【作者】 徐树玲；

【导师】 孙思修；

【作者基本信息】 山东大学 ， 无机化学， 2010， 博士

【摘要】 纳米材料的设计合成是纳米科学技术发展的热点领域,也是纳米科技得到进步研究并推广应用的基础。目前合成纳米材料的方法虽然很多,但是获得尺寸可控、颗粒均匀的纳米材料仍然存在一定的困难。探索发展纳米材料设计与合成的新途径、新方法,实现对纳米材料的尺寸大小、粒径分布以及形貌和表面修饰的控制仍然是纳米材料研究领域的一个重要课题。本论文以铜基无机材料为研究对象,发挥液相合成技术在控制材料的结构、形貌和尺寸方面的优势,对单质铜、氧化亚铜及铜基核壳结构纳米材料进行控制合成,探讨其控制机理及内在规律。论文的主要内容总结如下：1.水热法选择性合成铜纳米线和纳米片采用水热合成方法,在表面活性剂辅助下,通过控制Cu+离子的释放速率,调节溶液中有效单体的浓度,选择性合成了Cu纳米线和纳米片。当CTAC作为表面活性剂时,溶液中自由Cu+离子的释放速率和Cu+离子的还原速率由体系中的CuCl来决定,生成的产物为Cu纳米线。反应条件保持不变,当CTAB取代CTAC作为表面活性剂时,CTAB中的Br-与Cu+离子结合生成更难溶于水的CuBr。CuBr的生成使溶液中自由Cu+离子的浓度和Cu+的还原反应速率明显降低,为Cu纳米片的生成提供了有利的条件。2.水热合成多种形貌的氧化亚铜微米材料在水热条件下,次亚磷酸钠作为还原剂,柠檬酸三钠为配位剂,成功制备出多种形貌的Cu2O微米材料。次亚磷酸钠的还原性受溶液的酸碱性的影响,通过调节体系的pH值,可以控制还原反应的速率。对于面心立方晶系的Cu2O来说,立方体形貌的获得是由于六个<100>面生长较慢,而<111>生长较快所致。化学动力学实验表明,碱性条件下,次亚磷酸钠处于不活泼型,还原反应速率非常慢。因此,提高体系的pH值,使次亚磷酸钠的还原速率降低。在比较慢的还原反应速率下,Cu20晶体六个<100>面没有生长完全造成了立方体到八角花状过渡。3.溶剂热法合成氧化亚铜空心立方体利用溶剂热合成技术,不借助于任何模板和表面活性剂,成功制备了Cu2O空心立方体。通过对不同时间所得产物的TEM图像观察,我们认为Cu2O空心立方体的形成是定向聚集和奥氏熟化共同作用的结果。在反应的初期,溶剂热条件下,生成的小粒子聚集成大的颗粒以减少体系的表面能。随着反应的进行,小粒子的浓度逐渐降低,定向聚集变为次要因素。由于小粒子的起始聚集迅速,导致立方体内部结构疏松。在反应的后期,小的粒子或疏松的颗粒不断溶解,生成更大的、结晶性和致密性更好的颗粒。因为立方体内部的小粒子曲率更大,更容易溶解继而再结晶生长,所以最终所得产物为空心立方体。实验发现,反应温度、反应时间和体系中的含水量都对空心结构有影响。4.液相法合成氧化亚铜-金核壳纳米球和银-铜核壳纳米材料(a)室温条件下合成CuO2-Au核壳纳米球,该方法具有简单易行,反应时间短的特点。首先通过N2H2和Cu(NO3)2的反应得到CuO2纳米球,然后加入HAuCl4水溶液,HAuCl4与体系中过量的N2H2反应,Au3+还原为Au单质,以CuO2纳米球为“种子”,在其表面生成出一层Au单质壳层结构。同时HAuCl4带入的H+可以与作为“种子”的CuO2反应,CuO2的表面逐渐被消耗,核与壳之间的空隙逐渐生成,最终生成核与壳分离的CuO2-Au核壳纳米球。(b)在PVP作为表面活性剂的溶剂热反应体系中,DMF既做溶剂又做还原剂,合成了Ag-Cu核壳结构纳米材料。通过对不同反应阶段所得产物的TEM和XRD分析,可以推测在溶剂热反应体系中,单质Ag先被还原出来作为成核中心,使新生成的Cu2O附着在其上面生长,形成核壳结构。随着反应时间的延长,Cu2O逐渐被还原为单质Cu,同时伴随着奥氏熟化过程,逐渐生成Ag-Cu核壳结构纳米材料。更多还原

