Synthesis, magnetic and optical properties of core/shell Co1-x Zn x Fe2O4/SiO2 nanoparticles
© Girgis et al; licensee Springer. 2011
Received: 22 April 2011
Accepted: 20 July 2011
Published: 20 July 2011
The optical properties of multi-functionalized cobalt ferrite (CoFe2O4), cobalt zinc ferrite (Co0.5Zn0.5Fe2O4), and zinc ferrite (ZnFe2O4) nanoparticles have been enhanced by coating them with silica shell using a modified Stöber method. The ferrites nanoparticles were prepared by a modified citrate gel technique. These core/shell ferrites nanoparticles have been fired at temperatures: 400°C, 600°C and 800°C, respectively, for 2 h. The composition, phase, and morphology of the prepared core/shell ferrites nanoparticles were determined by X-ray diffraction and transmission electron microscopy, respectively. The diffuse reflectance and magnetic properties of the core/shell ferrites nanoparticles at room temperature were investigated using UV/VIS double-beam spectrophotometer and vibrating sample magnetometer, respectively. It was found that, by increasing the firing temperature from 400°C to 800°C, the average crystallite size of the core/shell ferrites nanoparticles increases. The cobalt ferrite nanoparticles fired at temperature 800°C; show the highest saturation magnetization while the zinc ferrite nanoparticles coated with silica shell shows the highest diffuse reflectance. On the other hand, core/shell zinc ferrite/silica nanoparticles fired at 400°C show a ferromagnetic behavior and high diffuse reflectance when compared with all the uncoated or coated ferrites nanoparticles. These characteristics of core/shell zinc ferrite/silica nanostructures make them promising candidates for magneto-optical nanodevice applications.
Synthesis of magnetic nanoparticles have been intensively pursued due to their unique functional properties and their wide variety of potential applications in high density magnetic recording [1–4], ferrofluids technology , biomedical drug delivery [6, 7], and magnetic resonance imaging [8, 9], data storage, biosensors , biocompatible magnetic nanoparticles for cancer treatment [11–14], and magneto-optical devices [15–17] among others.
In recent years, Spinel ferrite nanoparticles have been widely studied because of their excellent and convenient magnetic and electrical properties [18, 19]. Among spinel ferrites, CoFe2O4 is of interest due to its high intrinsic coercivity (5,400 Oe) and moderate saturation magnetization (about 80 emu/g) as well as remarkable chemical stability and mechanical hardness, which makes it a good candidate for recording media [20, 21]. Also, studies indicate that the magnetic properties of CoFe2O4 depend strongly on its morphology and are greatly affected by the size of the particles [22, 23]. In addition, the magnetic properties of spinel structure CoFe2O4 can be altered by cation substitution. According to recent research, Zn2+ substituting for Co2+ in CoFe2O4 nanoparticles (Co1-x Zn x Fe2O4) exhibited improvement in properties such as excellent chemical stability, high corrosion resistivity, magneto-crystalline anisotropy, magneto-striction, and magneto-optical properties. Cobalt zinc ferrites nanoparticles have been prepared by different methods, such as co-precipitation, usual ceramic technique, microwave-hydrothermal method, and the solvothermal method [24–30].
In the present decade, core/shell structured nanoparticles have received much attention, due to their enhanced combination of optical, electronic, and magnetic properties compared to those of single-component nanomaterials . Thus, coating magnetic nanoparticles with silica is becoming a promising and important approach in the development of magnetic nanoparticles for both fundamental studies as well as technological applications. Silica formed on the surface of magnetic nanoparticles could screen the magnetic dipolar attraction between magnetic nanoparticles, which improves the dispersion of magnetic nanoparticles in liquid media and protects them from leaching in an acidic environment. In addition, the core/shell structure enhances the thermal and chemical stability of the magnetic nanoparticles due to the silica shell which provides a chemically inert surface for magnetic nanoparticles in biological systems. Therefore, silica-coated magnetic nanoparticles can be easily allowed to conjugate its surface with various functional groups [32, 33]. Also, the silica shell can enhance the optical properties of the nanoparticles . The optical properties of the nanostructures have been investigated earlier using many techniques, among them is the diffuse reflectance spectroscopy .
The main objective of this study is to investigate the effect of Zn2+ partially substituting for Co2+ in CoFe2O4 nanoparticles (Co1-x Zn x Fe2O4; x = 0, 0.5, and 1) and shelling with silica on the magnetic and optical properties of the ferrite nanoparticles for a variety of magneto-optical nanodevice applications. From a synthesis point of view exploring the effect of firing temperatures (400°C, 600°C and 800°C) is of interest to investigate.
