Hydrothermal synthesis and characterization of α-Fe2O3 nanoparticles

Iron oxide (Fe₂O₃) nanoparticles were synthesized by a simple hydrothermal synthesis method using only Fe(NO₃)₃·9H₂O and NH₃·H₂O as raw materials. The effect of reaction temperature and time on the crystalline phase and morphology of Fe₂O₃ products was investigated. The products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and Fourier transform infrared (FTIR) spectroscopy. The XRD and TEM results show that reaction temperature and time play an important role in the formation of the crystalline phase and morphology of the products. With increasing reaction temperature and time, the diffraction peaks of α-Fe₂O₃ become stronger and sharper, and the morphologies of the samples have an obvious change from floccules to nanoparticles. FTIR peaks show that α-Fe₂O₃ nanoparticles have about a 25 cm^?1 shift to higher frequency compared with those of α-Fe₂O₃ with other morphologies.     

Optical properties and photoinduced superparamagnetism of γ-Fe2O3 nanoparticles formed in dendrimer

We are presenting the joint investigation of the optical and photoinduced superparamagnetic properties of a single-domain γ-Fe₂O₃ nanoparticles (NPs) formed in poly(propylene imine) (PPI)-dendrimer. The optical absorption studies indicated direct allowed transition with the band gap (4.5 eV), which is "blue"-shift with respect to the value of the bulk material. The influence of pulsed laser irradiation on the superparamagnetic properties of γ-Fe₂O₃ NPs was studied by Electron paramagnetic resonance (EPR) spectroscopy. It has been shown that irradiation of the sample in vacuo and cooled in zero magnetic field to 6.9 K leads to the appearance of a new EPR signal, which decays immediately after the irradiation is stopped. We suppose that the generation of conduction band electrons by irradiation into the band gap of the γ-Fe₂O₃ changes the superparamagnetic properties of NPs.     

α-Fe2O3表面结构的研究

像差校正透射电子显微镜拥有亚埃级的分辨率,并克服了物镜离域效应的影响,可以定量分析复杂氧化物表面的原子结构,如弛豫、缺陷等.本文利用像差校正高分辨透射电镜,结合多片层法像模拟,研究了α-Fe2O3纳米颗粒[0001]带轴下的内部结构和表面结构.结果表明α-Fe2O3[0001]带轴下以O3-Fe4-O3-…方式的(11(-2)0)表面终结,表现为非极性表面.     

The effect of temperature on the growth of Ag2O nanoparticles and thin films from bis(2-hydroxy-1-naphthaldehydato)silver(I) complex by the thermal decomposition of spin–coated films

Bis(2-hydroxy-1-naphthaldehydato)silver(I) complex (Ag-HNA) was prepared through the reaction of the ligand and silver nitrate. Silver oxide nanoparticles were synthesized via thermal decomposition at different temperatures by calcinating Ag complex inside a ceramic boat. The same metal precursor was used to prepare Ag₂O thin films at different temperatures by spin coating onto a glass substrate. The prepared silver complex was characterized by Fourier transform infrared (FTIR) spectroscopy, elemental analysis, nuclear magnetic resonance (NMR) and thermogravimetric (TGA) analysis. The effects of decomposition temperatures (150, 200, 250 and 300 °C) and of the annealing temperatures for the films at 200, 250, 300 and 350 °C were studied. The surface morphologies, structural and optical properties of the nanoparticles and films were investigated. The results shows that the temperature plays a significant role in controlling nature of the nanoparticles and thin films. The X-Ray diffraction patterns of Ag₂O nanoparticles and the prepared thin films prepared revealed the face-centred cubic structures.     

