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Metal–organic gels (MOGs) are an emerging class of materials and potential candidates for electrochemical applications because they have the advantages of large surface areas, designable and tailorable structures, active metal sites, and mild synthetic conditions. In addition to pristine MOGs, MOGs have been converted into derivatives such as porous carbons and nanostructured metal oxides. The utilization of MOGs, MOG derivatives, and MOG nanocomposites with graphene, conductive polymers, and others has been studied in various electrochemical applications and there is a need for an exhaustive review that covers all the genres of metal–organic gels for electrochemical applications. This review focuses on electrochemical studies of MOGs in energy conversion and storage techniques. The latest progress in MOG materials for electricity/ion conductors (electrolytes), energy storage, and conversion (electrocatalysis, supercapacitors, and batteries) is summarized, and future developments in this rapidly advancing field are presented. [ABSTRACT FROM AUTHOR]

Developing nonprecious electrocatalysts toward the oxygen evolution reaction (OER) remains one of the main challenges for large-scale electrocatalytic water splitting. Metal–organic gels (MOGs) have recently emerged as promising nonprecious electrocatalysts for the OER, which have the advantages of high surface areas, hierarchical porosity, good compatibility, and open metal active sites for electrocatalysis. Herein, multimetallic metal–organic aerogel electrocatalysts (MG–FeNiCo) are assembled from 1,3,5-benzenetricarboxylic acid and Fe3+, Co2+, and Ni2+ nitrates via a facile one-pot method. In this way, multiple metal ions react with 1,3,5-benzenetricarboxylic acid to yield a multimetallic metal–organic gel. The multimetal–organic gel is a self-sorting system rather than a co-assembled one, exhibiting mixed nanoparticle and tape morphology. The bimetallic and multimetallic metal–organic gels exhibit a partially amorphous structure together with regular nanoscale metal–organic framework phases. It is noted that the MG–FeNiCo aerogel shows thermoreversible stimulus-response and a low density of 52.8 mg cm−3, and can support about 770 times its weight. MG–FeNiCo exhibits excellent OER performance with a low overpotential of 248 mV and 272 mV at a current density of 20 mA cm−2 and 50 mA cm−2, respectively, and a small Tafel slope of 49 mV dec−1. Chronopotentiometry experiments revealed that MG–FeNiCo can retain a current density of 10 mA cm−2 for 48 h with only a ∼2.1% increase, indicating the excellent activity and stability of MG–FeNiCo in the OER. The excellent performance is attributed to the synergistic effect of multiple metal ions to obtain more abundant active sites, and there is more electron movement in the oxidation and reduction state transformation of multiple metal ions (Fe3+/Fe2+ and Ni3+/Ni2+). Additionally, a conductive substance (graphene oxide) was doped into the gel network to form MG–FeNiCo-xGO aerogels. MG–FeNiCo–xGO aerogels show improved OER performance and good stability and durability. This strategy provides a simple and efficient method to explore multimetallic electrocatalysts. [ABSTRACT FROM AUTHOR]

With increasing industrial development, heavy metal ions have been widely released, and fluorescence detection is an effective approach owing to its high selectivity and sensitivity. Herein, a water-soluble luminescent sensor based on a spirobifluorene-based imidazolium polymer (IMSPF-Br-COOH) is developed from tetraimidazole spirobifluorene and 3-bromo-2-bromomethylpropionic acid through a quaternization reaction. IMSPF-Br-COOH has an imidazolium cationic network and carboxyl coordination groups. Consequently, fluorescence quenching of IMSPF-Br-COOH exhibits high selectivity for Fe3+ and Cr2O72−via coordination and anion exchange. The corresponding quenching coefficient (Ksv) is 2.0772 × 103 L mol−1 for Fe3+ and 1.0081 × 104 L mol−1 for Cr2O72−. The detection limit (LOD) is calculated to be 170.56 μmol L−1 for Fe3+ and 100.81 μmol L−1 for Cr2O72−. This work provides a novel approach for metal ion detection by water-soluble polymers. [ABSTRACT FROM AUTHOR]