The chemicals used for preparation of the samples were ferric nitrate (Fe(NO3)3·9H2O, Mw = 404.00 g/mol, Alpha Chemika™, Mumbai, India), cobalt (II) nitrate (Co(NO3)2·6H2O, Mw = 291.04 g/mol, WinLab, UK), and zinc nitrate (Zn(NO3)2·6H2O, Mw = 297.47 g/mol, WinLab, Laboratory chemicals reagent fine chemicals), citric acid monohydrate gritty, puriss, (C6H8O7·H2O, Mw = 210.14 g/mol, Riedel-Dehaën, Sigma-Aldrich, Labor Chemika Lien, GmbH, St. Louis, MO, USA), ammonia solution (30%), and tetraethyl orthosilicate (TEOS, C8H20O4Si, Mw = 208.33 g/mol, Merck Schuchardt OHG, Hohenbrunn, Germany).
CoFe2O4, ZnFe2O4, and Co0.5Zn0.5Fe2O4 nanoparticles have been prepared using modified citrate gel method [36, 37]. Co(NO3)2·6H2O solution (0.25 M), Zn(NO3)2·6H2O solution (0.25 M), and Fe(NO3)3·9H2O solution (0.25 M) were prepared by dissolving the metal nitrates in distilled water. The prepared solutions were mixed in molar ratio of Me2+/Fe3+ = 0.5 (Me2+ = Co2+, Zn2+, and 0.5 Co2+ + 0.5 Zn2+ for CoFe2O4, ZnFe2O4, and Co0.5Zn0.5Fe2O4, respectively) under constant stirring to get homogeneous solution with the heating rate of 5°C/min up to 80°C for 1 h. This mixture solution was added to the citric acid solution (0.25 M) maintaining the molar ratio between metal nitrates solution and citric acid solution as 1:1 and stirred for 2 h. Ammonia was added to reach pH equal to 7.5. Increasing the temperature during the stirring process leads to form a viscous gel. The gel was dried and fired at temperatures of 400°C, 600°C, and 800°C for 2 h to form CoFe2O4 (CF), ZnFe2O4 (ZF), and Co0.5Zn0.5Fe2O4 (CZF) nanoparticles.
Silica-coated magnetic nanoparticles were prepared using the modified Stöber method. The nanoparticles (fired at 400°C) were first treated by citric acid solution (0.01 M) under constant stirring for 1 h. The presence of citrate increases the organosilane affinity of the particle surface. These particles were separated and washed with distilled water several times. After that, the particles were redispersed in a mixture of absolute ethanol (80 ml) and distilled water (20 ml) the ammonia was added to the solution as a catalyst. Subsequently, 6 ml of TEOS was injected to the above solution, drop by drop at constant stirring for 24 h at room temperature to ensure the hydrolysis, after that, the condensation of TEOS on the surface of nanoparticles was achieved. Finally, the core/shell CoFe2O4/SiO2, Co0.5Zn0.5Fe2O4/SiO2, and ZnFe2O4/SiO2 particles were separated using external magnet, and washed with ethanol and water several times. The samples have been dried at 40°C for 24 h and fired at temperatures 400°C, 600°C, and 800°C, respectively, for 2 h.
The morphology of uncoated and coated nanoparticles was studied using transmission electron microscopy, TEM (JEOL 1230, JEOL, Tokyo, Japan). The phase composition and average crystallite size of the core/shell ferrite nanoparticles were investigated using X-ray diffractometer (Model Bruker D8 Advance (Bruker AXS, Madison, WI, USA), Cu-Kα1 (λ = 1.54058 Å) radiation with secondary monochromator at a scanning speed of 1°/min). In addition, vibrating samples magnetometer (model is Princeton FM-1, Princeton Applied Research, Oak Ridge, TN, USA) and UV/VIS double-beam spectrophotometer (model is no. Lambda 35, Perkin Elmer, Waltham, MA, USA) were used to measure the magnetic properties and diffuse reflectance of the prepared ferrite nanoparticles, respectively.
