Preparation And Properties Of TiO₂ Nanomaterials By Hydrothermal Method

Nano titanium dioxide is an excellent inorganic functional material,which has been widely used in the application of environment protection in the recent years.Therefore,the demand for the preparation of TiO₂ nanomaterials with different morphologies and structures is increasing,and the problem of immobilization in the preparation of TiO₂ nanomaterials is also an important research direction.In this study,the immobilized one-dimensional TiO₂ nanotubes and TiO₂ nanorods with high performance,have been synthesized using Ti foil as titanium source and substrate by the simple and economical hydrothermal method in alkaline solution and acid solution,respectively.The growth mechanism was discussed,and the morphology,structure and properties of TiO₂ nanomaterials were investigated.Furthermore,the correlations between the technological parameters?concentration of solution,reaction temperature and reaction time?and the characterization of TiO₂ nanowires were investigated systematically.It showed that:?1?High-density anatase TiO₂ nanotubes network were successfully prepared by hydrothermal method on the surface of Ti foil in NaOH solution.The network were composed by size uniform,complete structure nanotubes with the diameter of 50 nm which highly twisted together in a disordered way,accompanied by a small amount of cross pores.?a?The formation mechanism of TiO₂ nanotubes network: First,the titanate hydrogel was formed by the reaction of the titanium foil with the NaOH solution,and then the Ti-O bond of the titanate hydrogel began to break to form the sodium titanate with Na-Ti-O lamellar structure.With the progress of the reaction,the nucleation of Na2Ti3O7 sodium titanate lamellar structure continued to grow,and finally the unstable lamellar structure ruptured on the surface of Ti and changed the growth direction of the product.After the acid washing process,the excess H+ proton makes the lamellar structure in an unbalanced unstable state and spontaneously crimps into a low-energy nanotube.And finally get the TiO₂ nanotubes network.?b?The increase concentration of NaOH solution is beneficial for the growth of TiO₂ nanotubes.When the concentration of NaOH solution reaches 7M,the nucleation rate and density of TiO₂ was high.TiO₂ nanotubes were crossed with each other with a small amount of micropores which the diameter of one single TiO₂ nanotube is about 50 nm.As the concentration increase to 10 M,the diameter of the nanotubes remain constant,but the content of crystal phase increased.The overlarge density of nanotubes lead to TiO₂ nanotubes excessive crossed to a flat film structure on the Ti foil,making the utilization rate of internal TiO₂ particles reduced.The result of photocatalytic degradation test shown that TiO₂ nanotubes prepared on 10 M NaOH solution have a higher instantaneous photocatalytic degradation rate before 60 min.But the photocatalytic degradation rate of TiO₂ nanotubes prepared on 7M NaOH solution was higher on 105 min due to the huge internal reaction space,which provided more TiO₂ active sites in the degradation process.So the photocatalytic degradation rate of TiO₂ nanotubes reached the best 80% when the concentration of NaOH solution was 7M.In order to show the best hydrophilic performance,it was essential to have the factors such as the high content and great morphology crystal phase.There is not much difference between the sample prepared at the concentration was 7M or 10 M,which water drop almost layed on the surface of sample,and the optical contact angle was below 10 °.?c?With the increase of hydrothermal temperature,the content of TiO₂ phase gradually increased,the morphology of nanotubes became uniform,pores were filled by dense network.From the results of photocatalysis,it was found that the the sample prepared at 160? have a higher photocatalytic degradation rate than 170?,owing to the higher utilization rate of the internal particles of sample with a small amount of micropores prepared at 160? than the over dense network prepared at 170?.The hydrophilic performance differences between the two samples were small,the water drop almost layed on the surface,the optical contact angle was between 5° to 8°.?2?High-density rutile three-dimensional TiO₂ nanorods tree structure were successfully prepared on the surface of Ti foil in HCl solution by hydrothermal method.The three-dimensional tree structure show huge surface area,which composed of many nanorods with diameter of 100nm-1?m.Coarser TiO₂ nanorods form "trunk",meanwhile many "branches" nanorods nucleated on the "trunk" nanorods,and the "branches" nanorods grown up and become "trunks" and have new "branches" grow.?a?The increased concentration of HCl solution is beneficial to the growth.The morphology and tree structure of TiO₂ nanorods were optimized when the concentration was 0.5M.But TiO₂ nanorods will be corroded by high concentration.Since the performance of the sample is closely related to the content of crystal phase,crystallinity,morphology and structure,so the best photocatalytic and hydrophilic properties of the samples were synthesized when the HCl concentration is 0.5M.?b?As the hydrothermal temperature increased,the content of crystal phase gradually rised and reached best tree morphology structure when temperature was 220?.However,excessive temperatures lead to the overgrowth nanorods,which reduced the specific surface area because overlarge nanorods were connected tightly to each other.Since the three-dimensional tree morphology structure can diffuse the incident light several times to make it full used by Ti O₂ nanorods.So the sample of temperature 220°C which shown the best tree morphology has optimum performance.In our study,the best photocatalytic degradation rate of methyl orange is 71% and the hydrophilicity also achieves the best,the optical contact angle was 13°.?c?When the reaction time was short,the atomic contact was not sufficient which lead to the poor crystal content and morphology of the samples.The best structure and morphology of nanorods were reached when the reaction time was 12 h.However,the size of nanorods increased excessively with the time.The nanorods grown at this moment became closely connected,which huge reduced the aspect ratio and specific surface area.So the available Ti O₂ surface area rapidly decreased.Correspondingly,the sample prepared at 12 h shown the best photocatalytic performance,the photocatalytic degradation rate was 71%.The sample prepared at 12 h also exhibited best hydrophilicity.After ultraviolet radiation,the water drop almost layed flat on the surface of the sample,and the optical contact angle was 13°.