Single Metal-organic Framework Research Articles

Tetracycline antibiotics and NH4+ detection by Zn-organic framework fluorescent probe.

A fluorescent probe based on single metal-organic framework material without additional fluorophores and active sites can significantly improve the stability of the probe for detection, and has very important application value in environmental analysis and detection. In this paper, a simple and rapid fluorescence detection method was established with Zn-MOF, which realized the highly sensitive detection of tetracycline antibiotics and NH4+ in water. The prepared Zn-MOF has abundant pores and can exist stably in water. When tetracycline antibiotics are present in Zn-MOF aqueous solution, based on the unique coordination ability between Zn and N, tetracycline antibiotics rich in N will be adsorbed into the pore canals of MOF, and aggregation-induced luminescence will occur. The original non-fluorescent Zn-MOF will immediately produce yellow fluorescence, realizing the detection of tetracycline antibiotics in water, with the limit of detection reaching 0.017 μM in a linear range of 0.02-13 μM. Zn-MOF is further used for the detection of tetracycline antibiotics in actual samples of milk and honey. Oxytetracycline (OTC) with the best fluorescence response of tetracycline antibiotics was coated on Zn-MOF to synthesize OTC@Zn-MOF fluorescent probe. NH4+ will replace the original ligand of Zn-MOF, which will disintegrate MOF and release OTC, resulting in a fluorescence decrease. Therefore, NH4+ can be detected with low limit of detection (0.038 μM) in a linear range of 0 to 3 mM. The probe is expected to be able to detect ammonia in the environment.

Dual-Metal N-Heterocyclic Carbene Complex (M = Au and Pd)-Functionalized UiO-67 MOF for Alkyne Hydration-Suzuki Coupling Tandem Reaction.

Metal N-heterocyclic carbene complexes (NHC-M) have been recognized as an important class of organometallic catalysts. Herein, we demonstrate that different NHC-M (M = Au and Pd) species can be simultaneously introduced into a single metal organic framework (MOF) by direct assembly of NHC-M-decorated ligands and metal ions under solvothermal conditions. The obtained UiO-67-Au/Pd-NHBC MOF with different organometallic NHC-M species can be a highly reusable dual catalyst to sequentially promote alkyne hydration-Suzuki coupling reaction. The potential utility of this strategy is highlighted by the preparation of many more new multicatalysts of this type for various organic transformations in a sequential way.

High Capacity and Rate Capability Binder‐less Ternary Transition Metal‐organic Framework as Anode Material for Lithium‐ion Battery

AbstractA novel metal‐organic framework (MOF) composition containing three cations (CoCuNi−MOF) grown directly on nickel foam substrate has been evaluated for its use as an anode material for lithium ion batteries (LIB) and benchmarked the performance with its single cation MOF counterparts. Equimolar concentrations of cobalt, copper, and nickel and 1,4‐benzenedicarboxylic acid are used as metal centers and organic linker, respectively, for synthesis of CoCuNi−MOF. The morphology, chemical structure, and electrochemical properties of the materials are studied and analyzed for their suitability for lithium ion storage. The cyclability performance of CoCuNi−MOF exhibit good behavior with retaining ∼490 (±3) and ∼396 (±3) mA⋅h⋅g−1 at ∼200 and ∼500 mA⋅g−1, respectively. During rate capability evaluation, CoCuNi−MOF proved to be the best material compared to its single component MOF: CoCuNi−MOF retained an average capacity of ∼565 (±3) mA⋅h⋅g−1 at current density as high as 1000 mA⋅g−1. The positive attributes of CoCuNi−MOF are shown to arise from the synergistic effect of the three transition metals. The output from this work is expected to provide useful insight into the design of new MOFs electrode for LIBs with high specific capacity and improved cycle stability.

