SYNTHESIS AND CHARACETRIZATION OF MIXED OXIDE BASED ON COBALT FERRITE NANOPARTICLES

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1 Nonconventional Technologies Review Romania, June, Romanian Association of Nonconventional Technologies SYNTHESIS AND CHARACETRIZATION OF MIXED OXIDE BASED ON COBALT FERRITE NANOPARTICLES P. Vlazan 1, C.-V. Irina-Moisescu 2, I. Miron 1*, P. Sfirloaga 1,3, I. Grozescu 1,2 1 National Institute for Research and Development in Electrochemistry and Condensed Matter, P. Andronescu Street, No.1, Timisoara, Romania 2 Politehnica University of Timisoara, Piata Victoriei, No. 2, , Timisoara, Romania 3 West University of Timisoara, 4 Bd. V. Pârvan, Timişoara, Romania Contact person mironiasmina@gmail.com ABSTRACT: Cobalt ferrite (CoFe 2 O 4 ) nanoparticles were synthesized by sol-gel method and thermally treated at 500ºC for 2 hours. The achieved nanoparticles were characterized by means of Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction analysis (XRD), scanning electron microscopy (SEM-EDX) and magnetic analysis. XRD analysis revealed a single crystalline phase for CoFe 2 O 4 nanoparticles thermally treated at 500ºC. The average crystallite size was calculated around 29.7 nm. SEM analysis showed the presence of agglomeration and the EDX analysis confirmed the stoichiometry, Co:Fe = 1:2. Magnetic measurements showed that the CoFe 2 O 4 nanoparticles thermally treated at 500ºC presents a high coercivity (1400 Oe). Also, the saturation magnetization was calculated of about 60 emu/g. KEY WORDS: Cobalt ferrite, Nanoparticles, Sol-gel, X-ray diffraction, Magnetic properties 1. INTRODUCTION In the last years, the synthesis of nano-sized ferrite magnetic materials have been extensively studied because of their potential applications in highdensity magnetic recording, microwave devices, drug delivery applications, etc. [1]. The complex metal oxides in the form of nanoparticles such as spinel ferrites have good chemical and thermal stability and possess great potentials for application in catalysis, gas sensors, high quality ceramics and super paramagnetic materials.[2,3,4] The magnetic properties of nanomaterials are influenced by a number of factors such as: synthesis method, composition, particle size, shape, surface morphology, purity and interactions between particles. Among magnetic materials, cobalt ferrite with spinel structure AB 2 O 4 type, is especially interesting owing to its magnetic properties such as strong anisotropy, high coercivity at room temperature and moderate saturation magnetization, good mechanical and chemical stability [5]. To date were used many conventional and nonconventional methods for obtaining magnetic materials, among these including coprecipitation [6,7], hydrothermal synthesis [8,9], sol gel techniques [10], microemulsion method [11,12], sonochemical [13] and combustion reaction [14]. In the present study, CoFe 2 O 4 nanoparticles are synthesized using a sol-gel method and thermally treated at 500ºC for 2 hours. 2. EXPERIMENTAL The synthesis of cobalt ferrite nanoparticles was achieved by sol-gel method. Cobalt nitrate (Co(NO 3 ) 2 6H 2 O), iron nitrate (Fe(NO 3 ) 3 9H 2 O), citric acid (C 6 H 8 O 7 ), ethylic alcohol and ammonia solution 25% (NH 4 OH) were used as precursors. Stoichiometric amounts of cobalt nitrate and iron nitrate were dissolved in 1% acid citric solution and stirred vigorous on a magnetic stirrer at 60ºC temperature for 10 minutes. Then, the 25% ammonia solution was added drop by drop. The final ph of the mixture was about 8. Then, the temperature was raised till 150ºC and was maintained at this value till a viscous solution was formed. The ethylic alcohol was added and the gel was formed. The obtained gel was dried at 80ºC. A part of the obtained gel was grinded in an agate mortar in order to obtain a powder sample (sample P1). The rest of the obtained gel was then thermally treated at 500ºC for 2 hours. After the thermal treatment the compound was, also, grinded in an agate mortar in order to obtain a powder sample (sample P2). The sample P1 was characterized by Fourier transform infrared spectroscopy (FT-IR) in order to identify the formation of organometallic compounds and by thermogravimetric analysis (TGA) in order to 62

