Electrochemical study of the corrosion behaviour of carbon steel in fracturing fluid

Corrosion behaviour of carbon steel (K-55) in fracturing fluid was studied with a rotation cylinder electrode, under static and rotation conditions by means of several electrochemical techniques which are as follows: open circuit potential (OCP) decay, potentiodynamic polarisation and electrochemical impedance spectroscopy (EIS). The corrosion rate was determined by weight loss measurements. The electrode surface after a prefixed immersion time was characterised by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results indicated that carbon steel showed anodic dissolution behaviour that increased under rotating condition. The cathodic polarisation current density also increased with the electrode rotation due to the increased oxygen diffusion on the electrode surface. Two different oxide layers were formed: a dark, thin layer of magnetite tightly adhering to the electrode surface, characterised by localised corrosion spots, and a porous reddish layer of poorly adhering hematite (Fe₂O₃) and maghemite (γ-Fe₂O₃). Under higher rotation rate, the developed oxide layer was not so stable, owing to the shear stress induced between the solution and the specimen surface, enhancing the corrosion rate.     

Electrochemical Monitoring of Methotrexate Anticancer Drug in Human Blood Serum by Using in situ Solvothermal Synthesized Fe3O4/ITO Electrode

Here, we reported on a one‐step fabrication of magnetite Fe₃O₄ nanoparticles/indium tin oxide (ITO) electrode based on the direct growing of Fe₃O₄ nanoparticles on the ITO surface by using a solvothermal process. The modified electrode was used as electrochemical methotrexate (MTX) biosensor with high sensitivity based on cyclic voltammetry and square wave voltammetry techniques. The results demonstrated a linear relationship between the MTX concentration and its oxidation current peak over a wide range from 10^?5 to 10^?14 mole/L with a limit of detection of 0.4×10^?15 M based on the square wave voltammetry (SWV) technique. In addition, Fe₃O₄/ITO electrode showed a good capability for measuring very low concentrations of MTX drug dissolved in human serum solution. Also, Fe₃O₄/ITO electrode was used for detecting MTX in blood serum samples collected from patients after their treatment with MTX. The prepared electrode showed the higher sensitivity that higher than the Viva‐E instrument, which opens the door for developing a cheap, simple and higher sensitive MTX sensor.     

Electrochemical synthesis of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanoparticles in alkaline aqueous solutions containing complexing agents

Ultrafine magnetite particles are prepared through an electrochemical process, at room temperature, from an iron-based electrode immersed in an alkaline aqueous medium containing complexing compounds. XRD and chemical analysis indicate that the product is pure magnetite, Fe₃O₄. The size and morphology of the particles are studied by SEM. The magnetite nanoparticles present a magnetoresistance of almost 3%, at 300 K, under a magnetic field of 1 T. A reactive mechanism for the electrochemical process is proposed.     

New insights into the magnetic properties of the Ca2Fe2O5 ferrite

Ca₂Fe₂O₅ powder samples, undoped and doped with Na⁺, Mg²⁺, Al³⁺, Ti⁴⁺, Ge⁴⁺, were prepared with different synthesis routes to investigate the origin of the weak ferromagnetic component reported in literature for calcium ferrite single crystals. XRPD and EPR measurements have shown the presence of Fe₃O₄ magnetite as impurity phase in all the samples. This ferrimagnetic phase deeply influences the magnetic behavior with features very similar to those reported in literature for Ca₂Fe₂O₅, both powders and single crystals. Our results support the hypothesis that the weak ferromagnetic component observed in Ca₂Fe₂O₅ can be also due to the presence of magnetite impurity traces in the samples.     

