3D Porous Carbon Framework Stabilized Ultra‐Uniform Nano γ‐Fe2O3: A Useful Catalyst System

We present a novel strategy for the scalable fabrication of γ‐Fe₂O₃@3DPCF, a three‐dimensional porous carbon framework (PCF) anchored ultra‐uniform and ultra‐stable γ‐Fe₂O₃ nanocatalyst. The γ‐Fe₂O₃@3DPCF nanocomposites were facilely prepared with the following route: condensation of iron(III) acetylacetonate with acetylacetonate at room temperature to form the polymer precursor (PPr), which was carbonized subsequently at 800 °C. The homogeneous aldol condensation offered an ultra‐uniform distribution of iron, so that the γ‐Fe₂O₃ nanoparticles (NPs) were uniformly distributed in the 3D carbon architecture with the average size of approximate 20 nm. The Fe₂O₃ NPs were capped with carbon, so that the iron oxide maintained its γ‐phase instead of the more stable α‐phase. The nanocomposite was an excellent catalyst for the reduction of nitroarene; it gave >99 % conversion and 100 % selectivity for the reduction of nitroarenes to the corresponding anilines at 100 °C. The fabrication of the γ‐Fe₂O₃@3DPCF nanocatalyst represents a green and scalable method for the synthesis of novel carbon‐based metal oxide nanostructures.     

Polyethylene Glycol‐(N‐Methylimidazolium) Hydroxide‐Grafted γ‐Fe2O3@HAp: A Novel Nanomagnetic Recyclable Basic Phase‐Transfer Catalyst for the Synthesis of Tetrahydrobenzopyran Derivatives in Aqueous Media

Polyethylene glycol‐(N‐methylimidazolium) hydroxide‐grafted hydroxyapatite encapsulated γ‐Fe₂O₃ nanoparticles, γ‐Fe₂O₃@HAp@PEG(mim)OH, were prepared and characterized by FTIR, SEM, TEM, TGA, and EDAX. This nanocomposite was applied as a novel, green, nanomagnetic, and recyclable basic phase‐transfer catalyst for the synthesis of tetrahydrobenzopyrans in high yields via the three‐component reaction of aromatic aldehydes, malononitrile, and dimedone or 1,3‐cyclohexanedione in aqueous media at ambient temperature.     

Novel synthesis of Fe2O3–Pt ellipsoids coated by double‐shelled La2O3 as a catalyst for the reduction of 4‐nitrophenol

A facile strategy is reported for the fabrication of Pt‐loaded core–shell nanocomposite ellipsoids (Fe₂O₃‐Pt@DSL) consisting of ellipsoidal Fe₂O₃ cores, double‐layered La₂O₃ shells and deposited Pt nanoparticles (NPs). The formation of the doubled‐shelled structure uses Fe₂O₃‐Pt@mSiO₂ as template sacrificial agent and it involves the re‐deposition of silica and self‐assembly of metal oxide units. The preparation methods of double‐shelled metal oxides avoid repeated coating and etching and could be utilized to fabricate other shaped double‐shelled composites. Characterization results indicated that the Fe₂O₃‐Pt@DSL nanocomposites possessed mesoporous structure and tunable shell thickness. Moreover, due to the formation of Fe₂O₃ and La₂O₃ composites, Pt NPs can also be stabilized via deposition on chemically active oxides with a synergistic effect. Therefore, as a catalyst for the reduction of 4‐nitrophenol, Fe₂O₃‐Pt@DSL showed superior catalytic activity and reusability due to structural superiority and enhanced composite synergy. Finally, well‐dispersed Pt NPs were encapsulated into the void between the shell layers to construct the Fe₂O₃‐Pt@DSL‐Pt catalyst.     

