Mechanistic investigation of chemical looping combustion of coal with Fe2O3 oxygen carrier

The reaction of three Chinese coals with Fe₂O₃ oxygen carrier (OC) was performed in a thermogravimetric analyzer (TGA), with special focuses on the effects of varying heating rate and coal rank on reactivity. Fourier transform infrared spectroscopy (FTIR) was used to in situ detect the emitted gases from TGA. Field scanning electron microscopy/energy-dispersive X-ray spectrometry (FSEM-EDX) was used to study the morphology and elemental compositions of the reaction residues collected from TGA and the related phase evaluation was further identified by X-ray diffraction (XRD). Through all these experiments, it was found that the pyrolysis of coal samples without Fe₂O₃ OC under N₂ atmosphere underwent the dehydration and the ensuing primary and secondary pyrolysis stages. The increasing heating rate shifted the characteristic temperature (T_m) of the primary pyrolysis to a higher temperature and favored a more rapid generation of volatile matters. When the three coals reacting with Fe₂O₃ OC, TGA results demonstrated even over 200 °C, the reaction still experienced the partial pyrolysis at the relatively low temperature and the ensuing two reactions of Fe₂O₃ with the pyrolysis products at the primary and secondary stages. The coal of low rank with high volatile content should be preferred for the full conversion of coal into CO₂. Furthermore, the activation energy of Fe₂O₃ OC reacting with PDS at its primary pyrolysis stage was the largest, more than 70 kJ/mol. Finally, SEM-EDX and further XRD analysis of the residues from the reaction of PDS with Fe₂O₃ OC indicated the reduced counterpart of Fe₂O₃ was Fe₃O₄, and some inert iron compounds such as Fe₂SiO₄ and FeAl₂O₄ were also generated, which might deteriorate the reactivity of Fe₂O₃ OC.     

聚乙二醇/聚乙烯吡咯烷酮修饰的纳米Fe3O4粒子的制备与表征

为了获得能够在水中稳定分散,具有广泛应用前景的磁性纳米粒子,以不同分子量的聚乙烯吡咯烷酮(PVP)作为修饰剂,在聚乙二醇(PEG)中高温热分解乙酰丙酮铁(Fe(acac)₃)制备了纳米Fe₃O₄粒子。采用X射线粉末衍射仪(XRD)、透射电镜(TEM)、高分辨透射电镜(HRTEM)、超导量子干涉仪(SQUID)、热重分析仪(TGA)、傅里叶变换红外光谱仪(FT-IR)、纳米粒度与zeta电位分析仪对样品进行了表征,并对样品在生理盐水和生理缓冲液中的稳定性进行了研究,结果表明:制备的纳米Fe₃O₄粒子具有高的结晶度以及单分散性,在300 K下,具有超顺磁性和较高的饱和磁化强度;PEG和PVP共同修饰于纳米Fe₃O₄粒子表面,为纳米Fe₃O₄粒子提供了良好的水分散性;制备的纳米Fe₃O₄粒子在生理盐水和多种生理缓冲液中能够高度溶解并稳定地分散。水中的纳米Fe₃O₄粒子表面呈电中性,表面修饰层的空间位阻效应是所制备的纳米粒子在水溶液中高分散的原因。     

A novel method for the synthesis of Fe3O4 nanoparticles/CdS nanowires heterostructure nanocomposite and uses in photodegradation of methylene blue

We report here a simple, efficient, practical, and novel method for the preparation of Fe₃O₄ nanoparticles (NPs)/CdS nanowires. The CdS nanowire/Fe₃O₄ NP reported here was characterized by transmission electron microscopy (TEM), X-ray Diffraction (XRD), vibrating sample magnetometer (VSM), and energy-dispersive X-ray. Cadmium diethyl dithiophosphate has been used as a 3 in 1 precursor (cadmium, sulfur, and ligand source) for the synthesis of high-quality one-dimensional Fe₃O₄ NPs/CdS nanowires using a simple hydrothermal method in the presence of Fe₃O₄ NPs in water. Photocatalytic activity studies show that the nanocomposite has good photocatalytic activity toward the photodegradation of methylene blue in an aqueous solution.     

