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Volatile organic compounds (VOCs) have harmful effects on human health and the environment but detecting low levels of VOCs is challenging due to a lack of reliable biomarkers. However, incorporating gold nanoparticles (Au NPs) into metal-organic frameworks (MOFs) shows promise for VOC detection. In this study, we developed nanoscale Au@UiO-66 that exhibited surface-enhanced Raman scattering (SERS) activity even at very low levels of toluene vapors (down to 1.0 ppm) due to the thickness of the shell and strong π-π interactions between benzenyl-type linkers and toluene. The UiO-66 shell also increased the thermal stability of the Au NPs, preventing aggregation up to 550 °C. This development may be useful for sensitive detection of VOCs for environmental protection purposes.
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Metal-organic frameworks (MOFs), a new type of porous material, have shown many possible applications in gas storage and separation, biomedicine, catalysis, and so on. While most MOFs are synthesized through solvothermal synthesis where a large quantity of organic solvent is used, the green synthetic approach using a minimized amount of solvent is important to prevent irreversible environmental compacts. In this study, we successfully synthesized Zr-MOFs with SBUs (e.g., UiO-66 and MIL-140A) using a simple metal source and investigated the role of organic modulators in modulating the MOF structures during solid-state synthesis. Meanwhile, UiO-66 rich in defects synthesized via a solid-state conversion strategy shows good catalytic performance for the ring-opening of epoxides with alcohols. This work contributes to the understanding of the role of organic modulators in the solid-state synthesis of MOFs.
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Safety issues associated with lithium-ion batteries are of major concern, especially with the ever-growing demand for higher-energy-density storage devices. Although flame retardants (FRs) added to electrolytes can reduce fire hazards, large amounts of FRs are required and they severely deteriorate battery performance. Here, we report a feasible method to balance flame retardancy and electrochemical performance by coating an electrolyte-insoluble FR on commercial battery separators. By integrating dual materials via a two-pronged mechanism, the quantity of FR required could be limited to an ultrathin coating layer (4 µm) that rarely influences electrochemical performance. The developed composite separator has a four-times better flame retardancy than conventional polyolefin separators in full pouch cells. Additionally, this separator can be fabricated easily on a large scale for industrial applications. High-energy-density batteries (2 Ah) were assembled to demonstrate the scaling of the composite separator and to confirm its enhanced safety through nail penetration tests.
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The artificial engineering of an enzyme's structural conformation to enhance its activity is highly desired and challenging. Anisotropic reticular chemistry, best illustrated in the case of multivariate metal-organic frameworks (MTV-MOFs), provides a platform to modify a MOF's pore and inner-surface with functionality variations on frameworks to optimize the interior environment and to enhance the specifically targeted property. In this study, we altered the functionality and ratio of linkers in zeolitic imidazolate frameworks (ZIFs), a subclass of MOFs, with the MTV approach to demonstrate a strategy that allows us to optimize the activity of the encapsulated enzyme by continuously tuning the framework-enzyme interaction through the hydrophilicity change in the pores' microenvironment. To systematically study this interaction, we developed the component-adjustment-ternary plot (CAT) method to approach the optimal activity of the encapsulated enzyme BCL and revealed a nonlinear correlation, first incremental and then decremental, between the BCL activity and the hydrophilic linker' ratios in MTV-ZIF-8. These findings indicated there is a spatial arrangement of functional groups along the three-dimensional space across the ZIF-8 crystal with a unique sequence that could change the enzyme structure between closed-lid and open-lid conformations. These conformation changes were confirmed by FTIR spectra and fluorescence studies. The optimized BCL@ZIF-8 is not only thermally and chemically more stable than free BCL in solution, but also doubles the catalytic reactivity in the kinetic resolution reaction with 99% ee of the products.