α-Fe2O3纳米棒的制备研究

采用压力-热晶法,制得棒状的前躯体后再在600℃焙烧8h,成功地制得直径在20．40nm,长度在300—500nnl之间,均匀分散、疏松多孔的六方结构的棒状Fe2O3纳米粒子,并用透射电子显微镜、电子衍射、X射线衍射等技术手段对样品进行了表征,考察了制备条件对产物粒径、形貌的影响．结果表明：初始铁盐浓度对产物粒径影响不明显,可以在较高初始浓度下制备Fe2O3纳米粒子;pH值、初始压力对粒子形貌和大小有一定的影响．     

Single-step synthesis of activated carbon/γ-Fe2O3 nano-composite at room temperature

Magnetically activated carbon (MAC) nano-composite was synthesized by a simple single-step wet chemical method at room temperature. The structure, surface area, morphology and magnetic properties of as-prepared composite were characterized by X-ray diffraction (XRD), Brunaure–Emmet–Teller analysis (BET), Fourier transform infrared spectrum, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and vibrating sample magnetometry. SEM and TEM analysis indicated that the spherical maghemite (γ-Fe₂O₃) nanoparticles of average particle size 22±2 nm were homogeneously dispersed onto Treated Activated Carbon (TAC). Also, using Scherrer's formula, the average crystallite maghemite nano-particles on the TAC were estimated to be about 19 nm. According to BET analysis, the MAC was of 356 m²/g surface area and 0.36 cm³/g pore volume. The MAC nano-composite exhibited a nearly superparamagnetic property with a saturation magnetization (Ms) of 3.15 A m²/kg. It is suggested that this method could be a more efficient and practical way to produce magnetically modified activated carbon for use as a magnetic adsorbent to remove contaminants.     

Shape controlled synthesis and formation mechanism of Y2(C2O4)3 and Eu3+–Y2O3 phases via hydrothermal microemulsion

The flat or truncated flat cube Y₂O₃ precursor powders were synthesized in a reverse microemulsion and hydrothermal. Hexadecyl Trimethyl Ammonium Bromide (CTAB) and Organophosphate (OP) were used as the mixed surfactants, n-pentanol was used as assistant, and cyclohexane was used as oil phase. Y(NO₃)₃ and Na₂C₂O₄ solution were used as the water-phrase and starting materials. The resulting products were characterized by X-ray powder diffraction (XRD), field emission scanning electron microscopy (FESEM), d thermogravimetric – differential scanning calorimetry (TG–DSC), and photoluminescence spectroscopy (PL). The results show that the monoclinic rod-like Y₂(C₂O₄)₃ have been obtained via hydrothermal microemulsion and the sizes of the particles were diameters of 100 nm and lengths up to about 1–2 μm. The precursor calcined products were doped with Eu³⁺, and the prepared phosphors showed well-defined red luminescence due to radiative transitions from ⁵D₀ to ⁷F_J (J=1, 2) levels of Eu³⁺ ions. Furthermore, We reported Eu³⁺–Y₂O₃ phases represented a new class of optically active materials.     

Physical properties of hematite -Fe2O3 thin films: Application to photoelectrochemical solar cells

The physical properties and photoelectrochemical characterization of aluminium doped hematite -Fe2O3, synthesized by spray pyrolysis, have been investigated in regard to solar energy conversion. Stable Al-doped iron (III) oxide thin films synthesized by spray pyrolysis technique reveals an oxygen deficiency and the oxide exhibits n-type conductivity confirmed by anodic photocurrent generation. The preparative parameters have been optimized to obtain good quality thin films which are uniform and well adherent to the substrate. The deposited iron oxide thin films shows the single hematite phase with polycrystalline rhombohedral crystal structure with crystallite size 20-40 nm. Optical analysis enabled to point out the increase in direct band-gap energy from 2.2 to 2.25 eV with doping concentration which is attributed to blue shift. The dielectric constant and dielectric loss are studied as a function of frequency. To understand the conduction mechanism in the films AC conductivity is measured. The conduction occurs by small polaron hopping through mixed valences Fe2+/3+ with an electron mobility 300K of 1.08 Vcm2s-1. The -Fe2O3 exhibits long term chemical stability in neutral solution and has been characterized photoelectrochemically to assess its activity as a photoanode for various electrolytes using white light to obtain I–V characteristics. The Al-doped hematite exhibited higher photocurrent response when compared with undoped films achieving power conversion efficiency of 2.37% at 10 at% Al:Fe2O3 ¬ thin films along with fill factor 0.38 in NaOH electrolyte. The flat band potential Vfb (-0.87 VSCE) is determined by extrapolating the linear part to C-2 = 0 and the slope of the Mott-Schottky plot.     

