [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. Therefore, the synthesis of magnetite, especially on a nanoscale, requires careful control of synthesis parameters and the use of inert or reducing atmospheres during the thermal treatment for crystallization in order to delay the transformation to more stable phases and ensure the complete crystallization of nanoparticles [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eIn the literature, chemical synthesis methods that ensure reduced control over particle size and morphology, such as controlled precipitation [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e], co-precipitation [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e], hydrothermal and solvothermal methods [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e], combustion [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e], and sol-gel [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan additionalcitationids=\"CR15\" citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e], have been utilized in recent years to obtain stable magnetite at temperatures below 350\u0026deg;C. Generally, in these methods involving thermal decomposition for crystallization, all thermal treatments must be conducted under controlled atmosphere conditions as mentioned earlier and discussed by Niculescu \u003cem\u003eet al.\u003c/em\u003e [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e] in the 2022 review on magnetite nanoparticle synthesis.\u003c/p\u003e \u003cp\u003eManikandan \u003cem\u003eet al.\u003c/em\u003e [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e], in the synthesis of magnetite using microwave-assisted combustion method (2.45 GHz 850 W) and conventional heating (500\u0026deg;C, 2 h, 5\u0026deg;C/min), observed that the nitrogen-rich atmosphere self-generated during the combustion process between the oxidizing reagent (Fe(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003e\u0026middot;9H\u003csub\u003e2\u003c/sub\u003eO) and urea (CO(NH\u003csub\u003e2\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e) as a fuel, favored the formation of pure magnetite phase in both heating methods, with microwave being energetically less costly. Similarly, Aali \u003cem\u003eet al.\u003c/em\u003e [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e], in obtaining pure magnetite by the combustion method evaluating the use of different fuels (glycine, urea, and citric acid), determined that glycine (C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e5\u003c/sub\u003eNO\u003csub\u003e2\u003c/sub\u003e) was the only fuel that provided a sufficiently reducing atmosphere rich in H\u003csub\u003e2\u003c/sub\u003e and CO\u003csub\u003e2\u003c/sub\u003e to ensure the stability of pure magnetite after the combustion process. On the other hand, Wan \u003cem\u003eet al.\u003c/em\u003e [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e] reported the use of ethylene glycol in the preparation of monodispersed nanometric magnetite mesocrystals by the solvothermal method at 200\u0026deg;C in the presence of NaOH, where they found that the formed Fe(OH)\u003csub\u003e2\u003c/sub\u003e hydroxide is balanced by the intercalation of the ethylene glycol anion, allowing the formation of primary magnetite particles ordered in spherical superstructures/mesocrystals. Similarly, C\u0026oacute;tica \u003cem\u003eet al.\u003c/em\u003e [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e] reported the synthesis of magnetite NPs by the thermal decomposition method using an ethylene glycol and ferric nitrate precursor solution, using temperatures of 300\u0026deg;C and 500\u0026deg;C in an argon atmosphere, the authors reported the stabilization of the phase even up to 500\u0026deg;C with particle sizes of 20 nm and saturation magnetization values of 67 emu/g close to those of bulk magnetite (92 emu/g).\u003c/p\u003e \u003cp\u003eIn the other hand, there are few reports in the literature on the use of ethyleneglycol as a chelating agent during sol-gel synthesis. Takai \u003cem\u003eet al.\u003c/em\u003e [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e] synthesized magnetite nanoparticles via the sol-gel method using ethylene glycol, FeCl\u003csub\u003e2\u003c/sub\u003e, and FeCl\u003csub\u003e3\u003c/sub\u003e as precursors. The authors employed thermal treatment temperatures of 200\u0026deg;C, 300\u0026deg;C, and 400\u0026deg;C under vacuum, obtaining crystallites with sizes ranging approximately between 2 and 25 nm. However, at temperatures of 300\u0026deg;C and 400\u0026deg;C, the authors observed the formation of secondary phases of maghemite and hematite alongside the magnetite phase. Polla \u003cem\u003eet al.