FR3062126A1 - NANOPARTICLES HAVING A HEART STRUCTURE IN A PRESS SHELL BLUE ANALOGUE, METHOD FOR THE PREPARATION THEREOF, MATERIALS COMPRISING SAME, AND PROCESS FOR EXTRACTING METAL CATIONS. - Google Patents

Abstract

Nanoparticles with a core-shell structure, in which: the core of each of said nanoparticles is constituted by a nanoparticle in a metal hexacyanometallate or octacyanometallate, corresponding to the formula [Alk + x] Mn + y [M '(CN) m] tz-, where Alk + is a monovalent cation selected from the alkali metal cations and the ammonium cation NH4 +, x is 0, 1 or 2, M is a transition metal, n is 2 or 3, y is equal to at 1, 2 or 3, M 'is a transition metal, m is 6 or 8, z is 3 or 4, and t is 1 or 2; the shell of said nanoparticles, which surrounds the core, is in at least one porous inorganic oxide. Process for the preparation of said nanoparticles with core-shell structure Metallic cation exchange material comprising said nanoparticles having a core-shell structure. A process for extracting at least one metal cation from a liquid medium containing it, wherein said liquid medium is brought into contact with said nanoparticles with shell core structure and / or said metal cation exchange material.

Description

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FR 3 062 126 - A1 ® NANOPARTICLES WITH A CORE STRUCTURE IN AN ANALOG OF PRUSSE-SHELL BLUE, THEIR PREPARATION METHOD, MATERIALS COMPRISING SAME, AND METHOD OF EXTRACTING METAL CATIONS.

@) Nanoparticles with a core-shell structure, in which:

the core of each of said nanoparticles consists of a nanoparticle of a metal hexacyanometallate or octacyanometallate, corresponding to the formula [Alk ⁺ xJM y [M '(CN) m] t ^z_ , where Alk ⁺ is a monovalent cation chosen from alkali metal cations and the ammonium cation NH4 ⁺ , x is equal to 0.1 or 2, M is a transition metal, n is equal to 2 or 3, y is equal to 1.2 or 3, M 'is a transition metal, m is 6 or 8, z is 3 or 4, and t is 1 or 2;

- The shell of said nanoparticles, which surrounds the core, is made of at least one porous inorganic oxide.

Process for the preparation of said nanoparticles with a core-shell structure.

Metal cation exchanger material comprising said nanoparticles with a core-shell structure.

Method for extracting at least one metal cation from a liquid medium containing it, in which said liquid medium is brought into contact with said nanoparticles having a shell-core structure and / or said metal cation exchange material.

NANOPARTICLES HAVING CORE STRUCTURE IN AN ANALOG OF PRUSSE-SHELL BLUE, THEIR PREPARATION METHOD, MATERIALS COMPRISING SAME, AND METHOD FOR EXTRACTING METAL CATIONS.

DESCRIPTION

TECHNICAL AREA

The invention relates to nanoparticles with a core-shell structure, each of these nanoparticles comprising a core consisting of a nanoparticle of alkali metal hexa- or octacyanometallate.

These alkali metal hexa- and octacyanometallates can be called Prussian Blue Analogues or ABP.

More specifically, the invention relates to nanoparticles with a core-shell structure, each of which comprises a core consisting of a nanoparticle consisting of metal cations, in particular transition metal cations, and optionally alkali cations, and hexa- anions. or octacyanometallates, in particular hexa- or octacyanoferrate anions, and a shell made of a porous inorganic oxide, such as silica.

The nanoparticles according to the invention can therefore be more simply defined as nanoparticles with a core-shell structure comprising, preferably a core consisting of a nanoparticle of at least one Prussian Blue Analog or ABP and a shell of at least one inorganic oxide. porous.

The nanoparticles with a core-shell structure according to the invention can be considered as purely inorganic, mineral or inorganic-inorganic nanoparticles.

The invention further relates to a metal cation exchange material comprising said nanoparticles with a core-shell structure according to the invention and a solid or liquid matrix.

This metal cation exchange material can in particular be in the form of a solid monolith, a gel, a hydrogel or a solid membrane.

The invention also relates to a process for the manufacture of core-shell nanoparticles with a core consisting of nanoparticles made of Prussian Blue Analog ABP and of a shell made of metal oxide or porous metalloid such as silica.

