Cobalt Iron Cyanide Research Articles

Construction of potassium cobalt iron cyanide double-hollow nanobubble prisms for high selective adsorption of cesium

A facile self-templating method is developed to synthesize potassium cobalt iron cyanide double-hollow nanobubble prisms (Co-PBA DHNP) with controllable morphologies by using ZIF-67 hollow prisms as templates. Uniform nanoparticles distributed on the surface of Co-PBA DHNP; a cavity is formed inside the nanoparticles, and these hollow ones crosslinked together, forming a bubble-like structure in the shell. Benefiting from the unique double-hollow structure, Co-PBA DHNP displays exceptional performance, including a top adsorption capacity (qm = 494.38 mg/g), a high capability, commendable selectivity to Cs+ even in natural lake brine (KdCs = 2.14 × 106 mL/g), and excellent recyclability. The adsorption kinetics indicate that the equilibrium can be reached in 10 min. Density functional theory calculations reveal that the incorporation energy of Cs+ is lower than that of Na+ or K+, so embedding into the Co-PBA structure of those three ions is thermodynamically feasible. The process where alkali metal ions can be directly dehydrated and enter the Co-PBA lattice is advantageous. The main reason for excellent selectivity in multicomponent aqueous solutions is the ion exchange mechanism between K+ ions in Co-PBA and hydrated Cs+ ions.

Anatase-driven charge transfer involving a spin transition in cobalt iron cyanide nanostructures.

A charge transfer between Fe and Co in cobalt hexacyanoferrate has been observed for the first time by anatase doping. The charge transfer, which involves a spin transition at the Co site, is supported by high-resolution XANES spectra. EXAFS evidenced a consistent change (10%) of the Co-N first shell.

Cobalt–iron cyanide hollow cubes: Three-dimensional self-assembly and magnetic properties

Cobalt–iron cyanide hollow cubes have been synthesized via a poly(vinylpyrrolidone) assisted solvothermal route. A unique formation process: self-assembly followed by Ostwald ripening process, has been put forward to take account for the construction of hollow cubes. The rod-like nanocrystals first assemble as porous cubes via an oriented attachment process. Then, the porous cubes undergo an Ostwald-ripening process, which create interior spaces and result in the formation of hollow cubes. The magnetic property investigation reveals that K 0.22Co 0.58Fe 2.2(CN) 6 hollow cubes exhibit a ferromagnetic behavior.

Mixed valences system in cobalt iron cyanide. Microporous structure stability

Divalent transition metal hexacyanoferrates(III) have a microporous framework appropriate for separation and storage of small molecules. The nature of such porous framework is found in the existence of systematic vacancies of the building unit, the hexacyanoferrate octahedral block, [Fe(CN)6], in the material structure. The relatively low thermal stability appears to be the main limitation of these materials for such applications. In the as-synthesized material the available free volume is occupied by water which, can be removed by moderated heating but always involving decomposition of at least a small sample fraction. For cobalt a unique behavior has been observed. The heating of cobalt(2+) hexacyanoferrate(III) leads to an inner charge transfer to form the mixed valences Co(2+)Co(III) hexacyanoferrate(II,III) system. Since this inner oxidation–reduction reaction does not modify the coordination environments for the involved metals, the porous nature of the parent compound could be preserved and at the same time with a higher thermal stability related to the formation of the most stable ferrous species. The porous structure of the obtained material was evaluated from CO2 adsorption, X-ray diffraction, thermo-gravimetric, and infrared and Mossbauer spectroscopic data. The heat-induced charge transfer is accompanied of a progressive fracture of the material crystallites and also of a decrease for the pore volume as detected by the CO2 adsorption. For comparative purposes, a parallel study on a porous Prussian blue (ferric hexacyanoferrate(II)) species was carried out. The porous framework of this last material is also related to systematic vacancies of the hexacyanoferrate building block but without the mentioned heat-induced charge transfer effect. In this case the sample heating has no effect on the material porous properties.

