Fine tuning of CoFe2O4 properties prepared by solution combustion synthesis

Fine tuning of CoFe2O4 properties prepared by solution combustion synthesis

Available online at www.sciencedirect.com CERAMICS INTERNATIONAL Ceramics International 40 (2014) 10223–10229 www.elsevier.com/locate/ceramint Fine...

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Available online at www.sciencedirect.com

CERAMICS INTERNATIONAL

Ceramics International 40 (2014) 10223–10229 www.elsevier.com/locate/ceramint

Fine tuning of CoFe2O4 properties prepared by solution combustion synthesis Robert Ianoşn, Marian Bosca, Radu Lazău “Politehnica” University of Timişoara, Faculty of Industrial Chemistry and Environmental Engineering, Piaţa Victoriei No. 2, Timişoara 300006, Romania Received 24 January 2014; received in revised form 24 February 2014; accepted 25 February 2014 Available online 6 March 2014

Abstract Single phase CoFe2O4 powders were prepared by solution combustion synthesis using β-alanine as fuel. By adding to the reaction mixture various amounts of oxalic acid, which act as a retarding agent and pore generator, properties of CoFe2O4 powders can be properly adjusted. Depending on the amount of oxalic acid, the average crystallite size of CoFe2O4 ranges between 13 and 41 nm, whilst the specific surface area varies between 1.8 and 34.4 m2/g. The combustion synthesized CoFe2O4 powders exhibit a hard ferimagnetic behavior. The CoFe2O4 coercivity varies between 71.8 and 126.0 kA/m and the saturation magnetization ranges between 53.0 and 70.6 emu/g. After uniaxial pressing and sintering at 1400 1C for 4 h, the pellets reached relative densities up to 90% of the CoFe2O4 theoretical density. & 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Keywords: A. Powders: chemical preparation; A. Sintering; C. Magnetic properties; D. Ferrites; Combustion synthesis

1. Introduction Cobalt ferrite, CoFe2O4, has an inverse spinel structure and it is an important material that has exceptional magnetic, optical and electrical properties, exploited in various applications, such as catalysis [1–3], adsorption and separation [1], microwave absorbers [2,4], photonic and electronic devices [3–5], ferrofluid technology [3,6–8], magnetocaloric refrigeration [6,7], medical diagnosis [6–9], drug delivery [7–9], magnetocytolysis [8,9], magnetic cell sorting schemes, hyperthermia [3], permanent magnets [2], and sensors [2]. Generally, the magnetic properties of cobalt ferrite namely coercivity, anisotropy and saturation magnetization, are highly dependent on several parameters, amongst which the preparation method is probably the most important. Therefore, by properly selecting the synthesis route one can obtain CoFe2O4 powders with high/moderate coercivity and high/moderate saturation magnetization, according to the desired applications [1,2,5,6,10]. Alongside the co-precipitation method [2,11] many other preparation routes have been reported for CoFe2O4 preparation: n

Corresponding author. Tel.: þ40 256 404167. E-mail address: [email protected] (R. Ianoş).

http://dx.doi.org/10.1016/j.ceramint.2014.02.110 0272-8842 & 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

hydrothermal and solvothermal method [3,4], microemulsion technique [7,12], reverse micelles [9], Massart [13], sonochemical method [14], sol–gel [15], organic precursors [16] etc. Although it has been reported that combustion synthesis has a great potential in the preparation of metal oxide nanopowders, little attention has been paid to the preparation of CoFe2O4. In a recent review on combustion synthesis of spinel-type ferrite nanomaterials, Sutka and Mezinskis [17] reported that the most popular fuels tested for combustion synthesis of CoFe2O4 are urea [5], glycine [6,18] and citric acid [10,19,20]. In this paper we investigated the solution combustion synthesis of CoFe2O4 using an alternative fuel (β-alanine) alongside with various amounts of oxalic acid. Properties of the resulting powders were investigated and explained in relation with the synthesis conditions. 2. Experimental 2.1. Powder preparation Based on combustion reaction (1) stoichiometric amounts of Co(NO3)2  6H2O (Fluka, 98%), Fe(NO3)3  9H2O (Roth, 96%) and C3H7NO2 (β-alanine, Fluka, 99%) were dissolved in