Perylene diimide‐modified magnetic γ‐Fe2O3/CeO2 nanoparticles as peroxidase mimics for highly sensitive colorimetric detection of Vitamin C

Perylene diimide‐modified magnetic γ‐Fe₂O₃/CeO₂ nanoparticles (γ‐Fe₂O₃/CeO₂‐PDI) were prepared and exhibited excellent peroxidase‐like activity. The samples were characterized by HR‐TEM, XRD, Raman, N₂ adsorption, magnetic strength and XPS. The obtained γ‐Fe₂O₃/CeO₂‐PDI had size of 10~20 nm with high specific surface area of 77 m²/g, and could be easily separated from the aqueous solution by using a magnet, which are in favor of its practical application. Due to the decoration of PDI, the γ‐Fe₂O₃/CeO₂‐PDI possessed more surface defects (Ce³⁺) and active oxygen species than that of γ‐Fe₂O₃/CeO₂, resulting in the outstanding catalytic performance. And the composite catalyst also showed highly sensitive and selectivity toward VC with a limit of detection of 0.45 μM. Based on the fluorescent results, a possible hydroxyl radical (?OH) catalytic mechanism was proposed. It is believed that the as‐prepared γ‐Fe₂O₃/CeO₂‐PDI nanoparticles are promising biosensors applied for biomedical and food analysis.     

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.     

Magnetic Resonance and Mössbauer Studies of Superparamagnetic γ‐Fe2O3 Nanoparticles Encapsulated into Liquid‐Crystalline Poly(propylene imine) Dendrimers

We present the first results of electron magnetic resonance (EMR) and Mössbauer spectroscopy studies of γ‐Fe₂O₃ nanoparticles (NPs) incorporated into liquid‐crystalline, second‐generation dendrimers. The mean size of NPs formed in the dendrimers was around 2.5 nm. A temperature‐driven transition from superparamagnetic to ferrimagnetic resonance was observed for the sample. Low‐temperature blocking of the NP magnetic moments has been clearly evidenced in the integrated EMR line intensity and the blocking temperature was about 60 K. The physical parameters of magnetic NPs (magnetic moment, effective magnetic anisotropy) have been determined from analyses of the EMR data. The effective magnetic anisotropy constant is enhanced relative to bulk γ‐Fe₂O₃ and this enhanced value is associated with the influence of the surface and shape effects. The angular dependence of the EMR signal position for the field‐freezing sample from liquid‐crystalline phase showed that NPs possessed uniaxial anisotropy, in contrast to bulk γ‐Fe₂O₃. Mössbauer spectroscopy determined that fabricated NPs consisted of an α‐Fe core and a γ‐Fe₂O₃ shell.     

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.     

Magnetically recyclable palladium nanoparticles (Fe3O4‐Pd) for oxidative coupling between amides and olefins at room temperature

A convenient method for the synthesis of magnetically recyclable palladium nanoparticles (Fe₃O₄‐Pd) is described. The catalytic application of the Fe₃O₄‐Pd nanoparticles was explored for the first time in oxidative coupling between amides and olefins. p‐Toluenesulfonic acid plays a significant role in the oxidative amidation reaction. The reaction proceeds at room temperature, resulting in (Z)‐enamides under ambient air in the absence of co‐catalyst and ligand. The superparamagnetic nature of Fe₃O₄‐Pd facilitates easy, quantitative recovery of the catalyst from a reaction mixture, and it can be reused for up to three consecutive cycles with a slight decrease in catalytic activity.     

γ‐Fe2O3@Cu3Al‐LDH‐TUD as a new Amphoteric,Highly Efficient and Recyclable Heterogeneous Catalyst for the Solvent‐free Synthesis of Dihydropyrano[3,2‐c]pyrazoles and dihydropyrano[3,2‐c]chromens

Thiourea dioxide was immobilized on γ‐Fe₂O₃@Cu₃Al‐LDH magnetic nanoparticles to prepare the γ‐Fe₂O₃@Cu₃Al‐LDH‐TUD MNPs. The structure and properties of these magnetic nanoparticles were established by FT‐IR, EDX, SEM, XRD, and hystogram of particle size analytical methods. The results obtained from these analytical methods confirmed the successful immobilization of the thiourea dioxide onto the magnetic support. The synthesized magnetic nanoparticles (MNPs) exhibited high catalytic activity in one‐pot three‐component reactions under mild and solvent‐free conditions for the synthesis of diverse ranges of dihydropyrano[3,2‐c]pyrazoles and dihydropyrano[3,2‐c]chromens. All the reactions proceeded smoothly to furnish the respective products in excellent yields. Simple isolation of the products, avoidance of harmful organic solvents, versatility of the catalyst and its easy magnetic separation and reusability with no significant loss of activity are the main advantages of the present method.     

