1. Introduction Different aspects of water treatment are considered the most urgent topics at the present and will influence our future life. Photocatalytic oxidation of organic compounds is an advanced method for removal of impurities from water. Polychlorobiphenyls (PCBs) are a group of man-made organic compounds with 1 to 10 chlorine atoms that are attached to a biphenyl molecule. There are 209 congeners of PCB, which all have low water solubility, but also have high solubilities in most organic solvents. The chronic toxic effects of PCBs include failure in reproduction, birth defects and brain damage, in addition to being carcinogenic. Titanium dioxide is close to being the ideal photocatalyst in several ways: relatively inexpensive, chemically stable, the light required to activate the catalyst may be long-wavelength UV such as the natural UV component of the sunlight and the produced oxidant is powerful with elimination potential of most types of microorganisms 1. The main problem of this process is the low efficiency due to high electron/hole recombination rate 2. The efficiency of the photocatalysis process depends on the amount of generated holes, which is typically low, due to the high electron-hole recombination rate. In order to enhance the efficiency of the process, an anodic bias was applied on nanotubular TiO 2 which was grown by anodization in aqueous solution with addition of fluoride ions. Photocatalytic Degradation of Polychlorobiphenyls Using Anodic Bias on Nano Tubular TiO 2 Tal Zaid, N. Baram, D. Starosvetsky, Y. Ein-Eli Department of Materials Engineering, Technion-Israel Institute of Technology, Haifa 32000, Israel Summary Anodic polarization is capable of growing thick, crystalline, nanotubular oxide layer with high surface area Anodic bias is also capable of reducing electron/hole pair recombination process i.e. increasing the efficiency of the photocatalytic process and the degradation rate. The combination of immobilize, electrochemically grown titania with an application of extremely high anodic bias and UV illumination led to a dramatic improvement in measured photocurrent. The size of the photocatalyst is an important factor on the degradation rate of PCBs. The intensity of the UV illumination determined the current density received in the experiment, and hence, can have a major influence on the degradation rate. Different PCB congeners will produce different degradation rate, depending on the number of chlorine substitutes. References 1.Serpone, N., Pelizzetti, E., Photocatalysis Fundamentals and Applications, A. Wiley, USA p. 126-157, 1989. 2.Hoffmann, M.R., Scot, T.M., Wonyong, C.H., Bahnemann, D.W., Chem. Rev., 95, 69-96 (1995). 3.Fujishima. A., Rao, T.N., Tryk, D.A., J. Photochem. & Photobio. C, 1, 1-21, 2000. 4.Sunada, K., Kikuchi, Y., Hashimoto, K., Fujishima, A., Enviro. Sci. &Tech., 32, 5 (1998). Characterization Top and cross section HRSEM micrographs of TiO 2 growth via anodization in 1M Na 2 SO 4 + 0.5%wt NaF solution Only Ti !  The oxide is Amorphous The oxide is crystalline: Anatase E g =3.1 eV The Principle of Photocatalysis Under UV illumination electrons and holes are produced 3,4 : The following reactions occur: Hydroxyl radicals have high oxidation potential: schematic diagram showing the potentials for various RedOx processes occurring on the TiO 2 surface at pH 7 Experimental Anodization in aqueous solutions Electrolyte – 1M Na 2 SO 4 + 0.5%wt NaF 2hr, constant potential of 20V, room temp. Photocatalysis of PCBs A Petri dish with working, counter and reference electrodes. PCB – 100ml of 10  g/L aqueous solution. Anodic bias – 0-5V Analysis The absorption of the samples were determined by spectrophotometer. UV lamp – =360nm Effect of Ti/TiO 2 catalyst size on the degradation rate Increasing the photocatalyst size enhances the degradation rate. Effect of the UV lamp intensity on the current density higher current density is achieved with the more intense UV lamp. Photocatalysis results Effect of Anodic Bias on the current density Effect of Anodic Bias on the degradation rate An increase in the applied anodic bias until potential of 4 V SHE has led to an increase in degradation rate. Higher anodic bias resulted in higher current density. The PCB with less Chlorine substitutes had an higher degradation rate. Comparison of the degradation rate of two PCB congeners 2-Chlorobiphenyl 2,2',3,4,4',5'-hexachlorobiphenyl