Impregnated copper on Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>: an efficient magnetically separable nanocatalyst for rapid and selective acylation of amines

The present paper describes the synthesis of N-arylacetamides through acetylation of arylamines with Ac₂O in the presence of magnetically recyclable Fe₃O₄/Cu NPs. All reactions were carried out efficiently in H₂O within 2–10 min to give the products in 89–95% yields. Selective acetylation of amines versus alcohols was carried out successfully with this acetylating system. In addition, acetylation of amines and phenols was taken place with the same reactivity. Reusability of the nanocatalyst was examined 5 times without significant loss of its catalytic activity.     

Facile ultrasonic-assisted preparation of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>/Ag<Subscript>3</Subscript>VO<Subscript>4</Subscript> nanocomposites as magnetically recoverable visible-light-driven photocatalysts with considerable activity

In this work, a facile ultrasonic-assisted method was applied for preparation of Fe₃O₄/Ag₃VO₄ nanocomposites with different compositions. The as-prepared products were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy-dispersive analysis of X-rays, UV–Vis diffuse reflectance spectroscopy, Fourier transform infrared spectroscopy, and vibrating sample magnetometery. Photocatalytic degradation of rhodamine B under visible-light irradiation was investigated, and it was found that weight ratio of Fe₃O₄–Ag₃VO₄ has significant influence on the photocatalytic activity and the nanocomposite with 1:4 weight ratio of Fe₃O₄–Ag₃VO₄ has superior activity. In addition, the nanocomposite showed great activities in degradations of methylene blue and fuchsine, which are comparable with activity of the pure Ag₃VO₄. More importantly, this nanocomposite displayed remarkable saturation magnetization, leading to easily and quickly separation of its suspension from treated system by applying a magnetic field.     

H<Subscript>3</Subscript>PMo<Subscript>12</Subscript>O<Subscript>40</Subscript> immobilized chitosan/Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> as a novel efficient,green and recyclable nanocatalyst in the synthesis of pyrano-pyrazole derivatives

A novel nanomagnetic composite heteropolyacid immobilized chitosan/Fe₃O₄ was prepared via a facile one-pot synthetic approach. This magnetically recoverable nanocatalyst, H₃PMo₁₂O₄₀/chitosan/Fe₃O₄ (PMo/chit/Fe₃O₄), was fully characterized by XRD, FTIR, SEM and EDX analysis methods. A rapid, efficient and the chemoselective synthesis of different pyrano-pyrazole derivatives was achieved in excellent yields via a one-pot four-component reaction in the presence of catalytic amount of PMo/Chit/Fe₃O₄.     

Optical,magnetic and photocatalytic properties of magnetically separable Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>-doped ZnO and pristine ZnO nanospheres

This work focussed on the optical, magnetic and photocatalytic properties of sol–gel-synthesized Fe₃O₄-doped ZnO nanospheres and was compared with pristine ZnO nanospheres. The crystalline phase of Fe₃O₄-doped ZnO nanospheres was studied with X-ray diffraction analysis and was well matched with standard pattern. Surface morphology was studied with HR-SEM images and EDAX spectrum. Furthermore, elemental mapping analysis was carried out to confirm the presence of Fe₃O₄ phase in Fe₃O₄-doped ZnO nanospheres. FT-Raman spectral studies show that a strong intense peak at 670 cm^?1 indicates the presence of Fe₃O₄ in Fe₃O₄-doped ZnO nanospheres. The mean crystallite size of Fe₃O₄-doped ZnO nanospheres was 34 nm as calculated by Debye–Scherrer’s formula which confirmed with HR-TEM image. The SAED pattern shows the presence of (100), (101), (102) and (202) of ZnO phase and (400) of Fe₃O₄ phase, confirming the crystalline nature of Fe₃O₄-doped ZnO nanospheres. The vibrating sample magnetometer (VSM) result shows that Fe₃O₄-doped ZnO nanospheres possess superparamagnetic nature and the composite nanospheres are magnetically separable. The optical properties have been studied by diffuse reflectance spectroscopy and time-resolved photoluminescence spectra. Implantation of Fe₃O₄ in ZnO nanospheres modifies the UV absorption edge, and it displays near-band gap emission and deep-level emission. The photocatalytic activity of Fe₃O₄-doped ZnO nanospheres studied against rhodamine B dye is found higher than that of pristine ZnO nanospheres which shows that Fe₃O₄-doped ZnO nanospheres are a promising photocatalyst.     

