Fabrication of oriented silver-functionalized RPM3 films for the selective detection of olefins

Lanthanide Metal-Organic Frameworks Exhibiting Fluoro-Bridged Extended Chains: Synthesis, Crystal Structures, and Magnetic Properties

Two fluoro-bridged lanthanide-containing metal-organic frameworks (MOFs) were synthesized using 2,2'-bipyridine-4,4'-dicarboxylic acid (BPDC), a fluorinated modulator, and a lanthanide nitrate. The syntheses of MOFs containing Gd3+ or Tb3+ and a closely related MOF structure containing Ho3+, Gd3+, or Tb3+ are presented. The presence of the fluorinated metal chains in these MOFs is shown through single crystal X-ray diffraction, energy dispersion X-ray spectroscopy, 19F nuclear magnetic resonance, and X-ray photoelectron spectroscopy. Magnetic measurements reveal weak antiferromagnetic exchange between the Ln3+ ions mediated by fluoride anions along the zigzag ladder chains present in the crystal structures of these MOFs.

Transformation of a copper-based metal-organic polyhedron into a mixed linker MOF for CO2 capture

A new mixed linker metal-organic framework (MOF) has been synthesized from a copper-based metal-organic polyhedron (MOP-1) and 2,2'-bipyridine (2,2'-bipy). The CuMOF-Bipy with a formula of [Cu₂(2,2'-bpy)₂(m-BDC)₂]_n is comprised of a binuclear Cu(II) node coordinated to 2,2'-bipy, and isophthalic acid (m-BDC), which bridges to neighboring nodes. The crystal structure of CuMOF-Bipy consists of a stacked two-dimensional framework with the sql topology. CuMOF-Bipy was characterized by single-crystal X-ray diffraction (SC-XRD), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and CO₂ sorption. CuMOF-Bipy was shown to have one-dimensional sinusoidal channels that allow diffusion of CO₂ but not N₂.

Thin Films of Metal-Organic Framework Interfaces Obtained by Laser Evaporation

Properties such as large surface area, high pore volume, high chemical and thermal stability, and structural flexibility render zeolitic imidazolate frameworks (ZIFs) well-suited materials for gas separation, chemical sensors, and optical and electrical devices. For such applications, film processing is a prerequisite. Herein, matrix-assisted pulsed laser evaporation (MAPLE) was successfully used as a single-step deposition process to fabricate ZIF-8 films. By correlating laser fluency and controlling the specific transfer of lab-synthesized ZIF-8, films with user-controlled physical and chemical properties were obtained. Films' characteristics were evaluated by scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) spectroscopy, X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). The analysis showed that frameworks of ZIF-8 can be deposited successfully and controllably to yield polycrystalline films. The deposited films maintained the integrity of the individual ZIF-8 framework, while undergoing minor crystalline and surface chemistry changes. No significant changes in particle size were observed. Our study demonstrated control over both the MAPLE deposition conditions and the outcome, as well as the suitability of the listed deposition method to create composite architectures that could potentially be used in applications ranging from selective membranes to gas sensors.

Functional metal–organic frameworks as effective sensors of gases and volatile compounds

This review summarizes the recent advances of metal organic framework (MOF) based sensing of gases and volatile compounds.

Fluorescent "Turn-on" Sensing Based on Metal-Organic Frameworks (MOFs)

Metal-organic frameworks (MOFs) have evolved as an exciting class of materials in the domain of porous materials. The unique features of these materials arise from the combined properties of metal ions/clusters and organic struts which form the building blocks of these fascinating architectures. Among other multifarious applications, MOFs have shown tremendous applications as sensory materials for a wide variety of species. The signal transduction induced mechanism in these confined nanospaces generate optical output in response to a particular analyte which can be detected by wide variety of detection techniques. Fluorometric methods of sensing is one of widely studied method over past few decades. MOF-based fluorometric detection is a key research theme developed over the past few years. In this review, we give a brief overview of the recent developments of MOFs as "turn-on" sensors for a wide range of analytes (viz. cations, anions, volatile organic compounds (VOCs), etc.).

Alkaline Hydrolysis Behavior of Metal-Organic Frameworks NH2-MIL-53(Al) Employed for Sensitive Immunoassay via Releasing Fluorescent Molecules

Nanosized metal-organic frameworks (MOFs) NH₂-MIL-53(Al) were synthesized from 2-aminoterephthalic acid (NH₂·H₂BDC) and AlCl₃ by a facile hydrothermal method. The synthesized MOFs displayed good stability and a uniform particle size in a netural medium and were hydrolyzed in alkaline medium to release a large amount of fluorescent ligand NH₂·H₂BDC. Therefore, they can act as large-capability nanovehicles to load signal molecules for investigating various biorecognition events. In this work, based on the alkaline hydrolysis behavior of MOFs NH₂-MIL-53(Al), a sensitive immunoassay method was developed for the detection of aflatoxin B₁ (AFB₁) by employing them as fluorescent signal probes. With a competitive immunoassay mode on microplate, AFB₁ can be detected within a linear range of 0.05-25 ng mL^-1. The method was successfully employed to detect AFB₁ spiked in Job tears, Polygala tenuifolia and with acceptable recovery values of 83.00-114.00%. The detection results for moldy Fructus xanthii displayed an acceptable agreement with those from the high-performance liquid chromatography method, with relative errors of -14.21 to 3.49%. With the merits of high sensitivity, facile manipulation, and ideal reliability, the approach can also be extended to other areas such as aptasensor and receptor-binding assay.

