节点文献
硫化物和硒微纳结构的溶液相合成及物性研究
Investigation of Solution-Phase Synthesis and Properties of Sulfide and Selenium Microstructures/Nanostructures
【作者】 张兵;
【导师】 谢毅;
【作者基本信息】 中国科学技术大学 , 无机化学, 2007, 博士
【摘要】 本论文发展了生物分子辅助法、可见光辅助法、溶液相沉积法、回流等方法,控制合成了各种形貌的硫化物和三方硒材料,研究了所制备材料的电化学储氢行为,并对材料的生长机理和充放电过程进行了较系统地研究。利用生物小分子半胱氨酸作硫源和生物导向分子,实现了硫化物纳米结构的控制合成,并详细地研究了其电化学储氢行为,探讨产物形貌对其电化学储氢容量的影响:首次发展β-胡萝卜素辅助法控制合成了三方硒纳米线和纳米带,提出了新的片碎裂机理;发展了一步水热法合成具有一定电化学储氢性能的超长亚微米硒管;开创性地设计了以可见光为光源的合成硒材料的新方法,并将这种新方法拓展到其它材料的合成上;采用回流法合成具有潜在特异电学性质的分支状的三方硒管,研究其在功能材料制备上的应用,并用第一性原理进行理论计算;发展新的溶液相沉积法制备了各种形貌的多孔三方硒材料,并研究其在电化学储氢上的应用;从细胞水平上对于无机纳米硒的一些生物活性进行初步的研究。详细内容归纳如下:1.在生物小分子半胱氨酸的辅助下,合成了硫化铋纳米棒束组成的花样纳米结构。研究表明,在硫化铋纳米结构的形成中,半胱氨酸不仅用作硫源,而且还用作结构导向分子。作者还进一步拓展这种生物分子辅助法到金属基片上硫化物纳米结构的制备,于120℃下在镍片基底上直接生长多孔海绵状的二硫化三镍纳米结构。这种纳米结构的电化学放电容量可达380mAh/g,相当于1.4wt%单壁碳纳米管的储氢量。通过改变实验条件,还获得了其它形貌的Ni3S2和Bi2S3纳米结构,并发现纳米结构的形貌对其电化学储氢行为有重要的影响。同时,作者也深入地研究了硫化物纳米结构的形成机理,分析了形貌对电化学储氢行为产生影响的原因。2.利用具有抗氧化性能的生物分子β-胡萝卜素作导向模板和还原剂,在低温水热条件下一步合成了单晶硒纳米线和纳米带,发现硒纳米线和纳米带的生长机理并非通常的球线过程,基于对中间体的TEM和IR分析,提出了一种新的片碎裂机理。研究表明,该方法可以拓展到碲和钯的一维纳米材料的合成,有望发展成一种合成一维纳米结构的简单、普适的方法。3.利用非离子表面活性剂吐温-20作软模板,首次实现了在水热条件下一步合成了超长高结晶性硒亚微米管(长度大于100μm)。作者还发现这种超长硒管有较好的电化学储氢性能(放电电容量达265mAh/g)。研究表明,硒材料的形貌对其电化学储氢行为有重要的影响,管状和多孔状的结构有利于增加硒的储氢容量。以前的电化学储氢材料的研究主要集中在碳纳米管、二硫化钼、BN等层状材料上,这是首次在具有各向异性结构上的电化学储氢性能的报道,因此这项工作无疑拓展了储氢材料领域的研究。4.创造性地发展了一种简单、新颖的可见光辅助溶液相合成方法,并成功地用来合成各种硒、碲的一维纳米结构。通过调节反应物的种类和配比,可以大规模地合成诸如硒亚微米管、硒纳米棒、硒梭标、硒纳米棒形成的海胆状结构、碲纳米线、碲纳米带、碲纳米管和棘状Te纳米丝等一维纳米组装结构。研究表明,在可见光辅助合成方法中,光照射和热效应二者共同作用影响产物的形貌。草地灯发出的可见光能够促进非晶硒/碲转变成结晶性的三方硒/碲,诱导并增强水溶性高分子在硒、碲形貌控制合成中所起的导向作用。作者还以所合成的碲纳米线为例,说明了所合成的产物可以用作模板来制备可控铂载量的Pt-Te纳米链、Te@碳纳米电缆、碳纳米管、Te-Pt@碳纳米电缆等复合材料。5.采用回流法,在低温下成功制备出了一系列各种形貌的多臂硒纳米管。这种多臂管状结构还可以用于生成其他多臂管状功能复合纳米材料。此外,作者发现这种多臂硒管中的不同分枝存在不同的生长方向,除了常见的[001]方向之外,还发现了存在一些新的生长方向,比如垂直于(102)和(0-12)晶面的生长方向。第一性原理计算表明枝状硒管具有不同生长方向的各分枝能够表现出不同的特异电学性质,且有些分枝具有准金属性。6.发展了一种新颖简单的溶液相沉积方法来合成多孔硒材料。通过选择锌片作沉积基底,N2H4.H2O和EDTA作还原剂和配位分子,成功地合成了多孔三方硒花样、苹果状多孔硒微结构、藕状多孔硒微球、坚果状的多孔硒微球及麦穗状的硒微结构。水热条件下从基底上所释放出的锌离子和配位分子作用所产生的软模板对得到产物的形貌和多孔结构起到了十分重要的作用。研究表明,多孔硒材料有较高的电化学储氢能力,放电曲线出现比较明显的电位平台,其中藕状的多孔硒的最高放电容量达166mAh/g。7.从细胞水平上对于无机纳米硒的一些生物活性进行初步的研究。结果表明,纳米硒比普通无机硒的生物毒性低;和有机硒相比较,也有着相似的低毒性。
【Abstract】 In this dissertation, various solution-based routes including biomolecule-assisted method, visible-light-assisted technique, solution-phase deposition approach, refluxing, were developed for the morphology-controlled synthesis of metal sulfides and trigonal selenium (t-Se) materials. The formation mechanism and the electrochemical hydrogen storage behaviors of the as-prepared samples were investigated in detail. A facile biological approach was developed to fabricate Bi2S3 and Ni3S2 nanostructures using L-cysteine as both the sulfur source and the directing molecule under hydrothermal conditions. The electrochemical hydrogen storage behaviors of those sulfides were studied systematically and the dependence of these nanostructures’ capacities of electrochemical hydrogen storage on their shapes was discussed; The biomolecule beta-carotene-assisted approach was developed, for the first time, to synthesize t-Se nanowires and nanoribbons with high crystallinity. The one-dimensional (1D) Se nanostructures formed via a novel flack-cracking mechanism rather than a typical sphere-wire process; The author developed a one-step solution method to generate ultra-long single-crystalline