Over two billion people worldwide do not have consistent access to safe drinking water. And one possible method for satisfying that requirement functions similarly to a sponge, absorbing clean water while leaving impurities behind.
Princeton University researchers have created the next generation of their solar absorber gel technology, a gadget that might help people all around the world have access to clean water. The sponge-like gel is low-cost and simple to use, requiring just sunlight to filter contaminants from water such as heavy metals, oils, microplastics, and certain microorganisms, making it an option for off-grid water filtration.
The gadget has almost four times the filtration rate of the first-generation technology, which was created in 2021. A square metre of the one-centimeter-thick material can create over a gallon of water in as little as 10 minutes, enough to fulfil daily demand in many regions of the globe. The specifics of the novel solar absorber gel were published in ACS Central Science on February 8th.
“Many efforts have been made to develop a technology that uses solar energy to create clean, potable drinking water,” said Rodney Priestley, Dean of the Graduate School, Pomeroy and Betty Perry Smith Professor of Chemical and Biological Engineering, and associated faculty at the Andlinger Center for Energy and the Environment. “This newest development of our technology brings us one step closer to our objective of having a solar-powered system that can truly create enough clean water to fulfil daily demand.”
A gel generated from a polymer known as poly(N-isopropylacrylamide) or PNIPAm, which can absorb or release water depending on temperature, lies at the heart of the device’s sponge-like look.
This hydrogel functions like a sponge to collect water from a source such as a lake when temperatures are below 33 degrees Celsius (91 degrees Fahrenheit). However, when the hydrogel is taken from the water and exposed to sunlight at temperatures over 33 degrees, it starts to leak the water. The device may filter pollutants such as oils, heavy metals, microplastics, and certain forms of bacteria from water by adding polymers such as polydopamine (PDA) to the gel’s surface.
The gel, according to the researchers, is less costly and easier to use than previous evaporation-based methods. Users just immerse the sponge-like gadget in water until saturated. Then they take it out of the water, set it in the sun, and wait for it to emit filtered water. Under noon sunlight, the gel may release up to 70% of the water it absorbs in only 10 minutes.
“Our initial solar absorber gel already had good performance,” said Xiaohui Xu, the study’s lead author and a presidential postdoctoral scholar at Princeton University. “However, we intended to keep improving the device’s water-filtering efficiency.”
According to Xu, the huge improvement in filtration speed is due to structural alterations made by the researchers to the hydrogel between the first and second generations, which improved its capacity to carry water. While both the first and second generations use the identical PNIPAm hydrogel, the researchers discovered that by manufacturing the polymer in a combination of water and ethylene glycol, they could modify the gel to have a more linked, fibrous structure.
According to Xu, the unusual technique resulted in a significant improvement over most current hydrogels, which have a honeycomb-like structure with walls that inhibit water movement. She likened the novel hydrogel’s linked, fibrous structure to that of a mature loofah fruit, which is often used as a scouring sponge in bathrooms and kitchens.
Néhémie Guillomaitre, co-author of the research and a PhD student in chemical and biological engineering, stated that the second-generation solar absorber gel had several advantages over its predecessor.
The researchers, for example, added the solar absorber gel anti-fouling capabilities by adding another polymer, poly(sulfobetaine methacrylate) (PSBMA), to the gel’s surface. PSBMA not only helps the device filter impurities from water more effectively, but it also forms a hydration layer at the gel’s surface that repels oil and germs, allowing the gadget to be self-cleaning.
“Having anti-fouling characteristics extends the life of the gel,” Guillomaitre said. “There is less need to be concerned about oils and bacterial films building on the gel’s surface and reducing its efficiency over time.”
Finally, the researchers think that the solar absorber gel might scale to become an appealing choice for water purification at the home level, providing access to clean water without relying on grid electricity.
“Ideally, this technology might one day be utilised by anybody worried about the quality of their water, no matter where they reside,” Guillomaitre said.
While the researchers said that they are currently working on prototypes to show that their gadget can be scaled to home usage, Priestley thinks that the solar absorber gel might be utilised in emergency scenarios to give on-demand access to clean water in the near future. With funding from the National Science Foundation, Priestley co-founded AquaPao, which will continue to iterate and enhance the design of the solar absorber gel, evaluate its long-term endurance, and seek ways to scale up the technology.
“This study is an excellent illustration of how university research can be used in the startup environment,” Priestley added. “Through our effort, we have shown that basic research can have a tremendous influence on society.”
The paper, “Quick Release Anti-Fouling Hydrogels for Solar-Driven Water Purification,” was published on February 8 in ACS Central Science. Princeton University writers include Kofi Christie, R. Kane Bay, Navid Bizmark, Sujit Datta, and Z. Jason Ren, in addition to Xu, Guillomaitre, and Priestley.
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