Ce-doped TiO2 for photocatalytic degradation of chlorophenol

Visible-light photoactive Ce-doped TiO2 catalysts are prepared by solvothermolysis, characterized by several techniques (DRIFT, DR UV–vis, XRD and HRTEM/SAED/EDXS) and tested in the degradation of 4-chlorophenol. TiO2 materials are modified with low amounts of cerium to extend its absorption spectrum into the visible region. The presence of cerium, in an excess of 0.6% (w/w), is found to inhibit the transition from amorphous to crystalline phase during calcination at 400 °C. The observed photocatalytic activity is strongly dependent on both visible-light response and structure of the material. Cerium has a positive effect in preventing electron–hole recombination only when the crystalline structure is maintained. Compared with the commercial P-25 TiO2 catalyst, the activity observed at the initial period of the reaction is higher for the prepared Ce-doped material. However, in the case of the latter catalyst, activity decreases after 15 min in an experiment carried out at natural pH (5.8). This decrease in activity is not observed for a higher pH value (10) and seems to be related with catalyst deactivation due to removal of ceria from the surface. Finally, in the case of Ce-doped TiO2 materials, the main intermediates of degradation are hydroquinone and benzoquinone, while with P-25 the main intermediate is 4-chlorocatechol, suggesting that different reaction mechanisms may take place depending on the nature of the catalyst.