Zeolitic-imidazolate-framework filled hierarchical porous nanofiber membrane for air cleaning

Severe environmental impact caused by particulate matters (PM) and chemical gaseous pollutants (SO₂, NO_x, VOCs) has become a global atmospheric issue. Seeking an effective way for both PM removal and other pollutants is urgent and remains a challenge. Herein, we introduced a zeolitic imidazolate framework (ZIF-67) trap-in polystyrene hierarchical porous nanofiber membrane (ZIF-67/PS HPNFM) for both PM and SO₂ filtration. By controlling the hierarchical porous structure we achieve highly-effective and multi-functional air cleaning membrane that has remarkably low resistance. The macropores interwoven by nanofibers offer high gas permeance of 1489 m³ m⁻² h⁻¹ kPa⁻¹ which ensure a low pressure drop of 91 Pa. Meanwhile, the filled ZIF-67 enhanced the PM capture so that the ZIF-67/PS HPNFM showed a very high PM (<0.3 μm) removal efficiency of 99.921%. The mesopores in each nanofiber provided the gas permeating channels that direct SO₂ to ZIF-67. Further, the micropores from ZIF-67 dramatically enhanced the surface area (236 m² g⁻¹) and porosity (0.259 cm³ g⁻¹) which resulted in a good SO₂ adsorption capacity (1362 mg g⁻¹) at room temperature and humidity of 55%. The hierarchical porous structure membrane with multifunction provides a new concept for synergistic removal of various air contaminants.