2 determine the temperature at which cobalt ferrite nanoparticles are formed. The sample P2 was characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM-EDX) and by magnetic measurements. The X-ray diffraction pattern was recorded using the PANalytical X Pert Pro MPD diffractometer with CuKα radiation (λ=1.54 Å) between 10 and 100 (2θ). The morphological analysis and energy dispersive x- ray analysis were obtained using scanning electron microscope (Model Inspect S). Magnetic analysis was performed by conventional magnetic measurements in alternating current (AC) [15]. range and the tip splitting is due to the overlapping of the symmetric vibration of the carboxyl groups and asymmetric vibration of the C- O-C- group [17]. cm -1 TGA curve of the sample P1 is presented in Figure 2. From evolution of TGA curve of the sample P1 it can be observed that in the range ºC there is a high speed mass loss attributed to the decomposition of the formed organometallic precursor. 3. RESULTS AND DISCUSSIONS 3.1 CoFe 2 O 4 (sample P1) obtained by sol-gel method at 150ºC FT-IR spectra of the sample P1 is presents in Figure 1. The bands that occur in the cm -1 range are corresponding to the characteristic vibration of - OH groups not associated with the hydrogen bonds provided by citric acid. Figure 2. TGA curve for the sample P1 The loss in mass of about 10% in the range ºC is due to the elimination of the volatile substances (water, alcohol). 3.2 CoFe 2 O 4 (sample P2) obtained by sol-gel method and thermally treated at 500ºC The decomposition process of the CoFe 2 O 4 (sample P2) obtained by sol-gel method and thermally treated at 500ºC was studied by FT-IR spectroscopy. FT-IR spectra presented in Figure 3 shows by intense band situated at 576 cm -1 that the complete combustion of the organic part occurred and the cobalt ferrite nanoparticles were formed [18]. Figure 1. FT-IR spectra of the sample P1 The broadband from this area probably include bands corresponding to CH and CH2 groups from the cm -1 range. The band located at 1612 cm -1 is due to the asymmetrical vibration of COOgroups, while the intense band from 1390 to 1350 cm -1 corresponds to the symmetric vibration of the - COO- groups [16]. The presence of these bands confirmed that the carboxyl groups are coordinated to the metal ions, namely the formation of carboxylates, chelates of metal ions with citric acids. The intensity of the band situated in the Figure 3. FT-IR spectra of the sample P2 63

3 In order to obtain a complete combustion of the organic part, the gels were thermally treated for 2 hours at 500ºC. After thermal treatment, a fine powder with high volume was obtained, as it can be seen in Figure 4. (a) Figure 4. The image of the sample P2 XRD pattern for CoFe 2 O 4 obtained by thermal treatment at 500ºC (sample P2) is presented in Figure 5. It can be seen that the pattern shows only the characteristic peaks of well crystallized cobalt ferrite. The average crystallite size obtained by using the Scherrer s equation [19] was about 29.7 nm. (b) Figure 6. SEM image (a) and EDX spectrum (b) for the sample P2 EDX analysis for CoFe 2 O 4 (sample P2) confirmed the stoichiometry, Co:Fe = 1:2 (Figure 6 b)). The magnetic behaviour of the cobalt ferrite (sample P2) synthesized by sol-gel method and thermally treated at 500ºC is presented in Figure 7. One can see, that the coercivity presents a high value (H c = 1400 Oe), meaning that the existence of a large internal stress determine a behaviour close to the micrometer cobalt ferrite [20]. An influence on this kind of behaviour may be due to the presence of fine carbon particles which covers magnetic ferrite surface. Figure 5. XRD pattern of the sample P2 SEM image (Figure 6 a)) of CoFe 2 O 4 nanoparticles (sample P2) shows an agglomeration of nanoparticles which may be due to the presence of residual carbon aggregates that covers the surface of the nanoparticles as a thin layer. Figure 7. Magnetization curve for the sample P2 64