\u003c/em\u003e [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e], using iron nitrate as a precursor for obtaining magnetite NPs for water treatment, also conducted thermal treatments at temperatures of 200\u0026deg;C, 300\u0026deg;C, and 400\u0026deg;C without atmosphere control, resulting in pure magnetite phase formation at the first two temperatures. Thus, the use of ethyleneglycol as a solvent in both solvothermal and sol-gel methods is highly promising for the production of magnetite nanoparticles.\u003c/p\u003e \u003cp\u003eThus, in this work, magnetite nanoparticles were synthesized by the sol-gel method using ethylene glycol as a chelating agent. Thermal treatments for decomposition/crystallization were conducted without atmosphere control, and different treatment times were evaluated to analyze their effects on the structural, microstructural, and magnetic behaviors of the nanoparticles.\u003c/p\u003e"},{"header":"Experimental","content":"\u003cp\u003eThe magnetite nanoparticles (NPs) were obtained through a modified sol-gel method, using ethylene glycol (C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e6\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e, Synth, 99%) as a chelating agent. Initially, ethylene glycol and iron nitrate (Fe\u003csub\u003e3\u003c/sub\u003e(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003e\u0026middot;9H\u003csub\u003e2\u003c/sub\u003eO, Merck, 99%) were mixed under constant stirring. Subsequently, the temperature was raised to 80\u0026deg;C and maintained for 1 hour with continuous stirring, resulting in the orange-colored solution transitioning into a dark brown gel. The gel was completely dehydrated at 100\u0026deg;C to obtain the xerogel. Thermal analysis was conducted using differential scanning calorimetry and thermogravimetric analysis (DSC/TG - NETZSCH STA 409 C/CD) with a heating rate of 5\u0026deg;C/min to examine the behavior of the xerogel with increasing temperature. Following this, the xerogel was subjected to thermal treatments ranging from 170\u0026deg;C to 250\u0026deg;C to determine the most suitable magnetite crystallization temperature. Since these temperatures are below the decomposition temperature of the organic phase, the material underwent chemical washing with a 3.0 M acetic acid solution to ensure complete removal of residual organic phase. Once the optimal magnetite crystallization temperature was determined (200\u0026deg;C), the xerogel was thermally treated in a furnace (EDG 3000) at this temperature for varying hold times: 4, 8, 16, 24, and 48 hours. All NPs obtained under different conditions underwent chemical washing with 3.0 M acetic acid (CH\u003csub\u003e3\u003c/sub\u003eCOOH). The structural analysis of all NPs was performed using a Bruker AXS diffractometer with CuKα radiation as the source. Approximate magnetite concentrations for each condition were estimated from the diffractograms using the intensity equation (Eq.\u0026nbsp;\u003cspan refid=\"Equ1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$$\\%Magnetite Phase= \\frac{{I}_{311 \\left(Magnetite\\right)}}{{I}_{311 \\left(Magnetite\\right)+{I}_{104 \\left(Hematite\\right) }}}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e1\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ewhere I\u003csub\u003e311\u003c/sub\u003e and I\u003csub\u003e104\u003c/sub\u003e correspond to the maximum intensity value of the main peak of magnetite (311) located at 2θ\u0026thinsp;=\u0026thinsp;35.6 and hematite (104) located at 2θ\u0026thinsp;=\u0026thinsp;33.2, respectively.\u003c/p\u003e \u003cp\u003eThe crystallite sizes (L) were calculated using the Scherrer equation (Eq.\u0026nbsp;\u003cspan refid=\"Equ2\" class=\"InternalRef\"\u003e2\u003c/span\u003e)\u003cdiv id=\"Equ2\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ2\" name=\"EquationSource\"\u003e\n$$L= \\frac{K\\lambda }{\\text{cos}\\theta \\beta }$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e2\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ewhere K is the dimensionless size factor, typically close to unity (K\u0026thinsp;~\u0026thinsp;0.9), λ is the wavelength, in this case, 0.15418 nm, β is the full width at half maximum, and θ is the value corresponding to the peak of highest intensity.\u003c/p\u003e \u003cp\u003eThe microstructural analysis of the NPs treated at different hold times was performed using a scanning electron microscope (SEM) FEI Quanta 650F, and transmission electron microscopy (TEM) in a Tecnai LaB6 - ASTAR. The resulting micrographs were analyzed using Image J software to determine the average NP size. The estimation was conducted by measuring 200 particles to ensure reliable statistics. Frequency histograms were adjusted using a LogNormal function to estimate both the average size and size distribution of the NPs. Nitrogen adsorption measurements using the BET technique for surface area analysis were carried out on a Micromeritics Gemini-2370, and the equivalent spherical diameter (D\u003csub\u003eBET\u003c/sub\u003e) was estimated using the relationship described by Eq.