High-performance air filtration materials are important for addressing the airborne pollutants. Herein, we propose an unprecedented access to biodegradable poly­(lactic acid) (PLA)-based MOFilters with excellent filtering performance and antibacterial activity. The fabrication involved a stepwise in situ growth of zeolitic imidazolate framework-8 (ZIF-8) crystals at the surface of microfibrous PLA membranes, followed by mechanical polarization under high pressure and low temperature (5 MPa, 40 °C) to trigger the ordered alignment of dipoles in PLA chains and ZIF-8. The unique structural features allowed these PLA-based MOFilters to achieve an exceptional combination of excellent tensile properties, high dielectric constant (up to 2.4 F/m), and enhanced surface potential as high as 4 kV. Arising from the remarkable surface activity and electrostatic adsorption effect, a significant increase (from over 12% to nearly 20%) in PM0.3 filtration efficiency was observed for the PLA-based MOFilters compared to that of pure PLA counterparts, with weak relation to the airflow velocities (10–85 L/min). Moreover, the air resistance was controlled at a considerably low level for all the MOFilters, that is, below 183 Pa even at 85 L/min. It is worth noting that distinct antibacterial properties were achieved for the MOFilters, as illustrated by the inhibitive rates of 87 and 100% against Escherichia coli and Staphylococcus aureus, respectively. The proposed concept of PLA-based MOFilters offers unprecedented multifunction integration, which may fuel the development of biodegradable versatile filters with high capturing and antibacterial performances yet desirable manufacturing feasibility.

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Despite the great potential in fabrication of biodegradable and eco-friendly air filters by electrospinning poly­(lactic acid) (PLA) membranes, the filtering performance is frequently dwarfed by inadequate physical sieving or electrostatic adsorption mechanisms to capture airborne particulate matters (PMs). Here, using the parallel spinning approach, the unique micro/nanoscale architecture was established by conjugation of neighboring PLA nanofibers, creating bimodal fibers in electrospun PLA membranes for the enhanced slip effect to significantly reduce the air resistance. Moreover, the bone-like nanocrystalline hydroxyapatite bioelectret (HABE) was exploited to enhance the dielectric and polarization properties of electrospun PLA, accompanied by the controlled generation of junctions induced by the microaggregation of HABE (10–30 wt %). The incorporated HABE was supposed to orderly align in the applied E-field and largely promote the charging capability and surface potential, gradually increasing to 7.2 kV from the lowest level of 2.5 kV for pure PLA. This was mainly attributed to HABE-induced orientation of PLA backbone chains and CO dipoles, as well as the interfacial charges trapped at the interphases of HABE–PLA and crystalline region–amorphous PLA. Given the multiple capturing mechanisms, the micro/nanostructured PLA/HABE membranes were characterized by excellent and sustainable filtering performance, e.g., the filtration efficiency of PM0.3 was promoted from 59.38% for pure PLA to 94.38% after addition of 30 wt % HABE at a moderate airflow capacity of 32 L/min and from 30.78 to 83.75% at the highest level of 85 L/min. It is of interest that the pressure drop was significantly decreased, mainly arising from the slip effect between the ultrafine nanofibers and conjugated microfibers. The proposed combination of the nanostructured electret and the multistructuring strategy offers the function integration of efficient filtration and low resistance that are highly useful to pursue fully biodegradable filters.

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