Metal-organic Framework Shell Research Articles

An insight Into Surface and Diffusion Characteristics of UiO‐66@ZIF‐8 Core–Shell MOF for Asymmetric Supercapacitors with Unprecedented Energy Density

AbstractIn this study, nanosized zeolitic imidazolate framework‐8 (ZIF‐8) crystal has been produced on the universitetet i oslo‐66 (UiO‐66) metal–organic framework (MOF) to make core–shell structure using a layer‐by‐layer deposition method. In comparison to the pristine UiO‐66 and ZIF‐8, the core–shell MOF exhibits superior performance in terms of specific capacitance. This enhanced performance is attributed to its remarkable ability to facilitate the rapid diffusion of electrolyte ions through nanosized ZIF‐8 and enhance the electron transfer process involving the inner and outer metal ions within the UiO‐66@ZIF‐8 structure. Remarkably, the core–shell structure achieves an impressive specific capacitance of 588.8 F g−1 at a current density of 0.5 A g−1 using 1 m sulfuric acid (H2SO4) aqueous electrolyte. Additionally, the UiO‐66@ZIF‐8 core–shell material is demonstrated as a positive electrode, coupled with activated carbon (AC) derived from waste tissue paper serving as the negative electrode, in the fabrication of an asymmetric supercapacitor (ASC) device. At a power density of 400 W kg−1, this assembled asymmetric device delivers a notably high energy density of 53 Wh kg−1 along with a cyclic stability of 94.8% after 10 000 cycles. This study substantiates the superior performance of the UiO‐66@ZIF‐8 core–shell MOF structure as a highly effective supercapacitor electrode material, surpassing the performance of its pristine MOF counterparts.

Rational Design of Coordination Polymers Composited Hollow Multishelled Structures for Drug Delivery.

Multifunctional drug delivery systems (DDS) are in high demand for effectively targeting specific cells, necessitating excellent biocompatibility, precise release mechanisms, and sustained release capabilities. The hollow multishelled structure (HoMS) presents a promising solution, integrating structural and compositional design for efficient DDS development amidst complex cellular environments. Herein, starting from a Fe-based metal-organic framework (MOF), amorphous coordination polymers (CP) composited HoMS with controlled shell numbers are fabricated by balancing the rate of MOF decomposition and shell formation. Fe-CP HoMS loaded with DOX is utilized for synergistic chemotherapy and chemodynamic therapy, offering excellent responsive drug release capability (excellent pH-triggered drug release 82% within 72h at pH 5.0 solution with doxorubicin (DOX) loading capacity of 284mg g-1). In addition to its potent chemotherapy attributes, Fe-CP-HoMS possesses chemodynamic therapy potential by continuously catalyzing H2O2 to generate ·OH species within cancer cells, thus effectively inhibiting cancer cell proliferation. DOX@3S-Fe-CP-HoMS, at a concentration of 12.5µg mL-1, demonstrates significant inhibitory effects on cancer cells while maintaining minimal cytotoxicity toward normal cells. It is envisioned that CP-HoMS could serve as an effective and biocompatible platform for the advancement of intelligent drug delivery systems in the realm of cancer therapy.

Engineering High-Performance Hypergolic Propellant by Synergistic Contribution of Metal-Organic Framework Shell and Aluminum Core.

Hypergolicity is a highly desired characteristic for hybrid rocket engine-based fuels because it eliminates the need for a separate ignition system. Introducing hypergolic additives into conventional fuels through physical mixing is a feasible approach, but achieving highly reliable hypergolic ignition and energy release remains a major challenge. Here, the construction of core-shell Al@metal organic framework (MOF) heterostructures is reported as high-performance solid hypergolic propellants. Upon contact with the liquid oxidizer the uniformly distributed hypergolic MOF (Ag-MOF) shell can induce the ignition of hypergolic-inert fuel Al, resulting in Al combustion. Such a synthetic strategy is demonstrated to be favorable in hotspot generation and heat transfer relative to a simple physical mixture of Al/Ag-MOF, thus producing shorter ignition delay times and more efficient combustion. Thermal reactivity study indicated that the functionalization of the Ag-MOF shell changes the energy release process of the inner Al, which is accompanied by a thermite reaction. The synergistic effect of implantation of hypergolic MOF and high energy Al contributes to high specific impulses of 230-270 s over a wide range of oxidizer-to-fuel ratios.

