Spray-Freezing-Templated Vertically-Graded Macroporous Aerogel Membranes for Ultrahigh-Flux Filtration of Polydisperse Microplastics.

Abstract

Vertical gradients in membrane structure and functionality are critical for achieving high filtration efficiency, precise size selectivity, and enhanced anti-fouling properties. However, the fabrication of vertically graded membranes with controlled micro-pore size distribution and directional functionality remains a significant challenge in both scalability and reproducibility. Herein, a gradient aerogel (GE) membrane was fabricated via a one-step temperature-gradient-controlled spray-freezing process that synergistically controls substrate temperature, suspension flow rate, and nozzle-to-substrate distance to match solidification front velocity with droplet accumulation dynamics. This approach generates a seamless pore gradient from ∼100 µm at the top surface down to ∼3 µm at the base, containing restrictive pore throats as small as ∼0.2 µm. The resulting GE membrane delivers ultra-high flux of 35 586 and 25 479 L m^- ² h^- ¹ bar^- ¹ for 10 and 5 µm microplastics, respectively, with >99.7% retention. Crucially, in sediment-rich environments, the GE membrane outperforms commercial counterparts, where its hierarchical architecture effectively manages sediment load to sustain significantly higher flux and retention efficiency for polydisperse microplastics (1-10 µm). This scalable platform technology provides a versatile foundation for next-generation separation materials and multifunctional composite architectures.