Magnetic Composite Microspheres Research Articles

Multifunctional Magnetic Composite Microspheres with in Situ Growth Au Nanoparticles: A Highly Efficient Catalyst System

Multifunctional magne-tic composite microspheres which possess the precise control of the size, morphology, surface chemistry, and assembly process of each component have been successfully prepared. These functional nanocomposite microspheres possess a core of silica-protected magnetite particles and in situ growth active gold nanoparticles (ca. 4 nm) on the outer shell by layer-by-layer electrostatic self-assembly. The well-designed microspheres have high magnetization (23.9 emu/g), uniform sphere size (ca. 500 nm), and stably confined and active small Au nanoparticles. As a result, the very little composite microspheres show high performance in catalytic reduction of 4-nitrophenol (with conversion of 95% in 12 min), special convenient magnetic separability, long life, and good reusability. The unique nanostructure makes the microsphere a novel stable and highly efficient catalyst system for various catalytic industry processes.

A Novel Route to Prepare Fe<SUB>3</SUB>O<SUB>4</SUB>/P(MAA-co-NVP) Cross-Linked Magnetic Composite Microspheres with Core–Shell Architecture by Surface-Initiated Radical Dispersion Polymerization

A novel route was proposed to design and construct a magnetic composite microsphere with a controllable and regular core-shell architecture, which consists of Fe3O4 nanoparticles chemical-covalently encapsulated with pH-smart poly(methacrylic acid-co-N-vinyl pyrrolidone) (P(MAA-co-NVP)) cross-linked copolymers by a surface-initiated radical dispersion polymerization approach. The multistep surface treatment was employed to improve the dispersity and surface-chemical reactivity of Fe3O4 nanoparticles, involving introduction of active -NH2 groups, coupling of 1,1-methylene bis-(4-isocyanato-cyclohexane) and immobilizing of 2,2'-azobis[2-methyl-N-(2-hydroxyethyl) propionamide]. The structure and morphological characterization were carried out by FTIR, TEM, SEM and XRD etc. The neat Fe3O4 nanoparticles take on an aggregated spherical shape with an average diameter of about 12 nm, while Fe3O4/P(MAA-co-NVP) magnetic microspheres assume regularly monodispersed spheres with a mean dimension of ca. 0.8 microm. The dimension of the microspheres is abruptly increased with increasing pH values of the media. The microspheres exhibit superparamagnetic properties. It is expected that this type of novel microspheres can be employed as a magnetic targeted and pH-sensitive drug carrier.

Preparation of core–shell Fe3O4/SiO2 microspheres as adsorbents for purification of DNA

Nearly monodisperse core–shell Fe3O4/SiO2 microspheres have been prepared via a glycol reduction method followed by a modified Stöber process. The thickness of the silica shells can be tuned in the range 33–53 nm by varying the amount of tetraethyl silicate (TEOS) during syntheses. The magnetic composite microspheres were characterized with XRD, XPS, FTIR, TEM, ICP–OES and VSM, and further tested as adsorbents for purification of plasmid DNA from Escherichia coli DH5α cells. The magnetic purification of plasmid DNA leads to satisfying integrity, yield and purity in comparison with those isolated by the traditional phenol–chloroform extraction.

Controlled preparation of Fe3O4/P (St-MA) magnetic composite microspheres by DPE method

In this work, controlled radical polymerization based on 1, 1-diphenylethylene (DPE method) was used to prepare magnetic composite microspheres. By this method, Fe3O4/P (St-MA) magnetic composite microspheres were prepared via copolymerization of styrene (St) and maleic anhydride (MA) using DPE as radical control agent in the presence of Fe3O4 nanoparticles. The structure and properties of the magnetic composite microspheres obtained were characterized by IR, 1H-NMR, SEC-MALLS, TEM, TGA, VSM, DLS and other instruments. It was found that the DPE method allows the controlled preparation of magnetic composite microspheres, and Fe3O4/ P(St-MA) microspheres possess perfect sphere-shaped morphology, homogeneous particle size, carboxylic surface, superparamagnetism with a saturation magnetization of 14.704 emu/g, and magnetic content with a value of 25%.

