Effect of Post-Thermal Treatment on the Crystalline Structure and Photocatalytic Performance of Plasma Electrolytic Oxidation–Derived Coatings on Brass Alloy - دانشکده فنی و مهندسی
Effect of Post-Thermal Treatment on the Crystalline Structure and Photocatalytic Performance of Plasma Electrolytic Oxidation–Derived Coatings on Brass Alloy
نوع: Type: Thesis
مقطع: Segment: masters
عنوان: Title: Effect of Post-Thermal Treatment on the Crystalline Structure and Photocatalytic Performance of Plasma Electrolytic Oxidation–Derived Coatings on Brass Alloy
ارائه دهنده: Provider: Mohammad Mehdi Rajabi
اساتید راهنما: Supervisors: Dr. Arash Fattah-alhossieni
اساتید مشاور: Advisory Professors: Dr. Minoo Karbasi
اساتید ممتحن یا داور: Examining professors or referees: Dr. Hassan Elmkhah - Dr. Omid Imantalab
زمان و تاریخ ارائه: Time and date of presentation: 2026
مکان ارائه: Place of presentation: سالن کنفرانس دانشکده مهندسی
چکیده: Abstract: In this study, the plasma electrolytic oxidation (PEO) process was employed to fabricate ceramic coatings on a brass alloy substrate using an aluminate-based electrolyte. The effect of post-heat treatment on the structural and morphological characteristics of the coatings, as well as on the photocatalytic degradation of methylene blue (MB) under visible-light irradiation, was systematically investigated. The results revealed that annealing at 425°C establishes an optimal balance between nanostructure development and micro-crack control, while significantly enhancing surface hydrophilicity, as evidenced by a reduction in the water contact angle from approximately 29° to 11.6°. Grazing-incidence X-ray diffraction (GIXRD) analysis confirmed the presence of ZnO, CuO, and CuAlO2 phases alongside substrate reflections. In addition, X-ray photoelectron spectroscopy (XPS) results indicated the existence of Cu2+ species and Al 2p signals consistent with the formation of the CuAlO2 phase. Optical measurements demonstrated a direct band gap of approximately 2.86 eV. Mott–Schottky analysis revealed dual semiconductor behavior, characterized by both positive slopes (indicative of predominantly n-type conductivity mainly associated with the ZnO phase) and negative slopes (indicative of p-type behavior related to CuO and CuAlO2 phases) in different potential regions. This behavior suggests the coexistence of n-type and p-type semiconductor domains within the coating structure. Based on photocatalytic performance tests, the sample annealed at 425°C for 2h was identified as the optimal condition, as extending the annealing duration did not result in a significant performance improvement. Under visible-light irradiation and at an MB concentration of 15 ppm, this sample achieved a degradation efficiency of 54%, representing an approximately 13% enhancement compared to the non-annealed coating. Furthermore, peroxymonosulfate (PMS) activation led to a pronounced synergistic effect, with a synergy factor of about 2.57, resulting in a substantial improvement in pollutant removal efficiency. The influence of coexisting ions in water revealed that the presence of PO_4^(-3) and Cl^- ions enhanced the degradation efficiency to 63% and 57%, respectively, whereas NO_3^- ions exerted an inhibitory effect, reducing the efficiency to approximately 44%. Reusability assessment indicated an initial degradation efficiency loss of about 13% after the second cycle, followed by stable performance up to the fourth cycle. Radical scavenging experiments identified the dominant reactive species involved in the photocatalytic process, and a plausible degradation pathway for methylene blue was proposed based on intermediate product analysis. Overall, the results demonstrate that post-heat treatment at 425 °C for 2h effectively optimizes the morphology, enhances surface hydrophilicity, and promotes charge separation through the formation of a ZnO/CuO/CuAlO2 composite coating, thereby enabling stable and efficient visible-light-driven photocatalytic performance of PEO coatings on brass substrate.