Facile Synthesis of ZnO Nanorods by Microwave Irradiation of Zinc–Hydrazine Hydrate Complex
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ZnO nanorods have been successfully synthesized by a simple microwave-assisted solution phase approach. Hydrazine hydrate has been used as a mineralizer instead of sodium hydroxide. XRD and FESEM have been used to characterize the product. The FESEM images show that the diameter of the nanorods fall in the range of about 25–75 nm and length in the range of 500–1,500 nm with an aspect ratio of about 20–50. UV–VIS and photoluminescence spectra of the nanorods in solution have been taken to study their optical properties. A mechanism for microwave synthesis of the ZnO nanorods using hydrazine hydrate precursor has also been proposed.
KeywordsZnO Nanorods Microwave irradiation Optical properties Hydrazine hydrate
Quasi one—dimensional nanostructured materials (nanotubes, nanobelts, nanorods and nanowires) have recently attracted considerable attention due to their novel properties and potential applications in numerous areas such as nanoscale electronics and photonics [1, 2, 3]. ZnO is an important electronic and photonic material because of its wide band gap of 3.37 eV and high mechanical and thermal stabilities at room temperature . The strong exciton binding energy of ZnO is much larger than that of GaN and the thermal energy of ZnO which can ensure an efficient exciton emission at room temperature [5, 6]. Room temperature UV lasing properties have been demonstrated from ZnO epitaxial films, nanoclusters and nanowires [2, 7, 8, 9]. Hence ZnO is a promising photonic material in the blue UV region. For example, as UV laser, it can allow reading compact disks with much more information and greatly increasing the amount of data stored . In addition, the low cost, high chemical stability and low threshold intensity make ZnO an ideal candidate for UV laser.
The synthesis of one-dimensional single crystalline ZnO nanostructures has been of increasing interest due to their promising applications in nanoscale optoelectronic devices [1, 11, 12, 13]. The traditional approaches to synthesize one-dimensional ZnO nanostructures are the vapour phase transport processes with the assistance of metal catalysts, thermal evaporation and template-assisted growth [14, 15, 16, 17]. But these processes may introduce impurities in the final product. Hence, it is conceived that preparation of one-dimensional ZnO nanostructures via chemical routes without involving catalysts or templates provides promising option for the large-scale production of well dispersed materials [18, 19]. Though single crystalline ZnO nanorods have been prepared by a modified microemulsion method , the diameters obtained were in the range of 150 nm only. Generally the preparation methods mentioned above involve complex procedures, sophisticated equipment and rigorous experimental conditions. Thus, the development of low cost and mild synthetic routes to ZnO nanorods or nanowires is of great significance.
Herein, a novel and facile method for the preparation of ZnO nanorods by microwave irradiation technique is presented. The method employs a novel hydrazine hydrate complex precursor route and mild conditions.
Zinc acetate and hydrazine hydrate were mixed in a molar ratio of 1:4 in water under stirring. Hydrazine readily reacted with zinc acetate to form a slurry-like precipitate of the hybrid complex between them. The stirring of the slurry was continued for 15 min and then the mixture was subjected to microwave irradiation at 150 W microwave power for 10 min. The slurry became clear with a white precipitate at the bottom. The precipitate was filtered off, washed with absolute ethanol and distilled water several times and then dried in vacuum at 60 °C for 4 h.
X-ray diffraction patterns were taken on a Japan Rigaku D/max rA X-ray Diffractometer equipped with graphite monochromatized high intensity Cu Kα radiation (λ = 1.54178 Å). The accelerating voltage was set at 0.06°/s in the 2θ range 10–80°. The field emission scanning electron microscopy (FE-SEM) images and energy dispersive X-ray analysis (EDXA) were carried out on a FEI Company FE-SEM. Electron diffraction (ED) patterns and the transmission electron microscope (TEM) images of the nanorods were recorded on a JEOL (JEM 3010) transmission electron microscope operating with an accelerating voltage of 300 kV. UV–VIS and photoluminescence spectra of the ZnO nanorods were measured at room temperature under carbon tetrachloride dispersion on a Perkin Elmer UV–VIS and Photoluminescence spectrometers.
Results and Discussion
X-ray Diffraction Pattern (XRD) of ZnO Nanorods
FESEM, EDXA, TEM and ED of the Nanorods
UV–VIS and Photoluminescence Spectra of ZnO Nanorods
Possible Formation Mechanism
It is worthwhile to note here that under microwave irradiation, zinc acetate with only ammonium hydroxide does not yield any nanomaterial. Hence it may be concluded that it is the hydrazine complex which does the magic by acting both as a ligand and as a capping agent to yield 1D nanomaterial.
A facile route for the synthesis of ZnO nanorod by microwave irradiation method has been reported. The method offers a very simple and low cost route for the production of ZnO nanorods. ZnO nanorods have been characterized by XRD, FESEM and EDXA. A possible formation mechanism has been proposed via a zinc acetate–hydrazine hydrate complex formation. Hydrazine hydrate complex acts as ligand and capping agent facilitating the formation of ZnO 1D nanomaterial. The method may also be extended for the preparation of other nanomaterials.
Financial support in the form of a young scientist project grant and a SERC visiting fellowship from DST, Government of India is gratefully acknowledged. The author is also thankful to Prof. CNR Rao of JNCASR, Bangalore, for laboratory facilities and encouragement.