Tailoring TiO2 finite nanotubes: Doping-induced modulation of electronic, optical, and hydrogen storage properties

Abstract

In this study, we employ density functional theory calculations to investigate the properties of finite single walled TiO2 finite nanotubes (TiO2NTs). The constructed nanotubes demonstrate geometric stability, as evidenced by positive binding energy and real positive vibrational frequencies obtained from the infrared spectra. Substitutional doping with various atoms (B, N, C, Si, Li, Sc, Fe, and Cu) introduces intriguing effects on the electronic and optical properties of TiO2NTs. Doping with Fe slightly reduces the wide energy gap (∼5 eV) of unmodified TiO2NTs to 4.2 eV, while Si doping significantly decreases the energy gap by half. Furthermore, we investigate the impact of doping TiO2NTs with boron, carbon, nitrogen, iron, cesium, and silicon on their UV–Vis absorption spectra. The introduction of these dopants induces significant redshifts in the absorption peaks, indicating alterations in the electronic energy gap and transitions between specific states. These findings provide valuable insights into the structural and electronic modifications of TiO2NTs. Moreover, we explore the adsorption properties of TiO2NTs for H2 molecules. While unmodified TiO2NTs exhibit low adsorption energy, doping with a small number of C or Si atoms leads to a substantial enhancement in the adsorption energy. Specifically, Si doping achieves adsorption energy of approximately 0.2 eV, accompanied by a hydrogen storage capacity of 6.1 wt%, exceeding the standard capacity of 6.0 wt%. Importantly, the desorption temperature remains comparable to room temperature, ensuring long-term recyclability. These results highlight the potential of doped single-walled TiO2 nanotubes as efficient hydrogen storage devices.