Enhanced photocatalytic degradation of sulfamethoxazole by stable hierarchical Fe2O3/Co3O4 heterojunction on nickel foam

A facile approach was successfully employed to prepare Fe₂O₃/Co₃O₄ nanosheet arrays on nickel foams (Fe₂O₃/Co₃O₄@NF), which owned such advantages as narrow band gap energies and high separation rate of photoexcited electron-hole pairs. The combination of Fe₂O₃ and Co₃O₄ dramatically enhanced the photocatalytic activity towards sulfamethoxazole (SMZ) degradation, with the highest catalytic efficiency of k = 0.0538 min⁻¹, which was much higher than that of Fe₂O₃@NF (0.0098 min⁻¹) and Co₃O₄@NF (0.0094 min⁻¹). The introduction of Ni foam could not only act as the support to anchor photocatalyst, but also work as the electron mediator to promote the transition of electron-hole pairs. Reactive species trapping experiments combined with electron paramagnetic resonance analysis confirmed ^•O₂⁻ was primarily responsible for SMZ degradation. Furthermore, Fe₂O₃/Co₃O₄@NF was effective and almost unaffected by inorganic cations and anions in aqueous solution. This study could provide a facile and promising path for the construction of self-supported metal oxide-based heterojunction with high efficiency and strong stability.     

Visible light induced efficient activation of persulfate by a carbon quantum dots (CQDs) modified γ-Fe2O3 catalyst

In this study, a carbon quantum dots modified maghemite catalyst (CQDs@γ-Fe₂O₃) has been synthesized by a one-step solvothermal method for efficient persulfate (PDS) activation under visible light irradiation. Transmission electron microscopy (TEM), scanning electron microscopy (SEM) and UV–vis diffuse reflectance spectroscopy (UV–vis DRS) characterization indicated that the formation of heterojunction structure between CQDs and γ-Fe₂O₃ effectively reduced the catalyst band gap (E_g), favoring the separation rate of electrons and holes, leading to remarkable efficient sulfamethoxazole (SMX) degradation as compared to the dark-CQDs@γ-Fe₂O₃/PDS and vis-γ-Fe₂O₃/PDS systems. The evolution of dissolved irons also demonstrated that CQDs could accelerate the in-situ reduction of surface-bounded Fe³⁺. Electron paramagnetic resonance (EPR) and radical scavenging experiments demonstrated that both OH and SO₄⁻ were generated in the reaction system, while OH was relatively more dominant than SO₄⁻ for SMX degradation. Finally, the reaction mechanism in the vis-CQDs@γ-Fe₂O₃/PDS system was proposed involving an effective and accelerated heterogeneous-homogeneous iron cycle. CQDs would enrich the photo-generated electrons from γ-Fe₂O₃, causing efficient interfacial generation of surface-bond Fe²⁺ and reduction of adsorbed Fe³⁺. This visible light induced iron cycle would eventually lead to effective activation of PDS as well as the efficient degradation of SMX.     

Infrared spectrum of several double oxides with corundum structure resulting from the transformation of lacunar γ phases with a spinel structure

When aluminum or chormium is substituted by Fe³⁺ ions in α-Fe₂O₃, all the ir bands gradually shift toward high frequencies. Alternatively, for the α phases of type (Fe₂Cr_4?yAl_y)O₉ the transition occurs sharply for a composition y close to 2. For α phases substituted by (Fe_6?yCr_y)O₉-type chromium a linear variation of frequency with chromium content is observed. From ir data it has been shown that, under given temperature and time conditions, an α phase less rich in chromium than the initial product could be obtained by oxidizing iron chromite. The ir spectrum of the oxidation of pure magnetites the size of which is between 1400 and 15000 Å evolves versus the latter to yield either the γ-Fe₂O₃ or the α-Fe₂O₃ phase which can be formed from γ-Fe₂O₃ or by direct oxidation of Fe₃O₄.     

Octahedral distortions in the homometallic Fe ludwigite

An extended Hückel high spin band approach is used to investigate the effects of oxygen octahedral distortions in the Fe₃O₂BO₃ ludwigite. Owing to distortion, a 0.2 eV stabilizing gap (above the spin down Fermi level) is found to appear in a 1D sub-unit, formed by the strongly interacting Fe³⁺-Fe²⁺-Fe³⁺ triad. Through a detailed analysis of the crystal wave functions, the gap is found to be a result of 3d(σ)-3d(π) orbital mixing, which generates a narrow band for the extra (spin down) Fe²⁺ electron. Charge localization is obtained in the 1D sub-unit but not in the whole crystal (3D) calculation. It is suggested that the high barrier for electron hopping, experimentally found in the literature to occur around 220 K, be related to the 1D gap.     

