טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentBaram Nir
SubjectEnhanced Photo-Electrochemical Efficiency of Immobilized
TiO2
DepartmentDepartment of Materials Science and Engineering
Supervisor Professor Yair Ein-Eli
Full Thesis textFull thesis text - English Version


Abstract

Over the last few decades, titanium dioxide has been recognized the main material for photocatalytic degradation of organic compounds for water purification. The mechanism of photocatalysis in the presence of TiO2 is the enhanced formation of hydroxyl (OH?) radicals, which are active in oxidation processes and have a significant effect on the chemical oxidation of organic compounds in the environment. Complete mineralization of many organic substances is possible in aqueous systems, when sufficient OH? radical flux can be generated.

The aim of this research is to enhance the photoefficiency of TiO2-catalyst by a novel electrochemical approach. This approach aims substantially to enhance the efficiency of this process by using electrochemical polarization in order to produce both TiO2 catalyst on metallic Ti sheet and to reduce electron/hole pair recombination process.

In this research, high surface area immobilized TiO2 were grown via several electrochemical anodization methods for photocatalytic applications. Mesoporous TiO2 was grown in a molten salts electrolyte and in a sulfuric acid solution above the microsparking potential. On the contrary, nanotubular TiO2 was grown in a sodium sulfate solution with the addition of fluoride ions, leading to the formation of fine elongated nano tubes with high surface area. The microstructure of the different types of photocatalysts was characterized by SEM and XRD. Electrochemical studies were performed on the photocatalysts using linear sweep voltammetry and open circuit potential relaxation to measure the photocurrents and the charge transfer kinetics respectively. Electrochemical Impedance Spectroscopy (EIS) was used to study the capacitance of the TiO2 in the dark and under UV illumination. The results were fitted to a suggested equivalent model that describes the electric structure of the system.

E.coli bacteria and MeO molecule have been used as indicators of disinfection efficiency in water systems. The efficiency of E.coli photo-inactivation under UV light was evaluated by using the different types of photocatalysts. As expected from the electrochemical characterization, the nanotubular photocatalyst was found to be the most efficient photocatalyst toward E.coli inactivation and degradation of MeO. The immobilized nanotubular system is proven to be the most potent electrode for water purification. The immobilized grown porous TiO2-catalyst can repeatedly be used, achieving extremely high efficiency, without any need for advanced filtration techniques for the removal of the TiO2. The use of the described combined methods is a powerful tool toward predicting and understanding the ideal anode for photocatalytic process.