EtOAc-dispersed magnetic nanoparticles (DMNPs) of γ-Fe2O3 in the single-pot domino preparation of 5-oxo-2-thioxo-3-thiophenecarboxylate derivatives

EtOAc-dispersed magnetic nanoparticles (DMNPs) of γ-Fe₂O₃ represent a straightforward and green catalyst for the rapid three-component synthesis of 5-oxo-2-thioxo-3-thiophenecarboxylate derivatives as rhodanine skeletons via a single-pot domino process. The rhodanines were prepared over magnetic nanoparticles of γ-Fe₂O₃ without any salt or additives. Dispersed nano-γ-Fe₂O₃ have many advantages, such as stability in air, reusability, reactions with high efficiency, simple separation with magnetic external field from mixture reactions, chemical stability, and also low toxicity.     

Synthesis and magnetic properties of the γ-Fe2O3/poly-(methyl methacrylate)-core/shell nanoparticles

The synthesis of γ-Fe₂O₃/poly-(methyl methacrylate)-core/shell nanoparticles and their magnetic properties are reported. Specific γ-Fe₂O₃ nanoparticles capable of initiating atom transfer radical polymerization (ATRP) were prepared by a ligand exchange reaction of ((chloromethyl)phenylethyl)-dimethylchlorosilane and caprylate-capped γ-Fe₂O₃ nanoparticles of 4 nm in diameter, and the ATRP of methyl methacrylate was carried out subsequently. These nanoparticles were characterized with Fourier transform infrared spectroscopy, transmission electron microscopy and Mössbauer spectroscopy. Low temperature magnetic properties investigated with SQUID magnetometry revealed that the coercivity and the blocking temperature changed slightly owing to surface effects.     

Magnetically recoverable γ-Fe2O3 nanoparticles as a highly active catalyst for Friedel–Crafts benzoylation reaction under ultrasound irradiation

A simple, facile and efficient method has been developed for the Friedel–Crafts benzoylation of arenes using magnetic γ-Fe₂O₃ nanoparticles under solvent-free sonication. The γ-Fe₂O₃ nanoparticles were used as an efficient and magnetically recoverable catalyst for the synthesis of aromatic ketones in good to excellent yields at room temperature under solvent-free. The reaction occurred with high regioselectivity under mild condition. The magnetic γ-Fe₂O₃ nanoparticles are economically synthesized in large-scale, easily separated from the reaction mixture by an external magnet and able to be reused several times without significant loss of the catalytic performance, which make them easy application to industrial processes.     

Synthesis,characterization and magnetic properties of γ-Fe2O3 nanoparticles via a non-aqueous medium

Acicular shaped γ-Fe₂O₃ nanoparticles (major axis: 17±2 nm; minor axis: 1.7±1 nm) have been prepared using lauric acid as a non-aqueous medium. The products were investigated by IR, TG-DTA, XRD, Raman, SEM, TEM and magnetization measurements. For the preparation of pure γ-Fe₂O₃ nanoparticles, the suitable condition of the molar ratio of lauric acid to iron nitrate is set 2:1 and the appropriate temperature lies in the range 573–673 K. Besides, either pure α-Fe₂O₃ or a mixture of γ-Fe₂O₃ and α-Fe₂O₃ can also be obtained with the change of the molar ratio of lauric acid to iron nitrate. The experimental results indicate that the particle sizes, thermal stability and magnetic properties of the iron oxide strongly depend on the conditions in the preparation.     

Nanomagnetically modified sulfuric acid (γ-Fe2O3@SiO2-OSO3H): an efficient, fast, and reusable green catalyst for the Ugi-like Groebke-Blackburn-Bienaymé three-component reaction under solvent-free conditions

Superparamagnetic nanoparticles of modified sulfuric acid (γ-Fe₂O₃@SiO₂-OSO₃H) represent a straightforward and green catalyst for the rapid synthesis of aminoimidazopyridine skeletons via the Ugi-like Groebke-Blackburn-Bienaymé three-component reaction. The γ-Fe₂O₃@SiO₂-OSO₃H catalyst could be recovered and reused in five reaction cycles, giving a total TON = 453. The products were prepared under solvent-free conditions without any additives.     

