Metal–Organic Frameworks in Solid–Gas Phase Catalysis

Self-powered photoelectrochemical aptasensor based on MIL-68(In) derived In2O3 hollow nanotubes and Ag doped ZnIn2S4 quantum dots for oxytetracycline detection

A self-powered photoelectrochemical (PEC) aptasensor was constructed based on MIL-68(In) derived indium oxide hollow nanotubes (In₂O₃ HNs) and Ag-doped ZnIn₂S₄ quantum dots (QDs) as sensing matrix for the ultrasensitive detection of oxytetracycline (OTC). The hollow tube structure of the designed photoelectric active platform provided abundant active sites and a larger specific surface area for the immobilization of target recognition unit. The coupling of Ag:ZnIn₂S₄ QDs and In₂O₃ HNs can accelerate the transmit and separation of photoinduced charge, and thus greatly increasing the intensity of photocurrent signal. Then, the well-constructed OTC-aptamer was anchored on the modified photoelectrode as an accurate capturing element, achieving the specific detection of analyte. Under optimal conditions, the photocurrent intensity of the PEC aptasensor decreases linearly, with a linear response range of 10^-4 -10 nmol/L, and a limit of detection (LOD) of 3.3 × 10^-5 nmol/L (S/N = 3). The developed self-powered aptasensor with excellent reproducibility, stability, and selectivity, provides a potential way to detect antibiotic residues in environmental media.

A Facile and General Approach to Enhance Water Resistance of Metal-Organic Frameworks by the Post-Modification with Aminopropyltriethoxylsilane

The water sensitivity of metal-organic frameworks (MOFs) as a common and crucial issue has greatly hindered their practical applications. Here, we present a facile and general approach to improve the water resistance of a typical MOF, i.e., CuBTC [Cu3(BTC)2(H2O)3]n (BTC = benzene-1,3,5-tricarboxylate) using a post-modification reaction with aminopropyltriethoxylsilane (APTES) at room temperature. The afforded material is denoted as CuBTC@APTES. Various spectroscopic methods reveal that the organosilicon linkers have been successfully grafted onto CuBTC by electrostatic attraction between acid and base groups and without affecting the original coordination mode and basic structure. Compared with CuBTC, the water stability of CuBTC@APTES was significantly improved. The pristine CuBTC almost lost all its crystallinity, morphology and pore structure after 3-day treatment in water, while CuBTC@APTES is able to retain its main crystal structure and basic porosity after the same treatment. This finding can be explained by the successful introduction of the organosilicon molecular overlayer on the periphery of CuBTC to slow down the destruction of weak metal coordination bonds by water molecules, thus improving the water stability of CuBTC. The solution of water sensitivity provides more opportunities for the practical applications of CuBTC, such as aqueous phase catalysis and gas separation in humid environments. This simple approach can certainly be expanded to improve the water resistance of other carboxylate-containing ligand-based MOFs.

Exploring mechanistic routes for light alkane oxidation with an iron-triazolate metal-organic framework

In this work, we computationally explore the formation and subsequent reactivity of various iron-oxo species in the iron-triazolate framework Fe₂(μ-OH)₂(bbta) (H₂bbta = 1H,5H-benzo(1,2-d:4,5-d')bistriazole) for the catalytic activation of strong C-H bonds. With the direct conversion of methane to methanol as the probe reaction of interest, we use density functional theory (DFT) calculations to evaluate multiple mechanistic pathways in the presence of either N₂O or H₂O₂ oxidants. These calculations reveal that a wide range of transition metal-oxo sites - both terminal and bridging - are plausible in this family of metal-organic frameworks, making it a unique platform for comparing the electronic structure and reactivity of different proposed active site motifs. Based on the DFT calculations, we predict that Fe₂(μ-OH)₂(bbta) would exhibit a relatively low barrier for N₂O activation and energetically favorable formation of an [Fe(O)]²⁺ species that is capable of oxidizing C-H bonds. In contrast, the use of H₂O₂ as the oxidant is predicted to yield an assortment of bridging iron-oxo sites that are less reactive. We also find that abstracting oxo ligands can exhibit a complex mixture of both positive and negative spin density, which may have broader implications for relating the degree of radical character to catalytic activity. In general, we consider the coordinatively unsaturated iron sites to be promising for oxidation catalysis, and we provide several recommendations on how to further tune the catalytic properties of this family of metal-triazolate frameworks.

