【作者】 高庆生；

【导师】 唐颐；

【作者基本信息】 复旦大学 ， 物理化学， 2010， 博士

【摘要】 近十年来,随着纳米科学技术的发展,纳米材料的制备和应用成为了众多自然科学领域,如物理学、化学、材料和生物医学等的研究热点。结构新颖、性质丰富的各种纳米材料在各领域中展示了优于块体材料的优良性能,具有广阔的开发前景。其中,有机-无机杂化纳米线是纳米材料和纳米科学中的新热点。该类型材料指的拥有一维纳米形貌的有机-无机杂化物,它具有一维纳米材料形貌规整、一维传输特性和容易组装等特点；同时作为有机-无机杂化物,它的晶体结构方便可调、物化性质丰富,因此在光学、电子学、光电电子学、传感、储能等领域有巨大的开发潜力。然而,目前该材料的研究存在种类有限、生长机理不明确等问题,而且对于利用有机-无机杂化结构设计其它纳米材料的领域仍然存在空白。这严重限制了有机-无机杂化纳米线的发展和应用开发。因此,丰富有机-无机杂化纳米线的种类,研究纳米形貌和杂化结构的形成机制,探索杂化结构对设计更多纳米材料的意义,是进一步完善该材料的合成方法论的关键,也满足为纳米材料的应用提供足够的选择资源和材料设计思想的需求。本论文工作以“有机-无机杂化纳米线”为主线,针对上述存在的问题,从“合成表征”、“利用杂化物制备金属氧化物一维纳米结构”和“基于杂化物设计金属碳化物催化剂”三方面入手。讨论了新型有机-无机杂化纳米线如GeOx/ethylenediamine和MoOx/amine等的合成和表征,通过对合成规律的细致考察,提出了新的生长机理。通过对杂化结构的不断认识,发现其有机、无机成分紧密接触的特点有助于在金属氧化物/碳化物材料合成中发挥独特作用,因此通过相应的实验,得到金属氧化物的一维纳米结构(如GeO2、MoO2/C纳米线等)以及一系列碳化钼催化剂(Mo2C纳米线、Mo2C/CNT和Co-Mo2C/CNT等)。在上述工作中,即拓展了有机-无机杂化纳米线的物种,丰富了现有的合成理论和机理,还成功利用该杂化材料设计合成多种氧化物/碳化物功能纳米材料,这些材料在催化以及电化学中都表现出突出的性能,为功能纳米材料的设计合成提供了新的思路。论文对上述研究工作将分六个章节进行讨论：第三章讨论GeOx/ethylenediamine纳米线的合成与结构表征。利用氧化铁辅助的水热法首次合成了GeOx/ethylenediamine纳米线,方法操作简单,成本低廉,具有量产的前景。通过系统表征,发现该纳米线具有全新的晶体结构和有机-无机杂化成分,GeOx与乙二胺之间通过弱相互作用形成了周期性亚纳米结构。该特征性的亚纳米结构可以导致强的量子效应,体现为紫外吸收光谱中的蓝移现象,而且该杂化纳米具有光致荧光性质,在光学、光电纳米器件等领域具有广阔的应用前景。第四章探索了GeOx/ethylenediamine纳米线的生长规律。细致考察了不同实验条件对纳米线生长的影响,如反应时间、温度、有机胺种类以及金属氧化物助剂等,优化了实验条件,提炼了规律。在此基础上,通过综合分析之后提出了“氧化铁诱导的界面-溶液-固体”机理,即Fe2O3诱导了乙二胺分子与GeOx在氧化铁表面产生GeOx/EDA杂化单元,再通过界面生长的限制,形成了一维方向的生长。拓展合成体系,获得了MoO2/ethylenediamine纳米片等新颖结构,验证了所提机理。第五章介绍了MoOx/anine一维纳米结构的合成。提出了“利用钼酸根一维生长特性合成MoOx/amine纳米线”的策略,即在钼酸根与有机胺离子结合的同时保持钼酸根的生长特性。通过共沉淀方法,得到了一系列的MoOx/amine纳米线,例如Mo3O10(C6H8N)2·2H2O、MoOx/1,6-hexanediamine和MoOx/imidazole等,研究了纳米线的形成规律,优化了实验条件。同时,利用Mo3O10(C6H8N)2·2H2O为前驱体,通过原位聚合方法,可控合成了MoOx/polyaniline纳米线/管。这部分工作对氧化钼杂化纳米线进行深化研究,提出更加简单的合成方法,不但丰富了该类型材料的种类,也为后面钼相关功能纳米材料的设计提供了选择和调变空间。第六章介绍利用有机-无机杂化纳米线制备金属氧化物一维纳米结构的方法。针对不具备各向异性生长的金属氧化物,一维结构难以合成的问题,提出“基于有机-无机杂化纳米线设计一维纳米氧化物”的策略。利用有机-无机杂化纳米线为前驱体,通过简单的后处理(如焙烧)等,可以获得相应的氧化物纳米结构,方法简单、安全易控；同时,其中的有机成分可以在惰性气氛中高温碳化,形成碳杂化结构,提高材料的某些应用。例如,在空气氛中焙烧GeOx/ethylenediamine纳米线,可得到具有光致荧光性质的α-GeO2纳米线。同时,利用MoOx/amine纳米线,经惰性气氛焙烧,获得MoO2/C纳米线,细致表征了纳米线结构,研究了转变规律。由于其一维形貌和碳杂化结构,MoO2/C纳米线应用于锂离子电池负极材料,表现了高的可逆容量和良好的循环性,特别是倍率性能突出,符合了对新能源高能量密度、高功率密度的需求。第七章探讨“利用有机-无机杂化纳米线合成多孔一维碳化钼”的新策略。金属碳化物具有类贵金属催化性质,在许多催化反应中应用,但传统的程序升温还原方法由于涉及气-固相界面反应,反应不充分,容易造成表面积碳,产量受限。本工作提出“利用有机-无机杂化纳米线合成多孔一维碳化钼”的策略,利用MoOx/amine中有机-无机成分紧密接触的特点,通过高温条件下贯穿整体的均匀反应,获得多孔的Mo2C纳米线。产品由纳米颗粒组成纳米线形貌,具有大比表面和丰富孔性,而且表面积碳较少。利用甲醇分解制氢气的探针反应,发现本方法所得的Mo2C纳米线具有类贵金属的催化性质,且具有比程序升温还原法所得催化剂长的催化寿命和高的氢气产率。本章工作不但证明了该方法对碳化钼纳米结构合成的普适性和可调性,而且进一步展示了相对TPRe方法的优越性,包括简单操作和优良的产品特征。第八章将“基于有机-无机杂化结构制备碳化物”的策略进一步拓展到负载型碳化钼催化剂的合成。通过浸渍负载、烘干、焙烧等步骤,可以获得一系列负载型的Mo2C催化剂,如Mo2C/CNT、Co-Mo2C/CNT和Co-Mo2C/AC等。通过结构表征证明催化剂组分在载体上以纳米颗粒分散,且不同催化剂之间相互独立,不以合金等形式存在。研究发现有机-无机杂化物前驱体是形成碳化钼的关键,这样的合成与传统方法比较具有操作简单安全、产品表面积碳少等优点。在甲醇分解制氢气的表征反应中,负载型催化剂表现出优于非负载型催化剂的性能,其中Co-Mo2C/CNT最为突出,展现了作为该反应高效催化剂的潜力。探讨Co金属修饰对Mo2C催化剂的作用,认为Co能过够将Mo2C表面积碳转化为碳纳米管,释放了活性表面,提高了催化剂的寿命。负载型Mo2C催化剂的突出性能预示其作为贵金属催化剂廉价替代品的前景,同时也为其它反应的催化剂设计提供了新的思路。综上所述,本论文以“有机-无机杂化纳米线”为主线,通过水热、共沉淀等方法构建了有机-无机杂化纳米线合成体系,同时,基于杂化结构设计合成了多种金属氧化物/碳化物纳米结构,探讨了它们在锂离子电池、甲醇催化制氢气中的应用。在获得一系列新颖结构的功能纳米材料的同时,通过系统研究,还提出了“氧化铁诱导的界面-溶液-固体”生长机理和“基于有机-无机杂化纳米线设计氧化物/碳化物”的策略,为新材料开发与设计提供了方法学上的借鉴意义。更多还原

