Zr and Hf oxoclusters as building blocks for the preparation of nanostructured hybrid materials and binary oxides MO2–SiO2				(M = Hf, Zr)

Lidia Armelao; Helmut Bertagnolli; Silvia Gross; Venkata Krishnan; Urska Lavrencic-Stangar; Klaus Müller; Boris Orel; Gokulakrishnan Srinivasan; Eugenio Tondello; Andrea Zattin

doi:10.1039/B501904D

Zr and Hf oxoclusters as building blocks for the preparation of nanostructured hybrid materials and binary oxides MO₂–SiO₂ (M = Hf, Zr)

Lidia Armelao,^a Helmut Bertagnolli,^b Silvia Gross,*^a Venkata Krishnan,^b Urska Lavrencic-Stangar,^c Klaus Müller,^b Boris Orel,^c Gokulakrishnan Srinivasan,^b Eugenio Tondello^d and Andrea Zattin^d

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* Corresponding authors

^a CNR–ISTM, University of Padova, via Marzolo, 1- I-35131 Padova, Italy
E-mail: silvia.gross@unipd.it

^b Institute of Physical Chemistry, University of Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart, Germany

^c National Institute of Chemistry, Hajdrihova 19, SI-1000 Ljubljana, Slovenia

^d Department of Chemistry, University of Padova, via Marzolo, 1-35131 Padova, Italy

Abstract

Silica materials embedding ZrO₂ or HfO₂ were prepared by copolymerisation of organically modified oxozirconium or oxohafnium clusters M₄O₂(OMc)₁₂ (M = Zr, Hf and OMc = methacrylate) with (methacryloxymethyl)triethoxysilane or (methacryloxypropyl)trimethoxysilane. Free radical copolymerisation of the oxoclusters bearing 12 methacrylate groups with the methacrylate-functionalized siloxanes allows stable anchoring of the clusters to the silica network formed by the hydrolysis and condensation of the alkoxy groups. This route represents a valuable strategy to yield a very homogeneous dispersion of the MO₂ precursors inside the silica matrix. The composition and the microstructural features of the starting hybrid gels were studied by solid state ¹³C and ²⁹Si NMR spectroscopy and FT IR transmission spectroscopy. Their evolution upon mild heating (up to 180 °C) was followed by FT-IR Attenuated Total Reflectance spectroscopy (ATR), while their thermal behaviour was studied by thermogravimetric analysis (TGA). The covalent incorporation of the clusters into the silica hybrid matrix was studied at several temperatures. Through X-Ray Diffraction (XRD) and Extended X-ray Absorption Fine Structure Spectroscopy (EXAFS) it is demonstrated that temperatures above 800 °C yield binary oxides MO₂–SiO₂ (M = Zr, Hf). Delayed crystallisation of HfO₂ and tetragonal ZrO₂ from 450 °C to at least 800 °C was detected, which is ascribed to the presence of a homogeneous dispersion of the guest oxide in the silica matrix.

Journal of Materials Chemistry

Zr and Hf oxoclusters as building blocks for the preparation of nanostructured hybrid materials and binary oxides MO₂–SiO₂ (M = Hf, Zr)

Abstract

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Zr and Hf oxoclusters as building blocks for the preparation of nanostructured hybrid materials and binary oxides MO₂–SiO₂ (M = Hf, Zr)

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