Quantum Dot–Based Composite Photocatalytic Coating for Organic Pollutant Degradation

نوع: Type: Thesis

مقطع: Segment: masters

عنوان: Title: Quantum Dot–Based Composite Photocatalytic Coating for Organic Pollutant Degradation

ارائه دهنده: Provider: Zeinab Rezaei

اساتید راهنما: Supervisors: Dr. Omid Imantalab

اساتید مشاور: Advisory Professors: Dr. Arash Fattah-Alhosseini, Dr. Payam Veisi

اساتید ممتحن یا داور: Examining professors or referees: Dr. Mohsen Sheikhi, Dr. Mazdak Izadi

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

مکان ارائه: Place of presentation: سالن کنفرانس

چکیده: Abstract: Abstract: Abstract: The objective of this research is to develop photocatalytic coatings based on quantum dots using the plasma electrolytic oxidation (PEO) method and to investigate their efficacy in removing organic pollutants under visible light irradiation. While titanium dioxide is one of the most widely used photocatalysts—owing to its chemical stability, low toxicity, and favorable photocatalytic activity its utility is constrained by its limited response to visible light and the rapid recombination of charge carriers, However, limited absorption of visible light and the rapid recombination of charge carriers restrict its effective utilization. In this context, the plasma electrolytic oxidation (PEO) process has been employed as a suitable method for forming a porous TiO2 coating. Given the limitations associated with the performance of PEO coatings, this study utilizes N-GQDs and α-Fe₂O₃ QDs to modify the coating surface and enhance its visible-light utilization capability. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) were used to characterize the samples. Initially, PEO coatings were applied to a titanium substrate; subsequently, N-GQDs were deposited onto the PEO surface via a hydrothermal post-treatment process. Additionally, α- Fe2O3 quantum dots were applied to the PEO-coated titanium substrate through a co-precipitation post- treatment method. The photocatalytic behavior of these coatings was investigated using UV-Vis spectroscopy. The TiO2-PEO/N-GQDs sample exhibited 83% degradation of methylene blue, with a first- order rate constant of 4.3 × 10⁻³ min⁻¹. This is attributed to a more hydrophilic surface, a greater contribution from the nitrogen-doped graphene quantum dots, and a higher degree of porosity in the coating. The photocatalytic behavior of the TiO2-PEO/α-Fe2O3 QDs heterostructure coating reduced the concentration of methylene blue by 73% under visible light. The formation of new photocatalytic phases in the TiO2-PEO/N- GQDs and TiO2-PEO/α-Fe2O3 QDs heterostructures—characterized by a reduced effective band gap, enhanced visible light absorption, and an increased active surface area—creates more favorable conditions for the separation and transfer of charge carriers, thereby improving the photocatalytic activity of titanium dioxide in the visible region. The electrochemical behavior of the coatings was investigated using electrochemical impedance spectroscopy (EIS) in an Na₂SO₄ solution under both dark and illuminated conditions. In the TiO₂-PEO/N-GQDs and TiO₂-PEO/α-Fe₂O₃ quantum dot (QD) heterostructures, charge carrier transfer is facilitated, and the charge transfer resistance at the interface is reduced. In other words, these quantum dot heterostructures promote electron and hole transfer, thereby reducing the probability of charge carrier recombination and increasing the number of carriers available to participate in surface reactions; this, in turn, enhances the photocatalytic activity of the plasma electrolytic oxidation (PEO) coatings formed on the titanium substrate. Key Words: Plasma Electrolytic Oxidation (PEO)–Photocatalyst–Titanium Dioxide–Quantum Do