Benzimidazole-linked Polymers Research Articles

Insights into micro-structure and separation mechanism of benzimidazole-linked polymer membrane for H2/CO2 separation

Separation of hydrogen from carbon dioxide for sustainable H2 production and CO2 capture still faces great challenges due to the smaller size of H2 and higher condensability of CO2. Herein, a high-performance benzimidazole-linked polymer (BILP) membrane for hydrogen separation was directly prepared on α-Al2O3 substrate through a facile interfacial polymerization approach at room temperature. The separation performance of the BILP membrane were regulated by controlling the reaction time and the microstructure was systematically characterized. Molecular simulations were performed to deep understand the separation mechanism in the BILP membrane. The best performance membrane displays an extraordinary mixed gas selectivity of 40 for H2/CO2 together with outstanding H2 permeance of 250 gas permeation units (GPU) at 473 K, far exceeding the Robeson’s upper bound. Besides, the membrane can withstand high temperature and pressure, and also shows good H2/N2 and H2/CH4 selectivity. The excellent separation performance, coupled with high temperature and pressure resistance and easy preparation, render BILP membranes great potential for economic H2 purification, H2 recovery, and natural gas treatment.

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.

High-efficient Ag(I) ion binding, Ag(0) nanoparticle loading, and iodine trapping in ultrastable benzimidazole-linked polymers

Interest in functional silver has rapidly grown over the years due to significant advances in separation, sensing, catalysis, and biomedical applications. Here we developed a new strategy to load single atomic silver species in the rigid and open unit of the fully conjugated benzimidazole-linked polymers (BILPs). Due to the well-defined chelating units of N-heterocycles, the Ag+ ion species can be coordinated by N ligands and stabilized in the atomic level without aggregating into nanoscale Ag clusters and nanoparticles. The obtained Ag+-BILP-101 exhibits a selective binding property of Ag+ ions from solutions. The ultrastable structure and the property of taking up metal species, endow BILPs with the advantages of functionalizing metal species. After the reduction by NaBH4, the Ag+ ions were transferred into Ag nanoparticles. The substantial and intrinsic porosity of BILPs also gives excellent accessibility to Ag species loaded in the frameworks. The plentiful N-heterocycles and loaded Ag species show a synergistic/coadsorption effect for iodine vapor, and the charge transfer from frameworks promotes the formation of iodide ions. The iodine capture capacities of Ag+-BILP-101 and Ag0-BILP-101 reach 3.3 g/g and 3.7 g/g at 80 ℃, and still maintain 3.2 g/g and 3.5 g/g at 150 ℃, respectively. After ethanol elution, the residual iodine/Ag molar ratios in Ag+/Ag0-BILP-101 samples are still more than one (about 1.5), suggesting their strong affinity toward iodine. This work highlights the excellent selective Ag+ ion binding and Ag species supporting properties of BILPs, which can extend to other porous organic framework platforms for various applications based on silver species-skeleton interactions.

Molecular‐scale hybrid membranes: Metal‐oxo cluster crosslinked benzimidazole‐linked polymer membranes for superior H2 purification

AbstractHydrogen (H2) purification requires separation membranes with excellent performance and high stability. Here, a few nanometer‐sized Zr‐oxygen clusters (CP‐2) abundant in amino groups were incorporated in benzimidazole‐linked polymers (BILPs) by interfacial polymerization (IP) to fabricate molecular‐scale hybrid membranes for efficient H2/CO2 separation. The amino groups in CP‐2 engage in IP. The structure of the BILPs polymer chains is regulated and more H2 selective channels are created. The hybrid membranes provide an H2/CO2 selectivity of up to 75.2 (with a corresponding H2 permeance of 318 GPU) and a high H2 permeance of up to 1470 GPU (with a corresponding H2/CO2 selectivity of 23.6). In addition, the membranes exhibit satisfactory separation performance and durability under industry‐relevant conditions (573 K, 11 bar, or steam treatment).

