Synthesis of acetone reduced graphene oxide/Fe3O4 composite through simple and efficient chemical reduction of exfoliated graphene oxide for removal of dye from aqueous solution

A simple and effective technique for reduction of graphene oxide at low temperature (70 °C) using acetone was reported for the first time. Magnetically recoverable acetone reduced graphene oxide (ARGO)/Fe₃O₄ composite was synthesized by uniformly decorating Fe₃O₄ on ARGO. The synthesized ARGO/Fe₃O₄ composite was characterized by the powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Fourier transform-infrared spectroscopy and thermogravimetric analysis. An organic dye rhodamine 6G was used as an adsorbate for investigating the adsorption characteristics of the composite. The adsorption kinetic data were best described by the pseudo-second-order model, and equilibrium was achieved within 2 h. Dye adsorption was favored in basic conditions (pH 9–11) and governed by intraparticle diffusion process. The maximum dye adsorption on the composite was 93.37 mg/g at 293 K, and it followed the Langmuir–Freundlich model. The calculated thermodynamic parameters (ΔG°, ΔH° and ΔS°) showed that the dye adsorption onto composite was feasible, spontaneous and exothermic. The ARGO/Fe₃O₄ composite was easily controlled in magnetic field for desired separation, leading to an easy removal of the dye from wastewater, which holds great potential for dye decontamination.     

A novel approach for synthesis of M-type hexaferrites nanopowders via the co-precipitation method

M-type hexaferrites; barium hexaferrite BaFe₁₂O₁₉ and strontium hexaferrite SrFe₁₂O₁₉ powders have been successfully prepared via the co-precipitation method using 5 M sodium carbonate solution as alkali. Effects of the molar ratio and the annealing temperature on the crystal structure, crystallite size, microstructure and the magnetic properties of the produced powders were systematically studied. The results indicated that a single phase of barium hexaferrite was obtained at Fe³⁺/Ba²⁺ molar ratio 12 annealed at 800–1,200 °C for 2 h whereas the orthorhombic barium iron oxide BaFe₂O₄ phase was formed as a impurity phase with barium M-type ferrite at Fe³⁺/Ba²⁺ molar ratio 8. On the other hand, a single phase of strontium hexaferrite was produced with the Fe³⁺/Sr²⁺ molar ratio to 12 at the different annealing temperatures from 800 to 1,200 °C for 2 h whereas the orthorhombic strontium iron oxide Sr₄Fe₆O₁₃ phase was formed as a secondary phase with SrFe₁₂O₁₉ phase at Fe³⁺/Sr²⁺ molar ratio of 9.23. The crystallite sizes of the produced nanopowders were increased with increasing the annealing temperature and the molar ratios. The microstructure of the produced single phase M-type ferrites powders displayed as a hexagonal-platelet like structure. A saturation magnetization (53.8 emu/g) was achieved for the pure barium hexaferrite phase formed at low temperature 800 °C for 2 h. On the other hand, a higher saturation magnetization value (M _s = 85.4 emu/g) was obtained for the strontium hexaferrite powders from the precipitated precursors synthesized at Fe³⁺/Sr²⁺ molar ratio 12 and thermally treated at 1,000 °C for 2 h.     

Laser raman spectroscopic studies of the surface oxides formed on iron chromium alloys at elevated temperatures

Binary iron-base alloys containing chromium additions of 3, 9, 12 and 18 % were oxidized in air at elevated temperatures. Laser Raman spectroscopy has been used to determine the chemical compounds of the oxides of these alloys. It is found that the oxides formed on Fe-3Cr alloy at various elevated temperatures consist mainly of iron. However, for Cr additions ≥12 %, the surface oxide formed at 400°C consists of αFe₂O₃, Fe₃O₄ and spinel phases. With increasing oxidation temperature up to 850°C, the oxide scale consists of Cr₂O₃ and spinel phases only.     

