Characterization and application of Fe3O4/SiO2 nanocomposites

A sol-gel procedure was used to cover Fe₃O₄ nanoparticles with SiO₂ shell, forming a core/shell structure. The core/shell nanocomposites were synthesized by a two-step process. First, Fe₃O₄ nanoparticles were obtained through co-precipitation and dispersed in aqueous solution through electrostatic interactions in the presence of tetramethylammonium hydroxide (TMAOH). In the second step, Fe₃O₄ was capped with SiO₂ generated from the hydrolyzation of tetraethyl orthosilicate (TEOS). The structure and properties of the formed Fe₃O₄/SiO₂ nanocomposites were characterized and the results indicate that the Fe₃O₄/SiO₂ nanocomposites are superparamagnetic and are about 30 nm in size. Bioconjugation to IgG was also studied. Finally, the mechanism of depositing SiO₂ on magnetic nanoparticles was discussed.     

Synthesis of pH‐responsive magnetic yolk–shell nanoparticles: A comparison between conventional etching and new deswelling approaches

Iron oxide (Fe₃O₄) magnetic nanoparticles as movable cores were used to synthesize yolk–shell nanoparticles with pH‐responsive shell composed of ethylene glycol dimethacrylate (EGDMA)‐crosslinked poly(acrylic acid) (PAA) via two different routes. In the first more common route, Fe₃O₄ nanoparticles were coated with silica layer via the Stöber process to yield Fe₃O₄@SiO₂ core–shell nanoparticles, subsequently used as seeds in the distillation precipitation copolymerization of AA and EGDMA to yield Fe₃O₄@SiO₂@P(AA‐EGDMA). The silica layer was selectively removed through alkali etching to yield Fe₃O₄@air@P(AA‐EGDMA). In the second route, Fe₃O₄ nanoparticles without any stabilization were used as seeds in the distillation precipitation copolymerization of AA and EGDMA to yield Fe₃O₄@P(AA‐EGDMA) core–shell nanoparticles. The nanoparticles were subsequently dispersed in acidic medium of pH = 2. Yolk–shell Fe₃O₄@air@P(AA‐EGDMA) nanoparticles were formed through deswelling of crosslinked PAA because of protonation of carboxyl groups at low pH values. Various techniques were utilized to investigate the characteristics of the synthesized core–shell nanoparticles. Formation of yolk–shell nanostructure was observed for both synthesis routes, namely etching of silica layer and deswelling approaches, from vibrating sample magnetometry and transmission electron microscopy results. Both types of nanoparticles showed pH‐responsive behaviour, i.e. decrease in absorption with increase in pH, as examined using UV–visible spectroscopy.     

Threonine stabilizer‐controlled well‐dispersed small palladium nanoparticles on modified magnetic nanocatalyst for Heck cross‐coupling process in water

We report the synthesis of magnetically separable Fe₃O₄@Silica‐Threonine‐Pd⁰ magnetic nanoparticles with a core–shell structure. After synthesis of Fe₃O₄@Silica, threonine as an efficient stabilizer/ligand was bonded to the surface of Fe₃O₄@Silica. Then, palladium nanoparticles were generated on the threonine‐modified catalyst. The threonine stabilizer helps to generate palladium nanoparticles of small size (less than 4 nm) with high dispersity and uniformity. Magnetically separable Fe₃O₄@Silica‐Threonine‐Pd⁰ nanocatalyst was fully characterized using various techniques. This nanocatalyst efficiently catalysed the Heck cross‐coupling reaction of a variety of substrates in water medium as a green, safe and inexpensive solvent at 80°C. The Fe₃O₄@Silica‐Threonine‐Pd⁰ catalyst was used for at least eight successful consecutive runs with palladium leaching of only 0.05%.     

