Terephthalate Metal Organic Framework Research Articles

Removal of Toxic Metal Ions from Sungun Acid Rock Drainage Using Mordenite Zeolite, Graphene Nanosheets, and a Novel Metal–Organic Framework

We evaluated the sorptive properties of mordenite zeolite (MOR), a copper terephthalate metal–organic framework (MOF), and graphene oxide (GO) and their potential use in treating acid rock drainage (ARD) containing Fe3+, Cu2+, Mn2+, Zn2+, Pb2+, and Cd2+ ions. MOR was prepared via a hydrothermal method, MOF was prepared via a solvothermal method, and few-layered GO nanosheets were synthesized using Hummers’ method. The aqueous contaminants were removed by chemico-physical sorption and ion exchange in batch tests. It proved possible to dramatically improve removal efficiency and sorptive capacity by optimizing experimental conditions. Magnetic MOF crystals were more efficient in removing metals than the MOR and GO. Sorption tests using ARD from the Sungun copper mine and a multi-component solution containing cationic metal species revealed that both GO nanosheets and magnetic MOF have great potential for ARD treatment.

Formation Mechanism of the Secondary Building Unit in a Chromium Terephthalate Metal–Organic Framework

A detailed mechanism, based on density functional theory calculations and simulation, is presented outlining the formation of the secondary building unit (SBU) of MIL-101, a chromium terephthalate metal organic framework (MOF). Formation of the metal core and of the SBU is key to MOF nucleation, the rate-limiting step in the synthesis process of many MOFs. A series of reactions that lead to the formation of the SBU of MIL-101 is proposed in this work. The highest barrier (∼35 kcal/mol) involves the formation of a dimetal-linker intermediate and high to low spin transition as a third Cr-linker moiety joins to form a three metal-linker group joined by a central oxygen. The terephthalate linkers play an important, key mechanistic role with the carboxylates first joining chromium atoms prior to the formation of bridging oxygens. Subsequent to metal core formation, stepwise linker addition reactions generate different assembly pathways due to structural isomers that are limited by the removal of water molecule...

Chromium terephthalate metal–organic framework MIL-101: synthesis, functionalization, and applications for adsorption and catalysis

The chromium terephthalate metal–organic framework, MIL-101 (MIL, Material Institut Lavoisier), is comprised of trimeric chromium(III) octahedral clusters interconnected by 1,4-benzenedicarboxylates, resulting in a highly porous 3-dimentional structure. The large pores (29 and 34 A) and high BET surface area (>3000 m2 g−1) with a huge cell volume (≈702 000 A3) together with the coordinatively unsaturated open metal sites that can be subjected to diverse post-synthesis functionalization or guest encapsulation, and excellent hydrothermal/chemical stability, make MIL-101 particularly attractive for applications, such as selective gas adsorption/separation, energy storage and heterogeneous catalysis. This paper reviews the current status of research and development on the synthesis, functionalization and applications of MIL-101 for adsorption/catalytic reactions.

Detailed Structure Analysis of Atomic Positions and Defects in Zirconium Metal–Organic Frameworks

We report the structure of the Zr metal–organic frameworks (MOFs) UiO-66 and UiO-67 to very fine detail using synchrotron single-crystal X-ray diffraction and the synthesis method used to obtain single crystals. Zr terephthalate MOF UiO-66 is known to have missing linkers, and the nature of these are shown to be coordinating water and solvent molecules. Single crystals of the isoreticular material UiO-67 does not show such missing linker defects.

Highly Dispersible and Stable Copper Terephthalate Metal–Organic Framework–Graphene Oxide Nanocomposite for an Electrochemical Sensing Application

A highly dispersible and stable nanocomposite of Cu(tpa)-GO (Cu(tpa) = copper terephthalate metal-organic framework, GO = graphene oxide) was prepared through a simple ultrasonication method. The morphology and structure of the obtained composite were characterized via scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV-vis, Fourier-transform infrared (FT-IR), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). On the basis of the characterization results, the binding mechanism of the Cu(tpa) and GO was speculated to be the cooperative interaction of π-π stacking, hydrogen bonding, and Cu-O coordination. The electrochemical sensing property of Cu(tpa)-GO composite was investigated through casting the composite on a glassy carbon electrode (GCE), followed by an electro-reduction treatment to transfer the GO in the composite to the highly conductive reduced form (electrochemically reduced graphene, EGR). The results demonstrated that the electrochemical signals and peak profiles of the two drugs of acetaminophen (ACOP) and dopamine (DA) were significantly improved by the modified material, owing to the synergistic effect from high conductivity of EGR and unique electron mediating action of Cu(tpa). Under the optimum conditions, the oxidation peak currents of ACOP and DA were linearly correlated to their concentrations in the ranges of 1-100 and 1-50 μM, respectively. The detection limits for ACOP and DA were estimated to be as low as 0.36 and 0.21 μM, respectively.

