Metal-organic Framework Composites Research Articles

Dual positive charging sites for MIL-101 enhanced adsorption of toluene under high humidity conditions: Experimental and theoretical studies

Highly efficient capture of volatile organic compounds (VOCs) under humid conditions is a significant yet formidable task for metal–organic frameworks (MOFs). Based on the material simulation technique, we proposed implanting a significantly positive-density ligand (DABA) to modify MIL-101 and constructing dual positive-charging centers to improve MIL-101 competitive adsorption of benzene VOCs over H2O vapors both thermodynamically and kinetically. The introduction of DABA containing two –NH2 groups with electrostatically positive charges into MIL-101 resulted in the formation of an open tetrahedral cage with a dual positive charging center. This facilitated strong N-H…π interactions with toluene molecules, leading them to accumulate firmly in MOF pores, and thus dramatically enhanced its adsorption capacity from 17 to 31 toluene molecules per unit cell compared to pristine MIL-101. Moreover, the open tetrahedral cage in D-MIL-101 preferentially captured toluene and occupied the strongest adsorption sites first, thus effectively preventing H2O entry into MOF pores to contact with hydrophilic metal sites. This realized high water resistance and toluene adsorption uptake under high humidity conditions. Results showed that D-MIL-101 had a high specific surface area of 2558 m2/g and a new microporous structure of 9.5 Å size. It presented higher toluene uptake of 4.69 mmol/g at lower vapor pressure of P/P0 = 0.013 and 298 K temperature, as well as 3.3 folds higher working capacity of toluene compared to pristine MIL-101 under 80 % RH. This study presents a novel approach for constructing hydrophobic MOFs using new positive charging ligands and delves deeper into the competitive adsorption of VOCs/H2O in MOF composites for large-scale applications.

Study on hydrogen evolution of heterojunction formed by MoO3/Ni-MOF metal-organic framework composite

In this paper, a Z-scheme heterojunction is constructed by the synthesis of MoO3/Ni-MOF (MNM(x),x = 20%, 30%, 40% and 50%) composite materials to effectively improve its photocatalytic hydrogen production efficiency. Among them, MNM(30) composite materials have the best performance, with a hydrogen production of 7.90 mmol within 1 h, which has a significant improve for MoO3. The X-Ray Diffraction(XRD), Fourier Transform infrared spectroscopy(FT-IR), X-Rayr Photoelectron Spectroscopy(XPS), Scanning Electron Microscope(SEM) and Transmission Electron Microscope (TEM) of MoO3, Ni-MOF, and MNM(x) were analyzed to determine composition and morphology. The photoresponse and electron mobility of the them were analyzed though UV-Visible Spectrophotometer(UV–vis), Photoluminescence(PL) and Photoelectrochemical tests. The construction of Z-scheme heterojunctions has achieved the separation of photo-generated electrons and holes, leading to a significant improvement in photocatalytic efficiency. The introduction of Ni-MOF compensates for the problem of excessive bandgap in MoO3, which improves the absorption efficiency of visible light and stability of photocatalytic materials. This study provides a new pathway for photocatalytic hydrogen production in Mo-based materials by constructing heterojunctions and introducing MOF materials.

Adsorption performance of magnetic metal–organic framework composites for Congo red and amino black 10B

Adsorption performance of magnetic metal–organic framework composites for Congo red and amino black 10B

Research Progress on Metal–Organic Framework-Based Electrode Materials for Supercapacitors

Supercapacitors play an important role in power systems since they are a key part of electrochemical energy storage devices. To assemble high-performance supercapacitors, it is crucial to discover and innovate high-capacitive electrode materials. Recently, metal–organic frameworks (MOFs) and their derivatives have received wide concerns as electrode materials for supercapacitors, not only because of their high pore volume and large surface area for ions and electrons insertion and transportation, but also due to the intrinsic metal active sites that possibly offer extra faradaic pseudocapacitance. Additionally, the abundant species of MOFs with various morphologies also feature advantages in enriching the structural diversity of electrodes. In this paper, we first report the latest research progress and demonstrate the feasibility of pure MOFs for directly constructing supercapacitor electrodes. Furthermore, different MOF derivatives, including porous carbons, transition metal oxides, metal hydroxides and MOF composites for supercapacitors, are summarized, and their electrochemical performances with corresponding energy storage mechanisms are presented in detail. Finally, the perspectives for MOF-based materials applied in supercapacitors are discussed, aiming to provide a guideline for further research based on these promising materials.

