Metal Organic Framework UiO-66 Research Articles

Understanding lead and mercury adsorption by post-synthetically modified linkers in UiO-66 MOF. A computational theoretical study

ABSTRACT UiO-66 Metal-Organic framework (MOF) has been highlighted since its synthesis for its stability and many potential applications. Lead (II) and mercury (II) water remediation are among them. In the present work, we used density functional theory calculations, cluster models, and density analysis tools to study the lead and mercury adsorption mechanism of modified UiO-66. We have included the SH (thiol), NCS (isothiocyanate), NMeTU (N-methylthiourea) and DMTD (2,5-dimercapto-1,3,4-thiadiazole) linker groups. The results show a clear trend in capturing both metals: DMTD > NMeTU > SH > NCS. For mercury adsorption, little energy difference for DMTD (bidentate) and NMeTU (monodentate) is found, while for lead, this gap is greater. Inspection of charges and descriptors as softness in conceptual DFT showed the relevance of charge transfer in mercury capture by NMeTU, making this interaction almost as strong as the bidentate fashion through sulfur and nitrogen atoms in DMTD. Lead capture shows charge transfers of lesser magnitude, so the preferred interaction fashion is bidentate. Electronic density difference maps show qualitative visualization of results and are consistent with interaction energies. Through non-covalent interaction (NCI) analysis, it was possible to conclude that at DMTD, the interaction for both metals was stronger with nitrogen atom than sulfur.

Fe3O4 supported UiO-66 (Zr) metal-organic framework for removal of drug contaminants from water: fuzzy logic modeling approach.

The increase in production and consumption of pharmaceuticals and personal care products causes environmental problems. In this study, naproxen and clofibric acid adsorption were studied using Fe3O4-supported UiO-66 (Zr) metal-organic framework (Mag-UiO-66). The adsorption processes were carried out in batch mode at pH value 3.0. The optimum adsorbent quantities, equilibrium periods, pseudo-first-order (PFO), pseudo-second-order (PSO), and intra-particles diffusion kinetic models were calculated. Non-linear Langmuir, Freundlich, Dubinin-Radushkevich (D-R), and Sips isotherm equations were applied to experimental data. Thermodynamic analyses of naproxen and clofibric acid adsorption were also carried out in this study. The Langmuir isotherm qm values were found as 14.15mg/g for naproxen at 308K and 41.87mg/g for clofibric acid at 298K. Both of the adsorption processes were exothermic. MISO (multi-input single-output) fuzzy logic models for removal of both naproxen and clofibric acid adsorptions were designed based on the experimental data to estimate the removal uptake values. It is noteworthy that the results obtained through designed fuzzy logic models matched well with the experimental data and the findings of this study emphasize the validity of designed fuzzy logic models.

Bi/UiO-66-derived electrocatalysts for high CO2-to-formate conversion rate

In the CO2 electrocatalytic reduction reaction (CO2RR) technology, high CO2 conversion rate is highly required for efficient CO2 utilization from the CO2 resource. In this study, we propose the strategy of combining UiO-66 metal organic framework (MOF) structure with Bi electrocatalyst for highly active CO2RR with selective formic acid production. The synthesized Bi/UiO-66 catalyst shows superior CO2 reduction property, 4.6 times higher current density at −0.7 V vs. reversible hydrogen electrode (RHE) than bare Bi without UiO-66 despite of low electrochemical surface area. Also, NH2 functionalized UiO-66 shows almost no effect on CO2RR as compared to without NH2 probably due to disassembled linkers during CO2RR. Various characterizations such as Fourier transform infrared (FTIR), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) indicate carbonate species captured form of CO2 at Zr-MOF site should contribute the high CO2 conversion rate. Our findings demonstrate the feasibility of Zr-MOF as a Supporting material to achieve efficient CO2 reduction.

In Operando Spectroscopic Ellipsometry Investigation of MOF Thin Films for the Selective Capture of Acetic Acid.

