Programmable kernel structures of atomically precise metal nanoclusters for tailoring catalytic properties.

The unclear structures and polydispersity of metal nanoparticles (NPs) seriously hamper the identification of the active sites and the construction of structure-reactivity relationships. Fortunately, ligand-protected metal nanoclusters (NCs) with atomically precise structures and monodispersity have become an ideal candidate for understanding the well-defined correlations between structure and catalytic property at an atomic level. The programmable kernel structures of atomically precise metal NCs provide a fantastic chance to modulate their size, shape, atomic arrangement, and electron state by the precise modulating of the number, type, and location of metal atoms. Thus, the special focus of this review highlights the most recent process in tailoring the catalytic activity and selectivity over metal NCs by precisely controlling their kernel structures. This review is expected to shed light on the in-depth understanding of metal NCs' kernel structures and reactivity relationships.

Recent Developments of Microscopic Study for Lanthanide and Manganese Doped Luminescent Materials.

Luminescent materials are indispensable for applications in lighting, displays and photovoltaics, which can transfer, absorb, store and utilize light energy. Their performance is closely related with their size and morphologies, exact atomic arrangement, and local configuration about photofunctional centers. Advanced electron microscopy-based techniques have enabled the possibility to study nanostructures with atomic resolution. Especially, with the advanced micro-electro-mechanical systems, it is able to characterize the luminescent materials at the atomic scale under various environments, providing a deep understanding of the luminescent mechanism. Accordingly, this review summarizes the recent achievements of microscopic study to directly image the microstructure and local environment of activators in lanthanide and manganese (Ln/Mn2+ )-doped luminescent materials, including: 1) bulk materials, the typical systems are nitride/oxynitride phosphors; and 2) nanomaterials, such as nanocrystals (hexagonal-phase NaLnF4 and perovskite) and 2D nanosheets (Ca2 Ta3 O10 and MoS2 ). Finally, the challenges and limitations are highlighted, and some possible solutions to facilitate the developments of advanced luminescent materials are provided.

Cooperative Catalysis between Dual Copper Centers in a Metal-Organic Framework for Efficient Detoxification of Chemical Warfare Agent Simulants.

Chemical warfare agents (CWAs) are among the most lethal chemicals known to humans. Thus, developing multifunctional catalysts for highly efficient detoxification of various CWAs is of great importance. In this work, we developed a robust copper tetrazolate metal-organic framework (MOF) catalyst containing a dicopper unit similar to the coordination geometry of the active sites of natural phosphatase and tyrosinase enzymes. This catalyst aided in phosphate ester bond hydrolysis and hydrogen peroxide decomposition, ultimately achieving high detoxification efficiency against both a nerve agent simulant (diethoxy-phosphoryl cyanide (DECP)) with a half-life of 3.5 min and a sulfur mustard simulant (2-chloroethyl ethyl sulfide (CEES)) with a half-life of 4.5 min, making it competitive with other reported materials. The dicopper sites in ZZU-282 provide versatile binding modes with the substrates, thereby promoting the activation of substrates and enhancing the catalytic efficiency. A combination of postmodified metal exchange control experiments, density functional theory calculations, and catalytic evaluations confirmed that dual Cu sites are the active centers promoting the catalytic reaction. This study offers a new design perspective to achieve advanced catalysts for CWA detoxification.

Electronically and Geometrically Modified Single-Atom Fe Sites by Adjacent Fe Nanoparticles for Enhanced Oxygen Reduction.

