Effect of hydrothermal time on the photocatalytic activity of the hierarchical TiO2-WO3 coatings produced by plasma electrolytic oxidation-hydrothermal on pure titanium

In this study, a hierarchical coating of titanium dioxide/tungsten trioxide (TiO2/WO3) was created using the synergistic methods of plasma/hydrothermal electrolytic oxidation on the surface of pure titanium. For this purpose, TiO2 coating was first created by plasma electrolytic oxidation (PEO) process in phosphate-base electrolyte on titanium substrate. , then WO3 particles were created by hydrothermal process on TiO2 coating. The effect of the duration of the hydrothermal process (12, 18 and 24 hours) on the photocatalytic behavior of the coatings was investigated. Phase studies and microstructural characteristics were performed using X-ray diffraction (XRD) and field emission scanning electron microscope (FESEM). Photocatalytic degradation of methylene blue under visible light in the presence TiO2-WO3 coatings and TiO2 coating were compared. The pure TiO2 PEO coating showed about 47% degradation of methylene blue, while the optimal TiO2-WO3 composite coating, created by the combination of the plasma electrolytic oxidation /hydrothermal methods, resulted in 83% MB degradation. The highest photocatalytic activity of the TiO2-WO3 coating after hydrothermal for 18 h can be attributed to the presence of the visible-light-driven WO3 phase and its appropriate rod microstructure. After 12 h hydrothermal, the morphology of WO3 phase consisted of the nanoparticles and nanorods, while increasing the processing time up to 18 h led to the morphology development including the increase of nanoparticle size increment and growth of the nanorods.