Magnetic properties of magnetite nanoparticles synthesized by forced hydrolysis

We report the synthesis of superparamagnetic nanoparticles of iron oxide in magnetite phase with diameters of approximately 15 nm. Nanoparticles of magnetite were synthesized by forced hydrolysis method, controlling the oxidation with a nitrogen atmosphere during the synthesis. Nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Mössbauer spectroscopy and vibrating sample magnetometry. Quantitative analysis of crystalline phases was done by performing Rietveld refinement of the XRD profiles. In order to obtain nanometers sizes of magnetite phase solely, the parameters of formation such a pH and molar concentration were analyzed and determined by an equilibrium thermodynamics model with the chemical computer code MINTEQA [Allison Geoscience Consultants, Inc., HydroGeoLogic, Inc., MINTEQA2 for Windows, Equilibrium Speciation Model. Ver 1.5(2003)].     

Strengthening liberation and separation of magnetite ore via magnetic pulse pretreatment: An industrial test study

Performing ore pretreatment before grinding is particularly crucial for improving mineral liberation and conserving energy. This study proposed an innovative magnetic pulse pretreatment (MPP) technology that primarily used the magnetostrictive effect in an alternating magnetic field to enhance mineral liberation. The effect of MPP on the liberation degree and magnetite separation for magnetite ore were systematically investigated. The results show that the size and volume of the magnetic mineral particles in the ore due to the stretching effect of the alternating magnetic field resulted in microcracks at the interface between different minerals. Compared with the unpretreated process in an industrial test, increment in the −0.043 mm content of the ball mill discharge increased by 3.33 percentage points, increment in the liberation degree of magnetite across the entire particle size range increased by 5.82 percentage points, and increment in the iron concentrate grade increased by 1.22 percentage points, with an error range of 0.1%, due to MPP. The industrial application of MPP brings an enormous economic benefit potential to iron ore utilization.     

Continuous synthesis of magnetite nanoparticles in supercritical methanol

Magnetite (Fe₃O₄) nanoparticles are synthesized continuously in supercritical methanol (scMeOH) without using reducing agents at 30 MPa, 400 °C and a residence time of 38 s. XRD analysis reveals that particles synthesized in scMeOH retain magnetite crystalline structure while particles synthesized in supercritical water retain hematite (α-Fe₂O₃) crystalline structure. The scMeOH acts both as a reaction medium and a reducing agent. The magnetite nanoparticles are spherical in shape with an average diameter of 21 ± 2 nm, as measured using SEM and TEM. The saturation magnetization of the magnetite nanoparticle is 76.6 emu/g.     

Mechanochemical preparation of magnetite nanoparticles by coprecipitation

A novel simple process for preparing magnetite (Fe₃O₄) nanoparticles by a coprecipitation route without using any additives (e.g., surfactant and oxidizing and reducing agents) has been developed. In this method, a cooled ball mill was used as a synthesis reaction field in order to inhibit progress of both the synthesis reaction and the particle growth by heat energy. The Fe₃O₄ nanoparticles were formed by ball-milling of the starting suspension consisting of ferrous hydroxide and goethite colloids, and the crystallization was simultaneously progressed without heating. The obtained nanoparticles were then characterized through the SEM observation, XRD analysis, EDS analysis and oxidation-reduction titration, and the magnetic properties were measured with a SQUID magnetometer. This preparation process can provide successfully the superparamagnetic Fe₃O₄ nanoparticles of about 10 nm with high crystallinity and saturation magnetization by mechanochemical effect.     

Size control of nanocrystalline magnetite thin films containing a small amount of Ge

This study investigated the preparation and particle size control of nanocrystalline magnetite (Fe₃O₄) containing a small amount of Ge. Thin films were prepared by radio-frequency sputtering with a composite target of Ge chips set on a Fe₃O₄ compound target in a mixed atmosphere of Ar and O₂. X-ray diffraction revealed that the diffraction peak of magnetite gradually broadened as the oxygen ratio increased, with the mean grain size ranging from 26 to 2 nm. Transmission electron microscopy also revealed that the magnetite structurally changed from polycrystalline single phase to isolated granular nanocrystals. Magnetization at 8 × 10⁵ A/m was monotonically reduced from 0.32 to 0.04 T, and coercivity was monotonically reduced from 4.2 × 10⁴ to 2.1 × 10³ A/m with increasing the oxygen ratio from 0 to 0.4%.     

