FR2852947A1 - INORGANIC MATERIAL WITH HIERARCHIZED STRUCTURE, AND PROCESS FOR ITS PREPARATION - Google Patents

Abstract

The invention relates to an inorganic material with a hierarchical structure and a sol-gel process for its preparation.The material is a monolith consisting of an inorganic matrix. The matrix is constituted by a polymer of a metal oxide, and it comprises macropores, mesopores and micropores, said pores being interconnected. The preparation process consists of preparing an emulsion by introducing an oily phase into an aqueous solution of surfactant, adding an aqueous solution of precursor metal alkoxide to the solution of surfactant, before or after the preparation of the emulsion, to be left the reaction mixture to stand until the condensation of the precursor, then to dry the mixture.

Description

The present invention relates to a material with a structure

  hierarchical and a process for its manufacture.

  It is known to prepare inorganic polymers, in particular of silica, having one or two types of porosity. Macroporosity is obtained by the shaping process by direct emulsification and microporosity is inherent in amorphous silica.

  Thus, A. Imhof, et al. (Nature, vol. 389, October 30, 1997, p. 948-951) describe the implementation of sol-gel processes starting from alkoxides dissolved in a lower alcohol and hydrolysed by addition of a small amount of water , it being recalled that most of the alkoxides are very reactive with water and do not give stable emulsions.

  This document further describes the preparation of monodisperse macroporous materials of titanium oxide, zirconia, or silica, with pore diameters between 50 nm and several hum, from a monodisperse oil emulsion in formamide. . It also describes a method of preparing an "oil in formamide" emulsion, fractionating the emulsion to obtain a uniform droplet size, preparing a metal oxide solution in formamide with a small amount of water to hydrolyze, i.e. dissolve the oxide, disperse the emulsion in the solution, centrifuge to adjust the volume of the droplets, gel through the addition of ammonia to increase the pH, wash with water, dry and then calcine. This process has many steps which make it uneconomic.

  B. P. Pinks (Adv. Mater. 2002, 14, no. 24, December 17) 30 describes the preparation of porous silica from an emulsion stabilized by silica particles only, in the absence of surfactant. Evaporation in air produces solids with varying degrees of porosity and inherent wettability.

  Gi-Ra Yi, et al. (Chem. Mater. 1999, 11, 2322-2325) describe a process which uses sodium dodecylsulfonate (SDS) as a surfactant. A silica sol is prepared by mixing tetraethoxysilane (TEOS) or tetra-B0500FR methoxysilane (TMOS) and HCl with stirring. The gelation is obtained by addition of ammonium hydroxide. The final product is obtained by calcination. In another embodiment, an "isooctane in formamide" emulsion is used as a system congruent with formamide. The emulsion is stabilized by a triblock PEG-PPGPEG copolymer.

  J. S. Beck, et al. (J. Am. Chem. Soc. 1992, 114, 1083410843) describe the preparation of mesoporous solids constituted by a silicate or an aluminosilicate. The solid compounds obtained have a specific surface of the order of 700 m2 / g and the pore size is between 15 and 100 A. The aim of the present invention is to provide a simple process for the preparation of an inorganic material with a large specific surface.

  The material according to the invention is a monolith constituted by an inorganic matrix. It is characterized in that said inorganic matrix consists of a polymer of a metal oxide, and that it comprises macropores having an average dimension dA of 1 pm to 20 pm, 20 of the mesopores having an average dimension dE of 20 to 30 A and micropores having an average dimension d, from 5 to 10 A, said pores being interconnected.

  By monolith is meant a solid object having an average dimension of at least 1 mm.

  The metal oxide is an oxide of one or more metals, at least one of the metals being of the type capable of forming an alkoxide. By way of example of metals capable of forming an alkoxide, mention may be made of Si, Ti, Zr, Th, Nb, Ta, V, W and Al.

  The metal oxide can be a simple oxide, and it is then an oxide of one of the above metals.

  The metal oxide can also be a mixed oxide of at least two metals, and at least one of the metals is then chosen from the above metals, the other metal or metals being able to be chosen from other metals, especially B and Sn.

