2 research outputs found

    Novel Synthesis of Gold Nanoparticles Supported on Alkyne-Functionalized Nanosilica

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    A novel, convenient method for the preparation of gold nanoparticles supported on alkyne-functionalized nanosilica is presented. Silica nanoparticles functionalized with alkynyl carbamate moieties (<b>SiO</b><sub><b>2</b></sub><b>@Yne</b>) were synthesized by co-condensation of the difunctional organosilane [3-(2-propynylcarbamate)­propyl]­triethoxysilane (PPTEOS) with tetraethoxysilane (TEOS) in an alkaline medium. The alkynyl-carbamate functionalities present on silica are able to capture the gold precursor HAuCl<sub>4</sub>, spontaneously reduce it, and stabilize the resulting supported Au<sub>NPs</sub>, having an average size of ca. 11 nm. The prepared <b>Au</b>-<b>SiO</b><sub><b>2</b></sub><b>@Yne</b> was thoroughly analyzed by X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), transmission electron microscopy (TEM), atomic absorption spectroscopy (AAS), FT-IR, and UV–vis spectroscopy. The catalytic activity of <b>Au</b>-<b>SiO</b><sub><b>2</b></sub><b>@Yne</b> was investigated for the reduction of 4-nitrophenol to 4-aminophenol by NaBH<sub>4</sub>, and kinetic constants <i>k</i> in the order of magnitude of about 10<sup>–2</sup> s<sup>–1</sup> were found

    Straightforward Synthesis of Gold Nanoparticles Supported on Commercial Silica-Polyethyleneimine Beads

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    Stable silica-supported gold nanoparticles (Au<sub>NPs</sub>) suitable for catalysis applications were conveniently obtained in a straightforward, one-step synthesis by simply adding an aqueous solution of HAuCl<sub>4</sub> to commercial polyethyleneimine-functionalized silica beads (SiO<sub>2</sub>-PEI) as the only reactant without any external reducing agent and/or conventional stabilizing moieties. Six different types of Au<sub>NPs</sub>/(SiO<sub>2</sub>-PEI) beads termed <b>Au</b><sub><b><i>x</i>–<i>y</i></b></sub><b>h</b>, where <i>x</i> is the initial HAuCl<sub>4</sub> concentration (1, 5, or 10 mM) and <i>y</i> is the reaction time (1 or 24 h), were prepared and characterized by UV–vis diffuse reflectance spectroscopy, X-ray fluorescence, FE-SEM microscopy, and X-ray absorption spectroscopy. The SEM micrographs of <b>Au</b><sub><b><i>x</i>–<i>y</i></b></sub><b>h</b> samples showed that the particle size distribution decreases with the increase of the starting gold concentration, i.e., 70–100 nm for <b>Au</b><sub><b>1–</b></sub><sub><b><i>x</i></b></sub><b>h</b>, 40–70 nm for <b>Au</b><sub><b>5</b><b>–</b></sub><sub><b><i>x</i></b></sub><b>h</b>, and <b>Au</b><sub><b>10</b><b>–</b></sub><sub><b><i>x</i></b></sub><b>h</b>, whereas on passing from 1 to 24 h the aggregation phenomena overcome the nucleation ones, promoting the formation of bigger aggregates at the expense of small Au<sub>NPs</sub>. The XAS analysis as a combination of XANES and EXAFS studies provided detailed structural information regarding the coordination geometry and oxidation state of the gold atoms present on the beads. Moreover, the catalytic activity of the modified silica beads in the reduction of 4-nitrophenol to 4-aminophenol by NaBH<sub>4</sub> was investigated and in one case the XAS analysis was repeated after recovery of the catalyst, demonstrating further reduction of the Au site to Au(0)
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