Researchers at Princeton Engineering have found a way to turn your breakfast food into a new material that can cheaply remove salt and microplastics from seawater.
The researchers used egg whites to create an aerogel. This lightweight and porous material can be used in many applications. That includes water filtration, energy storage, and sound and thermal insulation. Craig Arnold, the Susan Dod Brown Professor of Mechanical and Aerospace Engineering and vice dean of innovation at Princeton, worked with his lab to create new materials, including aerogels, for engineering applications.
One day, sitting in a faculty meeting, he had an idea.
“I was sitting there, staring at the bread in my sandwich,” said Arnold. “And I thought to myself. This is exactly the kind of structure that we need.” So he asked his lab group to make different bread recipes mixed with carbon to see if they could recreate the aerogel structure he was looking for. None of them worked quite right initially, so the team kept eliminating ingredients as they tested until, eventually, only egg whites remained.
“We started with a more complex system,” Arnold said, “and we just kept reducing, reducing, reducing until we got to the core of what it was. It was the proteins in the egg whites that were leading to the structures that we needed.”
Egg whites to remove microplastics
Egg whites are a complex system of almost pure protein. When freeze-dried and heated to 900 degrees Celsius in an environment without oxygen, they create a structure of interconnected strands of carbon fibres and sheets of graphene. In a paper published Aug. 24 in Materials Today, Arnold and his coauthors showed that the resulting material can remove salt and microplastics from seawater with 98% and 99% efficiency, respectively.
“The egg whites even worked if they were fried on the stove first or whipped,” said Sehmus Ozden, the paper’s first author. Ozden is a former postdoctoral research associate at the Princeton Center for Complex Materials and is now a scientist at Aramco Research Center. While regular store-bought egg whites were used in initial tests, Ozden said, other similar commercially available proteins produced the same results.
“Eggs are cool because we can all connect to them, and they are easy to get, but you want to be careful about competing against the food cycle,” said Arnold. Because other proteins also work, the material can be produced in large quantities relatively cheaply and without impacting the food supply. One next step for the researchers, Ozden noted, is refining the fabrication process so it can be used in water purification on a larger scale.
Microplastics can be filtered better by egg whites than activated carbon
If this challenge can be solved, the material will have significant benefits because it is inexpensive to produce, energy-efficient, and highly effective. “Activated carbon is one of the cheapest materials used for water purification. We compared our results with activated carbon, and it’s much better,” said Ozden. Compared with reverse osmosis, which requires significant energy input and excess water for operation, this filtration process requires only gravity and wastes no water.
While Arnold sees water purity as a “major grand challenge,” that is not the only potential application for this material. He is also exploring other uses related to energy storage and insulation.
The research included contributions from the chemical and biological engineering departments and geosciences at Princeton and elsewhere. “It’s one thing to make something in the lab,” said Arnold, “and it’s another thing to understand why and how.” Collaborators who helped answer the why and how questions included professors Rodney Priestley and A. James Link from chemical and biological engineering helped identify the transformation mechanism of the egg white proteins at the molecular level. Princeton colleagues in geosciences assisted with measurements of water filtration.
Susanna Monti of the Institute for Chemistry of Organometallic Compounds and Valentina Tozzi from Instituto Nanoscienze and NEST-Scuola Normale Superiore created the theoretical simulations that revealed the transformation of egg white proteins into the aerogel.
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