Investigation Of Fabrication, Modification, Characterization And Photocatalytic Activity Of Titanium Dioxide Nanotube Array

Heterogeneous semiconductor photocatalysis is an important technique valuable for solar energy conversion and environmental purification.Among various oxide semiconductors,titanium dioxide(TiO₂)has been proved to be one of the most suitable photocatalysts for widespread environmental applications because of its strong oxidization,non-toxicity and long-term stability against photo and chemical corrosion.However,the fast recombination rate of photogenerated electron-hole pairs in the bulk TiO₂ and the low quantum yield of photochemical conversion for solar energy severely hinder the industrialized applications of TiO₂ photocatalyst.In recent years,many attempts have been made to improve the photocatalytic activity of TiO₂.In the present work,we focus on the development of electrochemical anodic oxidation technique to directly fabricate highly ordered TiO₂ nanotube array films on the titanium substrate.Some preparation parameters of TiO₂ nanotube arrays were systemically investigated.The SEM,XRD,Raman spectroscopy,UV-Vis diffuse reflection spectroscopy,EIS,and photocurrent spectroscopy were performed to characterize the morphology,crystalline phase,photo-absorption ability and photoelectrochemical property of TiO₂ nanotube array.The photocatalytic activity of the TiO₂ nanotube array film was evaluated by the decolorization of methyl orange in aqueous solution.Some critical structure factors of TiO₂ nanotube array film in the photocatalytic activity was discussed as well.The TiO₂ nanotube array films were modified to enhance photocatalytic efficiency by using a wet doping method.The main results and progresses of this dissertation are outlined as following:1.A new fluorinated electrolyte system containing glycerol has been developed to fabricate the TiO₂ nanotube arrays in a much wider voltage range between 5 and 33 V.The influences of the applied potential,anodizing time,and electrolyte composition on the formation of TiO₂ nanotube arrays and dimension of the resulting nanotubes are investigated in detail.It is found that the diameters of the as-prepared TiO₂ nanotubes varies enormously from 20 to 150 nm and its thickness changed from a few hundreds nanometers to several micrometers, depending on the controllable experiment conditions.2.The kinetic analysis shows that the charge transfer step is a determined reaction for the photoreactions process on TiO₂ nanotube array films.The TiO₂ nanotube array films exhibit a drastically enhanced photoresponse compared with the TiO₂ nanoparticle film prepared by the regular sol-gel method,which suggests that TiO₂ nanotube array film has a greater photocatalytic activity.3.The photocatalytic activities of the high-aspect-ratio TiO₂ nanotube array films are evaluated by the decolorization of methyl orange.Compared with the TiO₂ nanoparticle film,the nanotube array films exhibit a higher photocatalytic activity, which is ascribed to the more effective separation for the photogenerated electron-hole pairs and the higher internal surface area of the special nanotube array structure.In addition,the photocatalytic degradation by TiO₂ nanotube array films is not only able to destroy the conjugate system in methyl orange,but also degrade totally the polyaromatic rings of methyl orange to CO₂ and H₂O.The experiment results indicate that the film thickness markedly influences the photocatalytic activity of nanotube array film.But the apparent rate constants are slightly affected by the diameter of nanotubes,if the thickness of the TiO₂ film is kept the same.It is found that the 2.5μm-thick TiO₂ nanotube array film annealed at 500℃appears a maximum photodegradation efficiency to methyl orange.4.The nitrogen-doped TiO₂ nanotube array,which possesses great photoabsorption in the visible light region,is fabricated by an electrochemical anodic oxidation followed a wet process.The XPS result indicates that the nitrogen atoms are doped into lattice oxygen of TiO₂ nanotubes.Compared with the TiO₂ nanotube array film,the N-doped TiO₂ nanotube array film exhibites a higher photocatalytic activity which is evaluated by the decomposition rate of methyl orange using the tungsten-halogen lamp as light source. 5.The silver-doped TiO₂ nanotube array films are fabricated by combining pulse current electrodeposition with anodic oxidation method for the first time.The Ag nanoclusters are uniformly deposited inside the nanotubes,which are expected to be of benefit to the separation of photogenerated electron-hole pairs and enhancement of photoresponse of TiO₂ nanotube array films.