RU2522883C2 - Production of metal iron-based composite nanomaterial in pores of mesoporous matrix with magnetic properties - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: composite nanomaterial based on metal iron in powers of mesoporous matrix of silica SBA-15 that feature magnetic properties. Mesoporous matrix is impregnated with iron salts to be, then, removed from outer surface and processed by hydrogen in matrix pores till metal iron. Prior to impregnating, said matrix is dried at 200°C, not over. Weight of dried mesoporous matrix is placed in quartz reactor and treated by vapours of trichloraluminium in the flow of dry inert gas for at least 2 hours. Then, feed of said vapours is terminated to go on processing by said inert gas flow for at least 12 hours. Then, weight of mesoporous matrix is processed with water steam in the flow of dry inert gas for at least 2 hours. Then, feed of said vapours is terminated to go on processing by said inert gas flow for at least 12 hours. Thereafter, obtained alumina monolayer is built up many times to preset size of pores and magnetic properties of mesoporous matrix.

EFFECT: stable magnetisation owing to controlled adjustment of pore sizes and thickness of walls between pores.

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Description

The invention relates to the field of nanotechnology of composite materials based on mesoporous matrices containing nanoscale isolated metal particles, and can be used to produce magnetic materials used as magnetic sorbents, means of transporting drugs and to create magnetic media for storing information.

Known methods for producing magnetic nanomaterials based on both porous amorphous matrices (silica, coal, etc.), and flat substrates and a magnetic dispersed phase (metals (Fe, Ni), oxide ferro- and ferrimagnets) [1-12]. However, in these works, known methods do not allow to obtain the nano-size of the resulting particles and a narrow particle size distribution at the same time, which limits the possibility of obtaining nanomaterial with desired properties. Moreover, in the case of obtaining materials for magnetic recording of information, to increase the recording density, it is necessary to obtain magnetic particles with a size not exceeding 10 nm.

More progressive, from the point of view of homogeneous nanoparticles, is the approach known in the scientific literature as the “matrix isolation” of nanostructures [13-15].

A known method of producing materials based on the formation of nanostructures of a certain chemical composition in the matrix volume, the process being carried out by introducing the necessary chemical compounds by chemical methods [16, 17]. This approach allows one to control the parameters of nanoparticles at the stage of their formation. The matrices used for these purposes must contain structural voids that can be filled with compounds; subsequent chemical transformations lead to the formation of nanoparticles of a certain chemical composition in them [18]. In this case, the matrix cavities limit the reaction zone with the participation of compounds embedded in them. Obviously, the selection of matrices with various shapes of structural voids allows the synthesis of nanostructures of various structures.

To obtain monodisperse and spatially ordered nanostructures, porous materials with an ordered pore structure, such as mesoporous silica, porous alumina, and zeolites having one-dimensional channels, two- or three-dimensional cavities, are used. Based on this approach, a method is known for producing filamentous, lamellar, or spherical nanoparticles with a narrow particle size distribution [19]. The disadvantage of this method is the inability to adjust the size of metal particles, which is important when creating magnetic materials.

A known method of producing materials and devices containing oriented particles of the nanostructure [20]. This method proposes the synthesis of filamentous metal nanoparticles, metal alloys and metal-containing nanoparticles in a matrix of mesoporous silicon oxide, including through the implementation of chemical reactions in the matrix, stabilization of the nanoparticles, and the formation of oriented ordered extended nanostructures. However, the known method has not sufficiently high and not stable ordering of the arrangement of particles, which leads to a relatively rapid degradation of their functional properties.

A known method of producing magnetic nanocomposite materials with an ordered structure [21], which is the closest to the proposed technical solution and is selected as a prototype. In the known method, common with the present invention is the synthesis of metal nanoparticles in a matrix of mesoporous silica, including through the formation of solutions of the starting reagents and compounds, the implementation of the processes of synthesis and stabilization of particles, and the formation of larger nanoparticles.

The disadvantage of this method is the insufficiently high magnetic properties (magnetization) of the materials obtained, the instability of the magnetic properties over time, the inability to directionally control the magnetic properties of the materials obtained. These disadvantages of the known method are primarily associated with the structural features of the mesoporous silica used, which have the following structural characteristics (pore diameter 3 nm, wall thickness between pores 0.55 nm). This minimum wall thickness leads to a decrease in the magnetic properties of the material due to the possibility of interaction of magnetic nanoparticles with each other due to dipole-dipole interaction of magnetic dipoles.

The claimed invention is free from these disadvantages; its technical result is the achievement of the stability of the magnetic characteristics (magnetization) of the material due to the directional regulation of the pore size and wall thickness of the separating pores.

