Transparent micrometer-thick TiO2 films on SiO2-coated glass prepared by repeated dip-coating/calcination:: Characteristics and photocatalytic activities for removing acetaldehyde or toluene in air

TiO2 films on silica-coated glass plates were obtained through dip- coating and subsequent calcination at 753 K; this temperature and the proportions of the dip- coating solution components ( tetraisopropyl orthotitanate, ethoxyethoxyethanol, propan-2-ol, R-terpineol, and a hydroxypropyl cellulose) were optimized. Depending on the number N ( 5 <= N <= 30) of dip-coating/ calcination procedures, the films characteristics were hardness, > 9 H; thickness, 0.9-5.4 Am; transmitted light, ca. 70% ( visible spectral region); absorbed light, 90-100% at 358 nm; surface area, 40-80 m(2) g(-1); pore volume 7-20 mL g-1; anatase particle size, 3.5- 4 nm (elemental crystallites) and 12-16 nm ( agglomerates). These tiny sizes, which did not increase for N 20, were obtained because of the use of hydroxypropyl cellulose. The photocatalytic removal rate of acetaldehyde ( 3.25 ppmv) or toluene ( 1 ppmv) in flowing air ( 50% RH) showed that the TiO2 minimum amount varied with the pollutant and that a 1-2 Am thickness was sufficient to achieve a near-maximum efficacy. In summary, this preparation produces anatase films having the mechanical, optical, and photocatalytic properties required to obtain self-cleaning ( water contact angle test) and air depolluting ( at least in relatively confined spaces) glass without using a binder, which can restrict the accessibility to TiO2 and alter the photocatalytic activity.