Effect of ferrous/ferric ions molar ratio on reaction mechanism for hydrothermal synthesis of magnetite nanoparticles

Magnetite nanoparticles were prepared by hydrothermal synthesis under various initial ferrous/ferric molar ratios without adding any oxidizing and reducing agents in order to clarify effects of the molar ratio on the reaction mechanism for the formation of magnetite nanoparticles. The magnetite nanoparticles prepared were characterized by a scanning electron microscope, powder X-ray diffractometer, and superconducting quantum interference device (SQUID). At the molar ratio corresponding to the stoichiometric ratio in the synthesis reaction of magnetite from ferrous hydroxide and goethite, the nucleation of magnetite crystals progressed rapidly in an initial stage of the hydrothermal synthesis, resulting in formation of the magnetite nanoparticles having a smaller size and a lower crystallinity. On the other hand, at higher molar ratios, the particle size and crystallinity increased with increasing molar ratio because using surplus ferrous hydroxide the crystallites of magnetite nanoparticles grew up slowly under hydrothermal conditions according to the Schikorr reaction. The magnetite nanoparticles prepared under various molar ratios had good magnetic properties regardless of the molar ratio.     

Size control of magnetite nanoparticles by organic solvent-free chemical coprecipitation at room temperature

This study provides a facile single-step coprecipitation method for preparing size-controlled high crystalline magnetite nanoparticles in water system without using any organic solvents. In this method, an iron ions solution and an alkaline solution are simply mixed at room temperature without using any additional heating treatment. The size of obtained magnetite nanoparticles greatly depended on the coexisting anionic species in the starting solution because the coexisting anions greatly influenced both the formation of crystal nuclei and the dispersion stabilisation of formed precipitates. The size control of magnetite nanoparticles having high crystallinity and ferromagnetic property could be successfully achieved by using the effects of coexisting anions. For synthesising finer magnetite nanoparticles, the presence of lactate ion in the starting solution was effective, and coarser ones could be synthesised under higher ferrous/ferric ions molar ratios.     

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.     

An experimental investigation of aqueous-phase synthesis of magnetite nanoparticles via mechanochemical reduction of goethite

A newly developed mechanochemical process for the simple aqueous phase synthesis of crystalline magnetite nanoparticles has been experimentally investigated. In this process, a suspension of ferric hydroxide precursor is milled at room temperature using a horizontal tumbling ball mill consisting of a stainless steel pot and balls. Ferric hydroxide is transformed to magnetite without the use of a reducing agent. As a model starting material for the investigation, a pH-adjusted suspension of crystalline goethite was used. As the milling time increased, goethite disappeared along with the simultaneous formation of magnetite. A single phase of magnetite was obtained after 16 h of milling. A reaction mechanism for the formation of magnetite has been proposed based on oxidation–reduction reactions, in which the corrosion of iron in the pot and balls plays an important role. Free electrons are generated by the release of ferrous ions from the stainless steel in an anodic reaction, which then reduce goethite to ferrous hydroxide in a cathodic reaction. The solid phase reaction between ferrous hydroxide and goethite produces magnetite. Not only could the mechanochemical effect induced by the collision of balls accelerate the corrosion even under alkaline conditions, it can also promote the formation and crystallization of magnetite.     

In Situ Synthesis of Silica-Coated Magnetite Nanoparticles by Reverse Coprecipitation Method

Silica-coated magnetite nanoparticles were synthesized by reverse coprecipitation of Fe²⁺ and Fe³⁺ with sodium hydroxide in the presence of sodium silicate solution. Effect of reaction conditions and various amounts of sodium silicate solution on the powder particle characteristics was investigated by X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), Fourier transform infrared spectroscopy (FT-IR), laser particle size analyzer (LPSA), streaming current potential and vibrating sample magnetometer (VSM) techniques. Also, stability of silica-coated magnetite nanoparticles in the acidic condition has been studied by titration method. FT-IR results revealed that silica chemisorbed on the surface of magnetite nanoparticles by Fe?CO?CSi bonds. Analysis of the XRD patterns confirmed the formation of magnetite having spinel structure in the presence of sodium silicate solution. FE-SEM micrographs revealed that the mean particle size of spherical magnetite decreased from 50 to less than 25?nm by adding sodium silicate solution. Agglomeration declined when the volume ratio of sodium silicate/sodium hydroxide was 0.1. This was attributed to the coating of magnetite nanoparticles by silica. Coating of magnetite by silica prevents the formation of hydrogen bondings between magnetite and water molecules. Further increase in the sodium silicate concentration revealed a reverse effect.     