Preparation of Magnetic Microspheres Based on Poly(<I>ε</I>-Caprolactone)-Poly(Ethylene Glycol)Poly(<I>ε</I>-Caprolactone) Copolymers by Modified Solvent Diffusion Method

Magnetic microspheres have promising application in biomedical field. In this paper, biodegradable poly(epsilon-caprolactone)-poly(ethylene glycol)-poly(epsilon-caprolactone) (PCEC) triblock copolymers were synthesized by ring-opening polymerization method. Through adjusting the epsilon-CL/PEG weight ratio in feed, PCEC copolymers with different block ratio were obtained. A novel modified solvent diffusion method was described to prepare magnetic PCEC composite microspheres containing magnetite nanoparticles. The particle size of microsphere decreased with increase in the PEG/PCL block ratio. The obtained microspheres could response to external magnetic field. This study described a novel method to prepare magnetic microspheres. The obtained magnetic polymeric microspheres might have potential application in drug delivery system or disease diagnosis field.

Monodisperse magnetic composite poly(glycidyl methacrylate)/La0.75Sr0.25MnO3 microspheres by the dispersion polymerization

Monodisperse magnetic poly(glycidyl methacrylate) microspheres were prepared by dispersion polymerization of glycidyl methacrylate in cyclohexane in the presence of La0.75Sr0.25MnO3 nanoparticles, surface of which was modified with penta(propylene glycol) methacrylate phosphate (PPGMAP). However, only agglomerates were formed by the dispersion polymerization in toluene. Sterical stabilizer was poly(styrene-block-hydrogenated butadiene-block-styrene) and initiators investigated were 2,2′-azobisisobutyronitrile (AIBN) and 4,4′-azobis(4-cyanovaleric acid) (ACVA). Effects of initiators and other reaction conditions on properties of the composite microspheres were evaluated. The phase composition of the magnetic polymer composite microspheres and the size of magnetic cores were determined by X-ray powder diffraction. The characterization was completed by magnetization measurements, atomic absorption spectroscopy, TEM, SEM and ATR FTIR spectroscopy.

Preparation of magnetic composite microspheres by surfactant free controlled radical polymerization: Preparation and characteristics

Submicron magnetic composite microspheres have been prepared by a new surfactant free controlled radical polymerization. This new approach is based on the use of diphenylethene (DPE) as radical controlling agent and no emulsifier is required. X-ray powder diffraction (XRD), thermogravimetric analysis (TGA) and transmission electron microscopy (TEM), etc. were conducted to characterize the magnetite particles and magnetic composite microspheres. The average size of the magnetic composite microspheres prepared by this new approach is 265 nm and the magnetite content of the composite microspheres is around 20%. Furthermore, the magnetic composite microspheres which surfaces have epoxy groups were also prepared.

Fabrication and magnetorheological property of core/shell structured magnetic composite particle encapsulated with cross-linked poly(methyl methacrylate)

Hybrid magnetic particle of carbonyl iron (CI) microsphere and cross-linked poly(methyl methacrylate) (PMMA) with core/shell structure was prepared to be adopted as a dispersed particle for a magnetorheological (MR) fluid. The magnetic hybrid composite microsphere was synthesized via a dispersion polymerization in the presence of CI, in which the PMMA was cross-linked using ethylene glycol dimethacrylate during polymerization for its enhancement in both chemical resistance and surface hardness. Magnetic property and morphology of the produced hybrid particles were examined via a vibrating sample magnetometer and scanning electron microscopy, respectively. The hybrid magnetic microsphere based MR fluids were then investigated under different external magnetic field strengths via a rotational rheometer. Their flow behaviors showing typical MR characteristics at a steady shear mode along with shear viscosity were examined under applied external magnetic field strength.

Effective adsorption and separation of lysozyme with PAA-modified Fe 3O 4@silica core/shell microspheres

Submicron-size Fe 3O 4@silica core/shell microspheres were prepared by sol–gel method. Through coating inert silica shell and adjusting the thickness, the dispersibility of magnetic microspheres in water was greatly improved. The resultant Fe 3O 4@silica microspheres with controllable saturation magnetization between 34.3 emu/g and 47.3 emu/g were superparamagnetic. All as-prepared magnetic composite microspheres possessed fleetly magnetic responsivity. The PAA-modified Fe 3O 4@silica microspheres were used for selective adsorption and separation of lysozyme, and the experimental results showed that the maximum binding capacity is about 127 mg/g. After surface modification of Fe 3O 4@silica with polyacrylic acid (PAA) flexible chains, the binding capacity of Fe 3O 4@silica-g-PAA microspheres for lysozyme were 22 times as much as that of pure Fe 3O 4@silica microspheres at the same pH condition.

