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wood into graphene via flash Joule synthesis
The flash treatment of wood, or any other biomass for that matter, is a very interesting process in regards to how it can be used in the production of graphene. The use of electrochemical synthesis to produce graphene from graphite was first explored by Andre Geim and Kostya Novoselov at the University of Manchester who were awarded the 2010 Nobel Prize in Physics for their discovery (Geim & Novoselov). They treated a small flake of graphite with adhesive tape and placed it onto an oxidized silicon wafer. The wafer had been prepared earlier by oxidation into silicon dioxide (SiO2) using nitrogen trifluoride plasma etching which created surface oxygen groups (-OH). The tape held down one side while current flowed through causing a carbon monoxide bubble which caused the edge to peel up. This left behind atomic layers only one atom thick making this leading example as purest material ever discovered on earth (Hausler 22–24). Although there are similar processes that involve chemical reactions like hydrothermal growth or pyrolysis there is no comparison between these techniques due to low quality monolayer formation via covalent bonds and poor electrical conductivity respectively. These methods will not be discussed here but will be later on.
The flash Joule treatment is a very unique method that was first developed by Y. Miyasaka and colleagues at the Tokyo University of Science (Miyasaka et al.). The process involves heating the material to around 1000 °C which causes an oxidation reaction converting lignin into carbon oxide as well as releasing water vapor. The heat makes the structure undergo a thermochemical phase change where it transforms from its natural structure into graphite-like form, thus allowing for open access to all of its surface area; this in turn allows for maximum exposure during the electrochemical synthesis procedure.
In the process of flash Joule treatment, there are several key factors that affect how well graphene is synthesized. Water vapor removed from biomass for example plays a significant role in this reaction during the thermochemical phase change as it eliminates any impurities within the structure while also serving to increase its surface area by three orders of magnitude (Sarkar et al.). It removes all traces of water molecules and organic molecules which would otherwise inhibit formation. The graphite-like structure created through flash Joule treatment allows for easy access to either side of the material due to no more crystals being present; after this stage oxygen plasma etching must be applied so that both sides can become exposed.
The exposure of both sides is crucial for a successful synthesis because the material must be prepared in such a way that any exposed carbon atoms will react with the Fe catalyst (Bohl et al.). This catalyst is applied to one side which then acts as bait by attracting graphene producing molecules towards it. These molecules are called carbocations and are formed through flash Joule treatment's thermochemical phase change.
Once the carbocations are within range, they will react with exposed hydroxyl groups on the material's surface which forms a C-O bond. This step is where flash Joule treatment's main contribution to producing graphene comes into play as it overcomes two of the biggest obstacles in previous techniques: low yield and poor electrical conductivity (Bohl et al.). The large amount of exposed carbon atoms created by flash Joule treatment makes this process much more feasible.
This new method of producing graphene has been tested and proven to be successful in various ways. It was found that the electrical conductivity was on average 300 times larger than any other technique and the yield of monolayer graphene was around 98 percent (Schmid et al.). These results show how effective flash Joule treatment is at synthesizing high quality, single layer graphene.