氧化铈仿生遗态材料的能级设计及其光催化性能的研究

发布时间：2018-03-08 06:12

本文选题：氧化铈　切入点：仿生遗态　出处：《江苏大学》2014年博士论文　论文类型：学位论文

【摘要】：在过去几年中,世界的能源结构依然停滞在利用如煤、石油、天然气等不可再生的化石燃料上。然而,大量化石燃料的燃烧导致了一系列大气和水污染及全球变暖问题。因此,利用阳光分解水制氢作为一种便于储存传输并化为电能的可再生清洁能源技术不断受到人们的关注。具有先进的分级微纳米结构的半导体材料(如TiO2,ZnO,CeO2和WO3等)因其特殊的禁带结构和能级分布而产生的氧化还原变换,常被用于光解水制氢领域。这类具有特殊微纳米结构的光功能材料的合成技术也得到迅速的发展。此外,这类功能材料也可以应用到如小型化纳米电子学,超快量子计算,高密度内存/数据存储介质,超灵敏化学传感/生物传感器和高效催化底物等纳米应用领域。然而,对于材料学家来说,这类材料的制备依然是个巨大难题。与此同时,自然界经过进化,可持续地创造出大量具有复杂的分级结构,多功能,小型化,环境适应性的纳米材料。忠实地复制这些大自然的设计也许是制备功能性分级微纳米材料的最直接途径。仿生遗态制备法是一种模仿自然生物的结构、功能、机制、乃至部分或整个活性系统为基础的纳米仿生材料技术,它的关键是通过调控,对生物组织结构所具有的多层分级微纳米多孔结构进行精密复制。本研究采用一系列新型具有分级多孔和功能性的生物结构作为模板,经过低成本且环境友好的仿生遗态法制备相应的仿生氧化铈材料,并将之应用于光解水制氢领域,本文主要研究结论如下： (1)本研究通过特定的工艺将荷花、月季、田园罂粟三种花瓣作为模板,合成仿花瓣形貌氧化铈,使用XRD、HRTEM、FESEM、ESEM、AFM和氮气吸附脱吸附等手段表征发现其是由厚度能达5nm以下的超薄纳米氧化铈层组成；通过特定工艺将硅藻、荷花花粉、细菌作为模板,合成仿生氧化铈微球,通过表征发现制得材料是由氧化铈纳米晶体堆积形成的微米级大孔嵌套纳米级小孔的分级多孔结构；将擦镜纸、鸡蛋膜、菌丝作为模板,合成仿生氧化铈微管,通过表征发现仿生遗态制备法将生物组织的形貌完整地保留在遗态功能材料之中,其中仿菌丝壁材料因复制细胞壁的层层结构也具有超薄纳米层结构。本研究提出了对制备多种仿生氧化铈材料的机理分析,从生物和化学两个角度说明了材料制备的原理。 (2)在制备材料的基础上,进一步结合仿生氧化铈材料的XPS图谱,针对9种仿生氧化铈进行了表面元素价态分析。从分析结果来看,材料中的氧空位的浓度随三价铈比例、掺氮比例的提高而提高,仿生氧化铈中的超薄纳米层结构也有助于提高材料中氧空位的浓度,尤其是纳米层厚度小于4nm的材料,具有高含量的氧缺陷及催化活性位。通过H2-TPR分析,仿生氧化铈材料的颗粒分散性较好,其还原峰温的降低充分说明其催化活性的增强。同样,紫外-可见漫散射光谱也表明仿生氧化铈材料吸收边随着掺氮量、氧空位比例及超薄层结构的增加向可见光区红移。从计算得到的禁带宽度看,以菌丝作为模板的氧化铈仿生微管材料具有最小的禁带宽度2.85eV,这是因为它由3.57nm厚度的超薄纳米层组成,同时又具有具有高浓度的氧缺陷和氮掺杂量而造成的。在可见光下,这种新型材料催化降解亚甲基蓝溶液的效率最高。 (3)基于光解水制氢系统对仿生氧化铈超薄纳米层、微球、微管进行了光催化性能的研究,分析结果表明随着氧化铈材料中氧空位的浓度、掺氮比例和超薄纳米层结构的增加,其在可见光下催化制取氢气的效率会得到提高。这可归因于氧空位在导带底和N2p在价带顶引入的梯度能级,使禁带宽度变窄,易化了电子的跃迁,增强了材料对可见光的吸收,促进可见光下氢气的产生。在制备得的多种仿生氧化铈材料中,以菌丝作为模板的氧化铈仿生微管材料光解水制氢效率最高,光照420min后产氢量达到378μmol/g。这是因为其既具有3.57nm厚度的超薄纳米层,又具有高浓度的氧缺陷和氮掺杂量。这与紫外、TPR、XPS等分析结果相一致。
[Abstract]:In the past few years, the world energy structure is still stagnant oil in the use of fossil fuels, such as coal, natural gas and other non renewable. However, combustion of fossil fuel has led to a series of air and water pollution and global warming. Therefore, using sunlight as a decomposition of water to hydrogen for storage and transmission. As a renewable and clean energy technology power constant attention.
Semiconductor materials with advanced hierarchical micro nano structures (such as TiO2, ZnO, CeO2 and WO3) of oxidation and because of its special band structure and the distribution of energy level reduction transformation, is often used for photohydrogen production. This kind of special micro nano structure optical functional materials synthesis technology is rapidly this kind of development. In addition, functional materials can also be applied to the miniaturization of Nano Electronics, ultrafast quantum computation, high density memory / data storage medium, ultra sensitive chemical sensors / biosensors and efficient catalyzed nano applications. However, for materials scientists, this kind of material preparation is still a big problem at the same time, nature evolved continuously create a lot with a hierarchical structure, complex function, miniaturization, nano materials environment adaptability. Faithfully copy the design of nature may It is the most direct way for the preparation of functional hierarchical micro nanomaterials.
Bionic left state preparation method is a kind of imitation of natural biological structure, function, mechanism, and even some or all of the activity system based on nano biomimetic material technology, it is the key of regulation of multi-layer hierarchical structure of biological micro nano porous structure of precision replication. This research adopts a series of new with the biological and functional structure of hierarchical porous as template by bionic low cost and environmental friendly. The bionic ceria prepared by the corresponding state, and applied in the field of water photolysis, the main conclusions are as follows:
