Removal of 1-naphthylamine from aqueous solution by multiwall carbon nanotubes/iron oxides/cyclodextrin composite

The adsorption of 1-naphthylamine on multiwall carbon nanotubes/iron oxides/β-cyclodextrin composite (denoted by MWCNTs/iron oxides/CD) prepared by using plasma-induced grafting technique was investigated by batch technique under ambient conditions. The effect of contact time, pH, adsorbent content, temperature and initial 1-naphthylamine concentration, on 1-naphthylamine adsorption to MWCNTs/iron oxides/CD was examined. The adsorption of 1-naphthylamine on MWCNTs/iron oxides/CD was dependent on pH, adsorbent content, and temperature. The 1-napthylamien was adsorbed rapidly at the first 50h, and thereafter attained the adsorption saturation at 80h. The adsorption kinetic data were well described by the pseuso-second-order rate model. The adsorption isotherms were fitted by the Langmuir model better than by the Freundlich model. The maximum adsorption capacity of 1-naphthylamine was 200.0mg/g. The adsorption thermodynamic parameters of standard enthalpy (ΔH(0)), standard entropy changes (ΔS(0)), and standard free energy (ΔG(0)) were calculated from temperature dependent adsorption isotherms. The values of ΔH(0) and ΔG(0) suggested that the adsorption of 1-naphthylamine on MWCNTs/iron oxides/CD was endothermic and spontaneous. The electron-donor-acceptor interaction, Hydrophobic interaction, and Lewis acid-base interaction may play an important role in 1-naphthylamine adsorption. The results show that MWCNTs/iron oxides/CD is a promising magnetic nanomaterial for the preconcentration and separation of organic pollutants from aqueous solutions in environmental pollution cleanup.     

Synthesis and magnetic property of silica/iron oxides nanorods

To better understand the shape dependent property of binary nanostructure, magnetic silica/iron oxides (α-Fe₂O₃ and Fe₃O₄) nanocomposites in rodlike shape have been synthesized using β-FeOOH nanorods as the starting material. The silica layer was coated on the surface of β-FeOOH nanorods, which were prepared by hydrolyzing of FeCl₃ under hydrothermal conditions. Silica/α-Fe₂O₃ nanorods were prepared by calcining silica/β-FeOOH nanorods, and magnetic silica/Fe₃O₄ nanorods were obtained after the reduction of silica/α-Fe₂O₃ nanorods in an inert atmosphere. The role of the silica layer during the phase transformation process was discussed. The magnetic properties of silica/iron oxides (α-Fe₂O₃ and Fe₃O₄) nanorods were investigated and the results revealed that silica/iron oxides nanorods showed higher magnetic saturation value compared with the reported data.     

Preparation and magnetization of hematite nanocrystals with amorphous iron oxide layers by hydrothermal conditions

Hematite nanocrystals modified with surface layers of amorphous hydrous iron oxides were prepared by hydrothermal conditions in the absence of alkali. The formation temperature was found to be ca. 130°C. When the temperature was lower than 130°C, no product was formed, while above this temperature, the amount of amorphous hydrous iron oxides at the surface of hematite nanocrystals was drastically decreased. The amorphous layers on the hematite nanocrystals obtained at 130°C were determined to be Fe₂O₃·1.64H₂O. The coercivity for the hematite nanocrystals with modified layers was 0.534 kOe, which is slightly larger than the values for hematite nanocrystals with few agglomerations.     

An efficient and clean utilization technique for red mud based on fluidized bed carbon monoxide reduction

In order to simulate the pre-reduction behavior of ore powder by coal gas produced by smelting reduction of coal-based electric furnace, an efficient and clean utilization technique for red mud based on fluidized bed carbon monoxide reduction was developed in the present study. Experimental results indicated that a metallization rate of 68.08 % and reduction degree of 78.72 was obtained under the optimal conditions of reduction temperature of 800 °C, CO concentration of 85 %, and reduction time of 30 min. Pre-reduced materials can be used as raw materials for electric furnace melting reduction. The order in which iron oxides were reduced is only related to temperature, and at 800 °C, iron oxides were reduced in the order of Fe₂O₃ to Fe₃O₄ to FeO to Fe. During different stages of prereduction, the surface structure of ore particles changes, which is related to the metallization rate of iron oxides in red mud.     