  Materials whose inorganic matrix is a polymer of silica or of a mixed silica oxide are particularly preferred.

  B0500FR The inorganic matrix can also contain a filler, for example a carbonaceous filler such as nanofilaments, nanotubes or carbon powder. The filler can also be a polymer of a monomer which has a marked hydrophilic character, chosen for example from acrylic acid, acrylamide, vinylpyrolidone, methacrylates carrying hydrophilic functions such as in particular OH, COOH, NH , (in particular hydroxymethyl methacrylate).

  A material according to the present invention is obtained by a solgel process, characterized in that an emulsion is prepared by introducing an oily phase into an aqueous solution of surfactant, an aqueous solution of at least one alkali metal precursor is added. the oxide forming the inorganic matrix in the surfactant solution, before or after the preparation of the emulsion, the reaction mixture is left to stand until the precursor has condensed, then the mixture is dried to obtain a monolith .

  The oxide precursor solution forming the inorganic matrix of the material of the invention contains at least one alkoxide. When the inorganic matrix consists of a mixed oxide, a mixture of precursors is used, of which at least one is an alkoxide.

  As examples of alkoxides, mention may be made of the compounds R'n (OR) m-nM in which M represents a metal having the valence m, and 0 n <m, R represents an alkyl radical having from 1 to 5 atoms carbon, R ′ represents an alkyl radical or an aryl radical which optionally carry one or more functional groups. We can cite for example 30 Si (OR) 4, Ti (OR) 4, Zr (OR) 4, Th (OR) 4, Nb (OR) 5, Ta (OR) 5 and Al (OR) 3. Mention may also be made of the compounds VO (OR) 3 and W (OR) 6. The alkoxides in which R is methyl or ethyl are particularly preferred.

  The precursors which can be used in combination with at least one alkoxide can be chosen, for example, from hydroxides such as Al (OH) 3, oxides such as B203 or V205, chlorides such as SnCl4, ZrCl4 or TiCl4, or B0500FR oxychlorides such as ZrOCl2.2H20, or mixed oxides such as sodium metavanadate.

  For example, a silica matrix is obtained from an aqueous solution of an alkoxide R'n (OR) 4-nSi in which 5 R, R 'and n have the previous meaning. When the inorganic matrix consists of a mixed oxide of silicon and of a metal M, a solution of silicon alkoxide and a metal precursor M which may be an alkoxide of M or a non-alkoxide precursor of M. La is used. oily phase consists of one or more compounds chosen from linear or branched alkanes having at least 12 carbon atoms. By way of example, mention may be made of dodecane and hexadecane. The oily phase can also consist of a silicone oil of low viscosity, that is to say less than 400 centipoise.

  When the surfactant solution is used in the form of a thick phase, it is preferable to introduce the oily phase dropwise into the surfactant solution. Drip is not essential when a device such as an ultraturax is used to mix the constituents which generates intensive stirring.

  The surfactant can be a cationic surfactant chosen in particular from tetradecyltrimethyl ammonium bromide (TTAB) or dodecyltrimethylammonium bromide.

  In this case, the reaction medium is brought to a pH of less than 3, preferably less than 1.

  The surfactant can be an anionic surfactant chosen from sodium dodecylsulfate, sodium dodecylsulfonate and sodium dioctylsulfosuccinate (AOT).

  In this case, the reaction medium is brought to a pH greater than 10.

  The surfactant can be a nonionic surfactant chosen from surfactants with an ethoxylated head, and nonylphenols. In this case, the reaction medium is brought to a pH greater than 10 or less than 3, preferably less than 1.

  B0500FR When the monolith contains a carbonaceous filler such as nanofilaments, nanotubes or carbon powder, this filler is introduced into the reaction medium by dispersion in the solution of surfactant. When the filler is a polymer of a monomer which has a hydrophilic character, it is introduced by dispersing nanofilaments or powder of said polymer into the surfactant solution.

  When preparing the emulsion, respective amounts of aqueous solution and oily phase are used such that the ratio of aqueous phase to oily phase is less than 1/4 to limit the undesirable phenomena of segregation.

