Eggs found to remove salt and microplastics from seawater

Craig Arnold, the Susan Dod Brown Professor of Mechanical and Aerospace Engineering and vice dean of innovation at Princeton, came up with the idea while sitting in a faculty meeting.

“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.”

He proceeded to ask his lab group to make different bread recipes mixed with carbon to see if they could recreate the aerogel structure he needed. To find the substance that worked right, 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 down to the core of what it was. It was the proteins in the egg whites that were leading to the structures that we needed.”

Pure protein

Egg whites consist 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 fibers and sheets of graphene. Arnold and his coauthors found that the resulting material can remove salt and microplastics from seawater with up to 99 percent efficiency.

“The egg whites even worked if they were fried on the stove first, or whipped,” said Sehmus Ozden, the first author of the paper.

“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,” added Arnold.

Other proteins also worked indicating that the material can potentially be produced in large quantities relatively cheaply and without impacting the food supply. Now, the researchers are focused on refining the fabrication process so it can be used in water purification on a larger scale.

“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.

Only gravity required

Better yet, this filtration process requires only gravity to operate and wastes no water. This is a major improvement on reverse osmosis, which requires significant energy input and excess water for operation.

Arnold is also exploring other uses for egg whites related to energy storage and insulation and exploring the reasons behind the food’s multipurpose uses.

“It’s one thing to make something in the lab,” said Arnold, “and it’s another thing to understand why and how.”

The paper was first published on August 24 in the journal Materials Today.

Study abstract:

The integration of 2D-graphitic carbon (G) with 1D-carbon nanofiber (CF) allows for the unique properties of 2D graphitic carbon to be combined with the low densities, mechanical performance, and high surface area required for applications across the energy and sustainability landscape. Through a combination of experiments and numerical modeling, we demonstrate the transformation of standard egg-white (EW) proteins into an ultralightweight G-CF aerogel with a multiscale structure. The resulting covalently-bonded hierarchical structure, derived from the complex underlying protein configuration, exhibits a density that is two orders of magnitude lower than existing state-of-the-art materials. We apply this material to the challenges of desalination and water purification, notably demonstrating that the G-CF aerogel significantly improves upon existing materials, capturing 98.2% of ionic impurities and 99.9% of nano/microplastic contamination from seawater.