Synthesis and photoluminescence of corn-like ZnO nanostructures under solvothermal-assisted heat treatment

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Abstract

Corn-like ZnO nanorods have been prepared by a solvothermal-assisted heat treatment method. The products were investigated by XRD, FE-SEM, TEM, TG-DTA, FT-IR and PL. It was found that the corn-like ZnO nanorods consisted of polycrystal nanoparticles with hexagonal wurtzite structure. The diameter and length of the nanorods are about 90–150 nm and 0.6–3 μm, respectively. The near-band ultraviolet emission spectrum of the corn-like ZnO nanorods has one peak at 400 nm under 250 nm excitation at room temperature. A possible mechanism for the formation of the corn-like ZnO nanorods is also discussed briefly.

Introduction

Since the discovery of carbon nanotubes [1], one-dimensional (1D) nanometer-sized materials have attracted much attention owing to their great potential for fundamental studies as well as for applications in nanodevices and functional materials [2]. Semiconductor oxide nanomaterials, such as ZnO, Ga2O3, In2O3 and SnO2, are hot subjects because of the wide use as basic materials for transparent conducting films, photoelectronics, gas sensors [3], [4], [5], [6], etc. Among these materials, ZnO with a wide and direct band gap of 3.37 eV and a large exciton binding energy of 60meV at room temperature, has been considered a promising material for electronic and photonics applications [7]. Currently, many interesting ZnO nanostructures, including nanobelts, nanobridges and nanonails have been fabricated [8], [9], [10]. These complex structures are expected to have potential applications in building functional nanoelectronics devices. A common challenge shared by these studies is that shape control of the ZnO products is difficult to achieve. It turns out to be a great challenge for the future. Different fabrication methods have been reported for ZnO nanostructures, therein, a vapor-phase transport process with the assistance of metal catalysts and chemical thermal evaporation are the two major vapor methods to fabricate 1D ZnO nanostructures (nanorods and nanowires) [8], [11], [12], [13], [14], [15], [16]. Furthermore, some wet chemical methods have been developed to synthesize ZnO nanostructures without any catalysts. In this Letter, we report a solvothermal-assisted heat treatment method to synthesize novel corn-like ZnO nanorods. The synthesis involved precursors of 1D ZnC2O4 · 2H2O nanorods gained at relatively low temperature (80 °C), followed by heating without the presence of any catalyst. The structures of these characteristic shapes have been fully characterized and a growth mechanism was proposed.

Section snippets

Experimental

The corn-like ZnO nanorods were prepared in the following process. About 0.025 mol zinc acetate dihydrate (AR) and 0.025 mol oxalic acid dihydrate (AR) were added into a stainless-steel autoclave with a teflon liner containing 40 ml alcohol. After 10 min stirring, the stainless-steel autoclave was sealed and then put into an oven, which was kept at 80 °C for 5 h. The precipitate in the autoclave was taken out and washed repeatedly with deionized water and alcohol. Then a white powder was

Results and discussion

Fig. 1 shows typical XRD patterns of the synthesized products. All the diffraction peaks of sample 1 (curve b) can be indexed as ZnC2O4 · 2H2O (JCPDS 25-1029). The diffraction peaks in curve a (sample 2) can be indexed as hexagonal ZnO with lattice constants a = 0.325 nm and c = 0.52 nm, which are consistent with the values in the standard card (JCPDS 36-1451). These results indicate that the products (sample 1) formed in the stainless-steel autoclave was ZnC2O4 · 2H2O and that the products formed when

Conclusions

In summary, corn-like ZnO nanorods have been successfully prepared by a two-step method, involving a low temperature solvothermal process and a heat treatment process. The advantage of this approach is that the corn-like ZnO nanorods are produced at low reaction temperature without catalyst and any surfactant. The proposed growth mechanism is qualitative, based on the SEM and TEM observations. Heat treatment is proved to have important effects on the formation and shape of the corn-like ZnO

Acknowledgment

This research work was supported by the National Natural Science Foundation of China (Grant No. 50302010).

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