Ordered Porous Poly(ionic liquid) Crystallines: Spacing Confined Ionic Surface Enhancing Selective CO2 Capture and Fixation

Enhanced CO2 conversion through confinement of cross-linked ionic polymer within the pores of porous carbon materials

It is crucial to employ an integrated catalyst to avoid the complications of the recovery process. This work reports the fabrication of porous carbon@ionic liquid (PC@IL) composites with readily accessible active ion sites, achieved by confining cross-linked ionic liquid (IL) within the channels of porous carbon (PC). The incorporation of porous carbon not only confines the IL within its framework, creating microsites for CO2 adsorption and conversion, but also simplifies catalyst recovery. The results indicate that PC@IL composites exhibit excellent cycloaddition activity towards CO2 in a co-catalyst- and solvent-free environment. Notably, PC@IL(C)-24 demonstrates remarkable catalytic performance across various epoxides under 1 bar of CO2, with yields above 90 % at 90 °C for 12 h, and achieving a remarkable styrene carbonate yield of up to 92.8 % under a CO2 pressure of 1 bar (at 100 °C for 12 h). Control experiments confirm that the confinement effect exerted by N,S co-doped carbon on cross-linked IL plays a pivotal role in enhancing both stability and activity of PC@IL composites, thereby providing novel insights for designing functionalized porous carbon catalysts for CO2 cycloaddition conversion.

CO2 fixation: cycloaddition of CO2 to epoxides using practical metal-free recyclable catalysts

The conversion of CO2 into valuable chemicals is a crucial field of research. Cyclic organic carbonates have attracted great interest because they can be prepared under mild conditions and because of their structural versatility which enables a large variety of applications. Therefore, there is a need for potent and yet practical catalysts for the cycloaddition of CO2 to cyclic carbonates that are able to combine availability, low cost and an adequate performance. We review here several recyclable catalytic systems that are readily available, easy to prepare, and inexpensive with an eye to the future development of more efficient practical catalysts through the provided guidelines.

Non-cationic hyper-crosslinked ionic polymers with hierarchically ordered porous structures: facile synthesis and applications for highly efficient CO2 capture and conversion

Hyper-crosslinked porous ionic polymers (HCPIPs) have garnered significant attention due to their unique ionic properties and high specific surface areas. However, the limited variety of monomers, low ionic density, and difficulty in functionalization restrict their development. Herein, a series of functionalized non-cationic HCPIPs with high ionic density are designed and directly synthesized via an innovative and straightforward approach - anion (and cation) hyper-crosslinking of tetraphenylborate-based ionic liquids (ILs). These HCPIPs offer controllable hydroxyl group content (0-2.40 mmol g-1), high IL content (1.20-1.78 mmol g-1), and large specific surface area (636-729 m2 g-1) with hierarchically ordered porous structures. These HCPIPs demonstrate exceptional CO2 adsorption capacities and CO2/N2 adsorption selectivities, reaching up to 2.68-3.01 mmol g-1 and 166-237, respectively, at 273 K and 1 bar. Furthermore, these ionic porous materials serve as highly efficient heterogeneous catalysts for CO2 cycloaddition to epoxides under mild conditions (1 bar CO2, 60-80 °C, 12-24 h). Notably, the CO2 adsorption performances and catalytic activities of these HCPIPs are regulated by the hydroxyl groups within their structures, with enhancements observed as the number of hydroxyl groups increases. This work presents a facile and widely applicable method for constructing high-performance and task-specific HCPIPs.

Modified melamine-based porous organic polymers with imidazolium ionic liquids as efficient heterogeneous catalysts for CO2 cycloaddition

