Moisture And Oily Molecules Stable Nanofibrous Electret Membranes For Effectively Capturing PM_2.5

In recent years,air particulate matter?PM?pollution has become increasingly serious,especially PM_2.5?aerodynamic equivalent diameter?2.5?m?has caused millions of premature deaths over the past few years.To effectively protect people against PM_2.5 pollution,ever-increasing efforts have been devoted to designing filter materials able to allow air flowing smoothly while particles being wipe out effectively.Conventional fibrous membranes?glass fibrous,melt-blown fibrous,electret fibrous?,benefitting from their tortuous porous structures,have been growing to be the most promising materials for air filtration.Unfortunately,conventional fibrous air filtration materials represented by spun-bonded nonwovens,melt-blown fibers,and glass fibers are usually subjected to either low capture efficiency for PM_2.5 due to the large pore size or high air resistance due to the dense accumulation of fibers.The balance between high efficiency and low air resistance remains a bottleneck in air filtration field.Now,micro electret fibrous materials,which can capture PM_2.5 relying on coulomb force and electrostatic force,possess the advantage of elevating filtration efficiency while keeping a low pressure drop.Consequently,they have been proved to be an excellent candidate for high-performance materials for air filtration.Up to now,a number of electret fibrous materials,such as polypropylene,polycarbonate,polyimide,and so on,have been developed using the technologies including corona charging,tribocharging,and electric breakdown charging.Nevertheless,these electret technologies grant materials with electret property via post-proceeding operation,leading to the fatal drawback of shallow ejection depth of charges,which will easily dissipate when affected by the environment,such as moisture and particulate deposit.Therefore,the available electret materials are incapable of restraining the escape of charges,resulting in a poor stability for effectively adsorbing particles in service.Electret nanofiber air filter materials greatly improve the filtering performance of the air filter materials due to the high specific surface area,small pore diameter,and high porosity.However,as a cutting-edge technology used for fabricating fibrous materials,electrospinning can inject charges in situ during the evolution from polymer fluid to solid fibers,bring about the advantage of deeply trapped charges within fibers.Obviously,electrospinning holds great promise for solving bottlenecks of current electret technologies.Up to now,some attempts have been committed to fabricating electrospun electret air filters,such as polyamide-6/boehmite,poly?phenylene ether?/polystyrene,and poly?ether imide?/silica,and so on.Unfortunately,the majority of researches are only focused on elevating the electret performance by regulating parameters,ignoring studying the mechanism of charge injection and dissipation.Therefore,we want to overcome two challenges:?1?the dissipation mechanism of electret charges endowed by electrospinning is unclear yet and?2?charge stability under the surroundings with water and oil molecules needs to be enhanced further.Herein,we report a novel strategy to create electret nanofibrous membranes with high capacity of charge storage and robust charge stability under the environment containing moisture and oily components via electrospinning for the first time.Polyvinyl butyral?PVB?was selected as matrix polymer due to its high electrical resistivity,and silicon nitride nanoparticles?Si₃N₄ NPs?was used as an inspiring charge enhancer because of their high dielectric constant.More importantly,fluorinated polyurethane?FPU?were chosen as a hydro-oleophobic modifier based on its low surface energy.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.Beside,we studied the influence of gram weight,air velocity and particulate matter on the filtration properties of the PVB/Si₃N₄-FPU fibrous membrane.As research shows,as the gram weight increases,the filtration efficiency increases.As the wind speed increases,the filtration efficiency decreases.The filtration efficiency of the fiber membrane to the oil particles is 99.900%.The filtration efficiency of c fiber membrane for Nacl particles is 99.950%.Furthermore,we studied the purification properties of the PVB/Si₃N₄-FPU-2 fiber membrane on PM_2.5.Meanwhile,to compare with other commercial air filter material,benefiting from the high mechanical filtration efficiency with extraordinary stability of charge,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.