Graphene to clean polluted water
doi:10.1038/nindia.2012.147 Published online 3 October 2012
Chemists at the Indian Institute of Technology Madras have discovered the exceptional ability of graphene to remove common pesticides from water1. The work can herald a cheap method of cleaning up sources of drinking water polluted by pesticides, a common problem worldwide.
Graphene is an 'allotrope' or a 2-dimensional form of carbon with atoms densely packed in a honeycomb fashion in a one-atom-thick sheet or layer. Scientists have found several uses for this amazing material including for making transistors, gas sensors and corrosion-resistant coatings. The IITM chemists' discovery adds one more to this list.
Toxicity and health hazards posed by pesticides, even at very low concentrations, are of concern in both developing and developed countries. The World Health Organization prescribes a maximum limit of 0.1 microgram per litre of drinking water for a single pesticide.
In their work, the team led by Thalappil Pradeep studied graphene's interaction with chlorpyrifos, endosulfan and malathion, widely detected in surface and groundwater samples in many countries.
Their study showed that graphene picks up these pesticides in very large quantities — in fact, more than its self weight. For instance one gram of graphene was found to adsorb 1.2 gram of the pesticide endosulfan "higher than any material investigated for the purpose." This unusual capacity of graphene for the uptake of pesticides can be used for water clean-up, Pradeep told Nature India.
Carbon nanotubes (CNTs), another category of carbon, have been investigated for pesticide uptake but CNTs are reported to be cancer causing which may limit their utility in drinking water purification, he says.
"Our work establishes that the new class of 2-dimensional carbon nanomaterials has enormous potential in water purification, in creating cheap, easily manufacturable substrates", the researchers report. The material, according to the researchers, is also attractive due to its high specificity to the pesticides and insensitivity to changes in pH values of water and less toxicity than CNTs.
"Besides, reduced graphene oxide can be easily immobilized on cheap substrates like sand and used as a filter," they say. The anti-bacterial properties of graphene means bacteria is unlikely to accumulate on the filter media using graphene. The research was funded by the Nano Mission of the Department of Science and Technology (DST).
- Maliyekkal, M. S. et al. Graphene: a reusable substrate for unprecedented adsorption of pesticides. doi: 10.1002/smll.201201125 (2012)