A Nanoprotein-Functionalized Hierarchical Composite Air Filter

Building nanostructured active materials and rational porous structures in air filters will be significant in realizing high filtration efficiency and low normalized pressure drop. The construction of nanofabrics by electrospinning can lead to large active surface areas, but it has been challenging to control the porous structures to reduce the normalized pressure drop, in particular for thick fabrics. To address this issue, here, we report a protein-functionalized composite air filter with hierarchical structures. This composite is made of bacterial nanocellulose coated by protein nanoparticles and microcellulose fibers from wood pulp. The protein-functionalized nanocellulose can not only help expose the functional groups of protein for trapping pollutants but also act as a binder to reinforce the composite fabrics. At the same time, the long microcellulose fibers form large pores, reducing normalized pressure drop and improving mechanical properties. By adjusting the component ratios, we demonstrate a high-performance protein/nanocellulose/microcellulose composite air filter with high filtration efficiency of above 99.5% for PM1-2.5 but extremely low normalized pressure drop of 0.194 kPa/g, which is only about 1% of that for protein nanofabrics constructed by electrospinning. This study brings about a cost-effective strategy based on protein-functionalized hierarchical composite fabrics for fabrication of an advanced, green, sustainable air filter.