Ozone Formation during Photocatalytic Oxidation of Nitric Oxides under UV Irradiation with the Use of Commercial TiO(2) Photocatalytic Powders

The application of photocatalytic materials has been intensively researched in recent decades. The process of nitric oxide (NO) oxidation during photocatalysis has been observed to result in the formation of nitric dioxide (NO(2)). This is a significant factor of the photocatalysis process, as NO(2) is more toxic than NO. However, it has been reported that ozone (O(3)) is also formed during the photocatalytic reaction. This study analyzed the formation and oxidationof O(3) during the photocatalytic oxidation of NO under ultraviolet irradiation using commercial photocatalytic powders: AEROXIDE(®) TiO(2) P25 by Evonik, KRONOClean(®) 7050 by KRONOS(®), and KRONOClean(®) 7000 by KRONOS(®). An NO concentration of 100 ppb was assumed in laboratory tests based on the average nitric oxide concentrations recorded by the monitoring station in Warsaw. A mix flow-type reactor was applied in the study, and the appropriateness of its application was verified using a numerical model. The developed model assumed an empty reactor without a photocatalytic material, as well as a reactor with a photocatalytic material at its bottom to verify the gas flow in the chamber. The analysis of the air purification performance of photocatalytic powders indicated a significant reduction of NO and NO(x) and typical NO(2) formation. However, no significant formation of O(3) was observed. This observation was verified by the oxidation of pure ozone in the process of photocatalysis. The results indicated the oxidation of ozone concentration during the photocatalytic reaction, but self-decomposition of a significant amount of the gas.