A vibrational spectroscopy study of the growth of silicate-1 films on noble metal surfaces

Abstract: The main objective of this thesis was to acquire a better understanding of the mechanisms involved in the preparation of Silicalite-1 films in general and on gold surfaces in particular. Molecular sieve films on gold surfaces were prepared using the seed film method. The deficiency of negative charge on a gold surface in aqueous solution was overcome by a coupling agent (gamma-mercaptopropyltrimethoxysilane or sodium hydrosulfide). The resulting negatively charged surface was modified by a cationic polymer, facilitating the adsorption of negatively charged colloidal silicalite-1 seed crystals. The seed crystals were grown into a continuous molecular sieve film during hydrothermal treatment in synthesis solution. Reflection absorption infrared spectroscopy was found to be an excellent method to gain insight about the structures formed after each step in this preparation procedure. The recorded vibrational spectra were compared with vibrational modes calculated from the dynamic matrix of the clusters concidered. These comparisons showed that the organic coupling agent was oriented with the methylene chain perpendicular to the gold surface, the cationic polymer introduces disorder in the silane layer, the silanol groups predominantly form 6-membered puckered Si-O rings upon condensation and that linear defects in the films are formed during the hydrothermal treatment. The effects of seed size and hydrothermal treatment time on the formation of linear defects were investigated.