Polyoxometalate-Based Metal-Organic Frameworks as the Solid Support to Immobilize MP-11 Enzyme for Enhancing Thermal and Recyclable Stability

The immobilization of enzymes has received much attention. Metal-organic framework (MOF) as the adsorbent for enzyme encapsulation provides an effective strategy. However, the encapsulation efficacy is not dependent solely on the specific surface area. Though leading into appropriate substrate with negative charge would enhance the encapsulation efficacy. Polyoxometalates (POMs) as the electron sponge would donate electrons without any structural change. In this study, Keggin-type phosphotungstic acid (PW₁₂) was encapsulated in Zirconium metal-organic framework (PW₁₂@UiO-67) as a heterogeneous adsorbent for the encapsulation of enzyme. Our following data proved that this composite cluster could enhance the adsorption of enzyme and the stability of MP-11 was then significantly improved after immobilization.

Patterned microfluidic devices for rapid screening of metal-organic frameworks yield insights into polymorphism and non-monotonic growth

Metal-organic frameworks (MOFs) are porous crystalline structures that are composed of coordinated metal ligands and organic linkers. Due to their high porosity, ultra-high surface-to-volume ratio, and chemical and structural flexibility, MOFs have numerous applications. MOFs are primarily synthesized in batch reactors under harsh conditions and long synthesis times. The continuous depletion of metal ligands and linkers in batch processes affects the kinetics of the oligomerization reaction and, hence, their nucleation and growth rates. Therefore, the existing screening systems that rely on batch processes, such as microtiter plates and droplet-based microfluidics, do not provide reliable nucleation and growth rate data. Significant challenges still exist for developing a relatively inexpensive, safe, and readily scalable screening device and ensuring consistency of results before scaling up. Here, we have designed patterned-surface microfluidic devices for continuous-flow synthesis of MOFs that allow effective and rapid screening of synthesis conditions. The patterned surface reduces the induction time of MOF synthesis for rapid screening while providing support to capture MOF crystals for growth measurements. The efficacy of the continuous-flow patterned microfluidic device to screen polymorphs, morphology, and growth rates is demonstrated for the HKUST-1 MOF. The effects of solvent composition and pH modulators on the morphology, polymorphs, and size distribution of HKUST-1 are evaluated using the patterned microfluidic device. Additionally, a time-resolved FT-IR analysis coupled with the patterned microfluidic device provides quantitative insights into the non-monotonic growth of MOF crystals with respect to the progression of the bulk oligomerization reaction. The patterned microfluidic device can be used to screen crystals with a longer induction time, such as proteins, covalent-organic frameworks, and MOFs.

MOF-enabled confinement and related effects for chemical catalyst presentation and utilization

A defining characteristic of nearly all catalytically functional MOFs is uniform, molecular-scale porosity. MOF pores, linkers and nodes that define them, help regulate reactant and product transport, catalyst siting, catalyst accessibility, catalyst stability, catalyst activity, co-catalyst proximity, composition of the chemical environment at and beyond the catalytic active site, chemical intermediate and transition-state conformations, thermodynamic affinity of molecular guests for MOF interior sites, framework charge and density of charge-compensating ions, pore hydrophobicity/hydrophilicity, pore and channel rigidity vs. flexibility, and other features and properties. Collectively and individually, these properties help define overall catalyst functional behaviour. This review focuses on how porous, catalyst-containing MOFs capitalize on molecular-scale confinement, containment, isolation, environment modulation, energy delivery, and mobility to accomplish desired chemical transformations with potentially superior selectivity or other efficacy, especially in comparison to catalysts in homogeneous solution environments.

Confined in-situ polymerization in nanoscale porphyrinic metal-organic framework for fluorescence imaging-guided synergistic phototherapy

Engineering a versatile nanoplatform integrating imaging and therapeutic functions for efficient cancer treatment remains grand challenge. Herein, a type of metal-organic framework (MOF)-based hybrid material for fluorescence imaging-guided synergistic phototherapy...

Unravelling the catalytic potential of a magnetic CoFe2O4/Cu–ABDC MOF composite in the sustainable synthesis of 2H-indazole motifs

A magnetic CoFe2O4/Cu–ABDC hybrid composite was fabricated for the synthesis of biologically active and pharmacologically significant 2H-indazole scaffolds.

