Cr Metal-organic Framework Research Articles

HP35 Protein in the Mesopore of MIL-101(Cr) MOF: A Model to Study Cotranslocational Unfolding.

The immobilization of enzymes in metal-organic framework (MOF) cages is important in biotechnology. In this context, the mechanism of translocation of proteins through the cavities of the MOF and the roles played by confinement and MOF chemistry in giving rise to stable protein intermediates that are otherwise transiently populated in the physiological environment are important questions to be addressed. These unexplored aspects are examined with villin headpiece (HP35) as a model protein confined within a mesopore of MIL-101(Cr) using molecular dynamics simulations. At equilibrium, the protein is located farther from the center of the cavity and closer to the MOF surface. Molecular interactions with the MOF partially unfold helix-1 at its N-terminus. Umbrella sampling simulations inform the range of conformations that HP35 undertakes during translocation from one cavity to another and associated changes in free energy. Relative to its equilibrium state within the cavity, the free energy barrier for the unfolded protein at the cage window is estimated to be 16 kcal/mol. This study of MOF-based protein conformation can also be a general approach to observing intermediates in folding-unfolding pathways.

Molecularly imprinted polymer based on MIL-101 (Cr) MOF incorporated polyvinylidene for selective adsorption and separation dye with improved antifouling properties

In this work, new membrane was fabricated from polyester fabric (PF) as a substrate which was coated by a casting solution containing polyvinylidene fluoride (PVDF) blending by addition of MIL-101 (Cr) metal-organic framework (MOF)-molecularly imprinted 3-aminophenolhexamethylenetetramine (MIAPH) as filler and sodium dodecyl sulfate (SDS) as hydrophilic agent. The membrane was fabricated by phase inversion method (PVDF/MIAPH). The MIAPH has selective functional groups and was applied as filler in the mixed matrix membrane. The as-prepared MIAPH was characterized by FE-SEM, EDS, XRD, FTIR and BET-BJH analyses. The hydrophilic property, dye adsorption and filtration properties of the MIAPH/PVDF/PF membrane were studied for removal Trypan blue (TB) based on central composite design (CCD) technique through investigating operational variables (pH, TB concentration, pressure). In the fabrication of membranes, the optimal filtration properties appear at the 30 μL of SDS solution and 0.005 g MIAPH fillers. The fabricated MIAPH/PVDF/PF membrane indicates a high removal efficiency up to 94.9 % for the TB removal and has high selectivity. The data of the adsorption equilibrium were described by the Langmuir, Freundlich, Temkin and Dubinin-Radushkevich isotherms. The findings illustrated that appropriate of MIAPH in membranes could be an efficient and selective technique for TB elimination.

Enhanced Ceftriaxone Determination using a Glassy Carbon Electrode Modified with a Cr‐Based Metal‐Organic Framework Film Stabilized by β‐Cyclodextrin Polymer

AbstractA selective amperometric sensor was developed to detect the antibiotic ceftriaxone (CEF) using a composite film of poly(β‐cyclodextrin) and a metal‐organic framework (MOF). The sensor was obtained by electro‐polymerizing β‐cyclodextrin (β‐CD) onto a glassy carbon electrode (GCE) previously coated with a MIL‐101(Cr) MOF film. This design prevents MOF particles’ loss during extended electrode use. The MOF was structurally characterized using scanning electron microscopy, X‐ray diffraction, N2 adsorption‐desorption isotherms (BET method) and FTIR spectroscopy. Electrochemical impedance spectroscopy and cyclic voltammetry were used to assess the GCE/MIL‐101(Cr)‐pβ‐CD sensor, revealing reduced charge transfer resistance and enhanced sensitivity to CEF. Differential pulse voltammetry was then employed for CEF determination. Under optimized conditions, the sensor exhibited high sensitivity, a broad linear working range of 0.5 to 6 μM (R2=0.991), and a low detection limit of 0.34±0.02 μM (0.19±0.01 mg L−1). The selectivity of the sensor was evaluated in the presence of potential interferences such as organic acids, antibiotics and selected ions expected to affect the CEF signal. In an application to quantify a pharmaceutical formulation, the sensor displayed an impressive recovery rate of 98.3 % compared to results obtained using high‐performance liquid chromatography.

