A group of Researchers at the University of Illinois at Urbana’s Department of Mechanical Science and Engineering have recently published their study in the Journal of Materials Chemistry which describes a new and sustainable approach to transfer graphene and recycle the copper substrate used in the production of graphene.
Sung Woo’s team utilized carbon dioxide for the process of electrochemical reduction of the interlayer between the substrate layer and the graphene formed by the chemical vapor deposition (CVD).1 Woo’s team of Researchers also utilized inexpensive food grade ethyl cellulose as a thin film handling layer for the transfer process instead of the polymeric thin films that are used in traditional processes1. This inexpensive and environmentally friendly method described here could be an answer for large scale production of graphene.
Since its isolation in 2004, the world’s first two-dimensional material (2D), graphene, continues to gain a tremendous amount of interest among Researchers and Industries around the world.2 This nanoscale allotrope of carbon, whose structure resembles a hexagonal honey comb lattice of carbon atoms, is extremely light, yet incredibly strong and transparent, while also acting as a great conductor2.
Due to these special properties, along with its impressive flexibility and durability, graphene can be used in a variety of applications including water purification technologies, electronics, wearable technology, energy storage devices and many more2.
Among the several ways to prepare graphene monolayers, the CVD process is by far the most popular one. The CVD process utilizes carrier gases to deposit gaseous reactants onto substrates, such as copper, in a reaction chamber set at ambient conditions to produce high quality, extremely thin films of graphene. Although this process facilitates in the production of high quality graphene, there are some challenges associated with the CVD process of making it.
Of these include difficulties in the formation of uniform layers of graphene on the substrate and the separation or exfoliation of graphene from the substrate layer without damaging the structure of graphene. Typical separation processes employ solvents including harmful acids are used to dissolve the substrate, which could compromise the quality of graphene due to the possibility of residues left behind.
Sung Woo’s team from the University of Illinois used carbon dioxide as a precursor to form carbonic acid, which was found to help in the electrochemical under-etching of the copper oxide (Cu2O) interlayer present between the copper catalyst substrate and the graphene layer deposited by the CVD process. This process eliminates the need to use harmful chemicals for exfoliation, while also preserving the copper substrate that could be recycled for developing more graphene layers on top of it.
While traditional CVD processes that employ harmful chemicals to dissolve the substrate require several subsequent rinsing steps to remove any residue of substrates, this new approach developed here need not require any rinsing steps as the substrate is not dissolved.
Sung Woo’s team used food grade ethyl cellulose as a thin film handle layer for the transfer process of the graphene sheets. While traditional transfer processes utilize polymeric thin films, such as polycarbonate or poly methyl methacrylate (PMMA) that require use of toxic and carcinogenic solvents to solvate them, this new approach utilizes environmentally benign and inexpensive ethyl cellulose, which could be simply solvated by ethanol.
Ethyl cellulose not only makes the process eco-friendly and inexpensive, but it is also compatible with a variety of polymeric and soft biological materials including plastics and hydrogels used in the process.
After the transfer process of graphene is completed, the carbonic acid used here evaporates by forming carbon dioxide and water requiring no further rinsing or washing saving water and valuable time while also saving a lot of money because the copper substrate could be reused and there is no need for the use of any harmful chemicals for solvating the substrate.
Overall, this novel process is inexpensive, cleaner, environmentally friendly and could be suitable for large-scale, therefore suggesting that this method has the potential to finally take the graphene production from laboratory scale to industrial scale.
- “A sustainable approach to large area transfer of graphene and recycling of the copper substrate” M. Wang, W. Moestopo, et al. Journal of Materials Chemistry. (2017). DOI: 10.1039.C7TC02487H.
- “What Can Graphene Do?” – The University of Manchester