טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentGrimberg Vered
SubjectDegradation of Volatile Contaminants by an Integrated
Photocatalytic-Adsorptive Approach
DepartmentDepartment of Chemical Engineering
Supervisor Professor Yaron Paz


Abstract

 Titanium dioxide can be photoexcited by near-UV illumination to provide electron-hole pairs, which can migrate to the surface. The holes react with adsorbed water to produce hydroxyl radicals and the electrons react with adsorbed oxygen, to produce O2- species.  Both of these radical species may participate in the degradation of organic molecules at the TiO2 surface.

The main advantages of photocatalytic degradation are the variety of contaminants that can be treated and the ability to use solar energy for the oxidation process. The main disadvantages of the process are low adsorbtivity of non-polar contaminants on the titania surface and low quantum efficiency. The photocatalytic degradation of trichloroethylene (TCE) is very efficient in the gas phase due to a free radical mechanism. This mechanism might also be responsible for faster degradation of other contaminants co-existing in the gas stream.

The purpose of the work was to examine the possibility of enhancing the photodegradation of toluene in the gas phase by two means. First, by mixing it with TCE in order to use the radical mechanism of TCE degradation. Second, by using composite particles combined of titania sites and activated carbon sites, thus concentrating the contaminants near the photocatalytic sites to allow surface diffusion towards these sites.

The photocatalytic performance of composite particles was measured and compared with that of non-composite particles. Measurments were performed directly by an FTIR spectrometer. It was observed that during the photodegradation of TCE over the composite particles intermediate products were hardly released to the gas phase, unlike photodegradation of TCE over P25 particles. It was also found that addition of TCE could enhance the mineralization efficiency of toluene over P25 particles. This effect was not observed over the composite particles, although it is expected to occur with higher titania loadings of the composite particles.