Controllable Preparation of Single-walled Carbon Nanotubes Based on Different Magnesium Oxide Supports
|Keywords||single-walled carbon nanotubes MgO support diameter sepatation|
As a perfect one dimensional nano-material, single-walled carbon nanotubes (SWNTs)have great potential applications in many fields with unique structural characteristics,excellent physical and chemical properties, including nano electronics, composite materials,hydrogen storage materials, biological, medical and military fields, etc. Since Iijima’slandmark studies, the preparation, characterization, purification and separation of SWNTshave been paid widespread attention in the scientific community. Now, the commonpreparation methods of SWNTs are arc discharge, laser evaporation, and chemical vapordeposition (CVD). Because of low cost, high efficiency, continuous preparation and someother characteristics, CVD is acknowledged as the most promising method for the large-scaleproduction of SWNTs. But the SWNTs sample prepared by conventional CVD is a mixture ofdifferent chiral (metallic and semiconducting) SWNTs, which greatly limits its further studyand application in some areas such as electrical, optical and so on. So, separation of metallicand semiconducting SWNTs (M/S) is an inevitable choice. Gel chromatography has theadvantages of simple operation, good effect of separation, low cost and continuous separationin the separation of M/S, is increasingly focus on by researchers. No doubt, the quality andpurity of SWNTs have a great effect on the separation’s results, moreover, gelchromatography also requires SWNTs with fine diameter (~1nm). So, preparation of highquality, high purity, fine diameter SWTNs by CVD method is an important job for realizingthe large-scale preparation of single conductive property SWNTs.Studies have shown that many factors might influence the growth of SWNTs in reseach,such as carbon source, support, reaction temperature and so on. We could realize thecontrollable preparation of SWNTs by tuning various reaction conditions and parameters. Theselection of support is very important, which has a close relationship with the realization oflarge scale production of SWNTs. Supports with large capacity for catalyst, good thermalstability, stable structure, easy purification processing, low cost supports are what people hope.With the deepening of the study, people are beginning to realize the obvious advantages ofMgO support, including efficient and stable growth of SWNTs, scalable synthesis of SWNTsat low cost, and easy removal of the support in mild acid, causing little harm to the products.Under this background, the article mainly has carried on the following work:1. With CH4as a carbon source, Ar as a shielding gas, MgO as a catalyst support, preparedSWNTs by CVD method. After optimization of reaction conditions, such as temperature,heating rate and catalyst, SWNTs with high purity and thin diameter were synthesizedfinally.2. Four different MgO powder were used as the support of catalyst for preparing SWNTs respectively, and the influence brought by different MgO in reseach was explored. Theresults indicated that four kinds of MgO have different microstructure, grain size, specificsurface area, average pore diameter size, which could affect the nucleation of the catalysts,then influence the growth of SWNTs. The MgO with porous structure, high specificsurface area and small pore size distribution is suitable as support for preparing finediameter’s SWNTs.3. Electrostatic spinning technique was used to prepare high specific surface area and porousstructure’s MgO nano-fiber, and next the MgO fiber was used as the support of catalystfor the preparation of SWNTs. The results indicated that fiber structure, metal catalysttype and the concentration of catalyst could influence the results. The MgO with smallerpore size distribution, after the adsorption of Co catalyst, is suitable for preparing finediameter’s SWNTs. In addition, by adjusting the concentration of the catalyst, we cancontrol adsorption quantity of catalysts on the fibers’ surface, that can control the diameterand yield of preparing SWNTs, and moderate concentration of catalyst is suitable forpreparing fine diameter’s SWNTs.4. Gel column chromatography separation technology was used for the separation of M/S.The influence brought by different ultrasonic time and the specifications of glucan in M/Sseparation was explored. The m-SWNTs and s-SWNTs separated were characterized byRaman spectrum and UV-Vis-NIR spectrum. At last, compared Self-regulation SWNTswith HiPco SWNTs, separation effect is summarized and evaluated.