Hierarchically porous polyimide nanofiber membranes with enhanced thermal stability for efficient high-temperature air filtration

“Process first, strengthen later” strategy for polyimide filtration membranes • NIPS-assisted wet spinning constructs hierarchical porous nanofiber structure • 99.4% PM 0.3 filtration efficiency with low pressure drop of 98.6 Pa • S to -SO 2 - conversion enhances Tg (248.3 °C) and T 5 % (479.5 °C) • P-OPSI membrane maintains stable performance up to 450 °C High temperature industrial flue gas containing PM 0.3 particles poses serious environmental and health risks, making the development of polymer filtration membranes that combine processability, thermal stability, and high filtration efficiency a key challenge. This work propose a strategy of “processing first, then strengthening”, utilizing the dual function of sulfide ( S ) groups: their conformational flexibility can improve solubility and solution processability during membrane preparation, while their oxidizability allows them to be converted into highly thermally stable sulfone (-SO 2 -) groups through mild conversion reactions after synthesis without damaging the formed nanofiber structure. Firstly, soluble sulfide containing polyimide resin (PSI) was synthesized, and then processed into a component level porous nanofiber membrane (P-PSI) through non-solvent induced phase separation (NIPS) assisted wet spinning. Subsequently, through mild liquid-phase oxidation treatment, the S group was selectively converted into sulfone (-SO 2 -) groups without damaging the nanofiber structure, resulting in the formation of an oxidized porous PSI membrane (P-OPSI). The resulting P-OPSI membrane exhibits high specific surface area (76.1 m 2 /g), large surface pore size (25.3 nm), and high porosity (38.5%). It achieves a PM 0.3 filtration efficiency of 99.4% at wind speed of 0.53 m/s, with low pressure drop of 98.6 Pa and quality factor of 0.052 Pa −1 . Crucially, the P-OPSI membrane demonstrates significantly enhanced thermal properties, with glass transition temperature of 248.3 °C and 5% thermal weight loss temperature of 479.5 °C. This work establishes that the S to -SO₂- conversion strategy offers powerful and universal approach for designing high-performance polymer membranes for harsh high-temperature particle control. Download: Download high-res image (322KB) Download: Download full-size image