Preparation and characterization of α-Fe2O3–CeO2 composite

In our previous study we attempted to see the effect of cerium doping (Ce/Fe ratio 0.015 to 0.074) on goethite matrix and conversion of doped goethite to hematite. In the present communication, nano-structured α-Fe₂O₃–CeO₂ composite with Fe/Ce weight ratio as 1.1 has been synthesized by calcination of goethite-cerium hydroxide precursor prepared by co-precipitation method. It was observed that co-precipitation of cerium along with iron in hydroxide medium resulted in hindering the formation of crystalline order as the precursor formed showed poorly crystallized goethite and almost no crystallinity in Ce(OH)₄. Calcination of the precursor at 400 °C showed the formation of hematite together with a broad peak corresponding to cerium oxide whereas at 800 °C, two distinct phases of α-Fe₂O₃ and CeO₂ were observed. The Mössbauer spectra showed the presence of a paramagnetic component both for the precursor as well as for the sample calcined at 400 °C but on raising the calcination temperature to 800 °C, the paramagnetic component disappeared and the spectrum corresponding to pure α-Fe₂O₃ phase was observed. The microstructure of the product obtained by calcining at 800 °C showed rod like structure (30 to 50 nm width and 300 to 500 nm length) of α-Fe₂O₃ having equi-dimensional CeO₂ particles on and around the surface. Besides the rods, equi-dimensional particles and agglomerates corresponding to CeO₂ were also observed. The results show that co-precipitation followed by calcinations gives nanorods hematite with CeO₂ particles bonded to its surface.     

Synthesis of Cu–CdIn2O4 nanoparticles decorated on nickel foam as a sensitive non-enzymatic electrochemical sensor for glucose detection

Fast and effective detection of glucose has important significance in clinical medicine and the diagnosis of diabetes. Electrochemical non-enzymatic glucose sensor has received extensive attention to detect glucose in the recent years due to its simple operation and low cost. In this paper, Cu–CdIn₂O₄ nanoparticles decorated on nickel foam electrode as a sensitive non-enzymatic electrochemical sensor for glucose detection are synthesized by a one-step non-aqueous sol–gel method. Different Cu-doping levels are designed as performance comparison analysis. The electrocatalytic performance of the Cu–CdIn₂O₄ nanoparticles/Ni foam electrodes towards glucose oxidation is evaluated by cyclic voltammetry and current time. The results show that 15% Cu–CdIn₂O₄/Ni foam electrode shows higher sensitivity, as well as an excellent anti-interference and long-term stability towards glucose detection compared with 10% and 20% Cu–CdIn₂O₄/Ni foam electrodes. Hence, 15% Cu–CdIn₂O₄/Ni foam can be regarded as an efficient and a promising sensing material for glucose detection. Such satisfactory performance is not only attributed to the synergistic effect of Cd, In, and Cu, but also benefits from the uniform distribution of 15% Cu–CdIn₂O₄ nanoparticles on the Ni foam, which provides more reactive sites for the electrochemical catalytic reaction.

     

Synthesis,characterization and electrochemical properties of three-dimensionally ordered macroporous α-Fe2O3

Three-dimensionally ordered macroporous (3DOM) α-Fe₂O₃ electrode materials with large pore sizes and interconnected macroporous frameworks were successfully synthesized by a simply modified colloidal crystal templating strategy. The obtained samples were characterized by means of thermogravimetry, powder X-ray diffraction, nitrogen physisorption, scanning and transmission electron microscopy. The electrochemical properties of the 3DOM α-Fe₂O₃ were evaluated with cyclic voltammetry and discharge–charge experiments in an organic electrolyte containing a lithium salt. The results showed that the 3DOM α-Fe₂O₃ possessed a potential to be used as an anode material for lithium ion batteries with high initial discharge and charge capacities of 1883 and 1139 mAh g⁻¹, respectively. After 60th cycle, the reversible capacity could still be as high as 681 mAh g⁻¹ with a stable Coulombic efficiency of around 95%.     

