Zr-based Metal Research Articles

Hydrangea-like architectures composed of Zr-based metal-organic framework nanosheets with enhanced iodine capture.

Zirconium-based metal-organic framework nanosheet assembled hydrangea-like architectures were reported and an enhanced iodine capture capacity was achieved.

Preferential adsorption of ethane over ethylene on a Zr-based metal–organic framework: impacts of C–H⋯N hydrogen bonding

C–H⋯N interactions are more important than C–H⋯π interactions for ethane-selective adsorption.

A thiol-functionalized zirconium metal–organic cage for the effective removal of Hg2+ from aqueous solution

The mercury ions in waste water have threatened public health and environmental protection. In this sense, novel materials with outstanding performances for removal of Hg2+ are imperative. Herein, we demonstrate a thiol-functionalized zirconium metal–organic cage (MOC-(SH)2) with excellent dispersion displays ideal properties for Hg2+ capture. MOC-(SH)2 exhibits the ability of removing Hg2+ in aqueous solutions with a capacity of 335.9 mgHg2+/gMOC-(SH)2, which surpasses that of classical Zr-based metal–organic framework Uio-66-(SH)2 by 1.89 folds. The higher loading capacity of MOC-(SH)2 is probably owing to the excellent dispersion of the discrete cage, which makes the accessibility of binding sites (thiol) easier. Additionally, 99.6% of Hg2+ can be effectively captured by MOC-(SH)2 with the concentration decreased from 5 to 0.02 ppm reaching the permissible limit for Hg2+, outperforming the performance of Uio-66-(SH)2. The excellent absorption property of MOC-(SH)2 is also achieved in terms of superior selectivity under the presence of competitive metal ions. Meanwhile, the regenerated MOC-(SH)2 can be reused without apparent loss of Hg2+ loading capacity. UV–vis absorption spectra, IR spectra and emission spectra further verified the strong chemical affinity between Hg2+ and the thiol of MOC-(SH)2. The study lays the groundwork for using Zr-MOCs in the removal of toxic metal ions and environmental sustainability.

Zr-Based Metal–Organic Nanoporous Adsorbents of High Density for Methane Storage

A Zr–BDC metal–organic framework was synthesized by the solvothermal method using N,N‑dimethylformamide as an organic solvent at the temperature 110°С. The adsorbent thus obtained is characterized by a developed porous structure with specific BET surface SBET = 1060 m2/g, micropore volume W0 = 0.44 cm3/g, and average micropore radius х0 = 0.54 nm, which is indicative of a potentially effective adsorbent for adsorbed natural gas storage systems. The shaping parameters were determined for the Zr–BDC-based composites with polyvinyl alcohol as a binder and without the use of any binder at various compacting pressures. The influence of the shaping pressure on the packing density and structural and energy characteristics of the obtained samples was investigated. Based on the Dubinin theory of volume filling of micropores, the pressure dependences of the methane deliverable capacity both in the initial powdered and shaped Zr–BDC adsorbents at the temperatures of 243, 273, and 303 K were calculated for the pressures up to 100 bar. The deliverable volumetric methane capacity of the adsorption system based on the shaped Zr–BDC samples was measured in the specified thermodynamic conditions.

Synthesis and dielectric behavior of zirconium based metal organic framework UiO-66 filled epoxy composites

Low-κ dielectric polymers are extensivelyutilized inthe microelectronic industries because of their excellent mechanical and good insulating properties. Zr-based metal organic frameworks (MOFs) have shown suitable MOF/Polymer bonding and offer better mechanical properties than pure polymer. The present paper comprehensively explained the methods of synthesis and dielectric behavior of UiO-66 filled epoxy (EP) composites. In this study, nano-sized fillers Zr-based MOFs, UIO-66 (0.1% and 0.2%) were successfully introduced intoEP to investigatethe dielectric behavior of the prepared samples. The results clearly showed the dielectric constant of EP/UiO-66 (0.2%) was decreased to 2.99 from 3.175 (pure EP) therefore, the dielectric loss was reduced to 0.056 from 0.068. From the motivating results, we can say that UiO-66 playeda substantial part in bringing down the polymer dielectric propertiesand shouldbe getting further developmentwithin thefuture for preparing low-k EP composites.

Evidence on Primary Pore Size Dependence of C–C Bond Coupling Inside Zr-Based Metal–Organic Frameworks

The effect of pore structures in porous catalysts on the catalytic behavior of guest molecules has been discussed for decades. However, there is still no clear evidence to show that the guest molec...

