Functionalized Double‐Gradient Janus Filters for Full‐Scale Capture and Inactivation of Multiscale Aqueous Bioaerosols

Abstract Exposure to bioaerosols can result in severe infection and even death, prompting the development of numerous air filters to capture and inactivate bioaerosols. Although the wettability of filter media determines its bioaerosol‐capture efficiency, the dynamic collision behavior of multiscale aqueous bioaerosols on most filter media is poorly understood. A double‐gradient Janus paper (Janus paper) with a pore‐size gradient, asymmetric wettability, and biocidal and bioadhesion properties is fabricated in this study using an industrially available papermaking process. The dynamic collision behavior at the micrometer and millimeter scales indicates that the Janus paper enables the full‐scale blocking and/or capture of aqueous aerosols by a two‐step mechanism where the water‐repellent top layer blocks large‐size aqueous aerosols, while the hydrophilic bottom layer permits the adherence of small‐size aerosols to its fibers. The Janus paper exhibits a higher capture and inactivation capacity (inactivation efficiency: 98.3%), better dust‐holding capacity (> 21 g m −2 ), and a longer lifetime than commercial filter media. Commercial air purifiers comprising the Janus paper exhibit high potential for large‐scale commercial applications owing to the facile, low‐cost, and scalable fabrication method. This study enables future research on efficient and practicable Janus‐paper filter media.