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Tiny cleaners
The research team with the purifying cartridge

It is difficult to grasp the fact that the dark liquid swirling inside a small laboratory flask is actually a solution of gold. Yet, it is indeed bits of gold that are so minuscule that they are not visible to naked eyes. The gold particles may be diminutive but their atoms are packed with properties, which display unusually strong chemical reactivity.

It is this extreme “reactive” nature of these ultra-small nanoparticles that is being tapped by Thalappil Pradeep — head of the Unit of Nanoscience at the Department of Chemistry, Indian Institute of Technology (IIT), Madras, —to rid water of harmful contaminants. A long-standing champion of using nanoparticles to purify water — an effort the scientific community at large mocked at first — this IIT professor has time and again proved that nanoparticles of gold, and silver too, are highly efficient in making water fit for drinking, cleaning up even dissolved pesticides.

The bearded, bespectacled Pradeep, who works out of a compact lab supported by the Department of Science and Technology, comes across as a man on a mission. The enthusiasiastic professor, who has penned several books on nanoscience that are now prescribed textbooks in different universities, never passes up an opportunity to wax eloquent about the “magical” properties of nanoparticles which could be harnessed for the benefit of society.

In 2001, the chemistry professor demonstrated that it is possible to completely break down halocarbons, a class of compounds to which many lethal pesticides belong, into relatively harmless carbon particles and metal compounds. What this discovery meant was that pesticides in drinking water could be removed by passing them over nanoparticles. This work led to the development of a revolutionary nanoparticle-based technology for water purification. This patented technology is currently in commercial use with Eureka Forbes, a firm specialising in water purification, marketing these filters as Silver Nano.

Recently, Pradeep’s team has tweaked this technology a bit could help tackle arsenic contamination in groundwater, a serious problem that afflicts most states in eastern India, including West Bengal. A nanoparticle-based cartridge developed in the IIT lab is capable of trapping arsenic and other dissolved contaminants in drinking water.

“All over the world, the permissible limit of arsenic in drinking water is 10 parts per billion (ppb), in India it is 50 ppb. There is actually no safe limit of this toxic compound. It is highly dangerous to consume arsenic contaminated water. It can trigger several diseases, including cancer,” says Pradeep.

It took Pradeep’s team three years to come up with filter to remove arsenic completely from drinking water. “What was challenging was to make the know-how affordable and create something that would not recontaminate water in the surrounding,” he says. Therefore, they used natural materials like biomimetic material and modified them with elements that have a natural affinity for arsenic.

What the IIT team has come up with is a 10cm “cartridge” made up of biomimetic material with nano structures embedded in them. This cartridge is capable or removing arsenic in 2,000 litres of water. To put that in context, a family of five can use the cartridge to purify its drinking water for a year. And it takes the cartridge less than a minute to purify the water — after passing through the filter, the arsenic level goes down to less than 2 ppb. “It is a product suitable for families in remote areas as it does not need electricity. It can be fitted into any kind of existing water storage facility,” points out Pradeep. This cartridge will not release any other element into the water, it will just remove the contaminants.

However, Pradeep is still not satisfied. He believes that more work needs to be done to constantly improve the use of nanomaterials to purify water. “We probably need to invent new sensors to detect ultra low concentration sensing in water; and create more sustainable purifying technologies.” Says Pradeep.

Here’s wishing that he can make his dream of providing safe drinking water throughout our country a reality.