【Abstract】 The design and synthesis of nanometerials is hot research fields for nanoscience, and is also the base of the application and future development of nanotechnology. Although there are many methods reported for preparing nanomaterials, it is still difficult to obtain materials with controllable morphologies and sizes. Therefore, it is an important task in the field of material that how to develop new methods to design and synthesis of nanomaterials and realize the control of nanoparticles size, distribution, morphology and surface modification.This paper is focused on the controlled synthesis of copper-based inorganic nanoparticles, such as Cu, Cu2O and copper-based core-shell nanostructures. Growth mechanism and primary characterizations of nanoparticles are conducted. The advantages of liquid chemical synthesis technology in controlling the materials microstructures, morphologies and size are used. The detailed information of the dissertation is listed as follows.1. Selective synthesis of copper nanowires and nanroplates via a hydrothermal processCu nanowires and nanoplates have been selectively synthesized by controlling the release rate and the concentration of the free Cu+ via a surfactant-assisted hydrothermal process. The experiments show that when CTAC was used as surfactant, the release rate of the free Cu+ and the reduction process were controlled by CuCl, and Cu nanowires were obtained. When CTAB was used as surfactant, while other conditions were kept constant, When CTAB was used as surfactant, CuBr formed via the combination of Cu+ ions and Br- ions from CTAB. The free Cu+ concentration in the solution was decreased duo to the less solubility of CuBr than CuCl in the aqueous solution, and the formation of Cu atoms becomes slower, under such a condition may favor the growth of Cu plate-like structures.2 Hydrothermal synthesis of Cu2O microcrystals with various morphologiesA hydrothermal process has been developed to prepare Cu2O particles by reducing the Cu(II)-citrate complex with NaH2PO2. It has been known that the reducing power and reaction rate of NaH2PO2 change with varying of pH in aqueous solution, so reduction kinetically of system could be controlled by adjusting pH. As a face-centered cubic structure, the formation of Cu2O cubic might result from the{111} facets of Cu2O were eliminated because of their higher growth rate and the{100} facets remained because they have the lower growth rate. So the cubes of CU2O enclosed with six{100} facets were obtained. The results of chemical kinetic tests indicate that under acidic condition NaH2PO2 in inactivated state and the reduction rate becomes slow. The formation of Cu2O eight-pod particles can attribute to the fact that the reduction rate becomes slower as the pH is increased and the growth of six {100} facets are incomplete.3 Synthesis of Cu2O hollow nanocubes under solvothermal conditionWe synthesized Cu2O hollow nanocubes through a simple hydrothermal method without templates and surfactant. It is believed that both oriented attachment and Ostwald ripening should be the main formation mechanisms for the hollow nanocubes through TEM images at different time. In the first stage, initial nanoparticles are assumed in order to reduce their high surface energy. As the reaction proceeds, the concentration of the nanoparticles is decreased and the factor of oriented attachment is dominant in the reaction system. The loose structure is formed due to the oriented attachment process finishes so fast. In the later stage, crystallites located in the outermost surface of aggregates are larger and would grow at the expense of smaller ones inside, so the solid evacuation occurred, and hollow nanocubes were obtained. The experiment results indicate that the reaction time, temperature and the amount of water in the reaction system have some effect on the final morphology of Cu2O hollow nanocubes.4. Synthesis of Cu2O-Au core-shell nanospheres and Ag-Cu core-shell nanoparticles through solution method.(a) Cu2O-Au core-shell nanospheres were successfully prepared on a large scale through simple solution methods at room temperature in a very short time. Cu2O-Au nanospheres with core-shell structure were prepared by coating Au shell over Cu2O core. Cu2O cores were first prepared via the reaction between Cu(NO3)2 and N2H4.Then addition and subsequent reduction of HAuCl4 with excess N2H4 resulted in the formation of Au nanoparticles, which deposited on the Cu2O surface to form core-shell structure. At the same time, the evolution of the gap between core and shell could be attributed to the gradual consumption of the outmost surface of Cu2O core by H+ from HAuCl4. (b) A simple method has been developed for the synthesis of Ag-Cu core-shell nanoparticles, based on the use of DMF as both reductant and solvent, in the presence of PVP. At the early reaction stage, Ag+ ions are reduced first forming the core of the core-shell structure. The Ag core is acting as the nucleic center for the growth of the Cu2O layer. With the further reaction, Cu2+ ions are reduced subsequently and the shell of Cu2O nanoparticles are formed surrounding the Ag core. With a longer process time, the void space between core and shell could be observed, we presume that the formation of the void space between core and shell could attribute to the Ostwald ripening mechanism, accompanying with the reductive conversion of Cu2O to Cu. At the same time, Cu2O nanoparticles were transformed to Cu nanoparticles gradually, and Ag-Cu core-shell nanoparticles were obtained.更多还原