You can tell a lot about a poacher by the way they dehorn a rhinoceros — was the horn hacked off crudely or was it removed skillfully with a sharp, scalpel-like instrument? As Saif Bhatti bumped along the dirt back roads of Thornybush Game Reserve in South Africa, he was unsure which one they might find.
In April 2010 an explosion on the Deepwater Horizon oil drilling rig spilled an estimated 134 million gallons of oil into the Gulf of Mexico — the largest oil spill in U.S. history.
The aftermath of the disaster inspired engineer Vinayak Dravid to focus his work on solving environmental problems. “I realized the scale of the problem was gigantic and that we needed commensurate solutions,” Dravid says. Somewhat by accident, he and his team designed a sponge that can soak up oil spills and help save marine life.
Dravid is one of many researchers at Northwestern who are leveraging basic science and fundamental research to address some of today’s most dangerous environmental threats. These researchers are developing new technologies and processes to improve our air, our water and our world.
“A lot of environmental pollution problems are manageable and treatable,” Dravid says, “if there’s a willingness to innovate and take some chances.”
Saving Our Seas With Sponges
PROBLEM: 20,000 oil spills annually
SOLUTION: A sponge that can soak up 30 times its weight in oil
Vinayak Dravid, the Abraham Harris Professor of Materials Science and Engineering at Northwestern’s McCormick School of Engineering, says he is developing “nanoscale solutions to gigaton problems,” such as water pollution.
In 2018 a senior member of his research group spilled a nanoparticle solution on a lab table. As the team prepared to clean up the mess, they noticed that water droplets rolled right over the solution, rather than being absorbed. Dravid and his team were intrigued. So they placed a drop of oil on the solution, and that oil was immediately absorbed. “We immediately knew there was something fishy going on,” he says.
Dravid’s team applied the nano-based coating to a polyurethane sponge, similar to a regular kitchen sponge or packaging foam. Remarkably, the sponge soaked up 30 times its weight in oil and could then be wrung out and reused dozens of times. With 4 million tons of sponges being thrown into landfills each year, Dravid realized he could effectively use trash to clean up oil spills.
“There are 20,000 oil spills [reported to the U.S. government] every year,” Dravid says, adding that current methods to mitigate spills in bodies of water — including burning or dispersing the oil — are themselves harmful to marine life. His sponge technology could provide a safe and scalable way to clean up spills while leaving the surrounding environment unscathed.
Dravid’s lab has been working with the U.S. Coast Guard to develop this sponge technology, and recent testing at the National Oil Spill Response Research & Renewable Energy Test Facility in New Jersey showed the sponges completely soak up spilled oil within 10 seconds. The research group is also working with nongovernmental organizations and regulators to develop accident mitigation strategies for companies that transport oil across bodies of water. In the same way that ships provide life jackets for passengers, Dravid says, they could also store sponges on board in case of an accidental oil spill.
“It’s not just about absorbing oil but also doing so quickly before the oil spreads,” Dravid says. “Not only can we clean up with high capacity but we can clean up fast. In most cases, if you don’t immediately attack the spill, it spreads and creates even more pernicious problems.”
In addition to oil cleanup, Dravid’s sponge can be engineered to capture microplastics or phosphate, a nonrenewable resource used in fertilizer. Dravid, who envisions his sponge as a “Swiss Army knife approach” to pollution mitigation, is also engineering coatings to capture nuclear waste.
Getting The Lead Out
PROBLEM: Pollutants in drinking water
SOLUTION: Nano-engineered water filters that target city-specific toxins
Contaminated drinking water has been a problem throughout human history, highlighted recently by the water crises in Flint, Mich., Jackson, Miss., and elsewhere. Chemist Omar Farha has developed a way to remove pollutants such as lead from water. Farha’s lab studies metal-organic frameworks (MOFs) — nanoscale materials that can be engineered to capture specific gases, vapors and other materials from air and water. To the naked eye, Farha’s MOFs look like vials of colored sand, each crystal containing millions of individual cavities.
