Intercalation of [Pt(NH3)4]2+ ions into layered sodium silicate magadiite: a useful method to enhance their stabilisation in a highly dispersed state

Al-free layered sodium silicate magadiite has been used as the host material for the stabilisation of [Pt(NH₃)₄]²⁺ ions via intercalation and/or ion-exchange reactions. The stabilisation of Pt(NH₃)₄]²⁺ ions in between the layers of Na-magadiite was confirmed by thermogravimetric analysis (TGA), where increased decomposition temperatures were observed for the intercalated materials. The intercalation behaviour of Na-magadiite was evident from the significant uptake of Pt ions (22.2 wt%). When silica gel was used as the host matrix, negligible uptake of Pt ions (1.3 wt%) was noticed. The X-ray diffraction (XRD) measurements revealed no appreciable change in the basal spacing of the intercalated materials. Nevertheless, the decrease in the intensity of the 001 peak with increasing Pt loadings (from 13.0 to 22.2 wt%) substantiated the intercalation of [Pt(NH₃)₄]²⁺ ions within the interlayer spaces of Na-magadiite. The transmission electron microscopy (TEM) studies of the intercalated materials revealed that [Pt(NH₃)₄]²⁺ ions were homogeneously intercalated in the magadiite matrix, ranging from 2 to 3 nm. Subsequent calcination of the intercalated materials at 600 °C in air led to the formation of Pt nanoparticles supported on silica. The results of XRD and TEM indicated that Pt nanoparticles were highly dispersed on the silica support and were in the range of 5–12 nm. Moreover, chemical analyses confirmed the high loading of Pt on silica in agreement with the TGA results.     

Role of holes states on metal to insulator transition and collapse of magnetic ordering in LaFe1−xNixO3 (x = 0.0–0.5)

Polycrystalline LaFe_1?xNi_xO₃ (x = 0.0, 0.1, 0.3 and 0.5) have been prepared by the standard solid state reactions method. The phase formation has been confirmed by the powerful synchrotron X-ray diffraction experiment. In order to investigate the effects of Ni doping on the oxidation state, spin state and the magnetic ordering of the iron cations, ⁵⁷Fe Mössbauer Spectroscopy has been carried out at room temperature. Iron is present as Fe³⁺ in high spin state in LaFeO₃. Ni doping has no effect on the spin state of the Fe³⁺ cations. However, a progressive increase in the concentration of Fe⁴⁺ cations has been inferred. Relatively stronger covalent character of the Fe⁴⁺–O^?2 bond causes a progressive collapse in the magnetic ordering and delocalization of the hole states.     

Boron-, nitrogen-, aluminum-, and phosphorus-doped graphite electrodes for non-lithium ion batteries

Intercalation of Li⁺, Na⁺, K⁺, Mg²⁺, Ca²⁺, Zn²⁺, and Al³⁺ ions into B-, N-, Al-, and P-doped graphite has been studied using density functional theory calculations. While the intercalation of Li⁺, K⁺, and Ca²⁺ ions into graphite is thermodynamically favorable, that of Na⁺, Mg²⁺, Zn²⁺, and Al³⁺ ions into graphite is unfavorable. When doped in the form of graphitic structure, B, Al, and P dopants significantly stabilize the ion-intercalated graphite compounds. As a result, Na⁺ ions that are unable to intercalate into graphite can intercalate into B-, Al-, and P-doped graphite. The electron transfer from B, Al, and P dopants to host C atoms reinforces the ion–graphene electrostatic interaction, enhancing the thermodynamic driving force for ion intercalation. The catalytic activity of the dopant to promote the ion intercalation increases in the order of N < B < P < Al, which is associated with the electronegativity of the dopant.     

Luminescence characteristics of Eu2+ activated Ca2SiO4 Sr2SiO4 and Ba2SiO4 phosphorsfor white LEDs

<正>This paper investigates the luminescence characteristics of Eu²⁺ activated Ca₂SiO₄,Sr₂SiO₄ and Ba₂SiO₄ phosphors. Two emission bands are assigned to the f-d transitions of Eu²⁺ ions doped into two different cation sites in host lattices,and show different emission colour variation caused by substituting M²⁺ cations for smaller cations.This behaviour is discussed in terms of two competing factors of the crystal field strength and covalence.These phosphors with maximum excitation of around 370 nm can be applied as a colour-tunable phosphor for light-emitting diodes（LEDs） based on ultraviolet chip/phosphor technology.     

