New Use For Supermaterial Graphene In Water Desalination Is Looking Promising

Seawater: A new graphene membrane may soon allow the efficient treatment of seawater to yield a drinkable result. Image by U.S. Fish and Wildlife Service Headquarters.Seawater: A new graphene membrane may soon allow the efficient treatment of seawater to yield a drinkable result. Image by U.S. Fish and Wildlife Service Headquarters.

A lack of fresh, potable water is a looming crisis as the human population, and associated energy demand, continues to expand. Despite the Earth’s surface being primarily water-covered, only a small fraction is suitable for consumption or crop irrigation with the vast majority being salted ocean water. This makes desalination technology a crucial development in order to sustain our current rate of growth and industrialization, and a new graphene membrane may be just the breakthrough we need.

Currently, desalination is a more expensive option when compared with more traditional water sources like groundwater. However, as our water reserves continue to shrink, it will become an increasingly viable alternative making the present the right time to develop the appropriate technology. Indeed, the UN suggests that “water scarcity is among the main problems to be faced by many societies and the World in the XXIst century.” 

Most desalination strategies at present rely on the phenomenon of reverse osmosis. Osmosis is the natural tendency of the water to move from a region of high salt concentration to low salt concentration when the regions are separated by a semipermeable membrane; that is, a membrane through which the water can flow, but salt ions cannot. Reverse osmosis overcomes this process by adding an applied pressure greater than the osmotic pressure and in the opposing direction. Much current research effort is directed toward optimizing the semipermeable membrane for this task.

Graphene: an electron microscope image shows a graphene membrane. Image by materialesnano.com.Graphene: an electron microscope image shows a graphene membrane. Image by materialesnano.com.

Graphene, a new material discovered in the past decade, has attracted enormous attention for a variety of applications ranging from quantum computing and solar cells to smart phone screens and condoms, and garnered its discoverers a Nobel Prize in 2010.  Consisting of just a single layer of carbon atoms, it is as thin as a material can be while also maintaining remarkable strength – 150x that of steel – and flexibility. All of which make it an excellent candidate as a desalination membrane. New work reported this month has now shown that graphene punctured by nanoscale holes – those that can admit water while excluding salt ions – is indeed an efficient means of filtering seawater. In fact, the graphene nanopore film was able to achieve nearly 100% salt exclusion while also maintaining a higher rate of water passage than comparable technologies.

While further advances will be required to bring this technology up to an industrial scale, this proof-of-concept is a key first step in demonstrating that graphene is an ideal choice for a next generation of water desalination devices. And with a global water crisis a near inevitability, each developmental step is a vital one.