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Séminaire MCMF

Lundi 15 décembre à 15h00,
Salle Erwin Bertaut, F418

Orateur : Vladimir PANKOV (Belarusian State University, Minsk, Belarus)
"Development of a new cryochemical method for graphene-like materials and magnetic nanoparticles and nanocomposites for low-frequency tumour hyperthermia"

Abstract

Expanded graphite (few-layer graphene) is considered as one of the most promising carbon material. Commercially it can be produced by pyrolysis of graphite intercalation (Hammer’s method). This synthesis scheme is related to various environmental problems : disposal of strong acids, release of toxic gases - nitrogen oxides and sulfur, disposal of highly toxic substances (hydroxylamine, hydrazine, etc). Due to the structural and chemical defects, thermally expanded graphite has a lower mechanical strength, electrical and thermal conductivity.

The cryochemical method was developed for the synthesis of few-layer graphene based on the usage of strong reducing properties of alkaline metal solutions in liquid ammonia. Such solution includes salvated electron-pseudoanion of a salt called eletride. Unlike most of the methods described, this one does not use the oxidation of graphite layers, both at the stage of intercalates formation, and at the stage of their destruction.

Graphite has a high value of affinity to electron, and therefore easily forms intercalations with strong electron donors, such as the alkaline metals. The main role in the intercalate formation is played by solvated electron that enters the structure of graphite. Solvated cations act as counterions compensating electric charge.

The method allows creation of nanomaterials with different structural organization and to functionalize them with various additives in the preparation process. Advantages of this technology : it’s high-performance, flexible, environmentally friendly and waste-free. By-products are hydrogen and sodium hydroxide, which are involved in commercial circulation. Obtained graphene-like materials have structural perfection and chemical purity.

Based on this method, a low-temperature oxidative dehydrocondensation reaction was performed, obtaining carbon-metal wireframe nanocomposite for hydrogen storage.

Nanosized magnetic particles with magnetic hysteresis having an ability to absorb the energy of low-frequency fields (ZnxFe 3-x O 4, Fe 3-x BaxO4) were synthesized using this method. A great attention has been paid to nanoparticles biocompatibility (Me 1-x ZnxFe2O4 (Me=Mg,Mn)). This new type of hyperthermia uses an alternating magnetic field with amplitude of up to 1000 Oe (above the particle coercivity) and a frequency of 10 kHz (audio-frequency fields). Heating effects related to hysteresis losses (hysteresis relaxation type).

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