Postsynthetically Modified Polymers of Intrinsic Microporosity (PIMs) for Capturing Toxic Gases

Advanced Materials for NH3 Capture: Interaction Sites and Transport Pathways

Ammonia (NH3) is a carbon-free, hydrogen-rich chemical related to global food safety, clean energy, and environmental protection. As an essential technology for meeting the requirements raised by such issues, NH3 capture has been intensively explored by researchers in both fundamental and applied fields. The four typical methods used are (1) solvent absorption by ionic liquids and their derivatives, (2) adsorption by porous solids, (3) ab-adsorption by porous liquids, and (4) membrane separation. Rooted in the development of advanced materials for NH3 capture, we conducted a coherent review of the design of different materials, mainly in the past 5 years, their interactions with NH3 molecules and construction of transport pathways, as well as the structure-property relationship, with specific examples discussed. Finally, the challenges in current research and future worthwhile directions for NH3 capture materials are proposed.

High-Performance Porous Organic Polymers for Environmental Remediation of Toxic Gases

Sulfur dioxide (SO2) is a harmful acidic gas generated from power plants and fossil fuel combustion and represents a significant health risk and threat to the environment. Benzimidazole-linked polymers (BILPs) have emerged as a promising class of porous solid adsorbents for toxic gases because of their chemical and thermal stability as well as the chemical nature of the imidazole moiety. The performance of BILPs in SO2 capture was examined by synergistic experimental and theoretical studies. BILPs exhibit a significantly high SO2 uptake of up to 8.5 mmol g-1 at 298 K and 1.0 bar. The density functional theory (DFT) calculations predict that this high SO2 uptake is due to the dipole-dipole interactions between SO2 and the functionalized polymer frames through O2S(δ+)···N(δ-)-imine and O═S═O(δ-)···H(δ+)-aryl and intermolecular attraction between SO2 molecules (O═S═O(δ-)···S(δ+)O2). Moderate isosteric heats of adsorption (Qst ≈ 38 kJ mol-1) obtained from experimental SO2 uptake studies are well supported by the DFT calculations (≈40 kJ mol-1), which suggests physisorption processes enabling rapid adsorbent regeneration for reuse. Repeated adsorption experiments with almost identical SO2 uptake confirm the easy regeneration and robustness of BILPs. Moreover, BILPs possess very high SO2 adsorption selectivity at low concentration over carbon dioxide (CO2), methane (CH4), and nitrogen (N2): SO2/CO2, 19-24; SO2/CH4, 118-113; SO2/N2, 600-674. This study highlights the potential of BILPs in the desulfurization of flue gas or other gas mixtures through capturing trace levels of SO2.

Construction of N-Rich Aminal-Linked Porous Organic Polymers for Outstanding Precombustion CO2 Capture and H2 Purification: A Combined Experimental and Theoretical Study

A large number of scientific investigations are needed for developing a sustainable solid sorbent material for precombustion CO2 capture in the integrated gasification combined cycle (IGCC) that is accountable for the industrial coproduction of hydrogen and electricity. Keeping in mind the industrially relevant conditions (high pressure, high temperature, and humidity) as well as good CO2/H2 selectivity, we explored a series of sorbent materials. An all-rounder player in this game is the porous organic polymers (POPs) that are thermally and chemically stable, easily scalable, and precisely tunable. In the present investigation, we successfully synthesized two nitrogen-rich POPs by extended Schiff-base condensation reactions. Among these two porous polymers, TBAL-POP-2 exhibits high CO2 uptake capacity at 30 bar pressure (57.2, 18.7, and 15.9 mmol g-1 at 273, 298, and 313 K temperatures, respectively). CO2/H2 selectivities of TBAL-POP-1 and 2 at 25 °C are 434.35 and 477.93, respectively. On the other hand, at 313 K the CO2/H2 selectivities of TBAL-POP-1 and 2 are 296.92 and 421.58, respectively. Another important feature to win the race in the search of good sorbents is CO2 capture capacity at room temperature, which is very high for TBAL-POP-2 (15.61 mmol g-1 at 298 K for 30 to 1 bar pressure swing). High BET surface area and good mesopore volume along with a large nitrogen content in the framework make TBAL-POP-2 an excellent sorbent material for precombustion CO2 capture and H2 purification.

Porous acid-base hybrid polymers for enhanced NH3 uptake with assistance from cooperative hydrogen bonds

Carboxylic acid-modified materials are a common means of achieving efficient NH3 adsorption. In this study, we report that improved NH3 adsorption capacity and easier desorption can be achieved through the introduction of substances containing Lewis basic groups into carboxylic acid-modified materials. Easily synthesized mesoporous acid-base hybrid polymers were constructed with polymers rich in carboxylic acid and Lewis base moieties through cooperative hydrogen bonding interactions (CHBs). The hybrid polymer PAA-P4VP presented higher NH3 capacity (18.2 mmol g-1 at 298 K and 1 bar NH3 pressure) than PAA (6.0 mmol g-1) through the acid-base reaction and the assistance from CHBs with NH3, while the NH3 desorption from PAA-P4VP was easier for the reformation of CHBs. Based on the introduction of CHBs, a series of mesoporous acid-base hybrid polymers was synthesized with NH3 adsorption capacity of 15.8-19.3 mmol g-1 and high selectivity of NH3 over CO2 (SNH3/CO2 = 25.4-56.3) and N2 (SNH3/N2 = 254-1068), and the possible co-existing gases, such as SO2, had a lower effect on NH3 uptake by hybrid polymers. Overall, the hybrid polymers present efficient NH3 adsorption owing to the abundant acidic moieties and CHBs, while the concomitant Lewis bases promote NH3 desorption.

