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Formation Mechanism Of Anodic TiO2Nanotube And Nanopore Arrays

Posted on:2014-01-08Degree:MasterType:Thesis
Country:ChinaCandidate:Z M TanFull Text:PDF
GTID:2231330398454508Subject:Materials Science and Engineering
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TiO2is one of the most extensively studied materials in the fields of photo catalysis, dye-sensitized solar cells, biomedical devices, etc. Compared to other forms of titanium dioxide, anodic titanium oxide nanotube arrays (TNTs) exhibit improved properties due to their high surface area and controllable nanoscale geometry. Specific size and morphology control and intensive investigation of the anodic TNTs are of great significance for the preparation of novel TiO2nanoporous film and exploration for further applications in new fields.In this study, first, morphologies of highly ordered titanium oxide nanotube and nanopore arrays fabricated by anodic oxidation of titanium foil in a glycol solution containing0.5%ammonium fluoride were studied under various water concentrations, anodizing voltages and electrode distances. By fine tuning the anodizing voltage, titanium oxide nanotube arrays with an inner diameter ranged from20nm to145nm were prepared. Also, highly ordered titanium oxide nanopore arrays were successfully prepared by controlling the distance between two electrodes. Moreover, the possible formation mechanism of morphology variation of titanium oxide porous film was studied by analyzing the current density distribution inside the titanium dioxide film simulated by finite element analysis (FEA). It seems the different current density at different position in the TiO2film is one of the important factors for the the morphology formation of porous TiO2films.Then, Ti4+ions produced from the titanium electrolysis were demonstrated to react with F-to from TiF4/[TiF6]2-and dissolve into the electrolyte. During the anodization, TiF4/TiF6]2-were found to hydrolyze, leading to the deposition of TiO2. In particular, this deposition could be occurred at the very early stage of the anodization in the aged electrolyte which contains sufficient TiF4/[TiF6]2-. TiO2mainly deposited on the wall of the original naotube arrays or the edge of the remained slot during the anodization. According to FEA result, this deposition changed the current density distribution and promoted the wall formation of TNTs. Accordingly, a new mechanism model, namely TiO2grown upward and etched downward, was proposed for anodic TNTs formation. Furthermore, based on this hydrolysis deposition, a variety of novel structures of TNTs including the TiO2nanotube with a close mouth, three-layered TNTs with connected and unconnected pores and TiO2microflowers decorated TNTs were synthesized.Through adjusting the TiF4/TiF62concentration and the anodizing time, optimized TiO2nanopore arrays and nanoribbons were prepared by a re-electrolysis of Ti plate after the first TNTs was removed. Morphologies of the nanotube. nanopore and nanoribbon at different formation stages were observed by Scanning Electric Microscopy and the forming process was discussed. Moreover, the results show that with the assistant of TiO2hydrolysis deposition, nanopore arrays can be transferred into nanotube arrays, and the nanoribbons can be derived from deposition of TiO2on the nanotubes, which further proved that the previous TiO2grown upward and etched downward model.Finally, copper oxide, iron oxide, cerium oxide and manganese oxide were separately loaded into the anodic titanium nanotube arrays and selective catalytic reduction of NOx was conducted over the catalysts. The results showed that the denitration performance of Mn/TNTs is best, the NO transition of which at low temperature (150℃-225℃) is up to more than90%while that of Cu/TNTs. Fe/TNTs and Ce/TNTs increased with temperature and reached80%.70%and60%at300℃. respectively.
Keywords/Search Tags:TiO2nanotube arrays, TiO2nanopore arrays, Anodic oxidation, Hydrolysis deposition, Selective catalytic reduction, De-NO_x
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