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Photocatalytic reduction of methylene blue by the heterostructure of Titanium (IV) oxide and symmetric cationic polymethine dye

The results of the spectral, electrochemical and energy characteristics of symmetric cationic polymethine dye 2 - [(1E) -1,3,5-hexatrienyl -] - 1- (phenylmethyl)-benzindolium boron fluoride (D) indicate the possibility of its use as an effective titanium(IV) sensitizer oxide. Comparison of the absorption spectra of the dye solution and the reflectance spectra of the D/TiO2 heterostructures showed that the deposition of the dye on the TiO2 surface leads to bathochrome and hypochromic shifts of the absorption bands, the value of which depends on the content of this component in the heterostructure (HS). The obtained changes in the spectra of heterostructures indicate the possibility of formation of both J- and H-aggregates. Cyclic voltammetry determines the oxidation and reduction potentials of the investigated polymethine dye and calculates their redox potentials in the excited state. They have been found to be sufficient for sensitization by electron transfer to the TiO2 conduction band. The photocatalytic activity of HS D/TiO2 in the model reaction of methylene blue reduction depending on irradiation conditions and dye concentration has been determined. It is shown that, when irradiated with D/TiO2 heterostructures with light with λ <400 nm, their photocatalytic activity decreases with increasing dye content in the whole concentration range of the studied concentrations. When irradiated with heterostructures by light absorbed by the dye (λ = 872 nm), the photocatalytic activity increases to a maximum value at a concentration of the dye equal to 0,20 mg/g, and then decreases with increasing concentration. The energy of possible electronic processes caused by the action of light absorbed by a semiconductor and a dye-sensitizer is considered. The possibility of using created heterostructures as functional materials with a given level of photocatalytic activity and extended range of light sensitivity is shown.