Synergic Cellulose Nanofiber/Tourmaline Nanoparticle-Assembled Layered Piezoelectric Cryogels for High-Performance Airborne Particulate Filtration.

Here, hybrid stimuli-responsive (exhibiting pyroelectricity and piezoelectricity) porous cryogels are engineered by embedding tourmaline nanoparticles (TNs) in a cellulose nanofiber (CNF) skeleton to generate high-performance CNF-TN-based airborne particulate matter (PM) filters. First, single-layer hybrid cryogels with varying TN contents (0-5% w v) are assembled, and the design principles for multilayered filters are established based on a novel sequential pre-freezing and freeze-drying technique. As observed, the embedded TNs transformed the CNF network into a more homogeneous, isotropic, and firm structure, thus improving the structural integrity and thermal stability of the assembled cryogels while maintaining their ultrahigh porosity and low density. The TN induced piezoelectric voltage in the cryogels during filtration significantly enhanced the filtration performance. Furthermore, the patterned surface texture of the cryogels notably improved quality factor (Q) and the reusability of the layered filters overall. The explored hybrid cryogels, particularly those exhibiting multilayered configurations, can be deployed for high-performance airborne particulates filtration owing to the synergistic effect of their mechanical robustness, stability, and high filtration efficiency. As far as it is known that, the Q values (>0.04) obtained by the three-layered cryogels are similar to or even higher than those of the reported best aerosol filters.