Facile Preparation of a Stable Fe3O4@LDH@NiB Magnetic Core‐Shell Nanocomposite for Hydrogenation

A novel NiB deposited layered double hydroxide (LDH ) coated ferroferric oxide (Fe₃O₄ @LDH @NiB ) magnetic core‐shell nanocomposite was successfully fabricated by the combination of coprecipitation and impregnation‐reduction. During the Fe₃O₄ @LDH preparation, a facile template‐free approach was employed to introduce the LDH shell, which was more efficient than the conventional method for the preparation of mesoporous materials that always needs to introduce and remove templates. The resulted Fe₃O₄ @LDH has a relatively high surface area and abundant surface hydroxyl group, which can adsorb metal ions, making it favorable to disperse and stabilize the active Ni species, as demonstraed by TEM , XPS , FT‐IR and BET characterizations. Therefore, it exhibited good activity in the selective hydrogenation of cinnamic acid to hydrocinnamic acid with the conversion and selectivity both approaching to 100%. Notably, the obtained Fe₃O₄ @LDH @NiB can be easily separated by an external magnetic field and recycled eleven times without appreciable loss of its initial catalytic activity.     

Anchored Ni-dimethylglyoxime complex on Fe3O4@SiO2 core/shell nanoparticles for the clean catalytical synthesis of dicoumarols

Ni-Dimethylglyoxime complex immobilized on functionalized Fe₃O₄ was synthesized by a post-grafting way and utilized as a novel, thermally stable, recoverable, and efficient for green synthesis of dicoumarols through reaction of 4-hydroxycoumarin with various aldehydes in excellent yields and higher rate. Fe₃O₄@SiO₂-silylcyclopropyl-dimethylglyoxime-Ni superparamagnetic nanoparticles (MNP_s) were investigated by Fourier transform infrared spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, vibrating sample magnetometer, and Brunauer–Emmett–Teller technique. This nanocatalyst could be conveniently recovered via the use of an external magnetic field and reused for subsequent reactions for at least 7 times without any remarkable change and decrease in catalytic activity.     

Synthesis and Infrared Multi‐band Absorption Properties of Core‐shell NaYF4:Yb3+, Er3+@SiO2 Nanoparticles

Due to the unique size effects, nanomaterials in infrared absorption have attracted much attention for their strong absorption in the infrared region. To achieve the infrared multi‐band absorption, we propose to synthesize a core‐shell structure nanomaterial consisting of NaYF₄:Yb³⁺, Er³⁺ core and a layer of SiO₂ as shell. A series of NaYF₄:Yb³⁺, Er³⁺ nanocrystals were synthesized through hydrothermal method by adjusting the ratio of citric acid(CA)‐to‐NaOH, and the effects of CA concentration, and NaOH concentration were studied in detail. NaYF₄:Yb³⁺, Er³⁺@SiO₂ nanoparticles were synthesized by sol‐gel method using TEOS as silica source. The results show that the core‐shell NaYF₄:Yb³⁺, Er³⁺@SiO₂ nanoparticles were successfully synthesized. Up‐conversion spectra of these nanoparticles were recorded with 980 nm laser excitation under room temperature. There are no changes of the emission centers of nanoparticles before or after silica coating, but the emission intensities of nanoparticles after silica coating are weakened. Furthermore, the property of infrared multi‐band absorption was tested through ultraviolet‐visible‐near infrared spectrophotometer and infrared absorption spectra. The results illustrate that the multi‐band infrared absorption nanomaterial was successfully synthesized.     

Hierarchical Fe3O4@TiO2 Yolk–Shell Microspheres with Enhanced Microwave‐Absorption Properties

A facile and efficient strategy for the synthesis of hierarchical yolk–shell microspheres with magnetic Fe₃O₄ cores and dielectric TiO₂ shells has been developed. Various Fe₃O₄@TiO₂ yolk–shell microspheres with different core sizes, interstitial void volumes, and shell thicknesses have been successfully synthesized by controlling the synthetic parameters. Moreover, the microwave absorption properties of these yolk–shell microspheres, such as the complex permittivity and permeability, were investigated. The electromagnetic data demonstrate that the as‐synthesized Fe₃O₄@TiO₂ yolk–shell microspheres exhibit significantly enhanced microwave absorption properties compared with pure Fe₃O₄ and our previously reported Fe₃O₄@TiO₂ core–shell microspheres, which may result from the unique yolk–shell structure with a large surface area and high porosity, as well as synergistic effects between the functional Fe₃O₄ cores and TiO₂ shells.     

