Development of a ZIF-91-Porous-Liquid-Based Composite Hydrogel Dressing System for Diabetic Wound Healing

Porous metal-organic framework (MOF) liquids with permanent porosity, good fluidity, and fine dispersion attract broad attention in catalysis, transportation, gas storage, and chemical separations. Yet, the design and synthesis of porous MOF liquids for drug delivery remain less explored. Herein, a simple and general strategy is reported to prepare ZIF-91 porous liquid (ZIF-91-PL) via surface modification and ion exchange. The cationic nature of ZIF-91-PL not only renders it antibacterial but also with high curcumin loading capacity and sustained release. More importantly, the acrylate group on the grafted side chain of ZIF-91-PL makes it feasible to crosslink with modified gelatin through light curing, and the obtained hydrogel shows a significantly improved healing effect on the wound of diabetes. This work demonstrates for the first time, a MOF-based porous liquid for drug delivery, and the further fabrication of composite hydrogel may have potential applications in biomedical science.

Calculations of adsorption-dependent refractive indices of metal-organic frameworks for gas sensing applications

Detection of volatile organic compounds (VOCs) is one of the most challenging tasks in modelling breath analyzers because of their low concentrations (parts-per-billion (ppb) to parts-per-million (ppm)) in breath and the high humidity levels in exhaled breaths. The refractive index is one of the crucial optical properties of metal-organic frameworks (MOFs), which is changeable via the variation of gas species and concentrations that can be utilized as gas detectors. Herein, for the first time, we used Lorentz-Lorentz, Maxwell-Ga, and Bruggeman effective medium approximation (EMA) equations to compute the percentage change in the index of refraction (Δn%) of ZIF-7, ZIF-8, ZIF-90, MIL-101(Cr) and HKUST-1 upon exposure to ethanol at various partial pressures. We also determined the enhancement factors of the mentioned MOFs to assess the storage capability of MOFs and the biosensors' selectivity through guest-host interactions, especially, at low guest concentrations.

Ultrahigh-Loaded Fe Single Atoms and Fe3C Nanoparticle Catalysts as Air Cathodes for High-Performance Zn-Air Batteries

Fe-based materials containing Fe-Nx sites have emerged as promising electrocatalysts in the oxygen reduction reaction (ORR), but they still suffer structural instability which may lead to loss of catalytic activity. Herein, a novel electrocatalyst Fe₃C-FeSA@3DCN with the coexistence of Fe₃C nanoparticles and Fe single atoms (FeSA) in a three-dimensional conductive network (3DCN) is prepared via lattice confinement and defect trapping strategies with an Fe atomic loading of as high as 4.36%. In the ORR process, the limiting current density of Fe₃C-FeSA@3DCN reaches 5.72 mA cm^-2, with an onset potential of 0.926 V and a Tafel slope of 66 mV/decade, showing better catalytic activity and stability than Pt/C catalysts. Notably, its assembled aqueous and solid-state Zn-air batteries (ZABs) achieve peak power densities of 166 and 56 mW cm^-2, respectively, with a long service life of up to 200 h at a current density of 5 mA cm^-2. In addition, the assembled ZAB can provide a constant voltage on activated carbon electrodes to perform capacitive deionization to adsorb different ions. The importance of the Fe species active sites generated by Fe₃C and FeSA in the material for ORR activity to boost the electron transfer and mass transfer is demonstrated by a simple selective poisoning experiment.

Ambient CO2/N2 Switchable Pickering Emulsion Emulsified by TETA-Functionalized Metal-Organic Frameworks

In recent years, metal-organic frameworks (MOFs) have been explored as emulsifiers for the fabrication of Pickering emulsions and then used for hybrid material synthesis and interface catalysis. Nevertheless, stimuli-responsive Pickering emulsions stabilized by MOFs have been rarely reported so far, although they are of great importance for fundamental research studies and practical applications. Herein, for the first time, triethylenetetramine (TETA)-functionalized MOFs (ZIF-90/TETA) have been designed, synthesized, and used for fabricating CO₂-/N₂-response Pickering emulsions. It is shown that even at the ZIF-90/TETA content of 0.25 wt %, the functional MOF can still efficiently emulsify n-hexane and water to form a high internal phase Pickering emulsion. Importantly, the Pickering emulsion can be easily and reversibly switched between emulsification and demulsification by bubbling of CO₂ and N₂ alternatively at atmospheric pressure. The possible mechanism of the CO₂/N₂ switchable emulsion is investigated by zeta potential, water contact angle, interfacial tension, ¹³C NMR spectroscopy, and an optical microscope. It is found that the acid-base reaction of CO₂ with TETA anchored on the surface of ZIF-90 leads to the production of hydrophilic ammonium bicarbonate and carbamate, which results in the emulsification of the Pickering emulsion. However, when N₂ is bubbled to remove CO₂, the reverse reaction takes place to cause the demulsification of the Pickering emulsion. Moreover, the CO₂/N₂ switchable Pickering emulsion has been successfully used as a microreactor for Knoevenagel reactions to demonstrate a highly efficient integration of chemical reaction, product separation, and ZIF-90/TETA recycling for a sustainable chemical process.