Mixed valence states in cobalt iron cyanide

Cobalt iron cyanide with both Co and Fe in mixed valence states were prepared and characterized. In this mixed valence system the cobalt atom is found both as high spin Co(2+) and low spin Co(III) while iron always appears in low spin state to form two solid solutions: Co(2+)Co(III) hexacyanoferrates (II,III), and Co(2+)Co(III) hexacyanoferrate (II). Such solid solutions have the following formula units: (Co 2+) x (Co III) 1− x K[(Fe II) 1− x (Fe III) x (CN) 6]· 1 2 H 2O and (Co 2+) 1.5 x (Co III) 1− x K[Fe II(CN) 6]· yH 2O ( 0 ⩽ x ⩽ 1 , 1 ⩽ y ⩽ 14 ). Compounds within these two series were characterized from Infrared, Mössbauer, X-ray diffraction and thermo-gravimetric data, and magnetic measurements at low temperature. A model for their crystal structure is proposed and the structure for a representative composition refined from XRD powder patterns using the Rietveld method. A simple and reproducible procedure to prepare these solid solutions is provided. Within hexacyanoferrates, such mixed valence states system in both metal centres shows unique features, which are discussed from the obtained data.

Heat-induced charge transfer in cobalt iron cyanide

The heating of Co(2+) ferricyanide above 801C induces an inner charge transfer from Co(2+) towards Fe(III) to form the mixed valence system Co(2+)Co(III) ferri- ferro-cyanide. This charge transfer takes place preserving the material framework and forming a solid solution of the initial and final species. The cell edge of the cubic cell (Fm-3m) of this solid solution follows a regular variation with

Observation of the Anisotropic Photoinduced Magnetization Effect in Co−Fe Prussian Blue Thin Films Fabricated by Using Clay Langmuir−Blodgett Films as a Template

Thin films of cobalt-iron cyanide (Co-Fe Prussian blue) have been fabricated by means of the modified Langmuir-Blodgett (LB) method using a smectite clay mineral (montmorillonite). In this combined method, clay LB films play a template role in the formation of the Co-Fe Prussian blue thin layer. The films were revealed to possess a well-organized structure not only in perpendicular directions to the film surface but also in parallel directions to the film surface. The photoinduced electron transfer from the iron ion to the cobalt through the bridging cyanide in the films occurred at low temperature (8 K), similar to that in the bulk Co-Fe Prussian blue. The films clearly exhibited magnetic anisotropy with regards to the direction of the applied magnetic field. Moreover, the photoinduced magnetization effect in the films was also found to be anisotropic.

Physicochemical investigation of cobalt?iron cyanide nanoparticles synthesized by a novel solid?solid reaction in confined space

Cobalt–iron cyanide (Cox[Fe(CN)6]) nanoparticles have been synthesized by a novel solid–solid reaction in the confined space of dry sodium bis(2-ethylhexyl)sulfosuccinate (AOT) reversed micelles dispersed in n-heptane. The reaction has been carried out by mixing two dry AOT/n-heptane solutions containing CoCl2 and K4Fe(CN)6 or K3Fe(CN)6 nanoparticles in the micellar core, respectively. By UV-Vis spectroscopy it was ascertained that, after the mixing process, the formation of stable nanoparticles is fast and complete. Microcalorimetric measurements of the thermal effect due to the Cox[Fe(CN)6] nanoparticle formation allowed the determination of the stoichiometric ratio (x) and of the molar enthalpy of reaction in the core of AOT reversed micelles. The observed behavior suggests the occurrence of confinement effects and surfactant adsorption on the nanoparticle surface. Further structural information was achieved by small-angle X-ray scattering (SAXS) measurements. From all liquid samples, interesting salt/AOT composites were prepared by simple evaporation of the apolar solvent. Size, crystal structure, and electronic properties of Cox[Fe(CN)6] nanoparticles containing composites were obtained by wide-angle X-ray scattering (WAXS) and X-ray photoelectron spectroscopy (XPS).

Theoretical Study of the Charge Transfer Absorption in Cobalt-Iron Cyanide

The photo-induced charge transfer followed by the bidirectional phase transition in Fe-Co Prussian blue compounds is theoretically discussed. The result of ab initio calculations indicates that both the forward and backward transitions are triggered by photo-induced charge transfer excitations between Co-dγ and Fe-dϖ orbitals, although different kinds of Co sites are excited. It is concluded that the charge transfer proceeds by way of the spσ-pπ transition on the nitrogen atom, which can explain such a long range charge transfer between Co and Fe separated by about 5Å.

