Cent. Eur. J. Chem. • 7(1) • 2009 • 155-158 DOI: 10.2478/s11532-008-0077-5
Central European Journal of Chemistry
Synthesis and characterization of nanosized NiO2 and NiO using Triton® X-100 Research Article
Mohammad Kooti*, Mehdi Jorfi Department of Chemistry, College of Science, Shahid Chamran University, 65355-141 Ahvaz, Iran Received 25 December 2007; Accepted 12 September 2008
Abstract: N anosized NiO2 particles with an average diameter of 15 nm are prepared by treating of Ni(NO3)2•6H2O with an aqueous solution of KClO in the presence of Triton® X-100. This black fine powder of nickel peroxide was characterized by XRD diffraction, energy dispersive spectroscopy (EDS) and scanning electron microscopy (SEM). The as-prepared NiO2 can be easily transformed to nanosized NiO merely by washing it with acetone. The obtained NiO has an average diameter of 40 nm and was characterized by the same means used for NiO2. The nanoparticles of NiO2 and NiO were obtained in high yields and purities. Keywords: Nanosized • NiO2 • NiO • Triton® X-100
© Versita Warsaw and Springer-Verlag Berlin Heidelberg.
1. Introduction Synthesis and characterization of nanostructures is of significant importance because of their fundamental role in basic research and technological applications [1,2]. Among the various nano materials, metal oxides nanoparticles have attracted increasing technological and industrial interest. This interest has mainly to do with their properties associated with general characteristics such as mechanical hardness, thermal stability or chemical passivity. Transition metal oxides can be prepared through various methods, such as chemical vapor deposition [3], laser vaporization [4], hydrothermal techniques [5], plane pyrolysis [6], sol-gel rout [7] and liquid-control precipitation [8]. Sun et al. [9] have recently reported the preparation of some crystalline metal oxides by ultrasonic spray pyrolysis technique. Among the metal oxides, nickel oxide attracts a great attention because of its wide applications. Ultra fine NiO particles with a uniform size and well dispersion are desirable for many applications in the manufacture of ceramic, magnetic, electrochromic, heterogeneous catalytic materials, preparation of alkaline batteries and p-type transparent conducting films, etc [10,11].
Nickel oxide has been successfully prepared by chemical liquid precipitation, electrodeposition and sol-gel technique [12-14]. In all these methods, calcinations at the minimum temperature of 250°C are needed to get the crystalline NiO, but other properties of this oxide such as particle size are hard to control. The chemical preparation of nano-particles NiO is composed of two stages: the formation of metstable nickel precursor precipitate and the subsequent transformation to nano-NiO by thermal treatment [15,16]. In addition to nickel oxide, Ni(II) can also form nickel peroxide (NiO2). This peroxide is easily made by oxidation of Ni(II) salt by hypochlorite solution [17,18]. Ji et al. [19] have reported the synthesis of nano-sized NiO2 powder by a wet chemical method followed by calcinations. This is the first and the only method, to our knowledge, reported for the fabrication of nano-sized NiO2. Although NiO2 was synthesized without using NaClO, as oxidant, but the prepared method is a lengthy procedure and the yield of obtained NiO2 is rather low. NiO2 has been used as an efficient oxidant for the oxidation of wide range of organic compounds [17-20]. In this study, nano-sized nickel peroxide is easily made via oxidation of Ni(II) by KClO in the presence of Triton® X-100 GR surfactant. The as-prepared nano NiO2 was used to prepare nano-sized NiO in a very simple and rapid process.
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Synthesis and characterization of nanosized NiO2 and NiO using Triton® X-100
2. Experimental Procedures
3. Results and Discussion
All the analytical chemicals were purchased from Merck Chemical Co. and used as received without further purification.
Nanoparicles of NiO2 can be only prepared in the presence of Triton® X-100 GR surfactant during the oxidation of Ni2+ by ClO- alkaline solution. Without addition of this surfactant to the reaction mixture, no nano-NiO2 was produced and only large size of NiO2 particles was obtained. The TEM image of this bulk NiO2 sample made in the absence of surfactant is shown in Fig. 1a. The presence of Triton® X-100 GR, in fact, prevented nanoparticles from the aggregation forming into larger ones. The exact role of the surfactant in this approach is not clear. However, one possible function of Triton® X-100 GR molecules is to kinetically control the growth rates of various faces of NiO2 nanoparticles by interacting with these faces through chemical adsorption and desorption. This kind of function is more or less similar to the function of other reported surfactants [21]. We are also studying the effect of altering Triton® X-100 GR concentration on the size of obtained nanosized NiO2 and NiO. Interestingly, washing of the as-prepared nano-NiO2 with acetone produced nanoparticles of NiO in almost quantitave yield. However, the size of the obtained NiO particles are larger than the size of NiO2 ones. In fact, NiO2 oxidizes acetone to acetyl acetate, and in turn it is reduced to NiO. The transformation of NiO2 to NiO causes a change in the color of the starting powder from black to olive-green, which is the color of nickel oxide. Fig. 1 shows the SEM images of as-prepared nanosized NiO2 (b) and NiO (c).