Fe-N-C materials exhibit excellent activity and stability for oxygen reduction reaction (ORR), as one of the most promising candidates to replace commercial Pt/C catalysts. However, it is challenging to unravel features of the superior ORR activity originating from Fe-N-C materials. In this work, the electronic and geometric structures of the isolated Fe-N-C sites and their correlations with the ORR performance are investigated by varying the secondary thermal activation temperature of a rationally designed NC-supported Fe single-atom catalyst (SAC). The systematic analyses demonstrate the significant role of coordinated atoms of SA and metallic Fe nanoparticles (NPs) in altering the electronic structure of isolated Fe-N-C sites. Meanwhile, strong interaction between isolated Fe-N-C sites and adjacent Fe NPs can change the geometric structure of isolated Fe-N-C sites. Theoretical calculations reveal that optimal regulation of the electronic and geometric structure of isolated Fe-N-C sites by the co-existence of Fe NPs narrows the energy barriers of the rate-limiting steps of ORR, resulting in outstanding ORR performance. This work not only provides the fundamental understanding of the underlying structure-activity relationship, but also sheds light on designing efficient Fe-N-C catalysts.

Construction of Core-Shell MOF@COF Hybrids with Controllable Morphology Adjustment of COF Shell as a Novel Platform for Photocatalytic Cascade Reactions.

Recently, novel core-shell MOF@COF hybrids display excellent performance in various fields because of their inherited advantages from their parent MOFs and/or COFs. However, it is still a grand challenge to adjust the morphology of MOFs and/or COFs for consequent performance improvement. Herein, a Ti-MOF@TpTt hybrid coated with ultra-thin COF nanobelt, which is different from the fibrillar-like parent COF, is successfully synthesized through a sequential growth strategy. The as-obtained Pd decorated Ti-MOF@TpTt catalyst exhibits much higher photocatalytic performance than those of Ti-MOF, TpTt-COF, and Ti-MOF@TpTt hybrids with fibrillar-like COF shell for the photocatalytic cascade reactions of ammonia borane (AB) hydrolysis and nitroarenes hydrogenation. These can be attributed to its high BET surface area, core-shell structure, and type II heterojunction, which offers more accessible active sites and improves the separation efficiency of photo-generated carriers. Finally, the possible mechanisms of the cascade reaction are also proposed to well explain the improved performance of this photocatalytic system. This work presents a constructive route for designing core-shell MOF@COF hybrids with controllable morphology adjustment of COF shell, leading to the improved photocatalytic ability to broaden the applications of MOF/COF hybrid materials.

Ozone Decomposition by a Manganese-Organic Framework over the Entire Humidity Range.

Ground-level ozone (O3) is one of the main airborne pollutants detrimental to human health and ecosystems. However, the designed synthesis of high-performance O3 elimination catalysts suitable for broadly variable air compositions, especially a variable water vapor content, remains daunting. Herein, we report a new manganese-based metal organic framework, [Mn3(µ3-OH)2(TTPE)(H2O)4]·2H2O (H4TTPE = 1,1,2,2-tetrakis(4-(2H-tetrazol-5-yl)phenyl) ethane), denoted as ZZU-281. ZZU-281 catalyzes O3 decomposition with a nearly constant 100% working efficiency over the entire humidity range from dry (≤5% relative humidity (RH)) to high humidity (90% RH). We found that the maintainable coordinated water molecules and OH groups are activated by Mn2+, becoming active sites for O3 transfer to O2 with a low activation energy. The unique open channels, water retainability, and water stability of ZZU-281 further support the high catalytic performance. This work opens a new avenue for designing efficient catalysts for O3 elimination in practice.

Pyrolysis Kinetic Study and Reaction Mechanism of Epoxy Glass Fiber Reinforced Plastic by Thermogravimetric Analyzer (TG) and TG-FTIR (Fourier-Transform Infrared) Techniques.

