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).