doi:10.1038/nindia.2014.124 Published online 17 September 2014
Researchers have developed a technique to form biocompatible, few-layered graphene oxide sheets from bio-ionic liquids — ionic liquids derived from biomolecules1. When dispersed in water, these ionic liquids reduce and stabilize graphene oxide sheets. Such sheets are potentially useful for fabricating energy-storage devices, biomedical devices and heat-resistant composite materials for the automobile and aircraft industries.
Graphene oxide is usually reduced using hydrazine, which is toxic. This chemical contaminates the graphene oxide, making it unsuitable for use in biomedical applications such as tissue engineering. The researchers developed a method for making biocompatible graphene oxide from non-toxic chemicals that involves synthesizing ionic liquids from choline and fatty acids. They prepared four ionic liquids with different counter anions: choline hydroxide, choline bicarbonate, choline formate and choline caproate.
To modify separately synthesized samples of graphene oxide, the researchers added these ionic liquids to aqueous solutions containing dispersed graphene oxide. On adding the ionic liquids, the colour of the dispersed graphene oxide changed from brownish to blackish, indicating modification of graphene oxide. These ionic liquids also converted many-layered graphene oxide sheets into few-layered sheets.
By performing absorption measurements, the researchers confirmed that the ionic liquids modified the graphene oxide sheets through reduction. The graphene oxide sheets modified by the ionic liquids exhibited low absorption to ultraviolet and visible light, suggesting that the graphene oxide sheets had been reduced. Choline hydroxide and choline bicarbonate were found to reduce graphene oxide sheets more efficiently than choline formate and choline caproate.
The ionic liquids stabilized graphene oxide sheets dispersed in water for up to one year through the formation of nanoscale sheets of graphene oxide. “This long-term stability of the graphene oxide sheets is promising for the large-scale production of non-toxic graphene,” says Kamalesh Prasad, a senior author of the study.
1. Sharma, M. et al. Studies on the affect of bio-ionic liquid structures on the spontaneous reduction and dispersion stability of graphene oxide in aqueous media. RSC Adv. 4, 42197–42201 (2014)