Elsevier

Ceramics International

Volume 39, Issue 4, May 2013, Pages 4619-4625
Ceramics International

Short communication
Microemulsion-mediated synthesis and characterization of monodispersed nickel molybdate nanocrystals

https://doi.org/10.1016/j.ceramint.2012.11.059Get rights and content

Abstract

The present work reports the preparation of nickel molybdate nanocrystals via a microemulsion method. The microemulsion system included cationic surfactant CTAB, 1-butanol as co-surfactant, isooctane as oil phase, and aqueous solutions of nickel chloride and sodium molybdate. The produced water pools in the microemulsion system act as nanoreactors for reaction of nickel and molybdate ions to produce nickel molybdate nanomaterial. After calcination, the structure and morphology of the product were characterized by Fourier-transform infrared (FT-IR) and UV–vis spectroscopies, X-ray diffraction (XRD), energy-dispersive X-ray analysis (EDX), transmission electron microscopy (TEM), and thermogravimetric analyses (TGA). The synthesized α-NiMoO4 nanocrystals have a monoclinic structure with lengths of 140–150 nm and widths of 60–70 nm.

Introduction

Metal molybdates are of great technological interest due to their attractive properties, especially potential applications in catalysis [1], [2], [3], [4], [5], [6], [7], [8], [9]. Among them nickel molybdates have become more important because of their application in catalysis such as oxidative dehydrogenation of light alkanes [10], [11], hydrodesulfurization, hydrodenitrogenation [12], [13], etc. There are two stable structures for stoichiometric NiMoO4 [14], in which the α-form is stable at room temperature and contains molybdenum in an octahedral environment. The β-form, which is stable at high temperature, has the molybdenum in a tetrahedral configuration. The α-NiMoO4 has monoclinic structure and its structural units are NiO6 and MoO6 octahedra, which share edges and form chains.

Up to now, many investigations have been carried out on the synthesis of nickel molybdate materials [8], [15], [16], [17]. The most common preparation method used for the preparation of nickel molybdate is the co-precipitation technique and the effects of various parameters on the resulting product have been investigated [8], [15]. Other techniques include reactive sputtering [16], thermal treatment of organic salts [17], and sonochemical synthesis [18].

On the other hand, the development of uniform nanoparticles has been greatly pursued in recent years [18], [19], [20], [21], [22], [23], [24]. Due to their interesting electronic, optical, magnetic, and chemical properties, these nanosized materials have promising applications in many areas such as microelectronic devices, catalysis, biomedicine and so on. As a result, the preparation of uniform sized nanoparticles has become a very important research area and various techniques have been used for this purpose.

There are some reports on the preparation of nickel molybdate nanostructures such as mechanochemical synthesis [25], complete evaporation of a polymer-based metal complex precursor solution [26], [27], sonochemical method [28], and hydrothermal method [29]. However, to the best of our knowledge, there is no report on the preparation of nickel molybdate nanoparticles with the microemulsion method. Recently, we reported successful preparation of bismuth and iron molybdate nanoparticles using the microemulsion method [30], [31]. Nanoparticle preparation in microemulsions has been an interesting research topic in recent years and a large number of different nanomaterials have been synthesized in water-in-oil microemulsions [32]. The microemulsion method provides good control over the size and shape of the prepared nanomaterials and produces uniform and monodispersed nanomaterials.

Herein we report for the first time the preparation and characterization of uniform nickel molybdate nanocrystals by using the microemulsion method. The advantage of this approach is better control over the size and shape of the final nickel molybdate nanocrystals in comparison to other methods.

Section snippets

Experimental

All chemical reagents (nickel nitrate, sodium molybdate, n-butanol, isooctane, and cetyltrimethyl ammonium bromide) were purchased from the Merck chemical company.

In a typical procedure 3 ml aqueous solution of Ni(NO3)2 (0.1 M) was added to a mixture of n-butanol (2 g)/isooctane (4 g)/CTAB (2 g) in water (2 ml) and the resulting mixture was stirred for 15 min until a transparent solution was obtained. After that, 3 ml aqueous solution of Na2MoO4 (0.1 M) was added to the above mixture to give a final

Result and discussion

It is well known that NiMoO4 could be formed through the reaction between Ni2+ and MoO42− ions [8]. We conducted the preparation of NiMoO4 with the reverse micelles acting as nanoreactors. Fig. 1 shows a schematic representation of all stages involved in the synthesis of NiMoO4 nanocrystals by the microemulsion method. Stoichiometric addition of the MoO42− solution to the microemulsion containing Ni2+ ions gives rise to the immediate formation of NiMoO4 precipitates within the reverse micelles.

Conclusion

Monodispersed α-NiMoO4 nanocrystals were synthesized by using a microemulsion system including cationic surfactant CTAB/1-butanol/isooctane and water. Our studies suggested that 400 °C temperature is adequate to obtain high quality α-NiMoO4 nanocrystals with good crystallinity and perfect morphology. The XRD results show the presence of pure monoclinic α-NiMoO4 nanocrystals and from EDX analysis the atomic ratio of Ni to Mo was shown to be 1:1.1. The TEM analysis shows that the α-NiMoO4

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