Superparamagnetic behavior of iron oxides supported on porous silica gels

Spinel iron oxide (Fe₃O₄-γ-Fe₂O₃) particles were supported on microbeads of silica gel by the calcination of the silica gel base adsorbing citric acid and Fe³⁺ ions. The X-ray diffraction patterns and the⁵⁷Fe Mössbauer spectra measured for the spinel iron oxide indicated that the particle size of the oxide was regulated by the mean pore diameter (4–82 nm) of the silica gel support employed. In the case of α-Fe₂O₃ particles prepared by using the same silica gel beads, it was revealed by the Mössbauer spectra and the electron micrographs that there were relatively large particles of the oxide on the surface of the beads, in addition to the particles in the silica gel micropores.     

Visible light activated catalytic effect of iron containing soda-lime silicate glass characterized by 57Fe-Mössbauer spectroscopy

A relationship between local structure and visible light activated catalytic effect of iron containing soda lime silicate glass with the composition of 15Na₂O·15CaO·xFe₂O₃·(70-x)SiO₂, x = 5–50 mass %, abbreviated as NCFSx 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 NCFSx 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^IIIO₄ 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-Fe₂O₃). The absorption area (A) of α-Fe₂O₃ 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-Fe₂O₃ varied with the Fe₂O₃ content of NCFSx glass. The precipitation of α-Fe₂O₃ 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 NCFSx 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-Fe₂O₃ 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-Fe₂O₃ and/or Fe_1.833(OH)_0.5O_2.5 precipitated in soda-lime silicate glass matrix.     

Influence of iron ions on the structural properties of some inorganic glasses

The effects of iron on the structural properties of Zn-borosilicate glass and Pb-metaphosphate glass were studied using X-ray diffraction,⁵⁷Fe Mössbauer spectroscopy and IR spectroscopy. Zn-borosilicate glass was prepared with varying amounts of Fe₂O₃ (up to 30% wt.). It was found that the chemical form of added iron (-FeOOH, -Fe₂O₃ or Fe₃O₄) affects the Fe³⁺/Fe²⁺ ratio, as well as the distribution of iron ions at different coordination sites. At high concentration of iron the crystallization of zinc ferrite in the glass matrix takes place. X-ray diffraction and⁵⁷Fe Mössbauer spectroscopy showed that the amount of zinc ferrite in Zn-borosilicate glass decreases with the following order of addition: -FeOOH-Fe₂O₃Fe₃O₄. In Pb-metaphosphate glass doped with high concentration of -Fe₂O₃, the crystallization of Fe₃(PO₄)₂ is pronounced. The assignments of IR band positions and the corresponding interpretation are given. The importance of this study for the technology of vitrification of high-level radioactive wastes is emphasized.     

Influence of the preparation history of α-Fe2O3 on its reactivity for hydrogen reduction

TG experiments on the hydrogen reduction of α-Fe₂O₃ were carried out to elucidate the influence of the preparation history of the oxide on its reactivity. α-Fe₂O₃ samples were prepared by the thermal decomposition of seven iron salts in a stream of oxygen, air or nitrogen at temperatures of 500–1200°C for 1 h. Thirteen metal ions such as Cu²⁺, Ni²⁺, etc. were used as doping agents. The reactivity of the oxide was indicated by the initial reduction temperature (T_i. α-Fe₂O₃ prepared at lower temperatures showed lower T_i values and the reduction proceeded stepwise (Fe₂O₃ → Fe₃O₄ → Fe). T_i values increased with the rise in the preparation temperature of the oxide. The oxides prepared at higher temperatures showed that two reduction steps (Fe₂O₃ → Fe₃O₄ → Fe) proceed simultaneously. the preparation in oxygen gave higher T_i than that in air or nitrogen. The doping by metal ions, except Ti⁴⁺, lowered the T_i of α-Fe₂O₃. The Cu²⁺ ion showed the lowest T_i, while Ti⁴⁺ showed the highest T_i and the inhibition effect.The reduction process was expressed by two equations; Avrami—Erofeev's equation for α-Fe₂O₃ → Fe₃O₄ and Mampel's equation for Fe₃O₄ → Fe.     