The emission of polar volatile organic compounds (VOCs) is a major worldwide concern of air quality and equally impacts the preservation of cultural heritage (CH). The challenge is to design highly efficient adsorbents able to selectively capture traces of VOCs such as acetic acid (AA) in the presence of relative humidity (RH) normally found at storage in museums (40-80%). Although the selective capture of VOCs over water is still challenging, metal-organic frameworks (MOFs) possess highly tunable features (Lewis, Bronsted, or redox metal sites, functional groups, hydrophobicity, etc.) suitable to selectively capture a large variety of VOCs. In this context, we have explored the adsorption efficiency of a series of MOFs thin films (ZIF-8(Zn), MIL-101(Cr), and UiO-66(Zr)-2CF3) for the selective capture of AA based on a UV/vis and FT-IR spectroscopic ellipsometry in operando study (2-6% of relative pressure of AA under 40% of RH), namely conditions close to the realistic environmental storage conditions of cultural artifacts. For that purpose, optical quality thin films of MOFs were prepared by dip-coating, and their AA adsorption capacity and selectivity were evaluated under humid conditions by measuring the variation of the refractive index as a function of the vapor pressures while the chemical nature of the coadsorbed analytes (water and AA) was identified by FT-IR ellipsometry. While thin films of ZIF-8(Zn) strongly degraded upon exposure to AA/water vapors, films of MIL-101(Cr) and UiO-66(Zr)-2CF3 present a high chemical stability under those conditions. It was shown that MIL-101(Cr) presents a high AA adsorption capacity due to its high pore volume but exhibits a poor AA adsorption selectivity under humid conditions. In contrast, UiO-66(Zr)-2CF3 was shown to overpass MIL-101(Cr) in terms of AA/H2O adsorption selectivity and AA adsorption/desorption cycling stability because of its high hydrophobic character, suitable pore size for adequate confinement, and specific interactions.

Mixed matrix membranes comprising 6FDA-based polyimide blends and UiO-66 with co-continuous structures for gas separations

Membrane gas separation is considered a highly promising alternative to conventional gas separation. Recently, mixed matrix membranes containing UiO-66 metal–organic frameworks (MOFs) have been demonstrated to achieve high gas separation performance, especially in CO2-related separation. To date, few studies have used morphological control strategies to enhance the gas transport properties of mixed matrix membranes. In this study, we fabricated mixed matrix membranes comprising porous UiO-66 nanoparticles and immiscible 6FDA-based polyimide blends with co-continuous structures. The selective location of UiO-66 nanoparticles within one polymer phase of the co-continuous polymer blend was observed. However, this co-continuous structure cannot be referred to as a double-percolative morphology since the percolative UiO-66 networks did not successfully form. The gas permeability and gas sorption properties of pure gases (H2, CO2, N2, O2, and CH4) in the dense membranes and mixed matrix membranes were measured using the constant-volume variable-pressure method and the dual-volume pressure decay method, respectively. On the basis of the solution–diffusion mechanism, the contributions of gas sorption and gas transport to the overall gas permeation properties were determined and examined. When the UiO-66 content reached 35 wt%, the CO2 permeability of the mixed matrix membranes was significantly increased from 16.5 Barrer to 104.7 Barrer (by 635 %) without scarifying the permeability selectivities of CO2/N2 (16.5 ± 1.5) and CO2/CH4 (31.7 ± 5.8). The results suggest that both the addition of porous UiO-66 nanoparticles and the co-continuous structures contributed to the strongly enhanced gas separation performance of the mixed matrix membranes.

The Impact of Functionality and Porous System of Nanostructured Carriers Based on Metal–Organic Frameworks of UiO-66-Type on Catalytic Performance of Embedded Au Nanoparticles in Hydroamination Reaction

New methods for the preparation of metal–organic frameworks UiO-66 and NH2-UiO-66 with a hierarchical porous structure were developed using the MW-assisted technique under atmospheric pressure. The synthesized nanostructured meso-UiO-66 and meso-NH2-UiO-66 matrices were utilized as Au nanoparticle carriers. The resulting Au@meso-UiO-66 and Au@NH2-UiO-66 nanohybrids were studied in the reaction of phenylacetylene hydroamination with aniline into imine ([phenyl-(1-phenylethylydene)amine]) for the first time. Their catalytic behavior is significantly determined by a combination of factors, such as a small crystal size, micro–mesoporous structure, and functionality of the UiO-66 and NH2-UiO-66 carriers, as well as a high dispersion of embedded gold nanoparticles. The Au@meso-UiO-66 and Au@NH2-UiO-66 nanocatalysts demonstrate high activities (TOF), with conversion and selectivity values over 90. This excellent catalytic performance is comparable or even better than that demonstrated by heterogeneous systems based on conventional inorganic and inorganic supports known from the literature.

