Abstract
The structural, electronic, and optical properties of metal (Si, Ge, Sn, and Pb) mono‐ and co‐doped anatase TiO2 nanotubes are investigated, to elucidate their potential for photocatalytic applications. It is found that Si‐doped TiO2 nanotubes are more stable than those doped with Ge, Sn, or Pb. All dopants lower the bandgap, except the (Ge, Sn) co‐doped structure, the decrease depending on the concentration and the type of dopant. Correspondingly, a redshift in the optical properties for all kinds of dopings is obtained. Even though a Pb mono‐ and co‐doped TiO2 nanotube has the lowest bandgap, these systems are not suitable for water splitting, due to the location of the conduction band edges, in contrast to Si, Ge, and Sn mono‐doped TiO2 nanotubes. On the other hand, co‐doping of TiO2 does not improve its photocatalytic properties. The findings are consistent with recent experiments, which show an enhancement of light absorption for Si‐ and Sn‐doped TiO2 nanotubes.
Highlights
Its photosensitivity for visible light is a mono- and co-doped anatase TiO2 nanotubes are investigated, to elucidate their potential for photocatalytic applications
We investigate the effect of the mono-dopants (Si, Ge, Sn, and Pb) on the structure and stability of anatase phase (8,0) titania nanotubes (TNTs) (Section 2)
For mono-dopants, Pb-doped TNTs have the lowest bandgap at the studied concentrations (1% to 3%) due to the presence of distinct Pb states below the conduction band
Summary
The total number of the atoms in the unit cell of a TNT is related to the number of atoms in one unit cell (48 atoms) in the surface layer. From this point of view, Ge- and Sn-doped TNTs are “out of order,” which can be related to the effect of electronegativity on the ionic radius, implying that the formation of Sn–O bonds is more favorable than Ge–O bonds This behavior of formation energies and bond lengths is very similar to the behavior of the corresponding dopant in bulk TiO2.[43]. Where EMÀTiO2 and ETiO2 are the total energies of the metal-doped TiO2 and the pristine TNT, respectively, whereas μTi and μM denote the chemical potentials for Ti and the dopant; the latter is assumed to be equal to the energy of one atom in its corresponding bulk structure. One note that the formation energy of Si is smaller than that of the other dopants, corresponding to the fact that Si has the smallest
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