Enhanced sorption in an indium-acetylenedicarboxylate metal-organic framework with unexpected chains of cis-µ-OH-connected {InO6} octahedra.

Single crystals of the new metal-organic framework (MOF) In-adc (HHUD-4) were obtained through the reaction of linear acetylenedicarboxylic acid (H2adc) with In(NO3)3·xH2O as a racemic conglomerate in the chiral tetragonal space groups P4322 and P4122. Fundamentally different from other MOFs with linear linkers and trans-µ-OH-connected infinite {MO6} secondary building units as in the MIL-53-type, the linear adc2- linker leads to the formation of cis-µ-OH connected {InO6} polyhedra, which have otherwise only been found before for V-shaped ligands, as in CAU-10-H. A far-reaching implication of this finding is the possibility that trans-µ-OH/straight MIL-53-type MOFs will have polymorphs of CAU-10-H cis-µ-OH/helical topology and vice versa. HHUD-4 is a microporous MOF with a BET surface area of up to 940 m2 g-1 and a micropore volume of up to 0.39 cm3 g-1. Additionally, HHUD-4 features good adsorption uptakes of 3.77 mmol g-1 for CO2 and 1.25 mmol g-1 for CH4 at 273 K and 1 bar, respectively, and a high isosteric heat of adsorption of 11.4 kJ mol-1 for H2 with a maximum uptake of 6.36 mmol g-1 at 77 K and 1 bar. Vapor sorption experiments for water and volatile organic compounds (VOCs) such as benzene, cyclohexane and n-hexane yielded uptake values of 135, 269, 116 and 205 mg g-1, respectively, at 293 K. While HHUD-4 showed unremarkable results for water uptake and low stability for water, it exhibited good stability with steep VOC uptake steps at low relative pressures and a high selectivity of 17 for benzene/cyclohexane mixtures.

The Complexity of Comparative Adsorption of C6 Hydrocarbons (Benzene, Cyclohexane, n-Hexane) at Metal-Organic Frameworks.

The relatively stable MOFs Alfum, MIL-160, DUT-4, DUT-5, MIL-53-TDC, MIL-53, UiO-66, UiO-66-NH2, UiO-66(F)4, UiO-67, DUT-67, NH2-MIL-125, MIL-125, MIL-101(Cr), ZIF-8, ZIF-11 and ZIF-7 were studied for their C6 sorption properties. An understanding of the uptake of the larger C6 molecules cannot simply be achieved with surface area and pore volume (from N2 sorption) but involves the complex micropore structure of the MOF. The maximum adsorption capacity at p p0-1 = 0.9 was shown by DUT-4 for benzene, MIL-101(Cr) for cyclohexane and DUT-5 for n-hexane. In the low-pressure range from p p0-1 = 0.1 down to 0.05 the highest benzene uptake is given by DUT-5, DUT-67/UiO-67 and MIL-101(Cr), for cyclohexane and n-hexane by DUT-5, UiO-67 and MIL-101(Cr). The highest uptake capacity at p p0-1 = 0.02 was seen with MIL-53 for benzene, MIL-125 for cyclohexane and DUT-5 for n-hexane. DUT-5 and MIL-101(Cr) are the MOFs with the widest pore window openings/cross sections but the low-pressure uptake seems to be controlled by a complex combination of ligand and pore-size effect. IAST selectivities between the three binary mixtures show a finely tuned and difficult to predict interplay of pore window size with (critical) adsorptive size and possibly a role of electrostatics through functional groups such as NH2.

Modulation of the Sorption Characteristics for an H-bonded porous Architecture by Varying the Chemical Functionalization of the Channel Walls.

