Shape-controllable formation of poly-imidazolium salts for stable palladium N-heterocyclic carbene polymers

Harmonizing Between Chemical Functionality and Surface Area of Porous Organic Polymeric Nanotraps for Tuning Carbon Dioxide Capture

The energy sector has demonstrated significant enthusiasm for investigating post-combustion CO2 capture, storage, and separation. However, the practical application of current porous adsorbents is impeded by challenges related to cost competitiveness, stability, and scalability. Intregation of heteroatoms in the porous organic polymers (POPs) dispense it more susceptible for CO2 adsorption to attenuate green house gases. In this regard, two hydroxy rich hypercrosslinked POPs, namely Ph/Tt-POP have been developed by one-pot condensation polymerization using a facile synthetic strategy. The high surface areas of both the Ph/Tt-POP (1057 and 893 m2g-1, respectively), and the heteroatom functionality in the POP framework instigated us to explore our material for CO2 adsorption study. The CO2 uptake capacities in Ph/Tt-POP are found to be 2.45 and 2.2 mmol g-1, at 273 K respectively. Further, in-situ static 13C NMR experiment shows that CO2 molecules in Tt-POP appear to be less mobile than those in Ph-POP which probably due to the presence of triazine functional groups along with high abundant -OH groups in the Tt-POP framework. An in-depth study of the CO2 adsorption mechanism by density functional theory (DFT) calculations also shows that CO2 adsorption at the cages formed by two benzyl rings represents the most stable interaction and CO2 molecule is more favorably adsorbed on the Ph-POP with the more negative interaction energies values compared to that of Tt-POP. Further, Non-covalent interaction (NCI) plot reveals that CO2 molecules adsorb more on the Ph-POP than Tt-POP, which can be explain by hydrogen bond formation in case of Tt-POP repeating units turning aside CO2 molecule to interact with the Ph component. Overall, our present study reflects the comprising effects of surface area of the solid adsorbents as well as their functionality can be beneficial for developing efficient hypercrosslinked porous polymers as solid CO2 adsorbent.

Unveiling the Impact of Diverse Morphology of Ionic Porous Organic Polymers with Mechanistic Insight on the Ultrafast and Selective Removal of Toxic Pollutants from Water

In recent years, detoxification of contaminated water by different types of materials has received a great deal of attention. However, lack of methodical in-depth understanding of the role of various physical properties of such materials toward improved sorption performance limits their applicable efficiencies. In perspective, decontamination of oxoanion-polluted water by porous materials with different morphologies are unexplored due to a shortfall of proper synthetic strategies. Herein, systematic optimization of sequestration performance toward efficient decontamination of toxic oxoanion-polluted water has been demonstrated by varying the morphologies of an imidazolium-based cationic polymeric network [ionic porous organic polymers (iPOP-5)]. Detailed morphological evolution showed that the chemically stable ionic polymer exhibited several morphologies such as spherical, nanotube, and flakes. Among them, the flakelike material [iPOP-5(F)] showed ultrafast capture efficiency (up to ∼99 and >85% removal within less than 1 min) with high saturation capacities (301 and 610 mg g^-1) toward chromate [Cr(VI)] and perrhenate [Re(VII)] oxoanions, respectively, in water. On the other hand, the spherical-shaped polymer [iPOP-5(S)] exhibited relatively slow removal kinetics (>5 min for complete removal) toward both Cr(VI) and Re(VII) oxoanions. Notably, iPOP-5(F) eliminated Cr(VI) and Re(VII) selectively even in the presence of excessive (∼100-fold) competing anions from both high- and low-concentration contaminated water. Further, the compound demonstrated efficient separation of those oxoanions in a wide pH range as well as in various water systems (such as potable, lake, river, sea, and tannery water) with superior regeneration ability. Moreover, as a proof of concept, a column exchange-based water treatment experiment by iPOP-5(F) has been performed to reduce the concentration of Cr(VI) and Re(VII) below the WHO permitted level. Mechanistic investigation suggested that the rare in situ exfoliation of flakes into thin nanosheets helps to achieve ultrafast capture efficiency. In addition, detailed theoretical binding energy calculations were executed in order to understand such rapid, selective binding of chromate and perrhenate oxoanions with iPOP-5(F) over other nonmetal-based anions.

