Sol–Gel Auto-combustion Preparation of M2+ = Mg2+, Mn2+, Cd2+ Substituted M0.25Ni0.15Cu0.25Co0.35Fe2O4 Ferrites and Their Characterizations

Journal of Superconductivity and Novel Magnetism - Cost-effective and controllable synthesis of M0.25Ni0.15Cu0.25Co0.35Fe2O4 (M2+ ?=?Mg2+, Mn2+, and Cd2+) ferrites via the sol–gel...     

Possible weak ferromagnetism in pure and M (Mn, Cu, Co, Fe and Tb) doped NiGa2O4 nanoparticles

We report on the structural and magnetic properties of nanoparticles of NiGa2O4 and 5 at.% M doped (M = Mn2+, Cu2+, Co2+, Fe3+ and Tb3+) at Ga site of NiGa2O4, synthesized by gel-combustion method. The particle size, as investigated by X-ray diffraction and transmission electron microscopy, could be fine tuned by a controlled annealing process. Weak ferromagnetism becomes significant, when the particles are in the nano regime (5-7 nm). The magnetization becomes insignificant at larger particle size ( 150 nm). Cu2+ and Tb3+ doped NiGa2O4 nanoparticles showed relatively large room temperature ferromagnetism compared to other doped (Fe, Mn and Co) and undoped NiGa2O4 samples. The weak ferromagnetism observed in the nanoparticles of NiGa2O4, which is antiferromagnetic in the bulk, is due to the surface disordered states with uncompensated spins.     

Synthesis of Fe-group metal oxide nanostructures by thermal oxidation and their magnetic properties

In this paper, we review the preparation of Fe-group metal oxide nanostructures by the thermal oxidation method developed in our lab. By this method, we have prepared several kinds of nanostructures, including nanowires and nanoleaves. The magnetic properties of these nanostructures have also been studied. By carefully controlling the reacting time, temperature, and humidity, we have prepared alpha-Fe2O3, gamma-Fe2O3, Fe3O4, and Co3O4 nanowires and alpha-Fe2O3 nanoleaves by heating the substrates in proper atmosphere. The alpha-Fe2O3 and Co3O4 nanowires are produced by directly oxygenating pure metal at 550 to approximately 650 degrees C and 480-520 degrees C, separately. The gamma-Fe2O3 and Fe3O4 nanowires are produced by reducing as-prepared alpha-Fe2O3 nanowires in a mixture of N2 and H2. The nanowires are about 10-20 microm, with diameter of about 20 to approximately 100 nm. Most of the nanowire arrays are grown vertically from the surface of the substrate at a high surface density (10(8)-10(9) cm(-2)). Compared with the nanowires prepared by hydrothermal process and template method, Most of our nanowires are structurally uniform and single crystallites. The magnetic properties of these nanostructures are also studied, and demonstrate some novel properties.     

Effect of Ni+2-substituted Fe2TiO5 on the H2-reduction and CO2 Catalytic Decomposition Reactions at 500℃

CO2 is a major component of the greenhouse gases, which causes the global warming. To reduce CO2 gas, high activity nanosized Ni＋2 substituted Fe2TiO5 samples were synthesized by conventional ceramic method. The effect of the composition of the synthesized ferrite on the H2-reduction and CO2-catalytic decomposition was investigated. Fe2TiO5 （iron titanate） phase that has a nanocrystallite size of -80 nm is formed as a result of heating Fe2O3 and TiO2 while the addition of NiO leads to the formation of new phases （-80 nm） NiTiO3 and NiFe2O4, but the mixed solid of NiO and Fe2O3 results in the formation of NiFe2O4 only. Samples with Ni^＋2=0 shows the lowest reduction extent （20%）; as the extent of Ni＋2 increases, the extent of reduction increases. The increase in the reduction percent is attributed to the presence of NiTiO3 and NiFe2O4 phases, which are more reducible phases than Fe2TiO5. The CO2 decomposition reactions were monitored by thermogravimetric analysis （TGA） experiments. The oxidation of the H2-reduced Ni＋2 substituted Fe2TiO5 at 500℃ was investigated. As Ni^＋2 increases, the rate of reoxidation increases. Samples with the highest reduction extents gave the highest reoxidation extent, which is attributed to the highly porous nature and deficiency in oxygen due to the presence of metallic Fe, Ni and/or FeNi alloy. X-ray diffraction （XRD） and transmission electron microscopy （TEM） of oxidized samples show also the presence of carbon in the sample containing Ni＋2〉0, which appears in the form of nanotubes （25 nm）.     