Ab initio study of sodium intercalation into metal oxides

Using the full-potential linearized augmented plane wave (FP-LAPW) method, we have studied the effect of chemistry on the average intercalation voltage (AIV) caused by the Na ions intercalating into transition metal oxides. The effect of transition metal was systematically studied by varying M=Co, Ni and Mn in NaMO₂ and fixing the α-NaFeO₂ layered structure. The effect of the guest atoms into the host material is discussed in terms of the structural and electronic properties. Comparatively to Li intercalation, a significant electron transfer towards transition metal was found. This observation suggests that the transition metal contribute to the AIV determination and confirms the common assumption that intercalated electron reduces M⁴⁺ to M³⁺.     

Surface structure of magnetite (111) under hydrated conditions by crystal truncation rod diffraction

X-ray crystal truncation rod (CTR) diffraction under hydrated conditions at circum-neutral pH was used to determine the surface structure of Fe₃O₄(111) following a wet chemical mechanical polishing (CMP) preparation method. The best-fit model to the CTR data shows the presence of two oxygen terminated domains that are chemically inequivalent and symmetrically distinct in the surface contribution ratio of 75% oxygen octahedral-iron (OOI) termination (^aO_2.61–^aO_1.00–^oh1Fe_2.55–^bO_1.00–^bO_3.00–^td1Fe_1.00–^oh2Fe_1.00–^td2Fe_1.00–R) to 25% oxygen mixed-iron (OMI) termination (^bO_1.00–^bO_3.00–^td1Fe₀–^oh2Fe_1.00–^td2Fe_1.00–^aO_3.00–^aO_1.00–^oh1Fe_3.00–R). An adsorbed water layer could not be constrained in the best-fit model. However, bond-valence analyses suggest that both of the surfaces are hydro-oxo terminated. Furthermore, the topmost iron layers of both domains are inferred to be occupied with the redox active Fe²⁺ and Fe³⁺ cations indicating that these irons are the principle irons involved in controlling the surface reactivity of magnetite in industrial and environmentally relevant conditions.     

Characterization of natural chromite ((Mg,FeII)(Al,FeIIICr)2O4) samples from the Bushveld Complex,South Africa

Fe³⁺/Fe²⁺ ratios were determined for a suite of chromite samples from the Bushveld Complex, South Africa, using⁵⁷Fe Mössbauer spectroscopy and a ceric sulphate titration method. Two distinctly different types of chromite were identified. Type I chromites have low Fe³⁺/Fe²⁺ ratios (between 0.2 and 0.4), and contain 3 cations for every 4 oxygen ions in the chemical formula unit. Type II chromites, on the other hand, have Fe³⁺/Fe²⁺ ratios between 0.7 and 1.3, and contain considerably less than 3 cations per 4 oxygen ions in the formula unit. Type II chromites result from the oxidation of type I chromites and can be reduced back to the latter by heating in a gas mixture containing 1% CO and 99% CO₂ at 1000 °C.     

Emission color variation of M2SiO4:Eu (M=Ba, Sr, Ca) phosphors for light-emitting diode

The luminescent properties of alkaline earth orthosilicates M₂SiO₄ (M=Ba, Sr, Ca) doped with Eu²⁺ ions are investigated. Two emission bands are assigned to the f-d transitions of Eu²⁺ ions doped into two different cation sites in host lattices confirmed by electron paramagnetic resonance signal. Two emission bands show the different emission color variation with substituting M²⁺ cations with smaller cations. This behavior is discussed in terms of two competing factors of the crystal field strength and covalence. Also the decay times are in order of 600-1000 ns. These phosphors with maximum excitation of around 370 nm can be applied as a color-tunable phosphor for light-emitting diode based on ultraviolet chip/phosphor technology.     