Cordierite as catalyst support for nanocrystalline CuO/Fe2O3 system

CuO, Fe₂O₃ and CuO–Fe₂O₃ samples supported on cordierite (commercial grade) were prepared by wet impregnation method using finely powdered support material, copper and/or iron nitrates. The extent of loading was varied between 5 and 20 wt.% CuO, Fe₂O₃ or CuO–Fe₂O₃. The physicochemical, surface and catalytic properties of the various solids calcined at 350–700 °C were investigated using XRD, EDX, nitrogen adsorption at 77 K and CO-oxidation by O₂ at 220–280 °C.The results obtained revealed that the employed cordierite preheated at 350–700 °C was well-crystallized magnesium aluminum silicate (Mg₂Al₄Si₅O₁₈). Loading of 20 wt.% CuO or Fe₂O₃ on the cordierite surface calcined at 350 °C led to a partial dissolution of the added oxides in the support lattice forming solid solutions. The other portions remained as separate nanocrystalline CuO or Fe₂O₃ phases. The dissolved portions of the transition metal oxide increased upon increasing the calcination temperature from 350 to 500 °C. Loading of 20 wt.% CuO–Fe₂O₃ on the cordierite surface followed by calcination at 350 °C resulted in a solid–solid interaction between some of CuO and Fe₂O₃ yielding iron cuprate Fe₂CuO₄, which decomposed at ≥500 °C yielding copper and iron oxides. The portion of Fe₂O₃ dissolved in the cordierite lattice at 500 °C is twice that of CuO.The S_BET of cordierite increased several times by treating with small amounts of Fe₂O₃ or CuO. The increase was more pronounced by treating with Fe₂O₃. The catalytic activity of the cordierite increased progressively by increasing the amount of oxide(s) added. The mixed oxides system supported on cordierite and calcined at 350–700 °C showed catalytic activities much bigger than those measured for the individual supported systems. The synergistic effect manifested in case of solids calcined at 350 °C was attributed to the formation of surface iron cuprate. The significant increase in surface concentration of copper species on top surface layers of the solids treated with mixtures of copper and ferric oxides could be responsible for the synergistic effect for the mixed oxide catalysts calcined at 500 or 700 °C.     

The influence of TiO2 polymorph, mechanical milling and subsequent sintering on the formation of Ti-substituted spinel-related Li0.5Fe2.5O4

Single-phased spinel-related titanium-substituted Li_0.5Fe_2.5O₄ has been synthesized by sintering in air a mechanically pre-milled mixture of lithium carbonate, corundum-related iron (III) oxide and the rutile polymorph of titanium (IV) oxide at 700 °C (12 h). This temperature is ca. 450–500 °C less than the temperatures at which the material is normally prepared by conventional ceramic techniques. On replacing the rutile polymorph of titanium (IV) oxide in the pre-milled mixture by the anatase form the formation of single-phased titanium-substituted Li_0.5Fe_2.5O₄ was not achieved even after sintering the mixture at 1,000 °C (12 h).     

Synthesis of Fe–4.6?wt% B alloy via electro-deoxidation of mixed oxides

Fe–4.6 wt% B alloy was synthesized via electro-deoxidation of the mixed oxide precursor. The oxides, Fe₂O₃ and B₂O₃, mixed in suitable proportions were sintered at 900 °C yielding pellets with a two-phase structure; Fe₂O₃ and Fe₃BO₆. The sintered pellets, connected as cathode, were then electro-deoxidized in molten CaCl₂ or in CaCl₂–NaCl eutectic, against a graphite anode at 3.1 V. The electrolysis at 850 °C has successfully yielded a powder mixture of Fe and Fe₂B. Sequence of changes during the electrolysis was followed by interrupted experiments conducted at 850 °C. This has shown that iron is extracted quite early during the electrolysis through the depletion of oxygen from the starting oxide; Fe₂O₃, forming the other iron oxides in the process. Boron follows a more complicated route. Fe₃BO₆, the initial boron-bearing phase, was depleted in the early stages due to its reaction with molten salt. This gave rise to the formation of calcium borate. Boron was extracted from calcium borate in later stages of electrolysis, which appeared to have reacted in situ with the iron forming compound Fe₂B. An erratum to this article can be found at     

