A green method for solvent-free conversion of epoxides to thiiranes using NH4SCN in the presence of NiFe2O4 and MgFe2O4 magnetic nanocatalysts

Nickel and magnesium ferrite magnetic nanoparticles were fabricated and applied as efficient and reusable catalysts in the solvent-free conversion of various epoxides to the corresponding thiiranes with ammonium thiocyanate under oil bath (60°C) conditions. NiFe₂O₄ and MgFe₂O₄ nanoparticles can catalyze the reactions at short times in high to excellent yields. The catalysts can also be recovered easily using an external magnetic field and be reused four times without any significant loss of activity.     

Growth,structure, morphology,and magnetic properties of Ni ferrite films

The morphology, structure, and magnetic properties of nickel ferrite (NiFe₂O₄) films fabricated by radio frequency magnetron sputtering on Si(111) substrate have been investigated as functions of film thickness. Prepared films that have not undergone post-annealing show the better spinel crystal structure with increasing growth time. Meanwhile, the size of grain also increases, which induces the change of magnetic properties: saturation magnetization increased and coercivity increased at first and then decreased. Note that the sample of 10-nm thickness is the superparamagnetic property. Transmission electron microscopy displays that the film grew with a disorder structure at initial growth, then forms spinel crystal structure as its thickness increases, which is relative to lattice matching between substrate Si and NiFe₂O₄.     

磁性Fe3O4纳米粒子用作靶向药物载体的制备及分析

Fe3O4 magnetic nanoparticles were prepared by the aqueous co-precipitation of FeCl3-6H2O and FeCl2-4H2O with addition of ammonium hydroxide. The conditions for the preparation of Fe3O4 magnetic nanoparticles were optimized, and Fe3O4 magnetic nanoparticles obtained were characterized systematically by means of transmission electron microscope （TEM）, dynamic laser scattering analyzer （DLS） and X-ray diffraction （XRD）. The results revealed that the magnetic nanoparticles were cubic shaped and dispersive, with narrow size distribution and average diameter of 11.4 nm. It was found that the homogeneous variation of pH value in the solution via the control on the dropping rate of aqueous ammonia played a critical role in size distribution. The magnetic response of the product in the magnetic field was also analyzed and evaluated carefully. A 32.6 mT magnetic field which is produced by four ferromagnets was found to be sufficient to excite the dipole moments of 0.05 g Fe3O4 powder 2 cm far away from the ferromagnets. In conclusion, the Fe3O4 magnetic nanoparticles with excellent properties were competent for the magnetic carders of targeted-drug in future application.     

Effect of surfactants (PVB/EDTA/CTAB) assisted sol-gel synthesis on structural,magnetic and dielectric properties of NiFe2O4 nanoparticles

Nanocrystalline NiFe₂O₄ was synthesized by sol-gel route using various surfactants such as PVP, EDTA and CTAB. The effect of different surfactants on structure, magnetic and dielectric properties of the NiFe₂O₄ nanoparticles (NPs) were investigated. The prepared samples were inspected by XRD, HRSEM, and TEM. Powder XRD studies confirmed the realization of single crystalline cubic structure of the NiFe₂O₄ nanoferrites. The addition of surfactants significantly modified the crystallite size of the final products. Dielectric features of NiFe₂O₄ NPs were slightly modified with different surfactants. The magnetic results revealed an enormous decrease in coercivity and a moderate reduction in the saturation magnetization when EDTA and CTAB were used as compared to PVP. The present results declare that the adding of various surfactants in the sample preparation controls the size of NiFe₂O₄ NPs and thus noticeably influences the magnetic parameters.     

Graphene‐supported nickel ferrite: A magnetically separable photocatalyst with high activity under visible light

A straightforward strategy is designed for the fabrication of a magnetically separable NiFe₂O₄‐graphene photocatalyst with different graphene content. It is very interesting that the combination of NiFe₂O₄ nanoparticles with graphene sheets results in a dramatic conversion of the inert NiFe₂O₄ into a highly active catalyst for the degradation of methylene blue (MB) under visible light irradiation. The significant enhancement in photoactivity under visible light irradiation can be ascribed to the reduction of GO, because the photogenerated electrons of NiFe₂O₄ can transfer easily from the conduction band to the reduced GO, effectively preventing a direct recombination of electrons and holes. The results of the kinetic study indicated that the rate‐determining stage is the adsorption process of MB molecules. NiFe₂O₄ nanoparticles themselves have a strong magnetic property, which can be used for magnetic separation in a suspension system, and, therefore, the introduction of additional magnetic supports is no longer necessary. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

