A brief discussion on the bulk production of graphene

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Abstract: The mass production of graphene is of great significance for advancing the development of the graphene industry. This paper summarizes the current status, existing problems, and future development trends of the mass production of graphene, and offers an outlook on its prospects. Keywords: Graphene ； Macroscopic preparation ； Multiple varieties ； Automation Chinese Library Classification Number: TQ127 Document Code: A Graphene is a novel two-dimensional nanocarbon material with a thickness of just one layer of carbon atoms (0.34 nm); it consists of carbon atoms arranged in a hexagonal, honeycomb-like lattice formed by sp2 hybridized orbitals. Since its discovery, graphene has attracted widespread attention from the scientific community and the investment sector due to its excellent properties. The significant interest in graphene has also spurred the development of a range of graphene-related industries. In the entire graphene industry chain, the preparation of graphene is a prerequisite; only by obtaining graphene products with excellent properties can we further advance the industrialization of graphene. Therefore, the mass production of graphene is of great significance to the entire graphene industry. There are currently many methods for preparing graphene, but not all of them are suitable for the large-scale production of graphene. Below, the preparation methods of graphene will be compared. (1) Comparison of graphene preparation methods Various methods for preparing graphene have been developed to date, including the commonly used methods: mechanical exfoliation, chemical vapor deposition (CVD), chemical oxidation, and graphite intercalation ； And other preparation methods: epitaxial growth, carbon nanotube cutting, ion implantation, high-pressure high-temperature HPHT growth, explosion method, and organic synthesis methods, etc. The properties of graphene obtained through different preparation methods vary significantly, allowing it to be applied in various fields. Among the common methods for preparing graphene, mechanical exfoliation yields graphene with intact crystals, making it suitable for analyzing its intrinsic properties. However, this method produces only small quantities of graphene, so it is not appropriate for large-scale production of graphene ； The CVD method can produce graphene films with a large area and good uniformity, and the graphene samples obtained using this method are suitable for applications such as transparent conductive films ； Graphene prepared by chemical oxidation methods contains many defects, but it allows for the mass production of graphene; the samples obtained using this method are suitable for applications in energy storage, composite materials, water purification materials, and other fields. Since this method enables the production of the intermediate product graphene oxide, the oxygen-containing functional groups present on it offer more possibilities for modifying graphene-based materials, thereby expanding the applications of graphene ； The intercalation method for preparing graphene has simple steps and enables the production of graphene in large quantities; however, the resulting material has a high number of layers. It is suitable for applications that require high conductivity from graphene, but not for those that demand a specific layer structure. Currently, preparing large-area, single-crystal graphene remains a significant challenge. Although the CVD method and the redox method can be used to produce graphene in large quantities, CVD involves a complex transfer process for graphene at the later stages of production, and its cost is high; moreover, defects often occur in the growth and bonding of carbon within the substrate. During preparation using the redox method, single-layer graphene is extremely thin and prone to agglomeration, which reduces its electrical conductivity and specific surface area and further affects its application in optoelectronic devices. Additionally, the redox process can cause defects in the crystal structure of graphene, such as the loss of carbon atoms from the carbon rings. However, chemical oxidation remains an effective method for the large-scale production of graphene at low cost. (2) Individual differences in graphene: Strictly speaking, graphene refers to a two-dimensional carbon material with a thickness of a single layer of carbon atoms. However, due to the incomplete standard definition for graphene materials, it now represents an entire class of materials. The differences between materials mainly lie in their thickness and dimensions, all of which affect certain inherent properties of the materials; for example, the size of graphene has a significant impact on its properties. When graphene is reduced to a certain size (a few nm), it can be referred to as graphene quantum dots, which possess special properties in terms of fluorescence, magnetism, and so on. For applications involving transparent conductive films, the smaller the size of graphene, the higher the contact resistance during the assembly of the transparent conductive film; consequently, the overall resistance of the assembled transparent conductive film becomes greater. Therefore, size control of graphene is essential for its applications. If the thickness exceeds 10 layers, its properties are similar to those of graphite; therefore, it should no longer be referred to as a graphene material. Strictly speaking, when referring to graphene materials, it is necessary to indicate the number of layers, such as single-layer graphene, double-layer graphene, multi-layer graphene, etc. The individual variations in graphene require that, throughout the large-scale production process, attention be paid to the different structures of the graphene material, and various parameters such as the size and number of layers of the graphene products must be controlled, in order to produce a variety of graphene products that can meet the needs of different application areas. II. Bulk Production of Graphene 1. Current Status of Bulk Production of Graphene The graphene industry is given great importance; graphene materials and the graphene industry are mentioned several times in the Ministry of Industry and Information Technology’s recently released \"Guidelines for the Development of the New Materials Industry\" as well as the country’s \"13th Five-Year Plan for Scientific and Technological Innovation\". Various regions also provide substantial policy support for the graphene industry; multiple graphene industrial parks have been established in cities such as Qingdao, Wuxi, Changzhou, and Chongqing. Graphene preparation, as the primary stage in the entire graphene industry chain, receives even more attention from researchers. Many research institutions and companies are also carrying out intensive research on the large-scale