Synthesis of magnetic,reactive, and thermoresponsive Fe3O4 nanoparticles via surface‐initiated RAFT copolymerization of N‐isopropylacrylamide and acrolein

A reversible addition‐fragmentation chain transfer (RAFT) agent was directly anchored onto Fe₃O₄ nanoparticles in a simple procedure using a ligand exchange reaction of S‐1‐dodecyl‐S′‐(α,α′‐dimethyl‐α″‐acetic acid)trithiocarbonate with oleic acid initially present on the surface of pristine Fe₃O₄ nanoparticles. The RAFT agent‐functionalized Fe₃O₄ nanoparticles were then used for the surface‐initiated RAFT copolymerization of N‐isopropylacrylamide and acrolein to fabricate structurally well‐defined hybrid nanoparticles with reactive and thermoresponsive poly(N‐isopropylacrylamide‐co‐acrolein) shell and magnetic Fe₃O₄ core. Evidence of a well‐controlled surface‐initiated RAFT copolymerization was gained from a linear increase of number‐average molecular weight with overall monomer conversions and relatively narrow molecular weight distributions of the copolymers grown from the nanoparticles. The resulting novel magnetic, reactive, and thermoresponsive core‐shell nanoparticles exhibited temperature‐trigged magnetic separation behavior and high ability to immobilize model protein BSA. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 542–550, 2010     

Stable aqueous dispersion of magnetic iron oxide core–shell nanoparticles prepared by biocompatible maleate polymers

A new method is applied to prepare stable aqueous dispersion of magnetic iron oxide nanoparticles (MNPs) by biocompatible maleate polymers. Fe₃O₄ magnetic core–shell nanoparticles are obtained via forming an inclusion complex between carboxylic acid groups of maleated biocompatible polymers shell and Fe₃O₄ MNPs core surface. Maleate polymers are synthesized via esterification of poly(ethylene glycol), poly(vinyl alcohol) and starch with maleic anhydride (MA). The Fe₃O₄ magnetic core–shell nanoparticles are characterized by Fourier transform infrared spectroscopy, X‐ray diffraction, transmission electron microscopy and vibrating sample magnetometer. The obtained magnetic core–shell nanoparticles exhibit superparamagnetic property and reveal long‐term aqueous stability. This work represents a valid methodology to produce highly stable aqueous dispersion of Fe₃O₄ MNPs ferrofluids which can be expected to have great potential as contrast agent for magnetic resonance imaging. Furthermore, the shell composition of biocompatible maleate polymers with double bond of MA as crosslinker agent allows the polymerization with other monomers to design preferred drug delivery systems. Copyright © 2014 John Wiley & Sons, Ltd.     

Nanorods of transition metal oxalates: A versatile route to the oxide nanoparticles

A versatile route has been explored for the synthesis of nanorods of transition metal (Cu, Ni, Mn, Zn, Co and Fe) oxalates using reverse micelles. Transmission electron microscopy shows that the as-prepared nanorods of nickel and copper oxalates have diameter of 250 nm and 130 nm while the length is of the order of 2.5 μm and 480 nm, respectively. The aspect ratio of the nanorods of copper oxalate could be modified by changing the solvent. The average dimensions of manganese, zinc and cobalt oxalate nanorods were 100 μm, 120 μm and 300 nm, respectively, in diameter and 2.5 μm, 600 nm and 6.5 μm, respectively, in length. The aspect ratio of the cobalt oxalate nanorods could be modified by controlling the temperature.The nanorods of metal (Cu, Ni, Mn, Zn, Co and Fe) oxalates were found to be suitable precursors to obtain a variety of transition metal oxide nanoparticles. Our studies show that the grain size of CuO nanoparticles is highly dependent on the nature of non-polar solvent used to initially synthesize the oxalate rods. All the commonly known manganese oxides could be obtained as pure phases from the single manganese oxalate precursor by decomposing in different atmospheres (air, vacuum or nitrogen). The ZnO nanoparticles obtained from zinc oxalate rods are ～55 nm in diameter. Oxides with different morphology, Fe₃O₄ nanoparticles faceted (cuboidal) and Fe₂O₃ nanoparticles (spherical) could be obtained.     

