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1.
Graphene aerogel-supported manganese ferrite (MnxFe3−xO4/GAs) and reduced-graphene oxide/manganese ferrite composite (MnFe2O4/rGO) were synthesized and studied as cathode catalysts for oxygen reduction reactions in urea/O2 fuel cells. MnFe2O4/GAs exhibited a 3D framework with a continuous macroporous structure. Among the investigated Fe/Mn ratios, the more positive oxygen reduction onset potential was observed with Fe/Mn=2/1. The half-wave potential of MnFe2O4/GAs was considerably more positive than that of MnFe2O4/rGO and comparable with that of Pt/C, while the stability of MnFe2O4/GAs significantly higher than that of Pt/C. The best urea/O2 fuel cell performance was also observed with the MnFe2O4/GAs. The MnFe2O4/GAs exhibited an OCV of 0.713 V and a maximum power density of 1.7 mW cm−2 at 60 °C. Thus, this work shows that 3D structured graphene aerogel-supported MnFe2O4 catalysts can be used as an efficient cathode material for alkaline fuel cells.  相似文献   

2.
Mn/Fe mixed oxide solids doped with Al2O3 (0.32-1.27 wt.%) were prepared by impregnation of manganese nitrate with finely powdered ferric oxide, then treated with different amounts of aluminum nitrate. The obtained samples were calcined in air at 700-1000 °C for 6 h. The specific surface area (SBET) and the catalytic activity of pure and doped precalcined at 700-1000 °C have been measured by using N2 adsorption isotherms and CO oxidation by O2. The structure and the phase changes were characterized by DTA and XRD techniques. The obtained results revealed that Mn2O3 interacted readily with Fe2O3 to produce well-crystallized manganese ferrite (MnFe2O4) at temperatures of 800 °C and above. The degree of propagation of this reaction increased by Al2O3-doping and also by increasing the heating temperature. The treatment with 1.27 wt.% Al2O3 followed by heating at 1000 °C resulted in complete conversion of Mn/Fe oxides into the corresponding ferrite phase. The catalytic activity and SBET of pure and doped solids were found to decrease, by increasing both the calcination temperature and the amount of Al2O3 added, due to the enhanced formation of MnFe2O4 phase which is less reactive than the free oxides (Mn2O3 and Fe2O3). The activation energy of formation (ΔE) of MnFe2O4 was determined for pure and doped solids. The promotion effect of aluminum in formation of MnFe2O4 was attributed to an effective increase in the mobility of reacting cations.  相似文献   

3.
The potential of the Fe3O4, Mn3O4, and MnFe2O4 nanophases for the removal of arsenic(III) and (V) from aqueous solutions was investigated using the batch technique. The structure and grain size of the nanoadsorbents were characterized using XRD and Secherrer's equation. The Fe3O4, Mn3O4, and MnFe2O4 had the crystal structure of magnetite, hausmannite, and Jacobsite, while the grain sizes were 28, 25, and 12 nm, respectively. It was found that the sorption determined using 100 ppb of either As(III) or (V) was pH independent from pH 2 through pH 6. However, at pH below 3 the nanomaterials released high concentrations of iron and manganese into solution. The amount of both As(III) and (V) per gram of adsorbent was found to increase with increasing concentration of As in solution. The XRD analysis showed no decrease in the average grain size of the nanoadsorbents reacted with 1000 ppm of either As(III) or (V) or a combination of 500 ppm of each As species. Finally Fe3O4, Mn3O4, and MnFe2O4 showed binding capacities (µg/g) of 32.2, 8.9, and 718 for As(III) and 1575, 212 and 2125 for As(V), respectively.  相似文献   