TG-FTIR combined technology was used to study the degradation process and gas phase products of epoxy glass fiber reinforced plastic (glass fiber reinforced plastic) under the atmospheres of high purity nitrogen. The pyrolysis characteristics of epoxy glass fiber reinforced plastic were measured under different heating rates (5, 10, 15, 20 °C min-1) from 25 to 1000 °C. The thermogravimetric analyzer (TG) and differential thermogravimetric analyzer (DTG) curves show that the initial temperature, terminal temperature, and temperature of maximum weight loss rate in the pyrolysis reaction phase all move towards high temperature, as the heating rate increases. Epoxy glass fiber reinforced plastic has two stages of thermal weightlessness. The temperature range of the first stage of weight loss is 290-460 °C. The second stage is 460-1000 °C. The above two weight loss stages are caused by pyrolysis of the epoxy resin matrix, and the glass fiber will not decompose. The dynamic parameters of glass fiber reinforced plastic were obtained through the Kissinger-Akahira-Sunose (KAS), Flynn-Wall-Ozawa (FWO) and advanced Vyazovkin methods in model-free and the Coats-Redfern (CR) method in model fitting. FTIR spectrum result shows that the main components of the product gas are CO2, H2O, carbonyl components, and aromatic components during its pyrolysis.

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

Developing efficient sensor materials with superior performance for selective, fast and sensitive detection of gases and volatile organic compounds (VOCs) is essential for human health and environmental protection, through monitoring indoor and outdoor air pollutions, managing industrial processes, controlling food quality and assisting early diagnosis of diseases. Metal-organic frameworks (MOFs) are a unique type of crystalline and porous solid material constructed from metal nodes (metal ions or clusters) and functional organic ligands. They have been investigated extensively for possible use as high performance sensors for the detection of many different gases and VOCs in recent years, due to their large surface area, tunable pore size, functionalizable sites and intriguing properties, such as electrical conductivity, magnetism, ferroelectricity, luminescence and chromism. The high porosity of MOFs allows them to interact strongly with various analytes, including gases and VOCs, thus resulting in easily measurable responses to different physicochemical parameters. Although much of the recent work on MOF-based luminescent sensors have been summarized in several excellent reviews (up to 2018), a comprehensive overview of these materials for sensing gases and VOCs based on chemiresistive, magnetic, ferroelectric, and colorimertic mechanisms is missing. In this review, we highlight the most recent progress in developing MOF sensing and switching materials with an emphasis on sensing mechanisms based on electricity, magnetism, ferroelectricity and chromism. We provide a comprehensive analysis on the MOF-analyte interactions in these processes, which play a key role in the sensing performance of the MOF-based sensors and switches. We discuss in detail possible applications of MOF-based sensing and switching materials in detecting oxygen, water vapor, toxic industrial gases (such as hydrogen sulfide, ammonia, sulfur dioxide, nitrous oxide, carbon oxides and carbon disulfide) and VOCs (such as aromatic and aliphatic hydrocarbons, ketones, alcohols, aldehydes, chlorinated hydrocarbons and N,N'-dimethylformamide). Overall, this review serves as a timely source of information and provides insight for the future development of advanced MOF materials as next-generation gas and VOC sensors.

Metal Organic Frameworks Based Materials for Heterogeneous Photocatalysis.

The increase in environmental pollution due to the excessive use of fossil fuels has prompted the development of alternative and sustainable energy sources. As an abundant and sustainable energy, solar energy represents the most attractive and promising clean energy source for replacing fossil fuels. Metal organic frameworks (MOFs) are easily constructed and can be tailored towards favorable photocatalytic properties in pollution degradation, organic transformations, CO2 reduction and water splitting. In this review, we first summarize the different roles of MOF materials in the photoredox chemical systems. Then, the typical applications of MOF materials in heterogeneous photocatalysis are discussed in detail. Finally, the challenges and opportunities in this promising field are evaluated.

Luminescent Lanthanide MOFs: A Unique Platform for Chemical Sensing.

In recent years, lanthanide metal-organic frameworks (LnMOFs) have developed to be an interesting subclass of MOFs. The combination of the characteristic luminescent properties of Ln ions with the intriguing topological structures of MOFs opens up promising possibilities for the design of LnMOF-based chemical sensors. In this review, we present the most recent developments of LnMOFs as chemical sensors by briefly introducing the general luminescence features of LnMOFs, followed by a comprehensive investigation of the applications of LnMOF sensors for cations, anions, small molecules, nitroaromatic explosives, gases, vapors, pH, and temperature, as well as biomolecules.

