Copper Foam As Filter Material for Masks and Air Cleaners Possible?

At the height of the global coronavirus pandemic, facemasks have become a part of daily life. Researchers are now looking into a new material - from copper foams - that is durable and can potentially filter out microbes.

Researchers have fashioned copper foams, with small pores and large surface areas, from copper nanowires, potentially using them for facemasks and air filtering systems. The scientists, from the University of California Davis and Georgetown University, published their findings in the latest ACS Nano Letters in the report titled "Efficient and Robust Metallic Nanowire Foams for Deep Submicrometer Particulate Filtration," published March 24.

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Copper foam as a highly efficient, durable filter for reusable masks and air cleaners.

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Copper Foams for Reusable, Efficient Filtration Devices

With the new facemasks and air filters based from copper foams, users can expect efficient filtration devices that can be decontaminated easily for reuse and are also recyclable.

In the ongoing effort against COVID-19, scientists have repeatedly warned that infected persons - as with other respiratory illnesses - coughs or sneezes, they release with it small droplets and aerosol particles into the air around them. Particles smaller than 0.3 micrometers, such as the coronavirus, can remain airborne for hours. Filtering materials that can trap these particles would be ideal for fabricating face masks and air filters.

Unfortunately, some filter materials in use today have drawbacks and limitations. Fiberglass, carbon nanotubes, and even polypropylene fibers are not strong enough to withstand repeated decontamination procedures. On the other hand, other materials rely on electrostatic procedures, meaning they are not washable, and therefore contribute to waste afterward.

This led to researchers turning to metallic foams, whose pores are in the microscale - creating porous materials that are more robust, resistant to deformation, and common cleaning agents like solvents, temperature, and pressure from repeated decontaminations. It led to the team of Kai Liu and colleagues to develop copper foams, testing whether these materials could be used to efficiently filter out aerosols and materials in the submicron and nanoscale ranges while being durable enough to survive multiple decontamination and reuse.

Fabricating the Nanoporous Copper Foam

To create their copper foams, they first harvested electrodeposited copper nanowires, casting them into a free-standing three-dimensional network. The cast copper was further solidified using heat, creating strong bonds. Researchers added another layer of copper for additional material strength.

Testing the fabricated copper foams, researchers found out that the material maintained its form even when subjected to increased pressure and air speeds, which suggests that copper foams are durable enough to be used for reusable face masks or air filters. With this material as the base, the products could be cleaned and decontaminated by washing or blowing with compressed air. Additionally, researchers also discovered that the copper foams were excellent filtering materials against particles in the 0.1 to 1.6-micrometer size range, making them ideal for filtering out SARS-CoV-2 - the virus that causes COVID-19.

Fabricating the same copper foams with varying parameters, they found that the 2.5 millimeter-thick version, composed of 15 percent copper, was the most effective. This fabricated version has a large surface area capable of trapping about 97 percent of aerosol salt particles measuring between 0.1 to 0.4 micrometers, also used in face masks tested.