Metal-Organic Frameworks for Dual Photo-Oxidation and Capture of Arsenic from Water.

Despite rapid technological progress, heavy metal water pollution, particularly arsenic contamination, remains a significant global challenge. The stabilization of trivalent arsenic as neutral arsenite (AsIII) species hinders its removal by conventional adsorption methods. While adsorption of anionic arsenate (AsV) species is in principle more feasible, there are only a few adsorbents capable of adsorbing both forms of arsenic. In this work we study the potential of two well-known families of Metal-Organic Frameworks (MOFs), UiO-66 and MIL-125, to simultaneously adsorb and photo-oxidize arsenic species from water. Our results demonstrate that the formation of AsV ions upon light irradiation promotes the subsequent adsorption of additional AsIII species. Thus, we propose the combined utilization of photocatalysis and adsorption technologies for water remediation purposes.

Linear Polyethyleneimine-Based and Metal Organic Frameworks (DUT-67) Composite Hydrogels as Efficient Sorbents for the Removal of Methyl Orange, Copper Ions, and Penicillin V.

This research explores the integration of DUT-67 metal organic frameworks into polyethyleneimine-based hydrogels to assemble a composite system with enough mechanical strength, pore structure and chemical affinity to work as a sorbent for water remediation. By varying the solvent-to-modulator ratio in a water-based synthesis path, the particle size of DUT-67 was successfully modulated from 1 µm to 200 nm. Once DUT-67 particles were integrated into the polymeric hydrogel, the composite hydrogel exhibited enhanced mechanical properties after the incorporation of the MOF filler. XPS, NMR, TGA, FTIR, and FT Raman studies confirmed the presence and interaction of the DUT-67 particles with the polymeric chains within the hydrogel network. Adsorption studies of methyl orange, copper(II) ions, and penicillin V on the composite hydrogel revealed a rapid adsorption kinetics and monolayer adsorption according to the Langmuir's model. The composite hydrogel demonstrated higher adsorption capacities, as compared to the pristine hydrogel, showcasing a synergistic effect, with maximum adsorption capacities of 473 ± 21 mg L-1, 86 ± 6 mg L-1, and 127 ± 4 mg L-1, for methyl orange, copper(II) ions, and penicillin V, respectively. This study highlights the potential of MOF-based composite hydrogels as efficient adsorbents for environmental pollutants and pharmaceuticals.

A State-of-the-Art of Metal-Organic Frameworks for Chromium Photoreduction vs. Photocatalytic Water Remediation.

Hexavalent chromium (Cr(VI)) is a highly mobile cancerogenic and teratogenic heavy metal ion. Among the varied technologies applied today to address chromium water pollution, photocatalysis offers a rapid reduction of Cr(VI) to the less toxic Cr(III). In contrast to classic photocatalysts, Metal-Organic frameworks (MOFs) are porous semiconductors that can couple the Cr(VI) to Cr(III) photoreduction to the chromium species immobilization. In this minireview, we wish to discuss and analyze the state-of-the-art of MOFs for Cr(VI) detoxification and contextualizing it to the most recent advances and strategies of MOFs for photocatalysis purposes. The minireview has been structured in three sections: (i) a detailed discussion of the specific experimental techniques employed to characterize MOF photocatalysts, (ii) a description and identification of the key characteristics of MOFs for Cr(VI) photoreduction, and (iii) an outlook and perspective section in order to identify future trends.

Exploring ionic liquid-laden metal-organic framework composite materials as hybrid electrolytes in metal (ion) batteries.

This review focuses on the combination of metal-organic frameworks (MOFs) and ionic liquids (ILs) to obtain composite materials to be used as solid electrolytes in metal-ion battery applications. Benefiting from the controllable chemical composition, tunable pore structure and surface functionality, MOFs offer great opportunities for synthesizing high-performance electrolytes. Moreover, the encapsulation of ILs into porous materials can provide environmentally benign solid-state electrolytes for electrochemical devices. Due to the versatility of MOF-based materials, in this review we also explore their use as anodes and cathodes in Li- and Na-ion batteries. Finally, solid IL@MOF electrolytes and their implementation into Li and Na batteries have been analyzed, as well as the design and advanced manufacturing of solid IL@MOF electrolytes embedded on polymeric matrices.