Magnetic PNIPA hydrogels for hyperthermia applications in cancer therapy

Temperature-sensitive Poly (N-isopropylacrylamide), PNIPA gels were synthesized with micron-sized iron and iron oxide (Fe₃O₄) particles to investigate their viability for combined hyperthermia and drug release applications. The ultimate goal is to combine hyperthermia and triggered drug release. Induction heating of the magnetic hydrogels with varying concentration of magnetic powder was conducted at a frequency of 375 kHz for magnetic field strength varying from 1.7 kA/m to 2.5 kA/m. It was observed that the maximum temperature induced in the magnetic hydrogels increased with the concentration of magnetic particles and magnetic field strength. The PNIPA gel underwent a collapse transition at 34 °C. The best combination was found for the PNIPA–Fe₃O₄ system, 2.5 wt.% Fe₃O₄ in PNIPA–Fe₃O₄ system took 260 s to be heated to 45 °C under a magnetic field strength of 1.7 kA/m and the specific absorption rate (SAR) was found to be 1.83. SAR of iron oxide was found to be higher than the SAR of iron.     

Hydrogen evolution kinetics during transition metal oxide-catalyzed ammonia borane hydrolysis

This paper examines the feasibility of using transition metal oxides (cobalt, iron, copper, molybdenum, and vanadium oxides) as catalysts for ammonia borane (AB) hydrolysis. In our experiments, we used an aqueous solution containing 0.24 wt % AB. The amount of oxide catalysts was 10–40 mg. The hydrolysis process was run in the temperature range from 35 to 80°C. The highest hydrogen evolution rate was observed at a temperature of 80°C in the presence of cobalt and iron oxides (Co₃O₄ and Fe₂O₃ · nH₂O). The data obtained for the cobalt and iron oxides demonstrate that the reaction is first-order in ammonia borane. We determined the rate constants of the process and its apparent activation energy: 47.5 kJ/mol for Co₃O₄ and 60.2 kJ/mol for Fe₂O₃ · nH₂O. The cobalt and iron oxides were shown to be efficient catalysts for hydrogen production from aqueous AB solutions.     

Recovery of metals from power plant fly ash by two‐stage preferential chlorination

Abstract

Preferential chlorination or pre‐chlorination of iron oxide in fly ash was investigated as one means for reducing the iron in the final product. The chlorination behavior of pure Fe₂O₃, pure Al₂O₃, pure SiO₂, a mixture corresponding in composition to that of non‐magnetic fly ash, and oxides mixtures with various combinations of Fe₂O₃, Al₂O₃ and SiO₂ were also studied to give a better understanding of the selective chlorination of the Fe₂O₃ and of the effects of oxides upon the chlorination of other oxides.

The results reveal that chlorine attacks preferentially upon iron oxide. In the presence of carbon at a moderate temperature, the addition of Al₂O₃ and/or SiO₂ to Fe₂O₃ generally decreases the chlorination extent of Fe₂O₃; however, the addition of SiO₂ to Al₂O₃ or to Fe₂O₃‐Al₂O₃ mixture increases the chlorination extent of Al₂O₃. The chlorination extents of Fe₂O₃ and of Al₂O₃ in the ash‐carbon mixture and in the ignited ash are generally lower than those in the corresponding Fe₂O₃‐Al₂O₃ mixture. Comparison of the extents of chlorination for fly ash at low to moderate temperatures in the presence of carbon to those at high temperatures without adding carbon has been made. The results indicate that the chlorination of ash to produce AlCl₃ with low iron contamination without losing significant amounts of aluminum can be best accomplished in a two‐stage process consisting of a selective chlorination of Fe₂O₃ at moderate temperature (say, 700°C) and a high temperature (say, 850°C) chlorination of Al₂O₃, both with addition of carbon.     

Thermally induced changes in the magnetic properties of iron oxide nanoparticles under reducing and oxidizing conditions

