A critical evaluation of the mode of incorporation of nitrogen in doped anatase photocatalysts

A range of sol-gel synthesis conditions were used to prepare high surface area N-doped TiO2 in the anatase phase. The N dopant was derived either from NH3 in solution or from NH3 gas bubbled through solution. Bulk N doping levels were determined by an inert gas fusion method and were compared with surface N doping levels determined by X-ray photoelectron spectroscopy. Comparison was also made with the concentration of paramagnetic species measured by electron spin resonance spectroscopy. It was found that both surface and bulk doping levels were typically around 3 orders of magnitude higher than the concentration of paramagnetic N-containing species. All N-doped samples showed higher visible region (lambda > 395 nm) photocatalytic activity than undoped anatase itself. It is argued that catalytic activity is associated with the presence of nitrogen bound to lattice oxygen to give (NO)(O)' which can be photoexcited to give (NO)(O)(x) .