【作者】 缪应纯；

【导师】 李和兴；

【作者基本信息】 华东师范大学 ， 物理化学， 2014， 博士

【摘要】 铋-基复合氧化物具有独特的层状结构,有利于光捕获以及光生载流子的传递,提高光催化活性,且能够通过层间分子或离子变化调变光催化性能,因此成为近期光催化材料研究领域的热点之一。将光催化应用于染料废水净化是未来的重要发展方向。一方面,由于染料的大规模需求和生产,染料废水是当前工业废水的主要部分,占35%以上；另一方面,染料分子结构稳定,一般化学方法难以降解。而光催化降解过程中会产生一些毒性比染料本身还强的中间产物,同时,染料废水对光产生屏蔽效应,影响光催化剂对光的吸收和利用。光催化效率不仅取决于光催化剂组成,而且与结构形貌密切相关。本论文合成了不同形貌的铋系列氧化物(BiOBr和Bi2MoO6),并以Bi2MoO6为母体,进一步设计稀土修饰和异质结结构的光催化剂,考察所制备的光催化剂在降解染料废水中有机污染物的光催化活性。通过纳米结构裁剪和组成调变,进一步优化光催化剂。在此基础上,结合系统表征,初步探索不同形貌结构光催化剂的形成机理和晶体生长机理,考察光催化反应动力学并研究其反应机理,讨论光催化剂的构效关系。主要研究工作分为以下四个部分：(1)微波辅助离子液体合成纳米片堆积形成的BiOBr微立方体及其光催化活性采用微波辅助离子液体成功地合成了不同形貌的BiOBr,离子液体发挥结构导向作用,同时,结合微波作用,能够实现高结晶度和规整形貌结构的BiOBr光催化剂的合成。光在纳米片层之间的多次反射可提高光利用率,从而提高光催化活性。同时还发现由于表面有机物的敏化作用导致BiOBr催化剂具有相对高的光催化活性。(2)喷雾干燥法合成笼状Bi2MoO6中空微球及其光催化活性以葡萄糖为模板剂,通过喷雾干燥法,合成了笼状Bi2MoO6中空微球,考察了喷雾温度和葡萄糖用量对Bi2MoO6晶型、形貌、空心球壳厚度、球壳的孔分布和结构影响。所制备的Bi2MoO6在可见光诱导光催化降解废水RhB溶液中显示高活性,归因于其高比表面积,且光在Bi2MoO6笼状空心球空腔中的多次反射,提高了光的利用率。动力学测量显示,在罗丹明B(RhB)降解过程中遵循的是一级动力学,HPLC-MS检测表明,RhB经脱乙基的过程,形成了5个中间产物最后完全矿化为C02。(3)稀土原位修饰Bi2MoO6高活性可见光催化剂采用原位法制备了系列稀土离子修饰的Bi2MoO6可见光催化剂并应用于RhB的光催化降解,RhB的降解历程与采用非修饰的Bi2MoO6可见光催化剂相同。在不同稀土离子中,Gd3+修饰效果最佳,可能与其独特的f层电子结构有关；原位法优于浸渍法,主要归因于Gd3+进入Bi2MoO6晶格,形成施主能级,导致能级带隙变窄,不仅有利于可见光活化光催化剂,而且阻碍电子-空穴复合并抑制修饰剂流失,从而提高光催化活性和稳定性。(4)溶剂热合成BiOBr/Bi2MoO6及其光催化活性的研究采用溶剂热法制备了花球状BiOBr/Bi2Mo06可见光催化剂,其高比表面积有利于提高对RhB的吸附,BiOBr的作用是利用其对染料的优异吸附性能,提高光催化剂对RhB的吸附速率和吸附量,同时通过与Bi2MoO6构建异质结,促进光生电子与空穴分离,抑制其复合。因此BiOBr/Bi2MoO6显示高活性。该光催化反应中光生空穴为主要活性物种,RhB的降解历程与非修饰的Bi2MoO6可见光催化剂存在时相同。更多还原

