本文關(guān)鍵詞：類球形金及金鈀納米晶的可控制備與其拉曼和電催化性能研究　出處：《山東大學(xué)》2017年博士論文　論文類型：學(xué)位論文

  更多相關(guān)文章： 金屬納米晶 表面增強(qiáng)拉曼 表面缺陷密度 電催化

【摘要】：金納米晶由于具有獨(dú)特的物理化學(xué)性質(zhì),在很多領(lǐng)域,如:醫(yī)學(xué)診斷學(xué)、探測(cè)器、催化、納米藥物學(xué)等都有巨大的應(yīng)用價(jià)值。其中,水溶性類球形金納米晶由于制備方法簡(jiǎn)單,易于被非材料專業(yè),如:生物、物理、化學(xué)等專業(yè)的研究者制備,在很多實(shí)際應(yīng)用中發(fā)揮著重要作用,從而引起了人們廣泛的關(guān)注。目前制備水溶性類球形金納米晶最常用的方法是1951年由Turkevich提出的,即使用檸檬酸鈉還原氯金酸來(lái)直接制備。后來(lái),Frens通過(guò)改變檸檬酸鈉和氯金酸的摩爾比制備出尺寸范圍為16-150nm的金納米晶。但是隨著尺寸的增大,金納米晶尺寸分布變寬、形貌變得不均一。后來(lái),我們課題組改善了傳統(tǒng)的Turkevich法,將檸檬酸鈉、氯金酸和硝酸銀的混合液加入到沸水中,制備出了尺寸范圍12-36 nm的單分散類球形金納米晶。但是隨著檸檬酸鈉濃度的降低,成核速率減慢,二次成核不可避免,在合成尺寸大于36nm的納米晶時(shí),開(kāi)始出現(xiàn)橢球形或者其他不規(guī)則形貌的副產(chǎn)物。目前制備尺寸范圍較大的金納米晶方法比較復(fù)雜,可重復(fù)性差,所以用一種簡(jiǎn)單的方法制備尺寸范圍大、形貌均一、重復(fù)性好的類球形金納米晶仍然是一個(gè)嚴(yán)峻的挑戰(zhàn)。雙金屬核殼納米晶由于不同組分間的協(xié)同作用使其物理化學(xué)性質(zhì)得到顯著增強(qiáng),從而在很多領(lǐng)域得到廣泛關(guān)注,尤其在直接燃料電池領(lǐng)域中成為了研究熱點(diǎn)。眾所周知,鈀基納米催化劑在堿性條件下對(duì)乙醇氧化有優(yōu)異的催化性能,將金引入到銷基納米催化劑中,可以有效的提高納米催化劑的催化活性和抗CO中毒能力。當(dāng)金納米晶上生長(zhǎng)厚度只有幾個(gè)原子層的鈀時(shí),由于兩種金屬間的晶格常數(shù)不匹配引起的應(yīng)力效應(yīng)和電子耦合產(chǎn)生的配位效應(yīng),使得金鈀核殼結(jié)構(gòu)納米晶的催化性能得到顯著提高。最近,很多報(bào)道認(rèn)為,納米晶表面存在的缺陷同樣可以提高納米催化劑的催化性能。但是,目前仍然很難解釋納米催化劑在質(zhì)量歸一化的電流密度(mass activity)和電化學(xué)比表面積歸一化的電流密度(specific activity)之間的差異。由于制備具有不同缺陷密度的納米催化劑比較困難,并且到目前為止,納米催化劑表面缺陷仍然缺少定量計(jì)算的公式,所以很少有報(bào)道定量分析納米催化劑的缺陷密度與其mass activity和specific activity之間的關(guān)系。因此用簡(jiǎn)單的方法制備出具有不同缺陷密度、薄鈀層的金鈀核殼結(jié)構(gòu)納米晶,對(duì)在乙醇燃料電池的應(yīng)用中有巨大的利用價(jià)值�；谝陨蠁�(wèn)題,本論文首先通過(guò)加入過(guò)渡金屬離子(如Fe2+/Cu+和Ag+離子),通過(guò)兩者的協(xié)同作用,成功制備出單分散、類球形的14-60nm的球形金納米晶;接著我們?cè)谌u甲基氨基甲烷體系中,用一步種子生長(zhǎng)法合成尺寸范圍為31-577 nm的類球形金納米晶,并且考察了以對(duì)巰基苯胺(4-AIP)為探針?lè)肿?類球形金納米晶的表面增強(qiáng)拉曼的尺寸效應(yīng);最后基于金納米晶所具有孿晶缺陷的本質(zhì),提出缺陷密度的概念并給出計(jì)算公式,并考察了金鈀核殼結(jié)構(gòu)納米晶中缺陷密度和尺寸與催化性能之間的關(guān)系。具體研究?jī)?nèi)容如下:在第二章中,通過(guò)將檸檬酸鈉與Fe2+或Cu+離子以及硝酸銀的混合液代替檸檬酸鈉加入到沸騰的氯金酸溶液中,成功制備出尺寸范圍為14-60nm的單分散、類球形金納米晶。