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• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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Definitions

• Composite material consisting of a porous matrix and nanoparticles of metal or metal oxide
• the present invention relates to a composite material consisting of a porous matrix and nanoparticles of metal or metal oxide.
• the composite materials constituted by a microporous or mesoporous mineral matrix in which monodisperse metal nanoparticles are distributed homogeneously and in high concentration, are of great interest in various fields such as optics, magnetoresistance, thermoelectricity and catalysis. .
• the problem is to control the size and distribution of the particles, as well as the distance between the particles inside the solid.
• Solution impregnation methods have many disadvantages.
• the impregnation rate with the precursor solution is low and heterogeneous within the solid matrix.
• the level of nanoparticles after reduction within the matrix remains relatively low, generally less than 30% by volume, and on the other hand that the nanoparticles are concentrated essentially close to the surface of the porous matrix. , sure a thickness of about twenty nanometers.
• particle size distribution is important.
• EP-I 187 230 discloses a process for preparing a thermoelectric material comprising a step in which a target material is irradiated with a laser beam and the particles are recovered under vacuum, and a second step during which the particles recovered under vacuum are deposited on a substrate.
• the main disadvantage of this method is that it does not make it possible to obtain a uniform distribution of the nanoparticles within the matrix, whose surface area is richer. No.
• 6,670,539 describes a process for preparing a composite material consisting of a porous matrix whose pores have an average size of 5 to 15 nm, and of nanowires of bismuth or of bismuth alloy.
• the process involves passing a bismuth vapor into the pores of the matrix.
• the porous matrix is then cooled to progressively condense the bismuth vapor in the pores between the steam inlet and the vapor outlet, so as to gradually form bismuth nanowires in the pores.
• the progressive condensation of bismuth vapor in the matrix is limited by the size of the mesopores, and it is inhomogeneous. The inhomogeneous condensation makes it difficult to control the nucleation and growth reactions of the nanowires.
• the object of the present invention is to provide an efficient method for the production of a composite material consisting of a microporous or mesoporous solid matrix, in the pores of which nanoparticles of metal or metal oxide are distributed uniformly and with a high rate. This is why the present invention relates to a process for preparing a composite material, as well as the composite material obtained.
• the process for preparing a composite material according to the present invention consists in impregnating a microporous or mesoporous solid material with a solution of one or more precursors of the metal nanoparticles or nanoparticles of metal oxide, and then reducing the precursors within said matrix-forming material. It is characterized in that the impregnation is carried out under pressure vacuum of saturating vapor and under reflux of the precursor solution, and in that the reduction is carried out radiolytically.
• the precursor solution (s) may further contain an oxidation radical intercepting agent, which intercepts the oxidative radicals formed in the solution upon irradiation, thereby preventing oxidation of the colloidal particles produced.
• the oxidant radical interceptor is preferably selected from primary alcohols, secondary alcohols and formates. By way of example, mention may be made of isopropanol and alkali metal formates. These oxidative radical interceptors have a double function: they not only capture the oxidative radicals that arise during radiolysis, but they also provide new reducing radicals, which arise from their reaction with oxidizing radicals. This makes it possible to increase the reduction efficiency of the metal.
• the precursor solution contains the intercepting agent in sufficient quantity, the nanoparticles formed are constituted by the metal.
• the nanoparticles formed after reduction are particles of a metal oxide of the precursor compound.
• concentration of the radical interceptor is determined according to the amount and nature of the metal to be reduced, and the nature of the desired particles.
• the nanoparticles are generally oxide nanoparticles.
• the nanoparticles are generally metal nanoparticles
• concentration "interceptor” / "precursor metal salt” at least equal to a value of the order of 10 3 to 10 4
• the nanoparticles are generally metal nanoparticles
• the determination of very precise concentration domains adapted to each type of metal to form either metal nanoparticles or nanoparticles of metal oxide, is within the reach of the skilled person.
• microporous or mesoporous material intended to form the matrix of the composite material may be chosen from silica, alumina, zeolites, metal oxides such as zirconia, titanium oxide, polymers which have a mesoporosity [such as for example polystyrene, copolymers divinylbenzene (DVB) - ethylene glycol dimethacrylate (EDMA)].