N-Heterocyclic carbenes and their precursors in functionalised porous materials

Though N-heterocyclic carbenes (NHCs) have emerged as diverse and powerful discrete functional molecules in pharmaceutics, nanotechnology, and catalysis over decades, the heterogenization of NHCs and their precursors for broader applications in porous materials, like metal-organic frameworks (MOFs), porous coordination polymers (PCPs), covalent-organic frameworks (COFs), porous organic polymers (POPs), and porous organometallic cages (POMCs) was not extensively studied until the last ten years. By de novo or post-synthetic modification (PSM) methods, myriads of NHCs and their precursors containing building blocks were designed and integrated into MOFs, PCPs, COFs, POPs and POMCs to form various structures and porosities. Functionalisation with NHCs and their precursors significantly expands the scope of the potential applications of porous materials by tuning the pore surface chemical/physical properties, providing active sites for binding guest molecules and substrates and realizing recyclability. In this review, we summarise and discuss the recent progress on the synthetic methods, structural features, and promising applications of NHCs and their precursors in functionalised porous materials. At the end, a brief perspective on the encouraging future prospects and challenges in this contemporary field is presented. This review will serve as a guide for researchers to design and synthesize more novel porous materials functionalised with NHCs and their precursors.

Task-Specific Tailored Cationic Polymeric Network with High Base-Resistance for Unprecedented 99TcO4 - Cleanup from Alkaline Nuclear Waste

Direct removal of 99TcO4 - from alkaline nuclear waste is desirable because of the nuclear waste management and environmental protection relevant to nuclear energy but is yet to be achieved given that combined features of decent base-resistance and high uptake selectivity toward anions with low charge density have not been integrated into a single anion-exchange material. Herein, we proposed a strategy overcoming these challenges by rationally modifying the imidazolium unit of a cationic polymeric network (SCU-CPN-4) with bulky alkyl groups avoiding its ring-opening reaction induced by OH- because of the steric hindrance effect. This significantly improves not only the base-resistance but also the affinity toward TcO4 - as a result of enhanced hydrophobicity, compared to other existing anion-exchange materials. More importantly, SCU-CPN-4 exhibits record high uptake selectivity, fast sorption kinetics, sufficient robustness, and promising reusability for removing 99TcO4 - from the simulated high-level waste stream at the U.S. Savannah River Site, a typical alkaline nuclear waste, in both batch experiment and dynamic column separation test for the first time.

Evaluation of an Ionic Porous Organic Polymer for Water Remediation

The targeted synthesis of a novel ionic porous organic polymer (iPOP) was reported. The compound (denoted as QUST-iPOP-1) was built up through a quaternization reaction of tris(4-imidazolylphenyl)amine and cyanuric chloride, and then benzyl bromide was added to complete the quaternization of the total imidazolyl units. It featured a special exchangeable Cl^-/Br^--rich structure with high permanent porosity and wide pore size distribution, enabling it to rapidly and effectively remove environmentally toxic oxo-anions including Cr₂O₇^2-, MnO₄^-, and ReO₄^- and anionic organic dyes with different sizes including methyl blue, Congo red, and methyl orange from water. Notably, QUST-iPOP-1 showed ultra-high capacity values for radioactive TcO₄^- surrogate anions (MnO₄^- and ReO₄^-), Cr₂O₇^2-, methyl blue, and Congo red, and these were comparable to some reported compounds of exhaustive research. Furthermore, the relative removal rate was high even when other concurrent anions existed.

Imidazolium-Functionalized Chemically Robust Ionic Porous Organic Polymers (iPOPs) toward Toxic Oxo-Pollutants Capture from Water

Fabricating new and efficient materials aimed at containment of water contamination, in particular removing toxic heavy metal based oxo-anions (e. g. CrO₄ ^2- , TcO₄ ^- ) holds paramount importance. In this work, we report two new highly stable imidazolium based ionic porous organic polymers (iPOPs) decorated with multiple interaction sites along with electrostatics driven adsorptive removal of such oxo-anions from water. Both the iPOPs (namely, iPOP-3 and iPOP-4) exhibited rapid sieving kinetics and very high saturation uptake capacity for CrO₄ ^2- anions (170 and 141 mg g^-1 for iPOP-3 and iPOP-4 respectively) and ReO₄ ^- (515.5 and 350.3 mg g^-1 for iPOP-3 and iPOP-4 respectively), where ReO₄ ^- anions being the non-radioactive surrogative counterpart of radioactive TcO₄ ^- ions. Noticeably, both iPOPs showed exceptional selectivity towards CrO₄ ^2- and ReO₄ ^- even in presence of several other concurrent anions such as Br^- , Cl^- , SO₄ ^2- , NO₃ ^- etc. The theoretical binding energy calculations via DFT method further confirmed the preferential interaction sites as well as binding energies of both iPOPs towards CrO₄ ^2- and ReO₄ ^- over all other competing anions which corroborates with the experimental high capacity and selectivity of iPOPs toward such oxo-anions.

