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 O-2 and H-2 on visible-light-active N-doped TiO2 has been examined in the intrinsic (lambda < 387 nm) and in the N-doping induced extrinsic absorption range (lambda > 387 nm). Rates of photoadsorption scaled linearly with photon flow rho 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 Phi 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. (c) 2008 Elsevier B.V. All rights reserved.