Photogenerated Charge Separation And Transfer Behavior And Photocatalytic Activity Of Bismuth-Based Semiconductors

In order to deal with the energy crisis and environmental pollution,a series of physical and chemical methods have been developed.Among these methods,photocatalytic technology,as an advanced chemical oxidation method,can use renewable solar energy and semiconductor photocatalyst to degrade pollutants and reduce environmental pollution.It is a green and environmentally friendly clean technology.This thesis mainly contains two important parts.One is effects of different anion layers on photocatalytic properties;the second part is the photocatalytic activities of Bi@Bi-doped TiO₂ for degrading Rhodamine B（RhB）.（1）In the first part,we have mainly investigated the photochemical properties of Bi₂O₂CO₃ and Bi（C₂O₄）OH.It is found that although with the similar layer structure,Bi₂O₂CO₃ shows an activity 1.2 and 2.5 times higher than Bi（C₂O₄）OH for the degradation of phenol and Rhodamine B（RhB）under UV light irradiation（λ?400 nm）,respectively,which has been mainly attributed to their different anion layers.For Bi₂O₂CO₃,the CO₃^2-ions connect with one another to form a linked anion layer,but the alternated[Bi₂O₂]²⁺and CO₃^2-layers are completely separate;whereas for Bi（C₂O₄）OH,the C₂O₄^2-ions do not link with each other,but the oxygen bridges form between the[Bi₂O₂]²⁺and C₂O₄^2-layers.The results demonstrate that an internal electric field（IEF）is favored by the separate[Bi₂O₂]²⁺and CO₃^2-layers,which can greatly improve the charge separation rate.In contrast,the oxygen bridges between[Bi₂O₂]²⁺and C₂O₄^2-layers does not favor to form an IEF,resulting in a low charge separation rate.This finding suggests that the layer semiconductors with the completely separate cation and anion layers could be developed as the efficient photocatalysts.（2）To dramatically enhance the strategies have been developed to enhance the activity of a photocatalyst,the integration of multiple modification strategy can greatly enhance the activity.In this study,abundant bismuth is used to synthesize the oxygen defect-enriched TiO₂-based Mott-Schottky junction（S_yD_x）samples for the first time,and the photocatalytic degradation of rhodamine B（RhB）is used to evaluate the activity.Under UV light irradiation（λ≤400 nm）,the degradation activities of oxygen defect-enriched TiO₂（D_x）and oxygen defect-free TiO₂-based Mott-Schottky junction（S_y）can only increase by 0.3 and 1.9times,respectively;however,the activity of S₁₀D₁ has increased by 4.5 times,compared with original TiO₂,showing an obvious synergistic effect between oxygen defect and Mott-Schottky junction.Herein,oxygen defect expands the light absorption range and changes the surface properties of TiO₂ and Mott-Schottky junction obviously promotes reduces the separation of electrons and holes.This work demonstrates that the simple integration strategy is remarkably efficient to improve the activity of a photocatalyst,compared to single strategy.