Nanoporous Organic Network Coating of Nanostructured Polymer Films with Enhanced Adsorption Performance toward Particulate Matter

Macroscale Conjugated Microporous Polymers: Controlling Versatile Functionalities Over Several Dimensions

Since discovered in 2007, conjugated microporous polymers (CMPs) have been developed for numerous applications including gas adsorption, sensing, organic and photoredox catalysis, energy storage, etc. While featuring abundant micropores, the structural rigidity derived from CMPs' stable π-conjugated skeleton leads to insolubility and thus poor processability, which severely limits their applicability, e.g., in CMP-based devices. Hence, the development of CMPs whose structure can not only be controlled on the micro- but also on the macroscale have attracted tremendous interest. In conventional synthesis procedures, CMPs are obtained as powders, but in recent years various bottom-up synthesis strategies have been developed, which yield CMPs as thin films on substrates or as hybrid materials, allowing to span length scales from individual conjugated monomers to micro-/macrostructures. This review surveys recent advances on the construction of CMPs into macroscale structures, including membranes, films, aerogels, sponges, and other architectures. The focus is to describe the underlying fabrication techniques and the implications which follow from the macroscale morphologies, involving new chemistry and physics in such materials for applications like molecular separation/filtration/adsorption, energy storage and conversion, photothermal transformation, sensing, or catalysis.

Advances in particulate matter filtration: Materials, performance, and application

Air-borne pollutants in particulate matter (PM) form, produced either physically during industrial processes or certain biological routes, have posed a great threat to human health. Particularly during the current COVID-19 pandemic, effective filtration of the virus is an urgent matter worldwide. In this review, we first introduce some fundamentals about PM, including its source and classification, filtration mechanisms, and evaluation parameters. Advanced filtration materials and their functions are then summarized, among which polymers and MOFs are discussed in detail together with their antibacterial performance. The discussion on the application is divided into end-of-pipe treatment and source control. Finally, we conclude this review with our prospective view on future research in this area.

Fabrication of Fiber@Microporous Organic Polymer with Amino Groups@Cu Films for Flexible and Metal-Economical Electromagnetic Interference Shielding Materials

Flexible and metal-economical electromagnetic interference (EMI) shielding films were fabricated based on microporous organic polymer (MOP) chemistry. MOP with amino groups (MOP-A) could be introduced to the surface of poly(ethylene terephthalate) (PET) fibers. Due to the microporosity and amino groups of MOP-A, Ag⁺ could be easily incorporated into PET@MOP-A. Through Ag-catalyzed electroless Cu deposition, PET@MOP-A@Cu films were fabricated. The morphological and chemical structures of the PET@MOP-A@Cu were characterized by scanning electron microscopy, X-ray diffraction studies, and X-ray photoelectron spectroscopy. Among the films, the PET@MOP-A@Cu-40 with 41 wt % Cu (a thickness of 0.64 μm) showed excellent EMI shielding performance with 64.3-73.8 dB against an EM of 8-12 GHz. Moreover, it showed retention of the original EMI shielding performance against 1000 bending (R = 5 mm) tests.

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

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.

Effect of Functional Groups of Metal-Organic Frameworks, Coated on Cotton, on Removal of Particulate Matters via Selective Interactions

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.

Hyper-Cross-Linked Polymer on the Hollow Conjugated Microporous Polymer Platform: A Heterogeneous Catalytic System for Poly(caprolactone) Synthesis

This work shows that the shape-controlled microporous organic polymer (MOP) can be utilized for the morphological engineering of another class of MOP materials. The morphology of a hyper-cross-linked polymer (HCP) was successfully engineered on the hollow conjugated microporous polymer (CMP). Through the postsynthetic modification of HCP bearing BINOLs (HCP-B) on the hollow CMP-like material (H-CMPL), the HCP bearing BINOL phosphoric acid (HCP-BP) was engineered on the H-CMPL platform. The resultant H-CMPL@HCP-BP showed good catalytic performance as a heterogeneous catalytic system and excellent recyclability in the ring-opening polymerization of ε-caprolactones to poly(caprolactone).