Differences in electrophysical and gas sensing properties of flame spray synthesized Fe2O3(gamma-Fe2O3 and alpha-Fe2O3)

Nanoscaled Fe2O3 powders as candidates for gas sensing material for hydrogen detection were synthesized by the high temperature flame spray assisted combustion of ferrocene dissolved in benzene. X-ray diffraction (XRD) and selected area electron diffraction (SAED) show that the as prepared nanopowder consists of maghemite (gamma-Fe2O3) with low crystallinity. Thermal post-treatment causes a phase transformation towards hematite (alpha-Fe2O3) accompanied by an increase in the crystallinity. Upon exposure to air and hydrogen at elevated temperatures, both phases show a significant variation of conductivity and activation energy-as evidenced by impedance spectra-and thus a favorable sensor response, surpassing even that of flame-synthesized nanocrystalline tin dioxide. The conductivity has been identified as of electronic origin, affected by trap states located in the region adjacent to grain boundaries. Quantitative analysis of the impedance spectra with equivalent circuits shows that the conductivity is thermally activated and affected by the interaction of hydrogen with the sensor material. The calculated Debye screening length of gamma-Fe2O3 and alpha-Fe2O3 is about 27 nm and 16 nm, respectively, what contributes significantly to the sensitivity of the material. Gamma-Fe2O3 and alpha-Fe2O3 exhibit high sensor response towards hydrogen in a wide concentration range. Gamma-Fe2O3 shows n-type semiconducting behavior up to 573 K. Alpha-Fe2O3 shows p-type semiconducting behavior, as reflected in the dynamic changes of the resistivity. For both sensor materials, 523 K was the optimal operating temperature.     

On the formation of M2+ -Sb3+ -alkoxide precursors and sol-gel processing of M-Sb oxides with M = Cr,Mn, Fe,Co, Ni,Cu and Zn

Binary alkoxide complexes of compositions close to MSb(OEt)₅, with M = Mn, Fe, Co and Ni, have been prepared and characterized by their i.r. and u.v.-VIS spectra, while Cr, Cu and Zn do not form similar ethoxide complexes with Sb(OEt)₃. The Mn and Fe complexes must be prepared in inert atmosphere as they are very easily oxidized. The Fe complex is metastable and decomposes within a few hours. The Co complex can only be prepared in the presence of acetonitrile. X-ray amorphous gels were formed upon hydrolysis of solutions containing M to Sb species in the ratio 12 for M = Mn, Fe, Co and Ni. The gels consisted of agglomerated particles of sizes from 75 to 300 nm. The decomposition of the gels in air and in nitrogen has been monitored by means of thermogravimetric measurements. Samples of heated gels were quenched from various temperatures in the region 50–950°C, and the formed oxides were characterized by their X-ray powder patterns and by their infrared spectra. At 950 °C MSb₂O₆ was formed in air, while in nitrogen MSb₂O₄ (M = Mn, Co and Ni) was formed at intermediate temperatures. At higher temperatures the latter compound decomposed and Sb₂O₃ sublimated.     

The reactivity of ethylene oxide in contact with iron oxide fines as measured by adiabatic calorimetry

Samples of various iron oxides suspended above ethylene oxide in an adiabatic calorimeter exhibit exothermic activity at temperatures as low as room temperature. A gamma-Fe(2)O(3) sample was found to show the highest reactivity with ethylene oxide. Ethylene oxide in combination with most of the iron oxide fines tested displayed exothermic activity below 100 degrees C. Self-heat rates near 2000 degrees C/min were observed for the gamma-Fe(2)O(3) fines while rates in excess of 100 degrees C/min were found for other fines (alpha-Fe(2)O(3) and hydrated alpha-Fe(2)O(3)). In two cases (alpha-Fe(3)O(4) and alpha-Fe(2)O(3)), pressurization rates above 1000 psi/min took place. No reactivity was observed for ethylene oxide with the FeO. Thermal inertia effects in commercial operation, such as heat uptake by the equipment to which fines are attached, are presumed to be a factor in limiting the occurrence of related exotherms in ethylene oxide manufacturing facilities.     

