"Solar steaming" is an eco-friendly form of water purification in which sunlight is used to heat tainted water, turning it to steam which condenses back into liquid. That clean liquid is then collected as drinking water. A new system offers improved performance, and it copies the structure of the rose flower.

Led by Assoc. Prof. Donglei (Emma) Fan, a team from The University of Texas at Austin started with round pieces of paper that were coated with a black polymer known as polypyrrole – it's particularly good at converting solar light into heat. Those papers were initially just placed flat on the ground in the sunlight, where they showed promise for solar steaming, although they weren't efficient enough for practical use.

Inspired by a book she had read called The Black Tulip, Fan proceeded to try placing multiple papers together in a rose petal-like arrangement, contained within a glass jar. Tainted water was then drawn up into them through a stem-like tube that extended down into a vessel below.

It was found that this setup allowed more sunlight to hit the polypyrrole, as light that wasn't absorbed by one paper got reflected onto another. Additionally, the surface area for water vapor dissipation was increased.

As a result, the rose-shaped solar steamer is now capable of producing over half a US gallon (1.9 liters) of purified water per hour, per square meter (10.7 sq ft) of material. Any heavy metals or bacteria present in polluted water get left behind when it turns to steam, along with any salt present in seawater.

The technology is cheap, too, as each structure costs less than two US cents to make. By contrast, the researchers state that other solar steaming systems tend to be costly, bulky, and produce comparatively small amounts of clean water.

"Our rational design and low-cost fabrication of 3D origami photothermal materials represents a first-of-its-kind portable low-pressure solar-steaming-collection system," says PhD candidate Weigu Li, lead author of a paper on the study. "This could inspire new paradigms of solar-steaming technologies in clean water production for individuals and homes."

The paper was recently published in the journal Advanced Materials.

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