Improvement of Thermostability and Activity of Firefly Luciferase Through [TMG][Ac] Ionic Liquid Mediator

Firefly luciferase catalyzes production of light from luciferin in the presence of Mg²⁺?CATP and oxygen. This enzyme has wide range of applications in biotechnology and development of biosensors. The low thermal stability of wild-type firefly luciferase is a limiting factor in most applications. Improvements in activity and stability of few enzymes in the presence of ionic liquids were shown in many reports. In this study, kinetic and thermal stability of firefly luciferase from Photinus pyralis in the presence of three tetramethylguanidine-based ionic liquids was investigated. The enzyme has shown improved activity in the presence of [1, 1, 3, 3-tetramethylguanidine][acetate], but in the presence of [TMG][trichloroacetate] and [TMG][triflouroacetate] activity, it decreased or unchanged significantly. Among these ionic liquids, only [TMG][Ac] has increased the thermal stability of luciferase. Incubation of [TMG][Ac] with firefly luciferase brought about with decrease of K _m for ATP.     

Thermal properties of the γ-Fe2O3/poly(methyl methacrylate) core/shell nanoparticles

Thermal properties of γ-Fe₂O₃/poly(methyl methacrylate) (PMMA) core/shell particles with an average core size of 4 nm were studied through measurements of thermogravimetry, powder X-ray diffraction and magnetization. The thermal degradation of the PMMA shell in the air was found to occur at temperatures lower by about 60 °C than that of free PMMA. Random scission of the PMMA chains seemed to be catalyzed by the core oxide. The γ-Fe₂O₃ to α-Fe₂O₃ structural transformation took place at different temperatures depending upon the shell material. Namely, α-Fe₂O₃ was the only product for the caprylate-capped γ-Fe₂O₃ nanoparticles treated at 400 °C, whereas γ-Fe₂O₃ still remained for the γ-Fe₂O₃/PMMA composite treated at 500 °C. It is possible that some species containing silicon of the polymerization initiator origin were formed on the surface and prevented interparticle atomic diffusions needed for the γ–α transformation.     

Effect of capping and particle size on Raman laser-induced degradation of γ-Fe2O3 nanoparticles

Diol capped γ-Fe₂O₃ nanoparticles are prepared from ferric nitrate by refluxing in 1,4-butanediol (9.5 nm) and 1,5-pentanediol (15 nm) and uncapped particles are prepared by refluxing in 1,2-propanediol followed by sintering the alkoxide formed. X-ray diffraction (XRD) shows that all the samples have the spinel phase. Raman spectroscopy shows that the samples prepared in 1,4-butanediol and 1,5-pentanediol and 1,2-propanediol (sintered at 573 and 673 K) are γ-Fe₂O₃ and the 773 K-sintered sample is Fe₃O₄. Raman laser studies carried out at various laser powers show that all the samples undergo laser-induced degradation to α-Fe₂O₃ at higher laser power. The capped samples are however, found more stable to degradation than the uncapped samples. The stability of γ-Fe₂O₃ sample with large particle size (15.4 nm) is more than the sample with small particle size (10.2 nm). Fe₃O₄ having a particle size of 48 nm is however less stable than the smaller γ-Fe₂O₃ nanoparticles.     

Silica iminopyridine-functionalized nanomaghemite enhances the oxygenation activity and durability of simple Co(II) salophen complex

A novel magnetically recoverable catalyst was produced by coordinative attachment of Co(II) salophen complex to silica iminopyridine (SIPy)-functionalized-γ-Fe₂O₃ magnetic nanoparticles (SMNP@SIPy/Co(II) salophen). The vibration spectra and compositional data provided sufficient evidences for the structural integrity of as-prepared organic–inorganic nanohybrid. The magnetic nanocatalyst proved to be an efficient and selective heterogeneous catalyst for oxidation of different benzylic alcohols and featured higher catalytic activity and stability than that of homogenous counterpart. A TOF of 151 h⁻¹ and TON of more than 322 were obtained for oxidation of 4-cholrobenzyl alcohol in this catalytic system. The supported catalyst could easily be recovered from the reaction mixture by an external magnetic field and reused for subsequent experiments with consistent catalytic activity.     