The specified technical result is achieved by the fact that in the method for producing a composite nanomaterial based on metallic iron in the pores of a mesoporous matrix having magnetic properties in accordance with the claimed invention, it is preliminarily dried at a temperature of not more than 200 ° C before impregnation of the mesoporous matrix, and then 1 g dried sample of the mesoporous matrix, place it in a quartz reactor and treated with aluminum trichloride vapor in a stream of dry inert gas for at least 2 hours, then continue processing the sample of the mesoporous matrix with pure dry inert gas for at least 12 hours, then it is sequentially treated first with water vapor in a stream of dry inert gas for at least 2 hours, then with pure dry inert gas for at least 12 hours, after whereby the obtained alumina-oxygen monolayer is repeatedly increased to the specified pore sizes and magnetic properties of the mesoporous matrix.

In addition, the specified technical result is achieved in that the thickness of each stacked layer is controlled by the formula: L = l · n,

where L is the thickness of several alumina-oxygen monolayers in the pores of the mesoporous matrix, and the number of deposited monolayers is determined by the number of matrix treatments with reagents (aluminum trichloride, water) nm;

l is the thickness of one alumina-oxygen monolayer, equal to 0.28, nm;

n is the number of matrix treatments with reagents (aluminum trichloride, water).

In addition, the indicated technical result is achieved in that the mesoporous matrix is impregnated with iron chloride (3) (it should be noted that other iron-containing compounds (in particular, iron chloride (2)) can be taken as the iron-containing reagent.

In addition, the specified technical result is achieved by the fact that argon is taken as an inert gas.

The solution to the technical problem of the claimed invention is based on a fundamentally new approach to regulating the structural characteristics of the SBA-15 mesoporous matrix, primarily due to the directional regulation of pore size and wall thickness of the separating pores, which allows to achieve an increase and time stability of the magnetic characteristic (magnetization) material.

In the claimed invention for the first time for additional fine-tuning of the structure of the mesoporous matrix, it is proposed to use the deposition of nanolayers of aluminum oxide of a given thickness based on conducting surface chemical reactions (chemisorption) in a certain sequence. Technologically, these reactions are described in example 1.

The claimed invention was tested in laboratory conditions of the Faculty of Chemistry of St. Petersburg State University. The results of studies confirming the achievement of a technical result are given in specific examples of the implementation of the claimed invention.

The essence of the claimed invention is illustrated by specific examples of the implementation of the method with tables and is illustrated in Fig.1-2.

Figure 1 presents the General scheme of the synthesis of nanoparticles in the pores of mesoporous silica; a is the original matrix; b is a matrix with an introduced iron compound; c - matrix with introduced particles of metallic iron

Figure 2 presents the model of the porous structure SBA-15 with deposited alumina monolayers: a) a lattice model; b) unit cell.

Example 1

The SBA-15 mesoporous matrices obtained by the standard method were pre-hydroxylated (i.e., treated with water vapor at a temperature of 200 ° C) in order to obtain on its surface the maximum amount of OH groups that are reactive upon chemisorption of aluminum trichloride (AlCl ₃ ) .

The synthesis of alumina monolayers was carried out due to the following reactions:

interaction of OH groups of silica with vapors of AlCl ₃

the interaction of the reaction product (1) with water vapor

as a result of reactions (1) and (2) on the pore surface of the matrix is formed

a monolayer of oxygen-oxygen groups, and during a further cycle of reactions (1) and (2), a diamond-oxygen monolayer (aluminum oxide) of a given thickness is formed on the pore surface of the matrix (see Fig. 2).

Technologically, the synthesis is as follows.

At the first stage, SBA-15 mesoporous silica with a certain porous structure is obtained according to the standard procedure, then the sample is dried at a temperature of no more than 200 ° C. This temperature regime was the most optimal, since an increase in temperature led to a decrease in oxygen groups. Next, a sample is taken (1 g), placed in a quartz reactor and treated with vapors of aluminum trichloride (AlCl ₃ ) in a stream of dry inert gas (argon) for at least 2 hours, then the flow of aluminum trichloride vapor is stopped, and then, in order to remove of physically adsorbed aluminum trichloride molecules, the sample is treated with a stream of dry inert gas, which was taken as argon in this example (it should be noted that any inert gas (in particular, nitrogen, helium, etc.) can be taken as an inert gas me it is 12 hours, then the sample is treated with water vapor (H ₂ O) in a stream of dry inert gas (argon) for at least 2 hours, then the flow of water vapor is stopped, and then, in order to remove physically adsorbed water molecules, the sample is treated with a dry stream inert gas (argon) for at least 12 hours, then the sample is impregnated with a solution of a metal complex, the impregnated sample is washed with a solvent (water in a mixture of methylene chloride) to remove residual metal complex solution from the surface of the sample, dried in an inert stream gas at a temperature not exceeding 200 ° C and reduced in a hydrogen stream at a temperature of 500-600 ° C.