The chemical conversion of carbon dioxide (CO2) into highly value-added products not only alleviates the environmental issues caused by global warming but also makes an impact on economic benefits in the world. The synthesis of cyclic carbonates by the cycloaddition of CO2 with epoxides is one of the most attractive methods for CO2 conversion. However, the development of green and highly efficient heterogeneous catalysts is considered to be a great challenge in catalysis. In this work, alkenyl-modified melamine-based porous organic polymer (MPOP-4A) was firstly synthesized by a one-pot polycondensation method, and it was again modified with imidazolium-based ionic liquids to obtain final modified catalyst (MPOP-4A-IL). Various analytical techniques were used to confirm structure and chemical composition of the prepared materials. The MPOP-4A-IL catalyst synthesized by the post-modification strategy with imidazolium-based ionic liquids exhibited enhanced catalytic activity for CO2 cycloaddition reaction. The enhanced catalytic performance could be attributed to the presence of abundant active sites in their structure such as hydrogen bond donors (HBD), nitrogen (N) sites, and nucleophilic groups for an effective chemical reaction. The MPOP-4A-IL catalyst was found to be metal-free, easy to recycle and reuse, and has good versatility for a series of different epoxides. The interaction of MPOP-4A-IL catalyst with epoxide and CO2 was further verified by density functional theory (DFT) calculations, and the possible mechanism of the CO2 cycloaddition reaction was proposed.

In situ rapid synthesis of ionic liquid/ionic covalent organic framework composites for CO2 fixation

IL/ICOF composites were in situ synthesized via a one-pot route in half an hour under ambient conditions for catalytic cycloaddition of CO2 with epoxides into cyclic carbonates. The prepared composites feature a decent CO2 adsorption capacity of 1.63 mmol g-1 at 273 K and 1 bar and exhibit excellent catalytic performance in terms of yield and durability. This work may pave a new way to design and construct functionalized porous organic frameworks as heterogeneous catalysts for CO2 capture and conversion.

Hydroxy-Rich Covalent Organic Framework for the Efficient Catalysis of the Cycloaddition of CO2

The cycloaddition of CO2 with epoxides to cyclic carbonates is one of the most promising and green pathways for CO2 utilization, and the development of highly efficient catalysts remains a challenge. In this work, a novel hydroxy-rich covalent organic framework (TFPB-DHBD-COF) was synthesized, and it served as an efficient heterogeneous catalyst for the reaction of CO2 with 1,2-epoxybutane under mild conditions, providing the desired products in 90% conversion. The abundant hydroxy groups in the pore channels of TFPB-DHBD-COF could not only activate epoxides and CO2 via hydrogen bonding but also obviously enhance its stability through intramolecular five-membered ring hydrogen bonding. Thus, this COF also exhibited outstanding stability and tolerance for diverse substrates. Undoubtedly, this work has enriched the application of tailored COFs in the activation and utilization of CO2.

Organocatalytic Polymers from Affordable and Readily Available Building Blocks for the Cycloaddition of CO2 to Epoxides

The catalytic cycloaddition of CO₂ to epoxides to afford cyclic carbonates as useful monomers, intermediates, solvents, and additives is a continuously growing field of investigation as a way to carry out the atom-economic conversion of CO₂ to value-added products. Metal-free organocatalytic compounds are attractive systems among various catalysts for such transformations because they are inexpensive, nontoxic, and readily available. Herein, we highlight and discuss key advances in the development of polymer-based organocatalytic materials that match these requirements of affordability and availability by considering their synthetic routes, the monomers, and the supports employed. The discussion is organized according to the number (monofunctional versus bifunctional materials) and type of catalytically active moieties, including both halide-based and halide-free systems. Two general synthetic approaches are identified based on the postsynthetic functionalization of polymeric supports or the copolymerization of monomers bearing catalytically active moieties. After a review of the material syntheses and catalytic activities, the chemical and structural features affecting catalytic performance are discussed. Based on such analysis, some strategies for the future design of affordable and readily available polymer-based organocatalysts with enhanced catalytic activity under mild conditions are considered.

Amino-Functionalized Ionic-Liquid-Grafted Covalent Organic Frameworks for High-Efficiency CO2 Capture and Conversion