Fenton-like oxidation of Rhodamine B in the presence of two types of iron (II,III) oxide

The catalytic efficiency of iron (II, III) oxide to promote Fenton-like reaction was examined by employing Rhodamine B (RhB) as a model compound at neutral pH. Two types of iron (II, III) oxides were used as heterogeneous catalysts and characterized by XRD, Mössbauer spectroscopy, BET surface area, particle size and chemical analyses. The adsorption to the catalyst changed significantly with the pH value and the sorption isotherm was fitted using the Langmuir model for both solids. Both sorption and FTIR results indicated that surface complexation reaction may take place in the system. The variation of oxidation efficiency against H₂O₂ dosage and amount of exposed surface area per unit volume was evaluated and correlated with the adsorption behavior in the absence of oxidant. The occurrence of optimum amount of H₂O₂ or of exposed surface area for the effective degradation of RhB could be explained by the scavenging effect of hydroxyl radical by H₂O₂ or by iron oxide surface. Sorption and decolourization rate of RhB as well as H₂O₂ decomposition rate were found to be dependent on the surface characteristics of iron oxide. The kinetic oxidation experiments showed that structural Fe^II content strongly affects the reactivity towards H₂O₂ decomposition and therefore RhB decolourization. The site density and sorption ability of RhB on surface may also influence the oxidation performance in iron oxide/H₂O₂ system. The iron (II, III) oxide catalysts exhibited low iron leaching, good structural stability and no loss of performance in second reaction cycle. The sorption on the surface of iron oxide with catalytic oxidation using hydrogen peroxide would be an effective oxidation process for the contaminants.     

Sand flower layered double hydroxides synthesized by co-precipitation for CO2 capture: Morphology evolution mechanism,agitation effect and stability

Magnesium–aluminum layered double oxides (Mg–Al-LDO) derived from calcination of layered double hydroxides (LDH) is one of the most capable candidates for CO₂ capture. LDHs with sand flower and dense layered morphology are prepared by co-precipitation method at pH = 10 under different condition with and without stirring. The sand flower LDH prepared with stirring has better CO₂ adsorption performance. Additionally, the sand flower morphology under calcination can be preserved very well, while the morphology can only remain stable below 100 °C after hydrothermal treatment and reconstruction. The formation process of the sand flower LDH is investigated in detail and the related morphology evolution mechanism is proposed. This study can provide insight into the effect of mechanical interaction on chemical reaction and give a new way to control the morphology of layered materials.     

Spreading of liquid lead droplets on metallic iron covered by silicon oxide particles or films

As well known, the spreading of a liquid metal droplet on a solid metal is very sensitive to the presence of chemical heterogeneities on the solid metal. In this study, wetting experiments with liquid lead on heterogeneous surfaces composed of iron and silicon oxide particles or films were performed using the dispensed drop technique. High purity iron and binary iron–silicon substrates with different silicon contents were studied. Before the wetting experiments, the substrates are annealed at 850 °C in a N₂–H₂ atmosphere in order to reduce iron oxides and to form silicon oxide particles or films on the surface. The liquid lead droplet is then released onto the metallic substrate partly or wholly covered by the oxides. The spreading of the liquid metal droplet strongly depends on the surface area fraction covered by the oxides.     

Natural and synthetic iron oxides for hydrogen storage and purification

In this paper, the hydrogen storage capacity of some synthetic and natural iron oxides is presented. The results of the activity tests and characterization techniques of natural and synthetic iron oxides (N₂ adsorption–desorption isotherms, temperature-programmed reduction, X-ray diffraction, and plasma atomic emission spectroscopy) suggest that the use of chromium on iron oxide systems improved their hydrogen storage capacity. This is related to the capacity of chromium to modify the iron oxide reduction profile when Cr was incorporated. A direct reduction from Fe₃O₄ to Fe was observed as the mechanism for H₂ storage. In addition, natural oxides as commercial Superfine and Densinox-L oxides are proved to be suitable materials to store and purify H₂ due to their high stability during different cycles of reduction and oxidation. The best results among the natural ones were Densinox-L and among the synthetic ones Fe–10Cr.     

