Thermal oxide synthesis and characterization of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanorods and Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> nanowires

Fe₃O₄ nanorods and Fe₂O₃ nanowires have been synthesized through a simple thermal oxide reaction of Fe with C₂H₂O₄ solution at 200–600°C for 1 h in the air. The morphology and structure of Fe₃O₄ nanorods and Fe₂O₃ nanowires were detected with powder X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The influence of temperature on the morphology development was experimentally investigated. The results show that the polycrystals Fe₃O₄ nanorods with cubic structure and the average diameter of 0.5–0.8 μm grow after reaction at 200–500°C for 1 h in the air. When the temperature was 600°C, the samples completely became Fe₂O₃ nanowires with hexagonal structure. It was found that C₂H₂O₄ molecules had a significant effect on the formation of Fe₃O₄ nanorods. A possible mechanism was also proposed to account for the growth of these Fe₃O₄ nanorods. Supported by the Fund of Weinan Teacher’s University (Grant No. 08YKZ008), the National Natural Science Foundation of China (Grant No. 20573072) and the Doctoral Fund of Ministry of Education of China (Grant No. 20060718010)     

Facile Synthesis of Fe<Subscript>x</Subscript>O<Subscript>y</Subscript>/Ag Nanocomposites for Multifunctional and Efficient Catalytic Applications

In this study, the iron oxide/silver (Fe_xO_y/Ag) nanocomposite has been successfully prepared by a facile one-step method using goethite (α-FeOOH) rods as support. The diameter of the as-synthesized goethite rods was between 250 and 500 nm and the silver nanoparticles sizes were about 10–50 nm. By varying the concentrations, the Fe_xO_y/Ag nanocomposite with different Ag contents are successfully obtained. The Fe_xO_y/Ag nanocomposite was characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and energy dispersive spectroscopy, respectively. Due to the unique nanostructure, these nanocomposites can catalyze degradation of both aromatic nitro compounds and organic dyes only within a few minutes, which show high catalytic performance.     

Comparison of the Solubility of ZnFe<Subscript>2</Subscript>O<Subscript>4</Subscript>, Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> and Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> in High Temperature Water

As the solubility is a direct measure of stability, this study compares the solubilities of ZnFe₂O₄, Fe₃O₄ and Fe₂O₃ in high temperature water. Through literature analysis and formula derivation, it is shown that it is reasonable to assume ZnFe₂O₄ and Fe(OH)₃ coexist when ZnFe₂O₄ is dissolved in water. Results indicated that the solubility of ZnFe₂O₄ is much lower than that of Fe₂O₃ or Fe₃O₄. The low solubility of ZnFe₂O₄ indicates that it is more protectively stable as an anticorrosion phase. Moreover, the gap between the solubility of ZnFe₂O₄ and that of Fe₃O₄ or Fe₂O₃ was enlarged with an increase of temperature. This means that ZnFe₂O₄ is more protective at higher temperatures. Further analysis indicated that with the increase of temperature, the solubility of ZnFe₂O₄ changed little while those of Fe₂O₃ or Fe₃O₄ changed a lot. Little change of the solubility of ZnFe₂O₄ with increase of temperature showed that ZnFe₂O₄ is stable. The very low and constant solubility of ZnFe₂O₄ suggests that it is more protective than Fe₂O₃ and Fe₃O₄, especially in water at higher temperature.     

Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>/Au composite nano-particles and their optical properties

Fe₃O₄/Au composite particles with core/shell structure were prepared by reduction of Au³⁺ with hydroxylamine in the presence of an excess of Fe₃ O₄ as seeds. The resultant colloids, with an average diameter of less than 100 nm, were obtained; the remaining non-reacted Fe₃O₄ seeds can be removed by treatment with diluted HCl solution. The Fe₃O₄/Au colloids exhibit a characteristic peak of UV-visible spectra, which largely depend on the size of the particle and the suspension medium. The localized surface plasmon resonance peaks red shift and broaden with increased nanoparticle diameter or increased solvent ionic strength. The optical property is very important in the establishment of means for the detection of biomolecules.     

