Decomposition of nonionic surfactant on a nitrogen-doped photocatalyst under visible-light irradiation

A visible-light-active N-containing TiO2 photocatalysts were prepared from crude amorphous titanium dioxide by heating amorphous TiO2 in gaseous NH3 atmosphere. The calcination temperatures ranged from 200 to 1000 °C, respectively. UV-vis/DR spectra indicated that the N-doped catalysts prepared at temperatures <400 °C absorbed only UV light (Eg = 3.3 eV), whereas samples prepared at temperatures ≥400 °C absorbed both, UV (Eg = 3.10-3.31 eV) and vis (Eg = 2.54-2.66 eV) light. The chemical structure of the modified photocatalysts was investigated using FT-IR/DRS spectroscopy. All the spectra exhibited bands indicating nitrogen presence in the catalysts structure. The photocatalytic activity of the investigated catalysts was determined on a basis of a decomposition rate of nonionic surfactant (polyoxyethylenenonylphenol ether, Rokafenol N9). The most photoactive catalysts were those calcinated at 300, 500 and 600 °C. For the catalysts heated at temperatures of 500 and 600 °C Rokafenol N9 removal was equal to 61 and 60%, whereas TOC removal amounted to 40 and 35%, respectively. In case of the catalyst calcinated at 300 °C surfactant was degraded by 54% and TOC was removed by 35%. The phase composition of the most active photocatalysts was as follows: (a) catalyst calcinated at 300 °C-49.1% of amorphous TiO2, 47.4% of anatase and 3.5% of rutile; (b) catalyst calcinated at 500 °C-7.1% of amorphous TiO2, 89.4% of anatase and 3.5% of rutile; (c) catalyst calcinated at 600 °C-94.2% of anatase and 5.8% of rutile.