Microbial synthesis of magnetite and Mn-substituted magnetite nanoparticles: influence of bacteria and incubation temperature

Microbial synthesis of magnetite and metal (Co, Cr, Ni)-substituted magnetites has only recently been reported. The objective of this study was to examine the influence of Mn ion on the microbial synthesis of magnetite nanoparticles. The reductive biotransformation of an akaganeite (beta-FeOOH) or a Mn-substituted (2-20 mol%) akaganeite (Fe(1-x)Mn(x)OOH) by Shewanella loiha (PV-4, 25 degrees C) and Thermoanaerobacter ethanolicus (TOR-39, 60 degrees C) was investigated under anaerobic conditions at circumneutral pH (pH = 7-8). Both bacteria formed magnetite nanoparticles using akaganeite as a magnetite precursor. By comparison of iron minerals formed by PV-4 and TOR-39 using Mn-mixed akaganeite as the precursor, it was shown that PV-4 formed siderite (FeCO3), green rust [Fe2+Fe3+(OH)16CO3 x 4H2O], and magnetite at 25 degrees C, whereas TOR-39 formed mainly nm-sized magnetite at 60 degrees C. The presence of Mn in the magnetite formed by TOR-39 was revealed by energy dispersive X-ray analysis (EDX) is indicative of Mn substitution into magnetite crystals. EDX analysis of iron minerals formed by PV-4 showed that Mn was preferentially concentrated in the siderite and green rust. These results demonstrate that coprecipitated/sorbed Mn induced microbial formation of siderite and green rust by PV-4 at 25 degrees C, but the synthesis of Mn-substituted magnetite nanoparticles proceeded by TOR-39 at 60 degrees C. These results indicate that the bacteria have the ability to synthesize magnetite and Mn-substituted magnetite nano-crystals. Microbially facilitated synthesis of magnetite and metal-substituted magnetites at near ambient temperatures may expand the possible use of specialized ferromagnetic nano-particles.     

Calorimetric study on the decomposition of hydroxylamine in the presence of transition metals

Hydroxylamine (HA), hydroxylamine chloride (HAC1), and hydroxylamine nitrate (HAN) were each mixed with aqueous solutions of Cr3+, Cr6+, Mn7+, Co2+, Co3+, and Cu2+, and their heat flow profiles were monitored by a small-scaled reaction calorimeter, SuperCRC. These mixing tests demonstrated that HA was less reactive than HACl and HAN with Mn7+ and Cr6+. Their UV-vis spectra confirmed that the substrates reacted when Mn7+ and Cr6+ were reduced. HA was more reactive with Cu2+ than HAC1 and HAN and exhibited the highest reactivity among the three substrates with regard to metals in the intermediate oxidation states: Cr3+, Co3+, and Co2+. During the reaction of HA and Co3+, an induction period was observed. All exothermic reactions were accompanied by precipitation or a change in the UV-vis spectra.     

Green synthesis of uniform magnetite (Fe3O4) nanoparticles and micron cubes

Single-crystalline Fe3O4 microcubes were obtained through a green hydrothermal procedure using Fe3+, Fe2+ and H2O2 as starting materials. The structures and morphologies of the as-prepared samples were characterized in detail by X-ray diffraction (XRD), Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) respectively. Magnetite (Fe3O4) cubes averaging 3 microm in diameter were synthesized by H2O2 oxidation of Fe3+ and Fe2+ under neutral conditions. The contrastive experiments were designed to elucidate the effects of Fe3+, Fe2+ and H2O2 on the morphology of the final products. Irregular and ellipsoidal Fe2O3 structures were obtained by H2O2 oxidation of Fe3+ and Fe2+ respectively. Meanwhile, Fe3O4 nanotubes and nanoparticles were obtained when H2O2 was replaced by NH4HCO3 and urea respectively. The results show that H2O2, Fe3+ and Fe2+ in the reactive system play critical roles in obtaining micrometric cube-like Fe3O4. While, other nanometric Fe2O3 and Fe3O4 particles with tube-like and other morphologies could also be developed by controlling the reaction parameters.     

Flux growth of crystals of MNb2O6 (M = Ni,Co, Mn,Fe)

The growth of crystals of MNb₂O₆ (M = Ni, Co, Mn, Fe) from fluxed melts is described. With M = Ni and Co, platinum crucibles were used, but with M = Mn and Fe, growth was carried out under nitrogen in molybdenum and iron crucibles respectively.     

Preparation and characterization of LiNi0.8Co0.15Al0.05O2 cathode material from (NH4)2C2O4·2H2O precipitant

Journal of Materials Science: Materials in Electronics - LiNi0.8Co0.15Al0.05O2 (NCA) cathode material was usually prepared with Ni2+, Co2+, Al3+ co-precipitation method using NaOH/NH3·H2O...     