Conventional pyrophosphate anode electrochemical performance is restrained by its phase impurity, and the inevitable phase impurity is attributed to the traditional pyrophosphate material being obtained through high temperature (∼1000 °C). Herein, we report a novel phase-control stratagem that can obtain pure phase Mn2P2O7 at 300 °C. The obtained pure phase Mn2P2O7 presents 428.5 mA h g−1 after long cycles with superior stability in lithium ion battery systems. Moreover, it delivers promising electrochemical performance in the Na/K ion battery system. Furthermore, we applied the phase-control stratagem to the synthesis of a few pyrophosphate anodes, and successfully obtained the Co2P2O7, Ni2P2O7, TiP2O7, and Fe2Fe(P2O7)2 anodes, revealing that phase-control chemosynthesis is of great potential to the wide application of pyrophosphate fabrication. The phase controlled stratagem breaks the high temperature and phase impurity limitation of the traditional pyrophosphate anode synthesis, allowing for the stable and promising electrochemical cycling of pyrophosphate materials, and expands the further application and fabrication of pyrophosphate research studies on energy storage materials. [ABSTRACT FROM AUTHOR]

Efficient heterogeneous gel catalysts have been developed based on dynamic covalent chemistry and post-modification methods for the chemical fixation of CO2. Various porphyrin-based imine gels are synthesized and subsequent reduction of imine bonds and metallation with various metal centers yields gel catalysts. The gels are characterized by a number of techniques including SEM, TEM, EDX, FT-IR, CP/MAS 13C NMR, and XPS. The resulting gels not only have network structures including micro-, meso- and macropores, but also show improved chemical stability and strong interactions between CO2 and pore channels. The gel catalysts show good catalytic activity towards the cycloaddition of epoxides with CO2 to cyclic carbonates using wet gels. Post-modified gel catalysts with a Zn(ii) center (ZnTAPP-Go-r) show a high product yield and high stability with recyclability over 5 cycles. [ABSTRACT FROM AUTHOR]

Searching for porous materials that can be employed as solid stationary phases for chromatographic separations, porous membrane matrixes and solid supports for catalysis has become an active research area. Strategies for embedding emerging porous materials in columnar systems and their subsequent applications (separation and catalysis) have been developed, which benefit from the remarkable progress in the discovery and development of porous materials based on metal–organic coordination or dynamic covalent bonding such as metal–organic frameworks (MOFs), covalent-organic frameworks (COFs), porous organic cages, and porous organic polymers. In this review, porous materials that have been confined within capillary columns as packed, monolithic and open tubular columns are discussed. Progress in chromatographic separation and continuous flow catalytic synthesis is reviewed according to three major strategies. Applications of porous materials in membrane-separation fibre membrane systems and microfluidic devices with various functions are also highlighted. [ABSTRACT FROM AUTHOR]

Since the discovery of metal–organic frameworks (MOFs), covalent–organic frameworks (COFs) and zeolite–imidazole frameworks (ZIFs), many of their outstanding properties have been explored such as their large specific surface area, significant gas adsorption, and high catalytic activity. Some kinds of porous coordination polymers (PCPs) and their derivatives have shown high photocatalytic or electrocatalytic activity; thus, they may be able to catalyze the degeneration of organic molecules, the production of hydrogen and oxygen, carbon dioxide reduction, and so on. This review mainly focuses on the electrocatalytic, photocatalytic and photoelectrocatalytic properties of PCPs including MOFs, ZIFs and COFs. Several experiments have been reported in this article to compare their catalyst properties. Moreover, the reasons why they show these differences have been analyzed. These PCPs can be applied for tackling environmental pollution in water, carbon dioxide reduction and the production of hydrogen, which can help solve the energy crisis, the greenhouse effect and facilitate the utilization of solar energy. [ABSTRACT FROM AUTHOR]