\u0026nbsp;\u003cspan refid=\"Equ3\" class=\"InternalRef\"\u003e3\u003c/span\u003e.\u003cdiv id=\"Equ3\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ3\" name=\"EquationSource\"\u003e\n$${D}_{BET}= \\frac{6}{{S}_{BET} x {\\rho }_{th}}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e3\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ewhere SBET is the surface area measured by the BET test and ρth is the theoretical density, which in this case is 5.216 g/cm\u003csup\u003e3\u003c/sup\u003e, as per PDF #75-1609.\u003c/p\u003e \u003cp\u003eThe dispersion of the NPs in liquid media (isopropyl alcohol, distilled water, and ethylene glycol) was performed via ultrasonication for 5 minutes at room temperature. The total collection time of the dispersed NPs in the three liquids when subjected to an external magnetic field was measured, as well as the stability time of the dispersion without the presence of an external magnetic field.\u003c/p\u003e \u003cp\u003eFinally, for the analysis of the magnetic behavior of the samples, magnetization measurements as a function of magnetic field were carried out using a Magnetic Property Measurement System (MPMS\u0026reg;3) combined with a dc SQUID sensor (Quantum Design\u0026reg;), with a maximum field of 80 kOe, at room temperature.\u003c/p\u003e"},{"header":"Results and Discussion","content":"\u003cp\u003eIn the thermal analyses TG-DTG/DSC in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, it's possible to verify that the xerogel lost a total of 75% of mass, a typical behavior in the decomposition of polymeric resins.\u003c/p\u003e \u003cp\u003eInitially, an endothermic peak was observed at approximately 74\u0026deg;C, corresponding to the elimination of residual water in the sample, followed by the decomposition and oxidation of the organic phase, which occurs in two distinct stages, marked by abrupt changes in the slope of the TG curve, with clear peaks indicated by the maxima of the DTG at 150\u0026deg;C and 340\u0026deg;C. It can be observed that the width of the peak at 340\u0026deg;C in the DTG is relatively narrow, indicating that the evolution of decomposition/oxidation of the organic phase at this temperature is relatively rapid, initiating the crystallization process, unlike the first peak (150\u0026deg;C) where the decomposition and oxidation of the organic phase are slower, possibly associated with the breakage of complex polymeric chains.\u003c/p\u003e \u003cp\u003eThrough DSC analysis, the maximum exothermic peak at 330\u0026deg;C and the endothermic peak at 350\u0026deg;C, accompanied by a mass loss of approximately 15%, possibly associated with the transformation of the crystalline phase from magnetite (Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e) to hematite (α-Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e) (the more stable polymorphic phase of iron oxide), followed by the complete decomposition of the xerogel, above 350\u0026deg;C, no thermal events or significant changes in mass loss were observed, indicating that the system is stable.\u003c/p\u003e \u003cp\u003eFrom the analysis of TG-DSC/DSC results, it was found that the thermal treatment temperature where the synthesized magnetite phase possibly retained by sol-gel is between 147\u0026deg;C and 330\u0026deg;C.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eTherefore, thermal treatments were carried out between 150\u0026deg;C and 300\u0026deg;C for 4 hours without atmosphere control, in order to evaluate the onset of magnetite crystallization. In Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, the X-ray diffractograms of the xerogel thermally treated at 150\u0026deg;C, 200\u0026deg;C, and 300\u0026deg;C for 4 hours are presented.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe thermal treatment at 150\u0026deg;C revealed little crystallization of the sample, indicating that there was no onset of magnetite phase crystallization at this temperature, corroborating the TG-DTG/DSC analysis in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, where the first exothermic peak is solely associated with the decomposition of the organic phase with a 60% mass loss. With the temperature increase to 200\u0026deg;C, it is possible to observe the presence of all diffraction peaks related to magnetite, namely (220), (311), (222), (400), (422), (511), and (440) according to crystallographic card PDF 75\u0026ndash;449, indicating that the onset of magnetite crystallization occurs shortly after the elimination of the organic phase and these are not concomitant events. The peak widths suggest the presence of magnetite nanoparticles. At 300\u0026deg;C, the formation of magnetite phase was also observed, with approximately 25% presence of hematite phase (PDF 85\u0026ndash;599), confirming the TG-DTG/DSC analysis in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e regarding the temperature range between 300 and 350\u0026deg;C where the complete phase transformation from magnetite (Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e) to hematite phase (α-Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e) would take place.