Preparation Of BaTiO₃/TiO₂Heterojunction Nanotube Arrays And Investigation Of Their Photoelectrochemical And Photocatalytic Activity

Among the photocatalysts, highly ordered and well aligned titania （TiO₂） nanotube arrays fabricatedby electrochemical anodization offer a large surface area and stronger adsorption capacity. TiO₂nanotubearrays have attracted much attention in various fields. However, the low photo conversion efficiency is stilla major barrier to restrict the practical application of TiO₂nanotube arrays. Numerous modificationmethods have been applied to TiO₂nanotube arrays to solve this problem. Particularly, coupling of TiO₂nanotube arrays with other semiconductors with a matching energy band structure will facilitate the transferand separation of photo-generated electron-holes, so as to achieve the purpose of improving the utilizationefficiency of the incident light. Ferroelectric materials have internal dipolar fields that could separatephotogenerated carriers, and this has motivated several investigations of their photochemical properties.BaTiO₃is one of the important semiconductors with high dielectric and ferroelectric properties. And moreinterestingly, the conduction band and valence band of BaTiO₃is higher than those of TiO₂. If the chargeseparating characteristics of BaTiO₃could be combined with the photocatalytic properties of TiO₂, it mightbe possible to increase the photocatalytic efficiency. In my thesis, the BaTiO₃/TiO₂（denoted as BT）heterojunction nanotube arrays were fabricated by the hydrothermal method using TiO₂nanotubes obtainedfrom the electrochemical anodization as both template and initial reactant. For further improve thephotoelectrochemical and photocatalytic properties, Ag nanoparticles and other cocatalysts were loaded onthe surface of BT heterostructures by different methods. The detailed contents are as follows:（1） BaTiO₃/TiO₂heterostructure nanotube arrays were fabricated by in situ hydrothermal methodusing TiO₂nanotubes as both template and reactant. Four kinds of different BaTiO₃/TiO₂heterojunctionnanotube arrays were obtained by adjusting the reaction temperature, time, and the concentaration of theprecursors,. The photocatalytic degradation of methylene blue （MB） was chosen as a model reaction toevaluate the photocatalytic activities of samples. In addition, the photoelectrochemical properties werestudied by I-V curves and electrochemical impedance spectra （EIS）. The results indicated that BaTiO₃/TiO₂heterojunction nanotube arrays showed an enhanced photocatalytic activity for MB photodegradation thanthe pure TiO₂nanotube arrays, especially for BT-1sample, its photocatalytic yield for MB degradation reached72%. Moreover, the EIS results showed that the impedance arc radius of BaTiO₃/TiO₂heterostructures was smaller, indicating an improved separation efficiency of the charge carriers wasachieved.（2） Ag nanoparticles were loaded on the surface of BaTiO₃/TiO₂heterostructure by two differentmethods. SEM images showed that the silver nanoparticles obtained by the chemical reduction had auniform size and dispersed very well on the surface of BT nanotube arrays. And those obtained by thephoto-reduction method were very large, which made the integrated nanotube architecture destroyed.UV-vis DRS spectra showed that Ag/BT-C had a stronger absorption both in UV and visible light range.And the photocatalytic activity for MB degradation on Ag/BT-C reached nearly95%within180min, whichis much higher than that of Ag/BT-P and the pure BT nanotube arrays. In addition, the electrochemicalimpedance spectra showed that the impedance arc radius of Ag/BT-C was smaller; indicating that anenhanced charge carrier separation was achieved on Ag/BT-C.（3） Several different cocatalyst nanoparticles （Pt, Pd, Cu, Ni） were loaded on the surface ofBaTiO₃/TiO₂heterostructure by chemical reduction methods. The results indicated that the photocatalyticactivity for MB degradation and photocurrent of BT heterostures were improved a lot after thesecocatalysts were loaded. And the order of the photocatalytic activity was in accordance with that of thephotocurrent. The order was follows: Pt/BT-C> Ni/BT-C> Cu/BT-C> Pd/BT-C> BT.