Five isostructural microporous supramolecular architectures prepared by H-bonded assembly between the hexa-anionic complex [Zr2 (Ox)7 ]6- (Ox=oxalate, (C2 O4 )2- ) and tripodal cations (H3 -TripCH2 -R)3+ with R=H, CH3 , OH and OBn (Bn=CH2 Ph) are reported. The possibility to obtain the same structure using a mixture of tripodal cations with different R group (R=OH and R=CH3 ) has also been successfully explored, providing a unique example of three-component H-bonded porous framework. The resulting SPA-1(R) materials feature 1D pores decorated by R groups, with apparent pore diameters ranging from 3.0 to 8.5 Å. Influence of R groups on the sorption properties of these materials is evidenced through CO2 and H2 O vapor sorption/desorption experiments, as well as with I2 capture/release experiments in liquid media. This study is one of the first to demonstrate the possibility of tuning the porosity and exerting precise control over the chemical functionalization of the pores in a given H-bonded structure, without modifying the topology of the reference structure, and thus finely adjusting the sorption characteristics of the material.

Sensitive Electrochemical Sensor Based On an Aminated MIL-101(Cr) MOF for the Detection of Tartrazine.

The aminated metal-organic framework H2N-MIL-101(Cr) was used as the carbon paste electrode (CPE) modifier for the determination of tartrazine (Tz) in soft drinks. The amino material was characterized by electrochemical impedance spectroscopy and showed significantly faster electron transfer with lower charge-transfer resistance (0.13 kΩ) compared to the electrode modified with the unfunctionalized MIL-101(Cr) material (1.1 kΩ). The H2N-MIL-101(Cr)-modified CPE [H2N-MIL-101(Cr)-CPE] was then characterized by cyclic voltammetry (CV) using [Fe(CN)6]3- and [Ru(NH3)6]3+ ions as the redox probes, showing good accumulation of [Fe(CN)6]3- ions on the electrode surface. A CV scan of Tz in Britton Robinson buffer solution revealed an irreversible system with an oxidation peak at +0.998 V versus Ag/AgCl/KCl. Using CV and differential pulse voltammetry, an electrochemical method for quantifying Tz in aqueous medium was then developed. Several parameters that affect the accumulation and detection steps were optimized. Optimal detection of Tz was achieved after 180 s of accumulation in Britton Robinson buffer solution (pH 2) using 2 mg of H2N-MIL-101(Cr) material. Under optimal conditions, the sensor exhibited a linear response in the concentration range of 0.004-0.1 µM and good detection sensitivity (35.4 µA µM-1), and the detection limit for Tz was found to be 1.77 nM (S/N = 3). Satisfactory repeatability, stability, and anti-interference performance were also achieved on H2N-MIL-101(Cr)-CPE. The sensor was applied to commercial juices, and the results obtained were approximately similar to those given by UV-vis spectrophotometry.

Synthesis and Characterization of a Crystalline Imine-Based Covalent Organic Framework with Triazine Node and Biphenyl Linker and Its Fluorinated Derivate for CO2/CH4 Separation.

A catalyst-free Schiff base reaction was applied to synthesize two imine-linked covalent organic frameworks (COFs). The condensation reaction of 1,3,5-tris-(4-aminophenyl)triazine (TAPT) with 4,4'-biphenyldicarboxaldehyde led to the structure of HHU-COF-1 (HHU = Heinrich-Heine University). The fluorinated analog HHU-COF-2 was obtained with 2,2',3,3',5,5',6,6'-octafluoro-4,4'-biphenyldicarboxaldehyde. Solid-state NMR, infrared spectroscopy, X-ray photoelectron spectroscopy, and elemental analysis confirmed the successful formation of the two network structures. The crystalline materials are characterized by high Brunauer-Emmett-Teller surface areas of 2352 m2/g for HHU-COF-1 and 1356 m2/g for HHU-COF-2. The products of a larger-scale synthesis were applied to prepare mixed-matrix membranes (MMMs) with the polymer Matrimid. CO2/CH4 permeation tests revealed a moderate increase in CO2 permeability at constant selectivity for HHU-COF-1 as a dispersed phase, whereas application of the fluorinated COF led to a CO2/CH4 selectivity increase from 42 for the pure Matrimid membrane to 51 for 8 wt% of HHU-COF-2 and a permeability increase from 6.8 to 13.0 Barrer for the 24 wt% MMM.

