In this study, tungsten-doped titanium oxide (TiO2) coatings were produced via plasma electrolytic oxidation (PEO), decorated with zinc oxide (ZnO) through immersion in a zinc acetate dihydrate (ZAD) ethanol solution, and subsequently heat-treated. Initially, the chemical composition of the coating was optimized through tungsten doping. Next, critical parameters for the sol-gel decoration method, including solution concentration, immersion time, and heat treatment temperature, were optimized. The resulting coatings were characterized using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), attenuated total reflectance infrared spectroscopy (ATR-IR), and diffuse reflectance spectroscopy (DRS). To investigate the photoelectrocatalytic properties, the methylene blue (MB) degradation efficiency of the coatings was measured over 3 hours using liquid spectrophotometry. The results indicated that the tungsten-doped coating, produced by 5 minutes of PEO, decorated by 3 minutes of immersion in a 0.5 M solution, and heat-treated at 400°C, exhibited the highest degradation efficiency. The ZnO decoration increased the TiO2 band gap to 3 eV, reducing the photocatalytic efficiency from 53.4% to 43.1%, but increasing the electrocatalytic degradation efficiency from 8.6% to 62%. Consequently, the photoelectrocatalytic degradation efficiency improved from 29.7% to 84.4%. To eva‎luate the photoelectrochemical behavior of the optimized coating, open circuit potential (OCP) tests, potentiostatic photocurrent measurements, electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV) were conducted under dark conditions and xenon lamp illumination. The results showed that the electrocatalytic process, with extensive production of free radicals and an increased lifespan of light-excited charge carriers, overcame the reduction in visible light absorption due to the increased band gap, resulting in improved degradation efficiency. The pigment degradation in solution was found to be controlled by Warburg diffusion, with the outer layer of the PEO coating participating in photocatalytic reactions and the inner layer, where extensive n-n heterojunction formation between TiO2 and ZnO occurred, participating in electrocatalytic reactions. The repeatability of the decorated coating was eva‎luated over six cycles in the dye degradation process, showing a 22.5% reduction in degradation efficiency. Despite the reduced photocatalytic property of TiO2 after ZnO decoration, it effectively prevented a decline in photoelectrocatalytic performance.

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فتح اله كريم زاده , مسعود عطاپور