Metal Organic Framework UiO-66 Research Articles

Determination of pyrethroids in water samples by dispersive solid-phase extraction coupled with high-performance liquid chromatography.

A metal-organic framework UiO-66 was prepared and used as a sorbent for dispersive solid-phase extraction combined with high-performance liquid chromatography (DSPE-HPLC) for extracting and determining four pyrethroids in water samples for the first time. The as-synthesized material was confirmed by Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and N2 adsorption-desorption analysis. In addition, several important parameters affecting DSPE efficiency, including sorbent dosage, extraction time, salt concentration, pH, elution solvent, elution volume, and elution time, were optimized. Under the optimum conditions, the UiO-66 based on the DSPE-HPLC method displayed a wide linear range (10-1000 ng/ml), low limits of detection (2.8-3.5 ng/ml), and good precision (relative standard deviations [RSDs] < 3%) for the four pyrethroids. The recoveries at different spiked levels ranged from 89.3% to 107.7%. In addition, UiO-66 featured good reusability and reproducibility. The results demonstrated that π-π stacking interactions, hydrophobic interactions, and van der Waals forces between UiO-66 and the four pyrethroids played a crucial role in the adsorption process. Meanwhile, the maximum extraction capability could be obtained within 5 min. Thus, the DSPE coupled with the UiO-66 sorbent can be successfully used in the analysis of four pyrethroids in environmental water samples. PRACTITIONER POINTS: Simultaneous determination of four pyrethroids using the developed UiO-66-based DSPE-HPLC method in water samples. The developed method had a short enrichment time, broad linear ranges, a low detection limit, and high enrichment factor. It is showed that π-π stacking interaction, hydrophobic interaction, and van der Waals forces were the main mechanism.

Reticular chemistry for the rational design of mechanically robust mesoporous merged-net metal-organic frameworks

Reticular chemistry for the rational design of mechanically robust mesoporous merged-net metal-organic frameworks

Fast Assembly of Metal Organic Framework UiO-66 in Acid-Base Tunable Deep Eutectic Solvent for the Acetalization of Benzaldehyde and Methanol.

Zirconium-based metal-organic frameworks (MOFs) have attracted extensive attention owing to their robust stability and facile functionalization. However, they are generally prepared in common volatile solvents within a long reaction time. Here, we introduced environmentally friendly, cheap, and acid-based tunable deep eutectic solvents (DESs) formed from 2-methyl imidazole (MIm) and p-toluenesulfonic acid (PTSA) which significantly accelerated the assembly of zirconium-based MOF (UiO-66) without any aggressive additives. PTSA in acidic DES and ZrOCl2 preliminarily formed Zr(IV) oxo organic acid framework, whereas basic DES completely dissolved the ligand of UiO-66. The strong hydrogen bond effect of PTSA and MIm efficiently accelerated the linker exchange between zirconium oxo organic coordination in acidic DES and benzenedicarboxylate linker in weak basic DES within a reaction time of 2 h at 50 °C. Thus, UiO-66 was quickly assembled with small particle sizes and used as an excellent catalyst for the acetalization of benzaldehyde and methanol. Therefore, the developed synthesis approach provides a new green strategy to quickly prepare and design various structures of metal-based compounds under mild reaction conditions.

Hybrid adsorptive nanofiltration hollow fiber membranes with charge-patterned UiO-66 incorporated thin-film nanocomposite selective layer for enhanced boron removal

Herein, hybrid adsorptive nanofiltration (NF) hollow fiber (HF) membranes with the charge-patterned structure were fabricated and characterized for enhanced boron removal application. Mg–Al layer double hydroxide (LDH) and bentonite nanoparticles (NPs) were used as adsorbents in the support layer, while pristine and novel amine modified UiO-66 metal-organic frameworks (MOFs) were used to synthesize thin-film nanocomposite polyamide (PA) selective layer. UiO-66 was modified using triethylamine (TEA) and polyethylene imine (PEI) and the modification was approved through FTIR, DLS, and FESEM analyses. Prior to the performance evaluation of the fabricated membranes, the feasibility of boron removal by PA, and pristine and modified UiO-66 was investigated using molecular dynamics (MD) simulation and the diffusion coefficients were estimated. The structure of the fabricated thin film composite (TFC) and thin film nanocomposite (TFN) membranes were characterized by AFM, zeta potential and FESEM analyses showing agglomeration of the MOFs at 0.1 wt%. Membrane performance in boron removal was evaluated through brackish water condition at 4 bar in neutral and alkaline pH. The results showed that the contribution of the adsorptive support is 8 and 4% for the supports containing LDH and bentonite, respectively. Boron removal of the UiO-66 TFN membrane was achieved up to 58%, while the charge-patterned UiO-66/PEI TFN membrane was able to remove boron up to 87 and 91% at neutral and alkaline pH conditions.

