Graphene membranes filter seawater into fresh water

Researchers have reached a major turning point in the search for effective desalination by successfully fabricating a screen of graphene oxide to remove salt from seawater.

At the current research stage, this technique is still limited within the laboratory, but it is a breakthrough to open up the possibility that we can quickly and easily turn one of our rich resources. The best, sea water, is one of our rarest resources - clean water.

The research team, led by TS. Rahul Nair from the University of Manchester in England has shown that the sieve made from graphene can effectively filter out salts, the next step is to test the application of this strainer to salt filters.

Filtering salt from seawater to clean water is no longer a new issue.

"Reducing the permeability of membrane filters to atomic scale is a significant step forward and will open new possibilities to improve the effectiveness of desalination technology , " Dr Nair said. proved that it is possible to scale up methods to describe and mass produce graphene-based filters with sieve sizes on demand ".

The membrane of graphene oxide has long been considered a promising candidate for filtration and desalination, but although many research groups have developed membranes that can sieve large particles out of water, however to remove salt requires jacks. even smaller sieve ruler. A big problem is, when the graphene oxide film is exposed to water, the size of the holes increases, allowing salt particles to pass through the holes.

The Manchester team overcame this by building epoxy resin walls on either side of the graphene oxide membrane , preventing it from swelling in water. This allows them to precisely control the hole size in the membrane, creating holes small enough to filter out all the salt particles that are common from seawater.

The key to doing this research is based on the fact that when salt is dissolved in water, they form a 'shell' of water molecules around them.

"Water molecules are free to move, but sodium chloride is impossible. It always needs the help of water molecules," Dr. Nair said. in sieve, so it can't go through ".

Not only does seawater filter to drink, this membrane also makes water molecules flow faster through filters, which is the perfect factor to put the use of water filters into practice.

The breakthrough in fixing the size of the holes in the membrane is the key to the problem.

"When the capillary size is about a nanometer, very close to the size of the water molecule, the molecules that form a connection are as flexible as a train , " said TS. Nair explains: "That makes the movement of water faster: if more powerful on one side, the molecules will move to the other side because of the hydrogen bonds between them. You can only get the situation. traveling in a train style when the channel size is very small ".

There have been a number of major desalination plants in the world that use polymer membranes to filter out salts, but the process is still inefficient and costly, so finding a way to make it faster, cheaper More and easier is a great goal for researchers.

Thanks to climate change, the sea level is expected to increase by 3.8cm (1.5 inches) by 2100 and if the entire Greenland Ice Block melts, future generations will face rising oceans. up to 7.3 meters (24 feet).

But clean drinking water is still extremely difficult in many parts of the world - the UN predicts that by 2025, 14% of the world's population will suffer from water scarcity. Many of these countries will not be able to afford large scale desalination plants.

Researchers are hoping that graphene-based sieves can be as effective as large plants on a small scale, so it's easier to hit the market.

Graphene oxide is also much easier and cheaper to perform in laboratories than single-layer graphene, which means the technology will be affordable and easy to produce.

The membrane will retain salt molecules, only passing water molecules.

"Selective separation of water molecules from ions by physical restriction of the gap will open the process for the synthesis of inexpensive membranes for desalination" , Ram Devanathan from the Northwest Thai Binh National Experiment Duong, who did not participate in the study, added.

The ultimate goal is to create a filtration device that can produce drinking water from seawater or waste water with minimum energy inputs. The next step will be to test the durability of the filter when used for a long time and maintenance costs.

This study was published in Nature Nanotechnology.