Influence of N sources on the photocatalytic activity of N-doped TiO2

Influence of nitrogen precursors urea, semicarbazide and N,N’-dimethyl urea on the photocatalytic activity of the N-doped TiO₂ were studied by a simple decomposition method. The nano N-TiO₂ catalysts were synthesized via two different modified approaches by calcination at 500 °C. The synthesized samples were characterized by IR, UV-DRS, Raman, TG-DTA, XRD, EDX, XPS, SEM, TEM and BET analysis. Of the synthesized six samples of N-TiO₂ five samples showed better photocatalytic activity towards direct sunlight photo-degradation of methylene blue (MB) and rhodamine B (RhB) than Degussa P25. The catalysts obtained using semicarbazide samples F3 and F4 having large surface area of 76 and 85.8 m²/g displayed maximum photocatalytic activity. The sample F4 was 1.5 times more active than Degussa P25 for the decolourisation of MB and 1.9 times more active for the decolourisation of RhB. The presence of nitrogen, large surface area and coupling of rutile-anatase phases were found to be the main responsible factors for the enhanced photocatalytic activity. The exclusive formation of the anatase phase in the case of urea precursor is attributed to the slow evaporation of urea due to the formation of melamine derived products. The calcination temperature is the deciding factor responsible for the photocatalytic activity of the N-TiO₂ samples prepared from precursors which can potentially form the melamine and its oligomerized products on the surface of TiO₂.