Polydopamine/ polyethyleneimine/ MOF ternary-coated poly (vinyl chloride) nanocomposite membranes based on green solvent for shale gas wastewater treatment

Large-scale nanofiltration (NF) membrane fabrication relies on the use of harmful solvents and dangerous monomers (e.g., piperazine and trimesoyl chloride). Herein, we employed greener polydopamine (PDA) and polyethyleneimine (PEI) co-deposition to construct NF selective layer on poly(vinyl chloride) (PVC) substrate prepared by using the green solvent methyl-5-(dimethylamino)-2-methyl-5-oxopentanoate (PolarClean). The metal-organic framework (MOF) UIO-66 was also co-deposited to tune the NF selective layer property by exploiting hydrogen bonds, Π-Π interaction, and coordination bonds between oxygen functional groups and zirconium (Zr) of UIO-66 and the PDA-PEI complex, as well as its intrinsic properties of high hydrophilicity and positive charge. It also improved the surface area of NF selective layer, contributing to higher permeability. However, excessive dosage, higher than 0.1 g/L, promoted PDA aggregation, thus reducing its deposition on membrane surfaces and causing defects. When the dosage was 0.05 g/L, the ternary coated NF membrane exhibited the best property with low molecular weight cut-off (MWCO, ∼350 Da), adequate hydrophilicity, high permeance (3.17 ± 0.3 L m−2 h−1 bar−1), and high MgCl2 rejection (>80%). When used for shale gas wastewater (SGW) treatment, the ternary coated membrane showed removal rates of 58.5% for dissolved organic carbon, 71.1% for fluorescent organics, and 6.2% for total dissolved solids, allowing the effluent to meet the standards of SGW internal reuse. This work helps to inspire the next-generation sustainable NF membrane fabrication.

Onion-Like nanoparticles of the metal–organic framework UiO-66 synthesized by sequential spike crystal growth

Reproducible size and morphology of metal–organic framework (MOF) particles are essential for tuning these materials for applications like heterogeneous catalysis. Particle size measurements from electron micrographs provide information about the impact of changing synthetic parameters on MOF growth, but reported data are usually limited to averages and statistical distributions. Further elucidating synthetic control parameters could facilitate studies of facet-dependent and non-classical growth mechanisms. In this work, phase-pure nanoparticles of the MOF UiO-66 were synthesized using alternating spikes of zirconium and hafnium-based nodes, forming an onion-like structure with alternating layers of Zr-UiO-66 and Hf-UiO-66. In conventional, bright-field transmission electron micrographs, Hf-UiO-66 and Zr-UiO-66 layers appeared darker and lighter, respectively. Alternating layers of Hf-UiO-66 and Zr-UiO-66 were also apparent in elemental maps obtained using scanning transmission electron microscopy with energy-dispersive X-ray spectroscopy. Average particle sizes increased monotonically with each spike, and no Zr-only or Hf-only particles were observed after the first spike, indicating that new material was consistently incorporated onto existing seeds. Surface area of the onion-like particles and their uptake of Ni2+ from solution were both between the values measured for Zr-UiO-66 and Hf-UiO-66. Results demonstrate the use of sequential spikes of nodes in monitoring crystal growth in MOFs.

Highly effective removal of methylene blue from wastewater by modified hydroxyl groups materials: Adsorption performance and mechanisms

The hydroxyl groups (-OH) was modified on the surface metal-organic framework UiO-66 to improve the adsorption capacity of cationic dye methylene blue (MB). In this work, a novel preparation method was adopted to obtain the adsorbents through adjusting the amount of hydrochloric acid (HCl), which is a regulator, in reactions to obtain non-crystalline materials (NCM-WIT) and crystalline materials (U-(OH)2) which is modified MOFs by -OH groups. They both showed excellent MB adsorption performance in the pH range of 3–11. From the experimental analysis, the results were shown that the zeta potentials of adsorbents surface are more negative improving the adsorption capacity of cationic dye MB. The fitting results of their adsorption isotherms and adsorption kinetics fit the Langmuir model and pseudo-second-order kinetic, respectively. It was found that U-(OH)2 has a more stable regeneration capacity just using solvent washing. This study provides a good idea for wastewater treatment containing cationic dyes.

