In situ Growth of a Cobalt‐based Metal‐organic Framework on Multi‐walled Carbon Nanotubes for Simultaneously Detection of Hydroquinone and Catechol.

In the present study, we report a facile method for preparing a porous MWCNTs/ZIF‐67 nanocomposite with the help of a morphology‐maintained ZIF‐67 in situ growth on multi‐walled carbon nanotubes. Interesting, the MWCNTs/ZIF‐67 nanocomposite demonstrated excellent electrochemical activity for hydroquinone (HQ) and catechol (CC) attribute to the effective interconnections ZIF‐67 crystals and MWCNTs. The analytical curves for HQ and CC obtained by differential pulse voltammetry (DPV) were linear in the range from 0.5 to 100 μM. Benefitting from the excellent conductivity of MWCNTs as well as the high surface area and porosity of ZIF‐67, the advanced nanocomposite displayed good reproducibility, high selectivity and excellent stability, and was successfully employed to assay the content of dihydroxybenzene isomers in the lake water samples.     

In Situ Fabrication of Inorganic/Organic Hybrid Based on Cu/Co‐ZIF and Cu2O

We successfully fabricate a well‐defined inorganic/organic hybrid Cu₂O@Cu/Co‐ZIF (ZIF=zeolitic imidazolate frameworks) by use of growth of dual‐metal Cu/Co‐ZIF on the obtained Cu₂O hollow spheres. The key point of the strategy is coupling the in situ self‐sacrificing template. Cu₂O and the coordination of metal ions (Cu⁺ and Co²⁺) with 2‐methylimidazole. This new hybrid was characterized by powder X‐ray diffraction, (scanning) transmission electron microscopy, energy‐dispersive spectroscopy mapping, in situ FT‐IR spectroscopy, UV/Vis diffuse reflection spectroscopy, N₂ sorption measurements, and electron spin resonance. It was evidenced that Cu/Co‐ZIF nanocrystals have been assembled to continuous shells surrounding the Cu₂O cores as well as in the voids between layers and inner pores. Cu₂O@Cu/Co‐ZIF exhibits visible light responsiveness and holds potential as narrow band gap semiconductor and visible photocatalyst.     

(110)‐Oriented ZIF‐8 Thin Films on ITO with Controllable Thickness

(110)‐oriented zeolitic imidazolate framework (ZIF)‐8 thin films with controllable thickness are successfully deposited on indium tin oxide (ITO) electrodes at room temperature. The method applied uses 3‐aminopropyltriethoxysilane (APTES) in the form of self‐assembled monolayers (SAMs), followed by a subsequent adoption of the layer‐by‐layer (LBL) method. The crystallographic preferential orientation (CPO) index shows that the ZIF‐8 thin films are (110)‐oriented. A possible mechanism for the growth of the (110)‐oriented ZIF‐8 thin films on 3‐aminopropyltriethoxysilane modified ITO is proposed. The observed cross‐sectional scanning electron microscopy (SEM) images and photoluminescent (PL) spectra of the ZIF‐8 thin films indicate that the thickness of the ZIF‐8 layers is proportional to the number of growth cycles. The extension of such a SAM method for the fabrication of ZIF‐8 thin films as described herein should be applicable in other ZIF materials, and the as‐prepared ZIF‐8 thin films on ITO may be explored for photoelectrochemical applications.     

Atypical Hybrid Metal–Organic Frameworks (MOFs): A Combinative Process for MOF‐on‐MOF Growth,Etching, and Structure Transformation

The structural, compositional, and morphological features of metal–organic frameworks (MOFs) govern their properties and applications. Construction of hybrid MOFs with complicated structures, components, or morphologies is significant for the development of well‐organized MOFs. An advanced route is reported for construction of atypical hybrid MOFs with unique morphologies and complicated components: 1) MOF‐on‐MOF growth of a 3D zeolitic imidazolate framework (ZIF) on a ZIF‐L template, 2) etching of a part of the 2D ZIF‐L template, and 3) structural transformation of 2D ZIF‐L into 3D ZIF. The formation of core–shell‐type MOF rings and plates is controlled by regulating the three processes. The formation route for the core–shell‐type MOF rings and plates was monitored by tracking changes in morphology, structure, and composition. Carbon materials prepared from the pyrolysis of the core–shell‐type hybrid MOFs displayed enhanced oxygen reduction reaction activities compared to their monomeric counterparts.     