MOFs can be especially useful in water remediation, says Farha, a chemistry professor at Northwestern’s Weinberg College of Arts and Sciences.
“Contamination in drinking water varies from one city to another, and generic water filters are typically mediocre. And most of us use generic filters,” Farha says. “I believe we should be aiming for ‘smart filters.’ Every city should test its water supply and use filters that can capture the toxins specific to each city. … MOFs can play a big role because we have the ability to change the components to make them selective for different pollutants.”
Farha first applied MOFs to the degradation of poisonous chemicals known as nerve agents. He’s working with the U.S. Department of Defense to develop fabrics containing nerve agent–destroying MOFs for use in conflict zones.
Based on that work, Farha started engineering MOFs to break down plastics, and in a project supported by the Defense Advanced Research Projects Agency, he has since developed MOFs to extract water from air in harsh and low-humidity environments.
Farha hopes one day to create MOFs that can capture carbon dioxide and convert it into fuel, as well as MOFs that can store hydrogen at room temperature, which could pave the way for hydrogen-powered cars and reduced dependence on fossil fuels.
“In my group, we do fundamental research that can benefit humanity and be translated into products,” Farha says.
Making Plastic More Recyclable
PROBLEM: Unrecyclable plastics, such as rubber tires
SOLUTION: Chemical process that creates recyclable plastic for rubber tires and other products
Each year, the world generates about 800 billion pounds of plastic waste. That’s about 100 pounds per person per year. Of that plastic waste, about 20% is deemed nonrecyclable, with much of it ending up in incinerators or landfills. But chemical engineer John Torkelson has found a means to break down and reuse these previously unrecyclable plastics.
Thermoplastics, such as the kind used for milk jugs and soda bottles, are made up of linear polymer chains that can be recycled and remelted into new products. Torkelson is working with a specific class of materials called thermosets, which are used to create a broad range of products, including rubber tires and mattresses. Thermosets are made up of permanently crosslinked polymer chains that make the materials more durable but also make recycling impossible.
“You could take an empty 2-liter soda bottle and cut that into bits, reprocess it and form another bottle from that material,” says Torkelson, the Walter P. Murphy Professor of Chemical and Biological Engineering and Materials Science and Engineering at McCormick. “You can’t do that with a rubber tire because the chains are chemically crosslinked, and those are permanent. That prevents them from being effectively recycled.”
Using simple chemistry, Torkelson’s research team used “dynamic covalent crosslinks” to create polymers that incorporate the durability of permanent crosslinks but also can be recycled, offering the best of both worlds. These dynamic crosslinks can come apart at high temperatures and come back together once they’re cooled. His lab is collaborating with Dow Chemical to develop this work.
Torkelson’s dynamic covalent crosslinks could be used to create crosslinked polymer materials, such as rubber tires and polyurethane foam mattresses, that can be recycled a number of times, significantly extending the life of the polymer and reducing landfill waste.
Repurposing Greenhouse Gas
PROBLEM: A dangerous greenhouse gas in the air
SOLUTION: Bacteria that convert methane into renewable fuel
Methane is a potent greenhouse gas that can have up to 84 times more warming power than carbon dioxide.
Amy Rosenzweig has spent much of her career studying methanotrophic bacteria, which consume methane. These bacteria convert methane to methanol, which can be used as an energy source. Rosenzweig’s team is looking specifically at enzymes in the bacteria, seeking to understand how they work in the hopes of harnessing them for methane conversion.
“These enzymes bind the methane and use either iron or copper to react with oxygen, … break the bond in methane and convert it to methanol,” says Rosenzweig, the Weinberg Family Distinguished Professor of Life Sciences and professor of molecular biosciences and chemistry at Weinberg College. “If you understood on the molecular level how these enzymes work, you could … make a catalyst that is modeled on what the enzyme does.”
