Among water and wastewater treatment methods and reducing pollutants, photocatalytic decomposition with semiconductors is a new, effective, fast, and destructive method for this purpose, and titanium dioxide is considered one of the best photocatalysts. In this research, the porous coating of titanium dioxide was created using the electrolytic plasma oxidation method on the pure titanium surface in a phosphate base bath. The coating was done under two conditions of constant voltage and constant current, and the effect of the presence of tungstate in the bath on the formed phases and as a result on the photocatalytic behavior of the coatings was investigated. To confirm the optimal performance of the catalyst, the photocatalytic degradation of methylene blue pigment with visible light irradiation was investigated. The prepared samples' phase analysis, morphology, structure, and band gap were investigated by X-ray diffraction, scanning electron microscopy, elemental analysis, and visible-ultraviolet reflection spectroscopy. The coating obtained from constant current conditions showed the phase structure of anatase doped with tungsten, while the coating obtained from constant voltage conditions was a TiO2-WO3 composite. The photocatalytic performance of the coatings for the degradation of methylene blue dye was eva‎luated by ultraviolet-visible spectroscopy. According to the X-ray diffraction pattern, the coatings obtained from the bath without tungstate additive obtained from constant current had both anatase and rutile phases, while the coating obtained from the bath containing tungstate showed only the anatase phase. The resulting coatings at constant voltage contained tungsten oxide phase, which seems that the presence of this phase along with the anatase phase has led to a sharp drop in their photocatalytic properties. The high photocatalytic activity under the color degradation test for the coating with anatase and rutile phases without tungsten is confirm the fact that only the anatase phase does not cause photocatalytic activity, therefore, among the photocatalysts coated with doped titanium under constant current conditions, during 180 minutes of the color degradation test , the tungsten-free sample showed the highest photocatalytic efficiency (60%) under xenon light (400˂ (nm)λ˂800) under the coating time of 5 minutes. According to the reusability test under xenon light for 5 cycles, tungsten-doped coatings showed higher porosity and active surface due to continuous immersion time, and as a result, showed much better performance than titanium oxide coatings without tungsten. In this case, the titanium oxide coating containing the highest amount of tungsten showed a destruction efficiency of about 70% after 5 cycles of three hours. The electrochemical impedance spectroscopy test showed that the presence of tungsten additive in the coating bath as a result of its doping in the coating has increased the barrier performance of the coating, which can be attributed to the creation of a barrier layer of tungsten hydroxide on the surface of the coating.

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محمدحسين عنايتي , مسعود عطاپور