Turn-off Fluorescence Chemosensor for Iron with Bis(2-aminoethyl)-2-(9-fluorenyl)malonamide Functionlized SBA-15

An bis(2-aminoethyl)-2-(9-fluorenyl)malonamide as fluorophore ligand was immobilized onto mesoporous silica type SBA-15 via post synthesis grafting. The obtained material was characterized by small and wide angle X-ray diffraction, N₂ adsorption–desorption, Fourier transform infrared spectroscopy, Raman spectroscopy and thermogravimetric analysis that indicate the successful immobilization of the ligand on the surface of mesoporous silica. The sensing ability of the obtained material was studied by addition of the cations Fe³⁺, Mg²⁺, Cr³⁺, Co²⁺, Ni²⁺, Cu²⁺, Hg²⁺ and Zn²⁺ to water suspensions of the assayed solid. Of all the cations tested addition of Fe³⁺ ion to a suspension of this material resulted in the largest decrease in the fluorescence intensity. Turn-off photoluminescence of this material was remarkably observed for iron ions in comparing of the other cations. A good linearity between the fluorescence intensity of this material and the concentration of Fe³⁺ ion is constructed, which enables it as a fluorescence chemosensor for detecting the Fe³⁺ ion with a suitable detection limit of 1.35?×?10^?5. It can be introduced as a novel fluorescent sensor in aqueous solution for a lot of practical applications in chemical, environmental and biological systems.     

Evidence for ammonia oxidation and the ionic nature of ammoniated titanium disulfide

In order to elucidate the nature of Lewis bases in layered transition metal dichalcogenides (TX₂), ammoniated titanium disulfide, (NH₃)_yTiS₂ with 0.4 ? y ? 0.6, has been synthesized using stoichiometric TiS₂ and investigated by X-ray diffraction, vapor pressure measurements, thermogravimetric analysis, differential scanning calorimetry, and SQUID magnetrometry. These intercalation compounds lose ammonia rapidly at ambient temperature to form primarily a stage II structure. Upon heating, about half of the ammonia is weakly bound (deintercalation enthalpy ?2.6 kcal/mol) and leaves the TiS₂ host at low temperatures (?75°C), whereas the other half is bound more strongly (deintercalation enthalpy ?6.3 kcal/mol) and deintercalates only at higher temperatures (?150°C). The more strongly bound ammonia is identified as NH₄⁺, and an electron is donated to the TiS₂ conduction band for each NH₄⁺-ion present. Hence, the ionic formulation (NH₄⁺)_y' (NH₃)_y'TiS₂^{y' -} best describes these materials, where the NH₄⁺ ions are analogous to alkali-metal cations M⁺ in metal-ammonia intercalation complexes. The presence of a substantial concentration of NH₄⁺ provides a simple explanation of the unusual observation that the C₃ axis of NH₃ is parallel to the TiS₂ layers. The results of this study show that redox reactions do indeed play an important role in ammonia intercalation into TiS₂ and probably also into other TX₂ hosts.     

Sodium Intercalation of Graphene Films on Re( $$10\bar 10$$ 10 1 ¯ 0 )

It is shown that during low-temperature (300–500 K) intercalation of sodium atoms into thin multilayer graphene and graphite films on rhenium the first graphene layer plays the role of a trap to which atoms coming on the surface diffuse through a graphite film. The intercalation phase of the interlayer space in the graphite bulk is actively filled at a sodium atoms concentration under the first graphene layer close to the maximum possible (2 ± 0.5) × 10¹⁴ cm^–2. This phase capacity is proportional to the graphite film thickness that can be varied in this work from one graphene layer to ~50 atomic layers. The diffusion energy E _d of Na atoms through the graphite film was estimated to be E _d ≈ 1.4 eV.

     

Infrared diffuse reflectance spectra of micropowders of Ni<Subscript>1–<Emphasis Type="Italic">x</Emphasis></Subscript>Zn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> ferrites

The results of experimental studies of the IR diffuse reflectance spectra in the range from 4000 to 50 cm^–1 of Ni_1–xZn_xFe₂O₄ ferrite micropowders with different concentrations of nickel and zinc are presented. The dependence of the intensity of the IR spectra of these ferrites on the changing concentrations of Fe²⁺ and Fe³⁺ cations in ferrites of different compositions is found. The features of change of the reflectance spectra are studied depending on the ferrite compositions, and an interpretation of the observed spectral structures is proposed.     