Structure and electrochemical properties of magnetite and polypyrrole nanocomposites formed by pyrrole oxidation with magnetite nanoparticles

Nanocomposite of magnetic Fe₃O₄ nanoparticles and polypyrrole was prepared under sonication by a new chemical polymerization method during which Fe₃O₄ nanoparticles acted both as a pyrrole oxidant and as a component in the composite material. Synthesis of this nanocomposite was carried out in aqueous solution acidified to pH 2, a prerequisite for the formation of these types of material and to facilitate pyrrole oxidation by Fe₃O₄ nanoparticles. In this way, two kind of materials were produced: Fe₃O₄/PPy nanocomposite in which magnetite nanoparticles were dispersed in PPy matrix and Fe₃O₄-aggregates@PPy nanocomposite that exhibits structure in which aggregates of magnetite nanoparticles are surrounded by a layer of polymeric phase. In the latter case, the polymerization process took place in the presence of a surfactant. These nanocomposites were characterized by electron microscopy techniques, IR spectroscopy, X-ray powder diffraction, X-ray photoelectron spectroscopy and thermogravimetry. Particular attention was focused on the study of the electrochemical properties of the formed composites. The composite of Fe₃O₄ and PPy exhibits reversible electrochemical behaviour upon oxidation. The electrode process of the polymeric component oxidation in organic solvents such as acetonitrile and dichloromethane is very similar to the process in an aqueous solution.

     

Determination of Staphylococcus aureus B-1266 by an Enzyme-Free Electrochemical Immunosensor Incorporating Magnetite Nanoparticles

A simple and inexpensive immunosensor is reported for the rapid determination of Staphylococcus aureus B-1266 that uses Fe₃O₄–SiO₂–NH₂ nanoparticles as the direct signal label. The electrochemical immunoassay procedure includes the incubation of bacteria with excess magnetite nanoparticles, the magnetic separation of the free nanoparticles, a labeled immunocomplex formation on the surface of a planar electrode, and the electrochemical response from the magnetite nanoparticles in the immunocomplex. The electrochemical immunosensor allows for the selective and accurate detection of S. aureus from 10 to 105?CFU?mL^?1 with a relative standard deviation lower than 10%. The limit of detection was 8.7?CFU?mL^?1.     

Hydrogen peroxide sensor based on a stainless steel electrode coated with multi-walled carbon nanotubes modified with magnetite nanoparticles

Multi-walled carbon nanotubes (MWCNTs) were decorated with magnetite (Fe₃O₄) nanoparticles and then used to modify a stainless steel electrode. The Fe₃O₄/MWCNTs composite was characterized by scanning electron microscopy, transmission electron microscopy, Raman spectroscopy and X-ray diffraction patterns. Electrochemical properties of the modified electrode revealed a substantial catalytic activity for the reduction of hydrogen peroxide. The relationship between peak current and the concentration of hydrogen peroxide was linear in the range from 0.06?mmol?L^?1 to 0.36?mmol?L^?1, and the lowest detectable concentration is 0.01?mmol·L^?1 (S/N?=?3). The modified stainless steel electrode displays excellent stability.

Anomalous currents under cyclic polarization of magnetite electrode in acidic medium

An anomalous phenomenon was observed in acidic solutions in cyclic voltammetric curves in the studies of electrochemical behavior of magnetite. It consisted in appearance of the reverse current: a cathodic response under the anodic potential sweep. It was shown that the direct and reverse currents follow the same regularities. Analysis of experimental data allows concluding that both currents correspond to the same process: Fe₃O₄ + 8H⁺ + 2e ?? 3Fe _aq ²⁺ + 4H₂O. Appearance of anomalous currents on polarization curves of magnetite occurs if the following conditions are observed: irreversibility of the given electrochemical reaction under the given mode experimental parameters; incompleteness of reaction at the cathodic halfcycle stage; layer-by-layer dissolution when the electrode surface is continually refreshed.     

