共查询到20条相似文献,搜索用时 234 毫秒
1.
Catalytic properties of superparamagnetic γ-ferric oxide nanoclusters, which are uniform in terms of size and magnetic properties were studied. The catalysts were supported on the activated silica gel matrix (AGM) prepared from the KSK-2 silica gel of globular structure and on the activated silica matrix (ASM) prepared from layered natural vermiculite. The clusters are active in some reactions of chloroolefin conversions: isomerization of dichlorobutenes and alkylation of benzene with allyl chloride. Their activity in these reactions is many times higher that of usual supported catalysts based on α-ferric oxide. Analysis of the Mössbauer spectra of the 2.5 wt.% Fe/AGM and 2.5 wt.%Fe/ASM samples before and after the reaction at T = 3–300 K shows that during the reaction some Fe III ions arranged in ~2–3-nm γ-Fe 2O 3 nanoclusters magnetically ordered at 6 K are reduced to form a high-spin Fe II complex in the paramagnetic state. According to the macroscopic magnetization data (SQUID) of the initial clusters, curves with hysteresis are observed at 2 K in the plots of forward and backward magnetization, while the 2.5 wt.%Fe/ASM catalyst after the reaction at T = 2 K demonstrates a linear field dependence of the magnetization passing through the coordinate origin. Analysis of the Mössbauer spectra and magnetic properties suggests that during the catalytic reaction the Fe III ions in the γ-Fe 2O 3 nanoclusters interact with chloroolefin with the allylic structure to be partially reduced to the Fe II ions that are bound in a complex containing chloride ions and O II ion(s) of the silicate matrix as ligands. This is a reason, probably, for the high catalytic activity of γ-Fe 2O 3 nanoparticles. 相似文献
2.
Tris(2-hydroxymethyl-4-oxo-4H-pyran-5-olato-κ 2O 5,O 4)iron(III) [Fe(ka) 3], has been characterised by magnetic susceptibility measurements Mössbauer and EPR spectroscopy. The crystal structure of [Fe(ka) 3] has been determined by powder X-ray diffraction analysis. Magnetic susceptibility and EPR measurements indicated a paramagnetic high-spin iron centre. Mössbauer spectra revealed the presence of magnetic hyperfine interactions that are temperature-independent down to 4.2?K. The interionic Fe 3+ distance of 7.31?Å suggests spin-spin relaxation as the origin of these interactions. 相似文献
3.
The effect of the addition of a second metals such as Zn and Ni on the calcinaton and reduction of alumina, magnesia and silicasupported iron catalysis with total iron loading of 5wt% is investigated by Mössbauer spectroscopy. It is shown that the reducibility of supported α-Fe 2O 3 is gradually increased by adding the second metal. The values of the magnetic hyperfine field obtained from Mössbauer spectra for the Zn or Ni-added α-Fe 2O 3 or Fe catalysts decreased with increasing second metal loading. 相似文献
4.
Magnetic nanoparticles and those doped with rare-earth metal ions having spinel structure were synthesized, possessing the average particles size of 11.3-13.4 nm. According to Mössbauer spectroscopy data it can be concluded that prepared iron oxide nanoparticles are γ-Fe 2O 3. For materials containing rare-earth elements the decrease of octahedral component surface was observed in comparison to non-doped material, what can be explained by Eu 3+, Sm 3+ и Gd 3+ ions occupying the octahedral position. 相似文献
5.
57Fe Mössbauer spectra of 30CaO·15Al 2O 3·5Fe 2O 3·25PbO·25P 2O 5 glass consist of two quadrupole doublets due to distorted Fe(III)O 6 and Fe(II)O 6 octahedra. Mössbauer spectra of the aluminophosphate glass irradiated with 60Co γ-rays (≈5·10 4Gy) were essentially the same as those of non-irradiated glass. Mössbauer spectra of γ-ray irradiated aluminophosphate glass, containing 10 stable isotopes (Sr, Y, Zr, Nb, Mo, Ba, La, Ce, Pr, and Nd) as the simulated nuclear waste, were also the same as those of non-irradiated glass. These results indicate that the aluminophosphate glass containing iron and lead has high radiation-durability, in addition to high heat resistivity and high water resistivity. 相似文献
6.
The chemical state of particles of 5wt% Fe in α-Fe 2O 3 and the subsequently reduced iron particles supported on different particle size (50–200 mesh) of silica (SiO 2), alumina (Al 2O 3), magnesium oxide (MgO) and carbon (C) was examined by Mössbauer spectroscopy at various stages of calcination and reduction. The particle size of the α-Fe 2O 3 supported on different mesh sizes (50, 100, 140, 200 mesh) of SiO 2 has been determined. The strength of metal-support interaction with respect to the kind of support was found to be MgO>SiO 2>Al 2O 3>C. 相似文献
7.