Structural and Acidic Characteristics of Multiple Zr Defect Sites in UiO-66 Metal-Organic Frameworks.

Although defects are prevalent in metal-organic frameworks (MOFs) and usually play a crucial role in modulating their performance in various applications, detailed structural characterizations of various defects remain a challenging task mainly due to their disordered, heterogeneous, and local nature. In this work, by using solid-state nuclear magnetic resonance spectroscopy (SSNMR) techniques in conjunction with density functional theory (DFT) calculations, it is clearly elucidated that the trimethylphosphine (TMP)-assisted 31P NMR strategy is capable of greatly facilitating the qualitative and quantitative description of the detailed structural and acidic characteristics as well as the evolution process of various Zr defects with subtle distinctions in UiO-66 upon moderate thermal treatment, hence surpassing most conventional analytical techniques. These results offer a fundamental understanding of the defect chemistry in MOFs.

Metal-Organic Framework UiO-66-Mediated Dual-Signal Ratiometric Electrochemical Sensor for microRNA Detection with DNA Walker Amplification.

Electrochemical nanotags with strong signal input are necessary for a ratiometric electrochemical sensor to overcome the drawbacks of inaccurate detection results. In this paper, the metal-organic framework (MOF) UiO-66 was utilized as an electrochemical signal tag. A stable and strong current response at +0.9 V can be detected in neutral conditions. MicroRNA (miRNA) was employed as the model analyte. Herein, an enzyme-free DNA-walker-based ultrasensitive ratiometric electrochemical biosensor in combination with Zr MOF (UiO-66) signal tags to detect miRNA was demonstrated. In the presence of miRNA, the autonomous walker movement can be initiated by miRNA, leading to the release of biotin-modified fragments. Thus, streptavidin-labeled UiO-66 nanomaterials were not bound to the electrode, generating a low signal response of UiO-66 at +0.9 V. However, the current signal of electrolyte solution as reference at +0.2 V was increased due to the enhancement of electrode conductivity. This ratiometic sensor demonstrated high sensitivity, selectivity, and reproducibility. It can eliminate the disturbance of environmental factors and basic electrode characteristics, providing more accurate signals. A limit of detection (LOD) of 0.17 fM was achieved. Moreover, the method was also used to detect miRNA-21 spiked in real serum samples.

Low-temperature propane oxidative dehydrogenation over UiO-66 supported vanadia catalysts: Role of support confinement effects

Overoxidation is the principal barrier against commercializing propane oxidative dehydrogenation (PODH) catalysts for propylene production. The current approach to reducing overoxidation, i.e., coating the non-selective support surface with a monolayer of active phase, can itself increase the probability of overoxidation of the produced propylene due to polymerization of active phase species. Incorporating the “confinement agents” onto the metal oxide support might be considered as an alternative solution to prevent hydrocarbons from reaching the support and overoxidizing. Herein, the UiO-66 metal–organic framework, which contains numerous organic ligands connected to the zirconia nodes, was used as support for the vanadia active phase to highlight the role of support's confinement effects on the overall catalytic performance toward the PODH. The UiO-66 supported vanadia catalysts with various vanadium loadings were fabricated via an ultrasonic-assisted wet impregnation procedure. The catalytic function is related to the underlying chemical processes at catalyst surfaces using physicochemical characterization techniques, PODH performance measurements, and machine learning tools. The results showed that the catalyst with a relatively low vanadia density of 2.7 nm−2, equivalent to less than half of the entire support surface coverage, could achieve propylene productivity of 4.43 gC3H6gcat-1h-1, propane conversion of 17.1%, and propylene selectivity of 49.7% at 350 °C.

Ion conduction in Na＋ containing ionogels based on the UiO-66 metal organic framework

▪ conducting materials are critical to the development of solid-state sodium batteries which may enable the use of sodium metal anodes. Ionogels are hybrid liquid–solid electrolytes that are made by embedding an ionic liquid into a suitable solid framework. In this study, ionogels based on the UiO-66 type metal organic framework (MOF) porous structure were prepared. Three isostructural MOFs were synthesized and used: (i) the UiO-66 material, (ii) an amine functionalized MOF (UiO-66- ▪ ) and iii) a hydroxyl functionalized MOF (UiO-66- ▪ ). A mixture of sodium bis(fluorosulfonyl)imide (NaFSI) and 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMIM-FSI) was embedded in the pores of the MOFs. FTIR and conductivity spectroscopy were used to asses the interaction of the mobile species with the MOF structure as well as ion transport and electric relaxation properties of the materials. We found that the conductivity of the ionogels is strongly influenced by the functionalized linker used. The UiO-66- ▪ -based ionogels present an encouraging conductivity increase trend when sodium ions are present, whereas the UiO-66- ▪ -based ionogels present the highest conductivity in the order of 0.3 mScm−1 at 293 K, albeit this is very likely due to highly mobile protons. While further studies are needed to understand which species are dominating the ion conduction, this investigation offers an insight into the behavior of MOF-based ionogels and may guide further work in the field.

