Sol–gel doped TiO2 nanomaterials: a comparative study

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.