Facile Synthetic Route to a Nitrogen-doped Titanium Oxide with Enhanced Photoelectrochemical Property via Proton Beam Irradiation

A layered titanate with a light harvesting property only in a UV region was irradiated with a proton beam in the presence of nitrogen source like ammonium cation, in order to modify its band gap from UV to visible region. According to X-ray diffraction and X-ray absorption spectroscopy results, a protonic titanate maintains its lamellar structure even after proton beam bombardment, showing that the crystal structure of layered titanate was preserved even after the ammonium adsorption and successive proton beam irradiation for nitrogen doping. However, UV–vis and X-ray photoelectron spectra clearly show that the proton beam irradiation could provide enough energy to introduce ~0.5 at. % of nitrogen atoms into the titanium oxide for absorbing not only UV but also visible light. Photocurrent measurement clearly reveals that the nitrogen-doped titanium oxide via the proton beam treatment shows highly enhanced photocurrent in comparison with that of the bare titanium oxide, suggesting that the proton beam irradiation could be a potential method for band gap engineering of a wide variety of semiconducting materials.