Using molecular straps to engineer conjugated porous polymer growth, chemical doping, and conductivity

Controlling network growth and architecture of 3D-conjugated porous polymers (CPPs) is challenging and therefore has limited the ability to systematically tune the network architecture and study its impact on doping efficiency and conductivity. We have proposed that π-face masking straps mask the π-face of the polymer backbone and therefore help to control π-π interchain interactions in higher dimensional π-conjugated materials unlike the conventional linear alkyl pendant solubilizing chains that are incapable of masking the π-face. Herein, we used cycloaraliphane-based π-face masking strapped monomers and show that the strapped repeat units, unlike the conventional monomers, help to overcome the strong interchain π-π interactions, extend network residence time, tune network growth, and increase chemical doping and conductivity in 3D-conjugated porous polymers. The straps doubled the network crosslinking density, which resulted in 18 times higher chemical doping efficiency compared to the control non-strapped-CPP. The straps also provided synthetic tunability and generated CPPs of varying network size, crosslinking density, dispersibility limit, and chemical doping efficiency by changing the knot to strut ratio. For the first time, we have shown that the processability issue of CPPs can be overcome by blending them with insulating commodity polymers. The blending of CPPs with poly(methylmethacrylate) (PMMA) has enabled them to be processed into thin films for conductivity measurements. The conductivity of strapped-CPPs is three orders of magnitude higher than that of the poly(phenyleneethynylene) porous network.

Non-solvent post-modifications with volatile reagents for remarkably porous ketone functionalized polymers of intrinsic microporosity

Chemical modifications of porous materials almost always result in loss of structural integrity, porosity, solubility, or stability. Previous attempts, so far, have not allowed any promising trend to unravel, perhaps because of the complexity of porous network frameworks. But the soluble porous polymers, the polymers of intrinsic microporosity, provide an excellent platform to develop a universal strategy for effective modification of functional groups for current demands in advanced applications. Here, we report complete transformation of PIM-1 nitriles into four previously inaccessible functional groups - ketones, alcohols, imines, and hydrazones - in a single step using volatile reagents and through a counter-intuitive non-solvent approach that enables surface area preservation. The modifications are simple, scalable, reproducible, and give record surface areas for modified PIM-1s despite at times having to pass up to two consecutive post-synthetic transformations. This unconventional dual-mode strategy offers valuable directions for chemical modification of porous materials.

Evaluation of an Imine-Linked Polymer Organic Framework for Storage and Release of H2S and NO

Hydrogen sulfide (H₂S) and nitric oxide (NO) are especially known as toxic and polluting gases, yet they are also endogenously produced and play key roles in numerous biological processes. These two opposing aspects of the gases highlight the need for new types of materials to be developed in addition to the most common materials such as activated carbons and zeolites. Herein, a new imine-linked polymer organic framework was obtained using the inexpensive and easy-to-access reagents isophthalaldehyde and 2,4,6-triaminopyrimidine in good yield (64%) through the simple and catalyst-free Schiff-base reaction. The polymeric material has microporosity, an A_BET surface area of 51 m²/g, and temperature stability up to 300 °C. The obtained 2,4,6-triaminopyrimidine imine-linked polymer organic material has a higher capacity to adsorb NO (1.6 mmol/g) than H₂S (0.97 mmol/g). Release studies in aqueous solution showed that H₂S has a faster release (3 h) from the material than NO, for which a steady release was observed for at least 5 h. This result is the first evaluation of the possibility of an imine-linked polymer organic framework being used in the therapeutic release of NO or H₂S.

Heteroatom-Doped Porous Carbons as Effective Adsorbers for Toxic Industrial Gasses

Ammonia (NH3), often stored in large quantities before being used in the production of fertilizer, and sulfur dioxide (SO2), a byproduct of fossil fuel consumption, particularly the burning of coal, are highly toxic and corrosive gases that pose a significant danger to humans if accidentally released. Therefore, developing advanced materials to enable their effective capture and safe storage is highly desired. Herein, advanced benzimidazole-derived carbons (BIDCs) with an exceptional capacity for NH3 and SO2 have been designed and tested. These heteroatom-doped porous carbon adsorbents were synthesized by thermolysis of imidazolate-potassium salts affording high surface area and controlled heteroatom content to optimize for rapid NH3 and SO2 gas uptake and release under practical conditions. According to gas uptake measurements, these nitrogen-doped carbons exhibit exceptional gas adsorption capacity, with BIDC-3-800 adsorbing 21.42 mmol/g SO2 at 298 K and 1 bar, exceeding most reported porous materials and BIDC-2-700 adsorbing 14.26 mmol/g NH3 under the same conditions. The NH3 uptake of BIDC-2-700 surpassed reported activated carbons and is among the best adsorbents including metal organic frameworks (MOFs). Our synthetic method allows for control over both textural and chemical properties of the carbon and enables heteroatom functionality to be incorporated directly into the carbon framework without the need for postsynthetic modification. These materials were also tested for recyclability; all adsorbents showed almost complete retention of their initial gas uptake capacity during recyclability studies and maintained their structural integrity and their previous adsorption capacity of both NH3 and SO2, highlighting their potential for practical application.

