Preparation of TiO2 hollow microparticles by spraying water droplets into an organic solution of titanium tetraisopropoxide

Hollow, spherical TiO2 microparticles several tens of micrometers in diameter were prepared by spraying water into an organic phase containing titanium tetraisopropoxide (TTIP) as a titanium source. The rapid hydrolysis of TTIP at the water–oil interface resulted in the formation of a TiO2 shell covering the water droplet. Hexane and cyclohexane were better solvents than isopropanol for fabricating hollow spherical microparticles, suggesting the importance of immiscibility of the solvent with water in this synthesis method. The average particle size increased as the distance from the nozzle to the surface of the TTIP solution was increased. The shell thickness was reduced by the addition of ethanol to the sprayed water droplet. These results demonstrate the controllability of the structure of TiO2 hollow microparticles, including the diameter and the shell thickness.