Nitrogen-doped titanium oxide films as visible light photocatalyst by vapor deposition

Nitrogen-doped titanium oxide (TiO2−xNx) films were prepared by ion-assisted electron-beam evaporation, using rutile powder as source material. The films deposited with nitrogen ion bombardment at various nitrogen partial pressures (PPN2), were investigated by X-ray diffraction patterns, Raman, UV–Vis absorption and X-ray photoelectron spectra. Well-crystallized anatase TiO2 was deposited first without the nitrogen ion bombardment. With nitrogen ion bombardment under increasing PPN2, the TiO2−xNx films with the absorption edges red-shifted toward 500 nm were formed. The films are still in anatase phase but possessed substitutional nitrogen atoms and chemisorbed molecular N2. The films exhibited significant photocatalytic and hydrophilic properties under visible light. The films with 1.8 at.% of nitrogen, deposited at PPN2=3.1×10−2 Pa, exhibit the lowest contact-angle of 3° and the best photocatalytic activity on the degradation of methylene-blue with a rate-constant (k) about 0.293 h−1. The series of films exhibit a consistent relationship among structures, red-shift in visible light absorption, and visible light-induced the hydrophilicity and photocatalysis.