Magnetic composites of conducting polyaniline/nano-sized magnetite and their magnetorheology

Magnetorheological (MR) fluids, composed of colloidal particles dispersed in a carrier liquid, possess controllable rheological properties by an external magnetic field, showing dramatic changes of yield stress and shear viscosity caused by transformation between solid-like to liquid-like state. As a new MR material, we synthesized conducting polyaniline (PANI)/nano-sized Fe₃O₄ composites which could be adopted as a dispersed phase of MR fluids. Composites containing nano-sized Fe₃O₄ were synthesized via a chemical reaction method. Microstructure of the PANI/Fe₃O₄ composites was characterized by SEM and XRD. Magnetic property of the composites was characterized by VSM. Furthermore, MR fluid based on PANI/Fe₃O₄ composites was investigated using a rotational rheometer equipped with a magnetic field generator, exhibiting a typical MR performance of which shear stress of the fluids increased abruptly under magnetic fields.     

Phosphate removal from solution using steel slag through magnetic separation

Steel slag with magnetic separation was used to remove phosphate from aqueous solutions. The influence of adsorbent dose, pH, and temperature on phosphate removal was investigated in a series of batch experiments. Phosphate removal increased with the increasing temperature, adsorbent dose and decreased with increasing initial phosphate concentrations, while it was at its peak at pH of 5.5. The phosphate removal predominantly occurred through ion exchange. The specific surface area of the steel slag was 2.09m2/g. The adsorption of phosphate followed both Langmuir and Freundlich isotherms. The maximum adsorption capacity of the steel slag was 5.3mgP/g. The removal rates of total phosphorus (TP) and dissolved phosphorus (DP) from secondary effluents were 62-79% and 71-82%, respectively. Due to their low cost and high capability, it was concluded that the steel slag may be an efficient adsorbent to remove phosphate both from solution and wastewater.     

Solvothermal synthesis and characterization of functionalized graphene sheets (FGSs)/magnetite hybrids

Novel functionalized graphene sheets (FGSs)/Fe₃O₄ hybrids were synthesized through a facile one-step solvothermal method using FeCl₃ as iron source, ethylene glycol as the reducing agent and graphene nanosheets as templates. The morphology, composition and phase structure of as-prepared hybrid materials were characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and transmission electron microscopy (TEM). These results showed that denseness, size and crystallinity of magnetite can be altered by controlling the reaction parameters. Magnetization measurement indicated that both coercivity and saturation magnetization increased linearly with increasing magnetite concentration in hybrid materials. The measured relative complex permittivity indicated that a high resistivity existed in the FGSs/Fe₃O₄ inorganic hybrids. The magnetic loss was caused mainly by ferromagnetic natural resonance, which is in agreement with the Kittel equation. The novel inorganic hybrid materials are believed to have potential applications in the microwave absorbing performances.     

The effect of reaction temperature on the particle size, structure and magnetic properties of coprecipitated CoFe2O4 nanoparticles

Magnetic nanoparticles of cobalt ferrite have been synthesized at different temperatures without any subsequent heat treatment. The particle size, crystal structure and magnetic properties of as-synthesized particles were investigated by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, Raman spectroscopy and vibrating sample magnetometer. The nanoparticles are of cubic spinel structure and equiaxial shape. The average size of nanoparticles increases with the increase of reaction temperature. Magnetic properties of nanoparticles show strong dependence on the particle size. A maximum coercivity of 3267 Oe and a maximum remanence ratio of 0.58 are obtained from the sample synthesized at 80 °C.     

Preparation and application of calix[4]arene-grafted magnetite nanoparticles for removal of dichromate anions

Magnetic Fe₃O₄ nanoparticles were prepared by the chemical co-precipitation of Fe(III) and Fe(II) ions. Then, the nanoparticles were modified directly by 3-aminopropyltrimethoxy silane (APTMS) to introduce reactive groups onto the particles' surface, and diester derivative of calix[4]arene was immobilized onto the surface of modified-Fe₃O₄ nanoparticles by aminolysis reaction. The prepared magnetite nanoparticles (Calix-GM) were characterized by a combination of IR, TGA and TEM analyses. The extraction properties of the new material toward dichromate anions were also studied. It was observed that the prepared magnetite nanoparticles were an effective extractant for the removal of dichromate anions at pH 2.5–4.5.     

Comparison of two methods for removal of arsenic from potable water

Arsenic, well known of its toxicity, is present in potable water in many areas in the world, as well as in underground water used for water supply in Vojvodina, a region in Serbia. Its removal from raw water is necessary before distribution. In this work two methods of arsenic removal from water are compared. First method is water ozonation by introducing ozone in water and then filtration. Second method is treatment of water in plasma reactor and then filtration. High efficiency of the second method was confirmed by low concentration of arsenic in filtrate (below detection limit).     

