Preparation of the hottest single wall carbon nano

Preparation of single-walled carbon nanotubes

the discovery of single-walled carbon nanotubes (hereinafter abbreviated as SWCNTs) has opened up a new field full of vitality for the research of Nano Electronics, nano chemistry and nano materials. Recently, the preparation of multi walled carbon nanotubes with neat arrangement, uniform structure, orderly and controllable structure has made a major breakthrough, while the research of carbon nanotubes seems to lag behind, and there are three main obstacles:

first, the preparation technology of SWCNTs. At present, the structure of SWCNTs is more dispersed, the preparation cost is high, and the yield and purity are low

second, chemical modification of SWCNTs. Generally, chemical modification is carried out in water and organic solvents, but SWCNTs is insoluble in water and organic solvents, so it is difficult to carry out chemical modification, which directly affects the study of SWCNTs at the molecular level

third, detection methods and characterization methods. Although scientists have used Raman spectroscopy, electron microscopy, scanning tunneling microscopy (STM), atomic force microscopy (AFM) and other technologies to conduct in-depth research on SWCNTs, effective and simple research methods need to be further explored and developed

I. preparation of single-walled carbon nanotubes

swcnts preparation requires many manufacturers to achieve the main goals when purchasing tensile testing machines: ① continuous mass production; ② The structure is evenly distributed and controllable; ③ Low cost, suitable for commercial production; ④ High purity, easy to disperse. In order to achieve this goal, several key factors of SWCNTs preparation must be optimized: ① carbon source; ② Catalyst and support; ③ Preparation conditions. How to optimize or find new conditions is the key to prepare high-quality and high-yield SWCNTs. The following are the explorations made by scientists in the past two years

(1) graphite arc discharge method. The research team of Iijima, a scientist from NEC, used carbon rods containing metal catalysts to obtain SWCNTs with a yield of more than 70% by arc discharge. They mainly discussed the effects of temperature and the type and composition of catalysts on SWCNTs. The results showed that using nickel (0.6%) - ytterbium (0.6%) as catalyst had the highest yield (>70%) at 600 ℃. Chinese scholar Cheng Huiming and others have recently made a breakthrough. They use carbon rods containing iron, cobalt, nickel and ferrous sulfide to prepare a large number of SWCNTs (2G/h) with uniform diameter (about 1.8 nm) by semi continuous hydrogen arc discharge method, which can store hydrogen at room temperature, attracting great international attention. The biggest defect of graphite arc discharge is that the purity of SWCNTs is not high, and it contains many amorphous carbon and metal particles, which are disordered and easy to knit

(2) chemical vapor deposition method (C can clear the value displayed by the number to zero VD). The research on the preparation of SWCNTs by chemical vapor deposition has been very active in the past two years. At present, scientists mainly want to obtain catalysts and supports with high density of active points, large surface area and pore volume. Stanford University scientist Hongjie Dai's team prepared a single SWCNT or SWCNTs beam with directional growth parallel to the plane of the substrate. The key to their preparation is to use sol-gel technology to synthesize a catalyst material containing iron and molybdenum, which can form a uniform film on silicon aluminum support and has good catalytic activity. Its metal and carrier space interaction force is strong, and the surface area and pore volume of silicon aluminum composites are large at high temperature. 10 grams of SWCNTs can be synthesized per gram of catalyst. The research team of Chinese scientists Xie Sishen used cobalt nickel alloy/zeolite as catalyst to obtain SWCNTs with rigidity, few defects and high graphite degree. Colomer et al. Synthesized SWCNTs with the smallest diameter (0.7 nm) so far. They focused on the influence of catalyst and support on the growth of single-walled carbon nanotubes (bundles). They found that cobalt and iron have higher catalytic activity than nickel, and alumina as support is better than silicon. Although high-yield, pure and controllable SWCNTs can be obtained by CVD method, the biggest obstacle to its application and commercial production is high cost, complex pretreatment process, harsh preparation conditions, and the temperature is usually as high as 900 ~ 1000 ℃. The treatment of catalyst and support is time-consuming and laborious

(3) laser evaporation method. Iijima et al. Recently made this discussion by using this method. They found that the shorter the laser pulse interval, the higher the yield of SWCNTs, and the structure of SWCNTs is not affected by the pulse interval. Kokai et al. Used CO2 laser evaporation to obtain SWCNTs at room temperature. For the first time, they used rapid imaging technology and emission spectroscopy to observe the morphology of evaporated smoke streams and carbon containing fragments in argon atmosphere. This diagnostic technology makes it possible to track and study the growth process of SWCNTs. The main defect of laser evaporation (ablation) method is the low purity and easy entanglement of SWCNTs

(4) solar energy method. It is of great significance to prepare SWCNTs using the sun as energy. French scientists have made many useful explorations, but this technology is still immature. SWCNTs has low yield, many impurities and uneven structure

Second, the application of single-walled carbon nanotubes

the integrity of structural molecules makes single-walled carbon nanotubes have unique electrical, mechanical properties and chemical stability. Scientists have made extensive research on the potential applications of SWCNTs, such as gas storage, quantum wires, electronic devices and catalyst carriers

(1) hydrogen storage material. As a kind of clean energy, hydrogen has been paid attention by countries all over the world. However, the high cost and difficult operation of storage and transportation methods restrict the development and utilization of hydrogen energy, so it is imperative to develop an excellent hydrogen storage material. Chinese scholars' research on hydrogen storage materials has been in the forefront of the world. SWCNTs synthesized by Cheng Huiming and others can store hydrogen at room temperature after proper treatment. It is found that the weight of hydrogen stored in SWCNTs weighing about 500 mg at room temperature can reach 4.2%, and 78.3% of the stored hydrogen can be released at room temperature and pressure, and the remaining hydrogen can also be released after heating. This kind of SWCNTs can be reused. This achievement opens up a broad prospect for the research of hydrogen storage materials

(2) nano electronic devices lap steel precision and other parts. Scientists recently observed the atomic structure of SWCNTs with high-resolution scanning tunneling microscope and found that the structure is closely related to the electrical conductivity. Therefore, how to prepare SWCNTs with corresponding structures according to the needs of practical applications is the biggest challenge for researchers. To put the application of SWCNTs into practice, there are still many technical problems that must be solved, such as the controllable preparation of dispersed (rather than tube bundle) SWCNTs, the uniform structure, and the control of the growth point and growth direction on a part of the substrate when the rebound force of SWCNTs is absorbed by the workpiece. Kasumov et al. Found the superconducting current of SWCNTs. The author used a special technology to grow a single wall tube (beam) between the slits of two superconducting metal gaskets. When the temperature was lower than 1K, superconductivity appeared. They also discussed the effect of magnetic field strength on critical transition (TC). This phenomenon is similar to C60 (TC