Relation between photocatalytic activity and preparation conditions for nitrogen-doped visible light-driven TiO2 photocatalysts

Nitrogen-doped visible light-driven TiO2 photocatalyst powders were prepared at different temperatures and with different calcination times in a cylindrical tubular furnace under a stream of ammonia gas. Band-gap energy was from 2.92 to 3.04 eV, corresponding to the visible light region. Optical absorbance and the intensities of electron spin resonance (ESR) spectra, which indicate the concentration of doped nitrogen, decreased with temperature and time of calcination in the visible light region, and were also independent of photocatalytic activity. We found that the temperature of preparation (673, 773, and 873 K) and calcination time were important factors governing the photocatalytic reactivity of the N-doped TiO2: the highest photocatalytic activities for samples prepared at 673 and 873 K were observed with calcination times of 5 and 10 min, while that for samples prepared at 773 K was observed with a calcination time of 60 min. Active species at each calcination temperature may be as follows: active species for samples prepared at 673 K for 5 and 10 min may mainly be nitrogen species (NO, NO2, NO2−, NH2, etc.); that for samples prepared at 773 K for 60 min may mainly be doped atomic nitrogen; and that for samples prepared at 873 K for 5 and 10 min may be doped atomic nitrogen and nitrogen species.