Overlooked Formation of Carbonate Radical Anions in the Oxidation of Iron(II) by Oxygen in the Presence of Bicarbonate

Iron(II), (Fe(H₂O)₆²⁺, (Fe^II) participates in many reactions of natural and biological importance. It is critically important to understand the rates and the mechanism of Fe^II oxidation by dissolved molecular oxygen, O₂, under environmental conditions containing bicarbonate (HCO₃⁻), which exists up to millimolar concentrations. In the absence and presence of HCO₃⁻, the formation of reactive oxygen species (O₂⋅⁻, H₂O₂, and HO⋅) in Fe^II oxidation by O₂ has been suggested. In contrast, our study demonstrates for the first time the rapid generation of carbonate radical anions (CO₃⋅⁻) in the oxidation of Fe^II by O₂ in the presence of bicarbonate, HCO₃⁻. The rate of the formation of CO₃⋅⁻ may be expressed as d[CO₃⋅⁻]/dt=[Fe^II[[O₂][HCO₃⁻]². The formation of reactive species was investigated using ¹H nuclear magnetic resonance (¹H NMR) and gas chromatographic techniques. The study presented herein provides new insights into the reaction mechanism of Fe^II oxidation by O₂ in the presence of bicarbonate and highlights the importance of considering the formation of CO₃⋅⁻ in the geochemical cycling of iron and carbon.     

Sub-nanometer,Ultrafine α-Fe2O3 Sheets Realized by Controlled Crystallization Kinetics for Stable,High-Performance Energy Storage

The development of energy devices based on iron oxides/hydroxides is largely hindered by their poor conductivity and large volume changes, especially with regard to specific capacitance and cycle stability. Herein, superior capacitance (1575 F g⁻¹ at 1.25 A g⁻¹) and high rate performance (955 F g⁻¹ at 25 A g⁻¹) were realized by synthesizing sub-nanometer, ultrafine α-Fe₂O₃ sheets loaded on graphene (SU-Fe₂O₃-rGO). An assembled asymmetric supercapacitor showed outstanding cycle stability (106 % retention after 30 000 cycles). This excellent performance arises from the unique structural characteristics of the α-Fe₂O₃ sheets, which not only enrich electrochemically reactive sites, but also largely eliminate the volume changes after long-term charge/discharge cycling. The synthesis of SU-Fe₂O₃-rGO critically depends on control of the crystallization kinetics during growth. A controlled heterogeneous nucleation mechanism results in the formation of atomically thin α-Fe₂O₃ sheets on graphene rather than large particles in solvent, as clarified by theoretical calculations. This strategy paves a new way to synthesizing atomically thin transition metal oxide sheets and low-cost, eco-friendly iron-based energy storage.     

Porous α-Fe2O3 hollow microspheres and their application for acetone sensor

Porous α-Fe₂O₃ hollow microspheres were synthesized through a simple and efficient carbon sphere template method. The samples were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy and N₂ adsorption-desorption. Structural characterization indicated that as-prepared α-Fe₂O₃ hollow microspheres had porous structure with around 200 nm in diameter and thin shell about 10 nm thick. The average pore size and Brunauer-Emmett-Teller specific surface area of α-Fe₂O₃ hollow microspheres were 6.5 nm and 111.6 m²/g, respectively. The gas sensing behavior investigation showed that as-synthesized α-Fe₂O₃ hollow microspheres exhibited very good gas sensing property to acetone vapor.     

Effect of the structural change of an iron–iron oxide mixture on the decomposition of trichloroethylene

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 Fe³⁺ species in tetrahedral (T _d) and the Fe²⁺ and Fe³⁺ 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 (Fe⁰) from 40.6. to 12.6, 13.2, 3.8 2.8, and 1.0_±0.5 % and an increase in A of Fe₃O₄ 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 Fe⁰ oxidation, 0.34 day^?1 for Fe₃O₄ production, and 0.30 day^?1 for TCE decomposition, which indicates that the oxidation of Fe⁰ was the rate-controlling factor for Fe₃O₄ 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.     