Structural and electronic switching of a single crystal 2D metal-organic framework prepared by chemical vapor deposition

The incorporation of metal-organic frameworks into advanced devices remains a desirable goal, but progress is hindered by difficulties in preparing large crystalline metal-organic framework films with suitable electronic performance. We demonstrate the direct growth of large-area, high quality, and phase pure single metal-organic framework crystals through chemical vapor deposition of a dimolybdenum paddlewheel precursor, Mo2(INA)4. These exceptionally uniform, high quality crystals cover areas up to 8600 µm2 and can be grown down to thicknesses of 30 nm. Moreover, scanning tunneling microscopy indicates that the Mo2(INA)4 clusters assemble into a two-dimensional, single-layer framework. Devices are readily fabricated from single vapor-phase grown crystals and exhibit reversible 8-fold changes in conductivity upon illumination at modest powers. Moreover, we identify vapor-induced single crystal transitions that are reversible and responsible for 30-fold changes in conductivity of the metal-organic framework as monitored by in situ device measurements. Gas-phase methods, including chemical vapor deposition, show broader promise for the preparation of high-quality molecular frameworks, and may enable their integration into devices, including detectors and actuators.

Visible Light–Initiated Synergistic/Cascade Reactions over Metal–Organic Frameworks

One‐pot synergistic/cascade reactions represent a promising direction for future catalysis. In particular, the use of solar light to initiate the synergistic/cascade reactions in one pot has attracted increasing attention, with the aim of developing renewable energy–based processes. Metal–organic frameworks (MOFs), are considered to be a promising type of multifunctional catalysts for light‐initiated synergistic/cascade catalysis, due to their excellent photoactive activity and unique structural characteristics, which enable the incorporation of functionally different catalytic active sites to work in concert. Herein, some recent developments on using MOFs as multifunctional catalysts for light‐initiated one‐pot synergistic/cascade reactions are summarized. This review starts with general background information on synergistic/cascade catalysis and the possibility of using MOFs as multifunctional catalysts for light‐initiated synergistic/cascade reactions. Then some examples of designing and fabricating of multifunctional MOFs, including single MOFs, doped MOFs, and metal nanoparticles (MNPs)/MOFs, for a variety of light‐initiated one‐pot synergistic/cascade reactions are demonstrated. Finally, the challenges and the perspective of the development of multifunctional MOFs for light‐induced one‐pot synergistic/cascade reactions are addressed. It is hoped that this review can stimulate future research on the designing and developing of more smart multifunctional MOFs for light‐initiated one‐pot synergistic/cascade reactions.

Asymmetric Supercapacitors Based on Hierarchically Nanoporous Carbon and ZnCo2O4 From a Single Biometallic Metal-Organic Frameworks (Zn/Co-MOF).

Metal-organic framework (MOF)-derived nanoporous carbons (NPCs) and porous metal oxide nanostructures or nanocomposites have gathered considerable interest due to their potential use in supercapacitor (SCs) applications, owing to their precise control over porous architectures, pore volumes, and surface area. Bimetallic MOFs could provide rich redox reactions deriving from improved charge transfer between different metal ions, so their supercapacitor performance could be further greatly enhanced. In this study, “One-for-All” strategy is adopted to synthesize both positive and negative electrodes for hybrid asymmetric SCs (ASCs) from a single bimetallic MOF. The bimetallic Zn/Co-MOF with cuboid-like structures were synthesized by a simple method. The MOF-derived nanoporous carbons (NPC) were then obtained by post-heat treatment of the as-synthesized Zn/Co-MOF and rinsing with HCl, and bimetallic oxides (ZnCo2O4) were achieved by sintering the Zn/Co-MOF in air. The as-prepared MOF-derived NPC and bimetallic oxides were utilized as negative and positive materials to assemble hybrid ASCs with 6 M KOH as an electrolyte. Owing to the matchable voltage window and specific capacitance between the negative (NPC) and positive (ZnCo2O4), the as-assembled ASCs delivered high specific capacitance of 94.4 F/g (cell), excellent energy density of 28.6 Wh/kg at a power density of 100 W/kg, and high cycling stability of 87.2% after 5,000 charge-discharge cycles. This strategy is promising in producing high-energy-density electrode materials in supercapacitors.

