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Template-free synthesis of magnetic CoNi nanoparticles via a solvothermal method
Materials Letters ∎ (∎∎∎∎) ∎∎∎–∎∎∎
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Q1 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Template-free synthesis of magnetic CoNi nanoparticles via a solvothermal method Chunju Xu n, Dan Nie, Huiyu Chen, Yujie Wang, Yaqing Liu School of Materials Science and Engineering, North University of China, Taiyuan 030051, China
art ic l e i nf o
a b s t r a c t
Article history: Received 8 August 2014 Accepted 1 October 2014
CoNi alloy nanoparticles were prepared via a solvothermal method, and ethanol and water mixed solution was used as solvent. No surfactant or template was employed during the entirely synthetic procedure. The dependences of product size and shape on the temperature and volume ratio of ethanol to water were investigated in details. As the volume ratio of ethanol to water decreased, the shape of CoNi alloy changes from particle to platelets. The obtained samples were characterized by XRD, SEM, and VSM techniques. Magnetic measurement at room temperature showed that the CoNi nanoparticles possessed ferromagnetic behavior, and these CoNi nanoparticles could be used in magnetic media, sensors, and other devices. & 2014 Published by Elsevier B.V.
Keywords: Metals and alloys Nanoparticles CoNi Solvothermal synthesis
1. Introduction Over the past decade, preparation of transition metal alloy nanoparticles has attracted increasing attention because of their unique size-dependent magnetic properties. Compared to the single type of metal, the alloys show more interesting structural, electronic, and magnetic properties because of the interaction between the two components [1]. As an important transition metal alloy, CoNi possesses high magnetocrystalline anisotropy and chemical stability, which make it possible candidate for the next generation of magnetic storage media and high-performance permanent magnetic [2]. In addition, CoNi alloy has been extensively used for decoration, corrosion resistance, biomedical microdevices, catalysis, and microwave absorbers [3–5]. It is widely accepted that the shape and size of nanocrystals have much influence on their physicochemical properties. Hence, much effort has been devoted to prepare CoNi nanostructures with controllable size and well-defined morphology. Up to now, several types of CoNi structures including nanoparticles [6], nanowires [7,8], chains [9], flowers [10], and nanotubes [11,12] were fabricated by various methods. Typically, Lu et al. prepared CoNi alloy nanoparticles with controlled size in the solvent of ethylene glycol with assistance of different surfactants [6]. CoNi nanowires and nanotube arrays could be obtained by electrodeposition using an anodized aluminum oxide (AAO) template [8,11]. One-dimensional (1D) CoNi chains and 3D
n
Corresponding author. Tel./fax: þ 86 351 3559669. E-mail addresses: [email protected] (C. Xu), zffl[email protected] (Y. Liu).
micro-flowers were also reported by two groups using magnetic field-induced synthetic approach [9,10]. Most of the above methods were involved in the usage of template or solvent with high viscosity, and magnetic field-induced synthesis needs expensive and special instruments. The tedious and costly procedure would hinder their industry-scale application. Therefore, it is necessary to find a versatile and low-cost methodology for preparation of CoNi on a large scale. Besides, systematic investigations on the formation process of bimetallic CoNi particles are still required in order to control and understand their growth mechanism. Solvothermal synthesis is known as a suitable method for the synthesis of magnetic particles. This method allows an accurate and reproducible control of the mean diameter of particles from a few tens of nanometers to a few micrometers and has the advantages of simplicity and low cost compared with physical approach. Herein, CoNi nanoparticles with controllable size were synthesized via a solvothermal route, and ethanol and water mixed solution was used as solvent. No template or surfactant was employed during the synthesis. It was found that temperature and volume ratio of ethanol to water played important role for controlling the size as well as shapes of CoNi alloy nanoparticles.
