Iron oxide nanotube film formed on carbon steel for photoelectrochemical water splitting: effect of annealing temperature

Carbon steels (CSs) were anodized in an ethylene glycol solution containing 3 vol.% H₂O and 0.1 m NH₄F to coat with nanotube arrays film. The as anodized nanotube arrays film were annealed in argon atmosphere at various temperatures ranging from 250 to 550 °C for 4 h. The morphology and crystal phases of the film developed after annealing processes were examined using field emission scanning electron microscopy, X‐ray diffraction. Morphology transforms from nanobube arrays to nanotube bundles at 250 °C, to nanobube bundles with nanoflakes at 350 and 450 °C, to nanotube bundles with nanobelts at 550 °C. Amorphous transformed completely into maghemite at 350 °C and hematite with minor magnetite at 450 and 550 °C. Diffuse reflectance ultraviolet and visible spectra revealed iron oxide nanotube film annealed at 350 °C, or higher than 350 °C behaved tremendous absorbance ability in visible spectra range. Mott–Schottky analysis and linear scan voltammetry were performed in 1 m NaOH to show that iron oxide nanotube film annealed at 450 °C exhibited best charge carrier transfer ability upon illumination and superior photoelectrochemical properties compared with the films annealed at other temperatures. The film annealed at 450 °C displayed the photocurrent density of 0.13 mA cm^?2 at 0.2 V_Ag/AgCl, but the film annealed at other temperatures with the photocurrent densities of lower than 0.05 mA cm^?2 at 0.2 V_Ag/AgCl. The morphology and phase transform of iron oxide nanotube film at different annealing temperature results in the change of their photoelectrochemical properties. Copyright © 2016 John Wiley & Sons, Ltd.     

Determination of Active Metal in Ultradispersed Iron Powders and TG Study of Their Oxidation

Two oxidation stages of electrolytic ultradispersed iron powder at the temperature range of 90–450°C have been stated. The contribution of increasing mass and evolving heat at the first oxidation stage due to changing Fe⁰ into Fe₂O₃ in the total oxidation effect is predominant. The thermal method of active metal determination in electrolytic iron powders has been developed. The coarse-grained reduced iron powder was not oxidized completely just to 900°C because of local sintering of big iron particles as a result of evolving heat at oxidation of high-dispersed iron particles. This revised version was published online in August 2006 with corrections to the Cover Date.     

Fabrication of a New Electrochemiluminescent Sensing Interface Based on Zinc Oxide Nanorod

A new electrochemiluminescence (ECL) sensing interface was established based on the zinc oxide nanorod in this paper. Firstly, the zinc oxide (ZnO) nanorod was prepared on an indium tin oxide (ITO) electrode surface by the method of constant current cathodic electrodeposition, on which the Nafion film was then modified, and finally ruthenium(II) tris(bipyridine) (Ru(bpy)₃²⁺) was immobilized at the ZnO nanorod/Nafion composite‐modified electrode. The sensing interface shows well ECL behaviors and perfect stability after being constant temperature treatment at 80 °C. The composite electrode was characterized by EIS, SEM and XRD. The results showed that the good stability maybe related to the water content of Nafion film.     

Reversible Topochemical Exsolution of Iron in BaFe2+2(PO4)2

BaFe²⁺₂(PO₄)₂ was recently prepared and identified as the first 2D‐Ising ferromagnetic oxide with an original reentrant structural transition driven by high‐spin Fe²⁺ ions arranged in honeycomb layers. Both long‐term air exposure and moderate temperature (T>375 °C) leads to topochemical oxidation into iron‐depleted compounds with mixed Fe²⁺/Fe³⁺ valence. This process is unique, as the exsolution is effective even from single crystal with preservation of the initial crystallinity, and the structure of the deficient BaFe_2?x(PO₄)₂ (xx=2/7 and 1/3 with creation of novel original depleted triangular lattices. Under flowing H₂/Ar, Fe is reincorporated in the structure above 480 °C, as reproduced under the electron beam in a transmission microscope. After Fe exsolution, the insulating ferromagnetic compound turns into an antiferromagnetic semiconductor.     

