Photocatalytic activity of nanostructured titanium dioxide from diffusion flame synthesis

Abstract

Vapour fed flame aerosol synthesis has been employed to synthesize TiO 2 photocatalyst by oxidation of titanium tetrachloride (TiCl 4). The effect of precursor loading on particle growth and rutile phase formation was studied using laminar premixed flame with (Ar + TiCl 4)/CH 4/O 2/N 2 configuration and synthesis temperature of around 900 °C. The increase in precursor flow rate, as key synthesis parameter, from 2.5 to 29.5 mmol h −1 increased the average particle diameter, d BET , from 11 to 22 nm and decreased the specific surface area from 145 to 71 m 2 g −1 respectively. The samples were anatase-rich (up to 98 wt.%) and of increasing rutile fraction, when the primary TiO 2 particles exceeded the critical size of d c ≈ 11.6 nm. Degradation rate of aliphatic dichloroacetic acid (DCA) and aromatic 4-chlorophenol (4-CP), used as model pollutants for evaluation of photocatalytic activity, was higher for diffusion flame aerosol powders than for commercial pyrogenic TiO 2 products, P25 and P90, Evonik, of comparable sizes and anatase fractions. This effect was attributed to a lower degree of agglomeration resulting in a higher specific surface area. Photocatalytic activity of nanopowders is exclusively coupled with the anatase fraction. A beneficial effect due to accompanying rutile was not detected. The photocatalytic efficiency of nanopowders was found to decrease strongly with increase in average particle sizes larger than d c but was not positively affected by d lower than d c .