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News | PlasCarb

Solar-Powered Graphene Evaporator Zaps Dirty Water … With Bacteria

The pesky bacteria Gluconacetobacter hansenii is known to oenophiles for its ability to turn wine into vinegar, but it looks like the little guy is ready for a star turn in the sparkling green world of the future. A team of researchers based at Missouri’s Washington University in St. Louis has figured out how to combine solar power, graphene, and Gluconacetobacter into one radically simple water purification system.

Graphene To The Rescue

Graphene is a one atom thick, superstrong material with unique electronic properties. It has captured the interest of clean tech researchers around the world ever since its discovery in 2004, especially when it comes to solar power and energy storage.

As researchers dig deeper into the mysteries of this unique material, new properties keep emerging. A thin membrane based on graphene, for example, makes a powerful barrier against gasses and vapors, but it will allow water to pass through.

One recent example is a seawater desalination system from the folks over at Oak Ridge National Laboratory, which deploys a graphene membrane tailored with nanoscale pores.

Over at the University of Manchester they’re working on a similar concept. Researchers there have created a graphene based “mesh” that could lead to a small-scale, rapid, hand-pumped water desalination system.

Graphene + Solar Power … And Biofoam, Too

If you caught that thing about hand pumping, you’re on to something. Conventional water purification and desalination systems based on membranes are expensive, partly because they suck up a lot of energy. That makes tackling water scarcity issues in energy-scarce regions a formidable task.

Add poverty to the mix and you’ve got the perfect recipe for an unhealthy, inadequate water supply.

Hand-powered membrane systems can provide a workaround, and renewable energy is also emerging as a relatively inexpensive option.

The Washington University team found a solution by tacking entirely away from membrane-based systems. Instead, they leveraged graphene to set solar power to work on evaporation.

You can get all the details on the new graphene/solar device from the journal Advanced Materials, but for those of you on the go here’s the rundown from the research team:

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.

Simple, right?

In addition to solar power, the new system leverages biofoam. That’s an emerging nanoscale, foam-like cellulose fiber produced naturally by certain bacteria such as Gluconacetobacter hansenii.

All you have to do is take a layer of bacterial nanocellulose tricked out with graphene oxide, and put it on top of another layer of pure nanocellulose to form one combined sheet. Then set that sheet on top of some dirty water, sit back, and watch the action.

The spongy layer underneath absorbs the dirty water and draws it up to the graphene oxide layer, where it quickly evaporates due to the high temperature engineered by graphene:

Light radiates on top of it, and it converts into heat because of the graphene oxide — but the heat dissipation to the bulk water underneath is minimized by the pristine nanocellulose layer. You don’t want to waste the heat; you want to confine the heat to the top layer where the evaporation is actually happening.

As for cost, biofoam is lightweight and relatively low cost, and apparently graphene oxide has come down in price. The team has also developed a scalable, low-cost method for introducing graphene oxide into biofoam, in tandem with the bacterial action that creates the foam.

Next steps for the research team include tailoring the bacterial synthesis process to incorporate water-purifying materials directly into the biofoam, so stay tuned.

Image: via Washington University in St. Louis.

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