Investigating photocatalytic and electrochemical activity of TiO2-WO3 hierarchical coatings created by PEO and hydrothermal methods on commercial pure titanium

نوع: Type: thesis

مقطع: Segment: PHD

عنوان: Title: Investigating photocatalytic and electrochemical activity of TiO2-WO3 hierarchical coatings created by PEO and hydrothermal methods on commercial pure titanium

ارائه دهنده: Provider: Maryamsadat sharifian

اساتید راهنما: Supervisors: arash fattahalhosseini

اساتید مشاور: Advisory Professors: minoo karbasi

اساتید ممتحن یا داور: Examining professors or referees: baba jale

زمان و تاریخ ارائه: Time and date of presentation: 2023

مکان ارائه: Place of presentation: seminar

چکیده: Abstract: The present study aims to develop plasma electrolytic oxidation (PEO) and hydrothermal composite coatings in order to remove the color pollutant methylene blue. In this research, firstly, the porous coating of titania (TiO2) was produced at a current density of 6 A/dm2, frequency of 1000 Hz, time of 10 minutes, duty cycle of 80%, alkaline electrolyte and pulsed direct current mode. The voltage-time response of the coating process was recorded. Then tungsten trioxide nanoparticles (WO3 ) were grown on TiO2 coating using tungsten precursor (Na2WO4) by hydrothermal method. Hydrothermal parameters including Na2WO4 concentration, temperature and time were optimized respectively. Field Scanning Electron Microscope (FE-SEM), X-ray Energy Diffraction Spectroscopy (EDS), X-ray Diffraction (XRD), Diffuse Reflectance Spectroscopy (DRS) and Photoluminescence Spectroscopy (PL) were used to analyze the physical and photocatalytic behavior of the coatings. . First, WO3 nanoparticles in different concentrations of 0.0025 M, 0.005 M and 0.05 M of Na2WO4 were created by hydrothermal method at 200 C for 24 hours on titania coating. Spherical and quasi-spherical nanoparticles and agglomerate were observed on the coating surface. XRD results showed that the resulting coatings include anatase and monoclinic WO3 phases, which confirmed the creation of WO3 particles. The photocatalytic behavior of the coatings was investigated using optical, visible-ultraviolet spectroscopy. The best photocatalytic behavior related to the composite coating created at a concentration of 0.005 M, which showed 67% degradation. The reason for the increase in photocatalytic performance was the effective participation of WO3 nanoparticles and the expansion of the light absorption range of TiO2 to the visible light range. Next, the hydrothermal temperature was changed at the optimal concentration of 0.005 M. The coated sample at 120 C showed 74% degradation of methylene blue, which performed better compared to TiO2 coating with 47% degradation. An increase in temperature led to a decrease in the specific surface area due to the growth of WO3 nanoparticles and a decrease in the porosity of the coating; Therefore, low temperatures were more suitable. Finally, at the optimized concentration and temperature, the hydrothermal time was evaluated. Changing the time from 12 to 18 h produced nanorods that grew between the nanoparticles. The presence of this type of microstructure, especially the presence of nanorods, contributed to 88% destruction due to the reduction of electron-hole recombination in the longitudinal direction. In addition, the inhomogeneous binding of TiO2-WO3 led to the improved photocatalytic behavior in delaying the fast recombination of charge carriers. In the following, different photocatalytic parameters, including the concentration of methylene blue, pH, and the trap were evaluated on the optimal sample. The results of recovery of samples showed the stability of photocatalysts after 4 periods. Electrochemical behavior was performed by electrochemical impedance spectroscopy test in a sea salt simulator solution, 3.5% by weight of NaCl. The created composite coating had a lower corrosion resistance than the TiO2 coating alone, which was related to the reduction in thickness. Finally, with the presence of cavity trappers, superoxide anion and hydroxyl radical, the mechanism of the process was presented

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