Terephthalate Ligands Research Articles

Ultrarapid and Sustainable Synthesis of Trimetallic-Based MOF (CrNiFe-MOF) from Stainless Steel and Disodium Terephthalate-Derived PET Wastes.

Designing easy and sustainable strategies for the synthesis of metal-organic frameworks (MOFs) from organic and inorganic wastes with the efficient removal of phosphate from water remains a challenge. The majority of the reported works have utilized costly precursors and nonsoluble ligands for the synthesis of MOFs. Herein, we have developed a low-cost, simple, and sustainable alternative approach using the coprecipitation method in water at room temperature for the synthesis of a new adsorbent-based trimetallic MOF. Poly(ethylene terephthalate) and stainless steel wastes were used as sources of water-soluble disodium terephthalate ligand and three metallic species (chromium, nickel, and iron salts) for the fabrication of trimetallic MOF (CrNiFe-MOF), respectively. The newly developed MOF demonstrates a superior space-time yield of 5760 g m-3 day-1, reaching a level allowing the industrialization production of this sustainable MOF. The scanning electron microscopy and adsorption studies revealed that the developed trimetallic MOF consists of aggregated nanoparticles and the presence of defective as well as mesoporous structures. This MOF showed an enhanced adsorption capacity of phosphate from real eutrophic water samples and higher stability in a range of pHs. The density functional theory calculations evidenced that the phosphate ions preferentially adsorb over H2O toward the metal oxo-trimers, with the adsorption energies increasing from H3PO4 to PO43- species in line with an improvement of the adsorption performance of CrNiFe-MOF when the pH increases, i.e., when HPO42- and PO43- become more predominant. These calculations also supported that the incorporation of Cr metal sites in the oxo-trimer is expected to boost the phosphate affinity of the MOF. Finally, our work provides an easy and eco-friendly approach for MOF designing to enhance phosphate removal from water.

A Significant Two-Dimensional Structural Transformation in a Coordination Polymer that Changes Its Electronic and Protonic Behavior.

A 2D-to-2D (2D: two-dimensional) structural transformation accompanying significant bond rearrangement and coordination environment change is demonstrated in a coordination polymer (CP) comprised of copper(II) ions and terephthalate (BDC2- ) ligands for the first time. When immersed in water, a free-standing membrane of 2D Cu(BDC)(DMF) (Cu-1; DMF: N,N-dimethylformamide) transforms into 2D Cu(BDC)(H2 O)2 (Cu-2) while maintaining its highly oriented layered structure. In the 2D sheet, paddlewheel-type CuII dimers coordinated with four bidentate BDC ligands in a square-planar array in Cu-1 were released to form uniform aqua-bridged CuII chains, which are cross-linked with each other by unidentate BDC ligands, in Cu-2. The present facile approach to implement the 2D-to-2D transformation accompanied by bond rearrangement, which is characteristic of CPs, leads to a marked increase in in-plane magnetic susceptibility and proton conductivity. In situ experiments in support of theoretical calculations unveiled the energy diagram that governs the unique structural transformation.

A Significant Two‐Dimensional Structural Transformation in a Coordination Polymer that Changes Its Electronic and Protonic Behavior

AbstractA 2D‐to‐2D (2D: two‐dimensional) structural transformation accompanying significant bond rearrangement and coordination environment change is demonstrated in a coordination polymer (CP) comprised of copper(II) ions and terephthalate (BDC2−) ligands for the first time. When immersed in water, a free‐standing membrane of 2D Cu(BDC)(DMF) (Cu‐1; DMF: N,N‐dimethylformamide) transforms into 2D Cu(BDC)(H2O)2 (Cu‐2) while maintaining its highly oriented layered structure. In the 2D sheet, paddlewheel‐type CuII dimers coordinated with four bidentate BDC ligands in a square‐planar array in Cu‐1 were released to form uniform aqua‐bridged CuII chains, which are cross‐linked with each other by unidentate BDC ligands, in Cu‐2. The present facile approach to implement the 2D‐to‐2D transformation accompanied by bond rearrangement, which is characteristic of CPs, leads to a marked increase in in‐plane magnetic susceptibility and proton conductivity. In situ experiments in support of theoretical calculations unveiled the energy diagram that governs the unique structural transformation.

