A reusable electret filter media based on water droplet charging/cleaning

Abstract

Electret filter media has been considered as the most effective and economical filtration material due to its additional electrostatic filtration effect. However, the regeneration and recycling of electret filter media is a great challenge, as its stored charge would dissipate during filtration process, resulting in a significant efficiency reduction after cleaning. To address this problem, based on liquid–solid contact electrification (C-E) theory and self-cleaning property of hydrophobic surface, we successfully designed and fabricated a reusable PTFE electret filter membrane. After water droplets charging/cleaning, the surface charge of the membrane can be recovered to 100–110%, and the pressure drop can be restored to > 93%, exhibiting an excellent regeneration performance. Then the effect of particle wettability on cleaning performance was investigated. The hydrophilic PM2.5 on hydrophobic surface was found to be easier to clean by droplets rolling than the hydrophobic PM2.5 due to its stronger adhesion to the droplets. Furthermore, based on the theory of ion transfer at the solid–liquid interface, the charge evolution of the hydrophobic PTFE surface during the triboelectric electrification of water droplets was modeled. The rate of ion transfer between water droplets and hydrophobic surfaces depends linearly on the actual liquid–solid contact area. The charge saturation value of a solid surface is related to its ionic binding sites and the dielectric properties. The study promotes the development of reusable electret filters, and advances the understanding of the triboelectric properties of droplets on hydrophobic surfaces.