Functionalized multi-effect air filters with bimodal fibrous structure prepared by direction growth of keratin nanofibers

Traditionally, nonwoven air filters have advantages of high filtration efficiency, simple processing technology and low costs. However, nonwoven air filters show poor capability of removing both PMs and harmful gases simultaneously due to the lack of the functional groups as well as inaccessible trade-off in efficiency and resistance, which limits their applications. Herein, an integrated air filter of keratin nanofibers (KNF) and bicomponent microfibers (BMF) nonwovens with bimodal structure has been fabricated via heterogeneous freeze-drying to effectively remove formaldehyde (HCHO) and realize high-efficient filtration. Interestingly, it was found that BMF can not only act as a reinforcement that can endow bimodal structure with excellent me-chanical properties but also regulate airflow resistance and filtration efficiency by inducing directional growth of KNF. Therefore, the results reveal that the KNF/BMF nonwovens possess high filtration efficiency (93.9%) for removing PMs of 0.26 mu m at low airflow resistance (94.92 Pa) and exceptional long-term filtration capability (25.2 g/m2). In addition, the KNF possessing many functional groups shows high removal efficiency for HCHO (>50%) in the 1L quartz closed reactor after 120 min. This study demonstrates that the KNF/BMF nonwovens show great potential applications in the field of multi-efficiency air filters and provide a sustainable strategy for the application of discarded feathers in air remediation.