Flexible hydroxyapatite ultralong nanowire-based paper for highly efficient and multifunctional air filtration

Abstract

Fine particulate matter (PM) air pollution has been attracting much attention due to its great threat to human health. Herein, we report a new kind of air filter paper with high removal efficiencies for PM_2.5 and PM₁₀ prepared using ultralong hydroxyapatite (HAP) nanowires and cotton (CT) fibers as building blocks through a simple vacuum filtration process. Flexible and biocompatible ultralong HAP nanowires with lengths over 200 μm and diameters of approximately 20 nm are employed for significant improvement of the air filtration performance of commercial CT fibers. The ultralong HAP nanowires intertwine with CT fibers and form the highly porous HAP/CT air filter paper. In addition, by optimizing the proportion of HAP and CT, the as-prepared HAP/CT air filter paper exhibits high removal efficiencies of over 95% for PM_2.5 and PM₁₀; more importantly, it shows a lower pressure drop and a smaller thickness than a commercial breathing mask. Moreover, the fabrication of a large-sized HAP/CT air filter paper with desirable properties through a commercial sheet former is demonstrated. As a proof-of-concept, a homemade breathing mask is fabricated by imbedding the HAP/CT air filter paper into a commercial breathing mask. Furthermore, benefiting from the unique characteristics of ultralong HAP nanowires, other functions such as antibacterial activity can be achieved by the immobilization of silver nanoparticles as the representative bactericide, enabling the fabrication of multifunctional air filter paper. The experimental results suggest that the ultralong HAP nanowire-based air filter paper is promising for various applications in the environmental field.