More efficient desalination with crystalline carbon dots

Why is it in news?

Researchers at Indian Institute of Technology (IIT) Guwahati are now able to create a more efficient desalination process by synthesising crystalline dots

Details

• Researchers at Indian Institute of Technology (IIT) Guwahati have been able to synthesise highly crystalline carbon dots by doping them with nitrogen, Sulphur and phosphorus.
• The amount of phosphorus defined the extent of crystallinity. Unlike an amorphous material, less light was scattered or reflected from crystalline carbon dots on shining light. Instead, the crystalline material efficiently converted the absorbed light energy into heat energy.
• The team led by Prof. Arun Chattopadhyay from the Department of Chemistry successfully used the crystalline carbon dots for desalinating seawater by exposing the carbon dots to simulated solar conditions. The doped carbon dots were not only able to convert light into heat energy but were also able to interact with water and transfer the heat energy to water thus raising its temperature.
• Compared with carbon dots that were doped with all the three elements, those doped with only nitrogen and Sulphur were amorphous in nature. When only nitrogen and Sulphur are present the polycyclic carbon does not arrange in a particular manner, making it amorphous. But phosphate esters that form when phosphoric acid is added bond the polycyclic fragments. That is what makes it crystalline.
• The three- and two-element carbon dots added to water (with concentration up to 250 mg per millilitre) and exposed to simulated sunlight under reduced pressure showed wide variability in their ability to transfer heat energy to water.
• There was 43.5% evaporation of water within 15 minutes in the case of carbon dots doped with three elements and only 38.3% with carbon dots doped with only nitrogen and sulphur. When the solar thermal evaporation efficiencies under standard atmospheric pressure was calculated, carbon dots doped with three elements had nearly 84% efficiency. It was about 44% with carbon dots doped with only nitrogen and Sulphur.
• The team tested the ability of the doped carbon dots to desalinate seawater samples from Bay of Bengal, Persian Gulf and a sample with average sea water salinity. Maximum desalination was achieved with carbon dots doped with three elements in the Bay of Bengal water sample ”” 43% evaporation of the initial volume in 15 minutes. Only 35.5% seawater evaporated during the same time in the case of carbon dots with two elements.
• They tested the doped carbon dots’ ability to desalinate seawater even when the salt concentration was in excess. To do this, more seawater was added to the residual seawater after each cycle and the desalination efficiency was tested for nine cycles. The doped carbon dots with nitrogen, sulphur and phosphorus elements retained up to 78% of the original desalination efficiency even at the end of the ninth cycle. The doped carbon dots can be reused by removing excess salt through dialysis.
• The team is now trying to make doped carbon dots that are super crystalline so that energy is even more efficiently converted into heat. We also trying to make a film or sponge-like device that floats on water and evaporates water by converting sunlight into heat.

Conclusion

• Water makes up two-thirds of the Earth’s surface but only a tiny fraction of it can be utilized for drinking and other essential process.
• At a time when India’s and worlds freshwater sources are dwindling, Desalination seems to be the only alternative to access the vast unused water resource. However, desalination is a very expensive and not-so-efficient process. And this property of desalination process has hampered the ability of humans to harness the vast water resource effectively.
• A technology like this will help in effectively utilizing the vast sea water resource. It will also reduce the burden on existing freshwater resources, it will provide crucial water resource to regions suffering from prolonged droughts and will greatly help in solving India’s and worlds water woes.

Source

The Hindu