The present invention also relates to a process for the separation of metal cations, in particular radioactive metal cations, contained in a liquid, such as a solution, in particular an aqueous solution, using said nanoparticles with a core-shell structure according to the invention, or said metal cation exchange material comprising said nanoparticles with a core-shell structure.

For example, the nanoparticles or the material according to the invention can be used for adsorption, selective extraction of radioactive cesium contained in an aqueous solution.

The technical field of the invention can be defined as that of the treatment of liquid effluents and more particularly as that of the decontamination of radioactive liquid effluents polluted by metal cations such as cesium cations.

PRIOR STATE OF THE ART

Nuclear facilities such as power reactors, spent nuclear fuel reprocessing plants, laboratories, research centers, and liquid effluent treatment stations generate radioactive liquid effluents.

These effluents, whose volumes are considerable, must be treated and decontaminated before being discharged into the environment.

The pollutants contained in these effluents and which must therefore be eliminated are mainly solid particles and radio-elements essentially present in the form of metal cations in solution.

Industrial processes for decontamination of liquid effluents, and in particular radioactive liquid effluents, are however few in number because of the complex composition of said effluents, their high ionic strength, and also the wide variety of pH values which they can exhibit. .

The currently most widespread treatments in the context of decontamination of liquid effluents are evaporation and chemical treatment by coprecipitation.

Thus, the first step of a process for decontamination of liquid solutions, in particular of low-concentration radioactive liquid solutions, on an industrial scale, generally consists in carrying out the evaporation of these solutions in order to concentrate all of the ions present in those in the form of solid waste, which therefore becomes a residue of the decontamination process.

However, this evaporation treatment cannot be envisaged for saline effluents because scaling of the installation then occurs.

In addition, the presence of certain ions in the liquid effluents generates hot corrosion during the evaporation treatment.

In the case of effluents, in particular highly saline radioactive, another possible treatment is chemical treatment by co-precipitation or entrainment which is a treatment by phase change. This involves transferring the radio elements present from a liquid phase to a solid phase either by coprecipitation or by entrainment from solid particles.

These solid particles are then rich in radio-elements and are then recovered by filtration or decantation before being confined in an adequate matrix.

These coprecipitation (for example with barium sulphate for the extraction of ⁹⁰ Sr) or entrainment (from potassium nickelhexacyanoferrate particles for ¹³⁷ Cs) have a number of drawbacks.

First of all, the volumes of sludge formed are substantial and can cause compatibility problems with the materials currently used to confine waste, such as glass or cement matrices. In addition, co-precipitation agents are often sensitive to the chemical composition and the ionic strength of the effluent, which leads to a significant drop in selectivity and therefore an increase in the volume of waste.

In order to overcome the drawbacks listed above of the treatment processes, decontamination of liquid effluents, many researchers and industrialists in particular in the nuclear industry are currently looking for other ways for the treatment of these effluents.

One of the solutions studied is the use of inorganic ion exchange materials, or more exactly inorganic cation exchange materials which have a high selectivity for the ions to be extracted. If there is a very large literature on the various inorganic ion-exchange materials selective for ⁹⁰ Sr, ¹³⁷ Cs, or ⁶⁰ Co, the majority of studies relate to tests carried out batchwise and using exchange materials in the form of powders .

In fact, the inorganic ion exchange materials currently used to adsorb the elements to be decontaminated are essentially in the form of relatively fine powders, having grain sizes of the order of a micrometer, which are not compatible with a process used. continuously.

These powders, when used in a process implemented continuously, in particular in columns, can cause a high pressure drop in these columns, which can go as far as their clogging, clogging, and stopping. the installation.

If the inorganic ion exchange materials are no longer used in the form of loose powders but of massive, compact powders, the problems of clogging are certainly then avoided, but the micron size implies a low adsorption capacity because the adsorption takes place in area.

In order to remedy the drawbacks of the aforementioned materials, document WO-A1-2015 / 091677 [1] describes a solid material in the form of a cellular monolith consisting of a matrix of an inorganic oxide with hierarchical and open porosity comprising macropores, mesopores, and interconnected micropores, and nanoparticles of at least one inorganic solid material exchanging a metal cation being distributed in said porosity. This solid inorganic metal cation exchanger material can in particular be an Analogue of Prussian Blue ABP.

Document [1] also describes a process for the preparation of these materials in which an aqueous colloidal suspension of nanoparticles of at least one solid inorganic cation-exchanging material such as ABP nanoparticles is used.

