氮掺杂长竹节状碳纳米管的制备及其生长机理

本文采用电弧放电法,通过阳极棒与不锈钢片的共蒸发,制备了氮掺杂长竹节状碳纳米管。借助扫描电子显微镜（SEM）、场发射高分辨透射电子显微镜（HRTEM）及其附带能量色散X射线（EDX）光谱仪和电子能量损失谱（EELS）、透射电子显微镜（TEM）等表征方法,对产物的形貌、结构和组成进行表征。表征结果表明,氮掺杂长竹节状碳纳米管的长度在640~835nm之间,其内径在23~35nm之间,外径在28~47nm之间;且在每一节“竹节”与另一节“竹节”的连接处形成的内腔中均有一个黑色纳米颗粒,其直径尺寸以及产物中的氮掺杂长竹节状碳纳米管的含量均与熔化、蒸发的不锈钢片的面积有关。本文还对氮掺杂长竹节状碳纳米管的生长机理进行了简单的探讨。     

氮掺杂竹节状碳纳米管的催化合成

以有机胺为碳和氮源, 用催化方法合成出了含氮大管径竹节状碳纳米管. Fe/SBA-15分子筛为催化剂, 有机胺经过973 K高温裂解得到氮掺杂竹节状碳纳米管材料(CN_X). 比较了铁含量、二乙胺和六次甲基四胺原料对合成氮掺杂碳纳米管形貌和氮掺杂量的影响; 合成出氮碳比(N/C原子比)为0.26的氮掺杂竹节状碳纳米管材料.     

以吡啶为原料制备氮掺杂碳纳米管

在700～800 ℃,以吡啶为原料用CVD方法制备出了管径在20～40 nm的竹节状碳纳米管. EDX和XPS结果都表明氮掺杂到碳纳米管中. HRTEM研究发现掺氮碳纳米管的竹节由数层石墨片弯曲而成,纳米管外层石墨层逐渐消失.从Raman谱图的对照中发现,与相似条件下制备出的纯碳纳米管相比,氮掺杂碳纳米管的D谱带对G谱带的相对强度增加, TGA研究发现掺杂纳米管在较低温度下即被氧化,这些结果都说明氮掺杂使得纳米管的缺陷增加.     

不同氮掺杂量碳纳米管的合成和表征

以不同氮含量的有机胺为碳和氮源，用催化方法合成出了不同氮含量的大管径碳纳米管。采用Fe/SBA-15分子筛为催化剂，有机胺经过1 073 K高温裂解得到氮掺杂碳纳米管材料(CN_x)。比较了苯、三乙胺、二乙胺、乙二胺四种原料对合成CN_x形貌、产率、掺氮量和吸水率的影响；以二乙胺为原料合成出适中的氮碳比(N/C原子比为0.15)和较高产率(2.2 g·（g·cat）^-1)的竹节状CN_x材料。     

铁基氮掺杂碳纳米管制备及其电催化性能

利用化学原位聚合法制备聚吡咯包覆碳纳米管, 然后以硫酸亚铁铵盐为铁前驱体, 采用液相沉淀法制备聚吡咯-碳纳米管-铁化合物复合材料(Fe-PPy-CNTs), 通过对复合材料Fe-PPy-CNTs 热处理, 成功制备出铁基氮掺杂碳纳米管催化剂FeNCNTs. X射线衍射分析表明, 热处理使Fe-PPy-CNTs 复合物中Fe₃O₄向Fe₃N和Fe转化, 700 ℃热处理制备的FeNCNT700中铁主要是Fe₃O₄相, 但也有Fe相. 800和900 ℃热处理制备的催化剂FeNCNT800和FeNCNT900则明显有Fe₃N和Fe形成. 随着热处理温度升高, FeNCNTs 催化剂氮含量降低, 其含氮官能团也由吡咯型氮向吡啶型和石墨型氮转化. 电化学分析表明, 含有Fe₃N 的FeNCNT800 和FeNCNT900催化剂具有明显的氧还原催化活性, 其中, FeNCNT800因其具有高的比表面积、高的氮含量和高比例的有利于增强氧吸附能力和弱化O―O键的石墨氮官能团, 而表现出优于FeNCNT900氧还原催化活性及稳定性.     