In order to increase the thickness of the applied alumina-oxygen nanolayer, additional cycles of reactions (1) and (2) were carried out, and the number of cycles to obtain a certain thickness of the alumina-oxygen monolayer can be preliminary estimated by the formula: L = l · n, where L is the thickness of several alumina-oxygen monolayers in the pores of the mesoporous matrix, and the number of applied monolayers is determined by the number of matrix treatments with reagents (aluminum trichloride, water), nm;

l is the thickness of one monolayer of alumina groups equal to 0.28 nm;

n is the number of cycles performed (the number of matrix treatments with reagents (aluminum trichloride, water)).

As can be seen from Figure 1, which shows the porous structure of SBA-15 mesoporous silica, this material is characterized by the size of the wall thickness of the silica (d ~ 1 nm), which, although larger than the wall thickness of the mesoporous silica (d ~ 0, 55 nm) obtained by the known method, however, in order to completely avoid the negative factor associated with the possibility of dipole-dipole interaction of magnetic dipoles of metal (iron) nanoparticles, it is necessary to increase the wall thickness to 3.8 nm. This thickness value is achieved after ten build-up cycles (L = l · n = 0.28 · 10 = 2.8 nm + 1.0).

According to gravimetric analysis, chemically bound water in the sample of the initial SBA-15 mesoporous matrix was 3.6%. The surface measured by the method of Klyachko-Gurvich was 500 m ² / g; thus, the surface population with hydroxyls was 4.8 OH / nm ² .

After 1 cycle of molecular layering, the weight fraction of aluminum was 6.5% by the ratio of the amount of the initial hydroxyl groups of silica.

A number of analytical methods were used to diagnose the obtained samples. A study of the channel geometry of the obtained mesoporous materials was carried out using small-angle x-ray diffraction. This method made it possible to determine the interplanar spacings between layers of hexagonal packed pores. The weight fraction of iron in the sample was determined by photometry of the solution obtained by boiling an aliquot of the sample with an aqueous solution of hydrochloric acid. The determination of the amount of aluminum contained in the alumina monolayers deposited on SBA-15 was determined photometrically.

The chemical state of iron in the sample was determined by Mössbauer spectroscopy.

The grain surface structure was studied using a scanning electron microscope. On the microscope attachment for microprobe analysis, the elemental composition of various regions of the sample was analyzed. The magnetic properties of the obtained composite materials were studied using a Foner vibromagnetometer.

Example 2

Illustrates the ability to directionally adjust the structural characteristics of SBA-15 mesoporous silica. The structural characteristics of SBA-15 are regulated by the deposition of an alumina nanolayer before the iron compounds are introduced into the matrix and then reduced with hydrogen. Figure 1 shows a General scheme for the synthesis of nanoparticles in the pores of mesoporous silica. We see that the volume of iron salts fills the pores as much as possible, and the reduced iron occupies only part of the volume.

For the initial SBA-15 and samples with 1, 3, and 7 supported alumina monolayers, the specific pore volume was 0.71, 0.65, 0.5, 0.32 cm ³ / g, respectively.

To determine the thickness of the deposited layer, adsorption porosimetry was used, based on an experimental study of the desorption branch of the adsorption loop of water hysteresis. Table 1 shows the geometric parameters of the studied SBA-15 samples obtained during the analysis of the initial SBA-15 sample, and samples with one (sample SBA-15-1), with three (sample SBA-15-2) and seven (sample SBA -15-3) alumina monolayers.

Table 1 sample The number of deposited monolayers of Al-O groups ^{* 2} r _adc , nm ^{* 3} t _w , nm ^{* 4} SBA-15 0 4,5 1.9 SBA-15-1 one 4.3 2,3 SBA-15-2 3 4.0 2.9 SBA-15-3 7 3.6 3,7

* 1 specific porosity * 3 experimentally determined pore radius * 2 number of applied monolayers * 4 wall thickness separating pores

As can be seen from table 1, with an increase in the number of deposited monolayers, the pore size decreases, and the wall thickness increases. These data show that the inventive method for fine-tuning the pore size and wall thickness is effective and can be used to regulate the structure of mesoporous silica.