Synthesis, Structure, and Thermal Stability of a Mesoporous Titanium(III) Amine-Containing MOF.

The first mesoporous bimetallic TiIII/Al metal-organic framework (MOF) containing amine functionalities on its linkers has been selectively obtained by converting the cheap commercially available (TiCl3)3AlCl3 into Ti3-xAlxCl3(THF)3 and reacting this complex with 2-aminoterephthalic acid in dimethylformamide (DMF) under soft solvothermal conditions. This compound is structurally related to the previously described NH2-MIL-101(M) (M = Cr, Al, and Fe) MOFs. Thermal gravimetric analyses and in situ powder X-ray diffraction (PXRD) measurements demonstrated that this highly air-sensitive TiIII-containing MOF is structurally stable up to 200 °C. Nuclear magnetic resonance (NMR) spectroscopy, elemental analysis, and inductively coupled plasma (ICP) revealed that NH2-MIL-101(TiIII) contains trinuclear Ti3(μ3-O)Cl(DMF)2(RCOO)6 clusters with strongly bound DMF molecules and a small amount of aluminum. Sorption experiments revealed a higher affinity of this MOF for hydrogen compared to the previously described monometallic unfunctionalized MIL-101(TiIII) MOF.

Evaluation of defect induced surface heterogeneity in Metal-Organic Framework materials with alkali dopants employing adsorption isotherm modelling

In this article, an assessment of surface structural heterogeneity in porous metal organic framework (MOF) structure has been demonstrated by employing the methane and carbon-dioxide adsorption isotherms data. The virgin MIL-101-(Cr) MOF was synthesized by the hydrothermal method and defects were induced in the MOF structure by doping with various alkali (K, Na, Li) cations. The synthesized MOFs were characterized by XRD, SEM, EDX and BET measurement techniques. In order to understand the defect induced surface heterogeneity by alkali cation dopants, the surface energy distributions for CH4 and CO2 adsorptions on MOFs were measured by Dubinin – Astakhov model equation. The surface heterogeneity is mainly controlled by the limiting uptakes of adsorbates, the polarizability of adsorbates and the adsorbate-adsorbent interaction energy.

Application of Cr-metal organic framework (MOF) modified polyaniline/graphene oxide materials in supercapacitors

Application of Cr-metal organic framework (MOF) modified polyaniline/graphene oxide materials in supercapacitors

Synthesis of MIL-101(Cr) Metal Organic Framework by Green Synthesis for CO2 Gas Adsorption

Global warming issue due to the excessive carbon dioxide gas emission have raised strong interest in capturing or reducing the CO2 from flue gas or atmosphere. Physisorption-based CO2 capture applying the metal organic framework (MOF) provides a promising alternative for capturing CO2 due to the simplicity, low operating cost, and low energy requirement of the adsorption approach combined with the high CO2 adsorption capacity MOF material. In this study, a series of Chromium based MIL MOF with a variety molar ratio of chromium metal to 1,4-Benzene Dicarboxylate (BDC) organic linker were prepared via the solvent-free method (mechanochemical) to develop a clean and efficient way of synthesising MOF samples as promising CO2 adsorbents. The XRD results and FTIR spectra have confirmed the successful fabrication of MIL-101(Cr) MOF using the solvent-free method. The SEM images illustrated fine growth of irregular shaped coarse particles for Cr MOF with equal mole ratio of Cr to BDC. The MIL-101(Cr) samples were also tested on their CO2 adsorption capacity to understand the influence of molar ratio of the starting materials on the CO2 adsorption capacity. It was found that the MIL-101(Cr)1 led to the formation of a product with the highest CO2 uptake capacity of 18.78 mmol/g. In contrast, the EDS analysis result revealed that all the samples synthesised in this work were well incorporated with the Chromium element. It is therefore suggested that the molar ratio of Cr to BDC plays a critical role in determining the CO2 gas adsorption capacity.

