【作者】 彭琳琳；

【导师】 王德军；

【作者基本信息】 吉林大学 ， 物理化学， 2010， 博士

【摘要】 光电功能材料铁基氧化物及其复合物,具有较好的光电性质,可以应用到光催化、太阳电池及光电子器件等领域。它们优异的光电活性是与光生电荷的迁移行为密切相关的。因此,研究材料的微观的光生电荷载流子的行为特性对于其在光电领域的应用是十分必要的。本论文的工作主要是探讨了光电材料的光生电荷行为特性所表现出来的光电性质与光电活性的关系。首先利用表面光电压技术、Kelvin探针技术及瞬态光电压技术研究了一维有序的α-Fe₂O₃纳米棒阵列结构区别于体相α-Fe₂O₃的特殊的光电性质,证明了α-Fe₂O₃纳米棒阵列结构的量子尺寸效应。然后在这种阵列结构的基础上,与TiO₂构筑成具有异质界面的FTO/TiO₂/Fe₂O₃复合材料电极结构,比较了复合材料电极与单层α-Fe₂O₃纳米棒阵列电极的光电催化活性,测试结果表明复合材料料电极具有较好的光电催化降解染料的活性,同时探讨了复合材料电极相对于单层薄膜电极光生电荷运动行为的变化。最后,设计制备了α-Fe₂O₃纳米粒子包覆锐钛矿型TiO₂微米棒的异质结构复合物粉体,测试了其可见光催化降解有机染料的活性,说明了异质结构复合物优于单独的α-Fe₂O₃和TiO₂微米棒的光催化活性,并利用表面光伏技术证明了材料的光电活性与其本身的光电压性质的内在关系。更多还原

