Preparation of TiO2-coated hollow glass microspheres from titania-hydrate-coated fine volcanic glass

TiO2-coated hollow glass microspheres (HGMSs) for use in lightweight photocatalysis were developed from titania-hydrate-coated fine volcanic glass (FVG) particles by heat treatment at 940 degrees C for a few seconds. FVG particles were coated with titania hydrate by adding a precipitant dropwise into a suspension in which a raw material of coating layer was dissolved. The change in pH of the suspension, due to decomposition of precipitant, and the stirring speed, had a pronounced effect on the nature of the surface layer and the crystal structure. At an addition rate of 0.6 ml/min of precipitant and a stirring speed of 1000 rpm, smooth coverage of the FVG particles was achieved, and the crystal structure was amorphous and had traces of the anatase phase. lit 0.1 ml/min and 300 rpm, a thick and rough layer developed on the FVG particles; its structure was amorphous and had traces of the rutile phase. The crystals of anatase and rutile increased in number with heat treatment temperature and finally the surface of HGMS was entirely covered by TiO2. TiO2-coated HGMSs from the titania-hydrate-coated FVG are advantageous in particles with low density and high strength, and can be used as photocatalytic fillers.