An iron (II) guanidinate compound: Synthesis,characterization, thermal properties and its application as a CVD precursor for iron oxide film

An iron compound containing guanidinate ligand [Fe((SiMe₃)₂NC(ⁱPrN)₂)₂] was synthesized using a conventional lithium‐salt‐elimination reaction, and its chemical structure was characterized through elemental analysis, ¹H‐NMR and single‐crystal X‐ray diffraction, respectively. The thermal properties of the compound were examined through thermogravimetric analysis (TGA), and the TGA results demonstrated that the compound possessed sufficient volatility and suitable thermal stability for the CVD process. Moreover, the deposition experiments were conducted using the synthesized compound as a precursor and O₂ as an oxygen source to confirm its applicability as a CVD precursor, and α‐Fe₂O₃ films were successfully deposited at a relatively low deposition temperature (300°C).     

Sol‐Gel Related Solvothermal Procedure to Prepare Iron Oxide Fibers

A sol‐gel‐related solvothermal process is developed to prepare iron oxide fibers. Continuous iron oxide gel fiber was drawn from spinnable sol using ferric alkoxide as the precursor, and hollow hematite fiber was obtained after the gel fiber was treated by hydroncarbon thermal reaction. The as‐prepared hollow fiber was several millimeters in length, 4～15 µm in outer diameter, and ～3 µm in wall thickness. Substituting the hydrocarbon with triethylamide, Fe₃O₄ solid fiber composed of nanorods can be obtained. Incubated at 200°C in air for only 1 hour, Fe₃O₄ was oxidated to γ‐Fe₂O₃ fiber. Possible mechanisms involved in formation of these nanostructured iron oxide fibers also are discussed.     

Application of TOF-SIMS Method in the Study of Wetting the Iron (111) Surface with Promoter Oxides

In the present work, a simplified model of the Fe(111) surface’s promoter-oxide system was investigated in order to experimentally verify the previously proposed and known models concerning the structure and chemical composition of the surfaces of iron nanocrystallites in the ammonia-synthesis catalyst. It was shown that efficient oxygen diffusion from metal oxides to the clean Fe(111) iron surface took place even at temperatures lower than 100 °C. The effective wetting of the iron surface by potassium oxide is possible when the surface is covered with oxygen at temperatures above 250 °C. In the TOF-SIMS spectra of the surface of iron wetted with potassium, an emission of secondary FeOK⁺ ions was observed that implies that potassium atoms are bound to the iron surface atoms through oxygen. As a result of further wetting the iron surface with potassium ions, a heterogeneous surface structure was formed consisting of a thin K₂O layer, next to which there was an iron-oxide phase covered with potassium ions. Only a limited increase in calcium concentration was observed on the Fe(111) iron surface upon sample annealing at up to 350 °C. As a result of wetting the iron surface with calcium ions, an oxide solution of CaO-Fe_xO_y was formed. In the annealing process of the sample containing alumina, only traces of this promoter diffusing to the iron surface were observed. Alumina formed a solution with a passive layer on the iron surface and under the process conditions (350 °C) it did not wet the pure iron (111) surface. The decrease in Fe⁺-ion emission from the Fe-Ca and Fe-Al samples at 350 °C implies a reduction in the oxygen concentration on the sample surface at this temperature.     

Fe‐, Co‐, and Ni‐Loaded Porous Activated Carbon Balls as Lightweight Microwave Absorbents

Porous activated carbon ball (PACB) composites impregnated with iron, cobalt, nickel and/or their oxides were synthesized through a wet chemistry method involving PACBs as the carrier to load Fe³⁺, Co²⁺, and Ni²⁺ ions and a subsequent carbothermal reduction at different annealing temperatures. The results show that the pyrolysis products of nitrates and/or the products from the carbothermal reduction are embedded in the pores of the PACBs, with different distributions, resulting in different crystalline phases. The as‐prepared PACB composites possessed high specific surface areas of 791.2–901.5 m² g^?1 and low densities of 1.1–1.3 g cm^?3. Minimum reflection loss (RL) values of ?50.1, ?20.6, and ?20.4 dB were achieved for Fe–PACB (annealed at 500 °C), Co–PACB (annealed at 800 °C), and Ni–PACB (annealed at 800 °C) composites, respectively. Moreover, the influence of the amount of the magnetic components in the PACB composites on the microwave‐absorbing performances was investigated, further confirming that the dielectric loss was the primary contributor to microwave absorption.     

