Effect Of Electrolyte On Preparation And Photocatalytic Property Of TiO₂ Nanotube Arrays On Pure Titanium Substrate

Electrolytes play an important role in the formation, the composition, the photocatalytic activity of TiO₂ nanotube arrays on pure titanium during anodic oxidation. The different morphology of TiO₂ nanotube arrays and even the doping of nitrogen and other nonmetal elements in TiO₂ structure could be obtained in some elcctrolytes.In this work, the TiO₂ films are prepared by constant voltage anodic oxidation on the surface of pure titanium, separately using HF(0.5wt%), HF(0.5wt%) + (NH₄)₂SO₄(1¹.5mol/L), HF(0.5wt%) + (NH₄)H₂PO₄(1¹.5mol/L), HF(0.5wt%)+ NaNO₃(1¹.5mol/L), HF(0.5wt%) + (NH₄)₃PO₄(1¹.5mol/L) as electrolytes. The morphology and the composition of the films are analyzed by FESEM, EDX and XPS. The crystal structures of TiO₂ films are investigated by XRD. It is found that the tube diameter of TiO₂ nanotube arrays reduces evidently with hydrous titanic oxide on the film surface when adding (NH₄)₂SO₄ or (NH₄)H₂PO₄ in the electrolytes. The morphology of TiO₂ nanotube arrays hardly changes when NaNO₃ is added. Nitrogen could be doped in TiO₂ nanotube arrays as the structure of N-Ti-O, but other nonmetal elements are difficultly doped in the films. Therefore, electrochemical method could be used in the doping of nitrogen. XRD analysis indicates that different compositions of electrolytes have little influence on the transition temperature of the crystallization of TiO₂. The TiO₂ films prepared in different electrolytes are also used as photocatalyst to degrade the methylene blue under UV irradiation. At approximately 400℃of heat treatment, the TiO₂ films with the structure of anatase and highly-ordered TiO₂ nanotube arrays have better photocatalysis performance. But when the TiO₂ nanotube arrays with deposits on the surface are not ordered, the photocatalysis performance is worse. The doping of nitrogen in TiO₂ nanotube arrays can improve photocatalytic activities.