和傳統(tǒng)的Frens方法相比,我們制備的金納米晶尺寸分布范圍較窄,且形貌為均一的類球形。加入還原性較強(qiáng)的Fe2+或Cu+離子,可以在檸檬酸鈉濃度較低時(shí),與氯金酸發(fā)生氧化還原反應(yīng),直接將Au3+離子還原成Au0原子,加入的Ag+離子作為催化劑,可以有效加快檸檬酸鈉的氧化從而加快成核速率;同時(shí)能夠?qū)⑿纬傻慕鸺{米晶的形貌重塑成球形,保證納米晶各項(xiàng)同性的生長(zhǎng)。這兩種離子之間的協(xié)同效應(yīng)使我們的體系可以合成出單分散、類球形的金納米晶。在第三章中,在具有生物相容性的三羥甲基氨基甲烷體系中,以在檸檬酸鈉體系合成的17nm類球形金納米晶作為種子,通過(guò)改變種子的濃度可以成功制備出31-577nm的單分散、類球形的金納米晶。和文獻(xiàn)報(bào)道的種子生長(zhǎng)法不同,本方法操作簡(jiǎn)單,只需要順次將17nm類球形金納米晶種子和氯金酸溶液加入到沸騰的三羥甲基氨基甲烷溶液中即可。在最佳的pH范圍內(nèi),金納米晶的尺寸和濃度可以簡(jiǎn)單的通過(guò)調(diào)節(jié)加入的金納米晶種子濃度或者氯金酸的濃度來(lái)調(diào)控,通過(guò)改變氯金酸的濃度可以制備出高產(chǎn)量的金納米晶。此外,以4-AIP作為探針?lè)肿?對(duì)制備出的不同尺寸的類球形金納米晶進(jìn)行表面增強(qiáng)拉曼測(cè)試,發(fā)現(xiàn)隨著尺寸的增加,表面增強(qiáng)拉曼呈"火山型"的變化趨勢(shì)。以不同尺寸的類球形金納米晶基底,在不同激發(fā)波長(zhǎng)的條件下對(duì)4-AIP分子進(jìn)行表面增強(qiáng)拉曼測(cè)試,結(jié)果表明,在633和785 nm激發(fā)波長(zhǎng)下,97nm 和408 nm的類球形金納米晶分別具有最大的表面增強(qiáng)拉曼散射。在第四章中,以檸檬酸鈉體系中合成的不同尺寸具有不同缺陷密度的類球形金納米晶(6,12,19,30,57nm)作為種子,用大量的AA作為還原劑,在室溫下還原氯鈀酸鈉制備出厚度具有幾個(gè)Pd原子層的金鈀核殼結(jié)構(gòu)納米晶,并測(cè)試它們?cè)趬A性條件下對(duì)乙醇的催化氧化的能力,結(jié)果表明殼層厚度影響它們的催化性能,具有一個(gè)Pd原子層厚度的金鈀納米晶具有最佳的催化性能。在這一章中,我們首次提出了表面缺陷的概念,并對(duì)缺陷做出定量的計(jì)算。計(jì)算結(jié)果和催化性能相比,我們得出:納米晶的specific activity隨著缺陷密度的增加逐漸增大,而它們的活性比表面積(ECSA)和mass activity是隨著尺寸的增加呈"火山型"的變化趨勢(shì)。C19S Au0.91@Pd0.09/C取得最佳的催化性能和穩(wěn)定性,它的ECSAC119.8 m2 g-1)、mass activity(11.0 A mgPd-1)和 specific activity(9.3 mA cm-2)值分別是商業(yè) 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,時(shí)間-電流穩(wěn)定測(cè)試7200s后,C19S Au0.91@Pd0.09/C的電流密度(0.337 AmgPd-1)是商業(yè) Pd/C(8.2mA mgPd-1)的 40.9 倍。在第五章中,我們進(jìn)行了總結(jié)與展望。綜上所述,我們制備出尺寸均一的14-577 nm的類球形金納米晶以及具有不同缺陷密度的金鈀核殼納米晶,可以大大擴(kuò)寬納米晶在生物和催化等方面的應(yīng)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.

【學(xué)位授予單位】：山東大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2017
【分類號(hào)】：O614.123;TB383.1
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本文編號(hào)：1409865