A molecularly imprinted polymer-coated nanocomposite of magnetic nanoparticles for estrone recognition

In this study, we synthesized Fe₃O₄ magnetic nanoparticles coated estrone-imprinted polymer with controlled size using a semi-covalent imprinting strategy. In this protocol, the estrone-silica monomer complex (EstSi) was synthesized by the reaction 3-(triethoxysilyl)propyl isocyanate with estrone, where the template was linked to the silica coating on the iron oxide core via a thermally reversible bond. The removal of the template by a simple thermal reaction produced specific estrone recognition sites on the surface of silica shell.The resulting estrone-imprinted polymer coating Fe₃O₄ magnetic hybrid nanoparticles exhibit a much higher specific recognition and saturation magnetization. The hybrid nanoparticles have been used for biochemical separation of estrone.     

Facile deposition of gold nanoparticles on core–shell Fe3O4@polydopamine as recyclable nanocatalyst

A simple and green method for the controllable synthesis of core–shell Fe₃O₄ polydopamine nanoparticles (Fe₃O₄@PDA NPs) with tunable shell thickness and their application as a recyclable nanocatalyst support is presented. Magnetite Fe₃O₄ NPs formed in a one-pot process by the hydrothermal approach with a diameter of ∼240 nm were coated with a polydopamine shell layer with a tunable thickness of 15–45 nm. The facile deposition of Au NPs atop Fe₃O₄@PDA NPs was achieved by utilizing PDA as both the reducing agent and the coupling agent. The satellite nanocatalysts exhibited high catalytic performance for the reduction of p-nitrophenol. Furthermore, the recovery and reuse of the catalyst was demonstrated 8 times without detectible loss in activity. The synergistic combination of unique features of PDA and magnetic nanoparticles establishes these core–shell NPs as a versatile platform for potential applications.     

Ni@Pd core–shell nanoparticles immobilized on yolk–shell Fe3O4@polyaniline composites as a highly efficient,magnetically separable and atom‐economical catalyst for reduction of nitrobenzenes

The preparation of Ni@Pd core–shell nanoparticles immobilized on yolk–shell Fe₃O₄@polyaniline composites is reported. Fe₃O₄ nanoclusters were first synthesized through the solvothermal method and then the SiO₂ shell was coated on the Fe₃O₄ surface via a sol–gel process. To prepare Fe₃O₄@SiO₂@polyaniline composites, polyvinylpyrrolidone was first grafted on to the surface of Fe₃O₄@SiO₂ composites and subsequently polymerization of aniline was carried out via an ultrasound‐assisted in situ surface polymerization method. Selective etching of the middle SiO₂ layer was then accomplished to obtain the yolk–shell Fe₃O₄@polyaniline composites. The approach uses polyaniline (PANI) conductive polymer as a template for the synthesis of Ni@Pd core–shell nanoparticles. The catalytic activity of the synthesized yolk–shell Fe₃O₄@PANI/Ni@Pd composite was investigated in the reduction of o‐nitroaniline to benzenediamine by NaBH₄, which exhibited conversion of 99% in 3 min with a very low content of the catalyst. Transmission electron microscopy, X‐ray photoelectron spectroscopy, TGA, X‐ray diffraction, UV–visible, scanning electron microscopy, X‐ray energy dispersion spectroscopy and FT‐IR were employed to characterize the synthesized nanocatalyst. Copyright © 2014 John Wiley & Sons, Ltd.     

The highly selective capture of phosphopeptides by zirconium phosphonate-modified magnetic nanoparticles for phosphoproteome analysis

The highly selective capture of phosphopeptides from proteolytic digests is a great challenge for the identification of phosphoproteins by mass spectrometry. In this work, the zirconium phosphonate-modified magnetic Fe₃O₄/SiO₂ core/shell nanoparticles have been synthesized and successfully applied for the selective capture of phosphopeptides from complex tryptic digests of proteins before the analysis of MALDI-TOF mass spectrometry with the desired convenience of sample handling. The ratio of magnetic nanoparticle to protein and the incubation time for capturing phosphopeptides from complex proteolytic digests were investigated, and the optimized nanoparticle-to-protein ratio and incubation time were between 15:1 to 30:1 and 30 min, respectively. The excellent detection limit of 0.5 fmol β-casein has been achieved by MALDI-TOF mass spectrometry with the specific capture of zirconium phosphonate-modified magnetic Fe₃O₄ nanoparticles. The great specificity of zirconium phosphonate-modified magnetic Fe₃O₄ nanoparticles to phosphopeptides was demonstrated by the selective capture of phosphopeptides from a complex tryptic digest of the mixture of α-casein and bovine serum albumin at molar ratio of 1 to 100 in MALDI-TOF-MS analysis. An application of the magnetic nanoparticles to selective capture phosphopeptides from a tryptic digest of mouse liver lysate was further carried out by combining with nano-LC-MS/MS and MS/MS/MS analyses, and a total of 194 unique phosphopeptides were successfully identified.     