A supramolecular gel based on dynamic covalent acylhydrazone bonding assembled from small molecules has been reported. The gel shows aggregation-induced emission for selective and sensitive Cu2+ and subsequent CN− detection. [ABSTRACT FROM AUTHOR]

Porphyrin-based imine gels assembled from small molecular precursors have been developed as a novel type of catalysts in hydrogen production from water splitting. The gels offer chemical variety and hierarchically porous structures and are susceptible to modification via porphyrin metal centres. The Pd gel shows cathodic electrocatalytic activity to produce H2 when coated on FTO electrodes. The gels are stable and active for visible-light driven hydrogen production in the presence of a sacrificial electron donor and a cocatalyst. Impregnation of the Pd metal centre greatly enhances the H2 evolution rate. The Pd gel enables efficient photocatalytic H2 evolution via photoinjection of electrons from the light-harvesting gel network into the Pt nanoparticles. When illuminated with visible light, the Pt-doped PdTAPP–TFPT gel produces hydrogen from aqueous sodium ascorbate solution without significant degradation during four runs (1.0744 × 105μmol g−1 for 120 h totally). Interestingly the wet gels show remarkably higher H2 production efficiency than their dried counterparts. [ABSTRACT FROM AUTHOR]

A synthetic strategy is developed to grow Au nanoparticles supported by imidazolium-based porous organic polymers (Au/IM-POPs) along the inner surface of a fused-silica microfluidic capillary. The thickness of the hybrid Au/IM-POP material layers can be tuned by changing the precursor concentration. A variety of imidazolium-based porous organic polymers are developed from tetrakis[4-(1-imidazolyl)phenyl]methane and bromo-functionalized linker molecules and fully characterized, which may be used to support Au nanoparticles. Additionally the IM-POPs and Au/IM-POPs show porosity and the ability to take up guest molecules. The capillary coated with Au/IM-POPs is further assembled to obtain a catalytic microfluidic reactor. The catalytic activity of Au nanoparticles supported by the porous imidazolium polymer is probed by using the reduction of nitrobenzene derivatives flowing through the microfluidic reactor. The catalytic microfluidic reactor demonstrates significantly enhanced turnover frequency magnitudes in comparison with the corresponding reactions under batch conditions. [ABSTRACT FROM AUTHOR]

This review explores the features and corresponding application of ZIF-67 and its derivatives. Thermally and chemically stable zeolitic imidazolate framework (ZIF) materials have received extensive research and application interest. In particular, ZIF-67 can be synthesized by a facile and environmentally friendly organic synthesis method. The nanostructures and mean particle sizes of ZIF-67 can be adjusted by controlling experimental conditions carefully. The resulting ZIF-67 possesses the characteristics of a tunable pore aperture, highly stable structure, catalytic activity and so on. Furthermore, by combining the advantages of ZIF-67 and various components or structures, the resulting compounds have a potentially better performance than pure ZIF-67. Therefore, ZIF-67 and its derivatives have aroused great interest of scientists and have the potential to be applied to gas adsorption, molecular separation, electrochemistry, catalysis and so on. [ABSTRACT FROM AUTHOR]

A series of (metallo)porphyrin imine gels have been synthesized based on imine chemistry. The resulting aerogels have sponge-like porous networked structures consisting of interconnected nanoparticles with hierarchical porosity. The aerogels have high specific surface areas (up to 719 m2 g−1) and large pore volumes (up to 2.60 cm3 g−1). The effect of metal ions on the uptake of gases in these aerogels was investigated. The impregnation of various metal ions (Pd(ii), Ni(ii), Mn(iii), Fe(iii) and Sn(iv)) enhances the uptake capacity of various gases (e.g., CO2) despite their higher densities. Among the metal ions, Pd(ii) is the best to increase the adsorption capacity and the isosteric heat of CO2 adsorption. The Pd-tapp–A4 aerogel exhibits CO2 volumetric uptake (1.62 mmol g−1, 7.13 wt% at 298 K, 1 bar) with a high isosteric heat of adsorption (40.0 kJ mol−1). The gels also show potential applications in catalysis because of their unique hierarchical porosity and the availability of metal centers. In combination with microfluidic technology, a catalytic gel capillary reactor has been assembled with the Pd-tapp–A4 gel supported on the inner surface of a functionalized capillary. [ABSTRACT FROM AUTHOR]

