The effect of particle shape on the activity of nanocrystalline TiO2 photocatalysts in phenol decomposition

Nanosized TiO2 photocatalysts were synthesized via hydrogen–air flame hydrolysis. X-ray diffraction (XRD) measurements revealed that the TiO2 samples thus prepared consisted mainly of anatase (79–98 wt%) and the rest is rutile. Average particle diameters from TEM measurements were found to vary between 48 and 63 nm. The specific surface area of the samples was found to be practically independent of the synthesis parameters employed (20–32 m2 g−1). Photocatalytic activity of the catalysts was studied by using various model compounds. In spite of their very similar properties, the initial decomposition rate of phenol and methanol showed up to threefold variations within the series of the samples, and it was significantly higher for the best catalyst than that determined for Degussa P25. Our TEM measurements demonstrated that in the less active catalysts the dominant morphology of the particles is spherical, while polyhedral (cubic or hexagonal) shapes predominate in the samples with superior photocatalytic activity. From these observations, we concluded, that the shape of the primary particles (both in the case of our home made ones and in various batches of Degussa P25) strongly influence the photocatalytic activity of titania nanoparticles.