Example 3

At the end of the synthesis and analysis of the composition of the SBA-15 samples modified with iron nanoparticles, their magnetic properties were investigated. The analysis of the magnetic properties of the obtained samples was carried out on a Foner vibromagnetometer. To estimate the magnetic properties, we used the value of maximum magnetization — the specific magnetization of the sample at a field of 10 kOe.

Studies of the magnetic properties of samples obtained on the basis of SBA-15 with deposited alumina-oxygen nanolayers illustrate the possibility of controlling the magnetic properties of synthesized SBA-15 / Fe materials by applying aluminum-oxygen nanolayers and fine-tuning the porosity of the existing matrix. Table 2 shows the magnetization of the samples obtained on the basis of SBA-15 matrices modified with alumina monolayers.

table 2 sample σ ₁₀ , Am ² / kg ^* pore diameter, nm ^{* 1} (SBA-15) - without Al-O nanolayers / Fe 31 12 (SBA-15) - with 1 Al-O nanolayer / Fe 45 eleven (SBA-15) -c 3 Al-O nanolayers / Fe 55 10 (SBA-15) -c 7 Al-O nanolayers / Fe 71 8 * magnetization of the sample in a field of 10 kOe ^{* 1} porosity

Example 4

The data in table 3 illustrate the good reproducibility of the magnetic properties of materials with prolonged use. As can be seen from table 3, which presents data on the stability of the magnetic characteristics of the SBA-15 / Fe sample and the sample obtained by a known method (prototype), with prolonged use, the magnetic properties practically do not change. This suggests a good stability of dispersed iron. In the known method (prototype), the magnetization of the compared samples lies in the range of 0.5-1.0 em / g, i.e. in translation into standard units, is equal to (0.5-1) Am ² / kg.

From a comparison of the values of maximum magnetization, we can state that the method we developed for producing composite nanomaterial allows us to increase the magnetization value by 70 times compared to the known method (prototype).

Table 3 Parameter Name Units rev. The measured value of the sample SBA-15 / Fe The measured value of the prototype sample Sample 1 (tested immediately after synthesis) Maximum magnetization Am ² / kg 71 one Sample 2 (tested after 3 months storage) Maximum magnetization Am ² / kg 72 No Sample 3 ((tested after 8-month storage) Maximum magnetization Am ² / kg 71 No

As can be seen from the results of testing (examples 1-4), the inventive method has significant advantages over known analogues, first of all, it is important for solving applied problems the possibility of directional regulation of the magnetic properties of the obtained nanocomposite material, as well as its high stability of magnetic properties.

The results obtained show that the obtained SBA-15 / Fe material, due to the high stability of nanoparticles and good magnetic properties, can be used to create magnetic sorbents, magnetic transport particles for drugs. In the case of creating SBA-15 film composites, a planar matrix with a perpendicular pore orientation relative to the substrate, the synthesis of iron nanoparticles in these matrices according to our developed technique, can provide new materials for superdense magnetic recording of information.

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20. RF patent No. 2160697; publ. 12/20/2000.

21. RF patent №2322384; publ. 04/20/2008 (prototype).

Claims (4)

1. A method of obtaining a composite nanomaterial based on metallic iron in the pores of the SBA-15 silica mesoporous matrix with magnetic properties, comprising impregnating the mesoporous matrix with a solution of iron salts and then removing them from the outer surface and treating the iron salts with hydrogen in the pores of the mesoporous matrix to metallic iron, characterized in that before impregnation of the mesoporous matrix, it is pre-dried at a temperature of not more than 200 ° C, a portion of the dried mesoporous matrix is placed in a square a ring reactor and is treated with aluminum trichloride vapors in a stream of dry inert gas for at least 2 hours, then the supply of aluminum trichloride vapors is stopped and treated with a stream of dry inert gas for at least 12 hours, then a sample of the mesoporous matrix is sequentially treated with water vapor in a stream dry inert gas for at least 2 hours, stop the flow of water vapor and continue to process with a stream of dry inert gas for at least 12 hours, after which the resulting alumoki the monolayer monolayer is repeatedly expanded to the specified pore sizes and magnetic properties of the mesoporous matrix. 2. The method according to claim 1, characterized in that the thickness of the obtained amount of alumina monolayers is calculated by the formula
L = ℓ
where L is the thickness of the obtained amount of alumina monolayers,
ℓ - the thickness of one alumina monolayer, equal to 0.28 nm,
n is the number of treatments of the mesoporous matrix. 3. The method according to claim 1, characterized in that the impregnation of the mesoporous matrix is carried out with iron chloride (3). 4. The method according to claim 1, characterized in that argon is used as an inert gas.

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