Visible light-active nitrogen-doped TiO2 thin films prepared by DC magnetron sputtering used as a photocatalyst

The visible light-active nitrogen-doped TiO2 has been prepared by dc-reactive magnetron sputtering using Ti target in an Ar+O2/N gas mixture. The preparation of highly crystallized anatase TiOxNy thin films with various nitrogen concentrations allowed us to identify the optimum nitrogen flow ratio for the photocatalytic oxidation (PCO) of 2-propanol. At higher nitrogen flow rate, nitrogen is found to be difficult to substitute for oxygen having been predicted to contribute the band gap narrowing, giving rise to undesired deep level defects. In addition, Raman spectroscopy and X-ray diffraction (XRD) studies revealed that highly crystallized anatase growth of nitrogen-doped TiOxNy thin films are difficult at higher nitrogen flow rate. The optical band gap was found to be lower for the films deposited at 2 sccm of nitrogen flow rate. The PCO of 2-propanol was studied as a function of nitrogen flow rate using in situ FTIR spectroscopy. The PCO of 2-propanol found to proceed along two routes: one was through the chemisorbed species, 2-propoxide to form the CO2 directly; the other was through conversion of 2-propanol to acetone, followed by formation of formate species, and finally CO2.