Oxygen‐Assisted Cathodic Deposition of Zeolitic Imidazolate Frameworks with Controlled Thickness

Processing metal–organic frameworks (MOFs) as films with controllable thickness on a substrate is increasingly crucial for many applications to realize function integration and performance optimization. Herein, we report a facile cathodic deposition process that enables the large‐area preparation of uniform films of zeolitic imidazolate frameworks (ZIF‐8, ZIF‐71, and ZIF‐67) with highly tunable thickness ranging from approximately 24 nm to hundreds of nanometers. Importantly, this oxygen‐reduction‐triggered cathodic deposition does not lead to the plating of reduced metals (Zn and Co). It is also operable cost‐effectively in the absence of supporting electrolyte and facilitates the construction of well‐defined sub‐micrometer‐sized heterogeneous structures within ZIF films.     

Poly(p‐vinylbenzoic acid)‐block‐polystyrene Self‐assembled Structures as Templates in the Synthesis of ZIF‐8

Hybrid nanocrystals of PVBA‐b ‐PS/ZIF‐8 were prepared by the growth of ZIF‐8 on the surface of the self‐assembled structures from poly(p ‐vinylbenzoic acid)‐block‐polystyrene. Two different morphologies—micelles and vesicles—were obtained in selective solvents owing to the different ratios of PVBA to PS blocks. The structure and morphology of the PVBA‐b ‐PS/ZIF‐8 composites were characterized by Fourier transform IR spectroscopy, thermogravimetric analysis, X‐ray diffraction, transmission electron microscopy and scanning electron microscopy. PVBA‐b ‐PS/ZIF‐8 showed high catalytic performance in Knoevenagel condensation reactions at room temperature, which were attributed to the more exposed active sites of the small ZIF‐8 nanocrystals grown in a confined space and a high concentration of reactants in the polymeric aggregates.     

Enzyme‐Embedded Metal–Organic Framework Colloidosomes via an Emulsion‐Based Approach

Improving the activity and stability of enzymes is significant in enzyme immobilization. Here a facile approach to prepare ring‐like ZIF‐8 colloidosomes and spherical catalase‐embedded ZIF‐8 colloidosomes is developed via one‐step emulsion‐based technique at the water/butanol interface. The influence of the concentrations of ZIF‐8 nanocrystals and Pluronic F127 as well as the oil‐water ratio was investigated. Compared with in situ biomineralization, the colloidosomes prepared via the pickering emulsion method show successful encapsulation of positively charged enzymes. By using catalase as an immobilized model, the immobilized catalase exhibits high biocatalytic activity, stability and recyclability compared with free catalase.     

Hollow Zn−Co Based Zeolitic Imidazole Framework as a Robust Heterogeneous Catalyst for Enhanced CO2 Chemical Fixation

The efficient chemical conversion of carbon dioxide (CO₂) into value‐added fine chemicals is an intriguing but challenging route in sustainable chemistry. Herein, a hollow‐structured bimetallic zeolitic imidazole framework composed of Zn and Co as metal centers (H‐ZnCo‐ZIF) has been successfully prepared via a post‐synthetic strategy based on controllable chemical‐etching of the preformed solid ZnCo‐ZIF in tannic acid. The creation of hollow cavities inside each monocrystalline ZIFs could be achieved without destroying the intrinsic frameworks, as characterized by field‐emission scanning electron microscopy, transmission electron microscopy, and X‐ray diffraction technologies. The as‐synthesized H‐ZnCo‐ZIF exhibited remarkable catalytic activity in the cycloaddition of CO₂ with epoxides to the corresponding cyclic carbonates, outperforming the solid ZnCo‐ZIF analogue due to the improved mass transfer originating from the hollow structure. More importantly, due to stabilization of metal centers in the ZIF framework by the tannic acid shell, H‐ZnCo‐ZIF exhibited good recyclability, and no activity loss could be observed in six runs. The present study provides a simple and effective strategy to enhance the catalytic performance of ZIFs by creating a hollow structure via chemical etching.     

Preparation of Cu nanoparticle‐doped ZIF‐8/RGO composites for effective photodegradation of organic pollutant

Cu nanoparticle‐connected ZIF‐8/reduced graphite oxide (RGO) composite was successfully prepared through a facile hydrothermal reaction using sulfate in this paper. The crossover mechanism of metal nanoparticles loading and RGO decoration to enhance the photocatalytic efficiency of pristine ZIF‐8 was studied. The results showed that the prepared Cu‐S@ZIF‐8/RGO has a strong ability to take advantage of sunlight, indicating an appreciable application prospect. RGO can act as a base to support the whole structure and serve as an electron sink to accept photoexcited electrons, realizing the formation of reactive oxygen species (ROS) and inhibition of electron–hole pair recombination. Cu nanoparticles act as connectors between ZIF‐8 and RGO to transfer electrons and realize the formation of partial ROS on its surface. The doped sulfate radical can promote to extend the utilization of the wavelength range by generating surface states. Cu‐S@ZIF‐8/RGO showed the best photocatalytic activity in simulated sunlight for eliminating rhodamine B and 4‐chlorophenol among all the prepared samples, the structure kept intact even in the presence of different kinds of anions. The crossover study of metal loading and RGO decoration can develop a new way for only UV‐responsive metal–organic frameworks to remove organic contaminants under sunlight irradiation.     

