Sieving water out of air
Two thirds of the world’s population are experiencing water shortages, despite an estimated 13 trillion litres of water hovering around us in the atmosphere. But is there a cheap and effective way to get hold of it? MIT’s Evelyn Wang thinks so, and she’s developed a device based on clever molecular sieves - called metal organic frameworks or MOFs - to do it. Izzie Clarke heard how it works.
Evelyn - Our device allows us to capture water from air, and the way it does it is using this special material a metal organic framework that acts like a sponge, absorbs a lot of this water into the pores of the material, and then releases it when we apply a small amount of heat using the sun.
Izzie - How does that metal organic framework actually capture the water?
Evelyn - It is a device that is basically a box that opens up and so exposes this metal organic framework to the environment. The metal organic framework can capture even very small amounts of water in the air down to humidity ranges of about 20%, which are in these very arid conditions such as desert areas where there is a significant shortage of water. Then it’s being able to get the water out of the material and to make it into the liquid form.
Izzie - So how do you do that?
Evelyn - We close the door of the device, and so now the material’s confined such that we can heat up the material and then releases the vapour into this local environment that is very humid. Because we’re releasing more of the water vapour into this box and then we can now easily condense it using a condenser from the vapour to the liquid form.
Izzie - How is that being powered; it sounds quite energy consuming?
Evelyn - It’s a completely passive process, and because the material is tailored in a way to allow for easy release of the water at relatively low temperatures, we can use the sunlight. Then in the condensation process itself, it’s also passive because we’ve created this local high relative humidity environments such that the condensation temperature can be near to ambient.
Izzie - How much water can this metal organic framework capture and produce?
Evelyn - This particular MOF 801 can capture about 25% of its weight in water. Right now we anticipate, even with this amount of water capture, we can achieve a device that’s about 30 litres in size or so - about the size of a carryon suitcase, maybe a little bit smaller than that, which can deliver about 12-15 litres of drinking water each day.
Izzie - So what does that mean for environments that are suffering severe drought and water loss?
Evelyn - We think that this can be an important technology to be able to now address problems in those regions where there really isn’t a lot of infrastructure other than the Sun, and often they’re in a very arid climates. So we hope that we can start to deploy this technology to those regions to really be able to give all these people clean drinking water. Right now we’ve demonstrated a single layer of this metal organic framework in this prototype where we want to start now to integrate a few stacks of these layers such that it can produce more significant amounts of water. The second is working with collaborators who have really been the experts in the chemistry and in the development of the materials is being able to now scale up these materials, such that we can have larger quantities of them to be able to them mass produce many devices.