Radius Of Fe3 Research Articles

Self‐sacrificial Templated Synthesis of Fe/N Co‐doping TiO2 for Enhanced CO2 Photocatalytic Reduction

AbstractAs a green photocatalyst, TiO2 has been widely used in adsorption, desorption and redox reactions, but the wide energy band and moderate visible light absorption have greatly inhibited its applications in photocatalysis. The effective method of enhancing the performance of catalysts is the development of heterojunction and metal‐nonmetal co‐doping. Herein, Fe−N co‐doped TiO2 heterojunction photocatalysts (FexTi@C) were successfully synthesized by calcining a self‐sacrificial template (NH2−MIL‐125(Ti)) injected with Fe3+ solution. X‐ray diffraction (XRD), transmission electron microscopy (TEM), X‐ray photoelectron spectroscopy (XPS), N2 adsorption/desorption analysis, and photoelectrochemical tests were used to characterize FexTi@C, showing multiple rutile/anatase TiO2 heterojunction structure, low bandgap, and significant absorption in visible light. In addition, the Ti−O−Fe tetrahedra and more oxygen vacancies were provided since the doped N is from the pristine MOF and the radii of Fe3+ and Ti4+ are similar, which improved the photocatalytic efficiency of CO2 reduction to CH4, especially the Fe0.8Ti@C reached 7.8‐fold and 10.2‐fold CH4 yield increase compared with the original TiMOF template and the undoped Ti@C, respectively. This work presents a simple method for the fabrication of low bandgap semiconductors, and also makes a new attempt at the synergistic effect between the in‐situ elements and valence bonds of MOF‐derived catalysts.

Efficiently enhanced energy storage performance of Ba2Bi4Ti5O18 film by co-doping Fe3+ and Ta5+ ion with larger radius

We present an efficient strategy, that is the co-substitution of Fe3+ and Ta5+ ions with large radius for Ti4+ ion, to enhance energy storage performance of Ba2Bi4Ti5O18 film. For the films co-doped with Fe3+ and Ta5+ ions, the maximum polarization under the same external electric field is improved because the radius of Fe3+ and Ta5+ ions is larger than that of Ti4+ ion. Moreover, due to the composition and chemical disorder, the relaxor properties are also slightly improved, which can not be achieved by the film doped with Fe3+ ions only. What is more, for the films doped with Fe3+ ion only, the leakage current density increases greatly due to the charge imbalance, resulting in a significant decrease in breakdown strength. It is worth mentioning that the breakdown strength of Fe3+ and Ta5+ ions co-doped film does not decrease due to the charge balance. Another important point is the recoverable energy storage density of the films co-doped with Fe3+ and Ta5+ ions has been greatly improved based on the fact that the maximum external electric field does not decrease and the maximum polarization under the same external electric field increases. On top of that, the hysteresis of the polarization has also been improved. Finally, the co-doped films with Fe3+ and Ta5+ ions have good frequency and temperature stability.

Effects of Ga Substitution on Micromorphology and Static Magnetic Properties of Self-Biased M-Type Sr Hexaferrites

The Sr hexaferrites with chemical formula Sr0.4La0.3Ca0.3Fe11.85-xGaxCo0.15O19 (x = 0.0 — 1.4) were manufactured by traditional ceramic method. The affect of Ga substitution on static magnetic properties and micromorphology of M-type Sr (SrM) hexaferrites have been presented in detail. In accordance with the experiment results, as Ga-substituted content x rises up from 0.0 to 1.4, all SrM hexaferrite samples are magnetoplumbite hexagonal structure. The difference between radius of Fe3+ and Ga3+ ions leads to the decrease of lattice constants. As the amount of Ga substitution x increases from 0.0 to 1.4, the 4πMs and 4πMr presents a trend of increasing, but the Hc shows the opposite trend. K1 and Ha of all samples are higher than 2.5×105 J/m3 and 21 kOe respectively, which manifests all samples possess the strong uniaxial anisotropy. The materials discussed in this paper possess huge potential in the application of high frequency self-biased microwave devices.

