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

Abstract

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 inhouse 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.

Improved recovery of captured airborne bacteria and viruses with liquid-coated air filters

“…30,41,[65][66][67] HEPA filters were selected due to their ubiquity in air filtration applications, importance as part of the COVID-19 pandemic response, and wide commercial availability. 29,[68][69][70] Finally, CNFMs were tested as they have been previously shown to be effective in air filtration applications and are made from biodegradable cellulose, 54 an increasingly interesting material in light of ongoing efforts to improve environmental sustainability. 71-73…”

“…The procedure used to manufacture the cellulose nanofibers was based on our prior publications. 54 Cellulose acetate (2.25 g) was dissolved in 15 mL of acetone (15% w/v) under ambient conditions using an Arma-Rotator A-1 (Bethesda, MA) mixing at 20 rpm for 24 h. This precursor solution was loaded into a 5 mL Luer-Lock tip syringe capped with an 18-gauge needle that was mounted on a PHD Ultra syringe pump (Harvard Apparatus, Plymouth, PA).…”

“…For CNFM and PTFE air filters, three 50 μm-thick disks were stacked to achieve a total thickness of 150 µm before liquid infusion to be consistent with our previous work. 54 Particulate matter was generated by simultaneously burning three Hem Precious Chandan incense sticks (Hicksville, NY) in a custom-built chamber to mimic extreme hazardous air quality (PM concentration >2000 μg m −3 ). A Model 3775 Condensation Particle Counter (CPC, TSI Incorporated, Shoreview, MN) and a Series 3080 Electrostatic Classifier (TSI Incorporated, Shoreview, MN) at a sample flow rate of 3.0 L m −1 were used to measure the downstream particle concentration and particle size distribution from 20 to 900 nm.…”

“…The results showed much larger fibers on the surface of the filters compared to either the PTFE or CNFM materials, in agreement with previous reports on the characterization of these systems. 54,79,84,85 It is known that the stability of liquid coatings is due not only to a chemical match between the surface and coating liquid, but also due to capillary action. 75 The difference in the CV staining results obtained for the HEPA-LNs, may therefore be due to an increased contribution of capillary forces to holding the liquid coating in place, further explaining their better performance in the recovery of bacterial aerosols.…”

In Situ Biosynthesis of Biodegradable Functional Bacterial Cellulose for High-Efficiency Particulate Air Filtration

“…The use of sustainable and environmentally friendly polymers is an effective approach to avoid new unsecure environmental concerns. , Recent studies have shown that biobased materials such as poly­(vinyl alcohol) (PVA), amino acids, soy protein, zein protein, − silk fibroin, microalgae film, chitosan, and cellulose − have been used as the filters. Other than biobased material precursors, cellulose is a sort of environment-friendly reproducible natural material and an almost inexhaustible resource with outstanding properties .…”