Brønsted Instead of Lewis Acidity in Functionalized MIL-101Cr MOFs for Efficient Heterogeneous (nano-MOF) Catalysis in the Condensation Reaction of Aldehydes with Alcohols

Porous chromium(III) 2-nitro-, 2-amino-, and nonfunctionalized terephthalate (MIL-101Cr) metal organic frameworks are heterogeneous catalysts for diacetal formation from benzaldehyde and methanol (B-M reaction) as well as other aldehydes and alcohols. MIL-101Cr-NO2 obtained by direct reaction between CrO3 and 2-nitro-terephthalate showed the highest activity with 99% conversion in the B-M reaction in 90 min and turnover numbers of 114. The activity decreased in the order MIL-101Cr-NO2 > MIL-101Cr > MIL-101Cr-NH2. Within different samples of nonfunctionalized MIL-101Cr the activity increased with surface area. Methanol gas sorption of the different MIL materials correlates with the BET surface area and pore volume but not with the diacetalization activity. Benzaldehyde adsorption from heptane showed no significant difference for the different MILs. Gas sorption studies of CD3CN to probe for a higher Lewis acidity in MIL-101Cr-NO2 remained inconclusive. A high B-M catalytic activity of wet MIL-101Cr-NO2 excluded significant contributions from coordinatively unsaturated Lewis-acid sites. pH measurements of methanol dispersions of the MIL materials gave the most acidic pH (as low as 1.9) for MIL-101Cr-NO2, which significantly increased over MIL-101Cr (3.0) to MIL-101Cr-NH2 (3.3). The increase in acidity is of short range or a surface effect to the heterogeneous MIL particles as protons dissociating from the polarized aqua ligands (Cr-OH2) have to stay near the insoluble counteranionic framework. The variation in Brønsted acidity of MIL-101Cr-NO2 > MIL-101Cr ≈ MIL-101Cr-NH2 correlates with the withdrawing effect of NO2 and the diacetalization activity. The catalytic B-M activity of soluble, substitution-inert, and acidic Cr(NO3)3·9H2O supports the Brønsted-acid effect of the MIL materials. Filtration and centrifugation experiments with MIL-101Cr-NO2 revealed that about 2/3 of the catalytic activity comes from nano-MOF particles with a diameter below 200 nm. The MIL-101Cr-NO2 catalysts can be recycled five times with very little loss in activity. The diacetalization activity of MIL-101Cr-NO2 decreases with the alcohol chain length from methanol over ethanol, n-propanol, n-butanol, to almost inactive n-pentanol, while conversions for benzaldehyde, paratolylaldehyde, 4-chlorobenzaldehyde, and cyclohexanone all reach 90% or more after 90 min.

Correlated defect nanoregions in a metal–organic framework

Throughout much of condensed matter science, correlated disorder is key to material function. While structural and compositional defects are known to exist within a variety of metal–organic frameworks, the prevailing understanding is that these defects are only ever included in a random manner. Here we show—using a combination of diffuse scattering, electron microscopy, anomalous X-ray scattering, and pair distribution function measurements—that correlations between defects can in fact be introduced and controlled within a hafnium terephthalate metal–organic framework. The nanoscale defect structures that emerge are an analogue of correlated Schottky vacancies in rocksalt-structured transition metal monoxides and have implications for storage, transport, optical and mechanical responses. Our results suggest how the diffraction behaviour of some metal–organic frameworks might be reinterpreted, and establish a strategy of exploiting correlated nanoscale disorder as a targetable and desirable motif in metal–organic framework design.

Copper‐Based Metal–Organic Frameworks as Reusable Heterogeneous Catalysts for the One‐Pot Syntheses of Imidazo[1,2‐a]pyridines

AbstractA copper terephthalate metal–organic framework (Cu(BDC) MOF, BDC=1,4‐benzenedicarboxylate) is used as a highly efficient heterogeneous catalyst for the one‐pot, atom‐economical synthesis of imidazo[1,2‐a]pyridines that proceeds through the three‐component coupling of aldehydes, aminopyridines, and nitromethane. This heterocyclic synthesis, which uses MOFs for the first time, involves an intermolecular aza‐Michael addition with a subsequent intramolecular cyclization and uses air as an environmentally benign oxidant. This heterogeneous Cu(BDC) MOF can be reused without the loss of its activity. Its catalytic efficiency was also highlighted by comparing it with other catalytic systems that have been used for the syntheses of imidazo[1,2‐a]pyridines. This procedure not only eliminates the use of environmentally hazardous reagents but also involves mild reaction conditions.

