Fotokatalytický rozklad oxidu dusného

Abstract

This doctoral thesis deals with photocatalytic decomposition of N2O, with the use of titanium dioxide based photocatalysts. Five series of photocatalysts were used altogether. The first set contained cerium modified photocatalysts, cerium content being 5 mol.% and 30 mol.%. The next set contained photocatalysts with low cerium contents (0.3 – 0.8 mol.%). In the third series, there were nitrogen modified photocatalysts, in which titanium dioxide was prepared by different methods. different methods. Another set that was investigated included photocatalysts modified by graphitic carbon nitride. Commonly available Evonik P25 was used as pure TiO2. TiO2/g-C3N4 photocatalysts were prepared in the ratio 0.3:1 – 2:1. For the last set that was investigated, graphitic C3N4 was used again, but titanium dioxide was prepared by the sol-gel method, and the TiO2 to g-C3N4 ratios were 1:2 – 1:6. The photocatalysts were characterised by means of different spectroscopic methods (XPS, XRF, UV-Vis, Raman, FT-IR), as well as RTG and TEM, SEM and nitrogen physisorption at 77 K. Photo-electrochemical properties were characterised by means of photometric measurement. Physico-chemical properties of the photocatalysts which were determined by the above mentioned characterisations were correlated with their activity in photocatalytic decomposition of N2O. Photocatalytic decomposition of nitrous oxide was performed in stirred batch photoreactors, while nitrous oxide in helium or nitrogen was used as a reactor. The source of irradiation was a 8 W Hg lamp, with wavelengths of 254 nm a 365 nm. The highest activity in the series of photocatalysts with a high cerium content was displayed by the photocatalyst Ce0,05Ti0,95O2. In the series of Ce/TiO2 photocatalysts with low cerium contents, the highest levels of N2O conversion were reached with the photocatalyst with 0,3 mol.% cerium content. The higher photocatalytic efficiency was the result of an ideal ratio of Ce3+/Ce4+ ions. In nitrogen modified photocatalysts, there was an increase in photocatalytic activity, in comparison with pure TiO2 prepared by means of the sol-gel method, followed by calcination or extraction. This is probably mainly due to the occurrence of vacancies in material structure. Modifying the commonly available TiO2, i. e. Evonik P25, with the use of graphitic C3N4 led to an increase in photocatalytic activity of the prepared nanocomposites, in comparison with pure TiO2 or g-C3N4. The increase in photocatalytic activity is related not only to the size of rutile crystallite and semiconductor band gap energy, but especially to charge carrier separation. In the case of modifying TiO2 prepared by the sol-gel method, the activity was studied in UVC and UVA radiation. When UVC radiation is used, activity of all the prepared photocatalysts is almost identical. while in the case of UVA, the highest photocatalytic activity was displayed by TiO2/g-C3N4 (1:2). Photocatalytic experiments were confirmed by measurement of photo-electro-chemical currents. In photocatalysts, a heterojunction was created between the TiO2 and g-C3N4, leading to a decrease in recombination rates of electrons and holes, which in turn resulted in higher photocatalytic activity. Some of the most active photocatalysts from each set were compared with each other, as well as with the commonly available TiO2 Evonik P25. All the investigated photocatalysts displayed higher activity in photocatalytic decomposition of N2O than Evonik P25.