Photocatalytic and bactericidal activities of hydrothermally and sonochemically prepared Fe2O3–SnO2 nanoparticles

Fe₂O₃–SnO₂ nanocomposites (NCs) were prepared by hydrothermal and sonochemical methods. Transmission electron micrographs confirmed that the composites comprise nanoparticles. Energy-dispersive X-ray analyses revealed compositions of 25 at.% Sn and 22 at.% Fe for hydrothermally prepared NC (HNC) and 4 at.% Sn and 56 at.% Fe for sonochemically prepared NC (SNC). X-Ray diffractograms revealed rutile SnO₂, γ-Fe₂O₃, and FeO(OH) as components of HNC, and rutile SnO₂, γ-Fe₂O₃, β-Fe₂O₃ and FeO(OH) of SNC. Both NCs absorb visible light and display red emission. The solid-state impedance spectrum for HNC is a half-semicircular arc and SNC exhibits a quasi-linear relationship between Z′′ and Z′. Both NCs are ferromagnetic. The saturation magnetization of HNC is much less than that of the SNC, which in turn is far less than that of the γ-Fe₂O₃ precursor. Both NCs display visible light photocatalysis and HNC is a better photocatalyst than SNC. Furthermore, both NCs exhibit bactericidal activity.     

Visible light photocatalytic activity of reduced graphene oxide synergistically enhanced by successive inclusion of γ-Fe2O3, TiO2, and Ag nanoparticles

Novel magnetic nanocomposites are synthesized by loading reduced graphene oxide (r-GO) with three brands of nanoparticles consisting of titanium dioxide (TiO₂), gamma-iron(III) oxide (γ-Fe₂O₃), and silver (Ag) with varying amounts. The resulting Ag/TiO₂/γ-Fe₂O₃@r-GO demonstrates synergistically enhanced visible light photocatalytic activity, on degradation of wastewater׳s toxic crystal violet (CV). Specifically, it exhibits higher photoactivity than those of neat graphene oxide (GO), TiO₂@GO, γ-Fe₂O₃@GO, and TiO₂/γ-Fe₂O₃@GO, possibly because of effective separation of photogenerated carriers via strongly coupled Ag/γ-Fe₂O₃@r-GO cocatalyst and the enrichment of organic molecules on the graphene nanosheets. A higher photocatalytic efficiency is observed when 11.5 wt% Ag nanoparticles are incorporated in TiO₂/γ-Fe₂O₃@GO. After 3 successive cycles, the latter nanocomposite maintains 97% removal efficiency with excellent stability and easy recovery. Considering its facile preparation and high photocatalytic activity, it is hoped that this photocatalyst will find its application in various fields such as air purification and wastewater treatment. The structure and properties of Ag/TiO₂/γ-Fe₂O₃@r-GO are characterized by Fourier-transform infrared (FTIR), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), ultraviolet–visible spectrometry (UV–vis) and Raman spectroscopy techniques.     

Controllable synthesis of metastable γ-Bi2O3 architectures and optical properties

Metastable γ-Bi₂O₃ were successfully prepared via a controllable, facile and mild solution precipitation synthesis method in ethylene glycol-water mixed solvent systems without adding surfactant or template agents, at 80 ℃ and ambient atmospheric pressure in 40 min. Ethylene glycol can facilitate the nucleation of γ-Bi₂O₃ as only α-Bi₂O₃ was observed in its absence. And by adjusting ethylene glycol (EG) volume fraction, metastable γ-Bi₂O₃ submicro hexahedrons, tetrahedrons, polyhedrons and three-dimensional self-assembled hierarchical flower-like architectures were obtained respectively. SEM, XRD, and EDS were used to characterize the microstructures. The flower-like metastable γ-Bi₂O₃ architectures with diameter of several micrometers were 3D self-assembled from tetrahedrons step by step. The formation of the hierarchical flower-like architectures was due to the controlling of crystal growth kinetics and the guidance of self-assembly approach by ethylene glycol. The possible formation mechanism of these metastable γ-Bi₂O₃ architectures was also discussed. And compared with α-Bi₂O₃, β-Bi₂O₃, δ-Bi₂O₃, and γ-Bi₂O₃ through other means reported previously, the as-prepared γ-Bi₂O₃ in this paper possesses more excellent optical performance.     

