Template-free hydrothermal synthesis of hollow hematite microspheres

Hollow hematite (α-Fe₂O₃) microspheres with an average diameter of 3-4 μm and a shell thickness of approximate 150 nm was synthesized by a simple hydrothermal route using FeCl₃·6H₂O solution and acetic acid without using any templates. The hollow microspheres were composed of α-Fe₂O₃ nanoparticles with the diameter range from 20 to 40 nm. The effects of reaction parameters such as reaction time, temperature, concentration of FeCl₃·6H₂O solution, and initial pH on the morphology of the final products were investigated. A possible formation mechanism of hollow α-Fe₂O₃ microspheres was also proposed, where the acetic acid played a role of etching in the formation of hollow structure.     

Preparation and characterization of hollow α-Fe2O3 irregular microspheres

Hollow α-Fe₂O₃ irregular microspheres were prepared at 160 °C from a hydrolyzing Fe(ClO₄)₃ solution by adding sodium polyanethol sulphonate. The particles were characterized by ⁵⁷Fe Mössbauer, X-ray diffraction, Fourier transform infrared spectroscopy, field emission scanning electron microscopy and energy dispersive X-ray spectroscopy. The walls of these hollow particles consisted of elongated subunits composed of elongated and thin α-Fe₂O₃ rods. The precipitation of hollow α-Fe₂O₃ irregular microspheres was governed by the preferential adsorption of sulphonate/sulphate groups. The lateral aggregation of elongated thin rods and subunits also played an important role in the formation of hollow α-Fe₂O₃ irregular microspheres.     

Preparation of γ-Fe2O3 nanopowders by direct thermal decomposition of Fe-urea complex: reaction mechanism and magnetic properties

In this work, a novel method of producing maghemite (γ-Fe₂O₃) nanopowders has been developed, which can be performed by the direct thermal decomposition of an Fe–urea complex ([Fe(CON₂H₄)₆](NO₃)₃) in a single step. The reaction mechanism, particle morphology, and the magnetic properties of the γ-Fe₂O₃ nanopowders have been studied by using thermogravimetric (TG), differential scanning calorimetry (DSC), fourier transformed infrared (FTIR) spectroscopy, elemental analysis, X-ray powder diffraction (XRD), transmission electron micrograph (TEM) observations, and magnetic measurements. Thermal analyses together with the results of XRD show that the formation of γ-Fe₂O₃ occurs at ~200 °C through a two-stage thermal decomposition of the [Fe(CON₂H₄)₆](NO₃)₃ complex. The resulting iron oxide phases (i.e., γ-Fe₂O₃ and α-Fe₂O₃) are strongly dependent on the synthesis conditions of the [Fe(CON₂H₄)₆](NO₃)₃. When the molar ratio of Fe(NO₃)₃ · 9H₂O to CON₂H₄ that is used for the synthesis of [Fe(CON₂H₄)₆](NO₃)₃ is 1:6 (i.e., molar ratio in stoichiometry), a mixed phase of γ-Fe₂O₃ and α-Fe₂O₃ is formed. When the molar ratio is 1:6.2 (i.e., using an excess CON₂H₄), on the other hand, a pure γ-Fe₂O₃ is obtained. Magnetic measurements show that resulting nanopowders exhibit a ferromagnetic characteristic and their maximum saturation magnetization increases from 47.2 to 67.4 emu/g with an increase in the molar ratio of Fe(NO₃)₃ · 9H₂O to CON₂H₄ from 1:6 to 1:6.2.     

Characteristics of α-Fe2O3 thick film gas sensors

Haematite (α-Fe₂O₃) with SO₄²⁻ and tin, as raw material, was prepared by a co-precipitation method. The α-Fe₂O₃-based thick film gas sensors were made by a screen printing technique. The microstructure of the raw material was affected by the hydrogen ion concentration which was controlled during the process of raw material preparation. Also, the pH value exhibited an effect on the sensitivity to gases for the thick film. It was thought that the sulphate ions localized in the thick film played an active role in hydrocarbon gas adsorption phenomena. Thick films of α-Fe₂O₃/α-Al₂O₃/Pd (78:20:2 by weight) had good adhesion to alumina substrates and exhibited relatively high sensitivity to CH₄ at 350°C.     