Preparation and characterization of magnetic composite microspheres using a free radical polymerization system consisting of DPE

In this paper, a free radical polymerization system consisting of DPE was used to prepare magnetic composite microspheres. Fe3O4/P(AA–MMA–St) core-shell magnetic composite microspheres have been synthesized by copolymerization of acrylic acid, methyl methacrylate and styrene using DPE as radical control agent in the presence of Fe3O4 nanoparticles. The structure and properties of the magnetic composite microspheres were analyzed by FTIR, 1H NMR, SEC-MALLS, TEM, TGA, VSM and other instruments, and the formation mechanism of composite microspheres was supposed by those results. It was found that the Fe3O4/P(AA–MMA–St) microspheres were nano-size with relatively homogeneous particle size distribution, perfect sphere-shaped morphologies, superparamagnetism with a saturation magnetization of 18.430emu/g, and high magnetic content with a value of 40%. 1H NMR and TEM analysis indicated that at the first stage of polymerization, a DPE-containing copolymer of acrylic acid, methyl methacrylate formed and was then absorbed on the surface of Fe3O4 nanoparticles. Contact angle analysis indicated that the DPE-containing copolymer improved hydrophobicity of Fe3O4 nanoparticles through chemical absorption. In the second step polymerization, certain amount of monomers of styrene and residue methacrylate were initiated by the DPE-containing copolymer on the Fe3O4 nanoparticles' surface and resulted in the formation of Fe3O4/P(AA–MMA–St) composite microspheres.

A simple approach to the synthesis of hollow microspheres with magnetite/silica hybrid walls

In this paper, we report a simple approach for templating synthesis of magnetic hollow composite microspheres with magnetite/silica walls. This approach is based on the co-sedimentation of polymer microspheres and magnetic colloids followed by impregnation with silica oligomer from tetraethyl orthosilicate and the further removal of the polymer microspheres by pyrolysis. The diameter of the hollow microspheres can be adjusted in range of 300 nm – 2.0 μm by using polymer microspheres of different sizes and the wall thickness is tunable from 10–50 nm by controlling ratio of magnetite to the polymer microspheres. Magnetic characterizations show that the hollow microspheres have superparamagnetism with magnetization saturation of 10–30 emu/g. HRTEM and N 2 adsorption–desorption isotherms reveal that the hollow microspheres have numerous nanopores in the walls with a broad distribution in the range of 2 to 80 nm, which results in a high BET surface (67.6 m 2/g) and pores volume (0.14 cm 3/g).

PREPARATION AND CHARACTERIZATION OF MAGNETIC COMPOSITE MICROSPHERES WITH CORE-SHELL STRUCTURE

Magnetic Fe_3O_4/P(MMA/DVB)_(core)-P(St/GMA/DVB)_(shell) composite microspheres with core-shell structure were prepared by a two-step method.(1) Preparation of the magnetic cores:First,the magnetic miniemulsion composed of organic ferrofluid droplets dispersed in water was obtained by rapid addition of an oil-based magnetite ferrofluid,with a solid content 60 wt%,into the aqueous solution using DNS-86(polymerizable surfactant) as surfactant in the condition of ultrasonic emulsification.Then,the copolymerization monomers of methyl mathacrylate(MMA) and divinyl benzene(DVB) were injected directly into the magnetic miniemulsion.Because of their hydrophobic character,once the monomers were added into the emulsion,the methyl mathacrylate(MMA) and divinyl benzene(DVB) would have a high tendency to diffuse inside the organic phase of the ferrofluid droplets to form monomer swelling magnetic miniemulsion,which were supposed to be the main locus for copolymerization.In succession,the temperature was rapidly increased to 70℃ and starting the miniemulsion copolymerization to form uniform magnetic latexes.(2) Preparation of the core/shell hybrid polymeric microspheres:Through varying the feeding amount of styrene(St),glycidyl methacrylate(GMA) and DVB,the core-shell structured microspheres were rationally fabricated by the seed emulsion copolymerization using the above magnetic latex as the core emulsion.This preparation process is convenient and effective.Extensive characterization by X-ray diffraction(XRD),high resolution transmission electron microscopy(HR-TEM),thermogravimetric analysis(TGA) and vibrating sample magnetometer(VSM) showed that the magnetite content of Fe_3O_4/P(MMA/DVB) composite microspheres was 84 wt%.The magnetite content of the magnetic composite microspheres with core-shell structure is varied from 20 wt% to 76 wt% by feeding different amounts of monomers.The average diameter of the magnetic seeded microspheres and the core-shell composite microspheres is 150 nm and 350 nm,respectively.The functional epoxy groups on the surface of the core-shell composite microspheres can be further modified to load biomolecules.

