Metal Organic Framework UiO-66 Research Articles

Size- and ion-selective adsorption of organic dyes from aqueous solutions using functionalized UiO-66 frameworks

In the current context of environmental degradation, the development of novel size- and ion-selective adsorption materials for efficient wastewater treatment is a pressing concern. In this study, the selective adsorption properties of the metal–organic frameworks UiO-66, sulfo-functionalized UiO-66, and amino-functionalized UiO-66 are investigated using the organic dyes methylene blue, rhodamine B, methyl orange, and acid red 52 as model pollutants. Owing to the different molecular size of the dyes, UiO-66 showed a high adsorption capacity for methylene blue and methyl orange, whereas large rhodamine B and acid red 52 were not easy to be adsorbed in the micropores of the UiO-66 framework. In addition, the sulfo- and amino-functionalization of the UiO-66 framework enhanced the adsorption capacity for methylene blue and methyl orange, respectively. The ion-selective adsorption properties of the UiO-66 framework were demonstrated using mixed solutions of methylene blue and methyl orange. Although both compounds were moderately adsorbed into UiO-66, methylene blue and methyl orange were selectively adsorbed using sulfo-functionalized UiO-66 and amino-functionalized UiO-66, respectively. This combined size-selectivity and ion-selectivity renders functionalized UiO-66 a promising adsorbent for the removal of organic pollutants from aqueous solutions.

Catalytic CO Oxidation by Cu Single Atoms on the UiO-66 Metal–Organic Framework: The Role of the Oxidation State

Catalytic CO Oxidation by Cu Single Atoms on the UiO-66 Metal–Organic Framework: The Role of the Oxidation State

Origin of the Boosting Effect of Polyoxometalates in Photocatalysis: The Case of CO2 Reduction by a Rh-Containing Metal–Organic Framework

The immobilization of polyoxometalates (POMs) near catalytic centers of metal–organic frameworks (MOFs) has been reported as an advantageous strategy to boost their photocatalytic activity toward strategic reactions such as CO2 reduction (CO2RR) or hydrogen evolution (HER), although the reasons for such enhancement are still poorly understood. Unveiling the role of POM guests in the reaction mechanisms is therefore a key step toward the development of the next generation of multicomponent catalytic materials with optimal photocatalytic performances. Here, we elucidate the remarkable role of encapsulated [PW12O40]3– (PW12) polyoxometalates in boosting the photocatalytic activity of the Rh-functionalized UiO-67 MOF toward CO2RR and HER by combining theoretical density functional theory and microkinetic modeling approaches with experimental photophysical and spectroscopic techniques. First, we characterized in detail the reaction mechanism for CO2RR and HER catalyzed by the PW12-containing Rh-functionalized MOF, using [Ru(bpy)3]2+ as the photosensitizer (PS) and triethanolamine (TEOA) as the sacrificial electron donor in acetonitrile. Our results reveal that the encapsulated POMs act as efficient electron reservoirs, which quench [Ru(bpy)3]+─the photogenerated reduced form of the PS─and transfer the electrons to the Rh catalytic sites of the MOF. Notably, this is shown to favor the regeneration of the oxidized PS over its unproductive degradation, boosting the turnover numbers of the photocatalytic system. Such a mechanism can explain not only the higher formate and H2 product yields in the POM-containing catalyst but also the experimentally observed higher impact on the HER pathway than that on the CO2RR one, as the source of protons is generated in the reductive quenching of the photoexcited PS by TEOA. Finally, our computational exploration was extended to a whole variety of POMs, which allowed establishing relationships between their redox potentials and the activity of the related POM-containing catalytic materials. The optimal activity is reached when both the ability of the POM to accept electrons and that of its reduced form to reduce the Rh catalyst are simultaneously maximized, leading to a volcano plot whereby POMs with a moderate redox potential display the highest impact on photocatalytic performances.

