Effect of the electronic state of Ti on M-doped TiO2 nanoparticles (M=Zn, Ga or Ge) with high photocatalytic activities: A experimental and DFT molecular study

In the pursuit of environmental sustainability, nanomaterials with specific characteristics that can improve the environment by various methods have been developed. In this work, M-doped TiO2 microspheres have been synthesized by a colloidal route and doped with 1% in wt. of M (M=Zn, Ga and Ge). The materials were calcined at 400 °C and they were characterized by means X-ray diffraction (XRD) analysis, UV-vis spectroscopy coupled with diffuse reflectance spectroscopy (DRS), N2 physisorption, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The catalytic activity of the materials was studied by evaluating the photocatalytic degradation of 2,4-dichlorophenoxyacetic acid in an aqueous solution. Moreover the photocatalytic activity of the doped materials were enhanced compared to pristine material, according the next trend:Ge:TiO2 >Ga:TiO2 >Zn:TiO2>TiO2. The presence of atoms of Zn, Ga or Ge in the structure of TiO2 was shown by XPS analysis, indeed these results reveal a diminution of the energy levels of the 2p3/2 and 2p1/2 electrons from doped materials compared with pristine material, which is evidence for a strong relationship between the doped cation valence of the TiO2 and the degradation of the 2,4-dichlorophenoxyacetic acid. Theoretical calculations within DFT framework were performed on two models of nanoparticles like-anatase in order to interpret the photocatalytic activity obtained experimentally by means the frontier orbitals (HOMO and LUMO), the morphology and electronic distribution.