Document [1] further relates to a method for separating at least one metal cation from a liquid medium containing it, in which said liquid medium is brought into contact with said solid material.

If the adsorption capacity of the document material [1] is high, it is still insufficient and needs to be improved.

In particular, it has been found that the ABP particles which are immobilized in the matrix of an inorganic oxide of the material of this document tend to aggregate, agglomerate, which deteriorates the adsorption performance of this material. material.

More precisely in document [1], nanoparticles, in particular ABP nanoparticles, which are initially presented in the form of a colloidal suspension of nanoparticles and which are then introduced into monoliths, such as silica monoliths, have tendency to agglomerate, to aggregate. This results in a decrease in the specific surface of the nanoparticles, for example ABP, accessible to metal cations, such as cesium cations, to be separated and, consequently, a deterioration of the adsorption capacity of the material.

There is therefore, in view of the above, a need for a solid nanocomposite material comprising nanoparticles of a hexacyanometallate or octacyanometallate of an alkali metal and a transition metal, or more simply ABP nanoparticles, which does not have the drawbacks, limitations, disadvantages and defects of the materials of the prior art, as represented in particular by document [1], and which solves the problems posed by the materials of these documents, and in particular the problems posed by the document material [1],

There is in particular a need for such a material in which the agglomeration of the ABP nanoparticles is reduced in particular compared to the material of document [1], or even eliminated, and which consequently has an increased adsorption capacity for metal cations, especially in relation to document [1],

This material must have kinetics of rapid extraction, namely a few minutes to reach equilibrium, to allow optimal use in a fixed bed.

The amount of nanoparticles within said material must be high.

The nanoparticles must be ABP nanoparticles preferably containing an alkaline cation in the cages of the structure in order to act as a pure ion exchanger between the alkaline cation of the structure and a cation to be extracted, such as a Cesium cation. The exchange reaction between the material and the pollutant must only involve the alkaline cation, without impacting the other metals constituting the structure of the nanoparticles.

There is, moreover, a need for a process for preparing a material having the properties mentioned above and meeting the requirements listed above.

This process must also satisfy the following requirements: it must preferably use steps, in particular synthesis steps, not using organic solvents or controlled atmospheres in order to limit the footprint environmental, to reduce the risks inherent in industrial manufacturing and to reduce manufacturing costs as much as possible;

it must be simple, reliable, reproducible, include a limited number of steps.

it must include short synthesis steps in order to reduce the time and therefore the manufacturing cost.

The object of the invention is to provide such a method and such a material which meet inter alia these needs and these requirements.

STATEMENT OF THE INVENTION

This object, and others still, are achieved in accordance with the invention, by providing nanoparticles with a core-shell structure, in which:

the core of each of said nanoparticles is constituted by a nanoparticle in a metal hexacyanometallate or octacyanometallate, corresponding to the formula [Alk \] M ^{n +} _y [M '(CN) m] t ^z ·, where Alk ⁺ is a chosen monovalent cation among the alkali metal cations and the ammonium cation NHY, x is equal to 0.1 or 2, M is a transition metal, n is equal to 2 or 3, y is equal to 1, 2 or 3, M 'is a transition metal, m is 6 or 8, z is 3 or 4, and t is 1 or 2;

the shell of said nanoparticles, which surrounds the heart, is made of at least one porous inorganic oxide.

The cores made of a metal hexacyanometallate or octacyanometallate (ABP) of nanoparticles with a core-shell structure according to the invention are not aggregated, agglomerated, due to the presence of the shell of porous inorganic oxide, for example of silica all around of these hearts. Therefore, even if the core-shell nanoparticles according to the invention aggregate, agglomerate, this is of no consequence, and does not harm their adsorption capacity.

By porous inorganic oxide, it is generally understood that this oxide which constitutes the shell has a porosity of 2 to 25% by volume, estimated using microscopy.

The pore sizes of this porous inorganic oxide are generally less than 2 nm, that is to say that the porosity of this porous inorganic oxide can be defined as being a microporosity.

In the formula given above, Alk ⁺ can represent a monovalent cation of an alkali metal such as Li, Na, or K, K being preferred; or an ammonium cation NH ₄ ⁺ .

The formula given above could possibly be written in a simplified manner: [Alk _x ] M [M '(CN) m] where M is at the degree of oxidation 2 or 3 and Alk is at the degree of oxidation 1.

