|M.Sc Student||Abbas Nijmeh|
|Subject||Cementitious Photocatalytic Surfaces for Self Cleaning and|
|Department||Department of Chemical Engineering||Supervisor||Professor Yaron Paz|
|Full Thesis text - in Hebrew|
Air pollution is a major problem faced by modern societies. Compared with other air treatment techniques, photocatalysis is considered as an environmental friendly technique. Titanium dioxide is widely used as a photocatalyst due to its superior characteristics. Many uses were proposed including the application of photocatalysis to construction materials. Here, the photocatalyst is utilized for two purposes: self-cleaning of construction materials and air purification.
There is a common notion in the field of photocatalysis, that the same requirements for air purification hold also for self- cleaning, and that the same product may be adequate for the two purposes. The presented work examines this assumption and tries to understand to what extent this assumption is reasonable. Furthermore, it tries to locate appropriate parameters for each application.
Along this line a large set of cementitious surfaces loaded with TiO2 were prepared. The photocatalytic activity was evaluated based on two experimental set-ups:
1. Air purification system, which was used for an in-situ study of the kinetics of NO oxidation using an FTIR spectrophotometer.
2. Self-cleaning system which was based on the measurements of changes in colors of surfaces colored by Rhodamine B.
It was found that the type of titania had a significant effect on the performance of the photocatalytic surfaces in both applications. This was reflected through large number of parameters that governed the activity.
The effect of the concentration of the photocatalyst within cementitious matrices varied according to the different types and the different applications. In self-cleaning experiments, activity was found to increase quite linearly with concentration. In contrast, in air purification the dependence of the activity on the concentration was more complex and depended upon the type of the specific photocatalyst used in these experiments. In air purification experiments, activity was found to correlate with surface’s micro roughness measured by Atomic Force Microscopy (AFM).
The last parameter which was checked was the macro roughness. Results showed that rough surfaces were favorable for air purification applications, while smooth surfaces were more favorable for self cleaning.
From these results it can be concluded that photocatalytic surfaces have to be adjusted for a required application. Surface roughness, titania type and concentration should be optimized for each application. Rough surfaces are more favorable for air purification while smooth surfaces are more suitable for self-cleaning applications.