Application of metal organic frameworks for the inhibition of CO2 hydrates in gas dominated pipelines

The flow assurance problem caused due to the hydrate blockage is a major challenge in gas dominated pipeline flow (natural gas pipelines and CO2 sequestration pipelines). To make the hydrate inhibition economical during the pipeline flow, the use of effective low dosage hydrate inhibitor is the most crucial factor. To prevent the CO2 hydrate formation and blockage in the gas dominated pipelines the use of metal organic frameworks (MOFs) UiO-66 and UiO-66-NH2 is presented in this research work. The UiO-66 and UiO-66-NH2 were synthesized using hydrothermal synthesis method and characterized using scanning electron microscopic (SEM) images, powder X-Ray diffraction (PXRD), Brunauer-Emmett-Teller (BET) analysis, Fourier transform infrared spectroscopy (FTIR) and Thermogravimetric analysis (TGA). The synthesized MOFs were tested for CO2 hydrate inhibition in sapphire rocking cell. Both the MOFs were tested at concentrations of 0.25% w/v and 0.5% w/v. The increase in concentration of UiO-66-NH2 showed enhanced CO2 hydrate inhibition efficiency. UiO-66-NH2 was found to be much more effective in CO2 hydrate inhibition in comparison to UiO-66 during the tests.

A simple and efficient method for determining the pyrethroid pesticide residues in freshly squeezed fruit juices using a water stable metal–organic framework

A simple and efficient method was developed to assay-four common pyrethroid pesticides in freshly squeezed fruit juices. In this method, the water stable metal–organic framework UiO-66 was employed as the sorbent to directly extract the pesticides from freshly squeezed fruit juices for its good hydrophilicity to liposoluble pesticides. The pesticides could be captured by UiO-66 within 2 min under optimized conditions. The linearity of the pure solvent and matrix calibration curves were both satisfied (0.9961 ∼ 0.9998), and the matrix effect could be neglected. The limits of detection and limits of quantitation were 0.8 ∼ 1.5 and 2.9 ∼ 4.6 ng/g, respectively, which were much lower than the maximum residue levels (MRLs) set by the government (10 ∼ 5000 ng/g). The average recoveries of these pesticides were 68.1 ∼ 119.7 %, and the intra-day and inter-day relative standard deviations for recoveries were 5.2 ∼ 14.8 %. Thus, the developed method is reliable and can be used to evaluate the pyrethroid pesticide residues in freshly squeezed fruit juices..

Preparation of cerium-based UiO-66 metal-organic framework (MOF) without addition of solvent for developing its sustainable synthesis

UiO-66(Ce) metal-organic framework (MOF) has been a promising material for broad applications, including gas adsorption, photocatalysis, water treatment and reaction catalysis. For its usual preparation, a large amount of solvent is required and added during its fabrication process. This solvent is harmful to the environment most of the time. It is neither recyclable nor reusable, indicating the difficulty in waste disposal after MOF fabrication and the challenges for its scaling-up production. Given this, a solvent-free way of synthesizing the UiO-66 MOF to develop its sustainable synthesis was reported here. The MOF can be obtained by mechanically grinding the cerium (IV) ammonium nitrate (CAN) and terephthalic acid (BDC) using mortar and pestle without the addition of any solvent. Then the mixture was transferred into an autoclave and heated at 100 °C for one day. In this work, UiO-66(Ce) MOF samples with varying Ce to BDC molar ratios were successfully fabricated using the solvent-free method, supported by the XRD, SEM, EDX and FT-IR analysis results. By looking at their XRD patterns, two characteristic peaks for UiO-66(Ce) MOF were observed at 8.4° and 9.1°. The SEM images revealed the spherical crystalline morphology of UiO-66 MOF. At the same time, the EDX analysis result found the elemental composition of UiO-66 MOF was coherent with the reactants used, suggesting the excellent purity of MOF product formed in this work. As verified by the thermal stability test, the UiO-66 MOF produced here is thermally stable up to 250 °C in the air atmosphere.

Mobility and separation of linear and branched C5 alkanes in UiO-66 (Zr) probed by 2H NMR and MD simulations.

