Ta2O5 coatings modified with CdS, ZnO, and Dy2O3 particles prepared by plasma electrolytic oxidation of tantalum for the photocatalytic degradation of methyl orange

Ta₂O₅/CdS, Ta₂O₅/ZnO and Ta₂O₅/Dy₂O₃ coatings for application in photocatalytic degradation of methyl orange were prepared by plasma electrolytic oxidation of tantalum in an alkaline electrolyte with different concentrations of CdS, ZnO, and Dy₂O₃ particles up to 2.0 g/L. The coatings were characterized by SEM/EDS, XRD, Raman spectroscopy, DRS and photoluminescence spectroscopy. The morphology, thickness, phase structure and absorption properties of all coatings are almost identical and independent of the content of CdS, ZnO, and Dy₂O₃ embedded in Ta₂O₅ coatings. The orthorhombic and monoclinic phases of Ta₂O₅ are the main constituents of the coatings. Due to the low content of embedded CdS, ZnO, and Dy₂O₃ in Ta₂O₅ coatings, they exhibit high absorption in the middle ultraviolet region, which is characteristic of Ta₂O₅. The photocatalytic activity (PA) of Ta₂O₅/CdS, Ta₂O₅/ZnO and Ta₂O₅/Dy₂O₃ is higher than that of pure Ta₂O₅ and depends on the amount of CdS, ZnO, and Dy₂O₃ in the electrolyte, respectively. The highest PA was observed for coatings formed in an electrolyte containing 0.5 g/L of CdS, ZnO, and Dy₂O₃. The improved PA of Ta₂O₅/CdS, Ta₂O₅/ZnO and Ta₂O₅/Dy₂O₃ compared to Ta₂O₅ is related to the reduction of photogenerated electron/hole recombination. The mechanism of the photogenerated electron/hole transfer process is presented and discussed.