A benzimidazole-linked polymer membrane in alkaline water electrolysis

Advanced alkaline water electrolysis for hydrogen production necessitates the development of new membranes with high ionic conductivity, gas-tightness, and structural robustness in the alkaline environment. To this end, a benzimidazole-linked polymer (BILP) based composite membrane is prepared by forming a BILP-101 dense layer via interfacial polymerization (IP) on top of a commercial porous polyethylene (PE) substrate membrane. The density and thickness of the dense layer are easily adjustable by changing the acid content in the aqueous phase and the IP time, respectively. The BILP-PE composite membranes exhibit an area resistance of only ∼75 mΩ cm2 at 30 °C and <30 mΩ cm2 at 80 °C in 1 M KOH. While their H2 gas crossover rate is ∼4 × 10−14 mol cm s−1 cm−2 kPa−1, nearly two orders of magnitude lower than that of commercial Zirfon UTP-500 diaphragm. The BILP-PE membranes also show a very low swelling ratio of ∼4% and high tensile strength of >100 MPa. Soaking in 30 wt% KOH solution at 60 °C, the BILP dense layers would lose their weight at an ever-decreased speed and come to a halt after ∼24 d of soak, with a total loss of <10% of their original weight. The BILP-PE composite membrane looks very promising in advanced alkaline water electrolysis.

Lithium-Conducting Organic Solid Electrolyte for Organic Rechargeable Batteries: Boronated Benzoimidazole-Linked Polymer

Some of the Benzimidazole-linked polymers (BILPs) are a class of porous organic polymers that have high porosities, large specific surface areas, and high thermal and chemical stability. Owing to these properties, BILPs can be used in various applications including solid electrolytes for renewable energy utilization. In this study, we carried out the boran-modification of a kind of BILPs, in order to increase the Li ion conductivity by decreases the interaction between lithium ions and the anion backbone. The resulting B-TFB-HAB-BILP materials have an ionic conductivity of 2.9 × 10−6 S cm−1 at 30 °C, which increases to 1.4 × 10−4 S cm−1 at room temperature with the addition of the ionic liquid, PP13[TFSA]. This can be attributed to the suppression of resistance at the grain boundary. A coin cell with an organic cathode active material, B-TFB-HAB-BILP/PP13[TFSA] as the quasi-solid electrolyte, and Li foil as the anode exhibited an initial discharge capacity of 223 mAh g−1 (76 % of theoretical capacity). Our study can aid in the realization of organic rechargeable batteries with high gravimetric energy density.

Crosslinked benzimidazole-linked polymer membranes for dehydration of organics

Pervaporation is an energy-saving membrane technology and has been used for organic dehydration in industry. Nevertheless, new membrane materials with high performance are still on demand. Here, a number of 20–50 nm thick, novel benzimidazole-linked polymer (BILP) membranes are fabricated by a facial interfacial polymerization (IP) protocol. The structures are characterized and dehydration performance of acid, alcohol and ester was evaluated. The relationships among preparation parameters, membrane structures and performance were established, revealing that the synergistic effect of post crosslinking and heating is mandatory and conducive to membrane selectivity. The membranes provide a separation factor > 10000, a total flux of 363 g/m2/h and an excellent stability for dehydration of ethyl acetate. The separation factor is ranked as the highest compared with other polymer membranes with equivalent flux.

Experimental and molecular simulation study of a novel benzimidazole-linked polymer membrane for efficient H2/CO2 separation

Developing novel materials for membrane separation is extremely crucial. Benzimidazole-linked polymers (BILPs) show great potential for H2 purification due to their high thermal and chemical stability, while only a few BILPs have been used for membrane-based gas separation. In this work, the BILP-5 composite membranes were prepared via a facile interfacial polymerization. Dense and smooth BILP-5 composite membranes were prepared on α-Al2O3 support and characterized by scanning electron microscope (SEM) and atomic force microscope (AFM). The effects of interfacial polymerization reaction duration, temperature, and pressure on the gas separation performance of BILP-5 membranes were systematically investigated. The resultant BILP-5 membrane shows good stability and a high H2/CO2 selectivity of 16 with a H2 permeance of 362 GPU under mixed gas test at room temperature, which exceeds the 2008 upper bound. Furthermore, the H2/CO2 separation mechanism of BILP-5 membranes was investigated through molecular dynamics simulations. Coupled with the merits of simple preparation, good stability, and excellent gas separation performance, BILP-5 is expected to be one of the most promising membrane materials for H2/CO2 separation.

Designed channels in thin benzimidazole-linked polymer membranes for hot H2 purification

High performance H2-selective polymer membranes are needed for hot H2 purification. Here, we have developed a series of 50 nm thick benzimidazole-linked polymer (BILP) membranes. H2-selective channels are designed in the membranes on the basis of synergistic effect of controllable formation of benzimidazole rings and precise manipulation of spacing among polymer chains. Highly-selective BILP membranes provide H2/CO2 selectivity up to 56.3 (with a corresponding H2 permeance of 127 GPU). H2 permeance up to 439 GPU (with a corresponding selectivity of 28.5) is delivered by highly-permeable BILP membranes. The superior performance far exceeds the upper bounds of traditional polymer membranes. In addition, the membranes possess outstanding thermal (e.g., 300 °C) and pressure resistance.

