The new device using graphene oxide, fashioned into a sieve formation. The design is highly efficient at filtering salts, as demonstrated in laboratory tests. The new development should be possible to recreate on an industrial scale and thus provide a source of clean water for parts of the world where there is no freshwater supply.
Despite the planet being made up of 70 percent water, almost all of this water is seawater (Seawater makes up 97.3 percent of the Earth’s water) and people cannot drink water from the sea. This is because seawater contains salt. When humans drink seawater the body cells are take in water and salt, with the salt at a very high concentration and this level of sodium would be deadly if it was consumed regularly. One reason is that human kidneys can only make urine that is less salty than salt water. This means that to get rid of all the excess salt taken in by drinking seawater the kidneys would need to take existing water from the body. The result is a person would need to urinate more water than they drank. which means eventual death by dehydration as a person becomes ever thirstier.
The basis of the new filter is graphene oxide. Graphene is a single atom thick layer of a from of carbon. It is transparent, stronger than steel, and it possess many properties, such as being highly conductive of electricity. Graphene oxide is graphite oxide, an oxidized form of a compound of carbon, oxygen, and hydrogen in variable ratios, arranged in sheets. When the sheets become monomolecular (one molecule thick) graphene oxide is formed. Graphene oxide sheets have been used to prepare a strong paper-like materials, membranes, thin films, composite materials.
With the new development, Dr Rahul Nair from the University of Manchester, U.K., as developed graphene oxide in an ink-like form which can be used to form a membrane as it hardens as it is layered onto a substrate or porous material. It is then possible to drill small holes in the membrane. Provided the holes are less-than-one-nanometre in size, seawater can pass through and salt are retained, producing clean water.
Following the success of the prototype the new sieve will be tested against existing desalination membranes. The research is described in the journal Nature Nanotechnology, in a paper titled “Tunable sieving of ions using graphene oxide membranes.”