A Metal-Organic Framework/DNA Hybrid System as a Novel Fluorescent Biosensor for Mercury(II) Ion Detection.

Mercury(II) ions have emerged as a widespread environmental hazard in recent decades. Despite different kinds of detection methods reported to sense Hg(2+) , it still remains a challenging task to develop new sensing molecules to replenish the fluorescence-based apparatus for Hg(2+) detection. This communication demonstrates a novel fluorescent sensor using UiO-66-NH2 and a T-rich FAM-labeled ssDNA as a hybrid system to detect Hg(2+) sensitively and selectively. To the best of our knowledge, it has rarely been reported that a MOF is utilized as the biosensing platform for Hg(2+) assay.

Encapsulation of Ln(III) Ions/Dyes within a Microporous Anionic MOF by Post-synthetic Ionic Exchange Serving as a Ln(III) Ion Probe and Two-Color Luminescent Sensors.

A new anionic framework {[Me2NH2]0.125[In0.125(H2L)0.25]⋅xDMF}n (1) with one-dimensional (1D) channels along the c axis of about 13.06×13.06 Å(2), was solvothermally synthesized and well characterized. Post-synthetic cation exchange of 1 with Eu(3+), Tb(3+), Dy(3+), Sm(3+) afforded lanthanide(III)-loaded materials, Ln(3+)@1, with different luminescent behavior, indicating that compound 1 could be used as a potential luminescent probe toward different lanthanide(III) ions. Additionally, compound 1 exhibits selective adsorption ability toward cationic dyes. Moreover, the RhB@1 realized the probing of different organic solvent molecules by tuning the energy transfer efficiency between two different emissions, especially for sensing DMF. This work highlights the practical application of luminescent guest@MOFs as sensors, and it paves the way toward other one/multi-color luminescent host-guest systems by rational selection of MOF hosts and guest chromophores with suitable emissive colors and energy levels.

A tetranuclear copper cluster-based MOF with sulfonate-carboxylate ligands exhibiting high proton conduction properties.

A tetranuclear copper cluster-based MOF with sulfonate-carboxylate ligands has been synthesized. It possesses one-dimensional irregular channels lined with sulfonate, carboxylate, and DMF molecules, which show a high proton conductivity of 7.4 × 10(-4) S cm(-1) at 95 °C and 95% relative humidity.

A Temperature-Responsive Smart Europium Metal-Organic Framework Switch for Reversible Capture and Release of Intrinsic Eu3+ Ions.

Stimuli-responsive structural transformations are emerging as a scaffold to develop a charming class of smart materials. A EuL metal-organic framework (MOF) undergoes a reversible temperature-stimulated single-crystal to single-crystal transformation, showing a specific behavior of fast capture/release of free Eu3+ in the channels at low and room temperatures. At room temperature, compound 1a is obtained with one free carboxylate group severing as further hook, featuring one-dimensional square channels filled with intrinsic free europium ions. Trigged by lowering the ambient temperature, 1b is gained. In 1b, the intrinsic free europium ions can be fast captured by the carboxylate-hooks anchored in the framework, resulting in the structural change and its channel distortion. To the best of our knowledge, this is the first report of such a rapid and reversible switch stemming from dynamic control between noncovalent and covalent Eu-ligand interactions. Utilizing EuL MOF to detect highly explosive 2,4,6-trinitrophenol at room temperature and low temperature provides a glimpse into the potential of this material in fluorescence sensors.

Assembly of three coordination polymers based on a sulfonic-carboxylic ligand showing high proton conductivity.