Interface synthesis of flexible benzimidazole-linked polymer molecular-sieving membranes with superior antimicrobial activity

Benzimidazole-linked polymers (BILPs) are a type of porous organic frameworks (POFs) that possess high microporosity, exceptional thermal and chemical stabilities. Uniform growth of BILP-101x layer (∼95 nm) directly on the hydrolyzed polyacrylonitrile (HPAN) substrate can be realized within 30 min. The microstructure and separation capability of BILPs membranes were feasibly regulated by the precise control of synthetic parameters. Molecular simulations were performed to reveal the inner structure and molecular transportation behavior of the BILPs membranes. The optimized composite membrane exhibits ultra-high water permeance (∼255 L m −2 h −1 bar −1 ) with extraordinarily high dye/divalent salt selectivity, e.g., Congo red (696.7 Da), Direct red 23 (814 Da) > 99.0%, Na 2 SO 4 < 9%. Furthermore, the resultant membranes evince distinct antimicrobial activity due to the abundant benzimidazole groups in the polymer networks, and the colonies of live Escherichia coli ( E. coli ) bacteria were drastically reduced by 98.4%. Therefore, the resultant BILP membranes which exhibit remarkable permselectivity and superior antimicrobial properties are promising candidate for many applications such as dye desalination and water purification. Facile manufacture of flexible BILP membrane for efficient dye/divalent salt separation with ultrahigh water permeability and superior antimicrobial properties. • Thin and flexible BILP membrane was synthesized on top of PAN substrate. • The microstructure and separation performance of BILP membrane have been explored. • The BILP membrane exhibits ultra-high water permeance and dye/salt selectivity. • Abundant benzimidazole groups endow the membrane superior antimicrobial properties.

Nitrogen-Enriched Porous Benzimidazole-Linked Polymeric Network for the Adsorption of La (III), Ce (III), and Nd (III)

A porous benzimidazole-linked polymer, synthesized by a microwave-assisted procedure, exhibits an adsorption capacity of 760 mg/g, 700 mg/g, and 840 mg/g, respectively, for three rare earth ions, L...

Microporous benzimidazole-linked polymer and its derivatives for organic solvent nanofiltration

Organic solvent nanofiltration (OSN) has emerged as a robust separation technology for solvent recovery and microporous polymer membranes are considered as promising OSN membranes. A molecular simulation study is reported here to investigate a new type of microporous membranes for OSN, including a benzimidazole-linked polymer (BILP-4) and its derivatives (PILP-1 and PILP-3). PILP-1 and PILP-3 are computationally designed, they consist of tetrahedral cores in BILP-4 and contorted linkers in polymer of intrinsic microporosity (PIM-1). From molecular dynamics simulations, three membranes are found to possess considerable stability in organic solvents (methanol, ethanol and acetonitrile). The mean pore sizes of the swollen membranes have a linear relationship with swelling degrees. Intriguingly, methanol, ethanol and acetonitrile exhibit distinctly different permeation behavior through the three membranes. Specifically, the permeation of methanol is solely governed by the pore size, whereas both the pore size and the membrane-solvent interaction play a role in the permeation of ethanol; for acetonitrile, the permeation is mainly determined by the membrane-solvent interaction. A dye molecule (methylene blue) is tested for OSN and complete rejection is observed by all the three membranes. This simulation study reveals the complex permeation behavior of different solvents, identifies the key factors governing permeation, and suggest the three microporous membranes as interesting candidates for OSN.

