Effect of TiO2 nanoparticles aggregation in silicate thin coating films on photocatalytic behavior for antifouling materials

Two types of disperser namely, a high speed agitation bead mill and a colloidal mill, were used for the dispersion behavior control of TiO₂ nanoparticles (20 nm in average primary diameter) in an aqueous suspension. A composite thin film raging in thickness from 90 to 400 nm was prepared from the coating suspension following the addition of a commercial ethyl silicate oligomer binder into the prepared suspension by means of a spray coating method. The mean aggregate size of TiO₂ nanoparticles in the aqueous suspension was found to be 80 nm and 290 nm in diameter, respectively, when using the agitated bead and colloidal milling methods. Large aggregates on the order of several hundred nanometers were found to remain in the suspension after colloidal milling. Further, a fine dispersion of TiO₂ nanoparticles in the thin film produced using the agitation bead milling process promoted the photocatalytic activity and enhanced transparency of the film for visible light. The aggregate structure of TiO₂ nanoparticles in an aqueous suspension was well maintained in the film prepared by a spray coating process.