Composite based on a lamellar material and a porous material comprising an active substance and/or a microorganism

Abstract

The present invention concerns a process for preparing a composite of porous material/compound/hybrid organic-inorganic material having a 2:1 lamellar structure, said hybrid material having the following general formula I:
Na.sub.x[(Mg.sub.3)(Al.sub.x(RSi).sub.4−x)O.sub.8+x(OH).sub.2]  (I)
wherein
x is a number such that 0≤x<1.2 and
R represents a C.sub.1-C.sub.30 alkyl group, an aryl group, a (C.sub.1-C.sub.30 alkyl)aryl group or an O—(C.sub.1-C.sub.30 alkyl) group, it being possible for the alkyl group to be substituted with a group chosen from a phenyl, vinyl, aminopropyl or mercaptopropyl group,
and said compound being chosen from the group constituted of at least one active substance and at least one microorganism and mixtures thereof the process comprising:
a) the step of sol-gel synthesis of the hybrid organic-inorganic material having a 2:1 lamellar structure in the presence of the compound and of the porous material saturated with the compound;
b) the recovery of the composite. It also concerns a composite obtainable by means of this process, a composition comprising it and its use in particular for the fertilization of plants.

Claims

1. A process for preparing a composite of porous material/compound/hybrid organic-inorganic material having a 2:1 lamellar structure, said hybrid material having the following general formula I:
Na.sub.x[(Mg.sub.3)(Al.sub.x(RSi).sub.4−x)O.sub.8+x(OH).sub.2]  (I) wherein x is a number such that 0≤x<1.2 and R represents a C.sub.1-C.sub.30 alkyl group, an aryl group, a (C.sub.1-C.sub.30 alkyl)aryl group or an O—(C.sub.1-C.sub.30 alkyl) group, the alkyl group being optionally substituted with at least one substituent selected from phenyl, vinyl or mercaptopropyl, and said compound being selected from the group consisting of at least one active substance and at least one microorganism and mixtures thereof, the process comprising: a) the step of sol-gel synthesis of the hybrid organic-inorganic material having a 2:1 lamellar structure in the presence of the compound and of the porous material saturated with the compound; and b) the recovery of the composite, wherein the silicon source required for the synthesis of the hybrid material of formula I of step a) is an organoalkoxysilane or a mixture of organoalkoxysilanes having the following general formula II: RSi(OR′).sub.3 (II); wherein R′ is a methoxy or ethoxy group.

2. The process as claimed in claim 1, wherein step a) comprises the following steps: a1) addition of a magnesium source, of the compound, of the porous material saturated with the compound, of the silicon source, in the case where x≠0, of the aluminum source, and of a solvent; a2) adjustment of the pH to between 8 and 14; a3) stirring of the mixture so as to obtain a gel; a4) recovery of the solid phase of the gel obtained in step a3); a5) drying of the solid phase of the gel obtained in step a4).

3. The process as claimed in claim 2, wherein the compound comprises a microorganism and the microorganism in step a1) is in the form of a preculture of said microorganism, and the process comprises a prior step, before step a), of preparation of the microorganism preculture.

4. The process as claimed in claim 1, wherein x=0.

5. The process as claimed in claim 1, wherein the compound is an amino acid active substance.

6. The process as claimed in claim 1, wherein the compound is a microorganism selected from the group consisting of a bacterium, a microalga, a fungus and mixtures thereof.

7. The process as claimed in claim 1, wherein the porous material is activated or non-activated carbon.

8. The process as claimed in claim 1, wherein the silicon source is selected from the group consisting of phenyltrimethoxysilane of the following formula (a): Phenyl-Si(OCH.sub.3).sub.3 (a), tetraethyl orthosilicate of the following formula (b): Si(OC.sub.2H.sub.5).sub.4 (b), hexadecyltrimethoxysilane of the following formula (c): CH.sub.3(CH.sub.2).sub.14CH.sub.2—Si(OCH.sub.3).sub.3 (c), methyltriethoxysilane (MTES) of the following formula (d): CH.sub.3—Si(OCH.sub.3).sub.3 (d) and mixtures thereof.

9. The process as claimed in claim 1, which comprises a prior step, before step a), of preparation of the porous material saturated with the compound.

10. The process as claimed in claim 1, wherein the compound is tryptophan.

11. The process as claimed in claim 1, wherein the porous material is activated carbon.

12. The process as claimed in claim 1, wherein the silicon source is hexadecyltrimethoxysilane of the following formula (c): CH.sub.3(CH.sub.2).sub.14CH.sub.2—Si(OCH.sub.3).sub.3 (c).

13. The process as claimed in claim 1, wherein the source of silicon is selected from the group consisting of phenyltrimethoxysilane (a) and hexadecyltrimethoxysilane (c).

