Structural modifications in Au/Al2O3–CeO2 mixed oxides as a function of Ce4+ content and its effects in the mineralization of the herbicide diuron

Nanocrystalline Au/Al2O3–CeO2 photocatalysts with different CeO2 contents were prepared by the sol–gel method. Gold was deposited by a deposition–precipitation approach. Nitrogen adsorption, X-ray diffraction, Rietveld refinement, radial distribution functions, UV–vis spectroscopy (diffuse reflectance), FT-IR and transmission electron microscopy (TEM) techniques were used for the characterization of the synthesized Au/Al2O3–CeO2 samples. The photodegradation of the herbicide diuron (C9H10Cl2N2O) in aqueous media using an UV light emission source was used to evaluate the photocatalytic behavior of these nanomaterials. High specific surface areas (326–124 m2/g) and a band gap in the UV region 3.25–3.15 eV were obtained in these solids. XRD patterns showed that Au/Al2O3–CeO2 mixed oxides contain crystal structures of ceria and γ-alumina. Although, both ceria and γ-alumina are cubic structures, ceria phase is remarkably predominant with respect to the alumina phase. Mineralization of diuron was determined by measuring the total organic carbon (TOC) remaining in the irradiated solution. All the samples, including bare Au/Al2O3 solid, are quite active for the decomposition of the herbicide; however, the analysis of the TOC after 2.5 h in irradiation showed that only photocatalysts containing CeO2 are capable to reach up to 77% of mineralization of the herbicide.