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15 mL of hot distilled water, according to the working procedure shown in Fig. 1. Recipes were designed assuming a yield of 0.03 mol of CoFe2O4. Various amounts of C2H2O4 (oxalic acid, Chimreactiv, 99.6%) were added to the reaction mixture in different proportions (0–175 wt%), in order to investigate its influence on the cobalt ferrite properties. The addition amount was

calculated with respect to CoFe2O4. 3CoðNO3 Þ2 þ 6FeðNO3 Þ3 þ 8C3 H7 NO2 ) 3CoFe2 O4 þ 24CO2 þ 28H2 O þ 16N2

ð1Þ

The resulting aqueous solution was placed inside a preheated heating mantle (400 1C). As water evaporated, combustion reaction took place leading to the formation of a fluffy black powder, which was hand-ground, washed with distilled water and dried at 110 1C. 2.2. Sample characterization Phase composition of the powders was determined by X-ray diffraction (XRD) using a Rigaku ULTIMA IV diffractometer (monochromated CuKα radiation – 0.15406 nm) operating at 40 kV and 40 mA. The average crystallite size (DXRD) was calculated based on the XRD patterns using the PDXL 2.0 software. BET (Brunauer–Emmett–Teller) surface area of the powders, SBET, was measured by the nitrogen gas adsorption technique using a Micromeritics ASAP 2020 instrument. BJH (Barrett–Joyner–Halenda) cumulative volume of pores, VBJH, was calculated from the adsorption branch of the isotherms. Assuming that the cobalt ferrite particles have a spherical shape, the equivalent diameter, DBET, was calculated using Eq. (2)

Fig. 1. Flowchart of the aqueous combustion synthesis and characterization of CoFe2O4.

DBET ¼

6000 ρSBET

ð2Þ

Table 1 Characteristics of combustion synthesized CoFe2O4 powders. Sample no.

C2H2O4 (wt%)

Reaction time (s)

DXRD (nm)

a (Å)

SBET (m2/g)

DBET (nm)

Ms (emu/g)

Hc (kA/m)

1. 2. 3. 4. 5.

0 50 100 150 175

20 45 50 80 120

41 31 22 18 13

8.385 8.387 8.372 8.386 8.387

1.8 2.1 6.5 20.0 34.4

629 539 174 57 33

66.6 70.6 63.5 53.1 53.0

103.7 126.0 118.2 109.1 71.8

Fig. 2. Images taken during the combustion reactions of samples 1 and 5.

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where DBET is the equivalent particle size (nm), ρ is the theoretical density of CoFe2O4 (5.3 g/cm3), and SBET is the BET surface area (m2/g). Magnetic properties were measured at room temperature by vibrating sample magnetometry, using a VSM 880 ADE/DMS magnetometer. Combustion synthesized powders were lubricated with 1 wt% of oleic acid, pressed into cylindrical pellets

(1.75 mm height  18.5 mm diameter) and then sintered at 1400 1C for 4 h (Fig. 1). Relative density of the sintered pellets was determined by the Archimedes technique. Morphology and elemental analysis of CoFe2O4 powders/sintered pellets were investigated by scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDAX), using a FEI Inspect S instrument.

Fig. 3. XRD patterns of samples 1–5, prepared by solution combustion synthesis.

Fig. 5. The evolution of BJH cumulative pore volume as a function of the oxalic acid addition.

Fig. 4. Adsorption–desorption isotherms of samples 1–5, prepared by solution combustion synthesis.

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Fig. 6. SEM images of samples 1, 2 and 5.