Three Aromatic Residues are Required for Electron Transfer during Iron Mineralization in Bacterioferritin

Ferritins are iron storage proteins that overcome the problems of toxicity and poor bioavailability of iron by catalyzing iron oxidation and mineralization through the activity of a diiron ferroxidase site. Unlike in other ferritins, the oxidized di‐Fe³⁺ site of Escherichia coli bacterioferritin (EcBFR) is stable and therefore does not function as a conduit for the transfer of Fe³⁺ into the storage cavity, but instead acts as a true catalytic cofactor that cycles its oxidation state while driving Fe²⁺ oxidation in the cavity. Herein, we demonstrate that EcBFR mineralization depends on three aromatic residues near the diiron site, Tyr25, Tyr58, and Trp133, and that a transient radical is formed on Tyr25. The data indicate that the aromatic residues, together with a previously identified inner surface iron site, promote mineralization by ensuring the simultaneous delivery of two electrons, derived from Fe²⁺ oxidation in the BFR cavity, to the di‐ferric catalytic site for safe reduction of O₂.     

New approaches to the preparation of highly efficient chromium-containing oxide catalysts for the water gas shift reaction

It was found experimentally that the solutions of Cr³⁺ nitrate and the nitrates of other metals that are the constituents of Cr-containing catalysts can be prepared by dissolving a corresponding metal (for example, cast iron and electrolytic copper) in a solution of chromic anhydride and nitric acid to reach the quantitative reduction of Cr⁶⁺ without the formation of nitrogen oxides. Analogously, the oxidation of Fe²⁺ cations to Fe³⁺ coupled with the reduction of hexavalent chromium can be performed. The precipitation of Fe³⁺, Cr³⁺, and Cu²⁺ ions at a ratio of Fe: Cr = 9 and a concentration of Cu²⁺ to 20 at % can result in the formation of a partially hydrated oxide with the hydrohematite structure—a dispersed and highly defective oxide structure with a high specific surface area more than 300 m²/g and a higher thermal stability, as compared with the goethite phase (α-FeOOH). The dehydration of hydrohematite occurred at a noticeable rate at temperatures higher than 400°C. Hydrohematite promoted with copper cations exhibited high activity below 400°C; this can decrease the starting temperature of the adiabatic high-temperature WGSR to 300°C or below.     

Gold/Wüstite Core–shell Nanoparticles: Suppression of Iron Oxidation through the Electron‐Transfer Phenomenon

Plasmonic Au and magnetic Fe are coupled into uniform Au@Fe core–shell nanoparticles (NPs) to confirm that electron transfer occurred from the Au core to the Fe shell. Au NPs synthesized in aqueous medium are used as seeds and coated with an Fe shell. The resulting Au@Fe NPs are characterized by using various analytical techniques. X‐ray photoelectron spectroscopy and superconducting quantum interference device measurements reveal that the Fe shell of the Au@Fe NPs mainly consists of paramagnetic Wüstite with a thin surface oxide layer consisting of maghemite or magnetite. Electron transfer from the Au core to the Fe shell effectively suppresses iron oxidation from Fe²⁺ to Fe³⁺ near the interface between the Au and the Fe. The charge‐transfer‐induced electronic modification technique enables us to control the degree of iron oxidation and the resulting magnetic properties.     

Thermally Stable Super Ionic Conductor from Carbon Sphere Oxide

A highly stable proton conductor has been developed from carbon sphere oxide (CSO). Carbon sphere (CS) generated from sucrose was oxidized successfully to CSO using Hummers’ graphite oxidation technique. At room temperature and 90 % relative humidity, the proton conductivity of thin layer CSO on microsized comb electrode was found to be 8.7×10^?3 S cm^?1, which is higher than that for a similar graphene oxide (GO) sample (3.4×10^?3 S cm^?1). The activation energy (E_a) of 0.258 eV suggests that the proton is conducted through the Grotthuss mechanism. The carboxyl functional groups on the CSO surface are primarily responsible for transporting protons. In contrast to conventional carbon‐based proton conductors, in which the functional groups decompose around 80 °C, CSO has a stable morphology and functional groups with reproducible proton conductivity up to 400 °C. Even once annealed at different temperatures at high relative humidity, the proton conductivity of CSO remains almost unchanged, whereas significant change is seen with a similar GO sample. After annealing at 100 and 200 °C, the respective proton conductivity of CSO was almost the same, and was about ～50 % of the proton conductivity at room temperature. Carbon‐based solid electrolyte with such high thermal stability and reproducible proton conductivity is desired for practical applications. We expect that a CSO‐based proton conductor would be applicable for fuel cells and sensing devices operating under high temperatures.     