Optical and Magnetic Properties of Conjugate Structures of PbSe Quantum Dots and γ‐Fe2O3 Nanoparticles

An investigation of the optical and magnetic properties of a unique hydrogen‐linked conjugate nanostructure, comprised of superparamagnetic γ‐Fe₂O₃ nanoparticles (NPs) and near‐infrared PbSe nanocrystal quantum dot (NQD) chromophores, is reported. The results show retention of the NQDs’ emission quantum efficiency and radiative lifetime, and only a small red shift of its band energy, upon conjugation to the dielectric surroundings of γ‐Fe₂O₃ NPs. The study also shows the sustainability of the superparamagnetism of the NPs after conjugation, with only a slight decrease of the ferromagnetic–superparamagnetic transition temperature with respect to that of the individual NPs. Thus, the conjugate nanostructure can be considered as a useful medical platform when PbSe NQDs act as fluorescent tags, while the γ‐Fe₂O₃ NPs are used as a vehicle driven by an external magnetic field for targeted delivery of tags or drugs.     

Preparation of novel palladium nanoparticles supported on magnetic iron oxide and their catalytic application in the synthesis of 2‐imino‐3‐phenyl‐2,3‐dihydrobenzo[d]oxazol‐5‐ols

Novel Pd nanoparticles were prepared in five successive stages: 1) preparation of the Fe₃O₄ magnetic nanoparticles (Fe₃O₄ MNPs), 2) coating of Fe₃O₄ MNPs with SiO₂ (Fe₃O₄@SiO₂), 3) functionalization of Fe₃O₄@SiO₂ with 3‐chloropropyltrimethoxy‐ silane (CPTMS) ligand (Fe₃O₄@SiO₂@CPTMS), 4) further functionalization with 3,5‐diamino‐1,2,4‐triazole (DAT) ligand (Fe₃O₄@SiO₂@CPTMS @DAT), and 5) the complexation of Fe₃O₄@SiO₂@CPTMS@DAT with PdCl₂ (Fe₃O₄@SiO₂@CPTMS@ DAT@Pd). Then, the obtained Pd nano‐catalyst characterized by different methods such as the elemental analysis (CHN), FT‐IR, XRD, EDX, SEM, TEM, TG‐DTA and VSM. Finally, the Pd catalyst was applied for the synthesis of various 2‐imino‐3‐phenyl‐2,3‐dihydrobenzo[d]oxazol‐5‐ols.     

Fe3O4‐SAHPG‐Pd0 nanoparticles: A ligand‐free and low Pd loading quasiheterogeneous catalyst active for mild Suzuki–Miyaura coupling and C?H activation of pyrimidine cores

This paper reports a green magnetic quasiheterogeneous efficient palladium catalyst in which Pd⁰ nanoparticles have been immobilized in self‐assembled hyperbranched polyglycidole (SAHPG)‐coated magnetic Fe₃O₄ nanoparticles (Fe₃O₄‐SAHPG‐Pd⁰). This catalyst has been used for effective ligandless Pd catalyzed Suzuki–Miyaura coupling reactions of different aryl halides with substituted boronic acids at room temperature and in aqueous media. Herein, SAHPG is used as support; it also acts as a reducing agent and stabilizer to promote the transformation of Pd^II to Pd⁰ nanoparticles. Also, this environmental friendly quasiheterogeneous catalyst is employed for the first time in the synthesis of new pyrimido[4,5‐b]indoles via oxidative addition/C? H activation reactions on the pyrimidine rings, which were obtained with higher yield and faster than when Pd(OAc)₂ was used as the catalyst. Interestingly, the above‐mentioned catalyst could be recovered in a facile manner from the reaction mixture by applying an external magnet device and recycled several times with no significant decrease in the catalytic activity.     