  The concentration of surfactant is preferably greater than 10% by mass relative to the total amount of water, in order to obtain an initial viscous reaction medium and to promote emulsification.

  The concentration of precursor of the inorganic matrix is preferably greater than 10% by mass relative to the aqueous phase, in order to obtain total mineralization of the material and good mechanical strength.

  During the condensation step, when the reaction medium is left to stand after mixing the inorganic precursor solution and the active surfactant solution, the alkoxide (s) undergo a hydrolysis which gives a hydroxylated compound, said hydroxylated compound condensing then to form the inorganic matrix of the material. The duration of the hydrolysis is typically a few minutes. The duration of the condensation depends on the pH of the medium. When the pH of the reaction medium is less than 1, or even negative, or else when the pH of the medium is very strongly basic (close to 14), the duration of the condensation is of the order of 2 to 3 hours. When the pH tends towards 1.2, (which represents the isoelectric point of silica), the condensation is slower and typically requires at least a fortnight. In the latter case, the final material obtained is a very hard inorganic polymer. The hydrolysis / condensation step of precursors of the alkoxide type is carried out B0500FR advantageously at a temperature close to room temperature.

  When the aqueous precursor solution also contains at least one precursor other than an alkoxide, the condensation can be carried out in two stages, the condensation of the alkoxide (s) being catalyzed by the pH of the medium, the condensation subsequent non-alkoxide precursor (s) being optionally catalyzed by heating.

  Drying can be carried out in air, or by freeze-drying.

  The monolith obtained after drying has the three degrees of porosity (microporosity, mesoporosity and macroporosity). However, the pores can be closed with organic residues. Organic residues from the oily phase are mainly found in macropores and can be removed by simple washing before drying, for example using a volatile organic solvent such as acetone, THF or their mixtures. The organic residues from the surfactant are mainly found in the mesopores and can be removed by calcination, for example carried out at a temperature between 6000C and 7000C. When the monolith contains a carbonaceous filler, it forms, after drying, a composite material consisting of the inorganic polymer matrix having the three degrees of porosity, within which the carbonaceous filler is distributed. The calcination of this composite material must be carried out in a reducing medium in order to avoid the elimination of the carbonaceous charge in the form of CO or CO 2.

  The proposed material can be used in various applications, in particular as a synthetic bone substitute.

  The present invention is described in more detail by the following examples, to which it is not, however, limited.

  The materials obtained were characterized on different size scales. Macroporosity and mesoporosity were qualitatively characterized B0500FR respectively by a scanning electron microscopy (SEM) technique, and by a transmission electron microscopy (TEM) technique.

  Mesoporosity and microporosity were quantified 5 and segregated by a nitrogen adsorption-desorption technique (B.E.T. method).

Example 1

  3.5 g of tetraethoxysilane (TEOS) were added to 16.5 g of a 35% aqueous solution of tetradecyltrimethyl ammonium bromide (TTAB) which was brought to pH 0.07. The solution was deposited in a mortar to which 30 g of dodecane was additionally added and it was emulsified using an ultraturax sold under the brand Polytron. The concentrated emulsion obtained was deposited in a mold in which the sol-gel reaction (i.e. the solidification of the inorganic polymer) took place. This condensation stage took place over a period of one week. The material obtained, designated A, was washed in an acetone / tetrahydrofuran (THF) mixture (3 times for 24 hours) and air dried. The organic part, which produces the imprint of the mesostructure, was extracted by calcination at 650 C. The mineral material with hierarchical porosity thus obtained is designated by AC.

  FIG. 1a represents a micrograph of the material A, showing the macroporosity, obtained by SEM. The scale bar represents 1.9 µm.

  FIGS. 2a and 2b represent a micrograph of the materials A and AC respectively, showing the mesoporosity, obtained by TEM. The scale bars 30 represent 100 nm and 50 nm respectively.

  FIG. 3a represents X-ray diffractograms at small angles of the material A (curve defined by solid squares), and of the material AC (curve defined by triangles).