CO2 adsorption at low pressure over polymers-loaded mesoporous metal organic framework PCN-777: effect of basic site and porosity on adsorption

Selective capture of CO2 from offgas is highly important for our sustainability, including mitigating global warming. Here, we investigated the CO2 and N2 adsorption under low pressure by using a mesoporous Zr-based metal organic framework PCN-777 with or without modification with polymers like polyethyleneimine (PEI) and polystyrene (PS). The polymers were applied in this study in order to reduce the pore size of PCN-777 (P777) and to introduce basic sites when PEI was used. PCN-777 s loaded with both the PEI and PS were effective in CO2 adsorption because of reduced pore size; and [email protected] s were highly effective in CO2 capture owing to basic sites on PEI. For example, the best adsorbent (among the studied PCN-777-based adsorbents), PEI(20%)@P777, showed around 2.3 and 5.7 times of adsorption capacity (at 0.15 atm) and selectivity (CO2/N2), respectively, as much as those of the pristine P777. Moreover, this MOF is recyclable and has the recommended heat of adsorption when adsorbed CO2 is not much. Therefore, it might be suggested that mesoporous MOFs, not suitable for CO2 capture under low pressure (because of too big pore), can be modified facilely for effective CO2 adsorption (especially under low pressure of 1 atm or less) by loading polymers with basicity onto the mesoporous MOFs.

Optimization studies and artificial neural network modeling for pyrene adsorption onto UiO-66(Zr) and NH2-UiO-66(Zr) metal organic frameworks

Optimization studies was conducted for the pyrene (PYR) adsorption onto Zr-based metal organic frameworks (MOFs), UiO-66(Zr) and NH2-UiO-66(Zr) in aqueous medium. Central composite design (CCD) model has shown good fittings of the coefficient of determination (R2) with non-significant lack of fit for both UiO-66(Zr) and NH2-UiO-66(Zr) MOFs. The optimized adsorption efficiency achieved by the UiO-66(Zr) and NH2-UiO-66(Zr) were 99.22 and 95.67% respectively. Artificial neural network (ANN) model was able to predict the experimental findings with high precision at topographic node of 5-4-2 structural layer. The kinetics and isotherms of the process was best described by pseudo-second-order Langmuir models respectively. The process was exothermic and spontaneous with the good reusability of the MOFs.

Au–Pt bimetallic nanoparticle catalysts supported on UiO-67 for selective 1,3-butadiene hydrogenation

Bimetallic nanoparticle (NP)-supported catalysts for use in the hydrogenation reaction has received growing attention on account their excellent catalytic performance. In the present work, bimetallic Au–Pt and monometallic Pt/Au NPs were supported on the Zr-based metal–organic framework UiO-67 via a simple impregnation–reduction method. The catalytic performance of the catalysts for selective 1,3-butadiene (1,3-BD) hydrogenation was influenced by the space velocity, reaction temperature and Au/Pt molar ratio. Whilst bimetallic AuPt/UiO-67-3 displayed catalytic activity similar to that of Pt/UiO-67 for selective 1,3-BD hydrogenation, the former also exhibited much higher selectivity toward total butenes than the latter. The AuPt/UiO-67-3 catalyst with a 1.1:1.0 Au/Pt molar ratio exhibited the best catalytic activity and butene selectivity for selective 1,3-BD hydrogenation at 100 °C with a space velocity of 117 L/(h gcat).This work provides a practical example of novel and efficient bimetallic supported catalysts.

Defect Control in Zr-Based Metal–Organic Framework Nanoparticles for Arsenic Removal from Water

In this study, water-stable Zr-metal–organic framework (MOF) (UiO-66) nanoparticles of various defect concentrations were successfully prepared and examined as the adsorbent for arsenate removal fr...

Nucleophilic versus Electrophilic Activation of Hydrogen Peroxide over Zr-Based Metal-Organic Frameworks.