t-Se submicrotubes with good electrochemical capacity of hydrogen storage; A novel visible-light-assisted solution-phase technique was developed to prepare t-Se microstructures with abundant morphologies and was extended to the morphology-controlled synthesis of trigonal tellurium (t-Te); A series of crystalline multiarmed tubular t-Se nanostructures with unique electrical properties were successfully synthesized using a facile refluxing approach. Applications of these multi-armed Se materials in preparing functional composite nanomaterials were discussed, and first-principles studies were also adopted to predict the as-prepared materials’ electronic properties; A novel and facile solution-phase deposition approach was developed, for the first time, to synthesize porous t-Se materials with various morphologies; The bio-activity of inorganic nano Se was investigated on the level of cell. Such t-Se materials’ applications in electrochemical hydrogen storage were studied. The details are summarized as follows.1. A simple L-cysteine-assisted method was developed to prepare Bi2S3 flowerlike patterns with well-aligned nanorods. L-cysteine, a small biomolecule, was found to serve as both the S source and the directing molecule in the formation of bismuth sulfide nanostructures. The author further extended this facile biomolecule-assisted approach to generate nanothread-based porous spongelike nanosturctures on Ni foil with a high yield at 120°C. These novel nickel sulfide nanomaterials grown on Ni foils could electrochemically charge and discharge with a maximum capacity of 380 mAh/g (corresponding to 1.4 wt% hydrogen in SWNTs). By varying the experimental parameters, other Bi2S3 and Ni3S2 nanostructures were obtained. It was demonstrated that these sulfides nanostructures’ morphologies had a noticeable influence on the capacity of electrochemical hydrogen storage. The formation mechanism of these sulfides nanostructures was discussed and the dependence of their electrochemical properties on the products’ morphologies was explained in detail.2. A simple beta-carotene-assisted method was developed for the first time to synthesize t-Se nanowires and nanoribbons with high crystallinity. It was demonstrated that beta-carotene served as not only the reducing agent, but also an in situ template in the preparation of t-Se 1D nanostructures. It is found that the growth mechanism of Se nanomaterials is different from the familiar sphere-wire process. A novel flake-cracking mechanism is proposed. By this biomolecule-assisted route, Te 1D nanostructures and Pd nanowires were also fabricated. Thus, this method is a new, facile, general method to prepare 1D nanomaterials.3. Ultra-long single-crystalline t-Se submicrotubes with the length of over 100μm) were synthesized using a hydrothermal approach with the assistance of nonionic surfactant Polyoxyethylene(20)sorbitan monolaurate (Tween-20). The author demonstrated that the as-prepared ultra-long t-Se submicrotubes could charge and discharge with the high capacity of 265 mAh/g. It was observed that the morphology of the synthesized Se products had a remarkable influence on their capacity of electrochemical hydrogen capacity. The tubular or porous structure was considered to be the main factor for the high electrochemical