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.     

Hydrothermal synthesis and electrochemical properties of alpha-manganese sulfide submicrocrystals as an attractive electrode material for lithium-ion batteries

A convenient hydrothermal synthetic route has been successfully developed to prepare stable rock-salt-type structure α-MnS submicrocrystals under mild conditions. In this synthetic system, hydrated manganese chloride (MnCl₄·4H₂O) was used to supply a highly reactive manganese source, thiourea ((NH₂)₂CS) was used to supply the sulfide source and aqueous hydrazine (N₂H₄·H₂O) was used as both alkaline and reducing agent. The results revealed that the electrochemical performance of the α-MnS submicrocrystals may be associated with the degree of crystallinity and particle size of samples. The initial lithiation capacity of the α-MnS submicrocrystals obtained at 120 °C is 1327 mAh g⁻¹ at 0.7 V versus Li/Li⁺, which exhibited α-MnS submicrocrystals is extremely promising anode material for lithium-ion batteries and has great potential applications in the future.     

The influence of the synthesis routes of MgAl2O4 on its properties and behavior as support of dehydrogenation catalysts

In order to synthesize MgAl₂O₄, three methods were used: (a) a solid phase reaction of MgO and γ-Al₂O₃ oxides at 900 °C for 24 h (ceramic method), (b) wet milling during 24 h of the mixture of oxides followed by the reaction at 900 °C for 12 h (mechanochemical synthesis), and (c) coprecipitation of Mg(NO₃)₂·6H₂O and Al(NO₃)₃·9H₂O with ammonia solution followed by a calcination in a flow of air at 800 °C during 4 h (coprecipitation method). The synthesized materials were characterized by XRD, BET isotherm, isopropanol dehydration reaction, TGA/DTA and SEM. The results indicate that in all the cases the MgAl₂O₄ spinel was formed. Besides, a residue of MgO in the samples obtained by the ceramic method and mechanochemical synthesis was found, which was eliminated by purification. The surface area of MgAl₂O₄ obtained by mechanochemical synthesis and coprecipitation method are much higher than that of the spinel synthesized by the ceramic method. Pt (0.3%) catalysts were prepared by impregnating the three supports with H₂PtCl₆. The metallic dispersion of Pt/MgAl₂O₄ obtained by mechanochemical synthesis was higher than that of Pt catalysts supported on the other spinels, in agreement with the catalytic behavior observed in n-butane dehydrogenation reaction and test reactions of the metallic phase.     

Optoelectronic properties of β-Fe2O3 hollow nanoparticles

The effect of hollow structure on the optoelectronic properties of β-Fe₂O₃ hollow nanoparticles (HNPs) was determined. Spectrophotometry showed that the optical transmittance of the β-Fe₂O₃ HNPs was less than 40% in the visible-light region. This opaqueness was suggested to be an optical characteristic, commonly found in the authors' previous studies of TiO₂ and δ-Al₂O₃ HNPs. In addition, β-Fe₂O₃ HNPs had a band gap (1.86 eV) between amorphous (1.73 eV) and polycrystalline (1.97 eV) β-Fe₂O₃ thin films, which was a 5–7 nm thick shell that embraced an intermediate volume of the crystal phase, in-between the two thin films.     

Templating synthesis of waxberried hematite hollow spheres

Novel hematite (α-Fe₂O₃) hollow spheres were prepared through a surfactant-assisted solvothermal process. The XRD, SEM and TEM characterization data confirm that the formation of α-Fe₂O₃ hollow spheres exhibits waxberry-like architectures with spindle nanoparticles, the length in the range of 150-400 nm, as building block. Their tips of these nanoparticles were concentrated on a center. The sizes of α-Fe₂O₃ waxberry are less than 3 µm. They possess good photocatalytic properties when used for the degradation of salicylic acid in water. The formation mechanism of α-Fe₂O₃ waxberry is also discussed.     

