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

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.