Robust Lignin-Based Aerogel Filters: High-Efficiency Capture of Ultrafine Airborne Particulates and the Mechanism

In this article, we report a new type of lignin-based wood-like aerogel filters composed of aligned micrometer-sized pores and cross-linked lignin-based cell walls, as well as their air filtration-related properties. The aerogel filters were prepared via facile unidirectional ice-crystal-induced self-assembly from an aqueous solution, followed by annealing at 300 °C. The cross-linking of lignin and reinforcement with a very small amount of graphene significantly enhance the mechanical stiffness, thermal stability, and humidity/water resistance of the aerogels. Simultaneously, abundant functional groups retained from lignin and the aligned pore channels lead to high filtration efficiency for ultrafine particles accompanied by fairly low pressure drop. Moreover, these low-cost and renewable biomass-based filters also exhibit outstanding long-term filtration efficiency. Through filtration tests with particles of various sizes, it is revealed that the air filtration by this type of aerogel filters is dominated by diffusion, rather than impaction or interception mechanism, which offers a new avenue for design of novel high-performance air filters.