Preparation of nanoplates assembled 4CaO·5B2O3·7H2O oval-like microspheres via a hydrothermal method

4CaO·5B₂O₃·7H₂O uniform oval-like microspheres morphology has been prepared at 120 °C by a simple hydrothermal method with the help of the surfactant polyethylene glycol(PEG-300). The result indicates that 4CaO·5B₂O₃·7H₂O oval-like microspheres are constructed by ladder-like layers, and each layer is made up of numerous densely packed nanoplates with the thickness of 50–100 nm and the diameter of several microns. The nanoplates in each layer are interconnected with the nanoplates in next layer, which leads to form the multilayered structural oval-like microspheres. The PEG-300 plays an important role in the formation of this oval-like microspheres morphology.     

Preparation of superhydrophilic α-Fe2O3 nanofibers with tunable magnetic properties

The paper describes a simple, effective method for producing α-Fe₂O₃ nanofibers by electrospun poly(vinyl alcohol)/ferrous acetate composite nanofibers precursors and high-temperature calcination in air. The experimental results show that the morphology and crystalline phase of α-Fe₂O₃ nanofibres are influenced by the content of ferrous acetate in composite nanofibres and the calcination temperature. The α-Fe₂O₃ nanofibres can generate superhydrophilic surface displaying the contact angle of water as 0°. By controlling the calcination temperature of electrospun composite nanofibers in the air, the magnetic property of α-Fe₂O₃ nanofibres could be tuned from superparamagnetic to ferromagnetic.     

Facile route to the synthesis of porous α-Fe2O3 nanorods

The requirements of simple and reliable protocols for the synthesis of anisotropic structures with controlled morphology continue to be a major challenge in nanoscience. In this paper we describe the facile synthesis of porous hematite (α-Fe₂O₃) nanorods using anionic surfactant as a rod-like template. α-FeOOH nanorods with diameters of 170–210 nm and lengths up to 3–5 μm were synthesized in high yield via hydrothermal method using sodium dodecyl sulphate as a template. The porous α-Fe₂O₃ was obtained after solvent extraction and calcining the as-obtained α-FeOOH nanorods at 500 °C for 6 h. Even after removal of template by solvent extraction and calcination the shape of the nanorods was intact except the generation of pores on the nanorods. The porous nanorods were analysed by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, transmission and high-resolution transmission electron microscopy (TEM & HRTEM), scanning electron microscopy (SEM) and superconducting quantum interference device (SQUID) measurements. SEM and TEM images showed that the morphology of hematite nanostructure is homogeneous in the shape of rods and full of porosity and magnetization measurements of the porous α-Fe₂O₃ nanorods showed weak ferromagnetic behavior. The surfactant SDS (sodium dodecyl sulphate) plays a key role in controlling the nucleation and growth of the nanorods and their use as a new class of inorganic scaffolds for the synthesis of nanomaterials are salient features of the work with implications in crystal engineering and nanocomposites design for various applications.     

Analyses of nano-crystalline LiCoVO4 prepared by solvothermal reaction

LiOH·H₂O, Co(NO₃)₂·6H₂O and NH₄VO₃ were used to prepare nano-crystalline LiCoVO₄ by 150 °C solvothermal reaction in isopropanol for 10–360 h and subsequent calcination at 300–500 °C for 6 h. XRD, TEM and selected area electron diffraction (SAED) revealed the presence of nano-crystalline LiCoVO₄ with inverse spinel structure. The V–O stretching vibration modes of VO₄ tetrahedrons were detected by FTIR over the range 617–835 cm^− 1 and by Raman spectrometer at 805.7 and 783.1 cm^− 1. Co, V and O were detected by EDX. TGA of solvothermal products shows weight loss due to the evaporation and decomposition processes at 40–648 °C.     

