Unconventional Technology To Prepare A Specific Structure And Morphology Of Efficient Visible Light Catalyst And Its Application

Photocatalysis is a comprehensive discipline relating to optics, electrochemistry, material science, surface chemistry and catalysis chemistry. The semiconductor photocatalyst are usually employed which can absorb the optical energy and produce the photo-induced holes and electrons which have strong oxidizability and reducing power as well, thus the direct and indirect oxidation and reducing reaction can be occurred at the surface of the catalyst. What causes the great interest of the semiconductor photocatalysis in the scientific research area is the potential value to the problem of the energy utility and environmental purification.During past 30 years, hotocatalysis has been extensively with great achievements. However, there still remain many problems to be solved. Efficient semiconductor photocatalyst need to be improved on the basis of fundamental research. As far as the general TiO₂ photocatalyst, the broad band gap and low quantum efficiency confine its development. There isn't the unitized cognition to the real reaction mechanism of photocatalysis.We have engaged in the photocatalyst reseach areas for many times and thus got much experience in the research of the interaction of the photocatalyst's structure and their activities. Our work begins from the high activity of photocatalyst in the visible light to optimizing the preparation methods and conditions to prepare a series of photocatalyst. The effect of crystal phase, texture and surface property to activity was explored. Thus provides a lot of experience to further develop practical photocatalysis technique. We also use new technology route to prepare high activity photocatalysis under visible light. The detailed works are as follows:1. Nanocrystalline Fe/TiO₂ (Fe/TiO₂) visible photocatalyst with a mesoporous structure prepared via a nonhydrolytic sol-gel routeThe Fe/TiO₂ was prepared via a facile nonhydrolytic sol–gel (NSG) route. During photodegradation of methylene blue under visible light irradiation, as-prepared Fe/TiO₂ exhibited a higher activity than either the undoped TiO₂ or the Fe/TiO₂ obtained via the traditional hydrolytic sol–gel route. The correlation of the photocatalytic performance to the structural characteristics is discussed based on detailed characterizations. The promoting effect of the Fe-doping on the photocatalytic activity could be attributed to the formation of intermediate energy levels that allow Fe/TiO₂ to be activated easily in the visible area. The optimum Fe-content in Fe/TiO₂ is determined as 0.1% (Fe/Ti molar ratio). The nonhydrolytic sol–gel method is superior to the traditional hydrolytic sol–gel method owing to the controllable reaction rate and the lack of surface tension, which ensure the formation of mesopores and well-crystallized anatase, leading to a higher activity since reactant molecules are easily adsorbed and the recombination between the photoelectrons and the holes is effectively inhibited. Meanwhile, the nonhydrolytic sol-gel process could strengthen the incorporation of Fe-dopants in the TiO₂ network, which may further enhance the promoting effect of Fe-doping on the photocatalytic activity.2. Mesoporous Bi³⁺-doped TiO₂ (Bi-CST) spheres with core-shell chamber and enhanced visibly photocatalytic activity prepared by Solvothermally alcoholysisThe Bi-CST is prepared by alcoholysis under solvothermal conditions. During photodegradation of 4-chlorophenol(4-CP) under visible light irradiation, the Bi-CST sample calcined at 773 K exhibits higher activity than either the undoped CST sample. The correlation of the photocatalytic performance to the structural characteristics is discussed based on detailed characterizations. The promoting effect of the Bi-doping on the photocatalytic activity could be attributed to the formation of the highly dispersed Bi2O3 on the surface of TiO₂ which allow the Bi-CST sample to be activated easily in visible area. The optimum Bi-content in the Bi-CST sample is determined as 1% (Bi/Ti molar ratio). The well crystallized anatase, the strong absorbance in the Bi-CST sample lead to higher activity. Meanwhile, the unique sphere-in-sphere structure allows multi-reflections of visible light, within their interior cavities, endowing these spheres with greatly enhanced photoactivity. 3. Supercritical preparation of CdS-TiO₂ composite photocatalyst with high activity under visible light irradiationHighly active CdS/TiO₂ coupled photocatalyst was prepared by pretreatment the TiO₂ precursor under Cd(NO3)3/thiourea/ethanol supercritical conditions. The highly photocatalytic activity was evaluated by the liquid-phase oxidative degradation of 4-chlorophenol under irradiation of visible light with light-focalized instrument which is cut off the light below 420 nm. The results showed that CdS/TiO₂ coupled photocatalyst is successfully got under the supercritical conditons. After calcined under the highly- purified N2 atmosphere, the CdS/TiO₂ coupled photocatalyst interaction can be enhanced which may result the high photocatalysis activity. The highly photocatalytic activity of coupled photocatalyst also could be attributed to its higher surface area, well-crystallized anatase, fouthermore, the much stronger absorption in the UV-visible range with a red shift in the band gap transition. The CdS/TiO₂ coupled photocatalyst under the supercritical conditons provides an effective transfer of photo-generated electrons from the conduction band of CdS to that of TiO₂. The optimal molar ratio of TiO₂/CdS is 5/1, more quantity is not suitable for the degradation of 4-chlorophenol for the corruption of CdS.4. The synthesis of new Bi₂WO₆ visible photocatalysts via solvent-thermal routeWe have successfully prepared the sphere-like Bi2WO6 via solvent-thermal route with the help of the surfactant. X-ray diffraction (XRD), scanning electron microscopy (SEM), and the UV-vis spectra were used to characterize the product. The result indicated that the sphere is resulted mainly from the solvent. The pore on the surface of the sphere was formed with the calcined process. The formation mechanism was discussed on the basis of the results of time-dependent and temperature-dependent experiments. UV-vis spectroscopy was further employed to estimate the band gap energy of the sphere-like structures. The sphere-like Bi2WO6 sample showed the relatively high photocatalysis in the degradation of 4-chlorophenol under irradiation of visible light with light-focalized instrument which is cut off the light below 420 nm. Our work may shed some light on the design of other well-defined complex nanostructures, and the as-grown architectures may have potential applications.