Microwave Synthesis of γ-Fe2O3

Fine-particle Fe₂O₃ is prepared via microwave processing of Fe(NO₃)₃ · nH₂O, followed by low-temperature annealing. The particle size of the resulting -Fe₂O₃ is 5–6 nm after microwave processing and 80–110 nm after subsequent low-temperature heat treatment.     

Hydrothermal synthesis,characterization and thermal stability studies of α-Fe2O3 hollow microspheres

A simple, cost-effective hydrothermal technique was used in this study to successfully fabricate hollow α-Fe₂O₃ microspheres, using only fructose and anhydrous ferric chloride without any organic solvent or additive. The synthesized α-Fe₂O₃ hollow microspheres were characterized by X-ray diffraction spectroscopy (XRD), field-emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR). Based on the results, the shell was composed of aggregated α-Fe₂O₃ nanoparticles, while the fructose-derived carbon core was decomposed during calcination, leaving a hollow interior. XRD analysis confirmed the presence of the α-phase and the absence of γ-phase Fe₂O_3. A mean diameter of 595 nm was estimated for the microspheres by the Gaussian fit of the histogram constructed from the diameters measured over the SEM images. EDX spectrum of the sample showed signals attributed to Fe and O, and a homogenous distribution of these elements was confirmed by elemental mapping studies. ATR-FTIR analysis confirmed the bending and stretching vibration modes of the Fe-O bond. TGA-DTA data depicted that thermal stability of α-Fe₂O₃ hollow microsphere was achieved at 480 °C and no weight loss was observed up to 1000 °C. High-temperature calcination results showed that the material can maintain its hollow morphology up to 700 °C. This material has potential applications in drug delivery, gas sensing, and lithium storage.     

Green synthesis of α-Fe2O3 nanoparticles for photocatalytic application

In this study, the preparation of α-Fe₂O₃ nanoparticles using curcuma and tea leaves extract are reported. The curcuma and tea leaves are acted as a reductant and stabilizer. The crystal structure and particle size of the as-synthesized materials were measured through X-ray diffraction. X-ray diffraction patterns revealed that the as-prepared samples were α-Fe₂O₃ nanoparticles with well-crystallized rhombohedral structure and the crystallite sizes of the α-Fe₂O₃ nanoparticles are 4 and 5 nm. Scanning electron microscopy images showed that the prepared samples have spherical shape. The purity and properties of the as-synthesized α-Fe₂O₃ nanoparticles were measured by Raman spectroscopy. The chemical compositions of the as-prepared α-Fe₂O₃ nanoparticles have been analyzed by Fourier transform infrared spectroscopy. The absorption edge of the α-Fe₂O₃ nanoparticles are 561 and 551 nm. The photocatalytic activity of the α-Fe₂O₃ nanoparticles was measured by degradation of methylene orange and the α-Fe₂O₃ nanoparticles showed the excellent photocatalytic performance.     

Synthesis of ferrite grade γ-Fe2O3

Iron(II) carboxylato-hydrazinates: Ferrous fumarato-hydrazinate (FFH), FeC₄H₂O₄·2N₂H₄; ferrous succinato-hydrazinate (FSH), FeC₄H₄O₄·2N₂H₄; ferrous maleato-hydrazinate (FEH), FeC₄H₂O₄·2N₂H₄; ferrous malato-hydrazinate (FLH), Fein4H₄O₅·2N₂H₄; ferrous malonato-hydrazinate (FMH), FeC₃H₂O₄·1.5N₂H₄·H₂O; and ferrous tartrato-hydrazinate (FTH), FeC₄H₄O₆·N₂H₄·H₂O are being synthesized for the first time. These decompose (autocatalytically) in an ordinary atmosphere to mainly γ-Fe₂O₃, while the unhydrazinated iron(II) carboxylates in air yield α-Fe₂O₃, but the controlled atmosphere of moisture requires for the oxalates to stabilize the metastable γ-Fe₂O₃. The hydrazine released during heating reacts with atmospheric oxygen liberating enormous energy, N₂H₄ + O₂ → N₂ + H₂O; ΔH₂O = −621 kJ/mol, which enables to oxidatively decompose the dehydrazinated complex to γ-Fe₂O₃. The reaction products N₂ + H₂O provide the necessary atmosphere of moisture needed for the stabilization of the metastable oxide. The synthesis, characterization and thermal decomposition (DTA/TG) of the iron(II) carboxylato-hydrazinates are discussed to explain the suitability of γ-Fe₂O₃ in the ferrite synthesis.     