Electro-Magnetic Polyfuran/Fe3O4 Nanocomposite: Synthesis,Characterization, Antioxidant Activity,and Its Application as a Biosensor

Herein, the authors report the synthesis of electro-magnetic polyfuran/Fe₃O₄ nanocomposites using Fe₃O₄ magnetic nanoparticles of different content as nucleation sites via in situ chemical oxidation polymerization method. Surface, structural, morphological, thermal, electrical and magnetic properties of the nanocomposites were studied by FT-IR, UV-visible spectroscopies, XRD, FESEM, TGA, four probe, and VSM, respectively. The effect of Fe₃O₄ nanoparticles content on the electrical conductivity and magnetization of nanocomposites was studied. The obtained polyfuran and polyfuran/Fe₃O₄ nanocomposites were analyzed for their antioxidant activity using 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay. In addition, polyfuran/Fe₃O₄ nanocomposites have been investigated for application as electrochemical biosensor.     

Multifuctional Fe3O4@C/YVO4:Dy nanopowers: Preparation,luminescence and magnetic properties

As-synthesized Fe₃O₄ nanoparticles were encapsulated with carbon layers through a simple hydrothermal process. Fe₃O₄/C nanoparticles were coated with YVO₄:Dy³⁺ phosphors to form bifunctional Fe₃O₄@C@YVO₄:Dy³⁺ composites. Their structure, luminescence and magnetic properties were characterized by XRD, SEM, TEM, HRTEM, PL spectra and VSM. The experimental results indicated that the as-prepared bifunctional composites displayed well-defined core–shell structures. The ∼12 nm diameter YVO₄:Dy³⁺ shell exhibited tetragonal structure. Additionally, the composites exhibited a high saturation magnetization (13 emu/g) and excellent luminescence properties, indicating their promising potential as multifunctional biosensors for biomedical applications.     

Reduction and oxidation properties of Fe2O3/ZrO2 oxygen carrier for hydrogen production

Fe₂O₃ is a promising oxygen carrier for hydrogen production in the chemical-looping process. A set of kinetic studies on reduction with CH₄, CO and H₂ respectively, oxidation with water and oxygen containing Ar for chemical-looping hydrogen production was conducted. Fe₂O₃ (20 wt.%)/ZrO₂ was prepared by a co-precipitation method. The main variables in the TGA (thermogravimetric analyzer) experiment were temperatures and gas concentrations. The reaction kinetics parameters were estimated based on the experimental data. In the reduction by CH₄, CO and H₂, the reaction rate changed near FeO. Changes in the reaction rate due to phase transformation were observed at low temperature and low gas concentration during the reduction by CH₄, but the phenomenon was not remarkable for the reduction by CO and H₂. The reduction rate achieved using CO and H₂ was relatively faster than achieved using CH₄. The Hancock and Sharp method of comparing the kinetics of isothermal solid-state reactions was applied. A phase boundary controlled model (contacting sphere) was applied to the reduction of Fe₂O₃ to FeO by CH₄, and a different phase boundary controlled model (contacting infinite slab) was fit well to the reduction of FeO to Fe by CH₄. The reduction of Fe₂O₃ to Fe by CO and H₂ can be described by the former phase boundary controlled model (contacting sphere). This phase boundary controlled model (contacting sphere) also fit well for the oxidation of Fe to Fe₃O₄ by water and FeO to Fe₂O₃ by oxygen containing Ar. These kinetics data could be used to design chemical-looping hydrogen production systems.     

