Innovations are where you find them. For Craig Arnold, a professor of mechanical and aerospace engineering and vice dean of innovation at Princeton, his inspiration for a new material using egg whites was a piece of bread in a sandwich he was about to eat. “I was sitting there, staring at the bread in my sandwich,” Arnold says in a Princeton press release. “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. The researchers used those egg whites to create an aerogel, a lightweight and porous material that can be used in many types of applications including water filtration, energy storage, and sound and thermal insulation.
“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.”
Egg whites are a complex system of almost pure protein that — when freeze dried and then heated to 900 degrees Celsius in an environment without oxygen — create a structure of interconnected strands of carbon fibers and sheets of graphene. In a paper published August 24 in Materials Today, Arnold and his co-authors 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, first author on the paper. 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 worked, the material can potentially 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.
If this challenge can be solved, the material has significant benefits because it is inexpensive to produce, energy-efficient to use 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 to operate and wastes no water. Here’s the abstract of the study for your edification and amusement:
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.
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.
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. Support for the research was provided in part by the Princeton Center for Complex Materials and the US National Science Foundation.
Who knows where this research may lead? Desalinaztion of ocean water could be a boon to many islands where clean water is a precious commodity. But the potential to remove microplastics from seawater is an exciting prospect if you are someone who wants to cut down on the amount of plastics suspended in seawater today.
We don’t have specifics on how much it would cost to desalinate a cubic meter of seawater using this process. Heating elements to 900º C will obviously require a lot of energy and if that energy comes from fossil fuels or nuclear, that’s a two steps forward and two steps back process. But the research is promising enough we thought you would want to know about it, and now you do. We will keep our eyes open for more information about this process and when we know more, you will know more.
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