Recently, the research group of Professor Du Pingwu from the School of Chemistry and materials of China University of Science and Technology, for the first time, used the template of "hat" sealed by the thick ring of the nanotubes to construct the curve fragments of the vertically cut nanotubes. This method of connecting two graphene units through three curved molecules can directly obtain the Nano cage structure, which provides a new idea for the construction of end-sealed serrated carbon nanotubes. The relevant research results are published in the latest issue of German Applied Chemistry.
Coincidentally. Almost at the same time, researchers from Los Alamos Laboratory, who is famous for developing the world's first atomic bomb, using Functionalized Carbon nanotubes to produce the first carbon nanotube material that can emit single photon using communication wavelength at room temperature. Why is the magic material carbon nanotubes so popular with scientists from various countries?
The spatial structure is like "hollow football"
In 1985, the C60 of "football" structure attracted the attention of the whole world once it was discovered. Hollowing the "football", keeping the pentagonal and hexagonal grid structure of the surface, then expanding the hexagonal grid along one direction, and endowing the plane grid with carbon-carbon atoms and covalent bonds, therefore, carbon nanotubes with hollow cylindrical structure are formed.
Carbon nanotubes are one-dimensional quantum materials with special structures. It is mainly composed of hexagonal carbon atoms to form several layers to dozens of layers of coaxial circular tube, with a fixed distance between the layers, about 0.34 nanometers, and the diameter is generally 2-20 nanometers.
"Carbon nanotubes can be associated with hair filaments, but in fact its diameter is only one in tens of thousands of that of hair filaments, that is, tens of thousands of carbon nanotubes are arranged side by side, which is equivalent to a hair filaments." Professor Du Pingwu told the reporter of Science and Technology Daily that as a typical one-dimensional nano-structure, single-walled and multi-walled carbon nanotubes formed by grid curling of single-layer carbon atoms and multi-layer carbon atoms, the diameter is usually 0.8-2 nanometers and 5-20 nanometers, and the diameter of the thinnest carbon nanotubes reported at present can be as small as 0.4 nanometers.
Du Pingwu told the reporter that carbon nanotubes can be regarded as the curling of graphene sheets, so according to the number of graphene sheets, they can be divided into single-walled carbon nanotubes and multi-walled carbon nanotubes. According to its structural characteristics, carbon nanotubes can be divided into armchair-shaped nanotubes and sawtooth-shaped nanotubes.
Preparation Method is a challenge
"The common preparation methods of carbon nanotubes mainly include arc discharge method, laser ablation method, chemical vapor deposition method, solid phase thermal method, Glow Discharge method, gas combustion method and polymerization synthesis method, etc." Du Pingwu told reporters that the arc discharge method is the main method to produce carbon nanotubes. In 1991, Japanese physicist Yoshida Yoshino was the first carbon nanotubes discovered from carbon fibers produced by arc discharge method. "This method is relatively simple, but it is difficult to obtain carbon nanotubes with higher purity, and the results are often multilayer carbon nanotubes, while in actual research, people often need single-layer carbon nanotubes."
"Later, researchers developed the chemical vapor deposition method, which overcame the defect of the arc discharge method to a certain extent. The carbon nanotubes obtained were of high purity, but the diameter was not neat, irregular shape." Du Pingwu said that the subsequent gradually developed solid-phase thermal solution and so on were all limited by the environment and conditions.
"The preparation process of carbon nanotubes is similar to the organic synthesis reaction, and its side effects are complex and diverse. It is difficult to ensure that the carbon nanotubes in the same furnace are armchair-shaped or sawtooth-shaped." Du Pingwu said, under the action of strong acid and ultrasonic wave, carbon nanotubes can be broken into several sections first, and then proliferate and extend under the action of certain nanometer scale catalyst particles, however, the carbon nanotubes obtained after extension have the same curl mode as the template.
"If carbon nanotubes are proliferated by a way similar to DNA amplification, then only a small number of armchair-shaped nanotubes or serrated nanotubes need to be found, which can be replicated in a short time, the number of carbon nanotubes of the same type that are millions times the number of templates was amplified." Du Pingwu said that this may become a new way to prepare high purity carbon nanotubes.
Performance and size beyond silicon-based materials
"Carbon nanotubes have a perfect one-dimensional tubular structure. Carbon atoms combine with carbon-carbon covalent bonds to form one of the strongest chemical bonds in nature. Therefore, axial direction has high strength and toughness. In addition, there is no hanging bond on the side of the tube wall enclosed by hexagonal plane honeycomb structure, so carbon nanotubes have stable chemical characteristics." Du Pingwu said that the excellent performance of carbon nanotubes is manifested in the aspects of electricity, thermodynamics and optics, etc., and it has the characteristics of conducting electricity and conducting heat beyond the tradition, etc.
In 2013, scientists at Stanford University prepared the world's smallest "computer" with parallel single-walled carbon nanotubes as its main components ". In the past two years, the performance and size of Carbon Nanotube electronic devices have been broken through again and again, surpassing and eventually replacing the current commercial silicon-based devices.
Carbon nanotubes can also be made into transparent conductive films as substitute materials for touch screens. And the raw materials are hydrocarbon gases such as methane, ethylene and acetylene, which are not restricted by rare mineral resources. Carbon nanotube touch screen has the characteristics of flexibility, anti-interference, waterproof, knocking and scratch resistance, etc. It can be made into curved surface and has been applied in wearable devices, intelligent furniture and other fields.
Carbon nanotubes also provide physicists with the thinnest capillary for studying capillary phenomenon, and provide chemists with the thinnest test tube for nano chemical reaction, scientists even developed a "nano scale" that can weigh a single atom ". "China is in a leading position in the basic research of carbon nanotube materials. The control methods and theories of structural homogeneity are continuously innovated, and the control indexes are also refreshed year by year." Du Pingwu said.
