Researchers develop desalination technique inspired by trees

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A research team from the Indian Institute of Technology Gandhinagar (IITGN) in Gujarat has developed a cost-effective, environmentally friendly water desalination technique that can successfully remove more than 99% of salt ions and other impurities with natural processing to make seawater potable.

Image shows control of fluid channel space by inserting K+ and Cl- ions (represented by white balls and red balls respectively). The small water molecules (two white and one blue ball) in between are transported through the space as there is enough space for them, but the bigger salt ions are blocked due to restricted space.  A hexagonal structure with carbon atoms represents the graphite layers.
Image shows control of fluid channel space by inserting K+ and Cl- ions (represented by white balls and red balls respectively). The small water molecules (two white and one blue ball) in between are transported through the space as there is enough space for them, but the bigger salt ions are blocked due to restricted space. A hexagonal structure with carbon atoms represents the graphite layers. - Image: IIT Gandhinagar

The research is inspired by trees’ natural intake of water that uses the capillary effect and can provide affordable, energy-efficient drinking water solutions compared to energy-intense, expensive RO technologies.

The research team, led by Gopinadhan Kalon, assistant professor, Physics and Materials Engineering, IITGN, created controllable water transport channels in graphite crystal with the help of an electric field and potassium chloride (KCl) ions, which allowed only fresh water to move through the crystal and blocked all the salt ions.

These findings were recently reported in Nature Communications and lead author, Lalita Saini, said: “Natural graphite is not absorptive to water or any ions including protons. However, by its nature, the graphite crystal also does not allow any water molecules to pass through it because there is not enough space for the movement of these molecules. This issue was solved by using an electric field and inserting potassium chloride (KCl) ions in it, which create some space inside the graphite crystal and provide a stable structure for easy passage of water molecules, at the same time hindering the movement of any salt ions, giving drinkable water.”

In addition to making seawater safe to drink, carbon materials like graphite are antimicrobial, reducing the number of filters required in the desalination process.

The method is cost-effective and environmentally friendly because carbon is abundant in nature, and India is the second largest producer of graphite in the world. The current experiment used natural graphite but the team is also devising a method that does not require the use of natural graphite; instead, they can synthesise graphene (one-unit layer of graphite) from waste, plastics, wheat, sugar, chocolate etc., and assemble it to make graphite-like structure.