The effect of the structure of a mixture of industrially produced iron and iron oxide on the decomposition of trichloroethylene (TCE) was investigated by gas chromatography, scanning electron microscopy, Fourier transform infrared spectroscopy, energy dispersive X-ray analysis, X-ray diffractometry, and 57Fe-Mössbauer spectroscopy. The concentration of 10 mg L ?1 TCE aqueous solution decreased to 0.41, 0.52, 0.26, and 0.09 mg L ?1 when stirred for 7 days with iron–iron oxide mixtures having mass ratios of 2:8, 3:7, 4:6, and 5:5, respectively. The Mössbauer spectra of the mixtures after leaching were composed of two sextets with respective isomer shifts (δ) and internal magnetic fields ( H) of 0.29 ±0.01 mm s ?1 and 48.8 ±0.1 T, and 0.64 ±0.01 mm s ?1 and 45.5 ±0.1 T, attributed to the Fe 3+ species in tetrahedral ( T d) and the Fe 2+ and Fe 3+ mixed species (Fe 2.5+) in octahedral ( O h) sites, respectively. Mössbauer spectra of a 3:7 mass ratio iron–iron oxide mixture showed a gradual decrease in the absorption area ( A) of zero valent iron (Fe 0) from 40.6. to 12.6, 13.2, 3.8 2.8, and 1.0 ±0.5 % and an increase in A of Fe 3O 4 from 31.8 to 59.4, 71.4, 93.2, 95.6, and 98.0 ±0.5 % after leaching with 10 mg L ?1 TCE aqueous solution for 1, 2, 3, 7, and 10 days, respectively. Consistent values of the first-order rate constant were calculated as 0.32 day ?1 for Fe 0 oxidation, 0.34 day ?1 for Fe 3O 4 production, and 0.30 day ?1 for TCE decomposition, which indicates that the oxidation of Fe 0 was the rate-controlling factor for Fe 3O 4 production and TCE decomposition. It is concluded from the experimental results that an iron–iron oxide mixture is very effective for the decomposition of TCE. 相似文献
8.
The tris(2-chloromethyl-4-oxo-4 H-pyran-5-olato-κ 2O 5,O 4)iron(III), [Fe(kaCl) 3], has been synthesized and characterized by the crystal structure analysis, magnetic susceptibility measurements, Mössbauer, and EPR spectroscopic methods. The X-ray single crystal analysis of [Fe(kaCl) 3] revealed a mer isomer. The magnetic susceptibility measurements indicated the paramagnetic character in the temperature range of 2 K–298 K. The EPR and Mössbauer spectroscopy confirmed the presence of an iron center in a high-spin state. Additionally, the temperature-independent Mössbauer magnetic hyperfine interactions were observed down to 77 K. These interactions may result from spin–spin relaxation due to the interionic Fe 3+ distances of 7.386 Å. 相似文献
9.
A Debye temperature θ D of 378 (±5K) has been obtained by applying a simplified Debye model to the 57Fe Mössbauer spectra of 60CaO·39Ga 2O 3· 57Fe 2O 3 glass. The θ D value is comparable to those (280–580 K) obtained so far in several oxide glasses, glass-ceramics, and ceramics in which Mössbauer atoms are covalently bonded to oxygen atoms and play a role of network former. It proves that Fe(III) atoms occupy the substitutional sites of Ga(III) constituting distorted GaO 4 tetrahedra. 相似文献
10.
Magnetic iron oxide (magnetite, Fe 3O 4) nanoparticles were encapsulated with polystyrene to give a stable water‐based magnetic polymer latex, using the miniemulsion polymerization technique. The resulting magnetic latexes were characterized with transmission electron microscopy (TEM), dynamic light scattering (DLS), vibrating sample magnetometer measurements (VSM), and 57Fe Mössbauer spectroscopy measurements. TEM revealed that all magnetite nanoparticles were embedded in the polymer spheres, leaving no empty polystyrene particles. The distribution of magnetite particles within the polystyrene spheres was inhomogeneous, showing an uneven polar appearance. The DLS measurements indicated a bimodal size distribution for the particles in the latexes. According to our magnetometry and Mössbauer spectroscopy data, the encapsulated magnetite particles conserve their superparamagnetic feature when they are separated in the polymer matrix. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4802–4808, 2004 相似文献
11.