Synthesis and characterization of K2NiF4-type phases Ln0.5Sr1.5Mn0.5Fe0.5O4 (Ln = La, Nd, Gd, and Dy)

A systematic investigation of layered perovskite oxides with general formula Ln_0.5Sr_1.5Mn_0.5Fe_0.5O₄ (Ln?=?La, Nd, Gd, and Dy) has been undertaken mainly to understand their structural, magnetic, as well as electrical behavior. The materials were prepared by the ceramic method. X-ray data have been analyzed by using program Checkcell and the variations of various parameters are explained. It has been concluded that not only A-site cation radius, <r _A>, but also the size variance factor (σ ²) influence electrical and magnetic properties. A systematic study of electrical resistivity of all the four materials was undertaken as a function of temperature to understand the conduction mechanism. On analyzing the electrical resistivity data, it has been concluded that variable range hopping model is found to fit well. The magnetic studies suggest that the phases are antiferromagnetic and this behavior could arise from Mn⁴⁺–O–Mn⁴⁺, and Fe³⁺–O–Fe³⁺ superexchange interaction.     

Theoretical explanation for the DNA cleavage by GO with cation: anti-cooperativity effect among the π⋯π, cation⋯π/σ and H-bonding interactions in cytosine⋯GO⋯Mn+ (Mn+ = Na+, Mg2+, Al3+)

In order to reveal the nature of DNA cleavage by inorganic intercalator GO (graphene oxide) with cation, the cooperativity effects among the π?π, cation?π/σ and H-bonding interactions were evaluated in the cytosine?GO?Mⁿ⁺ (Mⁿ⁺?=?Na⁺, Mg²⁺, Al³⁺) model systems using the M06-2X, MP2 and ω B97X-D methods with the 6-311++G(2d,p) and 6-311++G(3df,3pd) basis sets. The Mⁿ⁺?O (ether) and N–H?O interactions induce the formation of the π?π stacking between cytosine and GO, and the anti-cooperativity effect are dominant in controling of the aggregation process of cytosine, GO and Mⁿ⁺, which was confirmed by the AIM (atoms-in-molecules) and RDG (reduced density gradient) analyses. Furthermore, the solvent effects of H₂O weaken greatly the anti-cooperativity effects. Thus, a deduction on the DNA cleavage by GO?cation with the intercalation mode is put forward: due to the anti-cooperativity effect and solvent effect, the π?π stacking is weakened in the complexes with Na⁺ or broken in those with Mg²⁺ or Al³⁺. Then the GO?Mg²⁺ moiety is squeezed out from the intercalating sites, leading to an invalid cleavage of DNA, while Na⁺ or Al³⁺ is bound tightly to cytosine, with a notable DNA cleavage. This deduction was used to explain reasonably the previous experimental phenomena.     

A study on the effect of melt-intercalation of PEO in HNbWO6

Polyethylene oxide (PEO) has been introduced into HNbWO₆·1.5H₂O using melt-intercalation technique and its effect on the structure and properties of the host material studied using powder X-ray diffraction, FT-IR, impedance spectroscopy and TGA/DTA measurements. The intercalation reaction leads to loss of stacking coherence along the c-axis of the host layered material, as evidenced by the XRD data. FT-IR spectra of the nanocomposite show changes, indicative of complexing of the guest polymer with the host layered structure. TGA/DTA isothermal profiles exhibit marked changes upon prolonged periods of intercalation. The conductivity of the nanocomposite is found to be about 2×10⁻⁶ S/cm.     

Synthesis and electrochemical characterization of M2Mn3O8 (M = Ca,Cu) compounds and derivatives

M₂Mn₃O₈ (M = Ca²⁺, Cu²⁺) compounds were synthesized and characterized in lithium cells. The M²⁺ cations, which reside in the van der Waals gaps between adjacent sheets of Mn₃O₈⁴⁻, may be replaced chemically (by ion-exchange) or electrochemically with Li. More than 7 Li⁺/Cu₂Mn₃O₈ may be inserted electrochemically, with concomitant reduction of Cu²⁺ to Cu metal, but less Li can be inserted into Ca₂Mn₃O₈. In the case of Cu²⁺, this process is partially reversible when the cell is charged above 3.5 V vs. Li, but intercalation of Cu⁺ rather than Cu²⁺ and Li⁺/Cu⁺ exchange occurs during the subsequent discharge. If the cell potential is kept below 3.4 V, the Li in excess of 4 Li⁺/Cu₂Mn₃O₈ can be cycled reversibly. The unusual mobility of + 2 cations in a layered structure has important implications both for the design of cathodes for Li batteries and for new systems that could be based on M²⁺ intercalation compounds.     

