Synthesis and characterization of thin shell hollow sphere NiO nanopowder via ultrasonic technique
Highlights
► NiO hollow spheres have been synthesized via ultrasonic technique. ► These hollow spheres have particle size 12±2 nm and sphere shell 1.4±0.1 nm. ► These hollow spheres have highly pure single crystalline cubic structure. ► TBAB played a key role in the formation of NiO spheres with hollow interior.
Introduction
Nickel oxide is one of the most important metal oxides due to its fascinating anodic electro-chromicity, excellent durability, electrochemical stability and large spin optical density [1], [2]. Therefore, it can be used in different technological applications such as smart windows [3], electrochemical super-capacitors [4], [5], [6], transparent P-type semiconducting layers [7], [8] and as anti-ferromagnetic films [9]. The synthesis of nanostructure metal oxide materials with hollow interiors is highly promising for the generation of tailor made systems for applications in antireflection surface coatings, microwave absorption [10], encapsulating sensitive materials [11] and rechargeable batteries [12], owing to their unique characteristics such as low density, high surface-to-volume ratio, and low refractive index. These hollow nanostructures are ideal candidates for improving electrolyte diffusion in solar cells [13], drug carrier systems [14] and sensors [15]. Especially, the large pore volume in hollow-spheres could act as a reservoir with a permeable barrier for controlling diffusion. There are several methods for the preparation of hollow nanostructures by using different templates such as polymers [16], emulsion droplets [17], micelles [18], the Kirkendall effect [19], Ostwald ripening [20] or chemically induced self-transformation [21]. However, strategies enabling the fabrication of high quantities of mono-disperse hollow sphere nanostructures remain highly challenging. In this letter, we report a novel approach for the synthesis of mono-disperse NiO hollow spheres via ultrasonic technique by using tetrabutyl ammonium bromide for the first time.
Section snippets
Experimental
Nickel oxide nanospheres were synthesized with and without tetrabutyl ammonium bromide as follows. 100 mM of nickel chloride was dissolved into 40 mL of deionized water. 0.4 mL of polyvinylpyrrolidone (2 wt%, MW=40,000) and 2 mL of potassium hydroxide (100 mM) were added to the nickel chloride solution. The mixture was inserted into an ultrasonic water bath at power 800 W for 20 min. The solution was removed from the sonicator and kept for 30 min at ambient temperature without stirring. The resultant
Results and discussion
Fig. 1 depicts XRD patterns for the prepared nickel oxide powders by ultrasonic technique in the absence and presence of tetrabutyl ammonium bromide (TBAB). XRD analysis reveals that all the products obtained can be indexed to the pure cubic structure NiO (JCPDS 47-1049). No evidence was found for the existence of impurities in the products. One can also notice that the peak intensities are decreased and they become broader in the presence of TBAB. This indicates that TBAB strongly controls the
Conclusion
Nickel oxide nanospheres with hollow interiors have been synthesized via ultrasonic technique by using tetrabutyl ammonium bromide for the first time. The prepared NiO hollow spheres have average particle size diameter 12±2 nm and sphere shell thickness about 1.4±0.1 nm. These prepared hollow spheres have highly pure single crystalline cubic structures. The atomic weight ratio of Ni:O was found to be 47:53. According to the obtained results, TBAB played a key role in the formation of the
Acknowledgment
This project was funded by the Deanship of Scientific Research (DSR), King Abdulaziz University, Jeddah, under Grant no. MS-13–112-D1432. The authors, therefore, acknowledge with thanks DSR technical and financial support.
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