4 Saturation magnetization was estimated to be about 60 emu/g. 4. CONCLUSIONS Cobalt ferrite nanoparticles (CoFe 2 O 4 ) were successfully synthesized by sol-gel method and thermally treated at 500ºC for 2 hours. The TGA curve of cobalt ferrite synthesized by sol-gel method at 150ºC showed that the crystalline cobalt ferrite occurs at 500ºC. X-ray diffraction spectra of CoFe 2 O 4 thermally treated at 500ºC confirmed the results obtained by TGA analysis. The average crystallite size was found to be avout 29.7 nm. EDX analysis for CoFe 2 O 4 thermally treated at 500ºC confirmed the stoichiometry, Co:Fe = 1:2. The magnetization curve reveals a high coercivity value about 1400 Oe. Also, the saturation magnetization was about 60 emu/g. Acknowledgement This paper is supported by the Sectorial Operational programme Human Resources Development (SOP HRD), ID financed from the European Social Fund and by the Romanian Government. The paper is supported by the Sectoral Operational Programme Human Resource Development under the project: " Doctoral and postdoctoral programs - support for the research competitiveness in sciences" number POSDRU/159/1.5/S/ References: 1. I.H. Gul, A. Maqsood, Structural, magnetic and electrical properties of cobalt ferrites prepared by the sol gel route, J. Alloys Compd., 465, , (2008). 2. S.H. Xiao,W.F. Jiang, L.Y. Li, X.J. Li, Lowtemperature auto-combustion synthesis and magnetic properties of cobalt ferrite nanopowder, Mater. Chem. Phys., 106, 82-87, (2007). 3. L.J. Zhao, H.J. Zhang, Y. Xing, S.Y. Song, S.Y. Yu,W.D. Shi, X.M. Guo, J.H. Yang, Y.Q. Lei, F. Cao, Studies on the magnetism of cobalt ferrite nanocrystals synthesized by hydrothermal method, J. Solid State Chem., 181, , (2008). 4. B.P. Barbero, J.A. Gamboa, L.E. Cadus, Synthesis and characterisation of La 1-x Ca x FeO 3 perovskite-type oxide catalysts for total oxidation of volatile organic compounds, Appl. Catal. B, 65, 21-30, (2006). 5. J.G. Lee, J.Y. Park, Y.J. Oh, C.S. Kim, Magnetic properties of CoFe 2 O 4 thin films prepared by a sol-gel method, J. Appl. Phys., 84, , (1998). 6. Y.I. Kim, D. Kim, C.S. Lee, Synthesis and characterization of CoFe 2 O 4 magnetic nanoparticles prepared by temperature-controlled coprecipitation method, Physica B, 337, 42 51, (2003). 7. J.Wang, T. Deng, Y. Lin, C. Yang, W. Zhan, Synthesis and characterization of CoFe2O4 magnetic particles prepared by co-precipitation method: Effect of mixture procedures of initial solution, J. Alloys Compd., 450, , (2008). 8. [8] G.B. Ji, S.L. Tang, S.K. Ren, F.M. Zhang, B.X. Gu, Y.W. Du, Simplified synthesis of single-crystalline magnetic CoFe 2 O 4 nanorods by a surfactant-assisted hydrothermal process, J. Cryst. Growth, 270, , (2004). 9. Q. Liu, J. Sun, H. Long, X. Sun, X. Zhong, Z. Xu, Hydrothermal synthesis of CoFe 2 O 4 nanoplatelets and nanoparticles, Mater. Chem. Phys., 108, , (2008). 10. L. Ai, J. Jiang, Influence of annealing temperature on the formation, microstructure and magnetic properties of spinel nanocrystalline cobalt ferrites, Curr Appl Phys., 10, , (2010). 11. L.J. Zhao, Q. Jiang, Effects of applied magnetic fieldand pressures on the magnetic properties of nanocrystalline CoFe 2 O 4 ferrite, J. Magn. Magn. Mater., 322, , (2010). 12. C. Liu, A. J. Rondinone, Z. Zhang, Synthesis of magnetic spinel ferrite CoFe 2 O 4 nanoparticles from ferric salt and characterization of the sizedependent superparamagnetic properties, Pure Appl. Chem., 72, 37 45, (2000). 13. Kurikka V. P. M. Shafi and A. Gedanken, Sonochemical preparation and size-dependent properties of nanostructured CoFe 2 O 4 particles, Chem. Mater., , (1998). 14. X. Zhang,W. Jiang, D. Song, H. Sun, Z. Sun, F. Li, Salt-assisted combustion synthesis of highly dispersed superparamagnetic CoFe 2 O 4 nanoparticles, J. Alloys Compd., 475, L34 L37, (2009). 15. I. Mihalca, A.Ercuta, Structural relaxation in Fe 70 Cr 10.5 P 11.5 Mn 1.5 C 6.5 amorphous alloy, J. Optoelectron. Adv. Mater., 5, , (2003). 16. X.F. Chu, D.L. Jiang, Y. Guo, C.M. Zheng, Ethanol gas sensor based CoFe 2 O 4 nanocrystallines prepared by hydrothermal method, Sens. Actuators B, 120, , (2006). 65

5 17. S. Vivekanandhan, M. Venkateswarlu, N. Satyanarayana, Sol-gel mediated surface modification of nanocrystalline NiFe 2 O 4 spinel powders with amorphous SiO 2, Mater. Chem. Phys., 91, 54 59, (2005). 18. T. Caillof, G. Pourroy, D. Stuerga, Microwave hydrothermal flash synthesis of nanocomposites Fe Co alloy/cobalt ferrite, J. Solid State Chem., 177, , (2004). 19. T. Minami, H. Sato, K. Ohashi, T. Tomofuji, S. Takata, Conduction mechanism of highly conductive and transparent zinc oxide thin films prepared by magnetron sputtering, J. Cryst. Growth, 117, , (1992). 20. G. Pourroy, N. Viart, S. La Kamp, Magnetic characterization of composite Fe-Co alloy/co containing magnetite, J. Magn. Magn. Mater., 203, 37-40, (1999). 66