Song Rongjun, Jiang Zhiwei, Bi Wuguo, Cheng Wenxi, Lu Jun, Huang Baotong, Tang Tao
State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, 5625, Renmin Street, Changchun 130022, China.
Chemistry. 2007;13(11):3234-40. doi: 10.1002/chem.200601018.
The effects of both organically modified montmorillonite (OMMT) and Ni(2)O(3) on the carbonization of polypropylene (PP) during pyrolysis were investigated. The results from TEM and Raman spectroscopy showed that the carbonized products of PP were mainly multiwalled carbon nanotubes (MWNTs). Surprisingly, a combination of OMMT and Ni(2)O(3) led to high-yield formation of MWNTs. X-ray powder diffraction (XRD) and GC-MS were used to investigate the mechanism of this combination for the high-yield formation of MWNTs from PP. Brønsted acid sites were created in degraded OMMT layers by thermal decomposition of the modifiers. The resultant carbenium ions play an important role in the carbonization of PP and the formation of MWNTs. The degradation of PP was induced by the presence of carbenium ions to form predominantly products with lower carbon numbers that could be easily catalyzed by the nickel catalyst for the growth of MWNTs. Furthermore, carbenium ions are active intermediates that promote the growth of MWNTs from the degradation products with higher carbon numbers through hydride-transfer reactions. The XRD measurements showed that Ni(2)O(3) was reduced into metallic nickel (Ni) in situ to afford the active sites for the growth of MWNTs.
研究了有机改性蒙脱土（OMMT）和Ni₂O₃对聚丙烯（PP）热解过程中碳化的影响。透射电子显微镜（TEM）和拉曼光谱的结果表明，PP的碳化产物主要是多壁碳纳米管（MWNTs）。令人惊讶的是，OMMT和Ni₂O₃的组合导致了MWNTs的高产率形成。采用X射线粉末衍射（XRD）和气相色谱-质谱联用（GC-MS）研究了这种组合从PP高产率形成MWNTs的机理。通过改性剂的热分解在降解的OMMT层中产生了布朗斯台德酸位点。生成的碳正离子在PP的碳化和MWNTs的形成中起重要作用。碳正离子的存在诱导了PP的降解，形成主要是低碳数的产物，这些产物很容易被镍催化剂催化用于MWNTs的生长。此外，碳正离子是活性中间体，通过氢化物转移反应促进来自高碳数降解产物的MWNTs的生长。XRD测量表明，Ni₂O₃原位还原为金属镍（Ni），为MWNTs的生长提供了活性位点。
