The synthesis of mesostructured silica films and monoliths functionalised by noble metal nanoparticles

Abstract

A lyotropic AgNO₃, HAuCl₄ and H₂PtCl₆–silica liquid crystalline (LC) phase is used as a supramolecular template for a one-pot synthesis of novel noble metal or complex ion containing nanocomposite materials in the form of a film and monolith. In these structures, Ag⁺, AuCl₄⁻ and PtCl₆²⁻ ions interact with the head group of an oligo(ethylene oxide) type non-ionic surfactant (C₁₂H₂₅(CH₂CH₂O)₁₀OH, denoted as C₁₂EO₁₀) assembly that are embedded within the channels of hexagonal mesostructured silica materials. A chemical and/or thermal reduction of the metal or complex ions produces nanoparticles of these metals in the mesoporous channels and the void spaces of the silica. The LC mesophase of H₂O∶X∶HNO₃∶C₁₂EO₁₀, (where X is AgNO₃, HAuCl₄ and H₂PtCl₆), and nanocomposite silica materials of meso-SiO₂–C₁₂EO₁₀–X and meso-SiO₂–C₁₂EO₁₀–M (M is the Ag, Au and Pt nanoparticles) have been investigated using polarised optical microscopy (POM), powder X-ray diffraction (PXRD), transmission electron microscopy (TEM), nuclear magnetic resonance (NMR), Fourier transform infrared (FTIR), Fourier transform (FT) Raman and UV-Vis absorption spectroscopy. Collectively the results indicate that the LC phase of a 50 w/w% H₂O∶C₁₂EO₁₀ is stable upon mixing with AgNO₃, HAuCl₄ and H₂PtCl₆ salts and/or acids. The metal ions or complex ions are distributed inside the channels of the mesoporous silica materials at low concentrations and may be converted into metal nanoparticles within the channels by a chemical and/or thermal reduction process. The metal nanoparticles have a broad size distribution where the platinum and silver particles are very small (typically 2–6 nm) and the gold particles are much larger (typically 5–30 nm).