Preparation And Photocatalytic Properties Of Oxides Modified Titanium Oxide Nanotube Structures

In recent years, photocatalysis based on TiO2 materials has caused great research interest on the environment issues by researchers around the world. TiO2 photocatalysts are promising candidates to decompose the organic pollutions in wastewaters and to play an important role in the water splitting for the hydrogen production. Among the different kind of TiO2 nanostructures, TiO2 nanotube arrays(TNTs) compared to other nanostructures have greater surface areas, pore volume and higher surface energy, and they also have stronger adsorption capacity, showing better photocatalytic properties and higher performance photoelectric conversion efficiency in practical applications.In practical, TNTs photocatalysts still face some problems:(1) TiO2 have a wide band gap(3.2eV for anatase and brookite phase, 3.0eV for rutile phase), it can only absorb ultraviolet light of sunlight less than 387.5nm wavelength, so the utilization of solar energy is very low;(2) Pure TiO2 nanomaterials have a high carrier recombination rate, and therefore the quantum efficiency is low. Using non-metallic elements/metal element doping, surface modification, the photosensitizer and other ways, the formed composite materials can effectively expand the absorption spectra of TNTs and improve the quantum efficiency. However, the above-mentioned methods make the process more complicated, and theyare more expensive. Combined semiconductor oxides with TNTs, the photo-generated electrons and holes are well separated, and the absorption spectrum can be expanded, thereby quantum efficiency and catalytic activity will be greatly improved.In this thesis, we firstly prepared TiO2 nanostructures with electrochemical anodic oxidation method under different solution conditions, then we assembled Cu2 O, ZnO on TiO2 nanotube array using solvothermal method, dip coating, electrodeposition method, finally we characterized the samples and analyzed the structures carefully. The photocatalytic degradation experiments were conducted under different conditions, and the results were discussed.(1) Using anodic oxidation method, we prepared TiO2 nanostructures in three different solutions, and found that the titanium sheet is formed with the surface of porous cross-linked nanostructures in HF aqueous solution. In NH4 F ethylene glycol solution, TiO2 nanotube arrays were generated, and the length of the tube can reach tens of microns, however, TNTs fabricated in this way are easy to seperate from titanium substrates. In HF/DMSO solution, the well-alligned TNTs were fabricated, and the TNTs are separated each other, and they are well attached with titanium substrates. The TNTs wereannealed at different temperatures and the results showed that the samples annealing at 550?Cobtained anatase phase, and had good photocatalytic effects.(2) Cu2 O nanospheres were prepared by adjusting the reactants, temperature and reaction time, and we found it possible to prepare pure Cu2 O nanospheres, using an ethylene glycol solution with copper nitrate. By controlling the reaction time ranging from 4 hours to 10 hours, we can control the sizes of Cu2 O nanoparticles. We grow Cu2 O nanoparticles on TNTs, and the amounts of Cu2 O nanoparticles increase with the increament of reaction time.. Under visible light conditions, the pure Cu2 O nanoparticles showgood methyl orange degradation rate; the photocatalytic degradation Cu2O/TiO2 nanocomposite structure were carried out under UV and visible light conditions, the results displayed that Cu2O/TiO2 nanostructured composite samples significantly have an enhanced catalytic properties under UV light. The Cu2O-modified TNTS also exhibited greatly improvement of the photocatalytic performance under visible light irradiation.(3) We prepared ZnO/TiO2 nanotubes nano-composite structure usinghydrothermal method, a dip coating method and an electrodeposition method. the nano-composite structure prepared using hydrothermal method had a large number of larger volume ZnO particulates on sample surface.Because ZnO particulates can block TiO2 nanotube compounds fully contacting and combining well with organic in water, resulting the photocatalytic effect decline; ZnO/TiO2 nanocomposite structure prepared using dipping can effectively control the size of the ZnO, and got well photocatalytic activity; ZnO/TiO2 nanocomposite structures prepared using electrodeposition can be facilitate control the amount of the deposited ZnO in TiO2 nanotube arrays by control the length of depositing time, the photocatalytic experimental results show that the deposition time at about 30 s can get better catalytic effect.