Catechol-formaldehyde resin microspheres@UiO-66-NH2@ CdS core-shell nanohybrids as robust visible-light photocatalyst for multifunctional applications

Well-defined zirconium based metal-organic frameworks (MOFs) coated polymer core-shell nanohybrid (CFR@MOF) was constructed using catechol formaldehyde resin (CFR) microspheres as a support, followed by encapsulating CdS nanoparticles (NPs) into MOF (UiO-66-NH2) shell layers to obtain CFR@UiO-66-NH2@CdS nanohybrids to enhance visible photosensitization for multifunctional photocatalytic applications including organic pollutant degradation, water disinfection and photoinduced atomic transfer radical polymerization (photoATRP). The CFR microspheres with a regular spherical morphology (200–400 nm) provided a versatile initial platform for the growth of MOF shells through mononuclear coating. The impact of different loadings of CdS NPs incorporated into CFR@UiO-66-NH2 shells on photocatalytic performance was systematically investigated. CFR@UiO-66-NH2 @CdS demonstrated robust dye degradation and antibacterial ability. Especially, a remarkable inhibitory efficiency of 99.99 % and 99.7 % was achieved for S. aureus and E. coli, with a low photocatalyst dosage (100 μg/mL) under visible light. Furthermore, by combining CFR@UiO-66-NH2@CdS with CuBr2/L catalysts, a high-efficiency red-light triggered photoredox catalytic polymerization system was established in photoinduced atom transfer radical polymerization (photoATRP), achieving high conversion rate (>90 %) for various monomers in a short time.

A thorough investigation of the utilization of metal-organic framework (MOF) coated titanium dioxide in photocatalytic applications: A review

Overall, this review provides accessible information about Metal-organic frameworks (MOFs) coated on TiO2 surfaces that can advance the photocatalytic activity of designing and creating more efficient materials as well as promoting application. TiO2 photocatalyst has been extensively studied for the unraveling of various environmental issues. Despite its potential, the high rate of recombination of photogenerated charge carriers and its broad band-gap energy pose obstacles to its application in photocatalysis. In order to overcome these hurdles, our research has concentrated on the incorporation of MOF coatings. The production of photoactive MOF coatings is a key issue because they have excellent photocatalytic performance and offer many industrial opportunities for photocatalysis. Different methods have been applied to produce MOF shell or layer on TiO2 NRs, NTs, NWs, and hollow particles. The object of this review is to supply an overview of the research on applying the MOF coating to the titania surface.

Ultra-stable MOF@MOF nanoplatform for photodynamic therapy sensitized by relieved hypoxia due to mitochondrial respiration inhibition

Metal-organic frameworks (MOFs) with periodically arranged porphyrinic linkers avoiding the self-quenching issue of porphyrins in photodynamic therapy (PDT) have been widely applied. However, the porphyrinic MOFs still face challenges of poor stability under physiological conditions and limited photodynamic efficiency by the hypoxia condition of tumors. Herein, we fabricate the MOF@MOF structure with a protective MOF shell to improve the stability and relieve the hypoxia condition of tumors for sensitized PDT. Under protection of the MOF shell, the MOF@MOF structure can keep intact for 96 h under physiological conditions. Consequently, the tumoral accumulation efficiency is two folds of the MOF core. Furthermore, the MOF shell decomposes under acidic environment, and the loaded inhibitor of mitochondria pyruvate carrier (7-amino carboxycoumarins-2, 7ACC2) will be released. 7ACC2 inhibits the mitochondrial pyruvate influx and simultaneously blocks glucose and lactate from fueling the mitochondrial respiration, thereupon relieving the hypoxia condition of tumors. Under a 5-min laser irradiation, the 7ACC2 carrying MOF@MOF nanoplatforms induced doubled cellular apoptosis and reduced 70% of the tumor growth compared with the cargo-free MOF@MOF. In summary, the design of this stable and hypoxia self-relievable MOF@MOF nanoplatform will enlighten the future development of MOF-based nanomedicines and PDT. Statement of significanceThough widely used for photodynamic therapy (PDT) in previous studies, porphyrinic metal-organic frameworks (MOFs) still face challenges in poor stability under physiological conditions and limited photodynamic efficiency due to the hypoxia condition of tumors. In order to solve these problems, (1) we develop the MOF@MOF strategy to improve the physiological stability; (2) an inhibitor of mitochondria pyruvate carrier, 7-amino carboxycoumarins-2 (7ACC2), is loaded to inhibit the mitochondrial pyruvate influx and simultaneously block glucose and lactate from fueling the mitochondrial respiration, thereupon relieving the hypoxia condition of tumors. In comparison with previous studies, our strategy simultaneously improves stability and overcomes the limited PDT efficiency in the hypoxia tumor tissue, which will enlighten the future development of MOF-based nanomedicines and PDT.

