An ingenious off-grid water purifier inspired by pufferfish doesn’t just work in sunlight

Clean water is already a scarce resource in many parts of the world, and this shortage should worsen with climate change. In a new study, researchers report a simple, sustainable technology for producing drinking water from polluted sources. They made a sponge-like gel that can purify dirty water using only sunlight. Their inspiration? Fish buffers, which are filled with water when they sense danger and let the water blow into its original form.

Over a billion people worldwide do not have access to safe drinking water, and every year two million people, mostly children, die from diarrhea. By 2025, the World Health Organization predicts that half of the world’s population could face water scarcity.

“The solution to the problem of water scarcity must be environmentally sound and must not result in a further burden on the availability of clean water,” write Princeton University chemistry and biology engineer Rodney Priestley and colleagues.

They developed a spongy material like jelly, called a hydrogel. These gels retain water in the spaces created between long tangled rows of polymers. Researchers have chosen one that is elastic and reacts to heat: when heated, it turns from a water-loving material into a water-repellent one, squeezing it out. They added a layer of melanin-based molecule to this gel, which can absorb solar energy, and also has the ability to remove heavy metals and organic dyes by chemical binding. Finally, the third final layer is made of filter material that retains impurities and pathogens.

The researchers tested the gel by putting it in cold water from a nearby lake for an hour. The gel swelled absorbing clean water, leaving behind pathogens, salts, oils and all heavy metals. They then took it out of the water and placed it in a container in direct sunlight. As it warmed up and reached a critical temperature of 34 ° C, it released clean water. The team published their work in a journal Advanced materials.

Solar water purification techniques already exist, but they rely on the evaporation of sunlight water. But since the new purification mechanism does not require water evaporation, which is an energy-intensive process, the highest recorded speed of solar water purification.

“For me, the most exciting thing about this work is that it can work completely offline, both on a large and a small scale,” Priestley said in a press release. “It could also work in the developed world in locations where water purification is needed at no cost, without plant.”

Source: Xiaohui Xu et al. Bioinspired elastic hydrogel for solar water purification. Advanced materials, 2021.

Image: Saspotato / flickr