Preparation and characterization of Fe3O4 magnetic composite microspheres covered by a P(MAH-co-MAA) copolymer

A magnetic core–shell-layered polymer microsphere (MPS) was successfully synthesized by a dispersion polymerization route, where the modified Fe3O4 nanoparticles (MFN) were used as a core, while poly(maleic anhydride-co-methacrylic acid) P(MAH-co-MAA) as a shell was covered on the surface of the Fe3O4 nanoparticles. Environmental scanning electron microscope (ESME) and transmission electron microscope (TEM) measurements indicate that the magnetic P(MAH-co-MAA)/Fe3O4 composite microspheres assume sphericity and have a novel core–shell-layered structure. The crystal particle sizes of the unimproved Fe3O4 and the MFN samples vary from 8 to 16 nm in diameter, and the average size is about 10.6 nm in diameter. The core–shell magnetic composite microspheres can be adjusted by changing the stirring speed. Since multiple Fe3O4 cores were coated with a proper percentage of P(MAH-co-MAA) copolymers, and therefore lower density was acquired for the MPS, which improved sedimentation and dispersion behavior. The saturated magnetization of pure Fe3O4 nanoparticles reaches 48.1 emu g−1 and the value for composite nanoparticles was as high as 173.5 emu g−1. The nanoparticles show strong superparamagnetic characteristics and can be expected to be used as a candidate for magnetism-controlled drug release.

Preparation of poly(styrene–glucidylmethacrylate)/Fe 3O 4 composite microspheres with high magnetite contents

Magnetic polymer composite microspheres with high magnetite contents were prepared by dispersion polymerization of styrene (St) and glucidylmethacrylate (GMA), in which Fe 3O 4 nanoparticles were co-stabilized by oleic acid and silane surfactants. The microstructure of the composite microspheres was characterized by Fourier transform infrared (FTIR) spectrometry, X-ray diffraction (XRD) and transmission electron microscopy (TEM). Results demonstrated the presence of a hybrid morphology with organic polymer-encapsulated inorganic particles. Subsequently, thermogravimetric analysis (TGA) and vibrating sample magnetometry (VSM) were used to evaluate the magnetite content of the microspheres. It was found that an accordant magnetite content of about 70 wt%, could be obtained for the magnetic polymer microspheres, a value significantly higher than those reported thus far. The possible mechanism for the formation of the microspheres was proposed.

Synthesis of cross-linked magnetic composite microspheres containing carboxyl groups

Fe3O4 magnetic nano-particles were prepared by a co-precipitation method and were modified using oleic acid. Then, the cross-linked magnetic compsoite microspheres containing a carboxyl group were prepared by using an improved emulsion polymerization with divinylbenzene (DVB) as the cross-linking agent. The composite microspheres comprised the Fe3O4 magnetic nano-particles as cores and the copolymer of styrene and acrylic acid as shells. The morphology and structure of the composite microsphere were characterized by FT-IR, transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectrum (XPS) and so on. The results show that the composite microspheres were well dispersed in emulsion with uniform sizes and carboxyl groups on their surface. They were cross-linked and stable in 1 mol/L of HCl and DMF.