3D Metallo-organic coordination assembly-based anion-enriched supramolecular material for fast and efficient removal of Cr2O72

Chromium(VI), especially dichromate (Cr₂O₇^2-) contamination in wastewater due to rapid industrialization with uncontrolled effluent management is still a serious concern which needs focused attention. Multiprong approaches are practiced such as chemical precipitation, reverse osmosis, ion-exchange, adsorption by granular activated carbon etc. to capture and separate this "Group A" human carcinogenic effluent from water. However, low capture capacity, non-reusability, poor selectivity, pH-limited performance are some major limitations of these techniques. Recently, metal organic frameworks (MOFs), metal organic cages (MOCs), porous organic polymers (POPs) or covalent organic frameworks (COFs), covalent organic networks (CONs) etc. emerged as new-generation materials to overcome such limitations. However, the development is still in initial stage and issues related to structural stability and integrity of many MOFs in water and in wide pH range, as well as reusability need to be addressed. At this juncture, herein we report a novel [Zn(terpyridine)₂]²⁺-templated trisimidazolium-based highly cationic three-dimensional metal-organic coordination assembly (3D MOCA), serving as a new class of efficient, fast, robust and recyclable dichromate-removal material. Not only the highly cationic assembly is enriched with a high density of Br^- anions, but its three-dimensional propagation and flexibility also exposes the exchangeable Br^- ions for facile anion-metathesis with Cr₂O₇^2-. By virtue of the benefits of these attributes, the presented supramolecular material exhibits a high capture capacity (469 mg g^-1), fast exchange kinetics (0.028 g mg^-1 min^-1), wide working pH range (pH 2-12) and reusability up to a minimum of 10 cycles without much loss of efficiency. Key mechanistic examinations highlight the evidences in favor of ion-exchange-based chemistry to be responsible for dichromate removal with the present material.

A spirobifluorene-based water-soluble imidazolium polymer for luminescence sensing

A water-soluble luminescent sensor based on a spirobifluorene-based imidazolium polymer is developed for the selective sensing of Fe³⁺ and Cr₂O₇²⁻.

Removal of anionic hexavalent chromium and methyl orange pollutants by using imidazolium-based mesoporous poly(ionic liquid)s as efficient adsorbents in column

Poly(ionic liquid)s (PILs) are attractive for their various applications, but the use of porous PILs have rarely been reported in anionic pollutants removal via ion-exchange by column. Herein, we report a serial of crosslinked imidazolium-based mesoporous PILs with Cl^- and Br^- as anions for hexavalent chromium (Cr(VI)) and methyl orange (MO) removal. Among them, PDVIm-Cl-SCD, from the free-radical polymerization of a dicationic monomer (N,N'-methylene-bis(1-(3-vinylimidazolium)) chloride, DVIm-Cl) and further supercritical carbon dioxide drying (SCD), displayed a very high sorption capacity (328.2 mg g^-1 at 25 °C) and excellent utilization of adsorption sites (UOA, 86.2%) towards Cr(VI), and an unprecedentedly high sorption capacity (1615.0 mg g^-1 at 25 °C) with a UOA of 67.4% to MO. Moreover, PDVIm-Cl-SCD also exhibited a broad pH range, excellent regeneration and remarkable reusability. Regarding to Cr(VI) removal, the volume of saturated KCl aqueous used for regenerating the Cr(VI) saturated PDVIm-Cl-SCD column (7.5-9.5 mL) was much less than the volume of treated Cr(VI) solution (160-200 mL). For MO removal, the volume of saturated NaCl solution used for regenerating the MO saturated PDVIm-Cl-SCD column (10.5-13.5 mL) was also much less than the volume of treated MO solution (220-235 mL), implying the great potential of PDVIm-Cl-SCD in sustainable wastewater treatment.

Two-in-one: construction of hydroxyl and imidazolium-bifunctionalized ionic networks in one-pot toward synergistic catalytic CO2 fixation

Two-in-one hydroxyl-incorporated imidazolium ionic network was constructed in one-pot quaternization for enhancing synergistic catalytic conversion of CO₂ under mild conditions.