\u003c/p\u003e \u003cp\u003eThus, 200\u0026deg;C was defined as the minimum temperature for the crystallization and stabilization of magnetite without atmosphere control. One parameter taken into consideration was the fact that, according to the thermal analyses in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, at 200\u0026deg;C, the organic phase of the xerogel was not completely oxidized and decomposed, with 15% of organic material remaining. To overcome this situation, the material treated thermally at 200\u0026deg;C was subjected to a chemical washing step using acetic acid (CH\u003csub\u003e3\u003c/sub\u003eCOOH) at a concentration of 0.3 M. Figure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e presents a comparison of the diffractograms, with and without chemical washing of the NPs obtained at 200\u0026deg;C.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIt is possible to observe that the diffraction peaks became more evident after chemical washing, revealing that the 0.3 M acetic acid used favored the elimination of residual organic phase at 200\u0026deg;C. Similar to Manami \u003cem\u003eet al.\u003c/em\u003e [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e], who reported the use of chemical washing to promote the precipitation of iron oxyhydroxide. Meanwhile, Ali \u003cem\u003eet al.\u003c/em\u003e [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e], to promote magnetite synthesis, prepared a nanoemulsion containing iron sources and sodium hydroxide, and finally, chemical washing with ethanol was carried out to exhibit superparamagnetic behavior with magnetization values.\u003c/p\u003e \u003cp\u003eOnce the minimum crystallization temperature and parameters for eliminating residual organic phase were defined, different holding times were proposed: 4, 8, 16, 24, and 48 hours at 200\u0026deg;C, aiming to evaluate the effect of the thermal treatment time under uncontrolled atmosphere conditions on the structural, microstructural, and physical properties of magnetite.\u003c/p\u003e \u003cp\u003eThe XRD analysis of the NPs subjected to different thermal treatment times presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e (left) indicates the maintenance of the complete integrity of the magnetite phase for up to 8 hours of holding time at 200\u0026deg;C without atmosphere control. Above 16 hours, the formation of some traces of hematite phase (α-Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e) (PDF 85\u0026ndash;599) can be observed, as evidenced by the presence of the peak at 2θ\u0026thinsp;=\u0026thinsp;33.1 corresponding to the crystallographic plane (104), present at a concentration of approximately 22.5% (Eq.\u0026nbsp;\u003cspan refid=\"Equ1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). It is possible to observe a slight increase in the concentration of hematite phase with increasing holding time, reaching concentrations of 24.0% and 25.4% in the treatments of 24 and 48 hours, respectively, as listed in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. It's noticeable the narrowing of all crystallographic peaks with increasing holding time, suggesting the enlargement of NP sizes, as observed in the analysis in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e (right), which zooms in on the peak of highest intensity, corresponding to the crystallographic plane (311) adjusted using a Lorentz-type function. This indicates a smaller full width at half maximum (FWHM), and consequently, larger Scherrer crystallite size, as can be observed by calculating the crystallite size using the Scherrer equation (Eq.\u0026nbsp;\u003cspan refid=\"Equ2\" class=\"InternalRef\"\u003e2\u003c/span\u003e), as presented in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eXu \u003cem\u003eet al.\u003c/em\u003e [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e] also observed this effect for sol-gel synthesized magnetite using iron nitrate and ethylene glycol as precursors. The authors noted that with the increase in thermal treatment temperature in the range between 200\u0026deg;C and 400\u0026deg;C, the full width at half maximum decreases and the reflection peaks become narrower, indicating larger crystallite sizes and better crystallinity of the phase.