بررسی فعالیت فتوکاتالیستی پوشش‌های TiO2-V2O5 ای: Investigation of the Photocatalytic Activity of TiO₂–V₂O₅ Coatings Fabricated by Plasma Electrolytic Oxidation (PEO) and Hydrothermal Methods on Commercially Pure Titaniumجادشده به روش PEO و هیدروترمال روی تیتانیوم خالص تجاری

نوع: Type: Thesis

مقطع: Segment: PHD

عنوان: Title: بررسی فعالیت فتوکاتالیستی پوشش‌های TiO2-V2O5 ای: Investigation of the Photocatalytic Activity of TiO₂–V₂O₅ Coatings Fabricated by Plasma Electrolytic Oxidation (PEO) and Hydrothermal Methods on Commercially Pure Titaniumجادشده به روش PEO و هیدروترمال روی تیتانیوم خالص تجاری

ارائه دهنده: Provider: shiva zaheri shoja

اساتید راهنما: Supervisors: Dr. Arash fattah alhoseini

اساتید مشاور: Advisory Professors: Dr. Minoo karbasi

اساتید ممتحن یا داور: Examining professors or referees: Dr. Azizian- Dr. movahedi- Dr. Izadi

زمان و تاریخ ارائه: Time and date of presentation: 2026

مکان ارائه: Place of presentation:

چکیده: Abstract: Abstract: Considering the growing environmental concerns associated with organic pollutants, photocatalytic processes have attracted considerable attention as an effective approach for pollutant removal. However, powder photocatalysts suffer from several limitations, including difficult recovery, particle agglomeration, and rapid recombination of charge carriers. Immobilized photocatalytic coatings can provide a suitable solution to overcome these challenges. Therefore, the aim of the present study was to evaluate the photocatalytic activity of VOₓ/TiO₂ composite coatings fabricated on commercially pure titanium substrates for the degradation of methylene blue under visible-light irradiation. In this work, TiO₂ coatings were first synthesized on titanium substrates using the plasma electrolytic oxidation (PEO) process. Subsequently, hydrothermal treatment was carried out using vanadium oxide precursors under different conditions in order to form VOₓ/TiO₂ heterostructures. The motivation for combining the PEO and hydrothermal methods was to produce stable and practical photocatalytic coatings with improved visible-light absorption, enhanced charge separation, and suppressed electron–hole recombination. The effects of hydrothermal treatment time (12, 24, and 48 h) and vanadium precursor concentration (1/5, 3, and 6 mM) on the structural, optical, and photocatalytic properties of the coatings were systematically investigated. The synthesized samples were characterized using field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), μ-Raman spectroscopy, UV–Vis diffuse reflectance spectroscopy (UV–Vis DRS), photoluminescence spectroscopy (PL), X-ray photoelectron spectroscopy (XPS), and Mott–Schottky analysis. FE-SEM observations revealed that the porous TiO₂ coating generated by the PEO process provided a favorable surface for the growth of vanadium oxide species. Increasing the hydrothermal duration up to 24 h resulted in a more uniform distribution of VOₓ nanostructures and the formation of an effective heterojunction with TiO₂, whereas prolonged treatment for 48 h led to particle agglomeration and partial blockage of active surface sites. XRD and Raman analyses confirmed the formation of TiO₂, TiVO₄, and various VOₓ phases. The samples prepared with a 3 mM vanadium precursor concentration exhibited a more pronounced TiVO₄ phase, while higher vanadium concentrations promoted the formation of vanadium-rich phases such as VO and V₂O₅. UV–Vis DRS analysis demonstrated a significant reduction in band-gap energy from approximately 3/12 eV for pure TiO₂ to about 1/75 eV for the modified samples, indicating enhanced visible-light absorption. In addition, PL results showed a lower emission intensity for the optimized samples, suggesting reduced electron–hole recombination. Among all synthesized coatings, the sample prepared at 24 h hydrothermal treatment time and 3 mM vanadium precursor concentration (TV-24h-3m) exhibited the highest photocatalytic performance, achieving approximately 93% degradation of methylene blue under visible-light irradiation. The apparent reaction rate constant of the optimized sample was approximately 27 times higher than that of the pure TiO₂ coating. Reactive-species trapping experiments demonstrated that the photocatalytic degradation process was mainly governed by reactive oxygen species (ROS), including hydroxyl radicals (•OH), superoxide radicals (O₂•⁻), and photogenerated holes (h⁺). Based on the PL, XPS, and Mott–Schottky results, the charge-transfer mechanism in the TiO₂/TiVO₄/V₂O₅ heterostructure was found to be more consistent with a quasi S-scheme pathway rather than a conventional type-II heterojunction mechanism. Overall, the results of this study indicate that precise control of hydrothermal synthesis parameters plays a crucial role in tuning the phase composition, optoelectronic properties, and photocatalytic activity of VOₓ/TiO₂ coatings. Furthermore, the combination of the PEO and hydrothermal methods provides an effective strategy for designing stable and visible-light-active photocatalytic coating.