Articles

Among the great number of sol–gel prepared nanomaterials, TiO2 has attracted significant interest due to its high photocatalytic activity, excellent functionality, thermal stability and non-toxicity. The photocatalytic degradation of pollutants using un-doped and doped TiO2 nanopowders or thin films is very attractive for applications in environmental protection, as a possible solution for water purification. The present work describes a comparative structural and chemical study of un-doped TiO2 and the corresponding S- and Ag-doped materials. The photocatalytic activity was established by testing the degradation of organic chloride compounds from aqueous solutions. Sol–gel Ag-doped TiO2 coatings, prepared by co-gelation and sol–gel Ag-doped TiO2 coatings obtained from nanopowders were also compared. Their structural evolution and crystallization behaviour (lattice parameters, crystallite sizes, internal strains) with thermal treatment were followed by thermal analysis, X-ray diffraction, transmission electron microscopy, atomic force microscopy and specific surface areas measurements. X-ray photoelectron spectroscopy analyses were performed to characterize the surface composition and S or Ag speciation, which was used to interpret the catalytic data.

Sol–gel processing is one of the most common methods to produce TiO2 photocatalysts in both forms of coatings and gels. The electrons and holes photogenerated in the TiO2 photocatalyst have strong reduction and oxidation power, being able to drive a variety of reactions. This property allows the efficient decomposition of air and water pollutants. The photocatalytic degradation of pollutants using TiO2 photocatalysts is very attractive for applications to environmental protection, as a possible alternative to conventional water treatment technologies. Impurity doping is one of the typical approaches to extend the spectral response of a wide band gap semiconductor to visible light. In the present work pure and S-doped TiO2 nanometer films prepared by the alkoxide route of the sol–gel process have been studied. The influence of dopant, number of coatings and thermal treatment on the films structure was determined. One had in view the structural evaluation and crystallization behavior with thermal treatment by DTA/TG analysis, FTIR, spectroellipsometry (SE) and XRD. The sol–gel films were tested for the degradation of chloride organic compounds from aqueous solution. The photocatalytic activity was improved due to S-addition. A chlorobenzene removal yield of 97% has been obtained.