Said nanoparticles of a metal hexacyanometallate or octacyanometallate can also be optionally called “nanocrystals”.

The material according to the invention differs fundamentally from the materials of the prior art and in particular from the material which is the subject of document [1] in that:

it comes in the specific form of nanoparticles with a specific heart-shell structure;

the core of these shell core nanoparticles is made of a specific material, namely a metal hexacyanometallate or octacyanometallate, corresponding to the formula [Alk ⁺ _x ] M ^{n +} y [M '(CN) m] t ^z “, where Alk ⁺ is a monovalent cation chosen from alkali metal cations and the ammonium cation NHU, x is equal to 0.1 or 2, M is a transition metal, n is equal to 2 or 3, y is equal to 1, 2 or 3, M 'is a transition metal, m is equal to 6 or 8, z is equal to 3 or 4, and t is equal to 1 or 2;

the shell of said nanoparticles, which surrounds the heart, is also made up of a specific material, namely at least one inorganic oxide.

the inorganic oxide of the shell is porous. A liquid medium containing a metal cation to be extracted, separated from this liquid medium can therefore pass through the shell and come into contact with the heart to be thus separated, extracted from the liquid medium. The nanoparticles with a core-shell structure according to the invention have never been described or suggested in the prior art.

The nanoparticles according to the invention meet the needs listed above, they do not have the drawbacks of nanoparticles of materials of the prior art, such as the material which is the subject of document [1] and they provide a solution to the problems posed by the nanoparticles of materials of the prior art, such as the material which is the subject of document [1], In document [1], there is no mention or suggestion that the nanoparticles are or can be nanoparticles with a core-shell structure, and even less the specific nanoparticles with a core-shell structure according to the invention.

In nanoparticles with a core-shell structure according to the invention, the shell plays the role of physical barrier to the agglomeration of nanoparticles of the heart in ABP, which has certain advantages, in particular when these nanoparticles with a core-shell structure are used. in a decontamination process, for example for separating, extracting a metal cation, such as a cesium cation, from a liquid medium. In fact, the ABP cores of nanoparticles with a core-shell structure according to the invention not being agglomerated, aggregated, their surface is much more accessible to contaminants such as metal cations which pass through the porous shell. The adsorption capacity of nanoparticles with a core-shell structure according to the invention is greatly increased compared to conventional nanoparticles with a core structure which consist only of an ABP core without a porous inorganic oxide shell.

Advantageously, the inorganic oxide of the shell is chosen from the oxides of at least one metal or metalloid such as Si, Ti, Zr, Th, Nb, Ta, V, W, Y, Ca, Mg and Al; and their mixtures.

Preferably, the inorganic oxide of the shell is silica.

The metal hexa- or octacyanometallate of formula [Alk ⁺ x] M ^{n +} _y [M '(CN) m] t ^z “, given above is generally chosen according to the intended application, the nature of the liquid effluent to be treated, and in particular as a function of the metal cation (s) that it is desired to separate.

Advantageously, M ^{n +} is Fe ²⁺ , Ni ²⁺ , Fe ³⁺ , Co ²⁺ , Cu ²⁺ , or Zn ²⁺ .

Advantageously, M 'is Fe ²⁺ or Fe ³⁺ or Co ³⁺ and m is 6; or M 'is Mo ⁵⁺ and m is 8.

Advantageously, [M '(CN) _m ] ^z “is [Fe (CN) 6] ³ ', [Fe (CN) 6] ⁴ ', [Co (CN) 6] ³ or [Mo (CN) ₈ ] ³ ·.

Preferably, the metal hexacyanometallate or octacyanometallate corresponds to the formula K2M Fe (CN) 6, for example IÇCu Fe (CN) 6,! <2ZnFe (CN) 6, or K2C0 Fe (CN) 6.

One of the main applications targeted for nanoparticles and materials according to the invention is that of sorbents of radioactive cesium for nuclear decontamination purposes.

However, the nanoparticles of copper ferrocyanides (and ferricyanides) (FCCu) of general formula [K ⁺ x] Cu ²⁺ y [Fe (CN) 6] ^z_ , for example K2Cu Fe (CN) 6 are very selective for cesium. Their crystal structure is cubic face centered, and has the advantage of being able to selectively exchange a cesium atom with an unbound potassium atom, present in the mesh.