Integration of Noble Metal Nanocrystals in a Hollow Metal–Organic Framework Shell

Integration of Noble Metal Nanocrystals in a Hollow Metal–Organic Framework Shell

Synthesis, characterization, and selective gas adsorption performance of hybrid NH2-MIL-101(Fe)/ZIF-8 metal organic framework (MOF)

In this paper, an efficient NH2-MIL-101(Fe)/ZIF-8 metal organic framework (MOF) with tunable pore architecture was synthesized by an internal extended growth approach, using polyvinylpyrrolidone (PVP) as a regulator. In the resultant structure, the larger-pore MOF (NH2-MIL-101(Fe)) provides the facilitated transport pathways and the smaller-pore MOF (ZIF-8) acts as the shell, enhancing the molecular sieving properties. The synthesized MOFs were characterized by FESEM, EDS, HRTEM, FTIR, XRD, TGA, and BET analyses, and the hybrid structure formation was accordingly approved. Furthermore, the pure gas adsorption measurements were conducted for CO2, N2, CH4, C2H6, and C2H4 gases at 298 and 328 K and equilibrium pressures up to 4 bar. The CO2 adsorption capacity of 3.982 mmol g−1 at 298 K for NH2-MIL-101(Fe)/ZIF-8 was obtained, which is ∼43% and ∼127% higher than the values for the individual MOFs, respectively. This increase is mainly attributed to the favorable CO2 interactions with the unpaired electrons of nitrogen (amine functional groups and imidazole nitrogen) as well as oxygen atoms along with unsaturated metal sites present in the both MOFs. In addition, the beneficial size exclusion effect of the shell MOF, resulted in improved gas adsorption selectivity values. The synthesized hybrid structure displayed considerably higher CO2/N2 and CO2/CH4 adsorption selectivities, which were ∼3.8 and 1.7 times greater than those of the pristine NH2-MIL-101(Fe) MOF, respectively. Furthermore, the C2H6/C2H4 selectivity of NH2-MIL-101(Fe)/ZIF-8 was raised by ∼48%, compared to the NH2-MIL-101(Fe) MOF, owning to the molecular sieving effect of ZIF-8 for C2H6 with larger kinetic diameter compared to C2H4.

Parametric simulations of hierarchical core–shell MOF materials for direct air capture