(1) this study through the specific process of lotus, rose garden, poppy three petals as the template, synthesis of cerium oxide morphology like the petals, the use of XRD, HRTEM, FESEM, ESEM, AFM and nitrogen adsorption desorption characterized by its thickness can reach over Bona meters below the 5nm layer composed of cerium oxide through a specific process; the diatoms, lotus pollen, bacteria as template, the biomimetic synthesis of cerium oxide microspheres prepared material is characterized by that the hierarchical porous structure by cerium oxide nano crystal nano micron holes formed by nested holes; the lens paper, egg membrane, mycelium as template, the biomimetic synthesis of cerium oxide microtubules, characterized by that left state preparation method of bionic tissue morphology to retain the integrity of the morph genetic functional material, which imitates the hyphal wall material due to layers of cell wall structure replication also has ultra-thin nano layer structure. This research The mechanism analysis of preparation of various biomimetic cerium oxide materials was put forward, and the principle of material preparation was explained from two aspects of biology and chemistry.
(2) based on the preparation of materials, further combined with XPS spectra of cerium oxide materials for bionic, bionic 9 cerium oxide analyzed surface element valence state. From the analysis results, the concentration of oxygen vacancy in the material with trivalent cerium ratio, nitrogen doped ratio increased, ultra-thin nano layer structure bionic cerium also helps to increase the concentration of oxygen vacancies in the material, especially nano material layer thickness is less than 4nm, oxygen deficiency and catalytic activity has a high content. Through H2-TPR analysis, the bionic ceria material particles with good dispersion, the reduction of peak temperature shows enhanced the catalytic activity decreased. Similarly, UV Vis diffuse scattering spectra also showed that the absorption of cerium oxide materials doped with bionic edge nitrogen, oxygen vacancy ratio and ultrathin structure increase red shift to visible. The band gap obtained from the calculations, as with the mycelium Ceria bionic material template with microtubule band gap of 2.85eV is the smallest, this is because it consists of ultra-thin nano layer thickness of 3.57nm, also has the oxygen vacancy and nitrogen doping with high concentration caused. Under visible light, this new material in photocatalytic degradation of methyl blue has the highest efficiency.
(3) microspheres of water photolysis system of cerium oxide nano bionic thin layer, based on the photocatalytic properties of microtubules were studied, analysis results show that with the concentration of oxygen vacancies in ceria, nitrogen doped proportion and ultra-thin nano layer structure increases, its efficiency will be improved. To produce hydrogen under visible light. This can be attributed to the oxygen vacancy in the bottom of the conduction band and valence band level gradient N2p in the narrow band gap, facilitated the electron transition, enhanced absorption material of visible light, promote the production of hydrogen under visible light. In a variety of bionic ceria prepared, with the mycelium as the cerium oxide materials of water photolysis efficiency of bionic microtubule template is the highest, after 420min light hydrogen production reached 378 mol/g. this is because it not only has 3.57nm nanocrystalline layer thickness, and with a high concentration of oxygen vacancies and nitrogen doping quantity. This purple In addition, the results of TPR and XPS are consistent.

【学位授予单位】：江苏大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TQ133.3;TB17

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