Nanoparticle-Coated Sponge Removes Metals and Nutrients From Water

As waterways face increasing contamination from agricultural runoff and industrial waste, researchers continue to seek efficient and cost-effective ways to remove pollutants such as phosphate, copper and zinc. A team at Northwestern University has developed a reusable sponge that can absorb these contaminants and release them for reuse, offering a potential solution for reducing environmental pollution while recovering valuable resources.

The sponge, coated with nanoparticles designed to attract specific pollutants, builds on previous research that demonstrated its ability to extract lead, microplastics and oil from water. Unlike many current solutions, which are expensive and single-use, this material can be reused multiple times by altering the water’s pH to release the collected substances.

A study detailing the sponge’s capabilities and potential applications will be published on February 5 in Environmental Science & Technology Water, a journal of the American Chemical Society. The research, led by Professor Vinayak Dravid at Northwestern’s McCormick School of Engineering, highlights a method for tailoring the sponge’s properties to address pollution concerns in specific environments, such as Chicago’s waterways.

How the sponge works

The sponge platform has evolved from its original oil-absorbing polyurethane version to a more advanced design made of hydrophilic cellulose. The material’s porous structure provides a high surface area, maximizing pollutant capture. By modifying the nanoparticle coating, researchers can fine-tune the sponge’s selectivity, allowing it to target specific contaminants, including metals, nutrients and plastics.

Dravid describes the platform as a "Swiss Army knife" due to its versatility and ability to function across different applications. To facilitate commercialization, he founded Coral Innovations, a startup focused on developing the sponge technology for large-scale environmental remediation.

Separating and recovering valuable resources

Stormwater treatment equipment manufacturer StormTrap, LLC collaborated with the Northwestern team to explore the sponge’s ability to capture and remove three key pollutants affecting Chicago’s water systems: copper, zinc and phosphate. StormTrap sought to integrate absorbent materials into its existing filtration systems to lower pollutant concentrations to untraceable levels.

While existing environmental regulations, such as those set by the Environmental Protection Agency, establish pollutant limits based on human health, reducing concentrations to prevent harmful ecological effects – such as algae blooms – often requires even stricter control.

The research team successfully designed the sponge to trap these pollutants, but a critical next step was determining how to recover the captured resources for reuse. Lead researcher Kelly Matuszewski, a PhD student in Dravid’s group and the study’s first author, developed a process that involves adjusting the water’s pH in stages. Lowering the pH causes the sponge to release copper and zinc, while raising it allows phosphate to be recovered separately.

This method proved highly effective: after five cycles of pollutant absorption and release, the sponge maintained its performance, producing water with pollutant levels below detection limits.

“With global reserves of phosphate and metals being depleted, we need to shift away from treating these minerals as waste,” Matuszewski said. “By understanding their interactions and developing ways to recover them, we can support both environmental and resource sustainability.”

Matuszewski’s contributions have also earned her recognition outside the lab. She is a finalist in the FoundHer Spotlight, a competition for early-career women scientists at Northwestern’s Querrey inQbation Lab. She will present her research to the Northwestern Women’s Board on March 5, competing for funding against seven other researchers.

Scaling up for real-world applications

The collaboration with StormTrap has enabled the team to transition from lab-scale testing to industry applications. While initial studies were conducted in controlled environments with equal concentrations of each pollutant, the next phase will involve testing the sponge in real-world conditions, where pollutant levels vary.

By assessing how much material the sponge can retain and refining its deployment strategies, the researchers aim to develop a scalable solution for wastewater treatment, stormwater management and broader environmental cleanup efforts. They also plan to partner with other Northwestern researchers focused on improving water quality in urban and agricultural settings.

Reference: Matuszewski KE, Shindel B, Nandwana V, Dravid VP. Rinse, recover, repeat: pH-assisted selective extraction of phosphate and metals with a sponge nanocomposite. ACS EST Water. 2025. doi: 10.1021/acsestwater.4c01234

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