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This sponge soaks up pollutants but saves valuable minerals

Scientists reimagine the lifecycle for non-renewables like metals and phosphate
February 5, 2025 | By Win Reynolds
sponge
The sponge, coated with nanoparticles that have an affinity for pollutants, can collect metals like zinc and copper, as well as phosphate, and in previous iterations has successfully pulled lead from water, and microplastics and oil from lakes and oceans.

Northwestern researchers have developed a specialized sponge that slurps up pollutants, offering a reusable and cost-effective solution to water contamination.

The big picture: As more waterways contend with algae blooms and pollution caused by minerals from agricultural runoff and industrial manufacturing processes, new methods to remove pollutants like phosphate, copper and zinc are emerging across fields. While solutions exist, they tend to be costly and can be used just once.

How it works: The sponge, coated with nanoparticles that have an affinity for pollutants, can collect metals like zinc and copper, as well as phosphate, and in previous iterations has successfully pulled lead from water, and microplastics and oil from lakes and oceans. It then releases these valuable resources when it is exposed to different pH’s.

Built for Chicago

In the study, researchers define a method to tailor their platform to specific Chicago pollutants and then selectively release them, giving resources that typically must be mined a potential for a second life.

“The technology can be used as a universal sorbent or ‘catch-all,’ or it can be tailored to certain groups of contaminants like metals, plastics or nutrients,” said principal investigator Vinayak Dravid.

Dravid is the Abraham Harris Professor of Materials Science and Engineering at Northwestern’s McCormick School of Engineering and a faculty affiliate of the Paula M. Trienens Institute for Sustainability and Energy. He is also the founding director of the Northwestern University Atomic and Nanoscale Characterization (NUANCE) Center as well as the Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource, and also serves as the associate director for global programs at the International Institute of Nanotechnology.

Like a Swiss Army knife

In its first iteration, the sponge platform was made of polyurethane and coated with a substance that attracted oil and repelled water. The newest version is a highly hydrophilic (water-loving) cellulose sponge coated with particles tailored to other pollutants. The sponge platform works so effectively because of its pores, providing lots of surface area where pollutants can attach.

Dravid has at times referred to the technology as a “Swiss Army knife” thanks to its versatility and ability to be used again and again. He co-founded NU startup Coral Innovations (formerly MFNS-Tech) to begin the process of commercializing the sponge-based technology for environmental remediation.

Principal investigator Vinayak Dravid works in the lab with Kelly Matuszewski, a Ph.D. student in the Dravid group and the paper’s first author. Photo by Matthew Allen

But, we can’t keep flushing these minerals

Stormwater treatment equipment manufacturer StormTrap, LLC learned about the platform and approached the team, asking about three specific pollutants heavily impacting Chicago. Hoping to add absorbent materials to their portfolio, StormTrap representatives asked if Dravid could get the concentration of pollutants down to untraceable amounts.

The Environmental Protection Agency sets levels for minerals based on human health that are at times higher than the amount considered safe from an environmental perspective, typically setting drinking water limits in the parts per million range when preventing algae blooms and other environmental impacts would require much smaller concentrations.

Developing the platform to capture copper, zinc and phosphate was relatively easy, but then, Kelly Matuszewski, a Ph.D. student in the Dravid group and the paper’s first author, was tasked with determining a method to get the resources back. As stores of phosphate and metals in mines are depleted, this second step is becoming critical.

“We can’t just keep flushing these minerals down the toilet,” Matuszewski said. “We need to understand how they interact and find ways to actually utilize them.”

Matuszewski found that by lowering the pH, metals flush out of the sponge. Once copper and zinc are removed, the pH is then raised, at which point phosphate comes off the sponge. She found that even after five cycles of collecting and removing minerals, the sponge worked just as well, and she was able to deliver water with untraceable amounts of pollutants.

Matuszewski is a finalist in the FoundHer Spotlight, a competition for early career women scientists facilitated by Northwestern’s Querrey inQbation Lab. She will pitch on March 5 to the Northwestern Women’s Board, competing against seven other researchers.

Notes

The partnership with StormTrap, LLC has allowed the team to assess the technology’s effectiveness and move quickly from the lab to the industry. Using the platform in real-life scenarios will be an important next step, as Matuszewski was working in a controlled environment in which each pollutant had the same relative concentration. The next phase will help them determine the amount of minerals a sponge can hold and allow them to partner with other Northwestern researchers working on creating cleaner waterways.

The paper was funded by Trienens and StormTrap and is based on work related to The Great Lakes Water Innovation Engine supported by the National Science Foundation.

Vinayak Dravid and Northwestern have financial interests (equities, royalties) in Coral Innovations.

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