Method of obtaining magnetite nanoparticles, stabilised with polyvinyl alcohol

FIELD: chemistry.

SUBSTANCE: invention can be used in magnetic nanoelectronics for magnetic registering media with high recording density, for magnetic sensors, radio-absorbing screens, as well as in medicine. Method of obtaining magnetite nanoparticles, stabilised with polyvinyl alcohol, includes obtaining magnetite in alkali medium of mixture of salts of bi- and trivalent iron and polyvinyl alcohol with weight content in initial mixture from 4 to 18 wt %, dispersion, washing and carrying out all operations under continuous ultrasound impact. Process of sedimentation of salts of bi- and trivalent iron and polyvinyl alcohol is carried out in ammonia vapour, with application of aqueous ammonia (NH₄OH) or hydrazine hydrate (N₂H₄·H₂O).

EFFECT: invention makes it possible to reduce scatter of magnetite nanoparticles by size, reduce labour consumption and expenditures in the course of process.

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The invention relates to the field of nano technology (specifically, to the field of polymeric nanocomposite based on the polyvinyl alcohol) and can be used in magnetic nano-electronics for magnetic recording media for high density recording, magnetic sensors, stealth screens and the like, as well as in medicine.

A known method of obtaining magnetite by coprecipitation of salts of divalent or trivalent iron excess alkali (see: Patent 4430239, ISM H01F 10/10. Ferrofluid Composition. Wyman J.E. USA).

During the realization of this patent, it is advisable to use a 10%salt solution (FeSO₄·7H₂O and FeCl₃·6N₂On) and pour in a solution of alkali or hold fast neutralization of the salt with an excess of alkali, as in the slow draining of dilute solutions are formed larger particles. To prevent the formation of iron hydroxide and other adverse processes using preferably chloride and ferric sulfate, and instead of caustic soda aqueous solution of ammonia. What if this chemical reaction can be expressed by the following equation:

The use of ammonia allows you to create soft conditions coprecipitation oxide, which contributes to reaction with the formation of it is finely dispersed magnetite composition of Fe_{2 O4or Fe2O3·FeO, which has the best magnetic characteristics in comparison with other magnetites, such as mFe2O3·nFeO (where n≠m), and the resulting ammonium salt NH4Cl when heated easily decomposes with evolution of ammonia gas. Ions Cl^-and soluble salts are removed by repeated washing with distilled water. As a result, in the solution decreases the number of oppositely charged ions, causing coagulation of particles of magnetite or preventing their peptization in the carrier fluid (using the obtained magnetite in magnetic fluids).}

However, the foregoing method and obtained by this method, the nanoparticles have a number of disadvantages:

a) no way to adjust the particle size of magnetite in the reaction, to limit their growth;

b) the method does not prevent aggregation of the obtained nanoparticles of magnetite;

C) obtained by the above method, the nanoparticles are chemically not protected, are highly reactive and quickly lose their properties when in contact with air.

Closest to the proposed method (prototype) is a Method of obtaining the magnetite nanoparticles stabilized biocompatible polymer having functional formyl group" (patent RF №2431472; and the Torah Yamskov IA, Tikhonov V.E., Loginova the like, includes I.A.). This method of obtaining nanoparticles of magnetite stabilized biocompatible polymer having available functional formyl group, includes obtaining magnetite from a mixture of salts of divalent or trivalent iron adsorbed in the polymer matrix, with subsequent modification of the end groups of the polymer. Magnetite receive joint deposition in an alkaline medium a mixture of salts of divalent or trivalent iron and at least one polymer selected from the range of: chitosan, polyvinyl alcohol, block copolymers of polystyrene and polyethylene oxide. The weight content of the polymer in the composite from 4 to 18 wt.%. The resulting composite is dispersed, treated with an aqueous solution of glutaraldehyde and washed. All operations are performed under continuous ultrasound exposure.

The invention allows to obtain stable nanoparticles of magnetite, are reusable.

The above method and obtained by this method, the nanoparticles have a number of disadvantages:

1). The high content of stabilizer on the surface and inside the nanoparticles significantly lowers operational magnetic properties of magnetite and seriously limits its application in magnetic nano-electronics.

