Photodegradation of the herbicide 2,4-dichlorophenoxyacetic acid on nanocrystalline TiO2-CeO2 sol-gel catalysts

Nanocrystalline TiO2-CeO2 mixed oxides with different CeO2 contents have been prepared by the sol-gel method. On the samples calcined at 673 K the specific surface areas, crystalline structures, optical absorption spectra and photocatalytic activity for the 2-dichlorophenoxyacetic acid degradation were determined. An important effect on the specific surface area as a function of the cerium oxide content was found; the BET areas increased from 73 m(2)/g, for the bare TiO2 catalyst, to 174 m(2)/g on the catalysts containing 10 wt.% CeO2. A continuous diminution in the energy of the E, band gap, which varied from 3.14 eV, for TiO2, to 2.47 eV for the catalysts with the highest cerium oxide content, was observed. The XRD Rietveld refinement showed that the number of the calculated [V-Ti4+(+)] deficiencies diminished as the cerium oxide content increased. A strong dependence on the nanostructured crystallite size (8.4-33 nm) and the capacity for the herbicide photocatalytic degradation was observed. The highest activity corresponded to that of the catalysts with the smallest crystallite size. (C) 2007 Elsevier B.V. All rights reserved.