Effect of Precipitation Temperature on Structural and

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Generally, spinel ferrites of M. +2 ... magnetic properties of the spinel ferrite materials originate ..... S.B.: Synthesis of nanosized MgFe2O4 powders by microwave.

Effect of Precipitation Temperature on Structural and Magnetic Features of Polyethylene Glycol-Coated Mn0.8Zn0.2Fe2 O 4 Nanoparticles Sahira Hassan Kareem, Mustaffa Shamsuddin & Siew Ling Lee

Journal of Superconductivity and Novel Magnetism Incorporating Novel Magnetism ISSN 1557-1939 J Supercond Nov Magn DOI 10.1007/s10948-016-3599-7

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Author's personal copy J Supercond Nov Magn DOI 10.1007/s10948-016-3599-7

ORIGINAL PAPER

Effect of Precipitation Temperature on Structural and Magnetic Features of Polyethylene Glycol-Coated Mn0.8Zn0.2Fe2O4 Nanoparticles Sahira Hassan Kareem1 · Mustaffa Shamsuddin1,2 · Siew Ling Lee1,2

Received: 29 March 2016 / Accepted: 14 June 2016 © Springer Science+Business Media New York 2016

Abstract The effects of precipitation temperature on both structural and magnetic properties of polyethylene glycolcoated Mn0.8 Zn0.2 Fe2 O4 nanoparticles are presented. Samples were prepared via co-precipitation method at different precipitation temperatures ranged 25–100 ◦ C. X-ray diffraction analysis revealed that both crystallite size and lattice constant of the nanoparticles increased with increasing of temperature. FESEM images verified the existence of crystalline ferrites of diameter ranged 7.49–9.41 nm. FTIR spectra evidenced the effect of precipitation temperature on Fe3+ —O2− stretching vibration in the ferrites. These Mn0.8 Zn0.2 Fe2 O4 nanoparticles exhibited the highest saturation magnetization 20.938 emu/g at 75 ◦ C. Correlations among precipitation temperature alteration, structural morphology, and magnetic response are established. Keywords Mn–Zn ferrites · Co-precipitation · Magnetic · Polyethylene glycol · Precipitation temperature

1 Introduction Recently, development of magnetic nanoparticles (NPs) synthesis and precise characterization techniques has opened new avenues towards extensive fundamental and

 Siew Ling Lee

[email protected] 1

Department of Chemistry, Faculty of Science, Universiti Teknologi Malaysia, 81310 Johor Bahru, Johor, Malaysia

2

Center for Sustainable Nanomaterials, Ibnu Sina Institute for Scientific and Industrial Research, Universiti Teknologi Malaysia, 81310 Johor Bahru, Malaysia

technological implications. Certainly, the unique properties of magnetic NPs are highly suitable for fast-paced miniaturization of modern electronic devices and biomedical applications [1–3]. Traditionally, ferrites are widely exploited in high-frequency devices such as transformers and magnetic heads [3]. The ferrites are also useful for various diagnostic and therapeutic biomedical applications such as tracking cells using magnetic resonance imaging and drug delivery to targeted tumor cells or tissues [4]. In the presence of an alternating magnetic field these magnetic hyperthermia can be used as one of the most promising cancer therapeutic agents with minimum side effects [5]. Furthermore, ferrites are potential for microwave devices [6], recording media [7], magnetic fluids [8], highdensity information storage [9], gas sensors [10], ferro-fluids [11], and catalysts [12]. Considering the commercialization opportunities of the ferrites, several synthesis methods including solidstate reaction [13], sol–gel [14], highenergy ball milling [15], chemical coprecipitation [16], hydrothermal synthesis [17], microwave hydrothermal [18] and micro-emulsion [19] have been developed. Among these methods, the chemical co-precipitation technique has been widely used for the preparation of ferrites due to its several advantages such as simplicity, reliability, flexibility, costeffectiveness and less time consumption. Generally, spinel ferrites of M+2 Fe+3 2 O4 (M = Ni, Cu, Zn, Mn) with AB2 O4 structure are described as cubic closepack arrangement of oxygen ions, where the tetrahedral A and octahedral B interstitial lattice sites are occupied by cations. In the normal spinel, the tetrahedral sites are occupied by divalent cations while trivalent cations occupy octahedral sites. Conversely, in inverse spinel the divalent cations occupy the octahedral sites, whereas the trivalent cations are distributed equally among A- and B-sites. The magnetic properties of the spinel ferrite materials originate

