Magnetic Core/Shell Nanocomposites

Mohamed Darwish

Institute of Nanomaterials, Advanced Technology and Innovation

Technical University of Liberec

23/4/2013

Nanoencapsulation received considerable increasing

attention by providing the possibility of combining

the properties of different material types (e.g.,

inorganic and organic) on the nanometer scale

having a spherical or irregular shape.

Capsules can be divided into two parts, namely the core and

the shell. The core contains the active ingredient, while the

shell protects the core permanently or temporarily from the

external environment.

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• The protective shell does not only serve to protect the magnetic nanoparticles against degradation but can also be used for further functionalization with specific components, such as catalytically active species, various drugs, specific binding sites, or other functional groups.

• Depending on applications, a wide variety of core materials can be encapsulated, including pigments, dyes, monomers, catalysts, curing agents, flame retardants, plasticizers and nanoparticles.

• When the diameter of metal oxide particle acting as magnetic core is less than 20 nm, the particle has superparamagnetism.

Applications of Magnetic Polymer Nanocomposite

•Water treatment application

•Catalysis

•Drug delivery

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Magnetic polymer composite particles can be prepared using various methods.

•The separately performed synthesis of the magnetic particles and polymer materials and then mixing them.

•In situ precipitation of magnetic material in the presence of polymer.

•Monomer polymerization in the presence of the magnetite particles to form magnetic polymer composite particles.

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• Co-precipitation from aqueous Fe (II)/ Fe (III) solutions.

• Thermal decomposition of organo-metallic compounds

• Hydrothermal synthesis basing on a solid-liquid-solution phase transfer strategy.

• Sonochemical synthesis

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Synthesis of iron oxide nanoparticles (NPs)

• Emulsion polymerization • Dispersion polymerization• Suspension polymerization • Microemulsion polymerization • Miniemulsion polymerization

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Synthesis of polymer shell

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Nanocapsules formation in miniemulsion

• Synthesis of magnetic core nanoparticles (inorganic reaction by co-precipitation process) Fe3O4 Magnetite

• Synthesis of magnetite polyvinylbenzyl chloride nanocomposites

(miniemulsion polymerization ) (-Cl) group • Synthesis of bi-layered polymer magnetite by coating of magnetite

polyvinylbenzyl chloride with a hydrophilic layer of polyethylene glycol, 3-amino-1-propanol, hexamethylenediamine or butyl-l, 4-diamine

(condensation polymerization) (-OH) group (-NH2 ) group

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Applied methods for magnetic nanocomposites polymer particles

with different functionalities

• Formation step

• Stabilization Step

By addition of oleic acid at room temperature or at higher temperature

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Synthesis of magnetic core nanoparticles by a co-precipitation process

Magnetic nanoparticles stabilize by oleate layer

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The average particles size is between 10 nm to 20 nm with superparamagnetic properties

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IR indicates that oleic acid is bonded with iron oxide

Bonding at higher temperature seems to be stronger

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Prepared at room temperature Prepared at higher temperature

The magnetite content is (~60%) for the preparation of magnetic nano particles by co-precipitation process with supermagnetic properties (~10nm diameter) by addition of oleic acid at higher temperature.

SampleMagnetite content

Fe3O4 %Average particles

size by TEMResistance to

HClDispersion

Magnetite (higher temperature)

60.3 ~10 nm Seconds hydrophobic properties

Preparation of magnetic polyvinylbenzyl chloride nanoparticles by miniemulsion polymerization

Direct process by formation of a homogeneous mixture of magnetite, monomer and surfactant by an US-sonotrode, then direct polymerization by addition of potassium peroxodisulfate.

This preparation method leads to oleic acid coated magnetite and a polymer shell with (-Cl) as functional group

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SampleMagnetite content

Fe3O4 %Average particles

size by TEMResistance to

HClDispersion

Magnetic Polyvinylbenzyl chloride nanoparticles

28.6 ~20 nm Hours hydrophobic properties

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The core shell structure formed where the outer shell is polymer with average particles diameter ranges from 10 nm to 15 nm

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Polyvinylbenzylchloride coated magnetite dispersed in acetone and after influence of a magnetic bar after 3 seconds demonstrating easy separation by magnetic force

[Darwish, M. S., et al., J Poly Research, 2011, 18(1), 79-88]

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Auger Electron Spectroscopy (AES)

Is an analytical technique that is used for performing surface analysis and to determine elemental composition as a function of depth of a sample.

Layer structure confirmed by auger electron spectroscopy

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Bonding situation study of oleic acid (co-monomer or mechanical entanglement) in the formation of magnetic polyvinylbenzyl chloride

The bonding situation of oleic acid (co-monomer or mechanical entanglement) was studied by IR and 1H-NMR.