Integration and Synergy of Organic Single Crystals and Metal–Organic Frameworks in Core–Shell Heterostructures Enables Outstanding Gas Selectivity for Detection

AbstractControllable integration of two or more functional components is one of the most convenient and effective ways to obtain composite advanced materials with collective properties and improved performance. In this work, in combination with organic single crystals and metal–organic frameworks (MOFs), a novel 1D well‐defined core–shell heterostructure with single copper phthalocyanine (CuPc) ribbon cores coated with a uniform isoreticular MOF‐3 (IRMOF‐3) shell is successfully constructed. Impressively, thanks to performance the integration and synergy of the CuPc cores and the IRMOF‐3 shells, the sensor devices based on such single heterostructures exhibit outstanding selectivity for NH3 detection at ≈60% relative humidity at room temperature, the current response of which to NH3 is around 34–265 times the magnitude of response to ten potential interfering gases even in the case of the 1:100 concentration ratio of NH3 (5 ppm) and the interfering gases (500 ppm). Moreover, the detection limit of such CuPc@IRMOF‐3 sensors toward NH3 is estimated to be 52 ppb (signal to noise ratio = 3) based on 11 blank determinations, and good stability and reusability can also be achieved. This work highlights that the integration of organic single crystals and MOFs into well‐defined structures offers a new opportunity for high‐performance gas sensors.

Postmetalation of a new porphyrin ligand-based metal–organic framework for catalytic oxidative carboxylation of olefins

Heterogeneous catalytic reactions based on single metal–organic framework (MOF) material for the oxidative carboxylation of olefins following a tandem process, which involves the epoxidation of olefins and subsequent epoxide–CO2 cycloaddition, are highly desirable and economical for CO2 chemical fixation. In this work, a new trans-A2B2-type porphyrin ligand, 5,15-di(m-benzoato)-porphyrin (H2DMBP), was successfully synthesized and utilized for constructing a novel, highly porous, and stable Nd-porphyrin MOF, named CSUST-2. (CSUST stands for Changsha University of Science and Technology.) Furthermore, the coordinatively unsaturated Co(II) ions were implanted into the MOF by exploiting the innate non-metallated porphyrin ligands to generate Co(II)@CSUST-2 framework, which was evidenced to act as an efficient recyclable catalyst for oxidative carboxylation of olefins in the presence of tert-butyl hydroperoxide (TBHP) as an oxidant and tetrabutylammonium bromide (n-Bu4NBr) as a co-catalyst under mild conditions (1 atm CO2, 75 °C, and without solvent).

Surface imprinted CoZn-bimetalic MOFs as selective colorimetric probe: Application for detection of dimethoate

Designing simple and selective sensors for on-site recognition of organophosphate toxins (OPs) is of great importance. Here, molecularly imprinted polymer (MIP)-capped CoZn bimetal imidazolate framework (CoZn ZIF) has been introduced as a specific probe for the quantification of dimethoate. The detection is based on its diminishing effect on the catalytic action of ZIF in 3,3′,5,5′-Tetramethylbenzidine (TMB)-hydrogen peroxide (H2O2) reaction. CoZn ZIF catalyzes the dissociation of H2O2 to hydroxyl radicals, which can then oxidize TMB and create a blue colored product. It was demonstrated that the catalytic performance of bimetal metal organic framework (MOF) is higher than that of single metal MOF of Co (ZIF-67) or Zn (ZIF-8). On the other hand, adsorbing dimethoate in the specific MIP sites on the surface of CoZn ZIF declines its catalytic action. This effect was exploited to design a selective colorimetric assay for dimethoate determination in fruit and wastewater samples. The decrease in the absorption intensity of final solution was proportional to the dimethoate concentration in the range of 0.02–1.2 μM, with a detection limit of 5.6 nM. The high specificity of MIP technique and great catalytic activity of CoZn ZIF, as well as the simplicity of colorimetric method led to a reliable screening assay.

