ESR study on the visible photocatalytic mechanism of nitrogen-doped novel TiO2 Synergistic effect of two kinds of oxygen vacancies

The visible photocatalytic mechanism of nitrogen-doped novel TiO2 was studied by means of electron spin resonance spectroscopy (ESR). It was found that, under visible light irradiation, the concentration of single-electron-trapped oxygen vacancy (SETOV, V-o(center dot)) of novel TiO2 remained unchanged, but that of nitrogen-doped novel TiO2 increased and returned to original state when the light was turned off. This implies that, aside from V-o(center dot) in bulk of nitrogen-doped novel TiO2, oxygen vacancy without trapped electron (V-o(center dot center dot)) was formed on its surface. V-o(center dot center dot) as a surface electron trap captured photogenerated electron from the bulk to generate extra V-o(center dot), carrying out photocatalytic reaction on the surface. At the same time, nitrogen doping product NO was chemically adsorbed on the vicinity of V-o(center dot center dot) and inhibited the attack of oxygen, allowing V-o(center dot center dot) to remain stable in air. The synergistic action of the two kinds of active structures, i.e., bulk V-o(center dot)-NO-Ti and surface V-o(center dot center dot)-NO-Ti, accounted for the visible photocatalytic activity of N-doped novel TiO2. (C) 2011 Elsevier Inc. All rights reserved.