Electrostatic air filtration by multifunctional dielectric hetero-caking filters with ultra-low pressure drop.

In air filtration for creating healthy indoor air, there is an intrinsic conflict between high filtration efficiency and low wind pressure drop. In this study, we overcame this conflict by developing new dielectric hetero-caking (HC) filters, in which high relative dielectric constant (εr) materials were heterogeneously loaded on the traditional polymer fibers. The dielectric HC filter in an electrostatic polarizing field generate a great amount of charges on its surface, leading to a strong attraction to pre-charged aerosol particles and result in high filtration efficiency. Observing via a charged coupled device (CCD) camera, the migration speed of aerosol smoke particles towards the polarized HC fiber exceeded those towards the unpolarized HC fiber by a factor of 6. We loaded high εr HCs including manganese dioxide (MnO2), activated carbon (AC), zinc oxide (ZnO), copper oxide (CuO), and barium titanate (BaTiO3) on polyurethane (PU) foams by a fast and large-scale roll-to-roll gel squeezing method. Based on the experimental results, when HCs had εr larger than 5.1, an increased εr did not benefit much on electrostatic filtration efficiency for aerosol particles, but resulted in a larger net ozone production. We suggested MnO2-HC filter for efficient and multifunctional filtration of indoor particles, ambient ozone and formaldehyde with only 3.8 Pa pressure drop at 1.1 m/s filtration velocity. This efficient and cost-effective dielectric HC filter opens a new avenue for the design of multifunctional filters, which will facilitate its large-scale production and commercial application in the ventilation system of healthy buildings.