capacity. Previous investigations on electrochemical hydrogen storage mainly restricted to layered-like materials (e.g. CNT, BN nanotubes, MoS2 nanotubes, TiS2 nanotubes), and this is the first report for the helix-chain-like materials. Thus, this work undoubtedly extends the study of materials with the function of hydrogen storage.4. A novel and facile visible-light-assisted solution-phase technique was successfully developed to synthesize t-Se and t-Te 1D nanostructures with various morphologies. By varying the kind and relative amount of the reacting agent, Se submicrotubes, Se nanorods, Se shuttles, urchin-like assembly of Se nanorods, Te nanowires, Te nanobelts, Te nanotubes, thornlike 1D assembly of Te nanothreads can be fabricated on a large scale. Both light and thermal effects play significant roles in this visible-light-assisted technique. It was found that the light from a lawn lamp could accelerate the transformation of amorphous Se/Te to trigonal crystalline Se/Te and enhance the directing role of water-soluble polymers in the current method. The as-prepared Te nanowires were chosen as the example to investigate the products’ applications in fabricating various functional nanomaterials. Furthermore, using the Te nanowires as the template, Pt-Te nanochains with modulated Pt dopants, Te@carbon-rich nanocables, carbonaceous nanotubes, Pt-Te@carbon-rich nanomaterials could be successfully generated.5. A series of crystalline multiarmed tubular selenium nanostructures were successfully synthesized using a facile refluxing approach at 100°C. Such mutiarmed tubes could be utilized as the template to prepare CdSe-Se composite nanomaterials. In addition, different arms had different growth directions, and some new directions (e. g. the directions perpendicular to (102) and (0-12) crystal planes) were observed through TEM, SAED and HRTEM analyses. Furthermore, first-principles studies demonstrated that arms with different directions in the branched tubes exhibited different unusual electronic properties and some arms had a quasi-metal character.6. A novel and facile solution-phase deposition approach was developed, for the first time, to prepare porous t-Se materials. Porous flower-like Se patterns, porous apple-like Se microstructures, porous lotus-root-like microspheres, porous walnut-like spheres and ear-like materials could be fabricated on a large scale by choosing Zn foil as the deposition substrate, and either N2H4H2O or EDTA (ethylenediaminetetraacetic acid) as both the reducing and coordinating agents. It was demonstrated that both the zinc ions released on the Zn substrate and the soft template formed in situ through the coordination between the Zn2+ and organic molecules are significant in controlling the porous structures and morphologies of the final products in this solution-phase deposition method. The porous t-Se materials had been shown to electrochemically store hydrogen with good capacity, which was considered to be associated with the porous structure of the obtained samples.7. The bio-activity of inorganic nano Se was investigated on the level of cell. The results demonstrated that the toxicity of inorganic nano Se was lower than that of the familiar inorganic selenium (e.g. SeO2, SeO32-), similar to that of organic selenium.