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>Synthesis of chemically-modified single-walled carbon nanotubes by counter-current ammonia gas injection into the induction thermal plasma process.
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Synthesis of chemically-modified single-walled carbon nanotubes by counter-current ammonia gas injection into the induction thermal plasma process.
Pristine single-walled carbon nanotubes (SWCNTs) are poorly dispersible and insoluble in many solvents and need to be chemically modified prior to their use in many applications.;Effects of the catalyst type and content on the SWCNTs final product, synthesized by induction thermal plasma (ITP), were studied to replace toxic cobalt (Co) in the feedstock. In this regard, three different catalyst mixtures (i.e. Ni-Y2O3, Ni-Co-Y2O3, and Ni-Mo-Y2O3) were used. Experimental results showed that the catalyst type affects the quality of the SWCNT final product. Similar quality SWCNTs can be produced when the same amount of Co was replaced by Ni. Moreover, the results observed in this experimental work were further explained by thermodynamic calculation results.;Thermogravimetry (TG) was used throughout the work to characterize the SWCNTs product. TG was firstly standardized by studying the effects of three main instrumental parameters (temperature ramp, TR, initial mass of the sample, IM, and gas flow rate, FR) on the Tonset and full-width half maximum (FWHM) obtained from TG and derivative TG graphs of carbon black, respectively. Therefore, a two-level factorial statistical design was performed. The statistical analysis showed that the effect of TR, IM, and to a lower extent, FR, is significant on FWHM and insignificant on Tonset.;A methodology was then developed based upon the SWCNTs synthesis using the ITP system, through an in situ chemistry approach. Ammonia (NH3) was selected and counter-currently injected into the ITP reactor at three different flow rates and by four different nozzle designs. Numerical simulation indicated a better mixing of NH3 in the ITP reactor when a certain nozzle was used. The experimental results showed the increase of D-band intensity in the Raman spectra of SWCNT samples upon the NH3 injection. NH3 could increase the nitrogen content of the SWCNTs final product up to 10 times. The SWCNTs sample treated with 15 vol% NH3 showed an enhanced dispersibility in Dimethylformamide and Isopropanol. Onion-like and planar carbon nanostructures were also observed.;This work is focused on the investigation of the synthesis of chemically modified SWCNTs material through an in situ approach. The main objectives of the presented research are: 1) to explore the in situ chemical process during the synthesis of SWCNT and 2) to closely examine the effect of a reactive environment on SWCNTs.;Complementary characterization on the SWCNT samples treated by 15 vol% NH3 indicated the surface modification of nanotubes. Metallic tubes showed a higher reactivity with NH3 than semiconducting ones. The model including the reactor thermo-flow field and NH3 thermal decomposition kinetics suggested a two-step SWCNT surface modification in which nanotubes firstly react with H and NH2 intermediates and later, NH3 chemisorbs on the nanotubes. The model also suggested that the intermediate species, like NNH and N2H2, play a role primarily in driving the NH3 decomposition rather than the chemical modification of SWCNTs.;Keywords: Single-walled carbon nanotube, Induction thermal plasma, Thermogravimetry, Kinetic, Computational fluid dynamic, Thermodynamic, modification, Functionalization.
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机译：原始的单壁碳纳米管（SWCNT）分散性差，在许多溶剂中均不溶，在将其用于多种应用之前需要进行化学修饰;催化剂类型和含量对SWCNTs最终产品的影响，通过感应热等离子体合成（ITP）被研究以替代原料中的有毒钴（Co）。在这方面，使用了三种不同的催化剂混合物（即，Ni-Y 2 O 3，Ni-Co-Y 2 O 3和Ni-Mo-Y 2 O 3）。实验结果表明，催化剂类型影响SWCNT最终产品的质量。当相同量的Co被Ni替代时，可以生产出质量相似的SWCNT。此外，通过热力学计算结果进一步解释了该实验工作中观察到的结果。整个工作中均使用热重法（TG）表征SWCNTs产品。 TG首先通过研究三个主要仪器参数（温度斜率，TR，样品的初始质量，IM和气体流速，FR）对Tonset和从TG获得的全宽半峰（FWHM）的影响进行标准化。碳黑的衍生TG图。因此，进行了两级因子统计设计。统计分析表明，TR，IM和较低的FR对FWHM有显着影响，而对Tonset则无影响。;然后基于ICNT系统的SWCNTs合成，通过原位化学开发了一种方法方法。选择氨气（NH3），并以三种不同的流速和四种不同的喷嘴设计将其逆流注入ITP反应器。数值模拟表明，使用一定的喷嘴时，ITP反应器中的NH3混合效果更好。实验结果表明，注入NH 3后，SWCNT样品的拉曼光谱中D带强度增加。 NH3可使SWCNTs最终产品的氮含量增加多达10倍。用15％（体积）NH3处理的SWCNTs在二甲基甲酰胺和异丙醇中的分散性增强。还观察到了洋葱状和平面状的碳纳米结构。这项工作的重点是通过原位合成化学改性的SWCNTs材料的研究。本研究的主要目的是：1）探索SWCNT合成过程中的原位化学过程； 2）仔细检查反应性环境对SWCNTs的影响。;对经15 vol％处理的SWCNT样品进行补充表征NH3表示纳米管的表面改性。金属管对NH3的反应性比半导体管高。包含反应器热流场和NH3热分解动力学的模型提出了两步SWCNT表面改性，其中纳米管首先与H和NH2中间体反应，然后NH3在纳米管上化学吸附。该模型还表明，中间物种（如NNH和N2H2）主要在驱动NH3分解而不是对SWCNT的化学修饰中发挥作用。关键词：单壁碳纳米管；感应热等离子体；热重分析；动力学；计算流体动态，热力学，修改，功能化。
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