Research on Filtering Sea Water with Graphene
Graphene sieves can turn seawater into drinking water by filtering common salts from water to make it safe to drink. Graphene-oxide membranes have attracted lots of attention for new filtration technologies. These findings came from a group of scientists at the University of Manchester that were published in the journal Nature Nanotechnology on the 4th of April 2017. Previously graphene-oxide membranes had shown potential for gas separation and water filtration. Graphene-oxide membranes that were developed at the National Graphene Institute have already shown that they can be used to filter out small nanoparticles, organic molecules, and large salts. However, they couldn’t be used for sieving out common salts which would require smaller sieves. Previous research at the University of Manchester found that when in water, graphene-oxide membranes become slightly swollen and smaller salts flow through the membrane along with water, but larger ions or molecules are blocked. The group from Manchester have developed these graphene membranes and found a strategy so the membranes wont swell when in water. They can precisely control the pore size in the membrane which can sieve common salts out of water making it safe to drink. They use realisation of scalable membranes with uniform pore size down to atomic size to do this. When common salts are dissolved in water a ‘shell’ of water molecules will form around the salts molecules. The tiny capillaries of the graphene-oxide membranes can then block the salt from flowing along with water. Water molecules are able to pass through the membrane barrier and flow fast which is ideal for application of these membranes for desalination.
I chose this topic because it is a very important discovery that could be useful in the future especially in developing countries. Only 0.37 % of all the earth’s water is drinkable and as the earth’s population continues to rise the demand for water is going up. Water is already very scarce in developing countries and many people suffer from diseases such as cholera due to drinking dirty water. Being able to filter sea water would completely end the world water crisis as there is a huge supply of sea water. Graphene sieves would also be cheap making it easy for developing countries to afford.
The researchers are trying to achieve an affordable desalination technology which could be used by developing countries as well as developed countries. By 2025 the UN expects that 14% of the world’s population will encounter water scarcity. As the effects of climate change are reducing urban water supplies, wealthy modern countries are investing in desalination technologies. For example: the recent California floods. At the moment desalination plants around the world only use polymer-based membranes. These polymer-based membranes are very expensive so can’t be afforded by developing countries which need this technology the most. Making polymers also involves burning fossil fuels which causes pollution and is an unsustainable process. Ram Devanathan, from the Pacific Northwest National Laboratory in Richland, US said more work needed to be done to produce graphene oxide membranes inexpensively at industrial scales. This would allow many developing countries to buy lots of this technology to provide drinking water. He also added scientists need to make the membranes durable to prolonged contact with seawater and ensure the membranes was resistant to “fouling” by salts and biological material. This would require existing barriers to be periodically cleaned or replaced. The ultimate goal of the researchers is to create a filtration device that will produce potable water from seawater or wastewater with minimal energy input. https://www.bbc.co.uk/news/science-environment-39482342
The researchers overcame the struggle of needing smaller sieves to get rid of salt by building walls of epoxy resin on either side of the graphene oxide membrane which stopped it from swelling up in water. This allowed them to precisely control the pore size in the membrane, creating holes tiny enough to filter out all common salts from seawater. The shell of water that forms around the salt will be larger than the channel size and cannot go through. This leaves sea water fresh to drink and water molecules flow faster which is good for use in desalination. When the capillary size of the graphene oxide is around one nanometre, which is very close to the size of the water molecule, those molecules form a interconnected arrangement. This makes the movement of water faster. Pushing harder on one side means the molecules all move on the other side due to the hydrogen bonds between them. https://www.sciencealert.com/scientists-create-a-graphene-based-sieve-that-turns-seawater-into-drinking-water
Due to climate change, seawater levels are predicted to increase by around 3.8cm by 2100, and if the entire Greenland ice sheet melts, the oceans could go up to 7.3 metres higher.