Assuntos
Enzimas Imobilizadas/metabolismo , Lipase/metabolismo , Estruturas Metalorgânicas/química , Burkholderia cepacia , Catálise , Enzimas Imobilizadas/química , Regulação Bacteriana da Expressão Gênica , Regulação Enzimológica da Expressão Gênica , Lipase/química , Lipase/genéticaRESUMO
Applying metal-organic frameworks (MOFs) on the surface of other materials to form multifunctional materials has recently attracted great attention; however, directing the MOF overgrowth is challenging due to the orders of magnitude differences in structural dimensions. In this work, we developed a universal strategy to mediate MOF growth on the surface of metal nanoparticles (NPs), by taking advantage of the dynamic nature of weakly adsorbed capping agents. During this colloidal process, the capping agents gradually dissociate from the metal surface, replaced in situ by the MOF. The MOF grows to generate a well-defined NP-MOF interface without a trapped capping agent, resulting in a uniform core-shell structure of one NP encapsulated in one single-crystalline MOF nanocrystal with specific facet alignment. The concept was demonstrated by coating ZIF-8 and UiO-66-type MOFs on shaped metal NPs capped by cetyltrimethylammonium surfactants, and the formation of the well-defined NP-MOF interface was monitored by spectroscopies. The defined interface outperforms ill-defined ones generated via conventional methods, displaying a high selectivity to unsaturated alcohols for the hydrogenation of an α,ß-unsaturated aldehyde. This strategy opens a new route to create aligned interfaces between materials with vastly different structural dimensions.
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Safety issues in lithium-ion batteries have raised serious concerns due to their ubiquitous utilization and close contact with the human body. Replacing flammable liquid electrolytes, solid-state electrolytes (SSEs) is thought to address this issue as well as provide unmatched energy densities in Li-based batteries. However, among the most intensively studied SSEs, polymeric solid electrolyte and polymer/ceramic composites are usually flammable, leaving the safety issue unattended. Here, we report the first design of a fireproof, ultralightweight polymer-polymer SSE. The SSE is composed of a porous mechanic enforcer (polyimide, PI), a fire-retardant additive (decabromodiphenyl ethane, DBDPE), and a ionic conductive polymer electrolyte (poly(ethylene oxide)/lithium bis(trifluoromethanesulfonyl)imide). The whole SSE is made from organic materials, with a thin, tunable thickness (10-25 µm), which endorse the energy density comparable to conventional separator/liquid electrolytes. The PI/DBDPE film is thermally stable, nonflammable, and mechanically strong, preventing Li-Li symmetrical cells from short-circuiting after more than 300 h of cycling. LiFePO4/Li half cells with our SSE show a high rate performance (131 mAh g-1 at 1 C) as well as cycling performance (300 cycles at C/2 rate) at 60 °C. Most intriguingly, pouch cells made with our polymer-polymer SSE still functioned well even under flame abuse tests.
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We studied coordination-dependent surfactant binding on shaped MOF nanocrystals. Cetyltrimethylammonium bromide (CTAB) on the surface of ZIF-8 was used as a model system. Infrared spectroscopic analysis and molecular dynamics simulations reveal different coordination environments for Zn nodes on {100} and {110} facets, resulting in different CTAB adsorption. We found that we are able to fine-tune the ratio of {100} and {110} facets in the nanocrystals. We also observed that once the MOF nanocrystals are enclosed by pure {110} facets growth along the {100} facets is terminated because the MOF nanocrystal has no surface area for CTAB adsorption. Growth can then be reinitiated through the etching of these rhombic dodecahedral nanocrystals to form a small amount of undercoordinated sites. This work represents the first systematic study of the design principles underpinning the synthesis of shaped MOF nanocrystals.
