In a new study, researchers have demonstrated how copper foam could be used as a highly efficient, durable filter for reusable masks and air cleaners.
Researchers at Georgetown University and the University of California, Davis, have transformed copper nanowires into metal foam that is able to effectively filter out microbes. The team says the foam could be used in face masks and air filtration systems.
The findings have been published in the American Chemical Society’s Nano Letters.
Copper foam as a microbe filter
Since the COVID-19 pandemic began, people across the globe have been wearing face masks to protect themselves from catching the virus. However, many of these face masks are not easily disinfected.
With respiratory viruses, when a person cough or sneezes for example, they release small droplets and aerosolised particles into the air which can stay airborne for hours, so materials that are able to trap the particles are ideal for face masks and air filter use. Metal foams are durable, and their small pores and large surface areas suggest they would be an effective material.
Professor Kai Liu from Georgetown University, and colleagues, have developed and tested copper foams to see if 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 then added to further strengthen the material.
In the tests, the copper foam held its form when pressurised and at high air speeds, suggesting durability for reusable face masks or air filters. It could also be cleaned with washing or compressed air.
The researchers also found that the metal foams had excellent filtration efficiency for particles within the 0.1-1.6 μm size range, which is relevant for filtering out coronavirus particles. Their most effective material was a 2.5mm-thick version, with copper taking up 15% of the volume, which had a large surface area and trapped 97% of 0.1-0.4 μm aerosolised salt particles.
The breathability of the foams was also generally comparable to that of commercially available polypropylene N95 face masks. As well as the material being recyclable, the team highlighted that because the new material is copper-based, the filters should be resistant to cleaning agents, allowing for many disinfection options, and its antimicrobial properties will help kill trapped bacteria and viruses.