Results and discussion
On the other hand, the hysteresis loop is much wider for the cobalt ferrite samples coated with silica shell (CFS) and fired at 400°C compared with cobalt ferrite samples fired at 800°C. This confirms that by increasing the firing temperature, the crystallite size increases leading to decrease of the switching field. Also, it was found that, for the cobalt ferrite nanoparticles coated with silica (CFS), the magnetic moment increases with increasing the firing temperature from 400°C to 800°C. As mentioned earlier from the XRD analysis, with increasing the firing temperature, the amorphous silica starts to disappear and the diffraction peaks of spinel cobalt ferrite phase only are found at higher temperatures due to the formation of robust core/shell structure (Figure 1a). This leads to creation of a very thin layer of cobalt ferrite silicate at the surface of these cobalt ferrite nanoparticles which decrease the effect of the amorphous silica shell and hence increase the magnetic moment at higher firing temperature.
Figure 5b shows the hysteresis loops of core/shell zinc ferrite nanoparticles coated with silica shell (ZFS) fired at 400°C and 800°C. It is clear that at 400°C, the zinc ferrite/silica nanoparticles show a ferromagnetic behavior compared with the sample fired at 800°C which shows a paramagnetic behavior.
Summary of the magnetization saturation and switching field (HC) values at room temperature (27°C)
Core/shell Co1-x Zn x Fe2O4/SiO2 (x = 0, 0.5, and 1) nanoparticles were prepared using modified citrate gel technique and coated with silica shell. The samples have been fired at 400°C, 600°C, and 800°C, respectively. It is concluded that cobalt ferrite nanoparticles fired at 800°C showed the highest magnetic properties, while zinc ferrite nanoparticles coated with silica and fired at 800°C shows the best enhanced optical properties. X-ray diffraction patterns show the presence of spinel ferrite crystalline phase as the main phase in all prepared core/shell ferrite nanoparticles. In addition, the average crystallite size increases on increasing the firing temperature from 400°C up to 800°C. Zinc ferrite nanoparticles coated with silica shell and fired at 400°C show a ferromagnetic behavior and high diffuse reflectance compared with all uncoated and coated nanoparticles due to the presence of zinc ions and the silica shell which play an important role on the optical properties enhancement. The firing temperatures as well as the crystallite size parameters have great effect on the magnetic and the optical properties of core/shell ferrite nanoparticles. Core/shell ferrite nanoparticles coated with silica are found to enhance the optical properties of the magnetic nanoparticles. Core/shell zinc ferrite nanoparticles coated with silica shell and fired at 400°C show promising results for photo-magnetic nanodevice applications and for magneto-optical recording industry.
We would like to thank the Swedish Research Foundation SIDA for supporting the present work under grant # 348-2007-6992.
- Leslie-Pelecky DL, Rieke RD: Magnetic properties of nanostructured materials. Chem Mater 1996, 8(8):1770–1783. 10.1021/cm960077fView ArticleGoogle Scholar
- Himpsel FJ, Ortega JE, Mankey GJ, Willis RF: Magnetic nanostructures. Adv Phys 1998, 47(4):511–597. 10.1080/000187398243519View ArticleGoogle Scholar
- Sugimoto M: The past, present and future of ferrites. J Am Ceram Soc 1999, 82(2):269–280.View ArticleGoogle Scholar
- Bate G: Magnetic recording materials since 1975. J Magn Magn Mater 1991, 100(1–3):413–424. 10.1016/0304-8853(91)90831-TView ArticleGoogle Scholar
- Pileni MP: Magnetic fluids: fabrication, magnetic properties, and organization of nanocrystals. Adv Funct Mater 2001, 11(5):323–336. 10.1002/1616-3028(200110)11:5<323::AID-ADFM323>3.0.CO;2-JView ArticleGoogle Scholar
