Highly Improved Performance of Cotton Air Filters in Particulate Matter Removal by the Incorporation of Metal-Organic Frameworks with Functional Groups Capable of Large Charge Separation.

Abstract

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 -NO2) 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-NH2/cotton < Zr-MOF-NH-SO3H/cotton < Zr-MOF-NH3+Cl-/cotton < Zr-MOF-NO2/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-NO2 coating on cotton showed a very high increase in the performance of cotton in PM removal. QF and RE of Zr-MOF-NO2/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 -NO2. This work may pave a way to utilize a functionalized MOF in the effective removal of PMs from air.