1. Introduction

Traditionally, graphene has been synthesized using the mechanical exfoliation method, which involves peeling graphite layers one by one to obtain a single-layer graphene. However, this method is not suitable for large-scale production due to its low efficiency and high cost. With the increasing demand for graphene in various applications, it has become crucial to develop effective methods for the mass production of large-scale, high-quality graphene.

To address the need for large-scale, high-quality graphene production, researchers have explored various methods. However, there are also limitations associated with the current large-scale graphene production methods. One major problem is the scalability of the production process. Achieving uniform growth of large-area graphene films while maintaining high quality remains a significant challenge. Furthermore, the transfer process needs to be optimized to minimize defects and ensure the overall integrity of the graphene film. Additionally, the cost-effectiveness of large-scale graphene production needs to be improved to meet the industrial demand [1].

This article provides a review of the currently widely used methods for large-scale production of graphene. These methods include chemical vapor precipitation, epitaxial crystal growth, graphene oxide reduction and solvent exfoliation. The article also highlights the advantages and disadvantages of each method in terms of their suitability for meeting the demands of the current market. According to this review, understanding the comparative advantages and disadvantages of different production methods can drive further research and development in the field. It identifies areas where current methods may be lacking and points to potential avenues for improvement. This can lead to the development of more efficient and cost-effective methods for large-scale production of graphene.

2. Overview of large-scale, high-quality Graphene Production Methods

Graphene, a two-dimensional allotrope of carbon, has attracted significant attention due to its exceptional properties and wide-ranging applications in various fields. It possesses excellent electrical conductivity, high thermal conductivity, and exceptional mechanical strength, making it a promising material for electronics, energy storage, sensors, and biomedical applications [2-4]. The production of graphene on a large scale with high quality is crucial to meet the increasing demand and enable its widespread utilization. Here are four current mainstream methods of large-scale, high-quality graphene production.

2.1. Chemical vapor deposition (CVD)

Chemical vapor precipitation is a method of preparing materials by introducing one or more gaseous elements into a reactor to produce the desired material by undergoing a chemical reaction under certain conditions [5]. This method is widely used in the preparation of ceramics, alloys and other materials. In this method, a hydrocarbon gas, such as methane, is introduced into a high-temperature furnace, where it decomposes and forms carbon atoms that condense onto a substrate, such as copper foil [6]. During chemical vapor precipitation experiments, it is necessary to control the type, concentration, temperature, pressure and other parameters of gaseous elements to ensure that the resulting material has the required structure and properties. The key to this method lies in the control of reaction conditions and the monitoring of the reaction process [7, 8].

The CVD method allows for the synthesis of large-area graphene films with high crystallinity and controllable thickness. Additionally, it offers the advantage of scalability, making it suitable for industrial-scale production. However, CVD allows for the control of the thickness and quality of the graphene film, but it requires a metal catalyst, which may affect the electronic properties of the graphene [9]. Additionally, CVD requires high temperatures and is not suitable for some substrates.

2.2. Epitaxial crystal growth method

The epitaxial crystal growth method refers to the growth of single crystal materials with the same or similar structure as the substrate crystal through certain technical means, such as molecular beam epitaxy, chemical vapor deposition, etc., on a single crystal substrate. Epitaxial crystal growth method is to control the chemical vapor deposition process on the existing crystal surface, so that the new crystal layer grows according to the structure and orientation of the original crystal. This method can control the number of layers, size and crystal orientation of graphene, resulting in high-quality graphene. This method has a wide range of applications in semiconductor devices, lasers, and other fields.

The experimental process of epitaxial crystal growth method is highly demanding, and it needs to be carried out under high vacuum or certain atmosphere conditions. In the process of epitaxial growth, it is necessary to control parameters such as temperature, crystal orientation, and growth rate to ensure that high-quality single crystal materials are obtained.

Epitaxial crystal growth has significant advantages in fabricating high-performance graphene electronic and optoelectronic devices. For example, graphene field-effect transistors fabricated using this method have high mobility and low noise characteristics. In addition, by combining with other materials, a variety of new graphene optoelectronic devices can be prepared.

Although the epitaxial crystal growth method has made some progress in the preparation of graphene, it still faces many challenges, such as increasing the growth rate, reducing the cost, and achieving uniform growth over a large area. In the future, with the advancement of technology and the development of new materials, the epitaxial crystal growth method for preparing graphene will have more applications and breakthroughs.