Effects of adsorbent dose, its particle size and initial arsenic concentration on the removal of arsenic, iron and manganese from simulated ground water by Fe3+ impregnated activated carbon

This paper presents the observations of the study on arsenic removal from a contaminated ground water (simulated) by adsorption onto Fe³⁺ impregnated granular activated carbon (GAC-Fe). Fe²⁺, Fe³⁺ and Mn²⁺ have also been considered along with arsenic species in the water sample. Similar study has also been done with untreated granular activated carbon (GAC) for comparison. The effects of adsorbent dose, particle size of adsorbent and initial arsenic concentration on the removal of As(T), As(III), As(V), Fe²⁺, Fe³⁺ and Mn²⁺ have been discussed. Under the experimental conditions, the optimum adsorbent doses for GAC-Fe and GAC have been found to be 8 g/l and 24 g/l, respectively with an agitation time of 15 h. Particle size of the adsorbents (both GAC and GAC-Fe) has shown negligible effect on the removal of arsenic and Fe species. However, for Mn removal the effect of adsorbent particle size is comparatively more. Percentage removal of As(T), As(V) and As(III) increase with the decrease in initial arsenic concentration (As₀). However, the increase in percentage removal of all the arsenic species with decrease in As₀ are less for higher value of As₀ (3000–500 ppb) than those of the lower value of As₀ (500–10 ppb). The % removal of As(T), As(III), As(V), Fe, and Mn were 95%, 92.4%, 97.6%, 99% and 41.2%, respectively when 8 g/l GAC-Fe was used at the As₀ value of 200 ppb. However, for GAC these values were 55.5%, 44%, 71%, 98% and 97%. The pH and temperature of the study were 7 ± 0.1 and 30 ± 1 °C, respectively.     

Studies on the removal of arsenic (III) from water by a novel hybrid material

The present work provides a method for removal of the arsenic (III) from water. An ion-exchanger hybrid material zirconium (IV) oxide-ethanolamine (ZrO-EA) is synthesized and characterized which is subsequently used for the removal of selective arsenic (III) from water containing 10,50,100 mg/L of arsenic (III) solution. The probable practical application for arsenic removal from water by this material has also been studied. The various parameters affecting the removal process like initial concentration of As (III), adsorbent dose, contact time, temperature, ionic strength, and pH are investigated. From the data of results, it is indicated that, the adsorbent dose of 0.7 mg/L, contact time 50 min after which the adsorption process comes to equilibrium, temperature (25 ± 2), solution pH (5-7), which are the optimum conditions for adsorption. The typical adsorption isotherms are calculated to know the suitability of the process. The column studies showed 98% recovery of arsenic from water especially at low concentration of arsenic in water samples.     

Study of arsenic(V) adsorption on bone char from aqueous solution

Arsenic is a toxic element and may be found in natural waters as well as in industrial waters. Leaching of arsenic from industrial wastewater into groundwater may cause significant contamination, which requires proper treatment before its use as drinking water. The present study described the removal of As(V) on bone char in batch studies conducted as a function of pH, dosage of adsorbent, and contact time. Kinetics revealed that uptake of As(V) ion by bone char was very rapid in the first 30min and equilibrium time was independent of initial As(V) concentration. And the adsorption process followed a first-order kinetics equation. The arsenic removal was strongly dependent on pH and dosage of adsorbent. Fourier transform infrared spectra of bone char before and after As(V) adsorption demonstrated that Ca-OH functional group plays an important role for As(V) ions removal, and the mechanisms of the removal of As(V) on bone char was complex mechanism where both co-precipitation and ion exchange. The results suggested that bone char can be used effectively for the removal of As(V) ion from aqueous solution.     

The role of functionalised multiwalled carbon nanotubes based supercapacitor for arsenic removal and desalination of sea water

In order to investigate the simultaneous adsorption property of functionalised multiwalled carbon nanotubes (MWNTs) for sodium and arsenic, a new type of carbon fabric supported functionalised MWNTs (f-MWNTs) based supercapacitor was developed. In addition, this setup was tested for desalination of sea water. MWNTs were synthesised by chemical vapour deposition technique and purified, followed by functionalisation. MWNTs were characterised by different techniques. Performance of supercapacitor-based water filter was analysed for the adsorption of high concentration of arsenic (trivalent and pentavalent) and sodium as well as for desalination of sea water by using cyclic voltametry and inductively coupled plasma-optical emission spectroscopy techniques. Adsorption isotherms and kinetic characteristics were studied for the simultaneous removal of sodium and arsenic. High desalination (removal of sodium and magnesium) efficiency of sea water and cyclic repeatability for simultaneous removal of arsenic (arsenate and arsenite) and sodium have been demonstrated in this study. Easy handling and flexibility of this new type of electrodes-based setup provides a platform for the development of portable water filter.     