From polyethylene waste bottles to UIO-66 (Zr) for preconcentration of steroid hormones from river water

Metal–organic framework (UiO-66 (Zr) was synthesized using polyethylene terephthalate (PET) and used as an adsorbent for extraction and preconcentration of steroid hormones in river water. Polyethylene waste bottles were used as the source of polyethylene terephthalate (PET) ligands. The UIO-66(Zr), which the PET was made from recycled waste plastics, was used for the first time for the extraction and preconcentration of four different types of steroid hormones in river water samples. Various analytical characterization techniques were employed to characterize the synthesized material. The steroid hormones were detected and quantified using high-performance liquid chromatography coupled with diode array detector (HPLC–DAD). The results were further validated using ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS). Experimental variables, such as sample pH, the mass of adsorbent and extraction time, were optimized using Box-Behnken design (BBD). The dispersive solid phase extraction method combined with HPLC–DAD, displayed good linearity (0.004–1000 µg/L) low limits of detections (LODs, 1.1–16 ng/L for ultrapure water and 2.6–5.3 ng/L for river water) and limits of quantification (LOQs, 3.7–5.3 ng/L for ultrapure water and 8.7–11.0 ng/L for river water samples) and acceptable extraction recoveries (86–101%). The intraday (n = 10) and interday (n = 5) precisions expressed in terms of relative standard deviations (%RSD) were all less than 5%. The steroid hormones were detected in most of the river water samples (Vaal River and Rietspruit River). The DSPE/HPLC method offered a promising approach for simultaneous extraction, preconcentration and determination of steroid hormones in water.

Metal-Organic Framework Derived Terephthalate Ligand Decorated TiO2 with Various Morphologies for Efficient Photocatalytic H2 Evolution.

It has been rarely reported the morphological control of derivatives of metal-organic frameworks (MOFs) in hydrothermal conditions for photocatalytic applications. We report here a family of highly efficient composite photocatalysts composed of terephthalic acid/terephthalate (TPA) ligand and TiO2 with various morphologies (e. g., nanoparticles, nanosheets, and nanorods). The composites are synthesized by a simple one-step hydrothermal method in various solvents (i. e., H2 O, HF, H2 SO4 , HCl, and HNO3 ) using Ti-based MOF (MIL-125(Ti)) as precursor. The formation mechanism of composite materials with different morphological features is discussed. Impressively, the composite of TiO2 nanoparticles/TPA synthesized using H2 O as solvent under hydrothermal condition exhibits the highest photocatalytic H2 activity among the studied materials, with a photocatalytic H2 production rate of 6.38 mmol g-1 h-1 , which is approximately 7.5-fold higher than pure TiO2 (Degussa, P25) and prominent apparent quantum efficiency (AQE) of 65 % at 365 nm. Furthermore, the mechanism of boosted photocatalytic H2 production is discussed.

Carbon dioxide adsorption to UiO-66: theoretical analysis of binding energy and NMR properties.

UiO-66 is one of the most valuable metal-organic frameworks because of its excellent adsorption capability for gas molecules and its high stability towards water. Herein we investigated adsorption of carbon dioxide (CO2), acetone, and methanol to infinite UiO-66 using DFT calculations on an infinite system under periodic-boundary conditions and post-Hartree-Fock (SCS-MP2 and MP2.5) calculations on cluster models. Three to four molecules are adsorbed at each of four μ-OH groups bridging three Zr atoms in one unit cell (named Site I). Six molecules are adsorbed around three pillar ligands, where the molecule is loosely surrounded by three terephthalate ligands (named Site II). Also, six molecules are adsorbed around the pillar ligand in a different manner from that at Site II, where the molecule is surrounded by three terephthalate ligands (named Site III). Totally fifteen to sixteen CO2 molecules are adsorbed into one unit cell of UiO-66. The binding energy (BE) decreases in the order Site I > Site III > Site II for all three molecules studied here and in the order acetone > methanol ≫ CO2 in the three adsorption sites. At the site I, the protonic H atom of the μ-OH group interacts strongly with the negatively charged O atom of CO2, acetone and methanol, which is the origin of the largest BE value at this site. Although the DFT calculations present these decreasing orders of BE values correctly, the correction by post-Hartree-Fock calculations is not negligibly small and must be added for obtaining better BE values. We explored NMR spectra of UiO-66 with adsorbed CO2 molecules and found that the isotropic shielding constants of the 1H atom significantly differ among no CO2, one CO2 (at Sites I, II, or III), and fifteen CO2 adsorption cases (Sites I to III) but the isotropic 17O and 13C shielding constants change moderately by adsorption of fifteen CO2 molecules. Thus, 1H NMR measurement is a useful experiment for investigating CO2 adsorption.

