Process for preparing cellular inorganic monolithic materials and uses of these materials

Abstract

A process is provided for preparing an inorganic material in the form of an alveolar monolith of a silica matrix where the monolith includes interconnected macropores. The process includes at least one step of mineralizing an oil-in-water emulsion formed from droplets of an oily phase dispersed in a continuous aqueous phase and in which colloidal solid particles are present at the interface formed between the continuous aqueous phase and the dispersed droplets of oily phase. Such materials obtained according to this process may be used, especially for separative chemistry and filtration, for performing chemical reactions catalyzed in heterogeneous phase, as thermal or phonic insulators, or as templates for manufacturing controlled-porosity carbon skeletons.

Claims

1. Process for preparing an inorganic material in the form of an alveolar monolith of a silica matrix having interconnected and monodispersed macropores, said process being capable of producing monodispersed macropores with a mean dimension d.sub.A ranging from 1 m to 400 m and micropores with a mean dimension d.sub.I of from 0.7 to 2 nm, said process comprising: at least one step of mineralization of an oil-in-water emulsion formed from droplets of an oily phase dispersed in a continuous aqueous phase and in which colloidal solid particles are present at an interface formed between the continuous aqueous phase and the dispersed droplets of said oily phase, wherein a volume fraction of the oily phase is greater than 50%, wherein the said mineralization step is performed without stirring and at a pH less than or equal to 3, in the presence of at least one hydrolized silicon oxide precursor in an amount greater than or equal to 3% by mass relative to the mass of the continuous aqueous phase, and wherein said colloidal solid particles are silicon oxide nanoparticles, said colloidal solid particles being functionalized at their surface to make them hydrophobic, wherein said colloidal solid particles are adsorbed at said interface and said colloidal solid particles stabilize said oil-in-water emulsion, wherein a mass of the colloidal solid particles in the oil-in-water emulsion ranges from 0.05 mg of particles/mL of the oily phase to 16 g of particles/mL of the oily phase, and wherein when a surfactant is present in addition to said colloidal solid particles, the amount of said surfactant being of a mass ratio of a mass of said surfactant/mass of said colloidal solid particles ranges from 1 mg of said surfactant per gram of said colloidal solid particles to 0.8 g of said surfactant per gram of said colloidal solid particles.

2. Process according to claim 1, wherein the oily phase of the oil-in-water emulsion includes one or more compounds chosen from either one of linear or branched alkanes, containing from 7 to 22 carbon atoms.

3. Process according to claim 2, wherein said either one of linear or branched alkanes are chosen from either one of dodecane and hexadecane.

4. Process according to claim 1, wherein the volume fraction of the oily phase of the oil-in-water emulsion ranges from 60% to 90%.

5. Process according to claim 1, wherein in said oil-in water emulsion, the amount of the colloidal solid particles ranges from 0.05 mg of particles/mL of the oily phase to 8 mg of particles/mL of the oily phase.

6. Process according to claim 1, wherein the colloidal solid particles are functionalized with compounds attached to their surface via covalent bonds, the said compounds comprising hydrophobic groups.

7. Process according to claim 1, wherein said at least one silicon oxide precursors are selected from the group consisting of tetramethoxy-ortho-silane, tetraethoxy-ortho-silane, dimethyldiethoxysilane and mixtures of dimethyldiethoxysilane with tetraethoxy-ortho-silane and tetramethoxy-ortho-silane.

8. Process according to claim 1, wherein a concentration of said at least one hydrolized silicon precursor in said continuous aqueous phase of said oil-in water emulsion ranges from 25% to 35% by mass relative to a mass of the continuous aqueous phase.

9. Process according to claim 1, wherein the continuous aqueous phase of said oil-in water emulsion also comprises one or more precursors of a metal oxide of formula MeO.sub.2 in which Me is a metal is selected from the group consisting of Zr, Ti, Th, Nb, Ta, V, W, and Al in an amount ranging from 1% to 30% by mass relative to a mass of said at least one hydrolized silicon precursors.

10. Process according to claim 9, wherein said one or more metal oxide precursors are chosen from alkoxides, chlorides, and nitrates of metals selected from the group consisting of Zr, Ti, Th, Nb, Ta, V, W, and Al.