Zr-based metal-organic frameworks (Zr-MOF) UiO-66 and UiO-67 catalyze thioether oxidation in nonprotic solvents with unprecedentedly high selectivity toward corresponding sulfones (96-99% at ca. 50% sulfide conversion with only 1 equiv of H2O2). The reaction mechanism has been investigated using test substrates, kinetic, adsorption, isotopic (18O) labeling, and spectroscopic tools. The following facts point out a nucleophilic character of the peroxo species responsible for the superior formation of sulfones: (1) nucleophilic parameter XNu = 0.92 in the oxidation of thianthrene 5-oxide and its decrease upon addition of acid; (2) sulfone to sulfoxide ratio of 24 in the competitive oxidation of methyl phenyl sulfoxide and p-Br-methyl phenyl sulfide; (3) significantly lower initial rates of methyl phenyl sulfide oxidation relative to methyl phenyl sulfoxide (kS/kSO = 0.05); and (4) positive slope ρ = +0.42 of the Hammett plot for competitive oxidation of p-substituted aryl methyl sulfoxides. Nucleophilic activation of H2O2 on Zr-MOF is also manifested by their capability of catalyzing epoxidation of electron-deficient C═C bonds in α,β-unsaturated ketones accompanied by oxidation of acetonitrile solvent. Kinetic modeling on methyl phenyl sulfoxide oxidation coupled with adsorption studies supports a mechanism that involves the interaction of H2O2 with Zr sites with the formation of a nucleophilic oxidizing species and release of water followed by oxygen atom transfer from the nucleophilic oxidant to sulfoxide that competes with water for Zr sites. The nucleophilic peroxo species coexists with an electrophilic one, ZrOOH, capable of oxygen atom transfer to nucleophilic sulfides. The predominance of nucleophilic activation of H2O2 over electrophilic one is, most likely, ensured by the presence of weak basic sites in Zr-MOFs identified by FTIR spectroscopy of adsorbed CDCl3 and quantified by adsorption of isobutyric acid.

Selective CO2 adsorption over functionalized Zr-based metal organic framework under atmospheric or lower pressure: Contribution of functional groups to adsorption

Selective capture of CO2 from offgas is important to mitigate the global warming; and metal organic frameworks (MOFs) have been attractive in the capture because of huge porosity, ready functionalization and so on. In this study, a stable Zr-based MOF, MOF-808, was modified with ethylenediaminetetraacetic acid (EDTA) and further reacted with ethylenediamine (ED); and finally reduced with lithium aluminum hydride (LAH) to introduce several functional groups (FGs) onto the MOF. Moreover, the MOFs were applied in CO2 adsorption under low pressure. The efficiency of MOF-808 in CO2 capture was improved with EDTA loading; however, interestingly, further reaction of MOF-808-EDTA with ED causes a very much decrease in the efficiency. Importantly, the reduction of MOF-808-EDTA-ED with LAH (for MOF-808-EDTA-ED-R) leads to a remarkable increase in the performance of the MOF, for high CO2 adsorption capacity, CO2/N2 selectivity and isosteric heat of adsorption. For example, MOF-808, MOF-808-EDTA, MOF-808-EDTA-ED and MOF-808-EDTA-ED-R showed CO2/N2 IAST selectivity (from CO2/N2 = 15/75) of 40, 48, 19 and 197, respectively, under 298 K and 1 atm. This unusual observation could be explained with the contribution of FGs and porosity. Or, amides in cyclic rings might be formed during reaction with ED; and the MOF with amides was poor in CO2 capture partly due to decreased porosity of the MOF; however, can be very effective in adsorption, after further reduction of amides to amines. This work shows the importance of modifications or FGs on MOFs in CO2 adsorption, or a simple reduction can increase the adsorption selectivity as much as 10 times, which might be helpful to mitigate the global warming.

Self-Assembly of Imidazolium-Functionalized Zr-Based Metal-Organic Polyhedra for Catalytic Conversion of CO2 into Cyclic Carbonates.

Three cationic capsule-shaped Zr-based metal-organic polyhedra (MOPs) with different cavity sizes were successfully constructed through the self-assembly of trinuclear zirconocene clusters and imidazolium-functionalized dicarboxylic ligands. Owing to the imidazolium groups in the MOPs, they show good CO2 adsorption uptake. Moreover, the halogen anions of the imidazolium groups and Brønsted acid sites (-OH) in the Zr-based knots are in close proximity, making these MOPs able to catalyze synergistically the cycloaddition reaction of CO2 with epoxides into cyclic carbonates. This is the first report of using MOPs as catalysts for this reaction without the addition of a cocatalyst.

