Method for preparing a composition comprising functionalised mineral particles and corresponding composition

Abstract

A method for preparing a composition including mineral particles functionalized by at least one organic group and having a specific surface defined according to the BET method greater than 500 m.sup.2/g, involves: —choosing a phyllosilicate composition, including mineral particles having a thickness of less than 100 nm, a largest dimension of less than 10 μm and belonging to the family of lamellar silicates; —choosing at least one functionalizing agent, from the group formed from the oxysilanes and oxygermanes having at least one organic group, —bringing the phyllosilicate composition into contact with a functionalizing solution including the functionalizing agent, so as to obtain a phyllosilicate composition including mineral particles functionalized by the organic group, while choosing the organic group from the group formed from the cationic heteroaryl groups, the quaternary ammonium groups and the salts of same. The phyllosilicate composition obtained by the method is also described.

Claims

1. A method for preparing a composition comprising mineral particles functionalised by at least one organic group and having a specific surface area determined according to the BET method—standard AFNOR X 11—621 and 622—of greater than 500 m.sup.2/g, wherein: choosing a phyllosilicate composition, comprising mineral particles belonging to the family of the lamellar silicates, said mineral particles selected from the group consisting of non-swelling 2:1 phyllosilicate, kaolinites, serpentinites, and chlorites having a thickness of less than 100 nm and a largest dimension of less than 10 μm; choosing at least one compound comprising funtionalising agent from the group consisting of oxysilanes and oxygermanes having at least one organic group, said phyllosilicate composition is brought into contact with a functionalising solution comprising the functionalising agent, so as to obtain a phyllosilicate composition comprising mineral particles functionalised by said organic group, characterised in that the organic group is chosen from the group formed of cationic heteroaryl groups, and their salts, and in that said functionalising agent having the chemical formula: ##STR00008## wherein: A denotes said organic group, T is chosen from the group formed of silicon and germanium, and R1, R2 and R3 are identical or different and are chosen from the group formed of hydrogen and linear alkyl groups containing from 1 to 3 carbon atom(s).

2. The method according to claim 1, characterized in that said chemical organic group is chosen from cationic heteroaryl groups comprising at least one aromatic ring having from 5 to 18 ring members, said aromatic ring containing at least one nitrogen atom.

3. The method according to claim 2, characterised in that said organic group has the chemical formula: ##STR00009## wherein: R7 is chosen from linear or branched alkyl groups containing from 1 to 18 carbon atom(s), n is an integer from 3 to 11, X.sup.− is an anion selected from the group consisting of bromide ion, iodide ion, chloride ion, trifluoromethanesulfonate anion, acetate anion, nitrate anion and nitrite anion.

4. The method according to claim 3, characterised in that, after said phyllosilicate composition has been brought into contact with the functionalising solution, there is carried out an at least partial exchange of the anion X.sup.− by at least one anionic species which is different from X.sup.− and is selected from the group consisting of bromide ion, iodide ion, bis(trifluoromethanesulfonyl)amide anion, trifluoromethanesulfonate anion, hexafluorophosphate anion, tetrafluoroborate anion, acetate anion, nitrate anion and nitrite anion.

5. The method according to claim 3, characterised in that, after said phyllosilicate composition has been brought into contact with the functionalising solution, there is carried out an at least partial exchange of the anion X.sup.−, when X.sup.− is selected from the group consisting of chlorine, bromine and iodine, by adding at least one silver salt.

6. The method according to claim 1, characterised in that said phyllosilicate composition comprises mineral particles having the chemical formula:
(Si.sub.xGe.sub.1-x).sub.4 M.sub.3O.sub.10(OH).sub.2 Si denoting silicon, Ge denoting germanium, x being a real number of the interval [0;1], and M denoting a metal.

7. The method according to claim 1, characterised in that said functionalising agent is chosen from the group formed of oxysilanes and oxygermanes which are soluble in an aqueous medium.