A novel phosphine-based tetragonal Ag4L2 cage has been assembled from a tetraphenylethylene (TPE)-based tetraphosphine and Ag+ ions. The cage structure is maintained both in solutions and in the solid state. Ag4L2 emits strong fluorescence not only in dilute solutions but also in aggregated states. The turn-on fluorescence of TPE-P4 in dilute solutions is attributed to the formation of Ag4L2. Ag4L2 shows potential as a fluorescent sensor towards anions and olefin compounds, which arises from binding of the guest anions/olefin compounds by its labile silver centres. [ABSTRACT FROM AUTHOR]

A series of novel aerogels have been obtained based on imine chemistry. The aerogels were prepared by polycondensation of various bridging aldehydes and amines via a sol–gel process. The imine aerogels of tetrakis-(4-aminophenyl)methane (A1) consist of three-dimensional networks of interconnected nanometer-sized particles with hierarchically porous structures. The porosity of the areogels is tuneable by the choice of precursors, precursor concentration and reaction solvent. The aerogels exhibit BET surface areas up to 1021 m2 g−1 (A1-biformyl aerogel A1B1-0.030), as measured by N2 adsorption at 77 K. The A1B1-0.030 aerogel possesses a CO2 uptake of 1.5 mmol g−1 at 298 K and 1.0 bar with an isosteric heat of 38.1 kJ mol−1 and displays high CO2/N2 selectivity up to 70.9, which is derived from the ideal adsorbed solution theory. The A1B1-0.030 aerogel also shows a good capacity to uptake aromatic toluene molecules from an aqueous solution. Moreover, the hierarchically porous structure endows the A1B1-0.030 aerogel with good performance in enrichment of large molecules (polycyclic aromatic hydrocarbons PAHs and organochlorine pesticides OCPs) as the coating adsorbent in solid-phase microextraction (SPME) fibres. [ABSTRACT FROM AUTHOR]

Metal-organic skeleton based gel electrolytes are prepared for the first time for high efficiency quasi-solid-state DSSCs. The gel electrolytes feature in their sponge-like porous matrix of a metal-organic gel (MOG) assembled by coordination of Al3+ and 1,3,5-benzenetricarboxylate (H3BTC), which can provide an excellent ability to accommodate electrolyte ingredients, thus largely preserving the properties of the liquid electrolyte. Meanwhile, the MOG electrolyte can well penetrate into the photoanode film to ensure a good interfacial contact. The effects of the concentration of active species in the MOG electrolyte on the photoelectrical performances are investigated. On increasing the concentration, Jsc of gel-state cells improves gradually due to the enhanced I-/I3- redox couple content, while Voc undergoes an increase first but decreases subsequently. The synergistic function of cations (such as Al3+, Li+, etc.) and tert-butylpyridine (TBP), which can induce a conductive band (CB) shift of the TiO2 photoanode and affect the electron recombination, may contribute to the variation of Voc. By optimizing the composition of the gel electrolyte, a high conversion efficiency of over 8.60% can be obtained, which is a little lower than that of a liquid-state cell (9.13%). This research study will open up a new way to fabricate quasi-solid-state DSSCs with high efficiency. [ABSTRACT FROM AUTHOR]

Post-modification of supramolecular assemblies via covalent capture is an important strategy for the fabrication of functional materials. This paper describes the synthesis of supramolecular nanotubes with appended pyridyl groups based on N,N′,N′′-tris(3-methylpyridyl)trimesic amide (TMPTA), and their successful post-modification by 1,4-bis(bromomethyl)benzene. The original tubular morphology of the TMPTA nanotubes was found to stay intact following the modification process. The modified nanotubes are resistant to attack by strong acids and bases. The continuous network of covalent bonds throughout the tubular network is responsible for this stability. The formation of pyridinium cations upon modification results in positively charged surfaces of nanotubes that were found to be highly effective adsorbents for a range of anionic dyes, demonstrating both high adsorption capacity and selectivities over cationic and neutral dye species. These materials can be reused for dye capture without losses in their capture ability. [ABSTRACT FROM AUTHOR]

