Air filtration has seen a sizable increase in the global market this past year due to the COVID-19 pandemic. Nanofiber nonwoven mats are able to reach certain efficiencies with a low-pressure drop, have a very high surface area to volume ratio, filter out submicron particulates, and can customize the fiber material to better suit its purpose. Although electrospinning nonwoven mats have been very well studied and documented there are not many papers that combine them. This review touches on the various ways to manufacture nonwoven mats for use as an air filter, with an emphasis on electrospinning, the mechanisms by which the fibrous nonwoven air filter stops particles passing through, and ways that the nonwoven mats can be altered by morphology, structure, and material parameters. Metallic, ceramic, and organic nanoparticle coatings, as well as electrospinning solutions with these same materials and their properties and effects of air filtration, are explored.

The fabrication of Polyvinylpyrrolidone (PVP) electrospun layers for air filter applications is the target of this study. Solutions of 10% PVP containing 0, 3, 10 and 25 wt% nanoclay were used to fabricate electrospun fibers. Scanning electron microscopy showed that the fibers’ roughness increased by increasing the nanoclay content, and it was maximum at the nanoclay concentration of 25 wt%. Concurrently, nanoclay decreased the pore size considerably and increased the range of the fibers’ size distribution up to 100%. In addition, as the nanoclay concentration increased, the frequency distribution decreased abruptly for the larger fiber sizes and increased dramatically for the small fiber sizes. This phenomenon was correlated to the effect of nanoclay concentration on the conductivity of the solution. The solution’s conductivity increased from 1.7 ± 0.05 µS/cm for the PVP solution without nanoclay to 62.7 ± 0.19 µS/cm for the solution containing 25 wt% nanoclay and destabilized the electrospun jet, increasing the range of fiber size distribution. Therefore, the PVP solution containing 25 wt% nanoclay has potential characteristics suitable for air-filter applications, owing to its rougher fibers and combination of fine and thicker fibers.

This research aims to fabricate hydrophobic electrospun air filters with ultra-high performance against virions. In order to achieve this goal, constant basis weight electrospun poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) with low-bead, high-bead, and ultra-high-bead fibre structures were used to fabricate single and multilayer filters by controlling the Dimethylformamide (DMF)-to-acetone ratio of the solvent. The water contact angle of the fabricated layers ranged from 131° for low-bead structures to 135° for ultra-high-bead structures, indicating their overall high hydrophobicity. The size-resolved filtering efficiency and pressure drop tests on the fabricated filters showed that low-bead structure for both single and multilayer filters and high-bead structure for single-layer filters enhance the quality factor remarkably. The results showed that the single-layer ultra-high-bead structure air filters had a filtering efficiency of 99.33%, superior to N95 air filters (96.54%) and comparable to double N95 filters (99.86%). However, the electrospun air filter showed a pressure drop of 169.3 Pa and a quality factor of $27.6\times {10}^{-3} {\mathrm{P}\mathrm{a}}^{-1}$compared to a pressure drop of 388 Pa and quality factor of $16.9\times {10}^{-3} {\mathrm{P}\mathrm{a}}^{-1}$ for double N95 air filters. Therefore, it has a high potential to be used as the filtration media in hospitals, long-term care centers, and masks to provide superior protection against virions for healthcare providers and patients.