高温退火一步非破坏性纯化碳纳米管

针对催化化学气相法合成的碳纳米管含有金属、金属氧化物和碳杂质, 且缺陷较多进行了非破坏性纯化研究. 基于碳纳米管与碳杂质间结构、性质的微小差异, 1800 ℃使粗制的碳纳米管高温退火3 h, 为避免碳纳米管氧化, 高温退火过程在氩气气氛中完成. 运用扫描电镜、透射电镜观察碳纳米管的形貌和结构, 发现高温退火后, 碳纳米管的端帽大部分被打开. 能谱检测显示, 粗制的碳纳米管中的杂质(Al, Si, Ni, Cu 质量分数w分别为4.67%, 0.27%, 40.12%和1.34%)退火后被除去. 拉曼分析表明, 退火前后石墨D, G峰面积S_D, S_G分别从1314900降至474921, 767157降至566292, 退火不仅有效地去除了样品中的碳杂质, 而且使碳纳米管的缺陷得到一定程度的修复, 石墨化度随之大大提高. 研究提出了一种简单的、非破坏性的、便于规模化的纯化方法.

One-step Process for Non-Destructive Purification of Carbon Nanotubes by High-temperature Annealing

A process of non-destructive purification of carbon nanotubes (CNTs) was discussed. CNTs samples were produced by a catalytic chemical vapor deposition method, which have defects along the graphite tube walls and include impurities, such as catalyst particles, amorphous carbon, carbon nanoparticles, etc. Taking advantage of the fact that different structure and thermal oxidation rates exist between CNTs and other carbonaceous particles, samples were annealed at 1800 ℃ for 3 h in an Ar protective atmosphere. The morphologies of the as-received and high-temperature annealed samples were characterized by scanning electron microscopy. Most of CNTs cap were opened, which were in agreement with transmission electron microscopy observation. The elemental compositions of the specimens were identified by energy dispersive spectrometry. As-received sample impurities such as Al, Si, Ni and Cu (their mass fraction values were 4.67%, 0.27%, 40.12% and 1.34%, respectively) were efficiently removed. The purity and the graphitization were determined by Raman spectroscopy. After the annealing, the area of the D-line peak and the G-line peak decreased from 1314900 to 474921 and from 767157 to 566292, respectively. The intensity of D-line peak decreased, while that of G-line peak increased. These results imply that some defects have been healed. The purity and the graphitization of annealed CNTs are high. High-temperature annealing has been confirmed as an effective means of removing both the catalyst particles and microstructures defects within nanotubes.