Experimental and theoretical elucidation on the inhibition mechanism of 1-methyl-5-mercapto-1,2,3,4-tetrazole self-assembled films on corrosion of iron in 0.5 M H2SO4 Solutions

The self-assembled films of 1-methyl-5-mercapto-1,2,3,4-tetrazole (MMT) were prepared on the iron surface. By means of electrochemical impedance spectroscopy in 0.5 M H₂SO₄ solutions, the inhibition ability of the film was investigated. Results were discussed through changing the concentrations of the inhibitor and the pH values of the self-assembly solutions. Quantum chemical calculation was applied to elucidate the adsorption mechanism of the inhibitor molecule to iron atom. The study shows that MMT is a good inhibitor for iron in 0.5 M H₂SO₄ solutions. The self-assembled films formed in 10⁻² M acidic solutions have the best protection effect and the inhibition efficiency in 0.5 M H₂SO₄ solutions is 98.0%. Density functional theory proves that MMT molecule is adsorbed on the iron surface by the most negatively charged nitrogen atom and the adsorption can occur spontaneously.     

Influence of molybdenum on the stability of iron oxide materials for hydrogen production with cyclic water gas shift process

The redox behavior of iron oxide modified with various amount of molybdenum (Mo) was investigated in the present study. The modified iron oxides were prepared by co-precipitation using urea hydrolysis method. The influence of Mo on the hydrogen production capacity and the material stability was studied in detail employing temperature-programmed reduction (TPR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and BET analysis. Furthermore, the activity and the stability of the samples were tested in repeated reduction and re-oxidation for 100 cycles with diluted H₂ and H₂O. The results indicate that Mo enhances the stability of iron oxide material by mitigating the sintering process. The positive influence of Mo in stabilizing the iron oxide material is attributed to the dispersion of Fe–Mo oxide material. The dispersion in turn inhibits the neck formation responsible for the sintering.     

Effect of Fe2O3 crystallite size on its mechanochemical reaction with La2O3 to form LaFeO3

Fe₂O₃ powders with different crystallite sizes prepared by heating FeOOH at various temperatures were ground with La₂O₃ powder using a planetary ball mill to investigate the effect of crystallite size on mechanochemical synthesis of LaFeO₃. Fe₂O₃ powder with smaller crystallite size obtained by heating at lower temperature reacts more easily with La₂O₃ than that with larger size. The mechanochemical reaction proceeds with an increase in grinding time. Specific surface area of the LaFeO₃ powder synthesized has a large value of over 11 m²/g. The mechanochemical process can be also applied to synthesize other iron complex oxides with rare earth elements such as Pr, Nd and Sm.     

Spin conversion of hydrogen using supported iron catalysts at cryogenic temperature

Alumina-supported iron oxides have been prepared by incipient wetness impregnation method and employed for orthohydrogen to parahydrogen spin conversion at cryogenic temperature. These materials were characterized using a series of characterization techniques such as SEM, XRD, Raman and in situ FTIR spectroscopy. The spin conversion was investigated at low temperature by a batch mode of operation. The in situ FTIR spectra were collected in a transmission mode to obtain the spin conversion. While the iron oxide was highly dispersed over alumina support at low loading percent, a rodlike crystallite of iron oxide was formed at high loading percent. The 10 and 20 wt% iron oxides on alumina were proved to be the most active catalysts. The spin conversion process was very slow and time-dependent. It was concluded that the spin conversion was a function of various factors including the iron oxide loading percent, calcination temperature, and different supports.     

