The effect of Co dopant on TiO2 structure of sol–gel nanopowders used as photocatalysts

Abstract

Un-doped and Co-doped sol–gel TiO2 nanopowders have been prepared and structurally characterized. Three Co mass concentrations related to TiO2 content have been used: 0.5, 1 and 2wt%. The morpho-structural changes due to the thermal treatment and dopant presence were followed by: thermal analysis methods, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and magnetic measurements. A detailed XRD analysis, based on an own calculus program, has established the lattice constants, the average size of the crystallites, <D>, and the average lattice strains, <S>, which can give some information about the structural disorder. The values of the lattice constants lead to the conclusion that a solid solution of the CoxTi1−xO2 form was obtained. The Co concentration imprints the paramagnetic behavior to the solid solutions. It influences the evolution of the <D> and <S> factors by the competition between: the deficit of oxygen acquired by un-doped TiO2 in the sol–gel process (influenced by temperature), the dopant diffusion in the host lattice (influenced by ionic radius and valence) and the super-exchange interactions between the magnetic moments of the molecules of the solid solution (influenced by the concentration of Co). The sample with 1wt% Co thermally treated at 400°C ensures the best photocatalytic activity in the advanced degradation of nitrobenzene from water.