Pd Nanoparticles Supported on MIL-101: An Efficient Recyclable Catalyst in Oxidation and Hydrogenation Reactions

Pd nanoparticles supported on the chromium terephthalate metal organic framework MIL-101 (Pd/MIL-101) in different loadings (0.9 and 4.5 wt%) have been successfully prepared through a simple Pd-acetate adsorption and reduction in acetone, and tested as catalyst for selected liquid phase oxidation and hydrogenation reactions. The materials were characterized by XRD, N2 adsorption--desorption isotherm, TEM, SEM-EDX and ICP analysis. The parent MIL-101 structure was found well preserved after formation of Pd nanoparticles and after catalytic reaction runs. The present catalyst afforded good activity and selectivity for the oxidation of benzyl alcohol to benzaldehyde with 85% conversion and 97% selectivity using air (1 atm) at 85 degrees C after 14 h. The catalyst also showed good activity in the hydrogenation of the C=C bond in alkenes to corresponding alkanes and also benzaldehyde to benzyl alcohol at room temperature using H2 (1 atm). Rigorous test results confirmed that Pd-nanoparticles supported on MIL-101 are responsible for the catalytic reactions occurred. Pd/MIL-101 was reusable several times without losing the structural integrity and initial activity, and demonstrated significantly higher catalytic activities than those by a commercial Pd catalyst supported on activated carbon.

Cr-MIL-101 encapsulated Keggin phosphotungstic acid as active nanomaterial for catalysing the alcoholysis of styrene oxide

Mesoporous chromium-based terephthalate metal–organic framework (MIL-101) encapsulated Keggin phosphotungstic acid (HPW) [MIL-101(HPW)] was demonstrated to be an active heterogeneous catalyst for selective catalysis of the ring opening reaction of styrene oxide with methanol, achieving 99% yield of 2-methoxy-2-phenylethanol in 20 minutes at 40 °C. Similar MIL-101 samples prepared using one-pot microwave synthesis in the absence of HPW or in the presence of hydrofluoric acid (HF) were less active. The impact of fluoride and HPW polyanion incorporation on the acidity of MIL-101 was investigated by the in situ infrared spectroscopy technique using CO as a probe molecule. Additional hydroxyl groups and Lewis acid sites are present in MIL-101(HPW) explaining the observed superior catalytic performance in styrene oxide methanolysis.

Oxidative catalytic versatility of a trivacant polyoxotungstate incorporated into MIL-101(Cr)

The first immobilization of the trivacant Keggin-type polyoxometalate ([A-PW9O34]9−, PW9) to prepare a novel heterogeneous oxidative catalyst is here reported. PW9 was incorporated into the cavities of the chromium terephthalate metal–organic framework MIL-101(Cr). Characterization of the composite PW9@MIL-101 by powder X-ray diffraction, SEM-EDX, FT-IR, FT-Raman spectroscopy, N2 adsorption–desorption isotherms and 31P solid-state NMR confirmed that the structures of MIL-101 and the polyoxometalate anion were retained after immobilization. The composite PW9@MIL-101 revealed versatility as a heterogeneous catalyst to oxidize efficiently monoterpenes as well as to reach a complete desulfurization of a model oil containing the most refractory sulfur compounds in fuel, using in both systems acetonitrile as the solvent and H2O2 as the oxidant. Complete conversion of geraniol to 2,3-epoxygeraniol was achieved after the first 30 min at room temperature, while the total desulfurization of the model oil containing 1707 ppm of sulfur was attained after 2 h. In both systems the catalyst was recyclable for various cycles without a significant loss of activity. The stability and heterogeneity of the catalyst were confirmed by several techniques and by leaching tests.