Solution phase synthesis of t-ZrO2 nanoparticles in ZrO2–SiO2 mixed oxide

A solution phase synthesis is used to prepare tetragonal zirconia nanoparticles. Ammonia solution and zirconia precursor solution were prepared separately and then mixed together to get colloidal hydroxide precipitate. The colloidal hydroxide was treated with silica sol and then the precipitate was separated and dried. The dried powder was then calcined at different temperatures for 2 and 6?h. The mean particle size of the powder calcined at 1000°C was found to be around 8–10?nm. The thermal analysis of dried powder indicates the formation of bulk tetragonal zirconia phase at 780°C. X-ray diffraction (XRD) and infrared spectroscopic analyses confirm the presence of 100% tetragonal zirconia phase in the powder calcined at 1000°C. The addition of silica stabilised the tetragonal zirconia phase. It is advantageous to use this powder as catalyst or catalyst support that operates at high temperatures.     

Fe-EDTA Thermal Decomposition,a Route to Highly Crystalline Hematite (Alpha Fe2O3) Nanoparticle Synthesis

In this study, we develop an experimental procedure to synthesize hematite nanoparticles by hydrothermal decomposition of Fe-EDTA complex in the presence of hydrogen peroxide, starting from ferric ammonium sulfate and Na ₄ EDTA as main precursors. The product was investigated by X-ray diffraction, scaning electron microscopy, dispersive X-ray spectroscopy, magnetic measurements, and UV-vis optical absorption measurements. The size of nanoparticles was determined to be 42 nm evaluated by XRD patterns using the Scherrer equation. This method allowed the formation of pure hematite nanoparticles with good and stable crystallographic characteristics. This procedure can be an effective method for synthesizing hematite nanoparticles exhibiting good crystallinity, stoichiometry, magnetic, and optical band gap properties. A possible mechanism for the formation of hematite nanocrystals was suggested.     

Synthesis and physical characterization of magnetite nanoparticles for biomedical applications

Iron oxide nanoparticles for biomedical applications in the size range of 15–130 nm were prepared by either oxidative hydrolysis of ferrous sulfate with KOH or precipitation from ferrous/ferric chloride solutions. The magnetite particle size is controlled by variation of pH and temperature. The synthesized magnetite nanoparticles are partially oxidized as signaled by ferrous concentrations of below 24 wt% Fe²⁺ and lattice parameters of a₀ ≤ 8.39 Å which are smaller compared to 8.39 Å for stoichiometric magnetite. The extend of oxidation increases with decreasing particle size. Heating at 150–350 °C topotactically transforms the magnetite nanoparticles into stoichiometric tetragonal maghemite (ferrous ion concentration c_Fe²⁺=0 and a₀ = 8.34 Å) without significant particle growth. The magnetite–maghemite transformation is studied with thermal analysis, XRD and IR spectroscopy. The saturation magnetizations of the magnetite and maghemite particles decrease with decreasing particle size. The variation of M_s with particle size is interpreted using a magnetic core–shell particle model. Magnetite particles with d ≤ 16 nm show superparamagnetic behavior at room temperature whereas particles with diameter >16 nm display hysteresis behavior. These particles are candidates for biomedical applications, e.g. controlled drug release or hyperthermia.     

The low temperature synthesis and characterization of Bi3.25La0.75Ti3O12 powder by hydroxide coprecipitation in aqueous medium

The fine powders of Bi_3.25La_0.75Ti₃O₁₂ (BLT) were prepared by coprecipitaton method in aqueous medium at low temperature. The differential thermal analysis (DTA), thermo-gravimetric analysis (TG) and X-ray diffraction (XRD) were employed to evaluate the phase formation of BLT and TEM was used to characterize and observe the particle size and morphology of BLT powder obtained. The results show that the bismuth layer perovskite phase of BLT can begin to form at as low as 500 °C by the coprecipitation method. When the precipitates obtained were calcined at 600 °C for 2 h, the mono-phase and perfect BLT powder was synthesized. The BLT powder obtained consists of irregular or plate-like particles which are less than about 100 nm and is nearly aggregate free.     

Inorganic Magnetite Precipitation at 25?��C: A Low-Cost Inorganic Coprecipitation Method

An easy, low-cost coprecipitation method to inorganically produce magnetite nanoparticles from solutions, in free-drift experiments, under anoxic conditions, at 25?°C and 1 atm pressure is here presented. By using this method, pure magnetite is obtained as the final solid, which shows the typical magnetic properties and thermal stability behavior of magnetite produced by other methods. The size of the magnetite crystals produced by the present method varies from relatively big sizes (200?C300 nm), to sizes within the single magnetic domain range, just depending on the incubation time. The solution from which magnetite precipitates may be representative of certain natural environments where bacteria that produce magnetite may live and, thus, our magnetite may be used as an inorganic reference to compare to biologically produced magnetites.     

