Preparation And Properties Of Photocatalyst Materials Based On TNTAs Heterojunction Films

Photocatalytic oxidation technology has attracted much attention due to its high efficiency for degrading organic pollutants and pollution-free. How to improve the photocatalytic performance and realize the reusability has become two key problems in the photocatalysis field, which limits the application of photocatalytic oxidation technology. In this dissertation, BiOBr/TiO2 nano heteroj unction array films (BiOBr/TNTAs) composite photocatalyst has been obtained by forming heteroj unctions between BiOBr and ordered TiO2 nanotube arrays. BiOBr is a semiconductor photocatalyst with high visible photocatalytic performance and stability, while TiO2 nanotube arrays can be easily recycled for their tight adhesion to Ti foils. BiOBr/TNTAs photocatalyst combines the advantages of BiOBr and TiO2 nanotube arrays together. However, the band gap of the BiOBr is 2.73 eV, which limits its visible light absorption. To further improve its visible light photocatalytic performance, the Pt-BiOBr/TiO2 nano heterojunction array films are prepared by decoration of novel metal Pt. The main results of this article are as follows:(1) The ordered TiO2 nanotube arrays films (TNTAs) are prepared by anodization at 60 V for 2 h with ethylene glycol solution containing ammonium fluoride as electrolyte. The effect of water content on the spacings of TiO2 nanotubes is discussed by changing the volume fraction of water in the electrolyte. The results show that the tube spacings between the nanotubes are clear with the diameter of approximately 150 nm and the TNTAs films are closely adhered to the Ti substrate, when the TNTAs are prepared in the electrolyte with 7% vol water.(2) The BiOBr/TiO2 nano heterojunction array films (BiOBr/TNTAs) are prepared by sequential chemical bath deposition (S-CBD) method. The influences of different parameters on the morphology such as reactant concentration, water bath temperature, immersion time and immersion cycles have been studied. The optimal process parameters for preparing the BiOBr/TNTAs samples are achieved with the reactant concentration of 0.05 M, water bath temperature of 40 degree, immersion time of 2 min, and immersion cycles of 2. The morphologies of BiOBr/TNTAs samples prepared with the optimal process parameters are TiO2 nanotubes attached with a lot of tiny BiOBr nanoflakes on the inner and external walls. The photocatalytic performances of BiOBr/TNTAs samples are obeserved and the mechanism is analyzed. The result shows that the BiOBr/TNTAs-2 presents the best photocurrent and photocatalytic performance. The reason may be the synergistic effects of the visible light response of BiOBr nanoflakes, formation of the BiOBr/TNTAs heteroj unctions and high specific surface area, which broaden the light response region and promote the separation and transfer of the photo-induced chargers.(3) The Pt-BiOBr/TiO2 nano heteroj unction array films (Pt-BiOBr/TNTAs) are obtained by loading novel metal Pt with solventhermal method and BiOBr nnanoflakes with S-CBD method on the inner and external walls of nanotubes. The deposition sequence of Pt and BiOBr is determined by experimental analysis. The result shows that the deposition sequence is first Pt particles and then BiOBr nanoflakes. The influences of the chloroplatinic acid concentration on the morphology of Pt/TNTAs samples are discussed. Pt particles become more and bigger with increase of the concentration, and overloading Pt particles results in particle aggregation and tube-mouth blocking. The optimum concentration of chloroplatinic acid is achieved to be 2 mM. Furthermore, the influence of immersion cycles of BiOBr nanoflakes is discussed. BiOBr nanoflakes became more and bigger with increasing immersion cycles, and that overloading of BiOBr nanoflakes will make the tube-mouth blocking. The Pt-BiOBr/TNTAs-2 possesses the best photocatalytic performance. The superior photocatalytic performance is due to the synergistic effects of the following factors:the surface plasma resounance (SPR) effect of Pt particles, electron traps of Pt nanoparticles, the visible light response of BiOBr, and the formation of different heteroj unctions in Pt-BiOBr/TNTAs.