2. Experimental procedure Materials and method: All reagents were analytical grade and used without further purification. In a typical synthesis, 0.48 g of CoCl2 6H2O and 0.48 g of NiCl2 6H2O were dissolved in 30 mL ethanol and water mixed solution (v/v ¼1:1) with stirring. Then 10 mL (12.5 M) of sodium hydroxide and 5 mL hydrazine hydrate
http://dx.doi.org/10.1016/j.matlet.2014.10.007 0167-577X/& 2014 Published by Elsevier B.V.
Please cite this article as: Xu C, et al. Template-free synthesis of magnetic CoNi nanoparticles via a solvothermal method. Mater Lett (2014), http://dx.doi.org/10.1016/j.matlet.2014.10.007i
C. Xu et al. / Materials Letters ∎ (∎∎∎∎) ∎∎∎–∎∎∎
2
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66
were introduced orderly. The mixture was transferred into a Teflon-lined stainless steel autoclave, sealed, and maintained at 160 1C for 8 h. After reaction, the autoclave was cooled down naturally, and the product was collected, rinsed, and dried. Controlled experiments were carried out by changing the temperature and volume ratio of ethanol to water, respectively, while kept other parameters constant. Characterizations: XRD pattern was recorded on a Bruker D8 focus diffractometer with Cu Kα radiation (λ¼0.15406 nm). The morphology and compositions of the sample were investigated using a JSM-7001F scanning electron microscope (SEM) equipped with X-ray energy dispersive spectrometer (EDS). Room temperature magnetic measurements were carried out by a vibrating sample magnetometer (VSM, Lakeshore 7404) with a maximum magnetic field of 10 kOe.
3. Results and discussion Fig. 1a showed the SEM image of the CoNi obtained in the typical synthesis. The product was composed of a large amount of particles with size ranging from 120 to 160 nm. The magnified view in Fig. 1b gave more detailed information that these particles were aggregated by smaller nanoparticles with diameter of 21 7 1.2 nm. The crystalline phase was confirmed by XRD technique, and the four peaks in XRD pattern (Fig. 1c) were located at 2θ¼44.5, 51.7, 76.4, and 92.81, corresponding to the (1 1 1), (2 0 0), (2 2 0), and (3 1 1) planes of face-centered cubic (FCC) phase of CoNi alloy [13]. The EDS spectrum of the CoNi nanoparticles in Fig. 1d indicated that the atomic ratio of Co/Ni is about 51:49, which is very close to the ratio of corresponding cations in the starting solution. The emerged elements of Au and Pd came from the coating film (70% Au and 30% Pd alloy) for SEM measurement. Combined the analysis of XRD and EDS data, it
could be concluded that CoNi nanoparticles with high purity were obtained. Temperature was an important factor for controlling the size and morphology of CoNi nanoparticles. When the experiment was conducted at lower temperature of 120 1C, big particles constructed by many smaller nanoparticles were formed, and the size of these particles could reach about 100 nm (Fig. 2a). Interestingly, some CoNi sheets coexisted as the white arrows indicated. Less energy was supplied for the reaction when low temperature was employed, and the initially generated CoNi nuclei had sufficient time for anisotropic growth with the assistance of magnetic dipolar interaction. As temperature increased to 140 1C and 160 1C, the CoNi sheets disappeared gradually, and particles with irregular shapes were dominant (Fig. 2b and Fig. 1a). It is very difficult to separate the nuclei step from the crystal growth process at high temperature, and hence the anisotropic growth is hard to achieve. When we further increased the temperature to 180 1C, it seemed that the product was dominated by particles with smooth surface, and the nanoparticles were difficult to be observed (Fig. 2c). Obviously, the CoNi particles growth process was governed by Oswald ripening mechanism, in which the CoNi particles grow in large at the expense of smaller nanoparticles. Particularly, CoNi particles grew into together when the sample was solvothermally prepared at 200 1C (Fig. 2d). The interface between some particles disappeared and the surface seemed to be covered by a layer of coating. Solvent plays another important role in solvothermal treatment. When volume ratio of ethanol to water equals to 3, the CoNi particles and huge patches existed in the product (Fig. 3a). The pressure in the autoclave was very high when ethanol was dominant, which great influenced the behavior of nuclei and crystal growth. With the volume of ethanol decreasing, the sample was mainly composed of particles that were aggregated by smaller nanoparticles (Fig. 3b). However, many CoNi platelets formed as
Fig. 1. SEM images with (a) panoramic view and (b) high magnification view, (c) XRD pattern, and (d) EDS spectrum of CoNi nanoparticles synthesized at 160 1C for 8 h with the ratio between ethanol and water of 1:1.