Core-satellite metal-organic framework@upconversion nanoparticle superstructures via electrostatic self-assembly for efficient photodynamic theranostics

The nanoplatforms based on upconversion nanoparticles (UCNPs) have shown great promise in amplified photodynamic therapy (PDT) triggered by near-infrared (NIR) light. However, their practical in vivo applications are hindered by the overheating effect of 980 nm excitation and low utilization of upconversion luminescence (UCL) by photosensitizers. To solve these defects, core-satellite metal-organic framework@UCNP superstructures, composed of a single metal-organic framework (MOF) NP as the core and Nd3+-sensitized UCNPs as the satellites, are designed and synthesized via a facile electrostatic self-assembly strategy. The superstructures realize a high co-loading capacity of chlorin e6 (Ce6) and rose bengal (RB) benefitted from the highly porous nature of MOF NPs, showing a strong spectral overlap between maximum absorption of photosensitizers and emission of UCNPs. The in vitro and in vivo experiments demonstrate that the dual-photosensitizer superstructures have trimodal (magnetic resonance (MR)/UCL/fluorescence (FL)) imaging functions and excellent antitumor effectiveness of PDT at 808 nm NIR light excitation, avoiding the laser irradiation-induced overheating issue. This study provides new insights for the development of highly efficient PDT nanodrugs toward precision theranostics.

3D, eco-friendly metal-organic frameworks@carbon nanotube aerogels composite materials for removal of pesticides in water

To alleviate the secondary risks of using metal-organic frameworks (MOFs) nanoparticles as adsorbent, a novel method of loading two MOFs (ZIF-8 or UiO66-NH2) on the carbon nanotube aerogels (MPCA) by in situ nucleation and growth of MOFs nanoparticles onto carbon nanotubes were developed. The prepared MOFs@MPCA aerogels were well characterized via SEM, TEM, EDS, FT-IR, XRD and XPS to reveal the microstructure and formation mechanism of MOF@MPCA. Besides, the hydrophilia, mechanical property and thermostability of MOF@MPCA were investigated. The results showed that MOF@MPCA had good hydrophilia, compression resilience and thermostability. The study on the ability to adsorb herbicides (chipton and alachlor) showed that the adsorption capacity of MOF@MPCA was stronger compared with single MOFs nanoparticles, which indicated that there was a synergistic effect between MOFs and MPCA. The equilibrium adsorption capacity of chipton adsorbed by UiO66-NH2@MPCA was 227.3 mg/g, and can be expediently reused for 5 cycles without a significant decrease in adsorption performance. Moreover, the results of biosafety experiments showed that MPCA can reduce the risk of MOFs nanoparticles leakage into the environment and accumulation in organisms. This work can provide a new research idea, which has potential applications to remove pollutants effectively and safely from the environment.

Microwave absorption performance of 2D Iron-Quinoid MOF

The excellent properties including high porosity, large specific surface area, low density, and strong controllability of metal–organic frameworks (MOFs) make them one of the preferred materials for a plethora of applications. One particular intriguing application, among others, is microwave absorption, to which majority of research has been devoted by using MOF as templates to prepare porous carbon via carbonization. Contrary to such approach, in this study we propose a novel strategy based on leveraging the intrinsic attributes of MOF. Through a simple and rapid microwave solvothermal method, lamellar redox-active iron-quinoid MOFs were synthesized and their morphology and crystallinity are modulated as a function of reaction temperature. The conductivity of the prepared MOF reached up to 2 × 10−3 S/m, which is comparable to that of semiconductors. In addition, magnetic hysteresis was observed at 300 K. The reaction temperature proved pivotal to attain maximum microwave absorption of −73.5 dB at 13.8 GHz with a matching thickness of 3.3 mm. Effective absorbing bandwidth with a reflection loss below −10 dB can be also gained in a wide frequency range of 9.8–15.9 GHz. The optimal microwave absorbing performance was mainly attributed to the simultaneous implementation of magnetic and electrical loss in a single iron-quinoid MOF resulting in adequate impedance matching through modulable magnetic and electric properties. The developed iron-quinoid MOF material opens up new opportunities to achieve high-efficiency, lightweight and tunable microwave absorbers. The material-structure coupling strategy here is instrumental to developing next-generation high-performance microwave absorbing materials.

