类球形金及金钯纳米晶的可控制备与其拉曼和电催化性能研究

发布时间：2018-01-11 14:13

  本文关键词：类球形金及金钯纳米晶的可控制备与其拉曼和电催化性能研究　出处：《山东大学》2017年博士论文　论文类型：学位论文

  更多相关文章： 金属纳米晶 表面增强拉曼 表面缺陷密度 电催化

【摘要】：金纳米晶由于具有独特的物理化学性质,在很多领域,如:医学诊断学、探测器、催化、纳米药物学等都有巨大的应用价值。其中,水溶性类球形金纳米晶由于制备方法简单,易于被非材料专业,如:生物、物理、化学等专业的研究者制备,在很多实际应用中发挥着重要作用,从而引起了人们广泛的关注。目前制备水溶性类球形金纳米晶最常用的方法是1951年由Turkevich提出的,即使用柠檬酸钠还原氯金酸来直接制备。后来,Frens通过改变柠檬酸钠和氯金酸的摩尔比制备出尺寸范围为16-150nm的金纳米晶。但是随着尺寸的增大,金纳米晶尺寸分布变宽、形貌变得不均一。后来,我们课题组改善了传统的Turkevich法,将柠檬酸钠、氯金酸和硝酸银的混合液加入到沸水中,制备出了尺寸范围12-36 nm的单分散类球形金纳米晶。但是随着柠檬酸钠浓度的降低,成核速率减慢,二次成核不可避免,在合成尺寸大于36nm的纳米晶时,开始出现椭球形或者其他不规则形貌的副产物。目前制备尺寸范围较大的金纳米晶方法比较复杂,可重复性差,所以用一种简单的方法制备尺寸范围大、形貌均一、重复性好的类球形金纳米晶仍然是一个严峻的挑战。双金属核壳纳米晶由于不同组分间的协同作用使其物理化学性质得到显著增强,从而在很多领域得到广泛关注,尤其在直接燃料电池领域中成为了研究热点。众所周知,钯基纳米催化剂在碱性条件下对乙醇氧化有优异的催化性能,将金引入到销基纳米催化剂中,可以有效的提高纳米催化剂的催化活性和抗CO中毒能力。当金纳米晶上生长厚度只有几个原子层的钯时,由于两种金属间的晶格常数不匹配引起的应力效应和电子耦合产生的配位效应,使得金钯核壳结构纳米晶的催化性能得到显著提高。最近,很多报道认为,纳米晶表面存在的缺陷同样可以提高纳米催化剂的催化性能。但是,目前仍然很难解释纳米催化剂在质量归一化的电流密度(mass activity)和电化学比表面积归一化的电流密度(specific activity)之间的差异。由于制备具有不同缺陷密度的纳米催化剂比较困难,并且到目前为止,纳米催化剂表面缺陷仍然缺少定量计算的公式,所以很少有报道定量分析纳米催化剂的缺陷密度与其mass activity和specific activity之间的关系。因此用简单的方法制备出具有不同缺陷密度、薄钯层的金钯核壳结构纳米晶,对在乙醇燃料电池的应用中有巨大的利用价值。基于以上问题,本论文首先通过加入过渡金属离子(如Fe2+/Cu+和Ag+离子),通过两者的协同作用,成功制备出单分散、类球形的14-60nm的球形金纳米晶;接着我们在三羟甲基氨基甲烷体系中,用一步种子生长法合成尺寸范围为31-577 nm的类球形金纳米晶,并且考察了以对巯基苯胺(4-AIP)为探针分子,类球形金纳米晶的表面增强拉曼的尺寸效应;最后基于金纳米晶所具有孪晶缺陷的本质,提出缺陷密度的概念并给出计算公式,并考察了金钯核壳结构纳米晶中缺陷密度和尺寸与催化性能之间的关系。具体研究内容如下:在第二章中,通过将柠檬酸钠与Fe2+或Cu+离子以及硝酸银的混合液代替柠檬酸钠加入到沸腾的氯金酸溶液中,成功制备出尺寸范围为14-60nm的单分散、类球形金纳米晶。和传统的Frens方法相比,我们制备的金纳米晶尺寸分布范围较窄,且形貌为均一的类球形。加入还原性较强的Fe2+或Cu+离子,可以在柠檬酸钠浓度较低时,与氯金酸发生氧化还原反应,直接将Au3+离子还原成Au0原子,加入的Ag+离子作为催化剂,可以有效加快柠檬酸钠的氧化从而加快成核速率;同时能够将形成的金纳米晶的形貌重塑成球形,保证纳米晶各项同性的生长。这两种离子之间的协同效应使我们的体系可以合成出单分散、类球形的金纳米晶。在第三章中,在具有生物相容性的三羟甲基氨基甲烷体系中,以在柠檬酸钠体系合成的17nm类球形金纳米晶作为种子,通过改变种子的浓度可以成功制备出31-577nm的单分散、类球形的金纳米晶。和文献报道的种子生长法不同,本方法操作简单,只需要顺次将17nm类球形金纳米晶种子和氯金酸溶液加入到沸腾的三羟甲基氨基甲烷溶液中即可。在最佳的pH范围内,金纳米晶的尺寸和浓度可以简单的通过调节加入的金纳米晶种子浓度或者氯金酸的浓度来调控,通过改变氯金酸的浓度可以制备出高产量的金纳米晶。此外,以4-AIP作为探针分子,对制备出的不同尺寸的类球形金纳米晶进行表面增强拉曼测试,发现随着尺寸的增加,表面增强拉曼呈"火山型"的变化趋势。以不同尺寸的类球形金纳米晶基底,在不同激发波长的条件下对4-AIP分子进行表面增强拉曼测试,结果表明,在633和785 nm激发波长下,97nm 和408 nm的类球形金纳米晶分别具有最大的表面增强拉曼散射。在第四章中,以柠檬酸钠体系中合成的不同尺寸具有不同缺陷密度的类球形金纳米晶(6,12,19,30,57nm)作为种子,用大量的AA作为还原剂,在室温下还原氯钯酸钠制备出厚度具有几个Pd原子层的金钯核壳结构纳米晶,并测试它们在碱性条件下对乙醇的催化氧化的能力,结果表明壳层厚度影响它们的催化性能,具有一个Pd原子层厚度的金钯纳米晶具有最佳的催化性能。在这一章中,我们首次提出了表面缺陷的概念,并对缺陷做出定量的计算。计算结果和催化性能相比,我们得出:纳米晶的specific activity随着缺陷密度的增加逐渐增大,而它们的活性比表面积(ECSA)和mass activity是随着尺寸的增加呈"火山型"的变化趋势。C19S Au0.91@Pd0.09/C取得最佳的催化性能和稳定性,它的ECSAC119.8 m2 g-1)、mass activity(11.0 A mgPd-1)和 specific activity(9.3 mA cm-2)值分别是商业 Pd/C(24.9 m2 g-1,0.3 A mpd-1,and 1.2 mA cm-2)的 4.8 倍、36.7 倍和 7.8倍,时间-电流稳定测试7200s后,C19S Au0.91@Pd0.09/C的电流密度(0.337 AmgPd-1)是商业 Pd/C(8.2mA mgPd-1)的 40.9 倍。在第五章中,我们进行了总结与展望。综上所述,我们制备出尺寸均一的14-577 nm的类球形金纳米晶以及具有不同缺陷密度的金钯核壳纳米晶,可以大大扩宽纳米晶在生物和催化等方面的应用。
[Abstract]:Gold nanocrystals due to its unique physical and chemical properties, in many fields, such as medical diagnostics, detector, catalysis, nano pharmacology have great application value. Among them, water soluble spherical gold nanoparticles as the preparation method is simple, easy to be non professional materials, such as biology, physics, research chemical and other professional preparation, plays an important role in many practical applications, which caused widespread concern. At present, the preparation method of water-soluble spherical gold nanoparticles is the most commonly used 1951 proposed by Turkevich, using sodium citrate reduction of HAuCl4 to direct preparation of later. Frens, prepared with size of gold nanocrystals by changing the 16-150nm of sodium citrate and chloroauric acid molar ratio. But as the size increases, the nano gold crystal size distribution becomes wider, surface becomes uneven. Later, our research group improved the traditional Tur Kevich