The self-assembly, characterization and application of hemoglobin immobilized on Fe3O4@Pt core-shell nanoparticles

Direct electron transfer is demonstrated to occur between an electrode and hemoglobin that was immobilized on a film of Fe₃O₄@Pt-chitosan (Fe₃O₄@Pt-CS). Magnetic nanoparticles composed of Fe₃O₄ were prepared by a chemical coprecipitation method, and platinum nanoparticles were deposited on the Fe₃O₄ surface to form novel core-shell nanocomposites. In phosphate buffer solution of pH 7.0, the hemoglobin-Fe₃O₄@Pt-CS assembly on a modified glassy carbon electrode exhibited a couple of well-defined and quasi-reversible redox peaks. The formal potential E^0′ was about ?0.35 V. The electrode displayed excellent electrocatalytic activity towards oxygen and hydrogen peroxide reduction without the need for an electron mediator.     

Ultrasonic-assisted synthesis of magnetite/carbon nanocomposite for electrochemical supercapacitor

Iron oxides are considered as the promising pseudocapacitive materials for high-performance supercapacitors due to their high theoretical specific capacitance, low cost, environmental benignity, and natural abundance. In this work, we study capacitive behavior of different magnetite (Fe₃O₄) nanoparticles/carbon black (CB) composites ratios. These composites are synthesized by the coprecipitation method in the presence of ultrasonic waves. The structural and morphological characteristics of the magnetite/CB composites are investigated by X-ray diffraction and scanning electron microscopy, respectively. The electrochemical performance of magnetite/CB composite electrodes is tested by cyclic voltammetry and galvanostatic charge/discharge in a Na₂SO₄ electrolyte. The results indicate that the magnetite/CB electrodes show typical pseudo-capacitive behavior in Na₂SO₄ solution. Moreover, in comparison to the pure Fe₃O₄ (37 F g^?1) and carbon black (23 F g^?1), the as-prepared 45 % magnetite/CB nanocomposite electrode shows a higher specific capacitance (300 F g^?1). Additionally, the supercapacitor device of the magnetite/CB nanocomposite exhibits excellent long cycle life along with 98.5 % specific capacitance retained after 10,000 cycle tests.     

Electronic structure of products of interaction between Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> cluster and water and its association with the corrosion behavior of magnetite

Electronic structure of Fe₃O₄ cluster and the products of its interaction with water molecule hydrates H₄O₂ and H₅O₂⁺ and H₃O₂⁻ ions is calculated by the quantum-chemical method DFT B3LYP/6-31G**. The expected behavior of magnetite in the acidic, neutral, and alkaline media is analyzed in the approximation of parameters of their electronic structure (the effective charges, binding and free valences of iron and oxygen atoms). In the interaction between Fe₃O₄ and H₅O₂⁺ (acidic medium), a hydride bond Fe-H forms, and the remainder of magnetite cluster becomes more susceptible to the attack of reagents. By contrast, the interaction of Fe₃O₄ with H₃O₂⁻ (alkaline medium) yields an oxide structure with low chemical activity of both iron and oxygen atoms. The calculated data are in agreement with the experimental data on the corrosion behavior of magnetite.     

磁性壳聚糖/Fe3O4/氧化石墨烯吸附剂的制备及其多染料吸附性能

为了提高壳聚糖的多染料吸附性能并使其便于固液分离,采用共沉淀法制备了壳聚糖、磁铁矿纳米颗粒、氧化石墨烯复合磁性吸附剂(CS/Fe₃O₄/GO)。系统的结构表征显示,CS包覆的Fe₃O₄磁性纳米颗粒均匀地分布在GO的表面。CS/Fe₃O₄/GO具有高达42.5 emu·g-1的室温铁磁性,因此可在外加磁场中实现高效固液分离。研究表明,CS/Fe₃O₄/GO对亚甲基蓝(MB)、甲基橙(MO)和刚果红(CR)等多种染料具有良好的吸附性能,溶液的pH、初始浓度和吸附时间对其多染料吸附性能具有显著影响。在最佳条件下,CS/Fe₃O₄/GO对MB、MO和CR的吸附量分别达到210.6、258.6和308.9 mg·g-1。CS/Fe₃O₄/GO具有优异的循环利用性能,经5次循环后仍能保留90%以上的原始吸附量。采用吸附等温线和吸附动力学对...     

