Moisture and oily molecules stable nanofibrous electret membranes for effectively capturing PM2.5

The fabrication of electret air filter with robust charge stability towards moisture and oily molecules is becoming increasingly essential due to the severe haze pollution, which is featured with high relative humidity (80-90%) and contains oily components (30-40%); however, this remains an ongoing challenge. Herein, a nanofibrous electret membrane able to enduringly capture PM2.5 with high efficiency and low air resistance under the surroundings containing moisture and oily components is successfully designed via electrospinning. Benefiting from the high electrical resistivity of polyvinyl butyral (PVB) and high dielectric constant of silicon nitride nanoparticles (Si3N4 NPs), PVB/Si3N4 nanofibrous membranes are endowed with improved stable surface potentials from 1610 to 2010 V when the content of charge enhancer (Si3N4) increases from 0 to 1 wt%. More importantly, the charge dissipating mechanism under water and oil condition is revealed. Moreover, by further introducing hydro-oleophobic fluorinated polyurethane (FPU), the stable surface potentials of PVB/Si3N4-FPU membranes are elevated by 62.8% under high relative humidity (85%) and 48.4% towards oily components, compared with PVB/Si3N4 membranes. The resultant membranes achieve a high filtration efficiency of 99.950%, low air resistance of 55.0 Pa, and robust durability, providing a guidance for the design of electret air filtration materials used in haze environment.