Synthesis and characterization of novel conducting composites of Fe3O4 nanoparticles and sulfonated polyanilines

Surface charged iron oxide (Fe₃O₄) nanoparticles were used for the synthesis of sulfonated polyaniline (SPAN)‐Fe₃O₄ nanocomposites (SPAN/Fe₃O₄‐NCs). 2,5‐diaminobenzenesulfonic acid (DABSA) and 2‐aminobenzenesulfonic acid (ABSA) were independently polymerized with aniline to form SPAN. The structure of the composites was characterized by means of transmission electron microscopy (TEM), X‐ray diffraction (XRD), thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) spectra, conductivity and magnetic properties. TEM reveals that Fe₃O₄ nanoparticles are “glued” with SPAN in the composite. TGA indicates that SPAN/Fe₃O₄‐NCs are having better thermal stability. The room temperature conductivity of SPAN/Fe₃O₄‐NCs is higher than that of pristine PANI and SPAN. SPAN/Fe₃O₄‐NCs exhibits magnetic behavior. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 4127–4134, 2007     

磁性Fe3O4纳米粒子用作靶向药物载体的制备及分析

Fe3O4 magnetic nanoparticles were prepared by the aqueous co-precipitation of FeCl3-6H2O and FeCl2-4H2O with addition of ammonium hydroxide. The conditions for the preparation of Fe3O4 magnetic nanoparticles were optimized, and Fe3O4 magnetic nanoparticles obtained were characterized systematically by means of transmission electron microscope （TEM）, dynamic laser scattering analyzer （DLS） and X-ray diffraction （XRD）. The results revealed that the magnetic nanoparticles were cubic shaped and dispersive, with narrow size distribution and average diameter of 11.4 nm. It was found that the homogeneous variation of pH value in the solution via the control on the dropping rate of aqueous ammonia played a critical role in size distribution. The magnetic response of the product in the magnetic field was also analyzed and evaluated carefully. A 32.6 mT magnetic field which is produced by four ferromagnets was found to be sufficient to excite the dipole moments of 0.05 g Fe3O4 powder 2 cm far away from the ferromagnets. In conclusion, the Fe3O4 magnetic nanoparticles with excellent properties were competent for the magnetic carders of targeted-drug in future application.     

Preparation and property characterization of PAA/Fe3O4 nanocomposite

PAA/Fe₃O₄ nanocomposites were prepared by mixing nano-Fe₃O₄ and polyacrylic acid (PAA) ethanol solution and then evaporating the solvent. The materials were characterized by transmission electron microscope (TEM), Fourier transform infrared spectroscope (FTIR), thermogravimetry analysis (TGA), dynamic ultra-micro hardness tester (DUMHT) and superconducting quantum interference device (SQUID) magnetometer. Results showed that PAA coordinated with nano-Fe₃O₄ to form a cross-linking structure. The presence of nano-Fe₃O₄ enhanced the thermal stability of the nanocomposite. The elasticity and hardness of the nanocomposite increased, and the indentation depth reduced with the increase of Fe₃O₄ content in the composites. The nanocomposites showed superparamagnetic properties at 300 K. Translated from Acta Scientiarum Naturalium Universitatis Sunyatseni, 2006, 45(5): 47–50 [译自: 中山大学学报 (自然科学版)]     

Electrochemical biosensors utilizing the electron transfer of hemoglobin immobilized on cobalt-substituted ferrite nanoparticles–chitosan film

Cobalt ferrite nanoparticles (Co_xFe_3−xO₄) and chitosan (CS) film were used to immobilize/adsorb hemoglobin (Hb) to create a protein electrode to study the direct electron transfer between the redox centers of the proteins and the electrode. X-ray diffraction (XRD) and transmission electron microscopy (TEM) revealed that the Co_xFe_3−xO₄ particles were nanoscale in size and formed an ordered layered structure. The native structure of the immobilized Hb was preserved as indicated by Fourier-transform infrared (FTIR) and UV–visible (UV–vis) spectroscopy. The Hb-Co_xFe_3−xO₄–CS modified electrode showed a pair of well-defined and quasi-reversible cyclic voltammetric peaks at −0.373 V (vs. SCE) and exhibited appreciable electrocatalytic activity for the reduction of H₂O₂. The catalysis currents increased linearly with H₂O₂ concentration in a wide range of 5.0 × 10⁻⁸ to 1.0 × 10⁻³ mol L⁻¹ with a detection limit of 1.0 × 10⁻⁸ mol L⁻¹ (S/N = 3) and had long-term stability. Finally, the proposed method was applied to investigate the coexistence of hydrogen peroxide with the interfering substances. Experimental results showed that the ascorbic acid, glucose, l-cysteine, uric acid, and dopamine at corresponding concentrations did not influence the detection of H₂O₂.     