Magnetic diphase nanostructure of ZnFe2O4/γ-Fe2O3

Magnetic diphase nanostructures of ZnFe₂O₄/γ-Fe₂O₃ were synthesized by a solvothermal method. The formation reactions were optimized by tuning the initial molar ratios of Fe/Zn. All samples were characterized by X-ray diffraction, thermogravimetric analysis, infrared spectroscopy, and Raman spectra. It is found that when the initial molar ratio of Fe/Zn is larger than 2, a diphase magnetic nanostructure of ZnFe₂O₄/γ-Fe₂O₃ was formed, in which the presence of ZnFe₂O₄ enhanced the thermal stability of γ-Fe₂O₃. Further increasing the initial molar ratio of Fe/Zn larger than 6 destabilized the diphase nanostructure and yielded traces of secondary phase α-Fe₂O₃. The grain surfaces of diphase nanostructure exhibited a spin-glass-like structure. At room temperature, all diphase nanostructures are superparamagnetic with saturation magnetization being increased with γ-Fe₂O₃ content.     

Ethanol Gas Sensor Based on γ-Fe2O3 Nanoparticles Working at Room Temperature with High Sensitivity

Improving the sensing sensitivity and lowering the working temperature are the critical issues for the practical application of gas sensors. For a gas sensor, the sensing materials play important roles in determining the sensing properties. In the present work, γ-Fe₂O₃ microspheres composed of nanoparticles were successfully fabricated by a typical facile hydrothermal process and a following annealing treatment. Interestingly, the as-synthesized γ-Fe₂O₃ microspheres showed excellent sensing properties for the detection of ethanol gas with high sensitivity, and especially working temperature as low as room temperature. The gas sensing results showed that at the optimal operating temperature (200 °C), the response intensity of γ-Fe₂O₃ microspheres for 1000 ppm ethanol gas could reach 74.6 and the limit of detection (LOD) was about 0.026 ppm. At room temperature, the γ-Fe₂O₃ microspheres still demonstrated a good response to different concentrations of ethanol gas from 1 to 1000 ppm, with a very good selectivity over other gas species and a good stability. This study indicated that the γ-Fe₂O₃ phase could be a type of promising room-temperature gas sensing material for ethanol gas detection.     

Ni2+ supported on hydroxyapatite-core-shell γ-Fe2O3 nanoparticles: a novel,highly efficient and reusable lewis acid catalyst for the regioselective azidolysis of epoxides in water

In this research, Ni²⁺ supported on hydroxyapatite-core-shell magnetic γ-Fe₂O₃ nanoparticles (γ-Fe₂O₃@HAp-Ni²⁺) as a novel, efficient, reusable and heterogeneous catalyst was reported. In this protocol, we used this catalyst for the ring opening of epoxide with sodium azide in water. The catalyst can be readily isolated using an external magnet and no obvious loss of activity was observed when the catalyst was reused in seven consecutive runs. The mean size and the surface morphology of the nanoparticles were characterized by transmission electron microscopy, scanning electron microscope, vibrating sample magnetometry, X-ray powder diffraction and Fourier transform infrared techniques.     

Synthesis and electromagnetic properties of polyaniline-coated silica/maghemite nanoparticles

Polyaniline coated silica/maghemite nanoparticles (PANI/SiO₂/γ-Fe₂O₃ composites) were synthesized by the combination of a sol-gel process and an in-situ polymerization method, in which ferrous and ferric salts as well as tetraethyl orthosilica (TEOS) acted as the precursor for γ-Fe₂O₃ and silica, respectively. As a result, the SiO₂/γ-Fe₂O₃ particle showed a core-shell structure, with γ-Fe₂O₃ as the magnetic core and silica as the shell of the particle. The shell thickness can be controlled by changing the TEOS concentration. The PANI/SiO₂/γ-Fe₂O₃ composites revealed a multilayer core-shell structure, where PANI is the outer shell of the composite. The doping level and the conductivity of PANI/SiO₂/γ-Fe₂O₃ composites decreased with increasing the TEOS content due to the presence of the less coated PANI on the SiO₂/γ-Fe₂O₃ core at higher TEOS content. For a SQUID analysis at room temperature, all γ-Fe₂O₃ containing composites showed a typical superparamagnetic behavior. The saturation magnetization of SiO₂/γ-Fe₂O₃ nanoparticles decreased with increasing the TEOS content due to the increase in silica shell thickness, while the saturation magnetization of PANI/SiO₂/γ-Fe₂O₃ composites also decreased with increasing the TEOS content, which is attributed to the lower conductivity of PANI in the composites at higher TEOS content.     

