Role of Gas−Aerosol Mixing during in Situ Coating of Flame-Made Titania Particles

Rutile TiO 2 particles of 40 nm average diameter were made by flame spray pyrolysis (FSP) and in situ coated with ultrathin (2−4 nm) SiO 2 layers. The spray flame was enclosed by a quartz glass tube while hexamethyldisiloxane (HMDSO) vapor-laden N 2 was injected in swirling crossflow to and downstream of the flame through a metal torus pipe ring. The as-prepared powders were characterized by transmission electron microscopy (TEM), X-ray diffraction, and nitrogen adsorption. The effect of mixing between HMDSO-laden N 2 jets and freshly made titania aerosol on product coating quality was investigated by varying systematically the number and gas flowrate through these jets experimentally and by computational fluid dynamics. The coating quality of titanium dioxide was evaluated further by photocatalysis of isopropanol to acetone under UV light using suspensions of the above particles.