PHOTOCATALYTIC OXIDATION OF FOOD DYES IN THE PRESENCE OF TITANIUM DIOXIDE

The paper presents the results of a study of the photooxidation process of food dyes in the presence of titanium dioxide in aqueous solutions using the MUF-3 photomineralizer. All food dyes used for the experiment, which are food additives E102, E110, E122, E124, E129, E151, are azo dyes, i.e. they contain an azo group associated with aromatic rings. Titanium dioxide in the anatase phase, obtained by alkaline hydrolysis of titanium tetrachloride with subsequent drying and calcination of the sample at 600oC, was chosen as a photocatalyst. It has been established that in the absence of a catalyst, the intrinsic lightfastness of the dyes is not the same - tartrazine is the most resistant to UV exposure, while carmoisine is the least resistant - it is destroyed by more than 40% within half an hour. Adding TiO2 to dye solutions leads to the destruction of organic molecules, as evidenced by the absence of optical activity of the solutions after 30 minutes of contact with the catalyst. In neutral environments, it is possible to achieve the greatest decomposition of carmoisine, sunset yellow and brilliant black - by 90-95%. Considering that the reaction of catalytic oxidation of dyes is described by a first-order equation, the reaction rate constants are determined. According to the rate of photodestruction under UV irradiation, the dyes can be arranged in the following series: E102 < E124 < E129 < E110 < E151 < E122. It is shown that within 10-15 minutes almost all the studied dyes are mineralized to a greater extent and faster in an acidic medium, however, increasing the duration of photooxidation to half an hour levels out these differences - the effect of the pH of the medium becomes less noticeable and high values of the degree of decomposition are achieved. IR spectroscopy of the original dye samples and samples subjected to photodestruction indicates that in the first 15 minutes, the -N-C- bonds in the molecules of the studied azo dyes are destroyed, and then the resulting fragments are oxidized with the formation of oxo products of photodestruction. Catalytic oxidation of organic substances from aqueous media can serve as an alternative to sorption technologies for wastewater treatment.