Controllable synthesis and characterization of novel copper–carbon core–shell structured nanoparticles

https://doi.org/10.1016/j.materresbull.2011.02.012Get rights and content

Abstract

A facile hydrothermal method was developed for preparing copper–carbon core–shell structured particles through a reaction at 160 °C in which glucose, copper sulfate pentahydrate and cetyltrimethylammonium bromide were used as starting materials. The original copper–carbon core–shell structured particles obtained were sized of 100–250 nm. The thickness of carbonaceous shells was controlled ranging from 25 to 100 nm by adjusting the hydrothermal duration time and the concentrations of glucose in the process. Products were characterized with transmission electron microscopy, X-ray diffraction, energy dispersive spectroscopy, Fourier transform infrared spectroscopy. Since no toxic materials were involved in the preparation, particles with stable carbonaceous framework and reactive surface also showed promising applications in medicine, electronics, sensors, lubricant, etc.

Highlights

► We reported a facile, green and cheap hydrothermal method to obtain novel copper-carbon core-shell nanoparticles. ► The as-formed particles with controllable size and morphology are antioxidant. ► The particles with organic-group-loaded surfaces and protective shells are expected to be applied in fields of medicine, electronics, sensors and lubricant.

Introduction

Nano-sized copper particles have received much attention owing to their tremendous applications in the fields of catalysis, electronics and photoelectronics [1], [2], [3], [4], [5]. A large number of strategies including chemical reduction, hydrothermal process, vapor synthesis, laser ablation and γ-irradiation for preparing copper nanoparticles have been reported [6], [7], [8], [9], [10]. The main obstacle to apply copper nanoparticles in the industry arises from their instability toward oxidation in air [11]. Therefore, developing novel fabrication methods to stabilize copper nanoparticles attracts great interests of scientists and is still a big challenge.

The current methods to modify the stability of copper nanoparticles include the following three approaches: (1) using nonaqueous liquid as dispersing media, which minimize the copper surface oxidation [12], [13], [14]; (2) preparing copper nanoparticles in aqueous solution by introducing polymers or surfactants as stabilizer to prevent the reaction of oxygen with the surface copper atoms [15], [16], [17]; (3) encapsulating copper nanoparticles by protective shells to form core–shell structured composites in order to keep the oxygen molecules from contacting the metallic copper particles [18], [19], [20]. In the first two approaches, large amounts of toxic organic reagents are introduced, hence leading to environmental pollution and relatively high cost. The third approach is more attractive. The core–shell structure not only renders the ability to protect copper core from the oxidation or corrosion but also combines the distinct properties of the cores and shells arisen from the different chemical compositions. Due to the inherent difficulties in synthesizing encapsulated copper nanoparticles, limited successful examples were developed. Guo and co-workers have developed a catalytic oxidation approach to coat copper powder with polyaniline [19]. Copper–silica core–shell structured nanoparticles providing corrosion resistance in aqueous environments were obtained through a reduction–encapsulation pathway by Kobayashi and co-workers [20]. Wei's team has synthesized copper–platinum core–shell catalysts by an electrochemical method [21]. The above-mentioned composite particles were impervious to oxidation and, especially, can meet diverse application requirements.

In recent years, carbon has gained increasing interest as one of the metallic encapsulating materials [22], [23], [24], [25], [26]. In addition, due to the presence of functional groups on the surface of carbonaceous shells, it is believed that the composites of metal–carbon are promising for biochemical, optical, electrical and clinic diagnostical applications [27], [28]. Sun and co-workers have initiated a facile and green method to encapsulate noble metal nanoparticles in carbon shells [29], [30]. He and co-workers have prepared carbon encapsulated magnetic nanoparticles by a similar hydrothermal route [31]. Wang's team has synthesized amorphous carbon coating tin–stibium particles [32]. However, to the best knowledge of authors, limited research has been reported on the preparation of copper–carbon core–shell structured nanoparticles.

In this study, novel copper–carbon core–shell structured nanoparticles have been successfully prepared through a hydrothermal route for the first time. To our knowledge, it has never been reported before. The synthesis procedure took place in aqueous solutions and no toxic reagents were employed. The effects of the experimental conditions, such as the concentrations of reagents, hydrothermal reaction temperature and duration time, on the morphology of the samples were discussed in detail.

Section snippets

Chemicals

The reagents (glucose, copper sulfate pentahydrate, cetyltrimethylammonium bromide and alcohol) were all A.R. grade, bought from Beijing Chemical Reagent Factory and used without further purification.

Synthesis

In a typical procedure for the synthesis of copper–carbon nanoparticles, 10.80 g of glucose, 1.50 g of copper sulfate pentahydrate and 1.20 g of cetyltrimethylammonium bromide were dissolved in 600 ml deionized water to form a clear solution after vigorous stirring. Then the obtained solution was

General characterization of as-formed particles

Typical TEM image of as-formed particles is shown in Fig. 1a. It showed that nanoparticles with core–shell structured morphology were obtained. The size of particles was about 150 nm and the thickness of the shell layers was around 45–65 nm.

The EDS profile revealed the elemental constitution of the core–shell structured nanoparticles (Fig. 1b). The two major peaks corresponded to carbon and copper, and the two weak peaks indicated the presence of oxygen and nickel. The nickel peak was originated

Conclusions

Novel copper–carbon core–shell structured nanoparticles with tunable size and morphology have been successfully prepared via an environment-friendly hydrothermal method. The carbonaceous shells contributing to inhibit the oxidation and aggregation of metal copper would improve the catalytic performance of copper. The systematic study on fabrication parameters revealed that the size and morphology of copper–carbon core–shell structured nanoparticles can be effected mainly by hydrothermal

Acknowledgements

The authors would like to acknowledge NanoMaterials Technology Pte Ltd., the National “863” Program of China (No. 2009AA033301), the NSFC (Nos. 50642042, 20821004) and the NCET project (No. NCET-06-0102) for financial support.

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