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

A set of Al-doped titania x -Al-TiO 2 ( 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 TiO 2 samples have a mixed-phase rutile-anatase crystalline structure with linear increase of the anatase fraction from 0.0 wt % for 0.0-Al-TiO 2 up to 18 wt % for 1.1-Al-TiO 2 . 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 m 2 /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 TiO 2 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 TiO 2 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 %.