Iron terephthalate metal–organic framework: Revealing the effective activation of hydrogen peroxide for the degradation of organic dye under visible light irradiation

Metal–organic frameworks (MOFs), a new class of porous crystalline materials, have attracted great interest as a promising candidate for sustainable energy and environmental remediation. In this study, we demonstrate that an iron terephthalate metal–organic framework MIL-53(Fe) synthesized by a facile solvothermal reaction was capable of activating hydrogen peroxide (H2O2) to achieve high efficiency in photocatalytic process. It could completely decompose the 10mgL−1 Rhodamine B (RhB) in the presence of a certain amount of H2O2 under visible light irradiation within 50min. The catalytic activities were found to be strongly affected by the various operating parameters, such as solution pH, initial dye concentration, and H2O2 dosage. The activation effects of MIL-53(Fe) were investigated through the detection of hydroxyl radicals (OH) and transient photocurrent responses, which revealed that the H2O2 behaved in two ways during the catalytic process: (i) it could be catalytically decomposed by MIL(Fe)-53 to produce OH radicals through the Fenton-like reaction; (ii) it could capture the photogenerated electrons in the conduction band of excited MIL-53(Fe) to form OH radicals under visible light irradiation. The ability of such iron-based MOFs to activate H2O2 may enable rational design of advanced MOF-based catalysts for environmental remediation.

Nano-rod catalysts: Building MOF bottles (MIL-101 family as heterogeneous single-site catalysts) around vanadium oxide ships

Porous materials based on chromium (III) terephthalate metal organic frameworks (Cr-MIL(101)) and their new composites with vanadium oxide has emerged as a potential catalyst because of its high specific surface area, tunable pore size, and unique structure. The structural and textural characterization of V@MIL(101) were done using FTIR, X-ray diffraction, N2 adsorption–desorption, and TEM. XRD and adsorption–desorption analysis shows that the mesostructure of MIL-101 remains intact after vanadium oxide modifications, while spectral technique show the successful immobilizing of the neat vanadium oxide inside the MIL-101 cavities. These new catalysts were found to be highly effective for selective oxidation of sulfides to sulfoxides and sulfones with H2O2 at room temperature and the 4.2% V@MIL(101) catalyst showed the highest activity. The PW12@MCFim heterogeneous system showed high catalytic oxidative activity in the treatment of commodity gasoline.

Highly stable chromium(III) terephthalate metal organic framework (MIL-101) encapsulated 12-tungstophosphoric heteropolyacid as a water-tolerant solid catalyst for hydrolysis and esterification

A heterogeneous catalyst, chromium(III) terephthalate metal organic framework (MIL-101) encapsulated 12-tungstophosphoric heteropolyacid (HPW), HPW@MIL-101, was prepared by a simple one-step hydrothermal reaction of aqueous mixtures of Cr(NO3)3, terephthalic acid, and HPW. The obtained catalyst was systemically characterized by XRD, N2 adsorption, FT-IR, acid–base titration, and 31P MAS NMR techniques as well as by elemental analysis. The catalytic activity and reusability of HPW@MIL-101 were evaluated in the liquid-phase hydrolysis of ethyl acetate and in esterification of acetic acid with n-hexanol. In both reactions, water exists as a reactant/solvent and as a product. HPW@MIL-101 shows a high activity and excellent reusability in both of the reactions, behaving as a water-tolerant heterogeneous acid catalyst without agglomeration, leaching and deactivation of HPW during its repeated use. The unique characteristics of MIL-101 and the well-dispersed level of HPW confined as noncoordinating guests in the mesoporous cages of the MIL-101 matrix with the integrated protonic acidity of HPW may account for the high catalytic properties of HPW@MIL-101.

Organophophorous Ester Degradation by Chromium(III) Terephthalate Metal–Organic Framework (MIL-101) Chelated to N,N-Dimethylaminopyridine and Related Aminopyridines

Porous materials based on chromium(III) terephthalate metal organic frameworks (MOF) MIL-101(Cr) and their complexes with dialkylaminopyridines (DAAP) were synthesized via a DAAP-MOF complexation, and tested for hydrolytic degradation of organophosphorous esters such as diethyl 4-nitrophenyl phosphate (paraoxon). Elemental analysis, TGA, XRD, FT-IR, TEM, SEM, and nitrogen adsorption measurements indicated that the DAAP units were incorporated into MIL-101 pores by complexation, keeping the parent framework intact. The DAAP-MOF enabled facile paraoxon hydrolysis in water/acetonitrile mixtures under ambient conditions (100% conversion after 24 h at pH 10). The MOF-DAAP complexes showed synergistic effects, being 7-fold and 47-fold more active than the parent MIL-101 or DAAP materials, respectively. The high hydrolysis reaction turnover was realized by simultaneous action of the Lewis acid Cr(III) center of the MOF as well as the electron-rich nucleophile, DAAP. This study demonstrates a simple and efficient method of generating catalytically active MOF materials for environmental detoxification as well as defensive applications.

