Surface hydration of fibrous filters by using water-absorbing metal–organic frameworks for efficient ultrafine particulate matter removal

Air pollution, particularly from particulate matters (PMs), has become a serious global issue. Thus, there are increasing demands for improving PM filtering systems for public safety. Here, we have first demonstrated that the surface hydration of electrospun fiber-based filters significantly improves capturing ability of ultrafine PM_0.3 (PMs having a diameter of ∼ 0.3 µm). Aluminum-based metal–organic framework (MOF)–303, which is uniformly coated on the surface of polyimide nanofibers (PI NFs), provides sufficient surface hydration with PI NFs due to its high-water uptake capability, resulting in favorable trapping sites for polar molecules or particles in the air. Furthermore, the MOF–303-coated PI NF (PI@MOF–303) filters show relatively low pressure drops, which can be attributed to increasing fiber diameters after MOF–303 coating, resulting from enlarged spaces between fibers. Consequently, the PI@MOF–303 filters afford highly efficient PM_0.3 removal properties (95.70%) and low pressure drop (ΔP = 36.73 Pa). Our strategy offers new insights into the fabrication of high-performance electrospun fiber-based filters with desirable properties for filtering PMs.