Structural, Optical and EPR Study of Zn1−xFexO Nanocrystals

Iron-doped ZnO nanocrystals, ZnO (Zn1−xFexO), with doping atomic ratio x = 0.0–0.05, have been synthesized using the sol–gel method to obtain nanoparticles with an average crystal size of around 38.0 nm. Materials were characterized by X-ray fluorescence, Raman and Fourier transform infrared (FTIR) spectroscopies, diffuse reflectance spectroscopy and continuous-wave electron paramagnetic resonance (EPR). FTIR spectroscopies suggest minor change in the Zn–O band occurring in the ZnO environment when the ZnO is Fe doped. X-ray diffraction measurements indicate that lattice parameters of Fe-doped ZnO do not change for all doping levels x. Raman studies show that no peaks disappear when Fe concentration increases, indicating that the incorporation of Fe does not cause an important local structural disarray in the crystalline ZnO lattice. Two broad bands appear at ≈ 570 cm−1 and ≈ 650 cm−1, which are related to the Zn substitution by iron. The band gap does not seem to be influenced by the average crystal size or the cell parameter. It could be because the crystal size is large enough to prevent quantum confinement. X-band EPR spectra recorded at 10 K are similar for all doping levels, x = 0.01–0.05, and are consistent with a spin Hamiltonian composed by isotropic Zeeman and second-order axial symmetry zero-field splitting (ZFS) interactions. Due to the small size of the particles and the difference between the ionic radii of Fe3+ and Zn2+, the EPR spectra are strongly influenced by a static distribution of ZFS parameters, leading to a severe lineshape broadening. An efficient strategy for the simulation process is explained in detail.

Defects characterisation and studies of structural properties of sol–gel synthesised MgFe2O4 nanocrystals through positron annihilation and supportive spectroscopic methods

ABSTRACTMagnesium ferrite (MgFe2O4) nanocrystalline samples were prepared by sol–gel method and by sintering at temperatures from 300°C to 1000°C. X-ray diffraction and electron microscopic studies showed an increase in crystallite sizes and a decrease in lattice constants at higher sintering temperatures. UV-Vis absorption measurements depicted blue shift for samples of smaller crystallite sizes (dc) with a resultant increase of the band gap energies (Eg. = 2.07 eV at dc = 49 nm to 3.10 eV at dc = 6 nm, for samples sintered at 1000°C and 300°C, respectively). Fourier transform infrared spectroscopy of the samples proved the formation of the spinel structure while energy dispersive X-ray analysis pointed out the non-stoichiometric composition, which implied the presence of vacancy type defects that could modify the structural and magnetic characteristics of the compounds. This necessitated the use of positron annihilation lifetime and coincidence Doppler broadening spectroscopic studies for defect characterisation and the results indicated distinct redistribution of cations within the unit cells, making the compound overwhelmingly turn towards a normal spinel configuration at smaller nanocrystalline sizes. Positrons were trapped in larger vacancies of increasing numbers in smaller crystallites. The vacancies turned out to be formed at the octahedral sites where the increased ionic radius of Fe3+ became large enough to reduce the occupancy significantly. Mossbauer spectra analysis indicated an increase of the ferromagnetic properties in samples sintered at higher temperatures. At 300°C and 400°C, the samples dominantly showed paramagnetic behaviour.

Ni addition induced modification of structural, magnetic properties and antistructural modeling of Zn1-xNixFe2O4 (x = 0.0 - 1.0) nanoferrites

Nano-crystalline Zn1-xNixFe2O4 (x = 0.0 - 1.0) nano-ferrites were synthesized by using sol–gel auto-combustion method. X-ray diffraction (XRD), magnetic measurements were used to monitor the effect of Ni addition on structural, magnetic properties. XRD patterns confirm the formation of single phase nanocrystalline cubic spinel structure. For sample with x = 1.0, a small fraction of Fe2O3 was also detected. Calculated parameters revealed that Ni2+ addition changecrystallite sizes (Ds) and (DW-H) respectively in the range between 30.29 – 39.13 nm, and 37.52 – 64.57 nm. Observed changes in the cell volume (V), specific surface area (S), X-ray density (ρXRD), are attributed to the difference in ionic radii of Fe3+, Ni2+, Zn2+ ions. The Ni2+ ions migrate predominantly to octahedral sites (thus pushing ferric ions on A sites) leading to increased inversion parameter and decrease of oxygen parameter (u) from 0.3836 to 0.3796. Exact matching of aexp, ath suggests that the estimated cation distribution is in good agreement with the real distribution and with magnetic data obtained from VSM. Hc varies between 66.49 Oe– 185.20 Oe, while, migration of cations leads to changes in Ms. In order to explain the nature of the surface defects the antistructural model is used in the current study.