Metal–organic frameworks (MOFs) can separate and adsorb specific gases from a gas mixture, making them an ideal candidate for direct air carbon capture. However, MOFs that adsorb CO2 well often competitively adsorb the more abundant H2O molecules in the atmosphere, degrading their adsorptive performance and operational longevity. MOF-contained-in-MOF (MOF⊂MOF) core–shell materials may resolve this issue if a shell can be synthesized to reject water while the core receives CO2. This paper builds on our team’s prior computational screening and experimental synthesis of individual and core–shell MOFs by performing multiphysics simulations on a spherical MOF⊂MOF core–shell pellet exposed to atmospheric air. This core–shell pellet is endowed with our previously calculated and experimentally measured constituent MOF properties to demonstrate a high throughput methodology for scale-up analysis on composite adsorbent structures. We simulate and screen five UiO-67(Zr) MOF variants for use as either the core or shell materials that lead to 25 MOF⊂MOF core–shell pellet combinations, five of which are pellets whose core and shell are the same MOF. The resulting rankings suggest that adding a shell MOF to a pellet does not necessarily improve the adsorptive performance of that pellet when using these UiO-67(Zr) variants. The highest-ranked core–shell pellet combination was a pellet whose core and shell were the same MOF material. However, when considering only the core domain of the pellet as a frame of reference, the ranking results suggest that using hydrophobic MOFs as the pellet core and hydrophilic MOFs as the pellet shell show improvement compared to without the shell MOF. Using this second frame of reference, we identify the MOF⊂MOF core–shell combination UiO-67(Zr)⊂2(NH2)-UiO-67(Zr) as the highest-performing pellet of those that show improvement over their homogeneous pellet counterparts. A set of parametric simulations are performed comparing the core–shell pellet UiO-67(Zr)⊂UiO-67(Zr) against that of UiO-67(Zr)⊂2(NH2)-UiO-67(Zr) to investigate the impact of air CO2 concentration, relative humidity, and shell thickness on each respective core MOF’s performance. From these studies, the largest improvement in the core MOF’s performance was observed when using elevated CO2 concentrations of 1000 ppm, reduced relative humidity levels of 10%, and an increased shell thickness of 0.03 cm on a pellet core 0.12 cm in radius. Together, these results suggest that additional UiO-67(Zr) MOF variants will need to be screened to determine the use cases where the use of a shell is of water-rejecting benefit to the pellet in the DAC setting. Further adsorption and porosimetry experimentation is necessary to replicate the proposed pellet under DAC conditions and establish a means of comparative analysis between the simulated and measured pellet properties.

Zr-MOF-Induced Smart Accumulation Enables Surface-Enhanced Raman Spectroscopic Detection of Dioxin at ppt Level in Food Samples.

The fast and economical detection of trace polychlorinated dibenzo-p-dioxins (PCDDs) in food samples by current mass spectrum-based methods is hindered by tedious sample preparation and bulky & expensive analytical instruments. Surface-enhanced Raman spectroscopy (SERS) successfully detects many organic pollutants in foods but not dioxins because the employed metal nanoparticles weakly adsorb hydrophobic PCDDs. Herein, we report the detection of PCDDs in milk with SERS for the first time using a bifunctional substrate consisting of Au nanoparticles embedded in a zirconium-based metal-organic framework shell (AuNP/Zr-MOF). 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD), as the most toxic PCDD, is detected as low as 1.2 parts per trillion (ppt) in real milk samples with massive interfering substances in 30 min, which is the lowest among all reported methods. The aromatic rings of Zr-MOF promote the smart accumulation of TCDD through π-π interactions, and Au-Cl interactions drive TCDD onto Au surfaces. Zr-MOF shells with pore sizes of 12.7 and 20 Å block the accessibility of larger interfering molecules. A one-step apparatus and protocol are established to be superior to traditional methods in terms of time and cost. This work provides new insight into a rational screening method for the detection of persistent organic pollutants in a real sample matrix.

Preserving Macroporosity in Type III Porous Liquids

AbstractPreserving large permanent pore structures in a fluid may endow conventional liquids with emergent physical properties. However, such materials are challenging to make because of the tendency of the pores to be filled and occupied by the solvent molecules. Here, we report the design and synthesis of the first Type III porous liquid (PL) containing uniform yet stable 480 nm cavities. This was achieved by first constructing a single crystalline hollow metal–organic framework (MOF), UiO‐66‐NH2, through chemical etching. The thin yet defect‐free MOF shell effectively excludes the bulky poly(dimethylsiloxane) solvent molecules from entering the cavity through its 4 Å aperture, resulting in the preservation of both micro‐ and macroporosity in the PL. These enormous void spaces allow the PL to reversibly host and release up to 27 wt % water for up to 10 cycles. The switching between the “dry” state and the “wet” state led to a large changes of the thermal conductivity of the PL from 0.140 to 0.256 W m−1 K−1, affording a guest‐responsive liquid thermal switch with a switching ratio of 1.8.

Preserving Macroporosity in Type III Porous Liquids.