Rationally integrating desired functional components into a composite material can endow the tailored function to achieve the corresponding purpose. This is the first case where a series of [AeImBr]_X%-TAPT-COFs (X = 0, 17, 33, 50, 67, 83, 100) were fabricated by chemically integrating the amino-functionalized imidazole ionic liquid (NH₂-IL) onto channel walls of mesoporous covalent organic framework materials ([HO]_X%-TAPT-COFs). By virtue of the polar groups (amino groups) and abundant imidazole cations of NH₂-IL and its microporous nature, the obtained [AeImBr]_X%-TAPT-COFs exhibit higher CO₂ capture activity than [HO]_X%-TAPT-COFs. Correspondingly, the CO₂ equilibrium capture capacity increases from 62.6 to 117.4 mg/g, which is crucial to the storage of enough CO₂ around the catalytic active sites. Additionally, the synergistic effect of -NH₂ and Br^- in NH₂-IL can also improve the cycloaddition reaction rate. The characteristics of [AeImBr]_X%-TAPT-COFs contribute to the efficient generation of cyclic carbonate through heterogeneously catalyzing CO₂-epoxide cycloaddition without any solvents and cocatalysts. Specifically, [AeImBr]_83%-TAPT-COF has a CO₂ equilibrium capture capacity of 117.4 mg/g and cyclochloroallyl carbonate yield of 99.1%. As a result of the use of the chemical grafting method, [AeImBr]_X%-TAPT-COFs possess excellent stability and cycle life. The equilibrium capture capacity and cyclochloroallyl carbonate yield reach 112.7 mg CO₂/g adsorbent and 95.0% at the eighth cycle.

Ionic Conjugated Polymers as Heterogeneous Catalysts for the Cycloaddition of Carbon Dioxide to Epoxides to Form Carbonates under Solvent- and Cocatalyst-Free Conditions

The generation of cyclic carbonates by the cycloaddition of CO₂ with epoxides is attractive in the industry, by which CO₂ is efficiently used as C1 source. Herein, a series of catalysts were developed to efficient mediate the cycloaddition of CO₂ with epoxides to generate carbonates. The catalysts were easily synthesized via the amine-formaldehyde condensation of ethidium bromide with a variety of linkers. The newly prepared heterogeneous catalysts have high thermal stability and degradation temperatures. The surface of the catalysts is smooth and spherical in shape. The effect of temperature, pressure, reaction time and catalyst dosage on the cycloaddition of CO₂ with epoxide were investigated. The results show that the catalyst with 1,3,5-tris(4-formylphenyl)benzene as the linker can achieve 97.4 % conversion efficiency at the conditions of 100 °C, reaction time of 12 h, and the reaction pressure of 1.2 MPa in a solvent-free environment. Notably, the polymers serve as homogeneous catalysts during the reaction (reaction temperature above T_g ) and can be separated and recovered easily as homogeneous catalysts at room temperature. In addition, the catalyst is not only suitable for a wide range of epoxide substrates, but also can be recycled many times. Furthermore, DFT calculations show that the coordination between the electrophilic center of the catalyst and the epoxide reduces the energy barrier, and the reaction mechanism is proposed based on the reaction kinetic studies and DFT calculations.

Immobilization of Ionic Liquid on a Covalent Organic Framework for Effectively Catalyzing Cycloaddition of CO2 to Epoxides

Transforming CO2 into value-added chemicals has been an important subject in recent years. The development of a novel heterogeneous catalyst for highly effective CO2 conversion still remains a great challenge. As an emerging class of porous organic polymers, covalent organic frameworks (COFs) have exhibited superior potential as catalysts for various chemical reactions, due to their unique structure and properties. In this study, a layered two-dimensional (2D) COF, IM4F-Py-COF, was prepared through a three-component condensation reaction. Benzimidazole moiety, as an ionic liquid precursor, was integrated onto the skeleton of the COF using a benzimidazole-containing building unit. Ionization of the benzimidazole framework was then achieved through quaternization with 1-bromobutane to produce an ionic liquid-immobilized COF, i.e., BMIM4F-Py-COF. The resulting ionic COF shows excellent catalytic activity in promoting the chemical fixation of CO2 via reaction with epoxides under solvent-free and co-catalyst-free conditions. High porosity, the one-dimensional (1D) open-channel structure of the COF and the high catalytic activity of ionic liquid may contribute to the excellent catalytic performance. Moreover, the COF catalyst could be reused at least five times without significant loss of its catalytic activity.