Synthesis and uranium adsorption studies of UiO-66 (Ce) based metal organic frameworks from aqueous solutions

Ce based Metal Organic Framework (MOF) UiO-66 (Ce) and a MOF-composite CeO2@UiO-66 (Ce) were prepared by conventional heating and hydrothermal method respectively. Both the MOFs were characterized using X-ray Diffraction (XRD) technique, Fourier Transform Infra Red (FT-IR) spectroscopy, Field Emission-Secondary Electron Microscopy (FE–SEM), Small Angle X-ray Scattering (SAXS), Thermogravimetric Analysis (TGA), Differential Thermal Analysis (DTA) and Transmission Electron Microscopy (TEM). N2 adsorption-desorption isotherms of UiO-66 (Ce) showed large specific surface area of ∼981 m2/g and a reasonably large pore volume compared to the composite sample. Their uranium adsorption capacity in aqueous solutions was investigated in the pH range 2–6. Uranium adsorption experiments indicated reasonably higher uranium adsorption capacity of 239 mg/g for CeO2@UiO-66 (Ce) compared to UiO-66 (Ce) (190 mg/g). Kinetic studies revealed rapid uranium adsorption in pure MOF compared to the composite material which was attributed to the blocking of pores by CeO2 nanoparticles in the composite material. These frameworks showed good thermal stability as revealed by the thermogravimetric studies. The synthesized MOFs exhibit moderate recyclability using dilute acid and can be utilized in successive cycles. The selectivity studies showed that these MOFs are highly selective to U (VI) compared to Fe (III), Co (II), Ni (II) and Sr (II). This study could pave a way for more advanced material synthesis involving MOFs which could prove very beneficial for the wastewater remediation thus creating a safer environment to live in.

Hydroxylation of UiO-66 Metal-Organic Frameworks for High Arsenic(III) Removal Efficiency.

Zirconium clusters of UiO-66 have been hydroxylated with NaOH to generate strong binding sites for As(III) species in wastewater treatment. Hydroxylated UiO-66 provides high adsorption capacity over a wide range of pH from 1 to 10 with a maximum uptake of 204 mg g-1, which is significantly enhanced compared to those of pristine UiO-66, acid-modulated UiO-66, and other adsorbents for use in a wide pH range of treatment processes. The local structure of hydroxylated sites and As(III) adsorption mechanism are determined by extended X-ray absorption fine structure combined with density functional theory calculations.

Evaluation and development of GO/UiO-67@PtNPs nanohybrid-based electrochemical sensor for invisible arsenic (III) in water samples

Invisible arsenic is a highly toxic pollutant in water bodies. Therefore, a quick, simple, eco-friendly, and sensitive detection method is significant for environmental governance, toxicological evaluation, and human health. A novel platform has been put forward to the determination of arsenic (As3+) in the real wastewater. The sensing platform was established on the basis of octahedral UiO-67 metal–organic framework (UiO-67 MOF) and Platinum nanoparticles (PtNPs). The UiO-67 MOFs had a porous structure with a great specific surface area, which was beneficial to the adsorption and concentration of arsenic. Graphene oxide (GO) can be accelerated electron transfer and increased abundant active sites, while platinum nanoparticles (PtNPs) can be facilitated the selective recognition of As3+ due to their electrocatalysis. The electrochemical properties of the GO/UiO-67@PtNPs composites were studied. Under optimized conditions, the GO/UiO-67@PtNPs sensors can be applied to the ultrasensitive and selective monitoring of As3+ in an aqueous solution, and exhibited high electrochemical performance toward As3+, including a wider linear range of 2.7–33.4 nM, and a lower detection limit of 0.48 nM, which is lower than the safety standard of drinking water constructed by the World Health Organization (WHO, 10 μg L−1). In addition, the developed sensing platform displayed excellent anti-interference, reproducibility, reliability, and applicability for the determination of As3+ in different environmental samples.