Surfactant assisted Cr-metal organic framework for the detection of bisphenol A in dust from E-waste recycling area

Due to their highly porous structures, metal organic framework materials are widely used in analytic areas. In this paper, Cr-metal organic framework (MIL-101(Cr)) modified electrode was prepared and then was used as electrochemical sensor for the detection of bisphenol A (BPA). By using one kind of surfactant of cetyltrimethylammonium bromide (CTAB), the analytic performances of MIL-101 (Cr) towards BPA detection were greatly improved. Compared with pure MIL-101 (Cr), the differential pulse voltammetry (DPV) behavior of CTAB/MIL-101 (Cr) was improved 3.0 times in the presence of BPA. The hydrophobic long chain alkanes of CTAB can improve the enrichment and electrochemical oxidation for BPA. The CTAB/MIL-101 (Cr) sensor exhibited a linear range from 20 to 350 nM and a low detection limit of 9.95 nM (LOD = 3sb/S) and showed good reproducibility, stability and selectivity. Finally, real samples of dusts from E-waste recycling area in South China were collected and the CTAB/MIL-101 (Cr) sensor demonstrated satisfactory results for BPA detection from these dust samples.

Formaldehyde Electro‐catalytic Oxidation onto Carbon Paste Electrode Modified by MIL‐101(Cr) Nanoparticles

AbstractIn this paper, MIL‐101(Cr) metal‐organic framework (MOF) has been rapidly synthesized via microwave heating and fully characterized using powder X‐ray diffraction (PXRD), field emission scanning electronic microscopy (FESEM), Fourier transform infrared (FT‐IR) and nitrogen adsorption/desorption isotherm. FESEM image of MIL‐101(Cr) MOF displays spherical particles with a uniform morphology and particle size under 100 nm. The BET surface area and average pore diameter of synthesized MIL‐101(Cr) MOF were obtained to be 7.266 × 102 m2 g−1 and 3.28 nm, respectively. Nickel hydroxide dispersed onto MIL‐101(Cr) nanoparticles modified carbon paste electrode (Ni(OH)2‐MIL/CPE) was employed for electro‐catalytic oxidation of formaldehyde (CH2O) in the alkaline medium. The mean value of electron‐transfer coefficient, charge‐transfer rate constant and surface coverage of the Ni(OH)2‐MIL/CPE are found to be 0.517, 0.0058 s−1 and 7.88 × 10−8 mol cm−2, respectively. Also, the mean value of catalytic rate constant and diffusion coefficient of CH2O in the modified electrode surface are calculated to be 2.37 × 102 cm3 mol−1 s−1 and 1.288 × 10−6 cm2 s−1, respectively. The results indicate that Ni(OH)2‐MIL/CPE displays good electrocatalytic activity to the CH2O oxidation owing to porous structure and the large surface area of MIL‐101(Cr) MOF.

Enhancing the separation efficiency of a C2H2/C2H4 mixture by a chromium metal–organic framework fabricated via post-synthetic metalation

A new Cr metal–organic framework was fabricated via post-synthetic metalation, which exhibited enhanced separation performance for C2H2/C2H4 compared to its template of the isostructural Fe framework.

Magnetic metal-organic frameworks nanocomposites for negligible-depletion solid-phase extraction of freely dissolved polyaromatic hydrocarbons