Synthesis of MnFe2O4 nanocrystals by wet-milling under atmospheric conditions

This work reports an original method for synthesis of well-crystallized manganese ferrite (MnFe₂O₄) nanoparticles via a high energy wet milling technique under atmospheric conditions, starting from metallic Mn and Fe powders in the presence of distilled water. The effects of milling conditions on the formation and magnetic properties of MnFe₂O₄ nanoparticles were investigated in detail. Fully stoichiometric MnFe₂O₄ nanocrystals with an average crystallite size of 14.5 nm were produced after 24 h of milling. As-synthesized MnFe₂O₄ nanocrystals were found to show soft magnetic behavior at room temperature with saturation magnetization of 53 emu/g. Due to reduced thermal effects, the saturation magnetization increased to 68 emu/g at 5 K. Results show that this method is simple and efficient for the mass production of MnFe₂O₄ nanoparticles.     

Surface Oxidized Carbon Nanotubes Uniformly Coated with Nickel Ferrite Nanoparticles

We report a facile non-templated hydrothermal synthesis method for the production of nickel ferrite (NiFe₂O₄)/carbon nanotube nanocomposite comprised of oxidized multi-walled carbon nanotube (o-MWCNT) uniformly coated with nanoparticles of NiFe₂O₄ (1–5 nm). The carboxylate groups of the o-MWCNT coordinate the nanoparticles strongly at its surface, and the size of the NiFe₂O₄ particles can be controlled by the subtle variation of reaction time and the quantity of o-MWCNT used. We believe that this method can be extended to allow the uniform coating of different spinel-type materials onto o-MWCNT and other nanocarbon materials.     

Synthesis of Heterogeneous Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript> Nanostructured Anodes with Long-Term Cycle Stability

The 0D-1D Lithium titanate (Li₄Ti₅O₁₂) heterogeneous nanostructures were synthesized through the solvothermal reaction using lithium hydroxide monohydrate (Li(OH)·H₂O) and protonated trititanate (H₂Ti₃O₇) nanowires as the templates in an ethanol/water mixed solvent with subsequent heat treatment. A scanning electron microscope (SEM) and a high resolution transmission electron microscope (HRTEM) were used to reveal that the Li₄Ti₅O₁₂ powders had 0D-1D heterogeneous nanostructures with nanoparticles (0D) on the surface of wires (1D). The composition of the mixed solvents and the volume ratio of ethanol modulated the primary particle size of the Li₄Ti₅O₁₂ nanoparticles. The Li₄Ti₅O₁₂ heterogeneous nanostructures exhibited good capacity retention of 125 mAh/g after 500 cycles at 1C and a superior high-rate performance of 114 mAh/g at 20C.     

An Ultrasensitive Electrochemiluminescence Immunoassay for Carbohydrate Antigen 19-9 in Serum Based on Antibody Labeled Fe3O4 Nanoparticles as Capture Probes and Graphene/CdTe Quantum Dot Bionanoconjugates as Signal Amplifiers

The CdTe quantum dots (QDs), graphene nanocomposite (CdTe-G) and dextran–Fe₃O₄ magnetic nanoparticles have been synthesized for developing an ultrasensitive electrochemiluminescence (ECL) immunoassay for Carcinoembryonic antigen 19-9 (CA 19-9) in serums. Firstly, the capture probes (CA 19-9 Ab1/Fe₃O₄) for enriching CA 19-9 were synthesized by immobilizing the CA 19-9’s first antibody (CA 19-9 Ab1) on magnetic nanoparticles (dextran-Fe₃O₄). Secondly, the signal probes (CA 19-9 Ab2/CdTe-G), which can emit an ECL signal, were formed by attaching the secondary CA 19-9 antibody (CA 19-9 Ab2) to the surface of the CdTe-G. Thirdly, the above two probes were used for conjugating with a serial of CA 19-9 concentrations. Graphene can immobilize dozens of CdTe QDs on their surface, which can emit stronger ECL intensity than CdTe QDs. Based on the amplified signal, ultrasensitive antigen detection can be realized. Under the optimal conditions, the ECL signal depended linearly on the logarithm of CA 19-9 concentration from 0.005 to 100 pg/mL, and the detection limit was 0.002 pg/mL. Finally, five samples of human serum were tested, and the results were compared with a time-resolved fluorescence assay (TRFA). The novel immunoassay provides a stable, specific and highly sensitive immunoassay protocol for tumor marker detection at very low levels, which can be applied in early diagnosis of tumor.     

