Wavelength-dependent photostimulated adsorption of molecular O2 and H2 on second generation titania photocatalysts: The case of the visible-light-active N-doped TiO2 system

The wavelength-dependence of photostimulated adsorption of O2 and H2 on visible-light-active N-doped TiO2 has been examined in the intrinsic (λ < 387 nm) and in the N-doping induced extrinsic absorption range (λ > 387 nm). Rates of photoadsorption scaled linearly with photon flow ρ at 4 Pa at four selected wavelengths from 300 to 550 nm, but were independent of gas pressure and correspond to rates of photogeneration of surface-active centers. The spectral dependence of quantum yields Φ of surface photoprocesses displayed multi-band-like structural features in both the intrinsic and extrinsic regions ascribed to the existence of three (and perhaps four) different types of defect states, confirming the absorption edge red-shift in N-doped TiO2 to be due to electronic excitation of intragap localized states that leads to the photogeneration of electrons and/or holes.