Fe对Mn/CeO2-TiO2催化剂低温NH3选择性催化还原NO的影响

以锰氧化物为活性组分,CeO2-TiO2为载体制备了Mn/CeO2-TiO2催化剂.考察了Fe的加入对Mn/CeO2-TiO2的低温NH3-SCR活性的影响.并采用BET比表面积,H2程序升温还原(H2-TPR)和X射线光电子能谱(XPS)等手段对催化剂进行了表征.活性结果表明,Fe的引入显著改善了Mn/CeO2-TiO2的NH3-SCR活性,催化剂在113～250℃之间表现出良好的NO去除效率.表征结果表明,Fe的引入促进了锰物种在CeO2-TiO2表面的分散,降低了Mn-Fe/CeO2-TiO2中锰物种的还原温度.XPS分析指出Mn-Fe/CeO2-TiO2表面Mn以+4价存在,而Fe主要以+3价的Fe2O3存在,且Fe与载体表面间存在强相互作用.     

Synthesis and characterisation of polyol-capped transition metal oxide nanoparticles

In-situ capped nanocrystalline gamma-Fe2O3, Co3O4, and Cu2O were prepared in 1,4-butanediol in aerobic conditions. X-ray diffraction (XRD) patterns show that the synthesised samples are nanocrystalline cubic oxides with crystallite sizes 9.5 nm, 13.4 nm, and 11 nm, respectively. Raman spectroscopy shows peaks at 350 cm(-1), 500 cm(-1), and 700 cm(-1), indicating that the iron oxide is gamma-Fe2O3; M?ssbauer spectroscopy shows the presence of two Fe3(3+) sites. Transmission electron microscopy images show that the particle sizes of gamma-Fe2O3 and Co3O4 samples are 8.9 nm and 7 nm, respectively. The absence of agglomeration indicates that the synthesised nanoparticles are capped. FT-IR spectra show the presence of an organic moiety in the sample which acts as a capping agent. Thermogravimetry shows that the capping is stable up to 873 K in gamma-Fe2O3, and up to 400 K in Co3O4. The samples are soluble in water to form stable hydrosols. During synthesis of gamma-Fe2O3 a 6-line ferrihydrite is formed as an intermediate, which is stable in solution up to 473 K, and transforms to gamma-Fe2O3 at 483 K, by rapid dissolution-reprecipitation. In the syntheses of Co3O4 and Cu2O, no intermediates are formed.     

Ni doped Fe3O4 magnetic nanoparticles

In this work, the effect of nickel doping on the structural and magnetic properties of Fe3O4 nanoparticles is analysed. Ni(x)Fe(3-x)O4 nanoparticles (x = 0, 0.04, 0.06 and 0.11) were obtained by chemical co-precipitation method, starting from a mixture of FeCl2 x 4H2O and Ni(AcO)2 x 4H2O salts. The analysis of the structure and composition of the synthesized nanoparticles confirms their nanometer size (main sizes around 10 nm) and the inclusion of the Ni atoms in the characteristic spinel structure of the magnetite Fe3O4 phase. In order to characterize in detail the structure of the samples, X-ray absorption (XANES) measurements were performed on the Ni and Fe K-edges. The results indicate the oxidation of the Ni atoms to the 2+ state and the location of the Ni2+ cations in the Fe2+ octahedral sites. With respect to the magnetic properties, the samples display the characteristic superparamagnetic behaviour, with anhysteretic magnetic response at room temperature. The estimated magnetic moment confirms the partial substitution of the Fe2+ cations by Ni2+ atoms in the octahedral sites of the spinel structure.     

Nano/micro lithium transitionmetal (Fe, Mn, Co and Ni) silicate cathode materials for lithium ion batteries

Lithium transitionmetal (Fe, Mn, Co, Ni) silicate cathode materials are new promising substituting cathode materials for lithium ion batteries. They had caught the researchers' eyes in the past several years. Nowadays, there are growing interests for silicate cathode materials in the field of lithium ion batteries. Among the silicate cathode materials, Li2FeSiO4 is the most promising cathode materials because of its high structure stability, high reversible capacity, high electronic conductivity and the abundant resource of iron and silicon. Although Li2MnSiO4 and Li2CoSiO4 have much higher theoretic specific capacity than Li2FeSiO4, they all have inferior electrochemical behaviours due to different reasons. There are only calculation results about Li2NiSiO4 till now. This brief critical review firstly discussed some papers about the first-principle calculation of Li2MSiO4 (M=Fe, Mn, Co Ni), and then collects and discusses relevant papers and recent patents about the fabrication, structure, particle size and electrochemical performance of nano/micro Li2MSiO4 (M=Fe, Mn, Co Ni) and their composites. Finally, the future challenges of Li2FeSiO4 are also discussed.     

Effect of Ni+2-substituted Fe2TiO5 on the H2-reduction and CO2 Catalytic Decomposition Reactions at 500℃

CO2 is a major component of the greenhouse gases, which causes the global warming. To reduce CO2 gas,high activity nanosized Ni 2 substituted Fe2TiO5 samples were synthesized by conventional ceramic method.The effect of the composition of the synthesized ferrite on the H2-reduction and CO2-catalytic decomposition was investigated. Fe2TiO5 (iron titanate) phase that has a nanocrystallite size of ～80 nm is formed as a result of heating Fe2O3 and TiO2 while the addition of NiO leads to the formation of new phases (～80 nm)NiTiO3 and NiFe2O4, but the mixed solid of NiO and Fe2O3 results in the formation of NiFe2O4 only.Samples with Ni 2=0 shows the lowest reduction extent (20%); as the extent of Ni 2 increases, the extent of reduction increases. The increase in the reduction percent is attributed to the presence of NiTiO3 and NiFe2O4 phases, which are more reducible phases than Fe2TiO5. The CO2 decomposition reactions were monitored by thermogravimetric analysis (TGA) experiments. The oxidation of the H2-reduced Ni 2 substituted Fe2TiO5 at 500℃ was investigated. As Ni 2 increases, the rate of reoxidation increases. Samples with the highest reduction extents gave the highest reoxidation extent, which is attributed to the highly porous nature and deficiency in oxygen due to the presence of metallic Fe, Ni and/or FeNi alloy. X-ray diffraction (XRD) and transmission electron microscopy (TEM) of oxidized samples show also the presence of carbon in the sample containing Ni 2＞0, which appears in the form of nanotubes (25 nm).     

Degradation of C.I. Reactive Red 2 (RR2) using ozone-based systems: comparisons of decolorization efficiency and power consumption

This study investigated the decolorization efficiency of C.I. Reactive Red 2 (RR2) in O3, O3/H2O2, O3/Fe3+, O3/H2O2/Fe3+, UV/O3, UV/O3/Fe3+, UV/O3/H2O2 and UV/O3/H2O2/Fe3+ systems at various pHs. The effective energy consumption constants and the electrical energy per order of pollutant removal (EE/O) were also determined. The experimental results indicated that the energy efficiency was highest at [H2O2]0=1000mg/l and [Fe3+]0=25mg/l. Accordingly, the H2O2 and Fe3+ doses in the hybrid ozone- and UV/ozone-based systems were controlled at these values. This work suggests that the dominant reactant in O3, O3/Fe3+ and O3/H2O2 systems was O3 and that in the O3/H2O2/Fe3+ system was H2O2/Fe3+. The experimental results revealed that the combinations of Fe3+ or H2O2/Fe3+ with O3 at pH 4 and of H2O2 or H2O2/Fe3+ with UV/O3 at pH 4 or 7 yielded a higher decolorization rate than O3 and UV/O3, respectively. At pH 4, the EE/O results demonstrated that the UV/O3/H2O2/Fe3+ system reduced 85% of the energy consumption compared with the UV/O3 system. Moreover, the O3/H2O2/Fe3+ system reduced 62% of the energy consumption compared with the O3 system. At pH 7, the EE/O results revealed that the UV/O3/H2O2/Fe3+ system consumed half the energy of the UV/O3 system.     

Magnetic Fe(2)MO(4) (M:Fe, Mn) activated carbons: fabrication, characterization and heterogeneous Fenton oxidation of methyl orange

We present a simple and efficient method for the fabrication of magnetic Fe(2)MO(4) (M:Fe and Mn) activated carbons (Fe(2)MO(4)/AC-H, M:Fe and Mn) by impregnating the activated carbon with simultaneous magnetic precursor and carbon modifying agent followed by calcination. The obtained samples were characterized by nitrogen adsorption isotherms, X-ray diffraction (XRD), scanning electron microscopy (SEM) and vibrating sample magnetometer (VSM), and the catalytic activity in heterogeneous Fenton oxidation of methyl orange (MO) was evaluated. The resulting Fe(2)MnO(4)/AC-H showed higher catalytic activity in the methyl orange oxidation than Fe(3)O(4)/AC-H. The effect of operational parameters (pH, catalyst loading H(2)O(2) dosage and initial MO concentration) on degradation performance of the oxidation process was investigated. Stability and reusability of selected catalyst were also tested.