The UiO-66 (Zr) metal-organic framework (MOF) is of notable interest due to its facile synthesis, robustness under a wide range of chemical and physical conditions and its capability to separate industrially relevant hydrocarbons mixtures. However, the knowledge of the molecular mechanisms behind these process remains limited. Here, we present a combined experimental (2H NMR) and computational study of the molecular mobility, transport and adsorption of C5 alkanes isomers in a dehydroxylated UiO-66 (Zr) MOF. We show that the tetrahedral cages of the MOF are the preferred adsorption location for both n-pentane and isopentane. In a binary mixture of the isomers, isopentane interacts more strongly with the material leading it to occupy more of the tetrahedral cages than n-pentane, resulting in an isopentane/n-pentane adsorption selectivity of αads = 2 (at 373 K). At the same time, the microscopic diffusivity for n-pentane, Dn (En = 18 kJ mol-1), is significantly lower than for isopentane, Diso (Eiso = 28 kJ mol-1), which results in a high separation selectivity for a n-pentane/isopentane mixture of α ≈ 13 (at 300 K). This shows that the UiO-66 MOF is indeed a promising active material for use in light hydrocarbon separation processes.

Computational insights into the interaction of water with the UiO-66 metal–organic framework and its functionalized derivatives

UiO-66 small tetrahedral pores host the preferential water adsorption sites. Hydrophilic functional groups boost the affinity of the octahedral pores for water, explaining the higher water uptake of functionalized UiO-66 at low relative humidity.

Nanosilver-loaded metal–organic framework UiO-66 with strong fungicidal activity

Green functionalization of the metal–organic framework UiO-66 with a high loading of dispersed cationic silver species, having an outstanding antifungal action.

UiO-66 framework with an encapsulated spin probe: synthesis and exceptional sensitivity to mechanical pressure.

Probes sensitive to mechanical stress are in demand for the analysis of pressure distribution in materials, and the design of pressure sensors based on metal-organic frameworks (MOFs) is highly promising due to their structural tunability. We report a new pressure-sensing material, which is based on the UiO-66 framework with trace amounts of a spin probe (0.03 wt%) encapsulated in cavities. To obtain this material, we developed an approach for encapsulation of stable nitroxide radical TEMPO ((2,2,6,6-tetramethylpiperidin-1-yl)oxyl) into the micropores of UiO-66 during its solvothermal synthesis. Pressure read-out using electron paramagnetic resonance (EPR) spectroscopy allows monitoring the degradation of the defected MOF structure upon pressurization, where full collapse of pores occurs at as low a pressure as 0.13 GPa. The developed methodology can be used in and ex situ and provides sensitive tools for non-destructive mapping of pressure effects in various materials.

Investigation of storage environments on aminopolymer stabilization within UiO-67(Zr) for CO2 capture

Poly(ethylene imine) (PEI) and poly(propylene imine) (PPI) are supported within metal–organic framework UiO-67(Zr) pores and evaluated for CO2 capture from simulated flue gas and air.

A density functional theory study of Nix (x = 4–16) cluster impregnation effects in multi-metal (Ce, Ti) UiO-66 metal–organic frameworks

We used periodic density functional theory calculations to analyse the structural and energetic properties of Ni clusters impregnated in Ce/Zr-UiO-66 and Ti/Zr-UiO-66 MOFs, to assess their potential use as catalysts for tri-reforming reaction.

Correlated missing linker defects increase thermal conductivity in metal-organic framework UiO-66.

Thermal transport in metal-organic frameworks (MOFs) is an essential but frequently overlooked property. Among the small number of existing studies on thermal transport in MOFs, even fewer have considered explicitly the influence of defects. However, defects naturally exist in MOF crystals and are known to influence many of their material properties. In this work, we investigate the influence of both randomly and symmetrically distributed defects on the thermal conductivity of the MOF UiO-66. Two types of defects were examined: missing linker and missing cluster defects. For symmetrically distributed (i.e., spatially correlated) defects, we considered three experimentally resolved defect nanodomains of UiO-66 with underlying topologies of bcu, reo, and scu. We observed that both randomly distributed missing linker and missing cluster defects typically decrease thermal conductivity, as expected. However, we found that the spatial arrangement of defects can significantly impact thermal conductivity. In particular, the spatially correlated missing linker defect nanodomain (bcu topology) displayed an intriguing anisotropy, with the thermal conductivity along a particular direction being higher than that of the defect-free UiO-66. We attribute this unusual defect-induced increase in thermal conductivity to the removal of the linkers perpendicular to the primary direction of heat transport. These perpendicular linkers act as phonon scattering sources such that removing them increases thermal conductivity in that direction. Moreover, we also observed an increase in phonon group velocity, which might also contribute to the unusual increase. Overall, we show that structural defects could be an additional lever to tune the thermal conductivity of MOFs.

