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 m2/g for the bare TiO2 solid to 71–137 m2/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 Eg 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.