The effect of calcination temperature on the state of the active component of iron-containing catalysts prepared by the impregnation of silica gel with a solution of FeSO 4 and on their catalytic properties in selective H 2S oxidation to sulfur was studied. With the use of thermal analysis, XPS, and Mössbauer spectroscopy, it was found that an X-ray amorphous iron-containing compound of complex composition was formed on the catalyst surface after thermal treatment in the temperature range of 400–500°C. This compound contained Fe 3+ cations in three nonequivalent positions characteristic of various oxy and hydroxy sulfates and oxide and sulfate groups as anions. Calcination at 600°C led to the almost complete removal of sulfate groups; as a result, the formation of an oxide structure came into play, and it was completed by the production of finely dispersed iron oxide in the ?-Fe 2O 3 modification (the average particle size of 3.2 nm) after treatment at 900°C. As the calcination temperature was increased from 500 to 700°C, an increase in the catalyst activity in hydrogen sulfide selective oxidation was observed because of a change in the state of the active component. A comparative study of the samples by temperature-programmed sulfidation made it possible to establish that an increase in the calcination temperature leads to an increase in the stability of the iron-containing catalysts to the action of a reaction atmosphere. 相似文献
12.
Iron-57 Mössbauer spectroscopy confirms a high sensitivity of the three-dimensional magnetic ordering temperature (T Néel) for a series of new intergrowth phases to both oxygen stoichiometry and the partial substitution of iron by copper and aluminium in the Ruddlesden-Popper phase LaSr 3Fe 30 10?δ. The chemical isomer shifts suggest that significant covalent electron delocalization exists in these phases. Spectra for the paramagnetic phases indicate two distinct iron coordination environments consistent with x-ray and neutron diffraction structure determinations. The Mössbauer spectra at 4.8 K exhibit the overlap of two magnetic hyperfine patterns corresponding to cooperative magnetic order at the iron sites with internal fields of 45 and 27 Tesla for nominal Fe 3+ and Fe 4+ sites respectively. 相似文献
13.
Magnetic nanocomposites γ-Fe 2O 3/silica were prepared by a one-step sol-gel method. The sol was prepared by TEOS (tetraethyl orthosilicate) acid hydrolysis in the presence of an iron salt soluble in methanol. After gelation and drying, the transparent samples were characterized after treatment at different temperatures. The particle size, observed by HR TEM, was in the range of 2–10 nm and depended on Fe-concentration and heating temperature. Magnetic measurements showed either a ferromagnetic or a superparamagnetic behaviour and could be explained by the particle size. The dependence of the magnetic behaviour on the particle size was also studied by Mössbauer spectroscopy. The samples in which the Fe 2O 3 particle size was approximately 10 nm showed magnetic splitting (sextet) at room temperature, while smaller particles (2–3 nm) showed this splitting only at the temperature of liquid helium. The optomagnetic properties of the samples were also measured (Kerr effect). 相似文献
14.
The thermal decomposition of iron(III) succinate, Fe 2(C 4H 4O 4) 2(OH) 2 and iron(III) adipate pentahydrate, Fe 2(C 6H 8O 4) 3·5 H 2O, has been investigated at different temperatures for different time intervals in static air atmosphere using Mössbauer spectroscopy and nonisothermal techniques (DTG-DTA-TG). The reduction of iron(III) to iron(II) species has been observed at 533 K and 563 K in the case of iron(III) succinate and iron(III) adipate, respectively. At higher temperatures, α-Fe 2O 3 is formed as the final thermolysis product. 相似文献
15.
The phase composition of carbon nanotubes (CNTs) with encapsulated iron atoms was studied by 57Fe Mössbauer spectroscopy. The synthesis of CNTs was shown to stabilize iron atoms as both thermodynamically stable iron carbide and oxide phases and phases not characteristic under synthesis conditions (γ-Fe and γ-Fe 2O 3). In addition, an analysis of the data obtained led us to suggest the existence of Fe-CNT atomic complexes in interlayer positions. CNTs and iron-containing phases were shown to be stable when subjected to prolonged annealing in air at temperatures up to 670 K. 相似文献
16.
A series of nanostructured iron compounds including cubic Fe 3O 4 and orthorhombic FeOOH were synthesized via a facile low temperature (in the range of 60?100°C) solution method. In the whole process, the interaction between FeCl 2·4H 2O and methenamine (C 6H 12N 4) was carried out through a reflux device under different reaction conditions such as temperature, solvent, and duration. The samples were detected by XRD, TEM, SAED, physical property measurement system, and Mössbauer spectroscopy, separately. The experiments showed that magnetic mixture nanoparticles had flake and rod morphologies, and cubic Fe 3O 4 took on grain nanostructure. Magnetism measurements indicated that the saturated magnetization of the as-obtained magnetic mixture was lower than that of the cubic magnetite. Mössbauer spectroscopy testified the sample consisting of cubic magnetite rather than γ-Fe 2O 3. In addition, a possible growth mechanism of cubic magnetic nanoparticles under different conditions was discussed. 相似文献
17.
