Mussel-inspired approach to cross-linked functional 3D nanofibrous aerogels for energy-efficient filtration of ultrafine airborne particles

Polymer aerogels fabricated using conventional methods typically have relatively narrow mono-modal pore size distribution (PSD), and relatively thick and tight pore walls. Herein, inspired by mussel glue, cross-linked three-dimensional (3D) polyacrylonitrile (PAN) nanofibrous aerogels (NFAs) with ultrahigh porosity, hierarchical porous structures, and good compression resistance are successfully fabricated via electrospinning, facile polydopamine (PDA) coating and crosslinking by ferric ions (Fe3+) followed by freeze-drying. Morphology characterization and compression tests show that both multiple hydrogen bonding facilitated by the PDA coating and Fe3+-PDA coordination bonding could effectively induce the formation of inter-fiber junctions, enhancing compression resistance of the 3D NFAs and leading to hierarchical porous structures with a very wide PSD. When a thin layer of the optimized 3D NFA with a large specific surface area (85.7 m2 g−1) is combined with a commercial air filter, the composite filter obtained exhibits high filtration efficiencies of 99.72% and 99.85% for airborne particles with sizes of <100 nm and <500 nm, respectively, at a low pressure drop of only 54.1 Pa. The results show that the cross-linked NFAs could act as a highly efficient air filter for ultrafine particles while not increasing the overall pressure-drop significantly, which are due to the good adhesive properties of PDA, electrostatic charge induced by Fe3+, and high porosity and hierarchical porous structures of the 3D NFAs.