method, the sodium citrate, mixed solution of chloroauric acid and silver nitrate is added to the boiling water, prepared by the 12-36 nm size range of monodisperse spherical gold nanoparticles. But with the decrease of the concentration of sodium citrate, the nucleation rate slowed down, two times of nucleation is inevitable, in the synthesis of Nanocrystalline size more than 36nm, began to ellipsoid or other irregular morphology by-products. The preparation of the large size range of gold nanocrystals method is more complex, poor reproducibility, so using a simple preparation method of large size range, uniform morphology, the nano gold spherical crystal with good repeatability is still a serious challenge. The bimetallic shell nanocrystals due to the synergistic effect between different components of the physical and chemical properties are significantly enhanced, which is widely concerned in many fields, especially in the field of direct fuel cell has become a research hotspot. The As we know, palladium based catalysts have excellent catalytic performance for ethanol oxidation in alkaline conditions, will be introduced to the gold pin based nano catalyst, can effectively improve the catalyst catalytic activity and resistance to CO poisoning. When gold nanocrystals grown on the thickness of only a few atomic layers of palladium, because the lattice constant of two the metal not match between the stress caused by the electronic effect and the coupling effect of coordination of the catalytic performance of Au PD core-shell nanocrystals has been improved. Recently, many reports that the defects of nanocrystalline surface also can improve the catalytic performance of nanometer catalyst. However, it is still hard to explain current the density of nano catalyst on quality normalized (mass activity) than the current density and electrochemical surface area normalized (specific activity). The differences between the preparation with different defect density The catalyst is difficult, and so far, the surface defects of nano catalyst still lacks the quantitative calculation formula, so there is little relationship between nano catalyst analysis reports quantitative defect density with mass activity and specific activity. Therefore, with simple preparation method with different defect density, thin layer of gold palladium palladium core shell the structure of nanocrystalline, has great value in use in the application of ethanol fuel cell. Based on the above problems, this paper firstly by adding transition metal ions (such as Fe2+/Cu+ and Ag+ ions), through the synergy of the two, successfully prepared monodisperse, spherical crystal nano gold spherical 14-60nm; then we in three Tris system, with a step size in the range of seed growth method for the synthesis of nano gold spherical crystal 31-577 nm, and to investigate the mercapto amine (4-AIP) on. The needle molecules, enhance the size effect of Raman surface spherical gold nanocrystals; finally, based on the nature of gold nanocrystals with twin defects, put forward the concept of defect density and the calculation formula is given, and the relationship between the Au PD core-shell structure nano crystal defect density and size and catalytic performance between the specific contents. As follows: in the second chapter, the sodium citrate with Fe2+ or Cu+ ions and silver nitrate mixture instead of sodium citrate added to HAuCl4 solution boiling, prepared for the 14-60nm single size dispersed, spherical gold nanometer crystal. Compared with the traditional Frens method, we made the nano gold crystal size distribution range was narrow, and the morphology of uniform spherical. With a strong reduction of Fe2+ or Cu+ ion in sodium citrate concentration was low, redox