2004 年 22 巻 1 号 p. 47-52
NOx pollution in the environment has become of a remarkable concern in Japan. Photocatalytic property of TiO2 material is recognized to be effective for the elimination of NOx with low concentration in large quantity. Thermal spraying process is feasible in making a large area and thick coating on the surface of the large construction. Therefore, direct coating onto the surface of the existing infrastructures by thermal spraying seems to be advantageous. In this study, formation of photocatalyst TiO2 coating was tried by thermal spraying. In order to reduce the NO2 generation from NO in the oxidation stage, it is effective to add adsorption substances to TiO2. The effect of addition of various additives to TiO2 both on the elimination property of NOx and reduce property of NO2 was also investigated in this study.
Various adsorption substances were added to TiO2 and the photocatalytic properties were investigated. Improvements both in the elimination ratio of NOx of agglomerated powders with Ca3(PO4)2, CaCO3 and diatomite additives and in the generation ratio of NO2 was performed. In the case of additives of Ca3(PO4)2 and nickel to TiO2, the elimination ratio of NOx of agglomerated powder improved by about 15%, and generation ratio of NO2 was reduced to one third with compared to the pure TiO2 powder. Photocatalytic properties of the coatings with various additives were also investigated. Compared to TiO2 coating, generation ratio of NO2 was reduced in that with any kinds of additives. However, in the coating with nickel addition, elimination ratio of NOx decreased. It is inferred that melted nickel during spraying covers the surrounding TiO2 particles and interferes the contact between TiO2 and NOx. A possibility was confirmed that the photocatalytic characteristic can be improved greatly by adding the appropreate additives.