Gas-responsive two-dimensional metal–organic framework composites for trace visualization of volatile organic compounds

Highly sensitive and specific identification of complex volatile organic compound mixtures has always been a huge challenge in the field of gas detection. To address this issue, the gas-responsive two-dimensional metal–organic framework (MOF) composites have been designed for fabricating a colorimetric sensor arrays for extremely sensitive detection of volatile organic compounds (VOCs). The physically exfoliated MOF nanosheets Zn2(bim)4 with large surface area and abundant unsaturated active sites were used for loading various dyes to form dye/Zn2(bim)4 composites. Due to the protective effect on dye activity and preconcentration for VOCs, the dye/Zn2(bim)4 composites-based colorimetric sensor arrays showed significantly enhanced sensitivity compared with the corresponding dyes for the detection of various VOCs. The mechanical flexibility of the dye/MOF nanosheets endowed the excellent film-forming properties on various substrates for fabricating the colorimetric sensor arrays. Besides owing to the hydrophobic property and the protection of the Zn2(bim)4 nanosheets, the dye/Zn2(bim)4 sensor arrays exhibited excellent anti-interference including humidity and temperature influence. On the basis of the fantastic properties of dye/Zn2(bim)4 composites for VOCs detection, the dye/Zn2(bim)4 sensor arrays were applied for the early perception of the plant disease late blight via ultra-sensitive and highly specific sensing the VOCs released from the infected plants.

Metal organic framework composite (Ti3AlC2 @ZIF-67) for vortex assisted solid phase extraction of lead from water and food samples

A composite of Ti3AlC2 max phase and ZIF-67 metal-organic framework (Ti3AlC2 @ ZIF- 67) was synthesized by mixing Ti3AlC2 and ZIF-67 in dimethyl formamide and used for solid phase extraction of Pb(II). Fourier transformation infrared spectroscopy, scanning electron microscopy, x-ray diffraction, and energy dispersive x-ray were used to find functional group, surface morphology, surface area elemental composition, and crystalline structure of Ti3AlC2 @ ZIF-67. Factors like solution pH (7.0), adsorbent dose (10.0 mg), sample volume, eluent concentration and volume (0.5 M, 1.0 mL), and vortex time (1.0 min) were optimized. The effect of interfering ions has been checked to determine the method's selectivity. Analytical parameters such as limit of detection (LOD) 0.26 µg L−1, limit of quantification (LOQ) 0.86 µg L−1, preconcentration factor (PF) 21, enhancement factor (EF) 20 and relative standard deviation (RSD) 4.6% were calculated under optimized experimental condition. Certified reference materials TMDA-64.3 water samples and INCT-OBTL-5 tobacco leaves were used to validate the accuracy of the proposed method for trace metals detection. The technique was also used for lead determination in food and water samples with satisfactory recovery results.

Synthesis and characterization of Zn-based bimetallic microporous MOF composites for effective formaldehyde sensing at room temperature

In the present work, we fabricated 1:1 bimetallic ZnCu(NA); ZnCd(NA); and ZnCo(NA) metal organic frameworks (MOFs) using nicotinic acid (NA) as organic linker by solvothermal method. All the compounds were characterized by Fourier-transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) analysis, X-ray photoelectron Spectroscopy (XPS), and scanning electron microscopy (SEM).The drop-casting method used to develop a chemiresistive sensor to sense Volatile Organic Compounds (VOCs) at room temperature. These bimetallic sensors exhibited excellent sensitivity and good linearity in detecting formaldehyde at 1 to 50 ppm range. The responses of all sensing materials towards formaldehyde gas at 50 ppm concentration are Cu(NA) 3.74, ZnCu(NA) 18.6, Cd(NA) 3.13, ZnCd(NA) 8.36 and ZnCo(NA) 28.3.The sensing times of Cu(NA), ZnCu(NA), Cd(NA), ZnCd(NA) and ZnCo(NA) are 17, 9, 15, 18 and 17 respectively. These results demonstrate the potential applications of bimetallic Zn/Cu, Zn/Cd, and Zn/Co MOFs for sensitive and specific formaldehyde detection at ambient temperature. These results show that ZnCo(NA) sensing material is an excellent selective sensor for formaldehyde sensing.