8. The method according to claim 1, characterised in that said functionalising solution is an aqueous solution.

9. The method according to claim 1, characterised in that said mineral particles comprise 2:1 phyllosilicates.

10. The method according to claim 1, characterised in that said mineral particles are prepared by a hydrothermal treatment of a hydrogel precursor containing silicon and/or germanium and a metal, said hydrogel precursor comprising particles of the formula (Si.sub.xGe.sub.1-x).sub.4 M.sub.3 O.sub.11, n′H.sub.2O, wherein: Si denotes silicon, Ge denotes germanium, x is a real number of the interval [0; 1], M denotes a metal atom, n′ relates to a number of molecule(s) of water associated with said hydrogel.

11. The method according to claim 10, characterised in that the hydrogel precursor is prepared by a coprecipitation reaction between: at least one compound comprising silicon and/or germanium, such as sodium metasilicate or sodium metagermanate or also silicon, and at least one metal salt, so as to obtain a hydrated hydrogel precursor containing silicon and/or germanium and a metal comprising 4 silicon and/or germanium atoms for 3 atoms of at least one metal M.

Description

(1) Other objects, advantages and features of the invention will become apparent upon reading the description and the examples which follow and which make reference to the accompanying figures.

(2) FIG. 1 shows an RX diffractogram of a composition according to the invention on which there is shown the relative intensity of the signal (number of counts per second) as a function of the interplanar spacing in angstroms.

(3) FIG. 2 shows a proton NMR spectrum of a composition according to the invention, carried out by means of a BRUKER® Avance 400® spectrometer.

(4) FIG. 3 shows a carbon NMR spectrum of a composition according to the invention, carried out by means of a BRUKER® Avance 400® spectrometer.

(5) FIG. 4 shows a silicon NMR spectrum of a composition according to the invention, carried out by means of a BRUKER® Avance 400® spectrometer.

(6) FIG. 5 shows an image obtained by field effect scanning electron microscopy of a composition according to the invention.

(7) A phyllosilicate composition used in a method according to the invention can be prepared, for example, according to the following synthesis protocol.

(8) A/—General Protocol for Synthesis of a Composition Used in a Method According to the Invention

(9) 1/—Preparation of a Hydrogel Precursor Containing Silicon and/or Germanium and a Metal

(10) According to a first variant, the hydrogel containing silicon and/or germanium and a metal is prepared by a coprecipitation according to the following reaction equation:

(11) $4\left(\begin{array}{c}{\left(-{\mathrm{Na}}_2{\mathrm{OSiO}}_2\right)}_x\\ {\left({\mathrm{Na}}_2{\mathrm{OGeO}}_2\right)}_{1-x}\end{array}\right)+2\mathrm{HCl}+{mH}_{2}O+3\left(\begin{array}{c}\begin{array}{c}{y}_{\left(1\right)}\left({\mathrm{MgCl}}_2\right)+y_{\left(2\right)}\left({\mathrm{CoCl}}_2\right)+\\ y_{\left(3\right)}\left({\mathrm{ZnCl}}_2\right)\end{array}\\ \begin{array}{c}+y_{\left(4\right)}\left({\mathrm{CuCl}}_2\right)+y_{\left(5\right)}\left({\mathrm{MnCl}}_2\right)+\\ y_{\left(16\right)}\left({\mathrm{FeCl}}_2\right)\end{array}\\ +y_{\left(7\right)}\left({\mathrm{NiCl}}_2\right)+y_{\left(8\right)}\left({\mathrm{CrCl}}_2\right)\end{array}\right).Math.\left[{\left({\mathrm{Si}}_x{\mathrm{Ge}}_{1-x}\right)}_4{M}_3{O}_{11},n^{\prime }{H}_{2}O\right]+8\mathrm{NaCl}+\left(m-n^{\prime }+1\right)H_{2}O$

(12) This coprecipitation reaction allows a hydrated hydrogel containing silicon and/or germanium and a metal having the stoichiometry of talc (4 silicon (Si) and/or germanium (Ge) atoms for 3 atoms of said divalent metal M) to be obtained.

