Light-sensitive heterostructures based on TiO2 and squaraine dye-sensitizer

Abstract

On the basis of nanodispersed titanium(IV) oxide and squaraine dye-sensitizer (D), new heterostructures (HS) have been created with a given level of photocatalytic activity and an expanded range of photosensitivity. On the basis of the analysis of the results of the measurement of spectral, electrochemical and energy characteristics, it is concluded that it is possible to use the tested squaraine as an effective TiO2 sensitizer. For the first time, using the method of cyclic voltammetry, the redox potentials of squaraine dye were determined and the redox processes were checked for reversibility. It is shown that the plot of the peak current versus the square root of the velocity sweep rate is described by a linear function. It has been found that the electrochemical processes are reversible and diffusion controlled. It is established that the values ​​of redox potentials can be used to calculate the values ​​of standard potentials and free energy. Based on the measured oxidation and reduction potentials of polymethine, the values ​​of the HOMO and LUMO energies were calculated and diagrams of the energy levels of squaraine relative to the electrophysical characteristics of titanium (IV) oxide were constructed. The peculiarities of the sensitizing ability of the studied squaraine dye were analyzed, the mechanism of photocatalytic action was proposed and its confirmation was obtained during the study of the methylene blue recovery reaction. The dependences of the photocatalytic activity of HS D/TiO2 on the dye concentration and irradiation conditions were revealed. It is shown that, when irradiated with heterostructures by light absorbed by the dye, at low concentrations of the latter (0.02÷0.2 mg/g), the photocatalytic activity increases, and at the content of the sensitizer 1.0÷2.0 mg/g, it decreases. When irradiated with HS by light absorbed by titanium(IV) oxide, photocatalytic activity decreases with increasing squaraine content.