Facile Synthesis of FeCo/Fe3O4 Nanocomposite with High Wave-Absorbing Properties

The FeCo/Fe₃O₄ nanocomposite was synthesized using the hydrothermal approach, in which the FeCo alloy and Fe₃O₄ are formed by one step. The structure of the FeCo/Fe₃O₄ nanocomposite was characterized by means of Scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray energy-dispersive spectrometer spectroscopy (EDX). They show that the mass ratio of FeCo/Fe₃O₄ strongly depends on the reaction temperature. Such various architectures follow a stepwise growth mechanism of the composites prepared in various reaction temperatures were also discussed. It indicates that this strategy is facile, effective and controllable for the synthesis of FeCo/Fe₃O₄ by the one-step method. Furthermore, the magnetic and wave-absorbing properties of the nanocomposites with various structures were investigated in detail. The results show that the FeCo/Fe₃O₄ with higher mass ratio has higher magnetic properties. Moreover, the FeCo/Fe₃O₄ nanocomposite shows high wave-absorbing properties (e.g., −37.9 dB), which are expected to apply in microwave absorbing materials.     

Magnetic and sterilizing properties of Ag(II)O–Fe3O4 hybrids synthesized via mechano-chemistry

Ag(II)O–Fe₃O₄ hybrids with good magnetic and bactericidal activity were synthesized via mechano-chemistry. The resulted products were characterized by transmission electronic microscope, X-ray diffraction, X-ray photoelectron and Fourier transform infrared spectroscopy, atomic absorption spectrophotometer, vibrating sample magnetometry and the shake-flask method. The results indicated that magnetite nanoparticles were effectively grafted onto the surface of Ag(II)O submicron particles. The functionalized particles remained dispersed and superparamagnetic. The saturation magnetization increased with the amount of magnetite in the hybrids. Element Ag was released from Ag(II)O–Fe₃O₄ hybrids with a slow dissolution speed. Ag(II)O–Fe₃O₄ hybrids had strong antibacterial properties. When the concentrations of the two hybrids with the mass ratio of Ag(II)O to Fe₃O₄ of 1:2 and 2:1 were 10 mg/L, more than 99.9% of the Staphylococcus aureus or Escherichia coli bacteria were killed.     

Fe3O4@SiO2-SnCl4: An Efficient Catalyst for the Synthesis of Xanthene Derivatives under Ultrasonic Irradiation

Grafting of SnCl₄ on the Fe₃O₄@SiO₂ nanoparticles afforded Fe₃O₄@SiO₂-SnCl₄ as a novel inorganic heterogenous catalyst, which was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), vibrating sample magnetometry (VSM), Field Emission Scanning Electron Microscopy (FE-SEM), and transmission electron microscopy (TEM). In this research, we report a convenient and efficient direct protocol for the preparation of xanthene derivatives via condensation of β-naphthol, dimedone, or mixture of β-naphthol and dimedone with various aromatic aldehydes in the presence of the catalytic amount of Fe₃O₄@SiO₂-SnCl₄ under ultrasonic irradiation. This procedure has a lot of advantages such as: very easy reaction conditions, absence of any tedious workup, or purification, and much milder method. The corresponding products have been obtained in excellent yields, high purity, and short reaction times.     