4.
New data on the structure and reversible lithium intercalation properties of sodium-deficient nickel–manganese oxides are provided. Novel properties of oxides determine their potential for direct use as cathode materials in lithium-ion batteries. The studies are focused on Na x Ni0.5Mn0.5O2 with x?=?2/3. Between 500 and 700 °C, new layered oxides Na0.65Ni0.5Mn0.5O2 with P3-type structure are obtained by a simple precursor method that consists in thermal decomposition of mixed sodium–nickel–manganese acetate salts obtained by freeze-drying. The structure, morphology, and oxidation state of nickel and manganese ions of Na0.65Ni0.5Mn0.5O2 are determined by powder X-ray diffraction, SEM and TEM analysis, and X-ray photoelectron spectroscopy (XPS). The lithium intercalation in Na0.65Ni0.5Mn0.5O2 is carried out in model two-electrode lithium cells of the type Li|LiPF6(EC:DMC)|Na0.65Ni0.5Mn0.5O2. A new structural feature of Na0.65Ni0.5Mn0.5O2 as compared with well-known O3–NaNi0.5Mn0.5O2 and P2–Na2/3Ni1/3Mn2/3O2 is the development of layer stacking ensuring prismatic site occupancy for Na+ ions with shared face on one side and shared edges on the other side with surrounding Ni/MnO6 octahedra. The reversible lithium intercalation in Na0.65Ni0.5Mn0.5O2 is demonstrated and discussed.  相似文献   

5.
Magnetic nanoparticles represent emerging tools in biomedical and pharmaceutical research. Because in most cases, the surfaces of these nanoparticles are hydrophobic, surface modifiers are usually applied to stabilize the colloidal suspension in an aqueous media. This investigation reports a simple technique for the preparation of MnFe2O4 synthesized within polyvinylamine (PVAm) nanoparticle reactors. Magnetite nanoparticles were previously synthesized using a similar scheme; however, substituting MnFe2O4 for Fe3O4 improved nanoparticle magnetization properties and further established the synthetic approach. PVAm nanoparticles exhibited more than 18% manganese ferrite loading by weight, a saturation magnetization of ~ 40 emu/g of MnFe2O4, excellent colloidal stability, and reactive primary amines for possible drug conjugation or surface modification. Transmission electron micrographs revealed that the dispersions contained ~ 50 nm PVAm nanoparticles incorporating manganese ferrite particles with a size less than ~ 7 nm. This reaction scheme further justifies a unique synthetic methodology for magnetic nanoparticles offering potential use in contrast‐enhanced magnetic resonance imaging or drug delivery. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 991–996, 2010  相似文献   

6.
A spray pyrolysis of a water solution of iron, manganese and iron nitrates is applied to prepare Zn0.5Mn0.5Fe2O4 single-phase ferrite with a spinel-type structure. The samples are characterized by means of differential scanning calorimetry, scanning and transmission electron microscopy, X-ray diffraction, infrared and 57Fe Mössbauer spectroscopy. The mass magnetization σ and the magnetic susceptibility 1/χ of the ferrites are measured as a function of temperature over the range of 78–728 K. The obtained sample contains nanoparticles with an average diameter d ∼7 nm possessing MnxZnyFe3−(x+y)O4 spinel-type structure with a uniform distribution of manganese and zinc atoms over the ferrite lattice. The Curie temperature is determined to be 375 ÷ 380 K.  相似文献   

7.
The electron donating properties of manganese ferrospinels of various compositions (MnFe2O4, Mn1.2Fe1.8O4, Mn2FeO4 and Mn2.5Fe0.5O4) were studied from the adsorption of electron acceptors of various electron affinity values from acetonitrile as solvent. The limit of electron transfer from the oxide surface is from 1.77 to 2.40 eV in terms of the electron affinity of the electron acceptor. The data have been correlated with the catalytic activity of these oxides towards autoxidation of sulfites. Both weak and strong electron donor sites catalyze the reaction.  相似文献   