• Microporosity means an average pore size of less than one nanometer. By mesoporosity is meant an average pore size of 1 to 100 nanometers.
• the pore distribution at the nanoscale can be disordered or ordered.
• a disordered distribution is generally constituted by open cavities distributed in a disordered manner.
• An ordered pore distribution may be oriented or unoriented.
• An unoriented ordered pore distribution may be constituted by cavities connected by tunnels.
• An ordered and oriented distribution may be constituted for example by channels distributed in regularly hexagonal form with few defects.
• the precursors are chosen from compounds of the following metals: Bi, Au, Ag, Ti, Mg, Al, Be, Mn, Zn, Cr, Cd, Co, Ni, Mo, Sn, Pb.
• the compounds may be inorganic salts (such as, for example, sulphates or perchlorates), or organic salts such as formates or neodecanates.
• neodecanoate mention may be made of neo-decanoate of bismuth. Neodecanoates make it possible to carry out the reduction in a nonaqueous medium.
• the precursors may further be selected from organometallic compounds.
• the solvent of the precursor solution is chosen as a function of the precursor salt concerned.
• the radiolytic reduction can be carried out using a source of ⁇ -rays, x-rays or an accelerated electron source.
• a composite material obtained by the process of the invention consists of a matrix consisting of a microporous solid material having an average pore size of less than one nanometer or of a mesoporous solid material having an average pore size of 1 to 100 nm, and by nanoparticles of metal or metal oxide.
• the matrix material is either disordered or ordered and optionally oriented, and in that: the nanoparticles are monodisperse in size and they represent from 50% to 67% of the total pore volume of the matrix material when said matrix material is ordered and optionally oriented; the nanoparticles are either monodisperse in size or the same size as the porosity of the matrix material, and they represent at least 50% of the initial pore volume of the matrix material when said matrix material is disordered.
• the monodisperse character is characterized for the materials object of the present invention, by a ratio ⁇ d> / d max of less than 10%, where d is the diameter of the nanoparticle.
• the size of the nanoparticles depends in particular on the irradiation dose rate, the initial precursor concentration and the pore size.
• a high dose rate promotes the production of a large number of nucleation centers.
• Figures 1a and 1b show a schematic view of a composite material in which the pore distribution in the matrix material is disordered, respectively before and after impregnation.
• Figures 2a and 2b show a schematic view of a composite material in which the pore distribution in the matrix material is ordered and oriented, respectively before and after impregnation.
• the microporosity is in the form of cylindrical channels. When the nanoparticles are in contact with each other, the residual porosity corresponding to the empty spaces separating the nanoparticles is 33%. This embodiment is illustrated schematically in FIG.
• the solid matrix consists of a material chosen from silica, alumina, zeolites, metal oxides such as zirconia, titanium oxide, polymers such as polystyrene, and copolymers which have a mesoporosity.
• the nanoparticles are homogeneously distributed across the volume of the matrix.
• the nanoparticles are constituted by a metal chosen from Bi, Au, Ag, Ti, Mg, Al, Be, Mn, Zn, Cr, Cd, Co, Ni, Mo, Sn or Pb, or by an oxide of one of these metals.
• a material comprising an open-pore disordered mesoporous silica matrix containing nanoparticles of bismuth, gold or silver;
• a material comprising an ordered and optionally oriented mesoporous silica matrix having pores in the form of regular channels, containing nanoparticles of bismuth; • A material comprising an open-pore mesoporous alumina matrix containing nanoparticles of bismuth, gold or silver.
• the method according to the invention can be implemented in a device as shown in FIG. 4.
• Said device comprises an impregnation chamber and a pumping system.
• the impregnation chamber comprises an irradiation cell 1, a liquid nitrogen trap 2, a precursor solution tank 3, heating means 4, and irradiation means, not shown.
• a pipe comprising a valve 5 connects the irradiation cell 1 and the tank 3.
• a pipe comprising a valve 6 connects the irradiation cell 1 to the liquid nitrogen trap 2.
• the pumping system comprises a primary pump 7, a pump secondary 8, conduits provided with valves 9, 10 and 11, and a vacuum measuring device 12.
• the pumping system provides a secondary boundary vacuum of 10 ⁇ 7 mbar.
• the materials according to the invention can be used in various technical fields.
