2 INFLUENCE OF Fe:W RATIO IN TETRABORATE ELECTROLYTE ON CHARACTERISTICS OF OXIDE LAYERS FORMED ON TITANIUM BY PLASMA ELECTROLYTIC OXIDATION

The effect of the concentration of sodium tungstate in a tetraborate electrolyte containing chelate complexes of Fe (III) with EDTA on the composition, optical and photocatalytic properties of Ti/TiO2-WO3-Fe2(WO4)3 film composites formed by a one-stage method of plasma-electrolytic oxidation was studied. The research showed that sodium tungstate additives contribute to the production of high-quality and continuous PEO coatings. According to X-ray Diffraction Analysis (XRD), all formed coatings contain tungsten oxide WO3 in the cubic modification and Fe2(WO4)3 in the monoclinic modification. A change in the Fe:W molar ratio from 1:1 to 1:3 in the electrolyte due to an increase in the concentration of Na2WO4 leads to an increase in the thickness from 24 to 33 μm, a decrease in the iron concentration from 10 to 4 at.%, but has almost no effect on the tungsten concentration in the oxide layers. According to diffusion reflectance spectra, coatings without iron (TiO2-WO3) absorb only UV light. The presence of iron in coatings leads to a red shift of the spectrum, indicating their ability to absorb visible radiation. This is confirmed by the values of the band gap Eg determined by the Tauc method for direct allowed transitions. As the iron content in the samples decreases, Eg increases from 2.01 to 2.68 eV. For samples obtained in a tetraborate-tungstate electrolyte without iron complexes, Eg=3.0 eV. All obtained composites exhibit almost the same photocatalytic activity in the degradation of methyl orange ((10 mg/L, pH 6.8) in the presence of hydrogen peroxide (C(H2O2) = 10 mmol/L) under UV and visible light. For citation: Budnikova Yu.B., Vasilyeva M.S., Lukiyanchuk I.V. 2 influence of Fe:W ratio in tetraborate electrolyte on characteristics of oxide layers formed on titanium by plasma electrolytic oxidation. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2025. V. 68. N 1. P. 79-87. DOI: 10.6060/ivkkt.20256802.7072.