Design And Performs Of New Composite Photocatalytic Materials In Optical Fiber Reactor

TiO₂semiconductor has been considered a kind of ideal photocatalytic material due to itsnon-toxic, low cost, high stability and superior photocatalytic properties. However, TiO₂canutilize no more than5%of the total solar energy impinging on the surface of the earth due toits wide bandgap. Moreover, the photogenerated electrons and holes of TiO₂can recombinerapidly, which results in the low quantum efficiency. These restrict the practical application ofTiO₂. Therefore, much effort has been devoted to developing more efficient and stablephotocatalysts. In addition, the design of highly efficient photoreactors is also crucial to thewide range of needs for environmental remediation and clean-up. Conventionally usedphotoreactors for liquid phase oxidation are based on the heterogeneous slurry system withsuspended catalyst. The design offers ease of construction and high catalyst loading. However,slurry reactors are limited to the laboratory scale for wastewater treatment because ofdifficulty of separation of photocatalyst nanoparticles from the treated water and nonuniformlight irradiation and low light utilization efficiency. Therefore, we devote ourselves to designand development of new and efficient composite photocatalyst with higher photocatalyticactivity and a new photoreactor. The photocatalytic materials were well characterized bymany techniques. And the photocatalytic activities were investigated systemically in thedesigned photoreactor under simulated sunlight irradiation.1. H₃PW₁₂O₄₀/TiO₂composite photocatalytic material was prepared by combination ofthe methods of sol gel and hydrothermal treatment at a lower temperature. AndH₃PW₁₂O₄₀/TiO₂-coated optical fibers were prepared by dip coating method. The Agnanoparticles were photodeposited on the surface of H₃PW₁₂O₄₀/TiO₂films coated on theoptical fibers. The photocatalysts were characterized by X ray diffraction （XRD）, FourierTransform Infrared Spectrometer （FT IR）, Inductively Coupled Plasma Atomic EmissionSpectrometer （ICP AES）, X ray photoelectron spectroscopy （XPS）, transmission electronmicroscopy （TEM）, field emission scanning electron microscopy （FESEM）, UV Vis diffusereflectance spectra （UV Vis/DRS） and N2adsorption/desorption. Their photocatalyticactivities were evaluated by degradation of aqueous RB and4NP under the simulatedsunlight irradiation. The recyclability of the H₃PW₁₂O₄₀/TiO₂and Ag/H₃PW₁₂O₄₀/TiO₂1filmwas evaluated through six consecutive catalytic cycles. The optical fiber reactor was designedby puting H₃PW₁₂O₄₀/TiO₂or Ag/H₃PW₁₂O₄₀/TiO₂1film coated optical fiber bundlevertically in the quartz reactor. In this design, the optical fibers act as not only supporter of thecomposites film but also the medium of light transmission. Therefore, this new type optical fiber reactor enhances the light use efficiency, which results to the enhanced photodegradationefficiency.2. g-C₃N₄and Bi₅Nb₃O₁₅were prepared by polycondensation and hydrothermaltreatment method respectively. g-C₃N₄/Bi₅Nb₃O₁₅composite photocatalytic materials wereprepared by a simple milling heat treatment method with g-C₃N₄and Bi₅Nb₃O₁₅as rawmaterials. The g-C₃N₄/Bi₅Nb₃O₁₅composites were characterized by XRD, FT IR, TEM,UV vis/DRS and PL. The photocatalytic activities of g-C₃N₄/Bi₅Nb₃O₁₅were evaluated bydegradation of aqueous MO and4CP under the visible light irradiation. At proper g-C₃N₄loading, the photocatalytic activity of g-C₃N₄/Bi₅Nb₃O₁₅outperforms pure g-C₃N₄andBi₅Nb₃O₁₅. The main active species yielded in the g-C₃N₄-and g-C₃N₄/Bi₅Nb₃O₁₅-catalyzed4CP degradation systems were also investigated by the free radical and hole scavengingexperiments. Accordingly, the photodegradation mechanism was given. Andg-C₃N₄/Bi₅Nb₃O₁₅–70was chosen to evaluate the recyclability of the g-C₃N₄/Bi₅Nb₃O₁₅photocatalysts by five times’RB degradation reaction.The separation and transportation of photogenerated electrons and holes wereinvestigated by photoelectrochemistry experiments and fluorescence spectra analysis. Thespecific process of the transportation of photogenerated carriers was studied by the bandstructure, which provided theoretical basis for the design of composite photocatalysts.