Preparation Of Visible Light Activity TiO₂-Based Nanotube Arrays Composite And Their Performance In Degradation Of Organic Pollutants In Aqueous Solution

Human beings have to face the problems of global environmental pollution and energy crisis in twenty-first century. The photocatalytic method as a green chemistry technology has become a research hotspot on the removal of of persistent organic pollutants in the environment. TiO2as a representative and promising photocatalyst, especially TiO2nanotube arrays with a one-dimensional ordered structure caused widespread concern because of its unique and orderly array structure, high specific surface area and better charge transfer performance. However, the bandgap of TiO2is3.2eV, which means it can only be excited by UV light of wavelengths less than387nm. The utilization of visible light accounting for most of the solar spectrum is low. Furthermore, the photo-generated charge and holes of TiO2easily recombine within the crystal composite, leading to the low quantum efficiency. These two problems limit the application of TiO2in practice. In this dissertation, the TiO2nanotube arrays was modified by using a conductive polymer PANI, precious metals Ag nanoparticles and Ag/Ag3PO4nanoparticles, respectively. And the morphology, structure, and photoelectrochemical properties of the composite material were characterized and discussed in detail. The main contents and results are as follows:(1) The PANI-loaded TiO2nanotube arrays were prepared by anodic oxidation method combined with cyclic voltammetry. The obvious red shift absorption was observed after the modification of PANI. Meanwhile, the separation efficiency of photo-generated electrons and holes has been significantly improved after the PANI was loaded. The efficiency of photocatalytic degradation of Rhodamine B (RhB) of the PANI-loaded TiO2nanotubes electrode was more than5times when compared with pure TiO2nanotube array electrode under visible light irradiation. The efficient photocatalytic activity was mainly due to the visible light sensitivity of PANI, and the energy band matched well with TiO2.(2) The Ag-loaded TiO2nanotube arrays were prepared by anodic oxidation method combined with ultrasonic-assisted UV phococatalytic reduction technique. The Ag-loaded TiO2nanotube array has obvious photocurrent response under visible light irradiation. And the charge transfer rate was improved significantly. Compare with pure TiO2nanotube arrays, the2,4,6-trichlorophenol degradation efficiency of Ag-loaded TiO2nanotube array electrode was improved significantly under simulated sunlight irradiation. The reactive oxygen species were·OH during the photocatalytic reaction, which were detected by chemical fluorescence and electron paramagnetic resonance technology. The dechlorination of2,4,6-trichlorophenol was anlysed by the detection of C1-concentration in the solution. The intermediate products of2,4,6-trichlorophenol degradation were identified by DFT calculations and LC-MS technique. And the degradation pathways of2,4,6-trichlorophenol on the surface of Ag-loaded TiO2nanotube arrays electrode were confirmed.(3) A new visible light photocatalyst of Ag/Ag3PO4nanoparticles was fabricated by chemical precipitation combined with in situ solvent reduction method. The photocatalysts showed strong photocatalytic activity for decomposition of dyes under visible light irradiation. And they also had strong oxidation of chlorophenol wastewater. The generation of active species in the photocatalytic system was detected, and the results indicated that the degradation process of the pollutants was mainly due to the direct oxidation by the holes. Combined with DFT theoretical calculation method, Ag3PO4catalyst is a narrowband and indirect semiconductor. And the bandgap is about2.57eV. The electron can be excited from the O2p orbitals to the5s orbital of Ag under visible light. Because of the hybridization of O2p orbital and P3s orbital, the electron can be excited from the valence band to the conduction band more easily.(4) The Ag/Ag3PO4-loaded TiO2nanotube arrays were prepared by anodic oxidation combined with chemical impregnation method. The clusters of Ag/Ag3PO4nanoparticles formed on the surface of the TiO2nanotubes and caused no damage to their ordered structure, and the phenomenon of blocking did not happen. The UV-Vis absorption of Ag/Ag3PCO4-loaded light TiO2nanotube arrays electrode expanded to the visible light region. Photocurrent response of Ag/Ag3PO4-loaded TiO2nanotube arrays in the visible light was much higher than the pure TiO2. The degradation efficiency of2-chlorophenol (CP) can reach more than95%under visible light irradiation with the Ag/Ag3PO4-loaded TiO2nanotube arrays. However, the degradation efficiency of2-CP only reached20%with the pure TiO2nanotube arrays electrode under the same conditions. The reactive oxygen species were OH during the photocatalytic reaction, which were detected by chemical fluorescence and electron paramagnetic resonance technology.The TiO2nanotube arrays electrode loaded with PANI, Ag nanoparticles and Ag/Ag3PO4nanoparticles effectively improve the utilization of visible light. They have great significance for the development of the practical application of photocatalytic technology.