(13) It is carried out starting from: 1. an aqueous solution of penta-hydrated sodium metasilicate or an aqueous solution of sodium metagermanate, or a mixture of these two solutions in the molar proportions x:(1−x), 2. a metal chloride solution prepared with one or more metal salts (in the form of hygroscopic crystals) diluted in distilled water, and 3. a 1N hydrochloric acid solution.

(14) The hydrogel containing silicon and/or germanium and a metal is prepared according to the following protocol: 1. the hydrochloric acid solution and the metal chloride solution are mixed, 2. this mixture is added to the sodium metasilicate and/or metagermanate solution; the coprecipitation gel forms instantly, 3. the gel is recovered after centrifugation (at 7000 revolutions/minute for 15 minutes) and removal of the supernatant (sodium chloride solution that has formed), 4. the gel is washed with distilled or osmosed water or with tap water (a minimum of two cycles of washing/centrifugation are necessary).

(15) According to a second variant, the hydrogel containing silicon and/or germanium and a metal can be prepared by a coprecipitation reaction involving, as reagent, at least one compound comprising silicon, at least one dicarboxylate salt of the formula M(R9-COO).sub.2 (R9 being chosen from H and alkyl groups containing fewer than 5 carbon atoms) in the presence of at least one carboxylate salt of the formula R8-COOM′, wherein M′ denotes a metal chosen from the group formed of Na and K, and R8 is chosen from the group formed of H and alkyl groups containing fewer than 5 carbon atoms.

(16) This coprecipitation reaction allows a hydrated hydrogel containing silicon and/or germanium and a metal having the stoichiometry of talc (4 Si/Ge for 3 M, M having the formula Mg.sub.y(1)Co.sub.y(2)Zn.sub.y(3)Cu.sub.y(4)Mn.sub.y(5)Fe.sub.y(6)Ni.sub.y(7)Cr.sub.y(8); each y(i) representing a real number of the interval [0;1], and such that

(17) $\underset{i=1}{\overset{8}{.Math.}}y\left(i\right)=1)$
to be obtained.

(18) The hydrogel containing silicon and/or germanium and a metal is prepared by a coprecipitation reaction carried out starting from: 1. an aqueous solution of penta-hydrated sodium metasilicate or an aqueous solution of sodium metagermanate, or a mixture of these two solutions in the molar proportions x:(1−x), 2. a solution of dicarboxylate salt(s) prepared with one or more dicarboxylate salt(s) of the formula M(R9-COO).sub.2 diluted in a carboxylic acid, such as acetic acid, and 3. a solution of carboxylate salt(s) prepared with one or more carboxylate salt(s) of the formula R8-COOM′ diluted in distilled water.

(19) The hydrogel containing silicon and/or germanium and a metal is prepared according to the following protocol: 1. the sodium metasilicate solution and the solution of carboxylate salt(s) of formula R8-COOM′ are mixed, 2. the solution of dicarboxylate salt(s) of the formula M(R9-COO).sub.2 is added quickly thereto; the coprecipitation hydrogel forms instantly.

(20) At the end of this first phase, a hydrated hydrogel containing silicon and/or germanium and a metal—(Si.sub.xGe.sub.1-x).sub.4M.sub.3O.sub.11, n′H.sub.2O—of gelatinous consistency is obtained (optionally in the presence of the carboxylate salt(s) of the formula (e) R8-COOM′ and R9-COOM′ in the case of the second variant). The gel has thixotropic behaviour, that is to say it passes from a viscous state to a liquid state when it is stirred and then returns to its original state if it is allowed to rest for a sufficient time. The hydrogel precursor containing silicon and/or germanium and a metal therefore also corresponds to formula (II) 4 (Si.sub.xGe.sub.1-x) 3 M ((10−ε) O) ((2+ε) (OH)), wherein: x is a real number of the interval [0; 1], and ε is a real number of the interval [0; 10[.