【Abstract】 Nanomaterials with photoelectric properties are applied to the photocatalysis, solar cell, biological sensor and photoelectric device, etc., following the development of the technology. Iron oxide attracts much attention for its special photoelectric properties among the various nanomaterials. Iron oxide with low band gap of 2.2 eV could absorb most of visible light. Moreover, iron oxide has many morphologies and it will appear some new photoelectric properties for iron oxide with particular structure and dimension. At the same time, poor conductivity, facility to recombine for electron-hole pairs in iron oxide are inhibiting its promising applications. In recent years, many approaches against its drawbacks have been made to improve the photoelectric properties. Among these methods, more efforts have been focused on the polycrystalline heterostructures based on the iron oxide. For this heterogeneous structural material, we could not only utilize the virtues of the iron oxide, but also accelerate the separation of the electons and holes under the influence of heterojunction between two different materials, which could promote the photoelectric activity of the materials. Therefore, the behaviors of photogenerated charges, including the generation, separation, transportation and recombination of the photoexcited charge carriers, directly determine the photoelectric performance of the materials. The surface photovoltage （SPV） technique is a well-suitable and more direct method to characterize the behavior of the photoinduced charges.In this thesis, we studied the photoelectric properties of theα-Fe₂O₃ nanorod array that are different from the bulk Fe₂O₃ by Kelvin probe system, SPV technique and the transient photovoltage （TPV） technique at first. And then the FTO/TiO₂/Fe₂O₃ two-layered film electrode was prepared based on the FTO/Fe₂O₃ film eldctrode. We compared the photocatalytic activity of the two electrodes and discussed the behaviors of the photogenerated charge carriers at the FTO/TiO₂/Fe₂O₃ two-layered film electrode. At last, we synthesized the Fe₂O₃/TiO₂ composites by coating TiO₂ microrods with Fe₂O₃ nanoparticles and tested the photocatalytic activity of the heterogeneous composites. The relationship between the photocatalytic activity and the photoelectric properties was demonstrated by the SPV and TPV spectra.The main results of this paper are illustrated as follows:1. Anα-Fe₂O₃ nanorod array was prepared by the hydrothermal method, and we have studied the photoelectric property and the kinetics of this structure by the SPV and the TPV technology. When theα-Fe₂O₃ nanorod array is excited from the surface, the SPV response takes place only in the ultraviolet region where the photonic energy is much larger than the bulk band gap and exhibits a quantum size effect. The photogenerated electrons transfer to the nanorod surface as a result of the high density of surface states. When the light is incident from the interface between the substrate and the nanorod array, the SPV response extends from ultraviolet to visible region due to the influence of the built-in field at the interface between the substrate and the bottom of the nanorod array, which corresponds to the band-to-band transition and exhibits the bulk property of theα-Fe₂O₃. The photogenerated charges of theα-Fe₂O₃ nanorod array are prone to separate and also to recombine upon illumination. From the comparison of photovoltage properties between theα-Fe₂O₃ nanorod array and theα-Fe₂O₃ nanorod powders, we could find the SPV spectra of theα-Fe₂O₃ nanorod powders only reflect the properties of bulk Fe₂O₃. These results on the behaviors of the photogenerated charge transfer at the surface and the interface of theα-Fe₂O₃ nanorod array could reflect the photoelectric activity of this material. So the information provided in this chapter may provide useful supports for the practical application ofα-Fe₂O₃ nanorod array in solar cell, photocatalysis and sensors.2. Based on the Fe₂O₃ nanorod array, we prepared the FTO/TiO₂/Fe₂O₃ two-layered film electrode which had the heterogeneous structure. We tested the photoelectric activity by degrading orangeⅡvia combined electro-oxidation and photocatalysis and studied the photoelectric properties of the FTO/TiO₂/Fe₂O₃ two-layered film electrode by electrochemical system, the SPV and the TPV systems. The influences of the hetero-interface between the Fe₂O₃ and TiO₂ on the behaviors of photoexcited charges were discussed. We could obtain the conclusions as follows. The working electrode could generate more photogenerated charges under the excitation of the visible light. The photoelectric activity of the working electrode could be improved by combining the applied electric field on the base of visible light irradiation. Compared the experimental results of photoelectric catalytic （PEC） degradation of organic dye, the PEC activity of the FTO/TiO₂/Fe₂O₃ two-layered film electrode was superior to the FTO/Fe₂O₃ single-layered film electrode. From the TPV and SPV spectra, we could observe that the photogenerated electrons and holes were easier to separate and difficult to recombination under the effect of the hetero-interface in the FTO/TiO₂/Fe₂O₃ two-layered film electrode. Therefore, these results could provide useful information for the application of those two electrodes in photoelectric device.3. The Fe₂O₃/TiO₂ hetero-structural composites with three mass ratios （Fe₂O₃ vs. TiO₂） by Fe₂O₃ nanoparticles covered TiO₂ microrods were prepared. The photocatalytic experimental results revealed that the Fe₂O₃/TiO₂ composites with hetero-structure were more active than the corresponding bare Fe₂O₃ or bare TiO₂ in the photodegradation of orange II under visible light illumination. Furthermore, the higher the mass ratio of Fe₂O₃ vs. TiO₂ is, the better the photocatalytic activity is for the composites. By comparing the photovoltaic property of pure Fe₂O₃ with that of Fe₂O₃/TiO₂ heterogeneous composites, we observed that the hetero-interface between Fe₂O₃ and TiO₂ imposed an important influence on the behaviors of photogenerated charge carriers. Moreover, the characteristics of the photogenerated charges were associated with the photocatalytic activity. With respect to the pure Fe₂O₃, the photoexcited electrons and holes of the Fe₂O₃/TiO₂ composites were prone to separate under the effect of interfacial electric field under visible light irradiation, which resulted in the enhanced photocatalytic activity of Fe₂O₃/TiO₂ hetero-structural composites. The quantity of the Fe₂O₃ coated on the TiO₂ microrods influenced the interfacial electric field and thus the transfer behaviors of the photogenerated charges, as revealed by the SPS and TPV characterizations. As a result, the photodegrading rates towards orange II were distinct from each other for the Fe₂O₃/TiO₂ composites with different mass ratios. Therefore, the results presented in this work may provide well-suitable and more direct methods to evaluate the photoelectric activities of the advanced materials for practical application such as photocatalysis.更多还原