Aldehyde-Alcohol Reactions Catalyzed under Mild Conditions by Chromium(III) Terephthalate Metal Organic Framework (MIL-101) and Phosphotungstic Acid Composites

Porous materials based on chromium(III) terephthalate metal organic frameworks (MIL-101) and their composites with phosphotungstic acid (PTA) were studied as heterogeneous acid catalysts in aldehyde-alcohol reactions exemplified by acetaldehyde-phenol (A-P) condensation and dimethylacetal formation from benzaldehyde and methanol (B-M reaction). The MIL-101 was synthesized solvothermically in water, and the MIL101/PTA composite materials were obtained by either impregnation of the already prepared MIL-101 porous matrix with phosphotungstic acid solution or by solvothermic treatment of aqueous mixtures of Cr(NO(3))(3), and terephthalic and phosphotungstic acids. The MIL101/PTA materials appeared to be effective catalysts for both A-P and B-M reactions occurring at room temperature, with half-lives ranging from 0.5 h (A-P) to 1.5-2 h (B-M) and turnover numbers over 600 for A-P and over 2900 for the B-M reaction, respectively. A synergistic effect of the strong acidic moieties (PTA) addition to mildly acidic Brønsted and Lewis acid cites of the MIL-101 was observed with the MIL101/PTA composites. The ability of the PTA and MIL101/PTA materials to strongly absorb and condense acetaldehyde vapors was discovered, with the MIL101/PTA absorbing over 10-fold its dry weight of acetaldehyde condensate at room temperature. The acetaldehyde was converted rapidly to crotonaldehyde and higher-molecular-weight compounds while in contact with MIL-101 and MIL101/PTA materials. The stability of the MIL-101 and MIL101/PTA catalysts was assessed within four cycles of the 1-day alcohol-aldehyde reactions in terms of the overall catalyst recovery, PTA or Cr content, and reaction rate constants in each cycle. The loss of the catalyst over 4 cycles was approximately 10 wt % for all tested catalysts due to the incomplete recovery and minute dissolution of the components. The reaction rates in all cycles remained unchanged and the catalyst losses stopped after the third cycle. The developed MIL101/PTA composites appear to be feasible for industrial catalytic applications.

Adsorption and Separation of Xylene Isomers and Ethylbenzene on Two Zn−Terephthalate Metal−Organic Frameworks

Metal−organic frameworks (MOFs) with metal-containing secondary building units and organic linkers have great potential for the separation of isomers. In this work, the adsorption and separation of xylene isomers and ethylbenzene (EB) on two Zn−terephthalate MOFs (MOF-5 and MOF-monoclinic) were studied by means of pulse gas chromatography, static vapor-phase adsorption, and breakthrough adsorption. The two studied Zn−terephthalate MOFs showed different selectivity and efficiency for the separation of xylene isomers and EB. On MOF-5, EB eluted first, while other isomers eluted at the same time. MOF-monoclinic showed a preferable adsorption of p-xylene over other isomers. The adsorption and separation of xylene isomers and EB were equilibrium-constant-controlled on MOF-5 and diffusion-dominated on MOF-monoclinic. On the basis of the measured McReynolds constants, MOF-5 was characterized as a stationary phase of nonpolarity, whereas MOF-monoclinic as a stationary phase of intermediate polarity for gas chroma...

Synthesis and Structure Characterization of Copper Terephthalate Metal–Organic Frameworks

AbstractIn this paper, we report on a high‐throughput (gram quantities) solvothermal method for the synthesis of copper terephthalate metal–organic frameworks in dmf. While the structure of MOF‐2 and some of the associated polymorphs are well known, we know of no equivalent structural studies for the isostructural copper terephthalate (Cu–tpa). The material we have made crystallizes in the C2/m space group. Cu–tpa also exhibits reversible solvent‐exchange properties. These properties make this material useful for potential applications in gas storage and catalysis applications. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Selective oxidation of tetralin over a chromium terephthalate metal organic framework, MIL-101

MIL-101, a mesoporous chromium terephthalate metal organic framework, was found to be an efficient heterogeneous catalyst for selective oxidation of tetralin to 1-tetralone using tert-butyl hydroperoxide or acylperoxy radicals generated in situ from trimethylacetaldehyde and O(2) as an oxidant.