Enhanced photocatalytic activity of TiO2−xNx loaded with copper ions under visible light irradiation

Nitrogen-doped TiO2 (TiO2−xNx) photocatalysts loaded with various transition metal ions, including Cu, Pt, Ni, Zn and La, were prepared using a wet impregnation method. Photocatalytic activity of the catalysts under visible light irradiation (λ > 410 nm) for acetaldehyde oxidation was examined. As a result, it was found that photocatalytic activity over TiO2−xNx (concentration of nitrogen was found to be ∼0.25 at.%) was markedly enhanced by Cu or Pt loading, while Ni, Zn or La loaded TiO2−xNx showed similar photodegradation rate to the bare TiO2−xNx. Among them, the enhancement effect of Cu ion was found highest. The optimum concentration of Cu was found to be 0.5 wt%, and X-ray photoelectron spectroscopy (XPS) and X-ray induced Auger electron spectroscopy (XAES) analyses suggested the presence of Cu2O or Cu hydroxides on the catalyst surface. In terms of the long-term stability of the catalysts, it was confirmed that more than 2100 μmol of CO2 was produced when acetaldehyde was continuously photooxidized over 1100 μmol of Cu loaded TiO2−xNx under visible light for 100 consecutive days (>410 nm, 0.9 mW/cm2, in a 1 L vessel).