A sulfonic-acid-based covalent organic framework (TpPa-SO3H) has been synthesized that exhibits intrinsic proton conductivity under anhydrous conditions. The sulfonic acid groups are aligned on the ...two-dimensional (2D) layers at periodic intervals and promote the proton hopping inside the hexagonal one-dimensional channel. The intrinsic proton conductivity of TpPa-SO3H was measured as 1.7 × 10–5 S cm–1 at 120 °C under anhydrous conditions. To enhance the proton conductivity, we have synthesized a hybrid COF TpPa-(SO3H-Py) by a ligand-based solid-solution approach that contains sulfonic acid as the acidic site, as well as pyridine as the basic site, in order to immobilize acidic proton carrier molecules. Impregnation of phytic acid molecules inside the framework increases the anhydrous proton conductivity up to 5 × 10–4 S cm–1 at 120 °C. Such an approach highlights the advantage and first-time use of hybrid COF for interplaying intrinsic to extrinsic proton conductivity.
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Finding appropriate stimuli for controlling the breathing behavior of flexible metal–organic frameworks (MOFs) is highly challenging. Herein, we report the solvent‐induced changes in the particle ...size and stability of different breathing phases of the MIL‐53 series, a group of flexible MOFs. A water/dimethylformamide (DMF) ratio is tuned to synthesize members of the MIL‐53 series which have different behaviors. The breathing is explored by high‐pressure methane sorption tests. Increasing DMF concentration decreases MOF particle size and increases the stability of the porous phases, boosting the 5.8–65 bar sorption difference of methane, which is required for natural‐gas delivery.
Learning to breathe: Changing the water/DMF ratio in the synthesis of metal–organic frameworks (MOFs) of the flexible MIL‐53 series gave different breathing properties, which were explored by high‐pressure methane sorption tests. Increasing DMF concentration decreases particle size and increases the stability of the porous phases, affording an increase in the 5.8–65 bar natural‐gas deliverable capacity of the MOFs.
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Two new chemically stable functional crystalline covalent organic frameworkds (COFs) (Tp-Azo and Tp-Stb) were synthesized using the Schiff base reaction between triformylphloroglucinol (Tp) and ...4,4′-azodianiline (Azo) or 4,4′-diaminostilbene (Stb), respectively. Both COFs show the expected keto-enamine form, and high stability toward boiling water, strong acidic, and basic media. H3PO4 doping in Tp-Azo leads to immobilization of the acid within the porous framework, which facilitates proton conduction in both the hydrous (σ = 9.9 × 10–4 S cm–1) and anhydrous state (σ = 6.7 × 10–5 S cm–1). This report constitutes the first emergence of COFs as proton conducting materials.
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Proton conductivity has been studied thoroughly in two isomeric In(III)-isophthalate based MOFs. In-IA-2D-1 is capable of showing proton conductivity (3.4 × 10(-3) S cm(-1)) under humidified ...conditions (98% RH), whereas In-IA-2D-2 can conduct protons (2.6 × 10(-5) S cm(-1)) under humidified as well as anhydrous conditions.
A Cu(II)-phenanthroline connected Strandberg-type polyoxometalate based proton conducting MOF, Cu(3)Mo(5)P(2), that contains one dimensional parallel water channels has been reported. Cu(3)Mo(5)P(2) ...shows proton conduction at room temperature as well as elevated temperature.
A GdIII‐based porous metal–organic framework (MOF), Gd‐pDBI, has been synthesized using fluorescent linker pDBI (pDBI=(1,4‐bis(5‐carboxy‐1H‐benzimidazole‐2‐yl)benzene)), resulting in a ...three‐dimensional interpenetrated structure with a one‐dimensional open channel (1.9×1.2 nm) filled with hydrogen‐bonded water assemblies. Gd‐pDBI exhibits high thermal stability, porosity, excellent water stability, along with organic‐solvent and mild acid and base stability with retention of crystallinity. Gd‐pDBI was transformed to the nanoscale regime (ca. 140 nm) by mechanical grinding to yield MG‐Gd‐pDBI with excellent water dispersibility (>90 min), maintaining its porosity and crystallinity. In vitro and in vivo studies on MG‐Gd‐pDBI revealed its low blood toxicity and highest drug loading (12 wt %) of anticancer drug doxorubicin in MOFs reported to date with pH‐responsive cancer‐cell‐specific drug release.
MOF nanocarrier: A new GdIII‐based porous metal–organic framework, Gd‐pDBI, with an elongated rotatable linker (DBI=(1,4‐bis(5‐carboxy‐1H‐benzimidazole‐2‐yl)benzene) was synthesized. Gd‐pDBI is biocompatible, water‐stable, and acid/base‐tolerant. Mechanical grinding yielded nanocrystals with excellent water dispersibility, and they feature the highest loading of the anticancer drug doxorubicin (DOX) and cancer‐cell‐specific drug release.
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Three new alkaline earth metal based MOFs have been synthesized by using 4,4'-sulfobisbenzoic acid (SBBA) and alkaline earth metal salts M(NO(3))(2), M = Ca, Sr, Ba. These MOFs exhibit interesting ...structural diversity, variable chemical stability as well as proton conductivity.
Mechanochemistry has become an increasingly important synthetic tool for a waste-free environment. However, the poor quality of the so-derived materials in terms of their crystallinity and porosity ...has been their major drawback for any practical applications. In this report, we have for the first time successfully leveraged such characteristics to show that the mechanochemically synthesized bipyridine based covalent organic framework (COF) outperforms its conventional solvothermal counterpart as an efficient solid-state electrolyte in PEM fuel cells. Marking the first such attempt in COFs, a Membrane Electrode Assembly (MEA) fabricated using the mechanochemically synthesized COF was observed to inhibit the fuel crossover and build up a stable Open Circuit Voltage (OCV = 0.93 V at 50 degree C), thereby establishing itself as an effective solid electrolyte material (with a proton conductivity of 1.4 10 super(-2) S cm super(-1)), while the solvothermally synthesized COF proved ineffective under similar conditions.
Proton conductivity of five Ca-based MOFs which depends on the amount of water molecules coordinated to the Ca-centres has been reported. These MOFs show high temperature proton conductivity due to ...the strong hydrogen bonding between the lattice and coordinated water molecules.
Metal‐organic frameworks (MOFs) are a class of hybrid network supramolecular solid materials comprised of organized organic linkers and metal cations. They can display enormously high surface areas ...with tunable pore size and functionality, and can be used as hosts for a range of guest molecules. Since their discovery, MOFs have experienced widespread exploration for their applications in gas storage, drug delivery and sensing. This article covers general and modern synthetic strategies to prepare MOFs, and discusses their structural diversity and properties with respect to application perspectives.
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