Fe3O4@silica‐MCM‐41@DABCO: A novel magnetically reusable nanostructured catalyst for clean in situ synthesis of substituted 2‐aminodihydropyrano[3,2‐b]pyran‐3‐cyano

DABCO (1,4‐diazabicyclo[2.2.2]octane)‐modified magnetite with silica‐MCM‐41 shell (Fe₃O₄@silica‐MCM‐41@DABCO) as an effective, magnetic and novel heterogeneous reusable nanocatalyst was synthesized and analysed using various techniques. Evaluation of the catalytic activity of this nanocatalyst was performed in the clean synthesis of substituted 2‐aminodihydropyrano[3,2‐b]pyran‐3‐cyano in high yields via in situ reaction of azido kojic acid, malononitrile and various aldehydes.     

Exchange‐Coupled fct‐FePd/α‐Fe Nanocomposite Magnets Converted from Pd/Fe3O4 Core/Shell Nanoparticles

We report the controlled synthesis of exchange‐coupled face‐centered tetragonal (fct) FePd/α‐Fe nanocomposite magnets with variable Fe concentration. The composite was converted from Pd/Fe₃O₄ core/shell nanoparticles through a high‐temperature annealing process in a reducing atmosphere. The shell thickness of core/shell Pd/Fe₃O₄ nanoparticles could be readily tuned, and subsequently the concentration of Fe in nanocomposite magnets was controlled. Upon annealing reduction, the hard magnetic fct‐FePd phase was formed by the interdiffusion between reduced α‐Fe and face‐centered cubic (fcc) Pd, whereas the excessive α‐Fe remained around the fct‐FePd grains, realizing exchange coupling between the soft magnetic α‐Fe and hard magnetic fct‐FePd phases. Magnetic measurements showed variation in the magnetic properties of the nanocomposite magnets with different compositions, indicating distinct exchange coupling at the interfaces. The coercivity of the exchange‐coupled nanocomposites could be tuned from 0.7 to 2.8 kOe and the saturation magnetization could be controlled from 93 to 160 emu g^?1. This work provides a bottom‐up approach using exchange‐coupled nanocomposites for engineering advanced permanent magnets with controllable magnetic properties.     

Applications of iron and nickel immobilized on hydroxyapatite‐core‐shell γ‐Fe2O3 as a nanomagnetic catalyst for the chemoselective oxidation of sulfides to sulfoxides under solvent‐free conditions

In the present study, Fe²⁺ and Ni²⁺ immobilized on hydroxyapatite‐core‐shell γ‐Fe₂O₃ (γ‐Fe₂O₃@HAp‐Fe²⁺ and γ‐Fe₂O₃@HAp‐Ni²⁺) with a high surface area has been synthesized and characterized by Fourier transform infrared (FTIR), X‐ray diffraction (XRD), vibrating sample magnetometer (VSM), transmission electron microscopy (TEM), and scanning electron microscope (SEM) techniques. Then, γ‐Fe₂O₃@HAp‐Fe²⁺ and γ‐Fe₂O₃@HAp‐Ni²⁺ were used as a new and magnetically recoverable nano catalyst for the selective oxidation of sulfides to sulfoxides with 33% aqueous H₂O₂ (0.5 mL) as an oxidant at room temperature in good to excellent yields and short reaction time. Nontoxicity of reagent, mild reaction condition, inexpensive and high catalytic activity, simple experimental procedure, short period of conversion and excellent yields, and ease of recovery from the reaction mixture using an external magnet are the advantages of the present method.     

HAp‐encapsulated γ‐Fe2O3‐supported dual acidic heterogeneous catalyst for highly efficient one‐pot synthesis of benzoxanthenones and 3‐pyranylindoles

A novel method is reported for the synthesis of benzoxanthenone and 3‐pyranylindole derivatives via one‐pot three‐component reactions using a newly synthesized HAp‐encapsulated γ‐Fe₂O₃‐supported dual acidic heterogeneous catalyst, as a reusable and highly efficient nanocatalyst. In this protocol the use of the nanocatalyst provided a green, useful and rapid method to generate products in short reaction times (4–20 min) and in excellent yields (87–96%). The paramagnetic nature of the catalyst provided a simple, trouble‐free and facile approach for the separation of the catalyst by applying an external magnet, and it could be used in eight cycles without significant loss in catalytic efficiency.     

