Influence of anodization parameters in the development of TiO2 nanotube arrays for photocatalytic reduction of carbon dioxide into methane /
Aamina
- xiii, 162 pages : illustration ; 30 cm. + 1-CD ROM
Faculty of Civil Engineering Technology
Thesis (Master of Science) -- Universiti Malaysia Pahang – 2024
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One of the most researched areas in the 21st century is the improvement of the photocatalytic efficiency of nanostructured materials, which necessitates a variety of their advanced nanostructure morphological aspects. Titanium dioxide (TiO2) is considered a significant photocatalyst with some predominant challenges, which are accelerated charge carrier recombination and limited light absorption. It occurs due to a very narrow photocatalytic region that is (λ < 400 nm). The one-dimensional TiO2 nanotube arrays (TNTAs) prepared by the electrochemical anodization process are used to combat these morphological challenges. The primary focus of the study is to investigate the influence of anodization parameters on the morphological, chemical, and optical features of TNTAs, and its impact on photocatalytic reduction of carbon dioxide into methane. The parameters included in this study are anodization steps, type of electrolyte, electrolyte composition, applied potential, and duration. The graphite was selected as the electrode (cathode) as an economical approach. Two-step anodization was selected over one-step anodization, as it resulted in the growth of a homogenous nanotubular structure with a good length of TNTAs. Ethylene glycol was selected over diethylene glycol and glycerol as the best type of electrolyte, due to homogenous and reproducible morphological development. Ethylene glycol with a composition of 2.5% water content and 0.4% ammonium fluoride percentages exhibited the most homogenous structure. It achieved a nanotube length of 5.3±1.3μm with an open tube average diameter of 65.38±5.68 nm. As for the applied potential, 40V exhibited the most homogeneous structures over 20, 30, and 50V applied potentials. It was also observed that increasing the anodization durations and potential increased the lengths of the nanotubes such as 50V-2h achieved the highest nanotube length of 16.2 μm. While 40V-4h achieved 10.79μm of length due to achieving equilibrium caused by prolonged oxidation and decreased tube and mass transfer. The nanotube length and diameter play a crucial role in maximizing the radial path for reducing rapid e+ /hrecombination rate, which ultimately increases visible light efficiency. All the samples were analyzed using FE-SEM, observed using ImageJ software, and the readings of diameter and length were arranged using OriginPro software. XRD analysis reveals the distinct peaks located at 25.3°, 37.7°, 48.0°, 53.7°, 55.0°, and 62.9° correspond specifically to the planes (101), (004), (200), (105), and (211), respectively associated solely with the anatase phase of the annealed TNTAs prepared using the best anodization parameters. UV-DRS shows that the unannealed achieved up to 3.52eV bandgap, whereas the annealed sample achieved a 3.70 eV bandgap, which leads to high stability, resistance to e- /h+ recombination, and selective productivity. To evaluate the photocatalytic efficiency of prepared TNTAs highly purified CO2 (99.99%) was passed continuously through a gas-solid phase photoreactor and the product was periodically collected. Notably, the annealed catalyst (40V-1h) exhibited the most promising performance, achieving a methane formation rate of 72 μmol g-1 h -1 within 60 minutes and accumulating a concentration of 228μmolg-1 by the 240-minute mark, sustaining a rate of 57 μmol g-1 h -1 . Nonetheless, very few researchers have produced TiO2 catalysts using electrochemical anodization, investigating how anodizing parameters affect morphology, optical properties, and the yield of photocatalytic products. Notably, the resultant photocatalyst exhibited significant CO2 reduction under visible light, underscoring its importance in energy and environmental contexts. This promising development signals opportunities to employ the synthesized catalyst for addressing CO2 reduction challenges through photocatalysis, thus expanding its potential applications
THE0009975 (Local)
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