Thermal Conversion of Core–Shell Metal–Organic Frameworks: A New Method for Selectively Functionalized Nanoporous Hybrid Carbon

From Bimetallic Metal-Organic Framework to Porous Carbon: High Surface Area and Multicomponent Active Dopants for Excellent Electrocatalysis

Bimetallic metal-organic frameworks are rationally synthesized as templates and employed for porous carbons with retained morphology, high graphitization degree, hierarchical porosity, high surface area, CoNx moiety and uniform N/Co dopant by pyrolysis. The optimized carbon with additional phosphorus dopant exhibits excellent electrocatalytic performance for the oxygen reduction reaction, which is much better than the benchmark Pt/C in alkaline media.

Synthesis of Zeolitic Imidazolate Framework Core-Shell Nanosheets Using Zinc-Imidazole Pseudopolymorphs

Zeolitic imidazolate frameworks (ZIFs) are an emerging class of microporous materials that possess an organic flexible scaffold and zeolite-like topology. The catalytic and molecular-separation capabilities of these materials have attracted considerable attention; however, crystal-shape engineering in ZIF materials remains in its infancy. This is the first study to report an effective method for tailoring the near-spherical crystal morphology of ZIF-8 using its leaf-like pseudopolymorph, ZIF-L. A thin, uniform layer of ZIF-8 is formed on ZIF-L through heterogeneous surface growth to produce a ZIF-L@ZIF-8 core-shell nanocomposite. This results in ZIF-8 with a crystal morphology comprising two-dimensional nanoflakes. We characterized the resulting core-shell crystals using a number of solid-state techniques, including powder X-ray diffraction, scanning electron microscopy, thermogravimetric analysis, and nitrogen physisorption. Approximately 16 mass% of ZIF-8 in the core-shell composites heterogeneous surfacely grown on ZIF-L core crystals. We also investigated the effects of zinc salts, which were used as a source of zinc in the formation of the ZIF-L@ZIF-8 core-shell nanocomposites. Finally, we assessed the CO2 adsorption properties of ZIF-8, ZIF-L, and ZIF-L@ZIF-8 core-shell crystals, the results of which were used to deduce the dynamic and equilibrium adsorption characteristics of various microporous ZIF crystals. The core-shell materials present hybridized CO2 uptake and diffusivity of the parent crystals. The proposed method for the synthesis of core-shell nanocomposites using pseudopolymorphic crystals is applicable to other ZIF systems.

Thermal conversion of an Fe₃O₄@metal-organic framework: a new method for an efficient Fe-Co/nanoporous carbon microwave absorbing material

A novel FeCo nanoparticle embedded nanoporous carbon composite (Fe-Co/NPC) was synthesized via in situ carbonization of dehydro-ascorbic acid (DHAA) coated Fe3O4 nanoparticles encapsulated in a metal-organic framework (zeolitic imidazolate framework-67, ZIF-67). The molar ratio of Fe/Co significantly depends on the encapsulated content of Fe3O4 in ZIF-67. The composites filled with 50 wt% of the Fe-Co/NPC-2.0 samples in paraffin show a maximum reflection loss (RL) of -21.7 dB at a thickness of 1.2 mm; in addition, a broad absorption bandwidth for RL < -10 dB which covers from 12.2 to 18 GHz can be obtained, and its minimum reflection loss and bandwidth (RL values exceeding -10 dB) are far greater than those of commercial carbonyl iron powder under a very low thickness (1-1.5 mm). This study not only provides a good reference for future preparation of carbon-based lightweight microwave absorbing materials but also broadens the application of such kinds of metal-organic frameworks.

Asymmetric Supercapacitors Using 3D Nanoporous Carbon and Cobalt Oxide Electrodes Synthesized from a Single Metal-Organic Framework

Nanoporous carbon and nanoporous cobalt oxide (Co3O4) materials have been selectively prepared from a single metal-organic framework (MOF) (zeolitic imidazolate framework, ZIF-67) by optimizing the annealing conditions. The resulting ZIF-derived carbon possesses highly graphitic walls and a high specific surface area of 350 m(2)·g(-1), while the resulting ZIF-derived nanoporous Co3O4 possesses a high specific surface area of 148 m(2)·g(-1) with much less carbon content (1.7 at%). When nanoporous carbon and nanoporous Co3O4 were tested as electrode materials for supercapacitor application, they showed high capacitance values (272 and 504 F·g(-1), respectively, at a scan rate of 5 mV·s(-1)). To further demonstrate the advantages of our ZIF-derived nanoporous materials, symmetric (SSCs) and asymmetric supercapacitors (ASCs) were also fabricated using nanoporous carbon and nanoporous Co3O4 electrodes. Improved capacitance performance was successfully realized for the ASC (Co3O4//carbon), better than those of the SSCs based on nanoporous carbon and nanoporous Co3O4 materials (i.e., carbon//carbon and Co3O4//Co3O4). The developed ASC with an optimal mass loading can be operated within a wide potential window of 0.0-1.6 V, which leads to a high specific energy of 36 W·h·kg(-1). More interestingly, this ASC also exhibits excellent rate capability (with the highest specific power of 8000 W·kg(-1) at a specific energy of 15 W·h·kg(-1)) combined with long-term stability up to 2000 cycles.

Combination effect of ionic liquid components on the structure and properties in 1,4-benzenedicarboxylate based zinc metal–organic frameworks

Two types of eleven Zn–BDC compounds were synthesized by ionothermal reactions. The combination effects of RMI⁺ and X⁻ on the structure construction, TG, and fluorescence are observed.

Hydroxyl-rich nanoporous carbon nanosheets synthesized by a one-pot method and their application in the in situ preparation of well-dispersed Ag nanoparticles

Nanoporous carbon nanosheets (CNSs) with high surface area have been synthesized by pyrolysis of organic–inorganic precursor. The CNSs with rich hydroxyl groups display remarkable reactivity and capability for in situ loading ultrafine Ag NPs.

Soft nano-wrapping on graphene oxide by using metal–organic network films composed of tannic acid and Fe ions

Graphene oxide nanosheets were easily covered with uniform metal–organic network films composed of tannic acid and Fe ions. The graphene oxide in the composite sheets was reduced chemically without the collapse of the wrapped nanostructure.

Hollow Co@C prepared from a Co-ZIF@microporous organic network: magnetic adsorbents for aromatic pollutants in water

ZIF-67 nanoparticles containing Co²⁺ ions were coated with a microporous organic network (MON). The thermolysis of ZIF-67@MON resulted in the formation of hollow Co@C materials which showed good performance as magnetic adsorbents for aromatic pollutants in water.