Stable low resistance air filter under high humidity endowed by self-emission far-infrared for effective PM2.5 capture

•The sharp rise of pressure drop under high humidity is addressed.•Resonance effect of FIR and water was firstly introduced to air filtration field.•The effect of FIR emissivity on the stability of pressure drop is revealed.•The resultant membranes exhibited excellent performance.

Air filters have attracted increasing attention due to the lethal danger of haze pollution worldwide. However, it remains challenging to fabricate air filtration materials that can remove particles efficiently and especially allow air flowing easily under the high relative humidity (RH) of haze environment. Here we designed an air filter exhibiting low and stable resistance towards moisture by taking advantage of the resonance effect between far infrared ray (FIR) and water molecules. Polyacrylonitrile (PAN) fibers were endowed with high FIR emissivity via optimizing the content of far infrared nanoparticles (FIPs) and the typical multi-level rough structure of fibrous membranes. Significantly, benefitting from the improved FIR emissivity, the rising rate of pressure drop declined from 20 to 8.9% under high RH of 85%. The stabilization mechanism of pressure drop was revealed by means of low field nuclear magnetic resonance. Furthermore, a high filtration efficiency of 99.998%, low pressure drop of 79.5 Pa, and particularly low rising rate of pressure drop (6%) were achieved simultaneously by obtaining the balance of pore size (2.1 μm) and FIR emissivity (87%). The resultant membranes exhibited a rapid PM2.5 removal rate (~15 min) after 10 h, and a robust stability of low pressure drop (increased by 8.7% after 25 h) in the field test in Shanghai. The fabrication of such a promising material may provide a new insight to design air filtration materials with durable high performance.