Nickel-Based Metal-Organic Frameworks as Electrocatalysts for the Oxygen Evolution Reaction (OER).

The exploration of earth-abundant electrocatalysts with high performance for the oxygen evolution reaction (OER) is eminently desirable and remains a significant challenge. The composite of the metal-organic framework (MOF) Ni10Co-BTC (BTC = 1,3,5-benzenetricarboxylate) and the highly conductive carbon material ketjenblack (KB) could be easily obtained from the MOF synthesis in the presence of KB in a one-step solvothermal reaction. The composite and the pristine MOF perform better than commercially available Ni/NiO nanoparticles under the same conditions for the OER. Activation of the nickel-cobalt clusters from the MOF can be seen under the applied anodic potential, which steadily boosts the OER performance. Ni10Co-BTC and Ni10Co-BTC/KB are used as sacrificial agents and undergo structural changes during electrochemical measurements, the stabilized materials show good OER performances.

Biphenyl-Based Covalent Triazine Framework/Matrimid® Mixed-Matrix Membranes for CO2/CH4 Separation.

Processes, such as biogas upgrading and natural gas sweetening, make CO2/CH4 separation an environmentally relevant and current topic. One way to overcome this separation issue is the application of membranes. An increase in separation efficiency can be achieved by applying mixed-matrix membranes, in which filler materials are introduced into polymer matrices. In this work, we report the covalent triazine framework CTF-biphenyl as filler material in a matrix of the glassy polyimide Matrimid®. MMMs with 8, 16, and 24 wt% of the filler material are applied for CO2/CH4 mixed-gas separation measurements. With a CTF-biphenyl loading of only 16 wt%, the CO2 permeability is more than doubled compared to the pure polymer membrane, while maintaining the high CO2/CH4 selectivity of Matrimid®.

Cucurbit[6]uril@MIL-101-Cl: loading polar porous cages in mesoporous stable host for enhanced SO2 adsorption at low pressures.

The robust cucurbituril-MOF composite CB6@MIL-101-Cl was synthesized by a wet impregnation method and a concomitant OH-to-Cl ligand exchange {CB6 = cucurbit[6]uril, 31 wt% content in the composite, MIL-101-Cl = [Cr3(O)Cl(H2O)2(BDC)3], BDC = benzene-1,4-dicarboxylate}. MIL-101-Cl was formed postsynthetically from standard fluorine-free MIL-101 where Cr-OH ligands were substituted by Cl during treatment with HCl. CB6@MIL-101-Cl combines the strong SO2 affinity of the rigid CB6 macrocycles and the high SO2 uptake capacity of MIL-101, and shows a high SO2 uptake of 438 cm3 g-1 (19.5 mmol g-1) at 1 bar and 293 K (380 cm3 g-1, 17.0 mmol g-1 at 1 bar and 298 K). The captured SO2 amount is 2.2 mmol g-1 for CB6@MIL-101-Cl at 0.01 bar and 293 K (2.0 mmol g-1 at 298 K), which is three times higher than that of the parent MIL-101 (0.7 mmol g-1) under the same conditions. The near zero-coverage SO2 adsorption enthalpies of MIL-101 and CB6@MIL-101-Cl are -35 kJ mol-1 and -50 kJ mol-1, respectively, reflecting the impact of the incorporated CB6 macrocycles, having higher affinity towards SO2. FT-IR spectroscopy confirms the interactions of the SO2 with the cucurbit[6]uril moieties of the CB6@MIL-101-Cl composite and SO2 retention for a few minutes under ambient air. Comparative experiments demonstrated loss of crystallinity and porosity after dry SO2 adsorption for MIL-101, while CB6@MIL-101-Cl exhibits nearly complete retention of crystallinity and porosity under the exposure to both dry and wet SO2. Thus, CB6@MIL-101-Cl can be an attractive adsorbent for SO2 capture because of its excellent recycling stability, high capacity and strong affinity toward SO2 at low pressure.