Efficient and switchable aptamer “fluorescence off/on” method based on UiO-66@Cu for ultrasensitive detection of acetamiprid

Acetamiprid (ACE) is one of the primary pesticides used to control sucking-mouthpart pests, such as aphids, thrips, and whiteflies. However, owing to its internal absorption characteristics, ACE can easily form pesticide residues that harm human health and cause environmental pollution. Therefore, it is extremely important to establish an ultrasensitive, accurate, and rapid method to detect ACE and limit ACE residues within a specific range. In this study, a bilayer metal-organic framework UiO-66 @Cu was synthesized using a simple hydrothermal method, and a “fluorescence off/on” strategy was constructed for ACE detection. The FAM-modified aptamer (Apt-FAM) absorbed onto the UiO-66 @Cu surface via electrostatic interactions and the fluorescence of Apt-FAM to be quenched by UiO-66 @Cu through photoelectron transfer between UiO-66 @Cu and FAM. In the presence of ACE, it is tightly bound to Apt-FAM, drawing it away from theUiO-66 @Cu surface, and the fluorescence intensity of the entire system was restored. The results indicated that under the optimal conditions, the limit of detection (LOD) and linear range of the “fluorescent off/on” method were 0.36 μg/mL and 0.5–10 μg/mL, respectively. The method exhibits good sensitivity, selectivity and reproducibility, which provides an original approach for the direct detection of ACE.

Microwave-assisted synthesis of 2D Zr-MOF nanosheets supported gold nanocomposites as efficient catalysts for the reduction of 4-nitrophenol

Two-dimensional metal-organic framework nanosheets (2D MONs) are excellent heterogeneous catalysts owing to their high density and accessible catalytic sites, reduced diffusion pathways for reactants/products, and fast electron transport. Moreover, the employment of 2D MONs as supports to encapsulate noble nanoparticles can not only stabilize the noble nanoparticles, but also significantly improve their catalytic activity through the synergetic effect between 2D MONs and noble nanoparticles. Herein, we reported a microwave-assisted method for the rapid preparation of 2D UiO-67 metal-organic framework nanosheets (named UiO-67 NS). The Au nanoparticles modified UiO-67 nanocomposites (denoted as Au/UiO-67 NS nanocomposites) are formed by the in situ reduction of HAuCl4 in the pores of UiO-67 NS. The Au/UiO-67 NS nanocomposites show excellent catalytic activity for the reduction of 4-nitrophenol to 4-aminophenol, and only 20 equivalent sodium borohydride can completely reduce 10 mM 4-NP in 100 s, thanks to highly exposed Au NPs and reduced diffusion distance. In addition, XPS characterizations showed that the binding energy of Au 4 f in Au/UiO-67 NS nanocomposites displays a 0.48 eV less than that of Au nanoparticles on UiO-67 octahedral microcrystals (denoted as Au@UiO-67 OM), which is believed to be responsible for the enhanced catalytic activity toward the reduction of 4-nitrophenol.

Visible-Light-Responsive UiO-66(Zr) with Defects Efficiently Promoting Photocatalytic CO2 Reduction.

It is of great importance to understand the relationship between the structure and properties at the atomic level, which provides a solid platform for the design of efficient heterogeneous catalysts. However, it remains a challenge to elucidate the roles of the structure of reaction sites in the catalytic activity of active sites due to the lack of understanding of the structure of specific active site species. Herein, taking the metal-organic framework (MOF) UiO-66(Zr) as a prototype, MOF catalysts with all-solid-state frustrated Lewis pairs (FLPs) Zr3+-OH were synthesized in situ by adding acetic acid (HAc) as a modulator. By introducing missing linkers, UiO-66(Zr) first becomes a visible-light-responsive photocatalyst for CO2 reduction. The in situ Fourier transform infrared (FTIR) spectrum reveals that b-CO32- is the key intermediate for the activation of CO2 molecules through FLPs Zr3+-OH. Moreover, defective UiO-66(Zr) could "self-breath" by surface hydroxyls. This finding not only provides a new avenue for utilizing UV-responsive MOFs by defect engineering but also sheds light on its catalytic activity at the atomic level.

