Influence of the Dopant Concentration on the Photocatalytic Activity: AI-Doped TiO2

A set of Al-doped titania x-Al-TiO2, (x = 0.0, 0.1, 0.3, 0.5, 0.7, 0.9, 1.1 wt % Al) has been synthesized by a sol gel method and tested in the reaction of the photocatalytic degradation of phenol in aqueous suspension. XRD and Raman studies show that the TiO2 samples have a mixed-phase rutile-anatase crystalline structure with linear increase of the anatase fraction from 0.0 wt % for 0.0-Al-TiO2 up to 18 wt % for 1.1-Al-TiO2. A decrease of the particle size from 800 to 50 nm and an increase of the specific surface area from 1.7 m(2)/g up to 28 m2/g with increased content of Al have been observed. The data of XRD, XPS, Raman spectroscopy, and EDS techniques show rather homogeneous aluminum distribution with only the Al(3+) oxidation state of aluminum incorporated in the TiO2 lattice. The bandgap energy E-g = (2.93 +/- 0.1) eV corresponding to indirect allowed transitions does not depend on the aluminum content within the 0.0-1.1 wt % Al concentration range. The photocatalytic testing of Al-doped TiO2 samples in the reaction of phenol degradation shows the existence of a maximal initial rate of phenol degradation at an Al concentration of about 0.5 wt %.