Graphene may not immediately seem like the perfect candidate as a water filter. Despite being just one atom thick, it would appear to be impervious to practically every liquid and gas. However, scientists have been working on the creation of a membrane that will allow water to filter through the graphene, removing impurities along the way.
In a short film produced for Physics World magazine in 2013, Materials Characterisation expert at the University of Manchester Sarah Haigh explains: “Graphene is very impermeable, even very light gases don’t pass through.
Across the pond in a lab at Berkeley, Assistant Professor Baoxia Mi has worked on developing a membrane she believes could outperform today’s water filtration technology. Mi believes that a graphene membrane would be more effective in removing contaminants from water – including pharmaceuticals, bacteria, viruses and harmful chemicals – than existing methods. Like many scientists, she is confident that the technique could be used for effective water desalination, wastewater reuse and storm water treatment.
The two-dimensional structure of graphene allows scientists to stack sheets of it together to create the thin membrane. Mi explains that by adding oxygen to graphene to make graphene oxide, space is created in the structure for the water to flow through. One problem with this approach is that adding oxygen makes the graphene more likely to dissolve in water. However, when Mi adhered a chemical to the sheets of graphene oxide to join them together, she found the membrane stayed intact in water. The results of her work were published in a paper she co-authored for the Journal of Environmental Science and Technology in 2013. Since then, Mi has co-authored numerous papers examining various aspects of the technology.
A year later, a group of scientists including Geim (one of the original scientists who found a way to isolate graphene) co-authored a paper observing how water permeated through micrometre-thick laminates that had been prepared by vacuum filtration of graphene oxide suspensions. They noted that when dry, the laminates were ‘vacuum-tight’ but when immersed in water, they acted like molecular sieves. The laminates were able to block all particles within the solution that had a radii (once hydrated) of more than 4.5 angstroms. They also noted just how fast a graphene oxide filter can filter water for water purification and desalination –thousands of times faster than would be expected for simple diffusion.
The Future of Graphene in Water Treatment
Graphene oxide membranes have been shown in the laboratory to be effective at removing contaminants from water to an exceptional level. The research conducted on graphene membranes today is bringing the possibility of delivering clean, safe drinking water to millions in developing countries ever closer.
There is, of course, a huge difference between testing materials in a university lab and producing them on the factory floor. This gulf can prove difficult for emerging technologies and is sometimes referred to as ‘death valley’ for potential products – where both academic institutions and industries lose interest. Historically, EPSRC’s Chief Executive David Delpy believes the problem lies with British businesses who can be slow to recognise the potential of the new technology and run with it.
In the context of graphene, Delpy believes there is a need to grow new industries. For this reason, the EPSRC insisted that both the Manchester and Cambridge graphene centres work alongside businesses. The Cambridge Centre has the likes of Nokia, Dyson, Du Pont and Philips listed amongst its partners – while the Manchester Centre lists Samsung, Sharp and Siemens as collaborators. However, turning graphene technology into a commercial reality will not only require partnership – it will also require significant financing – which is why the EU has announced a ‘Graphene Flagship’ funding package for graphene research worth €1 billion over the coming 10 years.
With substantial funding and the continued efforts of some of the World’s most outstanding scientists, the use of graphene in delivering clean drinking water for millions could soon be a reality.