Benzimidazole linked polymers (BILPs) in mixed-matrix membranes: Influence of filler porosity on the CO2/N2 separation performance

The performance of mixed-matrix membranes (MMMs) based on Matrimid® and benzimidazole-linked polymers (BILPs) have been investigated for the separation CO2/N2 and the dependency on the filler porosity. BILPs with two different porosities (BILP-101 and RT-BILP-101) were synthesized through controlling the initial polymerization rate and further characterized by several techniques (DRIFTs, 13C CP/MAS NMR, SEM, TEM, N2 and CO2 adsorption). To investigate the influence of porosity, the two types of fillers were incorporated into Matrimid® to prepare MMMs at varied loadings (8, 16 and 24 wt%). SEM confirmed that both BILP-101 and RT-BILP-101 are well dispered, indicating their good compatibility with the polymeric matrix. The partial pore blockage in the membrane was verified by CO2 adsorption isotherms on the prepared membranes. In the separation of CO2 from a 15:85 CO2:N2 mixture at 308 K, the incorporation of both BILPs fillers resulted in an enhancement in gas permeability together with constant selectivity owing to the fast transport pathways introduced by the porous network. It was noteworthy that the initial porosity of the filler had a large impact in separation permeability. The best improvement was achieved by 24 wt% RT-BILP-101 MMMs, for which the CO2 permeability increases up to 2.8-fold (from 9.6 to 27 Barrer) compared to the bare Matrimid®.

Incorporation of benzimidazole linked polymers into Matrimid to yield mixed matrix membranes with enhanced CO2/N2 selectivity

Two different highly cross-linked benzimidazole linked polymers (BILPs) displaying high surface area were successfully incorporated into Matrimid polymer to form a series of new mixed matrix membranes (MMMs). The surface functionality of the BILPs, BILP-4 and BILP-101, were exploited to assure the interaction with the Matrimid matrix and produce robust MMMs, which displayed significantly improved CO2 gas permeability. The ideal selectivities for CO2/N2 were calculated with enhancements as high as 34% at 15 wt% BILP loading. While BILP-4 and BILP-101 have similar structures and functionality, the two materials have notably different surface areas and CO2 adsorption capacity. Despite the differences in their gas adsorption properties, MMMs composed of Matrimid/BILP-4 and Matrimid/BILP-101 had very similar gas transport properties. These results suggest that the functional groups of the filler particle and the resulting interaction with the polymer matrix may have had more influence on the gas separation properties of the mixed matrix membrane than the adsorption properties of the fillers.

Enhanced Carbon Dioxide Capture from Landfill Gas Using Bifunctionalized Benzimidazole-Linked Polymers.

Tuning the binding affinity of small gases and their selective uptake by porous adsorbents are vital for effective CO2 removal from gas mixtures for environmental protection and fuel upgrading. In this study, an amine-functionalized benzimidazole-linked polymer (BILP-6-NH2) was synthesized by a combination of pre- and postsynthetic modification techniques in two steps. Presynthetic incorporation of nitro groups resulted in stoichiometric functionalization (1 nitro/phenyl) in addition to noninvasive functionalization, where more than 80% of the surface area maintained compared to BILP-6. Experimental studies presented enhanced CO2 uptake and CO2/CH4 selectivity in BILP-6-NH2 compared to BILP-6, which are governed by the synergetic effect of benzimidazole and amine moieties. DFT calculations were used to understand the interaction modes of CO2 with BILP-6-NH2 and confirmed the efficacy of amine groups. Encouraged by the enhanced uptake and selectivity in BILP-6-NH2, we have evaluated its performance in landfill gas separation under vacuum swing adsorption (VSA) settings, which resulted in very promising working capacity and sorbent selection parameters outperforming most of the best solid adsorbent in the literature.

Effect of acid-catalyzed formation rates of benzimidazole-linked polymers on porosity and selective CO2 capture from gas mixtures.

Benzimidazole-linked polymers (BILPs) are emerging candidates for gas storage and separation applications; however, their current synthetic methods offer limited control over textural properties which are vital for their multifaceted use. In this study, we investigate the impact of acid-catalyzed formation rates of the imidazole units on the porosity levels of BILPs and subsequent effects on CO2 and CH4 binding affinities and selective uptake of CO2 over CH4 and N2. Treatment of 3,3'-Diaminobenzidine tetrahydrochloride hydrate with 1,2,4,5-tetrakis(4-formylphenyl)benzene and 1,3,5-(4-formylphenyl)-benzene in anhydrous DMF afforded porous BILP-15 (448 m(2) g(-1)) and BILP-16 (435 m(2) g(-1)), respectively. Alternatively, the same polymers were prepared from the neutral 3,3'-Diaminobenzidine and catalytic amounts of aqueous HCl. The resulting polymers denoted BILP-15(AC) and BILP-16(AC) exhibited optimal surface areas; 862 m(2) g(-1) and 643 m(2) g(-1), respectively, only when 2 equiv of HCl (0.22 M) was used. In contrast, the CO2 binding affinity (Qst) dropped from 33.0 to 28.9 kJ mol(-1) for BILP-15 and from 32.0 to 31.6 kJ mol(-1) for BILP-16. According to initial slope calculations at 273 K/298 K, a notable change in CO2/N2 selectivity was observed for BILP-15(AC) (61/50) compared to BILP-15 (83/63). Similarly, ideal adsorbed solution theory (IAST) calculations also show the higher specific surface area of BILP-15(AC) and BILP-16(AC) compromises their CO2/N2 selectivity.