Fig. 7. Magnetic hysteresis curves of solution combustion synthesized CoFe2O4 powders.

Fig. 8. The evolution of coercivity of CoFe2O4 powders as a function of crystallite size.

3. Results and discussion

combustion synthesized CoFe2O4. Analyzing the influence of the oxalic acid addition on the CoFe2O4 crystallite size, one can notice that the crystallite size decreases with increasing the oxalic acid amount (Table 1). This evolution may be assigned on one hand to the decrease of the maximum temperature achieved during the combustion reaction and on the other hand to the increase of the gas volume evolved during the reaction, which hinders the crystallite growth. The adsorption–desorption isotherms of CoFe2O4 powders prepared by combustion synthesis are shown in Fig. 4. According to IUPAC classification, the samples show Type IV isotherms with H3 hysteresis, which suggests the presence of fragile porous particle agglomerations. Depending on the amount of oxalic acid added to the reaction mixture, the BET surface area of the obtained powders varies between 1.8 and 34.4 m2/g. Basically, increasing the oxalic acid addition leads to increased BET surface area and smaller crystallite size (Table 1). This evolution confirms not only the pore generator role of the oxalic acid, but also the mechanism that makes this possible: lowering the combustion temperature and increasing the volume of the evolved gases. One may notice that the equivalent particle size, DBET, calculated from the BET surface area is larger than the crystallite size, DXRD, calculated from the XRD patterns

The evolution of the combustion reactions – present in all the 5 recipes – is highly influenced by the proportion of oxalic acid addition. Practically, increasing the oxalic acid addition leads to longer reaction periods (Table 1). The higher the addition amount, the more obvious this effect is. In the case of samples 4 and 5 this is directly correlated with the lack of incandescence during combustion reactions. As a result, one can say that the oxalic acid addition results in a reduction of the combustion reaction intensity. Thus, the combustion reaction evolution gradually moves from a strong incandescence process, which is accompanied by flames (sample 1) to a smoldering process, where no flames or incandescence appeared (sample 5). For example, in Fig. 2 are shown some images taken during the combustion reactions of the samples 1 and 5. XRD patterns of the samples resulted from all the combustion reactions indicate CoFe2O4 as the single crystalline phase (Fig. 3). The unit cell parameter varies between 8.372 and 8.387 Å, which is very close to the theoretical value of CoFe2O4 (8.3919 Å) mentioned in the PDF file 22-1086. The average crystallite size of CoFe2O4 ranges between 13 and 41 nm, which indicates the nanocrystalline feature of

R. Ianoş et al. / Ceramics International 40 (2014) 10223–10229 Table 2 Comparative presentation of CoFe2O4 characteristics obtained in this study with respect to other results reported for the same preparation route. Fuel

DXRD (nm)

Hc (kA/m)

Ms (emu/g)

β-alanine (this study) Urea [5] Glycine [6] Glycine [18] Citric acid [19] Citric acid [20] Citric acid [10]

13–41 66 38 37 22 15 23

71.8–126.0 50 7 84 83 97 60

53.0–70.6 – 76 45 41 67 9

Fig. 9. Relative density of samples 1–5 sintered at 1400 1C for 4 h.

(Table 1). This indicates that the resulted CoFe2O4 particles are not single crystals, but they contain several crystallites, are polycrystalline, as confirmed by the SEM images of the samples. The pore generator function of the oxalic acid may also be noticed from the evolution of the cumulative pore volume, calculated based on the adsorption isotherm using the BJH method (Fig. 5). There is a direct correlation between the oxalic acid addition and pore volume: the higher the oxalic acid amount, the higher the pore volume. Thus, sample 5 prepared with 175% oxalic acid has a cumulative pore volume more than 22 times higher than sample 1 prepared with no oxalic acid addition. The evolution of BET surface area and cumulative pore volume as a function of the oxalic acid addition is also confirmed by the SEM images presented for samples 1, 2 and 5 (Fig. 6). One may notice that in each case the particles are associated in agglomerations smaller than 40 μm, which is in accordance to the type H3 hysteresis shown by the adsorption–desorption isotherms (Fig. 4). In the case of sample 1, prepared without oxalic acid, the grain porosity is rather small, as already confirmed by the nitrogen adsorption–desorption investigations. By comparison, sample 2 prepared with 50% oxalic acid addition, exhibits a clearly porous hollow structure. Increasing the addition amount