Zn(II)-MOF derived N-doped carbons achieve marked ORR activity in alkaline and acidic media.

A highly efficient metal-free N-doped carbon electrocatalyst toward oxygen reduction was obtained by one-pot pyrolysis of a single Zn(II)-MOF with mixed azolate and terephthalate ligands, demonstrating E1/2 of 0.88 V (vs. RHE) in 0.1 M KOH, and 0.79 V (vs. RHE) in 0.5 M H2SO4. It represents one of the best metal-free N-doped carbon electrocatalysts for the acidic ORR.

Creating enzyme-mimicking nanopockets in metal-organic frameworks for catalysis.

Numerous efforts are being made toward constructing artificial nanopockets inside heterogeneous catalysts to implement challenging reactions that are difficult to occur on traditional heterogeneous catalysts. Here, the enzyme-mimetic nanopockets are fabricated inside the typical UiO-66 by coordinating zirconium nodes with terephthalate (BDC) ligands and monocarboxylate modulators including formic acid (FC), acetic acid (AC), or trifluoroacetic acid (TFA). When used in transfer hydrogenation of alkyl levulinates with isopropanol toward γ-valerolactone (GVL), these modulators endow zirconium sites with enhanced activity and selectivity and good stability. The catalytic activity of UiO-66FC is ~30 times that of UiO-66, also outperforming the state-of-the-art heterogeneous catalysts. Distinct from general consensus on electron-withdrawing or electron-donating effect on the altered activity of metal centers, this improvement mainly originates from the conformational change of modulators in the nanopocket to assist forming the rate-determining six-membered ring intermediate at zirconium sites, which are stabilized by van der Waals force interactions.

Sulfate removal by barium-terephthalate MOF synthesized from recycled PET-waste using Doehlert design optimization

In this study, barium-terephthalate metal–organic framework (Ba(BDC)) was synthesized as a new efficient adsorbent by an aqueous media method. Terephthalate ligand recovered from polyethylene terephthalate (PET) waste was used as a precursor in the synthesis process. Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), energy-dispersive X-ray (EDX), and field-emission scanning electron microscopy (FESEM) were applied to analyze the chemical and crystal structure of Ba(BDC). For the first time, the adsorption ability of this compound was investigated to remove sulfate ions from water. Experimental design optimization approach involving both screening the effective factors (i.e. pH, adsorbent dosage (m), initial concentration of sulfate ion (C), and temperature (T), except contact time (t)) and running Doehlert design was led to obtaining a regression model for the relation between the removal percent of sulfate ion (R%) and four effective factors as follows.R%=0.366pH-0.01328C+3.641m+0.2589T-0.02248pH2+0.000003C2-0.2991m2-0.003452T2+0.000437pH×C-0.01377pH×T-0.001821C×m+0.000102C×T The resulting model was employed for finding optimum conditions including T = 29 °C, pH = 2, m = 3.1 mg, and C = 200 mg+L−1 that maximize R% of sulfate ion to 99.43 value. Furthermore, kinetics, isotherms, and thermodynamics studies are complementary divisions of this research. Because of a non-linear R2 value closer to 1 (R2 = 0.9831), the Langmuir-Freundlich isotherm model better describes the adsorbent-adsorbate behavior and its maximum adsorption capacity is qmax of 549.5 mg·g−1. The kinetic experimental data obey the pseudo-second-order model (R2 = 0.9984). Based on the negative value of thermodynamic parameters including ΔH°, ΔS°, and ΔG°, the adsorption process is exothermic and spontaneous chemisorption at various temperatures (298, 308, 318, and 328 K).