Schiff base complex of Mo supported on iron oxide magnetic nanoparticles (Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>) as recoverable nanocatalyst for the selective oxidation of sulfides

In this work, a new tridentate Schiff base dioxo-molybdenum(VI) complex immobilized on silica-coated magnetic nanoparticles (MoO₂5CML–Fe₃O₄@SiO₂) has been synthesized and characterized using different techniques such as FTIR, TGA, AAS, ICP–AES, XRD, VSM, EDX and SEM analyses. The catalytic activity of synthesized complex was examined in the oxidation of various sulfides in the presence of H₂O₂ as cheap, green and eco-friendly oxidant. This catalytic system provides high conversion and selectivity toward either sulfoxides or sulfones under different conditions. Also, the nanocatalyst could be easily separated and regenerated from reaction media by external magnet and could be reused for ten times without significant loss of the activity and selectivity.     

Pd(II) anchored to modified Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanoparticles as a new magnetically recoverable catalyst for epoxidation of styrene

A new support for Pd(II) was synthesized via the functionalization of Fe₃O₄ nanoparticles with N-(2-aminoethyl)acetamide. PdCl₂ was anchored to the support for obtaining a heterogeneous magnetically recoverable catalyst for Pd(II). High yield and excellent selectivity were obtained for the green epoxidation of styrene derivatives using H₂O₂ as a green oxidant in H₂O as the solvent at 100 °C. Also, the recovered catalyst is applicable for four times without significant decrease in yield.     

Cis-dioxo-Mo(VI) salophen complex supported on Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@SiO<Subscript>2</Subscript> nanoparticles as an efficient magnetically separable and reusable nanocatalyst for selective epoxidation of olefins

In this work, paramagnetic Fe₃O₄/SiO₂ nanoparticles were synthesized, characterized and functionalized with dioxo-Mo(VI) tetradentate Schiff base complex and characterized using IR spectroscopy, X-ray powder diffraction spectroscopy, scanning electron microscopy, transmission electron microscopy, vibrating sample magnetometry, diffuse reflectance spectroscopy and atomic absorption spectroscopy. Catalyst was used for the selective epoxidation of cyclooctene, cyclohexene, styrene, indene, α-pinene, 1-hepten, 1-octene, 1-dodecen and trans-stilbene using tert-butyl hydroperoxide as oxidant in 1,2-dichloroethane. This catalyst is efficient for oxidation of cyclooctene with a 100% selectivity for epoxidation with 100% conversion in 1 h. After the reaction, the magnetic nanocatalyst was easily separated by simply applying an external magnetic field and was used at least five successive times without significant decrease in conversion.

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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)     

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)     

Synthesis of novel magnetic sulfur-doped Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanoparticles for efficient removal of Pb(II)

In this work, we report the synthesis of magnetic sulfur-doped Fe₃O₄ nanoparticles (Fe₃O₄:S NPs) with a novel simple strategy, which includes low temperature multicomponent mixing and high temperature sintering. The prepared Fe₃O₄:S NPs exhibit a much better adsorption performance towards Pb(II) than bare Fe₃O₄ nanoparticles. FTIR, XPS, and XRD analyses suggested that the removal mechanisms of Pb(II) by Fe₃O₄:S NPs were associated with the process of precipitation (formation of PbS), hydrolysis, and surface adsorption. The kinetic studies showed that the adsorption data were described well by a pseudo second-order kinetic model, and the adsorption isotherms could be presented by Freundlich isotherm model. Moreover, the adsorption was not significantly affected by the coexisting ions, and the adsorbent could be easily separated from water by an external magnetic field after Pb(II) adsorption. Thus, Fe₃O₄:S NPs are supposed to be a good adsorbents for Pb(II) ions in environmental remediation.     

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.     

Synthesis of N-2-aryl-substituted 1,2,3-triazoles mediated by magnetic and recoverable CuFe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoparticles

An efficient and economic system for the synthesis of N-2-aryl-substituted 1,2,3-triazoles in the presence of CuFe₂O₄ was developed. The corresponding products can be obtained in good to excellent yields. It is interesting to note that the catalyst could be reused for five consecutive trials without significant decreases in its activity.     

