A copper-based foam filter that could someday be used in facemasks or air cleaners sits on the bristles of a plant, illustrating its light-weight nature. (Credit: Adapted from Nano Letters 2021, DOI: 10.1021/acs.nanolett.1c00050)

Researchers have transformed copper nanowires into metal foams that could be used in facemasks and air filtration systems. The foams filter efficiently and decontaminate easily for reuse, and they are recyclable.

When a person with a respiratory infection, such as SARS-CoV-2, coughs or sneezes, they release small droplets and aerosolized particles into the air. Particles smaller than 0.3 µm can stay airborne for hours, so materials that can trap these tiny particles are ideal for use in facemasks and air filters. But some existing filter materials have drawbacks.

The metallic foams with microscopic pores are stronger and more resistant to deformation and solvents, as well as to high temperatures and pressures. The researchers wanted to develop and test copper foams to see whether they could effectively remove submicron-sized aerosols while also being durable enough to be decontaminated and reused.

They fabricated metal foams by harvesting electrodeposited copper nanowires and casting them into a free-standing 3D network, which was solidified with heat to form strong bonds. A second copper layer was added to further strengthen the material. In tests, the copper foam held its form when pressurized and at high air speeds, suggesting it’s durable for reusable facemasks or air filters and could be cleaned with washing or compressed air.

The team found the metal foams had excellent filtration efficiency for particles within the 0.1–1.6 µm size range, which is relevant for filtering out SARS-CoV-2. Their most effective material was a 2.5-mm-thick version, with copper taking up 15 percent of the volume. This foam had a large surface area and trapped 97 percent of 0.1–0.4 µm aerosolized salt particles, which are commonly used in facemask tests.