Light/pH dual-responsive magnetic metal-organic frameworks composites for phosphorylated peptide enrichment

Metal-organic frameworks (MOFs) combined with specific ligands are highly adaptable smart materials that can respond to external and physiological stimuli. In this study, we introduced a pyridinyl zwitterionic ligand with light/pH dual response into magnetic MOF composite (Fe3O4@ZW-MOF) for enrichment of phosphorylated peptides for the first time. The introduction of the developed ligand gives MOF material dual response properties. Light stimulation affects the generation/disappearance of free radicals of the pyridine derivative, resulting in a change in the charge gradient of the zwitterion, and zwitterion can also regulate the pH of the solution by adding acid or base. Therefore, the reversible capture and release of phosphorylated peptides can be easily achieved by adjusting light and pH. The established phosphorylated peptide enrichment platform exhibits high sensitivity (detection limit of 1 fmol), high selectivity (β-casein:BSA, 1:1000), and good reusability (7 cycles). In addition, the method was applied to the enrichment of phosphorylated peptides in complex systems (non-fat milk and human serum), demonstrating the feasibility of this method for phosphoproteom analysis. In conclusion, the synthesized Fe3O4@ZW-MOF is a promising MOF material, which provides the possibility to advance the application of responsive MOFs materials in proteomics.

Mixed Metal-Organic Framework Mixed-Matrix Membranes: Insights into Simultaneous Moisture-Triggered and Catalytic Delivery of Nitric Oxide using Cryo-scanning Electron Microscopy.

The fundamental chemical and structural diversity of metal-organic frameworks (MOFs) is vast, but there is a lack of industrial adoption of these extremely versatile compounds. To bridge the gap between basic research and industry, MOF powders must be formulated into more application-relevant shapes and/or composites. Successful incorporation of varying ratios of two different MOFs, CPO-27-Ni and CuBTTri, in a thin polymer film represents an important step toward the development of mixed MOF mixed-matrix membranes. To gain insight into the distribution of the two different MOFs in the polymer, we report their investigation by Cryo-scanning electron microscopy (Cryo-SEM) tomography, which minimizes surface charging and electron beam-induced damage. Because the MOFs are based on two different metal ions, Ni and Cu, the elemental maps of the MOF composite cross sections clearly identify the size and location of each MOF in the reconstructed 3D model. The tomography run was about six times faster than conventional focused ion beam (FIB)-SEM and the first insights to image segmentation combined with machine learning could be achieved. To verify that the MOF composites combined the benefits of rapid moisture-triggered release of nitric oxide (NO) from CPO-27-Ni with the continuous catalytic generation of NO from CuBTTri, we characterized their ability to deliver NO individually and simultaneously. These MOF composites show great promise to achieve optimal dual NO delivery in real-world medical applications.

Interfacial Bonding between a Crystalline Metal-Organic Framework and an Inorganic Glass.

The interface within a composite is critically important for the chemical and physical properties of these materials. However, experimental structural studies of the interfacial regions within metal-organic framework (MOF) composites are extremely challenging. Here, we provide the first example of a new MOF composite family, i.e., using an inorganic glass matrix host in place of the commonly used organic polymers. Crucially, we also decipher atom-atom interactions at the interface. In particular, we dispersed a zeolitic imidazolate framework (ZIF-8) within a phosphate glass matrix and identified interactions at the interface using several different analysis methods of pair distribution function and multinuclear multidimensional magic angle spinning nuclear magnetic resonance spectroscopy. These demonstrated glass-ZIF atom-atom correlations. Additionally, carbon dioxide uptake and stability tests were also performed to check the increment of the surface area and the stability and durability of the material in different media. This opens up possibilities for creating new composites that include the intrinsic chemical properties of the constituent MOFs and inorganic glasses.