Application of iron oxide nanoparticles in the fields of water purification, biomedicine or chemistry often requires controlled magnetic properties that can be modified by changing temperature and redox conditions. Therefore, this work investigates the changes in the magnetic properties of iron oxide nanoparticles in the FeOOH − Fe₂O₃ − Fe₃O₄ system (i.e. hematite, goethite, lepidocrocite, maghemite and magnetite) at heating under reducing and oxidizing conditions. The results show that heat treatment of hematite and goethite in the presence of a reducing agent (5% starch) leads to their conversion into high magnetic magnetite. The starting temperature of transformation is approximately 350 °C for both samples. The magnetization increases to 86 Am²/kg for hematite reduced at 700 °C and to 88 Am²/kg for goethite reduced at 900 °C. An intense reaction occurs within the first 10 min and then the conversion process decelerates. Thermal treatment of lepidocrocite under both oxidizing and reducing conditions leads to an increase in magnetization due to the formation of maghemite and magnetite, respectively. Regardless of the redox conditions, the formation of magnetic phase begins at a temperature of 250 °C and is associated with the formation of maghemite from lepidocrocite. Under oxidizing conditions, the magnetization begins to decrease at 350 °C, which is associated with the conversion of maghemite to hematite. On the contrary, under reducing conditions, the magnetization of lepidocrocite increases up to 900 °C, which is associated with the formation of magnetite. Maximum values of magnetization are 36 Am²/kg for maghemite obtained at 350 °C, and 88 Am²/kg for magnetite obtained at 900 °C from lepidocrocite. With the help of conventional heating, the magnetic properties of IONs can be altered by phase transformations in the FeOOH − Fe₂O₃ − Fe₃O₄ system. Temperature and redox conditions are the two most important factors controlling the transformation pathways and the magnetic properties of the resulting IONs.     

Optical and structural investigations on iron-containing phosphate glasses

The article reports the preparation and complex characterization of iron-containing phosphate glasses considered to be ecological materials, as they contain non-toxic compounds related to environment. The oxide system Li₂O?CMgO?C(CaO)?CAl₂O₃?CP₂O₅?C(FeO/Fe₂O₃) was investigated in respect to its structural changes caused by MgO replacement with CaO and by the iron addition. UV?Cvis?CNIR (ultraviolet?Cvisible?Cnear infrared) spectroscopy as well as thermo-gravimetric (TG) measurements, differential thermo-analysis (DTA), X-ray diffraction (XRD) analysis, electronic paramagnetic resonance (EPR), and Mossbauer (nuclear gamma resonance) spectroscopy have been used to investigate redox states and coordination symmetry of iron, together with vitreous network changes during the heat treatment up to 1000 °C. UV?Cvis?CNIR transmission spectroscopy revealed no structural modifications when MgO was substituted by CaO, but noteworthy absorption bands attributed to Fe²⁺/Fe³⁺ species. TG analysis made in the 20?C1000 °C range shows low weight loss accompanied by several thermal effects, as evidenced by DTA. XRD patterns for the glass samples heat treated at about 700 °C revealed the presence of different phosphate crystalline phases containing Mg, Al, and Fe ions. EPR spectroscopy revealed the presence of paramagnetic Fe³⁺ ions and the change of the first coordination symmetry, when the samples are heated below the vitreous transition temperature. Mossbauer spectroscopy has evidenced two paramagnetic species, Fe²⁺ and Fe³⁺, both in octahedral coordination symmetry and a clustering process supported by only Fe³⁺ ions.     

Alignment under Magnetic Field of Mixed Fe2O3/SiO2 Colloidal Mesoporous Particles Induced by Shape Anisotropy

When using the bottom‐up approach with anisotropic building‐blocks, an important goal is to find simple methods to elaborate nanocomposite materials with a truly macroscopic anisotropy. Here, micrometer size colloidal mesoporous particles with a highly anisotropic rod‐like shape (aspect ratio ≈ 10) have been fabricated from silica (SiO₂) and iron oxide (Fe₂O₃). When dispersed in a solvent, these particles can be easily oriented using a magnetic field (≈200 mT). A macroscopic orientation of the particles is achieved, with their long axis parallel to the field, due to the shape anisotropy of the magnetic component of the particles. The iron oxide nanocrystals are confined inside the porosity and they form columns in the nanochannels. Two different polymorphs of Fe₂O₃ iron oxide have been stabilized, the superparamagnetic γ‐phase and the rarest multiferroic ε‐phase. The phase transformation between these two polymorphs occurs around 900 °C. Because growth occurs under confinement, a preferred crystallographic orientation of iron oxide is obtained, and structural relationships between the two polymorphs are revealed. These findings open completely new possibilities for the design of macroscopically oriented mesoporous nanocomposites, using such strongly anisotropic Fe₂O₃/silica particles. Moreover, in the case of the ε‐phase, nanocomposites with original anisotropic magnetic properties are in view.     

