Magnetic resonance of the NiFe2O4 nanoparticles in the gigahertz range

We report an adjustable magnetic resonance frequency from 1.45 to 2.54 GHz for NiFe₂O₄ nanoparticles which were prepared by a sol–gel process. X-ray diffraction and scanning electron microscopy results indicate that the samples are polycrystalline nanoparticles, and the size of the particles increases obviously with the thermal treatment temperature. The consequence of the surface composition suggests that the oxygen defects are present in the nanoparticle surface, and this surface magnetic state can show a strong surface anisotropy. With decreasing size of the particle, the surface magnetic effect is predominant, resulting in an increase of resonance frequency for NiFe₂O₄ nanoparticles. This finding provides a new route for NiFe₂O₄ materials that can be used in the gigahertz range.     

Amino Functionalized Nano Fe3O4@SiO2 as a Magnetically Green Catalyst for the One-Pot Synthesis of Spirooxindoles Under Mild Conditions

(3-Aminopropyl)-triethoxysilane attached to Fe₃O₄@SiO₂ nanoparticles has been characterized by powder X-ray diffraction, vibrating sample magnetometer, scanning electronic microscope, transmission electron microscope, energy dispersive X-ray, thermal gravimetric analysis, and Fourier transform infrared spectroscopy. The prepared nanoparticles employed as a heterogeneous catalyst in the synthesis of spirooxindoles derivatives in one-pot four-component reactions of isatin, methyl cyanoacetate or malononitrile, hydrazine hydrate, and ethyl acetoacetate. Amino-functionalized magnetic nanoparticles showed high catalytic activity in mild reaction conditions and excellent yields of products in short reaction times. Also, this nanocatalyst can be easily recovered by a magnet and reused for subsequent reactions for at least 5 times without noticeable loss in catalytic activity.     

A Novel Catalyst Pt/CoAl2O4/Al2O3 for Combination CO2 Reforming and Partial Oxidation of CH4

Pt/CoAl₂O₄/Al₂O₃, Pt/CoO_x/Al₂O₃, CoAl₂O₄/Al₂O₃ and CoO_x/Al₂O₃ catalysts were studied for combination CO₂ reforming and partial oxidation of CH₄. The results indicate that Pt/CoAl₂O₄/Al₂O₃ is the most effective, and XRD results indicate that Pt species are well dispersed over the Pt/CoAl₂O₄/Al₂O₃. High dispersion is related to the presence of CoAl₂O₄, formed during calcining at high temperature before Pt addition. In the presence of Pt, CoAl₂O₄ in the catalyst could be reduced partially at 973 K. Based on these results, it appears that zerovalent platinum with high dispersion and zerovalent cobalt resulting from CoAl₂O₄ reduction are responsible for high activity in the Pt/CoAl₂O₄/Al₂O₃ catalyst.     

Catalytic Properties of Cr2O3 Doped with MgO Supported on MgF2 and Al2O3

Catalytic properties of Cr₂O₃ supported on MgF₂ or Al₂O₃ have been modified by magnesium oxide. The catalysts have been obtained by the co-impregnation method and characterised by: BET, XRD and TPR. As follows from the results, the oxides supported on magnesium fluorine react with each other already at 400 °C, leading to formation of an amorphous spinel-like phase. On the Al₂O₃ support such an MgCr₂O₄ spinel has appeared at much higher temperatures. The addition of magnesium oxide has a significant effect on the activity and selectivity of the catalysts studied in the CO oxidation reaction at room temperature and in the reaction of cyclohexane dehydrogenation. The magnesium–chromium catalysts supported on MgF₂ have been found to show much higher activity and selectivity than the analogous systems supported on Al₂O₃.     

Cooperative Activation in the Synthesis of Flavanone Antioxidants Using a Simple and Highly Efficient Magnetically Recoverable Nano-Cu-CoFe2O4 Catalyst

ABSTRACT

Double mixed Cu_0.5Co_0.5Fe₂O₄ ferrite nanoparticles were found as a highly efficient and magnetically separable nanocatalyst for the synthesis of varied flavanone antioxidants. A wide range of flavanone derivatives were prepared with excellent isolated yields within the short reaction times. The catalyst could be separated using a simple magnetic extraction and reused 6 times with no remarkable loss of activity. The high activity of the prepared catalyst was attributed to the cooperative activation of the carbonyl group by both copper and cobalt via a synergistic catalytic effect that facilitates the Micheal addition of the hydroxyl group to the α,β-unsaturated ketone.     

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.     