Rapid and Visual Detection and Quantitation of Ethylene Released from Ripening Fruits: The New Use of Grubbs Catalyst

Herein, we report on fluorophore-tagged Grubbs catalysts as turn-on fluorescent probes for the sensitive detection and quantitation of ethylene, a plant hormone that plays a critical role in many phases of plant growth and fruit ripening. The ruthenium-based weak fluorescent probes were prepared handily through the metathesis reaction between the first-generation Grubbs catalyst and selected fluorophores that have high quantum yields and contain terminal vinyl groups. Upon exposure to ethylene, fluorescence enhancement was observed via the release of fluorophore from the probe. Our probe shows an excellent limit of detection for ethylene at 0.9 ppm in air and was successfully applied for monitoring ethylene released during the fruit-ripening process. Our work opens up a new avenue of application of Grubbs catalysts for bioanalytical chemistry of ethylene, which is critically important in plant biology, agriculture, and food industry.

Visible light-enhanced thermal decomposition performance of ammonium perchlorate with a metal–organic framework-derived Ag-embedded porous ZnO nanocomposite

An Ag-embedded porous ZnO nanocomposite (Ag–ZnO NC) fabricated using an MOF exhibits high catalytic activity for the thermal decomposition of AP under the assistance of visible light.

Adsorptive removal and separation of chemicals with metal-organic frameworks: Contribution of π-complexation

Efficient removal and separation of chemicals from the environment has become a vital issue from a biological and environmental point of view. Currently, adsorptive removal/separation is one of the most promising approaches for cleaning purposes. Selective adsorption/removal of various sulfur- and nitrogen-containing compounds, olefins, and π-electron-rich gases via π-complex formation between an adsorbent and adsorbate molecules is very competitive. Porous metal-organic framework (MOF) materials are very promising in the adsorption/separation of various liquids and gases owing to their distinct characteristics. This review summarizes the literature on the adsorptive removal/separation of various π-electron-rich compounds mainly from fuel and gases using MOF materials containing metal ions that are active for π-complexation. Details of the π-complexation, including mechanism, pros/cons, applications, and efficient ways to form the complex, are discussed systematically. For in-depth understanding, molecular orbital calculations regarding charge transfer between the π-complexing species are also explained in a separate section. From this review, readers will gain an understanding of π-complexation for adsorption and separation, especially with MOFs, to develop new insight for future research.

Photoluminescent Metal-Organic Frameworks for Gas Sensing

Luminescence of porous coordination polymers (PCPs) or metal-organic frameworks (MOFs) is sensitive to the type and concentration of chemical species in the surrounding environment, because these materials combine the advantages of the highly regular porous structures and various luminescence mechanisms, as well as diversified host-guest interactions. In the past few years, luminescent MOFs have attracted more and more attention for chemical sensing of gas-phase analytes, including common gases and vapors of solids/liquids. While liquid-phase and gas-phase luminescence sensing by MOFs share similar mechanisms such as host-guest electron and/or energy transfer, exiplex formation, and guest-perturbing of excited-state energy level and radiation pathways, via various types of host-guest interactions, gas-phase sensing has its unique advantages and challenges, such as easy utilization of encapsulated guest luminophores and difficulty for accurate measurement of the intensity change. This review summarizes recent progresses by using luminescent MOFs as reusable sensing materials for detection of gases and vapors of solids/liquids especially for O₂, highlighting various strategies for improving the sensitivity, selectivity, stability, and accuracy, reducing the materials cost, and developing related devices.

Metal-Organic Frameworks as Chemical Sensors

Chemical sensing is of critical importance in today's society in a variety of applications from medicine to environmental pollution control, and from food safety monitoring to the detection of illicit substances and chemical weapons. Metal–organic frameworks (MOFs) have shown tremendous promise as a new class of chemical sensor materials that could be integrated into future devices. MOFs are microporous crystalline materials with infinite, periodic structures composed of organic ‘linkers’ connected to metal ‘nodes’. Their architectures can be fine-tuned by synthetic design for task-specific purposes: as chemical sensors, MOFs can be designed to interact with specific target analytes. Interest in MOFs as chemical sensors has grown significantly over the last decade, particularly given the increasing number of examples of luminescent lanthanide-based MOFs, and MOFs that display mechanochemical responses to external stimuli. In this chapter, we discuss some of the fundamental properties required to prepare MOFs for chemical sensing. We then present an extensive review of recent research in this area, showing how MOFs have been applied in a wide range of applications, including sensing of anions, cations, small organic molecules, biomolecules, as well as changes in physical conditions such as temperature and pH.

Structuring of metal-organic frameworks at the mesoscopic/macroscopic scale

The assembly of metal ions with organic ligands through the formation of coordination bonds gives crystalline framework materials, known as metal-organic frameworks (MOFs), which recently emerged as a new class of porous materials. Besides the structural designability of MOFs at the molecular length scale, the researchers in this field very recently made important advances in creating more complex architectures at the mesoscopic/macroscopic scale, in which MOF nanocrystals are used as building units to construct higher-order superstructures. The structuring of MOFs in such a hierarchical order certainly opens a new opportunity to improve the material performance via design of the physical form rather than altering the chemical component. This review highlights these superstructures and their applications by categorizing them into four dimensionalities, zero-dimensional (0D), one-dimensional (1D), two-dimensional (2D), and three-dimensional (3D) superstructures. Because the key issue for structuring of MOFs is to spatially control the nucleation process in desired locations, this review conceptually categorizes the available synthetic methodologies from the viewpoint of the reaction system.

Gas sensing using porous materials for automotive applications

The use of zeolites and metal–organic frameworks in the sensing of gases emitted from automobile exhausts is reviewed.

Luminescent metal–organic frameworks for chemical sensing and explosive detection

This review provides an update on the photoluminescence properties of LMOFs and their utility in chemical sensing and explosive detection.