Effect of grain size on the Néel temperature of nanocrystalline nickel ferrite

Thermally induced changes of nanocrystalline NiFe₂O₄ spinel synthesized by sol-gel auto-ignition method are investigated using X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and magnetization measurements (VSM). The average grain size of NiFe₂O₄ increases from about 29 to 50 nm as the calcination temperature increases from 500 to 1000 °C. The IR spectra show the absorption bands corresponding to stretching vibrations of tetrahedral and octahedral bonds. The Néel temperature of NiFe₂O₄ for various grain sizes were determined by the direct measurement of magnetization.     

Novel environmentally friendly synthesis of superparamagnetic magnetite nanoparticles using mechanochemical effect

A novel method for synthesizing superparamagnetic magnetite nanoparticles in water system via coprecipitation under an environmentally friendly condition has been developed. In this method, an almost neutral suspension containing ferrous hydroxide and goethite is used as the starting suspension and subjected to a ball-milling treatment. The product was characterized by transmission electron microscopy, X-ray diffraction, energy dispersive X-ray spectroscopy, dynamic light scattering, superconducting quantum interference device magnetometry, and Mössbauer spectroscopy. The mechanochemical effect generated by the ball-milling treatment promoted the reaction between ferrous hydroxide and goethite even at room temperature, resulting in the formation of homogeneous magnetite nanoparticles. Simultaneously, it also contributed to crystallize the formed magnetite nanoparticles while inhibiting the particle growth. This resulted in the formation of ultrafine magnetite nanoparticles of about 10 nm having a single crystal structure. This method could provide ferromagnetic magnetite nanoparticles with superparamagnetism under the moderate condition without neither heating nor any additives such as surfactant and organic solvent.     

Removal of arsenic from water streams: an overview of available techniques

Arsenic poisoning has become one of the major environmental worries worldwide, as millions of people, which have been exposed to high arsenic concentrations (through contaminated drinking water), developed severe health problems. The high toxicity of this element made necessary the enforcement of stringent maximum allowable limits in drinking water. So, the development of novel techniques for its removal from aqueous streams is a very important issue. This paper offers an overview of geochemistry, distribution, sources, toxicity, regulations and applications of selected techniques for arsenic removal. The contribution briefly summarizes adsorption processes and mechanism of arsenic species removal from water streams by means of iron oxide/oxyhydroxide based materials. Sorption capacities of various sorbents (e.g. akaganeite, goethite, hydrous ferric oxide, iron oxide coated sand, Fe(III) loaded resin, granular ferric hydroxide, Ce(IV) doped iron oxide, natural iron ores, iron oxide coated cement, magnetically modified zeolite, Fe-hydroxide coated alumina) have been compared.     

Effective induction of magnetite on suspension magnetization roasting of hematite and reaction kinetics verification

Suspension magnetization roasting is an effective method for processing complex refractory iron ores. During industrial production, it was found that the separation index after magnetization roasting could be better optimized than with hematite alone; however, no pertinent study has been reported on the induction mechanism of magnetite during the reduction kinetics of hematite. In this study, the effect of magnetite on the reduction of hematite in the process of suspension magnetization roasting was investigated, and the mechanism of the induction reduction process was revealed by XRD, VSM and isothermal kinetic analyses. The results show that the addition of magnetite increases the conversion degree and reduction rate of hematite, and the magnetic conversion rate increases from 16% to 46% in the presence of 16% magnetite. The XRD and VSM analyses confirm that the addition of magnetite promotes the reduction speed of hematite and enhanced the magnetic properties of the roasting products. Isothermal kinetic analysis reveals that the initial stage of hematite reduction is controlled by the shrinking core model R₄, and the final stage is controlled by the three-dimensional diffusion model D₆. Compared with pure hematite, the pre-exponential factor and apparent activation energy of the reduction reaction decrease with the addition of 16% magnetite, which indicates the acceleration and promotion of magnetite on the reduction of hematite. This study provides important insights into the efficient and clean reduction of hematite with magnetite.     

Grain size effect on the R-phase transformation of nanocrystalline NiTi shape memory alloys

Development of nanoscale actuators and sensors in recent years calls for functional materials with small dimensions and high strengths. High strength nanocrystalline NiTi alloys which experience the R-phase transformation with a small thermal hysteresis are ideal candidates for these applications. To facilitate the application of the R-phase transformation in nanocrystalline NiTi alloys, this study investigated the effect of grain size on the R-phase transformation of a nanocrystalline Ti-50.2at.%Ni alloy. The nanometric grain size was created by severe cold deformation and low temperature anneal. It was found that in the recrystallized state, achieving nanoscale grain sizes (<100 nm) was effective in suppressing the B2→B19’ martensitic transformation and revealing the B2?R transformation. The B2?R transformation temperature was found to increase with the decreasing grain size within the range of 22–155 nm. The suppression of the B19’ martensite in nanograins is attributed to the limited space within the grains to allow the formation of self-accommodation structures to contain the large lattice distortion of the martensite.