Anisotropic Magnetite Nanorods for Enhanced Magnetic Hyperthermia

There is an increasing need for new strategies to improve the heating efficiency or the specific absorption rate (SAR) of magnetite (Fe₃O₄), which is the only FDA approved magnetic material. We propose a facile approach to obtain well‐dispersed highly crystalline Fe₃O₄ nanorods (NRs) by the reduction of β‐FeOOH in an organic solvent and demonstrate that the SAR of Fe₃O₄ NRs can be enhanced by tuning their aspect ratios. Fe₃O₄ NRs with an aspect ratio of 4.5 have a much higher SAR as compared with 15 nm Fe₃O₄ nanoparticles and Fe₃O₄ NRs counterparts with an aspect ratio of 10. The highest SAR is greatly increased up to 1072 W g^?1 for an ac field of 33 kA m^?1 and a concentration of 5 mg mL^?1, which is mostly attributed to hysteresis losses. These findings pave a new pathway for the design and synthesis of novel anisotropic iron oxide nanostructures with an optimal heating efficiency for advanced hyperthermia.     

Hydrothermal synthesis of reduced graphene sheets/Fe2O3 nanorods composites and their enhanced electrochemical performance for supercapacitors

Reduced graphene nanosheets/Fe₂O₃ nanorods (GNS/Fe₂O₃) composite has been fabricated by a hydrothermal route for supercapacitor electrode materials. The obtained GNS/Fe₂O₃ composite formed a uniform structure with the Fe₂O₃ nanorods grew on the graphene surface and/or filled between the graphene sheets. The electrochemical performances of the GNS/Fe₂O₃ hybrid supercapacitor were tested by cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge–discharge tests in 6 M KOH electrolyte. Comparing with the pure Fe₂O₃ electrode, GNS/Fe₂O₃ composite electrode exhibits an enhanced specific capacitance of 320 F g⁻¹ at 10 mA cm⁻² and an excellent cycle-ability with capacity retention of about 97% after 500 cycles. The simple and cost-effective preparation technique of this composite with good capacitive behavior encourages its potential commercial application.     

Synthesis and characterization of micron‐sized monodisperse superparamagnetic polymer particles with amino groups

Micron‐sized monodisperse superparamagnetic polyglycidyl methacrylate (PGMA) particles with functional amino groups were prepared by a process involving: (1) preparation of parent monodisperse PGMA particles by the dispersion polymerization method, (2) chemical modification of the PGMA particles with ethylenediamine (EDA) to yield amino groups, and (3) impregnation of iron ions (Fe²⁺ and Fe³⁺) inside the particles and subsequently precipitating them with ammonium hydroxide to form magnetite (Fe₃O₄) nanoparticles within the polymer particles. The resultant magnetic PGMA particles with amino groups were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), X‐ray diffractometry (XRD), and vibrating sample magnetometry (VSM). SEM showed that the magnetic particles had an average size of 2.6 μm and were highly monodisperse. TEM demonstrated that the magnetite nanoparticles distributed evenly within the polymer particles. The existence of amino groups in the magnetic polymer particles was confirmed by FTIR. XRD indicated that the magnetic nanoparticles within the polymer were pure Fe₃O₄ with a spinel structure. VSM results showed that the magnetic polymer particles were superparamagnetic, and saturation magnetization was found to be 16.3 emu/g. The Fe₃O₄ content of the magnetic particles was 24.3% based on total weight. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3433–3439, 2005     

