Photocatalytic properties of the composition $\alpha$-Bi$_{2}$O$_{3}$/Bi in the visible light range, depending on the concentration of metallic bismuth and the degree of imperfection of the crystal lattice of bismuth oxide

The photocatalytic activity of the $\alpha$-Bi$_{2}$O$_{3}$/Bi heterostructure compositions obtained by the method of low-temperature pyrolysis of bismuth-sorbitol complexes was investigated. The effectiveness of catalysts is estimated by the rate of decomposition of methylene blue (MS) upon irradiation with light of the visible spectrum. The catalysts obtained by varying the amount of sorbitol in the composition of the precursor organo-mineral complex of bismuth and by varying the temperature of synthesis, differ in different contents of metallic Bi and have different degrees of defectiveness of the $\alpha$-Bi$_{2}$O$_{3}$/Bi crystal lattice. It is established that isothermal annealing of $\alpha$-Bi$_{2}$O$_{3}$/Bi compositions in air in the range of 400–600$^{\circ}$C leads to relaxation of defects and an increase in the volume of the $\alpha$-Bi$_{2}$O$_{3}$/Bi crystal lattice. An increase in the annealing temperature to 550$^{\circ}$С is accompanied by an increase in the catalytic activity of $\alpha$-Bi$_{2}$O$_{3}$/Bi. However, at higher temperatures, degradation of the heterostructure occurs as a result of the oxidation of metallic bismuth, and the catalytic activity of the composition decreases.