Microstructural Changes Induced by Thermal Treatment of Cobalt(II) Hexacyanoferrate(III) Compound

Molecular-based magnet cobalt–iron cyanide, K0.2Co1.4[Fe(CN)6]·7H2O, was prepared by coprecipitation. The powder X-ray diffraction indicates a FCC crystal structure with a unit cell constant of 10.25 Å. It has a transition temperature of 11 K. The effects of heat treatment on the microstructures as well as magnetic properties in the compound were studied. Several structures were encountered during the course of annealing from room temperature to 600°C. In the as-prepared (freeze–dried) sample, the majority of the structure was found to be FeIII–CN–CoII, with a minor amount of FeII–CN–CoIII structure. The amount of FeIII–CN–CoII structure decreased as a function of annealing temperature. The third structure, namely CoII–CN–FeIII began to show up after annealing the sample at 100°C. Total decomposition of the cyanide sample occurred at 500°C. A mixture of BCC Fe–Co and a significant amount of (25 wt%) amorphous carbon particles was found in the sample annealed at 600°C.

Ultrafine Cobalt-Iron Cyanide Particles Prepared by Microemulsion Method

Cobalt–iron cyanide particles having ferromagnetic behavior with a Curie temperature TC of 14 to 15 K can be precipitated by mixing CoIICl2 and K3FeIII(CN)6. This similar reaction was carried out in the water pools of reverse micelles. By using nonionic surfactant poly(oxyethylene)5 nonyl phenol ether (NP5) and poly(oxyethylene)9 nonyl phenol ether (NP9) and petroleum ether (PE), reverse micelles can be made with a water pool of specific size which can be usually varied by the water/surfactant ratio. Such combination of surfactant, oil and aqueous solution provides a unique reactor environment for the synthesis of molecular-based magnetic particles of narrow size distribution. Molecular-magnetic powders, K0.28Co1.29[Fe(CN)6] · 6.5 H2O with particle size ranging from 5 to 10 nm have been successfully synthesized by the water-in-oil microemulsion technique. These particles have a Curie temperature of ≈︂14 K as determined using the Curie-Weiss law. High coercivity of 1.8 kOe was also measured for the ultrafine powder at 4.2 K. Structural and magnetic properties of the resulting magnetic materials are reported. This work has shown that microemulsion can be a powerful process to synthesize ultrafine molecular magnet particles exhibiting high coercivity.

Optically induced magnetism in cobalt iron cyanide

Theoretical studies on the recently observed optically induced magnetization in nanoparticles of ${\mathrm{K}}_{0.2}{\mathrm{Co}}_{1.4}{[\mathrm{Fe}(\mathrm{CN})}_{6}{]\mathrm{\ensuremath{\cdot}}6.9\mathrm{H}}_{2}\mathrm{O}$ have been carried out by simulating the solid with representative clusters. Our studies, performed within the density-functional formalism, show that the ground state is supplemented by several excited states with varying spin multiplicities. Illumination of the solid by light results in excitations to different states depending on the photon energy. In particular, it is shown that while red light enhances the magnetization, blue light reduces it---in agreement with the observed changes.

External Magnetic Field Effect on the Photoinduced Magnetization in a Cobalt Iron Cyanide

Abstract We studied the external magnetic field effects on the photoinduced magnetization of a cobalt iron cyanide, K0.4Co1.3[Fe(CN)6]·5H2O. Photoinduced magnetization value was increased ca. 20 % at maximum under the magnetic field of 50000 G at 5 K. In addition, in the ferrimagnetic region (T < Tc = 26 K), the external magnetic field accelerated the rate of photoinduced spin generation. Those data suggest that external magnetic field increases magnetic interaction between the excited state and spin clusters.

Cation-Driven Electron Transfer Involving a Spin Transition at Room Temperature in a Cobalt Iron Cyanide Thin Film

The electronic structure of a cobalt iron cyanide thin film, Na0.4Co1.3[Fe(CN)6]5H2O, was switched from FeIII(low spin)−CN−CoII(high spin) to FeII(low spin)−CN−CoIII(low spin) by exchanging cations in interstitial sites from Na+ to K+. The reverse process was also induced by replacing Na+ with K+. That is, the alkali cations in the interstitial sites dominate the electronic and spin states of the host compound. This type of switching phenomenon can be achieved by choosing a compound with both electronic degeneracy and zeolitic properties.

Reversible Photoinduced Magnetization

Reversible photoinduced magnetization was observed in a cobalt iron cyanide thin film. Magnetic properties of the prussian blue analog, , can be switched between ferrimagnetic and paramagnetic by visible and near‐IR light illumination. The critical temperature after illumination was about 26 K. This material, obtained via an electrochemical route in the form of thin films on an electrode, provides a new system whose magnetic properties can be controlled by both photochemical and electrochemical redox reactions.