X-ray photoelectron spectroscopy investigation of perovskites La1−x Sr x FeO3−y (0 ≤x < 1.0), prepared via a mechanochemical route

Perovskite-structure oxides La_1?x Sr _x FeO_3?y (x = 0, 0.2, 0.6, 1) were synthesized by the mechanochemical method. In order to refine the stoichiometric composition and the charge state of ions, these samples were studied by X-ray photoelectron spectroscopy (XPS). An investigation of perovskites with x = 0, 0.2, and 0.6 in air at room temperature showed that these samples do not contain oxygen vacancies (y = 0), i.e., they are fully oxidized. Hence, to produce electrical neutrality, these samples should contain iron(4+) cations in an amount proportional to the degree of substitution (x) of strontium(2+) for lanthanum(3+). However, no Fe⁴⁺ cations were found in the oxides. All perovskites contain only Fe³⁺ cations, oxygen ions O^2? along with oxygen ions with reduced electron density (O^?). These data provid evidence of the possible electron density redistribution from oxygen ions to iron cations. The fact that the oxides contain oxygen ions with reduced electron density suggests that weakly bound lattice oxygen in substituted perovskites is represented by O^? ions.     

Energetics of binary iron nitrides

High-temperature solution calorimetry in molten sodium molybdate 3Na₂O·4MoO₃ was used to determine the energetics of formation of a series of binary iron nitrides: γ′-Fe₄N, ε-Fe₃N_1+y (y=0, 0.10, 0.22, 0.30, 0.33), ζ-Fe₂N and γ′′-FeN_0.91. The linear relation ΔH°_f (FeN_x)=−65.23x+13.48 kJ mol⁻¹ was found between the enthalpies of formation from the elements at 298 K of iron nitrides FeN_x and their nitrogen content x. Using this linear approximation, the enthalpy of formation of α′′-Fe₁₆N₂ has been estimated to ΔH°_f (Fe₁₆N₂)=85.2±46.8 kJ mol⁻¹.     

Decoration of carbon nanotubes with iron oxide

A magnetic composite of multiwalls carbon nanotubes (MWNTs) decorated with iron oxide nanoparticles was synthesized successfully by a simple and effective chemistry precipitation method. The composite was characterized by X-ray diffraction analysis (XRD), Mössbauer spectrum (MS), transmission electron microscopy (TEM), and Fourier transform spectroscopy (FTIR) techniques. The patterns of XRD and MS indicated that MWNTs, γ-Fe₂O₃, and Fe₃O₄ coexisted in the composite. The TEM observation indicated that the nanoparticles of iron oxide were attached on the surface of the MWNTs, and the sizes of the particles ranged from 25 to 80 nm. FTIR spectra showed that SO₄⁻ functional groups existed on the surface of MWNTs after modification by sodium dodecylbenzene sulfonic acid (SDBS), which could immobilize Fe³⁺ ions onto the MWNTs. The hysteresis loops of the MWNTs and decorated MWNTs were measured by vibrating sample magnetometer (VSM), and the results showed that the composite was ferromagnetism with the saturated magnetization of 20.07 emu/g, and the coercive of 163.44 Oe.     

Untersuchung der ferromagnetischen Produkte der explosiven reaktionen zwischen Ammoniumeisencyanid und Kupfernitrat

The wet mixtures of ammonium hexacyanoferrate, (NH₄)₄[Fe(CN)₆], and cupric nitrate, Cu(NO₃)₂, react explosively when heated at 220 ?C. Among the solid products studied by chemical analysis, magnetic measurements and X-ray diffraction there are magnetite (Fe₃O₄), iron nitride (Fe₄N), gamma iron oxide (γ-Fe₂O₃), cuprous oxide (Cu₂O), alpha iron oxide (α-Fe₂O₃), cupric oxide (CuO), cuprous ferrite and metallic copper. Furthermore cupric hexacyanoferrate (Cu₂[Fe(CN)₆]) and ferric ferrocyanide (Fe₄[Fe(CN)₆]₃) have been found in weakly ferromagnetic products. The presence of these phases and their quantitative contribution depend upon the proportion of the initial salts and air supply.     

The electrical,optical and photoconducting properties of Fe2−xCrxO3 (0 ⩽ x ⩽ 0.47)

A study has been made of the electrical, optical and photoconducting properties of pure and reduced single crystals of composition Fe_2?xCr_xO₃ where 0 ? x ? 0.47. It has been found that pure α-Fe₂O₃ is not a photoconductor. When defect-free crystals of α-Fe₂O₃ are reduced a surface layer of Fe₃O₄ is formed and the crystals exhibit photoconductivity. Removal of this layer resulted in the disappearance of photocurrents and an increase in the sample resistivity. A necessary condition for the observation of photocurrents in n-type Fe₂O₃ is that some Fe₃O₄ be present. In addition, it has been found that the substitution of chromium for iron in α-Fe₂O₃ results in a monotonically decreasing optical band gap as the chromium concentration, x, increases.     