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2 Material Synthesis and Characterizations Polyether compound of PEG (repeated element of –H– (O–CH2 –CH2 )n –OH–)-coated Mn0.8 Zn0.2 Fe2 O4 NPs were prepared using chemical co-precipitation method. First, stoichiometric amount of analytical grade raw materials of MnCl2 .4H2 O (99 %, Merck), ZnCl2 (98.5 %, QReC), FeCl3 (98.5 %, Merck), NaOH (99 %, Merck), and PEG-200 (99 %, sigma) were dissolved in deionized water and heated under constant stirring. Later, 0.2 M NaOH solution and PEG-200 surfactant was added to the former solution to obtain the so-called precursor solution II. After that, precursor solution II was added drop-wise into precursor solution I and stirred vigorously at 25 ◦ C for 1 h. In order to study the effect of the precipitation temperature on the structural and magnetic properties of the resulted materials, the temperature was varied from 25 to 100 ◦ C. The pH of the aqueous solution was maintained in the range of 11–12 during the co-precipitation process. Later, the precipitates were filtered, washed several times in deionized water and dried over night in the oven at 5 ◦ C to remove the water content. Finally, PEGcoated Mn0.8 Zn0.2 Fe2 O4 NPs in powder form were obtained. As-prepared samples were characterized at room temperature. Bruker D8 Advance X-ray diffractometer (XRD) was used to verify the nanocrystalline nature and purity of pre˚ with pared ferrites with Cu-Kα radiations (λ = 1.5418 A), ◦ ◦ the 2θ range from 20 to 75 at a scanning rate of 0.05◦ /s, operated at 40 kV and 100 mA. Surface morphology and the phase homogeneity of the samples were analyzed via field

(440)

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from the antiferromagnetic coupling between the octahedral and tetrahedral sublattices. Consequently, the A- and Bsublattice magnetization differences (staggered) with unlike cations produce the net magnetization [20, 21]. The agglomeration of magnetic NPs being the major limitation for many applications needs to be overcome. The negative effect of NP assemblage can be reduced through surfactant coating onto them [22]. It is acknowledged that polyethylene glycol (PEG) could be absorbed easily at the surface of metal oxide colloid. This in turn retards the colloid activity by confining its growth on certain facets [23], hence leading to enhanced magnetic properties in aqueous solution. Despite some efforts, the influence of synthesis parameters on properties of PEG coating on Mn–Zn ferrite NPs is yet to be studied. In this paper, PEG-coated Mn0.8 Zn0.2 Fe2 O4 NPs were prepared via co-precipitation method using varied precipitation temperatures. The samples were characterized to determine the effect of the temperature on their physical properties and magnetic behavior.

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Fig. 1 XRD patterns of PEG-coated Mn0.8 Zn0.2 Fe2 O4 NPs temperature of 25 ◦ C, 50 ◦ C, 75 ◦ C, and 100 ◦ C

emission scanning electron microscopy (FESEM) imaging (SU8020, Hitachi). Fourier transformed infrared (FTIR) spectra for these PEG-coated Mn–Zn ferrites were recorded using a Perkin Elmer 5DX FTIR instrument with resolution of 0.8 cm−1 . Magnetic properties were measured using a vibrating sample magnetometer (VSM, Lake Shore 73039309 VSM) with sweep width of external magnetic field from −1 to 1 tesla

3 Results and Discussion Figure 1 depicts the XRD patterns of PEG-coated Mn0.2 Zn0.8 Fe2 O4 samples prepared at different precipitation temperatures. Observed diffraction peaks were indexed to the cubic structure in accordance with the JCPDS card no. 75-0034, indicating formation of single-phase cubic ferrite lattice of these PEG-coated Mn0.2 Zn0.8 Fe2 O4 samples. No impurity was detected. The spinel ferrite phase revealed preferred growth direction along (220), (311), (400), (422), (440), and (511) crystal planes. As observed, the crystallinity of the samples increased with increasing of precipitation temperature. Similar finding was reported for Ni0.5 Zn0.5 Fe2 O4 magnetic material [24]. Based on the prominent XRD peak at (311), the average crystallite sizes of NPs were estimated using Scherer’s equation [25]: dλ D= β cos θ where D is average crystallite size, d is the Scherrer con˚ β is the full width of half stant (0.89), λ = 1.5418 A, maximum (FWHM) intensity, and θ is Bragg’s angle in degrees. Besides, the lattice constant (a) and cell volume (V ) were calculated from the XRD patterns using the following equations: a = [d 2 (h2 + k 2 + l 2 )]1/2

