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New material to make seawater drinkable

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Washington :Researchers, led by an Indian-origin scientist, have found an energy-efficient material for removing salt from seawater to yield drinkable water.

The material, a nanometre-thick sheet of molybdenum disulfide (MoS2) riddled with tiny holes called nanopores, is specially designed to let high volumes of water through but keep salt and other contaminates out, a process called desalination.

The researchers from University of Illinois in US modelled various thin-film membranes and found that MoS2 showed the greatest efficiency, filtering through up to 70 per cent more water than graphene membranes.

“Even though we have a lot of water on this planet, there is very little that is drinkable,” said study leader Narayana Aluru, professor at University of Illinois.

“If we could find a low-cost, efficient way to purify sea water, we would be making good strides in solving the water crisis,” said Aluru.

“Finding materials for efficient desalination has been a big issue, and I think this work lays the foundation for next-generation materials,” said Aluru.

“These materials are efficient in terms of energy usage and fouling, which are issues that have plagued desalination technology for a long time,” said Aluru.

Most available desalination technologies rely on a process called reverse osmosis to push seawater through a thin plastic membrane to make fresh water.

The membrane has holes in it small enough to not let salt or dirt through, but large enough to let water through. They are very good at filtering out salt, but yield only a trickle of fresh water.

Although thin to the eye, these membranes are still relatively thick for filtering on the molecular level, so a lot of pressure has to be applied to push the water through.

Using the Blue Waters supercomputer at the National Centre for Supercomputing Applications at the University of Illinois, the researchers found that a single-layer sheet of MoS2 outperformed its competitors thanks to a combination of thinness, pore geometry and chemical properties.

“MoS2 has inherent advantages in that the molybdenum in the centre attracts water, then the sulphur on the other side pushes it away, so we have much higher rate of water going through the pore,” said graduate student Mohammad Heiranian, the first author of the study.

The single-layer sheets of MoS2 have the advantages of thinness, requiring much less energy, which in turn dramatically reduces operating costs.

MoS2 also is a robust material, so even such a thin sheet is able to withstand the necessary pressures and water volumes.

The study was published in the journal Nature Communications.

PTI