Magnetic Properties and Mössbauer Investigations of La0.67Sr0.33FexMn1−xO3 (x = 0 and 0.5) Perovskites

We report magnetic phase separation in pure La0.67Sr0.33FexMn1−xO3 (x = 0 and 0.5) ceramic samples. Rhombohedral crystal structures obtained with R3C space group show no significant changes in the lattice structures due to the close values of ionic radii of Fe3+ and Mn3+ ions. However, significant changes occur in the magnetic properties due to competing ferromagnetic (FM) and antiferromagnetic (AFM) interactions because of the presence of Fe3+ substitution. The FM double exchange interactions (DE) (Mn3+–O–Mn4+) appears suppressed by AFM superexchange interactions (Fe3+–O–Mn4+, Fe3+–O–Fe3+, Mn4+–O–Mn4+). The saturation magnetization for x = 0 has the highest value of approximately 80 emu/g at 2 K, which dropped significantly to approximately 5 emu/g at 2 K for the x = 0.5 sample. The coercivity (Hc) for x = 0.5 increased from 161 Oe at 300 K to 786 Oe at 2 K compared with that of x = 0 which varied from 110 to 150 Oe. A value of Hc(0) = 1.5 ± 0.04 kOe was extrapolated from the model fit to the temperature dependence of Hc. The temperature-dependent 57Fe Mossbauer spectroscopy measurements show the presence of Fe in two different environments that have an AFM Fe3+–O–Mn4+ and Fe3+/2+–O–Fe3+/2+ coordination. The unequal fraction population of Fe ions at both AFM environments seems to increase the exchange bias effect.

Synthesis and Properties of Ni-doped Goethite and Ni-doped Hematite Nanorods

Ni-doped goethite (α-FeOOH) nanorods were synthesized from mixed Fe(III)-Ni(II) nitrate solutions with various Ni/(Ni+Fe) ratios (0, 5, 10, 20, 33 and 50 mol % Ni) by hydrothermal precipitation in a highly alkaline medium using the strong organic alkali, tetramethyl¬ammonium hydroxide (TMAH). Ni-doped hematite (α-Fe2O3) nanorods were obtained by calcination of Ni- doped goethite nanorods at 400 °C. The Ni2+- for-Fe3+ substitution in goethite and hematite was confirmed by determination of the unit cell expansion (due to the difference in the ionic radii of Fe3+ and Ni2+) using XRPD and determination of the reduction of a hyperfine magnetic field (due to the difference in magnetic moments of Fe3+ and Ni2+) using Mossbauer spectroscopy. Single- phase goethite nanorods were found in samples containing 0 or 5 mol % Ni. A higher Ni content in the precipitation system (10 mol % or more) resulted in a higher Ni2+-for-Fe3+ substitution in goethite, and larger Ni-doped goethite nanorods, though with the presence of low crystalline Ni-containing ferrihydrite and Ni ferrite (NiFe2O4) as additional phases. Significant changes in FT-IR and UV-Vis-NIR spectra of prepared samples were observed with increasing Ni content. Electrochemical measurements of samples showed a strong increase in oxygen evolution reaction (OER) electrocatalytic activity with increasing Ni content.

Structural and Dielectric Properties of La0.33Sr0.67M0.33Ti0.67O3±δ (M = Mn or Fe) Perovskites

