Facile fabrication of morphology-adjustable viologen-based ionic polymers for carbon dioxide immobilization and iodine vapor adsorption

Viologens, also referred as 1,1'-disubstituted-4,4'-bipyridinium salts, exhibit exceptional redox properties, identifying them as building blocks for functional organic polymer materials with a wide range of potential applications, including carbon dioxide (CO2) conversion and iodine capture. Herein, a series of viologen-derived ionic porous organic polymers (VIPOP-n), assembled from viologen derivatives, were designed and synthesized using a straightforward one-step strategy. The constructed polymer materials were subsequently characterized by Fourier Transform Infrared Spectroscopy (FT-IR), solid-state 13C nuclear magnetic resonance (13C NMR), X-ray photoemission spectroscopy (XPS), scanning electron microscopy (SEM), and nitrogen adsorption-desorption isotherms, among other techniques. Notably, the variation of synthetic solvents significantly influences the construction of polymer materials, resulting in observable changes in morphology and structure, which in turn affect their potential applications in CO2 cycloaddition reaction and iodine adsorption. The polymer VIPOP-3 exhibits superior catalytic performance under conditions of 80 °C and 1 atm CO2, producing valuable cyclic carbonates with yields reaching 94%. Density Functional Theory (DFT) calculations indicate that inert-hydrogen bonding can effectively activate both the epoxide and CO2, lowering the activation energy (Ea) of the cycloaddition reaction to 87.5 kJ mol-1, as corroborated by kinetic evaluations. Additionally, all polymers exhibited effective iodine vapor adsorption capacities, with VIPOP-7 emerging as the most efficient material, displaying an adsorption capacity of 2.96 g g-1. The adsorption process was investigated through various kinetic models, revealing that both physical and chemical adsorption were involved, with physical adsorption being the predominant process.

New Viologen-Based Ionic Porous Organic Polymers for Efficient Removal of Anionic Dyes and Hexavalent Chromium (Cr (VI)) from Water

Water pollution is a critical environmental issue in modern society, and adsorption is recognized as a straightforward and efficient water purification technique. In this study, three new viologen-based ionic porous organic polymers were designed and successfully synthesized via a simple approach, and their adsorption properties for water pollutants were evaluated. The cationic nature of these polymers, coupled with their large conjugated π-electron system, physicochemical stability, and aromatic backbone, contributes to their high adsorption capacity and rapid adsorption efficiency for anionic contaminants in water such as Methyl Orange, Congo Red, and Cr (VI). The polymers exhibited maximum adsorption capacities of 1617 mg/g for MO, 3734 mg/g for CR, and 530.22 mg/g for Cr (VI), surpassing most previously reported adsorbents. Furthermore, the polymers maintained a high removal rate even in the presence of competing anions. Effective separation of anionic dyes from mixed solutions could be achieved through simple filtration. These characteristics make them promising candidates for water purification applications.

Silver nanoparticles modified sulfur-containing POSS polymer membrane substrate for adsorption and surface-enhanced Raman scattering analysis of chrysoidine in food samples

In analysis of complex samples, the stability and sensitivity of surface-enhanced Raman scattering (SERS) substrates may be compromised by matrix interference. To address this issue, a membrane substrate was prepared for fast enrichment, separation, and detection of chrysoidine all-in-one. The silver nanoparticles modified sulfur-containing POSS polymer (AgNPs/POSS-P-S) SERS membrane substrate was fabricated using polyhedral oligomeric silsesquioxane (POSS) as support materials. Through in-situ growth, AgNPs were uniformly modified on POSS-P-S to ensure the stability and SERS activity of the membrane substrate. The enhancement factor of the malachite green was up to 5.3 × 105. By loading the AgNPs/POSS-P-S on membrane, on the other hand, the SERS membrane substrate can also serve as an adsorption medium for separating chrysoidine from sample matrix. Furthermore, the specific sensing mechanism of AgNPs/POSS-P-S for chrysoidine was investigated and a fast, sensitive, and selective method for its quantification was established, with a linear range of 0.010-2.0 mg/L and the limits of detection at 3.7 μg/L. In addition, the SERS method was successfully applied for the analysis of chrysoidine in beverages and chili products with the recoveries in the range of 83.5%-113.4 % and the relative standard deviations in 3.2%-9.0 %. The proposed AgNPs/POSS-P-S membrane based SRES method has great potential for rapid chrysoidine analysis in food samples.

