Synthesis Of Bismuth Complex Oxide And Their Photocatalytic Properties Under Visible Light Irradation

In this dissertation, a series of bismuth complex oxide with special nanostructure were synthesized via mild hydrothermal method, which all showed excellent photocatalytic activities under visible light irradation. Since 1972 Fujishima reported titanium oxide as photocatalyst under splitted water into oxygen and hydrogen ultraviolet light irradation, much admirable researches on the preparation of the environmentally friendly photocatalysts have been investigated to progress their activity of the photocatalysts by the energy shortage and environment pollution of the whole globe recently. Basing on investigating the relationships of the structure and properties, the crystal structure of the obtained functional materials were played a more key role for the proprieties performance, which is worth for developing the new functional materials with novel morphologies and superior properties. The photocatalytic process was very friendly, lost less energy and totally mineralized the organic pollutants which were as known the best process for the environment pollution. The previous works were most focusing on titanium dioxide or related complex as photocatalyst, which was limited its application at the visible light rang for the band-gap. Bismuth complex oxides with layered structure as a series new appealing photocatalysts have attracted considerable attention for their admirable photocatalytic properties under visible light irradiation. The photocatalysis mechanism of the materials and the related influence factors on the photocatalysis were investiged for preparing more novel photocatlysts and inhancing the photocatalytic activity, which was set up an ideal model for understanding the relationship of the crystal structure and the properties. The dominating related reports have put forward that the higher BET surface area is the main in·uencing factor of the photocatalysis. Nevertheless, recent researches have indicated that the particular surface may also be pivotal to the photocatalytic activity. Our photocatalytic experiments showed that the photocatalyst with higher effective surface area were promoted by the particular surface exposed. The monoclinic phase bismuth vanadate with hierarchical frame works were prepared assisted by the Gemini-surfactant; the Bi₂O₂CO₃ with different hierarchitecturs were achieved without any templates; theγ-Bi₂MoO₆ samples with different morphologies and surface structures were prepared for investigating the impact factors of the photocatalytic activities. The details are summarized briefly as follows:1. The m-BiVO₄ hierarchical frame works were synthesized using a novel Gemini surfactant-monoalkylated disulfonated di-phenyl oxide surfactant (C12-MADS) as the structure-directing reagent and as-obtained m-BiVO₄ nanomaterials exhibited good photocatalysis for degradation of rhodamineB (RhB) under visible light. The C12-MADS played a key role for the formation of the m-BiVO₄ hierarchical frame works, which were chelated with the bismuth ions. The growth rate of the crystal was directly controlled by the decomposition of the obtained chelating precursor. The bismuth vandate with branches showed its potential applications as photocatalystsf. The surfactants with functional groups can be used to chealting with the metal ion that provide a new method to prepare the nanostructure with hierarchical frame works. 2. In this work a novel Bi₂O₂CO₃ photocatalyst was first put forward by virtue of structural understanding. The internal layered structure of a material would guide the lower growth rate along certain axis compared with that for other axises, to form 2D morphologies such as sheet-like/plate-like morphologies. The highly anisotropic internal structure of Bi₂O₂CO₃ is obviously a benefit for controlling the formation of Bi₂O₂CO₃ sheet-like or plate-like nanounits with special surface. Previous work was indicated that controlled organization of primary building units into hierarchically structured nanoarchitecture represents another challenge for their high potential in applications. The Bi₂O₂CO₃ nanostructures with different morphologies were fabricated after the sol gel precuer solution was treated with various pH value or temperature. In particular, the flower-like Bi₂O₂CO₃ hierarchitecture with the controlled special {001} surface exposed was first synthesized via a mild route, showing more excellent photocatalytic activity than the sponge-like porous spheres with higher surface area, which was due to the large distortion of Bi-O on the exposed surface of the sheets that were arranged the flower-like sample. The Bi₂O₂CO₃ nanostructures have proved to be not only a new photocatalyst under solar light irradiation, but also a possible example for investigating the key factors of which may impact on the photocatalytic ability. The results confirmed that the higher efficiency of the photocatalytic activity should be contributed synergistically by the higher BET surface area and the special exposed surface.3. In this work,γ-Bi₂MoO₆ samples with different morphologies and surface structures were prepared via simple solution methods and their photocatalytic degradations of rhodamine-B (RhB) were investigated under visible light irradiation. As one of the three different crystalographic phases of bismuth molybdates, theγ-Bi₂MoO₆ showed the distinguished photocatalytic activity under visible light irradiation for its suitable bandgap and intrinsic structure. Therefore, it is still very necessary to investigate the influencing factors of theγ-Bi₂MoO₆ surface structure on their photocatalytic activity. In spite of their lower BET surface area, we found that theγ-Bi₂MoO₆ sheets with the preferentially exposed {010} surface exhibited the greatly enhanced photocatalytic activity. The mechanism study and structural analysis of stoichiometricγ-Bi₂MoO₆ indicated that the particular reactive surface with enhancing the concentration of·OH and/or·OOH radicals, derived from the larger distortion of the MoO₆ octahedra, play a more important role of the enhanced photocatalytic activity. The photocatalytic mechanism of degrading the organic pollutant indicated that improving the separation of the electronic and vacancy can inhance the photocatalytic activity. Hence,the photocatalytic property has a close relationship with the structure of the exposed surface plane, in that the particular reactive surface with much more oxygen defects and in-plane vacancies can greatly enhance the photocatalytic activity.