Dopant Spin States and Magnetic Interactions in Transition Metal (Fe3+)-Doped Semiconductor Nanoparticles: An EMR and Magnetometric Study

In this work, electron magnetic resonance (EMR) spectroscopy and magnetometry studies were employed to investigate the origin of the observed room-temperature ferromagnetism in chemically synthesized Sn_1?x Fe _x O₂ powders. EMR data clearly established the presence of two different types of signals due to the incorporated Fe ions: paramagnetic spectra due to isolated Fe³⁺ ions and broad ferromagnetic resonance (FMR) spectra due to magnetically coupled Fe³⁺ dopant ions. EMR data analysis and simulation suggested the presence of high-spin (S = 5/2) Fe³⁺ ions incorporated into the SnO₂ host lattice both at substitutional and at interstitial sites. The FMR signal intensity and the saturation magnetization M _s of the ferromagnetic component increased with increasing Fe concentration. For Sn_0.953Fe_0.047O₂ samples, well-defined EMR spectra revealing FMRs were observed only for samples prepared in the 350–600°C range, whereas for samples prepared at higher annealing temperatures up to 900°C, the FMRs and saturation magnetization were vanished due to diffusion and eventual expulsion of the Fe ions from the nanoparticles, in agreement with data obtained from Raman and X-ray photoelectron spectroscopy.     

Electrical conductivity and chemical bond of graphite intercalation compound with fluorine and metal fluoride

Graphite intercalation compounds with fluorine and metal fluoride (MgF₂ or CuF₂) were prepared from petroleum coke and pyrolytic graphite. With progress in the intercalation reaction, the first stage compound with identity period 9.4 Å changed to another structure of identity period 10.7 Å. It was found from ESCA measurements that the chemical interaction between intercalated fluorine and carbon was similar to the covalent bond around the surface and slightly ionic in the bulk. The maximum electrical conductivities in the direction of the ab-axis were (1.9–2.0) × 10⁵ (ωcm)^-1, which were 10–13 times that of the original pyrolytic graphite.     

Intercalation of [Fe8(μ3-O)2(μ2-OH)12(tacn)6] single molecule magnets in saponite clay

We have contacted Na-saponite with aqueous solutions containing a well-defined iron polycation with structuring ligands [Fe₈(μ₃-O)₂(μ₂-OH₂)₁₂(tacn)₆]⁸⁺, which is known as a promising candidate for molecular magnets. When the resulting suspensions were activated with either microwaves or ultrasound, macroscopic-level characterization of the solid phases obtained after centrifugation (elemental analysis, surface area, XRD) suggested the intercalation of stoichiometrically intact polycations in the interlayer space by cation exchange. Furthermore, ⁵⁷Fe Mössbauer spectroscopy and Fe K-edge EXAFS are compatible with a conservation of the structure of the polycations inorganic core: connectivity seems to be maintained, while the polycations must be somewhat flattened by strain due to intercalation. Magnetization curves also appear compatible with a conservation of the polycation nuclearity, although experiments with a magnetically clean clay sample are necessary to confirm this point.     

Localized magnon gap modes in the 2-d Ising antiferromagnets K2CoF4 and Rb2CoF4

The defect (Mn²⁺,Ni²⁺,Fe²⁺) induced magnon gap modes in the layered antiferromagnets K₂CoF₄ and Rb₂CoF₄ were investigated with the methods of FIR absorption-and IR emission spectroscopy. The anisotropic exchange-parameters describing the strongly localized Mn²⁺ spin excitations far below the host lattice magnon band and the Ni²⁺ excitations in the vacinity of this band are presented. In the diluted system K₂Co_1-cMn_cF₄ localized Mn²⁺ cluster modes up to about C≈0.1 were observed. The excitation energy of these modes can only be explained by assuming an anisotropic Mn²⁺-Mn²⁺ exchange which is in contrast to the pure isomorphous system K₂MnF₄. In the spin mismatch system K₂CoF₄: Fe the magnetic moments of the isolated Fe²⁺ impurities are pulled from the plane perpendicular to the c-axis and aligned parallel to the easy axis of the magnetic crystal.