A novel gradient structured nanofiber and silver nanowire composite membrane for multifunctional air Filters, oil water Separation, and health monitoring flexible wearable devices.

Particular matter (PM), oily wastewater, and microorganisms (e.g., bacteria) have caused serious environmental, health, and safety issues. However, the development of multifunctional filtration materials to address these problems remains a great challenge. Here, we present a series of gradient structured air filters by simply spray coating poly(vinyl alcohol-co-ethylene) (PVA-co-PE) nanofibers on nylon mesh, followed by silver nanowires (AgNWs). Interestingly, it is found that the ANF-6 air filter is an anisotropic Janus membrane with asymmetric wettability and translucency. The as-prepared ANF-6 air filter exhibits excellent water vapor transmission rate (4447.92 ± 184.78 g/(m. d)), PM filtration (96.42 ± 0.64 % for PM), photothermal (79.6 °C under 1sun in 150 s), thermal insulation, antibacterial, and oil water separation. Additionally, the obtained ANF-6 air filter was impregnated with carbon black (CB) dispersion and served as flexible pressure sensors to monitor human respiration rate (17 times/min) and wrist pulse rate (80 times/min). The gradient structured PVA-co-PE nanofibers and AgNWs network provides excellent air filtration, oil water separation, and sensitivity performance for the sensors. These results provide a new scheme for designing multifunctional filtration materials and wearable pressure sensors in the application of air filtration, oil water separation, and wearable electronics for monitoring human health.