Pd on composite chitosan bead containing a star-like hybrid metal-organic framework: A promising catalyst for hydrogenation of lubricants

A star-like hybrid composite of metal-organic framework with amino-functionalized Fe-based metal-organic framework and zeolitic imidazolate framework components was synthesized, characterized and then embedded in chitosan beads. The beads were cross-linked with glutaraldehyde to furnish robust beads, which were then utilized as supporting materials for stabilizing Pd nanoparticles. The obtained catalytic composite was characterized via XRD, FTIR, TGA, ICP, SEM, EDS, elemental mapping and utilized for the hydrogenation of polyalphaolefin oil. The effects of temperature, catalyst loading and hydrogen pressure were investigated to find the best reaction conditions. According to the results, the present catalyst promoted hydrogenation reaction under relatively mild conditions (P = 8 bar, T = 130 °C and 5 wt% catalyst loading) to give the product in 98% yield and bromine index of 50 mg-Br/100 g. Besides, the catalyst exhibited acceptable recyclability and insignificant Pd leaching, which is very promising for large-scale applications. Hot filtration test also affirmed heterogeneous catalysis.

Polymerization-induced assembly-etching engineering to hollow Co@N-doped carbon microcages for superior electromagnetic wave absorption

Hollow engineering is an effective approach to optimize impedance matching and modify magnetic-dielectric synergy for enhanced wave absorption capability, but the composition and microstructure manipulation of metal-organic frameworks (MOFs)-derived absorbers remains a challenge. Herein, a novel and facile polymerization-induced assembly-etching strategy is proposed for the manufacture of wrinkled zeolitic imidazolate framework-67@polypyrrole (ZIF-67@PPy) microcages using ammonium persulfate catalyzed pyrrole polymerization and concomitant acid etching. Then, hollow cobalt@N-doped carbon microcages (Co@NCMs) with distorted carbon shells, rich core-shell heterojunctions, highly dispersive Co nanoparticles, and abundant heterogeneous interfaces are produced via high-temperature pyrolysis process, which eliminates the need for additional templates and etching agents. Moreover, the hollow microcage structure with interior cavities and mesopores provides superior impedance matching and lightweight characteristics to the absorbers. Therefore, the hollow absorbers demonstrate a minimum reflection loss of −50.4 dB and an effective absorption bandwidth (EAB) of 3.85 GHz at 2.7 mm with a 10 wt% filler loading. In general, the polymerization-indued assembly-etching strategy inspires the hollow engineering of MOF derivatives, and facilitates the development of superior electromagnetic wave absorption (EMA) materials.

Preparation and application of nickel copper ferrate and its metal–organic framework composite in the decontamination of chemical indicator contaminated synthetic and raw laboratory wastewater

Inefficient decontamination of laboratory wastewater polluted by chemical indicators such as methyl orange (MO) and phenolphthalein (PH) is a challenge that requires attention in most developing countries. In response to this, nickel-copper ferrate (NiCuFeO4) and nickel-copper ferrate-terephthalic acid-zinc metal–organic framework composite (NiCuFeO4@MOF-5) were synthesised via simple chemical process and their activities compared for the removal of MO and PH from synthetic and raw laboratory wastewater colleccted from a science laboratory at Federal Polytechnic, Ede, Nigeria. The scanning electron micrograph (SEM) images, revealed the surfaces of NiCuFeO4 and NiCuFeO4@MOF-5 to be rough and homogeneous with tightly arranged particles that are agglomerated. The adsorption capacity of NiCuFeO4@MOF-5 expressed for the removal of MO (30.97 mg g−1) and PH (41.22 mg g−1) from aqueous solution is higher than that of NiCuFeO4 for MO (25.82 mg g−1) and PH (23.00 mg g−1). NiCuFeO4 and NiCuFeO4@MOF-5 exhibited a promising stability even at the 7th regeneration cycle for the removal of MO and PH from solution. Results obtained for the removal of MO and PH from aqueous solution by NiCuFeO4 and NiCuFeO4@MOF-5 compared favorably with reported adsorbents in literature. Conclusively, NiCuFeO4@MOF-5 is a potential and better adsorbent than NiCuFeO4 for decontaminating laboratory wastewater contaminated with MO and PH.