Nano‐Fe3O4 Encapsulated‐Silica Particles Bearing 3‐Aminopropyl Group as a Magnetically Separable Catalyst for Efficient Knoevenagel Condensation of Aromatic Aldehydes with Active Methylene Compounds

Knoevenagel condensation of aromatic aldehydes with active methylene compounds such as malononitrile, ethylcyanoacetate, benzimidazol‐2‐acetonitrile and benzothiazole‐2‐acetonitrile proceeded very smoothly, catalyzed by nano‐Fe₃O₄ encapsulated‐silica particles supported primary amine. Both reaction time and yield are satisfying. The advantages of this catalyst are ease of preparation, non‐toxicity, low cost, ease of handling and recyclability.     

Magnetic Fe3O4‐PS‐Polyacetylene Composite Microspheres Showing Chirality Derived From Helical Substituted Polyacetylene

This communication reports the first integration of two significant concepts, “macromolecular helicity‐derived chirality,” and “magneticity” in one single microsphere entity. The novel chiral magnetic composite microspheres consisted of magnetic Fe₃O₄ nanoparticles and optically active helical substituted polyacetylene. Therefore, they exhibited both remarkable optical activity and magneticity. The microspheres adsorbed (R)‐(+)‐1‐phenylethylamine much more quickly than the other enantiomer, demonstrating the potential applications of the chiral magnetic composite microspheres in chiral recognition and chiral resolution.     

Metallodendritic Grafted Core–Shell γ‐Fe2O3 Nanoparticles Used as Recoverable Catalysts in Suzuki C?C Coupling Reactions

The use of dendritic structures for the grafting of core–shell γ‐Fe₂O₃/polymer 300 nm superparamagnetic nanoparticles (MNPs) has been performed with four metallodendrons that were functionalized with diphosphinopalladium complexes. The catalytic performance of these nanocatalysts was optimized for the Suzuki C? C cross‐coupling reaction. These results demonstrated the importance of optimizing the catalytic efficiency of grafted MNPs by optimizing the dendritic structures and the nature of the peripheral phosphine ligands. All of these nanocatalysts showed remarkable reactivity towards bromoarenes and they were recovered and efficiently reused by magnetic separation with almost no loss of reactivity, even after 25 cycles.     

Synthesis of Bis‐Thiazolidinones Using Chitosan‐attached Nano‐CuFe2O4 as an Efficient and Retrievable Heterogeneous Catalyst

The preparation of bis‐thiazolidinones has been achieved by a one‐pot condensation reaction of araldehydes, ethylenediamine, and 2‐mercaptoacetic acid in the presence of nano‐CuFe₂O₄@chitosan under reflux conditions in toluene. The catalyst was characterized by powder X‐ray diffraction (XRD), scanning electronic microscopy (SEM), vibrating sample magnetometer (VSM) measurements, thermal gravimetric analysis (TGA), and FT‐IR spectroscopy. This method provides several advantages including excellent yields, wide range of products, reusability of the catalyst, and a low amount of the catalyst.     

