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Removal of aqueous manganese using the natural zeolitic tuff from the Vranjska Banja deposit in Serbia.

The natural zeolite tuff from the Vranjska Banja deposit (Serbia) has been studied as sorbent for Mn(II) ions from aqueous solutions. The zeolite sample containing mainly clinoptilolite (more than 70%) removes Mn(II) ions by ion-exchange process, which was confirmed by X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray analysis (EDXS). XPS showed that there is no surface accumulation of Mn but an almost uniform distribution inside the sorbent; EDXS confirmed that Mn(II) replaced the clinoptilolite Na counter ions. The sorption isotherms were studied at 298 K by batch experiments showing that the Mn(II) removal is best described by the Langmuir-Freundlich or Sips model. The kinetics followed the pseudo-second-order model, the activation energy being 128 kJ mol(-1). The intra-particle diffusion is not the rate-controlling step in the sorption of Mn(II) on clinoptilolite. Thermodynamic data suggest spontaneity of the endothermic ion-exchange process in the 298-338 K range.

Natural Zeolites in Water Treatment – How Effective is Their Use

The unique treedimensional porous structure gives natural zeolites various application possibilities. Because of the excess of the negative charge on the surface of zeolite, which results from isomorphic replacement of silicon by aluminum in the primary structural units, natural zeolites belong to the group of cationic exchangers. Natural zeolites have advantages over other cation exchange materials such as commonly used organic resins, because they are cheap, they exhibit excellent selectivity for different cations at low temperatures, which is accompanied with a release of non-toxic exchangeable cations (K+, Na+, Ca2+ and Mg2+) to the environment, they are compact in size and they allow simple and cheap maintenance in the full-scale applications. The efficiency of water treatment by using natural and modified zeolites depends on the type and quantity of the used zeolite, the size distribution of zeolite particles, the initial concentration of contaminants (cation/anion), pH value of solution, ionic strength of solution, temperature, pressure, contact time of system zeolite/solution and the presence of other organic compounds and anions. For water treatment with natural zeolites, standard procedures are used, usually a procedure in column or batch process. More careful consideration of their superb metal removal properties and awareness of possible regeneration or further use of contaminant/metal-loaded forms can considerably increase their environmental application possibilities, with a focus the reduction of high concentrations of cations and anions in drinking water and wastewater, for surface, underground and public municipal water treatment independently or in combination with others physical - chemical methods.

A novel open framework zincophosphate : synthesis and characterization

Abstract The crystallization of a reactive zincophosphate gel (which may contain Co(II) component) in the presence of sodium cations at ambient temperature and pressure yielded products (abbreviated ZnPO-HEX or CoZnPO-HEX) with a novel anionic open framework topology. The Co(II) ions isomorphously replace zinc(II) in this zincophosphate lattice up to 30%. The hopeite phase appears as a precursor in the crystallization of these new products. The single crystal structure determination of CoZnPO-HEX reveals that the structure belongs to the hexagonal P61 space group with unit cell parameters a = 10.447(3) and c = 15.049(5)A. The structure consists of a three-dimensional tetrahedral framework containing one-dimensional six-ring channels. An infinite helix built up of sodium cations and water molecules has been found inside the channel. The helix plays an important structural role because a complete dehydration of the materials is the cause for the transformation of the hexagonal structure to an unknown crystalline phase.

MnO(x) nanoparticles supported on a new mesostructured silicate with textural porosity.

A two-step synthesis of a novel mesostructured silicate, KIL-2, and its manganese-containing analogue, Mn/KIL-2, has been developed. KIL-2 possesses interparticle mesopores with pore dimensions between 5 and 60 nm and a surface area of 448 m(2). The mesopores are formed by the aggregation of silica nanoparticles, which creates a network with interparticle voids. The particle size and the pore diameters depend on the temperature of the ageing step (first step) and on the solvothermal treatment in ethanol (second step), respectively. Mn/KIL-2 contains octahedrally coordinated Mn(3+) (80%) and tetrahedrally coordinated Mn(2+) (20%) ions. Mn(3+) ions are present in the extra-framework MnO(x) nanoparticles with typical dimensions of 2 nm, which are homogeneously distributed throughout the material. Mn(2+) ions occur as isolated manganese framework sites. The material is also able to retain its structure characteristics after the hydrothermal treatment in boiling water. Because of its non-toxic nature and cost-effective synthesis, Mn/KIL-2 thus exhibits properties that are needed for an environment-friendly catalyst.