Detection and Sorption of Heavy Metal Ions in Aqueous Media by a Fluorescent Zr(IV) Metal-Organic Framework Functionalized with 2-Picolylamine Receptor Groups.

Increasing global environmental pollution due to heavy metal ions raises the importance of research on new multifunctional materials for simultaneous detection and removal of these contaminants from water resources. In this study, we report a microporous 8-connected Zr4+ metal-organic framework (MOF) based on a terephthalate ligand decorated with a chelating 2-picolylamine side group (dMOR-2), which shows highly efficient fluorescence sensing and sorption of heavy metal cations. We demonstrate by detailed fluorescence studies the ability of a water-dispersible composite of dMOR-2 with polyvinylpyrrolidone for real-time detection of Cu2+, Pb2+, and Hg2+ in aqueous media. The limits of detection were found to be below 2 ppb for these species, while the system's performance is not affected by the presence of other potentially competitive ions. In addition, sorption studies showed that a composite of dMOR-2 with calcium alginate (dMOR-2@CaA) is an excellent sorbent for Pb2+ and Cu2+ ions with capacities of 376 ± 15 and 117 ± 4 mg per gram of dMOR-2@CaA, respectively, while displaying the capability for simultaneous removal of various heavy metal ions in low initial concentrations and in the presence of large excesses of other cationic species. Structural and spectroscopic studies with model ligands analogous to our material's receptor unit showed chelation to the 2-picolylamine moiety to be the main binding mode of metal ions to dMOR-2. Overall, dMOR-2 is shown to represent a rare example of a MOF, which combines sensitive fluorescence detection and high sorption capacity for heavy metal ions.

Experimental design optimization and isotherm modeling for removal of copper(II) by calcium‐terephthalate MOF synthesized from recycled PET waste

AbstractIn this research, a calcium‐terephthalate metal–organic framework ([Ca(BDC)(H2O)3]) was synthesized by a new high yield solvothermal method as an efficient adsorbent. Terephthalate ligand recovered from polyethylene terephthalate (PET) waste was used as a precursor in the synthesis process. The adsorption ability of this compound to remove copper(II) from aqueous solutions was investigated. Experimental designs involving Plackett–Burman and Doehlert designs were used for the optimization of the adsorption process. Plackett–Burman design was used for screening the effective factors such as pH, adsorbent dosage, and initial concentration of Cu(II). Running Doehlert design (DD) as an optimization approach led to find a model for relation between response and effective factors and maximized uptake capacity (q) of Cu(II) (q = 351.3 mg˖g−1) under optimum conditions (pH = 5, adsorbent dosage = 1.50 mg and initial concentration of Cu(II) = 150 mgL−1). Infrared spectroscopy (FTIR), X‐ray diffraction (XRD), energy‐dispersive X‐ray (EDX), and field‐emission scanning electron microscopy (FESEM) analyses were applied to investigate the chemical and crystal structure of [Ca(BDC)(H2O)3]. Furthermore, kinetics, isotherms, thermodynamics, and desorption studies are complementary divisions of this research.

From Operando Raman Mechanochemistry to "NMR Crystallography": Understanding the Structures and Interconversion of Zn-Terephthalate Networks Using Selective 17O-Labeling.

The description of the formation, structure, and reactivity of coordination networks and metal–organic frameworks (MOFs) remains a real challenge in a number of cases. This is notably true for compounds composed of Zn2+ ions and terephthalate ligands (benzene-1,4-dicarboxylate, BDC) because of the difficulties in isolating them as pure phases and/or because of the presence of structural defects. Here, using mechanochemistry in combination with operando Raman spectroscopy, the observation of the formation of various zinc terephthalate compounds was rendered possible, allowing the distinction and isolation of three intermediates during the ball-milling synthesis of Zn3(OH)4(BDC). An “NMR crystallography” approach was then used, combining solid-state NMR (1H, 13C, and 17O) and density functional theory (DFT) calculations to refine the poorly described crystallographic structures of these phases. Particularly noteworthy are the high-resolution 17O NMR analyses, which were made possible in a highly efficient and cost-effective way, thanks to the selective 17O-enrichment of either hydroxyl or terephthalate groups by ball-milling. This allowed the presence of defect sites to be identified for the first time in one of the phases, and the nature of the H-bonding network of the hydroxyls to be established in another. Lastly, the possibility of using deuterated precursors (e.g., D2O and d4-BDC) during ball-milling is also introduced as a means for observing specific transformations during operando Raman spectroscopy studies, which would not have been possible with hydrogenated equivalents. Overall, the synthetic and spectroscopic approaches developed herein are expected to push forward the understanding of the structure and reactivity of other complex coordination networks and MOFs.