Compressive graphene aerogels were obtained by the one-step reduction and self-assembly of graphene oxide with ethylenediamine and then freeze-drying. The aerogels hold good compressibility, variable electrical resistance and fire-resistance. The high porosity with a hydrophobic nature, allows the aerogels to absorb different organic liquids, and the absorption–squeezing process has been demonstrated for oil collection. [ABSTRACT FROM AUTHOR]

A new piezofluorochromic aggregation-induced emission compound was synthesized. The compound had morphology-alterable emission property and its amorphous and crystalline aggregates with various emissions were obtained through evaporation from the solutions in different solvent systems. The spectroscopic properties and morphological structures of the compound were reversed upon pressing and annealing (or fuming). The results show that the piezofluorochromic nature is generated through crystalline–amorphous phase transformation under external pressure. The reason for the phase transformation is ascribed to the twisted conformation of the molecule which leads to poor solid molecular packing and formation of some cavities in the interfaces of lamellar layers, as confirmed by single crystal X-ray diffraction analysis. [ABSTRACT FROM AUTHOR]

Modification of Fe-tricarboxylate based metal–organic gels yielded tert-butyl substituted or phosphine-functionalised gels in alcohols or DMF, which were prepared from 5-tert-butylisophthalic acid and 5-diphenylphosphanylisophthalic acid, respectively. Owing to their permeability, such phosphine-functionalised metal–organic gels can act as a new type of functionalisable porous scaffold. The phosphorus-containing gel was subsequently functionalised with Pd(ii) by immersion in a solution of Pd(COD)Cl2(COD = 1,5-cyclooctadiene). The subsequently functionalised Pd(ii)-immobilised gel and its xerogel/aerogel showed high activity in the catalysis of Suzuki C–C coupling comparable to unsupported complexes. The gel/xerogels could be reused under ambient atmosphere. [ABSTRACT FROM AUTHOR]

Ag6L6-type coordination nanotubular structures have been assembled from 6 Ag(i) ions and 6 T-shaped ligands, 4-(3,5-bis(diphenylphosphino)phenyl)pyridine; the nanotubes represent a discrete molecular architecture of a number of polymeric structures assembled from dimeric building blocks. [ABSTRACT FROM AUTHOR]

An introduction is presented in which the authors discuss various reports within the issue on topics including nucleation theory behind supramolecular gelation, crystallisation of inorganic materials with gel matrices, and use of a salt gelator to reveal the kinetic nature of supramolecular gels.

V 6 O 13 with a nanosheet structure was employed as a cathode material for aqueous zinc metal batteries. V 6 O 13 delivered a high specific capacity of 425 mA h g -1 , outstanding rate performance and durable cycling with high capacity retention of 86% after 3000 cycles. Moreover, in situ X-ray diffractometer (XRD), ex situ X-ray photoelectron spectroscopy (XPS) and X-ray absorption near-edge structure (XANES) were employed to ascertain the reaction mechanism of Zn 2+ storage.

A Au(i)-N-heterocyclic-carbene (NHC)-edged Pd 6 L 12 molecular metal-organic cage is assembled from a Au(i)-NHC-based bipyridyl bent ligand and Pd 2+ . The octahedral cage structure is unambiguously established by NMR, electrospray ionization-mass spectrometry and single crystal X-ray crystallography. The electrochemical behaviour was analyzed by cyclic voltammetry. The octahedral cage has a central cavity for guest binding, and is capable of encapsulating PF 6 - and BF 4 - anions within the cavity., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

A novel phosphine-based tetragonal cage has been assembled from a tetraphenylethylene (TPE)-based tetraphosphine and Ag(+) ions. The cage structure is maintained both in solutions and in the solid state. emits strong fluorescence not only in dilute solutions but also in aggregated states. The turn-on fluorescence of TPE-P4 in dilute solutions is attributed to the formation of . shows potential as a fluorescent sensor towards anions and olefin compounds, which arises from binding of the guest anions/olefin compounds by its labile silver centres.