A Liquid-Liquid Interfacial Strategy for Construction of Electroactive Chiral Covalent-Organic Frameworks with the Aim to Enlarge the Testing Scope of Chiral Electroanalysis

Although electroactive chiral covalent-organic frameworks (CCOFs) are considered an ideal platform for chiral electroanalysis, they are rarely reported due to the difficult selection of suitable precursors. Here, a facile strategy of liquid-liquid interfacial polymerization was carried out to synthesize the target electroactive CCOFs Ph-Py+-(S,S)-DPEA·PF6- and Ph-Py+-(R,R)-DPEA·PF6-. That is, a trivalent Zincke salt (4,4',4″-(benzene-1,3,5-triyl)tris(1-(2,4-dinitrophenyl)pyridin-1-ium)) trichloride (Ph-Py+-NO2) and enantiopure 1,2-diphenylethylenediamine (DPEA) were dissolved in water and chloroform, respectively. The Zincke reaction occurs at the interface, resulting in uniform porosity. As expected, the cyclic voltammetry and differential pulse voltammetry measurements showed that the tripyridinium units of the CCOFs afforded obvious electrochemical responses. When Ph-Py+-(S,S)-DPEA·PF6- was modified onto the surface of a glassy carbon electrode as a chiral sensor, the molecules, which included tryptophan, aspartic acid, serine, tyrosine, glutamic acid, mandelic acid, and malic acid, were enantioselectively recognized in the response of the peak current. Very importantly, the discriminative electrochemical signals were derived from Ph-Py+-(S,S)-DPEA·PF6-. The best peak current ratios between l- and d-enantiomers were in the range of 1.31-2.68. Besides, a good linear relationship between peak currents and enantiomeric excess (ee) values was established, which was successfully harnessed to determine the ee values for unknown samples. In a word, the current work provides new insight and potential of electroactive CCOFs for enantioselective sensing in a broad range.

Eliminating Concentration Polarization with Cationic Covalent Organic Polymer to Promote Effective Overpotential of Nitrogen Fixation

Electrocatalytic nitrogen reduction reaction offers a sustainable alternative to the conventional Haber-Bosch process. However, it is currently restricted by low effective overpotential due to the concentration polarization, which arises from accumulated products, ammonium, at the reaction interface. Here, a novel covalent organic polymer with ordered periodic cationic sites is proposed to tackle this challenge. The whole network exhibits strong positive charge and effectively repels the positively charged ammonium, enabling an ultra-low interfacial product concentration, and successfully driving the reaction equilibrium to the forward direction. With the given potential unchanged, the suppressed overpotential can be much liberated, ultimately leading to a continuous high-level reaction rate. As expected, when this tailored microenvironment is coupled with a transition metal-based catalyst, a 24-fold improvement is generated in the Faradaic efficiency (73.74 %) as compared with the bare one. The proposed strategy underscores the importance of optimizing dynamic processes as a means of improving overall performance in electrochemical syntheses.

Ionic covalent organic framework for selective detection and adsorption of TcO4-/ReO4. Chem Commun (Camb) 2023. [PMID: 37455640 DOI: 10.1039/d3cc02429f]

Herein, a novel fluorescent ionic covalent organic framework (BTTA-BDNP) based on a linked carbazole unit was constructed for the synchronous monitoring and capture of TcO₄^-/ReO₄^-. BTTA-BDNP has a fast fluorescence response time with a low detection limit (66.7 nM) for ReO₄^- (a non-radioactive substitute for TcO₄^-). Meanwhile, the high charge density and hydrophobic skeleton of BTTA-BDNP enable it to exhibit rapid and selective trapping of ReO₄^- in complex environments.