(21) The gel containing silicon and/or germanium and a metal can also be recovered after centrifugation (for example from 3000 to 15,000 revolutions per minute for from 5 to 60 minutes) and removal of the supernatant, optionally washing with demineralised water (for example two successive washings and centrifugations) and then drying, for example in an oven (60° C., 2 days), by lyophilisation, by spray drying or also by drying with microwave irradiation. The particles containing silicon and/or germanium and a metal of the formula (Si.sub.xGe.sub.1-x).sub.4M.sub.3O.sub.11, n′H.sub.2O can thus be stored in the form of a powder with a view to a subsequent hydrothermal treatment. The particles obtained containing silicon and/or germanium and a metal are, if necessary, ground by means of a mortar (for example an agate mortar) in order to obtain a homogeneous powder.

(22) 2/—Hydrothermal Treatment of the Gel Containing Silicon and/or Germanium and a Metal

(23) The gel containing silicon and/or germanium and a metal as obtained hereinbefore is subjected to a hydrothermal treatment at a temperature of from 150° C. to 600° C., and especially at a temperature of from 150° C. to 400° C.

(24) In order to carry out the hydrothermal treatment: 1. the gel is placed in a reactor (of 400 ml); the water/solid ratio is optionally adjusted by adding water, especially in order to avoid calcination of the solid fraction); in order to avoid any problem of leakage from the reactor, the reactor is filled to ⅔ of its volume, 2. there is optionally added, with stirring, a solution comprising at least one carboxylate salt of the formula R8-COOM′, in hydrated or anhydrous form, X denoting a metal chosen from the group formed of Na and K, and R.sub.2 being chosen from the group formed of H and alkyl groups containing fewer than 5 carbon atoms, 3. the reactor is placed inside an oven or conduction oven at the reaction temperature (established at from 150° C. to 600° C., in particular from 150° C. to 400° C.) throughout the treatment (from 30 minutes to 60 days).

(25) At the end of this hydrothermal treatment, a colloidal talcose composition comprising phyllosilicate mineral particles, in solution in water, is obtained.

(26) The carboxylate salt optionally present during the hydrothermal treatment can be added at the time said hydrothermal treatment is carried out and/or can be obtained from the precipitation medium of the gel containing silicon and/or germanium and a metal according to the second variant for the preparation of the hydrogel containing silicon and/or germanium and a metal. Carrying out the hydrothermal treatment in the presence of a carboxylate salt allows the reaction of converting the hydrogel containing silicon and/or germanium and a metal into a talcose composition comprising phyllosilicate mineral particles to be improved, especially by accelerating it. In the case where the hydrothermal treatment is carried out in the presence of such a carboxylate salt, a temperature inside the oven or autoclave of from 150° C. to 400° C. is sufficient.

(27) At the end of this hydrothermal treatment, the contents of the reactor are recovered after filtration and/or optionally centrifugation (for example at from 3000 to 15,000 revolutions per minute for from 5 to 60 minutes) and removal of the supernatant. The recovered talcose composition is optionally dried, for example in an oven (60° C., 2 days), by lyophilisation, by spray drying or also by drying with microwave irradiation.

(28) At the end of such a hydrothermal treatment there is obtained a divided solid composition comprising, for example, particles of synthetic talc of the formula Si.sub.4Mg.sub.3O.sub.10(OH).sub.2.

(29) B/—Method for Preparing a Composition Comprising Functionalised Mineral Particles According to the Invention

(30) The mineral particles as prepared hereinbefore, for example particles of synthetic talc Si.sub.4Mg.sub.3O.sub.10(OH).sub.2, are brought into contact with a solution comprising at least one oxysilane and/or at least one oxygermane having at least one organic group chosen from the group formed of cationic heteroaryl groups, quaternary ammonium groups and their salts.

