High Filtration Efficiency Copper Nanowire Foams with Tailored Microstructures

The COVID-19 pandemic highlighted the needs for filtration media with high efficiency for particulate matter in the deep submicron range. Previous work has shown that nanoporous foams constructed from metallic nanowires can be utilized as efficient and multifunctional filtration media [1]. Interestingly, surface area alone does not dictate the particulate filtration efficiency. But rather, microstructure details of the surface features on the metallic nanowires resulted from a synthesis step also play an important role [2]. In this work we have modified the size distribution of such surface features by purposely introducing nanoparticles of given sizes to investigate the effect on the foam’s filtration performance. Copper nanoparticles were synthesized using a solution-based reduction method, whose sizes range from tens of nanometers to microns. Such Cu nanoparticles were successfully integrated into the Cu nanowire foams, resulting in a preferred size distribution of the surface features on the foam interior surface. Such foams exhibited up to 30% improvement in filtration efficiency, for airborne NaCl particulates close in size to the nominal size of the incorporated Cu nanoparticles. These results demonstrate an effective design strategy utilizing controlled surface features to improve the filtration efficiency of the foams by capturing particles of a target size, without adversely affecting the breathability of the foams.