Preserving large permanent pore structures in a fluid may endow conventional liquids with emergent physical properties. However, such materials are challenging to make because of the tendency of the pores to be filled and occupied by the solvent molecules. Here, we report the design and synthesis of the first Type III porous liquid (PL) containing uniform yet stable 480 nm cavities. This was achieved by first constructing a single crystalline hollow metal-organic framework (MOF), UiO-66-NH2 , through chemical etching. The thin yet defect-free MOF shell effectively excludes the bulky poly(dimethylsiloxane) solvent molecules from entering the cavity through its 4 Å aperture, resulting in the preservation of both micro- and macroporosity in the PL. These enormous void spaces allow the PL to reversibly host and release up to 27 wt % water for up to 10 cycles. The switching between the "dry" state and the "wet" state led to a large changes of the thermal conductivity of the PL from 0.140 to 0.256 W m-1 K-1 , affording a guest-responsive liquid thermal switch with a switching ratio of 1.8.

Implementation of a Core-Shell Design Approach for Constructing MOFs for CO2 Capture.

Adsorption-based capture of CO2 from flue gas and from air requires materials that have a high affinity for CO2 and can resist water molecules that competitively bind to adsorption sites. Here, we present a core-shell metal-organic framework (MOF) design strategy where the core MOF is designed to selectively adsorb CO2, and the shell MOF is designed to block H2O diffusion into the core. To implement and test this strategy, we used the zirconium (Zr)-based UiO MOF platform because of its relative structural rigidity and chemical stability. Previously reported computational screening results were used to select optimal core and shell MOF compositions from a basis set of possible building blocks, and the target core-shell MOFs were prepared. Their compositions and structures were characterized using scanning electron microscopy, transmission electron microscopy, and powder X-ray diffraction. Multigas (CO2, N2, and H2O) sorption data were collected both for the core-shell MOFs and for the core and shell MOFs individually. These data were compared to determine whether the core-shell MOF architecture improved the CO2 capture performance under humid conditions. The combination of experimental and computational results demonstrated that adding a shell layer with high CO2/H2O diffusion selectivity can significantly reduce the effect of water on CO2 uptake.

Designing a new method for growing metal-organic framework (MOF) on MOF: synthesis, characterization and catalytic applications.

Metal-organic frameworks as a unique class of high-surface-area materials have gained considerable attention due to their characteristic properties. In this perspective, herein, we report an eco-friendly and inexpensive route for the synthesis of 4(3H)-quinazolinones using magnetically separable core-shell-like bimetallic Fe3O4-MAA@Co-MOF@Cu-MOF NPs as environmentally-friendly heterogeneous catalysts. To the best of our knowledge, this is the first example of the integration of two different types of MOFs, which contain two different metal ions (Co2+ in the core and Cu2+ in the shell) using an external ligand. Our study not only introduces a novel nanostructured catalyst for the organic reaction but also presents a new strategy for the combination of two MOFs in one particle at the nanometer level. To survey the structural and compositional features of the synthesized nanocatalyst, a variety of spectroscopic and microscopic techniques including FT-IR, XRD, BET, TEM, HR-TEM, FE-SEM, EDX, EDX-mapping, TGA, VSM, and ICP-OES were employed. The combination of magnetic Co-MOF with Cu-MOF leads to achieving unique structural and compositional properties for Fe3O4-MAA@Co-MOF@Cu-MOF NPs with a particle size of 20-70 nm, mesostructure, and relatively large specific surface area (236.16 m2 g-1). The as-prepared nanostructured catalyst can be an excellent environment catalyst for the synthesis of a wide library of 4(3H)-quinazolinones derivatives, including electron-donating and electron-withdrawing aromatic, heteroaromatic, and aliphatic compounds under solvent-free conditions much better than the parent precursors. Moreover, by investigating the longevity of the nanocatalyst, the conclusion could be derived that the aforesaid nanocatalyst is stable under reaction conditions and could be recycled for at least seven recycle runs without a discernible decrease in its catalytic activity.

LnNP@ZIF8 Smart System for In Situ NIR-II Ratiometric Imaging-Based Tumor Drug Resistance Evaluation.