Synthesis,characterization and catalytic performance of core‐shell structure magnetic Fe3O4/P(GMA‐EGDMA)‐NH2/HPG‐COOH‐Pd catalyst

A strategy has been developed for the synthesis, characterization and catalysis of magnetic Fe₃O₄/P(GMA‐EGDMA)‐NH₂/HPG‐COOH‐Pd core‐shell structure supported catalyst. The P(GMA‐EGDMA) polymer layer was coated on the surface of hollow magnetic Fe₃O₄ microspheres through the effect of KH570. The core‐shell magnetic Fe₃O₄/P(GMA‐EGDMA) modified by ‐NH₂ could be grafted with HPG. Then, the hyperbranched glycidyl (HPG) with terminal ‐OH were modified by ‐COOH and adsorbed Pd nanoparticles. The hyperbranched polymer layer not only protected the Fe₃O₄ magnetic core from acid–base substrate corrosion, but also provided a number of functional groups as binding sites for Pd nanoparticles. The prepared catalyst was characterized by UV–vis, TEM, SEM, FTIR, TGA, ICP‐OES, BET, XRD, DLS and VSM. The catalytic tests showed that the magnetic Fe₃O₄/P(GMA‐EGDMA)‐NH₂/HPG‐COOH‐Pd catalyst had excellent catalytic performance and retained 86% catalytic efficiency after 8 consecutive cycles.     

A Core–Shell Fe/Fe2O3 Nanowire as a High‐Performance Anode Material for Lithium‐Ion Batteries

The preparation of novel one‐dimensional core–shell Fe/Fe₂O₃ nanowires as anodes for high‐performance lithium‐ion batteries (LIBs) is reported. The nanowires are prepared in a facile synthetic process in aqueous solution under ambient conditions with subsequent annealing treatment that could tune the capacity for lithium storage. When this hybrid is used as an anode material for LIBs, the outer Fe₂O₃ shell can act as an electrochemically active material to store and release lithium ions, whereas the highly conductive and inactive Fe core functions as nothing more than an efficient electrical conducting pathway and a remarkable buffer to tolerate volume changes of the electrode materials during the insertion and extraction of lithium ions. The core–shell Fe/Fe₂O₃ nanowire maintains an excellent reversible capacity of over 767 mA h g^?1 at 500 mA g^?1 after 200 cycles with a high average Coulombic efficiency of 98.6 %. Even at 2000 mA g^?1, a stable capacity as high as 538 mA h g^?1 could be obtained. The unique composition and nanostructure of this electrode material contribute to this enhanced electrochemical performance. Due to the ease of large‐scale fabrication and superior electrochemical performance, these hybrid nanowires are promising anode materials for the next generation of high‐performance LIBs.     

Laser Assisted Catalytic Growth of ZnS/CdSe Core‐Shell and Wire‐Coil Nanowire Heterostructures

ZnS/CdSe core‐shell and wire‐coil nanowire heterostructures have been synthesized by chemical vapor deposition assisted with pulsed laser ablation. Measurements from high‐resolution transmission electron microscopy and selected area electron diffraction have revealed that both ZnS/CdSe core‐shell and wire‐coil nanowires are of single‐crystalline hexagonal wurtzite structures and grow along the [0001] direction. While the lattice parameters of ZnS and CdSe in the core‐shell nanowires are nearly equal to those of bulk ZnS and CdSe, change of the lattice parameters in the CdSe‐coil is attributed to the doping of Zn into CdSe, resulting in the relaxation of compressive strain at the interface between CdSe‐coil and ZnS‐wire. Composition variation across the interfacial regions in the ZnS/CdSe nanowire heterostructures ranges only 10–15 nm despite the pronounced lattice mismatch between ZnS and CdSe by ?11%. Growth mechanisms of the ZnS/CdSe nanowire heterostructures are discussed.     

Preparation and ferromagnetic properties of Ni0.5Zn0.5Fe2O4/polyaniline core–shell nanocomposites

Magnetic Ni_0.5Zn_0.5Fe₂O₄‐crosslinked polyaniline composites with a core–shell structure were prepared in the presence of Ni_0.5Zn_0.5Fe₂O₄ magnetic powder in a toluene solution containing iron chloride as a surfactant and dopant. Structural characterization by Fourier transform infrared, X‐ray diffraction, scanning electron microscopy, and transmission electron microscopy proved that Ni_0.5Zn_0.5Fe₂O₄ in the composites was responsible for the ferromagnetic behavior of the composites. The effects of the polyaniline and temperature on the magnetic properties of the Ni_0.5Zn_0.5Fe₂O₄/polyaniline composites were studied with electron paramagnetic resonance and superconducting quantum interference device techniques. A clear evolution from ferromagnetic resonance to electron paramagnetic resonance was observed as a function of temperature, which was related to the passage through the Curie point (～420 K). The magnetic properties of the resulting composites showed ferromagnetic behavior, such as high‐saturated magnetization (saturation magnetization = 35–39 emu/g), low coercive force (coercivity = 22–28 G), and low blocking temperatures (～23 K). © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2657–2664, 2006     