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003ePercentage values of hematite phase, crystallite size according to Scherrer euqation, average particle size from SEM and TEM micrographs .\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHolding time (hours)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e% Magnetite Phase\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eCrystallite size (nm)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eSEM average particle size (nm) \u003csup\u003e**\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eTEM average particle size (nm) \u003csup\u003e***\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e35\u0026thinsp;\u0026plusmn;\u0026thinsp;3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e18\u0026thinsp;\u0026plusmn;\u0026thinsp;0,1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e39\u0026thinsp;\u0026plusmn;\u0026thinsp;5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e16\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e77.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e32\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e43\u0026thinsp;\u0026plusmn;\u0026thinsp;4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e32\u0026thinsp;\u0026plusmn;\u0026thinsp;0,5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e24\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e76.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e43\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e49\u0026thinsp;\u0026plusmn;\u0026thinsp;3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e48\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e74.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e52\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e54\u0026thinsp;\u0026plusmn;\u0026thinsp;4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e46\u0026thinsp;\u0026plusmn;\u0026thinsp;1,1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e*Calculated according to Eq.\u0026nbsp;\u003cspan refid=\"Equ1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, ** Based on SEM micrographs analysis, LogNormal fitting, *** Based on TEM micrographs analysis, LogNormal fitting.\u003c/p\u003e \u003cp\u003eFrom the microstructural analysis presented in the SEM micrographs in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e, it is possible to observe a high agglomeration degree, inherent to the synthesis method. Soft, easily pulverizable clusters with a heterogeneous size distribution are observed. It was also noted that at all evaluated holding times, the nanoscale size of the particles was retained, but there is evident nanoparticle growth with increasing holding time.\u003c/p\u003e \u003cp\u003eIt's possible to identify that the clusters consist of equiaxial primary particles with sizes between 35\u0026thinsp;\u0026plusmn;\u0026thinsp;3 nm at 4 hours of holding time and 54\u0026thinsp;\u0026plusmn;\u0026thinsp;4 nm at 48 hours, as presented in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e and depicted in the size vs. time curve in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e(f). Furthermore, it was noticeable that with longer holding times, the particles acquired a more spherical shape due to the higher energy expended in the process, assuming the thermodynamically more stable form, as verified by Cotica \u003cem\u003eet al.\u003c/em\u003e [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. The crystallite size was in line with the calculated average particle size inferred from SEM micrographs analysis. In this case, the same trend of larger average particle sizes with increasing holding time of the thermal treatment was observed.\u003c/p\u003e \u003cp\u003eFrom the microstructural analysis using transmission electron microscopy (TEM) in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e, the nanoscale nature of the particles is highlighted. With a holding time of 4 hours, as shown in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, the estimated average size of primary particles was 18\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1 nm, while with longer holding times, the estimated size of primary particles tripled in size, with an estimated value of 46\u0026thinsp;\u0026plusmn;\u0026thinsp;1.1 nm, as shown in the histograms of distribution measurements in dark-field micrographs in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e (bottom).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe SAED inset in the bright-field micrographs of 4 and 16 hours shows a characteristic pattern of continuous rings typical of nanocrystalline systems, while at 48 hours, a polycrystalline pattern composed of regular spots associated with larger crystals is observed, corroborating the difference in particle size with increasing holding time.