Current methods of methane-to-methanol conversion require large industrial plants and expensive materials. Harnessing methanotrophic bacteria could provide a more portable and less costly method of making fuel from methane.
“The hope is that these bacteria could be used to make a smaller, more deployable solution,” Rosenzweig says. “You’re not going to build a giant plant next to a fracking site to harvest methane, and it’s difficult to transport the methane because it’s a gas. But you could have a solution where a bioreactor filled with these bacteria goes to the site and grabs all the methane, and the bacteria convert it.”
These bacteria also could be used to eat methane at landfills, where the greenhouse gas leaches into the air.
Rosenzweig has made several key discoveries about the conversion process, but there is still more work to be done. “We need to learn more about how the enzyme works to make these processes much faster and much more efficient,” she says.
Fighting ‘Forever Chemicals’
PROBLEM: Harmful ‘forever chemicals’ that exist all around us
SOLUTION: Breaking apart these compounds through chemical processes
Organic chemist and open-water swimmer Will Dichtel develops materials that remove pollutants from water, including pesticides, pharmaceutical agents and industrial chemicals. In the course of that work, he learned about a class of compounds called per- and polyfluoroalkyl substances, or PFAS.
Found in nonstick cookware, firefighting foams, waterproof cosmetics, water-repellent fabrics and products resistant to oil and grease, PFAS have been in use since the 1940s and ’50s. Today, they can be detected in drinking water — and in the blood of 97% of the U.S. population.
Dubbed “forever chemicals” in popular media, PFAS are really alarming, Dichtel says. “They don’t break down quickly in the environment. They accumulate in living organisms, including people, and they are associated with many negative health effects,” including developmental effects in children, greater risk of several types of cancer, increased cholesterol levels, and decreased fertility and ability to fight infections. Similar to lead, several PFAS have been declared unsafe even at trace levels by the U.S. Environmental Protection Agency.
Dichtel’s team began working on ways to remove PFAS from the environment. Using cyclodextrin, a sugar derived from cornstarch, they designed a polymer that can remove PFAS from water.
And now Dichtel, the Robert L. Letsinger Professor of Chemistry at Weinberg College, has identified a way to destroy PFAS with simple chemistry. He and his team discovered that a significant portion of PFAS compounds have what they call a “head group” composed of oxygen atoms, and a “tail” of carbon-flourine bonds. Heating the PFAS in a solvent with sodium hydroxide, a common reagent, decapitated the head group so that only the tail remained.
“That was really the eureka moment,” Dichtel says. “When that head group falls off, … the tail falls apart like a row of dominos.” What’s left behind, Dichtel says, is fluoride, “the safest form of fluorine,” and carbon byproducts that are known to be safe.
Dichtel estimates that about half of PFAS have this particular structure and could be destroyed using his lab’s technique. The researchers are optimistic that other classes of PFAS compounds will fall apart using similar principles.
Supported by a grant through the Northwestern Center for Water Research, in collaboration with investigators in Israel and the U.S., Dichtel’s team is testing their PFAS removal and destruction techniques in wastewater in both Chicago and the Middle East. The aim of the grant is to enable wastewater reuse, particularly in Israel, which already uses wastewater for agriculture. Removing PFAS so that these compounds don’t end up in agricultural products or meat is a huge goal, Dichtel says.
“This is more than just an academic discovery,” says Dichtel. “We’re trying to push beyond. We’re trying to make an impact.”
Clare Milliken is senior writer and producer in Northwestern’s Office of Global Marketing and Communications.
Editor’s note: Companies have been formed to assist in translating technologies discussed in this article. Vinayak Dravid has financial interests in MFNS Tech Inc. Omar Farha has financial interests in NuMat Technologies Inc. Will Dichtel has financial interests in Cyclopure Inc. Northwestern University also has financial interests in these companies and intellectual property interests in technologies discussed in this article.
Illustrations by Gracia Lam.