Modification of superparamagnetic iron oxide nanoparticles with poly(diallyldimethylammonium chloride) at air atmosphere

Superparamagnetic iron oxide particles with average size less than 20 nm were prepared by chemical co‐precipitation method in the air atmosphere. After that, polydimethyldiallyl ammonium chloride (PDDA) was used for wrapping iron oxide particles to obtain the core/shell nanocomposites. The parameters influencing properties of iron oxide particles and iron oxide/PDDA nanocomposites were investigated and optimized. The prepared iron oxide and nanocomposites were characterized by X‐ray diffraction (XRD) measurement, transmission electron microscopy (TEM), particle size and Zeta potential analyzer, Fourier transform infrared (FTIR) spectroscopy, and vibrating sample magnetometry (VSM), respectively. It was found that the iron oxide particles are cubic inverse spinel Fe₃O₄ with spherical shape. Superparamagnetic behavior of Fe₃O₄ with 73.114 emu/g is produced with NH₄OH as precipitator, and decreased to 58.583 emu/g for Fe₃O₄/PDDA nanocomposites. The Zeta potential of nanocomposites is positive value. The results showed that Fe₃O₄/PDDA nanocomposites have excellent future using as a carrier for bonding with some negative charged particles. Copyright © 2016 John Wiley & Sons, Ltd.     

Preparation of copper and zinc sulfide nanoparticles and their modification with cysteine

A new method for the preparation of copper and zinc sulfides nanoparticles in homogeneous aqueous solutions using cysteine as a surface modifier was proposed. The size of the particles obtained is 5–7 and 1.5–3 nm for copper and zinc sulfides, respectively, depending on the concentration of the reactants. Associates of the nanoparticles 10–30 nm in size are formed in the system with an increase in the total concentrations of the sulfides. Sols of the nanoparticles obtained in cysteine solutions are resistant to oxidation and coagulation within several weeks. The variation of the synthesis conditions makes it possible to obtain zinc sulfide particles with optical properties related to size effects.     

Uniformly dispersed copper nanoparticles onto the modified magnetically recoverable nanocatalyst for aqueous synthesis of primary amides

Magnetically recoverable and environmentally friendly Cu‐based heterogeneous catalyst has been synthesized for the one‐pot conversion of aldehydes to their corresponding primary amides. The Fe₃O₄@SiO₂ nanocomposites were prepared by synthesis of Fe₃O₄ magnetic nanoparticles (MNPs) which was then coated with a silica shell via Stöber method. Bi‐functional cysteine amino acid was covalently bonded onto the siliceous shell of nanocatalyst. The Cu^II ions were then loaded onto the modified surface of nanocatalyst. Finally, uniformly dispersed copper nanoparticles were achieved by reduction of Cu^II ions with NaBH₄. Amidation reaction of aryl halides with electron‐withdrawing or electron‐donating groups and hydroxylamine hydrochloride catalyzed with Fe₃O₄@SiO₂@Cysteine‐copper (FSC‐Cu) MNPs in aqueous condition gave an excellent yield of products. The FSC‐Cu MNPs could be easily isolated from the reaction mixture with an external magnet and reused at least 8 times without significant loss in activity.     