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Fig. 2 Precipitation temperature dependent variation of a crystallite size and b lattice constant

V = a3 Figure 2a, b represents the influence of precipitation temperature on the lattice parameters. A rise in temperature from 25 to 100 ◦ C was found to increase the crystallite size from 7.497 to 9.406 nm and the lattice parameter from ˚ Apparently, both crystallite size and lat8.288 to 8.433 A. tice constant of the NPs increased linearly with increasing of temperature. The phenomenon could be explained by the increase of crystal growth and perfection crystallization at

Fig. 3 FESEM images of PEG-coated Mn0.8 Zn0.2 Fe2 O4 NPs prepared at precipitation temperature of 25 ◦ C, 50 ◦ C, 75 ◦ C, and 100 ◦ C

higher temperature. As a result, grain growth which caused the increase in size of grains (crystallites) in a material could happen. In the literature [22], the increase in grain size occurred at completion of recovery and recrystallization processes at high temperature. It was also stated that the further reduction in the internal energy could only be achieved by reducing the total area of grain boundary. Similarly, the cell volume of the samples increased from 569.5 ˚ 3 with the increase of precipitation temperature to 600.0 A from 25 to 100 ◦ C.

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Figure 3 shows the FESEM images of PEG-coated Mn1−x Znx Fe2 O4 samples. As the temperature increased, stronger agglomeration of NPs was evidenced. The aggregation of NPs to larger diameter could be attributed to the presence of PEG which has increased attraction among the polymer chains via the formation of coordination complexes, resulting in the rapid nucleation and growth [26]. Under higher magnification, the spherical particles with size in the range of 14–27 nm were detected, confirming attainment of nanoparticles even after the PEG coating. Figure 4 displays the FTIR spectra of Mn1−x Znx Fe2 O4 , pure PEG, and PEGcoated Mn–Zn ferrites. The spectrum of Mn1−x Znx Fe2 O4 exhibited two main absorption bands at 613 and 506 cm−1 which are corresponded to Fe–O bond for stretching vibrations in tetrahedral (ν1 ) and octahedral site (ν2 ), respectively, implying that the normal mode of vibrations of tetrahedral site is higher than that of octahedral site [27, 28] It was previously claimed that both Mn2+ and Fe3+ ions preferentially occupied octahedral and tetrahedral sites, while Zn2+ preferred to occupy octahedral site. The occurrence of bands around 1640 and 3400 cm−1 in all the samples is associated to H–O–H bending vibration and O–H stretching modes, respectively. On the other hand, the spectrum of pure PEG shows characteristic peaks at 570, 1107, 1388, 1405, 1460, 1641, 2900, and 3364 cm−1 , matching with the reported results [29]. Among the observed peaks, the absorption band at 1107 cm−1 was assigned to C– O group vibration modes [17], while the bands observed between 1405 and 1460 cm−1 were due to the bending vibration of the –CH2 – group. As can be seen in Fig. 4, all the spectra of PEGcoated Mn–Zn ferrites showed bands at 613 and 1030 cm−1 , implying co-existence of PEG and

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Fig. 5 Hysteresis loops of (a) Mn0.8 Zn0.2 Fe2 O4 and as-prepared PEG-coated Mn0.8 Zn0.2 Fe2 O4 nano-ferrites at precipitation temperature of (b) 25 ◦ C, (c) 50 ◦ C, (d) 75 ◦ C, and (e) 100 ◦ C

Mn–Zn ferrites in the samples. It was observed that the small band at 613 cm−1 slightly shifted to lower wavelength with the increasing precipitation temperature, indicating the temperature affected the Fe3+ —O2− stretching vibration. Furthermore, transmittance of H–O–H bending vibration (at 1640 cm−1 ) and O–H stretching (3400 cm−1 ) modes decreased after introduction of PEG, signifying successful coating of PEG on the surface of Mn1−x Znx Fe2 O4 NPs. Figure 5 depicts the room temperature magnetic hysteresis loops of all the prepared samples. The results indicated that Mn0.8 Zn0.2 Fe2 O4 and PEG-coated Mn0.8 Zn0.2 Fe2 O4 samples behaved as magnet under a magnetic field. The magnetic behavior of PEG-coated Mn0.8 Zn0.2 Fe2 O4 which was prepared at 25 ◦ C was slightly higher than that of uncoated Mn0.8 Zn0.2 Fe2 O4 . The saturation magnetization (Ms ) increased significantly from 2.706 to 20.668 emu/g when the temperature increased from 25 to 75 ◦ C, followed by a drop to 12.919 emu/g at 100 ◦ C. The increase in Ms could be associated to the enhanced surface spin effects which were due to the rise in crystallinity degree, crystallite size, and particles size as evidenced by the XRD and FESEM results. In previous report, it was claimed that high degree of crystallinity and grain size led to improved magnetization behavior [24]. However, at higher precipitation temperature of 100 ◦ C, the agglomeration of the

