7 septembre 2023

[Graphene] – Large-scale synthesis of graphene and other 2D materials

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[Graphene] Codex International

Since its first demonstration in 2004, the large-scale commercial production of graphene has proven difficult and costly (‘large scale’ usually defined as weights more than 200 mg or films larger than 200 cm2). For instance, at an estimated cost of $50 000 to $200 000 per ton for graphene powders and $45 000 to $100 000 per m2 of graphene film, industrial production methods and costs are restraining graphene utility.
The quality of the graphene produced in the world today is rather poor and not optimally suited for most applications. This is possibly the main reason for the slow development of wider-scale commercial graphene applications, which usually require a customized solution in terms of graphene properties (read more on this issue in our previous Nanowerk Spotlight « Beware the fake graphene »).
A review paper in Advanced Materials (« Large-Scale Syntheses of 2D Materials: Flash Joule Heating and Other Methods ») summarizes the current industrial graphene synthetic and analytical methods, as well as recent academic advancements in larger-scale or sustainable synthesis of graphene.
The authors, led by Prof. James M. Tour from Rice University, place specific emphasis on recent research in the use of flash Joule heating as a rapid, efficient, and scalable method to produce graphene and other 2D nanomaterials. They present reactor design, synthetic strategies, safety considerations, feedstock selection, Raman spectroscopy, and future outlooks for flash Joule heating syntheses.
Concluding their review, they discuss the remaining challenges and opportunities in the larger-scale synthesis of graphene and a perspective on the broader use of flash Joule heating for larger-scale 2D materials synthesis.
As illustrated in the figure below, a multitude of demonstrated and hypothesized applications of graphene exist: composites, energy storage, lubricants, coatings, gas storage and separations, flexible electronics, displays, sensors, catalysts, and water filtration are among the most published upon.Graphene production can be broadly classified into two different methodologies: the top-down and bottom-up strategies. The name of each method acknowledges whether the carbon atoms had their hexagonal molecular arrangement before the synthesis began.
The bottom-up method (which is used almost exclusively for industrial larger-scale synthesis of graphene) employs for instance chemical vapor deposition (CVD), in which CH4, C2H4, or other simple hydrocarbons are catalytically decomposed to form graphene films on Ni, Cu, or other metal surfaces. Thus, the films are grown with individual carbon atoms from the bottom up to graphene sheets, adding one or a few atoms at a time to the graphene crystal.
Conversely, the top-down method uses the exfoliation of graphite to form graphene sheets. Here, the graphene sheets are already fully formed and are merely separated physically or chemically, from the top down to the individual or a few graphene layers.
Market research (Nature Nanotechnology, « The lab-to-fab journey of 2D materials ») suggests that there are currently more than 800 companies producing various graphene products including graphene-enhanced composite materials, and some 300 producing graphene powders.
Approximately 75% of the world’s graphite supply is controlled by China, and most worldwide graphene-based patents also reside in China (Resources, Conservation and Recycling, « Dynamic material flow analysis of natural graphite in China for 2001-2018 »). Total production of graphene and graphene nanoplatelets is currently estimated to reach 3800 ton per year, a minuscule amount when compared to other materials.
As the authors point out, significant progress in graphene production capability has been achieved over the past decade. However, the highly variable properties of commercially available graphene would likely benefit from stronger characterization standards and closer interaction between end-users and producers, to specifically tailor the material for the desired application.
The review dedicates comprehensive chapters to discuss current academic advancements in bulk top-down graphene production, larger-scale bottom-up graphene production, and sustainable larger-scale graphene production.

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