Graphene Sieve May Help Solve The World's Water Woes

Though 70% of the Earth is covered in water, only about 2.5% is fresh. Even worse, just 1% of the fresh water is readily accessible, the rest being trapped in glaciers or deep underground. It is therefore not surprising to hear that over 780 million people worldwide currently do not have easy access to clean water. The problems are only expected to get worse with climate change and the burgeoning world population. While desalinating sea water is the most logical solution, current techniques are too expensive and cumbersome to deploy on a large scale.

One promising method that a University of Manchester research team, led by Professor Rahul Nair, has been working on for the past few years, entails using graphene, the world’s first 2-D material. Often touted as the new wonder material, the single layer of tightly packed carbon atoms is harder than a diamond, 200 times stronger than steel, one million times thinner than a strand of human hair, and extremely flexible. It, therefore, lends itself to a wide variety of uses from medicine to energy, electronics, and even desalination.

For their experiments, the researchers used a graphene oxide membrane developed at the National Graphene Institute. The membrane’s small capillaries proved to be excellent at filtering out all the small nanoparticles, organic compounds, and most of the salt particles from the water. However, exposure to water caused it to swell and widens its pores, enabling some of the smallest salt molecules to slip through.

Now, the research team has come up with a clever way to control the swelling by coating the membrane with an epoxy resin, a substance often used in adhesives. The report, published in the journal Nature Nanotechnology on April 3, states that this simple solution keeps the pores smaller than the diameter of unwanted salts and other molecules, allowing only fresh, drinkable water to seep through. The scientists believe that the ability to fine-tune the pore size will open up opportunities for more efficient desalination technology and allow the graphene membranes to be used in other applications that require selective filtration.

The next challenge is to create membranes that can be scaled up or down in size so that they can be used in desalination plants as well as for portable water filtration in remote areas or developing nations. The team also needs to test the graphene membrane further to ensure it can withstand the constant exposure to sea water and resist the constant buildup of salts or biological materials left behind.

Resources: newatlas.com, phys.org, nature nanotechnolgy.com