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A highly porous and stable Zr-MOF containing a planar porphyrin-based tetraphosphonic acid was synthesized and characterized regarding its sorption properties and chemical stability., The Ni-metallated porphyrin-based tetraphosphonic acid (Ni-tetra(4-phosphonophenyl)porphyrin, Ni-H8TPPP) was used for the synthesis of highly porous metal phosphonates containing the tetravalent cations Zr4+ and Hf4+. The compounds were thoroughly characterized regarding their sorption properties towards N2 and H2O as well as thermal and chemical stability. During the synthesis optimization the reaction time could be substantially decreased under stirring from 24 to 3 h in glass vials. M-CAU-30, [M2(Ni-H2TPPP)(OH/F)2]·H2O (M = Zr, Hf) shows exceptionally high specific surface areas for metal phosphonates of aBET = 1070 and 1030 m2 g–1 for Zr- and Hf-CAU-30, respectively, which are very close/correspond to the theoretical values of 1180 and 1030 m2 g–1. CAU-30 is always obtained as mixtures with one mol ZrO2/HfO2 per formula unit as proven by TEM, electron diffraction, TG and elemental analysis. Hence experimentally derived specific surface areas are 970 and 910 m2 g–1, respectively. M-CAU-30 is chemically stable in the pH range 0 to 12 in HCl/NaOH and thermally up to 420 °C in air as determined by variable-temperature powder X-ray diffraction (VT-PXRD). The crystal structure of M-CAU-30 was determined by combining electron diffraction tomography for structure solution and powder X-ray diffraction data for the structure refinement. The crystal structure consists of chains of corner sharing MO6 octahedra interconnected by the partly deprotonated linker molecules Ni-H2TPPP6–. Thus 1D channels with pore diameters of 1.3 × 2.0 nm are formed. The redox activity of Zr-CAU-30 was investigated by cyclic voltammetry resulting in a reversible redox process at a half-wave potential of E1/2 = –0.649 V.

The ability of zirconium metal–organic frameworks (MOFs) to gelate under specific synthetic conditions opens up new opportunities in the preparation and shaping of hierarchically porous MOF monoliths, which could be directly implemented for catalytic and adsorptive applications., The ability of metal–organic frameworks (MOFs) to gelate under specific synthetic conditions opens up new opportunities in the preparation and shaping of hierarchically porous MOF monoliths, which could be directly implemented for catalytic and adsorptive applications. In this work, we present the first examples of xero- or aerogel monoliths consisting solely of nanoparticles of several prototypical Zr4+-based MOFs: UiO-66-X (X = H, NH2, NO2, (OH)2), UiO-67, MOF-801, MOF-808 and NU-1000. High reactant and water concentrations during synthesis were observed to induce the formation of gels, which were converted to monolithic materials by drying in air or supercritical CO2. Electron microscopy, combined with N2 physisorption experiments, was used to show that irregular nanoparticle packing leads to pure MOF monoliths with hierarchical pore systems, featuring both intraparticle micropores and interparticle mesopores. Finally, UiO-66 gels were shaped into monolithic spheres of 600 μm diameter using an oil-drop method, creating promising candidates for packed-bed catalytic or adsorptive applications, where hierarchical pore systems can greatly mitigate mass transfer limitations.

Luminescent adenine-stabilized silver clusters were created by transforming adeninate bio-MOF-1 to MOF-69A., Bright luminescent silver-adenine species were successfully stabilized in the pores of the MOF-69A (zinc biphenyldicarboxylate) metal–organic framework, starting from the intrinsically blue luminescent bio-MOF-1 (zinc adeninate 4,4′-biphenyldicarboxylate). Bio-MOF-1 is transformed to the MOF-69A framework by selectively leaching structural adenine linkers from the original framework using silver nitrate solutions in aqueous ethanol. Simultaneously, bright blue-green luminescent silver-adenine clusters are formed inside the pores of the recrystallized MOF-69A matrix in high local concentrations. The structural transition and concurrent changes in optical properties were characterized using a range of structural, physicochemical and spectroscopic techniques (steady-state and time-resolved luminescence, quantum yield determination, fluorescence microscopy). The presented results open new avenues for exploring the use of MOFs containing luminescent silver clusters for solid-state lighting and sensor applications.

Metal−organic frameworks (MOFs) are investigated for the adsorption of aromatic amino acids L-phenylalanine (L-Phe), Ltryptophan (L-Trp), and L-tyrosine (L-Tyr) from aqueous solutions. After screening a range of water-stable MOFs, the hydrophobic Zr- MOF MIL-140C emerged as the best performing material, exhibiting uptakes of 15 wt % for L-Trp and 20 wt % for L-Phe. These uptakes are 5−10 wt % higher than those of large-pore zeolites Beta and Y. Both single-compound and competitive adsorption isotherms for L-Phe and L-Trp were experimentally obtained at the natural pH of these amino acid mixtures (pH 6.5−7) without additional pH modification. We find that the hydrophobic nature of MIL-140C and the capacity of LTrp to form hydrogen bonds favor the uptake of L-Trp with its larger indole moiety compared to the smaller phenyl side group of L-Phe. On the basis of literature and vibrational analysis, observations of hydrogen-bonded L-Trp within the MIL-140C framework are evidenced by red- and blue-shifted −NH vibrations (3400 cm−1) in Fourier transform infrared spectroscopy, which were attributed to types N−HL‑Trp···πMIL‑140C and N−HL‑Trp···OMIL‑140C, respectively. MIL-140C is shown to be recycled at least three times for both aromatic amino acids without any loss of adsorption capacity, separation performance, or crystallinity. Desorption of aromatic amino acids proceeds easily in aqueous ethanol. Substantial coadsorption of negatively charged amino acids L-glutamate and L-aspartate (L-Glu and L-Asp) was observed from a model solution for wheat straw protein hydrolysate at pH 4.3. On the basis of these results, we conclude that MIL-140C is an interesting material for the recovery of essential aromatic amino acids L-Tyr, L-Phe, and L-Trp and of L-Glu and L-Asp from waste protein hydrolysates. ispartof: ACS Applied Materials and Interfaces vol:9 issue:35 pages:30064-30073 ispartof: location:United States status: published

In comparison to conventional stationary phases like (functionalized) silica or alumina in High-Performance Liquid Chromatography (HPLC), MOFs can lead to chromatographic separations based on molecular size and shape due to a uniform pore size distribution and ordered pore structure. Hereby, the versatility of organic linkers and metal centers used in MOFs introduce different interactions with the analytes than those obtained with commercial stationary phases in HPLC, which opens possibilities to separate different kind of mixtures. In this work, the MIL-125 (a Ti-based MOF) framework was used as stationary phase in liquid chromatography to study the separation of different model and stereoisomer mixtures. MIL-125(Ti) has distorted octahedral (12.5 Å) and tetrahedral (6.1 Å) cages connected with triangular windows of around 6 Å in size. Monodisperse MIL-125(Ti) particles were synthesized and slurry packed into a stainless steel column for HPLC measurements. MIL-125(Ti) allowed separation of variousmodel mixtures in HPLC, but moreover, the structure displays a stereo selectivity for difunctionalized cyclohexane molecules. This remarkable selectivity could be attributed to the shape selective confinement in the cages of the structure, where the tetrahedral cages act as channels between the octahedral cages, favoring the trans isomer. In a next stage, a Van Deemter curve was measured and intraparticle diffusion coefficients of some components were calculated from peak parking experiments in order to characterize and to determine performance of the crystal packed column, as will be discussed in this work. For a better understanding of the molecular interactions that occur within the chromatographic process, simulation techniques have been used. We performed Monte Carlo simulations to study adsorption properties of the most interesting molecules inside the framework. For this purpose, models of 4-ethylcyclohexanol and 1,3-dimethylcyclohexane isomers have been developed to reproduce characteristic properties of the molecules as well as their interactions with MIL-125(Ti). Adsorption isotherms, selectivity, distribution of the molecules, and Radial Distribution Functions were obtained and discussed. In conclusion, the separation potential and applicability of MIL-125(Ti) in chromatography was demonstrated via an experimental and theoretical way. This could be a start for the separation of other cis/trans mixtures, giving possibilities for separation of diastereomers, which is of tremendous importance for the production of pharmaceuticals. Acknowledgements The authors are grateful to IWT Vlaanderen, for financial support for MOFSHAPE “Shaped Metal-Organic Frameworks for Adsorption, Energy and Catalysis Applications”.