99TcO4- remediation by a cationic polymeric network

Direct removal of ⁹⁹TcO₄^- from the highly acidic solution of used nuclear fuel is highly beneficial for the recovery of uranium and plutonium and more importantly aids in the elimination of ⁹⁹Tc discharge into the environment. However, this task represents a huge challenge given the combined extreme conditions of super acidity, high ionic strength, and strong radiation field. Here we overcome this challenge using a cationic polymeric network with significant TcO₄^- uptake capabilities in four aspects: the fastest sorption kinetics, the highest sorption capacity, the most promising uptake performance from highly acidic solutions, and excellent radiation-resistance and hydrolytic stability among all anion sorbent materials reported. In addition, this material is fully recyclable for multiple sorption/desorption trials, making it extremely attractive for waste partitioning and emergency remediation. The excellent TcO₄^- uptake capability is elucidated by X-ray absorption spectroscopy, solid-state NMR measurement, and density functional theory analysis on anion coordination and bonding.

Pd–Ni Bimetallic Nanoparticles Supported on Zro2 as an Efficient Catalyst for Suzuki–Miyaura Reactions

Pd–Ni bimetallic nanoparticles (BMNPs) supported on ZrO2 were prepared by an impregnation–reduction method. The BMNPs showed excellent catalytic performance in Suzuki carbon–carbon cross-coupling reactions and almost quantitative conversion of the substrates was obtained under mild conditions in the absence of ligand. The excellent catalytic performance of the bimetallic catalyst could be a result of the synergistic effect between the two metal components. The catalyst showed outstanding recyclability during the reaction process; no obvious decrease in catalytic performance was observed after five cycles.

Template Synthesis of Three-Dimensional Hexakisimidazolium Cages

A procedure for the synthesis of three-dimensional hexakisimidazolium cage compounds has been developed. The reaction of the trigonal trisimidazolium salts H₃ L(PF₆ )₃ , decorated with three N-olefinic pendants, and silver oxide yielded trinuclear trisilver(I) hexacarbene molecular cylinders of the type [Ag₃ L₂ ]³⁺ with the olefinic pendants from the two different tricarbene ligands arranged in three pairs. Subsequent UV irradiation gave three cyclobutane links between the two tris-NHC ligands in three [2+2] cycloaddition reactions, thereby generating a three-dimensional hexakis-NHC ligand. Removal of the metal ions resulted in the formation of three-dimensional hexakisimidazolium cages with a large internal cavity.

General Synthetic Route toward Highly Dispersed Ultrafine Pd-Au Alloy Nanoparticles Enabled by Imidazolium-Based Organic Polymers

Bimetallic Pd-Au nanoparticles (NPs) usually show superior catalytic performances over their single-component counterparts, the general and facile synthesis of subnanometer-scaled Pd-Au NPs still remains a great challenge, especially for electronegative ultrafine bimetallic NPs. Here, we develop an anion-exchange strategy for the synthesis of ultrafine Pd-Au alloy NPs. Simple treatment of main-chain imidazolium-based organic polymer (IOP) with HAuCl₄ and Na₂PdCl₄, followed by reduction with NaBH₄ generated Pd-Au alloy NPs (Pd-Au/IOP). These NPs possess an unprecedented tiny size of 1.50 ± 0.20 nm and are uniformly dispersed over IOP. The electronic structure of the surface Pd and Au atoms is optimized via electron exchange during alloying, a net charge flowing resulting from counteranions is injected into Au and Pd to form a strong ensemble effect, which is responsible for a remarkably higher catalytic activity of Pd-Au/IOP in the hydrolytic dehydrogenation of ammonia borane than those of monometallic counterparts.

A heterogenized cobaltate catalyst on a bis-imidazolium-based covalent triazine framework for hydroesterification of epoxides

A recyclable heterogeneous [bis-imidazolium-CTF][Co(CO)₄] complex that reduces decomposition of cobaltate by intramolecular anion stabilization effects and efficiently converts epoxides into β-hydroxyesters with excellent conversion (selectivity 93%).

Polyimidazolium Salts: Robust Catalysts for the Cycloaddition of Carbon Dioxide into Carbonates in Solvent-Free Conditions

There is a growing interest in sustainable heterogeneous catalysts based on organic polymers. Here, we describe a series of polyimidazolium salt catalysts, prepared from the direct reaction of arene-bridged bis- and tris-alkyl halides with trimethylsilylimidazole. The polyimidazolium salts were characterized by spectroscopic and analytical techniques and it was found that their morphology and porosity could be controlled by adjusting the steric parameters of the spacer in the alkyl-halide starting materials. Moreover, the polymers are excellent heterogeneous organocatalysts for the cycloaddition of CO₂ to epoxides to afford cyclic carbonates at atmospheric pressure under solvent-free conditions. The polymer catalysts exhibit long-term stability and may be recycled and reused at least 10 times.