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Solid-state Li-S batteries are attractive due to their high energy density and safety. However, it is unclear whether the concepts from liquid electrolytes are applicable in the solid state to improve battery performance. Here, we demonstrate that the nanoscale encapsulation concept based on Li2S@TiS2 core-shell particles, originally developed in liquid electrolytes, is effective in solid polymer electrolytes. Using in situ optical cell and sulfur K-edge X-ray absorption, we find that polysulfides form and are well-trapped inside individual particles by the nanoscale TiS2 encapsulation. This TiS2 encapsulation layer also functions to catalyze the oxidation reaction of Li2S to sulfur, even in solid-state electrolytes, proven by both experiments and density functional theory calculations. A high cell-level specific energy of 427 W·h·kg-1 is achieved by integrating the Li2S@TiS2 cathode with a poly(ethylene oxide)-based electrolyte and a lithium metal anode. This study points to the fruitful direction of borrowing concepts from liquid electrolytes into solid-state batteries.
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It has been reported that the biological functions of enzymes could be altered when they are encapsulated in metal-organic frameworks (MOFs) due to the interactions between them. Herein, we probed the interactions of catalase in solid and hollow ZIF-8 microcrystals. The solid sample with confined catalase is prepared through a reported method, and the hollow sample is generated by hollowing the MOF crystals, sealing freestanding enzymes in the central cavities of hollow ZIF-8. During the hollowing process, the samples were monitored by small-angle X-ray scattering (SAXS) spectroscopy, electron microscopy, powder X-ray diffraction (PXRD), and nitrogen sorption. The interfacial interactions of the two samples were studied by infrared (IR) and fluorescence spectroscopy. IR study shows that freestanding catalase has less chemical interaction with ZIF-8 than confined catalase, and a fluorescence study indicates that the freestanding catalase has lower structural confinement. We have then carried out the hydrogen peroxide degradation activities of catalase at different stages and revealed that the freestanding catalase in hollow ZIF-8 has higher activity.
Assuntos
Estruturas Metalorgânicas , Catalase , Enzimas Imobilizadas , Espalhamento a Baixo Ângulo , Difração de Raios XRESUMO
The large-scale implementation of lithium metal batteries (LMBs) has long been plagued by the uncontrollable Li deposition triggered safety issues. Herein, a lithiophilic three-dimensional Li anode scaffold, which is prepared by molten Li infusion aided by confined growth of low-cost Zn clusters, is rationally constructed for high-performance LMBs. Owing to the synergy of the carbon host and the effective regulation from the Zn nanoclusters, the large volumetric change of Li metal is well mitigated and shows a smooth and dendrite-free behavior. The Li anode scaffold can deliver much improved Coulombic efficiency, superior rate performance, and long cycle lifespan with much lower voltage polarization. Furthermore, the half cells of Li anode scaffold paired with LiFePO4 /LiCoO2 /sulfur can achieve a higher specific capacity and longer stable cycling life than those with conventional Li foil. The Li|LFP cells can achieve a stable cycling over 250 cycles at 1C with a higher capacity retention of ≈90.8%, and a higher initial discharge capacity of 924.6 mAh g-1 with a high capacity retention over 300 cycles can also be obtained in Li|S cells at 1C. This work demonstrates a cost-effective and scalable strategy for stable Li metal anode toward next-generation and high-performance LMBs.
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An oxidative linker cleaving (OLC) process was developed for surgical manipulation of the engraving process within single crystalline MOFs particles. The strategy relies on selective degradation of 2,5-dihydroxyterephthalic acid linker into small molecular fragments by oxidative ring-opening reactions, resulting in controllable scissoring of framework. By regulation of the generation and diffusion of oxidative species, the core MOFs will undergo divergent etching routes, producing a series of single crystalline hollow and yolk-shell MOF structures. In addition, the OLC process can be initiated and localized around the pre-embedded Pd NPs through on-site catalytic generation of oxidative species, leading to solitary confinement of multiple NPs within one single crystalline MOF particle, namely, a multi-yolk-shell structure. This unique architecture can effectively protect NPs from agglomeration while realizing size selective catalysis at the same time.