2). The method is very time-consuming, in particular, C is the operation of processing the magnetite nanoparticles in an aqueous solution of glutaraldehyde. Note that this operation is not necessary for the magnetite nanoparticles used in electronics.

3). For the magnetite used in the magnetic electronics, sensors and the like, there is no need to use such expensive polymers like chitosan, block copolymers of polystyrene and polyethylene oxide.

4). Obtained by this method magnetite particles have a substantial range of sizes (according to our research - from 8 nm to 230 nm).

5). Upon receipt of the composite nanoparticles of magnetite in the form of a thin film or bulk material this way is not always possible to obtain a uniform structure of composite material, get rid of agglomerates of unreacted (reacted poorly) the source of the reaction products.

The purpose of the present invention consists of:

a) increase in functional magnetic properties of the magnetite nanoparticles for effective use in electronics devices, magnetic recording media, sensors, etc.;

b) reduction of the dispersion of nanoparticles of magnetite in size;

C) reducing the complexity and cost of the method (by eliminating some operations, reduce waste production by reducing the number of agglomerates, unreacted (reacted poorly) the source of the reaction products, and so what.);

g) obtaining a uniform structure of magnetite in the synthesis of composite nanoparticles of magnetite in the form of a thin film or bulk material.

The technical result is achieved by a method for production of nanoparticles of magnetite stabilized polyvinyl alcohol, including the production of magnetite in an alkaline medium a mixture of salts of divalent or trivalent iron and polyvinyl alcohol with a weight content in the initial mixture from 4 to 18 wt.%, dispersing, washing and conducting all operations under continuous ultrasound exposure, characterized by the fact that the process of deposition of a mixture of two - and trivalent iron and polyvinyl alcohol is carried out in pairs ammonia, using an aqueous solution of ammonia (NH₄OH) or hydrazine-hydrate (N₂H₄·H₂O).

The method is implemented as follows. In the first stage, prepare a solution of the polymer. Polyvinyl alcohol (PVA) dissolved in deionized water at a certain concentration (weight content in the initial mixture from 4 to 18 wt.% to obtain the maximum magnetization) to obtain a homogeneous solution, to accelerate the dissolution process vessel heated at 70°C, constantly stirring the solution. Later in the polymer solution make a joint solution of the compounds of ferric chloride III (6N₂About·FeCl₃) and chloride jelly is and II (4H ₂O·FeCl₂or sulphide of iron II (FeSO₄·7H₂O) in a ratio of two to one, in accordance with the standard method of obtaining chemical coprecipitation. The concentration of the metal calculated relative to the weight of the polymer. Thus, get the source precursors with different concentrations of metal.

As a restorative environment for synthesis is an aqueous solution of ammonia (NH₄OH) with a concentration of 25% or hydrazine-hydrate (N₂H₄·H₂O). The process of synthesis of the composite is carried out in a desiccator, the bottom of which is poured a solution of the carrier vapor of ammonia, and the top have a container with a solution of the precursor. After placing the samples for research in the desiccator, the required shutter speed, which depends on the number of the source precursor. The average dwell time is day. At the end of the synthesis is accomplished nanoparticles of Fe₃O₄in the PVA matrix.

When the hydrazine-hydrate (N₂H₄·H₂O) allocates a pair of ammonia oxidation by the oxygen of the air in the desiccator, and oxidation can occur by the second type involving precursor.

Use this method as a restorative environment is vapor ammonia narrow distribution of particle sizes, due to uniform distribution of the reaction medium at su the mu volume of material, resulting in the closest samples to the regular structure. A pair of ammonia from the gas phase is easily dissolved in the aqueous environment of the precursor and uniformly impregnate the whole amount, without making changes to the initial ratio of the components, so there is no need for mixing. As a result, the entire volume of the precursor is the reaction, there is no concentration gradient (or the gradient - minimum) at all stations, which allows the particles to activate the process.

