Proceedings of the 5thInternational Conference on Nanostructures (ICNS5) 6-9 March 2014, Kish Island, Iran
Simple Solvothermal Synthesis of NiAl2O4 Nanoparticles P. Jafari, M. Abdollahifar * Young Researchers and Elite Club, Kermanshah Branch, Islamic Azad University, Kermanshah, 6718997551, Iran. *
[email protected]
Abstract: NiAl2O4 nanoparticles were successfully synthesized in low temperature by solvothermal method using ethanol as a solvent. The formation process of the resulting nanoparticles is described and characterized by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) analysis. Our results showed that NiAl2O4 spinel structure was formed at 600 °C. NiAl2O4 spinel synthesized via this method was homogeneous with uniform particle with average size of 30 nm.
Keywords: Spinel; Nanoparticles; NiAl2O4; Solvothermal. Introduction A spinel is a ternary oxide whose general chemical formula is XY2O4, where X represents a divalent metal cation that usually occupies a tetrahedral site and Y represents trivalent metal cations that normally occupy the octahedral sites of a cubic lattice [1]. The unit cell of the XAl2O4 (X= Co, Ni, Zn) spinels are considered a host cell capable of holding a large number of divalent and trivalent cations in solid solution [2-4]. Moreover, they are of great interest due to their combination of desirable properties such as high thermal stability, high mechanical resistance, and high ability of cations diffusion, low sintering temperature and low surface acidity. Therefore, they are used as high temperature ceramic material [5], optical coating or host matrix [6, 7]. In addition, they present catalytic properties, had been used for many catalytic reactions, such as dehydration [8], hydrogenation [9] dry reforming of methane [10], methanol steam reforming [11], reforming of ethanol [12]. NiAl2O4 is a transition metal spinel that has a usual spinel structure with nickel in the tetrahedral sites and aluminum in the octahedral sites. NiAl2O4 has been a subject of extensive research from preparation to properties. The conventional method of preparation (solid state reaction between metal oxides) needs high temperatures for sintering and large power time consumption [13]. Ultrasound irradiation [10], microwave heating [14], solgel [15], impregnation and co-precipitation [16], homogenous precipitation [17] methods have been used to synthesis nanocrystalline nickel aluminate with small particle size. The major problem of these five methods is the phase segregation due to the different reactivity of the individual precursors. Usually, it is more difficult to overcome the problem of phase segregation in the precipitation method than in the sol-gel method. Solvothermal have been used to synthesis of many nanomaterials, therefore, we anticipate which this route can be employ for preparation of spinels. In this paper, a
novel simple solvothermal route was used for synthesis of NiAl2O4 spinel nanoparticles.
Materials and method The Al(NO3)3*9H2O and Ni(NO3)2. 6H2O and NaOH (Scharlau, Spain, extra pure), and ethanol 98% were used without further purification. NiAl2O4 nanoparticles were prepared using the solvothermal method. In a typical procedure, Al(NO3)3*9H2O (7.5 g) and Ni(NO3)2. 6H2O (7.5 g) were dissolved into 150 mL of ethanol 98% at room temperature in a beaker and magnetically stirred to obtain a homogeneous solution. The NaOH (2 Molar) was subsequently added drop by drop to the solution to give lacteous precipitates immediately. At this point, the pH value of the reaction mixture was ~ 5. The final solutions were transferred into a Teflon-lined stainless-steel autoclave of 250 mL capacity. The autoclave was sealed and maintained at 180 °C for 24 h, then cooling with water to room temperature and a precipitates were recovered. The product was collected by centrifugation and washed with distilled water and ethanol several times. The sample was dried at 60 °C for 24 h in air and the dried sample was labelled (a). Finally, the (a) sample was calcined at 600 °C for 5 h, resulting in the NiAl2O4 nanoparticles was labelled (b). The X-ray Powder diffraction patterns (XRD) were recorded using Inel, model EQUINOX3000 (French), with Ni-filtered CuKα1 radiation (λ=1.540560 Å), and field emission scanning electron microscopy (FESEM) images were obtained on a HITACHI, model S-4160, Vacc=25 kV.
Results and Discussion XRD patterns of samples ((a) as-prepared and (b) NiAl2O4) are given in Fig. 1. All diffraction lines could be unequivocally assigned to a spinel-type structure; space group Fd3m [18] as shown in Fig. 1 (a), and the
Proceedings of the 5thInternational Conference on Nanostructures (ICNS5) 6-9 March 2014, Kish Island, Iran
pattern is NiAl2O4 cubic spinel-type (ICDD: 71-0963). NiAl2O4 peaks are visible and strong at 600 °C.
NiAl2O4
I F
(b)
(a)
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25
45
65
85
2Theta (°)
Fig.1: XRD patterns of (a) as-prepared and (b) NiAl2O4 samples.
FESEM micrographs of both samples are given in Fig. 2. Homogeneous and well defined spinel particles of nanometric in size were evidenced by FESEM images. The particle morphology is quite uniform for both samples suggesting that this method of synthesis yields a homogeneous material with uniform particle sizes.
The size of 60 and 88 particles were measured for asprepared and NiAl2O4 samples, respectively. The particle size distributions can be seen in Fig. 3. For as-prepared sample, the majority of the particles have sizes in the range of 40 nm to 100 nm with average size of 70 nm, and sizes were in the range of 10 nm to 60 nm with average size of 30 nm for NiAl2O4 spinel sample.
Fig.2: FESEM images of (a) as-prepared and (b) NiAl2O4 samples.
40
(a)
35
(b)
30 25 20 15
Conclusions
A new method for preparing NiAl2O4 nanoparticles with uniform particle sizes, using the Aluminum nitrate, NaOH and ethanol was achieved via solvothermal method. The FESEM image showed that the majority of the spinel particles have average size of 30 nm. The method described in this work can be generalized to synthesize nanoparticles with low and uniform particle size.
10 5 0
Particle Size (nm)
Fig.3: Particle size distribution of (a) as-prepared and (b) NiAl2 O4 samples measured by FESEM.
Proceedings of the 5thInternational Conference on Nanostructures (ICNS5) 6-9 March 2014, Kish Island, Iran
Acknowledgment The authors would like to thank the Islamic Azad University, Kermanshah branch for technical supports.
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