Magnetoelastic Resonance Sensors: Principles, Applications, and Perspectives.

Magnetoelastic resonators are gaining attention as an incredibly versatile and sensitive transduction platform for the detection of varied physical, chemical, and biological parameters. These sensors, based on the coupling effect between mechanical and magnetic properties of ME platforms, stand out in comparison to alternative technologies due to their low cost and wireless detection capability. Several parameters have been optimized over the years to improve their performance, such as their composition, surface functionalization, or shape geometry. In this review, the working principles, recent advances, and future perspectives of magnetoelastic resonance transducers are introduced, highlighting their potentials as a versatile platform for sensing applications. First, the fundamental principles governing the magnetoelastic resonators performance are introduced as well as the most common magnetoelastic materials and their main fabrication methods are described. Second, the versatility and technical feasibility of magnetoelastic resonators for biological, chemical, and physical sensing are highlighted and the most recent results and functionalization processes are summarized. Finally, the forefront advances to further improve the performance of magnetoelastic resonators for sensing applications have been identified.

Chromium Speciation in Zirconium-Based Metal-Organic Frameworks for Environmental Remediation.

Acute CrVI water pollution due to anthropogenic activities is an increasing worldwide concern. The high toxicity and mobility of CrVI makes it necessary to develop dual adsorbent/ion-reductive materials that are able to capture CrVI and transform it efficiently into the less hazardous CrIII . An accurate description of chromium speciation at the adsorbent/ion-reductive matrix is key to assessing whether CrVI is completely reduced to CrIII , or if its incomplete transformation has led to the stabilization of highly reactive, transient CrV species within the material. With this goal in mind, a dual ultraviolet-visible and electron paramagnetic spectroscopy approach has been applied to determine the chromium speciation within zirconium-based metal-organic frameworks (MOFs). Our findings point out that the generation of defects at Zr-MOFs boosts CrVI adsorption, whilst the presence of reductive groups on the organic linkers play a key role in stabilizing it as isolated and/or clustered CrIII ions.

Exploring new hydrated delta type vanadium oxides for lithium intercalation.

Three hydrated double layered vanadium oxides, namely Na0.35V2O5·0.8(H2O), K0.36(H3O)0.15V2O5 and (NH4)0.37V2O5·0.15(H2O), were obtained by using mild hydrothermal conditions. Their delta type structural frameworks were solved by high-resolution synchrotron X-ray powder diffraction and the interlayer spacings were interpreted from difference Fourier maps. The inter-slab distances are modulated by the water content and the special arrangements of the alkali and ammonium cations. The XPS measurements denote mixed valence systems with high contents of V4+ ions up to 40%. The monitoring of the V4+ EPR signal over time suggests a reduction of the electronic delocalization on account of the partial oxidation to V5+. The electrochemical performance of the active phases is strongly conditioned by the vacuum-drying process of the electrodes, showing better capacity retention when vacuum is not applied. In situ X-ray diffraction shows a structural mechanism of contraction/expansion of the bilayers upon lithium insertion/extraction where the alkali ions behave as structural stabilizers. Galvanostatic cycling at very low current density implies migration of the alkali "pillars" triggering the collapse of the structure.

Thermal activation of charge carriers in ionic and electronic semiconductor ß-AgIVVO3 and ß-AgIVVO3@VV 1.6VIV 0.4O4.8 composite xerogels.