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up to 175% makes the CoFe2O4 morphology extremely loose, which is related to the large BET surface area of sample 5. The SEM images presented in Fig. 6 illustrate the increase of CoFe2O4 porosity with increasing the oxalic acid addition (sample 1-2-5), which is also confirmed by the nitrogen adsorption–desorption investigations (Table 1). Energy dispersive X-ray analysis (EDAX) of samples 1, 2 and 5 evidenced Co, Fe and O as the only present elements. Considering the method accuracy, the elemental composition of samples 1 (16.3% Co, 31.3% Fe, and 52.5% O), 2 (12.4% Co, 25.3% Fe, and 62.3% O) and 5 (13.2% Co, 26.0% Fe, and 60.8% O), expressed in atomic percents, is close to the theoretical composition of CoFe2O4 (14.3% Co, 28.6% Fe, and 57.1% O). These results are very well correlated to the XRD patterns (Fig. 3) of the samples showing CoFe2O4 as the single phase. The hysteresis curves of the samples obtained from the combustion reactions are presented in Fig. 7. One may notice that none of the samples reach the saturation magnetization in the applied range of magnetic field. Therefore, the saturation magnetization was calculated by plotting M as a function of 1/H, followed by the extrapolation of the magnetic curve at the magnitude of M, when H-1 (1/H-0). The saturation magnetization of CoFe2O4 powders calculated by this method ranges between 53.0 and 70.6 emu/g (Table 1). The coercivity of CoFe2O4 powders ranges between 71.8 and 126.0 kA/m, which indicates a hard ferrimagnetic character. The coercivity evolution as a function of the crystallite size (Fig. 8) is similar to the one reported by other authors [20,21]: coercivity increases with the increase of the crystallite size up to a maximum value of 126.0 kA/m, which corresponds to a crystallite size of 31 nm. The coercivity of CoFe2O4 powders decreases for larger crystallites due to the multidomenial character of the grains, surface anisotropy and thermal energies [20,21]. However, for the same crystallite size the CoFe2O4 coercivity values reported in this paper are higher, which translates into enhanced magnetic properties. Making a comparison between our results and those obtained by other authors [5,6,10,18–20] using combustion synthesis (Table 2), one may notice that the solution of using β-alanine and oxalic acid addition allows the adjustment of crystallite size, surface area and magnetic properties of CoFe2O4 in a wide range. The coercivity value of CoFe2O4 powders prepared in this study should be especially highlighted, as it is much higher than the one of CoFe2O4 powders obtained via combustion method using other fuels, such as urea, glycine or citric acid [5,6,10,18–20]. The relative density of the pellets sintered at 1400 1C for 4 h varies between 86 and 90% of the theoretical density (Fig. 9). One may notice that the relative density of the samples decreases with the increase of BET surface area. This phenomenon is even more prominent in the case of samples 4 and 5 – which show the highest BET surface area. This behavior suggests that the main challenge in achieving a good compactness after sintering is to obtain high-density green pellets in the first place. Taking this into account, one may expect to achieve improved results when using isostatic pressing rather than

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Fig. 10. SEM image and elements distribution (Co – blue, Fe – green, O – red) for sample 2, sintered at 1400 1C for 4 h.