Ionic liquid supported nickel-based metal-organic framework for electrochemical sensing of hydrogen peroxide and electrocatalytic oxidation of methanol

Since metal-organic frameworks (MOFs) have low electrical conductivity, the application of single MOFs as electrochemical sensor materials is very rare, and the construction of high-performance hydrogen peroxide (H2O2) sensors based on MOFs is still a difficult challenge. In this paper, a nickel-based MOF (Ni-MOF) material was synthesized using an ionic liquid as both solvent and ligand through an ionothermal method. The morphological and structural characterizations were studied by scanning electron microscopy, X-ray diffraction, attenuated total reflectance Fourier transform infrared spectroscopy and thermogravimetric analysis. Electrochemical sensing performance of the Ni-MOF modified glassy carbon electrode towards H2O2 was evaluated by cyclic voltammogram and chronoamperometry in an alkaline solution. The electrochemical H2O2 sensor was found to lead to a linear response from 0.5 μM to 2.0 mM with a detection limit of 0.18 μM. Moreover, the sensor also revealed good anti-interference ability and stability. To further assess the electrochemical properties, electrochemical activity of the Ni-MOF to oxidation of methanol was investigated by cyclic voltammetry. During the methanol oxidation reaction measurement, the Ni-MOF not only exhibited a high current density, but also found a good electrochemical activity for intermediate oxidation products. The above studies proved that the Ni-MOF material synthesized using the ionic liquid as a ligand can be used not only as an electrochemical H2O2 sensor but also as an electrocatalyst for methanol oxidation.

Self-assembled acicular CuCo-MOF for enhancing oxygen evolution reaction

Metal-organic framework (MOF) materials have a topological structure, which helps the reactants to fully contact the active sites. This structure can effectively increase the number of active sites participating in the reaction and enhance their catalytic properties. Therefore, in this work, single metal MOF (Co-MOF), single metal MOF with Cu through electrodeposition (Cu/Co-MOF), and double metal MOF (CuCo-MOF) in the case of the same ligand and metal ion were prepared by a hydrothermal method and electrodeposition, which were then applied in the electrocatalytic oxygen evolution reaction (OER). A group of electrochemical tests showed that as-prepared CuCo-MOF exhibited lowest Rct value, highest electron transfer capability, and the best catalytic performance among the three catalysts. When the current density was 10 mA cm−2, the overpotential of CuCo-MOF was 0.38 V, and the slope of Tafel curve was 118 mV dec−1. Moreover, the CuCo-MOF had larger TOF values and better electrocatalytic property as compared with the other two MOF materials. Therefore, the self-assembled acicular CuCo-MOF material prepared in this work has the advantages of low overpotential, small initial potential, and good stability.

Second harmonic generation enhancement of 2D metal-organic framework using silicon nanoparticles

Here we report on the 10 times enhancement of nonlinear optical signal coming from layered Cu-based metal-organic frameworks (MOFs) by means of placing of optically resonant silicon nanoparticles on the top of MOFs. These nanoparticles placed on the top of single MOFs allow the optical field localization and enhancement inside the framework due to the generation of Mie-type modes.

Metal-Organic Frameworks with Multiple Luminescence Emissions: Designs and Applications.