Please cite this article as: Xu C, et al. Template-free synthesis of magnetic CoNi nanoparticles via a solvothermal method. Mater Lett (2014), http://dx.doi.org/10.1016/j.matlet.2014.10.007i
C. Xu et al. / Materials Letters ∎ (∎∎∎∎) ∎∎∎–∎∎∎
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66
3
Fig. 2. SEM images of the CoNi alloy obtained at (a) 120 1C, (b) 140 1C, (c) 180 1C, and (d) 200 1C.
Fig. 3. SEM images of the products prepared with different volume ratio of ethanol to water: (a) 3:1, (b) 2:1, (c) 1:2, and (d) 1:3.
the solvent was mainly served by water (Fig. 3c and d), especially for the sample obtained with ethanol/water of 1:3. Under such conditions, more Co(OH)2 and Ni(OH)2 were easily produced at early stage of the synthesis. Because of their intrinsic lamellar structure, these hydroxides tend to grow into Co(OH)2 and Ni(OH)2
platelets, which would be converted into CoNi platelets by co-reduction with hydrazine hydrate. Besides, the pressure generated in the autoclave was comparatively lower, and the movement of initially formed CoNi nuclei in water-based solution was less intense compared to that in ethanol-based one. It is beneficial for
Please cite this article as: Xu C, et al. Template-free synthesis of magnetic CoNi nanoparticles via a solvothermal method. Mater Lett (2014), http://dx.doi.org/10.1016/j.matlet.2014.10.007i
C. Xu et al. / Materials Letters ∎ (∎∎∎∎) ∎∎∎–∎∎∎
4
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40
template, and these nanoparticles had a strong tendency to aggregate. Temperature and volume ratio of ethanol to water played important roles for the size and shape control. CoNi platelets were dominated in the product when water served as the main solvent. Magnetic measurement revealed that these CoNi nanoparticles were ferromagnetic with high coercivity value. Due to the relatively excellent magnetic properties, the obtained CoNi nanoparticles and platelets are expected to exhibit some interesting physicochemical properties and have important applications in micro/nanodevices.
Acknowledgments Fig. 4. Hysteresis loops of the CoNi nanoparticles obtained with ethanol/water of 3:1 and 1:1, and CoNi nanoplatelets synthesized with ethanol/water of 1:3, respectively.
the crystal anisotropic growth, and would not seriously destroy the crystal surface. The detailed formation process of platelets needs further investigation and related work is currently underway. In order to determine the magnetic properties of the CoNi nanoparticles and platelets, magnetic measurement was carried out at room temperature and the results were shown in Fig. 4. The saturation magnetization (Ms) values of the samples obtained with ethanol/water of 3:1, 1:1, and 1:3 are 111.3, 105.4, and 104.3 emu/g, respectively, which are lower than that of bulk CoNi (112 emu/g) probably due to the surface oxidation and larger surface to volume ratio of the nanostructures. On the other hand, the coercivity value for the CoNi platelets is 243.8 Oe, which is higher than that of CoNi nanoparticles. It is widely accepted that shape anisotropy would lead to significant improvement in coercivity. Therefore, the CoNi platelets obtained in this work are predicted to possess enhanced coercivity due to their remarkable shape anisotropy. 4. Conclusions
This work was supported by Youthful Science Foundation of North University of China (NUC), and Shanxi Scholarship Council Q2 of China.