Preparation and characterization of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>composite particles

Using Fe₃O₄ nano-particles as seeds, a new type of Fe₃O₄/Au composite particles with core/shell structure and diameter of about 170 nm was prepared by reduction of Au³⁺ with hydroxylamine in an aqueous solution. Particle size analyzer and transmission electron microscope were used to analyze the size distribution and microstructure of the particles in different conditions. The result showed that the magnetically responsive property and suspension stability of Fe₃O₄ seeds as well as reduction conditions of Au³⁺to Au⁰are the main factors which are crucial for obtaining a colloid of the Fe₃O₄/Au composite particles with uniform particle dispersion, excellent stability, homogeneity in particle sizes, and effective response to an external magnet in aqueous suspension solutions. UV-Vis analysis revealed that there is a characteristic peak of Fe₃O₄/Au fluid. For particles with d(0.5)=168 nm, the λmax is 625 nm.     

Adsorption behavior of <Superscript>99</Superscript>Tc on Fe,Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> and Fe<Subscript>2</Subscript>O<Subscript>4</Subscript>

Summary The adsorption of ⁹⁹Tc on the adsorbers Fe, Fe₂O₃ and Fe₃O₄ was studied by batch experiments under aerobic and anoxic conditions. The effects of pH and CO₃^2- concentration of the simulated ground water on the adsorption ratios were also investigated, and the valences of Tc in solution after the adsorption equilibrium were studied by solvent extraction. The adsorption isotherms of TcO₄- on the adsorbers Fe, Fe₂O₃ and Fe₃O₄ were determined. Experimental results have shown that the adsorption ratio of Tc on Fe decreases with the increase of pH in the range of 5-12 and increases with the decrease of the CO₃^2- concentration in the range of 10^-8M-10^-2M. Under aerobic conditions, the adsorption ratios of ⁹⁹Tc on Fe₂O₃ and Fe₃O₄ were not influenced by pH and CO₃^2-concentration. When Fe was used as adsorbent, Tc existed mainly in the form of Tc(IV) after equilibrium and in the form of Tc(VII) when the adsorbent was Fe₂O₃ or Fe₃O₄ under aerobic conditions. The adsorption ratios of Tc on Fe, Fe₂O₃ and Fe₃O₄ decreased with the increase of pH in the range of 5-12 and increased with the decrease of the CO₃^2- concentration in the range of 10^-8M-10^-2M under anoxic conditions. Tc existed mainly in the form of Tc(IV) after equilibrium when Fe, Fe₂O₃ and Fe₃O₄ was the adsorbent under anoxic conditions. The adsorption isotherms of TcO_4- on the adsorbers Fe, Fe₂O₃ and Fe₃O₄ are fairly in agreement with the Freundlich’s equation under both aerobic and anoxic conditions.     

Synthesis and Characterization of Al(OH)<Subscript>3</Subscript>, Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Nanoparticles and Polymeric Nanocomposites

Applying of the most toxic halogenated and aromatic flame retardants is limited with respect to the environmental requirements. Nontoxic Al(OH)₃ nanoparticles were synthesized via a simple surfactant-free precipitation reaction at room temperature. The effect of various precipitation-agents on the morphology of the products was investigated. Al(OH)₃ nanoparticles were added to the polysulfone and poly styrene (PS) matrices. Electron microscope images show excellent dispersion of aluminium hydroxide in PS matrix. Nanoparticles appropriately enhanced both thermal stability and flame retardant property of the polymeric matrices. The enhancement of flame retardancy is due to endothermic decomposition of Al(OH)₃ that absorbs heat and simultaneously releases of water (makes combustible gases diluted and cold). Dispersed nanoparticles play the role of a barrier layer against flame, oxygen and polymer volatilization. Al(OH)₃ was converted to Al₂O₃ and its photo-catalyst property in degradation three different organic dyes as pollutants was investigated.     

Synthesis of hybrid nanoparticles based on magnetic Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanoparticles and luminescent CdS nanoparticles

A new approach to the synthesis of hybrid nanoparticles based on magnetic Fe₃O₄ nanoparticles and CdS quantum dots, combining magnetic and luminescence properties, has been suggested. Conditions for preparation of their stable aqueous suspensions have been found, and their optical properties have been studied. Nanocomposites produced at the molar ratio Fe₃O₄: CdS = 5: 1, which exhibited the luminescence properties) and gave stable aqueous suspensions, have turned out to be most promising. The results are evidence that the synthesized nanoparticles can be used for the development of visualizing agents for in vitro biomedical research.     