【Abstract】 In this decade, the synthesis and application of nanomateials have attracted much attention in the fields of physics, chemistry, material science, biology and etc., with the development of nanoscience and nanotechnology. The superior performance of various nanomaterials than bulky counterparts has been demonstrated in many fields, indicating the potential application in the future. Among them, organic-inorganic hybrid nanowires have become a new highlight because of the uniform 1D morphology, anisotropic transport, easy assembly, tunable structures and functional properties.However, there are still challenges in the urgent research on organic-inorganic hybrid nanowires. Firstly, the kind of organic-inorganic hybrid nanowires is limited; secondly, the growth mechanism of such materials is obscure; and thirdly, the employment of organic-inorganic nanowires to fabricate other nanostructures has been ignored in the previous work. These factors limit seriously the development of such materials. Therefore, the research dealing with synthesis and growth mechanism of novel organic-inorganic hybrid nanowires, as well as designing other nanostructures based on the hybrids, has been expected to promote the development and application of such nanomaterials.This dissertation focus on organic-inorganic hybrid nanowires, with the deep investigation into three parts including "synthesis and characterization", "fabricating 1D metal-oxides from organic-inorganic nanowires" and "designing metal-carbide catalysts based on organic-inorganic hybrids". To explore more hybrid nanowires, a series of GeOx/ethylenediamine and MoOx/amine nanowires were originally developed and well characterized. New growth mechanisms were proposed on the basis of systematic study about their synthesis. Meanwhile,the subnanometer contact between organic and inorganic components in the hybrids was found significant for preparing the nanostructures of metal oxides and carbides, and thus several 1D metal oxides (e.g. GeO2 and MoO2/C nanowires) and carbide catalysts (e.g. Mo2C nanowires, Mo2C/CNT and Co-Mo2C/CNT) were successfully achieved, which exhibit high performance in electrochemistry and catalysis, respectively. Besides, due to the facile process, low cost and novel product structures, the synthetic strategies proposed in this work will open opportunities for the synthesis and design of functional materials. The details of each chapter are list below. In chapter 3, GeOx/ethylenediamine nanowires were firstly synthesized via Fe2O3-assited hydrothermal method, which is possible to large-scale preparation for the low cost and easy control. Through the systematic