New Research Found a Way to Get Clean Water Via Solar-Powered Gel Filters

Us who are living in some parts of the world don’t think about water too much and almost take it for granted. But we know that in many other parts of the world, millions of people can’t have access to clean water that easily.

Moreover, climate change has also made it worse, as the change of the environment affects the quality of drinking water.

Researchers at Princeton University have developed a potential solution that works like a sponge, soaking up clean water, while at the same time not taking contaminants along. Should the researchers be able to produce this at a large scale and economically, it may help a lot of people in need of clean water across the globe.

The “sponge” takes the form of a gel that’s low-cost, user friendly, and solar powered. Yep, it needs only sunlight to filter many types of pollutants like heavy metals, oils, microplastics, and some bacteria from water.

Compared to the first generation of similar technology developed in 2021, this gel could filter almost four times better. A simple square meter of the sponge-like material can produce more than a gallon of water in 10 minutes.

According to Rodney Priestley, Dean of the Graduate School, Pomeroy and Betty Perry Smith Professor of Chemical and Biological Engineering, many previous developments and efforts have created devices using solar energy with the same results. However, they don’t all produce enough water to meet daily needs.

“This latest iteration of our technology gets us another step closer towards the goal of having a technology driven by solar energy that can actually produce enough clean water to meet daily demand,” Priestley said.


The decline of forests and its effect on water quality

As mentioned, climate change has made it more challenging for forests to grow. Heat waves, drought, floods, and forest fires have pushed forest dieback further.

According to a study from Helmholtz Centre for Environmental Research (UFZ) that assessed Rappbode reservoir in the eastern Harz region, the catchment area has lost over 50% of its forest and it will impact drinking water reservoir negatively.

If this continues, people who need clean water in different parts of the world with forest loss may meet more water scarcity in the future.

Forests are vital in the water cycle: they filter water and bind nutrients—all are needed for good water quality.

When there are only a few nutrients in the reservoir water, the water is better for drinking because it makes it more difficult for algae to grow. And in turn, it’s easier and more cost-effective to treat water in the waterworks.

You can imagine if Harz, a region in a well-developed country, can suffer from declining water quality due to forest loss, what will happen to the ones that lack proper forest management? Or areas which water has been contaminated or unreliable?

Although this gel is not a cure-for-all, it’s a new development that will be a good step to give more people their daily clean water, particularly in off-grid areas.


Photo of Rappbode reservoir, Harz. Photo by Kora27 Wikimedia Commons


Sponge-like gel

The gel is made from a polymer known as poly(N-isopropylacrylamide) or PNIPAm that can absorb or release water depending on the temperature. Below 33C (91F), the material absorbs water from a source (lake, for instance). When it’s removed from water and the sun heats it up to a temperature above 33C, it releases the water.

When polydopamine (PDA) is added to the gel’s surface, this gel then filters all the contaminants mentioned previously.

Per the researchers, the gel is simpler to use and less expensive than current systems which rely on evaporation. Users only need to toss the device in a water source, let it be filled with water, remove it from water, let it toast somewhere, and wait for it to release filtered water.

First author Xiaohui Xu said, “Our first solar absorber gel already had strong performance. But we wanted to continue making the device even more efficient at filtering water.”

Xu added that the gel’s ability to filter more (and at a faster rate) came from changes that the team made to the hydrogel’s structure between the first and second generations that enhanced its ability to transport water.

Although the first and second generation are made from the same PNIPAm hydrogel, the team discovered that they could change the gel to have a more interconnected, fibrous structure. Xu compared the structure of the new gel to that of a mature loofah-fruit.


Complete with anti-fouling properties

Co-author Néhémie Guillomaitre added that increased filtration capability and speed aren’t the only improvements from the second-generation gel.

For instance, not just adding new structures, the researchers added anti-fouling properties to the gel by adding another type of polymer called poly(sulfobetaine methacrylate) (PSBMA) to the surface of the gel.

Therefore, the material won’t only filter contaminants more efficiently. It’s also able to form a hydration layer that repels oil and bacteria. The device is then able to self-clean.

“Having anti-fouling properties helps the gel last longer. There is less of a need to worry about oils and bacterial films accumulating on the gel’s surface over time and lowering its efficiency,” Guillomaitre said.

Combined with the cost-effectiveness of this material (as the researchers claimed), surely this gel is a good alternative to get clean water. The researchers believe that their new development could scale to become an attractive option for water purification in off-grid regions.

Guillomaitre added, “Ideally, this technology could one day be used by anyone concerned about their water quality, regardless of where they live.”



What happens after the innovation?

The Princeton researchers stated that they’re still in the process of creating prototypes to demonstrate their device so that it can be scaled to household use.

Priestley believes that the team plans to further develop the water purification gel which could be used in emergency situations to provide on-demand access to clean water.

Additionally, the research has received support from the National Science Foundation to launch a startup called AquaPao which will improve the design of the solar absorber gel, test its long-term durability, and identify opportunities to scale up the technology.

“This work is a wonderful example of how academic research can be translated into the startup world. Through our work, we have been able to show that fundamental research may have significant impact on society,” said Priestley, who is also the co-founder of AquaPao.



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