Graphene Removes Salt From Water To Make It Drinkable

Graphene may save our planet by filtering the seawater to make it drinkable, according to CNN.

As the world's drinkable water resources dwindle, scientists try to find new ways to replenish fresh water for the planet. The most abundant source of water is in the oceans. The earth's surface is 71 percent water, with 96.5 percent found in our oceans. However, the ocean water is loaded with salt, making it unfit for most plants, animals, and people. Or is it?

For years, people have pondered and tried to find ways to remove the salt content from this water source and turn it into a drinkable liquid. In 2004, scientists at the University of Manchester identified an ultra-thin sheet of carbon atoms organized in a hexagonal lattice of carbon atoms. Dr. Rahul Nair led the research team.

Graphene is the first 2-D material, 1 million times thinner than a human hair, and although it is very flexible, graphene is 200 times stronger than steel. Even though graphene is just one atom thick, it has the ability to absorb 2.3 percent of light so it can be seen by the naked eye.

This isn't the first time that graphene has been used to filter water, but the researchers ran into problems. The membrane pores in graphene would swell up when submerged in water. So instead of keeping small particle out of the filtered water, it would let them pass through, but it would block the larger ions or molecules.

"In terms of scalability and the cost of the material, graphene oxide has a potential advantage over single-layered graphene. To make it permeable, you need to drill small holes in the membrane. But if the hole size is larger than one nanometre, the salts go through that hole. You have to make a membrane with a very uniform less-than-one-nanometre hole size to make it useful for desalination. It is a really challenging job."
Dr. Rahul Nair described how the process worked with using the single-layer graphene as a filter.

"Water molecules can go through individually, but sodium chloride cannot. It always needs the help of the water molecules. The size of the shell of water around the salt is larger than the channel size, so it cannot go through."

Now, thanks to Rahul Nair and his team, they have found a way to control the expansion of the graphene so the pores remain tight. A coating of an epoxy resin on the graphene was enough to stop it from expanding so the impurities and salt could not go through. The resin they used is the same substance that is often added to coatings and glues. The salt particles and other contaminants are filtered so completely that only clean uncontaminated drinking water can pass through.

"When the capillary size is around one nanometre, which is very close to the size of the water molecule, those molecules form a nice interconnected arrangement like a train. That makes the movement of water faster: if you push harder on one side, the molecules all move on the other side because of the hydrogen bonds between them. You can only get that situation if the channel size is very small."

Dr. Rahul Nair's graphene filtration system could save the world as the water supply continues to worsen. By 2025, it's predicted that two-thirds of the world's population will suffer from lack of fresh drinking water. Even the United States is not immune to water shortages as the nation suffers from drought conditions. Sections of California and the desert Southwest use more water than they have on hand.

Graphene almost sounds too good to be true, but if it does what they believe it will, this could save the planet from drying out and the people dying from dehydration.

Ram Devanathan, from the Pacific Northwest National Laboratory in Richland, Washington, said that they need to make sure that graphene is durable and will last after prolonged exposure to salt water. Of course, the graphene and coating would need to be cleaned and/or replaced periodically, and the water would have to be tested and monitored to ensure no salt or impurities come through the sieve. Another hurdle in this design is finding a low-cost way to produce the graphene oxide membranes on a large industrial scale.

Even though this would give the world more water to drink, especially in those areas that have no fresh drinking water available, it does come up against opposition. The environmentalists are seemingly against the idea because it will involve large amounts of energy that would produce greenhouse gasses. They believe this may lead to the harm or death of marine organisms.

[Featured Image by John McConnico/AP Images]