A Highly-Efficient Oxygen Evolution Electrocatalyst Derived from a Metal-Organic Framework and Ketjenblack Carbon Material.

The composite of the metal-organic framework (MOF) Ni(Fe)-MOF-74 and the highly conductive carbon material ketjenblack (KB) could be easily obtained from the in-situ MOF synthesis in a one-step solvothermal reaction. The composite material features a remarkable electrochemical oxygen evolution reaction (OER) performance where the overpotential at 10 mA/cm2 and the current density at 1.7 VRHE are recorded as 0.274 VRHE and 650 mA/cm2 , respectively, in 1 mol/L KOH. In particular, the activation of nickel-iron clusters from the MOF under an applied anodic bias steadily boosts the OER performance. Although Ni(Fe)-MOF-74 goes through some structural modification during the electrochemical measurements, the stabilized and optimized composite material shows excellent OER performance. This simple strategy to design highly-efficient electrocatalysts, utilizing readily available precursors and carbon materials, will leverage the use of diverse metal-organic complexes into electrode fabrication with a high energy conversion efficiency.

Cucurbituril-Encapsulating Metal-Organic Framework via Mechanochemistry: Adsorbents with Enhanced Performance.

The first examples of monolithic crystalline host-guest hybrid materials are described. The reaction of 1,3,5-benzenetricarboxylic acid (H3 BTC) and Fe(NO3 )3 ⋅9 H2 O in the presence of decamethylcucurbit[5]uril ammonium chloride (MC5⋅2 NH4 Cl⋅4 H2 O) directly affords MC5@MIL-100(Fe) hybrid monoliths featuring hierarchical micro-, meso- and macropores. Particularly, this "bottle-around-ship" synthesis and one-pot shaping are facilitated by a newly discovered Fe-MC5 flowing gel formed by mechanochemistry. The designed MC5@MIL-100(Fe) hybrid material with MC5 as active domains shows enhanced CH4 and lead(II) uptake performance, and selective capture of lead(II) cations at low concentrations. This shows that host-guest hybrid materials can exhibit synergic properties that out-perform materials based on individual components.

Cadaveric Study of a Z-Plasty Modification to the Moberg Flap for Increased Advancement and Decreased Morbidity.

BACKGROUND: The Moberg advancement flap is a well-established tool to provide sensate, vascularized tissue for thumb reconstruction. Modifications providing additional length have been described, but no studies have examined how much additional advancement can be achieved consistently, and at what cost. The authors hypothesized that Z-plasty modification at the base of the Moberg flap would allow additional advancement compared with the traditional technique, and maintain primary closure of the donor-site and avoid additional morbidity. METHODS: Standard Moberg flaps were performed and advancement was measured on 20 cadaver specimens. Ten flaps were then modified with the O'Brien technique of incising proximally and skeletonizing the neurovascular bundles. The other 10 flaps were modified with Z-plasties at the base of the thumb. Differences in distance of advancement were compared, as was the ability to primarily close donor sites. RESULTS: Average advancement for Moberg flaps was 7.3 ± 1.2 mm, compared with 15.0 ± 2.5 mm for the O'Brien modification (p < 0.01) and 11.3 ± 1.7 mm for the Z-plasty modification (p < 0.01). CONCLUSIONS: Although the O'Brien modification allows approximately 50 percent further advancement than the Z-plasty modification compared with the standard Moberg flaps, the increase correlates to a large area of exposed neurovascular bundles at the volar base of the thumb, which requires secondary coverage. However, all Z-plasty donor-sites could be closed primarily. Primary closure of all donor sites will decrease healing time, wound complications, digital nerve sensitivity, and cosmetic appearance. This study is the first to show a significant increase in Moberg flap advancement using Z-plasty lengthening at the thumb base while avoiding any increased morbidity.