Preparation and characterization of the graphene–carbon nanotube/CoFe2O4/polyaniline composite with reticular branch structures

A novel graphene–carbon nanotube (graphene–CNT)/CoFe₂O₄/polyaniline composite with reticular branch structures had been fabricated by in situ chemical polymerization method. The textured structures of the as-prepared composites were characterized by the fourier transform infrared (FTIR) and X-ray diffraction (XRD). The morphology was analyzed by the scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The electromagnetic properties were tested by vibrating sample magnetometer and four-probe conductivity tester. The results showed that the graphene–CNT/CoFe₂O₄/polyaniline composite had the unique reticular branch structures. When the mass ratio of the graphene–CNT/CoFe₂O₄ to aniline was 1:3, the magnetic saturation value of the composite achieved 39.6 emu g⁻¹, and the conductivity reached 1.957 S cm⁻¹. Based on the experimental results, a probable formation mechanism for the unique reticular branch structures was proposed.     

One-step facile fabrication of Ag/γ-Fe2O3 composite microspheres

Ag/γ-Fe₂O₃ composite microspheres were successfully prepared via a simple solvothermal reduction method under mild conditions. Electron and X-ray diffraction data revealed that these composites consisted of silver and maghemite. Through the optimization of processing conditions, Ag/γ-Fe₂O₃ composites with a spherical shape were successfully produced. The results from the transmission and scanning electron microscopy revealed that the composites were spherical with a diameter in the range of 200–300 nm. Magnetic measurements showed that the mixed microspheres exhibited a typical ferromagnetic behavior, a specific saturation magnetization of 56 emu/g and an intrinsic coercivity of 38 Oe at room temperature. The presence of Ag nanoparticles dispersed into γ-Fe₂O₃ microspheres was also confirmed by UV–Vis absorption. These composites with microspherical morphologies can be applied in a variety of areas, including catalysis, medicine, photonics, and new functional device assemblies.     

Structural behavior of laser-irradiated γ-Fe2O3 nanocrystals dispersed in porous silica matrix : γ-Fe2O3 to α-Fe2O3 phase transition and formation of ε-Fe2O3

The effects of laser irradiation on γ-Fe₂O₃ 4 ± 1 nm diameter maghemite nanocrystals synthesized by co-precipitation and dispersed into an amorphous silica matrix by sol-gel methods have been investigated as function of iron oxide mass fraction. The structural properties of γ-Fe₂O₃ phase were carefully examined by X-ray diffraction and transmission electron microscopy. It has been shown that γ-Fe₂O₃ nanocrystals are isolated from each other and uniformly dispersed in silica matrix. The phase stability of maghemite nanocrystals was examined in situ under laser irradiation by Raman spectroscopy and compared with that resulting from heat treatment by X-ray diffraction. It was concluded that ε-Fe₂O₃ is an intermediate phase between γ-Fe₂O₃ and α-Fe₂O₃ and a series of distinct Raman vibrational bands were identified with the ε-Fe₂O₃ phase. The structural transformation of γ-Fe₂O₃ into α-Fe₂O₃ occurs either directly or via ε-Fe₂O₃, depending on the rate of nanocrystal agglomeration, the concentration of iron oxide in the nanocomposite and the properties of silica matrix. A phase diagram is established as a function of laser power density and concentration.     