Water-assisted hydrogen spillover in Pt nanoparticle-based metal–organic framework composites

Hydrogen spillover is the migration of activated hydrogen atoms from a metal particle onto the surface of catalyst support, which has made significant progress in heterogeneous catalysis. The phenomenon has been well researched on oxide supports, yet its occurrence, detection method and mechanism on non-oxide supports such as metal–organic frameworks (MOFs) remain controversial. Herein, we develop a facile strategy for efficiency enhancement of hydrogen spillover on various MOFs with the aid of water molecules. By encapsulating platinum (Pt) nanoparticles in MOF-801 for activating hydrogen and hydrogenation of C=C in the MOF ligand as activated hydrogen detector, a research platform is built with Pt@MOF-801 to measure the hydrogenation region for quantifying the efficiency and spatial extent of hydrogen spillover. A water-assisted hydrogen spillover path is found with lower migration energy barrier than the traditional spillover path via ligand. The synergy of the two paths explains a significant boost of hydrogen spillover in MOF-801 from imperceptible existence to spanning at least 100-nm-diameter region. Moreover, such strategy shows universality in different MOF and covalent organic framework materials for efficiency promotion of hydrogen spillover and improvement of catalytic activity and antitoxicity, opening up new horizons for catalyst design in porous crystalline materials.

Epitaxial growth of metal-organic framework nanosheets into single-crystalline orthogonal arrays

Construction of two-dimensional nanosheets into three-dimensional regular structures facilitates the mass transfer and exploits the maximum potential of two-dimensional building blocks in applications such as catalysis. Here, we report the synthesis of metal-organic frameworks with an orthogonal nanosheet array. The assembly involves the epitaxial growth of single crystalline metal-organic framework nanosheets with a naturally non-preferred facet exposure as the shell on a cubic metal-organic framework as the core. The nanosheets, despite of two typical shapes and crystallographic orientations, also form a single crystalline orthogonally arrayed framework. The density and size of nanosheets in the core-shell-structured composite metal-organic frameworks can be well adjusted. Moreover, metal-organic frameworks with a single composition and hollow orthogonal nanosheet array morphology can be obtained. Benefiting from the unusual facet exposure and macroporous structure, the designed structure exhibits improved electrocatalytic oxygen evolution activity compared to conventional nanosheets.

Ferromagnetic metal organic framework (MOF)/alginate hybrid beads for atmospheric water capture and induction heating-enabled water release

Atmospheric water harvesting (AWH) using sorbents has been proposed as a promising alternative to tackle the pressing issue of freshwater scarcity, particularly in densely populated metropolitan cities. However, successful deployment of this technology hinges on two critical prerequisites: high water capture capacity and low energy consumption for quick water release. In this work, a novel hybrid ferromagnetic MOF-alginate composite (MOF-AG@IO) bead for atmospheric water harvesting is presented. Using an ionic gel polymerization technique, instantaneous formation of MOF-AG@IO bead was achieved. SEM-EDX and XRD analysis revealed successful incorporation of MOF-808 crystals in the hydrogel together with CaCl2 and Fe3O4 particles. The composite exhibited high water capturing capacity from the atmosphere (∼ 1.02 gH2O/gMOF-AG@IO, 75 % RH, 25 °C) and, owing to Fe3O4 presence, quick water releasing capability (∼ 85 % water release within the first 30 min.) when exposed to magnetic induction, a technology not limited by the natural day-light cycle. The composite also showed cyclic stability, high water uptake kinetics (∼0.8 g/g at 75 % RH and 25 °C within 4 h) and excellent feasible water productivity of ∼9.11 LH2O/kgMOF-AG@IO/day. This potential productivity surpasses any previously reported values for MOF and MOF composites. Further, the composite sorbent exhibited high stability in outdoor conditions with no decline in water uptake capacity for multiple cycles. In summary, the novel ferromagnetic composite, which demonstrates a synergy of its constituent properties, offers itself as an attractive candidate for next-generation water harvesting devices integrated with electrified heating technology.

