PREPARATION OF GOLD COLLOID-DISPERSED SILICA COATING FILMS BY THE SOL-GEL METHOD

Silica glass coatings containing dispersed colloidal gold particles have been prepared by dipping a slide, glass substrate into acid-catalyzed tetraethoxysilane (TEOS) solutions containing HAuCl4.4H2O, withdrawing it, and heating it at 500-degrees-C. Effects of the amount of water and/or hydrochloric acid used for hydrolysis of TEOS on the size and state of the gold particles formed have been investigated. Higher HCl contents were effective in suppressing the escape of gold from the film on heating. Gel films derived from the highly acid catalyzed TEOS solutions hydrolyzed with a larger amount of water were transformed into glass coatings containing dispersed gold particles larger in size; gold particles smaller than 200, 280, and 340 angstrom were formed in the silica coatings derived from the solutions of H2O/TEOS mole ratios of 2, 4, and 10, respectively. Soaking of the gel coatings in monoethanolamine (MEA) vapor prior to heat treatment was found to be effective in suppressing the escape of gold from the film and in formation of silica coatings containing smaller gold particles. Silica glass coatings containing dispersed colloidal gold particles smaller than 80 angstrom in diameter could be prepared from highly acidic solutions through the amine vapor treatment.