A dual-scale Janus filter for enhanced oil-aerosol filtration performance via oil-guiding transmission

Air pollution has necessitated the large-scale utilization of air filters in aerospace, healthcare, personal protection, and manufacturing sectors. However, high-efficiency filters often exhibit high airflow resistance, increasing energy costs, especially when filtering liquid airborne pollutants like oil aerosols. These pollutants tend to coalesce into liquid films on the filters. Although regulating the wettability of a filter can reduce airflow resistance, the dynamic coalescence behavior and its effects on airflow transport remain unclear. Herein, we present a dual-scale Janus filter for oil aerosol capture. This filter, produced using an industrial papermaking process, features a pore-size gradient and asymmetric wettability. The dynamic coalescence behavior between oil aerosols and filter surfaces at the micro/nanoscale indicates that the superoleophilic layer serves as an oil-guiding layer, destroying the integrity of the oil film deposited on the superoleophobic filter layer and thereby facilitating airflow transport across the Janus filter. The Janus filter exhibits a 30 % lower steady-state pressure drop, higher filtration efficiency (99.4 %), higher dust-holding capacity (286 g m −2 ), and >8 times longer lifetime than those of commercial filters. As a proof-of-concept, the performance of an air purifier comprising Janus filters is demonstrated. These findings promote the development of efficient, energy-saving coalescence filters.