Microwave-assisted acid-induced formation of linker vacancies within Zr-based metal organic frameworks with enhanced heterogeneous catalysis

Herein, we report a microwave-assisted acid-induced post-treatment method for the formation of linker vacancies within Zr-based metal organic frameworks (Zr-MOFs). The number of linker vacancies can be easily regulated with this method by changing the concentration of the HCl solution and the duration of microwave irradiation. The optimized defective UiO-66 showed higher linker defects with a higher specific surface area and thermal stability. The results of the catalytic cyclization of citronella showed that the Zr-MOFs with more defects exhibited enhanced catalytic performance. This work may provide a new method for the creation of defective MOFs with high activity and stability.

Removal of Particulate Matters with Isostructural Zr-Based Metal-Organic Frameworks Coated on Cotton: Effect of Porosity of Coated MOFs on Removal.

Effective removal of particulate matters (PMs) from air is very important for our safe environment, health, and sustainability. In this study, isostructural (with the same topology of fcu) Zr-metal-organic frameworks (Zr-MOFs) such as UiO-66, UiO-67, and DUT-52 (with different porosity) were coated onto cotton and utilized in PM removal from air to understand the contribution of MOFs in improving the performances of air filters. Moreover, UiO-66s with different porosities were also prepared under different conditions from the same reaction mixture. Experiments to remove PMs such as PM2.5 and PM10 showed a critical role of porosity of coated MOFs in the PM removal. Or, the removal efficiency or quality factor increased linearly with the increasing surface area of all the studied MOFs, irrespective of the applied linkers (for synthesizing different MOFs) and synthesis conditions (for different porosities of UiO-66s). Therefore, this work confirms, for the first time, that the porosity of MOF is one of the most important parameters to improve the performance of air filter (to remove PMs) that is modified with coated MOFs. Moreover, we could suggest why porous materials with small pores were effective in capturing PMs (larger in size than pores of porous materials) from air.

Using MOF-808 as a Promising Support to Immobilize Ru for Selective Hydrogenation of Levulinic Acid to γ-Valerolactone

A stable Zr-based metal–organic framework (MOF), MOF-808, was used as a promising support to immobilize metallic Ru for the first time. The skeleton structure of MOF-808 can be well preserved during the immobilization process. Ru nanoparticles existed both inside and outside of the MOF cavities with good dispersion. The developed Ru/MOF-808 composite was found to be an efficient catalyst for the hydrogenation of biomass-derived levulinic acid (LA) to γ-valerolactone (GVL). Under mild reaction conditions, full conversion of LA (100%) with high selectivity to GVL (> 99%) was achieved. The catalyst recycling and hot filtration experiments indicate that Ru/MOF-808 possesses a good catalytic stability for the LA hydrogenation reaction, although some catalyst structure changes were observed. The good immobilization effect of MOF-808 for Ru may be related to the high binding affinity between the Zr6 nodes and Ru particles.

Topology-Based Functionalization of Robust Chiral Zr-Based Metal-Organic Frameworks for Catalytic Enantioselective Hydrogenation.

The design and development of robust and porous supported catalysts with high activity and selectivity is extremely significant but very challenging for eco-friendly synthesis of fine chemicals and pharmaceuticals. We report here the design and synthesis of highly stable chiral Zr(IV)-based MOFs with different topologies to support Ir complexesand demonstrate their networkstructures-dependent asymmetric catalytic performance. Guided by the modulated synthesis and isoreticular expansion strategy, five chiral Zr-MOFs with a flu or ith topology are constructed from enantiopure 1,1'-biphenol-derived tetracarboxylate linkers and Zr6, Zr9, or Zr12 clusters. The obtained MOFs all show high chemical stability in boiling water, strongly acidic, and weakly basic aqueous solutions. The two flu MOFs featuring the dihydroxyl groups of biphenol in open and large cages, after sequential postsynthetic modification with P(NMe2)3 and [Ir(COD)Cl]2, can be highly efficient and recyclable heterogeneous catalysts for hydrogenation of α-dehydroamino acid esters with up to 98% ee, whereas the three ith MOFs featuring the dihydroxyl groups in small cages cannot be installed with P(NMe2)3 to support the Ir complex. Incorporation of Ir-phosphorus catalysts into Zr-MOFs leads to great enhancement of their chemical stability, durability, and even stereoselectivity. This work therefore not only advances Zr-MOFs as stable supports for labile metal catalysts for heterogeneous asymmetric catalysis but also provides a new insight into how highly active chiral centers can result due to the framework topology.

