Analysis of graphene prepared from anthracite
Graphene is known as the king of known materials. The thickness of single-layer graphene is only one carbon atom, about 0.335nm, which is the thinnest material known at present and has many of the world's highest material properties (strongest electrical conductivity, hardest material, ultra-high-strength, ultra-high thermal conductivity, ultra-high light transmittance). Therefore, graphene materials are expected to bring revolutionary applications in energy storage, electronic components, composite materials, and other fields.
Graphene, as a new carbon material, has many advantages, but its relatively high cost seriously hinders the development of downstream products. Therefore, the research and application of graphene require urgent reform of its raw materials and preparation methods. At present, graphite is the most important material for the preparation of graphene. Its price is as high as 5000-8000 yuan/ton. And as it is regarded as a strategic mineral resource, the price is still rising, which is unfavorable to the reduction of the cost of graphene. Coal resources in China are abundant and cheap and contain basic structural units such as condensed aromatic rings and minerals as catalysts. These characteristics determine that coal-based materials can be used as carbon source materials for the preparation of graphene. The use of coal or coke to prepare fullerenes and carbon nanotubes has been widely reported. However, there are not many public reports and literature about the preparation of graphene from coal-based materials.
Domestic and foreign progress of coal-based ink
In 2013, James Tour et al. prepared graphene quantum dots from anthracite, bituminous coal, and coke by strong acid oxidation for the first time and studied in depth the relationship between the preparation process and fluorescence properties. Sabyasachi Sarkar has improved its process to directly extract about 100 nm of go from coal as a carrier for drug transport of TPP, PBS, and other pharmaceutical macromolecules. In 2016, Cyril Aymonier prepared to go quantum dots with fluorescence properties and graphene nanoribbons with aspect ratio using supercritical fluids.
In 2013, Gerardine Botte et al. prepared a 1cm× 1cm graphene transparent film using sub-bituminous coal as raw material and copper foil as a catalyst by CVD method at 1050℃, with a light transmittance of 95%, but with a thick thickness of about 5 nm. They then improved the process to reduce the CVD growth temperature to 400℃ and also produced a large transparent film (96% transmittance, 5 nm thickness).
In 2014, Qiu Jieshan et al. prepared three-dimensional hollow porous graphene spheres with a specific surface area of up to 1800 m2/g and specific capacitance of up to 244 F/g (20 A/g current density) using coal pitch as raw material and nano magnesium oxide as a template by high-temperature activation with potassium hydroxide. In addition, Lin Qiang et al. also prepared graphene nanosheets using coal pitch as raw material and aluminum powder and nano alumina as catalysts, respectively.
In 2012, Qiu Jinshan et al. first prepared graphene powder from taxi anthracite in Ningxia by reoxidation reduction method, with a specific surface area of 306m2/g.Rosa Menendez et al. prepared graphene powder with a specific surface area of only 75 m2/g from coke by REDOX method and investigated the relationship between the grain size of coke and the yield and flake diameter of go intermediates.
In 2016, Chen Chengmeng et al. from Shanxi Coal Chemical Institute, Chinese Academy of Sciences successfully prepared high-quality graphene powder from Taixi anthracite and Shanxi anthracite, respectively, and completed laboratory test preparation with a specific surface area of 560 m2/g.
In 2017, Yating Zhang and others from Xi ' a University of Science and Technology unveiled a preparation method for coal-based graphene quantum dots. The natural coal is processed into an ultrasonic cell crusher, ultrasonic 2h at room temperature and atmospheric pressure, and then using 0.22μm polytetrafluoroethylene filter membrane filtration, and then by dialysis to remove N, N dimethylformamide, water-soluble coal bedrock ink quantum dots. Graphene quantum dots are mainly used in the field of fluorescence imaging. Still, they cannot be applied to energy storage, thermal management, and other fields that require high conductivity, thermal conductivity, and size.
The most recent paper on coal-based graphene was published in Carbon in July 2019 by the University of Missouri-Columbia: Coal is upgraded to a multifunctional graphene-based material by laser scribing, which is a graphene material synthesized from coal by direct CO2 in the next step under environmental conditions. What kind of coal is used to prepare graphene and the preparation process are not mentioned in the article.
Preparation of graphene from anthracite
The process adopted by Shanxi Coal Chemical Institute of the Chinese Academy of Sciences is 1) raw material pretreatment. The raw coal is crushed into 80-500 mesh coal powder, and then according to the coal powder: catalyst weight ratio of 1:0.0.1-0.1, the coal powder and catalyst are evenly mixed by ball milling to get the mixture;(2) graphitization. The mixture was kept at 2000-3000℃ for 1-24h to make it graphitized. (3) Oxidation-reduction stir 1 weight part of graphitized material and 40-120 weight parts of concentrated sulfuric acid evenly at -5 to 5℃, then add 3-5 weight parts of potassium permanganate, react 30-90min at 30-50℃, and then add 40-100 weight parts of deionized water, continue to react 15-30min at 90-100℃. Then 5-10 parts by weight of hydrogen peroxide are added, stirred evenly, purified by water washing, and dried to get graphite oxide powder, and treated at 400-1200℃ to get coal cornerstone ink.
Zhang Yang, Qiu Jinshan et al. from Xi 'a University of Science and Technology prepared graphene using Jincheng anthracite and Taixi anthracite as raw materials. The specific methods were as follows:
1. The raw coal was broken.
2. Acid leaching and deashing of pulverized coal samples.
3. The coal samples were graphitized at 2500℃.
4. Graphene was obtained by the REDOX method.
It can be seen from the above two processes that the preparation of graphene from anthracite must be made of high-purity graphite at high temperature and high pressure, and then graphene is prepared from graphite.
Advantages and disadvantages of graphene prepared from anthracite and existing problems
The advantages of preparing graphene from anthracite are as follows: 1) It can improve the vibration density of graphene products;2) The graphene prepared has a kneading structure.
Disadvantages: the need for high-temperature catalytic graphitization of raw coal, that is, compared with off-the-shelf graphite as raw material, the process route is longer and the total cost is higher.
The problem: The technology is still in the laboratory. The main reason is that the technical bottleneck of graphene's downstream application has not been opened, and graphene prepared with graphite as raw material is enough to meet the market.
Conclusion
Therefore, graphene can be prepared by using anthracite as raw material. Still, graphene can be prepared only by catalytic graphitization of coal samples at high temperatures and then removal of impurities in coal. Although my country is rich in coal resources, the price is low, but compared with graphite as raw material for the preparation of graphene, the process route and the study of anthracite coal preparation of graphene is not many, just limited to laboratory research at present, the main reason is that the graphene downstream application technology bottleneck has not open, with graphite as the raw material preparation of graphene is enough to meet the market. It is hoped that with the development of graphene research and technological progress, the downstream of graphene will be gradually expanded in the future, which can provide a driving force for the development of graphene technology prepared from anthracite.
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