Investigation of the effect of electrolyte concentration and chemical composition on the photocatalytic behavior of coatings formed on AZ31 magnesium alloy by plasma electrolysis

نوع: Type: Thesis

مقطع: Segment: masters

عنوان: Title: Investigation of the effect of electrolyte concentration and chemical composition on the photocatalytic behavior of coatings formed on AZ31 magnesium alloy by plasma electrolysis

ارائه دهنده: Provider: Leyla momeni

اساتید راهنما: Supervisors: Dr. Arash Fattah-alhossieni

اساتید مشاور: Advisory Professors: Dr. Minoo Karbasi

اساتید ممتحن یا داور: Examining professors or referees: Dr. omid imantalab _ Dr. mohsen sheikhi

زمان و تاریخ ارائه: Time and date of presentation: 2025

مکان ارائه: Place of presentation: آمفی تاتر دانشکده مهندسی

چکیده: Abstract: This research was conducted with the aim of developing visible light activated potassium hydroxide-based plasma electrolytic oxidation (PEO) coatings of magnesium oxide that are capable of removing methylene blue contaminants. Various methods including scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), wettability, and diffuse reflectance spectroscopy (DRS) were used to characterize these coatings. Also, the voltage-time response of the coating process was recorded. PEO coating of AZ31 magnesium alloy was produced at a frequency of 1000 Hz, a duty cycle of 50%, a duration of 7 minutes, and a current density of 0.7 A/dcm2 in a phosphate-based electrolyte with a concentration of 5 g/L and different concentrations of 1, 2, and 3 g/L of potassium hydroxide. Initially, the difference in photocatalytic behavior between different electrolytes of sodium phosphate, sodium aluminate and sodium silicate was investigated and the photocatalytic behavior of these coatings was studied using visible-ultraviolet spectroscopy. The results showed that the coating formed in the silicate-based electrolyte showed the best photocatalytic behavior with 89% degradation of methylene blue. Subsequently, different concentrations of 2, 3 and 4 g/L potassium hydroxide were added to 5 g/L sodium silicate electrolyte and the voltage-time diagram of the samples was investigated. To investigate the photocatalytic behavior of samples with different concentrations of potassium hydroxide, each sample was exposed to visible light in methylene blue solution for 5 hours and their degradation rate was investigated. The sample with a concentration of 3 g/L potassium hydroxide with 89% degradation had the highest degradation of methylene blue among the samples. This is due to the more hydrophilic surface and higher porosity of this coating. Next, the current density of PEO coating was changed from 0.7 A/dcm2 to 0.5 A/dcm2 to observe better photocatalytic behavior. Also, different additives of titanium dioxide, graphene oxide and cerium oxide were added to the base electrolyte and their photocatalytic behavior was compared with the optimized sample. Finally, the photocatalytic mechanism of the optimized sample was outlined using DRS and Mott-Schottky analyses.

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