  These figures show that the mesopores are separated by a characteristic distance (40 A on average). At the mesoscopic scale, the pores are organized and have a vermicular structure.

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Example 2

  4 g of TEOS was added to 10 g of a 35% aqueous TTAB solution which was brought to pH -0.2. The solution was placed in a mortar to which 530 g of dodecane was further added and emulsified using an ultraturax. The concentrated emulsion obtained was deposited in a mold in which the sol-gel reaction took place. This condensation stage took place over a 24-hour period.

  The material obtained, designated B, was washed in an acetone / THF mixture (3 times for 24 hours) and air dried. The organic part was extracted by calcination at 6500C. The mineral material with hierarchical porosity thus obtained is designated by BC.

  Figure 1b represents a SEM micrograph of material B, showing the macroporosity. The scale bar represents 1.9 µm.

  FIG. 3b represents X-ray diffractograms at small angles of the material B (curve defined by solid squares), and of the material BC (curve defined by triangles).

Example 3

  0.5 g of Ti (OEt) 4 was added, then 5 g of TEOS to 16.5 g of a 35% aqueous solution of TTAB which was brought to pH -0.05. The solution was placed in a mortar to which 30 g of hexadecane was further added and emulsified using an ultraturax. The concentrated emulsion obtained was deposited in a mold in which the sol-gel reaction took place, resulting in a solidification of the inorganic polymer SiO2. This condensation step took place over a 24 hour period. Then, the material obtained was brought to 750C to catalyze the condensation reaction of the TiO2 system. This second condensation stage lasted 2 hours.

  The material designated by C obtained was washed in an acetone / THF mixture (3 times for 24 hours) and air dried. The organic part was extracted by calcination at 6500C. The mineral material with hierarchical porosity thus obtained is designated by CC.

  B0500FR Figure lc represents a SEM micrograph of the material C, showing the macroporosity. The scale bar represents 8 pm.

  FIGS. 2c and 2d represent a MET 5 micrograph of the materials C and CC respectively, showing the mesoporosity. The scale bars each represent 20 nm.

  FIG. 3c represents X-ray diffractograms at small angles of the material C (curve defined by solid squares), and of the material CC (curve defined by 10 triangles).

  The specific surface of the CC material, measured by the B.E.T. method, is 1248 m2 / g.

Example 4

  5 g of TEOS was added to 15 g of a 35% aqueous solution of TTAB which was brought to pH -0.1. The solution was placed in a mortar to which 30 g of dodecane was further added and emulsified using an ultraturax. The concentrated emulsion obtained was deposited in a mold in which the sol-gel reaction took place. This condensation step 20 took place over a period of 48 hours.

  The material obtained, designated by D, was washed in an acetone / THF mixture (3 times for 24 hours) and air dried.

  The organic part was extracted by calcination at 650OC.

  The mineral material with hierarchical porosity thus obtained is designated by DC.

  FIG. 1d represents a SEM micrograph of the material D, showing the macroporosity. The scale bar represents 1.9 µm.

  FIG. 3d represents X-ray diffractograms at small angles of the material D (curve defined by solid squares), and of the material DC (curve defined by triangles).

Example 5

  3 g of TEOS was added to 16.5 g of a 35% aqueous solution of TTAB which was brought to pH +0.05. The solution was placed in a mortar to which 30 g of hexadecane was further added and emulsified using an ultratu-B0500FR rax. The concentrated emulsion obtained was deposited in a mold in which the sol-gel reaction took place. This condensation stage took place for a week. The material obtained, designated by E, was washed in an acetone / THF mixture (3 times for 24 hours) and air dried. The organic part was extracted by calcination at 6500C. The mineral material with hierarchical porosity thus obtained is designated by EC.

  The figure shows a SEM micrograph of the material C, showing the macroporosity. The scale bar represents 8 pm.

  Figures 2e and 2f represent a MET micrograph of materials E and EC respectively, showing the mesoporosity. The scale bars represent 15,100 nm and 20 nm respectively.

  FIG. 3E represents X-ray diffractograms at small angles of the material e (curve defined by solid squares), and of the material EC (curve defined by triangles).