TiO2 nanofibre-assisted photodecomposition of Rhodamine B from aqueous solution

Using liquid phase deposition method on cellulose substrate, TiO₂ nanofibres were prepared with TiCl₄ as a precursor. TiO₂ nanofibres were obtained after heat treatment of the cellulose template. The remaining product was composed of micron-size TiO₂ fibres with a nanofiber microstructure. It is shown that nanofibres are formed through the aggregation of TiO₂ nanoparticles. X-ray diffraction analysis of the as-prepared solution indicates the formation of crystalline TiO₂ anatase phase. EDX analysis was employed to measure the adsorbed mass of TiO₂ on cellulose substrate. The effect of deposition time on the growth and morphology was investigated by scanning electron microscopy. Transmission electron microscopy studies demonstrate fine microstructures composed of 10–15?nm?nanoparticles. Surface area of the TiO₂ fibres, measured by Brunauer, Emmett and Teller analysis, was about 104?m²?g^?1. Photodegradation of Rhodamine B as a standard dye shows that the prepared samples have a high photocatalytic activity due to large surface area.     

Synthesis of WO3 in nanoscale with the usage of sucrose ester microemulsion and CTAB micelle solution

WO₃ nanoparticles were successfully prepared using first the low temperature hydrolysis method and second the chemical reaction method in water-in-oil sucrose ester microemulsion consisting of S1570, 1-butanol, tetradecane and aqueous phase. In this study WO₃ nanoparticles also were prepared using the CTAB micelle solution. The resultant WO₃ nanoparticles have been investigated with X-ray diffraction (XRD), transmission electron microscopy (TEM), variable pressure scanning electron microscope (SEM) equipped with energy dispersive X-ray analysis (EDX) and X-ray photoelectron spectroscopy (XPS). The shape and particles size of the resultant WO₃ nanoparticles from both methods in sucrose ester microemulsion show similar spherical shape and size range between 10 and 50 nm. The WO₃ nanoparticles prepared with the CTAB micelle solution show spherical shape with the size range average of 25-50 nm.     

Nitric oxide donor superparamagnetic iron oxide nanoparticles

This work reports a new strategy for delivering nitric oxide (NO), based on magnetic nanoparticles (MNPs), with great potential for biomedical applications. Water-soluble magnetic nanoparticles were prepared through a co-precipitation method by using ferrous and ferric chlorides in acidic solution, followed by a mercaptosuccinic acid (MSA) coating. The thiolated nanoparticles (SH-NPs) were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), transmission electron microscopy (TEM), and vibrating sample magnetometry (VSM). The results showed that the SH-NPs have a mean diameter of 10 nm and display superparamagnetic behavior at room temperature. Free thiol groups on the magnetite surface were nitrosated through the addition of an acidified nitrite solution, yielding nitrosated magnetic nanoparticles (SNO-NPs). The amount of NO covalently bound to the nanoparticles surface was evaluated by chemiluminescense. The SNO-NPs spontaneously released NO in aqueous solution at levels required for biomedical applications. This new magnetic NO-delivery vehicle has a great potential to generate desired amounts of NO directed to the target location.     

The one-pot synthesis of dextran-based nanoparticles and their application in in-situ fabrication of dextran-magnetite nanocomposites

The dextran-based nanoparticles containing carboxyl groups were synthesized by a one-pot approach, without using any organic solvents and surfactants. The resultant dextran-based nanoparticles was used as a host for the growing and organization of Fe(3)O(4) nanoparticles. The approach consists of the mixture of ferrous/ferric ions aqueous solution and host nanoparticles and subsequent coprecipitation of ferrous/ferric ions in basic medium. The magnetic nanocomposite material obtained was characterized using transmission electron microscopy (TEM), dynamic light scattering (DLS), thermogravimetric analysis (TGA), X-ray diffraction techniques (XRD) and vibrating sample magnetometry (VSM). The data demonstrate that the carboxyls which can capture cationic ferrous/ferric by electronic interaction in the dextran-based hosts plays a crucial role in fabricating nanocomposites with a homogeneous spatial distribution of magnetite nanoparticles. The magnetic nanocomposites exhibit comparable saturation magnetizations to that of reported Fe(3)O(4) nanoparticles, and therefore display great potential in a large scope of biomedical fields.     

