Azo dyes decomposition on new nitrogen-modified anatase TiO2 with high adsorptivity

New vis active photocatalyst was obtained by the modification of commercial anatase TiO2 (Police, Poland) in pressure reactor in an ammonia water atmosphere at 100 °C for 4 h. The photocatalytic activity of new material was tested during three azo dyes decomposition: monoazo (Reactive Read), diazo (Reactive Black) and poliazodye (Direct Green). Obtained photocatalyst had new bands at 1430-1440 cm−1 attributed to the bending vibrations of NH4+ and at 1535 cm−1 associated with NH2 groups or NO2 and NO. UV-vis/DR spectra of photocatalyst had also insignificant decrease in visible region. Fluorescence technique was used for studying the amount of hydroxyl radicals produced on TiO2 surface during visible light irradiation. The hydroxyl radicals produced react with coumarin present in the solution to form 7-hydroxycoumarin which has fluorescent capacity. Photocatalytic activity of modified TiO2 was compared with commercial titanium dioxide P25 (Degussa, Germany). The photocatalytic activity of TiO2/N was higher than that of unmodified material and P25 under visible light irradiation. The ability for dye adsorption (Reactive Red) on photocatalyst surface was also tested. Unmodified TiO2 and P25 has isotherm of adsorption by Freundlich model, and nitrogen-modified TiO2 by Langmuir model. The presence of nitrogen at the surface of TiO2 significantly increased adsorption capacity of TiO2 as well as OH radicals formation under visible radiation.