Metal-organic framework supported single-site nickel catalysts for butene dimerization

Homotopic sites in a well-controlled environment are not only ideal systems for mechanistic studies, but also allow optimal control of catalytic transformations. Sites having only a single metal cation and sites consisting of metal oxo complexes with few nickel (Ni) cations supported on the nodes of UiO-66 metal–organic framework (Ni-UiO-66) are studied for 1-butene dimerization. Monomeric Ni sites, which bind to the Zr6 node via two Zr-OH(μ3) linkages, are active and selective for the dimerization of 1-butene to linear and mono-branched C8 isomers. Ni oxo complexes with few Ni cations show lower activity and promote the oligomerization of transiently formed C8 isomers. Kohn-Sham density function theory calculations combined with spectroscopic measurements and kinetic analyses indicate that dimerization follows a Cossee-Arlman reaction mechanism.

Preparation and application of a nanocomposite of dopamine modified zirconium metal organic framework and polythiophene for solid-phase microextraction/gas chromatography of phenols released from polycarbonate materials

The zirconium metal-organic framework (MOF) UiO-66 was modified by dopamine (DA) and electrodeposited with Poly (3,4-ethylenedioxothiophene) (PEDOT) on an etched stainless steel wire to prepare a UiO-66-DA/PEDOT nanocomposite coating. The coating was characterized by scanning electron microscopy, energy dispersive spectrometer, Fourier transform infrared and thermogravimetric analysis, respectively. The coating has high specific surface area and more porous structure, which can be used to extract eight phenols, including 2-chlorophenol, o-cresol, m-cresol, 2, 4-dichlorophenol, 4-tert-butylphenol, 4-chlorophenol, 4-tert-octylphenol and α-naphthol. The adsorption behavior of the phenols on the UiO-66-DA/PEDOT coating had significant correlation with Langmuir isothermal model. A determination method for the eight phenols was established by combining with direct immersion solid-phase micro extraction and gas chromatography. Under the optimal experimental conditions, the detection linear range (LRs) was 0.05–50 μg mL−1 and the detection limit (LODs) was 0.01–0.08 μg mL−1 (S/N = 3). The method was applied for the migration detection of eight phenols in polycarbonate cups, which showed satisfactory recovery.

Exploring the Photophysical Properties of UiO-67 MOF Doped with Rhenium Carbonyl Complexes

Directly coordinating transition metal catalysts to the linkers of stable metal organic frameworks (MOFs) is a sleek solution to increasing the longevity of the catalyst. Photoluminescence metal complexes incorporated in MOFs have risen in interest lately. Particularly, Re(bpydc)(CO)3Cl (bpydc = 2,2’-bipyridine-5,5’-dicarboxylic acid) doped zirconium-based MOFs (Re-UiO-67) and their use in the photocatalytic reduction of CO2 have attracted considerable attention. Nonetheless, the photophysical characteristics of Re-UiO-67 as a function of loading have not been well explored. Here we analyzed the structural and compositional properties of Re-UiO-67 and showed that the photoluminescence properties of rhenium doped MOFs, including emission intensity, maximum, and lifetime, can be tuned by changing the rhenium loading. The photoluminescence of the film made of Re-UiO-67 exposed to different vapors also exhibited vapoluminescence, luminescence vapochromism, and vapotemporism. Understanding of photophysical properties of the Re-doped MOFs material could provide guidance for further photocatalytic, solar energy conversion and sensing applications.

Aqueous-Phase Destruction of Nerve-Agent Simulants at Copper Single Atoms in UiO-66.

Metal-organic frameworks (MOFs) have shown great success in aqueous-phase hydrolysis of nerve agents, with some even showing promise in the gas phase. However, both aqueous-phase reactivity and gas-phase reactivity are hindered because of the binding of the hydrolyzed products to the MOF nodes in a stable, bridging configuration, which limits turnover. Single transition-metal atoms in MOFs have been a growing field of interest for catalytic applications, and single atoms have been proposed to prevent the unwanted bridged conformation and increase catalytic turnover. To date, there has been little experimental evidence to support the hypothesis. Herein, we report two copper single atom-modified UiO-66 MOFs for nerve-agent simulant degradation. Despite the capping of highly active Zr4+ nodes with fewer Lewis acidic Cun+ atoms, the reactivity of both CuMOFs approaches that of native UiO-66 under aqueous conditions. Computational studies reveal that the Cu coordination environment impairs product inhibition with respect to the native MOF.