Zr4+-terephthalate MOFs with 6-connected structures, highly efficient As(III/V) sorption and superhydrophobic properties.

The use of terephthalate ligands with CnH2n+1NH-chains (n ≥ 6) led to the isolation of the first examples of Zr4+-terephthalate MOFs with 6-connected frameworks. The material with hexyl-amino functional groups has been proved to be an exceptional sorbent for the removal of As(III/V) toxic species from aqueous media, whereas MOFs with heptyl to dodecyl-amino moieties are superhydrophobic with promising oil-water separation properties.

Facet Engineering in Ultrathin Two-Dimensional NiFe Metal–Organic Frameworks by Coordination Modulation for Enhanced Electrocatalytic Water Oxidation

Crystal facet engineering has been proved as a dramatically efficient strategy to optimize the intrinsic catalytic property of catalysts. However, because of the difficulty in precise construction, facet engineering of two-dimensional metal–organic frameworks (2D MOFs) is rarely reported. Herein, we propose a new and facile coordination modulation method to realize the controllable synthesis of 2D NiFe-MOFs with a highly exposed (001) crystal facet. Specifically, acetate ions, which possess the same coordination groups with the participated terephthalic ligand, have been adopted into the MOF construction as the morphology and facet regulator. Through competitive coordination effect and ion-induced self-assembly, the fabricated NiFe-MOFs reveal a hierarchical microsphere architecture consisting of ultrathin nanosheets with thickness ∼5 nm. Further benefiting from the structural advantages, e.g., abundant active sites, highly exposed catalytic facet, and enhanced mass/charge transport, the hierarchical NiFe-MOF nanosheets exhibit an attractive overpotential of 240 mV at the current density of 10 mA cm–2, a small Tafel slope of 73.44 mV dec–1, and satisfactory stability for 16 h toward oxygen evolution reaction (OER). Besides, the increased exposure of the (001) facet will increase the proportion of high-valent nickel oxyhydroxides during OER, which will enhance the electrocatalytic performance. The universality of the modulation method is further verified by the successful synthesis of a series of 2D MOFs (Ni, Co, Cu, Zn, and corresponding bimetal MOFs). This method may serve as an important inspiration for the preparation and crystal facet engineering of 2D MOFs.

Metalloenzyme-Inspired Ce-MOF Catalyst for Oxidative Halogenation Reactions.

The structure of UiO-66(Ce) is formed by CeO2–x defective nanoclusters connected by terephthalate ligands. The initial presence of accessible Ce3+ sites in the as-synthesized UiO-66(Ce) has been determined by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR)-CO analyses. Moreover, linear scan voltammetric measurements reveal a reversible Ce4+/Ce3+ interconversion within the UiO-66(Ce) material, while nanocrystalline ceria shows an irreversible voltammetric response. This suggests that terephthalic acid ligands facilitate charge transfer between subnanometric metallic nodes, explaining the higher oxidase-like activity of UiO-66(Ce) compared to nanoceria for the mild oxidation of organic dyes under aerobic conditions. Based on these results, we propose the use of Ce-based metal–organic frameworks (MOFs) as efficient catalysts for the halogenation of activated arenes, as 1,3,5-trimethoxybenzene (TMB), using oxygen as a green oxidant. Kinetic studies demonstrate that UiO-66(Ce) is at least three times more active than nanoceria under the same reaction conditions. In addition, the UiO-66(Ce) catalyst shows an excellent stability and can be reused after proper washing treatments. Finally, a general mechanism for the oxidative halogenation reaction is proposed when using Ce-MOF as a catalyst, which mimics the mechanistic pathway described for metalloenzymes. The superb control in the generation of subnanometric CeO2–x defective clusters connected by adequate organic ligands in MOFs offers exciting opportunities in the design of Ce-based redox catalysts.