A Simple NMR‐Based Method for Studying the Spatial Distribution of Linkers within Mixed‐Linker Metal–Organic Frameworks

The spatial distribution of different linkers within mixed-linker metal-organic frameworks crucially influences the properties of such materials. A simple and robust approach based on (1)H spin-diffusion magic-angle-spinning nuclear magnetic resonance measurements and modeling of spin-diffusion curves is presented; this approach facilitates the distinction between homogeneous and clustered distributions. The performance of the approach is demonstrated with an example of an aluminum-based metal-organic material DUT-5, which has framework consisting of biphenyl and bipyridyl dicarboxylic linkers. The distribution is shown to be homogeneous in this material. The approach could be applied to studying other spatially disordered crystalline materials.

Spectroscopic evidence for the structure directing role of the solvent in the synthesis of two iron carboxylates.

Crystal engineering: The synthesis of the known compounds MIL-100(Fe) and MIL-45(Fe) is characterized by spectroscopy. The products are obtained under identical conditions by varying the solvent from pure water to a mixture of water and acetone. The starting solution, the gel, and the final reaction product were characterized by X-ray absorption spectroscopy (see picture).

Preparation and characterization of iron(III) phosphate–oxalate using 1,2-diaminopropane as the structure-directing agent

Abstract Iron(III) phosphate–oxalate (FePO–DAP) crystallizes from a clear solution containing 1,2-diaminopropane (DAP) and oxalic acid at 120 °C under hydrothermal conditions. Doubly protonated DAP is present inside a large one-dimensional 12-membered channel in a disordered manner, its presence creating different environments for the Fe atoms situated across one another at the sides of the channel. This is evident by Mossbauer spectroscopy: the spectrum at 4.2 K exhibits two sextets with an identical isomer shift of about 0.42 mm/s. FePO–DAP undergoes magnetic ordering at a low temperature (19 K).

Synthesis and Catalytic Performance of Hierarchically Porous MIL-100(Fe)@polyHIPE Hybrid Membranes.

Metal-organic frameworks (MOFs) nanoparticles in combination with a nonionic surfactant (Pluronic L-121) are used to stabilize dicyclopentadiene (DCPD)-in-water high internal phase emulsions (HIPEs). The resulting HIPEs containing the MIL-100(Fe) nanoparticles (MIL: Materials of Institut Lavoisier) at the interface between the oil- and the water-phases are then cured, and 100 μm thick, fully open, hierarchically porous hybrid membranes are obtained. The properties of the MIL-100(Fe)@pDCPD polyHIPE membranes are characterized and it is found that up to 14 wt% of the MIL-100(Fe) nanoparticles are incorporated in the hybrid material resulting in an increase of the microporosity up to 130 m(2) g(-1). Hybrid membranes show an appealing catalytic activity in Friedel-Crafts alkylation in a batch mode as well as in a flow-through mode, thereby demonstrating the preserved accessibility of Lewis acidic sites in the MOF nanostructures.

A facile strategy towards a highly accessible and hydrostable MOF-phase within hybrid polyHIPEs through in situ metal-oxide recrystallization

HKUST-1(Cu) and MOF-5(Zn)@polyHIPE hybrid materials were prepared using a metal salt-free technique, wherein metal–organic frameworks were in situ generated from the CuO- and ZnO-nanoparticles through secondary recrystallization. The solid-to-MOF transformation has proven to be a feasible and effective technique for preparing MOF@polyHIPE hybrid materials with a high MOF content of more than 75 wt%. The MOF phase within the hybrid polyHIPEs as disclosed herein exhibits superior micropore accessibility, structure hydrostability and durable CO2 adsorption capacity under humid conditions, not achievable with any of the previously reported methods.

Structure and magnetic properties of a new iron(II) citrate coordination polymer

The new compound [Fe(H2cit)(H2O)]n (NICS-2) is the first neutral ferrous citrate carboxylate that has been synthesized up to now. The iron citrate coordination polymer was hydrothermally synthesized and the structure was solved using single-crystal X-ray diffraction. It crystallizes in an orthorhombic space group P2(1)2(1)2(1) (No. 19), with a = 5.9470 (4), b = 10.402(1) (5), c = 13.5773 (7) Å, V = 839.91 (8) Å(3), Z = 4. Its structure consists of one-dimensional chains of corner-sharing Fe(II)O6 octahedra that are additionally cross-linked with citrate ligands. Chains are additionally stabilized into a pseudo-three-dimensional structure by hydrogen bonds. The measurement of magnetic properties revealed that the magnetic moment is almost constant above 100 K (μeff = 5.1 µB), but decreases rapidly below this temperature most probably due to the appearance of weak antiferromagnetic interactions between Fe atoms. Additionally, analysis of Mossbauer spectra confirmed the presence of divalent Fe atoms in the structure. Thermogravimetrical and X-ray high-temperature diffraction analyses showed the thermal stability of the material up to 548 K.