characterization, the novel crystalline structure and hybrid components are well confirmed, in which the GeOx units are connected by ethylenediamine through hydrogen bonding, forming the subnanometer structure. Strong quantum confinement effect can be considerably leaded by this subnanometer structure, reflected by the blue shift in UV spectra. Furthermore, the bright blue light can be emitted by such as-obtained nanowire, suggesting the potential application in future integrated optical nanodevices.In chapter 4, the growth of GeOx/ethylenediamine nanowires was discussed in detail. Several factors in the synthesis process, such as reacting time, temperature, amines and metal-oxide assisting agents, are systematically analyzed, and thus the growth mechanism of Fe2O3-assisted Surface-Solution-Solid was proposed. Herein, Fe2O3 leads to the formation of GeOx/ethylenediamine hybrid units on the surface, which is followed by an anisotropic growth induced by the solid-liquid interface reactions. Meanwhile, another novel structure of MoO2/ethylenediamine nanosheets was obtained through the similar growth process, indicating the potential of this mechanism as a new route to fabricating organic-inorganic hybrid nanomaterials.In chapter 5, a series of MoOx/amine nanowires were fabricate based on the anisotropic growth of molybdate crystals, including Mo3O10(C6H8N)2·2H2O、MoOx/1,6-hexanediamine and MoOx/imidazole. Detailed study was carried out on the formation of such nanowires, and the synthesis was well optimized. Furthermore, employing Mo3O10(C6H8N)2·2H2O as precursors, the controllable synthesis of MoOx/polyaniline nanowires/tubes can be realized through in-situ polymerization. The work in this chapter, not only furthers the research into organic-inorganic hybrid nanowires of MoOx, but also proposes easy strategies to enrich the system of such hybrid nanostructures, aiming the following design of functional Mo-based oxides and carbides.In chapter 6, an easy strategy was proposed to fabricate 1D oxides from organic-inorganic hybrid nanowires, regarding that the 1D nanostructures of oxides without anisotropic growth were difficult to obtain. After the calcination in air or inert flow, nanowires of oxides or carbon-hybrid metal-oxides can be easily achieved, respectively. Especially, the carbon-hybrid structures in such nanowires may enhance and improve some application in electrochemistry. For example,α-GeO2 nanowires with photoluminescence properties were obtained through calcining GeOx/ethylenediamine in air flow. Meanwhile, novel MoO2/C nanowires were successfully fabricated via the calcination of MoOx/amine nanowires under inert flow, which exhibited the high rate capability even under high current density as anode materials for Li ion battery. The potential of the synthetic strategy in design functional nanomaterials is well revealed by the universality for