Elsevier

Chemical Physics Letters

Volume 537, 1 June 2012, Pages 113-117
Chemical Physics Letters

Synthesis of supported metal oxide nanoparticles with narrow size distribution

https://doi.org/10.1016/j.cplett.2012.04.014Get rights and content

Abstract

We report a versatile synthetic route allowing the formation of transition metal oxide nanoparticles supported on solid surfaces. Basically, the method lies on the complexation of metal cations with both anionic surfactant and hydroxilated surfaces, which results in the formation of small aggregates onto the surface. At thermodynamical equilibrium, the resulting balance between the loss of entropy due to the aggregation and the gain in enthalpy due to hydrophobic interactions between the alkyl chains of the surfactant governs the size of these aggregates. After calcination in air, metal oxide nanoparticles with very narrow size distribution are obtained.

Highlights

Surfactant assisted synthesis of supported metal oxide nanoparticles. ► Complexation of metal cations with both anionic surfactant and hydroxilated surfaces. ► An easy synthetic route using very common materials and chemicals. ► A nanoparticle size distribution of 1.1 ± 0.3 nm.

Introduction

Today, almost all of the applications of nanoparticles require precise control of their sizes with narrow size distributions, since their properties at the nanoscale are strongly dependent on their size [1]. This is particularly true for the catalytic activity of metal nanoparticles such as the oxidation of carbon monoxide by gold clusters [2] or the growth of carbon nanotubes by chemical vapor deposition [3] or for their optical properties such as surface plasmon resonance [4] or photoluminescence [5]. Several approaches, such as lithographic patterning techniques using electron or focused ion beams [6], soft lithography [7], colloidal lithography [8], self-assembly techniques [9], [10], have been developed to fabricate monodispersed nanoparticles and today the challenge is to find a cheap, easy and reproducible technique allowing one to get nanoparticles of precise size supported on wide surfaces.

We report a new route for the synthesis of metal oxide nanoparticle which is based on the free evolution of a system towards its thermodynamical equilibrium. Basically, a hydroxilated substrate is dipped in a mixture of metal salt and anionic surfactant. After 5 min, the system has reached its thermodynamical equilibrium and metal containing nanoparticles are formed onto the surface. A calcination step transforms these particles into metal oxide nanoparticles. Beside the very few steps of this process, its originality lies on the fact that nanoparticles are formed directly onto the substrate, avoiding further handling such as precipitation or deposition of a colloidal suspension [11].

Section snippets

Experimental section

Anhydrous Iron (III) Chloride (FeCl3; >97%), Nickel (II) Chloride (NiCl2; >98%), Sodium Dodecyl Sulfate salt (SDS; >99%), Ammonium Dodecyl Sulfate salt (ADS; solution ∼30% in water), Hydrochloric acid (HCl; ⩾37%), Sulfuric Acid (H2SO4, 95–97%) and Hydrogen Peroxide (H2O2, 35%) were purchased from Sigma–Aldrich. Zinc (II) Chloride was purchased from Fluka.

Polished oxidized silicon wafers with an oxide layer of 500 nm were purchased from Silchem Vertriebsgesellschaft mbH, Germany.

All surfaces were

Results

SiO2/Si wafers are first cleaned by sonication in acetone for 10 min then rinsed with pure water. In a second step, wafers are either dipped in a mixture of H2SO4 and H2O2 (ratio 3 to 1) at 40 °C for 20 min or exposed to a water plasma for 3 min to hydroxilate them (formation of Si–OH groups). In a typical experiment, 1 ml of a 10−2 M solution of SDS in pure water is added to 10 ml of a 10−3 M solution of FeCl3 at pH 2. The hydroxilated wafer is dipped in the ‘working solution’ for 5 min then copiously

Discussion

Our interpretation of the mechanism of formation of the nanoparticles is illustrated on Scheme 1. Fe (III) usually exists in dilute aqueous solutions in an octahedral configuration and has six sites of complexation [18], [19]. In our working solutions in presence of SDS, ferric ions can complex H2O, OH, Cl species, as well as the dodecylsulfate anions by linking with the sulfate groups of the latter [20]. Ferric ions have clear tendency to complex OH groups of silica too [21]. Thus when the

Conclusion

In summary, we have developed a simple and new route for synthezising metal oxide nanoparticles by the use of very common materials and chemicals. In the field of nanoparticles synthesis, our method is based on an original concept, the complexation of metal cations with both anionic surfactant and hydroxilated surfaces. This complexation leads to the formation of small aggregates onto the surfaces which size results from the balance between the loss of entropy due to the aggregation and the

Acknowledgements

This work was supported by a CNRS-Région Alsace PhD Grant (D. Salem). M. He is thanked for technical support. J. Quillé and P. Bernard are thanked for light scattering and for XPS measurements, respectively.

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