Preparation of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>-C18 nano-magnetic composite materials and their cleanup properties for organophosphorous pesticides

Magnetic Fe₃O₄-C18 composite nanoparticles of approximately 5–10 nm in size were synthesized and characterized by IR spectroscopy, atomic absorption spectroscopy, X-ray diffraction, and transmission electron microscopy. The magnetic Fe₃O₄-C18 composite nanoparticles were applied for cleanup and enrichment of organophosphorous pesticides. Comparative studies were carried out between magnetic Fe₃O₄-C18 composite nanoparticles and common C18 materials. Residues of organophosphorous pesticides were determined by gas chromatography in combination with a nitrogen/phosphorus detector. The cleanup and enrichment properties of magnetic Fe₃O₄-C18 composite nanoparticles are comparable with those of common C18 materials for enrichment of organophosphorous pesticides, but the cleanup and enrichment are faster and easier to perform. Figure Presumed mechanism for the adhesion of the OPs to the Fe₃O₄-C18 magnetic nanoparticles     

Fabrication of monodisperse luminescent nanoparticles with core/shell poly(styrene/thiophene) structure

Luminescent poly(styrene/thiophene) (PSt/PT) core/shell nanoparticles were prepared by oxidative polymerization in the presence of PSt seed particles. PSt seed particles with uniform size distribution were prepared with an anionic surfactant by an emulsion polymerization process, and were used as a template to prepare monodispersive PT‐coated nanoparticles. A luminescent Polythiophene (PT) layer was formed on the surface of PSt nanoparticles by oxidation polymerization with iron chloride (FeCl₃) and hydrogen peroxide (H₂O₂). The mechanism of core/shell formation was found to be the interface‐dominant polymerization induced by the electrostatic attraction between the sulfonate group of anionic surfactant and Fe³⁺ ions after the diffusion of thiophene monomer to the PSt nanoparticles. Field‐emission scanning electron microscopy and transmission electron microscopy (TEM) proved the core/shell structure, which provided key evidence that PT was incorporated onto the surface of PSt nanoparticles. In addition, the effect of the PT shell thickness on photoluminescent (PL) intensity was investigated by changing the shell thickness of PSt/PT nanoparticles. We observed that the PL intensity increased up to about 30 nm of PT shell thickness, and then decreased due to self‐absorption. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5968–5975, 2008     

Synthesis of orientedly bioconjugated core/shell Fe3O4@Au magnetic nanoparticles for cell separation

Orientedly bioconjugated core/shell Fe₃O₄@Au magnetic nanoparticles were synthesized for cell separation. The Fe₃O₄@Au magnetic nanoparticles were synthesized by reducing HAuCl₄ on the surfaces of Fe₃O₄ nanoparticles, which were further characterized in detail by TEM, XRD and UV-vis spectra. Anti-CD3 monoclonal antibody was orientedly bioconjugated to the surface of Fe₃O₄@Au nanoparticles through affinity binding between the Fc portion of the antibody and protein A that covalently immobilized on the nanoparticles. The oriented immobilization method was performed to compare its efficiency for cell separation with the non-oriented one, in which the antibody was directly immobilized onto the carboxylated nanoparticle surface. Results showed that the orientedly bioconjugated Fe₃O₄@Au MNPs successfully pulled down CD3⁺ T cells from the whole splenocytes with high efficiency of up to 98.4%, showing a more effective cell-capture nanostructure than that obtained by non-oriented strategy. This developed strategy for the synthesis and oriented bioconjugation of Fe₃O₄@Au MNPs provides an efficient tool for cell separation, and may be further applied to various fields of bioanalytical chemistry for diagnosis, affinity extraction and biosensor.     

In situ synthesis of plate-like Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> nanoparticles in porous cellulose films with obvious magnetic anisotropy

Nanocomposite cellulose films with obvious magnetic anisotropy have been prepared by in situ synthesis of plate-like Fe₂O₃ nanoparticles in the cellulose matrix. The influence of the concentrations of FeCl₂ and FeCl₃ solutions on the morphology and particle size of the synthesized Fe₂O₃ nanoparticles as well as on the properties of the composite films has been investigated. The Fe₂O₃ nanoparticles synthesized in the cellulose matrix was γ-Fe₂O₃, and its morphology was plate-like with size about 48 nm and thickness about 9 nm, which was totally different from those reported works. The concentration of FeCl₂ and FeCl₃ solution has little influence on the particle size and morphology of the Fe₂O₃ nanoparticles, while the content of Fe₂O₃ nanoparticles increased with the increase of the concentration of the precursor solution, indicating that porous structured cellulose matrix could modulate the growth of inorganic nanoparticles. The unique morphology of the Fe₂O₃ nanoparticles endowed the composite films with obvious magnetic anisotropy, which would expand the applications of the cellulose based nanomaterials.     

