Quantitative relation between photocatalytic activity and degree of < 001 > orientation for anatase TiO2 thin films

We demonstrate a quantitative relation between exposed crystal surfaces and photocatalytic activity of nanocrystalline anatase TiO2. Thin films with controlled amount of < 001 > preferential orientation were prepared by reactive DC magnetron sputtering in Ar/O-2 atmosphere with the partial O-2 pressure as control parameter. The samples were characterized with X-ray diffraction, transmission electron microscopy and atomic force microscopy, from which the degree of preferential < 001 > orientation and exposed facets were determined by an extension of the March-Dollase model. Photocatalytic degradation of methylene blue dye shows that the photocatalytic reaction rate increases approximately with the square of the fraction of < 001 > oriented surfaces, with about eight times higher rate on the {001} surfaces, than on {101}, thus quantifying the effect of crystal facet abundancy on the photocatalytic activity of anatase TiO2.