Modification Of TiO₂Nanotube Array And Its Application On Photoelectrocatalytic Degradation Of Methylene Blue

Because of the high surface-to-volume ratios and specific architectures, the TiO₂nanotube films had a series of unique properties in both physical and chemical areas,which made them of great applicable potential in the fields of photocatalysis, gassensing, photoelectrolysis and photovoltaics.Therefore, the fabrication of TiO₂nanotube films and the exploration of their potential in practical application had beenmore and more attractive. In this dissertation, highly ordered TiO₂nanotubes wereprepared via electrochemical anodic oxidation, and the photoelectrocatalyticalperformances of property TiO₂nanotube films were investigated and the Au/TiO₂,Pd/TiO₂, Cu/TiO₂and Sn/TiO₂nanotube composite films were prepared via reversemicroemulsion electrodeposition method. Moreover, the microstructure andphotoelectrochemical properties of TiO₂nanotube films were characterized andanalyzed through various methods.SEM images indicate that the top-opened TiO₂nanotube were well aligned andorganized into high-density uniform arrays, and the diameter size range from30to70nm. The XRD patterns showed that the samples fabricated by anodic oxidation wereamorphous without being annealed and the sample crystallized in the anatase phase,which had good photocatalytic activity. Effect of heat treatment on thephotoelectrocatalysis performance of TiO₂nanotube array films had been studied. Theamorphous films were crystallized annealing in different atmospheres such as theoxygen, air, argon, and hydrogen. The photoelectrocatalysis performance of theas-annealed nanotube arrays was investigated using methane blue dye （MB） as atarget pollutant. The results showed that the MB degradation kinetics fits the law offirst order reaction and the rate constants are4.967,3.127,1.989, and1.625h1at0.5V bias, respectively. Electrochemical impedance spectroscopy analysis revealed thatthe MB degradation behavior was governed by the charge transfer characteristic of thenanotube. The improvement of light absorbance and excitation as well as the lowertransfer impedance might be critical factors for the efficient photoelectrocatalysis ofTiO₂arrays annealed in oxygen.Au, Pd, Cu and Sn doped TiO₂nanotube array films had been successfullyfabricated by electrodeposition with reverse microemulsion method. The diffusereflectance spectroscopy test of this composite films indicate that compared to TiO₂nanotubes electrode, the start of the absorption edge of Au, Pd and Cu metal ions doped TiO₂nanotubes electrode appears red shift, and the excitation wavelength rangeis extended to visible light due to the doping of Pd, greatly improving the utilizationof sunlight.The photoelectrocatalytic properties of various TiO₂nanotube array films wereinvestigated degradation efficiency of MB dye. The critical factors ofphotoelectrocatalysis, for instance, bias potential, electrolyte, initial pH value,illumination intensity, the surface area of photoelectrode were analyzed. The resultsindicated that the degradation efficiency on MB was greatly enhanced by thesynergetic effect of photoelctrocatalysis and the superior adsorbility of nanotubularstructure. The photoelectrocatalytic degradation on MB was carried out in quartz glassreactor with aqueous solutions, and NaCl was used as the electrolyte, the applied biaswas0.5V, the pH=3.25, light intensity is1000μW/cm², the surface area of nanotubearray film was2cm×2cm, the samples was annealed in oxygen atmosphere, theefficiency of photoelectrocatalysis degradation of MB was to99.56%. The results ofEIS analyses revealed that the surface reaction step was the only controlling step forthe photoelectrocatalytic process. The bias potential could decrease the values of theelectron-transfer resistance and increase the separation efficiency of photogeneratedelectron-hole pairs.