Factors influencing magnetic polymer microspheres prepared by dispersion polymerization

AbstractMagnetic iron oxide (Fe3O4) was prepared by a coprecipitation method. Core–shell composite magnetic polymer microspheres with carboxyl groups were synthesized by the dispersion polymerization of styrene and acrylic acid in the presence of magnetic oxide, and dibenzoyl peroxide was used as an initiator. The synthesized magnetic polymer microspheres were characterized with X‐ray diffraction, transmission electron microscopy, scanning electron microscopy, Fourier transform infrared spectroscopy, and so forth. The results indicated that the product was single‐phase Fe3O4, and its average size was about 10 nm. The configuration of the microspheres, which contained carboxyl groups, was spherical, and the average size was about 2 μm. The results of vibrating sample magnetometry tests showed that the magnetic powders produced by different surfactants had different saturation magnetizations. When poly(ethylene glycol) with a weight‐average molecular weight of 4000 was used as a surfactant, the saturation magnetization of the samples reached 69.2 emu/g. The factors that affected the shape, magnetism, size, and distribution of the microspheres were also studied. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

Preparation and characterization of magnetic poly(ε-caprolactone)-poly(ethylene glycol)-poly(ε-caprolactone) microspheres

In this article, nano-magnetite particles (ferrofluid, Fe3O4) were prepared by chemical co-deposition method. A series of biodegradable triblock poly(epsilon-caprolactone)-poly(ethylene glycol)-poly(epsilon-caprolactone) (PCL-PEG-PCL, PCEC) copolymers were synthesized by ring-opening polymerization method from epsilon-caprolactone (epsilon-CL) initiated by poly(ethylene glycol) diol (PEG) using stannous octoate as catalyst. And the magnetic PCEC composite microspheres were prepared by solvent diffusion method. The properties of the ferrofluid, PCEC copolymer, and magnetic PCEC microspheres were studied in detail by SEM, VSM, XRD, Malvern Laser Particle Sizer, 1H-NMR, GPC, and TG/DTG. Effects of macromolecular weight and concentration of polymer, and the time for ultrasound dispersion on properties of magnetic microspheres were also investigated. The obtained magnetic PCEC microspheres might have great potential application in targeted drug delivery system or cell separation.

Preparation and Characterization of Composite Magnetic Microspheres

In this study, composite magnetic microspheres of tamarind gum and chitosan were prepared in a well-shaped spherical form with a size range of 230—46 0 μm by the suspension cross-linking technique for use in the application of magnetic carrier technology. The magnetic material used in the preparation of the microspheres was prepared by precipitation from FeCl3 and FeSO4 solutions in basic medium. The morphological, magnetic properties and the functional groups of the microspheres were characterized by different techniques (i.e., Scanning Electron Microscope (SEM), magnetometry, and FT-IR). The results demonstrated that the stirring rate of the suspension and the Fe3O4/chitosan ratio are the most effective parameters for the size/size distribution and the magnetic quality of the microspheres, while the amount of tamarind gum has no significant effect on these properties. The best magnetic quality of the microspheres is around 4.11 emu/g microspheres at 8 KG magnetic field intensity. The thermal stability was measured by using DSC methods.

An Investigation of Two Kinds of Magnetic Chitosan Composite Microspheres

In this study, two composite magnetic microspheres made of tamarind gum with chitosan and artemisia seed gum with chitosan were prepared by suspension cross-linking for magnetic carrier applications. The magnetic material used in the preparation of the microspheres was prepared by precipitating FeCl3 and FeSO4 solutions in a basic medium. The morphological, thermal stability, and magnetic properties of the two composite magnetic microspheres were characterized by scanning electron microscope, magnetometry, and differential scanning calorimeter (DSC). The swelling kinetics and pH responsive behavior of the two microspheres were also studied.

Composite Magnetic Microspheres of Tamarind Gum and Chitosan: Preparation and Characterization

In this study, composite magnetic microspheres have been synthesized based on tamarind gum and chitosan utilizing the suspension cross‐linking technique for use in the application of magnetic carrier technology. The properties of the composite magnetic microsperes, such as morphological, magnetic properties, thermal stability and the functional groups of the microspheres, were characterized by different techniques (i.e., SEM, magnetometry, DSC and FT‐IR). The swelling kinetics and pH responsive behaviors of the composite magnetic microspheres were also studied.