doi:10.1038/nindia.2012.167 Published online 19 November 2012
Researchers have designed a new kind of mercury sensor by chemically modifying multi-walled carbon nanotubes (MWCNTs) using an organic salt. The MWCNT-based sensor has shown efficacy in detecting minute traces of mercury in drinking water and treated industrial effluents.
Mercury is a toxic chemical that damages the nervous system of infants and humans, and also impairs vision, speech and movement. Existing methods to detect mercury are complex and expensive.
To overcome these drawbacks, the researchers modified the surface of MWCNT by attaching the organic salt Fast Violet B in the presence of hypophosphorous acid, yielding a mercury-sensing electrode. They then collected mercury-contaminated water samples from tap water, treated industrial effluent, and polluted lake water and filtered these water samples.
The pH of these filtered samples was maintained at 8 using phosphate buffer solution. They carried out electrochemical studies using these samples and the MWCNT-based electrode applying suitable potential. On applying a specific potential, mercury ions in samples were reduced to mercury atoms, which attached to the electrode surface.
Applying a specific positive potential, the reduced mercury atoms were detached from the electrode's surface, generating current signalling the presence of mercury. The electrode could detect .002 parts per billion of mercury in the studied samples, even in the presence of interfering ions such as cadmium, silver, iron, copper, manganese, lead, calcium and chromium.
"The study suggests that the sensor could detect mercury in a wide variety of mercury-contaminated samples," says lead researcher M. Pandurangappa from the Department of Chemistry, Bangalore University, Bangalore.