Facile mechanosynthesis of amorphous zeolitic imidazolate frameworks

A fast and efficient mechanosynthesis (ball-milling) method of preparing amorphous zeolitic imidazolate frameworks (ZIFs) from different starting materials is discussed. Using X-ray total scattering, N(2) sorption analysis, and gas pycnometry, these frameworks are indistinguishable from one another and from temperature-amorphized ZIFs. Gas sorption analysis also confirms that they are nonporous once formed, in contrast to activated ZIF-4, which displays interesting gate-opening behavior. Nanoparticles of a prototypical nanoporous substituted ZIF, ZIF-8, were also prepared and shown to undergo amorphization.     

Fabrication of ZIF‐8@Polyphosphazene core‐shell structure and its efficient synergism with ammonium polyphosphate in flame‐retarding epoxy resin

A novel zeolitic imidazolate framework (ZIF‐8) nanoparticles@polyphosphazene (PZN) core‐shell architecture was synthesized, and then, ZIF‐8@PZN and ammonium polyphosphate (APP) were applied for increasing the flame retardancy and mechanical property of epoxy resin (EP) through a cooperative effect. Herein, ZIF‐8 was used as the core; the shell of PZN was coated to ZIF‐8 nanoparticles via a polycondensation method. The well‐designed ZIF‐8@PZN displayed superior fire retardancy and smoke suppression effect. The synthesized ZIF‐8@PZN observably raised the flame retardancy of EP composites, which could be demonstrated by thermogravimetric analysis (TGA) and a cone calorimeter test (CCT). The chemical structure of ZIF‐8@PZN was characterized by X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). Compared with pure epoxy, with the incorporation of 3 wt% ZIF‐8@PZN and 18 wt% APP into the EP, along with 80.8%, 72.6%, and 64.7% decreased in the peak heat release rate (pHRR), the peak smoke production rate (pSPR), and the peak CO production rate (pCOPR), respectively. These suggested that ZIF‐8@PZN and APP generated an intumescent char layer, and ZIF‐8@PZN can strengthen the char layer, resulting in the enhancement in the flame resistance of EP.     

Metal‐organic framework ZIF‐8 nanocrystals as pseudostationary phase for capillary electrokinetic chromatography

The outstanding properties such as large surface area, diverse structure, and accessible tunnels and cages make metal organic frameworks (MOFs) attractive as novel separation media in separation sciences. However, the utilization of MOFs in EKC has not been reported before. Here we show the exploration of zeolitic imidazolate framework‐8 (ZIF‐8), one of famous MOFs, as the pseudostationary phase (PSP) in EKC. ZIF‐8 nanocrystals were used as the PSP through dispersing in the running buffer (20 mM phosphate solution containing a 1% v/v methanol (pH 9.2)) to enhance the separation of the phenolic isomers (p‐benzenediol, m‐benzenediol, o‐benzenediol, m‐nitrophenol, p‐nitrophenol, and o‐nitrophenol). ZIF‐8 nanocrystals in the running buffer were negatively charged, and interacted with the phenolic hydroxyl groups of the analytes, and thus greatly improved the separation of the phenolic isomers. Inclusion of 200 mg L?¹ ZIF‐8 in the running buffer as the background electrolyte gave a baseline separation of the phenolic isomers within 4 min. The relative standard deviations for five replicate separations of the phenolic isomers were 0.2–1.1% for migration time and 4.5–9.7% for peak area. The limits of detection varied from 0.44 to 2.0 mg L?¹. The results show that nanosized MOFs are promising for application in EKC.     