reaction with gold chloride acid, direct Au3+ ions The reduction of Au0 atoms, the addition of Ag+ ions as catalyst, can effectively accelerate the oxidation of sodium citrate and accelerates the nucleation rate; at the same time can reshape the morphology of the nano gold crystal will be formed into a spherical nanocrystals to ensure isotropic growth. The synergistic effect between these two ions so that our system can be synthesized dispersion of spherical gold nanoparticles. In the third chapter, the biocompatible three Tris system, gold nanoparticles as seeds for 17nm spherical grains synthesized in the sodium citrate system, by changing the concentration of the seed can be successfully prepared 31-577nm monodisperse gold nanocrystals. Spherical. And the seed growth method reported in the literature, this method has the advantages of simple operation, only need to turn 17nm spherical nano gold crystal seed and chloroauric acid solution can be added to boiling three Tris solution. The best pH range, size and concentration of gold nanocrystals can be added simply by adjusting the nano gold crystal seed or concentration of chloroauric acid concentration to control, by changing the concentration of chloroauric acid can be prepared by gold nanocrystals with high yield. In addition, using 4-AIP as a probe molecule of gold nanoparticles type of spherical grains with different sizes of prepared by surface enhanced Raman test, found that with the increase in size, surface enhanced Raman showed tendency of "Volcano". The substrate spherical gold nanoparticles of different sizes at different excitation wavelengths under the condition of 4-AIP molecules in surface enhanced Raman test results in 633, and 785 nm excitation wavelength, the nano gold spherical crystal 97nm and 408 nm respectively with maximum surface enhanced Raman scattering. In the fourth chapter, based on different sizes of synthesis of sodium citrate system with different defect density The class of spherical gold nanoparticles (6,12,19,30,57nm) as seed, with a large number of AA as a reducing agent, reduction of palladium chloride sodium was prepared with the thickness of several Pd atomic layer of Au PD core-shell structure nanoparticles at room temperature, and test their ability to catalyze the oxidation of ethanol in alkaline conditions, results show that the shell effect of the thickness of their catalytic properties, with a Pd atomic layer of gold palladium nano crystal has the best catalytic performance. In this chapter, we first proposed the concept of surface defects, and make a quantitative calculation of the defects. The calculation results and the catalytic performance compared, we conclude that: nano crystal specific activity gradually increases with increasing the density of defects, and their active surface area (ECSA) and mass activity is with the size increasing trend of ".C19S Au0.91@Pd0.09/C" Volcano "has the best catalytic performance and stability It's ECSAC119.8, M2 g-1), mass activity (11 A mgPd-1) and specific activity (9.3 mA cm-2) value is Pd/C (24.9 M2 g-1,0.3 A business mpd-1, and 1.2 mA cm-2) 4.8 times, 36.7 times and 7.8 times, the time current stability test of 7200s, current density of C19S Au0.91@ Pd0.09/C the (0.337 AmgPd-1) Pd/C (8.2mA mgPd-1) is a commercial 40.9 times. In the fifth chapter, we make a summary and prospect. In summary, we prepared the nano gold spherical crystal with uniform size of 14-577 and nm with different defect density of Au PD core-shell nanocrystals can greatly expand application of nanocrystalline in biological and catalytic fields.

【学位授予单位】：山东大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：O614.123;TB383.1
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本文编号：1409865