8.
The composite/nanocomposite powders of Mn0.5Ni0.5Fe2O4/Fe type were synthesized starting from nanocrystalline Mn0.5Ni0.5Fe2O4 (D = 7 nm) (obtained by ceramic method and mechanical milling) and commercial Fe powders. The composites, Mn0.5Ni0.5Fe2O4/Fe, were milled for up to 120 min and subjected to heat treatment at 600 °C and 800 °C for 2 h. The manganese-nickel ferrite/iron composite samples were subjected to differential scanning calorimetry (DSC) up to 900 °C for thermal stability investigations. The composite component phases evolution during mechanical milling and heat treatments were investigated by X-ray diffraction technique. The present phases in Mn0.5Ni0.5Fe2O4/Fe composite are stable up to 400–450 °C. In the temperature range of 450-600 °C, the interdiffusion phenomena occurs leading to the formation of Fe1?xMnxFe2O4/Ni–Fe composite type. The new formed ferrite of Fe1?xMnxFe2O4 type presents an increased lattice parameter as a result of the substitution of nickel cations into the spinel structure by iron ones. Further increases of the temperature lead to the ferrite phase partial reduction and the formation of wustite-FeO type phase. The spinel structure presents incipient recrystallization phenomena after both heat treatments (600 °C and 800 °C). The mean crystallites size of the ferrite after heat treatment at 800 °C is about 75 nm. After DSC treatment at 900 °C, the composite material consists in Fe1?xMnxFe2O4, Ni structure, FeO, and (NiO)0.25(MnO)0.75 phases.  相似文献   

9.
Photothermal therapy (PTT) has emerged as one of the promising cancer therapy approaches. As a representative photothermal agent (PTA), magnetite possesses many advantages such as biodegradability and biocompatibility. However, photothermal instability hampers its further application. Herein, we systematically synthesized three kinds of ferrite nanoparticles and detailedly investigated their photothermal effect. Compared with Fe3O4 and MnFe2O4 nanoparticles, ZnFe2O4 nanoparticles exhibited a superior photothermal effect. After preservation for 70 days, the photothermal effect of Fe3O4 and MnFe2O4 nanoparticles observably declined while ZnFe2O4 nanoparticles showed slight decrease. Furthermore, in vitro experiment, ZnFe2O4 nanoparticles showed little toxicity to cells and achieved outstanding effect in killing cancer cells under NIR laser irradiation. Overall, through synthesizing and studying three kinds of ferrite MFe2O4 nanoparticles, we obtained ferrites as PTAs and learned about their changing trend in photothermal effect, expecting it can inspire further exploration of photothermal agents.  相似文献   

10.
The effect of ferric and manganese oxides dopants on thermal and physicochemical properties of Mn-oxide/Al2O3 and Fe2O3/Al2O3 systems has been studied separately. The pure and doped mixed solids were thermally treated at 400–1000°C. Pyrolysis of pure and doped mixed solids was investigated via thermal analysis (TG-DTG) techniques. The thermal products were characterized using XRD-analysis. The results revealed that pure ferric nitrate decomposes into Fe2O3 at 350°C and shows thermal stability up to1000°C. Crystalline Fe3O4 and Mn3O4phases were detected for some doped solids precalcined at 1000°C. Crystalline γ-Al2O3 phase was detected for all solids preheated up to 800°C. Ferric and manganese oxides enhanced the formation of α-Al2O3 phase at1000°C. Crystalline MnAl2O4 and MnFe2O4 phases were formed at 1000°C as a result of solid–solid interaction processes. The catalytic behavior of the thermal products was tested using the decomposition of H2O2 reaction. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

