New material for water desalination

Engineers at the University of Illinois have developed an energy efficient material for desalinating seawater.

The research team used nanometre-thick sheet of molybdenum disulphide (MoS₂) riddled with nanopores and successfully designed a material that can let through high volumes of water but keep salt and other contaminates out.

“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 research leader Professor Narayana Aluru.

Most available desalination technologies rely on reverse osmosis to filter seawater through a thin plastic membrane that has holes small enough to not let salt or dirt pass through, but large enough to let water through. This method is considered as good at filtering out salt, but it yields only a small amount of fresh water.

“Reverse osmosis is a very expensive process. It’s very energy intensive. A lot of power is required to do this process, and it’s not very efficient. In addition, the membranes fail because of clogging. So we’d like to make it cheaper and make the membranes more efficient so they don’t fail as often. We also don’t want to have to use a lot of pressure to get a high flow rate of water,” said Professor Aluru.

In the study, published in the journal Nature Communications, the team used the Blue Waters supercomputer at the National Center for Supercomputing Applications and modelled various thin-film membranes. They found that a single-layer sheet of MoS₂ can filter up to 70% more water than other membranes such as graphene.

The researchers created a sheet of MoS₂ that has sulphur coating either side with the molybdenum atom in the centre. Then they created a pore in the sheet that left an exposed ring of molybdenum around the centre of the pore creating a nozzle-like shape that drew water through the pore.

Research associate 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.”

The results showed that single-layer sheets of MoS₂ have the advantages of thinness, requiring much less energy, and therefore reducing operating costs. MoS₂ also is a robust material, so even such a thin sheet is able to withstand the necessary pressures and water volumes.

Paper: http://www.nature.com/ncomms/2015/151014/ncomms9616/full/ncomms9616.html