Applications of Viologens in Organic and Inorganic Discoloration Materials

Viologen derived from 4,4'-bipyridine has attracted much attention because of its color changing properties with electron transfer, unique redox stability and structural diversity. These characteristics have led to its successful use in various applications, in particular in color-changing materials. In the past few years, researchers have been working on the syntheses of viologen-based color-changing functional materials, and such materials have been widely used in many fields. In photochromic materials, it is used as anti-counterfeiting material; in thermochromic, it is used as memory storage material, and in electrochromic, it is used as a battery material. This Review discusses the progress of viologen in organic and inorganic discoloration materials in recent years. The syntheses of viologen and its derivatives are summarized, and its application in the field of discoloration materials is introduced.

Construction of porphyrin and viologen-linked cationic porous organic polymer for efficient and selective gold recovery

Recycling precious metals from electronic waste not only benefits environmental protection, but is also favorable for alleviating resource shortages. Ionic porous organic polymers, as one type of burgeoning material, are regarded as excellent adsorbents due to their high ion density, but their application in precious metal recovery is still very limited. Here, V-PPOP-Br, a highly stable and easy-to-build cationic porous organic polymer, was successfully prepared for the first time. By linking porphyrins with viologens, V-PPOP-Br obtained the characteristics of a hierarchical porous structure, a high ion density skeleton, and a rich nitrogen content, which gave it an ultrahigh adsorption capacity (Q_max = 792.22 mg g^-1) and rapid adsorption rate for Au(III). V-PPOP-Br also had an effective Au(III) recovery capability from SIM cards. Mechanism investigation confirmed that this remarkable adsorption performance was attributed to the interplay of ion exchange, redox reactions and coordination. Moreover, V-PPOP-Br had excellent recyclability and could maintain an ultrahigh adsorption efficiency of 81% after eight consecutive adsorption-desorption experiments. These excellent performances as well as the roughly calculated gold recycling economics ($37.37/g V-PPOP-Br) confirmed that it possesses promising potential as an ionic porous material for gold recovery.

Highly Efficient and Selective Gold Recovery Based on Hypercross-Linking and Polyamine-Functionalized Porous Organic Polymers

With the continuous increase of electronic products, there is an urgent need to effectively recover gold from e-waste and other secondary resources other than the original mine. Here, hypercross-linking and polyamine-functionalized porous organic polymers (Pc-POSS-POP) were designed and facially synthesized based on multiple azo-coupling polymerizations between 2,9,16,23-tetraaminophthalocyanine (H₂Pc(NH₂)₄) and octa(aminophenyl)-t8-silsesquioxane (OAPS) for the first time. The reaction requires no metal as a catalyst, thereby benefiting the purification of the product and the industrial scalability. Pc-POSS-POPs possess a hypercross-linking structure, highly conjugated frameworks, nitrogen-rich active sites, and extensively visible and near-infrared light absorption, which was utilized as an absorbent to retrieve Au (III). The results demonstrated that Pc-POSS-POPs have a high adsorption capacity (862.07 mg g^-1) and a rapid adsorption rate toward gold recycling. The maximum adsorption capacity could reach up to 1026.87 mg g^-1 as in the case of light irradiation. Due to the strong N coordination sites and the electronic interaction between the -NH₄⁺ groups of Pc-POSS-POPs and AuCl₄^-, Pc-POSS-POPs also exhibited excellent selectivity toward gold over several coordinated metals [Cr (VI), Co (II), Cd (II), Ni (II), and Hg (II)]. These properties together with the good regenerative ability and superior recyclability demonstrated that Pc-POSS-POPs possess promising potential as hypercross-linking polymers for capturing and recycling of Au (III).

Coupling of CO2 with Epoxides by Bifunctional Periodic Mesoporous Organosilica with Ionic Liquid Frameworks under Solvent, Additive and Metal-Free Conditions

Despite huge catalytic systems which have already been introduced to the direct coupling of CO2 with the epoxide to obtain the corresponding cyclic carbonate, the design of new systems which...

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.