A cerium-based metal-organic framework as adsorbent for the 99Mo/99mTc generator

The cerium-based metal–organic framework UiO-66 (Ce) was examined as a potential adsorbent for the 99Mo/99mTc generator. The results showed that the adsorbent had an outstanding adsorption performance, reaching up to 475 mg/g adsorption capacity at pH 3. An adsorption mechanism was proposed, where the adsorption was governed by hydrogen bonds, Ce-O-Mo coordination, π-anions and electrostatic interaction. Additionally, the adsorbent exhibited excellent radiation stability and good adsorption performance when radioactive 99Mo was applied. A 99Mo/99mTc generator was fabricated with UiO-66 (Ce) as adsorbent and its performance was evaluated over two weeks. The elution results showed that 92 ± 3% of 99mTc elution efficiency could be obtained with negligible cerium breakthrough, showing the great potential of UiO-66 (Ce) as adsorbent for 99Mo/99mTc generators.

Water-stable metal–organic framework (UiO-66) supported on zirconia nanofibers membrane for the dynamic removal of tetracycline and arsenic from water

Water-soluble pollutants including pharmaceuticals and personal care products (PPCPs) and inorganic arsenic have posed challenges to water and the environment. In this work, the water-stable metal–organic framework UiO-66 was loaded on electrospinning zirconia nanofibers membrane via the in-situ solvothermal method. This novel composite membrane had increased surface area, good adsorption performance, and could dynamically remove contaminants from polluted water. Adsorption performance of the composite membrane for tetracycline (TC) and As(III) were investigated using batch experiments. The maximum adsorption capacities were 59.27 mg/g for TC and 143.95 mg/g for As(III). The membrane’s dynamic removal efficiency for TC and As(III) could reach over 90% and 80%, respectively, at a relatively high flux of 60 L/(m2·h), and could be generated and reused. pH values had strong impacts on the electrostatic interaction force, thus influenced the absorption efficiency. The adsorption mechanisms were studied by experimental characterizations and DFT calculations, and the results showed that direct interaction, hydrogen bond and ligand exchange were the main driving forces, and ZrO bond played a significant role in this process. Based on the self-supporting structure and good adsorption performance, we believe this novel composite membrane could find notable applications in wastewater decontamination.

UiO-66 metal-organic framework as a double actor in chitosan scaffolds: Antibiotic carrier and osteogenesis promoter.

Metal-organic frameworks (MOFs) have recently emerged as a useful class of nanostructures with well-suited characteristics for drug delivery applications, due to the high surface area and pore size for efficient loading. Despite their use as a nano-carrier for controlled delivery of various types of drugs, the inherent osteo-conductive properties have stolen a great attention as a growing area of investigation. Here, we evaluated the double function of UiO-66 MOF structure as a carrier for fosfomycin antibiotic and also as an osteogenic differentiation promoter when introduced in 3D chitosan scaffolds, for the first time. Our results revealed that the wet-spun chitosan scaffolds containing fosfomycin loaded UiO-66 nanocrystals (CHI/UiO-66/FOS) possessed fiber mesh structure with integrated micro-scale fibers and increased mechanical strength. In vitro antibacterial studies indicated that CHI/UiO-66/FOS scaffolds showed bactericidal activity against Staphylococcus aureus. Moreover, the scaffolds were biocompatible to MC3T3-E1 pre-osteoblasts and significantly up-regulated the expression of osteogenesis-related genes and facilitated the extracellular matrix mineralization, in vitro. Taken together, our results demonstrate UiO-66 MOFs can present double functionality and CHI/UiO-66/FOS scaffolds hold a significant potential to be further explored as an alternative approach in treating infected bone defects like osteomyelitis.