Engineering linker defects in functionalized UiO-66 MOF nanoparticles for oil-in-water Pickering emulsion stabilization.

Designing metal-organic framework (MOF)-based solid nanoparticles to stabilize Pickering emulsions by fine-tuning their hydrophobicity and lipophobicity is vital for essential applications and fundamental understanding. We demonstrate in situ grafting of palmitic acid in UiO-66 MOF through its linker defects. Our designed and activated nanoparticles (denoted as UP') stabilized the Pickering emulsions of n-heptane-in-water. Furthermore, we showed how UP' stabilized emulsion droplets disperse in media by covering each tiny droplet with a nanoscale layer made of UP'. To support our claim, we carried out the freeze-drying process to remove the liquid part from the emulsion, leaving behind the solid shell-like microstructures that we further characterized through several microscopic techniques. The stable n-heptane-in-water emulsion was confirmed by dilution (drop test), conductivity, zeta potential, and theoretical surface electrostatic potential measurements. Rheological studies indicate that the Pickering emulsions of n-heptane-in-water stabilized by UP' are much more resistant to deformation and flow imparting higher (mechanical) stability and shelf-life. Pickering emulsions stabilized by UP' emerged as a versatile way to design smart functional materials of UiO-66 through engineering linker defects that may have potential applications in interfacial catalysis, dye or contaminant separation, etc.

Adsorption and decolorization study of reactive black 5 by immobilized metal-organic framework of UiO-66 and Gloeophyllum trabeum fungus.

This study aimed to investigate immobilized metal-organic framework (MOF) UiO-66 and brown-rot fungus Gloeophyllum trabeum (GT) in PVA-SA matrices for adsorption and decolorization of reactive black 5 (RB5). Furthermore, UiO-66/GT@PVA-SA composite was successfully fabricated and obtained by immobilizing UiO-66 and GT mycelia into a mixture of PVA-SA. This composite demonstrated a decolorization ability of 80.12% for RB5 after 7 days. The composite's reusability was assessed for three cycles; at last, it only achieved 21%. This study reported that adsorption of RB5 by the composite followed a pseudo-second-order kinetic model with a correlation coefficient (R2) of 0.9997. The Freundlich model was found to be suitable for the isotherm adsorption. The process was also spontaneous and feasible, as indicated by the negative ΔG value. Subsequently, four metabolite products resulting from decolorization of RB5 by UiO-66/GT@PVA-SA composite were proposed, namely: C24H19N5Na2O13S4 (m/z = 762), C10H13N2O8S2- (m/z = 353), C12H9N4O7S2- (m/z = 384), and C10H13O8S2- (m/z = 325).

Towards the fastest kinetics and highest uptake of post-functionalized UiO-66 for Hg2+ removal from water.

Recent advances in adsorbents have improved the removal of mercury ions from wastewater. Metal-organic frameworks (MOFs) have been increasingly used as adsorbents due to their high adsorption capacity and ability to adsorb various heavy metal ions. UiO-66 (Zr) MOFs are mainly used because they are highly stable in aqueous solutions. However, most functionalized UiO-66 materials are unable to achieve a high adsorption capacity because of the undesired reactions that occur during post-functionalization. Herein, we report a facile post-functionalization method to synthesize a MOF adsorbent with fully active amide- and thiol-functionalized chelating groups, termed UiO-66-A.T. UiO-66-A.T. was synthesized via a two-step reaction by crosslinking with a monomer containing a disulfide moiety, followed by disulfide cleavage to activate the thiol groups. UiO-66-A.T. removed Hg2+ from water with a maximum adsorption capacity of 691 mg g-1 and a rate constant of 0.28 g mg-1 min-1 at pH 1. In a mixed solution containing 10 different heavy metal ions, UiO-66-A.T. has a Hg2+ selectivity of 99.4%, which is the highest reported to date. These results demonstrate the effectiveness of our design strategy for synthesizing purely defined MOFs to achieve the best Hg2+ removal performance to date among post-functionalized UiO-66-type MOF adsorbents.

Tuning the rare-earth UiO-66 metal–organic framework platform for white light emission

A trimetallic rare-earth cluster-based metal–organic framework is synthesized that emits red, green and blue emission simultaneously.