NEW DRINKING WATER FROM THE SEA

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Sunlight-powered sponge turns seawater into freshwater

A new aerogel from Hong Kong scientists could make clean water from the ocean using only sunlight
by Kurt Knutsson October 23, 2025

Researchers from The Hong Kong Polytechnic University have created a new material that could change how we make clean water. Their sponge-like aerogel turns seawater into drinkable freshwater using only sunlight and a simple plastic cover. It needs no electricity or complex filters. This breakthrough points to a sustainable path for low-energy desalination, one of the toughest challenges in solving global water scarcity.

 
Credit: Hong Kong Polytechnic University

 
Why this sunlight sponge innovation matters

Most of Earth’s water is locked in oceans and seas, too salty for human use. Traditional desalination plants rely on energy-intensive systems that require costly infrastructure and the use of fossil fuels. With billions of people projected to face water shortages by 2050, the search for a clean, affordable desalination method has become urgent. The Hong Kong team’s aerogel may be that answer. It captures solar energy to evaporate seawater, leaving salt behind. The condensed vapor becomes pure, drinkable water, and it all happens naturally under sunlight.
SEM images of (a) RFC aerogel and (b) UFC aerogel.

Credit: Hong Kong Polytechnic University

 
How this sunlight sponge works

Led by Xi Shen, the researchers mixed carbon nanotubes and cellulose nanofibers to create a paste. They used 3D printing on a frozen surface to form vertical holes only 20 micrometers wide, smaller than a human hair. These microchannels help move water vapor efficiently through the material. Unlike squishy hydrogels used in other water filters, this aerogel is rigid, lightweight, and packed with solid pores. Those features make it ideal for soaking up sunlight and speeding evaporation. Even better, the material performs consistently at any size, from a tiny 1-centimeter square to a full 8-centimeter panel, making it easy to scale for real-world use.
Digital photographs of custom-made solar-driven evaporation system, watercollecting device, and the AFP aerogel lattice in the device.

Credit: Hong Kong Polytechnic University

 
 
Real-world testing of the sunlight sponge

To test it outdoors, researchers placed the aerogel on seawater, covered it with a curved plastic lid, and let the sun take over. The heat from sunlight evaporated the water, while the plastic lid trapped and condensed the vapor. After six hours, they collected about three tablespoons of drinkable water, a small but promising proof of concept.

According to Shen, “Our aerogel allows full-capacity desalination at any size, providing a simple, scalable solution for energy-free desalination to produce clean water.”
Digital photographs of a large-size AFP aerogel lattice (L = 0.22 m) and asmaller sample (L = 0.08 m) tested under the same outdoor conditions for 4 hours from 11:00 am to 15:00 pm (23 May 2025, Hong Kong, China).

Credit: Hong Kong Polytechnic University

 
What this means for you

If scaled successfully, this technology could make off-grid clean water possible for coastal and island communities that struggle with drought or contamination. It could also reduce reliance on expensive desalination plants that burn fossil fuels and harm marine ecosystems. Imagine keeping a small, sunlight-powered water purifier on a boat, at a campsite, or in disaster zones, where access to clean water can mean the difference between survival and disaster.

 

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Kurt’s key takeaways

This solar-powered aerogel represents a hopeful step toward solving one of humanity’s most pressing problems: freshwater scarcity. By harnessing the power of the sun, this technology could one day make sustainable, low-cost desalination accessible to millions of people.
 

If sunlight could provide all the fresh water your community needed, how might that change the future of global water access? Let us know in the comments below. 

https://www.polyu.edu.hk/en/risud/news-and-events/events/2019/3/3/[code]
	[code]https://www.polyu.edu.hk/risud/search-result/?query=sunlight+sponge+innovation

https://www.polyu.edu.hk/en/kteo/knowledge-transfer/innovations-and-technologies/technology-search/2-construction-and-environmental-technology/2_ap_02_0918/