Superparamagnetic Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> Nanoparticles Decorated Multiwalled Carbon Nanotubes: Preparation via Cyclic Microwave Approach and Their Drug Release Behavior

Superparamagnetic Fe₃O₄ nanoparticles decorated multiwalled carbon nanotubes were synthesized by cyclic microwave method and the effect of different reaction parameters on the products were also investigated. The as synthesized products were characterized by XRD, TEM, SEM, EDS, FT-IR, VSM, and Uv–Vis spectroscopy. It was observed that precursors’ concentration ratio had great effect on the particle size and decorating quality. Also the effect of the other parameters including irradiation power and time on product size and uniformity of the product were also investigated. The best products with desired particle size distribution obtained when irradiation power and reaction time were 900 W and 6 min, respectively. Aspirin and acetaminophen were applied as a model drug and the drug release behavior of the composite was investigated. It was observed that the drug discharge was highly dependent to the pH and can be tuned by applying magnetic field.     

Magnetorheological characteristics of aqueous suspensions that contain Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanoparticles

This investigation examines the magnetorheological (MR) characteristics of Fe₃O₄ aqueous suspensions. Magnetite particles (Fe₃O₄) were synthesized using a colloidal process and their sizes were determined to be normally distributed with an average of 10 nm by TEM. Experimental results reveal that the MR effect increases with the magnetic field and suspension concentration. The yield stress increases by up to two orders of magnitude when the sample is subjected to a magnetic field of 146 Oe/mm. In comparison with other published results, concerning a concentration of approximately 10–15% v/v, this study demonstrates that the same increase can be obtained with a concentration of nano-scale particles as low as 0.04% by volume. The viscosity was increased by an order of magnitude while the shear rate remained low; however, the increase decayed rapidly as the shear rate was raised. Finally, the MR effect caused by DC outperformed that caused by AC at the same current.     

Surface chemistry of nanoscale Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> dispersed in magnetic fluids

The interaction between stabilizers and nanoparticles is one of the important factors to prepare stable magnetic fluids. The magnetic nano-size Fe₃O₄ core with single domain and the average grain size around 8–12 nm were prepared by chemical precipitation method. The O/Fe molar ratio of the particle surface was measured by X-ray photoelectron spectroscopy (XPS). The heat effects of stabilizers adsorption on nanoparticles were measured by solution calorimetry. The excess amount of oxygen was possibly the result of the hydroxygen formed on the surface of the nanoparticles. The heat effects showed that compounds containing carboxyl groups can be adsorbed chemically on magnetite by forming chemical bonds. The other stabilizers involving NH-groups, such as polyethylene-imine, can be adsorbed physically. The exothermic value is about half of the former case. Supported by the National Natural Science Foundation of China (Grant No. 50476039), and Guangdong Provincial Department of Science and Technology (Grant No. 2004A10-703001)     

Magnetic nanoparticles (Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> &amp; Co<Subscript>3</Subscript>O<Subscript>4</Subscript>) and their applications in urea biosensing

Nanobiotechnology has opened a new and exciting opportunities for exploring urea biosensor based on magnetic nanoparticles (NPs) mainly Fe₃O₄ and Co₃O₄. These NPs have been extensively exploited to develop biosensors with stability, selectivity, reproducibility and fast response time. This review gives an overview of the development of urea biosensor based on Fe₃O₄ and Co₃O₄ for in vitro diagnostic applications along with significant improvements over the last few decades. Additionally, effort has been made to elaborate properties of magnetic nanoparticles (MNPs) in biosensing aspects. It also gives details of recent developments in hybrid nanobiocomposite based urea biosensor.     

Synthesis and characterization of Co<Subscript>0.8</Subscript>Zn<Subscript>0.2</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoparticles

Cobalt zinc ferrite, Co_0.8Zn_0.2Fe₂O₄, nanoparticles have been synthesized via autocatalytic decomposition of the precursor, cobalt zinc ferrous fumarato hydrazinate. The X-ray powder diffraction of the ‘as prepared’ oxide confirms the formation of single phase nanocrystalline cobalt zinc ferrite nanoparticles. The thermal decomposition of the precursor has been studied by isothermal, thermogravimetric and differential thermal analysis. The precursor has also been characterized by FTIR, and chemical analysis and its chemical composition has been determined as Co_0.8Zn_0.2Fe₂(C₄H₂O₄)₃·6N₂H_4. The Curie temperature of the ‘as-prepared oxide’ was determined by AC susceptibility measurements.     