Coordination Polymers from 2-Chloroterephthalate Linkers: Synthesis, Structural Diversity, and Catalytic CO2 Fixation

In contrast to the broad use of terephthalic acid as a building block for generating metal-organic architectures, functionalized terephthalate ligands remain significantly less investigated. In the present study, 2-chloroterephthalic acid (CltaH2) was used as an unexplored linker for assembling a new series of metal(II) coordination polymers (CPs) formulated as {[Cu2(μ-Clta)(μ4-Clta)(bipy)2]·2H2O}n (1), {[Cu2(μ-Clta)(μ4-Clta)(phen)2]·2H2O}n (2), [Co3(μ4-Clta)3(phen)2]n (3), {[Zn4(μ3-Clta)2(μ4-Clta)(μ3-OH)2(phen)2]·2H2O}n (4), {[Cd(μ3-Clta)(phen)]·H2O}n (5), [Co2(μ-Clta)(μ4-Clta)(μ-bpa)2]n (6), [Zn2(μ4-Clta)(μ4-biim)]n (7), and [Cd(μ-Clta)(H2biim)2]n (8). These compounds were prepared hydrothermally from the respective metal(II) chlorides, CltaH2, and different N-donor supporting ligands acting as mediators of crystallization (i.e., bipy, 2,2′-bipyridine; phen, 1,10-phenanthroline; bpa, bis(4-pyridyl)amine; H2biim, 2,2′-biimidazole). The structures of the coordination polymers 1-8 range from one-dimensional chains (5 and 8) and two-dimensional layers (1-3) to three-dimensional (3D) frameworks (4, 6, and 7); the latter also include 3D + 3D interpenetrated examples (4, 6). Apart from different dimensionalities, the compounds also feature distinct topologies, namely, 3,4L13 in 1 and 2, 3,4,6L12 in 3, pcu in 4, SP 1-periodic net (4,4)(0,2) in 5, sqc65 in 6, 2C1 in 8, and a new kir1 topology in 7. Given the similarity of the reaction conditions, the obtained wide diversity of structures is primarily determined by the type of metal(II) node and/or crystallization mediator. All the CPs were also screened as heterogeneous catalysts in a model CO2 fixation reaction, namely, in the coupling of epoxide (epichlorohydrin) with carbon dioxide, under atmospheric pressure, and in the absence of added solvent, to produce the corresponding cyclic carbonate. The catalytic reactions were optimized for CP 4, which revealed the best activity (up to 71% product yields), good stability, and recyclability for up to four reaction steps. Finally, CPs 3-8 are the first examples of cobalt, zinc, and cadmium coordination compounds assembled from 2-chloroterephthalic acid, thus widening its very limited application in the design of functional metal-organic architectures. ©

Tuning the Pore Surface of an Ultramicroporous Framework for Enhanced Methane and Acetylene Purification Performance.

Both methane (CH4) and acetylene (C2H2) are important energy source and raw chemicals in many industrial processes. The development of an energy-efficient and environmentally friendly separation and purification strategy for CH4 and C2H2 is necessary. Ultramicroporous metal-organic framework (MOF) materials have shown great success in the separation and purification of small-molecule gases. Herein, the synergy effect of tritopic polytetrazolate and ditopic terephthalate ligands successfully generates a series of isoreticular ultramicroporous cadmium tetrazolate-carboxylate MOF materials (SNNU-13-16) with excellent CH4 and C2H2 purification performance. Except for the uncoordinated tetrazolate N atoms serving as Lewis base sites, the pore size and pore surface of MOFs are systematically engineered by regulating dicarboxylic acid ligands varying from OH-BDC (SNNU-13) to Br-BDC (SNNU-14) to NH2-BDC (SNNU-15) to 1,4-NDC (SNNU-16). Benefiting from the ultramicroporous character (3.8-5.9 Å), rich Lewis base N sites, and tunable pore environments, all of these ultramicroporous MOFs exhibit a prominent separation capacity for carbon dioxide (CO2) or C2 hydrocarbons from CH4 and C2H2. Remarkably, SNNU-16 built by 1,4-NDC shows the highest ideal adsorbed solution theory CO2/CH4, ethylene (C2H4)/CH4, and C2H2/CH4 separation selectivity values, which are higher than those of most famous MOFs with or without open metal sites. Dynamic breakthrough experiments show that SNNU-16 can also efficiently separate the C2H2/CO2 mixtures with a gas flow rate of 4 mL min-1 under 1 bar and 298 K. The breakthrough time (18 min g-1) surpasses most best-gas-separation MOFs and nearly all other metal azolate-carboxylate MOF materials under the same conditions. The above prominently CH4 and C2H2 purification abilities of SNNU-13-16 materials were further confirmed by the Grand Canonical Monte Carlo (GCMC) simulations.