25 C Table 1 Magnetic properties of PEGcoated Mn0.8 Zn0.2 Fe2 O4 NPs prepared at different precipitation temperatures

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2.706 ± 0.1082 9.027 ± 0.3610 20.668 ± 0.8267 12.919 ± 0.5167

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Fig. 6 Precipitation temperature dependent of a saturation magnetization and b remanent magnetization

particles occurred, hence minimizing the net surface spin [30, 31]. As a result, magnetization values of PEG-coated Mn0.8 Zn0.2 Fe2 O4 decreased when higher sintering temperature was applied in the preparation procedure. Table 1 enlists the precipitation temperature-dependent variation of coercivity (Hc ), remanence (Mr ), and saturation magnetization (Ms ) of PEG-coated Mn0.8 Zn0.2 Fe2 O4 NPs. The decrease in Hc at 100 ◦ C could be corresponded to the presence of a considerable volume fraction of super-paramagnetic particles. It was reported that small Hc and sharp increase in the magnetization of ferrites with the increase of applied field signified the super-paramagnetic nature of synthesized NPs [32]. Figure 6a, b clearly shows that PEG-coated Mn0.8 Zn0.2 Fe2 O4 achieved the highest Ms and Mr values at precipitation temperature 75 ◦ C. Obviously, temperature of 75 ◦ C was the optimum temperature for the synthesis of PEG-coated Mn0.8 Zn0.2 Fe2 O4 of high magnetic properties. At temperature 75 ◦ C), the thermal energy was adequate to change the direction of

+ Mn0.8Zn0.2Fe2O4

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Fig. 7 Schematic diagram showing PEG-coated Mn0.8 Zn0.2 Fe2 O4 formation

magnetization of the entire crystallite, resulting in magnetostriction and generation of more domains for the better magnetic properties of the materials. Figure 7 illustrates the schematic diagram showing formation of PEG-coated Mn0.8 Zn0.2 Fe2 O4 which was prepared at precipitation temperature of 75 ◦ C. It was proposed that PEG possessing amphiphilic characteristic sticks to the surface of the ferrite particles. Meanwhile, the long chain of hydrophobic tails heading out in all directions prevented the magnetite particles from agglomeration. This phenomenon was prime important to achieve a physically and chemically stable colloidal system [34]. Besides, the surface coating with PEG was crucial to increase the water-dispersibility of the materials. Therefore, stability and magnetic properties of Mn/Zn ferrites could be improved after PEG coating at 75 ◦ C. The research findings will definitely contribute to possible applications of these ferrites in clinical and pharmaceutical areas.

4 Conclusion Precipitation temperature-assisted modifications in the structures and magnetic response of highly crystalline PEGcoated Mn0.8 Zn0.2 Fe2 O4 NPs were inspected. These PEGcoated Mn–Zn ferrites were prepared via co-precipitation and characterized using XRD, FESEM, FTIR, and VSM. Crystalline sizes of the materials were found to increase from 7.5 to 9.4 nm with the increase of precipitation temperature from 25 to 100 ◦ C. This strong temperature-dependent NP growth was attributed to the enhanced crystallinity and their self-aggregation at higher precipitation temperature. FTIR analysis results implied successful synthesis of PEG-coated Mn0.8 Zn0.2 Fe2 O4 materials. Besides, the precipitation temperature influenced the Fe3+ —O2− stretching

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vibration in the materials, hence affecting the magnetic behavior of the materials. Precipitation temperature dependent in saturation magnetization could also be ascribed to the enhanced surface spin effects at small particle size. It was demonstrated that PEG-coated Mn0.8 Zn0.2 Fe2 O4 achieved the highest values of Mr (0.6686 emu/g) and Ms (20.668 emu/g) at precipitation temperature 75 ◦ C. Acknowledgments The authors thank the Ministry of Higher Education (MOHE), Malaysia, and Universiti Teknologi Malaysia for the financial supports through Fundamental Research Grant Scheme, FRGS (Vote No. R.J130000.7809.4F527) and Research University Grant (Vote No. Q.J130000.2526.12H77).

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