It is still difficult to produce large quantities of "wonder material" graphene using conventional chemical methods but researchers at Stanford University in the US may now have come up with a solution to this problem.
Hongjie Dai and colleagues have invented a new scalable exfoliation-reintercalation-expansion technique to make high-quality, single-layer graphene sheets suspended in organic solvents. The sheets can then be made into large transparent conducting films for use in potential applications such as electrodes for solar cells.
Reintercalated graphite
"The conductance of the graphene sheets made using our technique is pretty close to pristine graphene and is about 100 times higher than graphene obtained by reducing graphene oxide," Dai told
nanotechweb.org.
The exfoliation-reintercalation-expansion method consists of exfoliating commercially available graphite at 1000 °C and treating it with oleum to reintercalate the graphite. Next, a chemical called TBA is used to further expand the distance between two graphene layers, explains Dai. The researchers then sonicate the product in DMF with the help of a surfactant, phospholipid-PEG, and centrifuge it to produce a suspension of mostly single-layer graphene sheets.
Simple technique
"The technique is not difficult and contains almost 90% single-layer graphene sheets," said Dai. "It is easy to scale up and we are currently trying to do gram-scale production in our lab."
Compared with other methods to prepare graphene, the new technique can produce large-scale single-layer graphene sheets with high conductance. Dai says that the most common, "peeling-off" method to produce graphene is only useful for small-scale prototype devices.
As for epitaxial growth methods, the graphene here is grown on special substrates like silicon carbide or ruthenium, and the graphene needs to be collected and deposited. Methods that reduce graphene oxide produce graphene with high resistance and low quality.
The sheets produced by Dai's team might be useful in transparent electrodes for solar cells. Sensors or anode materials in lithium batteries might also benefit from graphene as a component.
The team is now working hard to further improve the quality of its graphene sheets, increasing yield and developing novel applications.
The work was reported in
Nature Nanotechnology.
source:
nanotechweb.org
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