Photoelectrocatalytic Oxidation of Formic Acid in the Visible Spectral Region on Films of Nanocrystalline Titanium Oxide Doped by Bismuth

A method of formation of film coatings of titanium dioxide doped by bismuth ions (Bi³⁺) is developed on the basis of sol–gel synthesis and used to form film coatings of titanium dioxide with the anatase structure on the photoanode surface. Thus, samples containing 0.5 to 20 wt % of Bi are obtained. It is shown that the doping of titanium dioxide by bismuth ions results in a shift of light absorption to the visible region of electromagnetic radiation spectrum. The absorption level depends on the concentration of bismuth and reaches its maximum for samples containing 0.5 and 1.0 wt % of Bi. It is suggested on the basis of the data of X-ray phase analysis that an increase in the content of bismuth to 20 wt % leads to destruction of crystalline regions and amorphization of bismuth oxide and titanium oxide. The obtained coatings are studied as catalysts of photoelectrocatalytic oxidation of formic acid under illumination by monochromatic and visible light. It is found that the highest catalytic effect is observed on samples containing 1.0 wt % of bismuth. The forbidden gap width is estimated on the basis of absorption of monochromatic (464 nm) light, and it is shown that photoelectrocatalytic oxidation of formic acid in the visible spectral range accompanied by formiate ion adsorption on the illuminated photoanode surface is probably due to a decrease in the forbidden gap width in doped titanium dioxide to 2.7 eV.