various nanostructures and high performance for energy-storage.In chapter 7, we proposed a novel strategy to synthesize nanostructures of carbides based on organic-inorganic hybrid composites with subnanometer periodic structures. By employing the uniform reactions between subnanometer-contacting organic and inorganic components throughout the whole hybrids, this strategy successfully avoids the disadvantages in traditional temperature-program-reduction (TPRe) method using solid-gas interface reactions. Nanoporous Mo2C nanowires can be well obtained via calcining MoOx/amine nanowires under Ar flow, which are composed of Mo2C nanoparticles and possesses large surface with little depositing carbon. These nanowires display higher H2 yield and longer lifetime than bulky Mo2C obtained by TPRe method in the probe reaction of producing H2 from methanol decomposition. Thus, the significance of synthetic strategy for fabricating carbides from organic-inorganic nanocomposites is well demonstrated.In chapter 8, the strategy of fabricating carbides from organic-inorganic nanocomposites was further extended to design of supported Mo2C catalysts, such as Mo2C/CNT, Co-Mo2C/CNT and Co-Mo2C/AC. The physical characterization shows that the active composites present individually as highly dispersive nanoparticles on the surface of support, and no alloy phase can be observed. The formation of Mo2C can be attributed to the organic-inorganic hybrid precursors, and thus this process is significant for the advantages discussed in chapter 7,such as easy control, safety and little depositing carbon on surface. In the catalytic reaction of producing H2 from methanol decomposition, supported Mo2C catalysts show the higher performance than unsupported catalysts. Significantly, the Co-Mo2C/CNT displays ultrahigh activity, selectivity and stability in such reaction, indicating the potential as efficient substitutes for the high-price noble-metal catalysts. Furthermore, the research into the effect of metallic Co during catalytic process shows that Co transfers the coke to format carbon nanotubes, improving remarkably the stability. This mechanism may benefit the design other carbide catalysts for relevant reactions. To sum up, this dissertation focus on organic-inorganic hybrid nanowires, and the organic-inorganic hybrid nanowires system of GeOx and MoOx have been established through facile hydrothermal and co-precipitation methods. Furthermore, various nanostructures of molybdenum oxides and carbides have been also realized based on the organic-inorganic hybrid nanowires, whose performance in Li ion battery and producing H2 from methanol decomposition are discussed. Besides the novel nanostructures with functional properties, several mechanism and synthetic strategies have been proposed in this work, which will open up opportunities for the synthesis and design of new nanomaterials.更多还原