- Liu C, Zou BS, Rondinone AJ, Zhang ZJ: Reverse micelle synthesis and characterization of superparamagnetic MnFe 2 O 4 spinel ferrite nanocrystallites. J Phys Chem B 2000, 104(6):1141–1145. 10.1021/jp993552gView ArticleGoogle Scholar
- Sun C, Lee JSH, Zhang M: Magnetic nanoparticles in MR imaging and drug delivery. Adv Drug Deliv Rev 2008, 60: 1252–1265. 10.1016/j.addr.2008.03.018View ArticleGoogle Scholar
- Shultz MD, Calvin S, Fatouros PP, Morrison SA, Carpenter EE: Enhanced ferrite nanoparticles as MRI contrast agents. J Magn Magn Mater 2007, 311: 464–468. 10.1016/j.jmmm.2006.10.1188View ArticleGoogle Scholar
- Zhen L, He K, Xu CY, Shao WZ: Synthesis and characterization of single-crystalline MnFe 2 O 4 nanorods via a surfactant-free hydrothermal route. J Magn Magn Mater 2008, 320: 2672–2675. 10.1016/j.jmmm.2008.05.034View ArticleGoogle Scholar
- Schmid G: Nanoparticles: from theory to application. Weinheim: Wiley-VCH; 2004.Google Scholar
- Jordan A, Scholz R, Wust P, Schirra H, Schiestel T, Schmidt H, Felix R: Endocytosis of dextran and silan-coated magnetite nanoparticles and the effect of intracellular hyperthermia on human mammary carcinoma cells in vitro. J Magn Magn Mater 1999, 194: 185–196. 10.1016/S0304-8853(98)00558-7View ArticleGoogle Scholar
- Kim DH, Nikles DE, Johnson DT, Brazel CS: Heat generation of aqueously dispersed CoFe 2 O 4 nanoparticles as heating agents for magnetically activated drug delivery and hyperthermia. J Magn Magn Mater 2008, 320: 2390–2396. 10.1016/j.jmmm.2008.05.023View ArticleGoogle Scholar
- Mornet S, Vasseur S, Grasset F, Duguet E: Magnetic nanoparticle design for medical diagnosis and therapy. J Mater Chem 2004, 14: 2161–2175. 10.1039/b402025aView ArticleGoogle Scholar
- Wada S, Tazawa K, Furuta I, Nagae H: Antitumor effect of new local hyperthermia using dextran magnetite complex in hamster tongue carcinoma. Oral Dis 2003, 9: 218–223. 10.1034/j.1601-0825.2003.02839.xView ArticleGoogle Scholar
- Bentivegna MF, Nyvlt M, Ferre J, Jamet JP, Brun A, Visnovsky S, Urban R: Magnetically textured γ -Fe 2 O 3 nanoparticles in a silica gel matrix: optical and magneto-optical properties. J Appl Phys 1999, 85(4):2270–2278. 10.1063/1.369537View ArticleGoogle Scholar
- Hocini A, Boumaza T, Bouchemat M, Royer F, Jamon D, Rousseau JJ: Birefringence in magneto-optical rib waveguides made by SiO 2 /TiO 2 doped with g-Fe 2 O 3 . Microelectron J 2008, 39: 99–102. 10.1016/j.mejo.2007.09.012View ArticleGoogle Scholar
- Jamon D, Donatini F, Siblini A, Royer F, Perzynski R, Cabuil V, Neveu S: Experimental investigation on the magneto optic effects of ferrofluids via dynamic measurements. J Magn Magn Mater 2009, 321: 1148–1154. 10.1016/j.jmmm.2008.10.038View ArticleGoogle Scholar
- Kaiser M: Effect of nickel substitutions on some properties of Cu-Zn ferrites. J Alloy Compd 2009, 468(1–2):15–21. 10.1016/j.jallcom.2008.01.070View ArticleGoogle Scholar
- Iqbal MJ, Siddiquah MR: Electrical and magnetic properties of chromium-substituted cobalt ferrite nanomaterials. J Alloy Compd 2008, 453(1–2):513–518. 10.1016/j.jallcom.2007.06.105View ArticleGoogle Scholar
- Lee JG, Park JY, Kim CS: Growth of ultra-fine cobalt ferrite particles by a sol-gel method and their magnetic properties. J Mater Sci 1998, 33(15):3965–3968. 10.1023/A:1004696729673View ArticleGoogle Scholar
- Okuno SN, Hashimoto S, Inomata K: Preferred crystal orientation of cobalt ferrite thin films induced by ion bombardment during deposition. J Appl Phys 1992, 71: 5926–5929. 10.1063/1.350442View ArticleGoogle Scholar
- Montana S, Santi M: Nanostructures and magnetic properties of cobalt ferrite (CoFe 2 O 4 ) fabricated by electrospinning. Appl Phys Mater Sci Process 2009, 97(1):167–177. 10.1007/s00339-009-5256-5View ArticleGoogle Scholar
