Dynamics of charge at water-to-semiconductor interface: Case study of wet [0 0 1] anatase TiO2 nanowire

• Dynamics of photoexcitations is computed for TiO2 nanowires in aqueous environment.
• Aqueous TiO2 nanowires gain brighter but short-lived optical transitions.
• Relaxation of electrons (holes) is 2 (4) times faster in water than in vacuum.
• Calculated and experimental absorption/emission spectra correlate well.

The behavior of water molecules on the surfaces of the TiO2 nanowire grown in [0 0 1] direction has been investigated by combining theoretical calculations and experiments. Calculated UV–visible absorption spectra reproduce the main features of the experimental spectra. Computations predict that a photoexcitation followed by a sequence of relaxation events results in photoluminescence across the gap. TiO2 nanowires in vacuum and aqueous environment exhibit different dynamics of photo-excited charge carriers. In water, computed relaxation of electrons (holes) is approximately 2 (4) times faster compared with vacuum environment. Faster relaxation of holes vs. electrons and specific spatial localization of holes result to formation of long lived charge transfer excitation with positive charge at the surface of the nanowire. Comparison of relaxation process in TiO2/water interfaces focusing on different surfaces and nanostructures has potential in identifying structural characteristics of TiO2 materials important for efficient photo-electrochemical water splitting.

Figure optionsDownload high-quality image (105 K)Download as PowerPoint slide