Science

Graphene-based sheets make dirty water drinkable simply and cheaply

A new system of bi-layered biofoam may provide the means to purify vast bodies of water simply by overlaying them with sheets of this new material
A new system of bi-layered biofoam may provide the means to purify vast bodies of water simply by overlaying them with sheets of this new material
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A new system of bi-layered biofoam may provide the means to purify vast bodies of water simply by overlaying them with sheets of this new material
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A new system of bi-layered biofoam may provide the means to purify vast bodies of water simply by overlaying them with sheets of this new material

Engineers at the Washington University in St. Louis (WUSTL) have developed graphene-based biofoam sheets that can be laid on dirty or salty dams and ponds to produce clean drinking water, using the power of the sun. This new technique could be a cheap and simple way to help provide fresh water in countries where large areas of water are contaminated with suspended particles of dirt and other floating matter.

The biofilm is created as a two-layered structure consisting of two nanocellulose layers produced by bacteria. The lower layer contains pristine cellulose, while the top layer also contains graphene oxide, which absorbs sunlight and produces heat. The system works by drawing up water from underneath like a sponge where it then evaporates in the topmost layer, leaving behind any suspended particulates or salts. Fresh water then condenses on the top, where it can be drawn off and used.

"The process is extremely simple," said Srikanth Singamaneni, associate professor of mechanical engineering and materials at WUSTL. "The beauty is that the nanoscale cellulose fiber network produced by bacteria has excellent ability to move the water from the bulk to the evaporative surface while minimizing the heat coming down, and the entire thing is produced in one shot."

Whilst this is a novel use of graphene, the researchers claim that the process used to make their bi-layered biofoam is actually the most innovative part of the whole experiment. Analogous to the process an oyster uses to create a pearl, where a small kernel of material is continually overlaid with layers of a fluid coating that eventually hardens, the bacteria used in the new material produces layers of nanocellulose fibers peppered with particles of graphene oxide flakes.

"While we are culturing the bacteria for the cellulose, we added the graphene oxide flakes into the medium itself," said Qisheng Jiang, a graduate student at WUSTL. "The graphene oxide becomes embedded as the bacteria produces the cellulose. At a certain point along the process, we stop, remove the medium with the graphene oxide and reintroduce fresh medium. That produces the next layer of our foam. The interface is very strong; mechanically, it is quite robust."

The researchers also claim that the material is exceptionally light, cheap to make, and can easily be produced in vast quantities. And, unlike even exceptionally simple systems designed to do similar things, the graphene biofoam material is simply laid over a body of water and does not require systems of pipes or energy to run the water through for decontamination.

"Cellulose can be produced on a massive scale," said Singamaneni. "And graphene oxide is extremely cheap — people can produce tons, truly tons, of it. Both materials going into this are highly scalable. So one can imagine making huge sheets of the biofoam."

The production system used to create the biofoam also has the ability to include other nanostructure materials that destroy bacteria and clean the water more thoroughly, allowing it to produce safe drinking water from almost any source.

"We hope that for countries where there is ample sunlight, such as India, you'll be able to take some dirty water, evaporate it using our material, and collect fresh water," said Singamaneni.

The results of this research were recently published in the journal Advanced Materials.

Source: Washington University in St.Louis

12 comments
SarvdeepSingh
Let's' clean up the water in the environment & oceans first ... With such wonderful Tech ... Leave a clean legacy !
Nik
Doesn't simple solar evaporation do the same? The water vapour will need something to condense it, what will that be? How would one collect the condensed vapour from a flat sheet?
Mzungu_Mkubwa
But how is the fresh water collected? It is certainly not made clear and I'm having trouble imagining any viable method. Maybe I just get down there and slurp it off with my drinking straw, knee deep in the miry bog that's my water source?
ThomasH
Has graphene actually delivered on any of it's promises yet? It seems like we've been hearing for years and years all of the things it can do cheaply and effectively. That it's going to revolutionize tech. But is there a single example of it actually being used in the real world? If so, I'd love to learn about it.
lon4
Is this really a high tech solar still, the fresh water collected as a condensate? The graphic seems to suggest water vapor, but the writer offers no explanation.
Agamemnon
Crux#1: 'dry' graphene oxide. Crux #2: mutations of active bacteria due to E. coli & their ilk. I hate nay-say thoughts, but still ....
HenryFarkas
You don't need a graphene and cellulose bilayer. Just leave it out of the thing that's using solar energy to distill water. The water will still evaporate. The water vapor will still condense on whatever surface is cool enough to make the water condense, and you still end up with distilled water. All the salt and other contaminants, other than volatile contaminants, will stay in the pond whether you put the graphene and cellulose sheet on top or not.
StWils
Have you tried to see how well this foam can desalinate sea water? How tolerant is this of contamination and when the pores are filled with debris can it be flushed or backwashed effectively? As this gets to a demonstration plant level of development one excellent test application would be to separate water at Fukushima Daichi. Tepco has absolutely thousands of gallons of contaminated water flushed through the damaged nuclear power plants. Right now Tepco has just been building and filling large tanks as rapidly as possible. It would be a lot better if Tepco could filtre the contaminated water well enough to return it to the sea.
Kenfrost
What is the clean water production rate per square foot of membrane per hour of sunshine? Is the purification of sea water possible with this membrane?
GopalakrishnanHari
A video clip could have helped better understanding. Any sample available for trials ?