Hierarchical isoporous membrane filters for simultaneous reduction of pressure drop and efficient removal of nanoscale airborne contaminants

•Isoporous structure has the potential to achieve high filtration efficiency as the pore sizes can be designed to achieve accurate size selectivity.•we report an approach to simultaneously maximize filtration efficiency and minimize pressure drop in multi-layer isoporous membranes via a built-in micro-spacer array.•Finite element analysis (FEA) reveals the effects of the micro-spacer geometries in controlling the air stream direction, the associated kinetic loss and hence the reduced pressure drop across bilayer isoporous membranes.•The FEA results corroborate the performance of experimentally fabricated bilayer isoporous membranes with built-in micro-spacer array; a low pressure drop of ∼300 Pa at 7 cm/s, and >95% filtration efficiency for particle between 300 nm and 2 µm has been achieved.•The introduction of micro-spacer array in multi-layer isoporous membranes extends the performance limit of traditional filtration media especially for challenging applications such as air purification and respiratory filtration under high workload conditions.