Hydrothermal synthesis and characterization of monodisperse α-Fe2O3 nanoparticles

Monodisperse α-Fe₂O₃ nanoparticles have been successfully prepared by hydrothermal synthetic route using FeCl₃, CH₃COONa as reagents and reacted at 200 °C for 12 h. The morphology and structure of products were characterized by powder X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The results showed that the α-Fe₂O₃ nanoparticles were single-crystalline hexagonal structure and average diameters were about 80 nm. Magnetic properties have been detected by a vibrating sample magnetometer at room temperature. The nanoparticles exhibited a ferromagnetic behavior with the coercive force (Hc), saturation magnetization (Ms) and remanent magnetization (Mr) was 185.28 Oe and 0.494 emu/g, 0.077 emu/g.     

Crystallization of Anhydrous Copper Sulfate From Sulfuric Acid—Ammonium Sulfate Mixtures

The growth of CuSO₄ crystals from a nonaqueous solvent, composed of (NH₄)₂SO₄ and H₂SO₄ is described. Solubility of CuSO₄ in solvents of varying (NH₄)₂SO₄ to H₂SO₄ ratio, at 200 °C, has been determined, as well as the temperature dependence of the solubility in 0.35(NH₄)₂SO₄ — 0.65H₂SO₄. Single crystal specimens, weighing up to 150 mg have been obtained.     

A low-temperature solution route to hollow NH4VO3 microspheres with controllable shells

NH₄VO₃ hollow microspheres with controllable shells have been synthesised by the interaction between AgNO₃ and NH₄VO₃ via a facile one-step low-temperature solution-based method. The diameters and surface roughness of NH₄VO₃ hollow spheres can be readily controlled by altering the molar ratios of NH₄VO₃ to AgNO₃. When the molar ratios of NH₄VO₃ to AgNO₃ increase from 6?:?1 to 8?:?1, the diameters of NH₄VO₃ hollow spheres increase from 500–600 to 800–900?nm and the building blocks of the shells are assembled by nanoparticles and nanorods. The introduction of AgNO₃ and H₂O₂ plays an important role in the formation of NH₄VO₃ hollow microspheres.     

Preparation and magnetic properties of hollow ferrite microspheres by a gas-phase diffusion method in an ionic liquid/H2O mixed solution

In this work, hollow ferrite microspheres were prepared using a gas-phase diffusion method with cobalt nitrate and ferric nitrate as metal salt sources, an ionic liquid 1-butyl-3-methylimidazolium-tetrafluoroborate and water-mixed solvent as medium and ammonium carbonate as precipitant. Their structures and magnetization were characterized by transmission electron microscopy, scanning electron microscopy, X-ray diffraction, thermogravimetry, infrared spectroscopy, and vibrating sample magnetometer. The effects of reaction time, reaction temperature, precipitant loading, and mole ratio of Co to Fe n(Co/Fe) on the structures and magnetization of the microspheres were studied. The results showed that ferrite hollow microspheres with uniform morphology and high-magnetic performance were obtained at 60–80 °C for 12–16 h, while the (NH₄)₂CO₃ loading was 0.15 g/ml, n(Co/Fe) was 0.5:1, and calcination temperature was 550 °C. The obtained products consisted of CoFe₂O₄ phase accompanied by ferric oxide phase, with an average particle size about 1 μm and magnetization intensity about 10 emu/g.     