Silver vanadium oxide (SVO) and Silver Vanadium Oxide/Vanadium Oxide (SVO@VO) composite hydrogels are formed from the self-entanglement of ß-AgVO3 nanoribbons and slightly reduced vanadium oxide (VO) (VV 1.6VIV 0.4O4.8) nanoribbons; respectively. Starting from randomly distributed nanoribbons within hydrogels, and after a controlled drying process, a homogeneous xerogel system containing tuneable SVO : VO ratios from 1 : 0 to 1 : 1 can be obtained. The precise nanoribbons compositional control of these composite system can serve as a tool to tune the electrical properties of the xerogels, as it has been demonstrated in this work by impedance spectroscopy (IS) experiments. Indeed, depending on the composition and temperature conditions, composite xerogels can behave as electronic, protonic or high temperature ionic conductors. In addition, the electric and protonic conductivity of the composite xerogels can be enhanced (until a critical irreversible point), through the temperature triggered charge carrier creation. As concluded from thermogravimetry, IR, UV-Vis and EPR spectroscopy studies, besides the SVO : VO ratio, the thermal induced oxidation/reduction of V5+ to V4+, and thermally triggered release of strongly bonded water molecules at the nanoribbon surface are the two key variables that control the electric and ionic conduction processes within the SVO and composite SVO/VO xerogels.

Open and closed forms of the interpenetrated [Cu2(Tae)(Bpa)2](NO3)2·nH2O: magnetic properties and high pressure CO2/CH4 gas sorption.

Two closed and one open structural forms of the interpenetrated [Cu2(Tae)(Bpa)2](NO3)2·nH2O (H2Tae = 1,1,2,2-tetraacetylethane, Bpa = 1,2-bis(4-pyridyl)ethane) cationic coordination polymer have been synthesized. Three crystallographically related interpenetrated "ths" cationic nets encapsulate water molecules and nitrate anions giving rise to the closed structural forms of [Cu2(Tae)(Bpa)2](NO3)2·nH2O. Depending on the location of water molecules and nitrate groups, two different closed forms with 5.5 and 3.6 crystallization water molecules have been obtained. The thermal activation of the closed structures gives rise to a 29% expansion of the unit cell. This closed to open transformation is reversible, and is triggered by the loss or uptake of solvent. The high pressure gas adsorption experiments show similar selectivity values towards CO2 for CO2/CH4 mixtures to that showed by some metal organic frameworks without unsaturated metal sites, and isosteric heats for CO2 adsorption similar to that for the HKUST-1 compound.

Catalytic Performance of a New 1D Cu(II) Coordination Polymer {Cu(NO3)(H2O)}(HTae)(4,4'-Bpy) for Knoevenagel Condensation.

The {Cu(NO3)(H2O)}(HTae)(4,4'-Bpy) (H2Tae = 1,1,2,2-tetraacetylethane, 4,4'-Bpy = 4,4'-Dipyridyl) 1D coordination polymer has been obtained by slow evaporation. The crystal structure consists of parallel and oblique {Cu(HTae)(4,4'-Bpy)} zig-zag metal-organic chains stacked along the [100] crystallographic direction. Copper(II) ions are in octahedral coordination environment linked to two nitrogen atoms of two bridging 4,4'-Bpy and to two oxygen atoms of one HTae molecule in the equatorial plane. The occupation of the axial positions varies from one copper atom to another, with different combinations of water molecules and nitrate anions, giving rise to a commensurate super-structure. By means of the thermal removal of water molecules, copper coordinatively unsaturated centres are obtained. These open metal sites could act as Lewis acid active sites in several heterogeneous catalytic reactions. The dehydrated compound, CuHTaeBpy_HT, has been tested as a heterogeneous recoverable catalyst for Knoevenagel condensation reactions. The catalyst is active and heterogeneous for the condensation of aldehydes with malononitrile at 60 °C using a molar ratio catalyst:substrate of 3 % and toluene as solvent. The catalyst suffers a partial loss of activity when reusing it, but can be reused at least four times.

