TiO sub(2) Anatase with a Bandgap in the Visible Region

TiO sub(2) anatase plays a central role in energy and environmental research. A major bottleneck toward developing artificial photosynthesis with TiO sub(2) is that it only absorbs ultraviolet light, owing to its large bandgap of 3.2 eV. If one could reduce the bandgap of anatase to the visible region, TiO sub(2)-based photocatalysis could become a competitive clean energy source. Here, using scanning tunneling microscopy and spectroscopy in conjunction with density functional theory calculations, we report the discovery of a highly reactive titanium-terminated anatase surface with a reduced bandgap of less than 2 eV, stretching into the red portion of the solar spectrum. By tuning the surface preparation conditions, we can reversibly switch between the standard anatase surface and the newly discovered low bandgap surface phase. The identification of a TiO sub(2) anatase surface phase with a bandgap in the visible and high chemical reactivity has important implications for solar energy conversion, photocatalysis, and artificial photosynthesis. Keywords: Photocatalysis; TiO sub(2) anatase; titanium-terminated surface phase; bandgap reduction to the visible; scanning tunneling microscopy and spectroscopy; density functional theory