Fabrication of ZIF‐8@SiO2 Core–Shell Microspheres as the Stationary Phase for High‐Performance Liquid Chromatography

The unique features of high porosity, shape selectivity, and multiple active sites make metal–organic frameworks (MOFs) promising as novel stationary phases for high‐performance liquid chromatography (HPLC). However, the wide particle size distribution and irregular shape of conventional MOFs lead to lower column efficiency of such MOF‐packed columns. Herein, the fabrication of monodisperse MOF@SiO₂ core–shell microspheres as the stationary phase for HPLC to overcome the above‐mentioned problems is reported. Zeolitic imidazolate framework 8 (ZIF‐8) was used as an example of MOFs due to its permanent porosity, uniform pore size, and exceptional chemical stability. Unique carboxyl‐modified silica spheres were used as the support to grow the ZIF‐8 shell. The fabricated monodisperse ZIF‐8@SiO₂ packed columns (5 cm long × 4.6 mm i.d.) show high column efficiency (23 000 plates m^?1 for bisphenol A) for the HPLC separation of endocrine‐disrupting chemicals (bisphenol A, β‐estradiol, and p‐(tert‐octyl)phenol) and pesticides (thiamethoxam, hexaflumuron, chlorantraniliprole, and pymetrozine) within 7 min with good relative standard deviations for 11 replicate separations of the analytes (0.01–0.39, 0.65–1.7, 0.70–1.3, and 0.17–0.91 % for retention time, peak area, peak height, and half peak width, respectively). The ZIF‐8@SiO₂ microspheres combine the advantages of the good column packing properties of the uniform monodisperse silica microspheres and the separation ability of the ZIF‐8 crystals.     

Hollow Zn/Co Zeolitic Imidazolate Framework (ZIF) and Yolk–Shell Metal@Zn/Co ZIF Nanostructures

Metal–organic frameworks (MOFs) feature a great possibility for a broad spectrum of applications. Hollow MOF structures with tunable porosity and multifunctionality at the nanoscale with beneficial properties are desired as hosts for catalytically active species. Herein, we demonstrate the formation of well‐defined hollow Zn/Co‐based zeolitic imidazolate frameworks (ZIFs) by use of epitaxial growth of Zn‐MOF (ZIF‐8) on preformed Co‐MOF (ZIF‐67) nanocrystals that involve in situ self‐sacrifice/excavation of the Co‐MOF. Moreover, any type of metal nanoparticles can be accommodated in Zn/Co‐ZIF shells to generate yolk–shell metal@ZIF structures. Transmission electron microscopy and tomography studies revealed the inclusion of these nanoparticles within hollow Zn/Co‐ZIF with dominance of the Zn‐MOF as shell. Our findings lead to a generalization of such hollow systems that are working effectively to other types of ZIFs.     

Improvement of thermoplastic polyurethane's flame retardancy and thermal conductivity by leaf‐shaped cobalt‐zeolitic imidazolate framework–modified graphene and intumescent flame retardant

In this work, a new type of leaf‐shaped cobalt‐zeolitic imidazolate framework–modified graphene (Co‐ZIF‐L@RGO) hybrid was successfully prepared and blended with an intumescent flame retardant (IFR). It was added into thermoplastic polyurethane (TPU) to study the effect of its combination with IFR on the thermal conductivity and flame retardant performance of TPU. The morphology and structure of the Co‐ZIF‐L@RGO hybrid were characterized by scanning electron microscope (SEM), Fourier transform infrared and X‐ray diffraction (XRD). The results showed that Co‐ZIF‐L were uniformly loaded on the surface of graphene. Furthermore, compared with pure TPU, the limiting oxygen index values of the composite material with 3 wt% Co‐ZIF‐L and 27 wt% IFR increased to 32.6%. Their UL‐94 rating reached V‐0 rating. Their peak heat release rate, total heat release, peak smoke production rate and total smoke production were also greatly reduced by 84.4%, 70.1%, 60.3% and 62.5%, respectively. The thermogravimetric‐infrared test results showed that the amount of toxic gas emissions was effectively suppressed. The residual carbon was analyzed by SEM, laser Raman spectroscopy and XRD, and flame retardant mechanism was further investigated. Besides, the addition of this hybrid improved the thermal conductivity of TPU.     

Ball‐Milling‐Induced Amorphization of Zeolitic Imidazolate Frameworks (ZIFs) for the Irreversible Trapping of Iodine

The I₂‐sorption and ‐retention properties of several existing zeolitic imidazolate frameworks (ZIF‐4, ‐8, ‐69) and a novel framework, ZIF‐mnIm ([Zn(mnIm)₂]; mnIm=4‐methyl‐5‐nitroimidazolate), have been characterised using microanalysis, thermogravimetric analysis and X‐ray diffraction. The topologically identical ZIF‐8 ([Zn(mIm)₂]; mIm=2‐methylimidazolate) and ZIF‐mnIm display similar sorption abilities, though strikingly different guest‐retention behaviour upon heating. We discover that this guest retention is greatly enhanced upon facile amorphisation by ball milling, particularly in the case of ZIF‐mnIm, for which I₂ loss is retarded by as much as 200 °C. It is anticipated that this general approach should be applicable to the wide range of available metal–organic framework‐type materials for the permanent storage of harmful guest species.     