Stable Porous Organic Polymers Used for Reversible Adsorption and Efficient Separation of Trace SO2

The development of porous solid adsorbents for selective adsorption and separation of SO₂ has attracted much attention recently. Herein, we design porous organic polymers (POPs) decorated with pyridine ligands as building units (POP-Py) through a radical polymerization of the 2,5-divinylpyridine (v-Py) monomer. Due to its high BET surface area, nanoporosity, and excellent stability, the prepared POP-Py can be used for reversible adsorption and efficient separation of SO₂. The POP-Py possesses a SO₂ capacity of 10.8 mmol g^-1 at 298 K and 1.0 bar, which can be well retained after 6 recycles, showing an excellent reversible adsorption capacity. The POP-Py also shows superior separation performance for SO₂ from a ternary SO₂/CO₂/N₂ mixture (0.17/15/84.83v%), giving a breakthrough time and a saturated SO₂ capacity at 178 min g^-1 and 0.4 mmol g^-1. The retention time was well maintained even under high moisture conditions, confirming its superior water resistance. Furthermore, when other vinyl-functionalized organic ligand monomers (bipyridine, pyrimidine, and pyrazine) were employed for radical polymerization, all of the resultant porous organic ligand polymers (POP-BPy, POP-PyI, and POP-PyA) exhibited superior performance for reversible adsorption and efficient separation of SO₂. The combined features of reversible adsorption, efficient separation, and water resistance are important for the industrial applications of these materials as SO₂ adsorbents.

Functional Porous Ionic Polymers as Efficient Heterogeneous Catalysts for the Chemical Fixation of CO2 under Mild Conditions

The development of efficient and metal-free heterogeneous catalysts for the chemical fixation of CO2 into value-added products is still a challenge. Herein, we reported two kinds of polar group (-COOH, -OH)-functionalized porous ionic polymers (PIPs) that were constructed from the corresponding phosphonium salt monomers (v-PBC and v-PBH) using a solvothermal radical polymerization method. The resulting PIPs (POP-PBC and POP-PBH) can be used as efficient bifunctional heterogeneous catalysts in the cycloaddition reaction of CO2 with epoxides under relatively low temperature, ambient pressure, and metal-free conditions without any additives. It was found that the catalytic activities of the POP-PBC and POP-PBH were comparable with the homogeneous catalysts of Me-PBC and PBH and were higher than that of the POP-PPh3-COOH that was synthesized through a post-modification method, indicating the importance of the high concentration catalytic active sites in the heterogeneous catalysts. Reaction under low CO2 concentration conditions showed that the activity of the POP-PBC (with a conversion of 53.8% and a selectivity of 99.0%) was higher than that of the POP-PBH (with a conversion of 32.3% and a selectivity of 99.0%), verifying the promoting effect of the polar group (-COOH group) in the porous framework. The POP-PBC can also be recycled at least five times without a significant loss of catalytic activity, indicating the high stability and robustness of the PIPs-based heterogeneous catalysts.

Polymeric ionic liquid with carboxyl anchored on mesoporous silica for efficient fixation of carbon dioxide

The utilization of carbon dioxide (CO₂) has drawn much attention because of the increasing serious environmental problems. In order to promote the cycloaddition reaction of CO₂ to epoxides, a new synthesis strategy for friendly nonmetal catalyst to combine polymeric ionic liquid (PIL) with mesoporous silica (mSiO₂) was proposed. By thorough characterizations, those catalysts (mSiO₂-PIL-n, n = 1, 2, 3, 4) were verified that PIL with multiply catalytic active sites such as carboxyl group, imidazole ring and Br^-, was mainly anchored in mesoporous SiO₂ structures. Therefore, mSiO₂-PIL-n exhibited excellent catalytic activity for CO₂ cycloaddition reaction to epoxides under solventless and cocatalyst-free conditions. Typically, the appropriate PIL loading and specific surface area guaranteed mSiO₂-PIL-2 could efficiently catalyze the cycloaddition reaction with 96% yield and 99% selectivity to the target product of propylene carbonate under the conditions of 120 °C, 2 MPa and 6 h. Additionally, the mSiO₂-PIL-2 catalyst showed superior recyclability and there was no catalytic activity decrease for 10 runs of recycling due to the tightly anchored PIL on mesoporous SiO₂ by copolymerization. And the catalytic activity to other substituted epoxides over mSiO₂-PIL-2 was also expanded. Therefore, PIL anchored on mesoporous SiO₂ by copolymerization could be a promising synthetic strategy for the efficient catalyst to combine multiple active components in a single catalyst, meanwhile, mSiO₂-PIL-n exhibited an appealing catalyst candidate for the effective fixation and utilization of CO₂.