11. Process according to claim 1, wherein the mineralization step is performed at a pH of less than or equal to 1.

12. Process according to claim 1, wherein said process also comprises a step of impregnating said alveolar monolith using a solution containing a functionalizing agent.

13. A process according to claim 1, said process further comprising a step of employing an inorganic material obtained according to claim 1 for separative chemistry and filtration, for performing chemical reactions catalysed in heterogeneous phase, as material for thermal or phonic insulation, or as templates for manufacturing controlled-porosity carbon skeletons.

14. Process according to claim 13, further comprising the step of employing said inorganic material as high-frequency-selective acoustic insulator.

15. Process according to claim 13, further comprising a step of employing said inorganic material for the preparation of chromatography columns with a macropore size gradient, wherein a chromatography column includes several macroporous alveolar monoliths stacked on each other, said macroporous alveolar monoliths comprising different macropore sizes resulting from the mineralization of oil-in-water emulsions comprising droplets of different sizes and mineralized to create a chromatography column with a macropore size gradient.

16. Process according to claim 1, wherein the dispersed droplets of oily phase in the oil-in-water emulsion have a mean diameter ranging between 1 m and 1 mm.

17. Process for preparing an inorganic material in the form of an alveolar monolith of a silica matrix having interconnected and monodispersed macropores, said process being capable of producing monodispersed macropores with a mean dimension d.sub.A ranging from 1 m to 400 m and micropores with a mean dimension d.sub.I of from 0.7 to 2 nm, said process comprising: at least one step of mineralization of an oil-in-water emulsion formed from droplets of an oily phase dispersed in a continuous aqueous phase and in which colloidal solid particles are present at an interface formed between the continuous aqueous phase and the dispersed droplets of said oily phase, wherein a volume fraction of the oily phase is greater than 50%, and wherein the said mineralization step is performed at a pH less than or equal to 3, in the presence of at least one silicon oxide precursor in an amount greater than or equal to 3% by mass relative to the mass of the continuous aqueous phase, and wherein said colloidal solid particles are silicon oxide nanoparticles, said colloidal solid particles being functionalized at their surface to make them hydrophobic, wherein said colloidal solid particles are adsorbed at said interface and said colloidal solid particles stabilize said oil-in-water emulsion, wherein a mass of the colloidal solid particles in the oil-in-water emulsion ranges from 0.05 mg of particles/mL of the oily phase to 16 g of particles/mL of the oily phase, and wherein the oil-in-water emulsion is prepared in a single step by mixing: i) said continuous aqueous phase containing at least one silicon oxide precursor in an amount of greater than or equal to 3% by mass relative to the mass of the aqueous phase, at least one acid in a sufficient amount to bring the continuous aqueous phase to a pH of less than or equal to 3, and the colloidal solid particles in an amount of greater than or equal to 3% by mass relative to the mass of the aqueous phase, and mechanically stirring it with ii) said oily phase in an amount such that the volume fraction of the oily phase in the resulting oil-in-water emulsion is greater than 50%; the said oil-in-water emulsion then being left to stand until the said inorganic material is obtained in the form of a silica monolith with monodispersed macroporosity.

18. Process for preparing an inorganic material in the form of an alveolar monolith of a silica matrix having interconnected and monodispersed macropores, said process being capable of producing monodispersed macropores with a mean dimension d.sub.A ranging from 1 m to 400 m and micropores with a mean dimension d.sub.I of from 0.7 to 2 nm, said process comprising: at least one step of mineralization of an oil-in-water emulsion formed from droplets of an oily phase dispersed in a continuous aqueous phase and in which colloidal solid particles are present at an interface formed between the continuous aqueous phase and the dispersed droplets of said oily phase, wherein a volume fraction of the oily phase is greater than 50%, and wherein the said mineralization step is performed without stirring and at a pH less than or equal to 3, in the presence of at least one silicon oxide precursor in an amount greater than or equal to 3% by mass relative to the mass of the continuous aqueous phase, and wherein said colloidal solid particles are silicon oxide nanoparticles, said colloidal solid particles being functionalized at their surface to make them hydrophobic, wherein said colloidal solid particles are adsorbed at said interface and said colloidal solid particles stabilize said oil-in-water emulsion, wherein a mass of the colloidal solid particles in the oil-in-water emulsion ranges from 0.05 mg of particles/mL of the oily phase to 16 g of particles/mL of the oily phase, and wherein said process does not include a surfactant so as to stabilize the oil-in-water emulsion.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIGS. 1(a) and 1(b) are photographs of monolith M.sub.75 in side view (FIG. 1a) and in top view (FIG. 1b) from example 1, in accordance with one embodiment;

(2) FIG. 2 is an SEM photograph of monolith M.sub.64 before calcination from example 1, in accordance with one embodiment;

(3) FIG. 3 is an SEM photograph of monolith M.sub.75 before calcination from example 1, in accordance with one embodiment;

(4) FIG. 4 is an SEM photograph of monolith M.sub.80 before calcinations from example 1, in accordance with one embodiment;

(5) FIG. 5 is an SEM photograph of monolith M.sub.64 before calcinations from example 1, in accordance with one embodiment;

(6) FIG. 6 is an SEM photograph of monolith M.sub.64 after calcinations from example 1, in accordance with one embodiment;

(7) FIG. 7 is an SEM photograph of monolith M.sub.75 after calcinations from example 1, in accordance with one embodiment;

(8) FIG. 8 is an SEM photograph of monolith M.sub.80 after calcinations from example 1, in accordance with one embodiment;

(9) FIG. 9 is an SEM photograph of monolith M.sub.85 after calcinations from example 1, in accordance with one embodiment;

(10) FIGS. 10 and 11 are, respectively, SEM photographs of monoliths M.sub.0.025 and M.sub.0.075 after calcinations from example 2, in accordance with one embodiment; and

(11) FIG. 12 is a chart showing the change in pore diameter (in m) as a function of the mass of particles (in g) from example 2, in accordance with one embodiment.

DETAILED DESCRIPTION

(12) The present invention is illustrated by the following implementation examples, to which it is not, however, limited.

EXAMPLES

(13) The starting materials used in the examples that follow are listed below: 98% tetradecyltrimethylammonium bromide (TTAB): from Alfa Aesar; 98% tetraethoxy-ortho-si lane (TEOS): from Aldrich; 99% hexadecane (mass per unit volume: 0.773 g/cm.sup.2): from Sigma-Aldrich; commercial acetone; tetrahydrofuran; 37% hydrochloric acid of ISO quality for analyses: from Carlo Erba Reagent; silica nanoparticles functionalized with hexadecylsilane groups, sold under the trade name AEROSIL R816 by the company Evonik Degussa (diameter: 12 nm, specific surface area: 19020 m.sup.2/g); demineralised water.

(14) These starting materials were used as received from the manufacturers, without additional purification.

(15) In the examples that follow, each of the emulsions prepared had a total volume of 20 mL.

(16) In the text hereinbelow, m.sub.p indicates the amount in grams of silica nanoparticles used per 20 mL of emulsion and is the volume fraction of oil (hexadecane) in the emulsion.

(17) The macroporosity was characterized qualitatively by an SEM technique using a TM-1000 microscope from the company Hitachi. The samples were coated with gold or carbon by plasma deposition before being characterized.

Example 1

Preparation of Macroporous Silica Monoliths from Emulsions of Varied

(18) In this example, various silica monoliths were prepared from water-in-oil emulsions having different volume fractions of oil.

(19) The general protocol below was used:

(20) i) The aqueous phase was prepared by mixing the water in an amount suited to the desired volume fraction of oil (), the nanoparticles in an amount m.sub.p, 0.29 g of HCl and 2.24 g of TEOS. This mixture was left to stand to the point of hydrolysis of the TEOS. The suspension was optionally sonicated using an ultrasonic bath in order better to disperse the particles. Hexadecane was added in an amount corresponding to . The whole was stirred using a homogenizer of ULTRA-TURRAX type (sold by the company Janke-Kunkel IKA Labortechnik) at a speed of 24 000 rpm for about 30 seconds.

(21) ii) The solidification of the emulsions took place at rest for 10 days to allow polycondensation of the silica precursor (TEOS) in the continuous phase of the emulsion in the form of a silica monolith.