References [1] Stahl B, Gajbhiye NS, Wilde G, Kramer D, Ellrich J, Ghafari M, et al. Adv Mater 2002;14:24–7. [2] Zeng H, Li J, Liu JP, Wang ZL, Sun S. Nature 2002;420:395–8. [3] Hong R, Fischer NO, Emrick T, Rotello VM. Chem Mater 2005;17:4617–21. [4] Liu Q, Guo X, Wang T, Li Y, Shen W. Mater Lett 2010;64:1271–4. [5] Kurlyandskaya GV, Bhagat SM. J Appl Phys 2006;99:104308. [6] Lu WH, Sun DB, Yu HY. J Alloys Compd 2013;546:229–33. [7] Rheem Y, Yoo BY, Beyermann WP, Myung NV. Nanotechnology 2007;18: 125204. [8] Talapatra S, Tang X, Padi M, Kim T, Vajtai R, Sastry GVS, et al. J Mater Sci 2009;44:2271–5. [9] Hu MJ, Lin B, Yu SH. Nano Res 2008;1:303–13. [10] Li H, Liao JY, Du YC, You T, Liao WW, Wein LL. Chem Commun 2013;49:1768–70. [11] Zhang HM, Zhang XL, Zhang JJ, Li ZY, Sun HY. J Magn Magn Mater 2013;342:69–73. [12] Li XZ, Wei XW, Ye Y. Mater Lett 2009;63:578–80. [13] Nie D, Xu CJ, Chen HY, Wang YJ, Li JW, Liu YQ. Mater Lett 2014;131:306–9.
In summary, CoNi nanoparticles with high purity were prepared through a solvothermal method without using any surfactant or
Please cite this article as: Xu C, et al. Template-free synthesis of magnetic CoNi nanoparticles via a solvothermal method. Mater Lett (2014), http://dx.doi.org/10.1016/j.matlet.2014.10.007i
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Q1 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Template-free synthesis of magnetic CoNi nanoparticles via a solvothermal method Chunju Xu n, Dan Nie, Huiyu Chen, Yujie Wang, Yaqing Liu School of Materials Science and Engineering, North University of China, Taiyuan 030051, China
art ic l e i nf o
a b s t r a c t
Article history: Received 8 August 2014 Accepted 1 October 2014
CoNi alloy nanoparticles were prepared via a solvothermal method, and ethanol and water mixed solution was used as solvent. No surfactant or template was employed during the entirely synthetic procedure. The dependences of product size and shape on the temperature and volume ratio of ethanol to water were investigated in details. As the volume ratio of ethanol to water decreased, the shape of CoNi alloy changes from particle to platelets. The obtained samples were characterized by XRD, SEM, and VSM techniques. Magnetic measurement at room temperature showed that the CoNi nanoparticles possessed ferromagnetic behavior, and these CoNi nanoparticles could be used in magnetic media, sensors, and other devices. & 2014 Published by Elsevier B.V.
Keywords: Metals and alloys Nanoparticles CoNi Solvothermal synthesis
1. Introduction Over the past decade, preparation of transition metal alloy nanoparticles has attracted increasing attention because of their unique size-dependent magnetic properties. Compared to the single type of metal, the alloys show more interesting structural, electronic, and magnetic properties because of the interaction between the two components [1]. As an important transition metal alloy, CoNi possesses high magnetocrystalline anisotropy and chemical stability, which make it possible candidate for the next generation of magnetic storage media and high-performance permanent magnetic [2]. In addition, CoNi alloy has been extensively used for decoration, corrosion resistance, biomedical microdevices, catalysis, and microwave absorbers [3–5]. It is widely accepted that the shape and size of nanocrystals have much influence on their physicochemical properties. Hence, much effort has been devoted to prepare CoNi nanostructures with controllable size and well-defined morphology. Up to now, several types of CoNi structures including nanoparticles [6], nanowires [7,8], chains [9], flowers [10], and nanotubes [11,12] were fabricated by various methods. Typically, Lu et al. prepared CoNi alloy nanoparticles with controlled size in the solvent of ethylene glycol with assistance of different surfactants [6]. CoNi nanowires and nanotube arrays could be obtained by electrodeposition using an anodized aluminum oxide (AAO) template [8,11]. One-dimensional (1D) CoNi chains and 3D
n
Corresponding author. Tel./fax: þ 86 351 3559669. E-mail addresses: [email protected] (C. Xu), zffl[email protected] (Y. Liu).