Unravelling free volume in branched-cation ionic liquids based on silicon

The branching of ionic liquid cation sidechains utilizing silicon as the backbone was explored and it was found that this structural feature leads to fluids with remarkably low density and viscosity. The relatively low liquid densities suggest a large free volume in these liquids. Argon solubility was measured using a precise saturation method to probe the relative free volumes. Argon molar solubilities were slightly higher in ionic liquids with alkylsilane and siloxane groups within the cation, compared to carbon-based branched groups. The anion size, however, showed by far the dominant effect on argon solubility. Thermodynamic solvation parameters were derived from the solubility data and the argon solvation environment was modelled utilizing the polarizable CL&Pol force field. Semiquantitative analysis was in agreement with trends established from the experimental data. The results of this investigation demonstrate design principles for targeted ionic liquids when optimisation for the free volume is required, and demonstrate the utility of argon as a simple, noninteracting probe. As more ionic liquids find their way into industrial processes of scale, these findings are important for their utilisation in the capture of any gaseous solute, gas separation, or in processes involving the transformation of gases or small molecules.

The branching of ionic liquid cation sidechains utilizing silicon as the backbone was explored and it was found that this structural feature leads to fluids with remarkably low density and viscosity.

Catalytic properties of the ferryl ion in the solid state: a computational review

This review summarises the last findings in the emerging field of heterogeneous catalytic oxidation of light alkanes by ferryl species supported on solid-state systems such as the conversion of methane into methanol by FeO-MOF74.

Ethylene polymerization with a crystallographically well-defined metal–organic framework supported catalyst

Crystallographic characterization of a heterogeneous ethylene polymerization catalyst elucidates a chromium–carbon bond after alkyl aluminum activation and provides mechanistic insights.

Stepwise synthesis of Zr-based metal–organic frameworks: incorporating a trinuclear zirconocene-based metallo-pyridine ligand

Based on a presynthesized Zr3 precursor, two isostructural 2D heterometallic ZrMOFs have been synthesized by a step synthesis strategy.

Three novel metal-organic frameworks with different coordination modes for trace detection of anthrax biomarkers

Dipicolinic acid (DPA) is an anthrax biomarker. Its serious consequences make its detection a great need. In this paper, three novel metal-organic frameworks (MOFs) with different coordination modes were synthesized by a simple solvothermal method, which can be used as highly efficient fluorescence sensors for the highly selective and sensitive trace detection of DPA. MOFs 1-3 showed rapid responses to DPA (<30 s), and the limits of detection (LODs) were calculated to be 1.01 × 10^-6 M^-1 (MOF 1), 1.17 × 10^-6 M^-1 (MOF 2) and 2.07 × 10^-6 M^-1 (MOF 3). DPA detection based on MOFs 1-3 in fetal bovine serum is highly reliable based on the high recovery rates (90% to 115%). Hence, the three MOF-based sensors can be used in the real-time detection of DPA.

Functionalized Carbon Materials in Syngas Conversion

Functionalized carbon materials are widely used in heterogeneous catalysis due to their unique properties such as adjustable surface properties, excellent thermal conductivity, high surface areas, tunable porosity, and moderate interactions with guest metals. The transformation of syngas into hydrocarbons (known as the Fischer-Tropsch synthesis) or oxygenates is an exothermic reaction and is typically catalyzed by transition metals dispersed on functionalized supports. Various carbon materials have been employed in syngas conversions not only for improving the performance or decreasing the dosage of expensive active metals but also for building model catalysts for fundamental research. This article provides a critical review on recent advances in the utilization of carbon materials, in particular the recently developed functionalized nanocarbon materials, for syngas conversions to either hydrocarbons or oxygenates. The unique features of carbon materials in dispersing metal nanoparticles, heteroatom doping, surface modification, and building special nanoarchitectures are highlighted. The key factors that control the reaction course and the reaction mechanism are discussed to gain insights for the rational design of efficient carbon-supported catalysts for syngas conversions. The challenges and future opportunities in developing functionalized carbon materials for syngas conversions are briefly analyzed.

The Encounter of Biomolecules in Metal-Organic Framework Micro/Nano Reactors

In nature, biochemical reactions often take place in confined spaces, as typically exemplified by cells. As numerous cellular reactors can be integrated to maintain the living system, researchers have made constant efforts to construct cell-like structures for achieving similar transformations in vitro. Micro/nano reactors engineered by polymers and colloids are becoming popular and being applied in many fields, especially there has been an increasing trend toward constructing metal-organic framework (MOF) micro/nano reactors with the thriving of MOF nanotechnologies. Because of the uniform pores of MOFs, the transmission of substances can be regulated more accurately. Along with properties of large specific surface area, functional diversity and precise control of the particle size, MOFs are also ideal platforms for building distinct microenvironments for biological substances. Compared with traditional polymersomes and colloidosomes, the unique characteristics of MOFs render them potent micro/nano reactor shell materials, mimicking cells for applications in enzymatic catalysis, sensing, nanotherapy, vaccine, biodegradation, etc. This review highlights recent signs of progress on the design of MOF micro/nano reactors and their applications in biology, discusses the existing problems, and prospects their promising properties for smarter multifunctional applications.

