Lotus leaf-inspired poly(lactic acid) nanofibrous membranes with enhanced humidity resistance for superefficient PM filtration and high-sensitivity passive monitoring

The biomimetic design principles offer promising solutions to fabrication of multifunctional nanofibrous membranes (NFMs) with on-demand hierarchies and properties. Herein, a combined electrospinning electrospray approach was employed to firmly anchor MOF nanocrystals onto poly(lactic acid) (PLA) nanofibers, resembling the naturally occurring dense protrusions at the lotus leaf. The formation of unique MOF-protruding superstructures gave rise to an exceptional combination of increased electroactivity, in-situ electret properties and charge regeneration mechanisms, as well as remarkable humidity resistance. With 8 wt% bioinspired MOF-protrusions for the electrospun electrosprayed PLA NFMs (BM-PLA8), the initial surface potential was elevated to 3.0 kV and slightly decreased to 2.6 kV after 7-day ageing, in clear contrast to only 1.1 and 0.6 kV for the normal PLA, respectively. Moreover, the tribo-output voltage and current were significantly promoted for BM-PLA8 (64.5 V and 151.6 nA), demonstrating high humidity resistance and long-term robustness even at 90 % RH. It conferred distinct improvements in air filtration performance for BM-PLA8 even at the highest airflow velocity of 85 L/min (below 250 Pa, 99.9 % and 95.0 % removal of PM 2.5 and PM 0.3 , respectively), far surpassing the normal PLA counterpart (nearly 350 Pa, 89.5 % and 75.8 %). Arising from the respiration-driven charge regeneration mechanisms, passive respiratory monitoring of high sensitivity was demonstrated for BM-PLA8, showing great promise for efficient healthcare under the challenging circumstances.