About 4 billion tires sit in landfills and junkyards around the world, according to the Tire Industry Project. From there, they leach many harmful chemicals and small microplastic pieces into the environment. Finding a way to recycle old tires is on many a scientist’s agenda.
Now, researchers at Dalhousie University in Canada have turned old tires into a material that produces clean water by harnessing solar energy. Their new floating device can purify over 3.5 liters of water a day, for only 0.86 per liter. What’s more, it also generates a small amount of electricity, the team reports in the journal iScience.
The low-cost device is a version of the well-known solar still. These devices use solar energy to evaporate water, which separates out the salt and impurities. The water vapor is condensed on a cold surface and then collected as pure water.
The Dalhousie researchers made a floating solar sill from a piece of foam. And then, to keep costs low, they made the key ingredient of their solar still from discarded tires. They ground tires into crumbs, which they heated to 500°C in the absence of oxygen. This converts them into a char made of fine carbon particles.
Next, the team mixed the char with titanium dioxide powder and processed it to make tiny titanium carbide nanoparticles. These particles are excellent at absorbing sunlight and turning it into heat. Previously, the team had studied various types of carbon waste, such as coffee grounds and lobster shells, to make the nanoparticles. But tire rubber works best, they found.
The researchers coated the tire-derived material on the foam. Finally, they covered the foam with a see-through plastic dome to make their solar sill.
When they placed the device on salty water, it wicked into the foam and evaporates on the surface by the titanium carbide material. The water vapor rises and condenses on the dome, from where it flows down the sides into a bag for collection.
“Most floating solar desalination research has been done only in controlled lab environments, with real-world studies remaining scarce,” the team writes in the paper. So they took their device out into the field.
They placed the device on the Atlantic Ocean off the Halifax harbor for five full days. The device converted solar energy to vapor with an efficiency of 40% at a calculated rate of 3.67 liters for each square meter each day.
The researchers say that they could modify the device to produce a small amount of electricity using a phenomenon called the thermoelectric effect. The electricity should be enough to power small water quality sensors. Next summer, the researchers plan to test the device further in South Asia.
Source: Margeson, M.J. et al. Refractory Plasmonic Material based Floating Solar Still for Simultaneous Desalination and Electricity Generation, ISCIENCE, 2024.
Image: ©Anthropocene Magazine