碳纳米管的最新制备技术及生长机理

结合笔者的工作综述了碳纳米管的制备技术及生长机理的最新研究进展，重点介绍了近两年来碳纳米管制备的进展情况，包括传统制备方法的改进（电弧放电法、化学气相沉积法和激光蒸发法）、新型制备技术、特殊结构的碳纳米管制备；同时探讨了碳纳米管的各种生长机理；最后提出了碳纳米管制备技术和生长机理的发展方向。     

聚苯胺改性氮掺杂碳纳米管制备及其超级电容器性能

利用苯胺原位化学聚合合成聚苯胺包覆碳纳米管(CNTs), 再炭化处理制备氮掺杂碳纳米管(NCNTs).激光拉曼(Raman)光谱和X射线光电子谱(XPS)分析及透射电镜(TEM)观察表明, 苯胺包覆碳纳米管经炭化处理后, 得到以碳纳米管为核、氮掺杂碳层为壳, 具有核-壳结构的氮掺杂碳纳米管, 而碳纳米管本征结构未遭破坏. 研究表明, 随着苯胺用量的增大, 氮掺杂碳纳米管的氮掺杂碳层变厚, 氮含量从7.06%(质量分数)增加到8.64%, 而作为超级电容器电极材料, 随着氮掺杂碳层厚度降低, 氮掺杂碳纳米管在6 mol·L^-1氢氧化钾电解液中的比容量从107 F·g^-1增大到205 F·g^-1, 远高于原始碳纳米管10 F·g^-1的比容量, 且聚苯胺改性氮掺杂碳纳米管表现出较好的充放电循环性, 经1000次充放电循环后仍保持初始容量的92.8%~97.1%, 表明氮掺杂碳纳米管不仅通过表面氮杂原子引入大的法拉第电容和改善亲水性使电容量显著增大, 其具有的核壳结构特征也使循环稳定性增强。     

氮掺杂碳纳米管的制备及其电化学性能

采用弱反应性含氮有机物水合肼、二乙烯三胺对碳纳米管进行氮掺杂处理. 结合X射线光电子谱(XPS)分析和扫描电镜(SEM)观察, 发现两种含氮有机物处理均可使碳纳米管表面成功连接上含氮基团, 并保持了碳纳米管的本征形貌和结构. 水合肼处理的碳纳米管的氮含量(碳/氮原子比为95/2)明显高于二乙烯三胺处理的碳纳米管(碳/氮原子比为96/0.5). 氮掺杂后碳纳米管在水溶液中分散性明显改善, 且分散性随着氮含量增加进一步增强, 因此水合肼处理的碳纳米管分散性明显优于二乙烯三胺处理的碳纳米管. 作为电化学电容器电极材料, 碳纳米管含氮官能团贡献了赝电容, 但其循环性仍需进一步改进. 氮掺杂碳纳米管较好的亲水性, 改善了电解液的浸润, 循环后氮掺杂碳纳米管电极的比容量仍略高于纯碳纳米管电极的比容量.     

Ni基催化剂上未掺杂和氮掺杂的碳纳米纤维生长机理的比较

研究了Ni催化剂上碳纳米纤维,以及Ni和Ni-Cu催化剂上N掺杂的碳纳米纤维的生长机理.结果表明,这两个过程的机理均包含了表面非计量碳化镍的形成,然后是碳或碳和氮通过催化剂颗粒体相的溶解和扩散.     

竹节状碳纳米管有序阵列的合成和表征

用1,4-偶氮二异丁基腈作碳源,以载有催化剂Co的多孔Al₂O₃膜作模板,用化学气相沉积法在较低温度(600℃)下方便地制得了单分散碳纳米管有序阵列。透射电子显微分析表明,所得碳纳米管的形态为竹节形状,端口是闭合的,这和同样用Al₂O₃膜作模板但以乙烯或乙炔作碳源热分解制得的中空碳纳米管的情形明显不同。对该纳米管的生成机理进行了初步探讨。     

MWPCVD低温合成纳米碳管的生长机理

The synthesis of carbon nanotubes (CNTs) at low temperature has received a great deal of attention and be-comes a challenging issue. But few model which accounts for the growth of CNTs is suited for the synthesis of CNTs by microwave plasma chemical vapor deposition (MWPCVD) at low temperature because most researchers conclude that the growth mechanism is determined by the catalyst-supporter interaction while ignored the diffusion of carbon in the catalyst. In this paper, under the catalytic effect of cobalt supported by SiO₂ and Al₂O₃, CNTs are synthe-sized by MWPCVD at about 500℃, and tip-growth, the model which accounts for the catalytic growth of CNTs is outlined. It is the temperature difference between the upper and bottom of the catalytic particle that results in the diffusion of carbon atoms from upper to the bottom, and precipitation of saturated carbon on the bottom surface to form CNTs.     

