Degradation of the herbicide 2,4-dichlorophenoxyacetic acid over TiO2-CeO2 sol-gel photocatalysts: Effect of the annealing temperature on the photoactivity

TiO2-CeO2 mixed oxides were synthesized by the sol-gel method and calcined at 473, 673 and 873 K. The preparation method enabled us to obtain TiO2-CeO2 mixed oxides with specific surface areas of 250, 174 and 99 m2/g. An important effect of the thermal treatment on the band gap of the TiO2-CeO2 mixed oxides was observed. The Eg band gap shifts from 3.1 to 3.2 eV, for the TiO2 bare catalysts, to 2.3-2.5 eV on the annealed mixed oxides. The X-ray Rietveld refinement shows that the calculated titanium deficiency diminishes as the annealing temperature of the mixed oxides is increased. A relationship between the titanium deficiency per unit cell (from 44.8 to 20.0%) the Eg band gap (2.3-2.5 eV) and the capacity for the herbicide photodegradation (from 85.6 to 94.5%) was observed.