Chemically Mechanical entanglement

Magnetic polyvinylbenzyl chloride nanoparticles based on the performed characterization

Two possible binding situations: chemical or mechanical binding with hydrophobic properties

20[Darwish, M. S., et al., Journal of Materials Science, 2011, 46(7), 2123-34]

Bi-layered polymer magnetic core nanoparticles

This preparation method leads to oleic acid coated magnetite and bi-layered polymer shell with (-OH or -NH2) group as functional group

Bi-layered polymer magnetic core was prepared by coating of magnetic core hydrophobic polymer shell composites with a hydrophilic layer of butyl- l, 4-diamine , hexamethylenediamine or 3-amino-1-propanol by polycondensation

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The core shell structure formed where average particles diameter ranges from 20 nm to 50 nm

Magnetic (III) Magnetic (II) Magnetic (I)

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bi-layered polymer magnetic core of butyl-l, 4-diamine gives higher in thermal stability

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Dispersion of Bi-layered polymer magnetic core /shell in water phase

Magnetic (III) ` Magnetic (II) Magnetic (I)

Hydrophilic properties of bi-layered polymer magnetic core composites

[Darwish, M. S., et al., Advanced Materials Research, 2013, Vols. 622-623, 254-258]

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Magnetic polymer as nano-carriers for enzyme immobilization

There are different property requirements and evaluation standards in accordance with different target substances and application system. Generally, certain parameters about magnetic carriers. should be taken into consideration: magnetic response capability, surface functional groups, biocompatibility, the size and its distribution of particles.

As a suitable enzyme for immobilization is alcohol dehydrogenase A (ADH-‘A’) and covalent immobilization was carried out. The standard enzyme buffer is potassium-phosphate-buffer (0.1 M, pH 7.0) the standard substrate is acetophenone, the reaction product is phenylethanol. Analysis was carried out using gas chromatography.

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Solubility test of magnetic carriers in Ppb (Potassium-phosphate Buffer ) and Toluene

Some pre-testing of the particles was done to make sure the particles are ready for use in the enzymatic environment.

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Reaction of the standard-substrate acetophenone by ADH-A immobilised on magnetic polyvinylaniline

The particles of magnetic polyvinylaniline with immobilized enzyme ADH-‘A’ have been tested with the standard substrate acetophenone (80 mM) dissolved in potassium-phosphate-buffer. During the test the enzyme showed poor activity. The product concentration didn’t show any increase for the first 50 minutes. However, the final concentration is at about 18 mM after 270 minutes which indicate that conversion has taken place but rather slow.

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Reaction of 2,5-hexandione by ADH-‘A’ immobilised on magnetic polyvinylaniline

The concentration of the substrate 2,5-Hexandione decreased slightly from 40 mM to 38 mM while the concentration of the product 2,5-hexandiol didn’t show any changes for the first 100 minutes of incubation. Only at the end, the sample indicated an increase of product up to 5mM. The immobilization results show that immobilization occurred but in a small extent.

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Batch test 10 mL of amino-linked ADH-A, production of phenylethanol at 30 °C

Batch test 10 mL of EDAC-linked ADH-A to chloro-magnetic beads, production of phenylethanol at 30 °C

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Catalytic application

Metal nanoparticles have attracted a special attention due to their use in catalysis. The catalytic reactivity depends on size and shape of nanoparticles and therefore synthesis of controlled shapes and size of colloidal platinum particles could be critical for these applications. Pt nanoparticles show high activity as catalyst in organic synthesis.

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One of the most known methods used for preparing nanostructred metal particles is the transition metal salt reduction method. In most methods of preparation two or four valence platinum are reduced to zero valence metal atoms with reducing agent e.g. sodium borohydride (NaBH4). The most popular procedure is the reduction of H2PtCl6.

Catalytic activity is tried to be added on polymer support of magnetic polyvinylbenzyl chloride nanoparticles. Pt is used to form Pt-Fe nanocomposites for using it as a catalyst for organic synthesis

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The polymer supported Pt-catalyst on magnetite polyvinylbenzyl chloride nanoparticles gives improved in thermal stability which indicates the lower amount of polymer included in the sample.

Atomic absorption spectroscopy was used for the determination of Pt metal in the sample. Pt loading in polymer-supported Pt catalyst on magnetite poly-vinylbenzyl chloride nanoparticles was found to be 17 wt %.

Characterization of Pt @ magnetic core/shell nanocomposite

Polymer supported Pt-catalysts on magnetic core/shell were prepared with fine homogeneous distribution with an average particle diameter of 5 nm

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[Darwish, M. S., et al., J. Appl. Polym. Sci. 2012, DOI: 10.1002/APP.38864]

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Catalysis in reduction reaction of cinnamaldehyde to cinamylalcohol

The catalytic activity of the catalyst is increased at high temperature and the reduction reaction of cinnamaldehyde to cinnamon alcohol is nearly finished in 15 min.

Conclusion and outlook

•Stable magnetic nanoparticles were prepared with superparamagnetic properties (<20 nm) by a co-precipitation process.

•The magnetite nanoparticles prepared by addition of oleic acid at higher temperature resulted in higher stability and also in higher magnetite content compared to the samples prepared at room temperature.

•Miniemulsion polymerization was successfully used in the preparation of magnetic polymer core shell nanoparticles functionalized with (-Cl, -NH2 and -OH) groups with a diameter range of 20 nm - 50 nm.

•Bi-layered magnetic core composites show better resistance against HCl than magnetite, which gives evidence that the magnetic composite has a core/shell-structure where the shell protects the core.

•The resulting nano-composite particles can be used for chemical engineering applications, water treatment and for binding enzymes on the functionalized surface sites.

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