Effect of microwave heating on the microstructures and kinetics of carbothermal reduction of pyrolusite ore

This article focuses on the development of phase transformation and morphology of low-grade pyrolusite during carbothermal reduction using microwave heating. The XRD, SEM and EDS results show that selective carbothermal reduction of Mn_xO_y and Fe_xO_y in pyrolusite is easy to realize with microwave heating, which can reduce MnO₂ to MnO, and Fe₂O₃ to Fe₃O₄, rather than FeO. It was also observed that the phases of Mn₂O₃, Mn₃O₄ and MnO appear at 300?°C, 450?°C and 500?°C, respectively. The MnO phase, formed by the accumulation of MnO sphere particle with a diameter of 266.75–420.05?nm, is loose and porous. At a temperature of 750?°C, the Mn₂SiO₄ layer of about 316?nm in thickness, tightly wrapping SiO₂ particle is generated at the interface between MnO and SiO₂ embedded with MnO. Above 650?°C, Fe₂O₃ in pyrolusite can be transformed into a very dense Fe₃O₄ phase.     

Scale growth on 2·25Cr–1 Mo steel

Abstract

A 2·25Cr–1 Mo steel was oxidised at 600°C in dry flowing oxygen for periods of up to 100 h. The change in the structure of the oxide scale with time was studied thermogravimetrically and microstructurally by use of SEM and EDX analyses. It was shown that an oxide layer of Fe₃O₄ nucleated and spread laterally between layers of α-Fe₂O₃ and a doped spinel oxide.

MST/931     

Sb‐Doped SnO2 Nanorods Underlayer Effect to the α‐Fe2O3 Nanorods Sheathed with TiO2 for Enhanced Photoelectrochemical Water Splitting

Here, a Sb‐doped SnO₂ (ATO) nanorod underneath an α‐Fe₂O₃ nanorod sheathed with TiO₂ for photoelectrochemical (PEC) water splitting is reported. The experimental results, corroborated with theoretical analysis, demonstrate that the ATO nanorod underlayer effect on the α‐Fe₂O₃ nanorod sheathed with TiO₂ enhances the PEC water splitting performance. The growth of the well‐defined ATO nanorods is reported as a conductive underlayer to improve α‐Fe₂O₃ PEC water oxidation performance. The α‐Fe₂O₃ nanorods grown on the ATO nanorods exhibit improved performance for PEC water oxidation compared to α‐Fe₂O₃ grown on flat fluorine‐doped tin oxide glass. Furthermore, a simple and facile TiCl₄ chemical treatment further introduces TiO₂ passivation layer formation on the α‐Fe₂O₃ to reduce surface recombination. As a result, these unique nanostructures show dramatically improved photocurrent density (139% higher than that of the pure hematite nanorods).     

Magnet–PNIPA hydrogels for bioengineering applications

Temperature-sensitive Poly (N-isopropylacrylamide), PNIPA gels were synthesized with micron-sized iron and iron oxide (Fe₃O₄) particles to investigate their viability for hyperthermia applications. Induction heating of the magnetic hydrogels with varying concentration of magnetic powder was conducted at a frequency of 375  kHz for magnetic field strength varying from 1.7 kA/m (21 Oe) to 2.5 kA/m (31.4 Oe). It was observed that the maximum temperature induced in the magnetic hydrogels increased with the concentration of magnetic particles and magnetic field strength. The PNIPA gel underwent a collapse transition at 34 °C. It was found that a 2.5 wt.% Fe₃O₄ in PNIPA composite took 260 s to be heated to 45 °C under a magnetic field strength of 1.7 kA/m, the specific absorption rate (SAR) was found to be 1.83. SAR of iron oxide was found to be higher than the SAR of iron.     