Synthesis and electrochemical characterization of Li2MnO3–LiNixCOyMnzO2 cathode for lithium battery using co-precipitation method

The Li_xNi_0.23Co_0.12Mn_0.65O₂ electrode system with various compositions (x = 1.19, 1.33, 1.46, 1.58) was synthesized from a metal oxide precursor synthesized by co-precipitation method. The XRD patterns of the prepared powders revealed a hexagonal α-NaFeO₂ structure (space group: R-3m, 166) and the existence of a Li₂MnO₃ phase in the composite structure. In particular, the low Li content sample shows a three integrated structure (spinel, Li₂MnO₃, LiMO₂) for a Li/Metal(Ni/Co/Mn) mol ratio of 1.2. Scanning electron microscopy showed that all the synthesized samples contained spherical agglomerates with a size of 8–10 μm. Among the samples tested, Li_1.46Ni_0.23Co_0.12Mn_0.65O₂ shows relatively high charge and discharge capacity for the first cycle is 287, 192.9 mA h g^?1, respectively. Also, charge transfer resistance was also significantly improved compare with other samples.     

Fabrication, growth mechanism, and characterization of α-Fe(2)O(3) nanorods

This work reports the facile synthesis of α-Fe(2)O(3) nanorods and nano-hexagons and its application as sunlight-driven photocatalysis. The obtained products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), scanning electron microscopy (SEM), diffused reflectance spectroscopy (DRUV-vis), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). The phase and crystallinity were confirmed from the XRD study. Electron microscopy study clearly indicates the formation of different morphologies of nanocrystals. These hematite nanostructures were used as a model system for studying the shape-dependent photocatalytic degradation of phenol, methylene blue, and congo red. Amongst all the nanostructured semiconductors, Pt-doped hematite nanorod showed 55% efficiency towards the decolonization of methylene blue and 63% toward congo red under sun light illumination. The difference in photocatalytic activity is discussed in terms of their crystallize size and morphological ordering.     

Synthesis of α-Fe2O3 via oxidative hydrolysis of iron(II) sulphate

The influence of the main reaction parameters (temperature, pH and concentration) in the oxidative hydrolysis of iron (II) sulphate in an acid medium on the properties of the obtained -Fe₂O₃ and its applicability in ferrite production has been studied. The addition of manganese(II) ions catalyses the process in the homogeneous phase, probably by activation of oxygen. The obtained results are discussed within the framework of the assumed reaction mechanism, which includes an homogeneous reaction and a heterogeneous one with the participation of the oxidative hydrolysis product -FeOOH.     

Facile solution synthesis of α-FeF3·3H2O nanowires and their conversion to α-Fe2O3 nanowires for photoelectrochemical application

We report for the first time the facile solution growth of α-FeF(3)·3H(2)O nanowires (NWs) in large quantity at a low supersaturation level and their scalable conversion to porous semiconducting α-Fe(2)O(3) (hematite) NWs of high aspect ratio via a simple thermal treatment in air. The structural characterization by transmission electron microscopy shows that thin α-FeF(3)·3H(2)O NWs (typically <100 nm in diameter) are converted to single-crystal α-Fe(2)O(3) NWs with internal pores, while thick ones (typically >100 nm in diameter) become polycrystalline porous α-Fe(2)O(3) NWs. We further demonstrated the photoelectrochemical (PEC) application of the nanostructured photoelectrodes prepared from these converted hematite NWs. The optimized photoelectrode with a ~400 nm thick hematite NW film yielded a photocurrent density of 0.54 mA/cm(2) at 1.23 V vs reversible hydrogen electrode potential after modification with cobalt catalyst under standard conditions (AM 1.5 G, 100 mW/cm(2), pH = 13.6, 1 M NaOH). The low cost, large quantity, and high aspect ratio of the converted hematite NWs, together with the resulting simpler photoelectrode preparation, can be of great benefit for hematite-based PEC water splitting. Furthermore, the ease and scalability of the conversion from hydrated fluoride NWs to oxide NWs suggest a potentially versatile and low-cost strategy to make NWs of other useful iron-based compounds that may enable their large-scale renewable energy applications.     