(22) iii) The silica monoliths thus obtained were washed 3 times, at 24 hours per time, in baths consisting of an acetone/THF mixture (30/70 v/v) in order to remove the residual oil present in the macropores of the monolith, and dried in a desiccator at room temperature for 7 days.

(23) iv) The monoliths were then calcined in a tubular oven (of the brand Nabertherm, manufacturer code LT311P330) in air and according to the following temperature programme: temperature rise up to 200 C. at a rate of 2 C./min, steady stage at 200 C. for 2 hours, rise to 650 C. at a rate of 2 C./min, steady stage at 650 C. for 6 hours, stoppage of the oven and return to room temperature via the oven inertia. This calcination step makes it possible to remove the remaining traces of organic matter (oil, solvents, etc.) but also to densify the material by sintering the silica.

(24) Table I below gives the characteristics of the monoliths manufactured according to this protocol:

(25) TABLE-US-00001 TABLE I Size of the Monolith m.sub.p (in g) (in %) macropores (in m) M.sub.64 0.050 64 144 M.sub.70 0.055 70 208 M.sub.75 0.059 75 136 M.sub.80 0.062 80 154 M.sub.85 0.066 85 178 M.sub.87 0.068 87 143

(26) The monoliths M.sub.64; M.sub.75; M.sub.80 and M.sub.85 were examined by scanning electron microscopy (SEM) using a microscope sold under the reference TM-1000 by the company Hitachi, before and after the calcination step.

(27) The attached FIG. 2 is the SEMI photograph of monolith M.sub.64 before calcination.

(28) The attached FIG. 3 is the SEM photograph of monolith M.sub.75 before calcination.

(29) The attached FIG. 4 is the SEM photograph of monolith M.sub.80 before calcination.

(30) The attached FIG. 5 is the SEM photograph of monolith M.sub.85 before calcination.

(31) The attached FIG. 6 is the SEM photograph of monolith M.sub.64 after calcination.

(32) The attached FIG. 7 is the SEM photograph of monolith M.sub.75 after calcination.

(33) The attached FIG. 8 is the SEM photograph of monolith M.sub.80 after calcination.

(34) The attached FIG. 9 is the SEM photograph of monolith M.sub.85 after calcination.

(35) These results show that the macropore volume increases with the volume fraction of the oily phase.

Example 2

Preparation of Macroporous Silica Monoliths with Varied Pore Sizes Starting with Emulsions Containing Colloidal Particles Functionalized with a Surfactant

(36) In this example, a cationic surfactant, TTAB, was used to functionalize the AEROSIL R816 particles used above in Example 1. The amount of particles was varied to vary the size of the pores while keeping the ratio m.sub.SA/m.sub.p constant and equal to 0.0107. In this example, was kept constant and equal to 64%, i.e. the oily phase is composed of a fixed amount of 12.8 ml of hexadecane.

(37) The composition of the aqueous phase was as follows: 2.85 g of HCl, 2.24 g of TEOS, m.sub.p grams of particles, m.sub.SA=0.0107m.sub.p grams of TTAB and a sufficient amount of water for 7.2 ml.

(38) Besides these differences, the protocol for preparing the monoliths is identical to that used and described above in Example 1.

(39) Table II below gives the characteristics of each of the monoliths thus prepared:

(40) TABLE-US-00002 TABLE II Size of the Monolith m.sub.p (in g) macropores (in m) M.sub.0.025 0.025 167 M.sub.0.050 0.050 87 M.sub.0.075 0.075 56 M.sub.0.10 0.10 43 M.sub.0.15 0.15 24 M.sub.0.20 0.20 17

(41) After calcination, the monoliths M.sub.0.025 and M.sub.0.075 were examined by scanning electron microscopy (SEM) using a microscope sold under the reference TM-1000 by the company Hitachi.

(42) The attached FIGS. 10 and 11 are, respectively, the SEM photographs of monoliths M.sub.0.025 and M.sub.0.075 after calcination.

(43) Finally, the attached FIG. 12 shows the change in pore diameter (in m) as a function of the mass of particles (in g).

(44) Using surfactant to functionalize the particles allows better adsorption of these particles to the oil/water interface and good control of the size, as may be seen in FIG. 12.