Aptamer-functionalised metal-organic frameworks as an ‘on–off–on’ fluorescent sensor for bisphenol S detection

Bisphenol S (BPS) is an industrial chemical that is widely used to manufacture daily items, such as plastic water bottles, milk bottles, water cups, and paper products. BPS is a biologically toxic environmental endocrine disruptor. Long-term exposure to BPS can disrupt the reproductive system, endanger health, and increase the risk of cancer. The metal-organic framework UiO-66 is characterised with high thermal and chemical stability, a simple synthetic route, and low preparation cost. In this study, we modified UiO-66 with nucleic acid aptamers to prepare an ‘on–off–on’ fluorescent sensor for the simple and rapid detection of BPS. The FAM-labelled aptamer was selected as the fluorescent probe (i.e. ‘on’). In the presence of UiO-66, the FAM-labelled aptamer adsorbed onto the surface of the UiO-66 material, and the fluorescence of FAM was quenched by photoinduced electron transfer (i.e. ‘off’). When BPS was introduced into the system, the configuration of the FAM-labelled aptamer changed after binding to BPS, and the adsorption of FAM on UiO-66 weakened, resulting in fluorescence recovery (i.e. ‘on’).Based on this principle, the reaction system was optimised, and the BPS content was analysed according to the change in the fluorescence signal. The signals changed linearly in the BPS concentration range of 2.0 × 10−4–4.0 × 10−2 mmol L−1, and the system had a detection limit of 1.84 × 10−4 mmol L−1. The sensor was successfully used to detect the BPS content in commercial plastic bottled water.

Smart Multifunctional UiO-66 Metal-Organic Framework Nanoparticles with Outstanding Drug-Loading/Release Potential for the Targeted Delivery of Quercetin.

Herein, UiO-66 and its two functional analogs (with -NO2 and -NH2 functional groups) were synthesized, and their potential ability as pH stimulus nanocarriers of quercetin (QU), an anticancer agent, was studied. UiO-66 is a low-toxicity, biocompatible metal-organic framework with a large surface area and good stability, which can be prepared through a facile and inexpensive method. Before and after drug loading, various analyses were conducted to characterize the synthesized nanocarriers. Moreover, Monte Carlo simulations were performed to investigate their structures and interactions with quercetin. The most promising drug loading potential and prolonged drug release (over 25 days) were observed in QU@UiO-66-NO2 with 37% drug loading content, which was the best-tested sample that exhibited a higher release rate under acidic conditions (pH = 5) than that in normal cells (pH = 7.4). This behavior is known as pH-stimulus-controlled ability. The cell treatment with free QU, UiO-66-R, and QU@UiO-66-R (R = -H, -NO2, and -NH2) was performed, and an MTT assay was conducted on HEK-293 and MDA-MB-231 cells for the cytotoxicity study. Additionally, the kinetic modeling of drug release was investigated on the basis of the analysis of the drug release profiles.

A comprehensive review on water remediation using UiO-66 MOFs and their derivatives.

Metal-organic frameworks (MOFs) are a versatile class of porous materials offering unprecedented scope for chemical and structural tunability. On account of their synthetic versatility, tunable and exceptional host-guest chemistry they are widely utilized in many prominent water remediation techniques. However, some of the MOFs present low structural stabilities specifically in aqueous and harsh chemical conditions which impedes their potential application in the field. Among the currently explored MOFs, UiO-66 exhibits structural robustness and has gained immense scientific popularity. Built with a zirconium-terephthalate framework, the strong Zr-O bond coordination contributes to its stability in aqueous, chemical, and thermal conditions. Moreover, other exceptional features such as high surface area and uniform pore size add to the grand arena of porous nanomaterials. As a result of its stable nature, UiO-66 offers relaxed admittance towards various functionalization, including synthetic and post-synthetic modifications. Consequently, the adsorptive properties of these highly stable frameworks have been modulated by the addition of various functionalities. Moreover, due to the presence of catalytically active sites, the use of UiO-66 has also been extended towards the degradation of pollutants. Furthermore, to solve the practical handling issues of the crystalline powdered forms, UiO-66 has been incorporated into various membrane supports. The incorporation of UiO-66 in various matrices has enhanced the rejection, permeate flux, and anti-fouling properties of membranes. The combination of such exceptional characteristics of UiO-66 MOF has expanded its scope in targeted purification techniques. Subsequently, this review highlights the role of UiO-66 in major water purification techniques such as adsorption, photocatalytic degradation, and membrane separation. This comprehensive review is expected to shed light on the existing developments and guide the inexhaustible futuristic scope of UiO-66 MOF.

