Making Salt Water Drinkable!

Even though we have a lot of water on this planet, there is very little that is drinkable and finding materials for efficient desalination has been a big issue. Most available desalination technologies rely on a process called reverse osmosis to push seawater through a thin plastic membrane to make fresh water. However, reverse osmosis is a very expensive process. A lot of energy is required to do this process, and it’s not very efficient. 

The membranes that are currently available for the reverse osmosis process are very good at filtering out salt, but yield only a trickle of fresh water. The membrane has holes in it small enough to not let salt or dirt through, but large enough to let water through. 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.

Nanotechnology could play a great role in reducing the cost of desalination plants and making them energy efficient. University of Illinois engineers have found a more energy-efficient material for removing salt from seawater that  could deliver huge advantages in terms of providing people with access to drinking water and help combat problems like drought. 

“If we could find a low-cost, efficient way to purify sea water, we would be making good strides in solving the water crisis. ...... Finding materials for efficient desalination has been a big issue, and I think this work lays the foundation for next-generation materials. These materials are efficient in terms of energy usage and fouling, which are issues that have plagued desalination technology for a long time,” said study leader Narayana Aluru, a U. of I. professor of mechanical science and engineering.

The researchers have developed a material that allows high volumes of water to pass through extremely tiny holes called ‘nanopores’ while blocking salt and other contaminants. The material they’re using – a nanometre-thick sheet of molybdenum disulphide (MoS2) riddled with these nanopore holes – is the most efficient of a number of thin-film membranes that the engineers modelled, filtering up to 70 percent more water than graphene.

Simulation box and different pore architectures.

Simulation box and different pore architectures.

MoS2 has inherent advantages in that the molybdenum in the centre attracts water, then the sulphur on the other side pushes it away, so the system has a much higher rate of water going through the pore. In addition to the chemical properties, 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. Read More>

The first step to actualising this system will be testing, but they’re confident their findings – which are published in Nature Communications – could be applied on an industrial scale for everybody’s benefit. The next steps for the researchers will be joint venturing with manufacturers who can bring their modelled desalination technique to life.