| Due to its properties of high chemical stability, no photo-corrosion and environmental friendly, TiO2 nanomaterials become the research focus in the field of wastewater treatment by photocatalysis in the past few decades. But wide bandgap and high recombination ratio of photo-generated carriers make it is impossible to directly use TiO2 materials as high performance visible light photocatalyst. Narrowing the bandgap and inhibiting the recombination of the carriers are the only way to improve the photocatalytic performance of the TiO2 materials. In this thesis, we found that both doping and heterojunction structure modified TiO2 based photocatalysts have their own disadvantages through studying their photocatalytic performances. In order to obtain high performance TiO2 based photocatalysts, we studied the influence of carbon materials for the photocatalytic performance of TiO2 materials. The result demonstrate that the rational structure of the TiO2/C composite can not only improve the photocatalytic performance of TiO2 materials, but also achieve the recycling of the catalyst, which is the key to realize the actual application of TiO2 based photocatalysts. And in the further study on the effective separation of the photo-generated carriers, we conceive and complete the design of a new photocatalysis device, which is named photon-driven fuel cells. Photon-driven fuel cells can achieve the photodegradation of the organic matter and the generation of electricity simultaneously, which ideally combines the wastewater treatment with the production of energy. Lots of experiments are needed to study the preparation of the high performance electrode because the requirement of electrode materials is harsh. For narrowing the bandgap and inhibiting the recombination of the carriers, we studied the photocatalytic performance of TiO2 based photocatalysts, which were modified respectively by doping, surface treatment and attached on carbon materials, and analyzed its device development. The main content are as follows:(1) Fe-doped TiO2 nanoparticles have been prepared by hydrothermal method, and their photocatalytic performances were also tested with methylene blue (MB) as the degradation target. The result demonstrate that doping can indeed enhance the absorption of visible light, but Fe ions in the crystal of TiO2 also play the role in the recombination center of carriers, which would decrease the photocatalytic performance of TiO2. Then we obtained black TiO2 nanomaterials after the pure TiO2 nanoparticles had been treated in the hydrogen plasma atmosphere. The black TiO2 belongs to the self-doped TiO2 material, which can absorb visible light, even partial near infrared light. And its excellent photocatalytic performance under visible light is determined by the absorption of visible light, large amounts of oxygen vacancies and the Ti-H bond, which as the capture agent of electrons can enhance the separation of carriers.(2) In order to avoid the increase of the recombination ratio caused by the dopant, we prepared some heterojunction structures, which are consisted of TiO2 and other common narrow bandgap transition metal oxides, to achieve the absorption of visible light and enhance the separation of carriers simultaneously. The result demonstrate that though the Type I heterojunction structure can absorb visible light, it cannot achieve the effective separation of carriers, which leads to its poor photocatalytic performance. And the Type II heterojunction structure can enhance the effective separation of carriers due to its proper bandgap structure, but its photocatalytic performance is not very ideal. This phenomenon demonstrates that the effective separation of carriers is not the only factor to enhance the photocatalytic performance of the photocatalyst, the last energy-level site of the hole in photocatalysts may be a more important factor to improve the photocatalytic performance of photocatalyst.(3) Through measuring the photocatalytic performance of TiO2/C composites with different carbon coating content, we find that proper carbon coating could control the content of surface oxygen vacancies on the TiO2 nanoparticles during the calcination process. And it also can enhance the separation of photo-generated carries in the photocatalysis test, which results in the high photocatalytic performance of photocatalysts. Then we prepared different TiO2/C composites with reduction oxide graphene (rGO) microsphere, graphite powder and carbon fiber as carbon matrix respectively, which can be separated from the aqueous solution easily via natural subsidence effect. Through testing the photocatalytic performance of these composites, we find that the TiO2/rGO composite has good dye adsorption property, but its photocatalytic performance is not very stable, which is harmful to its actual application. And the TiO2/graphite powder composite has better photocatalytic performance than the original TiO2 nanoparticles, and its cycling performance is very stable. But because the force between TiO2 nanoparticles and graphite powder is the simplest physical adsorption, its structural stability is not very good. Finally, we obtained TiO2/porous carbon fiber composite by self-template method. The adsorption property of porous carbon fiber and the chemical bond between TiO2 particles and carbon fiber make the composite have good photocatalytic performance, which provide new sight for the subsequent preparation of high performance TiO2 based photocatalyst.(4) Through detailed analyzing the development course of the enhancement process on the separation of photo-generated carriers and refering the structure of the existing electrochemical cell, we design a new electrochemical cell, which is named photon-driven fuel cell. The reaction on the cathode of traditional fuel cell is replaced by the photo-degradation reaction of organic matter in the photo-driven fuel cell. And the photon-driven fuel cell achieves the ideal separation of photo-generated carriers, and realizes the preliminary design of the photocatalysis device, which provides new route for the actual application of photocatalysis. Because the requirement of the photoanode structure and performance is harsh, which caused by the entire reaction process, lots of experiments about the preparation of photoanode are still needed to carry out in future. |
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