11.
The alkali sodium ferrate (IV) Na4FeO4 has been prepared by solid-state reaction of sodium peroxide Na2O2 and wustite Fe1−xO, in a molar ratio Na/Fe=4, at 400°C under vacuum. Powder X-ray and neutron diffraction studies indicate that Na4FeO4 crystallizes in the triclinic system P−1 with the cell parameters= a=8.4810(2) Å, b=5.7688(1) Å, c=6.5622(1) Å, α=124.662(2)°, β=98.848(2)°, γ=101.761(2)° and Z=2. Na4FeO4 is isotypic with the other known phases Na4MO4 (M=Ti, Cr, Mn, Co and Ge, Sn, Pb). The solid solution Na4FexCo1−xO4 exists for x=0-1 and we have followed the evolution of the cell parameters with x to determine the lattice parameters of the triclinic cell of Na4FeO4. A three-dimensional network of isolated FeO4 tetrahedra connected by Na atoms characterizes the structure. This compound is antiferromagnetic below TN=16 K. At 2 K the magnetic cell is twice the nuclear cell and the magnetic structure is collinear (μFe=3.36(12) μB at 2 K). This black compound is highly hygroscopic. In water or on contact with the atmospheric moisture it is disproportionated in Fe3+ and Fe6+. The Mössbauer spectra of Na4FeO4 are fitted with one doublet (δ=− 0.22 mm/s, Δ=0.41 mm/s at 295 K) in the paramagnetic state and with a sextet at 8K. These parameters characterize Fe4+ high-spin in tetrahedral FeO4 coordination.  相似文献   

12.
Halka Bilinski 《Polyhedron》1983,2(5):353-358
The precipitation of manganese from aqueous solution of manganese perchlorate and sodium pyrophosphate was investigated in a broad concentration range of both precipitation components and at various pH values, at 295 K and I = 0.5 mol dm?3. Tyndallometric technique was used. A soluble range has been observed in ten-fold excess of pyrophosphate and at 7 < pH < 10, where manganese forms complex with pyrophosphate. In the precipitation range the following precipitates were identified: Na2MnP2O7, Mn2P2O7 and MnOx. Quantitative solubility experiments have been performed at I ≈ 0 mol dm?3. From experimental data the following values for equilibrium constants have been obtained:
  相似文献   

13.
Summary The thermal decomposition of manganese tris(malonato)ferrate(III) hexahydrate, Mn3[Fe(CH2C2O4)3]2 . 6H2O has been investigated from ambient temperature to 600 °C in static air atmosphere using various physico-chemical techniques, i.e., simultaneous TG-DTG-DSC, XRD, M?ssbauer and IR spectroscopic techniques. Nano-particles of manganese ferrite, MnFe2O4, have been obtained as a result of solid-state reaction between a-Fe2O3 and MnO (intermediate species formed during thermolysis) at a temperature much lower than that for ceramic method. SEM analysis of final thermolysis product reveals the formation of monodisperse manganese ferrite nanoparticles with an average particle size of 35 nm. Magnetic studies show that these particles have a saturation magnetization of 1861G and Curie temperature of 300 °C. Lower magnitude of these parameters as compared to the bulk values is attributed to their smaller particle size.  相似文献   

14.
Studies on the structural changes and catalytic behavior of iron-manganese catalysts for CO hydrogenation were conducted using Mossbauer spectroscopy, X-ray diffraction, temperature programmed reduction and kinetic measurements. It was observed that the reduction of the mixed oxide catalyst precursors proceeds via the formation of Fe3-xMnxO4,Mn3-xFexO4 mixed spinel and Fe1-zMn2O mixed oxide to α-iron and MnO. After use for CO hydrogenation, catalysts are oxidized as well as carburized. The Mn3-yFeyO4 mixed spinel and Fe1-2MnzO mixed oxide are the most powerful phases for olefin production. The highest attainable 2–4 low carbon olefin selectivity is 41% with an 86% conversion level. Higher manganese content or lower reduction temperatures may change the carbide formed from χ-Fe5C2 to the more unstable ?′-Fe22C. Carbide formation is greatly dependent on manganese content and activation procedure used.  相似文献   