Computational study of Brønsted acidity in the metal–organic framework UiO-66

UiO-66 is one of the most popular metal–organic framework materials for catalysis. The Brønsted acidity of its Zr6-node is often critical to its catalytic power, but the acidity of each individual proton is difficult to measure directly in experiments. Here, we used density functional theory calculations to quantify the Brønsted acidity of different protons on both pristine and defective Zr6-nodes. The calculated acidities were in a different order than the previously reported results that were indirectly assigned from titration. Additional computational analyses were performed to help explain the results and reveal the underlying factors that could affect the acidity.

Role of Lewis Acid Metal Centers in Metal–Organic Frameworks for Ultrafast Reduction of 4-Nitrophenol

Metal–Organic Frameworks (MOFs) can be a good alternative to conventional catalysts because they are non-toxic and can be selective without compromising efficiency. Nano MOFs such as UiO-66 have proven themselves to be competitive in the catalytic family. In this study, we report the excellent catalytic behavior of UiO-66 MOF in the reduction of a model reaction: 4-Nitrophenol (4-NP) to 4-Aminophenol (4-AP) over MOF-5 (Zn-BDC) and MIL-101 (Fe-BDC). Nano UiO-66 crystals were synthesized by a hydrothermal process and characterized by Powder X-ray Diffraction, Diffused Reflectance UV-Vis spectroscopy, Scanning Electron Microscopy, and Transmission Electron Microscopy. The catalysts’ performance during the hydrogenation reduction reaction from 4-NP to 4-AP was investigated in the presence of a reducer, NaBH4. The UiO-66 nano crystals exhibited excellent catalytic behavior owing to its large surface area and Lewis acidic nature at the metal nodes. Furthermore, UiO-66 showed excellent recyclability behavior, verified during repeated consecutive use in a sequence. The catalyst yielded similar catalytic behavior during the reduction of nitrophenols at each cycle, which is a novel finding.

Screening of Suitable Size/Pore Dependent IL/UiO-66 Composite for Selective Gas Separation Application

The separation of toxic gases is the imperative environmental demand for which the isostructural UiO-66 metal-organic framework (MOF) has captivated, due to its exceptional thermal and chemical stability. There are two types of pores, the larger octahedral (Oh) pore (i.e., ~16 Å) and the smaller tetrahedral (Td) pore (i.e., ~10 Å), and they both perform differently in adsorbing the gas molecules. To enhance the gas separation application, green solvent ionic liquids (IL) are impregnated. The enormous application lies in its cation-anion tunability. Our interest is to find the most suitable pore for IL occupancy in UiO-66 for effectual CO2 separation. To comprehend the IL interaction inside the pores, [BMIM]+[X]- and [EMIM]+[X]- (Where X = Cl, BF4, PF6, HCOO, and CF3COO) in Oh and Td pores of UiO-66 are studied using the first principle approach. We observe the selectivity and adsorption of composites for selecting the suitable composite for gas separation application. Among the high BE composites, we found [BMIM][PF6]Oh@UiO-66 shows promising selectivity and adsorption.

Dual responsive molecularly imprinted polymers based on UiO-66-DOX for selective targeting tumor cells and controlled drug release

The preparation of synthetic drug delivery systems free of antibody modifications that can effectively recognize tumor sites and control drug delivery is essential for cancer therapy. In this study, UiO-66 metal–organic framework (MOF) modified with amino and phenylboronic acid groups was used as substrate to load the anti-cancer drug doxorubicin (DOX). Then a molecularly imprinted polymer (UiO-66-DOX@MIP) with sialic acid (SA) as the template molecule was further prepared on the surface of the synthesized nanoparticles using surface molecular imprinting technique (MIT). This polymer combines the excellent properties of UiO-66 and molecularly imprinted polymer (MIP). It was simple to prepare, economical and easy to obtain, and had a regular morphology. UiO-66-DOX@MIP containing molecularly imprinted binding sites that match the template molecule SA, could specifically recognize target tumor cells. The imprinted layer prevented drug leakage in normal body fluids while degrading and drug release under tumor microenvironment, with pH and glutathione (GSH) dual-responsive drug release properties. The UiO-66-DOX@MIP showed excellent biocompatibility and great cellular uptake efficiency to cancer cells without influence of interfering substances.