2.3. Graphene oxide reduction

Graphene oxide (GO) reduction method is a method to prepare graphene through a two-step reaction of oxidation and reduction, by reducing graphene oxide into graphene, to obtain materials with excellent properties. The experimental process of graphene oxide reduction method is relatively simple. It mainly includes two steps: preparation and reduction of graphene oxide. The preparation of graphene oxide can be obtained by a variety of methods, and the reduction process usually uses chemical or thermal reduction. Care needs to be taken to control the degree of oxidation and reduction in the experiment to ensure that the purity and quality of graphene are obtained.

Firstly, graphite is oxidized to graphite oxide in the presence of strong acid and strong oxidant, and then exfoliated to form graphene oxide by ultrasound. Next, graphene oxide is reduced to graphene by a reduction reaction. This process mainly includes the following steps:

Oxidation: Graphite is mixed with a strong acid (such as concentrated sulfuric acid) and a strong oxidizing agent (such as sodium nitrate) to form graphite oxide after an oxidation reaction.

Ultrasonic exfoliation: the obtained graphite oxide is dispersed in water and exfoliated into a single layer of graphene oxide by ultrasonic treatment.

Reduction: graphene oxide is reduced to graphene by using appropriate reducing agents (such as hydrogen, hydrazine hydrate, etc.) [10].

Compared with other methods for the preparation of graphene, such as chemical vapor deposition and epitaxial crystal growth method, graphene oxide reduction has the advantages of simple operation and low cost. However, graphene produced by this method usually has a high defect density and, in some applications, may perform slightly worse than graphene produced by other methods.

Graphene prepared by graphene oxide reduction has been widely used in energy storage, sensors, electrode materials and other fields because of its good electrical conductivity and mechanical properties. However, its large-scale application still faces some technical challenges, such as improving the yield, purity and electrical properties of graphene. In addition, finding environmentally friendly and efficient reducing agents is also a major challenge.

With the deepening of the research, the technology of preparing graphene by graphene oxide reduction will continue to improve. In the future, by improving the preparation process, optimizing the reaction conditions and developing new reducing agents, it is expected to further improve the performance of graphene and reduce its preparation cost. In addition, the combination with other preparation methods will also provide new possibilities for large-scale preparation of high-quality graphene.

2.4. Solvent stripping method

Solvent stripping method is a method to reduce graphene oxide (GO) from its original oxidation state to graphene by selecting suitable solvent. In the stripping process, the interaction force between solvent molecules and GO lamellae must be greater than the van der Waals force between GO lamellae in order to achieve effective peeling. Common solvents include water, ethanol, acetone and so on. Temperature and time are two key factors that affect the peeling effect. With the increase of temperature, the stripping effect of solvent is enhanced, but too high temperature may lead to the decrease of graphene quality. The length of time will also affect the peeling effect, usually need to maintain a certain amount of stirring intensity in a certain period of time to ensure the peeling effect.

(1) preparation phase: prepare an appropriate amount of graphene oxide solution, which can be prepared by Hummer’s method [11].

(2) Solvent selection: select the appropriate solvent, such as water, ethanol, acetone, etc.

(3) Stirring and reduction: add the solvent to graphene oxide solution and stir at a certain temperature for a certain time to reduce graphene oxide to graphene.

(4) Centrifugation and washing: centrifuge the mixture to remove large particles of impurities, and then wash with water or ethanol to remove excess salt and unpeeled graphene oxide.

(5) Drying: the washed graphene is dried in a drying box to obtain graphene products.

The advantages of solvent exfoliation are as follows: Firstly, high quality graphene can be prepared on a large scale. Secondly, the choice of solvent and preparation conditions can be adjusted, and graphene with different morphologies and sizes can be obtained. Thirdly, the exfoliated graphene sheet layer is thin, which is conducive to its excellent performance. However, this method also has some problems. For example, it needs to use a large number of organic solvents, which may cause pollution to the environment. Secondly, in the preparation process, it is necessary to go through steps such as centrifugal separation and drying, which is complicated and costly. Thirdly, it is still impossible to achieve the directional growth of graphene and control the crystalline quality [12].

3. Similarities and differences analysis of Existing large-scale, high-quality Production Method

Another purpose of this paper is to compare and analyze the four methods of chemical vapor precipitation, epitaxial crystal growth, graphene oxide reduction and solvent exfoliation, and clarify their similarities and differences in experimental operation, influencing factors, application fields, etc., in order to provide reference for the selection of methods in practical application.