纳米碳管负载Co催化生长纳米碳管

In this paper, carbon nanotubes (CNTs) used as support and cobalt as catalyst to prepare new CNTs was studied. CNTs could grow well if the precursor CNTs were supported with Co on its surface. On the contrary, CNTs couldn’t grow at all if the precursor CNTs were not supported with Co. The TEM images showed that diameters of the obtained CNTs were different from those of the precursor CNTs. The pure CNTs could be prepared in this method without further purifying. The amount of Co on the precursor CNTs could affect the growth of CNTs greatly. When the content of metal on precursor CNTs was less than 16.2%, the amount of the obtained CNTs increased with the increasing amount of Co, and the maximum growth amount of 625% of CNTs could be obtained. But if the content of metal was more than 16.2%, the amount of Co had no influence on the growth of CNTs.     

分叉碳纳米管的催化生长

Branching carbon nanotubes were synthesized by pyrolysis of acetylene at 700℃ over oxygen-free copper and γ-Al₂O₃-supported Cu unitary or Cu/Fe binary catalysts. The morphologies of the as-grown products were charac-terized by transmission electron microscopy. The results indicated that the branching structures were closely related to the Cu component of the catalysts. We proposed that the special electronic structure (3d¹⁰4s¹) of Cu play the crucial role in the formation of the heptagon defects related to the branching structures.     

简易法制备竹节状非晶态碳纳米管

以正硅酸乙酯为碳源,采用简易热分解法,在无催化剂的条件下合成了竹节状非晶态碳纳米管。运用扫描电镜(SEM)和透射电镜(TEM)对样品进行表征,结果表明竹节状非晶态碳纳米管长几个微米,其外径和内径分别是30~40 nm和8~15 nm。该方法在无催化剂条件下制备出非晶态碳纳米管,对科学研究有着重要的意义和潜在的应用前景。     

纳米碳管的制备

纳米碳管是一种新型的纳米材料和碳分子,其独特的分子结构和性能引起了人们的广泛关注。本文综述了纳米碳管的几种制备方法和相关的生长机理。     

Growth Mechanism of Vertically Aligned Carbon Nanotube Arrays

Vertically aligned multi-walled carbon nanotube arrays grown on quartz substrate are obtained by co-pyrolysis of xylene and ferrocene at 850 oC in a tube furnace. Raman spectroscopy and high resolution transmission electron microscopy measurements show that the single-walled carbon nanotubes are only present on top of vertically aligned multi-walled carbon nanotube arrays. It has been revealed that isolated single-walled carbon nanotubes are only present in those floating catalyst generated materials. It thus suggests that the single-walled carbon nanotubes here are also generated by floating catalyst. Vertically alignedcarbon nanotube arrays on the quartz substrate have shown good orientation and good graphitization. Meanwhile, to investigate the growth mechanism, two bi-layers carbon nan-otube films with di erent thickness have been synthesized and analyzed by Raman spectroscopy. The results show that the two-layer vertically aligned carbon nanotube films grow “bottom-up”. There are distinguished Raman scattering signals for the second layer itself, surface of the first layer, interface between the first and second layer, side wall and bottom surface. It indicates that the obtained carbon nanotubes follow the base-growth mechanism, and the single-walled carbon nanotubes grow from their base at the growth beginning when iron catalyst particles have small size. Those carbon nanotubes with few walls (typically <5 walls) have similar properties, which also agree with the base-growth mechanism.     

多壁碳纳米管的制备及改性处理

用自制的镍 硅二元气凝胶作催化剂,合成了多壁碳纳米管.甲烷在680℃催化裂解120min,再升温至800℃继续裂解20min,得到多壁碳纳米管.TEM、HRTEM和Raman光谱分析表明,所得多壁碳纳米管与高定向石墨具有相似的层状结构,其管径分布均匀,约15～30nm左右,长径比大,管端封闭,并含有金属催化剂粒子;采用不同方法改性处理,发现经过稀硝酸浸泡和空气氧化处理后,能去除碳管中金属催化剂,同时碳纳米管管长变短,端帽开口,能有效利用内表面,比表面积增大.     

Hollow Nanotubes of N‐Doped Carbon on CoS

Low‐cost, single‐step synthesis of hollow nanotubes of N‐doped carbon deposited on CoS is enabled by the simultaneous use of three functionalities of polyacrylonitrite (PAN) nanofibers: 1) a substrate for loading active materials, 2) a sacrificial template for creating hollow tubular structures, and 3) a precursor for in situ nitrogen doping. The N‐doped carbon in hollow tubes of CoS provides a high‐capacity anode of long cycle life for a rechargeable Li‐ion or Na‐ion battery cell that undergoes the conversion reaction 2 A⁺+2 e^?+CoS →Co+A₂S with A=Li or Na.