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DOI: 10.1002/admi.201800628 For example, porous polymeric monoliths have been prepared for the removal of PMs.[3] Recently, various membranes consisting of fibers have been engineered.[4–7] Especially, electrospinning is a powerful method used to fabricate polymer fibers for porous membranes.[8] For example, poly(ethylene terephthalate) (PET) fibers have been extensively engineered.[9] However, the application of PET membrane for the capture of PMs has rarely been reported, possibly due to its poor adsorption behavior.[4–14] To capture the PM2.5 efficiently, electrospun fibers have been engineered to small diameters of sub μm, although they can suffer from a permeability issue.[4–7,10–14] As another chemical strategy, the adsorption performance of fibrous membranes can be enhanced through the introduction of additive materials.[10–14] For example, porous materials such as metal–organic frameworks (MOFs) have been incorporated in the engineering of fibers by electrospinning.[10,13] However, the amounts of additive MOF materials in efficient fibrous membranes were quite high up to ≈50–100 wt%.[10,13] Because the PM2.5 capture is related to the surface properties of fibrous membranes, thin coating approach may be atom-economically efficient. However, reports on efficient thin coating chemistry for fibrous membranes are insufficient.[14–17] Recently, microporous organic networks (MONs) have been synthesized by the coupling of organic building blocks.[18–26] For example, the click reaction of multiazidoarenes with multiethynylarenes resulted in MONs through the formation of triazole rings, showing high surface areas and microporosities.[27–33] Although the click-based MONs (C-MONs) have been tested as gas adsorbents, as far as we are aware, there were no reports on the engineering of C-MONs on fibers. We considered that the coating of PET fibers with C-MONs can enhance adsorption performance. In this work, we report the engineering of C-MONs on the surface of PET fibers (PET@C-MON) and their enhanced adsorption performance toward PMs. Figure 1 shows a synthetic scheme for PET@C-MON fibrous membranes. First, metallic copper with a thickness of 200–300 nm was introduced to the surface of PET fibers with ≈13 μm diameter through electroless deposition.[34] The white PET membrane turned reddish brown through Cu deposition (Figure 2a,b). It is well known that various Cu(I) species including Cu2O can catalyze the click reaction of azide–alkyne cycloaddition.[35] Thus, we partially oxidized metallic copper on This work shows that the adsorptive performance of fibrous membrane can be enhanced by microporous organic network (MON) chemistry. Copper species are introduced into the surface of poly(ethylene terephthalate) (PET) fibers through electroless deposition. Through the Cu2O-catalyzed click reactions of tetra(4-ethynylphenyl)methane with 1,4-diazidobenzene, clickbased MON (C-MON) layers are formed on the PET@Cu@Cu2O. Etching of copper species results in the formation of PET@C-MON membranes that show enhanced removal performance by up to 13.3 times for particulate matters with smaller sizes than 2.5 μm (PM2.5), compared with pristine PET fibers.