Dispersant-assisted hydrothermal synthesis of MnZn ferrites from raw oxides

MnZn-ferrite powders were prepared using hydrothermal syntheses of a homogenous mixture of the raw oxides, i.e., Fe₂O₃, ZnO and Mn₃O₄, at 280°C in air. The hydrothermal synthesis was performed in the presence of various amounts of an anionic dispersant. The final results of the hydrothermal reaction between the raw oxides were fine powders with a heterogeneous phase composition mostly composed of iron oxide and spinel products. The composition of the spinel products depended to a great extent on the amount of dispersant in the hydrothermally treated suspension. Without the dispersant addition, Zn ferrite and Zn manganate spinel products were formed, while in the presence of the dispersant, the ferrimagnetic MnZn-ferrite spinel product was obtained. A larger amount of the dispersant in the reaction mixture increased the conversion rate of the raw oxides into the Mn,Zn ferrite spinel product. Additionally, polyvinyl alcohol (PVA) was used during the hydrothermal synthesis in order to bind the chlorine impurities, introduced into the hydrothermally prepared powder with the raw Fe₂O₃. With the PVA burnout, the level of chlorine impurities was decreased by approximately 50%.     

Comparative study of the surface oxidation behaviour of amorphous and crystallized Fe67Co18B14Si1 metallic glass

The oxidation of amorphous and crystallized specimens of the metallic glass Fe₆₇Co₁₈B₁₄Si₁ were studied under controlled conditions using Auger electron spectroscopy and X-ray photo-electron spectroscopy. The different oxides were characterized as boron and iron oxide forming in that sequence for both the amorphous and crystalline specimens. No cobalt oxide was detected. A higher oxygen uptake was measured for the amorphous than for the crystalline specimens. Comparison with the literature shows that the difference in oxygen uptake is heavily composition dependent. The oxidation of the amorphous specimens constitutes a driving force for boron to segregate to the surface and causes a boron enriched layer. Segregation of boron and cobalt occurs during annealing and the sequence of the enriched layers is influenced by environmental conditions.     

Phase composition of ceramics in systems with oxides of rare-earth elements, manganese, and titanium

Ceramics based on systems with oxides of rare-earth elements (REE: Y₂O₃, Sm₂O₃, Gd₂O₃), manganese, and titanium, considered as hosts for immobilization of REE- and actinide-containing radioactive wastes (RAW), were prepared by cold pressing and sintering at 1300–1400°C, and also by plasma treatment. Phases of the pyrochlore-murataite series are prevalent in the ceramics, and perovskite-pyrophanite-type phases are impurity phases, as well as the hibonite-loveringite- and garnet-type phases revealed in the ceramics prepared with addition of iron and aluminum oxides. The formation of murataite or, more precisely, of structures consisting of murataite and pyrochlore modules is more typical of the yttrium-containing systems. With an increase in the radius of the REE ion, the tendency toward formation of pyrochlore-type phases is enhanced, and the presence of large REE cations (La) stimulates formation of a perovskite-type phase.     

Dielectric behaviour of MgFe2O4 prepared from chemically beneficiated iron ore rejects

Chemically beneficiated high silica/alumina iron ore rejects (27–76% Fe₂O₃) were used to synthesize iron oxides of purity 96–98% with SiO₂/Al₂O₃ ratio reduced to 0.03. The major impurities on chemical beneficiations were Al, Si, and Mn in the range 2–3%. A 99.73% purity Fe₂O₃ was also prepared by solvent extraction method using methyl isobutyl ketone (MIBK) from the acid extracts of the ore rejects. The magnesium ferrite, MgFe₂O₄, prepared from these synthetic iron oxides showed high resistivity of ∼ 10⁸ ohm cm. All ferrites showed saturation magnetization, 4πM_s, in the narrow range of 900–1200 Gauss and the Curie temperature,T, _cof all these fell within a small limit of 670 ± 30 K. All ferrites had low dielectric constants (ε′), 12–15, and low dielectric loss, tan δ, which decreased with the increase in frequency indicating a normal dielectric dispersion found in ferrites. The presence of insignificant amount of polarizable Fe²⁺ ions can be attributed to their high resistances and low dielectric constants. Impurities inherent in the samples had no marked influence on the electrical properties of the ferrites prepared from the iron ore rejects, suggesting the possibility of formation of ferrite of constant composition, MgFe₂O₄, of low magnetic and dielectric losses at lower temperatures of 1000°C by ceramic technique.     

