The Preparation And Properties Of Single Crystal Like TiO₂ Nanotube Arrays With Different Preferential Orientation

Single crystal like TiO2 nanotube(SC-ATONA)has attracted much attention owing to its excellent properties,like superior charge transport and a large surface area.However,most of the prepared TiO2 nanotubes are polycrystalline structure,which leads to recombination of photo-generated electrons and holes at the grain boundaries.Therefore,it is necessary to prepare a single-crystal TiO2 nanotube array by a simple method.However,the current preparation methods are complicated and there is no clear mechanism to explain the formation process.Herein,we report a facile method to prepare one dimensional SC-ATONAs.And the mechanism of the preferential orientation of single crystallization of TiO2 nanotubes is also proposed.Accordingly,the preferential orientation of SC-ATONAs could be controlled precisely.(1)Based on the influence of F-ion on the crystallization temperature of amorphous TiO2,the single-crystal TiO2 nanotube arrays were successfully prepared by controlling the temperature and heating rate.When the temperature is slowly increased,the amorphous TiO2 on the upper end of nanotubes will be crystallized by the anatase TiO2 which is preferentially crystallized at the bottom of the nanotubes in a short time.Thus,a TiO2 nanotube array with single crystal structure is formed.Through the change of concentration of NH4F in the electrolyte,the selective orientation exposure of anatase(001)and(101)crystal planes can be used to control the preferential orientation.(2)The prepared SC-ATONA were tested for degradation of MO under UV-light.It was found that the sample ATONA0.5(S)has the best photocatalytic activity,and the reaction constant K is 1.93 times that of the polycrystalline sample.The optical properties of ATONA0.5(S)and the polycrystalline sample ATONA0.5(R)were also elevated.The results show that the sample ATONA0.5(S)has a faster response speed and a bigger ratio of light and dark current.(3)Through the method of photocatalytic oxidation reduction,FeOx and Ag were successfully loaded on the surface of TiO2 nanotubes,further improving the photocatalytic performance of the sample ATONA0.5(S).By adjusting the concentration of the solution and the time of illumination,the best samples of the photocatalytic performance of fe-50 mL/3 h and Ag-20 mL/1 h were obtained,and their performance improved by 30.73%and 44.55%respectively.