Modulation of the charge transfer behavior of Ni(II)-doped NH2-MIL-125(Ti): Regulation of Ni ions content and enhanced photocatalytic CO2 reduction performance

Regulation of the electronic structure of metal oxo clusters in metal organic frameworks (MOFs) is a promising way to modulate charge transfer efficiency and photocatalytic performance. Herein, a series of Ni2+ doped NH2-MIL-125-Ti (NH2-MIL-125-Nix/Ti) with different Ni2+/Ti4+ molar ratio (x = 0.5%–1.5%) are prepared via an in-situ doping method. Correlations between the electronic structure of (Ti/Ni)8O8(OH)4 nodes and charge transfer efficiency, bandgap and energy position of band edges of the NH2-MIL-125-Nix/Ti are systematically investigated based on experimental and computational method. The doped Ni2+ was confirmed to be an efficient mediator to promote the electron transfer from photoexcited terephthalate ligand to the (Ti/Ni)8O8(OH)4 nodes in NH2-MIL-125-Nix/Ti. The NH2-MIL-125-Ni1%/Ti exhibited the highest CO2 conversion rate with 98.6% CO selectivity and the factors affecting the photocatalytic CO2 reduction performance are also studied. It provides some guidance for developing MOFs photocatalyst with targeted performance via modification of the electronic structure of metal oxo clusters.

MIL-101(Cr)-NO2 as efficient catalyst for the aerobic oxidation of thiophenols and the oxidative desulfurization of dibenzothiophenes

A series of MIL-101(Cr)-X functionalized with electron withdrawing (NO2, SO3H or Cl) or electron donor (NH2 or CH3) groups has been tested for the solvent-free oxidative coupling of thiophenol to disulfides. No byproducts were observed. A relationship between the catalytic activity of these MOFs with the substituent meta Hammet constant on the terephthalate ligand and with their redox potential was found, MIL-101(Cr)-NO2 being the most active catalyst. NO2-substituted MIL-101 is also more efficient than the parent MIL-101(Cr) to promote the aerobic desulfurization of dibenzothiophenes in n-dodecane or commercial Diesel as solvent. No byproduct formation was observed. Mechanistic studies reveal that MIL-101(Cr)-NO2 is acting as heterogeneous catalyst in thiophenol oxidation and as radical initiator for the aerobic desulfurization. For both reactions, the catalyst can be reused without deactivation, maintaining its crystallinity and with negligible metal leaching.

The Effect of Hydrogen Peroxide on the Synthesis of Terephthalate‐Based Metal‐Organic Frameworks

AbstractMetal‐organic frameworks (MOFs) are versatile materials for applications in fields including the environment, energy and health. A synthetic route for improving the formation of MOFs has been developed and is triggered by hydrogen peroxide (H2O2) to promote the formation of terephthalate‐based MOFs of MIL‐53 and MIL‐68 types, specifically those made from Fe3+ and Al3+ and mixtures of both. Different characterization techniques (TGA, XRD, SEM, TEM, N2 porosimetry and Raman, mass and NMR spectroscopies) gave insights into the effect of H2O2 on the MOF synthesis. The reaction yield was significantly improved (the highest yield being 74 % for MIL‐53(Al)), while crystallinity and N2 adsorption properties were mostly maintained for phases based on Al and Al/Fe. Furthermore, a reaction mechanism was envisaged from the mass spectroscopic analysis of the reaction solutions, thus suggesting that H2O2 plays the role of a μ‐hydroxo bridge promoter, favoring the link between terephthalate ligands and aluminum‐containing species to give rise to the μ‐carboxylate bridges, leading to a faster growth of the final MOF, and offering a novel MOF synthesis approach.