Magnetoelectricity in CoFe2O4 nanocrystal-P(VDF-HFP) thin films

Transition metal ferrites such as CoFe₂O₄, possessing a large magnetostriction coefficient and high Curie temperature (T_c > 600 K), are excellent candidates for creating magnetic order at the nanoscale and provide a pathway to the fabrication of uniform particle-matrix films with optimized potential for magnetoelectric coupling. Here, a series of 0–3 type nanocomposite thin films composed of ferrimagnetic cobalt ferrite nanocrystals (8 to 18 nm) and a ferroelectric/piezoelectric polymer poly(vinylidene fluoride-co-hexafluoropropene), P(VDF-HFP), were prepared by multiple spin coating and cast coating over a thickness range of 200 nm to 1.6 μm. We describe the synthesis and structural characterization of the nanocrystals and composite films by XRD, TEM, HRTEM, STEM, and SEM, as well as dielectric and magnetic properties, in order to identify evidence of cooperative interactions between the two phases. The CoFe₂O₄ polymer nanocomposite thin films exhibit composition-dependent effective permittivity, loss tangent, and specific saturation magnetization (M_s). An enhancement of the effective permittivity and saturation magnetization of the CoFe₂O₄-P(VDF-HFP) films was observed and directly compared with CoFe₂O₄-polyvinylpyrrolidone, a non-ferroelectric polymer-based nanocomposite prepared by the same method. The comparison provided evidence for the observation of a magnetoelectric effect in the case of CoFe₂O₄-P(VDF-HFP), attributed to a magnetostrictive/piezoelectric interaction. An enhancement of M_s up to +20.7% was observed at room temperature in the case of the 10 wt.% CoFe₂O₄-P(VDF-HFP) sample.     

Fabrication of PLA/MWCNT/Fe3O4 composite nanofibers for leukemia cancer cells

The efficient delivery of daunorubicin loaded poly (lactic acid) (PLA)/multiwalled carbon nanotubes (MWCNT)/Fe₃O₄ composite nanofibers was investigated. The synthesized nanofibers were characterized using SEM, TEM, and XRD analysis. The proliferation inhibition effect of PLA/MWCNT/Fe₃O₄ nanofibrous scaffolds on leukemia K562 cell lines was investigated. The effect of nanofiber concentration on the daunorubicin delivery in the absence and presence of external magnetic field was also evaluated. The results indicated that the incorporation of daunorubicin into the prepared nanofibrous scaffold under applied magnetic field could have synergistic cytotoxic effect on leukemia cancer cells. The drug release mechanism followed the non-Fickian transport.     

Studies on electrical properties of La0.8Sr0.2Ga0.8Mg0.2O2.80 (LSGM) and LSGM-SrSn1−xFexO3 (x = 0.8; 0.9) composites and their chemical reactivity

We report the electrical conductivity properties of solid-state synthesized perovskite-like La_0.8Sr_0.2Ga_0.8Mg_0.2O_2.80 (LSGM) and LSGM-SrSn_1−xFe_xO₃ (x = 0.8; 0.9) composites. LSGM exhibits both bulk and grain-boundary contribution in the ac impedance plots. The grain-boundary conductivity (σ_gb) is slightly (≤half-order of magnitude) higher than that of the bulk oxide ion conductivity (σ_bulk). Powder XRD study reveals that no chemical reaction occurs between LSGM and SrSn_1−xFe_xO₃ (1:1 wt.%) at 1000 °C (48 h) and forms a single-phase perovskite-like compound at 1300 °C (48 h) in air, while in hydrogen atmosphere, at 800 °C for 48 h, a growth of LaSrGaO₄ and LaSrGa₃O₇ impurity phases and formation of metallic Fe was observed. The LSGM-SrSn_1−xFe_xO₃ (x = 0.8; 0.9) composites show a single or part of semicircle in air at low-temperature regime. The electrical conductivity of the composites were found to be much higher compared to pure LSGM and lower about an order of magnitude than those of pure Sn-doped SrFeO₃ perovskite.     

Mn2O3/TiO2 nanofibers with broad-spectrum antibiotics effect and photocatalytic activity for preliminary stage of water desalination

Composite nanofibers consisting of Mn₂O₃ and TiO₂ were prepared by the electrospinning process, and tested as Gram-class-independent antibacterial agent and photocatalyst for organic pollutants degradation. Initially, electrospinning of a sol–gel consisting of titanium isopropoxide, manganese acetate tetrahydrate and poly(vinyl pyrrolidone) was used to produce hybrid polymeric nanofibers. Calcination of the obtained nanofibers in air at 650 °C led to produce good morphology Mn₂O₃/TiO₂ nanofibers. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were employed to characterize the as-spun nanofibers and the calcined product. X-ray powder diffractometry (XRD) analysis was also used to characterize the chemical composition and the crystallographic structure of the sintered nanofibers. The antibacterial activity of Mn₂O₃/TiO₂ nanofibers against Gram negative and Gram positive bacteria was investigated by calculating the minimum inhibitory concentration after treatment with the nanofibers. Investigations revealed that the lowest concentration of Mn₂O₃/TiO₂ nanofibers solution inhibiting the growth of Staphylococcus aureus ATCC 29231 and Escherichia coli ATCC 52922 strains is 0.4 and 0.8 μg/ml, respectively. Incorporation of Mn₂O₃ significantly improved the photodegradation of methylene blue (MB) dye under the visible light irradiation due to enhancing rutile phase formation in the TiO₂ nanofibers matrix.     

