# Cation mono- and co-doped anatase TiO$_2$ nanotubes: An {\em ab initio} investigation of electronic and optical properties

## TL;DR

This study uses ab initio methods to analyze how mono- and co-doping of TiO2 nanotubes with various metals affects their electronic and optical properties, aiming to improve photocatalytic applications.

## Contribution

It provides a comparative analysis of different metal dopants in TiO2 nanotubes, highlighting stability and optical property changes relevant for photocatalysis.

## Key findings

- Si doping enhances stability of TiO2 nanotubes.
- All dopants lower the band gap except Ge, Sn co-doping.
- Pb doping reduces band gap but is unsuitable for water splitting.

## Abstract

The structural, electronic, and optical properties of metal (Si, Ge, Sn, and Pb) mono- and co-doped anatase TiO$_{2}$ nanotubes are investigated, in order to elucidate their potential for photocatalytic applications. It is found that Si doped TiO$_{2}$ nanotubes are more stable than those doped with Ge, Sn, or Pb. All dopants lower the band gap, 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 TiO$_{2}$ nanotube has the lowest band gap, 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 TiO$_{2}$ nanotubes. On the other hand, co-doping of TiO$_{2}$ does not improve its photocatalytic properties. Our findings are consistent with recent experiments which show an enhancement of light absorption for Si and Sn doped TiO$_{2}$ nanotubes.