The relationship between local structure and visible-light activated photocatalytic effect of simulated domestic waste slag glass–ceramics (R-NaWSFe) was investigated. The largest pseudo-first-order rate constant of 9.75?×?10?3 min?1 was estimated for methylene blue decomposition test under the visible-light irradiation using R-NaWSFe with additional 30 mass% of Fe2O3 heat-treated at 900 °C for 100 min. The reason for the high photoactivity of this sample was mainly due to nanoparticles of CaFe2O4 and α-Fe2O3 confirmed by the Mössbauer spectrum measured at 77 K. It is concluded that the nanoparticles of magnetic components in silica are essential for exhibiting visible-light activated catalytic effect. 相似文献
18.
The Mössbauer spectra of 57Fe 3+ substituted in 0.2 to 0.4 atom % of the octahedral sites in the host lattices Na 0.9Mg 0.45Ti 1.55O 4, TiO 2, Sc 2O 3, LiScO 2 and MgAl 2O 4 have been examined. Hyperfine splittings of the spectra were observed for all cases except Sc 2O 3. In all cases the electron spin resonance spectrum was found, or has been shown to be highly anisotropic as a result of the presence of strong axial or rhombic fields and consequent splitting of the 3 d5 ground state energy levels. In several cases resolution of the and Mössbauer spectra was observed. Mössbauer spectra of the solid solutions Na 0.9Mg 0.45Ti 1.55O 4Na 0.9Fe 0.9Ti 1.1O 4, LiScO 2LiFeO 2 and TiO 2FeNbO 4 have also been examined. 相似文献
19.
Mullite-type Bi 2(Ga 1-xFe x) 4O 9 solid solutions, with 0.1 ≤ x ≤ 0.9, have been synthesized by a combination of mechanical and thermal treatments of a Bi 2O 3/Ga 2O 3/α-Fe 2O 3 stoichiometric mixture. The microstructure of the as-prepared materials on the long-range and local atomic scales was investigated by X-ray diffraction and 57Fe Mössbauer spectroscopy, respectively. The XRD data analysis revealed in all cases linear dependence of the lattice parameters related on x. Due to the ability of the applied Mössbauer spectroscopy to probe the local environment of Fe cations, the local structural disorder in investigated solid solutions is provided. It was shown that the presence of Fe 3+ cations in octahedral sites of the orthorhombic structure causes a local distortion of polyhedra in the material. The preferential occupation of Fe in octahedral site was revealed. Detailed quantitative information on both the cation distribution and the bond lengths provided is discussed in relation to the derived hyperfine parameters. 相似文献
20.
A relationship between local structure and visible light activated catalytic effect of iron containing soda lime silicate glass with the composition of 15Na 2O·15CaO· xFe 2O 3·(70- x)SiO 2, x = 5–50 mass %, abbreviated as NCFS x was investigated by means of 57Fe-Mössbauer spectroscopy, X-ray diffractometry (XRD), small angle X-ray scattering (SAXS), electrospray ionization mass spectrometry (ESI–MS) and ultraviolet–visible light absorption spectroscopy (UV–Vis). Mössbauer spectra of NCFS x glass with ‘ x’ being equal to or larger than 30 after isothermal annealing at 1,000 °C for 100 min consisted of a paramagnetic doublet and a magnetic sextet. The former had isomer shift ( δ) of 0.24 mm s ?1 and quadrupole splitting ( Δ) of 0.99 mm s ?1 due to distorted Fe IIIO 4 tetrahedra, and the latter had δ of 0.36 mm s ?1 and internal magnetic field ( H int) of 51.8 T due to hematite (α-Fe 2O 3). The absorption area ( A) of α-Fe 2O 3 varied from 47.2 to 75.9, 93.1, 64.8 and 47.9 % with ‘ x’ from 30 to 35, 40, 45 and 50, indicating that the amount of precipitated α-Fe 2O 3 varied with the Fe 2O 3 content of NCFS x glass. The precipitation of α-Fe 2O 3 was also confirmed by XRD study of annealed NCFS glass with ‘ x’ larger than 30. A relaxed sexted with δ, H int and Γ of 0.34 mm s ?1 and 37.9 T and 1.32 mm s ?1 was observed from the Mössbauer spectra of annealed NCFS x glass with ‘ x’ of 45 and 50, implying that the precipitation of non-stoichiometric iron hydroxide oxide with the composition of Fe 1.833(OH) 0.5O 2.5 having the similar structure of α-Fe 2O 3 and α-FeOOH. A remarkable decrease in the concentration of methylene blue (MB) from 10 to 0.0 μmol L ?1 with the first-order rate constant ( k) of 2.87 × 10 ?2 h ?1 was observed for 10-day leaching test using annealed NCFS50 glass under visible light irradiation. ESI–MS study indicated that existence of fragments with m/ z value of 129, 117 and 207 etc. originating from MB having m/ z of 284. This result evidently showed that the MB concentration decreased due to visible light induced decomposition caused by the visible light activated catalytic effect of α-Fe 2O 3 and/or Fe 1.833(OH) 0.5O 2.5 precipitated in soda-lime silicate glass matrix. 相似文献
|