Optimizing the Packing Density and Chemistry of Cellulose Nanofilters for High-Efficiency Particulate Removal

The global spread of COVID-19 as well as the worsening air pollution throughout the world have brought tremendous attention to the development of materials that can efficiently capture particulate matter. We suggest that the high porosity of electrospun filters composed of nanofibers could provide minimal obstruction to air flow, while their high tortuosity and surface area-to-volume ratio present an excellent platform to capture particulates. In this study, the removal of nanoscale particles via in-house fabricated cellulose nanofilters is significantly enhanced by chemically functionalizing the fibers' surface via the deposition of the bioinspired glue polydopamine (PDA) or the polycation poly(diallyldimethylammonium chloride) (PDADMAC). The effects of filter packing density, layering thickness, and chemistry on their performance, i.e., their filtration efficiency, most penetrating particle size (MPPS), particle fractional penetration percent, and performance in a high relative humidity environment, were investigated. When evaluated in an extremely hazardous environment (PM concentration ∼2000 μg m-3), the filtration efficiency, pressure drop, and quality factor for the cellulose nanofilters were measured to be >98.0%, <200 Pa, and ∼0.03 Pa-1, respectively. When we evaluated the performance of a composite hydrophobic/hydrophilic filter in an 80% relative humidity environment, a 99.8% filtration efficiency was achieved. We have demonstrated that the removal of nanoscale particulates can be effectively captured using cellulose-based nanofilters, even in a nonideal high humidity environment. These fundamental investigations into the structure-property-chemistry relationships of in-house electrospun nanofilters on nanoscale particulate removal hold the potential to help drive the future engineering of nanofilters for air purification applications, which is a timely and extremely important concern. © 2021 American Chemical Society.