• materials having a mesoporous matrix and bismuth nanoparticles are particularly useful in thermoelectricity and magnetoresistance.
• thermoelectric materials In the field of thermoelectric materials, bismuth is known for its good thermoelectric properties, especially in the case of 2D and ID quantum confinement. In this type of confinement, the merit factor remains below 2. This limit is essentially due to phonon propagation. In a material according to the present invention, comprising a mesoporous matrix and nanoparticles of bismuth, phonon propagation is decreased.
• the present invention also relates to the use of the materials according to the invention comprising a mesoporous matrix and nanoparticles of bismuth as a thermoelectric material, especially as a cold generator, or conversely as a voltage generator.
• a cold generator the composite material containing nanoparticles of bismuth can be used for example in the design of a refrigerator, an air-conditioned car seat, a car air conditioner, a cooler, a thermostatically controlled enclosure, or a radia ⁇ tor for electronic circuit.
• the composite material containing nanoparticles of bismuth can be used for example as a direct energy source or as a component of an accumulator.
• a magnetoresistance value is called "large” when it represents a relative increase of 50% compared to mate rials values ⁇ conventional magnetoresistive.
• This increase is defined according to the formula: (RR (H)) / R> 50% where R is the resistance of the material without a magnetic field and R (H) is the resistance of the material subjected to the magnetic field.
• R is the resistance of the material without a magnetic field
• R (H) is the resistance of the material subjected to the magnetic field.
• this increase reaches 50% in the case of bismuth for a temperature of 300K with a field of 32 Tesla.
• the composite material according to the invention can be used as a magnetic sensor, for example in the manufacture of read heads or the detection of magnetic fields.
• the invention is illustrated below by an example of preparation of a composite material, to which it is however not limited.
• the preparation was carried out in a device similar to that described above.
• the irradiation cell was pre-steamed at 80 ° C. on a water bath in order to degas and decontaminate the surfaces of the cell to prevent the formation of particles on the walls.
• a precursor solution bismuth perchlorate in water at a concentration of 0.06 mol / l
• a solution of oxidizing radical intercepting agent isopropanol in water at 7 mol / l.
• a mesoporous silica sample was prepared according to the method described by Dongyuan Zhao, Qisheng Huo, Jianglin Feng, Bradley F. Chmelka, and Galen D. Stucky, [J. Am. Chem. Soc. 1998, 120, 6024-6036].
• 4.0 g of Brij 96® surfactant was dissolved in 20 g of water and 80 g of 2M HCl with stirring. To the homogeneous solution thus obtained, then 8.80 g of tetraethoxysilane was added at room temperature maintaining stirring for 20 h. The solid product was recovered, washed and dried at room temperature. The material thus obtained was heated from ambient temperature to a temperature of 500 ° C. over a period of 8 hours. It was then carried out for 6 hours before allowing the material to cool to room temperature.
• the dimensions of the sample are a few millimeters.
• the pore size is 6 nm and the total porosity of the sample is 80% of the total volume.
• the BET surface is 342 g / m 2 .
• the valves 5 and 6 of the device being closed, the precursor solution was introduced into the reservoir 3 and the silica sample into the irradiation cell 1.
• the valve 6 was opened, and the silica sample was treated under a vacuum of 10 ⁇ 6 mbar by heating at a temperature of 80 0 C using the heating means 4, to desorb all impurities and water present on the surface.
• the valve 6 was closed, which put the cell under static vacuum.
• the valve 5 was opened to introduce the precursor solution into the irradiation cell.
• the precursor solution vaporized immediately.
• the valve 5 was closed, the valve 6 was partially opened to evacuate the irradiation cell using the primary pumping system, until total pumping of the dissolved gas characterized by the cooling of the irradiation cell 1.
• valve 6 was closed to isolate the irradiation cell 1, and it was heated up to pressure saturating vapor of the precursor solution under partial vacuum. A reflux phenomenon was observed in cell 1. The heating was maintained for a period of 2 hours. This duration is a function of both the size and the porosity of the monolith forming the sample.
• the isopropanol solution is introduced into the cell 1, by opening the valve 5.
• the valve 5 was closed again after the introduction of 1-isopropanol. again the vacuum until cooling of the irradiation cell 1.