micro-flowers were also reported by two groups using magnetic field-induced synthetic approach [9,10]. Most of the above methods were involved in the usage of template or solvent with high viscosity, and magnetic field-induced synthesis needs expensive and special instruments. The tedious and costly procedure would hinder their industry-scale application. Therefore, it is necessary to find a versatile and low-cost methodology for preparation of CoNi on a large scale. Besides, systematic investigations on the formation process of bimetallic CoNi particles are still required in order to control and understand their growth mechanism. Solvothermal synthesis is known as a suitable method for the synthesis of magnetic particles. This method allows an accurate and reproducible control of the mean diameter of particles from a few tens of nanometers to a few micrometers and has the advantages of simplicity and low cost compared with physical approach. Herein, CoNi nanoparticles with controllable size were synthesized via a solvothermal route, and ethanol and water mixed solution was used as solvent. No template or surfactant was employed during the synthesis. It was found that temperature and volume ratio of ethanol to water played important role for controlling the size as well as shapes of CoNi alloy nanoparticles.
2. Experimental procedure Materials and method: All reagents were analytical grade and used without further purification. In a typical synthesis, 0.48 g of CoCl2 6H2O and 0.48 g of NiCl2 6H2O were dissolved in 30 mL ethanol and water mixed solution (v/v ¼1:1) with stirring. Then 10 mL (12.5 M) of sodium hydroxide and 5 mL hydrazine hydrate
http://dx.doi.org/10.1016/j.matlet.2014.10.007 0167-577X/& 2014 Published by Elsevier B.V.
Please cite this article as: Xu C, et al. Template-free synthesis of magnetic CoNi nanoparticles via a solvothermal method. Mater Lett (2014), http://dx.doi.org/10.1016/j.matlet.2014.10.007i
C. Xu et al. / Materials Letters ∎ (∎∎∎∎) ∎∎∎–∎∎∎
2
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66
were introduced orderly. The mixture was transferred into a Teflon-lined stainless steel autoclave, sealed, and maintained at 160 1C for 8 h. After reaction, the autoclave was cooled down naturally, and the product was collected, rinsed, and dried. Controlled experiments were carried out by changing the temperature and volume ratio of ethanol to water, respectively, while kept other parameters constant. Characterizations: XRD pattern was recorded on a Bruker D8 focus diffractometer with Cu Kα radiation (λ¼0.15406 nm). The morphology and compositions of the sample were investigated using a JSM-7001F scanning electron microscope (SEM) equipped with X-ray energy dispersive spectrometer (EDS). Room temperature magnetic measurements were carried out by a vibrating sample magnetometer (VSM, Lakeshore 7404) with a maximum magnetic field of 10 kOe.