Polyamine-functionalized imidazolyl poly(ionic liquid)s for the efficient conversion of CO2 into cyclic carbonates

The synergistic effect of polyamine groups and nucleophile (Br−) significantly improved the catalytic performance of N4-PIL-2, which can convert epoxides into cyclic carbonates with excellent yields and selectivity under ambient pressure.

Porous polyelectrolyte frameworks: synthesis, post-ionization and advanced applications

Porous organic polymers (POPs), which feature high surface areas, robust skeletons, tunable pores, adjustable functionality and versatile applicability, have constituted a designable platform to develop advanced organic materials. Endowing polyelectrolytes with the distinct characteristics of POPs will attract mounting interest as the structural diversity of polyelectrolytes will bring the new hope of intriguing applications and potential benefits. In this review, the striking progress in ionized POPs (i-POPs) has been systematically summarized with regard to their synthetic strategies and applications. In the synthesis of i-POPs, we illustrate the representative ionic building blocks and charged functional groups capable of constructing the polyelectrolyte frameworks. The synthetic methods, including direct synthesis and post-modification, are detailed for the i-POPs with amorphous or crystalline structures, respectively. Subsequently, we outline the distinctive performances of i-POPs in adsorption, separation, catalysis, sensing, ion conduction and biomedical applications. The survey concerns the interplay between the surface chemistry, ionic interaction and pore confinement that cooperatively promote the performance of i-POPs. Finally, we conclude with the remaining challenges and promising opportunities for the on-going development of i-POPs.

Hydrogen bond donor functionalized poly(ionic liquid)s for efficient synergistic conversion of CO2 to cyclic carbonates

The development of metal-free, high effective and recyclable catalysts plays a pivotal role in transforming CO2 into high value-added products such as cyclic carbonates. In this paper, we introduced the hydrogen bond donor (HBD) groups into poly(ionic liquid)s via free radical polymerization, which successfully combined the HBD and ionic liquids (ILs) into one heterogeneous catalyst. The HBD could synergistically activate epoxides with hydroxyl functionalized ionic liquids and efficiently catalyze the cycloaddition of CO2 into cyclic carbonates. The yield of propylene carbonate (PC) reached 94% (at 105 °C, 2 MPa CO2, 3 h), which far exceeded poly(ionic liquid)s without HBDs functionalization (PC yield 72%), and even approached bulk ionic liquids (PC yield 95%). Moreover, HBD-functionalized poly(ionic liquid)s (HPILs) exhibited excellent recyclability after five runs and afforded wide substrate scope. According to the experimental results, 1H NMR spectra and density functional theory (DFT) calculations showed 2-hydroxyethyl methacrylate (HEMA) and the hydroxyl of ILs would form strong H-bonds with epoxides contributing to the ring-opening process of epoxides, and a possible HBD and nucleophilic anion synergistically catalytic mechanism was proposed. The method herein paved a brand new way for green technology and utilization of poly(ionic liquid)s.

Covalent organic frameworks: an ideal platform for designing ordered materials and advanced applications

Covalent organic frameworks offer a molecular platform for integrating organic units into periodically ordered yet extended 2D and 3D polymers to create topologically well-defined polygonal lattices and built-in discrete micropores and/or mesopores.

Emerging Ionic Polymers for CO2 Conversion to Cyclic Carbonates: An Overview of Recent Developments

In this mini review, we highlight some key work from the last 2 years where ionic polymers have been used as a catalyst to convert CO2 into cyclic carbonates. Emerging ionic polymers reported for this catalytic application include materials such as poly(ionic liquid)s (PILs), ionic porous organic polymers (iPOPs) or ionic covalent organic frameworks (iCOFs) among others. All these organic materials share in common the ionic moiety cations such as imidazolium, pyridinium, viologen, ammonium, phosphonium, and guanidinium, and anions such as halides, [BF4]–, [PF6]–, and [Tf2N]–. The mechanistic aspects and efficiency of the CO2 conversion reaction and the polymer design including functional groups and porosity are discussed in detail. This review should provide valuable information for researchers to design new polymers for important catalysis applications.