\u003c/p\u003e \u003cp\u003eFrom the BET analysis, it is possible to observe the trend of decreasing surface area with increasing holding time, while the values of equivalent spherical diameter calculated using Eq.\u0026nbsp;\u003cspan refid=\"Equ2\" class=\"InternalRef\"\u003e2\u003c/span\u003e were close to those obtained by TEM analysis. This result indicates the high dispersion of magnetite NPs obtained under all evaluated holding time conditions.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eShaker \u003cem\u003eet al.\u003c/em\u003e [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e] studied the synthesis of magnetite with ethylene glycol at different thermal treatment temperatures ranging from 200 to 400\u0026deg;C, where an average particle size in the range of 30 to 90 nm was observed. Temperatures above 400\u0026deg;C failed to retain the magnetite phase, resulting in the formation of hematite phase. On the other hand, Nkurikiyimfura \u003cem\u003eet al.\u003c/em\u003e [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e] investigated the synthesis of magnetite by co-precipitation-reduction, where the average particle diameter was around 11 nm, exhibiting superparamagnetic behavior as expected.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eSurface area and equivalent spherical diameter of the NPs obtained at different holding times.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHolding time (hours)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSurface area (BET) (m\u003csup\u003e2\u003c/sup\u003e/g)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eEquivalent spherical diameter (nm) *\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e106.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e11.0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e114.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e10.0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e16\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e105.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e11.0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e24\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e104.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e11.0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e48\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e67.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e17.0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"3\"\u003e* Eq.\u0026nbsp;\u003cspan refid=\"Equ3\" class=\"InternalRef\"\u003e3\u003c/span\u003e\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe magnetite NPs obtained at 200\u0026deg;C for 8 and 48 hours were dispersed in isopropyl alcohol, distilled water, and ethylene glycol via ultrasonication for 5 minutes at room temperature. All resulting suspensions responded to an external magnetic field, as shown in the photographs of Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e. From the assays, it was possible to observe the high dispersion of both samples (8 and 48 h) in the three liquid media evaluated, indicating their reduced particle size, an important characteristic, especially for suspensions in water, specifically for biomedical applications, where a high dispersion of magnetite NPs in body fluids is required. In the case of the magnetic fluid used in cancer therapy, which requires high dispersion and suspension stability for a certain period, in order to improve heating efficiency to ensure the elimination of tumor cells. The total collection of NPs obtained in 8 hours when subjected to an external magnetic field occurred at times of 5, 15, and 120 minutes in alcohol, water, and ethylene glycol media, respectively. For the NPs obtained in 48 hours, which exhibit 25.4% hematite phase (α-Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e), according to XRD analysis (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e), as expected, the total collection times were doubled, being 15, 30, and 240 minutes in alcohol, water, and ethylene glycol media, respectively. These results indicate the good magnetic behavior of the obtained NPs.\u003c/p\u003e \u003cp\u003eThe stability of the suspensions was observed through the precipitation of the samples over a period of 2 days, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e. These results indicate that the synthesized NPs offer a long suspension stability characteristic both in water and in ethylene glycol, an important feature for applications where prolonged dispersion is required, such as in magnetic fluids used in cancer therapy as mentioned earlier.