Emissive species are powerful for luminescent detection with high sensitivity and simple procedure and for light-emitting diode (LED) lighting because of their high efficiency, long lifetime, and low energy consumption. Here we propose the concept of multiple luminescence emissions from a single matrix or species under single-wavelength excitation. Multiemission not only realizes the high sensitivity of luminescence sensing but also possesses the capacity of self-reference for environment-free interferences. The color change is also convenient for visible detection. In multiemission species, every emissive center responds to a specific analyte to improve the efficiency for multiple-target detection. Multiemission also extends the applications to anticounterfeiting, colorful LEDs, and information storage. To date, it is still challenging to combine more than one type of emissive center in a single matrix or species. Obtaining multiemission under single-wavelength excitation also needs exquisite design. Metal-organic frameworks (MOFs) are porous hybrid assemblies prepared with metal ions and organic ligands. Metal nodes and ligands with large π-conjugated systems have the potential for the construction of luminescent MOFs. Abundant and diverse precursors provide the possibility to prepare MOFs with multiple luminescence emissions. The pores or channels of MOFs also act as hosts to encapsulate luminescent guest species as additional emissive sites. In this Account, we propose the concept of multiple-luminescence MOFs (ML-MOFs) and summarize the recent research progress on their designs, constructions, and applications reported by our group and others. ML-MOFs are MOFs that possess more than one emissive center under single-wavelength excitation. Six different kinds of construction strategies of ML-MOFs are introduced: (1) multiemission from both metal nodes and ligands in single MOFs; (2) use of mixed-metal nodes as multiemission centers in single MOFs; (3) combination of different emissive MOFs as a whole to achieve multiemission application; (4) host-guest emissions from emissive MOFs after encapsulation of luminescent guest species; (5) organization of different emissive ligands in a single MOF for multiemission; and (6) use of single ligands exhibiting dual emission to prepare ML-MOFs. We also discuss the mechanisms that realize multiple emissions from MOFs under single-wavelength excitation, such as the antenna effect and excited-state intramolecular proton transfer. The applications of ratiometric sensing, LED lighting, anticounterfeiting, and information storage are summarized. With this Account, we hope to spark new ideas and to inspire new endeavors in the design and construction of ML-MOFs, especially with postsynthetic techniques such as postsynthetic modification, postsynthetic exchange, and postsynthetic deprotection, to promote the applications of MOFs in sensing, lighting, information storage, and others.

Multi-shelled hollow metal-organic frameworks for optimizing the adsorption performance of antibiotics

Antibiotics have been widely used in the prevention and treatment of diseases such as humans, poultry and aquaculture due to their remarkable antibacterial effects. Nowadays, the infections caused by antibiotic-resistant bacteria are increasing, and resistance to antibiotics is probably the major public health problem. Therefore, the effective removal of trace antibiotic technology and materials in water has gradually attracted the attention of all parties in recent years. However, due to the difficulty in pore size, porosity, physical and chemical properties modification, the application of traditional porous materials, such as activated carbon, zeolites and silicates, are limited to some extent. As a new type of porous materials, metal-organic frameworks (MOFs) are considered as a promising platform for the adsorption applications. Inspired by the favorable structure and morphology of inorganic materials, hollow structures are promising materials for enhancing the adsorption performance. Herein, we fabricated multi-shelled hollow MOFs through step-by-step crystal growth and subsequent etched by acetic acid. The solid MOFs particles size about 200 nm, and the hollow cavity of single shell hollow MOFs (SSHM) about 100 nm. The diameters of double shell hollow MOFs (DSHM) inner cavity and outer shell were 50 and 50 nm, respectively. Triple shell hollow MOFs (TSHM) inner cavity and outer shell diameters were 20 and 70 nm, respectively. Powder X-ray diffraction (XRD) and N2 sorption confirmed the crystallographic structure and porosity of the resulting hollow MOFs. The hollow MOFs showed similar diffraction peaks position and intensity with pristine MOFs, which indicated that the high phase purity of the product MOFs. The BET surface of solid, single, double and triple shell MOFs were 2389.1, 2454.2, 2052.7 and 2396.2 m2/g, respectively. The hollow structured MOFs exhibited higher adsorption capacity than the solid MOFs, and the adsorption capacity increased with the number of layers. Particularly, the triple-shelled hollow MOFs (TSHM) for oxytetracycline and tetracyclines adsorption capacity is about 76 and 95 mg/g, respectively, which is three times higher than the solid MIL-101. The high adsorption capacity and removal efficiency may be attributed to the enhanced active site in each layer of multi hollow structure that can sorption more molecules. The recycling experiment showed that the adsorption efficiency of antibiotics in water by TSHM was relatively stable, and it still showed good crystallinity and morphological stability after reuses of up to 4 cycles. The enhanced adsorption capacity and excellent reusability obtained in this study demonstrated the potential of multi-shelled hollow MOFs structures as a novel adsorbent for the removal of organic molecules.

In Situ Confined Bimetallic Metal-Organic Framework Derived Nanostructure within 3D Interconnected Bamboo-like Carbon Nanotube Networks for Boosting Electromagnetic Wave Absorbing Performances.

