Electronic Origin of Enhanced Photocatalytic Activity at the Anatase/Rutile Boundary: A Case of Acetic Acid on the TiO₂ Surface

The photocatalytic activity of titanium dioxide (TiO2) was investigated with a particular focus on the band-bending profile at the anatase/rutile (A/R) boundary. Various microfocused X-ray spectroscopic techniques were employed, including X-ray photoemission and absorption spectroscopies, as well as X-ray photoemission electron microscopy. The photocatalytic degradation of acetic acid adsorbed on a biphasic TiO2 surface was monitored both with and without ultraviolet irradiation. The study found that the photocatalytic activity at the A/R boundary was higher compared to that of either the anatase or the rutile monophase. Additionally, the bending profiles of both the valence and conduction bands across the A/R boundary were experimentally determined. Notably, a steep potential gradient of more than 1 eV/μm at the boundary was revealed for the first time, which is likely responsible for the observed enhancement in photocatalytic activity.