15.
Carbonate is a somewhat enigmatic anion in static secondary ion mass spectrometry (SIMS) because abundant ions containing intact CO32? are not detected when analyzing alkaline‐earth carbonate minerals common to the geochemical environment. In contrast, carbonate can be observed as an adduct ion when it is bound with alkali cations. In this study, carbonate was detected as the adduct Na2CO3·Na+ in the spectra of sodium carbonate, bicarbonate, hydroxide, oxalate, formate and nitrite and to a lesser extent nitrate. The appearance of the adduct Na2CO3·Na+ on hydroxide, oxalate, formate and nitrite surfaces was interpreted in terms of these basic surfaces fixing CO2 from the ambient atmosphere. The low abundance of Na2CO3·Na+ in the static SIMS spectrum of sodium nitrate, compared with a significantly higher abundance in salts having stronger conjugate bases, suggested that the basicity of the conjugate anions correlated with aggressive CO2 fixation; however, the appearance of Na2CO3·Na+ could not be explained simply in terms of solution basicity constants. The oxide molecular ion Na2O+ and adducts NaOH·Na+ and Na2O·Na+ also constituted part of the carbonate spectral signature, and were observed in spectra from all the salts studied. In addition to the carbonate and oxide ions, a low‐abundance oxalate ion series was observed that had the general formula Na2?xHxC2O4·Na+, where 0 < x < 2. Oxalate adsorption from the laboratory atmosphere was demonstrated but the oxalate ion series also was likely to be formed from reductive coupling occurring during the static SIMS bombardment event. The remarkable spectral similarity observed when comparing the sodium salts indicated that their surfaces shared common chemical speciation and that the chemistry of the surfaces was very different from the bulk of the particle. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

16.
Three new α-hydroxy carboxylate group functionalized MnFe2O4 nanoparticles (NPs) have been developed to explore the microscopic origin of ligand modified fluorescence and magnetic properties of nearly monodispersed MnFe2O4 NPs. The surface functionalization has been carried out with three small organic ligands (tartrate, malate, and citrate) having different number of α-hydroxy carboxylate functional group along with steric effect. Detailed study unveils that α-hydroxy carboxylate moiety of the ligands plays key role to generate intrinsic fluorescence in functionalized MnFe2O4 NPs through the activation of ligand to metal charge transfer transitions, associated with ligand–Mn2+/Fe3+ interactions along with dd transition corresponding to d–orbital energy level splitting of Fe3+ ions on NP surface. Further, MnFe2O4 NPs show a maximum 140.88% increase in coercivity and 97.95% decrease in magnetization compared to its bare one upon functionalization. The ligands that induce smallest crystal field splitting of d–orbital energy level of transition metal ions are found to result in strongest ferrimagnetic activation of the NPs. Finally, our developed tartrate functionalized MnFe2O4 (T-MnFe2O4) NPs have been utilized for studying DNA binding interaction and nuclease activity for stimulating their beneficial activities toward diverse biomedical applications. The spectroscopic measurements indicate that T-MnFe2O4 NPs bind calf thymus DNA by intercalative mode. The ability of T-MnFe2O4 NPs to induce DNA cleavage was studied by gel electrophoresis technique where the complex is found to promote the cleavage of pBR322 plasmid DNA from the super coiled form I to linear coiled form II and nicked coiled form III with good efficiency.  相似文献   

17.
The reduction of chromium, nickel, and manganese oxides by hydrogen, CO, CH4, and model syngas (mixtures of CO + H2 or H2 + CO + CO2) and oxidation by water vapor has been studied from the thermodynamic and chemical equilibrium point of view. Attention was concentrated not only on the convenient conditions for reduction of the relevant oxides to metals or lower oxides at temperatures in the range 400–1000 K, but also on the possible formation of soot, carbides, and carbonates as precursors for the carbon monoxide and carbon dioxide formation in the steam oxidation step. Reduction of very stable Cr2O3 to metallic Cr by hydrogen or CO at temperatures of 400–1000 K is thermodynamically excluded. Reduction of nickel oxide (NiO) and manganese oxide (Mn3O4) by hydrogen or CO at such temperatures is feasible. The oxidation of MnO and Ni by steam and simultaneous production of hydrogen at temperatures between 400 and 1000 K is a difficult step from the thermodynamics viewpoint. Assuming the Ni—NiO system, the formation of nickel aluminum spinel could be used to increase the equilibrium hydrogen yield, thus, enabling the hydrogen production via looping redox process. The equilibrium hydrogen yield under the conditions of steam oxidation of the Ni—NiO system is, however, substantially lower than that for the Fe—Fe3O4 system. The system comprising nickel ferrite seems to be unsuitable for cyclic redox processes. Under strongly reducing conditions, at high CO concentrations/partial pressures, formation of nickel carbide (Ni3C) is thermodynamically favored. Pressurized conditions during the reduction step with CO/CO2 containing gases enhance the formation of soot and carbon-containing compounds such as carbides and/or carbonates.  相似文献   