A Synergic Activity of Urea/Butyl Imidazolium Ionic Liquid Supported on UiO-66-NH2 Metal–Organic Framework for Synthesis of Oximes

An efficient supported ionic liquid catalyst is designed for condensation reaction of aldehydes and ketones. The Zr-based metal–organic framework (MOF), UiO-66-NH2, was initially functionalized with N,N′-dibutyl imidazolium ionic liquid (UiO-66-NH2-ILBr–), and then urea was attached to the ionic liquid (IL) to form a task-specific IL. Bromide was exchanged with tetrafluoroborate and the catalyst exhibits excellent performance for the synthesis of oximes. The ionic liquid/urea coupling showed a synergistic effect on the efficiency of the reaction. The supported catalyst system was recycled simply by filtration and reused for five times without significant decrease in its activity. The catalyst was characterized with PXRD, FTIR, TGA, XPS, BET, FE-SEM, EDS, elemental mapping and elemental analysis (CHN). MOF/IL/urea catalytic system was used for the synthesis of oximes

Iodine Capture Using Zr-Based Metal-Organic Frameworks (Zr-MOFs): Adsorption Performance and Mechanism.

The effective capture of radioiodine, produced or released from nuclear-related activities, is of paramount importance for the sustainable development of nuclear energy. Here, a series of zirconium-based metal-organic frameworks (Zr-MOFs), with a Zr6(μ3-O)4(μ3-OH)4 cluster and various carboxylate linkers, were investigated for the capture of volatile iodine. Their adsorption kinetics and recyclability were investigated in dry and humid environments. The structural change of Zr-MOFs during iodine trapping was studied using powder X-ray diffraction and pore structure measurements. Experimental spectra (Raman and X-ray photoelectron spectroscopy) and density functional theory (DFT) calculations for the linkers and Zr clusters were performed to understand the trapping mechanism of the framework. When interacting with iodine molecules, MOF-808, NU-1000, and UiO-66, with highly connected and/or rigid linkers, have better structural stability than UiO-67 and MOF-867, which have flexible linkers with less connectivity. Particularly, MOF-808, with a rigid and tritopic benzenetricarboxylate linker, has the highest iodine adsorption capacity (2.18 g/g, 80 °C), as well as the largest pore volume after iodine elution. In contrast, UiO-67, with long linear ditopic linkers, exhibits the weakest stability and lowest adsorption capacity (0.53 g/g, 80 °C) because of its most serious collapse of pore structures. After incorporating with strong electron-donating imidazole/pyridine ligands, both the stability and adsorption capacity of MOF-808/NU-1000 decrease. DFT calculations verify that the N-heterocycle groups could enhance the affinity toward iodine by strong charge transfer. DFT calculations also suggest that the terminal -OH in MOF-808 has a strong affinity toward iodine (-54 kJ/mol I2) and water (-63 kJ/mol H2O) and a weak affinity toward NO2 (-27 kJ/mol NO2). With high adsorption capacity and excellent stability, MOF-808 shows great potential for the sustainable removal of radioiodine.

High-efficiency adsorption of norfloxacin using octahedral UIO-66-NH2 nanomaterials: Dynamics, thermodynamics, and mechanisms

Antibiotics abuse has been a significant threat to the environment and human health. In this study, we successfully synthesized highly stable amino-functionalized Zr-based metal–organic frameworks (UiO-66-NH2) and studied the adsorption behaviors of norfloxacin (NOR) in water. The adsorption capacities of UiO-66-NH2 reached a maximum of 222.5 mg/g for NOR, which were considerably higher than that of most reported adsorbents. Moreover, the equilibrium time (6 h) was less than that of several previously reported adsorbents. Ionic-strength-influenced experiments showed that NaCl and CaCl2 aqueous solutions could improve the removal efficiency of NOR. The presence of humic acid could barely affect the adsorption amount. At a concentration of 10 mg/L, the highest partition coefficient of 20.9 mg/g/µM was obtained, and the removal rate of NOR was as high as 91.6%, implying that UiO-66-NH2 offered considerable adsorption performance at a low concentration of NOR. In addition, UiO-66-NH2 exhibited good regeneration efficiency, thus offering the possibility to remove norfloxacin from sewage. Finally, several credible adsorption mechanisms were proposed. The results will aid us to comprehend the surface interaction between organic micropollutants and UiO-66-NH2 and prefigure the potential of UiO-66-NH2 as a novel adsorbent for the removal of NOR.