Cu(II) immobilized on guanidinated epibromohydrin‐functionalized γ‐Fe2O3@TiO2 (γ‐Fe2O3@TiO2‐EG‐Cu(II)): A highly efficient magnetically separable heterogeneous nanocatalyst for one‐pot synthesis of highly substituted imidazoles

A simple, efficient and eco‐friendly procedure has been developed using Cu(II) immobilized on guanidinated epibromohydrin‐functionalized γ‐Fe₂O₃@TiO₂ (γ‐Fe₂O₃@TiO₂‐EG‐Cu(II)) for the synthesis of 2,4,5‐trisubstituted and 1,2,4,5‐tetrasubstituted imidazoles, via the condensation reactions of various aldehydes with benzil and ammonium acetate or ammonium acetate and amines, under solvent‐free conditions. High‐resolution transmission electron microscopy analysis of this catalyst clearly affirmed the formation of a γ‐Fe₂O₃ core and a TiO₂ shell, with mean sizes of about 10–20 and 5–10 nm, respectively. These data were in very good agreement with X‐ray crystallographic measurements (13 and 7 nm). Moreover, magnetization measurements revealed that both γ‐Fe₂O₃@TiO₂ and γ‐Fe₂O₃@TiO₂‐EG‐Cu(II) had superparamagnetic behaviour with saturation magnetization of 23.79 and 22.12 emu g^?1, respectively. γ‐Fe₂O₃@TiO₂‐EG‐Cu(II) was found to be a green and highly efficient nanocatalyst, which could be easily handled, recovered and reused several times without significant loss of its activity. The scope of the presented methodology is quite broad; a variety of aldehydes as well as amines have been shown to be viable substrates. A mechanism for the cyclocondensation reaction has also been proposed.     

Preparation of magnetic Fe3O4/P (GMA‐DVB)‐PEI/Pd highly efficient catalyst with core‐shell structure

In this paper, a simple route for palladium (Pd) nanoparticles attached to the surface of hollow magnetic Fe₃O₄/P (GMA‐DVB)‐polyethyleneimine (PEI) microspheres was established. Due to the large amount of imidogen groups and tertiary amine groups presenting in the PEI, Pd²⁺ ions could be anchored to the support by complexation with a polyfunctional organic ligand. Thereafter, a magnetic Pd catalyst having a high loading amount and good dispersibility was obtained by reducing Pd²⁺ ions. Afterwards, the prepared catalyst was characterized by TEM, SEM, FTIR, XRD, TGA, VSM, and UV–vis in detail. Ultimately, their catalytic activity was evaluated using the reduction of 4‐nitrophenol (4‐NP). Research showed that the Fe₃O₄/P (GMA‐DVB)‐PEI/Pd catalyst possessed high catalytic performances for the reduction of 4‐NP with a conversion rate of 98.43% within 540 s. Furthermore, the catalyst could be easily recovered and reused at least for nine successive cycles.     