纳米磁性四氧化三铁的制备及表征

采用化学共沉淀法制备了纳米磁性Fe3O4粒子.选用NH3@H2O作为沉淀剂,加入到Fe2+和Fe3+的混合溶液中,制得了纳米磁性Fe3O4粒子.考察了Fe2+和Fe3+溶液浓度、沉淀剂的浓度、Fe2+/Fe3+/OH-、温度及搅拌速度等因素对产物粒径及性能的影响,并对其进行了初步的性能表征.     

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.     

Mesoporous TiO2 thin films embedded with Au nanoparticles for the enhancement of the photocatalytic properties

Mesoporous TiO₂ thin films were prepared by hydrothermal-oxidation of titanium metal thin films, which were obtained by DC magnetron sputtering technique. Gold nanoparticles, which were prepared by reduction of HAuCl₄, were embedded into the holes of the mesoporous TiO₂ films by capillary method followed by annealing in air up to 400 °C. The size of pore of TiO₂ films is about 100 nm and that of Au nanoparticles is about 10 nm in average. The morphology of the films was analyzed by field emission scanning electron microscope (FE-SEM) and scanning probe microscopes (SPMs). Subsequently, the photocatalytic performances of the obtained nanosystems in the decomposition of methylene blue solution are discussed. The obtained results show that the dispersion of Au nanoparticles on the mesoporous TiO2 matrix will help enhancing the photocatalytic activity with respect to pure TiO₂ under visible light irradiation.     

Synthesis and characterization of ultrafine poly(vinylalcohol phosphate) coated magnetite nanoparticles

Nanosized magnetite (Fe3O4) particles showing superparamagnetism at room temperature have been prepared by controlled coprecipitation of Fe2+ and Fe3+ in presence of highly hydrophilic poly(vinylalcohol phosphate)(PVAP). The impact of polymer concentration on particle size, size distribution, colloidal stability, and magnetic property has been extensively studied. The aqueous suspension of magnetite, prepared using 1% PVAP solution is stable for four weeks at pH 5-8. X-ray diffractograms show the formation of nanocrystalline inverse spinel phase magnetite. Transmission Electron Microscopy confirmed well dispersed cubic magnetite particles of size of about 5.8 nm. Dynamic Light Scattering measurement shows narrow distribution of hydrodynamic size of particle aggregates. Infrared spectra of samples show strong Fe--O--P bond on the oxide surface. UV-visible studies show aqueous dispersion of magnetite formed by using 1% PVAP solution is stable at least for four weeks without any detoriation of particle size. Magnetization measurements at room temperature show superparamagnetic nature of polymer coated magnetite nanoparticles.     

Novel mechanochemical process for synthesis of magnetite nanoparticles using coprecipitation method

A novel coprecipitation method using a high mechanical energy field as the synthesis reaction system of magnetite (Fe₃O₄) has been developed for preparing the superparamagnetic Fe₃O₄ nanoparticles with high crystallinity in water system. In the synthesis process, the suspension containing the precipitates of ferrous hydroxide and goethite was treated in a tumbling ball mill under a cooling condition. The mechanical energy generated by collision of ball media promoted the Fe₃O₄ formation reaction and simultaneously crystallized the formed Fe₃O₄ nanoparticles without using any conventional heating techniques by means of the mechanochemical effect. The collision energy of ball media was numerically analyzed by discrete element simulation of their motion in the ball mill. Size, crystallinity and magnetization of the Fe₃O₄ nanoparticles obtained under different ball-milling conditions were almost the same regardless of the amount of the collision energy. However, the reaction rate of Fe₃O₄ formation increased with the collision energy, which was analogous to increase of the reaction rate caused by increase of the heat energy applied to the reaction system. The reaction rate depended strongly on the number of collisions with the energy larger than a threshold value corresponding to the activation energy in this reaction system.     

Surface mechanical attrition treatment-induced dissolution of Cu4Ti precipitates in Cu–4wt-%Ti alloy

ABSTRACT

The microstructural evolution of an overaged Cu-4wt-%Ti alloy associated with surface mechanical attrition treatment (SMAT) has been studied by X-ray diffraction, scanning electron microscope and transmission electron microscopy. The results show that β-Cu₄Ti precipitates in the topmost surface layer were dissolved after SMAT, and Cu solid solution phase with a fine grain size of approximately 25?nm was observed. Dislocation activities were the main deformation mechanism of lamellar structure in the overaged Cu–4wt-%Ti alloy. The twinning in lamellar Cu phase was inhibited by the β-Cu₄Ti precipitates.