Stretchable and Compressible Si₃N₄ Nanofiber Sponge with Aligned Microstructure for Highly Efficient Particulate Matter Filtration under High-Velocity Airflow

Particulate matter (PM) is one of the most severe air pollutants and poses a threat to human health. Air filters with high filtration efficiency applied to the source of PM are an effective way to reduce pollution. However, many of the present filtration materials usually fail because of their high pressure drop under high-velocity airflow and poor thermal stability at high temperatures. Herein, a highly porous Si₃N₄ nanofiber sponge (Si₃N₄ NFS) assembled by aligned and well-interconnected Si₃N₄ nanofibers is designed and fabricated via chemical vapor deposition (CVD). The resulting ultralight Si₃N₄ NFS (2.69 mg cm⁻³) processes temperature-invariant reversible strechability (10% strain) and compressibility (50% strain), which enables its mechanical robustness under high-velocity airflow. The highly porous and aligned microstructure result in a Si₃N₄ NFS with high filtration efficiency for PM_2.5 (99.97%) and simultaneous low pressure drop (340 Pa, only <0.33% of atmospheric pressure) even under a high gas flow velocity (8.72 m s⁻¹) at a high temperature (1000 °C). Furthermore, the Si₃N₄ NFS air filter exhibits good long-term service ability and recyclability. Such Si₃N₄ NFS with aligned microstructures for highly efficient gas filters provides new perspectives for the design and preparation of high-performance filtration materials.