Study of sensitivity and selectivity of α-Fe2O3 thin films for different toxic gases and alcohols

This paper presents a detailed study on the sensitivity and selectivity of α-Fe₂O₃ thin films produced by deposition of Fe and post-deposition annealed at two temperatures of 600 °C and 800 °C with flow of oxygen for application as a sensor for toxic gases including CO, H₂S, NH₃ and NO₂ and alcohols such as C₃H₇OH, CH₃OH, and C₂H₅OH. The crystallographic structure of the samples was studied by X-ray diffraction (XRD) method while an atomic force microscope (AFM) was employed for surface morphology investigation. The electrical response of the films was measured while they were exposed to various toxic gases and alcohols in the temperature range of 50–300 °C. The sample annealed at higher temperature showed higher response for different gases and alcohols tested in this work which can be due to the higher resistance of this sample. Results also indicated that the α-Fe₂O₃ thin films show higher selectivity to NO₂ gas relative to the other gases and alcohols while the best sensitivity is obtained at 200 °C. The α-Fe₂O₃ thin film post-deposition annealed at 800 °C also showed a good stability and reproducibility and a detection limit of 10 ppm for NO₂ gas at the operating temperature of 200 °C.     

Visible-light-responsive γ-Fe2O3/PMMA/S-TiO2 core/shell nanocomposite: Preparation,characterization and photocatalytic activity

Organic-inorganic composite materials have demonstrated many potential applications in environmental field. This paper presented a facile preparation method for γ-Fe₂O₃/PMMA/S-TiO₂ nanocomposite with core-shell structure and its application in degradation of phenanthrene under visible light irradiation. Firstly, γ-Fe₂O₃/PMMA nanoparticles were synthesized by the modified-suspension-polymerization method. Then γ-Fe₂O₃/PMMA/S-TiO₂ core-shell nanocomposites were prepared by adding as-synthesized γ-Fe₂O₃/PMMA nanoparticles into the sol solution formed by sol-gel method using tetrabutyltitanate as Ti source and thiourea as sulfur source. The characterization result of the obtained products by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy indicated that the layer of sulfur doped titania was successfully coated onto the surface of γ-Fe₂O₃/PMMA nanoparticles. Thermogravimetry (TG) analysis presented that the layer of sulfur doped TiO₂ could efficiently reduce the decomposition of polymethylmethacrylate (PMMA) even at higher temperature up to 500 °C. UV–vis diffuse reflectance spectroscopy showed that γ-Fe₂O₃/PMMA/S-TiO₂ nanocomposite clearly exhibits the red-shift of the absorption edge compared with γ-Fe₂O₃/PMMA/TiO_2. The photocatalytic activity evaluation showed that the γ-Fe₂O₃/PMMA/S-TiO₂ nanocomposite exhibited the best photocatalytic activity for degradation of phenanthrene under the conditions of 0.8 mol% of sulfur doping, calcination temperature at 300 °C and the addition concentration of 1.0 g/L. Moreover, the nanocomposites have good recovery ability by the recovery experiment.     

Carbon and silica interlayer influence for the photocatalytic performances of spindle-like α-Fe2O3/Bi2O3 p–n heterostructures

The p–n heterojunction is an effective structure to suppress the recombination of photogenerated charge carriers due to the built-in internal electric field. Herein, we successfully synthesize a spindle-like α-Fe₂O₃/Bi₂O₃ core–shell heterostructure, in which α-Fe₂O₃ is an n-type semiconductor and Bi₂O₃ is a p-type semiconductor. In comparison with pure α-Fe₂O₃ seeds, the α-Fe₂O₃/Bi₂O₃ p–n heterojunction photocatalyst exhibits tremendous photocatalytic performance on the degradation of Rhodamine B (RhB) under illumination of visible light. In addition, we insert an interlayer between p–n heterostructure, similar to p–i–n heterostructure. The silicon oxide and carbon are selected as the interlayer due to its different conductivity. The as-obtained α-Fe₂O₃/C/Bi₂O₃ exhibits higher degradation rate than α-Fe₂O₃/SiO₂/Bi₂O₃. The reason is attributed to the mesoporous structure of carbon layer and its high conductivity so that the photogenerated electrons can be easily transferred from the conduction band of α-Fe₂O₃ to the conduction band of Bi₂O₃ thereby promoting an effective separation of photogenerated electrons and holes. However, the introduction of interlayer reduces the photocatalytic activity due to the alteration of internal built-in electric field in the heterojunction. We envision that these results have potential applications for designing the heterostructural photocatalysts.     