The bioavailability of a pollutant is usually evaluated based on its freely dissolved concentration (Cfree), which can be measured by negligible-depletion equilibrium extraction that is commonly suffered from long equilibration time. Herein, metal-organic framework (MOF) composites (Fe3O4@MIL-101), consists of a magnetic Fe3O4 core and a MIL-101 (Cr) MOF shell, is developed as sorbents for negligible-depletion magnetic solid-phase extraction (nd-MSPE) of freely dissolved polyaromatic hydrocarbons (PAHs) in environmental waters. The freely dissolved PAHs in 1000 mL water samples are extracted with 1.5 mg MOF composites, and desorbed with 0.9 mL of acetonitrile under sonication for 5 min. The MOF composites exclude the extraction of dissolved organic matter (DOM) and DOM-associated PAHs by size exclusion. Additionally, the combined interactions (hydrophobic, π-π and π-complexation) between PAHs and composites markedly reduced the extraction equilibration time to < 60 min for all the studied PAHs with logKOW up to 5.74. Moreover, the porous coordination polymers property of the MOFs makes the proposed nd-MSPE based on the partitioning of PAHs and thus excludes the competitive adsorption of coexisting substances. The developed nd-MSPE approach provides low detection limits (0.08–0.82 ng L−1), wide linear range (1–1000 ng L−1) and high precision (relative standard deviations (RSDs) (3.3–4.8%) in determining Cfree of PAHs. The measured Cfree of PAHs in environmental waters are in good agreement with that of verified method. Given the large diversity in structure and pore size of MOFs, various magnetic MOFs can be fabricated for task-specific nd-MSPE of analytes, presenting a prospective strategy for high-efficiency measuring Cfree of contaminants in environments.

A Chromium Hydroxide/MIL‐101(Cr) MOF Composite Catalyst and Its Use for the Selective Isomerization of Glucose to Fructose

AbstractA metal–organic framework (MOF)‐based catalyst, chromium hydroxide/MIL‐101(Cr), was prepared by a one‐pot synthesis method. The combination of chromium hydroxide particles on and within Lewis acidic MIL‐101 accomplishes highly selective conversion of glucose to fructose in the presence of ethanol, matching the performance of optimized Sn‐containing Lewis acidic zeolites. Differently from zeolites, NMR spectroscopy studies with isotopically labeled molecules demonstrate that isomerization of glucose to fructose on this catalyst, proceeds predominantly via a proton transfer mechanism.

A Chromium Hydroxide/MIL-101(Cr) MOF Composite Catalyst and Its Use for the Selective Isomerization of Glucose to Fructose.

A metal-organic framework (MOF)-based catalyst, chromium hydroxide/MIL-101(Cr), was prepared by a one-pot synthesis method. The combination of chromium hydroxide particles on and within Lewis acidic MIL-101 accomplishes highly selective conversion of glucose to fructose in the presence of ethanol, matching the performance of optimized Sn-containing Lewis acidic zeolites. Differently from zeolites, NMR spectroscopy studies with isotopically labeled molecules demonstrate that isomerization of glucose to fructose on this catalyst, proceeds predominantly via a proton transfer mechanism.

Activated carbon (type Maxsorb-III) and MIL-101(Cr) metal organic framework based composite adsorbent for higher CH4 storage and CO2 capture

We have designed and developed carbon-based metal organic framework (MOF) composite for CH4 storage and CO2 capture. The proposed composite structure namely MAX-MIL was synthesized by in situ incorporation of activated carbon powder (type Maxsorb-III) in MIL-101(Cr) MOF structure via fluorine free hydrothermal reaction method. The porous properties, structure, morphology and thermal stability, chemical functionalities of MAX-MIL composite were measured by N2 adsorption/desorption data, X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FTIR) analysis. The gravimetric and volumetric uptakes of CH4 and CO2 onto Maxsorb-III, MIL-101(Cr) MOF and MAX-MIL composite were experimentally measured. The results show that the composite MAX-MIL adsorbs more CH4 and CO2 as compared with original MIL-101(Cr) MOF. The isotherm results provide a basis to identify the importance of addition of small amount of Maxsorb-III into the metal organic frameworks for increasing both volumetric and gravimetric uptakes of CH4 and CO2.