Generally, the metal hexacyanometallate or octacyanometallate nanoparticles have a sphere or spheroid shape.

Generally, nanoparticles with a core-shell structure have a sphere or spheroid shape.

Generally, the nanoparticles (core) of metal hexacyanometallate or octacyanometallate have an average size, such as a diameter, from 2 to 20 nm, preferably from 2 to 10 nm, more preferably from 2 to 5 nm.

Generally, the shell has a thickness of 2 to 100 nm, preferably 5 to 20 nm.

Consequently, the nanoparticles with a core-shell structure according to the invention have an average size, such as a diameter, from 4 to 120 nm, preferably from 4 to 50 nm, more preferably from 4 to 20 nm.

Generally, the content of metal hexacyanometallate or octacyanometallate nanoparticles of the nanoparticles according to the invention is from 0.5% to 15% by weight, preferably 0.5% to 5% by weight.

The invention further relates to a metal cation exchange material comprising said nanoparticles with a core-shell structure according to the invention and a solid or liquid matrix.

This matrix can in particular be in the form of a solid monolith, a gel, a hydrogel or a solid membrane.

It can be considered that, in this metal cation exchange material, the nanoparticles with a core-shell structure according to the invention are used as functionalizing agents for the matrix which is, for example, in the form of a solid monolith, a gel, hydrogel or solid membrane.

The invention relates, in particular, to a solid metal cation exchange material in the form of a cellular monolith consisting of a matrix of an inorganic oxide with hierarchical and open porosity comprising macropores, mesopores, and micropores, said macropores, mesopores and micropores being interconnected, and the nanoparticles with a core-shell structure according to the invention being distributed in said porosity.

This solid metal cation exchanger material according to the invention in the form of a cellular monolith is distinguished from the solid material in the form of a cellular monolith described in document [1], in that the nanoparticles which are distributed in the porosity of the matrix, are the specific nanoparticles with a core-shell structure according to the invention as they have been described above. The ABP cores of these nanoparticles with a core-shell structure are therefore not agglomerated, aggregated, on the contrary ABP nanoparticles without the shell of the document material [1] which do not have such a core-shell structure but simply a structure "Heart".

As a result, this solid metal cation exchange material according to the invention, in the form of a cellular monolith, has all the advantages due to nanoparticles with a core-shell structure according to the invention, the ABP cores of which are not not agglomerated, compared to the ABP nanoparticles - which do not have a core-shell structure - distributed in the porosity of the matrix of the document material [1], In particular, this solid material according to the invention is presented under the shape of a honeycomb monolith has a higher adsorption capacity for metal cations than the honeycomb monolith of document [1],

This solid metal cation exchange material according to the invention is in the form of a cellular monolith, if it overcomes the drawbacks in particular in terms of aggregation of ABP nanoparticles and of still limited adsorption capacity, of the material of document [1] retains all the other advantageous properties of this material which are exposed in document [1]. In other words, the material of document [1] is greatly improved due to the use of nanoparticles. specific to a core-shell structure according to the invention instead of the conventional nanoparticles with a core structure, which consist only of an ABP core without a shell of porous inorganic oxide, used in the material of document [1],

The inorganic oxide of said solid metal cation exchange material according to the invention, in the form of a cellular monolith, is generally chosen from the oxides of at least one metal or metalloid such as Si, Ti, Zr, Th, Nb, Ta, V, W, Y, Ca, Mg and Al; and their mixtures.

Preferably, the inorganic oxide is silica.

The invention also relates to a process for preparing nanoparticles with a core-shell structure according to the invention, which comprises at least the following successive steps:

a) a water-in-oil microemulsion C is prepared, formed of droplets of an aqueous phase constituted by a suspension of nanoparticles of [Alk ⁺ _x ] M ^{n +} y [M '(CN) m] t ^z , said droplets being dispersed in a continuous oily phase;

b) adding a base to the microemulsion C obtained in step a) so that the pH of the aqueous phase of the water-in-oil microemulsion C is greater than or equal to 8, preferably is 8 to 10, provided that which gives a microemulsion D;

c) adding a precursor of the inorganic oxide to the microemulsion D obtained in step b), whereby a microemulsion E is obtained;

d) maturation, mineralization of the microemulsion E obtained in step c) is carried out, whereby the porous inorganic oxide shell is formed around the nanoparticles of [Alk ⁺ x] M ^{n +} y [M '(CN) m ] t ^z and the nanoparticles with a core-shell structure are formed;

e) adding one or more organic solvent (s) to the mineralized microemulsion E obtained in step d), whereby the microemulsion E is broken;

f) the nanoparticles with a core-shell structure are separated from the broken microemulsion E obtained in step e);

g) washing the nanoparticles with a core-shell structure separated in step f).

