Scientists develop ‘nanopores’ that can inexpensively filter salt out of seawater

In order to help people get access to drinking water and help fight natural calamities like drought, engineers in the University of Illinois have been working to come up with a new significant and more energy-efficient way of taking the salt out of seawater.

‘Nanopores’, a material developed by the researchers allows high volumes of water to pass through very tiny holes while blocking salt and other contaminants. Nanometre, the material used by the engineers is a thick sheet of molybdenum disulphide (MoS2) pierced with these nanopore holes is the most efficient of a number of thin-film membranes that they fashioned filtering up to 70 percent more water than graphene.

Narayana Aluru, a professor of mechanical science and engineering at the University of Illinois and leader of the study, said “Even though we have a lot of water on this planet, there is very little that is drinkable. If we could find a low-cost, efficient way to purify sea water, we would be making good strides in solving the water crisis.”

The solution to this could be MoS2 coupled with nanopores. While removing salt from water is not something new, it could make a huge difference when it comes to processing large amounts of seawater. With this new material, there is a gain in efficiency in terms of the energy needed to make the filtration work, and also the cost of keeping a desalination system running.

“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.”

Conventional desalination depends on reverse osmosis to direct seawater through a thin plastic membrane, but the process has to face a number of blockages. While it may look like a more tube- or tunnel-like than a sheet that’s only a nanometre in thickness from a microscopic perspective, even though the membrane may appear thin to the eye. This means that to operate it needs more pressure (and thus energy). They are also exposed to more clogging, which increases the operational costs.

In comparison, many of the above flaws are reduced or negated due to the extreme thinness of the molybdenum disulphide membrane, as it lets water to move through with much less resistance. However, behind the system the ingenuity is not just in its engineering.

The first author of the study, Mohammad Heiranian said “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. It’s inherent in the chemistry of MoS2 and the geometry of the pore, so we don’t have to functionalise the pore, which is a very complex process with graphene.”

So, here is the world’s first thirsty water filter. The researchers are collaborating with manufacturers which is their next step who can bring their modelled desalination technique to life. While the first step will be testing, they are sure that their findings could be applied on an industrial scale for everybody’s benefit, which are published in Nature Communications.

Amir Barati Farimani, a postdoctoral fellow at Stanford University who worked on the research at Illinois as a graduate student, said “I’m in California now, and there’s a lot of talk about the drought and how to tackle it. I’m very hopeful that this work can help the designers of desalination plants.”

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