- Chiu WS, Radiman S, Abd-Shukor R, Abdullah MH, Khiew PS: Tunable coercivity of CoFe 2 O 4 nanoparticles via thermal annealing treatment. J Alloy Compd 2008, 459(1–2):291–297. 10.1016/j.jallcom.2007.04.215View ArticleGoogle Scholar
- Vaidyanathan G, Sendhilnathan S: Characterization of Co1-xZnxFe2O4 nanoparticles synthesized by co-precipitation method. Phys B: Phys Condens Matter 2008, 403: 2157–2167. 10.1016/j.physb.2007.08.219View ArticleGoogle Scholar
- Akther Hossain AKM, Tabata H, Kawai T: Magnetoresistive properties of Zn 1-x Co x Fe 2 O 4 ferrites. J Magn Magn Mater 2008, 320(6):1157–1162. 10.1016/j.jmmm.2007.11.009View ArticleGoogle Scholar
- Islam MU, Aen F, Niazi SB, Azhar Khan M, Ishaque M, Abbas T, Rana MU: Electrical transport properties of CoZn ferrite-SiO 2 composites prepared by co-precipitation technique. Mater Chem Physic 2008, 109(2–3):482–487. 10.1016/j.matchemphys.2007.12.021View ArticleGoogle Scholar
- Arulmurugan R, Vaidyanathan G, Sendhilnathan S, Jeyadevan B: Thermomagnetic properties of Co 1-x Zn x Fe 2 O 4 (x = 0.1–0.5) nanoparticles. J Magn Magn Mater 2006, 303(1):131–137. 10.1016/j.jmmm.2005.10.237View ArticleGoogle Scholar
- Tawfik A, Hamada IM, Hemeda OM: Effect of laser irradiation on the structure and electromechanical properties of Co-Zn ferrite. J Magn Magn Mater 2002, 250: 77–82.View ArticleGoogle Scholar
- Kim CK, Lee JH, Katoh S, Murakami R, Yoshimura M: Synthesis of Co-, Co-Zn and Ni-Zn ferrite powders by the microwave-hydrothermal method. Mater Res Bull 2001, 36(12):2241–2250. 10.1016/S0025-5408(01)00703-6View ArticleGoogle Scholar
- Hou C, Yu H, Zhang Q, Li Y, Wang H: Preparation and magnetic property analysis of monodisperse Co-Zn ferrite nanospheres. J Alloy Compd 2010, 491(1–2):431–435. 10.1016/j.jallcom.2009.10.217View ArticleGoogle Scholar
- Lu QH, Yao KL, Xi D, Liu ZI, Luo XP, Ning Q: A magnetic separation study on synthesis of magnetic Fe oxide core/Au shell nanoparticles. Nanoscience 2006, 11(4):241–248.Google Scholar
- Deng YH, Wang CC, Hu JH, Yang WL, Fu SK: Investigation of formation of silica-coated magnetite nanoparticles via sol-gel approach. Colloid Surface Physicochem Eng Aspects 2005, 262(1–3):87–93. 10.1016/j.colsurfa.2005.04.009View ArticleGoogle Scholar
- Sounderya N, Zhang Y: Use of core/shell structured nanoparticles for biomedical applications. Recent Patents on Biomedical Engineering 2008, 1: 34–42.View ArticleGoogle Scholar
- Huaiping C, Toftegaard R, Arnbjerg J, Ogilby PR: Silica - coated gold nanorods with a gold overcoat: controlling optical properties by controlling the dimensions of a gold - silica - gold layered nanoparticle. Langmuir 2010, 26(6):4188–4195. 10.1021/la9032223View ArticleGoogle Scholar
- Morales AE, Mora ES, Pal U: Use of diffuse reflectance spectroscopy for optical characterization of un-supported nanostructures. Revista Mexicana De Fisica S 2007, 53(5):18–22.Google Scholar
- Turtelli RS, Duong GV, Nunes W, Grössinger R, Knobel M: Magnetic properties of nanocrystalline CoFe 2 O 4 synthesized by modified citrate-gel method. J Magn Magn Mater 2008, 320: e339-e342. 10.1016/j.jmmm.2008.02.067View ArticleGoogle Scholar
- Varma PCR, Manna RS, Banerjee D, Varma MR, Suresh KG, Nigam AK: Magnetic properties of CoFe 2 O 4 synthesized by solid state, citrate precursor and polymerized complex methods: A comparative study. J Alloy Compd 2008, 453: 298–303. 10.1016/j.jallcom.2006.11.058View ArticleGoogle Scholar
- Torrent J, Barrόn V: Diffuse reflectance spectroscopy of iron oxides. In Encyclopedia of Surface and Colloid Science. New York: Marcel Dekker, Inc.; 2002:1438–1446.Google Scholar
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.