The method according to the invention comprises a specific series of specific steps which has never been described or suggested in the prior art.

In particular, steps b) to g) during which an inorganic oxide shell is prepared around the nanoparticles of [Alk ⁺ x] M ^{n +} y [IVI '(CN) m] t ^z are neither described nor suggested in l prior art.

It turned out that the process according to the invention made it possible to easily prepare, and with a high yield, the nanoparticles according to the invention, which have a high adsorption capacity for metal cations such as cesium cations (see examples) .

The water-in-oil microemulsion C, formed of droplets of an aqueous phase constituted by a suspension of nanoparticles of [Alk ⁺ x] M ^{n +} y [IVI '(CN) m] t ^z , said droplets being dispersed in a phase Continuous oily can be prepared by the following steps:

al) reacting an anionic organic surfactant with cations M ^{n +} , whereby an anionic surfactant modified by the cations M ^{n +} is obtained;

bl) a water-in-oil microemulsion A is prepared, stabilized by the organic surfactant, and formed of droplets of an aqueous phase containing [Alk ⁺ _X ] [M '(CN) m] t ^z ', for example K4Fe (CN) 6, dispersed in a continuous oily phase;

cl) preparing a water-in-oil microemulsion B, stabilized by the modified organic surfactant prepared in step a1), and formed of droplets of an aqueous phase consisting of water, dispersed in a continuous oily phase;

dl) mixing the microemulsion A and the microemulsion B, whereby the water-in-oil microemulsion C is obtained, formed of droplets of an aqueous phase constituted by a suspension of nanoparticles of [Alk ⁺ x] M ^{n +} y [ IVI '(CN) m] t ^z , said droplets being dispersed in a continuous oily phase.

In step a1), the anionic organic surfactant is generally chosen from anionic surfactants which comprise cations, such as cations of alkali metals such as Na ⁺ cations which can be exchanged with the M ^{n +} cations of transition metals described more high, such as copper or zinc cations.

An example of such an anionic surfactant is sodium dioctyl sulfosuccinate also known by the abbreviation "AOT" and which is in the form of a whitish gel.

To react the anionic organic surfactant with the cations M ^{n +} , it is possible to mix a solution of this surfactant in an organic solvent, and an aqueous solution containing the cation M ^{n +} , such as M ²⁺ , generally in the form of a salt of metal M.

Preferably, the water of the aqueous solution containing the cation M ^{n +} is ultra pure water.

The salt of the metal M contained in this solution B is a salt in which the metal M is generally chosen from the metals capable of giving a cyanometallate of this metal M, such as a hexacyanoferrate of this metal, which is insoluble.

This metal M can be chosen from all the transition metals, for example from copper, cobalt, zinc, nickel and iron etc.

The ion M ^{n +} can therefore be chosen from the ions Fe ²⁺ , Ni ²⁺ , Fe ³⁺ , Co ²⁺ , Cu ²⁺ , and Zn ²⁺ .

The salt of the metal M can be for example a nitrate, a sulfate, a chloride, an acetate, a tetrafluoroborate, optionally hydrated, of one of these metals M.

The preferred salts are the nitrates, for example of formula MfNChh, for example CufNChh.

The concentration of the metal salt M in the solution is preferably at saturation.

The mixture of the surfactant solution in an organic solvent and the aqueous solution containing the cation M ^{n +} , such as M ^{2+, is} then separated into two phases.

These two phases are an organic phase which contains the surfactant such as ΙΆ0Τ modified by the cations M ^{n +} and an aqueous phase.

The aqueous phase is eliminated and the organic phase is washed several times with water until complete elimination of the salts, for example nitrates.

The organic phase containing the modified surfactant is then dried, for example at 35 ° C. under vacuum for 48 hours, to give the modified surfactant.

For example, to prepare modified ΙΆ0Τ, one can mix a given volume of AOT at 1 mol / L in absolute ethanol with a saturated aqueous solution of metal salt M such as Cu, for example metal nitrate of formula Μ ²⁺ (ΝΟ3 ^_ ) 2, such as copper nitrate, a homogeneous mixture is thus obtained.