production of graphene. It is reported that numerous research institutions and companies are currently conducting studies on the bulk production of graphene, and there have been several reports on the construction and operation of production lines for bulk graphene manufacturing. Relevant research institutions such as the Metal Research Institute, Shanxi Coal Chemistry Research Institute, Peking University, Tsinghua University, Zhejiang University, Nankai University, etc ； Enterprise entities such as: Beijing Shengmeng Technology, Ningbo Messi Technology, Changzhou Sixth Element, Beijing Carbon Century, etc. **Policy and corporate investment have greatly driven the industrialization of graphene. There are several methods used for the mass production of graphene. The main methods currently available for this purpose include chemical oxidation, graphite intercalation, and CVD. Methods used by the research team led by Academician Cheng Huiming at the Institute of Metals for the mass production of graphene include the CVD method and the graphite intercalation method ； Beijing Shengmeng Technology and Changzhou Sixth Element primarily use chemical oxidation and graphite intercalation methods for bulk production. Regarding the preparation scale, since the scale of graphene produced via the CVD method cannot be measured in terms of mass, we will use the chemical oxidation method and the graphite intercalation method as examples for illustration. Currently, graphene is mainly produced in kilogram quantities; however, some companies claim to have production lines capable of producing graphene in ton quantities, such as Changzhou Sixth Element, Beijing Shenglian Technology, and Beijing Carbon Century. Looking at the industrial distribution of large-scale graphene production, the development of graphene is currently concentrated in the eastern region, with provinces such as Jiangsu, Shandong, Zhejiang, and Beijing showing strong efforts in this field as well as substantial investment in research and development. 2. Current problems in the mass production process: Although significant breakthroughs and progress have been made in the mass production of graphene, there are still many issues that hinder further development of the graphene industry. Firstly, the industry for graphene production is of uneven quality. Many investors are eager to enter this industry and rush in without a proper understanding of graphene, which results in significant variations in the quality of the graphene products produced. Due to the incomplete standard-setting for graphene at present, some graphene products available on the market do not match the specifications indicated, and these issues affect the widespread adoption of graphene. Secondly, graphene products are relatively limited in variety. Although the CVD method offers the possibility for large-scale production of thin films, the most commonly used methods at present are chemical oxidation and graphite intercalation. The limited variety of methods for producing graphene in bulk also results in a limited range of graphene products available on the market, which fails to meet the needs of various customers. Many manufacturers fail to recognize the impact that variations in the size and number of layers of graphene products have on their performance, and they are also unable to provide effective technical support. This leaves buyers confused when choosing graphene products, making it difficult for them to find suitable options, which ultimately leads to a decrease in customers’ trust in graphene products. All of these will affect the development of the graphene industry. Again, there are still some issues with the design of large-scale graphene production lines. Current large-scale production lines for graphene only ensure the availability of the product; they are not well-designed in terms of environmental impact, energy consumption, and time requirements, which results in high costs for graphene. At the same time, the current graphene production lines have a low level of automation; errors caused by manual operations can affect the quality of graphene products. All of these require further improvement. These problems existing in the large-scale preparation of graphene have hindered the development of the graphene industry; they need to be further addressed in future efforts to produce graphene on a large scale. III. Development directions for the mass production of graphene 1. Development trends of graphene In light of the problems existing in the field of mass production of graphene at present, we believe that there are several development directions for the mass production of graphene. (1) The improvement in the quality of graphene products and the diversified development of graphene-based materials have led to enhanced quality control over these products, thereby improving their quality. At the same time, a range of graphene materials has been developed to meet the needs of various customers, by controlling parameters such as the size and thickness of graphene as well as the degree of modification. Develop graphene-derived materials (graphene quantum dots, 3D graphene, graphene rolls, etc.) to expand the application fields of graphene. (2) Developing new green macro-scale preparation methods for graphene to address issues such as wastewater generation in current graphene production processes. The diverse development of large-scale production methods for graphene can meet the application requirements of graphene in various fields, and it will play a positive role in advancing the exploration of new applications for graphene. (3) Improve and optimize the graphene production line: enhance the functions of this line and increase its level of automation. It ensures that a single production line can be used to manufacture different graphene products. At the same time, while ensuring the quality of graphene products, adjustments to the equipment are made to reduce energy consumption and shorten the production cycle during graphene manufacturing, thereby further lowering the production costs of graphene. It offers the possibility for graphene to be used on a large scale. 2. Development prospects: The mass production of graphene is an important part of the graphene industry chain, and it is also the first issue that needs to be resolved for the development of the entire graphene industry. Only by being able to produce large quantities of different graphene materials with excellent properties and reducing the cost of graphene can we ensure the feasibility of its applications. Although significant progress has been made in the bulk production of graphene, there are still many limitations, and researchers worldwide need to work together to address a range of issues. It is believed that in the near future, significant breakthroughs will be achieved in the industrial-scale production of graphene, enabling the development of industries that utilize this material.