Green synthesis of thiiranes from epoxides catalyzed by magnetically separable CuFe2O4/Mg(OH)2 nanocomposite in water under benign conditions

The magnetically separable CuFe₂O₄/Mg(OH)₂ nanocomposite was prepared and characterized by FT-IR, XRD, SEM, EDS, and VSM techniques. The synthesized nanoparticles were used as a new and efficient heterogeneous catalyst for the conversion of various epoxides to the corresponding thiiranes with thiourea in water solvent at room temperature. The reactions were completed within 1–3.7?h to give thiiranes in 70–99% yields. The applied CuFe₂O₄/Mg(OH)₂ nanocomposite was separated easily using an external magnet and reused for several times without any considerable loss of activity.     

CoFe2O4@SiO2/PrNH2 nanoparticles as highly efficient and magnetically recoverable catalyst for the synthesis of 1,3-thiazolidin-4-ones

An efficient three-component synthesis of 1,3-thiazolidin-4-ones is described by one-pot condensation of aldehydes, aromatic amine and thioglycolic acid with nano-CoFe₂O₄@SiO₂/PrNH₂ as a robust heterogeneous catalyst. The significant advantages of this protocol are the use of magnetically recoverable catalyst, high to excellent product yields, operational simplicity and the use of CoFe₂O₄@SiO₂/PrNH₂ nanoparticles as an environment-friendly catalyst.     

Catalytic Activities of Al2O3-promoted NiSO4/TiO2 for Acid Catalysis

A series of catalysts, NiSO₄/Al₂O₃–TiO₂, for acid catalysis was prepared by the impregnation method, where support, Al₂O₃–TiO₂ was prepared by the coprecipitation method using a mixed aqueous solution of titanium tetrachloride and aluminum nitrate solution followed by adding an aqueous ammonia solution. The addition of nickel sulfate (or Al₂O₃) to TiO₂ shifted the phase transition of TiO₂ from amorphous to anatase to higher temperature because of the interaction between nickel sulfate (or Al₂O₃) and TiO₂. 15-NiSO₄/5-Al₂O₃–TiO₂ containing 15 wt% NiSO₄ and 5 mol% Al₂O₃, and calcined at 400°C exhibited maximum catalytic activities for both reactions, 2-propanol dehydration and cumene dealkylation. The catalytic activities for both reactions were correlated with the acidity of catalysts measured by the ammonia chemisorption method. The charge transfer from Ti atoms to the neighboring Al atoms strengthens the Al–O bond between Al and the surface sulfate species. The addition of Al₂O₃ up to 5 mol% enhanced the acidity, thermal property, and catalytic activities of NiSO₄/Al₂O₃–TiO₂ gradually due to the interaction between Al₂O₃ and TiO₂ and consequent formation of Al–O–Ti bond.     

Dehydrogenation of ethylbenzene over TiO2-Fe2O3 and ZrO2-Fe2O3 mixed oxide catalysts

The mixed metal oxides TiO₂-Fe₂O₃ and ZrO₂-Fe₂O₃ were examined as potential catalysts for the dehydrogenation reaction of ethylbenzene. The acidic and basic properties and surface area, pore volume and pore size distribution of these catalysts were measured. The catalytic activities can be correlated very well with the surface area and the acidity and basicity of ZrO₂-Fe₂O₃ catalysts. However, for TiO₂-Fe₂O₃ catalysts, the surface area, the amount of acidic and basic sites and TiFe₂O₅ crystallinity are all important factors affecting the catalytic activities for ethylbenzene dehydrogenation. A synergistic effect was found for the TiO₂-Fe₂O₃ and ZrO₂-Fe₂O₃ catalyst system and also for the TiO₂-Fe₂O₃-ZrO₂ system, i.e. the activities of these catalysts can be ranked in the following order: TiO₂-Fe₂O₃-ZrO₂>TiO₂-Fe₂O₃ >ZrO₂>Fe₂O₃>TiO₂. Meanwhile, all of these catalysts showed higher activities than the conventional potassium-promoted iron catalysts.     

Fe3O4@SiO2-SnCl4: An Efficient Catalyst for the Synthesis of Xanthene Derivatives under Ultrasonic Irradiation

Grafting of SnCl₄ on the Fe₃O₄@SiO₂ nanoparticles afforded Fe₃O₄@SiO₂-SnCl₄ as a novel inorganic heterogenous catalyst, which was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), vibrating sample magnetometry (VSM), Field Emission Scanning Electron Microscopy (FE-SEM), and transmission electron microscopy (TEM). In this research, we report a convenient and efficient direct protocol for the preparation of xanthene derivatives via condensation of β-naphthol, dimedone, or mixture of β-naphthol and dimedone with various aromatic aldehydes in the presence of the catalytic amount of Fe₃O₄@SiO₂-SnCl₄ under ultrasonic irradiation. This procedure has a lot of advantages such as: very easy reaction conditions, absence of any tedious workup, or purification, and much milder method. The corresponding products have been obtained in excellent yields, high purity, and short reaction times.     

