Microwave cooking for soluble CNTs

The industrial processing of carbon nanotubes (CNTs) could become much easier with the development of a quick and simple way to make them highly soluble. 

Normal single-wall CNTs are effectively insoluble, forming huge clumps that sink to the bottom. US researchers have worked on increasing this solubility by attaching various different water-soluble compounds, including fluorine, aryl radicals and sugars, to the tubes. Unfortunately, none of these mechanisms has increased solubility much, and they usually involve time-consuming reaction processes.

Chemists at the New Jersey Institute of Technology, led by Somenath Mitra, have now used microwaves to create CNTs that are up to 125 times more soluble than forerunners. Their method involves adding CNTs to a mixture of nitric acid and sulphuric acid and then heating it in a microwave for just three minutes. The chemists found that the resultant CNTs could dissolve in water at concentrations as high as 10mg/mL, compared with only around 0.08mg/mL for most other methods.

Detailed studies of the CNTs showed that they now contained carboxylated and acid sulfonated groups on their surface, transforming them into polyelectrolyte salts that readily dissolved in polar solvents such as water. And the transformed CNTs were still able to conduct electricity at similar levels to normal CNTs.

Mitra’s team is now exploring practical applications for these soluble CNTs, including nano-composites, organic solar cells and thin films. The researchers have formed a company called Nanopulse to commercialise them. ’We are [also] using microwaves to alter nanotubes in several different ways, including attaching different functional groups, polymers and ceramic composites,’ Mitra told Chemistry World.

Jon Evans