Ionic Polyureas-A Novel Subclass of Poly(Ionic Liquid)s for CO2 Capture

The growing concern for climate change and global warming has given rise to investigations in various research fields, including one particular area dedicated to the creation of solid sorbents for efficient CO2 capture. In this work, a new family of poly(ionic liquid)s (PILs) comprising cationic polyureas (PURs) with tetrafluoroborate (BF4) anions has been synthesized. Condensation of various diisocyanates with novel ionic diamines and subsequent ion metathesis reaction resulted in high molar mass ionic PURs (Mw = 12 ÷ 173 × 103 g/mol) with high thermal stability (up to 260 °C), glass transition temperatures in the range of 153-286 °C and remarkable CO2 capture (10.5-24.8 mg/g at 0 °C and 1 bar). The CO2 sorption was found to be dependent on the nature of the cation and structure of the diisocyanate. The highest sorption was demonstrated by tetrafluoroborate PUR based on 4,4'-methylene-bis(cyclohexyl isocyanate) diisocyanate and aromatic diamine bearing quinuclidinium cation (24.8 mg/g at 0 °C and 1 bar). It is hoped that the present study will inspire novel design strategies for improving the sorption properties of PILs and the creation of novel effective CO2 sorbents.

Silicon and Phosphorus Co-doped Bipyridine-Linked Covalent Triazine Framework as a Promising Metal-Free Catalyst for Hydrogen Evolution Reaction: A Theoretical Investigation

Electrocatalytic water spliting is the most attractive route for hydrogen production, but the development of nonprecious, stable, and high-performance catalysts for hydrogen evolution reaction (HER) to replace the scarce platinum group metal-based electrocatalysts is still a challenging task for the scientific community. In this work, within the framework of density functional theory computations, we have predicted that a silicon and phosphorus co-doped bipyridine-linked covalent triazine framework, followed by substitution of bipyridine hydrogens at the P-site with fluorine atoms, may be a potential catalyst for HER. Our predicted model system (SiPF-Bpy-CTF) exhibits a very low band gap (7 meV), which may exhibit facile charge transfer kinetics during HER. Using the Gibbs free energy for the adsorption of atomic hydrogen ([Formula: see text]) as the key descriptor, we have found that our proposed model system (SiPF-Bpy-CTF) exhibits superior HER catalytic activity, with its [Formula: see text] being close to the ideal value (0 eV).

Imidazolium-Functionalized Ionic Hypercrosslinked Porous Polymers for Efficient Synthesis of Cyclic Carbonates from Simulated Flue Gas

The rapid growth of CO₂ emissions, especially from power plants, has led to the urgent need to directly capture and fix CO₂ in the flue gas after simple purification rather than energy-intensive gas separation. Herein, imidazolium-functionalized ionic hypercrosslinked porous polymers (HCPs) bearing adjustable surface groups were straightforwardly synthesized through co-hypercrosslinking of benzylimidazole salts and crosslinker through Friedel-Crafts alkylation. Abundant microporosity and relatively high ionic moieties were obtainable in the ethyl-group-tethered ionic HCP, giving a remarkably selective CO₂ capture performance with a CO₂ uptake of 3.05 mmol g^-1 and an ideal adsorbed solution theory (IAST) CO₂ /N₂ selectivity as high as 363 (273 K, 1 bar). This ionic polymer demonstrated high efficiency in the synthesis of cyclic carbonates from the coupling of various epoxides with the simulated flue gas (15 % CO₂ and 85 % N₂ ), giving high yields, large turnover numbers (up to 4800), and stable reusability under additive- and solvent-free conditions.

Cobalt-Salen-Based Porous Ionic Polymer: The Role of Valence on Cooperative Conversion of CO2 to Cyclic Carbonate

Cobalt-salen-based porous ionic polymers, which are composed of cobalt and halogen anions decorated on the framework, effectively catalyze the CO₂ cycloaddition reaction of epoxides to cyclic carbonates under ambient conditions. The cooperative effect of bifunctional active sites of cobalt as the Lewis acidic site and the halogen anion as the nucleophile responds to the high catalytic performance. Moreover, density functional theory results indicate that the cobalt valence state and the corresponding coordination group influence the rate-determining step of the CO₂ cycloaddition reaction and the nucleophilicity of halogen anions.

Zinc 2-N-methyl N-confused porphyrin: an efficient catalyst for the conversion of CO2 into cyclic carbonates

A zinc 2-N-methyl N-confused porphyrin (Zn(NCP)Cl) catalyst was developed for the solvent-free synthesis of cyclic carbonates from epoxides and CO₂.