In-situ growth of metal-organic framework (Cu–UiO-66) within wood scaffold for improved flame retardancy

ABSTRACT In this work, a novel Cu–UiO-66/wood composite was successfully fabricated by a facile in situ growth strategy, and the influence of Cu–UiO-66 metal-organic framework (MOF) loading on the wood substrate thermal stability and flame retardancy were investigated. Scanning electron microscopy images indicated that the octahedral Cu–UiO-66 microparticles were uniformly and firmly decorated on the lumen surface within the balsa wood scaffold. The incorporation of only 6.5 wt% Cu–UiO-66 MOF remarkably enhanced the thermal stability and flame retardancy of the natural wood. Compared with the untreated wood, the peak heat release rate of the Cu–UiO-66/wood composite exhibited a drastic decline by 73.1% from 94.5 to 25.4 W·g−1 and the total heat release from 7.7 to 5 kJ·g−1. Meanwhile, the treated wood had a strong self-extinguishing ability and the char residue rate of the Cu–UiO-66/wood is significantly increased by 132.7%. Therefore, this work provided an effective means of achieving the fire safety wood via introducing and constructing Cu–UiO-66 MOF flame retardants material.

Ligand-mediated band structure engineering and physiochemical properties of UiO-66 (Zr) metal-organic frameworks (MOFs) for solar-driven degradation of dye molecules

In this study, Zr-based metal organic frameworks (Zr-MOFs) with different ligands such as terephthalic acid (UiO-66), 2-aminoterephthalic (UiO-66-NH2) and 2-methylimidazole (UiO‐66‐2M) are synthesized using hydrothermal method in order to investigate their ligand-dependent properties towards photocatalytic degradation of dyes molecules under solar light. The structural analysis by XRD revealed the fundamental cubic-topology of the UiO-66 structure for all the synthesized MOFs, and the presence of respective functional groups is confirmed via their ART-IR spectra. A spherical morphology with average size of ~80 and 200 nm are observed for UiO-66 and UiO-66-NH2 MOFs, respectively, whereas, bricks-like morphology is observed for UiO‐66‐2M, which is attributed to the binding habit of the respective ligands. Band gap energy of the synthesized UiO-66, UiO-66-NH2 and UiO‐66‐2M is estimated to be ~3.85, 2.92 and 2.77 eV, respectively. Among the synthesized MOFs, the photocatalytic degradation efficiency of UiO-66-NH2 MOFs is found to be greater towards the cationic rhodamine B (RhB) dye (~95% in 120 min), while it is relatively less efficient in degrading the anionic Congo red (CR) dye, (~64% in 120 min). The insights gained from the fundamental characterizations, Mott-Schottky, scavenger and electrochemical impedance analysis revealed that the amino-groups in UiO-66-NH2 MOFs offered the band edge potentials suitable for the effective generation of energetic radical species with the improved carrier delocalization, recombination resistance and charge transfer properties in the MOFs. The further parametric studies revealed that the UiO-66-NH2 MOFs can be effectively scaled-up and used for dye degradation applications in real-time.