18.
Structural and magnetic properties were studied on La1−xMnOδ nanocrystalline powders exhibiting different La/Mn ratios. These compounds were prepared using a gel combustion method based on a cation solution soaking by acrylamide polymerization. Structural properties were studied both by transmission electron microscopy and X-ray diffraction (XRD). Complete chemical composition analyses were performed by induced coupled plasma spectroscopy and by iodometric titration. Proportions of parasitic phases in samples, as La2O3 or Mn3O4, and actual compositions of La1−xMnOδ phases were then determined from refinements of XRD data and sample chemical compositions. As a result, perovskite structure is not any more stable for La/Mn<0.9 as it decomposes into a mixing of La0.9MnO3 and of Mn3O4 phases, in agreement with results on thermodynamic equilibrium in the La-Mn-O phase diagram. For La/Mn>0.9, a high oxygen excess is observed and leads to consider the creation of vacancies on both lanthanum and manganese sites, whose concentrations are evaluated. Magnetic properties agree well with the proposed structures and sample compositions since for La/Mn<0.9, for which a La0.9MnO3 phase is always found, the Curie temperature remains constant and equal to 295 K (the highest temperature never observed before in such series of compositions), while for La/Mn>0.9, there is a formation of Mn vacancies giving rise to a lowering of Curie temperature resulting of a frustration of ferromagnetic interactions.  相似文献   

19.
Phase composition of the V2O5-NaVO3-Ca(VO3)2-Mn2V2O7 system was studied, and a subsolidus phase diagram constructed. The tetrahedration of the diagram is determined by the fact that the end-member of Ca1–x Mn x (VO3)2 solid solution is in equilibrium with all compounds of the system (V2O5, NaVO3, Ca(VO3)2), vanadium β-bronzes Na x V2O5 (0.22 ≤ x ≤ 0.40) and κ-bronzes (0.25 ≤ x ≤ 0.45, 0 ≤ y ≤ 0.16), Mn2V2O7, and Na2Mn3(V2O7)2 and with the end-members of reciprocal solid solutions based on calcium and sodium metavanadates. At 20°C, the degree of vanadium dissolution α for Na2Ca(VO3)4 is 100% for 0.5 ≤ pH ≤ 10; for the other phases of the system, vanadium dissolution ranges from 100 to 10% for pH below 3.5; in the alkaline pH range, ≤ 10%. Sodium for calcium substitution in Ca(VO3)2 increases α in aqueous NaOH to 20%. For Na2Mn3(V2O7)2, α decreases from 92 to 80% as pH changes from 0.5 to 2.5; at pH above 4, α = 30%.  相似文献   

20.
The First T5‐Supertetrahedron in Oxide Chemistry: Na26Mn39O55 Na26Mn39O55 has been obtained from a redox reaction between manganese metal, CdO in the presence of Na2O and Na2SO4 as a flux component as red single crystals with octahedral shape. The crystal structure has been determined from single crystal data (Fd3¯m, Z = 8, a = 2377.4(3) pm at 293 K and a = 2372.5(2) pm at 130 K). The rare characteristic structural feature of a T5‐Supertetrahedron, [Mn35O56], is observed for this new mixed‐valent sodium‐oxomanganat(II, III), Na26Mn39O55. First investigations of the magnetic properties are reported.  相似文献   

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