Commensurate Superstructure of the {Cu(NO3)(H2O)}(HTae)(Bpy) Coordination Polymer: An Example of 2D Hydrogen-Bonding Networks as Magnetic Exchange Pathway.

The average and commensurate superstructures of the one-dimensional coordination polymer {Cu(NO3)(H2O)}(HTae)(Bpy) (H2Tae = 1,1,2,2-tetraacetylethane, Bpy = 4,4'-bipyridine) were determined by single-crystal X-ray diffraction, and the possible symmetry relations between the space group of the average structure and the superstructure were checked. The crystal structure consists in parallel and oblique {Cu(HTae)(Bpy)} zigzag metal-organic chains stacked along the [100] crystallographic direction. The origin of the fivefold c axis in the commensurate superstructure is ascribed to a commensurate modulation of the coordination environment of the copper atoms. The commensurately ordered nitrate groups and coordinated water molecules establish a two-dimensional hydrogen-bonding network. Moreover, the crystal structure shows a commensurate to incommensurate transition at room temperature. The release of the coordination water molecules destabilizes the crystal framework, and the compound shows an irreversible structure transformation above 100 °C. Despite the loss of crystallinity, the spectroscopic studies indicate that the main building blocks of the crystal framework are retained after the transformation. The hydrogen-bonding network not only plays a crucial role stabilizing the crystal structure but also is an important pathway for magnetic exchange transmission. In fact, the magnetic susceptibility curves indicate that after the loss of coordinated water molecules, and hence the collapse of the hydrogen-bonding network, the weak anti-ferromagnetic coupling observed in the initial compound is broken. The electron paramagnetic resonance spectra are the consequence of the average signals from Cu(II) with different orientations, indicating that the magnetic coupling is effective between them. In fact, X- and Q-band data are reflecting different situations; the X-band spectra show the characteristics of an exchange g-tensor, while the Q-band signals are coming from both the exchange and the molecular g-tensors.

Ax(H3O)2-xMn5(HPO3)6 (A = Li, Na, K and NH4): open-framework manganese(ii) phosphites templated by mixed cationic species.

Ax(H3O)2-xMn5(HPO3)6 (A = Li, x = 0.55 (1-Li); A = Na, x = 0.72 (2-Na); A = K, x = 0.30 (3-K); A = NH4, x = 0.59 (4-NH4)) phases were synthesized by employing mild hydrothermal conditions. 1-Li was studied by single crystal X-ray diffraction, while sodium, potassium and ammonium containing analogues were obtained as polycrystalline samples and characterized by powder X-ray diffraction. The four compounds were characterized by ICP-Q-MS, thermal analysis and XPS, IR, UV/Vis and EPR spectroscopy. Single crystal data indicate that 1-Li crystallizes in the P3[combining macron]c1 space group with lattice parameters a = 10.3764(1) Å and c = 9.4017(1) Å with Z = 2. The crystal structure of these phases is constituted by a three-dimensional [Mn(ii)5(HPO3)6](2-) anionic skeleton templated by alkali metal and ammonium cations together with protonated water molecules. Such an inorganic framework is formed by layers of edge-sharing MnO6 octahedra placed in the ab plane and joined along the c direction through phosphite pseudotetrahedra. The sheets display 12-membered ring channels parallel to the c-axis, ca. 5 Å in diameter, where the extraframework species display a strong disorder. EPR measurements point to the existence of short range ferromagnetic interactions around 12 K. Magnetic susceptibility and heat capacity measurements show that all the compounds exhibit long range antiferromagnetic order below circa 4 K, with a significant magnetocaloric effect around the Neel temperature.

Thermal response, catalytic activity, and color change of the first hybrid vanadate containing Bpe guest molecules.