• the isopropanol solution diffused rapidly into the precursor solution, the mixture was then refluxed again for one hour and then sealed under vacuum. Vacuuming at the end of the refluxing step of the mixture can be replaced by isolating the sample in cell 1 at atmospheric pressure by flushing under argon for 30 minutes.
• the impregnated silica monolith was then subjected to irradiation with a cesium 137 ⁇ -ray source having a power of 1.8 kGy ⁇ hr -1 for one hour, after which the monolith was dried directly. in cell 1 under primary vacuum, then secondary The sample obtained was characterized by TEM, BET and RX.
• the BET surface of the sample after the end of the treatment is 60 m 2 / g, which represents a decrease of 87% compared to the initial value.
• Figure 5 shows a darkfield TEM micrograph of the silica-based mesoporous matrix in which bismuth nanoparticles have been formed. This micrograph clearly shows the presence of crystallized nanoparticles throughout the mesoporous matrix. The nanoparticles appear in white and have a size of 6.0 ⁇ 0.5 nm. Under the electron beam of the transmission electron microscope, the nanoparticles undergo rotations on themselves. Thus, depending on their orientation, they diffract or not. This explains why, on this type of image, only a part of the totality of the nanoparticles present in the network of silica. FIG. 5 shows that crystallized nanoparticles which are stable, in high concentration and slightly spaced apart can be produced in the organized mesoporous silica.
• FIG. 3 The structure of this silica / bismuth sample in which the microporosity of the matrix is of the ordered type and oriented in the form of cylindrical channels is also represented in FIG. 3 above.
• the upper part is a Transmission Electron Microscopy (TEM) micrograph of a sample of material showing the alignment of the metal bismuth nanoparticles in a channel. This is an enlarged view of the sample shown in FIG. 5.
• the bottom portion is a diagram of a portion of this channel. It specifies the evolution and the limits of the percentage of impregnation as a function of the periodic distance a between the spherical bismuth nanoparticles.
• the X-ray diffraction pattern is shown in Fig. 6, which also indicates the intensity of the lines according to JCPDS sheet 05-0519.
• the intensity I is indicated on the ordinate, and the angle ⁇ is indicated on the abscissa.
• the curve corresponds to the material according to the invention of the present example.
• the four diffraction peaks of the metal bismuth can be distinguished.
• the intensity of the lines, with respect to the continuous background, is low, which is related to the high absorption capacity of bismuth, whose mass absorption coefficient, for a source X Cu K-alpha of 1.6 KWatt under 40 KeV, is 15 cm 2 / g.
• the comparison of the spectrum with data from sheet 05-0519 of the JCPDF file confirms the formation of nanoparticles of metal bismuth and not of bismuth oxide.
• the disordered silica matrix was obtained by the method described by Polartz, et al. [Chemical Communication,
• the irradiation was carried out using a cesium-137 ⁇ -ray source having a power of 1.8 kGy ⁇ h -1 for a duration of 2 hours, and Figure 7 shows a TEM micrograph of the material obtained.
• the image analysis confirms an impregnation rate greater than 70% in a material whose initial porosity, measured by BET, was 80% . The sizes and shapes of the particles are adjusted to those of the porosity, the has a high level of irradiation.
• a disordered silica monolith was prepared according to the method cited in Example 2. The procedure for impregnating the silver salt is identical to that of Example 1. The cells 1 and 3 were covered with a sheet of aluminum to protect the precursor from light rays. The impregnated silica monolith was then subjected to irradiation with a cesium 137 ⁇ -ray source having a power of 1.8 kGy ⁇ hr -1 for one hour, after which the monolith was dried directly. in cell 1 under primary vacuum, then secondary.

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• 2005
  • 2005-02-24 FR FR0501879A patent/FR2882371B1/fr not_active Expired - Fee Related
• 2006
  • 2006-02-16 EP EP06709332A patent/EP1851359A2/fr not_active Withdrawn
  • 2006-02-16 JP JP2007556629A patent/JP5230206B2/ja not_active Expired - Fee Related
  • 2006-02-16 WO PCT/FR2006/000357 patent/WO2006090046A2/fr active Application Filing
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• 2007
  • 2007-08-13 US US11/889,454 patent/US20080176059A1/en not_active Abandoned

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