POSS and imidazolium-constructed ionic porous hypercrosslinked polymers with multiple active sites for synergistic catalytic CO2 transformation

In this work, we reported a facile one-pot approach to construct polyhedral oligomeric silsesquioxane (POSS) and imidazolium-based ionic porous hypercrosslinked polymers (denoted as iPHCPs) with multiple active sites towards efficient catalytic conversion of carbon dioxide (CO₂) to high value-added cyclic carbonates. The targeted iPHCPs were synthesized from a rigid molecular building block octavinylsilsesquioxane (VPOSS) and a newly-designed phenyl-based imidazolium ionic crosslinker through the AlCl₃-catalyzed Friedel-Crafts reaction. The desired multiple active sites come from the mixed anions including free Cl^- and Br^- anions, and in situ formed Lewis acidic metal-halogen complex anions [AlCl₃Br]^- within imidazolium moieties and POSS-derived Si-OH groups during the synthetic process. The typical polymer iPHCP-12 possesses a hierarchical micro-/mesoporous structure with a high surface area up to 537 m² g^-1 and shows a fluffy nano-morphology. By virtue of the co-existence of free nucleophilic Cl^- and Br^- anions, the metal complex anion [AlCl₃Br]^- with both electrophilic and nucleophilic characters and electrophilic hydrogen bond donor (HBD) Si-OH groups, iPHCP-12 is regarded as an efficient recyclable heterogeneous catalyst for synergistic catalytic conversion of CO₂ with various epoxides into cyclic carbonates under mild conditions. The present work provides a succinct one-pot strategy to construct task-specific ionic porous hypercrosslinked polymers from easily available modules for the targeted catalytic applications.

Azine Steric Hindrances Switch Halogen Bonding to N-Arylation upon Interplay with σ-Hole Donating Haloarenenitriles

An interplay between 4-bromo- and 4-iodo-5-nitrophthalonitriles (XNPN, X=Br or I) and any one of the azines (pyridine 1, 4-dimethylaminopyridine 2, isoquinoline 3, 4-cyanopyridine 4, 2-methylpyridine 5, 2-aminopyridine 6, quinoline 7, 1-methylisoquinoline 8, and 2,2'-bipyridine 9) proceeds differently depending on steric and electronic effects of the heterocycles. Sterically unhindered azines 1-3 underwent N-arylation to give the corresponding azinium salts (characterized by ¹ H and ¹³ C{H} NMR and high-resolution ESI-MS). In contrast, azines 4-9 with sterically hindered N atoms or bearing an electron-withdrawing substituent, form stable co-crystals with XNPN, where two interacting molecules are bound by halogen bonding. In all obtained co-crystals, X⋅⋅⋅N structure-directed halogen bonds were recognized and theoretically evaluated including DFT calculations (PBE0-D3/def2-TZVP level of theory), QTAIM analysis, molecular electrostatic potential surfaces, and noncovalent interaction plot index. Estimated energies of halogen bonding vary from -7.6 kcal/mol (for 6 ⋅ INPN) to -11.4 kcal/mol (5 ⋅ INPN).

A silsesquioxane-porphyrin-based porous organic polymer as a highly efficient and recyclable absorbent for wastewater treatment

Effective capture of pollutants from wastewater is crucial for protecting the environment and human health. An azo-based porous organic polymer (AzoPPOP) containing porphyrin and inorganics cage polyhedral oligomeric silsesquioxane units was synthesized via a catalyst-free coupling reaction. Results showed that AzoPPOP possess a high surface area, a hierarchically porous structure, good thermal stability, abundant adsorption sites, and an electronegative nature. Based on these properties, AzoPPOP had an extremely high adsorption capacity (1357.58 mg g^-1) for RhB, a fast adsorption rate, and good selectivity. Study of the mechanism revealed that in addition to electrostatic interactions, the high specific surface area, existence of -NH₂, and the strong π-π interaction between AzoPPOP and RhB also play important roles for the adsorption of RhB. AzoPPOP also displayed excellent adsorption properties for heavy metal ions (230.45, 192.24 and 162.11 mg g^-1 for Ag⁺, Hg²⁺, and Pb²⁺, respectively). More importantly, simulation of the purification experiment of waste water and the recycling regeneration experiment revealed that AzoPPOP has good high-level recyclability and could remove multi-pollutants in one pass through a simple adsorption column.