The next step after synthesis is washing the samples with deionized water to remove the reaction products. Particles themselves are collected using a magnet.

All operations are performed under continuous ultrasound exposure with a frequency of 22 kHz.

To expedite the process of obtaining composite replacement solution of ammonia to hydrazine hydrate (N₂H₄·H₂O). Our studies showed that the choice of matrix are the best on the reproducibility of the results hold when using polyvinyl alcohol. The operation of the modification with glutaraldehyde in the proposed technical solution is excluded as unnecessary operation.

Thus, the proposed method is compared with the prototype has the following distinctive features:

1). The process of deposition of a mixture of sole is bivalent and trivalent iron and polyvinyl alcohol is carried out in vapor ammonia, but as the media reaction gas is an aqueous solution of ammonia (NH₄OH) or hydrazine-hydrate (N₂H₄·H₂O).

2). The operation of the modification with glutaraldehyde excluded.

The use of these distinctive features to achieve their goal, the authors are unknown.

It should be noted another advantage of using vapors of ammonia as a restorative environment. Use the vapors of ammonia allows the reaction recover successfully from a precursor in the liquid state and the gel state and in a state of powder.

Figure 1 presents the scheme of obtaining nanoparticles of magnetite by the proposed method in a desiccator with the prepared precursor using vapors of ammonia (NH₄OH) or hydrazine-hydrate (N₂H₄·H₂O). 1 - desiccator, 2 - table, 3 - Petri dish, 4 - precursor.

Figure 2 presents x-ray diffraction analysis of the obtained nanocomposites nanocomposite.

Example 1. In 150 ml of deionized water was dissolved 11,25 g FeCl₃·6H₂O and 4.61 in g FeCl₂·4H₂O. In the prepared solution was poured a solution of polyvinyl alcohol (10 ml) was dissolved 0.2 g of dry powder mixtures of PVA). Then, the solution was stirred until a homogeneous consistency.

Thus obtained precursor solution was poured in a Petri dish and services is enableval on the table holder desiccator (see 1). At the bottom of the table poured into about 300 ml of an aqueous solution of ammonia of 25%. The desiccator was closed and passed the day. By the end of the day the reaction products from the Petri dishes were thoroughly washed in deionized water, and the nanoparticles were collected by a magnet. Data mössbauer spectroscopy showed that the obtained nanoparticles are nanoparticles of Fe₃O₄in the super-paramagnetic state. The results of mössbauer spectroscopy was confirmed by the results of x-ray analysis (see Figure 2). According to transmission electron microscopy, as a result of the work were obtained nanoparticles of Fe₃O₄size 8-16 nm in a matrix of polyvinyl alcohol.

Example 2. In 150 ml of deionized water was dissolved 11,249, FeCl₃·6N₂Oh and br4.61 .FeCl₂·4H₂O. To the resulting solution was poured prepared solution of polyvinyl alcohol (10 ml) was dissolved 1 g of dry powder mixtures of PVA). Then, the solution was stirred until a homogeneous consistency.

The resulting precursor solution was poured in a Petri dish and set on the table the holder of the desiccator. At the bottom of the desiccator poured into about 100 ml. of hydrazine hydrate. The desiccator was closed and kept it as a Petri dish containing precursor 20 hours.

The reaction products from the Petri dishes were thoroughly washed in deionized water, and NAS the particles were collected by a magnet.

According to transmission electron microscopy, as a result of the work were obtained nanoparticles size 10-18 nm. The results of x-ray analysis allowed us to conclude that this is magnetite particles.

The method of obtaining the magnetite nanoparticles stabilized polyvinyl alcohol, including the production of magnetite in an alkaline medium a mixture of salts of divalent or trivalent iron and polyvinyl alcohol with a weight content in the initial mixture from 4 to 18 wt.%, dispersing, washing and conducting all operations under continuous ultrasound exposure, characterized in that the deposition process of the mixture of salts of divalent or trivalent iron and polyvinyl alcohol is carried out in a vapor of ammonia using an aqueous solution of ammonia (NH₄OH) or hydrazine-hydrate (N₂H₄·H₂O).