uniaxial pressing. The SEM images (Fig. 10) of sample 2 sintered at 1400 1C for 4 h reveal the presence of the interconnected grains, smaller than 10 mm, and also the residual pores located at the grain boundaries. These observations are in agreement with the relative density of sample 2 (89% of the theoretical density). After the sintering process, the elemental composition of sample 2 (15.1 at% Co, 31.3 at% Fe and 53.6 at % O) is very close to the theoretical composition of CoFe2O4. At the same time, one may notice a homogeneous distribution of cobalt, iron and oxygen in the sintered sample. 4. Conclusions Single phase CoFe2O4 powders were prepared by solution combustion synthesis, without any annealing step, using βalanine as fuel. Properties of the resulted CoFe2O4 powders may be adjusted by adding various amounts of oxalic acid, which acts as a retarding agent and pore generator. Depending on the amount of oxalic acid, the average crystallite size of CoFe2O4 ranges between 13 and 41 nm, whilst the BET surface area varies between 1.8 and 34.4 m2/g. The combustion synthesized CoFe2O4 powders exhibit a hard ferrimagnetic behavior, having a coercivity that ranges between 71.8 and 126.0 kA/m. The saturation magnetization varies between 53.0 and 70.6 emu/g. After hydraulic uniaxial pressing and sintering at 1400 1C for 4 h, the pellets reached relative densities up to 90% of the CoFe2O4 theoretical density. The superior magnetic properties of the CoFe2O4 powders obtained directly from the combustion reaction (with no subsequent annealing), as well as their sintering behavior represent strong arguments for using the combustion method in the synthesis of CoFe2O4 powders with tailored properties. Acknowledgments This paper is supported by the Sectoral Operational Programme Human Resources Development, financed from the

European Social Fund and by the Romanian Government under the Contract number POSDRU/86/1.2/S/58146 (MASTERMAT). Authors would like to acknowledge Paula Sfîrloagă (National Research Institute for Electrochemistry and Condensed Matter, Timişoara) and Oana Marinică (National Center for Engineering of Systems with Complex Fluids, University “Politehnica” Timişoara) for performing the SEMEDAX and VSM analysis.

References [1] Y. Xingbin, C. Jiangtao, X. Qunji, M. Philippe, Synthesis and magnetic properties of CoFe2O4 nanoparticles confined within mesoporous silica, Microporous Mesoporous Mater. 135 (2010) 137–142. [2] W. Jing, D. Tong, L. Yulong, Y. Caiqin, Z. Wenhong, Synthesis and characterization of CoFe2O4 magnetic particles prepared by coprecipitation method: effect of mixture procedures of initial solution, J. Alloys Compd. 450 (2008) 532–539. [3] L. Xing-Hua, X. Cai-Ling, H. Xiang-Hua, Q. Liang, W. Tao, L. Fa-Shen, Synthesis and magnetic properties of nearly monodisperse CoFe2O4 nanoparticles through a simple hydrothermal condition, Nanoscale Res. Lett. 5 (2010) 1039–1044. [4] Z. Shusen, M. Dongxu, Preparation of CoFe2O4 nanocrystallites by solvothermal process and its catalytic activity on the thermal decomposition of ammonium perchlorate, J. Nanomater. (2010) 1–5 (article ID 842816). [5] K. Nermin, B. Abdülhadi, K. Yüksel, S.T. Muhammet, Microwaveassisted combustion synthesis of CoFe2O4 with urea, and its magnetic characterization, Scr. Mater. 57 (2007) 441–444. [6] A.B. Salunkhe, V.M. Khot, N.D. Thorat, M.R. Phadatare, C.I. Satish, D.S. Dhawale, S.H. Pawar, Polyvinil alcohol functionalized cobalt ferrite nanoparticles for biomedical applications, Appl. Surf. Sci. 264 (2013) 598–604. [7] L. Chao, A.J. Rondinone, Z.J. Zhang, Synthesis of magnetic spinel ferrite CoFe2O4 nanoparticles from ferric salt and characterization of the sizedependent superparamagnetic properties, Pure Appl. Chem. 72 (2000) 37–45. [8] J. Unyong, T. Xiaowei, W. Yong, Y. Hong, X. Younan, Superparamagnetic colloids: controlled synthesis and niche applications, Adv. Mater. 19 (2007) 33–60. [9] V.L. Calero-DdelC, C. Rinaldi, Synthesis and magnetic characterization of cobalt-substituted ferrite (CoxFe3  xO4) nanoparticles, J. Magn. Magn. Mater. 314 (2007) 60–67.