We have investigated the structural and dielectric properties of La0.33Sr0.67Mn0.33Ti0.67O3+δ (LSMTO) and La0.33Sr0.67Fe0.33Ti0.67O3−δ (LSFTO) perovskites synthesized by the solid-state reaction method at 1500 ∘C Rietveld analysis of X-ray diffraction (XRD) data shows pure crystalline phase with cubic \(Pm\bar {3}m\) structure, with no change in the unit cell volume due to the same ionic radii of Fe3+ and Mn3+. Scanning electron microscopy (SEM) micrographs show that the average grain size is slightly larger for LSMTO than for LSFTO. The electrical response of samples was studied at room temperature using the impedance spectroscopy technique over a broad frequency range (0.1Hz1MHz). The conductivity curves for the two samples were well fitted by the Jonscher law. For the LSFTO sample the hopping process occurs at long distance whereas for LSMTO compound, it occurs between neighboring sites. Variation of the dielectric parameter (e′) and that of the loss factor (e″) for both samples were explained by the different polarization and conductivity mechanisms. For both compounds, the variation of the imaginary part Z? shows a peak at a relaxation frequency (fr) related to the relaxation time (τ) by τ = 1/2πfr. Cole-Cole plots of impedance show the presence of two semicircles for LSMTO sample, whereas LSFTO compound shows one semicircle. To explain the impedance results, an appropriate electrical equivalent circuit has been proposed for each sample.

The Influence of Fe<sup>3+ </sup>Doping on the Crystallization of TiO<sub>2</sub> and their Photocatalytic Activity

TiO2 photocatalysts doped by Fe3+ with different contents were prepared by adsorption phase synthesis. The influence of Fe3+ doping with various concentrations on the crystallization of TiO2 was explored by XRD. Then photodegradation experiments of methyl-orange were employed to evaluate the activity of these photocatalysts. The results indicated that the crystallization of TiO2 was restricted after doping, due to replacement of Ti4+ in TiO2 lattice structure by Fe3+ ions. And the restriction became stronger with doping concentration of Fe3+ ions increasing. Since radius of Fe3+ was close to Ti4+, the restriction of Fe3+ doping on crystallization of TiO2 was so stronger that the photocatalytic activity of most TiO2 doped with Fe3+ ions was lower than that of TiO2 without doping.

Crystallization and Photocatalytic-Activity of TiO<sub>2</sub> Doped with Metal Ions Prepared by Adsorption Phase Synthesis

TiO2 photocatalysts doped with different metal ions were prepared by adsorption phase synthesis. The influence of different dopant metal ions with various concentrations on the crystallization of TiO2 was ex-plored by XRD. Then photodegradation experiments of methyl-orange were employed to evaluate the activity of these photocatalysts. The results indicated that the crystallization of TiO2 was restricted after doping, due to replacement of Ti4+ in TiO2 lattice structure by other metal ions. And the restriction became stronger with radius and concentration of doping ions increasing. There was an optimum dopant concentration appeared during preparation of TiO2 doped with Cd2+ and Fe3+. When dopant concentration was less or more than this optimum value, the photocatalytic activity of TiO2 doped with metal ions was lower than that of TiO2 without doping. Since radius of Fe3+ was close to Ti4+, the influence of Fe3+ dopant concentration on crystallization and activity of TiO2 was more obvious than that of Cd2+ doping.

Optical absorption and EPR study of the octahedralFe3+center in yttrium aluminum garnet

The optical-absorption and EPR spectra of octahedral Fe3+ center in yttrium aluminum garnet have been studied by diagonalizing the complete energy matrices for a d(5) configuration ion in a trigonal ligand field. It is shown that the local lattice structure around an octahedrally coordinated Fe3+ center has an expansion distortion. The expansion distortion may be attributed to the fact that the radius of Fe3+ ion is larger than that of Al3+ ion, and the Fe3+ ion will push the oxygen ligands outwards. Simultaneously, the local lattice structure distortion parameters Delta R=0.0907 A and Delta theta=1.940 degrees for the octahedral Fe3+ center in the crystal are determined. From optical spectra calculation, we confirm that two strong sharp transitions at 407 and 415 nm, which are apparent in the optical absorption spectra for lightly doped YAG:Fe3+ system, should be ascribed to the tetrahedral Fe3+ center. This is also in accord with the conclusion of Rotman [J. Appl. Phys. 66, 3207 (1989)].

Molecular structure of [trans-FeCl2(imidazole)4]Cl·THF·H2O

The structure of [trans-FeCl2(imidazole)4]Cl has been determined as the THF/H2O solvate. The Fe-Cl and Fe-N distances in the cation are shorter than analogous trans-FeCl2(L)4 compounds, concomitant with the decreased ionic radius of Fe3+ versus Fe2+. Crystal data: orthorhombic, Pnma, a = 8.456(2), b = 20.991(4), c = 13.288(3) A, V = 2358.6(8), andZ = 4.