Micro/Nanoengineered α-Fe2O3 Nanoaggregate Conformably Enclosed by Ultrathin N-Doped Carbon Shell for Ultrastable Lithium Storage and Insight into Phase Evolution Mechanism

The Fe-based transition metal oxides are promising anode candidates for lithium storage considering their high specific capacity, low cost, and environmental compatibility. However, the poor electron/ion conductivity and significant volume stress limit their cycle and rate performances. Furthermore, the phenomena of capacity rise and sudden decay for α-Fe₂O₃ have appeared in most reports. Here, a uniform micro/nano α-Fe₂O₃ nanoaggregate conformably enclosed in an ultrathin N-doped carbon network (denoted as M/N-α-Fe₂O₃@NC) is designed. The M/N porous balls combine the merits of secondary nanoparticles to shorten the Li⁺ transportation pathways as well as alleviating volume expansion, and primary microballs to stabilize the electrode/electrolyte interface. Furthermore, the ultrathin carbon shell favors fast electron transfer and protects the electrode from electrolyte corrosion. Therefore, the M/N-α-Fe₂O₃@NC electrode delivers an excellent reversible capacity of 901 mA h g⁻¹ with capacity retention up to 94.0 % after 200 cycles at 0.2 A g⁻¹. Notably, the capacity rise does not happen during cycling. Moreover, the lithium storage mechanism is elucidated by ex situ XRD and HRTEM experiments. It is verified that the reversible phase transformation of α↔γ occurs during the first cycle, whereas only the α-Fe₂O₃ phase is reversibly transformed during subsequent cycles. This study offers a simple and scalable strategy for the practical application of high-performance Fe₂O₃ electrodes.     

Efficient reduction of hexavalent chromium with microscale Fe/Cu bimetals: Efficiency and the role of Cu

Microscale zero valent iron (mFe⁰) is one of the most potential water pollution remediation materials, but the effective utilization ability of electrons released by mFe⁰ in the reduction of hexavalent chromium (Cr(VI)) is not satisfactory. Here, we find the microscale iron-copper (mFe/Cu) bimetals coated with copper on the surface of mFe⁰ can significantly improve the effective utilization of electrons released by mFe⁰. Electrochemical analysis displays that copper plating on the surface of mFe/Cu can promote the release the electrons from mFe⁰ and reduce the impedance of mFe⁰. Spin-polarized density functional theory (DFT) calculation reveals that Cu on the surface of mFe/Cu bimetals promotes the release of electrons from mFe⁰ and reduces the adsorption energy of Fe to Cr. As the electron transporter, moreover, Cu can always attract Cr to the hollow position near itself of the Fe surface, which could promote the effective utilization of electrons released by Fe. Effective utilization ability of electrons in mFe/Cu system is 12.5 times higher than that in mFe⁰ system. Our findings provide another basis for the efficient reduction of Cr(VI) by mFe/Cu bimetals, which could promote the application and popularization of mFe/Cu bimetals.     

Porous α-Fe_2O_3/SnO_2 nanoflower with enhanced sulfur selectivity and stability for H_2S selective oxidation

Being abundant and active,Fe_2O_3 is suitable for selective oxidation of H_2S.However,its practical application is limited due to the poor sulfur selectivity and rapid deactivation.Herein,we report a facile template-free hydrothermal method to fabricate porous α-Fe_2O_3/SnO_2 composites with hierarchical nanoflower that can obviously improve the catalytic performance of Fe_2O_3.It was disclosed that the synergistic effect between α-Fe_2O_3 and SnO_2 promotes the physico-chemical properties of α-Fe_2O_3/SnO_2 composites.Specifically,the electron transfer between the Fe~(2+)/Fe~(3+) and Sn~(2+)/Sn~(4+) redox couples enhances the reducibility of α-Fe_2O_3/SnO_2 composites.The number of oxygen vacancies is improved when the Fe cations incorporate into SnO_2 structure,which facilitates the adsorption and activation of oxygen species.Additionally,the porous structure improves the accessibility of H_2 S to active sites.Among the composites,Fe1 Sn1 exhibits complete H_2 S conversion with 100% sulfur selectivity at 220℃,better than those of pure α-Fe_2O_3 and SnO_2.Moreover,Fe1 Sn1 catalyst shows high stability and water resistance.