Oxidation of magnesium in the systems NaClO4-Mg-Metal oxide (peroxide)

Oxidation of magnesium in mixtures NaClO₄ + Mg + metal oxide or peroxide has been investigated using differential thermal analysis (DTA). In the systems with peroxides Na₂O₂, Li₂O₂, BaO₂, CaO₂ or ZnO, magnesium oxidizes simultaneously with decomposition of NaClO₄ in the region 380–520°C, which is 100–200°C below the oxidation temperature of magnesium in air. In the ternary systems with transition-metal oxides NiO, CuO, FeO, and Fe₂O₃, magnesium transforms into oxide at above 600°C after sodium perchlorate had been decomposed completely. The low-temperature oxidation of magnesium occurs in the systems in which sodium chlorate is accumulated during the catalytic decomposition of NaClO₄.     

A New Iron‐Based Carbon Monoxide Oxidation Catalyst: Structure–Activity Correlation

A new iron‐based catalyst for carbon monoxide oxidation, as a potential substitute for precious‐metal systems, has been prepared by using a facile impregnation method with iron tris‐acetylacetonate as a precursor on γ‐Al₂O₃. Light‐off and full conversion temperatures as low as 235 and 278 °C can be reached. However, the catalytic activity strongly depends on the loading; lower loadings perform better than higher ones. The different activities can be explained by variations of the structures formed. The structures are thoroughly characterized by a multimethodic approach by using X‐ray diffraction, Brunauer–Emmett–Teller surface areas, and Mössbauer spectroscopy combined with diffuse reflectance UV/Vis and X‐ray absorption spectroscopy. Consequently, isolated tetrahedrally coordinated Fe³⁺ centers and phases of AlFeO₃ are identified as structural requirements for high activity in the oxidation of carbon monoxide.     

Electrical,optical, and structural characterization of p‐type N‐doped SnO thin films prepared by thermal oxidation of sputtered SnNx thin films

We present a study of electrical and optical properties of nitrogen‐doped tin oxide thin films deposited on glass by the DC Magnetron Sputtering method. The deposition conditions to obtain p‐type thin films were a relative partial pressure between 7% and 11% (N₂ and/or O₂), a total working pressure of 1.8 mTorr and a plasma power of 30 W. The deposited thin films were oxidized after annealing at 250°C for 30 minutes. X‐ray diffraction results showed that the as‐deposited thin films exhibit a Sn tetragonal structure, and after annealing, they showed SnO tetragonal structure. X‐ray photoelectron spectroscopy results showed the presence of nitrogen in the samples before and after annealing. The measured physical parameters of the thin films were optical band gap between 1.92 and 2.68 eV, resistivity between 0.52 and 5.46 Ωcm, a concentration of p‐type carriers between 10¹⁸ and 10¹⁹ cm^?3, and a Hall mobility between 0.1 and 1.94 cm²V^?1s^?1. These thin films were used to fabricate p‐type thin film transistors.     

Highly Oxidized Platinum Nanoparticles Prepared through Radio‐Frequency Sputtering: Thermal Stability and Reaction Probability towards CO

Platinum‐oxide nanoparticles were prepared through the radio‐frequency (RF) discharge sputtering of a Pt electrode in an oxygen atmosphere. The structure, particles size, electronic properties, and surface composition of the RF‐sputtered particles were studied by using transmission electron microscopy and X‐ray photoelectron spectroscopy. The application of the RF discharge method resulted in the formation of highly oxidized Pt⁴⁺ species that were stable under ultrahigh vacuum conditions up to 100 °C, indicating the capability of Pt⁴⁺–O species to play an important role in the oxidation catalysis under real conditions. The thermal stability and reaction probability of Pt⁴⁺ oxide species were analyzed and compared with those of Pt²⁺ species. The reaction probability of PtO₂ nanoparticles at 90 °C was found to be about ten times higher than that of PtO‐like structures.     

