Enhanced 3D sponge with asymmetric wettability: an efficient solution for ultra-low resistance oil aerosol filtration over extended durations

Oil aerosols frequently lead to air pollution, health concerns, and the corrosion of equipment. The removal of oil aerosol from the atmosphere is critical in both industrial manufacturing and everyday living. Despite the prevalent use of 2D fibrous filters for the capture of oil aerosols, achieving efficient filtration with minimal resistance remains a significant hurdle. Herein, we report a novel method for creating 3D porous filters, which substantially diminishes the pressure drop during filtration. Employing a dip-coating technique, we produced superamphiphilic sponges (SALS) and superamphiphobic sponges (SABS), which were then combined to engineer thickness-directional asymmetric wettability. The most effective filtration was observed when the sponge arrangement consisted of SALS in the front and SABS in the rear, both with thickness of 3.5 cm. Under optimal conditions, the filtration efficiency reached 96.16% with a pressure drop of merely 0.048 kPa, yielding an ultra-high quality factor of 67.71 kPa⁻¹. Additionally, this material is capable of continuous oil mist separation for at least 24 hours, a duration significantly longer than that reported for previously studied 2D fibrous filters. This unforeseen development may offer a novel paradigm for the design of 3D porous filters that are not only high-performing but also energy-efficient and long-lasting.