Stability and cytotoxicity study of NiFe2O4 nanocomposites synthesized by co-precipitation and subsequent thermal annealing

In this article, NiFe₂O₄ nanoparticles (NPs) were prepared by co-precipitation method with subsequent thermal annealing leading to obtainment NPs with average sizes of 78 nm. Structure and magnetic analysis were performed by X-ray diffraction, transmission electron microscopy, Mössbauer spectroscopy and vibrating sample magnetometry techniques. Stability of NiFe₂O₄ NPs was evaluated in PBS solution during 20 days. The toxicity of prepared NPs was evaluated in vitro using different cancer cell lines: HeLa (cervical cancer cell), PC-3 (prostate cancer cell). Fibroblasts like cells of L929 obtained from subcutaneous adipose tissue of mouse were used as normal cells. Results indicate successful synthesis of NiFe₂O₄ NPs that exhibit low cytotoxicity in concentration range from 1 to 100 μg/ml. Presented physical and biological results indicate the possibility of application investigated magnetic nanoparticles in hyperthermia, targeted drug delivery, magnetic resonance imaging or cell separation.     

Synthesis of magnetically separable core–shell structured Ni<Subscript>x</Subscript>Fe<Subscript>1−x</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript>@TiO<Subscript>2</Subscript> nanoparticles photocatalysts for the degradation of organic dyes

In this paper, the core–shell structured NiFe₂O₄@TiO₂ nanoparticles and nanochains as photocatalysts were successfully prepared through hydrothermal and hydrolysis method. The as-prepared core–shell structure was composed of a magnetic NiFe₂O₄ core and photocatalytic titanium oxide coating shell. SEM and TEM images characterized the morphology of NiFe₂O₄@TiO₂ nanoparticles. Moreover, the results of XRD patterns proved that the TiO₂ coating shell consisted of anatase. The VSM measurements showed that the saturation magnetization values of NiFe₂O₄ and NiFe₂O₄@TiO₂ nanoparticles was 65 and 53 emu/g, respectively. The photocatalyst of NiFe₂O₄@TiO₂ nanoparticles exhibited the outstanding recyclable performance for RhB. And, the photo_degradation ration of maintained 69 % after the photocatalyst experienced ten photocatalysis experiments, which is better than that of Fe₃O₄@TiO₂ photocatalysts.     

Sonochemical synthesis of magnetic core–shell Fe3O4@ZrO2 nanoparticles and their application to the highly effective immobilization of myoglobin for direct electrochemistry

In this study, bifunctional Fe₃O₄@ZrO₂ magnetic core–shell nanoparticles (NPs), synthesized by a simple and effective sonochemical approach, were attached to the surface of a magnetic glassy carbon electrode (MGCE) and successfully applied to the immobilization/adsorption of myoglobin (Mb) for constructing a novel biosensor platform. With the advantages of the magnetism and the excellent biocompatibility of the Fe₃O₄@ZrO₂ NPs, Mb could be easily immobilized on the surface of the electrode in the present of external magnetic field and well retained its bioactivity, hence dramatically facilitated direct electron transfer of Mb was demonstrated. The proposed Mb/Fe₃O₄@ZrO₂ biofilm electrode exhibited excellent electrocatalytic behaviors towards the reduction of H₂O₂ with a linear range from 0.64 μM to 148 μM. This presented system avoids the complex synthesis for protecting Fe₃O₄ NPs, supplies a simple, effective and inexpensive way to immobilize protein, and is promising for construction of third-generation biosensors and other bio-magnetic induction devices.     