The chemistry and thermal stability of HfTaO/Si interface by x‐ray photoelectron spectroscopy

The chemistry and thermal stability of HfTaO/Si interface as a function of annealing temperature have been investigated by x‐ray photoelectron spectroscopy. For the as‐deposited sample, the formation of Hf‐silicate bond is observed on Hf 4f core‐level spectra, which contributes to bulk HfO₂ and SiO₂. Besides, the suboxide of tantalum (Ta⁺¹) is formed at the interface at room temperature because of oxygen‐deficient conditions. HfSi₂, Hf_xSi_yO_4, and HfO₂ coexists in interfacial region at 850 °C, meanwhile, an evidence for transforming from the Ta¹⁺ to tantalum oxide (Ta⁵⁺) is verified. The peaks of Hf–O–Si and Hf–O have disappeared, only one peak of Hf silicide remained after the annealing at 950 °C. A stable SiO₂ phase in HfTaO/Si is formed under different annealing conditions. Copyright © 2011 John Wiley & Sons, Ltd.     

Role of Iron Carbonyls in the Inhibition of Oxygen Activation for the Oxidation of CO Catalyzed by Iron Oxide‐Supported Gold

Iron oxide‐supported gold samples were prepared by co‐precipitation from HAuCl₄ and Fe(NO₃)₃. The activities of the samples as CO oxidation catalysts were tested without thermal treatment and following treatments in flows of He and O₂ at various temperatures. It was found that the untreated samples and those treated in a flow of He at 150 °C were more active than samples that had been treated at 400 °C in either a flow of O₂ or of He. Infrared spectra recorded during CO oxidation catalysis indicate the presence of bonded CO molecules to cationic gold on all samples, whereas spectra of the least active catalysts indicate a predominant presence of Fe²⁺ carbonyls, which were highly stable under the conditions of our experiments. Our results indicate that in the least active samples the Fe²⁺‐bound CO blocks sites that would otherwise be available for oxygen activation.     

Methyl orange degradation enhanced by hydrogen spillover onto platinum nanocatalyst surface

Following a thermal reduction method, platinum nanoparticles were synthesized and stabilized by polyvinylpyrrolidone. The colloidal platinum nanoparticles were stable for more than 3 months. The micrograph analysis unveiled that the colloidal platinum nanoparticles were well dispersed with an average size of 2.53 nm. The sol–gel‐based inverse micelle strategy was applied to synthesize mesoporous iron oxide material. The colloidal platinum nanoparticles were deposited on mesoporous iron oxide through the capillary inclusion method. The small‐angle X‐ray scattering analysis indicated that the dimension of platinum nanoparticles deposited on mesoporous iron oxide (Pt‐Fe₂O₃) was 2.64 nm. X‐ray photoelectron spectroscopy (XPS) data showed that the binding energy on Pt‐Fe₂O₃ surface decreased owing to mesoporous support–nanoparticle interaction. Both colloidal and deposited platinum nanocatalysts improved the degradation of methyl orange under reduction conditions. The activation energy on the deposited platinum nanocatalyst interface (2.66 kJ mol^?1) was significantly lowered compared with the one on the colloidal platinum nanocatalyst interface (40.63 ± 0.53 kJ mol^?1).     

Investigating the oxidation state of Fe from LiFePO4-based lithium ion battery cathodes via capillary electrophoresis

A capillary electrophoresis (CE) method with ultraviolet/visible (UV–Vis) spectroscopy for iron speciation in lithium ion battery (LIB) electrolytes was developed. The complexation of Fe²⁺ with 1,10-phenantroline (o-phen) and of Fe³⁺ with ethylenediamine tetraacetic acid (EDTA) revealed effective stabilization of both iron species during sample preparation and CE measurements. For the investigation of small electrolyte volumes from LIB cells, a sample buffer with optimal sample pH was developed to inhibit precipitation of Fe³⁺ during complexation of Fe²⁺ with o-phen. However, the presence of the conducting salt lithium hexafluorophosphate (LiPF₆) in the electrolyte led to the precipitation of the complex [Fe(o-phen)₃](PF₆)₂. Addition of acetonitrile (ACN) to the sample successfully re-dissolved this Fe²⁺-complex to retain the quantification of both species. Further optimization of the method successfully prevented the oxidation of dissolved Fe²⁺ with ambient oxygen during sample preparation, by previously stabilizing the sample with HCl or by working under counterflow of argon. Following dissolution experiments with the positive electrode material LiFePO₄ (LFP) in LIB electrolytes under dry room conditions at 20°C and 60°C mainly revealed iron dissolution at elevated temperatures due to the formation of acidic electrolyte decomposition products. Despite the primary oxidation state of iron in LFP of +2, both iron species were detected in the electrolytes that derive from oxidation of dissolved Fe²⁺ by remaining molecular oxygen in the sample vials during the dissolution experiments.