Carbon Dioxide Sensitivity of Zeolitic Imidazolate Frameworks

Zeolitic imidazolate frameworks of zinc, cobalt, and cadmium, including the framework ZIF‐8 commercially sold as Basolite Z1200, exhibit surprising sensitivity to carbon dioxide under mild conditions. The frameworks chemically react with CO₂ in the presence of moisture or liquid water to form carbonates. This effect, which has been previously not reported in metal–organic framework chemistry, provides an explanation for conflicting reports on ZIF‐8 stability to water and is of outstanding significance for evaluating the potential applications of metal–organic frameworks, especially for CO₂ sequestration.     

Continuous‐Flow Synthesis of ZIF‐8 Biocomposites with Tunable Particle Size

Zeolitic imidazolate framework (ZIF) biocomposites show the capacity to protect and deliver biotherapeutics. To date, the progress in this research area is based on laboratory batch methods. Now, the first continuous flow synthetic method is presented for the encapsulation of a model protein (bovine serum albumin, BSA) and a clinical therapeutic (α1‐antitrypsin, AAT) in ZIF‐8. The in situ kinetics of nucleation, growth, and crystallization of BSA@ZIF‐8 were studied by small‐angle X‐ray scattering. By controlling the injection time of ethanol, the particle growth could be quenched by ethanol‐induced crystallization from amorphous particles to ZIF‐8 crystals. The particle size of the biocomposite was tuned in the 40–100 nm range by varying residence time prior to introduction of ethanol. As a proof‐of‐concept, this procedure was used for the encapsulation of AAT in ZIF‐8. Upon release of the biotherapeutic from the composite, the trypsin inhibitor function of AAT was preserved.     

HPW/PDMAEMA‐b‐PMAA/ZIF‐8 Ternary Lamellar Composite and the Photocatalytic Degradation of Methylene Blue

PDMAEMA‐b‐PMAA block copolymers were prepared by the sequential RAFT polymerization of DMAEMA and tBMA, followed by hydrolysis. Phosphotungstic acid (HPW) was anchored to the PDMAEMA blocks through electrostatic interactions and the as‐obtained HPW/PDMAEMA‐b‐PMAA was added to the synthesis of ZIF‐8. During the formation of ZIF‐8, the PMAA blocks coordinated to the Zn²⁺ ions through their carboxy groups, along with the HPW groups that were anchored to the PDMAEMA blocks. In this way, the block copolymer could consolidate the interactions between HPW and ZIF‐8 and prevent the leakage of HPW. Finally, the HPW/PDMAEMA‐b‐PMAA/ZIF‐8 ternary lamellar composite was obtained and the structure of the HPW/PDMAEMA‐b‐PMAA/ZIF‐8 hybrid material was characterized by using powder X‐ray diffraction (PXRD), X‐ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). As a photocatalyst, the HPW/PDMAEMA‐b‐PMAA/ZIF‐8 ternary lamellar composite showed excellent photoactivity for the degradation of methylene blue (MB). The rate of degradation of MB was 0.0240 min^?1, which was 7.5‐times higher than that of commercially available P25 (0.0032 min^?1). In the presence of H₂O₂, the kinetic degradation parameters of the composite reached 0.0634 min^?1, which was about 19.8‐times higher than that of P25.     

Hollow Zn/Co ZIF Particles Derived from Core–Shell ZIF‐67@ZIF‐8 as Selective Catalyst for the Semi‐Hydrogenation of Acetylene

The rational design of metal–organic frameworks (MOFs) with hollow features and tunable porosity at the nanoscale can enhance their intrinsic properties and stimulates increasing attentions. In this Communication, we demonstrate that methanol can affect the coordination mode of ZIF‐67 in the presence of Co²⁺ and induces a mild phase transformation under solvothermal conditions. By applying this transformation process to the ZIF‐67@ZIF‐8 core–shell structures, a well‐defined hollow Zn/Co ZIF rhombic dodecahedron can be obtained. The manufacturing of hollow MOFs enables us to prepare a noble metal@MOF yolk‐shell composite with controlled spatial distribution and morphology. The enhanced gas storage and porous confinement that originate from the hollow interior and coating of ZIF‐8 confers this unique catalyst with superior activity and selectivity toward the semi‐hydrogenation of acetylene.