A tetraphenylethylene-based phosphine, 1,1,2,2-tetrakis((4-diphenylphosphino)phenyl)ethylene (TPE-P4), was synthesized and showed novel aggregation-induced and mechano-responsive emission. A mixture of TPE-P4 and Ag(+) could fix atmospheric CO2in situ as carbonate ions in neutral solution to yield a rare 3D metal-organic framework with zeolite-like SOD topology, [Ag2(TPE-P4)CO3]x⊃nH2O (Ag-TPE-P4). Ag-TPE-P4 showed turn-on luminescence of TPE-P4, emitting bright bluish green light in the solid state.

A novel dynamic covalent gel has been prepared via the imine bond formation reaction of tetraamine building blocks with luminescent tetraphenylethene tetraaldehyde units. The gel shows high hierarchical porosity (SBET = 512 m(2) g(-1)) and remarkable aggregation-induced emission enhancement, which has been demonstrated to be a selective sensor.

Rigid bridging terpyridyl phosphine and AgOTf form nanofibres to induce gelation of organic solvents, and the gel emits blue luminescence by suppressing π-π interactions between ligands.

Ag(6)L(6)-type coordination nanotubular structures have been assembled from 6 Ag(I) ions and 6 T-shaped ligands, 4-(3,5-bis(diphenylphosphino)phenyl)pyridine; the nanotubes represent a discrete molecular architecture of a number of polymeric structures assembled from dimeric building blocks.

M(2)L(2) type metallacyclic complexes, [Pd(2)(L1)(2)Cl(4)]·1.5CH(2)Cl(2) (1), [Pd(2)(L1)(2)Cl(4)]·2CHCl(3) (2), [Pd(2)(L2)(2)Cl(4)]·2CH(2)Cl(2)·2CH(3)CN (3), [Pd(2)(L2)(2)Cl(4)]·2CHCl(3)·2CH(3)CN (4) and [Pd(2)(L3)(2)Cl(4)]·CH(2)Cl(2)·2CH(3)CN (5), have been prepared from three semi-rigid benzimidazol or benzotriazol ligands, 1,4-bis(benzimidazol-1-ylmethyl)-2,3,5,6-tetramethylbenzene (L1), 1,4-bis(5,6-dimethylbenzimidazol-1-ylmethyl)-2,3,5,6-tetramethylbenzene (L2) and 1,4-bis(benzotriazol-1-ylmethyl)-2,3,5,6-tetramethylbenzene (L3). All the complexes were structurally characterized by single-crystal X-ray diffraction and the phase purity was confirmed by powder X-ray diffraction (PXRD) measurements. The solution structure of representative complex 1 was studied by (1)H NMR titration and ESI mass spectroscopy. The thermal stability and guest-exchange properties of 1, 3 and 4 were investigated, revealing that the Pd(2)L(2) metallacycles can act as a selective receptor for CH(2)Cl(2) or CHCl(3) guest molecules. The catalytic activity of 1 in Suzuki-Miyaura coupling reaction was also studied and 1 could be recycled at least 5 times under heterogeneous conditions, indicative of a potential self-supported catalyst.

In the absence of coordinating solvents and anions, silver salts and triphosphines form viscous, thixotropic coordination polymers in solution, which aggregate into unusual wormlike macroscopic structures and undergo cage-polymer interconversions depending on the stoichiometry and presence of templating anions.

The combination of directionality and unsaturated metal sites in bowl-shaped coordination clusters [Ag(4)L(3)(SbF(6))](3+){L = 2,4,6-tris(diphenylphosphino)triazine} results in the formation of discrete dimers on reaction with additional bridging ligands.