Just-in-time evaluation of drug resistance in situ will greatly facilitate the achievement of precision cancer therapy. The rapid elevation of reactive oxygen species (ROS) is the key to chemotherapy. Hence, suppressed ROS production is an important marker for chemotherapy drug resistance. Herein, a NIR-II emission smart nanoprobe (LnNP@ZIF8, consisting of a lanthanide-doped nanoparticle (LnNP) core and metal-organic framework shell (ZIF8)) is constructed for drug delivery and in vivo NIR-II ratiometric imaging of ROS for tumor drug resistance evaluation. The drug-loaded nanoprobes release therapeutic substances for chemotherapy in the acidic tumor tissue. As the level of ROS increases, the LnNPs shows responsively descending fluorescence intensity at 1550 nm excited by 980 nm (F1550, 980Ex), while the fluorescence of the LnNPs at 1060 nm excited by 808 nm (F1060, 808Ex) is stable. Due to the ratiometric F1550, 980Ex/F1060, 808Ex value exhibiting a linear relationship with ROS concentration, NIR-II imaging results of ROS change based on this ratio can be an important basis for determining tumor drug resistance. As the chemotherapy and resistance evaluation are explored continuously in situ, the ratiometric imaging identifies drug resistance successfully within 24 h, which can greatly improve the timeliness of accurate treatment.

Synthesis, characterization, and gas adsorption performance of an efficient hierarchical ZIF-11@ZIF-8 core–shell metal–organic framework (MOF)

In this paper, the solvent-assisted linker exchange (SALE) technique was successfully applied for the synthesis of porous ZIF-11@ZIF-8 core–shell composite structure metal–organic framework (MOF). The RHO-type ZIF-11 owing to larger cavities along with higher freedom in linker rotation, acts as the core and contributes in adsorption capacity enhancement. On the other hand, the SOD-type ZIF-8 provides greater molecular sieving features due to its lower degree of linker flexibility and thereby results in an improvement of the adsorption selectivity. The morphology and structure of the fabricated MOFs were characterized by XRD, FTIR, FESEM, EDS, TEM, BET, and TGA analyses and formation of the core–shell structure was confirmed. The BET surface area and micropore volume of the synthesized ZIF-11@ZIF-8 MOF were obtained as high as 1023.4 m2/g and 0.435 cm3 g−1, respectively. Gas adsorption measurements were carried out for CO2, N2, CH4, C2H6, and C2H4 gases at 298 and 328 K and equilibrium pressures up to 4 bar. The results revealed a remarkable rise (∼100 %) in CO2 adsorption capacity of ZIF-11@ZIF-8 nanoparticles (8.21 mmol g−1), compared to the pristine ZIF-11 (4.35 mmol g−1) at 298 K. The CO2/N2 and CO2/CH4 adsorption selectivity values were also augmented by 131 % and 92 %, respectively. In addition, the fabricated core–shell MOF, exhibited greater ethane (C2H6) adsorption capacity by ∼ 65 %, along with ethane to ethylene (C2H4) adsorption selectivity enhancement by ∼ 50 %. The higher adsorption capacity values without sacrificing adsorption selectivity suggests that the controlled core–shell MOF structures would be promising candidates for effective separation of CO2 from CH4 and N2 as well as C2H6 from C2H4.

SERS Monitored Kinetic Process of Gaseous Thiophenol Compound in Plasmonic MOF Nanoparticles.

Benefiting from the electromagnetic enhancement of noble metal nanoparticles (NPs) and the capture ability of organic frameworks, plasmonic metal-organic framework (MOF) structures have greatly promoted the development of gas detection by surface-enhanced Raman spectroscopy (SERS). In those detections, the kinetic process of gaseous molecules in plasmonic-MOF structures has a great influence on SERS spectra, which is still lacking intensive investigation in previous reports. In this work, the kinetic processes of gaseous thiophenol compounds (TPC) in the plasmonic Zeolitic Imidazolate Framework (Ag@ZIF) core-shell NPs are studied by SERS spectra. The experimental data demonstrate that the SERS intensities of gaseous TPC could be enhanced once more in an H2 mixed gas environment with different functional groups of TPC. Further results reveal that the two-step enhancement of SERS intensities is not only related to the thicknesses of the MOF shell but also affected by the ambient mixed gas. To understand this novel phenomenon, the binding energy between the gaseous molecule and ZIF is calculated based on first-principles computation. In combination with the plasmonic properties of the Ag core, a molecular collision model is introduced here to show the distribution of gaseous TPC molecules in ZIF, which could be responsible for this interesting two-step enhancement of SERS intensities. Furthermore, the H2 assisted kinetic process of gaseous p-aminothiophenol (PATP) is also analyzed by the classical pseudo-first-order kinetic model, which is consistent with our experimental SERS data. Our work not only reveals the novel phenomenon of plasmonic-MOF structures to improve the gas detection by SERS spectra but also enriches the understanding of the microcosmic process of gaseous molecules in the mixed gas environment to optimize MOF structures for gas capture and storage.