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A bio-inspired design of using metal-organic framework (MOF) microcrystals with well-defined multi-shelled hollow structures was used as a matrix to host multiple guests including molecules and nanoparticles at separated locations to form a hierarchical material, mimicking biological structures. The interactions such as energy transfer (ET) between different guests are regulated by precisely fixing them in the MOF shells or encapsulating them in the cavities between the MOF shells. The proof-of-concept design is demonstrated by hosting chromophore molecules including rhodamine 6G (R6G) and 7-amino-4-(trifluoromethyl)coumarin (C-151), as well as metal nanoparticles (Pd NPs) into the multi-shelled hollow zeolitic imidazolate framework-8 (ZIF-8). We could selectively establish or diminish the guest-to-framework and guest-to-guest ET. This work provides a platform to construct complex multifunctional materials, especially those need precise separation control of multi-components.
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We demonstrate a molecular-level observation of driving CO2 molecules into a quasi-condensed phase on the solid surface of metal nanoparticles (NP) under ambient conditions of 1 bar and 298 K. This is achieved via a CO2 accumulation in the interface between a metal-organic framework (MOF) and a metal NP surface formed by coating NPs with a MOF. Using real-time surface-enhanced Raman scattering spectroscopy, a >18-fold enhancement of surface coverage of CO2 is observed at the interface. The high surface concentration leads CO2 molecules to be in close proximity with the probe molecules on the metal surface (4-methylbenzenethiol), and transforms CO2 molecules into a bent conformation without the formation of chemical bonds. Such linear-to-bent transition of CO2 is unprecedented at ambient conditions in the absence of chemical bond formation, and is commonly observed only in pressurized systems (>105 bar). The molecular-level observation of a quasi-condensed phase induced by MOF coating could impact the future design of hybrid materials in diverse applications, including catalytic CO2 conversion and ambient solid-gas operation.
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We show that an enzyme maintains its biological function under a wider range of conditions after being embedded in metal-organic framework (MOF) microcrystals via a de novo approach. This enhanced stability arises from confinement of the enzyme molecules in the mesoporous cavities in the MOFs, which reduces the structural mobility of enzyme molecules. We embedded catalase (CAT) into zeolitic imidazolate frameworks (ZIF-90 and ZIF-8), and then exposed both embedded CAT and free CAT to a denature reagent (i.e., urea) and high temperatures (i.e., 80 °C). The embedded CAT maintains its biological function in the decomposition of hydrogen peroxide even when exposed to 6 M urea and 80 °C, with apparent rate constants kobs (s-1) of 1.30 × 10-3 and 1.05 × 10-3, respectively, while free CAT shows undetectable activity. A fluorescence spectroscopy study shows that the structural conformation of the embedded CAT changes less under these denaturing conditions than free CAT.
Assuntos
Catalase/química , Imidazóis/farmacologia , Estruturas Metalorgânicas/farmacologia , Desdobramento de Proteína/efeitos dos fármacos , Zeolitas/farmacologia , Catalase/metabolismo , Imidazóis/química , Estruturas Metalorgânicas/química , Tamanho da Partícula , Porosidade/efeitos dos fármacos , Conformação Proteica/efeitos dos fármacos , Espectrometria de Fluorescência , Propriedades de Superfície/efeitos dos fármacos , Temperatura , Zeolitas/químicaRESUMO
We develop a new concept to impart new functions to biocatalysts by combining enzymes and metal-organic frameworks (MOFs). The proof-of-concept design is demonstrated by embedding catalase molecules into uniformly sized ZIF-90 crystals via a de novo approach. We have carried out electron microscopy, X-ray diffraction, nitrogen sorption, electrophoresis, thermogravimetric analysis, and confocal microscopy to confirm that the ~10 nm catalase molecules are embedded in 2 µm single-crystalline ZIF-90 crystals with ~5 wt % loading. Because catalase is immobilized and sheltered by the ZIF-90 crystals, the composites show activity in hydrogen peroxide degradation even in the presence of protease proteinase K.