Effect of Micropores of a Porous Coordination Polymer on the Product Selectivity in RuII Complex-catalyzed CO2 Reduction

To develop an efficient CO2 reduction catalyst, hybridizing a molecular catalyst and a porous coordination polymer (PCP) is a promising strategy because it can combine both advantages of the precise reactivity control of the former and the CO2 adsorption property of the latter. Although several PCP hybrid catalysts have been reported to date, the CO2 sorption behavior and the CO2 reduction reactivity have been investigated separately, and the CO2 enrichment during the catalysis is still unclear. We report CO2 photoreduction under different temperatures and pressures using a PCP-RuII complex hybrid catalyst. The product selectivity (CO or HCOOH) varied depending on the reaction conditions. The altered selectivity could be interpreted in terms of the CO2 capture in the micropores of a PCP.

Recent advances in molecular logic gate chemosensors based on luminescent metal organic frameworks

Luminescent metal-organic frameworks (LMOFs) as chemosensors, can sense various analytes, such as heavy metal ions, antibiotics, pesticides, and small biological molecules. Based on the fluorescence characteristics of LMOFs, a variety of logic gates have been developed. In this review, we mainly discuss some common logic systems based on LMOFs, and then summarize the strategies of constructing logic gates from two perspectives. One is based on superior characteristics of MOFs, which can be synthesized from Ln³⁺ based MOFs (Ln-MOFs) or form hybrids by encapsulating different materials, including metal ions, dyes, and quantum dots (QDs). The other is to control the presence of inputs by reactions between different reactants and then further control switches of logic gates. Additionally, the common sensing mechanisms of LMOFs in logic gates are discussed. In the end, we have envisioned MOFs that possess a promising future in logic computing areas.

Multifunctional luminescence sensing and white light adjustment of lanthanide metal-organic frameworks constructed from the flexible cyclotriphosphazene-derived hexacarboxylic acid ligand

Considering that cyclotriphosphazene polycarboxylic acid is a kind of organic ligand with fantastic structures and performances and the unique luminescence characteristics of rare earth ions, a series of porous lanthanide metal-organic frameworks (Ln-MOFs) (CH₃)₂NH₂[Ln₃(HCPCP)_1.5(CH₃COO)]·6DMA (Ln = Ce (1), Sm (2), Eu (3), Tb (4), HCPCP = hexa(4-carboxyphenoxy)cyclotriphosphazene, and DMA = N,N-dimethylacetamide) were synthesized with novel topological network structures. Compound 4 exhibited a sensitive recognition of -NO₂, and had a fluorescence quenching phenomenon for seven kinds of nitro aromatic compounds (NACs). In particular, it showed the best fluorescence response to 2,4,6-trinitrophenol (TNP) and 2,4-dinitrophenol (DNP), and the K_SV values were 2.86 × 10⁵ M^-1 and 8.21 × 10⁴ M^-1, and the limit of detection (LOD) values were 0.20 μM and 0.71 μM, respectively. At the same time, we successfully doped different concentrations of Eu³⁺ into compound 4 to obtain a series of doped Ln-MOF materials x%Eu³⁺@4 (x = 0.5, 2.5, 5, 7.5, 10, 15 and 20). With the increase of Eu³⁺ doping ratios, the characteristic peaks of Tb³⁺ and Eu³⁺ changed regularly, and the energy transfer from Tb³⁺ to Eu³⁺ ions occurred. By changing the excitation wavelength of the samples with different Eu³⁺ doping concentrations, a higher quality white light emitting material 7.5%Eu³⁺@4 (λ_ex = 340 nm) was finally obtained, with a CIE coordinate of (0.3268, 0.3212).

A novel 3D terbium metal-organic framework as a heterogeneous Lewis acid catalyst for the cyanosilylation of aldehyde

A novel 3D lanthanide(iii) metal-organic framework (MOF) (namely Tb-MOF), was synthesized by self-assembly from Tb(iii) ion nitrate and the rigid organic ligand H₂sbdc (H₂sbdc = 5,5-dioxo-5H-dibenzo[b,d]thiophene-3,7-dicarboxylic acid), and could work as an efficient heterogeneous catalyst for the cyanosilylation of aromatic aldehydes at room temperature. The obtained Tb-MOF has been characterized and analysed in detail by single crystal X-ray diffraction, powder X-ray diffraction, thermogravimetric analysis and so on. The pores of Tb-MOF provided a microenvironment that was beneficial for the substrates to be close to the Lewis acid catalytic sites. The IR spectrogram and the fluorescence titration proved that the substrates could be activated inside the channel of Tb-MOF. The heterogeneous Tb-MOF catalyst with fine catalytic efficiency exhibited a high TON (TON = 460), and could be recycled at least three times without significantly reducing its activity.

