There is perhaps no greater humanitarian potential in graphene than its ability to filter water. What, for instance, could be more compelling than the prospect of a graphene drinking straw that removes the impurities in water and produces crystal clear refreshment in the remotest of locations? Surely such a possibility shows us, in as stark and as matter a fact a way as possible, why every pound of the British government’s recent pledge of support for the industry is worthy of applause. Yet, as you may have come to expect, the story of graphene’s world changing potential does not end there.
The filtration potential of graphene first came to the world’s attention during the middle of last year when David Cohen-Tanugi and Jeffrey Grossman reported the use of nanoporous graphene to filter salt ions from seawater. Reverse osmosis, up till then the most effective method of removing salt ions, was shown to be 2-3 times slower at desalination than the graphene alternative. Graphene was also shown to require less energy input and to provide the potential of smaller desalination modules; improvements in functionality that made graphene an almost certain replacement for the old technology.
It is never plain sailing when it comes to new scientific discoveries and some challenges remain that make the use of nanoporous graphene in desalination currently not viable. The first difficulty is in achieving the structure of nanopore size distribution required for the task; but, unsurprisingly when the benefits are so clearly arrayed, research to improve the fabrication of highly ordered nanoporous graphene is currently being undertaken. The second of the challenges faced by anyone wishing to commercialise graphene as a desalination product is the stability of nanoporous graphene under applied pressure. Hope of a solution with respect to this second difficulty may lie in the use of a thin-film support layer similar to those currently used in the RO technique.
So, difficult as it may be for some, we will have to wait longer for those life saving straws than we had hoped. What matters though is the proof of concept that Tanugi and Grossman’s work has provided. And in the world of innovation proof of concept is what gains researchers further funding.
Updating the story of graphene’s use in water purification brings us to the latest piece of research from a collaboration between Rice University and Lomonosov Moscow State University. The work currently revealed in the Royal Society of Chemistry journal Physical Chemistry Chemical Physics places graphene oxide at the forefront of our attempts to decontaminate radioactive sites. Graphene oxide, it has been shown, is an excellent binder that clumps radionuclides into solids that can be removed by filtration.
James Tour from the research team at Rice University has suggested that the discovery paves the way for the use of graphene at sites like the Fukushima nuclear plant and at fracking sites where radioactive materials are brought up inadvertently. The current solution employed in the fracking process is simply storage of the contaminated water, however, the graphene oxide solution seems to promise a leaner and more efficient means of capture and disposal.
Where nuclear waste is concerned graphene oxide is also thought to have the potential to be faster acting, meaning that the risk of seepage and further contamination of clean water supplies is reduced.
“Graphene oxide introduced to simulated wastes coagulated within minutes, quickly clumping the worst toxins. The high retention properties are not surprising to us, but what is astonishing is the very fast kinetics of sorption, which is key,” said chemist Stepan Kalmykov.
The researchers showed how plutonium, uranium and radioactive isotopes from the lanthanide and actinide group of elements – the 30 rare earth elements in the periodic table – could be easily removed from contaminated water. It should be noted that the process does not render the resultant clumps non-radioactive, but it does provide a valuable means of dealing with nuclear spillage and contamination.
“Where you have huge pools of radioactive material, like at Fukushima, you add graphene oxide and get back a solid material from what were just ions in a solution,” he said. “Then you can skim it off and burn it. Graphene oxide burns very rapidly and leaves a cake of radioactive material you can then reuse.”
What’s more the researchers believe that the findings could be of benefit to the mining industry where the extraction of rare earth materials has all but been stopped.
Environmental requirements have “essentially shut down U.S. mining of rare earth metals, which are needed for cell phones,” Tour said. “China owns the market because they’re not subject to the same environmental standards. So if this technology offers the chance to revive mining here, it could be huge.”