Rice University graduate student Mohamad Kabbani grinds nanotubes with a mortar and pestle. A chemical reaction takes place as the altered nanotubes are forced together, unzipping them into graphene nanoribbons. (Credit: Jeff Fitlow/Rice University)A team of international collaborators led by scientists at Rice University has developed a basic technique for producing nanoribbons by grinding nanotubes in a mortar and pestle. In this first solid state reaction of carbon nanotubes, it was shown the very smooth manual grinding method can induce a chemical reaction that unzips the nanotubes into graphene nanoribbons, avoiding the usual harsh chemical and heating conditions that can cause ripples, wrinkles and defects in the graphene, making it less convenient for electronic devices.
The observed reaction also provides highly conductive graphene with good quality and yield, and it is versatile enough to tune for graphene production for specific needs, useful since nanoribbons are finding increasing commercial applications in composite materials due to their electronic properties and/or strength.
The study, published in Nature Communications [Kabbani et al. Nat. Commun. (2015) DOI: 10.1038/ncomms8291], involved an exothermic reaction from the mixing of two types of chemically modified nanotubes that, on coming into contact during the grinding, reacted and unzipped. The team prepared two batches of multi-walled carbon nanotubes, one with carboxyl groups and the other with hydroxyl groups attached. When these were ground together for up to 20 minutes using a mortar and pestle, the chemical additives reacted with each other, triggering the nanotubes to unzip into nanoribbons, with water as a byproduct.
“Using different functionalities in different nanoscale systems could revolutionize nanomaterials development”.Mohamad Kabbani
The tests were confirmed at participating labs under standard lab conditions as well as in a vacuum, outside in the open air, and at variable humidity, temperatures, times and seasons through spectroscopic measurements, thermal analysis and molecular dynamic simulations. Although the team remain unsure about what exactly is taking place at the nanoscale, and the new process is a chemical reaction that depends on molecules purposely attached to the nanotubes, a process known as functionalization, it is crucial that the grinding can achieve a strong chemical coupling between the solid nanostructures to produce new types of nanostructured products that offer specific properties.
Much work still needs to be carried out to see if it would be possible to use a large number of possible nanostructures and chemical functional groups and to understand the reactions of different types of functionalized nanoparticles other than carbon nanotubes. The researchers hope this will lead to further systematic studies of nanotubes reactions in solid state. As lead author Mohamad Kabbani said, “Using different functionalities in different nanoscale systems could revolutionize nanomaterials development”.