3.1. Experimental conditions:

Chemical vapor precipitation method and epitaxial crystal growth method need to be carried out under certain atmosphere and temperature conditions, graphene oxide reduction method has relatively low requirements, and solvent stripping method is usually carried out at room temperature and pressure.

3.2. Influencing factors

The results of chemical vapor precipitation method are affected by the type, concentration, temperature and pressure of gaseous elements, the epitaxial crystal growth method is affected by temperature, crystal orientation, growth rate and other factors, the graphene oxide reduction method is affected by the degree of oxidation and reduction conditions, and the solvent stripping method is affected by the solvent type and polymer solubility.

3.3. Material quality

The quality of the material prepared by the epitaxial crystal growth method is high, the quality of the material prepared by the chemical vapor precipitation method depends on the reaction conditions, the quality of the graphene prepared by the graphene oxide reduction method depends on the oxidation and reduction conditions, and the quality of the graphene prepared by the solvent stripping method is related to the difference in polymer solubility and compatibility.

3.4. Applications

The materials prepared by chemical vapor precipitation method are widely used in ceramics, alloys and other fields, the epitaxial crystal growth method is widely used in semiconductor devices, lasers and other fields, the graphene prepared by graphene oxide reduction method is widely used in electronic devices, energy storage and other fields, and the graphene prepared by solvent stripping method are widely used in flexible electronics, energy storage and sensors are broad.

3.5. Evaluation of advantages and disadvantages

The advantages of chemical vapor precipitation method and epitaxial crystal growth method are that high-quality materials can be prepared, but the experimental conditions are harsher, and the advantages of graphene oxide reduction method and solvent exfoliation method are advantages. The preparation process is relatively simple, but the quality of the material needs to be improved. Compared with other methods of graphene preparation, solvent stripping method has the advantages of simple operation and low cost. Compared with chemical vapor deposition and epitaxial growth, solvent stripping method does not need high vacuum or high temperature environment, and the equipment cost is lower. However, the performance of graphene prepared by solvent stripping method is relatively low, so it is not suitable for the application field with high performance requirements. In terms of application, the appropriate method should be selected according to the nature of the required material and the application scenario.

4. Development trends and challenges

With the continuous advancement of science and technology, the requirements for material properties are getting higher and higher, which provides the impetus for the improvement of the above methods. In the future, new gas sources and more advanced reactor designs may further improve the efficiency and material quality of chemical vapor precipitation. Epitaxial growth techniques may combine new materials and technologies for wider applications. For the graphene oxide reduction method, improving the purity and continuity of graphene will be the main development direction. The solvent stripping method may explore more kinds of solvents and polymer materials to obtain more kinds of nanofibers.

5. Conclusion

In conclusion, the four methods of chemical vapor precipitation, epitaxial crystal growth, graphene oxide reduction and solvent stripping have their own advantages and disadvantages, and their application fields are also different. In practical applications, the appropriate method should be selected according to the nature of the required material and the application scenario. In the future, the development of technology will pay more attention to the performance and application of materials, and we should flexibly use these methods in specific applications to improve the level of results. For example, for applications that require high-quality single-crystal materials, such as semiconductor devices and lasers, epitaxial crystal growth may be the best choice. For large-scale preparation of ceramic or alloy materials, chemical vapor precipitation may be more suitable. In terms of the preparation of graphene, the graphene oxide reduction method may be an ideal method for large-scale preparation of graphene due to its simple operation and low cost [13].

However, how to improve the purity and continuity of graphene is still an important problem that needs to be solved. For the preparation of high-performance fibrous materials, the solvent stripping method provides an easy method. However, how to control the solubility of polymers in solvents and how to quickly and uniformly precipitate polymers are still problems that need further research.

In this paper, four methods, namely chemical vapor precipitation, epitaxial crystal growth, graphene oxide reduction and solvent stripping, were compared and analyzed. There are significant differences in experimental conditions, influencing factors, material quality, etc., each with its own advantages and disadvantages and application fields. In practical applications, the appropriate method should be selected according to the nature of the required material and the application scenario. In the future, the development of technology will pay more attention to the performance and application of materials, so further improving these methods to improve the quality and application range of materials will be an important research direction in the future.

Overall, this study provides valuable insights into the production of large-scale, high-quality graphene and serves as a reference for future research and development in this field. By addressing the existing problems and challenges, as well as exploring new production methods, the industrial-scale production of high-quality graphene can be achieved, fulfilling the increasing demand for this versatile material.