JSI - Synthesis of Materials K8

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Head of Department 

Prof. Dr. Darko Makovec
darko.makovec@ijs.si 
Telephone: +386 1 477 35 79

 

 

Secretary

Bernarda An┼żelak
bernarda.anzelak@ijs.si
Telephone: +386 1 477 33 23

Nanocomposite particles

 

Nanocomposite particles are a special class of composite materials. They are composite materials in the form of small particles, typically less than 100 nm in size. Within the individual nanocomposite particles the magnetic nanoparticles are usually fused with particles or layers of other functional materials. Normally, the materials that exhibit different applicable properties are fused; therefore, they are classified as multifunctional materials.

 

Nanocomposite particles are synthesized in various ways:

 

1.     By the hetero-agglomeration (self-assembly) of nanoparticles of different materials in suspensions. The driving force is the attractive electrostatic force between nanoparticles with an opposite surface charge or the chemical reactions between surface molecules.

2.     Nanoparticles of one material are coated by a layer of the other material.

3.     By mini-emulsion polymerization of a suspension of nanoparticles in a monomer MMA, nanocomposite particles that contain nanoparticles dispersed in a polymer matrix are prepared.

 

 

 

The company Cinkarna Celje d.d. co-financed a project in which in collaboration with researchers from the Institute for Public Health Maribor we developed two procedures for the preparation of multifunctional, superparamagnetic, photocatalytic nanocomposite particles. Nanocomposite particles are composed of agglomerates of maghemite Fe2O3 nanoparticles coated by a layer of photocatalytic anatase TiO2. For the purpose of photocatalytic purification the nanocomposite particles are dispersed in polluted water. The surface layer provides a high photocatalytic activity and because they are magnetic the particles are magnetically separated from the suspension and reused. Two approaches were used for the preparation of such nanocomposite particles:

  1. Nanocomposite particles were prepared by the hetero-agglomeration of anatase and maghemite nanoparticles in an aqueous suspension. The attractive electrostatic force between oppositely charged nanoparticles is the reason for the hetero-agglomeration.
  2. Already formed agglomerates of superparamagnetic nanoparticles were coated by a layer of nanocrystalline anatase. The process is based on the hydrolysis of an aqueous solution of TiSO4.

 

Mixing of the suspensions of anatase and maghemite nanoparticles with opposite surface charge which leads to the hetero-agglomeration and formation of the nanocomposite particles. The nanocomposite acts as photocatalyst that can be magnetically separated from the suspension.

 

Nanocomposite particles composed of agglomerates of superparamagnetic nanoparticles coated by a layer of nanocrystalline anatase.

 

For the preparation of multifunctional nanocomposite particles the method based on coating the functional core material with a magnetic layer is of special interest. The iron oxide maghemite magnetic layer is coated on core (nano)particles by the precipitation of iron ions from an aqueous solution. In order to induce the heterogeneous nucleation of the coating on the core particles the supersaturation of the product material, which determines the chemical reactions kinetics, must be carefully controlled. The slow release of hydroxyl ions needed for precipitation is achieved by the slow dissolution of Mg(OH)2, whereas Fe3+ ions are slowly released by decomposition of the Fe-urea complex. Iron oxy(hydroxide) coating on the core particles is transformed to magnetic maghemite at the end of the process.

In this way we have synthesized nanocomposite particles composed of the magnetically hard hexaferrite core particles, coated by a magnetically soft maghemite. Such nanocomposite particles should display an optimal hysteresis loop for the magnetic hyperthermia cancer treatment. Under the appropriate synthesis conditions the maghemite was epitaxially grown on the structurally similar hexaferrite. The spinel {111} planes were parallel to the hexaferrite {0001} basal planes.

 

Nanocomposite particle composed of hexaferrite (HF) core coated by a spinel maghemite (S).

JSI - Synthesis of Materials K8