Heavy metal contaminant remediation study of western Xiamen Bay sediment, China: Laboratory bench scale testing results

A surface sediment sample (<5 cm) was collected from a sewage sludge contaminated site (118°02.711′E, 24°32.585′N) within western Xiamen Bay, China, in July 2005 for a sediment decontamination study. A series of laboratory-based experiments under various conditions were performed using chemical complexation reagents (e.g., H₂C₂O₄, EDTA–2Na, etc.) and their combination in order to provide information for sediment remediation technology development. In this study, the results suggest that aeration and agitation of the sediment samples in distilled–deionized water (DDW) have either no or weak (<30%) effect on metal removal, whereas agitation, aeration and rotation of the samples in chemical complexation solutions yield much better metal removal efficiency (up to 90%). A low pH condition (e.g., pH < 3) and a low solid to liquid ratio (e.g., S:L = 1:50) could increase metal removal efficiency. The experimental results suggest that 0.20 M (NH₄)₂C₂O₄ + 0.025 M EDTA combination with solid:liquid ratio = 1:50 and 0.50 M ammonium acetate (NH₄Ac) + 0.025 M EDTA combination with solid:liquid ratio = 1:50 are the most effective methods for metal removal from the contaminated sediments. This research provides additional useful information for sediment metal remediation technology development.     

Optical, electrical and magnetic properties of Co3O4 nanocrystallites obtained by thermal decomposition of sol–gel derived oxalates

Nanocrystallites of tricobalt tetraoxide (Co₃O₄) have been synthesized by sol–gel process using cobalt acetate tetrahydrate, oxalic acid as precursors and ethanol as a solvent. The process comprises of gel formation, drying at 80 °C for 24 h to obtain cobalt oxalate dihydrate (α-CoC₂O₄·2H₂O) followed by calcination at or above 400 °C for 2 h in air. These results combined with thermal analysis have been used to determine the scheme of oxide formation. The room temperature optical absorption spectra exhibits blue shift in both (i) ligand to metal (p(O²⁻) → e_g(Co³⁺), 3.12 eV), and (ii) metal to metal charge transfer transitions (a) t_2g(Co³⁺) → t₂(Co²⁺), 1.77 eV, (b) t₂(Co²⁺) → e_g(Co³⁺), 0.95 eV together with the d–d transitions (0.853 and 0.56 eV) within the Co²⁺ tetrahedra. The temperature dependent ac electrical and dielectric properties of these nanocrystals have been studied in the frequency range 100 Hz to 15 MHz. There are two regimes distinguishing different temperature dependences of the conductivity (70–100 K and 200–300 K). The ac conductivity in both the temperature regions is explained in terms of nearest neighbor hopping (NNH) mechanism of electrons. The carrier concentration measured from the capacitance (C)–voltage (V) measurements is found to be 1.05 × 10¹⁶ m⁻³. The temperature dependent dc magnetic susceptibility curves under zero field cooled (ZFC) and field cooled (FC) conditions exhibit irreversibilities whose blocking temperature (T_B) is centered at 35 K. The observed Néel temperature (T_N  25 K) is significantly lower than the bulk Co₃O₄ value (T_N = 40 K) possibly due to the associate finite size effects.     

Microwave dielectric properties and sintering behavior of nano-scaled (α + θ)-Al2O3 ceramics

The dielectric properties at microwave frequencies and the microstructures of nano (α + θ)-Al₂O₃ ceramics were investigated. Using the high-purity nano (α + θ)-Al₂O₃ powders can effectively increase the value of the quality factor and lower the sintering temperature of the ceramic samples. Grain growth can be limited with θ-phase Al₂O₃ addition and high-density alumina ceramics can be obtained with smaller grain size comparing to pure α-Al₂O₃. Relative density of sintered samples can be as high as 99.49% at 1400 °C for 8 h. The unloaded quality factors Q × f are strongly dependent on the sintering time. Further improvement of the Q × f value can be achieved by extending the sintering time to 8 h. A dielectric constant (_r) of 10, a high Q × f value of 634,000 GHz (measured at 14 GHz) and a temperature coefficient of resonant frequency (τ_f) of −39.88 ppm/°C were obtained for specimen sintered at 1400 °C for 8 h. Sintered ceramic samples were also characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM).