Photoelectrochemical and theoretical investigation of the photocatalytic activity of TiO2 : N

Abstract

Electrochemical and photoelectrochemical techniques have been employed to investigate the electronic energy level modification of N-doped TiO₂ and to elucidate its properties and roles, particularly the electron transfer rate and influence on recombination, in a simple and facile manner. However, the results obtained cannot be easily interpreted and they need comparisons with theoretical calculations. In this study, photoelectrochemical measurements were conducted to investigate the effect of N-doping on TiO₂ nanomaterials, and the results obtained were compared with theoretical calculations. Band-gap values calculated by diffuse reflectance UV-vis spectroscopy were used together with photoelectrochemical measurements of TiO₂ and TiO₂ : N flat-band potentials to create a scheme of the energy-level band edges. In addition, this method confirmed the creation of energetic inter-levels by the N-doping process, as predicted by theoretical calculations. The replacement of an oxygen atom by nitrogen atom in the anatase structure shows a modification of the energetic levels, caused by a shift of the upper energy level; this shift was caused by local structural disorder. From the photoelectrochemical results, it is possible to confirm that the electron concentration in the TiO₂ photoelectrode is higher than that in the TiO₂ : N photoelectrode; due to an increase in the recombination of electrons and holes because of the creation of inter-levels in the TiO₂ : N band-gap. In addition, theoretical analysis indicated a possibility of direct transfer of electrons into the band-gap of TiO₂ : N. This combined approach was useful for interpreting many unclear results with respect to the photocatalytic activity of TiO₂ : N.