The photocatalytic activity of semiconductor metal oxides can be improved by the addition of sensitizer which enhances the band gap by considerable red shift of the absorption edge of semiconductor. In the present study, the effect of ascorbic acid as sensitizer on the photocatalytic activity of titania-silica binary mixtures was studied. The SiO2-TiO2 mixtures having 50wt%Ti:Si composition were prepared with sol-gel method. The surface area and porosity of the samples were modified by using various amounts of polyethylene glycol (PEG) as template. The thin films of the samples were obtained by dip coating of glass plates to colloidal solutions. The samples were characterized by methylene blue adsorption method and UV-Vis spectrophotometry. The photocatalytic activities of the samples were measured with methylene blue degradation, methyl orange degradation and direct water splitting in the presence and absence of ascorbic acid. Increase in the surface area and reaction rate with increasing PEG addition until a threshold value was observed. Highest methylene blue degradation activity was observed for 27g PEG added sol-gel derived film and surface area of this film is measured as 44m2/m2. Ascorbic acid presence shows a significant increase in the photocatalytic degradation activity of methyl orange. The sensitization effect of ascorbic acid was also compared with the effect of EDTA. It was found that the effect of ascorbic acid on the methyl orange degradation rate is significantly higher than the effect of EDTA. However, the effect of EDTA is more pronounced in water splitting reaction.

This diploma thesis deals with photoelectrochemical cells containing photoactive titanium dioxide anode and their use for photocatalytic degradation of organic compound from water solutions. The electrical properties of the produced photoelectrochemical cells were determined by the use of voltamperometric characteristics, the oxidation ability of the cells was monitored by measuring the fluorescence of the oxidative intermediates. To study these reactions, benzoic acid was used as the fluorescence probe for OH˙ radicals. The aim of the study was to study the influence of material composition and spatial arrangement of the cathode and the relationship between irradiation, current and rate of electrode processes.