Structure and reactivity of highly reduced titanium oxide surface layers on TiO₂: A first-principles study

Area of Science:

• Materials Science
• Surface Science
• Computational Chemistry

Background:

• Reduced titanium oxide (TiO_x) films on TiO₂ are promising for photocatalysis and electronic devices.
• Understanding the structure and properties of TiO_x/TiO₂ interfaces is crucial for optimizing performance.
• The behavior of these interfaces in aqueous environments is particularly important for photocatalytic applications.

Purpose of the Study:

• To investigate the structure and properties of titanium monoxide (TiO) layers on anatase TiO₂ (001).
• To analyze the interface between TiO/TiO₂ and liquid water using first-principles calculations.
• To understand the implications of TiO layer formation on TiO₂ properties and stability.

Main Methods:

• First-principles calculations were employed to study the epitaxial growth of TiO on anatase TiO₂ (001).
• The electronic properties, including work function and surface conductivity, were calculated.
• First-principles molecular dynamics simulations were used to examine the TiO/water and TiO₂/water interfaces.

Main Results:

• Epitaxial growth of TiO on anatase TiO₂ (001) is limited to a single layer; subsequent growth forms islands.
• TiO layers reduce the work function and increase surface conductivity of TiO₂, potentially enhancing photocatalysis.
• The TiO/TiO₂ interface is thermodynamically unstable in humid/aqueous environments, leading to partial reoxidation.
• A dense, tightly packed first water layer forms on the TiO surface, unlike the multilayer structure on anatase.

Conclusions:

• A single layer of TiO on anatase TiO₂ (001) offers beneficial electronic properties for photocatalysis but lacks stability.
• The observed dense water layer on TiO suggests a pathway for surface reoxidation in aqueous conditions.
• These findings provide insights into the design and stability of reduced titanium oxide structures for advanced applications.