Sensitive and selective detection of chromium (VI) based on two-dimensional luminescence metal organic framework nanosheets via the mechanism integrating chemical oxidation-reduction and inner filter effect

Two-dimensional luminescence metal organic framework nanosheets (LMOF) named NH₂-CuMOFs were synthesized using Cu (II) nodes coordinated with negatively charged 2-aminoterephthalic acid (NH₂-BDC) via a bottom-up strategy, which were first used as the fluorescent probes for the detection of chromium Cr (VI). The nanosheets possess stable fluorescence with the maximum emission wavelength of 436 nm at excitation of 338 nm that can be effectively quenched by hexavalent chromium Cr (VI). The NH₂-CuMOFs nanosheets show superior advantage over the linker of NH₂-BDC for the excellent selectivity to Cr (Ⅵ) without the interferences of other metal ions. The mechanism investigation suggested that the sensitive detection of Cr (VI) was attributed to the chemical oxidation-reduction (redox) reaction and internal filtration effect (IFE) between Cr (VI) and NH₂-CuMOFs nanosheets. Based on this mechanism, the quantitation of Cr (VI) was realized in the linear range of 0.1-20 μM with a detection limit of 18 nM. Moreover, the detection of Cr (VI) in real samples was also conducted with good recovery. This work provides an optical sensing nanoplatform for heavy metal ions based on two-dimensional LMOFs via a novel mechanism integrating chemical redox reaction and IFE, which may promise broad application prospect for two-dimensional luminescence nanosheets.

A novel approach for the preparation of core-shell MOF/polymer composites as mixed-mode stationary phase

The nickel organic framework capped with polyvinylpyrrolidone was prepared and synergistically immobilized onto porous silica surface as the mixed-mode stationary phase for high-performance liquid chromatography. Here, polyvinylpyrrolidone firstly was chosen as functional molecules to change morphology and size of the metal organic framework. The silica microspheres were then modified by them via a simple bonding method rather than in-situ growth method with the aid of electrostatic interaction commonly used before. The stationary phase showed flexible selectivity for separation of both hydrophilic and hydrophobic compounds, especially for hydrophilic compounds such as carbohydrates, alkaloids and sulfonamides etc. The chromatographic behaviors were evaluated by investigating various factors, and a typical mixed-mode retention feature of the column was observed. The composites could be prepared repetitively, and relative standard deviations of retention time of objective compounds among different batches were less than 1.75%. It also showed excellent chromatographic reproducibility, stability and potentiality for application in real samples. In short, the composites can be used for a feasible option for analysis of multiple compounds as the mixed-mode stationary phase and it provides a general approach for preparing MOFs-based composites by changing morphology and size of MOFs.

Host-Guest Interactions Between Metal-Organic Frameworks and Air-Sensitive Complexes at High Temperature

The host-guest chemistry of metal–organic frameworks (MOFs) has been attracting increasing attention owing to the outstanding properties derived from MOFs-guests combinations. However, there are large difficulties involved in the syntheses of the host-guest MOF systems with air-sensitive metal complexes. In addition, the behaviors on host-guest interactions in the above systems at high temperature are not clear. This study reported the synthetic methods for host-guest systems of metal–organic framework and air-sensitive metal complexes via a developed chemical vapor infiltration process. With the synchrotron X-ray powder diffraction (XRPD) measurements and Fourier Transform infrared spectroscopy (FTIR), the successful loadings of Fe(CO)₅ in HKUST-1 and NH₂-MIL-101(Al) have been confirmed. At high temperatures, the structural and chemical componential changes were investigated in detail by XRPD and FTIR measurements. HKUST-1 was proven to have strong interaction with Fe(CO)₅ and resulted in a heavy loading amount of 63.1 wt%, but too strong an interaction led to deformation of HKUST-1 sub-unit under heating conditions. NH₂-MIL-101(Al), meanwhile, has a weaker interaction and is chemically inert to Fe(CO)₅ at high temperatures.