Metal-organic framework (MOFs) derived magnetic nanoparticles/porous carbon (M/C) composites featuring efficient interfacial engineering and spatially continuous three-dimensional (3D) networks are desirable electromagnetic wave (EMW) absorbing materials due to multiple transmission path and well impedance matching. However, it is challenging to construct such 3D interconnected carbon networks from a single MOF precursor. Herein, FeNi3 and N embedded 3D carbon networks comprising bamboo-like carbon nanotubes connected carbon nanorods (FeNi@CNT/CNRs) were prepared via one-step pyrolyzing of the composite of melamine and FeNi-MIL-88B. Attributed to the synergistic contributions of 3D interconnected carbon nanotube networks and MOFs derived M/C for multiple transmission path, impedance matching, and dielectric loss (especially for multiple polarization and micro-current), the FeNi@CNT/CNRs nanoarchitectures have demonstrated superior EMW absorbing performance. In particular, the optimized FeNi@CNT/CNR-0.9 has exhibited strong absorption (-47.0 dB, 2.3 mm in thickness) and broadband effective absorption (4.5 GHz, 1.6 mm in thickness). This attractive strategy holds promise as a general approach to fabricate the carbon hybrid network constituted of MOFs derived nanopolyhedron and CNTs for the target application.

Rotation Restricted Emission and Antenna Effect in Single Metal-Organic Frameworks.

Aggregation induced-emission (AIE) and antenna effects are important luminescence behaviors. Thus, investigating their emission mechanisms and revealing their behaviors have become critical but challenging. Here we design and prepare metal-organic frameworks (MOFs) with an AIE ligand (i.e., tetrakis(4-carboxyphenyl)pyrazine (L1)) and Ln3+ ions (including Eu3+, Tb3+, and Gd3+). The emission from L1 is gradually enhanced during the formation of the MOFs because coordination restricts the intramolecular rotation. Thus, the emission is called as coordination-induced emission (CIE) with the same restriction of intramolecular rotation mechanism as AIE. Meanwhile, benzene rings twist to adapt to the MOFs' rigid structure, so the emission blueshifts gradually, as an additional evidence of CIE. Both AIE and CIE are "rotation-restricted emission (RRE)". Eu3+ ions exhibit the strongest emission with gradually enhanced intensity during the formation of L1-Eu MOF. Combined with emission properties from Tb3+ and Gd3+ ions, the antenna effect is verified. We also validate the conditions for the efficient sensitization of Ln3+ ions experimentally and refresh the threshold value of the energy gap between triplet state of a ligand and excited state of Ln3+ ions to 3000 cm-1. Thus, RRE and antenna effects are revealed and validated simultaneously. Because CIE of L1 and antenna effect emission from Eu3+ ions are enhanced simultaneously as strong dual emissions, ratiometric fluorescence detection is realized with the detection of arginine as a model. Our results incorporate AIE and CIE into RRE, which provides explicit information for the construction and application of emission systems with AIE ligands as building blocks. MOFs are also extended to explore the emission mechanism and the energy transfer between ligands and metal ions.

Van der Waals Heterostructured MOF-on-MOF Thin Films: Cascading Functionality to Realize Advanced Chemiresistive Sensing.

Heterostructured metal-organic framework (MOF)-on-MOF thin films have the potential to cascade the various properties of different MOF layers in a sequence to produce functions that cannot be achieved by single MOF layers. An integration method that relies on van der Waals interactions, and which overcomes the lattice-matching limits of reported methods, has been developed. The method deposits molecular sieving Cu-TCPP (TCPP=5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin) layers onto semiconductive Cu-HHTP (HHTP=2,3,6,7,10,11-hexahydrotriphenylene) layers to obtain highly oriented MOF-on-MOF thin films. For the first time, the properties in different MOF layers were cascaded in sequence to synergistically produce an enhanced device function. Cu-TCPP-on-Cu-HHTP demonstrated excellent selectivity and the highest response to benzene of the reported recoverable chemiresistive sensing materials that are active at room temperature. This method allows integration of MOFs with cascading properties into advanced functional materials.