2.1. Preparation of Nanosized NiO2
Chlorine gas (generated from 10 g of KMnO4 and 60 mL of concentrated HCl) was slowly bubbled into a chilled solution of KOH (11.2 g) in 50 mL of water over a one hour period with stirring. To the resulting yellow solution of KClO, 5 mL of Triton® X-100 GR was added and the mixture was stirred magnetically for 15 min. A quantity of 5.8 g (0.02 mol) of Ni(NO3)2•6H2O was then added portion-wise in 60 min with continuous stirring under cooling conditions (0°C). A fine black precipitate formed which was then filtered off and washed with deionized water (ten times 10 mL) and dried at 200°C for 6 h to afford 1.7 g of NiO2 nonoparticles (94% yield). The final product was dried for 18 h under room temperature vacuum.
2.2. Preparation of Nanosized NiO
In this approach, NiO2 was prepared by the same procedure, which was mentioned above. The fine black precipitate of NiO2 was filtered off and washed with deionized water (ten times 10 mL) and acetone (five times 10 mL) to obtain nano-NiO, then dried at 200°C for 6 h to afford 1.42 g of NiO nonoparticles (95% yield). The final product is dried for 18 h under room temperature vacuum.
2.3. Characterization
The as-prepared nano-NiO2 and nano-NiO were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS). The XRD patterns were obtained on a Philips Analytical X-ray diffractometer, operating with CuK a radiation (l=1.54056 Å), with a flat sample holder mounted on a PW1830 spectrogonimeter. The EDS measurements were carried out on a LEO 1455 VP energy dispersive spectrometer. The TEM images were taken using a LEO 906 E transmission electron microscope. FT-IR spectra of the nanoparticles NiO2 and NiO (using KBr disks) were recorded using a BOMEN MB 102 spectrometer. Figure 1. TEM image of bulk NiO2 (a), SEM images of as-prepared nanosized of NiO2 (b) and NiO (c) 156
M. Kooti, M. Jorfi
The elemental analysis with EDS, as shown in Fig. 2, demonstrates that both the nano-sized NiO2 and NiO products contain only Ni and O elements. The obtained results of the EDS are given in the Table 1. Table 1.
The average nanoparticles sizes were calculated from the full-width at half maximum (FWHM) of the reflection using the Scherer equation: (1)
Results obtained from the elemental analysis with EDS Experimental
Calculated
Ni
O
Ni
O
NiO2
64.02
35.98
64.71
35.29
NiO
79.56
20.44
78.58
21.42
The IR spectra of as-prepared NiO and NiO2 exhibits a band absorption maximum located in the range of 415 - 425 cm-1, corresponding to the stretching vibration of the bond Ni-O [22]. The location of the peaks are suggestive of nanocrystalline as-prepared samples, since the bulk NiO shows an absorption in the range of 390 - 405 cm-1 [23]. The XRD patterns for the as-prepared NiO and NiO2 nano-sized are given in Fig. 3. Obviously, NiO2 and NiO have the same crystal structure, with five peaks at 37.26°, 43.29°, 62.88°, 75.42° and 79.41°, corresponding to (111), (200), (220), (311) and (222) planes. The only difference between the XRD spectra of nanosized NiO and NiO2, as can be seen from Fig. 3, is the intensity of the peaks, which is lower for NiO2 compared with NiO sample. Our finding is in agreement with the synthesized sample reported by H. Ji et al. [19].
Where K* is a constant (ca. 0.9); l is the X-ray wavelength (1.54056 Å); qB is the Bragg angle; q1/2 is the pure diffraction broadening of a peak at half-height. The grains sizes which evaluated from X-ray line broading were found to be 21 nm (NiO2) and 36 nm (NiO), which are in close agreement with the scanning electron microscopic (SEM) studies which show grains of 15 nm (NiO2) and 40 nm (NiO).
4. Conclusions We have shown that NiO2 and NiO nanoparticles can be readily produced by a surfactant-assisted chemical reaction. The nanoparticles NiO2 can be only obtained by the addition of Triton® X-100 GR to the reaction mixture of Ni(NO3)2•6H2O and ClO-. The produced nano-NiO2 can be converted to NiO nanoparticles simply by washing with acetone. The nanoparticles of NiO2 and NiO were obtained in high yields and purities. There was no need for calcinations as it is usually applied in other reported methods of NiO nanoparticle preparation.
NiO
NiO2
Figure 2. Elemental analysis of as-prepared nanosized NiO2 (a) and NiO (b)
Figure 3. X-ray diffraction patterns of nanosized NiO and NiO2 157
Synthesis and characterization of nanosized NiO2 and NiO using Triton® X-100
Acknowledgments The authors are grateful to the Research Council of Shahid Chamran University, Ahvaz, Iran, for the financial support of this research.
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