Fabrication and characterization of YBa2Cu3O7−x /Sn composite superconductors

YBa₂Cu₃O_7–x /Sn (YBCO/Sn) composites sintered at 230 °C exhibited a percolation threshold for electrical conductivity at 20 vol% Sn, with semiconducting and metallic behaviour below and above it, respectively. The simultaneous decrease in =d/dT and ₀ with increase in Sn content was related to formation of defect-free interfaces. The diamagnetic shielding property of the composites weakened with Sn content, as deduced from magnetic levitation experiments.     

Biomimetic fabrication of α-Fe2O3 with hierarchical structures as H2S Sensor

A facile sol–gel method is developed for the fabrication of α-Fe₂O₃ with quasi-honeycomb like structures inherited from Papilio paris butterfly wings. The exquisite hierarchical architecture is faithfully maintained in α-Fe₂O₃ from the skeleton of butterfly wings at the levels from macro to nano-scales. When used as a chemical sensor, the obtained α-Fe₂O₃ replica (P-α-Fe₂O₃) showed a much higher performance than that of the compared α-Fe₂O₃ nanoparticles synthesized under the same condition without biotemplate (S-α-Fe₂O₃). The P-α-Fe₂O₃-based sensor has a sensitivity of 19.2–50 ppm H₂S, which is four times more than that of S-α-Fe₂O₃, accompanied by a rapid response/recovery time within 1/10 s even at a relatively low working temperature of 180 °C. Compare to the S-α-Fe₂O₃, surface area of which cannot be detectable, the high sensing feature of P-α-Fe₂O₃ would be attributed to the relatively high-specific surface area 24.12 m²/g thus fabricated together with the unique 3D-network structures, which provide channel for the diffusion of H₂S. This strategy is expected to be used in fabrication of other kinds of metal oxide with unique structures for the potential application in gas sensor.     

Synthesis and gas sensing properties of α-Fe(2)O(3)@ZnO core-shell nanospindles

α-Fe(2)O(3)@ZnO core-shell nanospindles were synthesized via a two-step hydrothermal approach, and characterized by means of SEM/TEM/XRD/XPS. The ZnO shell coated on the nanospindles has a thickness of 10-15 nm. Considering that both α-Fe(2)O(3) and ZnO are good sensing materials, we have investigated the gas sensing performances of the core-shell nanocomposite using ethanol as the main probe gas. It is interesting to find that the gas sensor properties of the core-shell nanospindles are significantly enhanced compared with pristine α-Fe(2)O(3). The enhanced sensor properties are attributed to the unique core-shell nanostructure. The detailed sensing mechanism is discussed with respect to the energy band structure and the electron depletion theory. The core-shell nanostructure reported in this work provides a new path to fabricate highly sensitive materials for gas sensing applications.     

Three and one-dimensional hierarchical α-Fe2O3 nanostructures for photoelectrochemical water oxidation

Journal of Materials Science: Materials in Electronics - Herein, we report the synthesis of three-dimensional (3D) and one-dimensional (1D) hierarchical hematite (α-Fe2O3) nanostructures on...     

Improvements in α-Fe2O3 ceramic sensors for reducing gases by addition of Sb2O3

The microstructure, electrical properties and gas-sensing characteristics of Sb-doped -Fe₂O₃ were investigated. Powder precursors with Sb/Fe = 0–0.1 were prepared by chemical coprecipitation method. Sb-doped -Fe₂O₃ powders were characterized by means of thermal gravimetric-differential thermal analysis (TG-DTA), X-ray diffraction (XRD), BET surface area and scanning electron microscope (SEM). It was found that the raw powders underwent crystallization into the corundum structure of -Fe₂O₃ at a temperature which increased somewhat with increasing Sb content; a proper amount of Sb doping suppressed both crystallite growth and the formation of hard agglomerates. The doping of Sb₂O₃ decreased the sensor resistance by one order of magnitude and increased the sensitivities to some hydrocarbon gases markedly. The former can be attributed to the substitution of Sb⁵⁺ for Fe³⁺ sites in -Fe₂O₃ generating more free electrons; the latter is closely related to Sb-doped samples accommodating a higher density of chemisorbed oxygen.