磁性壳聚糖/Fe3O4/氧化石墨烯吸附剂的制备及其多染料吸附性能

为了提高壳聚糖的多染料吸附性能并使其便于固液分离,采用共沉淀法制备了壳聚糖、磁铁矿纳米颗粒、氧化石墨烯复合磁性吸附剂(CS/Fe₃O₄/GO)。系统的结构表征显示,CS包覆的Fe₃O₄磁性纳米颗粒均匀地分布在GO的表面。CS/Fe₃O₄/GO具有高达42.5 emu·g^-1的室温铁磁性,因此可在外加磁场中实现高效固液分离。研究表明,CS/Fe₃O₄/GO对亚甲基蓝(MB)、甲基橙(MO)和刚果红(CR)等多种染料具有良好的吸附性能,溶液的pH、初始浓度和吸附时间对其多染料吸附性能具有显著影响。在最佳条件下,CS/Fe₃O₄/GO对MB、MO和CR的吸附量分别达到210.6、258.6和308.9 mg·g^-1。CS/Fe₃O₄/GO具有优异的循环利用性能,经5次循环后仍能保留90%以上的原始吸附量。采用吸附等温线和吸附动力学对CS/Fe₃O₄/GO的多染料吸附性能进行了拟合分析,并详细讨论了其吸附机理。     

The influence of the oxidative dehydrogenation of butene-1 on the phase composition of the nickel ferrite/γ-Al2O3 catalyst

The influence of the oxidative dehydrogenation of butene-1 on the phase composition of a ferrite-containing catalyst on γ-Al₂O₃ with a Ni: Fe atomic ratio of 1: 4 was studied. It was found by X-ray diffraction, EPR, IR absorption spectroscopy, and derivatography that the reduction of Fe³⁺ to Fe²⁺ with the formation of The Fe₃O₄ magnetite phase occurred under various conditions of olefin (reaction mixture)-catalyst surface contact. The treatment of the catalyst with the reaction mixture and its oxidation decrease the degree of spinel phase imperfection.     

Construction of an Amperometric Glucose Biosensor by Immobilization of Glucose Oxidase on Nanocomposite at the Surface of FTO Electrode

Fluorine? tin oxide (FTO) nanostructure was developed on the surface of a glass plate using spray payroliziz method. A new electrochemical biosensor was fabricated based on a layer by layer process. In this process chitosan? Fe₃O₄ (CH? Fe₃O₄) nanocomposite film was prepared at the surface of FTO electrode by dip? coating method. In the next step, the glucose oxidase (GOx) was immobilized on the CH? Fe₃O₄/FTO nanocomposite electrode. The GOx/CH? Fe₃O₄/FTO bioelectrode has a linear range of 10–270 µM and a detection limit of 5 µM. The highest sensitivity was obtained at 1.2 µA mM^?1 cm^?2.     

Controlled synthesis of core-shell Fe2O3@N-C with ultralong cycle life for lithium-ion batteries

Development of low-cost electrode materials with long cycle life and high volumetric capacity is important for large-scale applications of lithium-ion batteries （LIBs）.Here,an electrode made from Fe₂O₃encapsulated with N-doped carbon （Fe₂O₃@N-C） via ZIF-8 coating and carbonization process is reported.A cavity was generated between the Fe₂O₃and N-C material during the carbonization process that is conducive to alleviating the volum...     

Effect of sintering temperature on electrochemical performance of porous SrTi1-xFexO3-δ (x = 0.35, 0.5, 0.7) oxygen electrodes for solid oxide cells

This work evaluates the effects of the sintering temperature (800 °C, 900 °C, 1000 °C) of SrTi_1-xFe_xO_3-δ (x = 0.35, 0.5, 0.7) porous electrodes on their electrochemical performance as potential oxygen electrode materials of solid oxide cells. The materials were prepared by a solid-state reaction method and revealed the expected cubic perovskite structure. After milling, the powders were characterised by a sub-micrometre particle size with high sinter-activity. It was shown that the lowest area specific resistance was achieved after sintering SrTi_0.65Fe_0.35O₃ electrodes at 1000 °C, and SrTi_0.5Fe_0.5O₃ and SrTi_0.30Fe_0.70O₃ electrodes at 800 °C, which can be considered to be a relatively low temperature. In general, EIS measurements showed that increasing the Fe content results in lowered electrode polarisation and a decrease of the series resistance. Even though the studied materials have much lower total conductivities than state-of-the-art electrode materials (e.g. (La,Sr)(Co,Fe)O₃), the polarisation resistances obtained in this work can be considered low.