Facile Regulation of Shell Thickness of the Au@MOF Core-Shell Composites for Highly Sensitive Surface-Enhanced Raman Scattering Sensing.

Metal-organic frameworks (MOFs)-based core-shell composites have advanced the development of surface-enhanced Raman scattering (SERS) analysis, which originates from the promising structural characteristics of the outer framework material as well as the inherent plasmonic properties of the novel metal structure core (for example, nanoparticle, MNP). However, the SERS effect only exists directly in the surface of MNP or restricted around the plasmonic MNP surface. Consequently, the nanoscale control of the thickness of MOF shell in hybrid core-shell substrates is highly desirable. Despite the great effects which have been made to integrate various MOF matrices with MNP for the purpose of improving the SERS activity, the nanoscale thickness control of MOF shell remains a significant challenge. Here, we report a facile regulation method that enables the Au NP to be encapsulated by a zirconium-based MOF (BUT-17) with different thickness through the controlling of synthesis parameters. This method provides a promising strategy for optimizing the activity of core-shell SERS substrates for potential trace detection.

Achieving surface-sealing of hematite nanoarray photoanode with controllable metal–organic frameworks shell for enhanced photoelectrochemical water oxidation

Surface engineering of hematite (α-Fe2O3) photoanode by coupling electrocatalytically active metal–organic frameworks (MOFs) is an efficient way of boosting surface charge transfer for photoelectrochemical (PEC) water oxidation. However, the precise and controllable coating of conformal MOFs overlayer through a facile approach on photoelectrode still faces a challenge. In this work, NiFe metal–organic frameworks (NiFe-MOFs) are conformally deposited on zirconium-doped hematite (Zr-Fe2O3) by a novel indirect ligand-assisted transformation method, in which the well-coupled NiFe-layered double hydroxides (NiFe-LDHs) on photoanode act as self-templates due to their special layered structure and suitable interlayer spacing to provide with large specific area for the in-situ etching and coordinating, thus achieving the in-situ transformation of NiFe-LDHs layer into conformal NiFe-MOFs shell. Then, detailed investigations reveal that this conformal NiFe-MOFs shell endows the photoanode with a larger electrochemical active area, higher stability, and longer charge carrier lifetime compared to that of crystalline NiFe-MOFs on Zr-Fe2O3 from traditional solvothermal, resulting in outstanding PEC water oxidation performance of the target core–shell Zr-Fe2O3@NiFe-MOFs photoanode.

Interface-Sensitized Chemiresistor: Integrated Conductive and Porous Metal-Organic Frameworks

Research to develop ideal sensing devices for toxic gases is on the rise, and amongst various materials, metal–organic frameworks (MOFs) have opened up promising vistas as chemiresistive sensors due to their high structural and functional tunability. Here, we report the composites of dimensionally (2D and 3D) and functionally (conductive and porous) different two MOFs in the form of a well-integrated core–shell structure. The hierarchically assembled 2D-MOF@3D-MOF exhibits new interfacial properties that are responsible for synergetically enhanced sensing performances toward toxic H2S gas with the lowest recorded limit of detection (1.4 ppb), superior sensitivity (ΔR/R0 = 3.37), and outstanding selectivity at room temperature in air. The sensing mechanisms are proposed by combinational studies of experiments and calculation, which indicates that multiple changes (e.g., local structural change of the shell MOF, secondary binding sites generation from the core MOF, and free radicals formation) play a critical role in achieving synergetic chemiresistive sensing.