Methanobactin-Mediated Synthesis of Gold Nanoparticles Supported over Al2O3 toward an Efficient Catalyst for Glucose Oxidation

Methanobactin (Mb) is a copper-binding peptide that appears to function as an agent for copper sequestration and uptake in methanotrophs. Mb can also bind and reduce Au(III) to Au(0). In this paper, Au/Al₂O₃ catalysts prepared by a novel incipient wetness-Mb-mediated bioreduction method were used for glucose oxidation. The catalysts were characterized, and the analysis revealed that very small gold nanoparticles with a particle size <4 nm were prepared by the incipient wetness-Mb-mediated bioreduction method, even at 1.0% Au loading (w/w). The influence of Au loading, calcination temperature and calcination time on the specific activity of Au/Al₂O₃ catalysts was systematically investigated. Experimental results showed that decomposing the Mb molecules properly by calcinations can enhance the specific activity of Au/Al₂O₃ catalysts, though they acted as reductant and protective agents during the catalyst preparation. Au/Al₂O₃ catalysts synthesized by the method exhibited optimum specific activity under operational synthesis conditions of Au loading of 1.0 wt % and calcined at 450 °C for 2 h. The catalysts were reused eight times, without a significant decrease in specific activity. To our knowledge, this is the first attempt at the preparation of Au/Al₂O₃ catalysts by Mb-mediated in situ synthesis of gold nanoparticles.     

Nano-CuFe2O4@SO3H Catalyzed Efficient One-Pot Cyclo-Dehydration of Dimedone and Synthesis of Chromeno[4,3-b]chromenes

Chlorosulfonic acid immobilized on CuFe₂O₄ nanoparticles (nano-CuFe₂O₄@SO₃H) was evaluated as a recoverable catalyst for the one-pot cyclo-dehydration of dimedone and synthesis of chromeno[4,3-b]chromene derivatives by reaction of arylaldehydes, dimedone or 1,3-cyclohexanedione, with 3-hydroxycoumarine or 4-hydroxycoumarine in good to excellent yield. Also, 2,2′-Arylmethylene bis(3-hydroxy-5,5-dimethyl-2-cyclohexene-1-one) was synthesized by the reaction of aromatic aldehyde and dimedone using nano-CuFe₂O₄ in ethanol at room temperature. The catalyst could be recycled several times without significant loss of its catalytic activity. Clean methodologies, easy work-up procedure, high yield and simple preparation of the catalyst are some advantages of this procedure.     

Structure and photocatalytic performance of magnetically separable titania photocatalysts for the degradation of propachlor

A magnetic photocatalyst was prepared by modification of TiO₂ nanoparticles (Degussa P25) with nanocrystalline γ-Fe₂O₃ nanoparticles through a protective lining made up of two oppositely charged polyelectrolytes. As-prepared magnetically separable photocatalysts differing in γ-Fe₂O₃ loading (3, 8, 13, 20 and 30 wt.%) were characterized by XRD, TEM, thermal analysis, Mössbauer and magnetic measurements. The photocatalytic efficiency of the nanocomposite catalysts was evaluated using a chloroacetanilide herbicide (propachlor) in water as model compound. The primary degradation of propachlor followed pseudo-first-order kinetics according to the Langmuir–Hinshelwood model. Generally, all magnetic photocatalysts exhibit good catalytic activity towards organic pollutants, do not suffer from photodissolution and can be reused several times without any decrease in their photocatalytic activity.     

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.     

Synthesis of MIL-Modified Fe3O4 Magnetic Nanoparticles for Enhancing Uptake and Efficiency of Temozolomide in Glioblastoma Treatment

