Plasma-electrolytic synthesis and characteristics of Ti/TiO2–WO3–CoWO4 composites

Abstract

Photocatalysts based on TiO2–WO3–CoWO4 oxide layers on titanium were formed by plasma-electrolytic oxidation in tetraborate-tungstate electrolytes with the addition of cobalt acetate and EDTA at W:Co ratios of 3:1, 1:1, and 1:3. All formed coatings contain crystalline phases of CoWO4 and WO3. According to the results of energy dispersive analysis, the concentration of tungsten in the composition of PEO coatings varies within 11–17 at.%, the content of cobalt is ~4–9 at.%. The W:Co ratio in the resulting coatings corresponds to the ratio of these elements in the electrolytes. The band gap values determined by the Tauc method for a direct allowed transition are 2.4–2.5 eV and do not depend on the W:Co ratio in the coating composition. It is shown that all the formed coatings exhibit photocatalytic activity in the reaction of MO decomposition under visible and UV irradiation. The photocatalytic activity of Ti/W:Co samples largely depends on the W:Co ratio in their composition. The highest activity is shown by samples in which the ratio W:Co = 3:1, χMO in their presence is ~82 %.