14. A composite of porous material/compound/hybrid organic-inorganic material having a 2:1 lamellar structure of formula (I), obtained by means of the process as claimed in claim 1.

15. A composition comprising the composite as claimed in claim 14 and an excipient.

16. The composition as claimed in claim 15, which is in solid form, in liquid form or in gel form.

17. The composition as claimed in claim 16, wherein the solid form is in powder, granule or microgranule form.

18. The composition as claimed in claim 15 which allows the controlled release of the compound in the soil.

19. The composition as claimed in claim 15, which also comprises nutrients, organic raw materials and/or mineral raw materials.

20. A method for the fertilization, nutrition, growth stimulation and/or prophylaxis of plants and/or the improvement of the physical, chemical and/or biological properties of the soil or of the culture substrate of plants comprising the administration of an effective amount of the composite as claimed in claim 14, or of a composition comprising the composite as claimed in claim 14 and an excipient, to a plant in need thereof or to the soil or culture substrate of a plant in need thereof.

21. The method as claimed in claim 20 application to the leaves, the roots, in an open field or in soilless culture of the plant in need thereof.

Description

EXAMPLE 1: COMPOSITE OF ACTIVATED CARBON/TRYPTOPHAN/HYBRID MATERIAL OF FORMULA (I) OF TALC TYPE OBTAINED FROM AN 80 MOL % PHENYITMS AND 20 MOL % TEOS ORGANOALKOXYSILANE MIXTURE (REFERRED TO AS CA/TRP/80PH-20TEOS)

(1) 1.A—Preparation of the Activated Carbon Saturated with Tryptophan (M25)

(2) A carbon (denoted CA1) physically activated with steam (Bioconservacion, Spain) is milled. The particles having a size of less than 250 μm are used for the remainder of the treatments. 10 g of this carbon are brought into contact, with stirring, with one liter of an aqueous solution of tryptophan having a concentration equal to 10,000 mg.Math.L.sup.−1. After filtration using syringe filters with a porosity of 0.2 μm, the filtrate is assayed and the product is dried at 40° C. in an oven; the amount of tryptophan adsorbed is 309.3 mg.Math.g.sup.−1 of carbon, the amount of tryptophan in the carbon-based material is 236.2 mg.Math.g.sup.−1 of material (carbon+tryptophan). This compound is called CA1+TRP. The comparison between the X-ray diffractograms of the CA1 and CA1+TRP samples indicates that the tryptophan adsorption induces no structural modification of the activated carbon which contains quartz as impurity. Furthermore, the absence of diffraction peaks characteristic of tryptophan indicates that the latter is well adsorbed onto the activated carbon and does not crystallize at the surface.

(3) 1.B—Preparation of the CA/TRP/80pH-20TEOS Composite (C004)

(4) 2.16 g of magnesium nitrate hexahydrate (99%, Sigma Aldrich) are added to 20 mL of absolute ethanol (99.9%, Carlo Erba) and the mixture is kept stirring until complete dissolution. 200 mg of L-tryptophan (TRP) (>98%, Sigma Aldrich) are introduced with stirring, then 1 g of the CA1+TRP reference sample is introduced before the addition of a mixture consisting of 1.646 g of phenyltrimethoxysilane (98%, ABCR) and of 0.432 g of tetraethylsilane (98%, ABCR) (mixture by mass of 79.2% of PhenyITMS and 20.8% of TEOS which represents 80 mol % of PhenyITMS and 20 mol % of TEOS). The whole mixture is left to stir and then the pH of the solution is brought to a value of 10 by addition of 15 mL of an aqueous sodium hydroxide solution (>97%, Sigma Aldrich) having a concentration of 1M. After stirring for 24 h at ambient temperature, the solid is separated from the solution by centrifugation (speed of 10,000 rpm for 10 min). The solid is washed three times with ethanol, before being dried in an oven at 40° C. for 48 h. The compound (2.21 g) obtained is then ground in an agate mortar before being characterized. The X-ray diffractogram indicates that the structure of talc type of formula Mg.sub.3(RSi).sub.4O.sub.8(OH).sub.2 wherein R represents a mixture of phenyl group and of O-ethyl group is formed (presence of reflections characteristic of the lattice planes (001), (020,110), (130,220) and (060)) and that it comprises the carbon-based compound (presence of reflections characteristic of carbon and of quartz) (degree of incorporation: 115.9 mg of tryptophan/g of composite).