Four isomorphic compounds with formula [{Co2(H2O)2(Bpe)2}(V4O12)]·4H2O·Bpe, CoBpe 1; [{CoNi(H2O)2(Bpe)2}(V4O12)]·4H2O·Bpe, CoNiBpe 2; [{Co0.6Ni1.4(H2O)2(Bpe)2}(V4O12)]·4H2O·Bpe, NiCoBpe 3; and [{Ni2(H2O)2(Bpe)2}(V4O12)]·4H2O·Bpe, NiBpe 4, have been obtained by hydrothermal synthesis. The crystal structures of CoBpe 1 and NiBpe 4 were determined by single-crystal X-ray diffraction (XRD). The Rietveld refinement of CoNiBpe 2 and NiCoBpe 3 XRD patterns confirms that those are isomorphic. The compounds crystallize in the P1̅ space group, exhibiting a crystal structure constructed from inorganic layers pillared by Bpe ligands. The crystal structure contains intralayer and interlayer channels, in which the crystallization water molecules and Bpe guest molecules, respectively, are located. The solvent molecules establish a hydrogen bonding network with the coordinated water molecules. Thermodiffractometric and thermogravimetric studies showed that the loss of crystallization and coordinated water molecules takes place at different temperatures, giving rise to crystal structure transformations that involve important reduction of the interlayer distance, and strong reduction of crystallinity. The IR, Raman, and UV-vis spectra of the as-synthesized and heated compounds confirm that the structural building blocks and octahedral coordination environment of the metal centers are maintained after the structural transformations. The color change and reversibility of the water molecules uptake/removal were tested showing that the initial color is not completely recovered when the compounds are heated at temperatures higher than 200 °C. The thermal evolution of the magnetic susceptibility indicates one-dimensional antiferromagnetic coupling of the metal centers at high temperatures. For NiCoBpe 3 and NiBpe 4 compounds magnetic ordering is established at low temperatures, as can be judged by the maxima observed in the magnetic susceptibilities. CoNiBpe 2 was proved as catalyst being active for cyanosilylation reactions of aldehydes.

Amine templated open-framework vanadium(III) phosphites with catalytic properties.

Four novel amine templated open-framework vanadium(III) phosphites with the formula (C(5)N(2)H(14))(0.5)[V(H(2)O)(HPO(3))(2)], 1 (C(5)N(2)H(14) = 2-methylpiperazinium), and (L)(4-x)(H(3)O)(x)[V(9)(H(2)O)(6)(HPO(3))(14-y)(HPO(4))(y)(H(2)PO(3))(3-z)(H(2)PO(4))z]·nH(2)O (2, L = cyclopentylammonium, x = 0, y = 3.5, z = 3, n = 0; , L = cyclohexylammonium, x = 1, y = 0, z = 0.6, n = 2.33; , L = cycloheptylammonium, x = 1, y = 0, z = 0, n = 2.33) were synthesized employing solvothermal reactions and characterized by single-crystal X-ray diffraction, ICP-AES and elemental analyses, thermogravimetric and thermodiffractometric analyses, and IR and UV/vis spectroscopy. Single-crystal data indicate that 1 crystallizes in the triclinic system, space group P1, whereas 2, 3 and 4 crystallize in the hexagonal space group P6(3)/m. Compound 1 has a two-dimensional motif with anionic sheets of [V(H(2)O)(HPO(3))(2)](-) formula, whose charge is compensated by the 2-methylpiperazinium cations embedded between the layers. In contrast, 2, 3 and 4 present a pillar-layer network giving rise to a three-dimensional framework containing intersecting 16-ring channels with the primary amine templates and the crystallization water molecules enclosed in them. 1, 2, 3 and 4 behave as heterogeneous catalysts for the selective oxidation of alkyl aryl sulfides, with tert-butylhydroperoxide (TBHP) as the oxidizing agent, being active, selective and recyclable for several successive cycles of reaction.

Synthesis and comparative study of Co(pym)(VO3)2 and [Co(H2O)2(VO3)2]·2H2O.