(31) The functionalising agent (oxysilane and/or oxygermane) has the chemical formula:

(32) ##STR00004##
wherein: A denotes said organic group rom the group formed of cationic heteroaryl groups, quaternary ammonium groups and their salts, T is chosen from silicon and germanium, and R1, R2 and R3 are identical or different and are chosen from the group formed of hydrogen and linear alkyl groups containing from 1 to 3 carbon atom(s).

(33) The functionalising agent can optionally polymerise in the functionalising solution and be in a small proportion in the following form:

(34) ##STR00005##
or also in the form of other products of that polymerisation.

(35) To that end:

(36) 1. 1 gram of phyllosilicate mineral particles previously dried in an oven is placed in 40 ml of an aqueous solution in which there is dissolved at least one functionalised oxysilane and/or at least one functionalised oxygermane as defined hereinabove, for 1 hour, with stirring, the concentration of that compound in the solution being, for example, 0.015 mol/l,

(37) 2. the particles are recovered by centrifuging the solution, for example for 10 minutes at 10,000 revolutions/minute, and removing the supernatant solution,

(38) 3. the particles are rinsed one to two times with distilled water, by centrifugation, for example for 10 minutes at 10,000 revolutions/minute, and removal of the supernatant solution each time, so as to remove excess oxysilanes and/or oxygermanes, and

(39) 4. the particles obtained are dried, for example by lyophilisation.

(40) In particular, said oxysilane can be a trialkoxysilane which is soluble in an aqueous medium and has the following formula:

(41) ##STR00006##
wherein: R1, R2 and R3 are identical or different and are chosen from linear alkyl groups containing from 1 to 3 carbon atom(s), R7 is chosen from linear alkyl groups containing from 1 to 18 carbon atom(s), n is an integer from 1 to 5, and X.sup.− is an anion, wherein X is chosen from the group formed of chlorine, iodine and bromine.

(42) It is then possible to carry out an at least partial exchange of the anion X.sup.− by at least one anionic species which is different from X.sup.− and is chosen from the group formed of the bromide ion Br.sup.−, the iodide ion I.sup.−, the bis-trifluoromethanesulfonamide anion, the trifluoromethanesulfonate anion, the hexafluorophosphate anion, the tetrafluoroborate anion, the acetate anion, the nitrate anion NO.sub.3.sup.− and the nitrite anion NO.sub.2.sup.−. Such an exchange by metathesis allows the more or less hydrophilic or hydrophobic nature of the functionalised mineral particles that are prepared to be modulated in a customised manner. It is possible to use, for example, a metal salt such as a silver salt (especially a silver nitrate AgNO.sub.3) or a lithium salt (such as lithium bis-trifluoromethanesulfonamide, for example).

(43) C/—Analysis and Structural Characterisation

(44) The size and particle size distribution of the phyllosilicate mineral particles composing them were evaluated by observation by field effect scanning electron microscopy.

(45) It is found that the particle size of the elementary particles varies from 20 nm to 100 nm. In particular, the phyllosilicate mineral particles have a thickness of less than 100 nm and a largest dimension of less than 10 μm.

(46) Moreover, measurements of the specific surface area (surface area of the particles relative to a unit of mass) of the mineral particles that were prepared, determined according to the BET method by the quantity of nitrogen adsorbed at the surface of said particles so as to form a monomolecular layer covering said surface completely (measurement according to the BET method, standard AFNOR X 11—621 and 622) were carried out. It is found that the specific surface area of the phyllosilicate mineral particles contained in a composition obtained by a method according to the invention is approximately 700 m.sup.2/g.

(47) Such a specific surface area value, while the specific surface area of a natural talc is approximately 20 m.sup.2/g, is indicative not only of a very small particle size and of the lamellar nature of the particles, but also of the divided or deagglomerated state of the particles, and especially of an exfoliation of the elementary lamellae forming said particles.