EXAMPLE 2: COMPOSITE OF ACTIVATED CARBON/TRYPTOPHAN/HYBRID MATERIAL OF FORMULA (I) OF TALC TYPE OBTAINED FROM THE ORGANOALKOXYSILANE C16TMS (REFERRED TO AS CA/TRP/C.SUB.16.TMS2.5 (C005))

(5) 1.13 g of magnesium nitrate hexahydrate (99%, Sigma Aldrich) are added to 20 mL of absolute ethanol (99.9%, Carlo Erba), and the mixture is kept stirring until complete dissolution. 200 mg of L-tryptophan (TRP) (>98%, Sigma Aldrich) are introduced with stirring, then 2.5 g of the CA1+TRP reference sample obtained according to example 1-A are introduced, before the addition of 2 g of hexadecyltrimethoxysilane (>85%, Sigma). The whole mixture is left to stir, and then the pH of the solution is brought to a value of 10 by addition of 15 mL of an aqueous sodium hydroxide solution (>97%, Sigma Aldrich) having a concentration of 1M. After stirring for 24 h at ambient temperature, the solid is separated from the solution by centrifugation (speed of 10,000 rpm for 10 min). The solid is washed three times with ethanol before being dried in an oven at 40° C. for 48 h. The compound obtained (4.11 g) is then ground in an agate mortar before being characterized.

(6) The scanning electron microscopy image indicates that the CA1+TRP sample is totally encapsulated (degree of encapsulation: 119.7 mg of tryptophan/g of composite).

EXAMPLE 3: COMPOSITES CA/TRP/C.SUB.16.TMS5, CA/TRP/C.SUB.16.TMS1, CA/TRP/MTES AND CA/TRP/100% PHENYL

(7) Using a process identical to that used to prepare the CA/TRP/C16TMS compound, other compounds according to the invention were prepared by replacing the hexadecyltrimethoxysilane as silicon source with methyltriethoxysilane (MTES) or phenyltrimethoxysilane (PhenyITMS) or by modifying the hexadecyltrimethoxysilane/CA1 (activated carbon) ratio. The compounds obtained were called, respectively, CA/TRP/MTES, CA/TRP/100% Phenyl, CA/TRP/C16TMS1 and CA/TRP/C16TMS5. The amount of compounds used and recovered and the degrees of encapsulation are collated in table 1 below.

(8) TABLE-US-00001 TABLE 1 Mass Mass talc-type Degree of activated Mass hybrid encapsulation Silicon carbon recovered material (mg TRP/g Compound source (g) (g) (g) composite) CA/TRP/MTES MTES 1 2.08 1.08 107.8 (C001) CA/TRP/100% Phenyl PhenylTMS 1 2.04 1.04 125.1 (C003) CA/TRP/C16TMS1 C.sub.16TMS 1 2.66 1.66 76.7 (C002) CA/TRP/C16TMS5 C.sub.16TMS 5 6.52 1.52 148.6 (C006) It should be noted that, at equal carbon mass, the composite synthesized with PhenylTMS contains more tryptophan. However, the encapsulation is better with the composite synthesized with C.sub.16TMS. There is also a correlation between the mass of carbon integrated into the composite and the mass of talc-type hybrid material synthesized with C.sub.16TMS.

EXAMPLE 4: DYNAMIC-MODE RELEASE KINETICS

(9) The properties of tryptophan release from the composite according to the invention were studied according to the following protocol:

(10) 15 mg of the composite according to the invention were suspended in 50 ml of demineralized water, or 300 mg of the composite according to the invention were suspended in 1 L of demineralized water, so as to obtain a concentration of 300 mg/L.

(11) Regular 5 ml specimens were taken and filtered immediately (cut-off threshold 0.2 μm).

(12) UV-spectroscopy analyses were carried out on these specimens. A scan was thus performed in order to check that the UV signature is indeed that of tryptophan, then the tryptophan was quantified by analysis at 280 nm.

(13) After analysis, the specimen is redissolved in the stock solution. When the tryptophan concentration stabilizes in the stock solution, the latter is filtered on a Büchner funnel and then the carbon-based material or the composite is again suspended in demineralized water. Thus, the protocol is repeated until there is no longer any tryptophan release. This mode is therefore referred to as dynamic mode.

(14) The results are presented in FIG. 1.

(15) It is noted (FIG. 1) that the release is very rapid for the activated carbon saturated with tryptophan (CA1+TRP (M25)) and for some composites (CA/TRP/MTES (C001) and CA/TRP/80Ph-20TEOS (C004)).

(16) On the other hand, the release kinetics are slightly slower for the CA/TRP/100% Phenyl composite (C003) and even slower for the CA/TRP/C.sub.16TMS2.5 (C005) and CA/TRP/C.sub.16TMS5 (C006) composites. The release also varies as a function of the CA/talc-type hybrid material ratio as demonstrated in FIG. 1 for the CA/TRP/C.sub.16TMS2.5 and CA/TRP/C16TMS5 composites: it increases if the ratio increases.