Preparation of CuO nanoparticles by microwave irradiation

https://doi.org/10.1016/S0022-0248(02)01571-3Get rights and content

Abstract

CuO nanoparticles with an average size of ca. 4 nm have been successfully prepared by microwave irradiation, using copper (II) acetate and sodium hydroxide as the starting materials and ethanol as the solvent. The CuO nanoparticles are characterized by using techniques such as X-ray powder diffraction, transmission electron microscopy, selected area electron diffraction, X-ray photoelectron spectroscopy and UV–Visible absorption spectroscopy. The as-prepared CuO nanoparticles have regular shape, narrow size distribution and high purity. The band gap is estimated to be 2.43 eV according to the results of the optical measurements of the CuO nanoparticles.

Introduction

Nanocrystalline semiconductor particles have drawn considerable interest in recent years because of their special properties such as a large surface-to-volume ratio, increased activity, special electronic properties and unique optical properties as compared to those of the bulk materials [1], [2]. The oxides of transition metals are an important class of semiconductors, which have applications in magnetic storage media, solar energy transformation, electronics and catalysis [3], [4], [5], [6], [7], [8], [9], [10], [11], [12]. Among the oxides of transition metals, CuO has attracted much attention because it is the basis of several high-Tc superconductors. CuO is a semiconducting compound with a narrow band gap and used for photoconductive and photothermal applications [13]. However, up to now, the reports on the preparation and characterization of nanocrystalline CuO are relatively few to some other transition metal oxides such as zinc oxide, titanium dioxide, tin dioxide and iron oxide. Some methods for the preparation of nanocrystalline CuO have been reported recently such as the sonochemical method [14], sol–gel technique [15], one-step solid state reaction method at room temperature [16], electrochemical method [17], thermal decomposition of precursors [18], and co-implantation of metal and oxygen ions [19], and so on.

Microwaves are electromagnetic waves containing electric and magnetic field components. It is well known that the interaction of dielectric materials, liquids or solids, with microwaves leads to what is generally known as dielectric heating. Electric dipoles present in such materials respond to the applied electric field. In liquids, this constant reorientation leads to the friction between molecules, which subsequently generates heat [20]. Claimed effects of microwave irradiation include thermal effects and non-thermal effects. Microwave irradiation as a heating method has found a number of applications in chemistry. The microwave synthesis, which is generally quite fast, simple and efficient in energy, has been developed and is widely used in various fields such as molecular sieve preparation, radiopharmaceuticals, the preparation of inorganic complexes and oxide, organic reactions, plasma chemistry, analytical chemistry and catalysis [21]. The applications of microwave irradiation in the preparation of nanoparticles have been reported in recent years [22], [23], [24], [25], [26], [27], [28], [29], [30]. Microwave irradiation has shown very rapid growth in its application to material science due to its unique reaction effects such as rapid volumetric heating and the consequent dramatic increase in reaction rates, etc. Compared with the conventional methods, the microwave synthesis has the advantages of short reaction time, small particle size, narrow particle size distribution and high purity.

In this paper, we report a novel method for the preparation of monoclinic CuO nanoparticles by microwave irradiation. It is found to be a fast, convenient, mild, energy-efficient and environmentally friendly route to produce CuO nanoparticles in only one step. The product has regular shape, small size, narrow size distribution and high purity.

Section snippets

Materials

Cu(CH3COO)2 and NaOH of analytical purity were purchased from Shanghai Chemical Reagent Factory (China). Absolute ethanol of analytical purity was purchased from Nanjing Chemical Reagent Factory (China). Polyethylene glycol-19000 (PEG) was purchased from Tianjing Third Reagent Factory (China). All the reagents were used without further purification. Distilled water was used in our experiments.

Instruments

A microwave oven with 650 W power (Sanle general electric corp. Nanjing, China) was used. A refluxing

XRD analysis

The XRD pattern (Fig. 1) of the product obtained is identical to the single-phase CuO with a monoclinic structure. The intensities and positions of the peaks are in good agreement with literature values [31]. No peaks of impurity are found in the XRD pattern. The broadening of the peaks indicates that the crystal size is small. The average size of the CuO nanoparticles is estimated to be ca. 4 nm according to the Debye–Scherer formula [32].

TEM and SAED measurements

The size and morphology of the product are analyzed by

Conclusions

Nanocrystalline CuO particles with a monoclinic structure have been prepared successfully by a novel method using microwave irradiation. It is a simple and efficient method to produce CuO nanoparticles with regular shape, small size, narrow size distribution and high purity. We can foresee the upscaling of the process to form large quantities of nanosized CuO particles, which have wide applications in various fields such as photics, catalysis and biosensors.

Acknowledgements

This work is supported by the Jiangsu Advanced Science and Technology Program of China (BG 2001039), National Natural Science Foundation of China (No. 50072006) and Analytical Foundation of Nanjing University. The authors also thank Ms. Xiaoning Zhao and Ms. Xiaoshu Wang from Modern Analytic Center of Nanjing University for extending their facilities to us.

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