3. Results and discussion Fig. 1a showed the SEM image of the CoNi obtained in the typical synthesis. The product was composed of a large amount of particles with size ranging from 120 to 160 nm. The magnified view in Fig. 1b gave more detailed information that these particles were aggregated by smaller nanoparticles with diameter of 21 7 1.2 nm. The crystalline phase was confirmed by XRD technique, and the four peaks in XRD pattern (Fig. 1c) were located at 2θ¼44.5, 51.7, 76.4, and 92.81, corresponding to the (1 1 1), (2 0 0), (2 2 0), and (3 1 1) planes of face-centered cubic (FCC) phase of CoNi alloy [13]. The EDS spectrum of the CoNi nanoparticles in Fig. 1d indicated that the atomic ratio of Co/Ni is about 51:49, which is very close to the ratio of corresponding cations in the starting solution. The emerged elements of Au and Pd came from the coating film (70% Au and 30% Pd alloy) for SEM measurement. Combined the analysis of XRD and EDS data, it
could be concluded that CoNi nanoparticles with high purity were obtained. Temperature was an important factor for controlling the size and morphology of CoNi nanoparticles. When the experiment was conducted at lower temperature of 120 1C, big particles constructed by many smaller nanoparticles were formed, and the size of these particles could reach about 100 nm (Fig. 2a). Interestingly, some CoNi sheets coexisted as the white arrows indicated. Less energy was supplied for the reaction when low temperature was employed, and the initially generated CoNi nuclei had sufficient time for anisotropic growth with the assistance of magnetic dipolar interaction. As temperature increased to 140 1C and 160 1C, the CoNi sheets disappeared gradually, and particles with irregular shapes were dominant (Fig. 2b and Fig. 1a). It is very difficult to separate the nuclei step from the crystal growth process at high temperature, and hence the anisotropic growth is hard to achieve. When we further increased the temperature to 180 1C, it seemed that the product was dominated by particles with smooth surface, and the nanoparticles were difficult to be observed (Fig. 2c). Obviously, the CoNi particles growth process was governed by Oswald ripening mechanism, in which the CoNi particles grow in large at the expense of smaller nanoparticles. Particularly, CoNi particles grew into together when the sample was solvothermally prepared at 200 1C (Fig. 2d). The interface between some particles disappeared and the surface seemed to be covered by a layer of coating. Solvent plays another important role in solvothermal treatment. When volume ratio of ethanol to water equals to 3, the CoNi particles and huge patches existed in the product (Fig. 3a). The pressure in the autoclave was very high when ethanol was dominant, which great influenced the behavior of nuclei and crystal growth. With the volume of ethanol decreasing, the sample was mainly composed of particles that were aggregated by smaller nanoparticles (Fig. 3b). However, many CoNi platelets formed as
Fig. 1. SEM images with (a) panoramic view and (b) high magnification view, (c) XRD pattern, and (d) EDS spectrum of CoNi nanoparticles synthesized at 160 1C for 8 h with the ratio between ethanol and water of 1:1.
Please cite this article as: Xu C, et al. Template-free synthesis of magnetic CoNi nanoparticles via a solvothermal method. Mater Lett (2014), http://dx.doi.org/10.1016/j.matlet.2014.10.007i
C. Xu et al. / Materials Letters ∎ (∎∎∎∎) ∎∎∎–∎∎∎
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66
3
Fig. 2. SEM images of the CoNi alloy obtained at (a) 120 1C, (b) 140 1C, (c) 180 1C, and (d) 200 1C.
Fig. 3. SEM images of the products prepared with different volume ratio of ethanol to water: (a) 3:1, (b) 2:1, (c) 1:2, and (d) 1:3.