Bowl-shaped poly(3,4-ethylenedioxythiophene)/γ-Fe2O3 composites with elecromagnetic function

In this paper, electromagnetic poly(3,4-ethylenedioxythiophene)/γ-Fe2O3 (PEDOT/γ-Fe2O3 ) micro-bowls, 1 2 μm in diameter, were prepared by a simple environment-friendly process. In this method, the aqueous solution of cetyltrimethylammonium bromide (CTAB) instead of any organic solvent was used. FeCl3 acted as a source of Fe Ⅲ for the formation of γ-Fe2O3 and as an oxidant for the polymerization of 3,4-ethylenedioxythiophene (EDOT). The bowl-shaped morphology of PEDOT/γ-Fe2O3 composites was strongly influenced by the concentration of CTAB, FeCl2 , ammonia solution and the reaction temperature. The saturation magnetization of PEDOT/γ-Fe2O3 micro-bowls increased with the increase of FeCl2 concentration and reached 6.20 Am2 /kg at the FeCl2 concentration of 0.30 mol/L. The conductivity of the PEDOT/γ-Fe2O3 composites was in the range of 101 S/cm. The electrical and magnetic sources of PEDOT/γ-Fe2O3 micro-bowls were confirmed by SEM-EDX, TEM, XRD and XPS spectra. And the possible formation mechanism of PEDOT//γ-Fe2O3 was proposed.     

Synthesis,characterization and application of sulfonic acid supported on ferrite–silica superparamagnetic nanoparticles

In this study, the synthesis of sulfonic acid supported on ferrite–silica superparamagnetic nanoparticles (Fe₃O₄@SiO₂@SO₃H) as a nanocatalyst with large density of acidic groups is suggested. This nanocatalyst was prepared in three steps: preparation of colloidal iron oxide magnetic nanoparticles (Fe₃O₄ MNPs), coating of silica on Fe₃O₄ MNPs (Fe₃O₄@SiO₂) and incorporation of sulfonic acid as a functional group on the surface of Fe₃O₄@SiO₂ nanoparticles (Fe₃O₄@SiO₂@SO₃H). The properties of the prepared magnetic nanoparticles were characterized using transmission electron microscopy, infrared spectroscopy, vibrating sample magnetometry, X‐ray diffraction and thermogravimetric analysis. Finally, the applicability of the synthesized magnetic nanoparticles was tested as a heterogeneous solid acid nanocatalyst for one‐pot synthesis of diindolyloxindole derivatives in aqueous medium. Oxindole derivatives were produced by the coupling of indole and isatin compounds with good to high yields (60–98%). Copyright © 2016 John Wiley & Sons, Ltd.     

Efficient and selective oxidation of hydrocarbons with tert-butyl hydroperoxide catalyzed by oxidovanadium(IV) unsymmetrical Schiff base complex supported on γ-Fe2O3 magnetic nanoparticles

The catalytic activity of an oxidovanadium(IV) unsymmetrical Schiff base complex supported on γ-Fe₂O₃ magnetic nanoparticles, γ-Fe₂O₃@[VO(salenac-OH)] in which salenac-OH?=?[9-(2′,4′-dihydroxyphenyl)-5,8-diaza-4-methylnona-2,4,8-trienato](-2), was explored in the oxidation of hydrocarbons with tert-butyl hydroperoxide (TBHP, 70% aqueous solution) as oxidant. High catalytic activity and selectivity were demonstrated by this magnetic nanocatalyst in alkane hydroxylation and alkene epoxidation, and the corresponding products were obtained with good to excellent yields in acetonitrile at 50 °C. Reasonable catalytic activity was presented by this supported catalyst in the epoxidation of linear alkenes under optimal reaction conditions. In addition, alkylbenzene derivatives and cycloalkanes can be oxidized to their corresponding alcohols and ketones with good yields in this catalytic system. It is possible to magnetically separate the γ-Fe₂O₃@[VO(salenac-OH)] catalyst and reuse it four times without losing the activity significantly. Moreover, the catalyst structure and morphology do not change after recovery, as indicated by comparing scanning electron microscopy (SEM) image, Fourier transform infrared (FT-IR) and diffuse reflectance spectrum (DRS) of the recovered catalyst with those of the fresh catalyst.

