IIT Gandhinagar develops cost-effective, eco-friendly water desalination technique to make seawater drinkable

 

The whole earth is surrounded by 71% water, out of which 97.5% water is in the oceans but still  we are facing a water shortage because it is saline. Now, the  Indian Institute of Technology Gandhinagar (IITGN) researchers team have developed a cost-effective and environment-friendly water desalination technique that can successfully remove more than 99% of salt ions and other impurities with natural processing to make seawater potable.

This research team headed by Prof 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. The research team also includes IITGN PhD scholars Lalita Saini, Aparna Rathi, Suvigya Kaushik, and a Postdoctoral fellow Siva Sankar Nemala.

IITGN team took inspiration by Trees’ Natural Intake of water using Capillary Effect,

The research has been motivated and guided  by trees’ natural intake of water using capillary effect. Selective transport of molecules and ions is commonly observed in biological systems. Mimicking these biological channels could result in highly efficient filtration systems. The research team used a capillary process in the technique, which does not cost any energy, and in fact, the evaporation of water happened spontaneously without the need of any external pressure. The evaporation rates provided a back-calculated pressure of 50-70 bar arising from the capillary and other forces that are present inside the nanoscale channels.

The  team said, adding it can prove useful in designing filters for gas purification, proton exchange in a fuel cell, chemical separation, recovery of precious metal from waste among others. It can also be suitable for dehumidification applications as expanded graphite has high water evaporation rates.

© Provided by The Financial Express "The evaporation rates provided a back-calculated pressure of 50-70 bar arising from the capillary and other forces that are present inside the nanoscale channels," IITGN team said

International Journal ‘Nature Communications’ has published the findings,

The finding has been published in the international journal ‘Nature Communications’. Explaining the technique further, first author of the research paper, 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 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 and providing drinkable water" Saini added.

What makes the technique cost-effective and environment-friendly?,

According to the team, “The present 2mm x 2mm sized device made by the research team has flow rates comparable to RO technology, that too without using electricity. This is the first such method that could controllably manipulate graphite, without damaging its structural integrity, inside aqueous solutions. The water evaporation and filtration processes used in this technique do not involve any electricity, and therefore it does not produce any gas emissions, making it environment-friendly. The team is now working to develop a direct point-of-use water filter using this technique to make it accessible for the people.”

“Continuous rise in population and enormous energy demands has put immense pressure on conventional clean water resources. The widely used reverse osmosis technique for desalination is expensive, wastes more water, and is highly energy-intensive, which typically requires hydrostatic pressures of 60-80 bar, as the freshwater resources continuously shrinking, there is a high need of such kind of water purification methods who can recycle  desalination and impurities of seawater into drinkable” Gopinadhan Kalon, Assistant Professor, Physics and Materials Engineering, IITGN told PTI.

"Our method is not only limited to graphite but also to a large number of layered materials like clay that could be explored for high performance separation applications. With abundant seawater and appropriate plant design optimization, our method holds a bright future in realizing the dream of drinking water for everyone on the planet." - Gopinath added.

Carbon is abundant in nature, and India is the second largest producer of graphite in the world. The current experiment has utilized natural graphite. However, the team is also devising a method that does not require the use of natural graphite; instead, they can synthesize  graphene (one-unit layer of graphite) from waste, plastics, wheat, sugar, chocolate etc., and assemble it to make graphite-like structure. This technique can also prove to be useful in designing filters for gas purification, proton exchange in a fuel cell, chemical separation, recovery of precious metal from waste etc.