Rapid synthesis of copper nanoparticles by sodium hypophosphite reduction in ethylene glycol under microwave irradiation

doi:10.1016/j.jcrysgro.2004.07.008

Journal of Crystal Growth

Volume 270, Issues 3–4, 1 October 2004, Pages 722-728

https://doi.org/10.1016/j.jcrysgro.2004.07.008 Get rights and content

Abstract

This paper presents a rapid method for preparation of copper metal nanoparticles by reducing CuSO₄·5H₂O with NaH₂PO₂·H₂O in ethylene glycol under microwave irradiation. The influences of the reaction parameters, such as the concentrations of reducing agent and protective polymer time of microwave irradiation, on the size and agglomeration of copper nanoparticles were investigated by X-ray powder diffraction and transmission electron microscope. Well-dispersed copper nanoparticles with diameter of about 10 nm were obtained. The use of microwave irradiation accelerated the reaction rate and benefited the dispersion and the particle size distribution of the nanoparticles.

Introduction

Copper metal nanoparticles have received considerable attention in the past two decades due to their unusual properties and potential applications in nanomaterials, thermal conducting, lubrication, nanofluids and catalysts [1], [2], [3], [4], [5], [6]. Diverse approaches to the preparation of copper metal powders have been reported, such as microemulsion [7], reverse micelles [8], reduction of aqueous copper salts [9], γ-irradiation [10], UV-light irradiation [11] and polyol process [12], etc. Among the various methods, the chemical reduction of copper salts in aqueous systems is characterized by a quick reaction rate, but the agglomeration of particles is often serious. So it is very difficult to obtain nanoscale copper metal powders. On the other hand, the polyol process, in which liquid polyol acts as both solvent and reducing agent [12], is one of the successful methods for preparing uniform and well-dispersed copper nanoparticles. However, compared with the aqueous chemical reduction method, it takes place slowly and requires high temperature and refluxing for several hours or even days.

Microwaves are electromagnetic waves containing electric and magnetic field components. Recently, microwave irradiation has shown very rapid growth in its application in materials science due to its thermal and non-thermal effects [13]. It is well known that the interaction of dielectric materials, liquids or solids, with microwaves leads to dielectric heating. Compared with the conventional methods, microwave synthesis has the advantages of short reaction time, small particles size and narrow particles distribution.

The present investigation was performed to synthesize well-dispersed metal copper nanoparticles rapidly by a modified polyol process in which sodium hypophosphite was used as reducing agent and microwave irradiation was used as heating source. Reaction parameters such as the concentrations of reducing agent and protective polymer (polyvinylpyrrolidone, PVP), the time of microwave irradiation were varied to control the size and agglomeration of copper nanoparticles.

Section snippets

Materials and instruments

Copper sulfate pentahydrate (CuSO₄·5H₂O) was obtained from Jinan Chemical Corporation. Sodium hypophosphite (NaH₂PO₂·H₂O) and ethylene glycol were the product of Tianjin Guangcheng Chemical Corporation. Polyvinylpyrrolidone (PVP K30, polymerization degree 360) was obtained from Shanghai Dongsheng Chemical Corporation. Other reagents were purchased from Huadong Chemical Corporation. All the reagents used in our experiments were of analytical purity and were used without further purification.

Copper nanoparticle size and structure

Fig. 1a,–c, are the TEM image, selected area electron diffraction (SAED) pattern and size distribution of the typical product, respectively. The TEM graph reveals that the product consists of spherical particles, and all nanoparticles are dispersed very well. The average diameter estimated from TEM image analysis is 10.4 nm (Fig. 1c). The standard deviation and relative standard deviation are 1.8 nm and 0.17 , respectively. Four fringe patterns with plane distances of 2.08, 1.80, 1.28, 1.09 Å can

Conclusions

In summary, a rapid method to synthesize copper metal nanoparticles by reducing CuSO₄ with NaH₂PO₂ in ethylene glycol under microwave irradiation was developed. The use of microwave irradiation not only accelerated the reduction rate, but also benefited the dispersion and the size distribution of the nanoparticles. It was shown that the molar ratio of NaH₂PO₂/CuSO₄ plays an important role in determining the phase and grain size of the product, and optimum quantities of PVP were one of the keys

Acknowledgements

This work is supported by the National Nature Science Foundation of China (50242008) and Shandong Nature Science Foundation of China (Z2002F02). We are grateful for the kind assistance from Dr. De-Bao Wang, Prof. Zheng-shui Hu and Xun Fu, Institute of Chemistry and Molecular Engineering, Qingdao University of Science and Technology.

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Rapid synthesis of copper nanoparticles by sodium hypophosphite reduction in ethylene glycol under microwave irradiation

Abstract

Introduction

Section snippets

Materials and instruments

Copper nanoparticle size and structure

Conclusions

Acknowledgements

Int. J. Heat Fluid Flow

J. Colloid Interface Sci.

Nanostructureed Mater.

Chem. Phys. Lett.

J. Solid State Chem.

Science

Wear

Appl. Phys. Lett.