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30% of the world’s population does not have access to clean, safe, and affordable drinking water. To tackle a growing water crisis, reduce stress on groundwater usage, and avoid expensive water imports, researchers are seeking a cheap and environmentally friendly way to sanitize domestic and industrial wastewater.

A laser-etched aluminum panel that can evaporate and purify water at greater than 100% efficiency could help solve the water crisis in drought-stricken regions and provide safe drinking water for U.S. soldiers in the field. 

A research team at the University of Rochester led by optics professor Chunlei Guo recently published a paper describing a new solar water purification technique made possible with laser etching.

A quadrillionth-of-a-second burst of laser pulses can etch the surface of a normal — cheap and plentiful — sheet of black aluminum into a “super-wicking, super-light-absorbing” (SWSA) material.

When the three-centimeter-square panel is placed in water at an angle facing the sun, a thin film of water is drawn upwards over the metal’s surface through open capillary channels, a bit like a synthetic tree. There, the water is quickly heated, evaporated, and collected while retaining more than 100% of the energy absorbed from the sun.

“This is a simple, durable, inexpensive way to address the global water crisis, especially in developing nations,” wrote Guo.

The panel has been used in lab conditions with the water collected in a glass box. It took two hours to gather 5 milliliters of purified water, so the process will require scaling up to purify worthwhile volumes. Making the panels double-sided would further improve efficiency.

Why not just use the power of the sun to boil water for purification? While this would eliminate microbial pathogens, boiling will not eliminate heavy metals and other contaminants like detergent, urine, and glycerin.

To reduce contaminants, it is necessary to evaporate the water, then condense and collect it. Doing so will leave nearly all impurities behind and decrease the level of contaminants to well below the WHO and EPA standards for drinkable water.

The etched-aluminum panel technique has two advantages over the other main methods of solar-based water evaporation: volume heating and interfacial heating.

Firstly, it is much more energy-efficient, as only the water drawn up through the channels is heated, and the angle of the panel can be continually adjusted to directly face the sun. Secondly, other wicking materials become clogged with contaminants left behind, which requires frequent replacement, whereas the panel’s open channels are easy to clean.

The cheap, plentiful nature of aluminum means it is available all over the world and could be a valuable tool in tackling chronic water shortages in developing countries. The sheets can be combined with existing solar-panel tracking systems to bolster their effectiveness and could also be useful for water desalinization projects. 

U.S. soldiers have carried iodine tablets for decades, but Army researchers are interested in reducing the amount of water soldiers have to carry by giving them the ability to generate and purify water in situ.

Guo’s laser etching technology has also been used to create super-water-repellent, super-water-attracting, and super-energy-absorbing materials, as well as metallic structures that can never sink no matter how punctured they are. The process can also be used to change the color of a range of metals.

This research was supported by the U.S. Army Research Office, the National Science Foundation Partnership for Innovation Grant, and the Bill & Melinda Gates Foundation.

Image Credit: L Jones / Shutterstock

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