The effects of Fe, Co and Ni dopants on TiO2 structure of sol–gel nanopowders used as photocatalysts for environmental protection: A comparative study

This paper highlights the effects of iron, cobalt and nickel dopants on the structure and photocatalytic properties of the sol–gel TiO2 nanopowders and performs a comparative study of their behavior. Undoped TiO2 and 0.5, 1 and 2 wt% Fe, Co and/or Ni-doped TiO2 nanopowders have been prepared. The compositions with 0.5 wt% dopant were selected for this study considering that the best results have been obtained using iron dopant with this concentration. A detailed XRD analysis, based on an own calculus program, has established the lattice parameters, the average size of the crystallites (D), the unit cell volume (UCV) and the average lattice strains (S), which can give some information about the structural disorder. The structural changes due to the thermal treatment and the type of the dopant were established. The dopants addition is responsible for supplementary defects in the crystalline lattice. Besides the mobile single point defects due to the thermal treatment, the dopants induce the paramagnetic ones. The increase of temperature does not significantly influence the unit cell volume (UCV). This fact could be considered as a proof of the acceptance of the dopant by the anatase lattice, where MexTi1–xO2–δ type solid solutions are formed. The variation of the (D) and (S) values with temperature, calculated for both undoped and doped TiO2 samples indicates the fact that the highest disorder state was found at 400 °C. The photocatalytic activity of the prepared nanopowders has been tested in the degradation of nitrobenzene from water. The sample with 0.5 wt% Fe dopant concentration thermally treated at 400 °C presented the best photocatalytic activity.