Nature Inspired Technique to Help Turn Seawater into Freshwater

Efforts to develop more efficient desalination techniques for converting seawater into freshwater are slated to get a major boost with researchers gaining new insights into the molecular working of aquaporins, the water channels in human cell membranes.

Growing population and climate change pose a major global challenge in terms of water availability in the coming times. Scientific communities worldwide are looking for better ways to convert the saline water in seas and oceans into freshwater for household and industrial use. Though various desalination technologies exist in the market today, the high energy expenditure by these technologies restricts their widespread use.

A research team at the Indian Institute of Technology (IIT) – Madras has been exploring the use of carbon nanotubes and graphene nanopores to overcome the problems. Although studies have shown that graphitic carbon materials show a large water permeation capability than the conventional reverse osmosis membranes, their tube-like structures reduce the rate of permeation due to the hydrodynamic resistance at their entrance. To solve this issue, the team took inspiration from nature.

Efforts to develop more efficient desalination techniques for converting seawater into freshwater are slated to get a major boost with researchers gaining new insights into the molecular working of aquaporins, the water channels in human cell membranes.

They observed that the hourglass shape of aquaporins helps in the simultaneous passage of water and exclusion of ions/salts from it and decided to check if the same structure could enhance the desalination efficiency of carbon nanomaterial-based membranes. The team specifically found how and why water conduction in carbon nanotubes is enhanced with the introduction of a conical or hourglass-shaped inlet.

Team leader, Prof. Sarith P Sathian said, “Our study reveals the mechanisms responsible for the enhanced water permeation inside hourglass-shaped nanopores. It is possible that the same mechanisms be reproduced in a different system of nanopores which can provide a higher desalination efficiency. Secondly, ion rejection of the membrane is a crucial aspect when it comes to desalination through such nanoporous membranes. From our study, we find that the ion rejection is chiefly dependent on the CNT sizes. Hence, it could be possible to conceive a nanopore geometry with a very high permeation capacity without compromising the ion rejection.”

The study was conducted in collaboration with Swinburne University of Technology, Australia, and The Netherlands-based Delft University of Technology. It was a sponsored project of the Department of Science and Technology, Government of India, as part of its Water Technology Initiative (WTI).

The team included Mr. Vishnu Prasad Kurupath from IIT Madras, Dr. Sridhar Kumar Kannam from Swinburne University of Technology, Australia, and Dr. Remco Hartkamp, Delft University of Technology, The Netherlands. The findings of this study have been published in the journal Desalination.