Synthesis of spiro[pyrazoloquinoline-oxindoles] and spiro[chromenopyrazolo-oxindoles] promoted by guanidine-functionalized magnetic Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanoparticles

Magnetic nanoparticles (MNPs) Fe₃O₄-immobilized guanidine (Fe₃O₄ MNPs-guanidine) have been used as an efficient catalyst for the preparation of spiro[pyrazoloquinoline-oxindoles] and spiro[chromenopyrazolo-oxindoles] by four-component reactions of phenylhydrazine or hydrazine hydrate, isatins, ketoesters and naphthylamine or 2-naphthol under reflux condition in ethanol. This method provides several advantages including mild reaction conditions, the applicability to a wide range of substrates, the reusability of the catalyst and low catalyst loading.     

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.     

Highly chemiluminescent magnetic mesoporous carbon composites Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@void@C with yolk-shell structure

In this work, highly chemiluminescent magnetic mesoporous carbon with yolk-shell structure was synthesized by encapsulating N-(4-aminobutyl)-N-ethylisoluminol (ABEI) and Co²⁺ into the magnetic mesoporous carbon composites (Co²⁺-ABEI-Fe₃O₄@ void@C). The synthetic Co²⁺-ABEI-Fe₃O₄@void@C showed a good magnetic separation property, which could remove residual ABEI molecules and Co²⁺ in less than 3 min under an external magnet. Moreover, the synthetic Co²⁺-ABEI-Fe₃O₄@void@C demonstrated good chemiluminescence (CL) property and good stability when interacted with alkaline H₂O₂ solution. The CL intensity of such Co²⁺-ABEI-Fe₃O₄@void@C was about 120 times higher than that of ABEI-Fe₃O₄@void@C. The Co²⁺-ABEIFe₃O₄@ void@C also exhibited good electrochemiluminescence (ECL) property in alkaline solution. The outstanding CL/ECL performance of the Co²⁺-ABEI-Fe₃O₄@void@C was attributed to the Co²⁺ immobilized in the Co²⁺-ABEI-Fe₃O₄@void@C, which catalyzed the decomposition of H₂O₂ to generate O₂^?? and HO^?, expediting the CL/ECL reaction. The synthetic Co²⁺-ABEI-Fe₃O₄@void@C may be of great application for the development of new methodologies in bioanalysis.     

One-pot sequential synthesis of magnetically separable Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>/AgCl photocatalysts with enhanced activity and stability

Magnetically separable Fe₃O₄/AgCl photocatalysts were prepared by a one-pot sequential method. A series of techniques proved the hybrid structure of Fe₃O₄/AgCl composites. Fe₃O₄/AgCl composites had a much higher photocatalytic activity toward Rhodamine B (RhB) degradation than pure AgCl under the simulated solar light irradiation. The existence of metal Ag resulted in high photocatalytic activity of Fe₃O₄/AgCl, which was related with the amount of metallic Ag. The scavenging experiments showed that the degradation reaction most probably was initiated by the photoinduced single-electron transfer, and the generation of superoxide anion (O ₂ ^-· ) played a significant role. The composite photocatalysts could be recycled by applying an external magnetic field, and the reused composites maintained their original photocatalytic activity. Fe₃O₄/AgCl composites were highly efficient, magnetically separable, and recoverable. This proves their potential applications in the photodegradation of organic pollutants.     

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.     

Effect of the polymeric coating over Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> particles used for magnetic separation

In this work, the synthesis of magnetite nanoparticles by two variant chemical coprecipitation methods that involve reflux and aging conditions was investigated. The influence of the synthesis conditions on particle size, morphology, magnetic properties and protein adsorption were studied. The synthesized magnetite nanoparticles showed a spherical shape with an average particle size directly influenced by the synthesis technique. Particles of average size 27 nm and 200 nm were obtained. When the coprecipitation method was used without reflux and aging, the smallest particles were obtained. Magnetite nanoparticles obtained from both methods exhibited a superparamagnetic behavior and their saturation magnetization was particle size dependent. Values of 67 and 78 emu g⁻¹ were obtained for the 27 nm and 200 nm magnetite particles, respectively. The nanoparticles were coated with silica, aminosilane, and silica-aminosilane shell. The influence of the coating on protein absorption was studied using Bovine Serum Albumin (BSA) protein.      

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.