Enhancement of photocatalytic activity of nano TiO2 by doping with nitrogen and its stain removal properties

Abstract

Nano Titanium dioxide is widely studied as a photocatalyst under UV light. But its wide band gap and recombination of electrons and holes, reduce the photocatalytic efficiency. Wide band gap limits the photocatalytic activity to ultra violet radiation. There are metal-TiO2 core shell nano structures which reduces the electron hole recombination. In order to utilize the wider range from solar radiation nano TiO2 can be doped with metal or non-metal elements. Transition metal doping of TiO2 has strongly localized states within the band gap which causes thermal instabilities and formation of carrier recombination centers. Therefore doping TiO2 with non metal elements has been proved as a better structure to enhance the photocatalytic efficiency.

When introducing Nitrogen to nano TiO2, oxygen atoms are substituted with nitrogen atoms. Hybridization of N 2p states with the O 2p state derived valence band is supposed to achieve a band gap narrowing. Therefore it is possible for the N-doped TiO2 to absorb energy from visible light and act as a photocatalyst. In this paper N-doped TiO2 was synthesized by addition of ammonia water. Synthesized particles were characterized with X-ray diffraction techniques and it was observed that obtained TiO2 was in anatase form. UV-visible spectra showed nano TiO2 absorbs in the UV region between 240 nm to 350 nm range and the absorption of N- TiO2 has been shifted to the visible region (340 nm to 530 nm). Photocatalytic action of N- TiO2 was compared with anatase nano TiO2 (bought commercially from Sigma-aldrich) by analyzing the colour reduction of Methylene blue under sunlight. UV-Vis analysis of this system proved that the photocatalytic activity of N-TiO2 is greater than nano TiO2 under sunlight. Also UV-Visible analysis showed that N - TiO2 in dispersion form has higher stain removal properties than the nano TiO2 dispersion (bought commercially from Sigma-Aldrich) for stained fabrics under sunlight.