Example 6

  4 g of TEOS were added to 16 g of a 35% aqueous TTAB solution which was brought to pH +0.5. The solution was deposited in a mortar to which 30 g of dodecane was further added and emulsified using an ultra-turax. The concentrated emulsion obtained was deposited in a mold in which the sol-gel reaction took place. This condensation stage took place over a period of fifteen days. The material obtained, designated F, was washed in an acetone / THF mixture (3 times for 24 hours) and air dried. The organic part was extracted by calcination at 650 C. The mineral material with hierarchical porosity thus obtained is designated by FC.

  FIG. 1f represents a SEM micrograph of the material F, showing the macroporosity. The scale bar 35 represents 4 µm.

  FIG. 3f represents X-ray diffractograms at small angles of the material F (curve defined by solid square B0500FR), and of the material FC (curve defined by triangles).

  The specific surface of the FC material, measured by the B.E.T. method, is 837.82 m2 / g.

Example 7

  3.5 g of TEOS was added to 16 g of a 35% aqueous TTAB solution in which 0.3 g of carbon nanofilaments were dispersed beforehand and which was brought to pH +0.04 .

  The solution was placed in a mortar to which 30 g of dodecane was further added and emulsified using an ultraturax. The concentrated emulsion obtained was deposited in a mold in which the sol-gel reaction took place. This condensation stage took place over a period of fifteen days. The material obtained, designated as G, 15 was washed in an acetone / THF mixture (3 times for 24 hours) and air dried. The mineral material thus obtained is a composite material constituted by a matrix of Sio2 in which the carbon nanofilaments are distributed. It is calcined under a reducing atmosphere to obtain a GC material in which the mineral filler is kept.

Example 8

  3.5 g of TEOS was added to 16 g of a 35% aqueous TTAB solution in which 0.03 g of carbon nanofilaments were dispersed beforehand and which was then brought to pH +0 , 04. The solution was placed in a mortar to which 30 g of dodecane was further added and emulsified using an ultraturax. The concentrated emulsion obtained was deposited in a mold in which the sol-gel reaction took place. This condensation stage took place over a period of fifteen days. The material obtained, designated by H, was washed in an acetone / THF mixture (3 times for 24 hours) and air dried. The organic part was extracted by calcination at 17000C. The mineral material with hierarchical porosity thus obtained, designated by HC 35 is, as in the previous example, a composite material constituted by a matrix of Sio2 in which the carbon nanofilaments are distributed. The increase in the carbon nanofilament content B0500FR makes it possible to optimize the conduction properties of the material.

Example 9

  3.5 g of TEOS were added to 16 g of a 35% aqueous solution of TTAB in which 0.3 g of sodium metavanadate was previously dispersed and which was then brought to pH +0, 04. The solution was placed in a mortar to which 30 g of dodecane was further added and emulsified using an ultraturax. The concentrated emulsion 10 obtained was deposited in a mold in which the sol-gel reaction took place. This condensation stage took place over a period of fifteen days. The material obtained, designated by I, was washed in an acetone / THF mixture (3 times for 24 hours) and air dried. The organic part was extracted by calcination at 650 C. The mineral material with newly hierarchical porosity is designated by IC.

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Claims (29)