Synthesis of the Magnetically Nanoporous Organic Polymer Fe3O4@SiO2-NH2-COP and Its Application in the Determination of Sulfonamide Residues in Surface Water Surrounding a Cattle Farm

Efficient extractions of trace antibiotic residues in the environment are a key factor for accurate quantification of the residues. A new nanoporous material, namely, magnetically covalent organic polymer (MCOP, Fe₃O₄@SiO₂-NH₂-COP) was synthesized in this work and was used for magnetic solid-phase extraction (MSPE). The combination of MSPE with high-performance liquid chromatography separation together with ultraviolet detection (HPLC-UV) was established as an effective method for the determination of four sulfonamide (SA) residues in surface water surrounding a cattle farm. The synthesized magnetic material was characterized by SEM, TEM, FT-IR, magnetic properties measurement system (MPMS), and nitrogen gas porosimetry. The material possessed many attractive features, such as a unique microporous structure, a larger specific surface area (137.93 m²·g⁻¹) than bare Fe₃O₄ (24.84 m²·g⁻¹), high saturation magnetization (50.5 emu·g⁻¹), open adsorption sites, and high stability. The influencing parameters, including pH, the used amount of MCOPs, the type of eluent, adsorption solution, and desorption time, were optimized. Under the optimized conditions, the method conferred good linearity ranges (R² ≥ 0.9990), low detection limits (S/N = 3, LOD, 0.10–0.25 μg·L⁻¹), and satisfactory recoveries (79.7% to 92.2%). The enrichment factor (EF) for the four SAs was 34.13–38.86. The relative standard deviations of intraday (n = 5) and of interday (n = 3) were less than 4.8% and 8.9%, respectively. The equilibria between extraction and desorption for SAs could be reached within 150 s. The proposed method was sensitive and convenient for detecting SA residues in complex environmental matrices, and the successful application of the new MCOPs as an adsorbent was demonstrated.

A Catalytically Accessible Polyoxometalate in a Porous Fiber for Degradation of a Mustard Gas Simulant

Polyoxometalates (POMs) are versatile materials for chemical catalysis due to their tunable acidity and rich redox properties. While POMs have attracted significant attention in homogeneous catalysis, challenges regarding aggregation and instability in solvents often prevent the wide implementation of POMs as heterogeneous catalysts. Therefore, the successful incorporation of a POM into a solid support, such as a polymer, is desirable for practical applications where unique functionalities of the POM combine with the advantages of the polymer. In this work, we showcase how polymers of intrinsic microporosity (PIMs) can serve as matrices for anchoring a pure inorganic Keggin-type POM (H₃PW₁₂O₄₀) to fabricate PIM-based composite materials. Specifically, we found that PIMs installed with amidoxime functionalities could successfully attach POMs (PW₁₂@PIM-1-AO) without self-segregation. Furthermore, we fabricated porous fibrous mats via electrospinning of the PIM-POM composites. Comprehensive characterization confirmed the integrity of the POM in the composite material. Following this, we demonstrated that the incorporated POMs in the composite fibers maintained their innate catalytic activity for the oxidative degradation of 2-chloroethyl ethyl sulfide, a sulfur mustard simulant, in the presence of hydrogen peroxide as the oxidant. Ultimately, our work highlights that PIM-based hybrid materials provide a potential route for implementing these reactive fiber mats into protective equipment.

A Pressure Swing Approach to Selective CO2 Sequestration Using Functionalized Hypercrosslinked Polymers

Functionalized hypercrosslinked polymers (HCPs) with surface areas between 213 and 1124 m²/g based on a range of monomers containing different chemical moieties were evaluated for CO₂ capture using a pressure swing adsorption (PSA) methodology under humid conditions and elevated temperatures. The networks demonstrated rapid CO₂ uptake reaching maximum uptakes in under 60 s. The most promising networks demonstrating the best selectivity and highest uptakes were applied to a pressure swing setup using simulated flue gas streams. The carbazole, triphenylmethanol and triphenylamine networks were found to be capable of converting a dilute CO₂ stream (>20%) into a concentrated stream (>85%) after only two pressure swing cycles from 20 bar (adsorption) to 1 bar (desorption). This work demonstrates the ease with which readily synthesized functional porous materials can be successfully applied to a pressure swing methodology and used to separate CO₂ from N₂ from industrially applicable simulated gas streams under more realistic conditions.