POSS nanostructures in catalysis

In this review we highlight the use of appealing POSS-based nanostructures for both homogeneous and heterogeneous catalytic applications.

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.

Facile synthesis of crystalline viologen-based porous ionic polymers with hydrogen-bonded water for efficient catalytic CO2 fixation under ambient conditions

In this work, we report a series of crystalline viologen-based porous ionic polymers (denoted VIP-X, X = Cl or Br), that have in situ formed dicationic viologens paired with halogen anions and intrinsic hydrogen-bonded water molecules, towards metal-free heterogeneous catalytic conversion of carbon dioxide (CO₂) under mild conditions. The targeted VIP-X materials were facilely constructed via the Menshutkin reaction of 4,4′-bipyridine with 4,4′-bis(bromomethyl)biphenyl (BCBMP) or 4,4′-bis(chloromethyl)biphenyl (BBMBP) monomers. Their crystalline and porous structures, morphological features and chemical structures and compositions were fully characterized by various advanced techniques. The optimal catalyst VIP-Br afforded a high yield of 99% in the synthesis of cyclic carbonate by CO₂ cycloaddition with epichlorohydrin under atmospheric pressure (1 bar) and a low temperature (40 °C), while other various epoxides could be also converted into cyclic carbonates under mild conditions. Moreover, the catalyst VIP-Br could be separated easily and reused with good stability. The remarkable catalytic performance could be attributed to the synergistic effect of the enriched Br⁻ anions and available hydrogen bond donors –OH groups coming from H-bonded water molecules.

Viologen-based porous ionic polymers with halogen anions and hydrogen-bonded water were constructed for efficient catalytic CO₂ fixation under mild conditions.

Metalated-bipyridine-based porous hybrid polymers with POSS-derived Si–OH groups for synergistic catalytic CO2 fixation

ZnBr₂ metalated-bipyridine porous hybrid polymers with POSS-derived Si–OH as “all-in-one” heterogeneous catalysts for synergistic catalytic CO₂ fixation.

The Preparation and Chemical Structure Analysis of Novel POSS-Based Porous Materials

In this work, we reported the preparation and chemical analysis of novel polyhedral oligomeric silsesquioxane (POSS)-based porous materials, which were prepared according to Friedel-Crafts chloromethylation by using aluminum chloride as the catalyst and dichloromethane as the solvent. Through controlling the treatment solvent (water or methanol) and kinds of POSS, several materials with different morphologies were conveniently obtained. The chemical structure of porous materials was systematically characterized by Fourier-transform infrared (FTIR) spectra, ²⁹Si Nuclear Magnetic Resonance (NMR), ¹³C NMR, and X-ray photoelectron spectroscopy (XPS). The samples were further characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA) to study their crystallinity, morphology, and thermal properties, respectively. The work systematically demonstrated the chemical structure of the porous materials. Moreover, the advantages and disadvantages of the preparation method and typical properties of the material were evaluated through a comparative analysis with other related research works.

Design Strategies and Redox-Dependent Applications of Insoluble Viologen-Based Covalent Organic Polymers

Dicationic quaternary salts of 4,4'-bipyridine, also referred to as the viologen family, are well-known for their interesting redox chemistry, whereby they can be reversibly reduced into radical cationic and neutral moieties. Because of this ability to switch between different redox states, viologens have frequently been incorporated into covalent organic polymers (COPs) as molecular switches to construct stimuli-responsive materials. Although many viologen-based COPs have been reported, hyper-conjugated insoluble COPs started to emerge fairly recently and have not been comprehensively reviewed. In this review, we investigate the design strategies employed in the synthesis of insoluble viologen-based COPs, which can be broadly classified as those with viologen in the backbone and those with viologen as pendant groups. Chemical reactions used in the synthesis of each category, including Sonogashira-Hagihara cross-coupling, Menshutkin and Zincke reactions, are highlighted. Diverse applications of these COPs are discussed with particular reference to the redox state of viologen in each material. Uses of these materials for gas adsorption, organic and inorganic pollutant removal, catalysis, sensing and film fabrication are explored.