EXAMPLE 1

(48) A suspension comprising particles of talc of the formula Si.sub.4Mg.sub.3O.sub.10(OH).sub.2 comprising 100 g of talc gel (that is to say 10 g of dry talc) in 300 ml of water is prepared. The suspension is stirred magnetically and at the same time subjected to ultrasound until a suspension having a homogeneous consistency and a milky appearance is obtained.

(49) The functionalised oxysilane is then added to the suspension comprising talc particles. 1 g of 1-(trimethoxy-silyl-propyl)-3-methyl-imidazolium chloride previously diluted in 20 ml of water is added. The oxysilane and the talc particles are thus brought into contact in the functionalising solution so that the molar ratio between the oxysilane and the talc particles is 0.13. Magnetic stirring and sonication are maintained for 10 minutes.

(50) 1-(Trimethoxy-silyl-propyl)-3-methyl-imidazolium chloride has the following structural chemical formula:

(51) ##STR00007##

(52) The suspension is then centrifuged at 10,000 revolutions/minute for 10 minutes, and the supernatant solution composed of water and excess functionalised oxysilane.

(53) The functionalised talcose composition that is recovered is then subjected to washing with demineralised water and centrifugation.

(54) Finally, the talcose composition recovered after centrifugation is dried by lyophilisation (trap at −52° C. and vacuum of 0.087 mbar).

(55) The talcose composition obtained comprises 0.03 mmole of oxysilane per gram of talc (measurement carried out by elemental analysis).

(56) The specific surface area of the talcose composition obtained, measured according to the BET method, is 764 m.sup.2/g.

(57) The X-ray diffractogram of the talc composition so obtained is shown in FIG. 1. The X-ray diffractogram of this talcose composition has diffraction peaks corresponding to the diffraction peaks of the functionalised talc, and in particular the following characteristic diffraction peaks: a plane (001) situated at a distance of 11.074 Å (I=100); a plane (020) situated at a distance of 4.554 Å (I=33); a plane (003) situated at a distance of 3.173 Å (I=67); a plane (060) situated at a distance of 1.512 Å (I=16).

(58) The proton NMR spectrum (FIG. 2) of the mineral particles prepared makes it possible to identify the presence of the Hs of the Mg(OH) groups of the talc lamellae (chemical shifts between 0 and 1 ppm), the Hs of the imidazolium ring (chemical shifts between 6 ppm and 9 ppm) and of water (chemical shifts between 3 and 5 ppm).

(59) The carbon NMR spectrum (FIG. 3) of the mineral particles prepared makes it possible to identify the presence of an imidazolium group (chemical shifts between 115 ppm and 140 ppm) as well as the presence of a methyl group and of methylene groups (chemical shifts between 0 ppm and 60 ppm, including the methylene of the CH.sub.2—Si bond between 9 ppm and 10 ppm).

(60) The silicon NMR spectrum (FIG. 4) of the mineral particles prepared makes it possible to identify the presence of Si—O—Si groups (chemical shifts between −80 ppm and −100 ppm).

(61) The proton, carbon and silicon NMR spectra were obtained with a magnetic field of 9.4 tesla.

(62) FIG. 5 is an image obtained by field effect scanning electron microscopy (SEM-FEG) of the mineral particles prepared.

(63) These analyses therefore show that the functionalisation of the talc is successfully carried out by the fixing of an oxysilane carrying an imidazolium group by covalent bonding with the talc. They are in particular bonds of the Si—O—Si type between a silicon atom of the talc and the silicon of the oxysilane. Furthermore, the functionalised talcose composition prepared by a method according to the invention comprises individualised and deagglomerated talc particles which have a very large specific surface area.

(64) The invention can be the subject of many other applications and of different variants with respect to the embodiments and examples described above. In particular, other oxysilanes and oxygermanes can likewise be used as the functionalising agent for the phyllosilicate mineral particles.