Due
to the extraordinarily high surface to volume ratio and enormous
structural and chemical diversities, metal–organic frameworks
(MOFs) have drawn much attention in applications such as heterogeneous
catalysis, gas storage separation, and drug delivery, and so on. However,
the potential of MOF materials as mechanical metamaterials has not
been investigated. In this work, we demonstrated that through the
concerted effort of molecular construct and mesoscopic structural
design, hierarchical MOFs can exhibit superb mechanical properties.
With the cutting-edge in situ transmission and scanning
electron microscope (TEM and SEM) techniques, the mechanical properties
of hollow UiO-66 octahedron particles were quantitatively studied
by compression on individual specimens. Results showed that the yield
strength and Young’s modulus of the hierarchical porous framework
material presented a distinct “smaller is stronger
and stiffer” size dependency, and the maximum yield
strength and Young’s modulus reached 580 ± 55 MPa and
4.3 ± 0.5 GPa, respectively. The specific strengths were measured
as 0.15 ± 0.03 to 0.68 ± 0.11 GPa g–1 cm3, which is comparable to the previously reported state-of-the-art
mechanical metamaterials like glassy carbon nanolattices and pyrolytic
carbon nanolattices. This work revealed that MOF materials can be
made into a new class of low-density, high-strength mechanical metamaterials
and provided insight into the mechanical stability of nanoscale MOFs
for practical applications.
Understanding the atomistic mechanisms of non-equilibrium
processes
during solid-state synthesis, such as nucleation and grain structure
formation of a layered oxide phase, is a critical challenge for developing
promising cathode materials such as Ni-rich layered oxide for Li-ion
batteries. In this study, we found that the aluminum oxide coating
layer transforms into lithium aluminate as an intermediate, which
has favorable low interfacial energies with the layered oxide to promote
the nucleation of the latter. The fast and uniform nucleation and
formation of the layered oxide phase at relatively low temperatures
were evidenced using solid-state nuclear magnetic resonance and in
situ synchrotron X-ray diffraction. The resulting Ni-rich layered
oxide cathode has fine primary particles, as visualized by three-dimensional
tomography constructed using a focused-ion beam and scanning electron
microscopy. The densely packed fine primary particles enable the excellent
mechanical strength of the secondary particles, as demonstrated by
in situ compression tests. This strategy provides a new approach for
developing next-generation, high-strength battery materials.
Thermoplastic polyurethane (TPU) is widely used in daily life due to its characteristics of light weight, high impact strength, and compression resistance. However, TPU products are extremely flammable and will generate toxic fumes under fire attack, threatening human life and safety. In this article, a nanohybrid flame retardant was designed for the fire safety of TPU. Herein, Co3O4 was anchored on the surface of exfoliated ultra-thin boron nitride nanosheets (BNNO@Co3O4) via coprecipitation and subsequent calcination. Then, a polyphosphazene (PPZ) layer was coated onto BNNO@Co3O4 by high temperature polymerization to generate a nanohybrid flame retardant named BNNO@Co3O4@PPZ. The cone calorimeter results exhibited that the heat release and smoke production during TPU combustion were remarkably restrained after the incorporation of the nanohybrid flame retardant. Compared with pure TPU, the peak heat release rate (PHRR) decreased by 44.1%, the peak smoke production rate (PSPR) decreased by 51.2%, and the peak CO production rate (PCOPR) decreased by 72.5%. Based on the analysis of carbon residues after combustion, the significant improvement in fire resistance of TPU by BNNO@Co3O4@PPZ was attributed to the combination of quenching effect, catalytic carbonization effect, and barrier effect. In addition, the intrinsic mechanical properties of TPU were well maintained due to the existence of the PPZ organic layer.
As a kind of excellent multifunctional metal oxide semiconductor, KxNa1-xNbO3 (KNN) has been widely applied in a variety of fields such as photocatalysis and energy harvesting due to their superb...
Water pollution has always been a serious problem across the world; therefore, facile pollutant degradation via light irradiation has been an attractive issue in the field of environmental protection. In this study, a type of Zn-based metal–organic framework (ZIF−8)-wrapped BiVO4 nanorod (BiVO4@ZIF−8) with high efficiency for photocatalytic wastewater treatment was synthesized through a two-step hydrothermal method. The heterojunction structure of BiVO4@ZIF−8 was confirmed by morphology characterization. Due to the introduction of mesoporous ZIF−8, the specific surface area reached up to 304.5 m2/g, which was hundreds of times larger than that of pure BiVO4 nanorods. Furthermore, the band gap of BiVO4@ZIF−8 was narrowed down to 2.35 eV, which enabled its more efficient utilization of visible light. After irradiation under visible light for about 40 min, about 70% of rhodamine B (RhB) was degraded, which was much faster than using pure BiVO4 or other BiVO4-based photocatalysts. The synergistic photocatalysis mechanism of BiVO4@ZIF−8 is also discussed. This study might offer new pathways for effective degradation of wastewater through facile design of novel photocatalysts.
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