Matrix-Assisted Formation of Metal Nanoparticles in Organosilica Sol-Gels
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Matrix-Assisted Formation of Metal Nanoparticles in Organosilica Sol-Gels Sandie H. Cheung and Bakul C. Dave Department of Chemistry and Biochemistry Southern Illinois University Carbondale, IL 62901-4409. ABSTRACT The use of organosilica sol-gels for controlled in-situ formation of metal nanoparticles is investigated. The use of an organically-modified alkoxysilane precursor provides chemically interacting nanopores for the sequestration and binding of metal ions followed by chemical reduction to form metal nanoparticles. The sol-gel matrix acts as a structural template to enable growth of the metal nanoparticles within its porous silica framework, and prevents clustering to form precipitate. Furthermore, simple redox chemistry is used to convert pre-formed copper nanoparticles in the sol-gel matrix into silver and gold nanoparticles. A particularly important aspect of this synthesis method is that all the reaction chemistry is performed under ambient conditions. The particles are characterized by high resolution transmission electron microscopy for their sizes and size distribution. The elemental composition of the particles is determined by energy dispersive X-ray analysis.
INTRODUCTION Formation of metal nanoparticles with controlled dimensions is an important issue in nanotechnology, and in the design of electronic and optical devices because of their novel and unusual properties [1]. The controlled formation of metal nanoparticles with a reasonable degree of control over their size, shape and size distribution remains an important issue in synthesis and processing [2]. A variety of wet and dry methods of preparation of such particles are employed [3]. In this direction, the nanopores of the sol-gel glasses offer a physical nanocavity that can be effectively used as a physical template for synthesis of nanoclusters and particles [4]. We have recently shown that the pores of sol-gel can be used for controlled formation of metal-oxo clusters [5]. In this report, we extend this approach to fabricate nanoparticles of metals with sizes on the order of 4-8 nm. The strategy used in this work is based on use of an organically-modified sol-gel precursor with ligating atoms that can be used for sequestration and binding of metal ions [5]. These matrix-bound metal ions when chemically reduced, give rise to metal particles whose size and distribution can be controlled. Furthermore, by means of simple redox chemistry, it is possible to exchange one metal ion with other. As part of this work, we used the organosilane precursor bis[3-(trimethoxysilylpropyl)]ethylenediamine (enTMOS) whose molecular formula is given as [(OCH3)3Si(CH2)3NH(CH2)2NH(CH2)3Si(OCH3)3]. The precursors was used because 1) it provides ligating atoms in the form of amino groups for sequestration and binding of metal ions, 2) it provides a porous matrix with majority pores having size on the order of 4-8 nm [5], 3) it provides a hydrophobic matrix (due to organic groups) which prevents extensive aggregation of particles and spatially isolates them [6], an
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