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e, the magnetization curves (emu/g) as a function of the applied magnetic field (Oe) of the hematite NPs obtained at different holding times are presented. The magnetization curves revealed the superparamagnetic behavior of all NPs, which was expected for materials with particle sizes below 50 nm. As reported by several authors, superparamagnetic behavior is common in magnetite nanoparticles [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e presents the values of saturation magnetization, remanent magnetization, and coercive field of the magnetite NPs subjected to different thermal treatment times (4\u0026ndash;48 hours), resulting in different initial particle sizes ranging from 30 nm to 50 nm.\u003c/p\u003e \u003cp\u003eIt is possible to observe an increase in saturation magnetization when the sample is subjected to holding times of 8 hours, possibly due to the increased crystallinity of the magnetite phase. On the other hand, for holding times above 16 hours, there is a gradual decrease in saturation magnetization, associated with the presence of hematite phase in the sample, corroborating the XRD results presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eMagnetization properties NPs\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHolding time (hours)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eInital Particle size (nm)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSaturation magnetization (emu/g)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eRemanent magnetization (emu/g)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eCoercitive field (kOe)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e35\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e13\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.82\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e22.5 x10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e39\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e57\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.90\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e6.1x10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e16\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e43\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.31\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e13.95 x10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e24\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e49\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.42\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e25.35 x10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e48\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e54\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e13\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.085\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e25.14 x10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e"},{"header":"Conclusions","content":"\u003cp\u003eThe sol-gel synthesis using ethylene glycol was effective in forming and stabilizing the magnetite (Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e) phase at 200\u0026deg;C without the use of controlled atmosphere. Up to 8 hours of thermal treatment, 100% integrity of the pure phase was maintained, while above 16 hours, the presence of 22.5% hematite phase (α-Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e) was observed, reaching up to 25.4% of this phase after 48 hours of thermal treatment. The estimated average particle sizes of the NPs varied from approximately 20 nm for 4 hours of treatment to approximately 50 nm for 48 hours of treatment where the magnetite/hematite heterostructures were presente.\u003c/p\u003e \u003cp\u003eThe magnetite NPs exhibited high dispersion for both samples (8 and 48 h) in the three evaluated liquid media (ethyl alcohol, water, and ethylene glycol), indicating their reduced particle size and remaining dispersed for a long period of time, 24\u0026ndash;48 hours in water and ethylene glycol. The total collection of NPs obtained in 8 hours when subjected to an external magnetic field occurred within 5, 15, and 120 minutes in alcohol, water, and ethylene glycol media, respectively. For the NPs obtained in 48 hours, the total collection times were doubled, with these samples containing 25.4% hematite phase.\u003c/p\u003e \u003cp\u003eAll NPs exhibited superparamagnetic behavior due to their particle sizes being below 50 nm. The maximum saturation magnetization value obtained was 57 emu/g in the 8-hour treatment sample, which still maintained stable pure magnetite. Above 16 hours of thermal treatment, there was a gradual decrease in saturation magnetization associated with the presence of hematite phase, as expected.