Preparation, Characterization And Application Of Some Semiconductor Materials With Photocatalytic Property

Among semiconductor photocatalytic materials, TiO₂ becomes a most important photocatalytic semiconductor material because of its advantages of high photocatalytic activity, strong ultraviolet radiation shielding, good thermal conductivity, good dispersibility and cheap, non-toxic, no secondary pollution, etc. And Cu₂O is a rare semiconductor materials excited by visible light. Its band gap is about 2.1eV, so it could be excited by 400-800nm wavelength of the visible light; in addition to, Cu₂O is nontoxic, low-cost preparation and higher theory efficiency. So these two semiconductors have broad application prospects in the field of photocatalytic due to their advantages. Therefore, different morphology of TiO₂ nanomaterials, submicron size Cu₂O octahedron and their doping were synthesized by simple methods in this paper. And the degradation studies of the typical organic pollutants and the actual sewage were completed by using these semiconductor photocatalytic materials. The purpose is to provide the necessary theoretical basis for ascientific research and practical applications in the future.This paper consists of two parts. The synthesis and characterization of these two semiconductor materials of TiO₂ and Cu₂O and their dopings were introduced in the first part. Photocatalytic materials were prepared by hydrothermal synthesis and liquid at room temperature respectively. Rules morphology, uniform photocatalytic materials with different size were prepared by changing the reaction conditions and controlling system parameters. In the first chapter, crystal and morphology controllable TiO₂ nano particles were compared by hydrothermal synthesis. The size, crystal and morphology of TiO₂ nanoparticles are different with changing the pH of system. When pH<10, uniform distribution spherical TiO₂ nanoparticles with consistent size could be compared. The stronger the acidity system is, the smaller the size of the nano-particles is, and the minimum size is up to 7 nm and the produce is anatase; When pH=11, the aspect ratio of TiO₂ nanorobs prepared with more regular is about 6 - 1 and the crystal is still anatase. When the pH becomes bigger, butterfly-shaped TiO₂ nanomaterials prepared would change from anatase into brookite.Separation and recovery are difficult when particles directly applied to wastewater treatment. The TiO₂ nanotubes and nanofibers can not only solve the difficulties of separation and recycling, but also can guarantee good photocatalytic activity. Therefore, in the second chapter, the nano-tubes were prepared by using TiO₂ nanoparticles as raw materials. By changing conditions, the outer diameter and inside diameter of nano-tubes are respectively about 10nm and 8nm and their lengths are about 100-200nm. And the diameters of TiO₂ nanofibers are about 40-60nm and their lengths are about 10-20μm. The products have uniformity size and good morphology.Cu₂O as a semiconductor material can be triggered photocatalytic reaction in the sunlight irradiation. It is one of environmental protection photocatalysts with great prospects. In the protection of environment, the application in the degradation of organic pollutants has a lot of development, and its importance is increasingly shown. In the third chapter, the sub-micron size Cu₂O octahedrons were prepared by using a simple method of liquid at room temperature. The experimental carried out at room temperature is simple and the reaction period is short; raw materials are cheap and easy to get without additives and any complex apparatus. The shape and size of Product can be changed by regulating the concentration of NaOH; in addition to, the product is friendly to environment without organic pollutants except acetate; the yield is higher and easy to carry out industrial production.The study also synthesized Cu₂O/TiO₂ and TiO₂/Cu₂O doping bodies in order to improve the photocatalytic properties of materials. The products were characterized by XRD, TEM, SEM, and SAED.The second part is photocatalytic degradation. In the fifth and sixth chapters, phenol and nitrobenzene as the simulated water samples are respectively degraded by using the prepared nano-TiO₂ materials as photocatalyst. The initial concentration of the degradation products, the pH of reaction system, the amount of photo-catalyst and the different morphology of photocatalyst as the factors were reviewed. The reactor of photocatalytic degradation was the ring reactor, and the light source of degradation was UV. In the process of degradation, we took the sample timing, and monitored by GC / MS after extraction and concentration enriched.Demotion mechanism of phenol and nitrobenzene were speculated through literature research and the monitoring of intermediates in the process of degradation.In the seventh chapter, we use sub-micron size Cu₂O and TiO₂/Cu₂O doping as the photocatalyst to degrade methylene blue under visible. The results show that the photocatalytic properties of TiO₂/Cu₂O doping has been enhanced than before doping, and when the doping of TiO₂ is 3%, the efficiency of photocatalytic degradation for methylene blue is the highest. The degradation rate can reach to 95% after 2h.In the eighth chapter, we use TiO₂-doped fiber and Cu₂O/TiO₂ doping to degrade the actual industrial wastewater, and we reviewed the degradation efficiency of before and after TiO₂-doped fiber for the wastewater under the same conditions. Through the determination of COD, the photocatalytic properties of TiO₂-doped fiber slightly increased. When the doping of the Cu₂O is 5%, the degradation efficiency for industrial wastewater is the highest. The degradation rate can reach to 90% after 5h.