The words “sponges” and “cleanup” might evoke dirty dishes and kitchen duty. But to a team of materials scientists, they are the inspiration for a way to remediate aquatic oil spills. Researchers at Northwestern University have developed an inexpensive way to convert ordinary sponges to ones that selectively soak up oil from water. The oil can be recovered simply by squeezing the sponges.
Oil leaking from tankers and pipelines harms marine life and the environment. Existing methods for treating the spills have significant shortcomings. On-site burning, for example, emits pollution and greenhouse gases. Chemical dispersants, which break up the oil into tiny droplets and scatter them throughout the water, can harm wildlife. Other methods don’t discriminate well between oil and water, or they leave the water covered with an oily sheen.
Several research groups have proposed alternatives to these commercial cleanup methods, such as soaking up the oil with sponges coated with silanes, fluorocarbons, or graphene. But these lab-scale studies rely on reagents and procedures that are expensive, toxic, or unscalable.
Vikas Nandwana, a research associate working with Northwestern’s Vinayak P. Dravid, and coworkers developed a simple dip-coating method to apply a composite film of graphite and iron oxide nanoparticles to polyurethane and other sponges. The coating, which can also be prepared with iron manganese oxide, is made from inexpensive, abundant, and environmentally benign starting materials and is formulated as an aqueous slurry. Applying it to standard polyurethane furniture cushions that are typically landfilled creates a sponge that selectively absorbs a wide variety of oils from oil-water mixtures while excluding water (Ind. Eng. Chem. Res. 2020, 10.1021/acs.iecr.0c01493).
Tests with reference oils and crude-oil samples showed that the coated sponges can absorb up to 30 times their weight in oil and work well across wide-ranging pH values and water salinity. After squeezing to recover the oil, the sponges can be reused dozens of times with little change in uptake capacity. The nanoparticles make the sponges magnetic, so they can be steered to oil spills and later drained of their oily cargo via radio-frequency heating without physical contact.
Debra Shore, commissioner of Chicago’s Metropolitan Water Reclamation District (MWRD), notes that not only do the sponges “have potentially interesting applications in pollution reduction,” they also might be used to recover phosphorus and other nutrients, which she notes, “is a broad concern for wastewater treatment plants.”
Justin Hart, a water-science and policy specialist with MWRD, is encouraged by the study, but says he’d like to see the sponges tested with diluted bitumen from Canadian tar sands, a dangerous and tough-to-remediate form of oil that flows through the Chicago region.
Nandwana says the team is studying other cleanup applications and working to commercialize the sponges.