Graphene Sieves Could Make Sea Water Potable

Several years ago now, I remember reading a BBC article which highlighted the amazing potential of a material called ‘graphene’, which saw Nobel Prizes issued to its inventors including Professor Kostya Novoselov who claimed that it would have future applications that would change medicine and information technology. Fast forward five years and the BBC have published another article that makes the incredible claim that graphene filters could potentially make sea water drinkable. Let’s take a look at just how this could happen and analyse the evidence that substantiates this bold assertion.

What is graphene?

Graphene is lauded as the ‘thinnest material ever created’ – so thin in fact that it is virtually only 2 dimensional. It is made from a single layer of atoms. When stretched, graphene is stronger than steel or diamonds, and conducts electricity more efficiently than copper. It is incredibly flexible and can be folded, which has led to ideas including foldable computer screens. Exciting stuff indeed.

The sea water filter

Being the world’s thinnest material, graphene has been investigated for the ways in which this property can overcome age old problems. The most staggering claim to date is that scientists are capable of devising a graphene-based sieve capable of removing salt crystals from seawater. The ramifications of such an invention would be staggering – potentially giving access to drinking water to millions of people for whom water is not yet a basic human right. The next step in what could prove to be a laborious route to product design is testing the prototype graphene oxide sieves against the efficacy of existing desalination membranes. Notice the reference to ‘graphene oxide’, a version of graphene that was applied to the problem of manufacturing graphene sieves on an industrial scale by scientists from the University of Manchester, led by Dr Rahul Nair. Graphene oxide is produced in lab conditions by simple oxidation and as a chemical derivative of graphene and has been fundamental in their successes to date.

Overcoming the problems

Previously, while graphene has been useful in filtering many nanoparticles and organic molecules it has fallen down when confronted with saltwater as graphene oxide membranes were found to swell slightly when underwater, which meant that smaller salt particles could flow through the pores with the water molecules. However, Dr Nair’s team proved that science always finds a way by experimenting with attaching walls constructed out of epoxy resin (which helps make many glues) on each side of the graphene oxide membrane. This has enabled the membranes to be altered to allow water molecules through, but not salt. Water can go through unassisted, but salt always needs the help of a watery shell to push them through. The scientists were able (with this information) to fine tune the sieves to allow water molecules to pass through freely, but sodium chloride, coated in its watery ride was shut out!

Future need and application

The United Nations has projected that by 2025 14% of the world’s human population will suffer from a water scarcity issue. This means that many of the world’s scientific resources are being channelled into solutions, of which graphene is certainly one. While polymer-based membranes are currently used in desalination plants the world over, they are energy intensive and not cheap to run. Graphene oxide replacements could one day in the near future, thanks to the fantastic work at Manchester University, enable cheaper, more energy efficient examples to be manufactured. One potential stumbling block is that the durability of the material if used under seawater has yet to be fully tested – a fact that Dr Nair et al are aware of and in the process of rectifying.