A nanometric hybrid system consisting of a Fe₃O₄ magnetic nanoparticles modified through the growth of Fe-based Metal-organic frameworks of the MIL (Materials Institute Lavoiser) was developed. The obtained system retains both the nanometer dimensions and the magnetic properties of the Fe₃O₄ nanoparticles and possesses increased the loading capability due to the highly porous Fe-MIL. It was tested to load, carry and release temozolomide (TMZ) for the treatment of glioblastoma multiforme one of the most aggressive and deadly human cancers. The chemical characterization of the hybrid system was performed through various complementary techniques: X-ray-diffraction, thermogravimetric analysis, FT-IR and X-ray photoelectron spectroscopies. The nanomaterial showed low toxicity and an increased adsorption capacity compared to bare Fe₃O₄ magnetic nanoparticles (MNPs). It can load about 12 mg/g of TMZ and carry the drug into A172 cells without degradation. Our experimental data confirm that, after 48 h of treatment, the TMZ-loaded hybrid nanoparticles (15 and 20 μg/mL) suppressed human glioblastoma cell viability much more effectively than the free drug. Finally, we found that the internalization of the MIL-modified system is more evident than bare MNPs at all the used concentrations both in the cytoplasm and in the nucleus suggesting that it can be capable of overcoming the blood-brain barrier and targeting brain tumors. In conclusion, these results indicate that this combined nanoparticle represents a highly promising drug delivery system for TMZ targeting into cancer cells.     

Magnetic CuFe2O4 Prepared by Polymeric Precursor Method as a Reusable Heterogeneous Fenton-like Catalyst for the Efficient Removal of Methylene Blue

The heterogeneous Fenton-like catalysts based on CuFe₂O₄ were prepared by polymeric precursor method at several annealing temperatures. The obtained catalysts were respectively characterized by X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, point of zero charge measurement, and vibrating sample magnetometer. The Fenton-like catalytic activity was evaluated via the oxidation of methylene blue with H₂O₂. The results show that the CuFe₂O₄ phase content and the particle size increase with the annealing temperatures whereas the surface OH groups and the surface acidity decrease. The prepared powders possess typical ferromagnetic properties which allow them to be easily recovered and reused. These catalysts also present highly catalytic activities for the oxidation of methylene blue, which is principally attributed to the catalysis of the CuFe₂O₄ phase. When the annealing temperature increased, the catalytic performance was reduced, corresponding to the increase of particle size and the decrease of surface OH groups.     

Preparation and characterisation of closed-pore Al2O3-MgAl2O4 refractory aggregate utilising superplasticity

ABSTRACT

A novel high closed porosity Al₂O₃-MgAl₂O₄ refractory aggregate has been successfully fabricated by utilising superplasticity with Al₂O₃ and MgO as raw materials, SiC as high temperature pore-forming agent. The effects of the addition amounts of MgO and SiC on porosity, sintering behaviours, phase composition, pore size distribution and microstructure of the refractory aggregate have been investigated. The formation mechanism of the closed pore in the refractory aggregate has been discussed. The results showed that the MgO can improve the superplastic deformation ability of Al₂O₃-based ceramic at high temperature. With the content of MgO and SiC increased, the closed porosity and the pore size increased. The oxidation of SiC improved the sinterability of materials at the initial stage of sintering, and then the released gases due to the further oxidation of SiC promoted the formation of closed pores by motivating the superplastic deformation ability of Al₂O₃-based materials.     

The Magnetism Properties and Surface Microstructure of NBR/Fe3O4 Composites

For preparing the good magnetism properties of rubber, NBR/Fe₃O₄ composites are prepared. In the experiment, the surface microstructure of NBR/Fe₃O₄ and distribution of nano-Fe₃O₄ particles are analyzed. The results showed that after the addition of nano-Fe₃O₄, the surface microstructure of NBR/Fe₃O₄ is greatly improved. The interface bonding of nano-Fe₃O₄ and NBR are close-knit. With adding different mass fractions of nanoparticles, the maximum elongation 300% stress at definite elongation and the tensile strength of composites are decreased, but the shore A hardness of composites is improved. The magnetic property of composites can only rely on mass fraction of nano-Fe₃O₄, while uncorrelated to the degree of scatter of nano-Fe₃O₄.     

Hydrothermal solvothermal synthesis and microwave absorbing study of MCo2O4 (M = Mn,Ni) microparticles

ABSTRACT

MCo₂O₄ (M?=?Mn,Ni) microparticles were synthesised by a simple hydrothermal solvothermal method. The samples were characterised by X-ray diffraction, X-ray energy dispersive spectroscopy and scanning electron microscopy, which showed that MnCo₂O₄ microparticles with spherical particles aggregated by a large number of small cubes and cubic shaped NiCo₂O₄ microcubes were obtained. The microwave absorption properties of these products were systematically investigated by vector network analysis. Results indicated that the minimum reflection loss value of MnCo₂O₄ microparticles was ?26.34?dB at 11.04?GHz with the absorber thickness of 2.5?mm, which was much lower than that of NiCo₂O₄ microcubes with the same absorber thickness. The possible mechanism was analysed, indicating that the geometry and size of MCo₂O₄ (M?=?Mn,Ni) microparticles played a key role in microwave absorption.