R. Ianoş et al. / Ceramics International 40 (2014) 10223–10229 [10] S.H. Xiao, W.F. Jiang, L.Y. Li, X. Li, Low-temperature auto-combustion synthesis and magnetic properties of cobalt ferrite nanopowder, Mater. Chem. Phys. 106 (2007) 82–87. [11] S.Y. Zhao, D.K. Lee, C.W. Kim, H.G. Cha, Y.H. Kim, Y.S. Kang, Synthesis of magnetic nanoparticles of Fe3O4 and CoFe2O4 and their surface modification by surfactant adsorption, Bull. Korean Chem. Soc. 27 (2006) 237–242. [12] P. Pulišová, J. Kováč, A. Voigt, P. Raschman, Structure and magnetic properties of Co and Ni nano-ferrites prepared by a two step direct microemulsions synthesis, J. Magn. Magn. Mater. 341 (2013) 93–99. [13] C. Chifiriuc, V. Lazăr, C. Bleotu, I. Călugărescu, A.M. Grumezescu, D.E. Mihăiescu, D.E. Mogoşanu, A.S. Buteică, E. Buteică, Bacterial adherence to the cellular and inert substrate in the presence of CoFe2O4 and Fe3O4 /oleic acid–core/shell, Dig. J. Nanomater. Biostruct. 6 (2011) 37–42. [14] K.V.P.M. Shafi, A. Gedanken, Sonochemical preparation and sizedependent properties of nanostructured CoFe2O4 particles, Chem. Mater. 10 (1998) 3445–3450. [15] T. Meron, Y. Rosenberg, Y. Lereah, G. Markovich, Synthesis and assembly of high-quality cobalt ferrite nanocrystals prepared by a modified sol–gel technique, J. Magn. Magn. Mater. 292 (2005) 11–16.

10229

[16] R.N. Panda, J.C. Shih, T.S. Chin, Magnetic properties of nano-crystalline Gd- or Pr-substituted CoFe2O4 synthesized by the citrate precursor technique, J. Magn. Magn. Mater. 257 (2003) 79–86. [17] A. Sutka, G. Mezinskis, Sol–gel auto-combustion synthesis of spinel-type ferrite nanomaterials, Front. Mater. Sci. 6 (2012) 128–141. [18] A.B. Salunkhe, V.M. Khot, M.R. Phadatare, S.H. Pawar, Combustion synthesis of cobalt ferrite nanoparticles—influence of fuel to oxidizer ratio, J. Alloys Compd. 514 (2012) 91–96. [19] U. Kurtan, R. Topkaya, A. Baykal, M.S. Toprak, Temperature dependent magnetic properties of CoFe2O4/CTAB nanocomposite synthesized by sol–gel auto-combustion technique, Ceram. Int. 39 (2013) 6551–6558. [20] B.G. Toksha, S.E. Shirsath, S.M. Patange, K.M. Jadhav, Structural investigations and magnetic properties of cobalt ferrite nanoparticles prepared by sol–gel auto combustion method, Solid State Commun. 147 (2008) 479–483. [21] K. Maaz, A. Mumtaz, S.K. Hasanaina, A. Ceylan, Synthesis and magnetic properties of cobalt ferrite (CoFe2O4) nanoparticles prepared by wet chemical route, J. Magn. Magn. Mater. 308 (2007) 289–295.