Nanostructured GdAlO3 perovskite, a new possible catalyst for combustion of volatile organic compounds

The purpose of this paper was to obtain nanosize GdAlO₃ perovskite powders for catalyst applications. Two different thermal treatments (900 °C for 1 h and 1000 °C for 7 h) were applied to amorphous powder obtained by combined sol–gel and self-combustion method to promote crystallization of GdAlO₃ perovskite. The structural and phase transformations after each thermal treatment have been studied by scanning electron microscopy (SEM), X-ray diffraction (XRD), and N₂ adsorption. After treatment at 900 °C the formation of perovskite phase, GdAlO₃ (with orthorhombic structure) in mixture with other phases (Gd₂O₃, Al₂O₃, Gd₄Al₂O₉, and Gd₃Al₅O₁₂) was detected. A monophase crystalline material, GdAlO₃ pure perovskite, with crystallite size of 40 nm and S_BET of 10 m²/g was obtained after a longer treatment, 7 h at 1000 °C. The catalytic activity of the two nanocrystalline samples in the combustion reaction of acetone, propane, benzene, and Pb free gasoline was studied. Both samples exhibit the best catalytic activity for acetone combustion (80 % acetone conversion at 500 °C) and proved poor catalytic performance in catalytic combustion of Pb free gasoline (24 % conversion at 500 °C). Although S_BET value for sample treated at 900 °C is higher (22 m²/g) than that of the sample treated at 1000 °C (10 m²/g), the treatment at 1000 °C for 7 h assures a good thermo-chemical stability of GdAlO₃ perovskite required by low temperature catalyst applications. GdAlO₃ perovskite seems to be a promising catalyst for low temperature acetone combustion (T < 500 °C).     

The influence of equilibration time on the physical properties of B2O3PbOFe2O3 glasses

The 20Fe₂O₃ 80[3B₂O₃·PbO] glasses equilibrated at 1250°C, for times ranging between 0.5 and 10 hrs are studied by X-rays, electron-microscope, Mössbauer effect, electron paramagnetic resonance and magnetic measurements. The iron valence states as well as the distribution of iron ions in the glass matrix are analysed.     

The oxidation of Fe3Al–(0, 2, 4, 6%)Cr alloys at 1000 °C

Thermomechanically treated Fe₃Al–(0, 2, 4, 6at.%)Cr alloys were isothermally oxidized at 1000 °C in air, and their oxidation characteristics were studied using thermogravimetric analyzer, X-ray diffractometer, scanning electron microscope, electron probe microanalyzer, and TEM/EDS. It was found that Cr decreased the oxidation resistance of Fe₃Al alloys to a certain extent. The oxide scales that formed on the unalloyed Fe₃Al alloys consisted primarily of α-Al₂O₃ containing a small percentage of dissolved iron ions. Less than 1% of dissolved chromium ions was additionally present in the oxide scale formed on the Fe₃Al–Cr alloys. An Al-free, Fe-enriched zone was formed beneath the oxide scale, owing to Al consumption to form the oxide scale. The oxide scale on all alloys had poor adherence.     

Preparation and properties of glass-ceramic materials obtained by recycling goethite industrial waste

The recycling of toxic goethite waste, originated in the hydrometallurgy of zinc ores, in glass-ceramic matrices has been studied. Oxide compositions suitable to form glasses were prepared by mixing the goethite waste with granite scraps and glass cullet, yielding the following oxide composition (wt%): SiO₂, 44.6; Al₂O₃, 3.3; Fe₂O₃, 25.5; MgO, 1.6; CaO, 4.5; Na₂O, 5.9; PbO, 3.1; ZnO, 6.5; K₂O, 1.0; TiO₂, 2.0; other 2.0. By proper addition of carbon powder, the initial Fe³⁺/Fe²⁺ ratio (12) of glasses melted in air at 1450 °C was approximated to the stoichiometric value of magnetite (2) to obtain high nucleation and crystallization rates. The heat treatment of iron supersaturated goethite glasses above 630 °C led to the formation of magnetite nuclei with a high tendency to grow and coalesce with time. The crystallization of pyroxene, occurring on the magnetite crystals above 800 °C, was found to be influenced by the nucleation period, so that the highest crystalline volume fraction, V _f (0.80–0.85), was obtained for 90–120 min nucleation time at 670 °C and 120 min crystallization at 860 °C. This revised version was published online in November 2006 with corrections to the Cover Date.