Ag nanoparticles decorated Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>/chitosan nanocomposite: synthesis,characterization and application toward electrochemical sensing of hydrogen peroxide

We studied a rapid, sensitive and selective amperometric sensor for determination of hydrogen peroxide by electrodeposited Ag NPs on a modified glassy carbon electrode (GCE). The modified GCE was constructed through a step by step modification of magnetic chitosan functional composite (Fe₃O₄–CH) and high-dispersed silver nanoparticles on the surface. The resulted Ag@Fe₃O₄–CH was characterized by various analytical methods including Fourier transform infrared spectroscopy, X-ray diffraction, transmission electron microscopy, scanning electron microscopy and cyclic voltammetry. The proposed sensor employed Ag@Fe₃O₄–CH/GCE as the working electrode with a linear current response to the hydrogen peroxide concentration in a wide range from 0.01 to 400 µM with a low limit of detection (LOD = 0.0038 µM, S/N = 3). The proposed sensor showed superior reproductivity, sensitivity and selectivity for the detection of hydrogen peroxide in environmental and clinical samples.     

Synthesis of NiO/Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> nanocomposites as substrate for the construction of electrochemical biosensors

The exploration of substrate materials to construct electrochemical biosensors for glucose monitoring in the field of clinical diagnosis, especially for diabetes is still being investigated extensively. In this paper, NiO/Fe₂O₃ nanocomposites are designed and synthesized by two-step hydrothermal approach in combination with calcinations. The morphology and microstructure are studied by SEM, XRD, XPS, and TEM systematically. Optimized NiO/Fe₂O₃ nanocomposites are employed as substrate to construct glucose biosensors, and the electrochemical properties are carried out by cyclic voltammetric and chronoamperometric techniques. The results indicate as-prepared biosensors achieve a high sensitivity of 230.5 μA cm^?2 mM^?1, wide linear range between 50 and 2867 μM, and low detection limit of 3.9 μM towards glucose detection. The synergistic effect between NiO and Fe₂O₃ as substrate to construct glucose biosensors is elucidated. The selectivity is acceptable based on the detection of glucose concentration for diabetics.     

Preparation and Characterization of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@SiO<Subscript>2</Subscript> Nanoparticles Incorporated Polymer Monolithic Column for Gas Chromatography

We report on the synthesis of Fe₃O₄@SiO₂ nanoparticles incorporated poly(divinylbenzene) monolithic column via in situ polymerization. The monolith had larger specific surface area and relatively uniform porous structure and was characterized by scanning electron microscopy, nitrogen adsorption–desorption, and Fourier transform infrared spectroscopy. The monolith was then applied for the evaluation of gas chromatography separation properties. Here, an electromagnetic induction heating technique was employed to control the column temperature with the thermal effect of eddy current in ferromagnetic materials Fe₃O₄. The monolith offered good separation efficiency for benzene and toluene and a higher column efficiency was obtained up to 4481 and 9216 plates per meter, respectively. In addition, the injection volume and column capacity of the proposed system are as much as 5 µL and 100 ng. This makes it possible to use a UV detector. The fabricated Fe₃O₄@SiO₂ nanoparticles incorporated poly(divinylbenzene) monolithic column has been shown to be very promising for gas chromatography separation.

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Microstructure and Magnetic Behaviour of Nanosized Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> Powders and Polycrystalline Films

Summary.  The object of investigation were the magnetic interactions in nanostructured Fe₃O₄ assemblies of two kinds (powder and film) where particles of similar size present nearly uniform domains in a close to planar arrangement with spacings sufficient for magnetic interactions. We discuss the use of the soft-chemistry method, i.e. the modified ‘ferrite plating’ (MFP) technique, for the synthesis of polycrystalline films of magnetite with nanosized crystallites. Received October 22, 2001. Accepted January 21, 2002     

Study of electrochemical behavior of the Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanoparticles in aprotic media

Peculiarities of electrochemical behavior of the Fe₃O₄ magnetic nanoparticles immobilized on the surface of a platinum electrode in aprotic organic media were investigated. Possible scheme of electrochemical behavior of nanoparticles depending on pre-electrolysis potential (–1.3,–2.5 V) was suggested. The effect of pre-electrolysis time, potential scan rate and nature of supporting electrolyte on the processes investigated was determined. A linear dependence of electrochemical oxidation signal versus the concentration of nanoparticles in modifying suspension in the concentration range of 0.05—0.5 g L^–1 was observed. The results of the performed research allow using magnetite nanoparticles as a direct signal-generating label in electrochemical immunoassay.