The three-dimensional Co(pym)(VO(3))(2), 1, hybrid compound, where pym is pyrimidine, has been synthesized under mild hydrothermal conditions at 120 °C. The compound has been characterized by FT-IR spectroscopy, elemental analysis, thermogravimetric measurements, thermodiffractometry, UV-Vis spectroscopy, temperature-dependent magnetic susceptibility and magnetization, and finally a study of specific heat has been performed. The crystal structure of 1 was solved using single-crystal X-ray diffraction data, taking into account that the crystals of this compound are twins of two components. It crystallizes in the monoclinic system, space group C2/c, a = 12.899(5) Å, b = 9.859(2) Å, c = 7.051(1) Å, ß = 111.41(3)°, Z = 4. The crystal structure is built up from edge sharing VO(5) trigonal bipyramid double chains and [CoO(4)pym](n) chains. This resembles the structure of the [Co(H(2)O)(2)(VO(3))(2)]·2H(2)O compound, 2. For this reason a comparative study of their properties was carried out. Magnetic measurements of 1, performed in the 2.0 to 300 K range, reveal the existence of a weak ferromagnetic order near 3 K. This fact was confirmed with magnetization measurements, which show irreversibility characteristic of soft ferromagnets. Magnetic measurements of 2 show a 3D antiferromagnetic ordering at 2.5 K. The magnetization shows a small change of curvature indicating the occurrence of a metamagnetic transition. Specific heat measurements of both compounds confirm the 3D nature of the magnetic order. The comparative study of the magneto-structural correlations reveals that the pyrimidine molecules are responsible for the different magnetic behaviour between 1 and 2.

Flexible and dynamic thermal behavior of self-catenated [{Ni3(H2O)3(Bpa)4}(V6O18)]·8H2O constructed from 10-c heterometallic inorganic-organic clusters.

The hydrothermal treatment of Ni(NO(3))(2)·6H(2)O, NaVO(3), and Bpa (1,2-Di(pyridyl)ethane) (C(12)H(12)N(2)) at 120 °C during 3 days leads to green single crystals of the title compound. The single crystal X-ray diffraction reveals that [{Ni(3)(H(2)O)(3)(Bpa)(4)}(V(6)O(18))]·8H(2)O crystallizes in the monoclinic system, P2(1)/c space group, with a = 13.5536 (2), b = 19.0463 (2), c = 27.7435 (3) Å, ß = 112.3880 (10)°, V = 6622(3) Å(3), with R1(obs) = 0.0558, wR2(obs) = 0.1359, for 10278 observed reflections. The complexity of the crystal structure is based on different points, as the existence of: both "gauche" and "trans" conformations of the organic ligand, the [V(12)O(36)](-12) cycles, formed by 12 corner-sharing VO(4) tetrahedra, and, finally, the combination of both three-dimensional metal-organic and inorganic substructures, giving rise to a self-catenated highly connected net. The crystallization water molecules are semi-encapsulated in the channels along the [100] direction, and their loss gives rise to a dynamical and reversible structural contraction. Moreover, after the removal of the crystallization water molecules, the compound exhibits a negative thermal behavior in the 85-155 °C temperature range, and irreversible structural transformation due to the loss of coordinated water molecules up to 200 °C. The IR and UV-vis spectra were determined for the as-synthesized sample, after the removal of crystallization water molecules and after the irreversible transformation due to the loss of coordinated water molecules. The thermal evolution of χ(m) was adjusted to a magnetic model considering an isotropic dimer plus two Ni(II) d(8) isolated octahedra.

Tris[4,4'-(ethene-1,2-di-yl)dipyridinium] deca-vanadate dihydrate.

The asymmetric unit of the title compound, (C(12)H(12)N(2))(3)[V(10)O(28)]·2H(2)O, contains one half of a deca-vanadate anion, one and a half trans-1,2-bis-(4-pyridinio)ethene cations and one water mol-ecule. The V(10)O(28) groups are involved in a three-dimensional hydrogen-bonding network through Ow-H⋯O, N-H⋯O and C-H⋯O inter-actions.