Green synthesis of Fe3O4/ZnO magnetic core-shell nanoparticles by Petasites hybridus rhizome water extract and their application for the synthesis of pyran derivatives: Investigation of antioxidant and antimicrobial activity

In this research, Fe₃O₄/ZnO magnetic core-shell nanoparticles (Fe₃O₄/ZnO MCNPs) were synthesized through a green method using Petasites hybridus rhizome water extract as a reducing and stabilizing agent. The morphology and size of the Fe₃O₄/ZnO MCNPs was identified by X-ray diffraction, scanning electron microscopy, and Energy-dispersive X-ray spectroscopy (EDX) analysis. The catalytic activity of the Fe₃O₄/ZnO MCNPs was evaluated in the efficient and green preparation of pyran derivatives in excellent yield using three-component reactions of dimedone, aldehydes, and malononitrile in ethanol at room temperature. The ability of some synthesized compounds to scavenge the 2,2-diphenyl-1-picrylhydrazyl radical was measured and the results proved this observation. Moreover, the antimicrobial activity of some synthesized compounds was proved by employing the disk diffusion test on Gram-positive and Gram-negative bacteria. The results for the disk diffusion test showed that compounds ( 4c, 4d, 4f and 4g ) prevented bacterial growth.     

Preparation and characterization of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>composite particles

Using Fe₃O₄ nano-particles as seeds, a new type of Fe₃O₄/Au composite particles with core/shell structure and diameter of about 170 nm was prepared by reduction of Au³⁺ with hydroxylamine in an aqueous solution. Particle size analyzer and transmission electron microscope were used to analyze the size distribution and microstructure of the particles in different conditions. The result showed that the magnetically responsive property and suspension stability of Fe₃O₄ seeds as well as reduction conditions of Au³⁺to Au⁰are the main factors which are crucial for obtaining a colloid of the Fe₃O₄/Au composite particles with uniform particle dispersion, excellent stability, homogeneity in particle sizes, and effective response to an external magnet in aqueous suspension solutions. UV-Vis analysis revealed that there is a characteristic peak of Fe₃O₄/Au fluid. For particles with d(0.5)=168 nm, the λmax is 625 nm.     

Superparamagnetic POT/Fe3O4 nanoparticle composites with supported Au nanoparticles as recyclable high-performance nanocatalysts

A novel method has been developed to successfully synthesize Fe₃O₄ nanoparticles with tunable size and morphology supported on shells of poly(o-Toluidine)(POT) hollow microspheres. The as-prepared POT/Fe₃O₄ nanoparticle composites can be used as novel and magnetic-responsive catalyst supports to produce highly efficient and recyclable noble metal catalysts. The size of Fe₃O₄ nanoparticles supported on shells of POT hollow microspheres can be tuned from 4 to 12 nm by changing the concentration of Fe ions. The roles of the doping acid of POT and Zeta potentials of Fe₃O₄ nanoparticles and POT in the formation of the POT/Fe₃O₄ nanoparticle composites were discussed. Furthermore, gold nanoparticles that were supported on the as-synthesized POT/Fe₃O₄ nanoparticle composites have been achieved by utilizing the reactivity of POT towards Au ions. The size of gold nanoparticles can be tuned by altering the concentration of HAuCl₄. Finally, the catalytic activity of the obtained POT/Fe₃O₄/Au composites for 4-nitrophenol (4NP) reduction is investigated. The results demonstrate that such magnetic-responsive polymer-supported gold nanoparticles can be easily recovered and reused five times still remains high catalytic performance, which indicate their potential applications in the field of catalysis.