Effects of various polyoxyethylene sorbitan monooils (Tweens) and sodium dodecyl sulfate on reflux synthesis of copper nanoparticles
Introduction
Owing to the quantum size effect of metal nanoparticles, they exhibit unique physical and chemical properties that are significantly different from their bulk. These properties have attracted considerable interest because of their potential applications in optical, magnetic, calorific, electronic, catalytic, memory, sensor, and so on [1], [2]. In order to obtain highly qualified and good stabilized nanoparticles, it is crucial to control their particle size, particle size distribution, external shape, internal structure, and chemical composition.
With their unique performance, the applications of Cu nanoparticles span over catalyst, electron conduction slurry, microelectronics, metal alloy, solid lubricant, and so on [3], [4], [5]. Now the main methods to produce Cu nanoparticles have been categorized as gas phase evaporation [6], plasma [7], γ-radiation-hydrothermal [8], machine-chemical [9], ultrasonic-chemical [10], electron beam irradiation [11], photocatalytic decomposition [12], electrolysis [13], sol–gel [14], inverse micro emulsion [15], chemical reduction [16], microwave irradiation [17], supercritical extraction [18], and hydrothermal method [19]. Among them, reflux chemical reduction method is most commonly used because of the simple equipments, the short technology processes, the low investment, and the convenient for industrialization.
Cu nanoparticles have the characteristics of surface atom ligand deficiency, giving a high surface energy, which makes them easily congregate and oxidize during the synthetic process [2]. Therefore, polyelectrolytes such as polyimide [20], polyvinylpyrrolidone [21], polyvinyl acohol [22], and polyacrtylene [23], and surfactants such as didecyl phthalate [24], sulfur alcohol [25], and acetyltrimethyl ammonium bromide [16], were applied to the synthetic system as dispersants or modifiers. These materials were used not only to prevent the as-synthesized Cu nanoparticles from further oxidation and aggregation, but also to control their particle size, particle size distribution, and shape. Usually hydrazine hydrate [16], sodium borohydride [26], hypophosphite, formaldehyde were used as reductants. Unfortunately, some of the used organic modifiers and reductants are not environmentally benign.
In the present research, we reported the reflux synthesis of Cu nanoparticles using eco-friendly Tweens or sodium dodecyl sulfate (SDS) or both as organic modifiers and ascorbic acid as a reductant. High concentrated Cu nanoparticles aqueous suspensions were achieved starting from copper sulfate (0.25 M). The effects of single modifier and composite modifiers on the morphology of the resulting Cu nanoparticles were also investigated.
Section snippets
Materials
Copper sulfate pentahydrate (99.0%) and ascorbic acid (99.7%) were analytical reagent grade. SDS, polyoxyethylene 20 sorbitan monolaurate (Tween-20), polyoxyethylene 40 sorbitan monopalmitate (Tween-40); and polyoxyethylene sorbitan monooleate (Tween-80) were chemical reagent grade. All of them were purchased from Shanghai Chemical Reagent Company, China, and used as received. Distilled water was used as solvent throughout all the experiments.
Preparation of Cu nanoparticles
Aqueous solutions of different organic modifiers,
Chemical structure of Cu nanoparticles
Fig. 1 shows the XRD patterns of the synthesized Cu samples. Samples R1-R7 were synthesized using Tweens, SDS, and the composites of SDS and Tweens as modifiers, respectively. From the XRD patterns, it can be found that diffraction peaks with strong intensities appear at 2θ = 43.3°, 50.4°, and 74.1°, belonging to the 1 1 0, 2 0 0, and 2 2 0 crystal plane diffractions of metal Cu (fcc), respectively. Moreover, there are no other diffraction peaks except those of Cu, which means that modifiers are
Conclusions
In conclusion, phase pure Cu nanoparticles with different average particle sizes and size distributions can be conveniently synthesized using eco-friendly SDS or Tweens or both, and ascorbic acid as modifiers and reductant, respectively, starting from copper sulfate.
The coordinative interactions between SDS or Tweens and the resulting Cu nanoparticles were certified by FT-IR analyses. The stabilizing ability of Tweens on Cu nanoparticles was increased with increasing the hydrophobicity of
Acknowledgements
The authors would like to show sincere thanks for financial supports from Chinese Education Ministry (2003406), Jiangsu Province (200470), and Jiangsu University (1281310001).
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