     

Synthesis of Fe3O4@SiO2@polymer nanoparticles for controlled drug release

Novel multifunctional nanoparticles containing a magnetic Fe₃O₄@SiO₂ sphere and a biocompatible block copolymer poly(ethylene glycol)-b-poly(aspartate) (PEG-b-PAsp) were prepared. The silica coated on the superparamagnetic core was able to achieve a magnetic dispersivity, as well as to protect Fe₃O₄ against oxidation and acid corrosion. The PAsp block was grafted to the surface of Fe₃O₄@SiO₂ nanoparticles by amido bonds, and the PEG block formed the outermost shell. The anticancer agent doxorubicin (DOX) was loaded into the hybrid nanoparticles via an electrostatic interaction between DOX and PAsp. The release rate of DOX could be adjusted by the pH value.     

Polyphosphoric acid supported on silica-coated NiFe2O4 nanoparticles: An efficient and magnetically-recoverable catalyst for N-formylation of amines

A rapid, green and simple method for the N-formylation of various aromatic amines with formic acid using polyphosphoric acid supported on silica-coated NiFe₂O₄ magnetic nanoparticles (NiFe₂O₄@SiO₂–PPA) under solvent-free conditions at room temperature has been developed. The magnetic catalyst can be easily removed by a simple magnet and reused at least three times without any loss of its high catalytic activity. In addition to its facility, this protocol enhances product purity and promises economic and also environmental profits.     

Role of surface spins on magnetization of Cr2O3 coated γ-Fe2O3 nanoparticles

Effect of surface spins in chromium oxide (Cr₂O₃) coated maghemite (γ-Fe₂O₃) nanoparticles (13 nm) as prepared by microwave plasma technique have been studied in detail. The temperature dependent zero field cooled/field cooled (ZFC/FC) measurements revealed the blocking temperature at T_B = 75 K. Simulated ZFC/FC curves exhibited large value of effective anisotropy of Cr₂O₃ coated γ-Fe₂O₃ nanoparticles as compared to bulk γ-Fe₂O₃ but less than bare γ-Fe₂O₃ nanoparticles. Bloch's law was fitted on M_S-T data and revealed the values of Bloch's constant B = 3.523 × 10⁻⁴ K^−b and Bloch's exponent b = 1.10. The higher value of B than in bulk is due to weaker exchange coupling J (B ̴ 1/J) on the surface of nanoparticle due to disorder surface spins, while lower value of b is due to no spin wave excitation in presence of large energy band gap at nanoscale. Kneller's law fit on H_C-T data deviated in all temperature range which is due to strong surface anisotropy, core-shell interactions and superparamagnetism. Interparticle interactions and spin glass behavior were investigated by using different physical laws for f-dependent ac susceptibility and they confirmed the presence of spin glass behavior which is due to disordered frozen surface spins and random interparticle interactions.     

Simultaneous photocatalytic oxidation and adsorption for efficient As(III) removal by magnetic BiOI/γ-Fe2O3 core–shell nanoparticles

Addressing arsenite pollution in groundwater has drawn great attention. It is attractive to pre-oxidize highly mobile As(III) to relatively low-toxic As(V) with a subsequent adsorption separation process. Herein, BiOI anchoring on γ-Fe₂O₃ is performed to synthesize BiOI/γ-Fe₂O₃ core–shell nanoparticles for efficient removal of As(III) via a simultaneous photocatalytic oxidization–adsorption process. The physical and chemical structures of BiOI/γ-Fe₂O₃ are investigated by transmission electron microscopy, Fourier transform infrared spectroscopy, and X-ray diffraction measurements. The photoluminescence and electron spin resonance (ESR) characterization were employed to ascertain the possible reaction mechanism of visible-light-driven photocatalytic oxidation of As(III). Such BiOI/γ-Fe₂O₃ delivers a superior As(III) removal capability under visible light irradiation with an arsenic removal efficiency of 99.8% within 180 min, higher than those of BiOCl/γ-Fe₂O₃ (81.7%) and BiOBr/γ-Fe₂O₃ (98.9%). The optimal BiOI/γ-Fe₂O₃ (molar ratio of 2:1) is obtained by rationally adjusting the molar ratio of BiOI to γ-Fe₂O₃. The as-synthesized BiOI/γ-Fe₂O₃ performs well in a wide pH range of 2–8. Only coexisting PO₄^3? anions have a significant effect on the As(III) removal. The free radical trapping experiment and ESR results demonstrate that the ?O₂^? and h⁺ are the main active substances for the photocatalytic oxidation of As(III) on BiOI/γ-Fe₂O₃. This work not only gives a novel magnetic core–shell nanoparticle photocatalyst for efficient photocatalytic oxidation and adsorption of As(III) but also offers a new strategy to rationally design BiOX for its related practical applications.