Enhanced cycling performance of Fe3O4-graphene nanocomposite as an anode material for lithium-ion batteries

Fe₃O₄-graphene nanocomposite was prepared by a gas/liquid interface reaction. The structure and morphology of the Fe₃O₄-graphene nanocomposite were characterized by X-ray diffraction, scanning electron microscopy and high-resolution transmission electron microscopy. The electrochemical performances were evaluated in coin-type cells. Electrochemical tests show that the Fe₃O₄-22.7 wt.% graphene nanocomposite exhibits much higher capacity retention with a large reversible specific capacity of 1048 mAh g⁻¹ (99% of the initial reversible specific capacity) at the 90th cycle in comparison with that of the bare Fe₃O₄ nanoparticles (only 226 mAh g⁻¹ at the 34th cycle). The enhanced cycling performance can be attributed to the facts that the graphene sheets distributed between the Fe₃O₄ nanoparticles can prevent the aggregation of the Fe₃O₄ nanoparticles, and the Fe₃O₄-graphene nanocomposite can provide buffering spaces against the volume changes of Fe₃O₄ nanoparticles during electrochemical cycling.     

Effect of TiO2 supporting layer on Fe2O3 photoanode for efficient water splitting

For an electrochemical water splitting system, titanate nanotubular particles with a thickness of ∼700 nm produced by a hydrothermal process were repetitively coated on fluorine-doped tin oxide (FTO) glass via layer-by-layer self-assembly method. The obtained titanate/FTO films were dipped in aqueous Fe solution, followed by heat treatment for crystallization at 500 °C for 10 min in air. The UV–vis absorbance of the Fe-oxide/titanate/FTO film showed a red-shifted spectrum compared with the TiO₂/FTO coated film; this red shift was achieved by the formation of thin hematite-Fe₂O₃ and anatase-TiO₂ phases verified using X-ray diffraction and Raman results. The cyclic voltammetry results of the Fe₂O₃/TiO₂/FTO films showed distinct reversible cycle characteristics with large oxidation–reduction peaks with low onset voltage of I–V characteristics under UV–vis light illumination. The prepared Fe₂O₃/TiO₂/FTO film showed much higher photocurrent densities for more efficient water splitting under UV–vis light illumination than did the Fe₂O₃/FTO film. Its maximum photocurrent was almost 3.5 times higher than that obtained with Fe₂O₃/FTO film because of the easy electron collection in the current collector. The large current collection was due to the existence of a TiO₂ base layer beneath the Fe₂O₃ layer.     

Metal oxides nanoparticles on SBA-15: Efficient catalyst for methane combustion

Catalysts based on crystalline nanoparticles of Mn and Co metal oxides supported on mesoporous silica SBA-15 have been developed. These materials were characterized by XRD, BET and transmission electron microscopy (TEM) techniques. SBA-15 mesoporous silica was synthesized by a conventional sol–gel method using a tri-block copolymer as surfactant. Supported Mn₃O₄ and Co₃O₄ nanoparticles were obtained after calcination of as-impregnated SBA-15 by a metal salt precursor. The catalytic activity was evaluated in the combustion of methane at low concentration.Co₃O₄/SBA-15 (7 wt.%) exhibits the highest performance among the different oxides. Furthermore, this novel generation of catalysts appeared as active as conventional LaCoO₃ perovskite, usually taken as reference for this reaction. Thanks to its organized meso-structures, SBA-15 material creates peculiar diffusion conditions for reactants and/or products.