Visible light absorption ability and photocatalytic oxidation activity of various interstitial N-doped TiO2 prepared from different nitrogen dopants

Nitrogen-doped TiO2 was developed to enable photocatalytic reactions using the visible range of the solar spectrum. This work reports on the synthesis, characterisation and kinetic study of interstitial N-doped TiO2 prepared by the sol–gel method using three different types of nitrogen dopants: diethanolamine, triethylamine and urea. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy and UV–visible spectroscopy were used to analyse the titania. Different interstitial N-doped TiO2 properties, such as absorption ability in the UV–visible light region, redshift in adsorption edge, good crystallisation and composition ratio of titania structures (anatase and rutile) could be obtained from different nitrogen dopants. Amongst investigated nitrogen precursors, diethanolamine provided the highest visible light absorption ability of interstitial N-doped TiO2 with the smallest energy bandgap and the smallest anatase crystal size, resulting in the highest efficiency in 2-chlorophenol degradation. The photocatalytic activity of all N-doped TiO2 can be arranged in the following order: TiO2/diethanolamine > TiO2/triethylamine > TiO2/urea > un-doped TiO2. The initial rate of 2-chlorophenol degradation using the interstitial N-doped TiO2 with diethanolamine was 0.59 mg/L-min and the kinetic constant was 2.34 × 10−2 min−1 with a half-life of 98 min. In all cases, hydroquinone was detected as a major intermediate in the degradation of 2-chlorophenol.