Controllable Synthesis,Modification Of TiO₂ Nanotube Arrays And Their Photocatalytic Properties

High specific surface area,dense and orderly structure,strong adsorptive power and rapid electronic transmission contribute to the excellent application value of TiO₂ nanotube arrays prepared by anodic oxidation method working in Dye Sensitized Solar Cell?DSSC?,gas sensitive sensor materials,photochromic behaviors,photocatalytic degradation and photolysis of water hydrogen production.In this paper,highly ordered TiO₂ nanotube arrays were produced via the electrochemical anodic oxidation process.From the electrochemical mechanism of anodic oxidation,we investigated the parameters of anodic oxidation process which influenced its morphology structure.Also,an new and efficient in situ two-step anode oxidation process was explored,and the TiO₂ nanotubes with butterfly-wing strengthened hierarchical shape could be controlled well.On the base,noble metals such as Ag,Au and Pt were fabricated onto those very nanotube arrays separately.Furthermore,we tested the photocatalytic degradation properties of modified nanotubes arrays through gas phase methanol and methanal catalytic oxidation.We deeply discussed the relations between anodic oxidation process parameters?anodic oxidation voltage and ratio of electrolyte?and TiO₂ nanotube arrays morphology by means of many characterization methods?SEM,EDS and XRD,etc.?,and probed into the controllablepreparation rule of TiO₂ nanotube arrays.With the growth of voltage,the average diameter of nanotubes increased,and the best voltage range was 20 V-50 V,The composition ratio of electrolyte affected its smooth level,the optimal ratio was ethylene glycol solution with 0.3 wt%NH4F and 2 H20 vol%.TiO₂ nanotubes arrays were shaped as butterfly-wing enhanced hierarchical structure was created through a novel in situ anodic two-step oxidation method by changing second oxidation voltage.These very TiO₂ nanotubes arrays owned unique double-wall,the top layer showed hexagonal pore shape and the bottom presented tube form,the whole emerged the compact feature with several tubes hided in one bigger pipe.The lager gap between the first anodic oxidation voltage and the second was,the more tubes came out in the bottom layer,and the structure was much tighter.The gas phase methanol photocatalytic degradation experiments results demonstrated that photocatalytic activity of TiO₂ nanotube arrays prepared under the condition of two-step anodic oxidation voltage?50 V/20 V?was higher than one-step method.Due to bigger specific surface area,the reaction rate constant of the former was three times as much as the latter.Ag,Au and Pt nanoparticles were successfully deposited onto butterfly-wing hierarchical structured TiO₂ nanotubes surface by way of photo-deposition process.Gas phase methanol and methanal were taken as target degradation objects,and photocatalytic performances of TiO₂ nanotubes before and after decoration were estimated by infrared spectrometer?FTIR?,Moreover,we deeply analyzed their degradation mechanism.It was revealed that the oxidative decomposition time of gas phase methanal was shorter than methanol;TiO₂ nanotubes doping with noble nanoparticals expressed wider spectral absorption scale and displayed significant photocatalytic properties because of Schottky barrier formation between noble metal particles and TiO₂,and the photocatalytic property order is Pt/TiO₂>Au/TiO₂>Ag/TiO₂.