Grafted NiO on natural olivine for dry reforming of methane

Natural olivine is used for gasification of biomass in a fluidised bed. Characterisations by X-raydiffraction and electron microscopies (SEM and TEM) have proved the presence of a (Mg,Fe)₂SiO₄ structure (Mg/Fe ratio: 9/1) with a rather broad distribution in elemental composition. Temperature programmed reduction has revealed equally the presence of iron oxides outside of this structure. The nature of free iron oxides can be both modified by increasing the temperature of calcination and confirmed by measurements of magnetism.

The introduction of nickel oxide upon natural olivine is obtained by impregnation with a nitrate salt. The type of interaction of nickel oxide with olivine is different depending upon the preparationmethod and the calcination temperature. For calcination at 1100 ºC, the effects of the amount ofNiO and the number of impregnation have been studied. At a high temperature of calcination (1400 ºC), NiO is integrated into the olivine structure and the amount of free iron increases. Integrated NiO on olivine is non-reducible, resulting in an inactive catalyst. At lower calcination temperatures grafted NiO is formed, a species which is reduced under catalytic test conditions without aggregation of particles. A single impregnation of nickel (5.5 wt% of NiO) gives a stable catalyst activated directly under reaction conditions (CH₄ + CO₂) yielding 96% CO and 76% H₂. Catalysts with lower amounts of NiO or a double impregnation of nickel salt lead to a less stable system.

Analysis reveals that no change in olivine structure nor size of nickel deposit occurs under test conditions. Equally there are no carbon deposits formed on these catalysts. A model of the evolution of each catalytic system arising from the different preparation methods is proposed. The observed deactivation of such catalysts is attributed to the increase in the amount of free iron, which favours the oxidative properties of the catalytic system.     

Synthesis and photocatalytic activity of nano-sized iron oxides

Nano-sized iron oxide powder with average crystallite sizes 35, 100 and 150 nm was prepared by thermal evaporation and co-precipitation techniques. The synthesized powders were characterized by X-ray diffraction analysis technique, transmission electron microscope (TEM) and scanning electron microscope (SEM). The prepared powders were tested as catalysts for the photo catalytic decomposition of Congo red dye. The effect of crystal size of iron oxides on the rate of decomposition of Congo red dye was investigated in visible light as well as in the absence of light. The experimental results show that both iron oxides with crystallite size 35 and 150 nm cause complete decomposition of Congo red dye while iron oxide particles with crystallite size 100 nm were unable to decompose the dye.     

Characterization of nano-crystalline Mg–Ni–Al hydrotalcite derived mixed oxides as hydrogen adsorbent

A promising energy storage material containing magnesium, nickel and aluminum metals has been synthesized using conventional coprecipitation method. The physio-chemical properties, morphology and microstructure of hydrotalcite based mixed oxides (MNAM) have been characterized using ICP-MS, XRD, BET, FESEM and TEM techniques. The characterizations revealed that the adsorbent are highly dispersed, poly crystalline, homogenously distributed and interactive. Temperature programmed techniques have been used to explore the sorption capacities of mixed oxides. Nano-crystalline mesoporous and interactive reduced mixed oxides exhibit a 3.9 wt% H₂ adsorption capacity at ambient conditions. Temperature programmed desorption study predicted a desorption capacity of 1.9 wt% H₂. Different hydrogen adsorbed phases of magnesium and nickel have been characterized using HRTEM, Raman and FT-IR techniques.     

Cubic and tetragonal maghemite formation inside carbon nanotubes under chemical vapor deposition process conditions

Abstract

Carbon nanotubes filled with iron oxides can be a promising material for medicine. In this paper, carbon nanotubes containing iron oxides were synthesized by chemical vapor deposition method. Cubic and tetragonal modifications of maghemite Fe₂O₃ were found inside the nanotubes along with α- and γ-phases of iron and iron carbides by electron microscopy studies. Twins were identified in the tetragonal maghemite with the {103} twinning plane.