Currently, the contamination of air with particulate matters (PMs such as PM2.5 and PM10) is very severe, especially in Asian countries. Metal–organic frameworks (MOFs), with or without extra functional groups such as −NH2 and −NH-SO3H, were coated on conventional cotton to improve the efficiency of filters (composed of cotton fabric) in the removal of PMs from air. More importantly, the effect of the functional group of MOFs on the effective PM removal was analyzed quantitatively for the first time and could be interpreted via selective interactions. The removal efficiency was increased on the order: cotton < UiO-66/cotton < UiO-66-NH2/cotton < UiO-66-NH-SO3H/cotton, and the efficiency of the UiO-66-NH-SO3H-coated cotton was more than three times that of the pristine cotton. Moreover, the quality factor of cotton was more than doubled (or, 2.5–3 times) by UiO-66-NH-SO3H (only 20%) coating. The plausible mechanism for PM removal could be suggested based on the characterization of captured PM and introduced functional groups on MOFs. Based on the removal efficiency, pressure drop, and quality factor, coating of MOFs with functional groups, especially that are effective for charge separations (such as −SO3H), is one of the promising ways to improve the performance of PM filters. Moreover, the suggested strategy might be applied in capturing most of PMs composed of oxides, ammonium species, and carbons with polar outside.

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Currently, air contamination, especially with particulate matters (PMs), is severe in several countries. To increase the efficiency of air filters in PM removal, metal−organic frameworks (MOFs, here, Zr-MOFs, especially with functional groups (FGs) such as −NO 2 ) were coated, after synthesis, onto cotton using covalent bonding for the first time. The removal efficiencies (REs) and quality factors (QFs) of cottons with or without MOFs were in the order: cotton < Zr-MOF/cotton < Zr-MOF-NH 2 /cotton < Zr-MOF-NH-SO 3 H/cotton < Zr-MOF-NH 3 + Cl − /cotton < Zr-MOF-NO 2 /cotton. This monotonic increase in the PM removal efficiency or QF could be explained with the order of charge separation or developed charges (total, in absolute value: ∼0 to 2.0) on FGs of MOFs. Importantly, Zr-MOF-NO 2 coating on cotton showed a very high increase in the performance of cotton in PM removal. QF and RE of Zr-MOF-NO 2 /cotton were 4.6 times and 6.2 times of the bare cotton, respectively, for PM2.5 removal, even with a very small increase in pressure drop (3 Pa or less) with MOF coating. Based on the research, it can be suggested that coating MOFs on substrates is a promising way to improve the performances of air filters for PM removal, especially when MOFs have FGs that can have large charge separation such as −NO 2 . This work may pave a way to utilize a functionalized MOF in the effective removal of PMs from air.

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