NiFe<Subscript>2</Subscript>O<Subscript>4</Subscript>@SiO<Subscript>2</Subscript> Nanoparticles Stabilized by Porous Silica Shells

Abstract  

NiFe₂O₄ nanoparticles stabilized by porous silica shells (NiFe₂O₄@SiO₂) were prepared using a one-pot synthesis and characterized for their physical and chemical stability in severe environments, representative of those encountered in industrial catalytic reactors. The SiO₂ shell is porous, allowing transport of gases to and from the metal core. The shell also stabilizes NiFe₂O₄ at the nanoparticle surface: NiFe₂O₄@SiO₂ annealed at temperatures through 973 K displays evidence of surface Ni, as verified by H₂ TPD analyses. At 1,173 K, hematite forms at the surface of the metallic cores of the NiFe₂O₄@SiO₂ nanoparticles and surface Ni is no longer observed. Without the silica shell, however, even mild reduction (at 773 K) can draw Fe to the surface and eliminate surface Ni sites.     

Synthesis and characterization of monodisperse NiFe2O4 nanoparticles

Narrow size distribution nickel ferrite nanoparticles with average particle size of around 6 nm has been synthesized via rapid thermo-decomposition method in the presence of oleylamine in solution which acted as neutralizing, stabilizing and reducing agent OAm coated NiFe₂O₄ NPs. X-ray powder diffraction (XRD), Fourier Transform Infrared Spectra (FT-IR), Thermal Gravimetric Analysis (TGA), Scanning Electron Microscopy (SEM), Transmission electron microscopy (TEM), Vibrating Simple Magnetometer (VSM) and also Mössbauer Spectroscopy were used for structural, morphological, spectroscopic and magnetic characterization of the product. The XRD analysis revealed the formation of single phase nickel ferrite with Fd-3m space group. Both FT-IR and TGA analyses confirmed the formation of desired nanocomposite. FT-IR analysis also showed characteristic IR absorption bands of the spinel nickel ferrite phase and oleylamine. TEM and SEM analysis showed that product have almost spherical structural morphology. TEM images showed that NiFe₂O₄ nanoparticles have narrow size distribution and Energy Dispersive X-ray (EDX) analysis confirmed the presence of metal ions in the required stoichiometric ratio. Superparamagnetic property of the product was confirmed by VSM. From ⁵⁷Fe Mössbauer spectroscopy data, the variation in line width, isomer shift, quadrupole splitting and hyperfine magnetic field values have been determined. The Mössbauer spectra for OAm coated NiFe₂O₄ NPs. is consisting of one paramagnetic central doublets and one magnetic Zeeman sextet. Finally, the synthetic procedure can be extended to the preparation of high quality metal or alloy nanoparticles.     

Electrostatic complexation of polyelectrolyte and magnetic nanoparticles: from wild clustering to controllable magnetic wires

We present the electrostatic complexation between polyelectrolytes and charged nanoparticles. The nanoparticles in solution are γ-Fe₂O₃ (maghemite) spheres with 8.3 nm diameter and anionic surface charges. The complexation was monitored using three different formulation pathways such as direct mixing, dilution, and dialysis. In the first process, the hybrids were obtained by mixing stock solutions of polymers and nanoparticles. A ‘destabilization state’ with sharp and intense maximum aggregation was found at charges stoichiometry (isoelectric point). While on the two sides of the isoelectric point, ‘long-lived stable clusters state’ (arrested states) were observed. Dilution and dialysis processes were based on controlled desalting kinetics according to methods developed in molecular biology. Under an external magnetic field (B = 0.3 T), from dialysis at isoelectric point and at arrested states, cationic polyelectrolytes can ‘paste’ these magnetic nanoparticles (NPs) together to yield irregular aggregates (size of 100 μm) and regular rod-like aggregates, respectively. These straight magnetic wires were fabricated with diameters around 200 nm and lengths comprised between 1 μm and 0.5 mm. The wires can have either positive or negative charges on their surface. After analyzing their orientational behavior under an external rotating field, we also showed that the wires made from different polyelectrolytes have the same magnetic property. The recipe used a wide range of polyelectrolytes thereby enhancing the versatility and applied potentialities of the method. This simple and general approach presents significant perspective for the fabrication of hybrid functional materials.     

