A protein-functionalized microfiber/protein nanofiber Bi-layered air filter with synergistically enhanced filtration performance by a viable method

Realization of high filtration efficiency and low pressure drop is in critical need for advanced air filters. Electrospun nanofiber-based air filters create high surface area which can efficiently capture pollutants, but the production rate is difficult to improve and it's challenging to reduce the pressure drop. In this study, we demonstrate that a protein-functionalized cotton-fiber composite air filter with high filtration efficiency and low normalized pressure drop can be fabricated via an evaporation-controlled strategy. It is the first report that a green solvent system (ethanol aqueous), an optimized protein concentration, and evaporation temperature can lead to protein-functionalized cotton filters with improved air filtration efficiency. The resulting loose micro fibrous structure and large pores of cotton fiber mats give rise to a low normalized pressure drop. The high filtration performance results from the unique protein morphology on the cotton fiber surface, e.g. homogeneously distributed protein particles via denaturation process, creating an optimized surface area for interactions between protein and pollutants. In addition, to enhance the filtration efficiency for capturing fine particulate pollutants (i.e. PM1.0, PM0.3), a synergistic bi-layered air filter which combines the zein-functionalized cotton fibers with a thin layer of protein nanofibers is fabricated. It is further demonstrated that the unique configuration of the composite air filter at the upstream side for airflow and protein nanofiber at the downstream side leads to remarkable filtration efficiencies over 99.0% for PM of a broad range of sizes due to a synergistic effect. This study provides a new and cost-effective method with a green solvent involved for efficiently fabricating green and efficient air filters by combining microfibers and nanofibers.