【Abstract】 Bismuth-containing complex oxides, as excellent visible light photocatalysts, that were layer structure composed of [Bi2O2]2+slabs interleaved by double slabs of different atoms which could diversify the photocatalytic activity of bismuth-containing complex oxides, have attracted extensive attention these days. The layered structure endowed the complex oxides with high carrier mobility and small probability of the recombination of photogenerated electrons and holes. On the one hand, dyes were demanded and produced in a large scale in industry. On the other hand, traditional chemical methods were difficult in decomposing dyes due to the steady molecule structure of dyes. Hence, the application of photocatalytic method in dye wastewater cleaning could be important development in future. Unluckily, in the photodecomposition process of dye wastewater treatment, the yielded intermediates could be more toxic than the dye molecule itself. Furthermore, the light shielding effect of dyes wastewater could affect the absorption and utilization of light. The photocatalytic efficiency could not only depend on the catalyst composition, but also closely relate to the structure and morphology. This thesis focused on the synthesis of bismuth-containing complex oxides (BiOBr and Bi2MoO6) with various morphologies and the hierarchical flower-like RE/Bi2MoO6and BiOBr/Bi2MoO6spheres by solvothermal technology, and then the cleaning wastewater by photocatalysis for various organic compounds. The photocatalysts were further optimized by the cutting and adjusting of the structure. Based on the above results and the systematic characterization, the formation and crystal growth mechanism of the photocatalysts with various morphologies were studied. Meanwhile, the reaction kinetics and reaction mechanism of photocatalytic process was disclosed. Then, the correlation of the photocatalytic performances or the mineralization ability to the morphology has been discussed based on the photocatalytic activity with various morphologies. The research work could be described in the following four parts:(1) Microwave-assisted ionic liquid self-assembly of BiOBr nanosheets in microcube with enhanced photocatalytic activityBiOBr with various morphologies has been successfully synthesized via microwave-assisted ionic liquid self-assembly method. Ionic liquid, which could play the oriented role, could help to achieve BiOBr with the high crystallinity and regular morphology structure, combined with microwave. The visible light reflection among the nanosheets of microcube could enhance light absorption, and then increase the photocatalytic activity of BiOBr nanosheets in microcube. Simultaneously, it was observed that the photocatalytic performance of the uncalcined hierarchical BiOBr microcube was superior to that of the calcined hierarchical BiOBr due to the sensitization effect of the organics on the surface.(2) Aerosol-spraying preparation of Bi2MoO6, A visible photocatalyst in hollow microspheres with a porous outer shell and enhanced activityBi2MoO6hollow microspheres with cage-like pores on the outer shell were synthesized by aerosolspraying with glucose as a template. The aerosol-spraying temperature and the amount of glucose played key roles in determining the crystal phase and the Bi2MoO6morphology including outer shell thickness and number of cage-like pores on the outer shell. The photocatalytic degradation of rhodamine B under visible-light irradiation was examined which revealed that the reaction followed first order kinetics with respect of rhodamine B concentration and rhodamine B was completely degraded into CO2via de-ethylation process with the formation of5intermediates. The as-prepared Bi2MoO6exhibited high activity owing to the high surface area and additionally because of multiple light reflections in the hollow chamber.(3) In situ rare-earth doped Bi2MoO6visible light photocatalyst with enhanced activityA series of Bi2MoO6visible light photocatalysts were doped with various rare-earth via in-situ synthesis and used for photocatalytic degradation of RhB. The Gd3+-modification was superior over other rare-earth due to Gd3+with particular4f electron structure, and the in-situ synthesis was better than traditional impregnation method since the Gd3+was incorporated into the Bi2MoO6crystal lattice to form donor level, which facilitated photocatalystic activation with visible lights illuminating, retarded the photo-induced electron-hole recombination, and inhibited the leaching of dopants, leading to the enhanced activity and stability.(4) Solvothermal preparation of BiOBr/Bi2MoO6heterostructures with enhanced photocatalytic propertyThe flower-like BiOBr/Bi2MoO6microsphere was synthesized by a simple solvothermal method. The0.20-BiOBr/Bi2MoO6sample exhibited excellent adsorption, photocatalytic abilities, and mineralization ability for the degradation of RhB under visible light irradiation (>420nm), due to the heterojunction structure, higher SBET and the BiOBr strong adsorption abilities for RhB. In this system, h+was the dominant reactive specie. The photocatalyst degradation processes of RhB for before and after modified were uniform.更多还原