Top-down synthesis of graphene: New Methods

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To supply all the potential applications of graphene, highly efficient and cost-effective industrial-scale processes must be established to produce superior quality graphene. Various graphene production technologies and methods have been reported, including exfoliation, chemical oxidation–reduction, arc-discharge, CVD, epitaxial growth, thermal pyrolysis, direct organic synthesis, and laser-assisted production. These methods have potential roadblocks to upscaling and commercialization, including their high cost, process complexity, and low yields. Initially, researchers had only one goal: to produce graphene at any price. This practice resulted in very expensive graphene with unpredictable properties; the production methods were not scalable, and some were not environmentally friendly. Therefore, to achieve universal adoption of graphene, research on graphene production methods that can address present obstacles, including cost, scalability, and environmental concerns, is ongoing. In addition to finding ways to reduce the cost of graphene production, the graphene-based industry will be driven by the development of cutting-edge applications of graphene, in which the performance and functions of graphene must be exceptional. It is thus expected that high-value applications of graphene still need to be developed. The slow penetration of graphene products into global markets could be due to its comparatively high cost and unreproducible functions relative to existing material technologies. In the chemical industry, various lower-grade graphene products are sold in the open market, which often contain high levels of metal and oxygen contamination, lower graphene content, and a high percentage of thick graphene particles (multiple layers). Considerable misinformation and misunderstanding in the graphene market result in unreliable graphene availability and irrational pricing schemes. The classification of graphene according to a standardized universal protocol is necessary because it will allow the quantitative comparison of samples produced by different laboratories and manufacturers as well as help accelerate the adoption of graphene in real-world applications. The ISO 2017 graphene standards describe graphene based on the number of layers, which is not appropriate for the present graphene market, and further advanced standardization is required. For example, various properties of SLG, such as sheet resistance and electrical and thermal conductivity, vary between SLG produced by different suppliers and perform differently in a particular application. Thus, the advanced standardization of graphene and its derivatives must be developed and should include the magnitude of the properties. Furthermore, the progress of full-scale graphene commercialization will depend on the development of low-cost production methods, transparent communication between the producers and buyers, and standardization of graphene products. However, it must be recognized that the development of commercial products based on graphene is still in its infancy stage. Perhaps the main reason for this slow uptake can be found in the price vs. benefit ratio, which may be acceptable for advanced applications but remains unfavorable for bulk lower-cost applications. In addition, it is crucial to consider that each application will require a different grade (type) of graphene and at a different price. Each of the material characteristics controls how the graphene material will perform in a specific application. Thus, the well-suited application of available graphene materials is driven by the quality of graphene and the selected graphene production method. Consequently, the future of application development will primarily depend on whether manufacturers are able to supply material that will meet this demand. While there are currently over 3000 entities worldwide that produce graphene, not all can meet the standards, and many produce poor quality material. Thus, continued research and development in this nascent field should remain focused on the development of an affordable graphene production method, and the full-scale commercialization of graphene and graphene-enabled products. Finally, we hope that this comprehensive review will be helpful and valuable in determining the scalability of existing top-down methods based on their respective advantages and disadvantages and in discovering new ways to produce graphene and related materials on a large scale.

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