Promotion of Proton Conductivity by Encapsulation of Metal-Organic Polyhedra in Metal-Organic Frameworks

A Zr-based metal-organic polyhedron (MOP) was self-assembled in a porous MOF host, DUT-68, successfully to synthesize MOP-1@DUT-68. The MOP guest (MOP-1) has a diameter of about 20 Å, larger than that of the square windows (pore sizes of ∼14 Å) of DUT-68 but smaller than that of the rhombicuboctahedral cage (27.7 Å), which means that the migration and leaching of MOP-1 could be effectively prohibited if MOP-1 is encapsulated in the MOF's cavities. The proton conductivity of MOP-1@DUT-68 is 1.14×10^-3  S cm^-1 (at 80 °C under 98 % relative humidity), which is three orders of magnitude higher than that of DUT-68. Compared with MOP-1⊂DUT-68, which was synthesized by impregnation, MOP-1@DUT-68 is more prone to form faster proton-conduction pathways and thus provides higher proton conductivity.

Green Conversion of CO2 and Propargylamines Triggered by Triply Synergistic Catalytic Effects in Metal-Organic Frameworks

Cyclization of propargylamines with CO₂ to obtain 2-oxazolidone heterocyclic compounds is an essential reaction in industry but it is usually catalyzed by noble-metal catalysts with organic bases as co-catalysts under harsh conditions. We have synthesized a unique Cu^I /Cu^II mixed valence copper-based framework {[(Cu^I ₆ I₅ )Cu₃ ^II L₆ (DMA)₃ ](NO₃ )⋅9DMA}_n (1) with good solvent and thermal stability, as well as a high density of uncoordinated amino groups evenly distributed in the large nanoscopic channels. Catalytic experiments show that 1 can effectively catalyze the reaction of propargylamines with CO₂ , and the yield can reach 99 %. The turnover frequency (TOF) reaches a record value of 230 h^-1 , which is much higher than that of reported noble-metal catalysts. Importantly, this is the first report of heterogeneously catalyzed green conversion of propargylamines with CO₂ without solvents and co-catalysts under low temperature and atmospheric pressure. A mechanistic study reveals that a triply synergistic catalytic effect between Cu^I /Cu^II and uncoordinated amino groups promotes highly efficient and green conversion of CO₂ . Furthermore, 1 directly catalyzes this reaction with high efficiency when using simulated flue gas as a CO₂ source.

Remodelling a shp: Transmetalation in a Rare-Earth Cluster-Based Metal-Organic Framework

Postsynthetic modification of metal-organic frameworks (MOFs) is an important strategy for accessing MOF analogues that cannot be easily synthesized de novo. In this work, the rare-earth (RE) cluster-based MOF Y-CU-10 with shp topology was modified through transmetalation using a series of RE ions, including La(III), Nd(III), Eu(III), Tb(III), Er(III), Tm(III), and Yb(III). In all cases, metal exchange higher than 70% was observed, with reproducible results. All transmetalated materials were fully characterized and compared to the parent MOF Y-CU-10 with regard to crystallinity, surface area, and morphology. Additionally, single-crystal X-ray diffraction measurements were performed to provide further evidence of transmetalation occurring in the nonanuclear cluster nodes of the MOF.

Syntheses, Structures and Luminescent Properties of Eu- and Tb-MOFs with 3,5-Pyridinedicarboxylate and 1,2-Benzenedicarboxylate

Two lanthanide-based MOFs (Ln-MOFs) were synthesized by reaction of Eu(III) or Tb(III) perchlorates with mixed dicarboxylates of 3,5-pdc and 1,2-bdc (3,5-H₂pdc = 3,5-pyridinedicarboxylic acid; 1,2-H₂bdc = 1,2-benzenedicarboxylic acid) by hydrothermal method. The chemical formulas of the two complexes were [Eu₂(3,5-pdc)(1,2-bdc)₂(H₂O)₄]_n (1) and {[Tb₂(3,5-pdc)(1,2-bdc)₂(H₂O)₄]·2H₂O}_n (2). IR spectra and element analyses were tested to characterize the two compounds. The crystal structures were determined by X-ray single crystal diffraction. MOF 1 was 3D porous network structure but MOF 2 was 2D layered structure. The two MOFs emitted the characteristic fluorescence of Eu(III) or Tb(III) ion with the excitations of UV-rays. Their lifetimes of excited states for Eu(III) (⁵D₀) and Tb(III) (⁵D₄) were 0.31 and 0.82 ms. The absolute quantum yields (Ф_a) of MOF1 and 2 were also tested and the Ф_a(1) (λ_ex = 320 nm) and Ф_a(2) (λ_ex = 296 nm) were 15% and 48%, respectively.