Assuntos
Biocatálise , Catalase/química , Catalase/metabolismo , Nanoporos , Compostos Organometálicos/química , Tamanho da Partícula , Enzimas Imobilizadas/química , Enzimas Imobilizadas/metabolismo , Peróxido de Hidrogênio/metabolismo , Imidazóis/química , Cinética , Modelos Moleculares , Conformação Proteica , Zeolitas/químicaRESUMO
Fracture-free and conformal Pd-UiO-66@ZIF-8 core-shell metal-organic framework material is synthesized by a surfactant-mediated method. The hierarchical nanoporous material exhibits great size-selective hydrogenation catalysis and demonstrates potentials for many different applications.
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Composite nanomaterials are attractive for a diverse range of applications in catalysis, plasmonics, sensing, imaging, and biology. In such composite nanomaterials, it is desired, yet still challenging to create a controlled alignment between components with lattices in disparate scales. To address this challenge, we report a new concept of colloidal synthesis, in which self-assembled molecular layers control the alignment between materials during the synthesis. To illustrate this concept, self-assembled cetyltrimethylammonium bromide (CTAB) molecules are used to control interfaces in a core-shell nanocomposite with a well-defined metal nanocrystal core and a metal-organic-framework (MOF) shell, which differ in structural dimensions by orders of magnitude. We show that single metal nanocrystals are captured individually in single-crystalline MOFs, and an alignment between the {100} planes of the metal and {110} planes of the MOFs is observed. By utilizing the same concept, a layer of mesostructured silica is formed over MOF crystals. These multilayered core-shell structures demonstrate a controlled alignment across a wide range of materials, from the metal nanocrystals, extending to nanoporous MOFs and mesostructured silica.
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The Li-O2 battery promises high capacity to meet the need for electrochemical energy storage applications. Successful development of the technology hinges on the availability of stable cathodes. The reactivity exhibited by a carbon support compromises the cyclability of Li-O2 operation. A noncarbon cathode support has therefore become a necessity. Using a TiSi2 nanonet as a high surface area, conductive support, we obtained a new noncarbon cathode material that corrects the deficiency. To enable oxygen reduction and evolution, Ru nanoparticles were deposited by atomic layer deposition onto TiSi2 nanonets. A surprising site-selective growth whereupon Ru nanoparticles only deposit onto the b planes of TiSi2 was observed. DFT calculations show that the selectivity is a result of different interface energetics. The resulting heteronanostructure proves to be a highly effective cathode material. It enables Li-O2 test cells that can be recharged more than 100 cycles with average round-trip efficiencies >70%.
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Under linker exchange conditions, large guests with molecular diameters 3-4 times the framework aperture size have been encapsulated into preformed nanocrystals of the metal-organic framework ZIF-8. Guest encapsulation is facilitated by the formation of short-lived "open" states of the pores upon linker dissociation. Kinetic studies suggested that linker exchange reactions in ZIF-8 proceed via a competition between dissociative and associative exchange mechanisms, and guest encapsulation was enhanced under conditions where the dissociative pathway predominates.
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Encapsulating enzymes within metal-organic frameworks has enhanced their structural stability and interface tunability for catalysis. However, the small apertures of the frameworks restrict their effectiveness to small organic molecules. Herein, we present a green strategy directed by visible linker micelles for the aqueous synthesis of MAF-6 that enables enzymes for the catalytic asymmetric synthesis of chiral molecules. Due to the large pore aperture (7.6 Å), double the aperture size of benchmark ZIF-8 (3.4 Å), MAF-6 allows encapsulated enzyme BCL to access larger substrates and do so faster. Through the optimization of surfactants' effect during synthesis, BCL@MAF-6-SDS (SDS = sodium dodecyl sulfate) displayed a catalytic efficiency (Kcat/Km) that was 420 times greater than that of BCL@ZIF-8. This biocomposite efficiently catalyzed the synthesis of drug precursor molecules with 94-99% enantioselectivity and nearly quantitative yields. These findings represent a deeper understanding of de novo synthetic encapsulation of enzyme in MOFs, thereby unfolding the great potential of enzyme@MAF catalysts for asymmetric synthesis of organics and pharmaceuticals.