Researchers have found copper foam as a reusable filter for face masks and air purifiers

During the COVID-19 pandemic, people have become accustomed to wearing masks, but numerous of the covers are fragile and not easily sterilized. Metal foams are durable, and their tiny holes and large surface area suggest they are effective at filtering microbes. Now, researchers report in ACS 'Nano Letters that converting copper nanowires into metal foam can be used in face masks and air filtration systems. The foam is effectively filtered, easily decontaminated, reusable, and recyclable.

When people with respiratory infections, such as SARS-CoV-2, cough or sneeze, they release tiny droplets and aerosol particles into the air. Particles smaller than 0.3μm can remain in the air for hours, so materials capable of capturing these tiny particles are ideal for face masks and air filters. However, some existing filtration materials also have disadvantages. For example, fiberglass, carbon nanotubes and polypropylene fibers are not durable enough to undergo repeated decontamination procedures, while some materials additionally rely on static electricity and therefore cannot be cleaned, leading to significant waste.

a82c7ead73d1bd56a37101430bfde88dRecently, researchers have developed metal foams with microphones that are stronger and more resistant to deformation, solvents, elevated temperatures and pressures, while also durable enough to be decontaminated and reused. The researchers created the metal foam filter by taking electrodeposited copper nanowires and casting them into a stand-alone 3D network that was heated and solidified to form strong bonds. A second copper layer was added to help strengthen the material. In tests, the copper foam maintained its shape under pressure and elevated air speeds, indicating that it is durable for reusable face masks or air filters and can be cleaned with washing or compressed air.

The research team found that the metal foam has a excellent filtration efficiency for particles in the size range of 0.1-1.6μm, which is relevant for filtering SARS-CoV-2. Their most effective material is the 2.5mm thick version, in which copper makes up 15% of the volume. The foam has a large surface area and can trap up to 97% of the 0.1-0.4μm air-soluble salt particles commonly used in mask testing. According to the team's calculations, their foam is roughly as breathable as commercially available polypropylene N95 masks.

Because the original material is copper-based, the filters should be resistant to cleaners, allowing for numerous disinfection options whose antimicrobial properties will help kill trapped bacteria and viruses, the researchers claimed. Plus, they can be recycled. The researchers estimate that the material currently costs about $2 per mask, while disinfecting and reusing it would extend its life and make it economically competitive with existing products.

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