Exceptional Gas Adsorption Properties by Nitrogen-Doped Porous Carbons Derived from Benzimidazole-Linked Polymers

Heteroatom-doped porous carbons are emerging as platforms for use in a wide range of applications including catalysis, energy storage, and gas separation or storage, among others. The use of high activation temperatures and heteroatom multiple-source precursors remain great challenges, and this study aims to addresses both issues. A series of highly porous N-doped carbon (CPC) materials was successfully synthesized by chemical activation of benzimidazole-linked polymers (BILPs) followed by thermolysis under argon. The high temperature synthesized CPC-700 reaches surface area and pore volume as high as 3240 m2 g–1 and 1.51 cm3 g–1, respectively, while low temperature activated CPC-550 exhibits the highest ultramicropore volume of 0.35 cm3 g–1. The controlled activation process endows CPCs with diverse textural properties, adjustable nitrogen content (1–8 wt %), and remarkable gas sorption properties. In particular, exceptionally high CO2 uptake capacities of 5.8 mmol g–1 (1.0 bar) and 2.1 mmol g–1 (0.15 bar) at ambient temperature were obtained for materials prepared at 550 °C due to a combination of a high level of N-doping and ultramicroporosity. Furthermore, CPCs prepared at higher temperatures exhibit remarkable total uptake for CO2 (25.7 mmol g–1 at 298 K and 30 bar) and CH4 (20.5 mmol g–1 at 298 K and 65 bar) as a result of higher total micropores and small mesopores volume. Interestingly, the N sites within the imidazole rings of BILPs are intrinsically located in pyrrolic/pyridinic positions typically found in N-doped carbons. Therefore, the chemical and physical transformation of BILPs into CPCs is thermodynamically favored and saves significant amounts of energy that would otherwise be consumed during carbonization processes.

Highly porous and photoluminescent pyrene-quinoxaline-derived benzimidazole-linked polymers

Successful incorporation of pyrene-quinoxaline building units into benzimidazole-linked polymers leads to highly porous frameworks that are semiconducting and photoluminescent.

Highly Selective CO2 Capture by Triazine-Based Benzimidazole-Linked Polymers

Triazine-based benzimidazole-linked polymers (TBILPs), TBILP-1 and TBILP-2, were synthesized by condensation reaction of 2,4,6-tris(4-formylphenyl)-1,3,5-triazine (TFPT) with 1,2,4,5-benzenetetraamine tetrachloride (BTA) and 2,3,6,7,14,15-hexaaminotriptycene (HATT), respectively. The Ar sorption isotherms at 87 K revealed high surface areas for TBILP-1 (330 m2 g–1) and TBILP-2 (1080 m2 g–1). TBILP-2 adsorbed significantly high CO2 (5.19 mmol g–1/228 mg g–1) at 1 bar and 273 K. Initial slope selectivity calculations demonstrated that TBILP-1 has very high selectivity for CO2 over N2 (63) at 298 K, outperforming all triazine-based porous organic polymers reported to date. On the other hand, the larger surface area of TBILP-2 leads to relatively lower selectivity for CO2/N2 (40) and CO2/CH4 (7) at 298 K. TBILPs showed moderate isosteric heats of adsorption for CO2: TBILP-1 (35 kJ mol–1) and TBILP-2 (29 kJ mol–1) enabling high and reversible CO2 uptake at ambient temperature. In addition, TBILPs displayed promising working capacity, regenerability, and sorbent selection parameter values for CO2 capture from gas mixtures under vacuum swing adsorption (VSA) and pressure swing adsorption (PSA) conditions.

New insights into carbon dioxide interactions with benzimidazole-linked polymers

A synergistic experimental and theoretical study (DFT) highlights the impact of material design at the molecular and electronic levels on the binding affinity and interaction sites of CO2 with benzimidazole-linked polymers (BILPs); CO2 is stabilized by benzimidazole units through Lewis acid-base (N···CO2) and aryl C-H···O=C=O interactions.