Large-scale preparation of micro-gradient structured sub-micro fibrous membrane with narrow diameter distribution for high-efficiency air purification
Micro-gradient structured polyacrylonitrile (PAN) sub-micro fibrous membrane composed of coarse, medium, and fine (C, M, and F) fiber layers with different fiber diameters in submicron scale range was fabricated via one-step free surface electrospinning with large-scale productivity, which was first demonstrated as air filter. The sub-micro fibers with narrow diameter distribution for each layer were regulated precisely in micro-gradient structure, also, the influence of the arrangement for layers on performance of the membrane was analyzed systematically, among which the membrane with F-M-C displayed the optimal performance (filtration efficiency of 99.28% and pressure drop of 55.86 Pa). Besides, the filtration performance of composite membrane could be further improved to efficiency of 99.99% and drop of 92 Pa only by surface modification of the finest fibrous layer. Furthermore, the micro-gradient structure of membrane could be regulated and fabricated arbitrarily with different gradient degree, even at nanometer level. Via polymer blending, the upgraded micro-gradient structured filter (the average fiber diameters of each layer were only 200, 110 and 70 nm) possessed ~1 μm average pore size, larger specific surface area (53.12 m2 g-1) and excellent efficiency of 99.97% (F-M-C) with resistance of 106.8 Pa, superior to those of the homogeneous PAN filter. The results suggested that the micro-gradient structured fibrous membrane composed of C, M, and F layers with tortuous channels could efficiently separate different sized PMs from the airstream through the capturing mechanisms. The cost-effective micro-gradient filter media produced by one-step free surface electrospinning was promising for the industrial production and commercial application.