טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentEpshtein Marina
SubjectPhotocatalytic Inactivation of Microorganisms in Water Using
Embedded TiO2 and Anodic Bias
DepartmentDepartment of Civil and Environmental Engineering
Supervisors Professor Robert Armon
Dr. Jeanna Starosvetsky
Full Thesis text - in Hebrew Full thesis text - Hebrew Version


Abstract

Present study describes a novel electrochemical approach to photocatalytic decontamination of water using TiO2-catalyst. In order to improve the photocatalytic water purification it was proposed to use a highly developed-surface-area TiO2 catalyst grown via anodization process on a Ti substrate. The TiO2-catalyst was prepared by various methods of anodization and was used in order to purify the water of microbial contamination. The immobilized TiO2 produced on a metal substrate, can be repeatedly used and can be easily regenerated, which makes the process cheaper and more attractive compared to use of TiO2 powder suspension. The efficiency of photocatalytic treatment depends on the amount of generated holes that is typically low due to the high electron-hole recombination rate. Holes concentration may be enhanced by retarding the electron-hole recombination process. Semiconductor electrochemistry suggests that electron-hole recombination could be reduced more effectively under electrochemical polarization. In the present study, suppression of electron/hole recombination process and correspondingly enhancement of the holes concentration on UV irradiated catalyst surface was carried out by anodically applied voltage.

The first task of the study was to test the influence of various factors on the rate of the photocatalytic reaction, such as suspension medium types, pH, organic matter content, and TiO2 oxide layer, different microorganisms, initial microorganisms’ concentrations and anodic potential.

The second task was to find the optimal parameters of the photocatalytic process that are the most efficient for inactivation of the selected microorganisms. The highest effective inactivation was obtained with water containing 0.01% NaCl at pH=5, at an initial microorganisms concentration - 106 CFU/ml , an anodic potential of 1.5V and with TiO2 nanotubular electrode.

The third task was to compare the effectiveness of the new TiO2 nanotubular electrode with TiO2 P25 powder suspension. The experimental data revealed that the new TiO2 nanotubular electrode is highly effective in the inactivation of viable bacterial cells in spite of the fact that TiO2 P25 powder has much higher surface area than TiO2 nanotubular electrode.

As the fourth task the possibility of repeated use of embedded TiO2 was examined. It revealed that immobilized grown porous TiO2-catalyst can be repeatedly used, achieving extremely high efficiency.

In conclusion, the new method utilizing extreme anodic polarization to produce both TiO2 catalysts and to reduce electron/hole pair recombination process proved its feasibility by increasing the photocatalysis efficiency.