Nature often plays a mean trick on thirsty people. Unless you’re stranded in the desert, there’s often water, water everywhere, yet nary a drop to drink.
The problem isn’t ever the water itself, but the things suspended in it. The grit, organic matter and larger particles are just the start of the problem. In even the clearest running streams, disease-causing microbes, industrial compounds or naturally occurring arsenic can pose serious health risks.
Then there’s nature’s biggest barb—more than 97 percent of the water on Earth is too salty to drink. Whether it’s seawater or saline groundwater, imbibing salt causes the body to dehydrate and start shutting down.
Significantly less than one percent of the planet’s total supply of water is available fresh water for the 7.2 billion people living today, the animals and the wild and crop plants. While that supply stays about the same over time, our growing, urbanizing population and expanding industrial footprint means ever more demand. Societies around the world must deal with freshwater scarcity every day—the UN says some 1.2 billion people live where water is physically scarce.
Yet with saltwater all around, the answer to the problem has always seemed so close.
Researchers in Switzerland say they have punched precisely shaped holes in films of graphene, a two-dimensional sheet of linked carbon atoms. Their development means graphene, a material that is lightweight and strong, can be made into the thinnest possible membrane with pores of exact size to exclude specific molecules.
Engineers at ETH Zurich created the membrane out of two graphene sheets pressed together. Their prototypes were 100,000 times thinner than a human hair.
"With a thickness of just two carbon atoms, this is the thinnest porous membrane that is technologically possible to make," said Jakob Buchheim, a nanoscience doctoral student in the university’s Department of Mechanical and Process Engineering. He is a lead author of the study published today in the journal Science.
Along with major applications like filtering water, separating gaseous mixtures and removing impurities from liquids, graphene membranes could be a game changer in rain gear and waterproofing. The researchers say the material could be manufactured to make a coating that excludes liquids while letting gases right on through.