claims   1. Material in the form of a monolith consisting of an inorganic matrix, characterized in that said inorganic matrix consists of a polymer of a metal oxide and in that it comprises macropores having an average dimension dA of 1 μm at 20 μm, mesopores having an average dimension dE of 20 to 30 A and micropores having an average dimension d, of 5 to 10 A, said pores being interconnected.   2. Material according to claim 1, characterized in that the metal oxide is an oxide of one or more metals, at least one of the metals being of the type capable of forming an alkoxide.   3. Material according to claim 2, characterized in that at least one of the metals is chosen from Si, Ti, Zr, Th, Nb, Ta, V, W and Al.   4. Material according to one of claims 2 or 3, characterized in that the oxide is a mixed oxide further containing B and Sn.   5. Material according to one of claims 1 to 4, characterized in that the inorganic polymer is a polymer of silicon oxide or of a mixed oxide of silicon.   6. Material according to claim 1, characterized in that the inorganic matrix also contains a filler.   7. Material according to claim 6, characterized in that the filler is a carbonaceous filler.   8. Material according to claim 6, characterized in that the filler is a polymer of a monomer which has a hydrophilic character.   9. A method of preparing a material according to claim 1 by a sol-gel process, characterized in that an emulsion is prepared by introducing an oily phase into an aqueous solution of surfactant, an aqueous solution of at least a metal alkoxide precursor of the oxide forming the inorganic matrix to the surfactant solution, before or after the preparation of the emulsion, the reaction mixture is left to stand until the precursor is condensed, then the mixture to obtain a monolith.   10. Method according to claim 9, characterized in that it comprises a washing step before drying, carried out using a volatile organic solvent.   11. Method according to claim 9, characterized in that the solution of precursors contains at least one alkoxide R'n (OR) m-nM in which M represents a metal having the valence m, and 0 <n <m, R represents an alkyl radical having from 1 to 5 carbon atoms, R ′ represents an alkyl radical or an aryl radical which optionally carry one or more functional groups.   12. Method according to claim 11, characterized in that the alkoxide is chosen from Si (OR) 4, Ti (OR) 4, Zr (OR) 4, 15 Th (OR) 4, Nb (OR) 5, Ta (OR) 5 and Al (OR) 3.   13. Method according to claim 9, characterized in that the alkoxide is VO (OR) 3 OR W (OR) 6, R representing an alkyl radical having from 1 to 5 carbon atoms.   14. Method according to claim 9, characterized in that a mixture of precursors comprising at least one alkoxide is used, the other precursor (s) being chosen from oxides, mixed oxides, hydroxides, chlorides and oxychlorides.   15. Method according to claim 9, characterized in that the oily phase consists of one or more compounds chosen from linear or branched alkanes having at least 12 carbon atoms, or by a silicone oil having a viscosity of less than 400 centipoise.   16. Method according to claim 9, characterized in that the surfactant solution is used in the form of a thick phase, and the oily phase is introduced dropwise into the surfactant solution.   17. Method according to claim 10, characterized in that a device which generates intensive stirring is used to make the mixture of the constituents.   18. The method of claim 9, characterized in that the surfactant is a cationic surfactant and the reaction medium is brought to a pH below 3.   B0500FR 19. The method of claim 9, characterized in that the surfactant is an anionic surfactant and the reaction medium is brought to a pH greater than 10.   20. The method of claim 9, characterized in that the surfactant is a nonionic surfactant and the reaction medium is brought to a pH greater than 10 or less than 3.   21. The method of claim 9, characterized in that the reaction medium before the hydrolysis and condensation step is at a pH less than 1 or close to 14, and in that the duration of the condensation is 2 at 3 o'clock.   22. Method according to claim 14, characterized in that the condensation is carried out in two stages, the condensation of the alkoxide (s) being catalyzed by the pH 15 of the medium, the subsequent condensation of the precursor (s) non-alkoxide (s) being catalyzed by heating.   23. The method of claim 9, characterized in that a carbonaceous filler is introduced into the reaction medium by dispersion in the solution of surfactant.   24. The method of claim 9, characterized in that a polymer of a monomer which has a hydrophilic nature is introduced as a filler, by dispersion of nanofilaments or powder of said monomer in the surfactant solution.   25. The method of claim 9, characterized in that respective amounts of aqueous solution and oily phase are used such that the ratio of aqueous phase / oily phase is less than 1/4.   26. The method of claim 9, characterized in that the concentration of surfactant is greater than 10% by mass relative to the total amount of water.   27. The method of claim 9, characterized in that the concentration of precursor of the inorganic matrix is greater than 10% by mass relative to the aqueous phase.   B0500FR 28. The method of claim 9, characterized in that it comprises, after drying, a calcination step carried out at a temperature between 600 and 7000C.   29. Method according to claim 23, characterized in that it comprises, after drying, a calcination step carried out under a reducing atmosphere. B0500FR