Polymerized Ionic Networks with High Charge Density: Quasi-Solid Electrolytes in Lithium-Metal Batteries

Polymerized ionic networks (PINs) with six ion pairs per repeating unit are synthesized by nucleophilic-substitution-mediated polymerization or radical polymerization of monomers bearing six 1-vinylimidazolium cations. PIN-based solid-like electrolytes show good ionic conductivities (up to 5.32 × 10(-3) S cm(-1) at 22°C), wide electrochemical stability windows (up to 5.6 V), and good interfacial compatibility with the electrodes.

Fabrication of Ruthenium Nanoparticles in Porous Organic Polymers: Towards Advanced Heterogeneous Catalytic Nanoreactors

A novel strategy has been adopted for the construction of a copolymer of benzene-benzylamine-1 (BBA-1), which is a porous organic polymer (POP) with a high BET surface area, through Friedel-Crafts alkylation of benzylamine and benzene by using formaldehyde dimethyl acetal as a cross-linker and anhydrous FeCl3 as a promoter. Ruthenium nanoparticles (Ru NPs) were successfully distributed in the interior cavities of polymers through NaBH4, ethylene glycol, and hydrothermal reduction routes, which delivered Ru-A, Ru-B, and Ru-C materials, respectively, and avoided aggregation of metal NPs. Homogeneous dispersion, the nanoconfinement effect of the polymer, and the oxidation state of Ru NPs were verified by employing TEM, energy-dispersive X-ray spectroscopy mapping, cross polarization magic-angle spinning (13)C NMR spectroscopy, and X-ray photoelectron spectroscopy analytical tools. These three new Ru-based POP materials exhibited excellent catalytic performance in the hydrogenation of nitroarenes at RT (with a reaction time of only ≈ 30 min), with high conversion, selectivity, stability, and recyclability for several catalytic cycles, compared with other traditional materials, such as Ru@C, Ru@SiO2, and Ru@TiO2, but no clear agglomeration or loss of catalytic activity was observed. The high catalytic performance of the ruthenium-based POP materials is due to the synergetic effect of nanoconfinement and electron donation offered by the 3D POP network. DFT calculations showed that hydrogenation of nitrobenzene over the Ru (0001) catalyst surface through a direct reaction pathway is more favorable than that through an indirect reaction pathway.

Solvent-Induced Facile Synthesis of Cubic-, Spherical-, and Honeycomb-Shape Palladium N-Heterocyclic Carbene Particles and Catalytic Applications in Cyanosilylation

The facile synthesis of palladium N-heterocyclic carbene (NHC) particles with spherical, cubic, and honeycomb morphologies is accomplished. The structures of cubic and honeycomb particles are defined as an unprecedented trinuclear palladium-NHC complex. An obvious effect of particle morphologies on catalytic activity and recyclability is observed in hetero-geneous cyanosilylation.

Spherical core-shell magnetic particles constructed by main-chain palladium N-heterocyclic carbenes

The encapsulation of the functional species on magnetic core is a facile approach for the synthesis of core-shell magnetic materials, and surface encapsulating matrices play crucial roles in regulating their properties and applications. In this study, two core-shell palladium N-heterocyclic carbene (NHC) particles (Fe3O4@PNP1 and Fe3O4@PNP2) were prepared by a one-pot reaction of semi-rigid tripodal imidazolium salts and palladium acetate in the presence of magnetite nanoparticles. The magnetite nanoparticles are encapsulated inside the main-chain palladium, which act as cores. The conjugated effects of triphenyltriazine and triphenylbenzene in the imidazolium salts have important influence on their physical properties and catalytic performances. Fe3O4@PNP2 shows better recyclability than Fe3O4@PNP1. Unexpectedly, Pd(ii) is well maintained after six consecutive catalytic runs in Fe3O4@PNP2, and Pd(0) and Pd(ii) coexist in Fe3O4@PNP1 under the same conditions; moreover, the morphologies of these spherical core-shell particles show no significant variation after six consecutive catalytic runs.

In situ formation of well-dispersed palladium nanoparticles immobilized in imidazolium-based organic ionic polymers

A new strategy for the synthesis of well-dispersed palladium nanoparticles (NPs) immobilized in imidazolium-based porous organic ionic polymers was presented in this study. The as-synthesized polymers showed excellent catalytic activity and reusability in the hydrogenation of nitroarenes without extra addition of palladium species.