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgments\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors would like to thank the Structural Characterization Laboratory (LCE/DEMa/UFSCar) for the general facilities, the Hydrogen in Metals Laboratory (LHM/CPqMaE/UFSCar) for the DSC/TG results, Prof. Dr. Adilson de Oliveira and Leonardo Dalla Costa from the Superconductivity and Magnetism Group (GSM/DF/UFSCar) and the Interdisciplinary Laboratory of Electrochemistry and Ceramics, Department of Chemistry, Federal University of S\u0026atilde;o Carlos (LIEC/DQ/UFSCar) for the magnetic measurements, and the funding agencies CAPES (PNPD20131474 \u0026ndash; 33001014004P9), CNPq (Proc. 431304/2016-5), and FAPESP (Proc. 2017/2509-0) for the scholarships and general support. This work was supported by the Coordination for the Improvement of Higher Education Personnel (CAPES) - Financing Code 001.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eAdelina-Gabriela Niculescu, CristinaChircov, Alexandru Mihai Grumezescu. Magnetite nanoparticles: Synthesis methods \u0026ndash; A comparative review, 199, 202ages 16-27. https://doi.org/10.1016/j.ymeth.2021.04.018.\u003c/li\u003e\n\u003cli\u003eBhole, R., Gonsalves, D., Murugesan, G. et al. Superparamagnetic spherical magnetite nanoparticles: synthesis, characterization and catalytic potential. Appl Nanosci (2022). https://doi.org/10.1007/s13204-022-02532-4\u003c/li\u003e\n\u003cli\u003eEtemadifar, R., Kianvash, \u003cu\u003eA\u003c/u\u003e., Arsalani, N., Abouzari-Lotf E., Hajalilou A. Green synthesis of superparamagnetic magnetite nanoparticles: effect of natural surfactant and heat treatment on the magnetic properties. \u003cem\u003eJ Mater Sci: Mater Electron\u003c/em\u003e 29, 17144\u0026ndash;17153 (2018). https://doi.org/10.1007/s10854-018-9805-6\u003c/li\u003e\n\u003cli\u003eInnocent Nkurikiyimfura, Yanmin Wang, Bonfils Safari, Emmanuel Nshingabigwi, Temperature-dependent magnetic properties of magnetite nanoparticles synthesized via coprecipitation method, Journal of Alloys and Compounds, 846, 2020, 156344, https://doi.org/10.1016/j.jallcom.2020.156344\u003c/li\u003e\n\u003cli\u003eDrienn J. Szalai, Nithyapriya Manivannan, George Kaptay, Super-paramagnetic magnetite nanoparticles obtained by different synthesis and separation methods stabilized by biocompatible coatings, Colloids and Surfaces A: Physicochemical and Engineering Aspects, 568, 2019, 113-122. https://doi.org/10.1016/j.colsurfa.2019.02.006\u003c/li\u003e\n\u003cli\u003eP. Tipsawat, U. 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Rep. 11 (2021) 1\u0026ndash;13. https://doi.org/10.1038/s41598-021-91334-9\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Nanoparticles, Magnetite, Fe3O4, sol-gel, heterostructure, thermal treatment","lastPublishedDoi":"10.21203/rs.3.rs-4178101/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4178101/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThis study describes the synthesis of magnetite (Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e) nanoparticles (NPs) using the sol-gel method with ethylene glycol as a chelating agent. The use of this agent allowed for the complete crystallization of pure magnetite phase at 200°C, without atmosphere control during the thermal treatment for crystallization. Different thermal treatment times (4, 8, 16, 24, and 48 hours) and their effects on the structure, microstructure, and magnetic properties of the nanoparticles were evaluated. The results showed that the magnetite phase remained stable and pure up to 8 hours of thermal treatment in an air atmosphere, with nanoparticles exhibiting a crystallite size of 30 nm and saturation magnetization of 57 emu/g. After 16 hours, the presence of a magnetite/hematite heterostructure was observed, with approximately 22.5% hematite (α-Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e). The presence of hematite increased with the thermal treatment time, reaching 25.4% at 48 hours, and the saturation magnetization decreased with the reduction of magnetite phase in the nanoparticles. Additionally, the NPs dispersion in different liquid media (isopropyl alcohol, distilled water, and ethylene glycol) was verify to evaluated suspension stability and total magnetic collection time, aiming for potential applications as a magnetic fluid.\u003c/p\u003e","manuscriptTitle":"Effect of heat treatment time in oxygen atmosphere on the stabilization of magnetite NPs: synthesis, characterization, and magnetic response","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-04-01 10:39:43","doi":"10.21203/rs.3.rs-4178101/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"3315e44f-cfa9-41d4-8e8a-01ae62a1ca40","owner":[],"postedDate":"April 1st, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2024-11-01T14:08:50+00:00","versionOfRecord":[],"versionCreatedAt":"2024-04-01 10:39:43","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4178101","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4178101","identity":"rs-4178101","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}