Magnetically separable g‐C3N4 hybrid nanocomposite: Highly efficient and eco‐friendly recyclable catalyst for one‐pot synthesis of α‐aminonitriles

A magnetically separable graphitic carbon nitride nanocomposite (Fe₃O₄/g‐C₃N₄) as a catalyst for the three‐component condensation reactions of carbonyl compounds, amines and trimethylsilylcyanide was thoroughly investigated. The reaction of these three components was found to be efficient, economical and green and took place in the presence of a catalytic amount of the magnetically separable catalyst to yield the corresponding α‐aminonitriles in good to excellent yields. The prepared nanocomposite was characterized using scanning electron microscopy and energy‐dispersive X‐ray and Fourier transform infrared spectroscopies. The nanocomposite was also found to be reusable could be recovered easily and reused several times without distinct deterioration in its catalytic activity.     

Pd embedded N,S co‐doped graphene wrapped core‐shell magnetic nanospheres: Engineered stable nanocatalyst for Suzuki couplings

Designed nitrogen and sulfur co‐doped graphene wrapped magnetic core‐shell supported Pd nanoparticles were synthesized through the following steps. Firstly, Fe₃O₄ was prepared, coated with silica and then functionalized with amine groups to create a positive charge on the structure for enhancing the interaction of the Fe₃O₄@SiO₂ with graphene oxide. Secondary, the pre‐catalyst wrapped with graphene to enhance adsorption of aromatic substrates through π–π stacking. Thirdly, graphene was doped with nitrogen and sulfur to increase the grafting of Pd in hybrid. Finally, Pd NPs were attached on the surface of pre‐engineered structure to produce Fe₃O₄@SiO₂@N,S‐wG@Pd which exhibited high performance in Suzuki reactions. This superior activity can be indexed to the incorporation of N and S atoms into graphene led to high anchoring and well‐dispersion of Pd NPs on the nanocomposite surface offering large amounts of active centers, that strongly increased the interaction between Pd and substrates to decreases Pd leaching.     

α‐Fe2O3 Polyhedral Nanoparticles Enclosed by Different Crystal Facets: Tunable Synthesis,Formation Mechanism Analysis,and Facets‐dependent n‐Butanol Sensing Properties

Three kinds of polyhedral α‐Fe₂O₃ nanoparticles enclosed by different facets including oblique parallel hexahedrons (op‐hexahedral NPs), cracked oblique parallel hexahedrons (cop‐hexahedral NPs), and octadecahedral nanoparticles (octadecahedral NPs), were successfully prepared by simply changing only one reaction parameter in the hydrothermal process. The structural and morphological of the products were systematically studied using various characterizations including X‐ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM), revealing that the three kinds of α‐Fe₂O₃ nanoparticles were enclosed by {104}, {110}/{104}, and {102}/{012}/{104} crystal planes, respectively. The exposed facets and shape of the nanocrystals were found to be affected by the adding amount of ethylene glycol in the solvent. The gas‐sensing properties and mechanism of the α‐Fe₂O₃ samples were studied and analyzed, which indicated that the sensitivity of the three samples followed the order of octadecahedral NPs > cop‐hexahedral NPs > op‐hexahedral NPs due to the combined effects of specific surface area and oxygen defects in the nanocrystals.     

Silver nanoparticles supported on ionic‐tagged magnetic hydroxyapatite as a highly efficient and reusable nanocatalyst for hydrogenation of nitroarenes in water

A novel chemically modified magnetic hydroxyapatite (MHAp) was prepared and used as support and stabilizer for the synthesis of silver nanoparticles. First, 1,4‐diazabicyclo[2.2.2]octane (DABCO) was successfully grafted onto the surface of MHAp, and then silver nanoparticles were homogeneously loaded on mesoporous MHAp‐DABCO (ionic‐tagged MHAp) nanocomposite by in situ chemical reduction of silver nitrate using sodium borohydride. The structure and properties of the resulting MHAp‐DABCO‐Ag nanocomposite were confirmed using various techniques. The catalytic activity of ionic‐tagged MHAp‐Ag nanocatalyst was investigated for the hydrogenation reaction of nitroarenes in aqueous media. The results reveal that the Ag‐containing inorganic–organic nanocomposite is highly efficient for the reduction of a wide range of aromatic nitro compounds under green conditions. The superparamagnetic nature of the nanocatalyst leads to its being readily removed from solution via application of a magnetic field, and it can be easily stored and reused.