【作者】 郑艳；

【导师】 陈明清； 谢毅；

【作者基本信息】 江南大学 ， 应用化学， 2011， 博士

【摘要】 本论文旨在利用简单温和的液相水热合成法来制备得到一系列具有规则有序纳米结构的光催化功能材料。自发现二氧化钛在经紫外光照射后,可以催化分解水以及降解有机物,光催化功能材料在解决全球面临的能源危机和废水废气等环境污染治理方面表现出的优越性能,激励了人们不断的开发和研究光催化材料,通过对制备得到的催化功能材料的结构表征与相关物理化学性质的分析,进一步深入地研究了功能材料的纳米结构对材料的性能应用方面将会产生的影响。光催化的过程能耗少,可直接利用太阳光的能源,转化为新能源或者可彻底矿化有机污染物,解决人类在能源和环境方面所面临的问题。目前关于光催化纳米材料的研究,大多数集中在二氧化钛或者二氧化钛的改性方面,但是由于TiO₂能带较宽,对可见光的响应能力差,其应用前景受到一定的限制。铋复合氧化物由于具有可见光响应性能,近年来一直受到国内外许多科研工作者们的广泛关注,制备高催化效率的光催化材料以及研究相应材料的光催化机理和影响催化效率的因素等都是人们研究的焦点。对光催化机理以及催化效率影响因素的研究,不仅有利于更好的研究开发更多的新型功能材料,还为材料的应用提供了更为广泛的空间,同时也为研究功能材料的结构与性能之间的关系提供了一个可供讨论的理想模型。在本论文中,制备的一系列铋复合氧化物都具有优越的可见光光催化性能,利用新型的双子表面活性剂辅助合成得到了m-BiVO₄的多级支晶结构;通过自组装过程,合成得到了大小均一的花状碳酸氧铋的纳米结构;为了研究结构与性能之间的影响因素,合成了系列不同形貌与表面结构的γ-Bi₂MoO₆材料,并对其结构和光催化性质进行了深入的分析;通过光催化降解染料的研究,将光催化降解有机污染物的反应从紫外光区扩展到可见光区,并为利用太阳光去除难降解的染料污物提供了一种新的途径。本论文的主要研究内容如下:1.在水热的条件下,通过利用十二烷基二苯醚二磺酸钠阴离子双子表面活性剂对金属离子的螯合作用,制备得到了具有多级分枝结构的单斜相钒酸铋枝晶。通过不同反应时间段所得的中间产物的物相和结构分析,观察到了单斜相钒酸铋多级分权结构的生长过程,双子表活剂的螯合作用控制了晶体的生长方向和生长速率,由此推测出了多级支晶机构的可能的生长机理。通过在可见光照射下,利用所得的枝晶结构钒酸铋材料作为光催化剂,降解有机染料罗丹明B溶液的光催化实验,得到的实验结果表明了枝晶结构的单斜相钒酸铋比一般块材具有更为优越的光催化性能,是具有应用前景的可见光光催化功能材料。利用双子表面活性剂等多官能团分子的螯合作用,辅助合成得到多级结构的方法,也为其他材料的多级支晶结构的制备提供了一种可行的思路。2.根据碳酸氧铋的晶体结构的剖析,首次提出了具有层状结构的碳酸氧铋材料作为光催化剂的潜在可能性。通过柠檬酸根络合金属铋离子生成溶胶-凝胶的前驱液,再经过调节前驱液的pH值,改变反应体系的温度等制备得到了具有不同纳米结构的碳酸氧铋材料。由不同时间段的中间产物的对比分析实验,推测出了不同纳米结构的生长机理。在实验室中,通过利用不同的碳酸氧铋纳米结构作为光催化剂,在可见光照射下降解罗丹明B溶液的光催化实验,表明了碳酸氧铋材料确实是具有可见光响应的功能材料。其中花球状的碳酸氧铋纳米结构,表现出了最高的催化效率,这是由于组成花球的片状基本单元结构所暴露出的{001}晶面具有很高的反应活性,在此晶面上由于Bi-O多面体的极大程度的扭曲变形,使得Bi-O键非常不稳定,从而促进了花球状纳米结构的光催化活性能力。光催化实验结果表明,优越的光催化活性是高比表面积与特殊晶面裸露的协同作用,即具有较高的有效的比表面积的功能材料对应用性能的提高起着积极的促进作用。因此,制备得到的碳酸氧铋材料可以应用于光催化降解有机物,不仅拓宽了开发新型可见光光催化材料的思路,还为探索研究光催化性能的影响因素提供了一个潜在的可行的途径与理论模型。3.通过简单的水溶液加热合成法,制备得到了具有不同形貌、尺寸与表面结构的γ-Bi₂MoO₆材料,并通过对这一系列所得产物用于降解有机染料罗丹明B溶液的光催化性能实验,研究了对于γ-Bi₂MoO₆作为光催化剂时其可见光光催化活性能力,并深入地讨论了影响光催化性能的可能因素。通过实验,发现暴露出{010}晶面的片状γ-Bi₂MoO₆虽然具有较低的比表面积却表现出了较高的光催化活性能力。通过进一步对γ-Bi₂MoO₆作为光催化剂降解有机染料罗丹B溶液的光催化机理的研究和γ-Bi₂MoO₆晶体结构的深入分析,表明由于γ-Bi₂MoO₆片状材料裸露出的特殊活性晶面{010}面上MoO₆八面体发生了很大程度上的扭曲变形,使得在此晶面上具有非常多的氧缺陷和平面空位,这对促进材料光催化活性能力的提高有着重要的作用。因此,通过对γ-Bi₂MoO₆光催化降解有机物的机理分析,如果催化剂材料的表面晶面能够有效地促进光生电子与空穴的分离,提高溶液中过氧自由基和过羟基自由基的浓度,将会促进功能材料的催化效率的提高,这样的表面晶面的暴露对光催化作用的加强才是有效的,具有较高的有效的比表面积的纳米材料的制备,将对研究高效的光催化材料有着深远的意义。更多还原

【Abstract】 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.更多还原