Ligand-engineered Ru-doped cobalt oxides derived from metal-organic frameworks for large-current-density water splitting

The influence of the preorganized structure and chemical composition of metal-organic frameworks (MOFs) on the morphology, surface properties, and catalytic activity of the MOFs-derived metal oxides is yet to be revealed. In this work, two types of Co-MOFs with different coordination configurations are synthesized for the preparation of the structure-engineered ruthenium (Ru)-doped cobalt oxides. The effect of the preorganized coordination structure of the MOFs on the morphology and surface properties is investigated. Interestingly, the oxalate-based MOFs derived Ru-doped cobalt oxide (OX-Co3O4-Ru) exhibits much better surface wettability and more oxygen vacancies than the zeolitic imidazolate framework-67 derived Ru-doped cobalt oxide. As expected, the OX-Co3O4-Ru owns excellent catalytic properties towards both hydrogen evolution reaction and oxygen evolution reaction with an overpotential of 49 and 286 mV, respectively at a current density of 100 mA cm−2 in 1.0 M KOH. Importantly, the bifunctional OX-Co3O4-Ru catalyst offers an extremely high current density of 500 mA cm−2 at a cell voltage of 1.71 V for overall water splitting and as well demonstrates robust working stability.

Metal-organic framework composite Mn/Fe-MOF@Pd with peroxidase-like activities for sensitive colorimetric detection of hydroquinone

The construction of highly sensitive detection methods for hydroquinone (HQ) in environment and cosmetics is of great significance for environmental protection and human health. In this work, a novel detection method for HQ was successfully developed by constructing a metal-organic framework mimic enzyme colorimetric sensor (Mn/Fe-MOF@Pd1.0) with excellent peroxidase-like activity, which was synthesized by doping manganese ions into Fe-MOF by introducing bimetallic active centers, thereby improving the peroxidase-like activity of Fe-MOF, and the acid resistance and stability of Mn/Fe-MOF were improved by supporting palladium (Pd NPs). It is proven that Mn/Fe-MOF@Pd1.0 promoted the decomposition of hydrogen peroxide (H2O2) to generate active species, therefore, oxidized chromogenic substrate discoloration. On this basis, the detection of HQ based on the Mn/Fe-MOF@Pd1.0 colorimetric sensor was constructed, in which the limit of detection (LOD) was 0.09 μM in the linear range of 0.3–30 μM. Furthermore, Mn/Fe-MOF@Pd1.0 was successfully used for detecting HQ in hydroquinone whitening cream and actual water samples. The successful synthesis of Mn/Fe-MOF@Pd1.0 may provide new insights for further study of the enzyme-like activity of metal-organic framework composites, and the constructed facile and sensitive sensor system could broaden the application prospects of HQ detection.

Adsorption investigation of a composite of metal-organic framework and polyethylene oxide hydrogel

Though adsorption techniques are eco-environmentally friendly, most lack the effectiveness of complete contaminant elimination leading to increasing concerns about the presence of aqueous contaminants on humans. Thus, synergistic combination of low adsorption capacity adsorbents may be an effective method to enhance their aqueous contaminant uptake. Sol-gel synthesized lanthanum-1,4-benzene dicarboxylate metal organic framework (LaBDC MOF) and polyethylene oxide (PEO) hydrogel were combined to prepare a synergistic composite adsorbent (PEO-LaBDC) for aqueous methylene blue (MB) adsorption. Major properties of the pristine LaBDC MOF and PEO hydrogel were expressed in the characterized composite indicating successful preparation. PEO-LaBDC composite MB removal rate of MB was at least twice as fast (60 min) to those of the pristine LaBDC MOF (120 min) and PEO hydrogel (125 min). The fitting of kinetics model was fractal in nature, and optimum adsorption was on the alkaline end of the pH spectrum for all adsorbents (pH = 12, 10, and 10, respectively). Comparatively, the composite exhibited a better adsorption performance of ≈177% higher than the pristine LaBDC MOF; buttressing the idea that synergistic combination of adsorbents in composites could enhance adsorption processes. Therefore, the PEO-LaBDC composite is a promising adsorbent for the remediation of aqueous MB.

A composite of metal-organic framework and MXene for efficient and rapid uranium extraction from seawater

A composite of metal-organic framework and MXene for efficient and rapid uranium extraction from seawater