Preparation, characterization, and photocatalytic activity under UV and visible light of Co, Mn, and Ni mono-doped and (P,Mo) and (P,W) co-doped TiO2 nanoparticles: a comparative study.

In this work, TiO2-based nanomaterials have been successfully synthesized by doping TiO2 with Co, Mn, and Ni and by co-doping it with (P,Mo) or (P,W). The structural, optical, and morphological properties of the synthesized nanomaterials have been investigated using various techniques such as XRD, FTIR spectroscopy, UV-vis diffuse reflectance spectroscopy, XPS, and SEM-EDS. The obtained results showed that the crystalline structure of the doped TiO2-based nanomaterials depends strongly on the nature of the doping ions. The obtained band gap energy of TiO2 co-doped with (P,Mo) changes to a level below the band gap energy of TiO2 anatase indicating a high ability to absorb visible light. The obtained photocatalytic activity results of methyl orange degradation showed that, under visible light, the mono-doping of TiO2 with Co and its co-doping with (P,Mo) or (P,W) improve significantly the photocatalytic activity of TiO2 in comparison with undoped TiO2. The activity order obtained under UV-A irradiation for the used photocatalysts is TiO2 > > 1%Ni-TiO2 > 1%Co-TiO2 > 30%(P,Mo)-TiO2 ≈ 30%(P,W)TiO2 > 1%Mn-TiO2 while under visible light, it is 1%Co-TiO2 > 30%(P,Mo)-TiO2 > 30%(P,W)TiO2 ≈ TiO2 > 1%Ni-TiO2 > 1%Mn-TiO2. The high photocatalytic activity observed for these samples could be the result of a synergetic effect of the high visible light absorption capacity and the low recombination rate of photoexcited electrons and holes.