Degradation of the herbicide 2,4-dichlorophenoxyacetic acid over Au/TiO2-CeO2 photocatalysts: Effect of the CeO2 content on the photoactivity

Au/TiO2-CeO2 photocatalysts were studied in the photodegradation of the 2,4-dichlorophenoxyacetic acid (2,4-D) in aqueous medium under UV light emission source. The TiO2-CeO2 supports (2.5-10 wt.% CeO2) were prepared by the sol-gel method using titanium alkoxide and cerium nitrate as starting precursors. Gold nanoparticles were prepared by the deposition-precipitation method with urea and deposed on the supports to obtain Au/TiO2-CeO2 photocatalysts. The BET area increases as function of the CeO2 content from 64 m(2)/g for the bare TiO2 solid to 71-137 m(2)/g for the TiO2-CeO2 mixed oxides. TEM and HRTEM images showed Au nanoparticles ranking from 8.1 to 3.4 nm. Additionally well defined gold plasmon and a red shift in the E-g band gap energy (3.14-2.47 eV) was observed by UV-vis spectroscopy on the mixed oxides. For the photodegradation of 2,4-D it has been observed an important effect of cerium oxide in the photoactivity, it varies from 78 to 99% of 2,4-D conversion and from 61 to 88% of total organic carbon conversion for the Au/TiO2 and Au/TiO2-CeO2 photocatalysts respectively. A synergetic effect where gold plays the role of electrons tramp and the cerium oxide the role of oxidizing agent is proposed. (C) 2010 Elsevier B. V. All rights reserved.