Graphene is a layer of carbon atoms, one atom thick, arranged as a hexagonal sheet. It very quickly revealed itself as the most exceptional material known in terms of strength, electrical conductivity and optical properties, plus quite a few that only physicists have ever heard of.
Surely this staggeringly gifted substance could be put to use? The first idea was that graphene would replace silicon as the power behind IT. But there was a problem: graphene lacks the bandgap that allows silicon to switch billions of bits of information in a nanosecond. Electronic graphene-based devices have been made as small-scale lab demonstrations but its killer app has yet to emerge.
But perhaps the wait will soon be over? André Geim’s approach to doing science is famously screwball. His track record includes levitating frogs in diamagnetic fields (both as a wacky thing to do – no frogs are harmed in this experiment – and as a demonstration of the power of magnetism in areas you might not have thought susceptible) and sticking a model spider man to the ceiling with a dry synthetic tape derived from the principle of the gecko’s foot.
To sustain the spirit of such free-floating enquiry, Geim’s team hold off-piste Friday evening meetings, one of which a few years ago they enlivened with a particularly strong and pure vodka produced using yet another of graphene’s amazing properties. Strictly this wasn’t graphene but its cousin, graphene oxide. It has the same hexagonal structure as graphene but the attached oxygen atoms give it some unusual properties when water is around. Graphene itself, although only one atom thick, is completely impermeable to other molecules. Not even helium can get through a graphene membrane. But graphene oxide can allow water molecules through, in a super-slippery way that researchers are still trying to understand, whilst holding back everything else. So vodka can be “distilled” through graphene oxide to increase its strength.
The Friday Meeting trick instantly suggested a serious application. A substance with graphene oxide’s extreme filtration properties could surely be used in industrial processes: cleaning up wastewaters, for instance and, above all, desalination – the possible saviour of a world running out of water.
Desalination already exists as a viable if expensive technology. In less than a decade since the introduction of large-scale desalination in Israel, 40 percent of its water now comes from the sea. But the economics of desalination are fiendish: having reached that landmark, Israel has recently experienced two wet years and the expensive desalination plants are being run at only 70% capacity. It might be wise, though, to retain a high capacity through apparently wet years as insurance. In any case, as a world leader in desalination, Israel exports the technology and, with climate change increasing its grip, there is always going to be somewhere in dire need.
California currently looks to be the likeliest market. The State of California, with its 38 million people, has always had a problem with water supply. Many thought it folly to build the city of Los Angeles in the first place and all sorts of skulduggery were employed to keep it lubricated. Now with global warming expected to further dry out the arid southwest of North America and the state currently struggling with a three-year drought that has left some communities within months of a total loss of water supply, California might be in need of a miracle. And so the Israeli firm IDE is currently building the biggest desalination plant in the USA: a $1 billion facility at Carlsbad, San Diego. Soberingly, large though this is, it will supply only 7 % of San Diego’s water.
The point about graphene desalination technologies is that they could be significantly cheaper and more efficient than the existing reverse osmosis plants. One of the giant Californian aerospace companies, Lockheed Martin, has already patented a graphene reverse osmosis filter called Perforene. This is the original graphene itself with many engineered perforations to allow the water through. But punching holes in graphene is not as elegant as, and is likely to be more expensive than, graphene oxide technology. In a recent paper in Science, the Manchester team describes their latest work with graphene oxide. Instead of punching holes in graphene they use several layers of graphene oxide to fine tune the permeability of the membrane.
No doubt there will be many more contenders before a mature technology emerges but no one can now say that graphene is a solution looking for a problem (as some hard-headed venture capitalists have alleged): indeed it could be the answer to the age-old problem of a real, physical solution: the 97 % of the water on the planet that is useless for drinking water and irrigation – sea water. Solving this will not as much fun as vodka at the Friday Meetings but it could be a matter of life or death for the world’s arid regions.
You can read more about graphene, graphene oxide and desalination in my new book, with sculptor Tom Grimsey, Nanoscience: Giants of the Infinitesimal (Papadakis), published on May 7th.