04/14/2017

A Water Widget For The World’s Driest Places

7:37 minutes

Photo by Public Domain Photography/flickr/CC BY-SA 2.0

People in the United States don’t worry about having enough water. It’s in the ground, coming out of your faucet, or bottled in the refrigerator at the grocery store. But for people living in the hottest, driest climates on the planet, water is a scarce resource.

[A few key tips to keep your drinking water clean.]

In a study published in the journal Science this week, engineers at MIT describe a device that can extract three liters of water vapor from the air in conditions as low as 20 percent humidity. Evelyn Wang, Associate Professor of Mechanical Engineering at MIT, joins Science Friday to talk about how the new water widget uses a new technology—metal organic frameworks—to harvest water from dry air using very little energy.


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Segment Guests

Evelyn Wang

Evelyn Wang is an associate professor of Mechanical Engineering at the Massachusetts Institute of Technology in Cambridge, Massachusetts.

Segment Transcript

IRA FLATOW: This is Science Friday. I’m Ira Flatow. Water, it’s the one thing they’re not making any more of. Fresh water is precious, so people are always looking for novel ways of finding fresh water. And now, scientists at MIT have designed a device that can extract three liters of water vapor from the air, even really, sort of, dry air, Humidity as low as 20%.

And it uses the climate’s most abundant resource to do it, the sun. Wow. Joining us to talk about her new water widget is Dr. Evelyn Wang, Associate Professor of mechanical engineering at MIT. Welcome to Science Friday Dr. Wang.

DR. EVELYN WANG: Hi, Ira. Thanks a lot.

IRA FLATOW: You’re welcome, and can you give us a little thumbnail sketch of how your device works, even in such low humidity conditions?

DR. EVELYN WANG: Sure, the device works based on a really special material called a metal-organic framework. And that has been developed by my collaborator at UC Berkeley, Professor Omar Yaghi. And the key to this material is the fact that it can capture a lot of water from the air. And so you can tailor these types of materials in that way, such that it can really soak up a lot of that water. And the key then is once you capture the water with this material, then how do you actually extract it from that and then make it into the drinking water? And the way we–

IRA FLATOW: I’m sorry, go ahead. No, I was going to ask you, why the water vapor is attracted to the material to begin with?

DR. EVELYN WANG: Right. It has a lot of special, kind of, features of the material itself. First of all, it’s kind of this three-dimensional porous type framework. And the way design these materials, in particular this one, has these zirconium metal clusters with these organic linkers, and it creates this kind of very porous metal frame– this framework that has a lot of surface area. That particularly attracts the water molecules and doesn’t attract as well, say CO2.

And this way, it’s really great in terms of soaking up or capturing the water. However, an important part is then releasing also this water. There are a lot of materials that are really good at capturing water and a lot of that water. However, this material is also nicely tailored, such that you can release the water relatively easily with very little energy and at low temperatures. And that’s why we can use the sunlight in this case to do that. To be able to now extract the water, and then now then condense it back from the vapor to the liquid phase in this particular device.

IRA FLATOW: What does the sunlight do? We’re not thinking of a solar cell here making electricity, are we?

DR. EVELYN WANG: No, in this case, we’re thinking more of like a solar thermal type process. So in fact, the sun is allowing you to heat up this material. And typically, when you think about how much sunlight there is, it can’t heat up material that much. But that’s enough, in particular for this material, to now release the water molecules from the surface, and then allow it to condense with a condenser design.

IRA FLATOW: So how big is this? Is it bigger than a breadbox, as we’ve said? Looks like about the size of a breadbox.

DR. EVELYN WANG: It is about, I would say, that’s exactly the size of our prototype right now. It’s kind of more of a proof-of-concept type prototype, in that this kind of approach to harvesting water can work.

IRA FLATOW: How much water can it harvest?

DR. EVELYN WANG: So this device, I would say, is not something in terms of large quantities. So because the amount of material we use is about a gram-type scale, so you can imagine that based on the numbers, it’s only a fraction of a gram type water. But when we’re thinking about really creating an actual practical device, as you mentioned these numbers of about three liters per day, we can start to think about actually incorporating many layers of this type of material into a more practical type configuration. And such that you can in fact extract a reasonable amount of water, say about three liters per day in a typical size scale, as you suggest of like say a breadbox.

IRA FLATOW: Wow. How common are a 20% humidity environments in the areas that need better sources of drinking water?

DR. EVELYN WANG: So we’ve looked at the world map, and you can see that in fact, there are many regions in say Africa, as well as India. There are a lot of arid-type conditions all over the map that really we’re trying to target the type of technology– where there is also abundant sun.

And in a lot of these regions, obviously, the infrastructure is very limited. So there aren’t really many approaches that can really address the water scarcity problem. And really, the opportunity that we have with our technology is the fact that it can be completely passive. So as long as we have sunlight, and we have this material in this kind of designed device, we can now have clean drinking water.

IRA FLATOW: Have you gone out and tested it in the desert yet?

DR. EVELYN WANG: We have not. In fact, that has been really our next target. It’s really taking our prototype out now and going to different target areas within the US, as well as elsewhere around the world, that really could benefit from this kind of technology.

IRA FLATOW: All right, so who’s got the patent on this one? And who’s going to buy the patent or work with you on that?

DR. EVELYN WANG: That’s a good question. So the materials are very special, and the material patents belong to my collaborator at Berkeley, Omar Yaghi. And we have a patent for the design of the types of devices that you can make from using these materials. So–

IRA FLATOW: So it’s all different. It’s not just that little breadbox. You could come up with all kinds of different designs for this.

DR. EVELYN WANG: That’s right. And I think there is a lot of kind of nuances to be able to maximize the kind of output of the water that you want. And so, for example, we have these special materials, but they’re incorporated into a matrix that’s made of a metal. So it’s actually a copper foam matrix that we have this material in.

The reason we do that is because an important part of this is in fact the heat transport. Because when we shine the sun on this material, the material itself, the metal-organic framework has a relatively low thermoconnectivity. And so you can have a pretty large temperature gradient across the material. And so it takes a lot longer to be able to remove the water molecules and to actually be able to then collect it in the form of liquid.

And so by incorporating this kind of metal matrix within it then enhances the overall kind of heat transfer processes, such that it could more easily, kind of, remove the water. And we can design the kind of the geometries of the layers, such that we can maximize that kind of extraction process of the water.

IRA FLATOW: So when might we see the first one out there ready?

DR. EVELYN WANG: We hope that we can see really like more of a real practical device in the next couple years or so. That’s what we are aiming for. So we’re really hoping whether we take this technology out as a start-up, or we work with other kind of companies that can help us kind of take it to the market and to really make it a product. That’s what we’re hoping.

IRA FLATOW: Well, good luck. Good luck to you, and we’ll wait to get the first one online somewhere.

DR. EVELYN WANG: Great. Thanks a lot, Ira.

IRA FLATOW: Dr. Evelyn Wang, Associate Professor of mechanical engineering at MIT.

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