the solvent was mainly served by water (Fig. 3c and d), especially for the sample obtained with ethanol/water of 1:3. Under such conditions, more Co(OH)2 and Ni(OH)2 were easily produced at early stage of the synthesis. Because of their intrinsic lamellar structure, these hydroxides tend to grow into Co(OH)2 and Ni(OH)2
platelets, which would be converted into CoNi platelets by co-reduction with hydrazine hydrate. Besides, the pressure generated in the autoclave was comparatively lower, and the movement of initially formed CoNi nuclei in water-based solution was less intense compared to that in ethanol-based one. It is beneficial for
Please cite this article as: Xu C, et al. Template-free synthesis of magnetic CoNi nanoparticles via a solvothermal method. Mater Lett (2014), http://dx.doi.org/10.1016/j.matlet.2014.10.007i
C. Xu et al. / Materials Letters ∎ (∎∎∎∎) ∎∎∎–∎∎∎
4
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40
template, and these nanoparticles had a strong tendency to aggregate. Temperature and volume ratio of ethanol to water played important roles for the size and shape control. CoNi platelets were dominated in the product when water served as the main solvent. Magnetic measurement revealed that these CoNi nanoparticles were ferromagnetic with high coercivity value. Due to the relatively excellent magnetic properties, the obtained CoNi nanoparticles and platelets are expected to exhibit some interesting physicochemical properties and have important applications in micro/nanodevices.
Acknowledgments Fig. 4. Hysteresis loops of the CoNi nanoparticles obtained with ethanol/water of 3:1 and 1:1, and CoNi nanoplatelets synthesized with ethanol/water of 1:3, respectively.
the crystal anisotropic growth, and would not seriously destroy the crystal surface. The detailed formation process of platelets needs further investigation and related work is currently underway. In order to determine the magnetic properties of the CoNi nanoparticles and platelets, magnetic measurement was carried out at room temperature and the results were shown in Fig. 4. The saturation magnetization (Ms) values of the samples obtained with ethanol/water of 3:1, 1:1, and 1:3 are 111.3, 105.4, and 104.3 emu/g, respectively, which are lower than that of bulk CoNi (112 emu/g) probably due to the surface oxidation and larger surface to volume ratio of the nanostructures. On the other hand, the coercivity value for the CoNi platelets is 243.8 Oe, which is higher than that of CoNi nanoparticles. It is widely accepted that shape anisotropy would lead to significant improvement in coercivity. Therefore, the CoNi platelets obtained in this work are predicted to possess enhanced coercivity due to their remarkable shape anisotropy. 4. Conclusions
This work was supported by Youthful Science Foundation of North University of China (NUC), and Shanxi Scholarship Council Q2 of China.
References [1] Stahl B, Gajbhiye NS, Wilde G, Kramer D, Ellrich J, Ghafari M, et al. Adv Mater 2002;14:24–7. [2] Zeng H, Li J, Liu JP, Wang ZL, Sun S. Nature 2002;420:395–8. [3] Hong R, Fischer NO, Emrick T, Rotello VM. Chem Mater 2005;17:4617–21. [4] Liu Q, Guo X, Wang T, Li Y, Shen W. Mater Lett 2010;64:1271–4. [5] Kurlyandskaya GV, Bhagat SM. J Appl Phys 2006;99:104308. [6] Lu WH, Sun DB, Yu HY. J Alloys Compd 2013;546:229–33. [7] Rheem Y, Yoo BY, Beyermann WP, Myung NV. Nanotechnology 2007;18: 125204. [8] Talapatra S, Tang X, Padi M, Kim T, Vajtai R, Sastry GVS, et al. J Mater Sci 2009;44:2271–5. [9] Hu MJ, Lin B, Yu SH. Nano Res 2008;1:303–13. [10] Li H, Liao JY, Du YC, You T, Liao WW, Wein LL. Chem Commun 2013;49:1768–70. [11] Zhang HM, Zhang XL, Zhang JJ, Li ZY, Sun HY. J Magn Magn Mater 2013;342:69–73. [12] Li XZ, Wei XW, Ye Y. Mater Lett 2009;63:578–80. [13] Nie D, Xu CJ, Chen HY, Wang YJ, Li JW, Liu YQ. Mater Lett 2014;131:306–9.
In summary, CoNi nanoparticles with high purity were prepared through a solvothermal method without using any surfactant or
Please cite this article as: Xu C, et al. Template-free synthesis of magnetic CoNi nanoparticles via a solvothermal method. Mater Lett (2014), http://dx.doi.org/10.1016/j.matlet.2014.10.007i