Enhanced photocatalytic decolorization of methyl orange by gallium-doped α-Fe2O3

Gallium (Ga)-doped hematite (α-Fe₂O₃) with different molar ratios of Ga/Fe (1%, 2%, 3% and 4%) was prepared by a facile parallel flow co-precipitation method. The photocatalysts prepared were characterized by the Brunauer–Emmett–Teller method, X-ray diffraction, UV/vis diffuse reflectance spectroscopy, and scanning electron microscope. The photo-generated charges separation efficiency of different photocatalysts was investigated using benzoquinone as scavenger. The formation rate of OH radicals produced during the photocatalytic reaction process was studied by a terephthalic acid photoluminescence probing technique. Doping Ga³⁺ into α-Fe₂O₃ increases the specific surface area and the separation efficiency of photo-induced charges. The catalytic activity of the photocatalysts for decolorization of methyl orange aqueous solution was investigated. The results show that α-Fe₂O₃ doped with 3% Ga possesses the best photocatalytic activity. The underlying mechanism is suggested.     

钇掺杂纳米α-Fe2O3的合成及气敏性能研究

采用柠檬酸sol-gel法制备了不同掺杂量的Y2O3-Fe2O3(w(Y2O3)=0~7%)纳米粉体材料,并用X射线衍射仪、透射电镜等测试手段分析了材料的微观结构,并进行了气敏性能测试。研究发现:掺杂适量Y2O3可抑制α-Fe2O3晶粒的生长,提高粉体材料的气敏性能,其中掺杂量为5%的烧结型气敏元件在160℃的较低温度条件下,对汽油有较高的灵敏度,较好的选择性及响应–恢复特性,且线性检测范围较宽。     

Ni掺杂α-Fe2O3纳米材料的制备及气敏性能研究

采用水热法合成了Ni掺杂α-Fe2O3纳米材料,通过XRD、TEM等手段对产物的物相、形貌等进行了表征,并探讨了材料的气敏性能。结果表明:工作温度为300℃时,元件对50×10–6的H2S气体的灵敏度可达122.8,H2S气体对其他几种被测气体的选择性系数均在9以上,响应恢复时间分别为5s和14s。最后提出了Ni掺杂对α-Fe2O3气敏元件性能影响的机理。     

AC conductivity of nanoparticles CoxFe(1−x)Fe2O4 (x=0, 0.25 and 1) ferrites

Nanoparticles of Co_xFe_(1−x)Fe₂O₄ (x=0, 0.25 and 1) were prepared by the chemical co-precipitation method. X-ray diffraction and scanning electron microscopy were used to determine the average particle size and morphology of the prepared samples. AC conductivity is found to vary as ω^s in the frequency range 42–5×10⁶ Hz. The impedance analysis reveals that low conductivity and high impedance values are observed at low temperatures. The Nyquist impedance plots of the present investigation clearly depict the inherent phenomenon involved in the conduction mechanism of Co doped Fe₃O₄ ferrites. Regarding frequency dependence of Co_xFe_(1−x)Fe₂O₄ AC conductivity the observed behavior clearly indicates that the present ferrites are semiconductor-like.     

Dzyaloshinskii-Moriya Torque-Driven Resonance in Antiferromagnetic α-Fe2O3

The high-frequency optical mode of α-Fe₂O₃ is examined, and it is reported that Dzyaloshinskii−Moriya (DM) interaction generates a new type of torque on the magnetic resonance. Using a continuous-wave terahertz interferometer, the optical mode spectra is measured, where the asymmetric absorption with a large amplitude and broad linewidth is observed near the magnetic transition point, Morin temperature (T_M ≈ 254.3 K). Based on the spin wave model, the spectral anomaly is attributed to the DM interaction-induced torque, enabling to extract the strength of DM interaction field of 4 T. This work opens a new avenue to characterize the spin resonance behaviors at an antiferromagnetic singular point for next-generation and high-frequency spin-based information technologies.