Neighboring Zn-Zr Sites in a Metal-Organic Framework for CO2 Hydrogenation

ZrZnO_x is active in catalyzing carbon dioxide (CO₂) hydrogenation to methanol (MeOH) via a synergy between ZnO_x and ZrO_x. Here we report the construction of Zn²⁺-O-Zr⁴⁺ sites in a metal-organic framework (MOF) to reveal insights into the structural requirement for MeOH production. The Zn²⁺-O-Zr⁴⁺ sites are obtained by postsynthetic treatment of Zr₆(μ₃-O)₄(μ₃-OH)₄ nodes of MOF-808 by ZnEt₂ and a mild thermal treatment to remove capping ligands and afford exposed metal sites for catalysis. The resultant MOF-808-Zn catalyst exhibits >99% MeOH selectivity in CO₂ hydrogenation at 250 °C and a high space-time yield of up to 190.7 mg_MeOH g_Zn^-1 h^-1. The catalytic activity is stable for at least 100 h. X-ray absorption spectroscopy (XAS) analyses indicate the presence of Zn²⁺-O-Zr⁴⁺ centers instead of Zn_mO_n clusters. Temperature-programmed desorption (TPD) of hydrogen and H/D exchange tests show the activation of H₂ by Zn²⁺ centers. Open Zr⁴⁺ sites are also critical, as Zn²⁺ centers supported on Zr-based nodes of other MOFs without open Zr⁴⁺ sites fail to produce MeOH. TPD of CO₂ reveals the importance of bicarbonate decomposition under reaction conditions in generating open Zr⁴⁺ sites for CO₂ activation. The well-defined local structures of metal-oxo nodes in MOFs provide a unique opportunity to elucidate structural details of bifunctional catalytic centers.

Zeolitic imidazolate framework-8/ fluorinated graphene coated SiO2 composites for pipette tip solid-phase extraction of chlorophenols in environmental and food samples

In this work, a novel composite adsorbent was successfully prepared by zeolite imidazolate framework-8/fluorinated graphene layer-by-layer covalently bonded on SiO₂ microspheres, and followed to be packed into micro pipette tip for extraction of trace chlorophenols prior to their detection by high performance liquid chromatography (HPLC). The morphology and structure of adsorbent material was characterized by field emission scanning electron microscopy with energy dispersive spectrometer, X-ray diffraction, and N₂ adsorption. The parameters including the amount of adsorbent, sampling volume, sampling rate, sample pH, and desorption solvent affected the extraction performance was systematically investigated by pipette tip solid-phase extraction (PT-SPE) coupled with HPLC analysis. Under the optimized condition, the linearity of this method ranged from 20 to 2000 ng mL^-1 for chlorophenols (CPs) with determination coefficient higher than 0.99. The limit of detection (at a signal-to-noise ratio of 3) were in the range 2-20 ng mL^-1 for tap water and black tea drinks, 0.2-2 μg g^-1 for honey. The relative recoveries of the CPs from spiked samples ranged from 71.8% to 104.7%, with relative standard deviations less than 6.2%. The filled extraction tube exhibited good stability and reproducibility. The proposed method has been successfully used to detect CPs in water and drinks with satisfactory recoveries.

Metal-organic frameworks as catalytic selectivity regulators for organic transformations

Selective organic transformations using metal-organic frameworks (MOFs) and MOF-based heterogeneous catalysts have been an intriguing but challenging research topic in both the chemistry and materials communities. Analogous to the reaction specificity achieved in enzyme pockets, MOFs are also powerful platforms for regulating the catalytic selectivity via engineering their catalytic microenvironments, such as metal node alternation, ligand functionalization, pore decoration, topology variation and others. In this review, we provide a comprehensive introduction and discussion about the role of MOFs played in regulating and even boosting the size-, shape-, chemo-, regio- and more appealing stereo-selectivity in organic transformations. We hope that it will be instructive for researchers in this field to rationally design, conveniently prepare and elaborately functionalize MOFs or MOF-based composites for the synthesis of high value-added organic chemicals with significantly improved selectivity.

Evaluating the Robustness of Metal-Organic Frameworks for Synthetic Chemistry

Metal-organic frameworks (MOFs) are emerging as sustainable reagents and catalysts with promising applications in synthetic chemistry. Although the hydrothermal stabilities of MOFs have been well studied, their robustness toward various reagents, including acids, bases, nucleophiles, electrophiles, oxidants, and reductants, remains poorly characterized. As such, heterogeneous platforms for promising catalysts are generally identified on an ad hoc basis and have largely been limited to carboxylate frameworks to date. To address these limitations, here we systematically characterize the robustness of 17 representative carboxylate, salicylate, and azolate MOFs toward 30 conditions representing the scope of synthetic organic chemistry. Specifically, analysis of the full width at half-maximum of powder X-ray diffraction patterns, as well as infrared spectroscopy, 77 K N2 adsorption measurements, and scanning electron microscopy in select cases are employed to appraise framework degradation and dissolution under a range of representative conditions. Our studies demonstrate that azolate MOFs, such as Fe2(bdp)3 (bdp2- = 4,4'-(1,4-phenylene)bis(pyrazolate)), generally possess excellent chemical stabilities under myriad conditions. In addition, we find that carboxylate and salicylate frameworks possess complementary stabilities, with carboxylate MOFs possessing superior robustness toward acids, electrophiles, and oxidants, and salicylate MOFs demonstrating improved robustness toward bases, nucleophiles, and reductants. The guidelines provided herein should facilitate the rational design of robust frameworks for applications in synthetic chemistry and guide the development of new strategies for the postsynthetic modification of MOFs as well.

Zinc Metal-Organic Framework Growing on the Surface of Fruit Peels and Its Photocatalytic Activity

The development of water treatment materials using environmentally friendly natural biomasses as substitutes plays an increasingly important role in environmental protection. Zeolitic imidazolate framework-8 (ZIF-8) is often used for the catalytic degradation of dye wastewater, but due to its small particle size, its disadvantage of easy agglomeration prevents it from being fully functional. Herein, we report an efficient method for synthesizing biomasses/ZIF-8 using four different fruit peels as carriers. ZIF-8 nanoparticles are in-situ grown uniformly on their surface. The Brunauer-Emmett-Teller surface area of shaddock peel/ZIF-8 was found to be 752.15 m²g^-1. After catalytic activity comparison, the loose shaddock peel/ZIF-8 showed the fastest and most significant degradation efficiency of 94% in methylene blue aqueous solution and could be used multiple times through a simple washing process.

Design and evaluation of novel MOF-polymer core-shell composite as mixed-mode stationary phase for high performance liquid chromatography

A general method was developed for preparing a metal-organic framework-polymer composite coated silica core-shell stationary phase. Silica microspheres were comodified with metal-organic framework and polyvinylpyrrolidone rather than the in situ method of silica modification by original metal-organic framework particles. Metal-organic framework particles and polyvinylpyrrolidone on silica surface were beneficial to suppress silanol activity and enhance composite material tolerance, as well as increasing the water compatibility of the original metal-organic framework-based stationary phases. The stationary phase exhibited superior hydrophilic and hydrophobic performance in terms of separation for various analytes including seven alkaloids, six sulfonamides, five antibiotics, and five polycyclic aromatic hydrocarbons. Moreover, the composite material also showed excellent stability with the relative standard deviation of the retention time of 0.4 to 0.7%. The separation performance with real samples proved that the column has good practical application potential. In summary, the poposed method provides a general way for preparing metal-organic framework-polymer composite material and changed the current status of original metal-organic framework particles modified silica as a single mode chromatographic stationary phase.

Catalytic Hydrogenation of CO2 to Methanol Using Multinuclear Iridium Complexes in a Gas-Solid Phase Reaction

We report a novel approach toward the catalytic hydrogenation of CO₂ to methanol performed in the gas-solid phase using multinuclear iridium complexes at low temperature (30-80 °C). Although homogeneous CO₂ hydrogenation in water catalyzed by amide-based iridium catalysts provided only a negligible amount of methanol, the combination of a multinuclear catalyst and gas-solid phase reaction conditions led to the effective production of methanol from CO₂. The catalytic activities of the multinuclear catalyst were dependent on the relative configuration of each active species. Conveniently, methanol obtained from the gas phase could be easily isolated from the catalyst without contamination with CO, CH₄, or formic acid (FA). The catalyst can be recycled in a batchwise manner via gas release and filling. A final turnover number of 113 was obtained upon reusing the catalyst at 60 °C and 4 MPa of H₂/CO₂ (3:1). The high reactivity of this system has been attributed to hydride complex formation upon exposure to H₂ gas, suppression of the liberation of FA under gas-solid phase reaction conditions, and intramolecular multiple hydride transfer to CO₂ by the multinuclear catalyst.

A turn-on fluorescence sensing strategy for rapid detection of flumequine in water environments using covalent-coordination functionalized MOFs

With high output and large use of antibiotics in the process of aquaculture, pollution caused by antibiotics in water environments is becoming a thorny problem, and its ecological risk has aroused widespread concern.