Highly efficient adsorption desalination employing protonated-amino-functionalized MOFs

The MOFs (metal organic frameworks) namely MIL-101 (Cr), MIL-125 (Ti) and UiO-66 (Zr) are found suitable for desalination and cooling applications. To improve both cooling and desalination performances, these MOFs were embedded with amino (–NH2) functional groups. For further improvement of water adsorption capacity and rates, the amino-functionalized MOFs can be protonated with hydrochloric acid (HCl). This article at first deals with the synthesis and characterization of protonated-amino-functionalized (NH3+Cl−) MIL-101 (Cr), MIL-125 (Ti) and UiO-66 (Zr) MOFs. Secondly, under adsorption and desorption conditions, the H2O loadings on these adsorbents are evaluated from transient to steady states. The experimental results show that the protonation (NH3+Cl−) based MIL-101 (Cr), MIL-125 (Ti) and UiO-66 (Zr) MOFs show the greater water distribution of 0.35, 0.31 and 0.4 kg/kg of MOFs. According to experimental results (heat exchanger performance, adsorption isotherms and kinetics data), the performance criteria such as specific cooling capacity (SCP), daily water production (SDWP) and coefficient of performance (COP) are evaluated for various desorption temperature (60 to 80°C) and cycle time (100 to 1000 s). The simulation results show a remarkable improvement in water production i.e., SDWP > 50 m3 desalinated water/t of adsorbents/day for protonated UiO-66 (Zr) MOFs. Additionally, the SCP improves from 0.006 to 0.72 kW/kg of MOFs.

One‐pot synthesis of copper nanocluster/Tb‐MOF composites for the ratiometric fluorescence detection of Cu2+

The increasing degradation of ecosystems due to heavy metal residues has led to environment and food contamination, prompting the development of convenient platforms for monitoring heavy metals. Here, a new dual-emission fluorescent sensor CuNCs@Tb@UiO-66-(COOH)2 for the detection of copper ions (Cu2+ ) has been synthesized using one-pot encapsulation of Tb(III) and glutathione-stabilized copper nanoclusters (CuNCs) into metal-organic frameworks (MOFs) UiO-66-(COOH)2 . In this ratiometric sensor, the fluorescence intensity of Tb3+ decreased significantly upon the addition of Cu2+ , whereas that of CuNCs showed good stability, together with an apparent colour change. Therefore, ratiometric fluorescence detection of Cu2+ can be accomplished by measuring the ratio of the fluorescence intensity at the 450 nm (F450 ) wavelength of CuNCs to the 548 nm (F548 ) emission of Tb3+ in the fluorescence spectra of the CuNCs@Tb@UiO-66-(COOH)2 suspension. Moreover, the obtained fluorescent probe showed good results in the detection of actual samples. This work can provide the basis of method for the exploration of ratiometric fluorescence and visual sensors of trace pollutants analysis in complicated samples.

The Use of Uio-66 Metal–Organic Frameworks as a High-Performance Catalyst for the Isomerization Process of endo- to exo-Dicyclopentadiene in a Solvent-Free Condition

Exo-tetrahydrodicyclopentadiene (tricyclo[5.2.1.02,6]decane) or JP-10 is a synthetic jet fuel, which can be used as a high-density fuel in the air-breathing missile engineers and supersonic combustion ramjets. It can be produced from the fully saturated version of exo-dicyclopentadiene (exo-DCPD). This work introduces a new green method for isomerization of endo-dicyclopentadiene (endo-DCPD) to exo- form in the presence of metal–organic frameworks (MOFs). The synthesized UiO-66 and UiO-66-vac as two suitable MOF catalysts are used for the isomerization process in a solvent-free condition. The design of the experiment is used to optimize reaction conditions including time, temperature and catalyst loading. High yield and excellent conversion of endo- to exo-DCPD are obtained by reacting with UiO-66-vac at lower levels of time and temperature. Solvent-free, environmentally friendly, simple reaction process, reusable catalyst, and availability of materials are advantages of this process.

Zirconium-oxo Nodes of MOFs with Tunable Electronic Properties Provide Effective ⋅OH Species for Enhanced Methane Hydroxylation.

Direct conversion of methane to high value-added oxygenates under mild conditions has attracted extensive interest. However, the over-oxidation of target products is usually unavoidable due to the easily excessive activation of C-H bond on the sites of supported metal species. Here, we identified the most efficient Zr-oxo nodes of UiO-66 metal-organic frameworks (MOFs) catalysts for the selective oxidation of methane with H2 O2 . These nodes were modified by three types of benzene 1, 4-dicarboxylates (NH2 -BDC, H2 BDC, and NO2 -BDC). Detailed characterizations and DFT calculations revealed that these ligands can effectively tune the electronic properties of Zr-oxo nodes and the H2 BDC ligand led to optimal electronic density of Zr-oxo nodes in UiO-66. Thus the UiO-66-H catalyst promoted the formation of ⋅OH species that adsorbed on Zr-oxo nodes, and facilitated the activation of methane with a lower energy barrier and subsequent conversion to hydroxylation oxygenates with 100 % selectivity.