Production of Galactooligosaccharides Using β-Galactosidase Immobilized on Chitosan-Coated Magnetic Nanoparticles with Tris(hydroxymethyl)phosphine as an Optional Coupling Agent

β-Galactosidase was immobilized on chitosan-coated magnetic Fe₃O₄ nanoparticles and was used to produce galactooligosaccharides (GOS) from lactose. Immobilized enzyme was prepared with or without the coupling agent, tris(hydroxymethyl)phosphine (THP). The two immobilized systems and the free enzyme achieved their maximum activity at pH 6.0 with an optimal temperature of 50 °C. The immobilized enzymes showed higher activities at a wider range of temperatures and pH. Furthermore, the immobilized enzyme coupled with THP showed higher thermal stability than that without THP. However, activity retention of batchwise reactions was similar for both immobilized systems. All the three enzyme systems produced GOS compound with similar concentration profiles, with a maximum GOS yield of 50.5% from 36% (w·v⁻¹) lactose on a dry weight basis. The chitosan-coated magnetic Fe₃O₄ nanoparticles can be regenerated using a desorption/re-adsorption process described in this study.     

Synthesis and Characterization of NiFe2O4 Nanoparticles via Solid‐State Reaction

NiFe₂O₄ nanoparticles were synthesized via solid‐state reaction. The effects of the reaction parameters, namely dispersant content, calcination temperature and annealing time on particle size and morphology were investigated. Magnetic properties of NiFe₂O₄ nanoparticles were tested. The formation mechanism of nanoparticles by solid‐state reaction was also discussed. The results indicated that the synthesized nickel ferrite particles were of nanometer size with different morphologies by slight variation of the reaction conditions. The solid‐state reaction technique is a simple, convenient, inexpensive and effective preparation method of NiFe₂O₄ in high yield.     

Effect of MnO2 addition on properties of NiFe2O4-based cermets

The impact of MnO₂ as an additive on the properties of NiFe₂O₄-based cermets prepared by the two-steps sintering method has been investigated. The new material was characterized in terms of the crystal structure, microstructure, linear shrinkage, relative density and porosity. Moreover, the bending strength of NiFe₂O₄-based cermets was measured. Differential scanning calorimetry (DSC) and X-ray diffraction analysis (XRD) shows that the addition of MnO₂ has no obvious influence on the crystal structure of the cermets. Scanning electron microscope (SEM) studies reveals that the grain sizes of cermets decreases slightly with doped MnO₂. The results show that the linear shrinkage, relative density and bending strength increase at first and then decrease slightly. A high-density (99.56%) and high-strength (84.28 MPa) NiFe₂O₄-based cermets has been obtained by adding 0.50 wt% MnO₂ into the matrix.     

Synthesis and characterization of polyrhodanine/nickel ferrite nanocomposite with an effective and broad spectrum antibacterial activity

Nickel ferrite nanoparticles were successfully synthesized via a co-precipitation approach, and then polyrhodanine/nickel ferrite nanocomposite (PRh/NiFe₂O₄) as an antimicrobial agent was fabricated by a chemical polymerization method. The synthesized NiFe₂O₄ nanoparticles and PRh/NiFe₂O₄ nanocomposite were chemically, magnetically and morphologically characterized using FTIR, FESEM, DLS, VSM and XRD techniques. The FESEM analysis showed that the NiFe₂O₄ nanoparticles had a polygon structure with an average diameter of 50 nm. According to disc diffusion as well as MIC and MBC tests, the PRh/NiFe₂O₄ nanocomposite had better antibacterial effects on killing Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli in comparison with the NiFe₂O₄ nanoparticles.     

Spinels as cathodes for the electrochemical reduction of O2 and NO

Spinels were synthesised and investigated as electro-catalyst for the electrochemical reduction of oxygen and nitric oxide using cyclic voltammetry and cone shaped electrodes. The following four spinels were investigated; CoFe₂O₄, NiFe₂O₄, CuFe₂O₄ and Co₃O₄. The composition CuFe₂O₄ revealed the largest difference in activity between reduction of oxygen and the reduction of nitric oxide, the activity being highest for the reduction of nitric oxide. The material is probably not stable when polarised cathodically. However it seems that the electrode material can be regenerated upon oxidation. NiFe₂O₄ is also more active for the reduction of nitric oxide than for the reduction of oxygen, whereas the cobalt containing spinels have a higher activity for the reduction of oxygen than for the reduction of nitric oxide.