MoS2 Nanopores Desalination
MoS2 Nanopores, developed by the University of Illinois, seems to be an energy-efficient technique for removing salt from seawater. The material, a nanometer-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 thin-film membrane MoS2 showed the greatest efficiency, filtering through up to 70 percent more water than graphene membranes.
The image is a schematic representation of how the filter works.
- (a) shows the MoS2 sheet with the molybdenum in blue and the sulfur in yellow.
Water appears transparent blue.
- In (b) we see three types of pores, one molybdenum only, one mixed and one sulfur only.
The study tested all three types to determine relative performance.
The membrane was compared with graphene-based rigid technology with better than 70% improvement. The molybdenum-only pores allowed the greatest flow-through rate but overall the MoS2 mix performed two to five times better than current conventional desalination technology.
Compared to reverse osmosis
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.
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. Illinois wanted to make it:
- the membranes more efficient so they don’t fail as often
- avoid a lot of pressure to get a high flow rate of water
Illinois has previously studied MoS2 nanopores as a platform for DNA sequencing and decided to explore its properties for water desalination. Using the Blue Waters supercomputer they 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 center attracts water, then the sulfur 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. “It’s inherent in the chemistry of MoS2 and the geometry of the pore, so we don’t have to functionalize the pore, which is a very complex process with graphene.”
Thin, green and cheap
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.
There’s a lot of talk about the drought and how to tackle it. Illinois is very hopeful that the MoS2 nanopores can help the designers of desalination plants. This type of thin membrane can increase return on investment because they are much more energy efficient.
- Clean Drinking Water
- PH2OG water from the air
- WaterSeer produces water from air
- Virgin Islands tackles water shortage with desalination technology with solar power
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