Preparation of Ag‐doped g‐C3N4 Nano Sheet Decorated Magnetic γ‐Fe2O3@SiO2 Core–Shell Hollow Spheres through a Novel Hydrothermal Procedure: Investigation of the Catalytic activity for A3, KA2 Coupling Reactions and [3 + 2] Cycloaddition

Taking advantageous of both g‐C₃N₄ and magnetic core‐shell hollow spheres, for the first time a heterogeneous and magnetically separable hybrid system was prepared through a novel and simple hydrothermal procedure and used for immobilization of bio‐synthesized Ag(0) nanoparticles. The hybrid system was fully characterized by using SEM/EDS, FTIR, VSM, TEM, XRD, TGA, DTGA, ICP‐AES, BET and elemental mapping analysis. The catalytic utility of the obtained system, h‐Fe₂O₃@SiO₂/g‐C₃N₄/Ag, for promoting ultrasonic‐assisted A³, KA² coupling reactions and [3 + 2] cycloaddition has been confirmed. The results established that the catalyst could efficiently catalyze the reaction to afford the corresponding products in high yields in short reaction times. The reusability study confirmed that the catalyst could be recovered and reused for at least five reaction runs with only slight loss of the catalytic activity. The hot filtration test also proved low silver leaching, indicating the heterogeneous nature of the catalysis.     

Magnetically Separable and Versatile Pd/Fe3O4 Catalyst for Efficient Suzuki Cross‐Coupling Reaction and Selective Hydrogenation of Nitroarenes

Magnetic nanoparticle‐supported Pd/Fe₃O₄ was readily prepared and proved to be versatile catalyst for efficient Suzuki cross‐coupling reaction, and the reduction of nitroarenes under mild conditions (balloon H₂ pressure and room temperature). The catalyst could be conveniently recovered and reused several times with sustained catalytic activity.     

Electrochemical Sensor for Detection of Glucose Based on Ni@Pt Core‐shell Nanoparticles Supported on Carbon

In this work, Ni@Pt core‐shell nanoparticles with diameter of 3–4 nm and thin Pt shell was synthesized by a successive reduction approach using carbon as support to develop high‐performance non‐enzymatic glucose sensor. The resulting electrochemical sensor displayed good catalytic activity toward glucose oxidation, presenting a high current density of 66.9 µA mM^?1 cm^?2 at an applied potential of ?0.1 V. It showed a wide linear range of 0.1–30.1 mM and the limit of detection was down to 30 µM (S/N=3). Notably, it was found that the proposed sensor exhibited good selectivity to avoid the interference from ascorbic acid, uric acid, fructose and acetamidophenol. Furthermore, the feasibility of the as‐prepared non‐enzymatic glucose sensor in the determination of glucose in serum samples was successfully implemented.     

Controlled Synthesis of Fe3O4/ZIF‐8 Nanoparticles for Magnetically Separable Nanocatalysts

Fe₃O₄/ZIF‐8 nanoparticles were synthesized through a room‐temperature reaction between 2‐methylimidazolate and zinc nitrate in the presence of Fe₃O₄ nanocrystals. The particle size, surface charge, and magnetic loading can be conveniently controlled by the dosage of Zn(NO₃)₂ and Fe₃O₄ nanocrystals. The as‐prepared particles show both good thermal stability (stable to 550 °C) and large surface area (1174 m²g^?1). The nanoparticles also have a superparamagnetic response, so that they can strongly respond to an external field during magnetic separation and disperse back into the solution after withdrawal of the magnetic field. For the Knoevenagel reaction, which is catalyzed by alkaline active sites on external surface of catalyst, small Fe₃O₄/ZIF‐8 nanoparticles show a higher catalytic activity. At the same time, the nanocatalysts can be continuously used in multiple catalytic reactions through magnetic separation, activation, and redispersion with little loss of activity.     

Chitosan‐Based Hydrothermal Nanocarbon: Core‐Shell Characteristics and Composite Electrodes

Low cost sustainable hydrothermal nanocarbon from chitosan is investigated for anion binding and electrochemical sensing. Raman analysis suggests amorphous carbon core components but film electrodes show insulator characteristics due to incomplete “core‐shell carbonisation”. Anion adsorption capability is exploited in a composite with negatively charged carbon nanoparticles. The accessible positive surface charge is estimated as 14, 70, 20 C g^?1 for hydrothermal nanocarbon obtained at 180 °C, 200 °C, 230 °C, respectively (Langmuirian binding constant ca. 10⁵ mol^?1 dm³), which suggests that up to 15 % of nitrogen can be present in the form of accessible surface or shell ammonium functionalities.