The role of crystal phase in determining photocatalytic activity of nitrogen doped TiO2

Two series of nitrogen doped TiO2 samples with different ratios of anatase to rutile phases were prepared by milling the mixture of P25 TiO2 and C6H12N4 in air and gaseous NH3 atmosphere, respectively. Compared to air, NH3 atmosphere plays an important role in delaying the crystallite transformation from anatase to rutile in the mechanochemical reaction of TiO2 and C6H12N4. In contrast to the previously reported results for pure TiO2, it is found that nitrogen doped TiO2 with higher content of rutile phase demonstrates higher photocatalytic activity in photodegrading pollutant Rhodamine B under both UV light and visible light irradiation (λ>420 nmλ>420 nm), and the amount of the surface-adsorbed water and hydroxyl groups on nitrogen doped TiO2 have little correlations with their crystallite phases (anatase or rutile) and photocatalytic activity. The more abundant surface states characterized by photoluminescence spectroscopy together with the lowered valence band maximum of rutile TiO2 by nitrogen doping are considered as the key factors for the higher activity of nitrogen doped TiO2 with higher content of rutile phase.

A favorable surface structure of nitrogen doped TiO2 facilitating surface transfer of carriers, i.e. with abundant surface states, can be more important in determining photocatalytic activity of nitrogen doped TiO2. Abundant surface adsorbed water and hydroxyl groups can be advantageous only if such favorable surface structure exists in the photocatalyst.Figure optionsDownload as PowerPoint slide