Three new coordination polymers (CPs)/metal-organic frameworks (MOFs) with different structures have been synthesized using 4,8-disulfonyl-2,6-naphthalenedicarboxylic acid (H4L) and metal ions, Cu(2+), Ca(2+) and Cd(2+). The Cu compound features a one-dimensional chain structure, further extending into a 2D layer network through H-bond interactions. Both the Ca and Cd compounds show 3D frameworks with (4,4)-connected PtS-type topology and (3,6)-connected bct-type topology, respectively. These CPs/MOFs all exhibit proton conduction behavior, especially for the Cu compound with a proton conductivity of 3.46 × 10(-3) S cm(-1) at 368 K and 95% relative humidity (RH). Additionally, the activation energy (Ea) has also been investigated to deeply understand the proton-conduction mechanism.

A stable, pillar-layer metal-organic framework containing uncoordinated carboxyl groups for separation of transition metal ions.

A 3D pillar-layer framework (1) with uncoordinated carboxyl groups exhibits exceptional stability. It can effectively and selectively adsorb Cu(2+) ions and has been applied as a chromatographic column for separating Cu(2+)/Co(2+) ions.

A new type of double-chain based 3D lanthanide(III) metal-organic framework demonstrating proton conduction and tunable emission.

A new type of 3D lanthanide(III) metal-organic framework directly constructed by double-chain motifs was synthesized. It shows a proton conductivity of 1.6 × 10(-5) S cm(-1) at 75 °C at 97% RH, and tunable emission including white light.

A multifunctional proton-conducting and sensing pillar-layer framework based on [24-MC-6] heterometallic crown clusters.

3D pillar-layer framework with [24-MC-6] heterometallic crown clusters exhibits proton conductivity and selective sensing of acetone as well as Cu(2+) ions.

Employing tripodal carboxylate ligand to construct Co(II) coordination networks modulated by N-donor ligands: syntheses, structures and magnetic properties.

Hydrothermal reaction of a tripodal bridging ligand, 5-(4-carboxyphenoxy)isophthalic acid (H3cpia) with cobalt salts modulated by N-donor neutral ligands leads to the formation of six novel coordination networks formulated as {[Co(1.5)(cpia)(o-bix)](H2O)(1.5)}n (1), {[Co2(cpia)(µ-OH)(m-bix)]H2O}n (2), {[Co(1.5)(cpia)(m-bix)]}n (3), {[Co(1.5)(cpia)(p-bix)(0.5)(H2O)]H2O}n (4), {[Co(2.5)(cpia)(Hcpia)(4,4'-bpy)(2.5)](H2O)3}n (5), and {[Co3(cpia)2(bpp)2]H2O}n (6). Compound 1 exhibits a two-dimensional, (3,8)-connected layered architecture composed of trinuclear cobalt clusters. Compound 2 possesses a three-dimensional dense framework with (3,8)-connected tfz-d topology built from butterfly-shaped tetranuclear Co4(µ3-OH)2(6+) clusters. Similar to compound 1, trinuclear Co clusters act as secondary building units to construct the final 2D layered structure modulated by m-bix and bpp ligands in compounds 3 and 6. In compound 4, trinuclear Co clusters connected by cpia(3-) anions give rise to two-dimensional layers, which are further pillared by p-bix ligands to the three-dimensional framework. Compound 5 features a 2D, (3,4,6)-connected molecular network assembled from alternate binuclear and mononuclear Co building blocks. The magnetic investigation indicates that strong antiferromagnetic interactions between cobalt ions are dominant in compounds 2 and 6.

Two high-connected metal-organic frameworks based on d10-metal clusters: syntheses, structural topologies and luminescent properties.

The d(10)-metal-oxo clusters connected by the asymmetric tricarboxylate and linear neutral ligands give rise to two novel high-connected MOFs. They feature the highest (3,16)- and (3,8)-connected three-dimensional frameworks based on cube-like octanuclear [Zn8(µ2-OH)4(CO2)12] clusters and butterfly-like tetranuclear [Cd4(µ3-OH)2(CO2)6] clusters as the secondary building units, respectively.