Urchin-Inspired TiO2@MIL-101 Double-Shell Hollow Particles: Adsorption and Highly Efficient Photocatalytic Degradation of Hydrogen Sulfide

Titanium dioxide (TiO2) is a commonly used photocatalysis for the oxidation of hydrogen sulfide (H2S). However, the low surface area and adsorption ability of TiO2 limit the photocatalytic decomposition rate. Here, a tunable metal–organic framework (MOF) coating is applied to hollow TiO2 nanoparticles using a versatile step-by-step self-assembly strategy. The hollow structure provides a high surface area, and the selected MIL-101 (Cr) MOF has a high and regenerable adsorption ability for H2S. The TiO2@MIL-101 double-shell hollow particles enable a catalytic cycle involving simultaneous adsorption and degradation of H2S, with considerably enhanced photocatalytic reaction rate. This work provides a method for improving photocatalytic performance through the design of hollow MOF-based materials that rationally combine the power of MOF and TiO2.

Prediction of phase transitions by investigating CO2 adsorption on 1% lithium doped MIL-101 (Cr) MOF with anomalous type isosteric heat of adsorption

The amount of adsorbate uptakes and heats of adsorption (Qst) for CO2 + 1% Li doped MIL-101 (Cr) metal organic framework (MOF) system are measured at wide ranges of pressures and temperatures. Some data are reported for the regions below the triple point (200 K–216.5 K). The multilayer CO2 adsorption uptakes in a series of discontinuous jump are found in the sub-triple region. Various types and shapes of Qst are observed and the unexpected differences in Qst at sub-triple, sub-critical and super critical regions are explained. At sub-triple zone, two sharp spikes of Qst against uptakes are found for identifying the transitions of adsorbate layer from the gaseous phase to the solid phase. The gas – liquid transition is also observed from the uptake dependence Qst data at 220 K and 240 K. A monotonic decrease in Qst is found at higher temperatures.

Study of metal-organic framework MIL-101(Cr) for natural gas (methane) storage and compare with other MOFs (metal-organic frameworks)

Natural gas, containing mainly methane (CH4), has the potential to substitute petroleum as fuel for vehicles. However, the storage of natural gas at adequately high densities to fulfil the requirement of driving range is a challenging task. One prospective solution is the use of porous materials to adsorb natural gas at lower pressures and temperatures resulting in higher density storage. In this article, we present an extensive study on synthesis, characterization and property evaluation of MIL-101(Cr) MOF (metal-organic framework) for CH4 adsorption. At 298 K, it is observed that the total volumetric uptake of CH4 on MIL-101(Cr) MOF is about (i) 150 cm3/cm3 at 35 bar, (ii) 215 cm3/cm3 at 65 bar, and (iii) 30 cm3/cm3 at 5 bar. Further, we have demonstrated a novel idea to store CH4 on MOFs in an ANG (adsorbed natural gas) vessel below critical point temperature employing LNG (liquefied natural gas) regasification. This LNG–ANG coupling improves the competitiveness of ANG storage and increases the CH4 working capacity. Employing LNG-ANG coupling, it is found that MIL-101(Cr) exhibits high CH4 delivery or working capacity which is (i) 240 cm3/cm3 for the operating parameters ranging from 6 bar at 160 K to 5 bar at 298 K, and (ii) 125 cm3/cm3 for the operating parameters varying from 1.2 bar at 160 K to 5 bar at 298 K.

Molecular Insight into the Adsorption and Diffusion of Water in the Versatile Hydrophilic/Hydrophobic Flexible MIL-53(Cr) MOF

Prior to envisage any implication of metal–organic framework (MOF) materials in industrial applications such as gas storage/separation, it is of primary importance to examine beyond their stability under humidity, the interactions between water and MOF surfaces. Regarding the MOF type MIL-53(Cr), the situation becomes more complex due to the breathing of its structure upon water adsorption that induces a structural transition between a narrow pore (NP) and a large pore (LP) forms. The resulting shrinkage/reopening of the framework leads to crucial modifications of the hydrophobicity/hydrophilicity character of the material. A combination of molecular simulations (Grand Canonical Monte Carlo and molecular dynamics) and experimental techniques (quasi-elastic neutron scattering and gravimetry/volumetry) allows a complete elucidation of the adsorption and diffusion mechanisms in play in this structure. It also provides a microscopic explanation of the hydrophilic and mildly hydrophobic behaviors of the NP and...