The addition of diethyl ether to this mixture causes the mixture to be separated into two phases, namely an organic phase which contains the surfactant as ΙΆ0Τ modified by the cations M ^{n +} and an aqueous phase.

The aqueous phase is eliminated and the organic phase is washed several times with water until complete elimination of the salts, for example nitrates.

The organic phase containing the modified surfactant is then dried, for example at 35 ° C. under vacuum for 48 hours, to give the modified surfactant.

In the case where the surfactant is sodium sulfosuccinate, the modified surfactant is the sulfosuccinate of metal M, for example copper sulfosuccinate which is in the form of a paste or gel of blue color due to the Cu ²⁺ ions.

During step b1), a water-in-oil microemulsion A is prepared, stabilized by the organic surfactant, and formed of droplets of an aqueous phase containing [Alk ⁺ _X ] [M '(CN) _m ] t ^z “, for example KUFefCNk, dispersed in a continuous oily phase.

For this, one can for example mix a solution of the unmodified surfactant, such as ΓΑΟΤ (unmodified), in an organic solvent and an aqueous solution of [Alk ⁺ _X ] [M '(CN) m] t ^z ', by example of K4Fe (CN) 6.

This mixture is generally carried out with ultrasonic stirring.

The organic solvent generally consists of one or more liquid alkane (s) chosen from linear or branched alkanes having from 5 to 22 carbon atoms, preferably from 7 to 22 carbon atoms such as isooctane, and dodecane and hexadecane; cyclic alkanes of 5 to 22 carbon atoms such as cyclohexane; and their mixtures.

The concentration of the surfactant in the solution is generally 0.01 to 5 M, preferably 0.1 M.

The concentration of [Alk ⁺ _X ] [M '(CN) m] t ^z ', for example K4Fe (CN) 6 in the aqueous solution is generally from 0.005 M to 0.5 M, preferably 0.05 M .

The volume of the aqueous solution of [Alk ⁺ _X ] [M '(CN) m] t ^z ', for example K4Fe (CN) 6, is generally adapted so that the ratio w = [H2O] / [Surfactant ] designated by wa when this ratio relates to microemulsion A, ie from 1 to 30, preferably from 10.

In step c1), a water-in-oil microemulsion B is prepared, stabilized by the modified organic surfactant prepared in step a1, and formed of droplets of an aqueous phase consisting of water dispersed in a continuous oily phase.

For this, one can for example mix a solution of the modified surfactant, such as ΙΆ0Τ (modified), in an organic solvent with pure water.

This mixture is generally carried out with ultrasonic stirring.

The organic solvent generally consists of one or more liquid alkanes chosen from linear or branched alkanes having from 5 to 22 carbon atoms, preferably from 7 to 22 carbon atoms such as isooctane, and dodecane and hexadecane; cyclic alkanes of 5 to 22 carbon atoms such as cyclohexane; and their mixtures.

The concentration of surfactant in the solution is generally from 0.001 to 2.5 M, with the presence of 0.044 M.

The volume of pure water is generally adapted so that the ratio w = [H2O] / [Surfactant] designated by wb when this ratio relates to microemulsion B, ie from 2.5 to 15, preferably from 5. Generally wb = wa / 2.

In this emulsion B, the modified surfactant is instead placed at the interface between the two phases and the metal M, such as copper, which modifies the surfactant which is thus placed on the side of the aqueous phase.

During step dl), the microemulsion A and the microemulsion are mixed

B, whereby the water-in-oil microemulsion C is obtained, formed of droplets of an aqueous phase constituted by a suspension of nanoparticles of ferrocyanides [Alk ⁺ _x ] M ^{n +} y [IVI '(CN) m] t ^z , for example K2MFe (CN) 6, in particular KzCuFe (CN) 6, said droplets being dispersed in a continuous oily phase. In this microemulsion

C, the aqueous phase is therefore a suspension.

The ratio w = [H2O] / [Surfactant] designated by wc when this ratio relates to microemulsion C generally ranges from 3.75 to 22.5, preferably wc is equal to

7.5. Indeed, we mix microemulsion A and microemulsion B to give microemulsion C, and consequently wc = (wa + wb) / 2 = 3 wa / 4.

These ferrocyanides are crystalline coordination polymers, the structure of which is cubic face centered. These compounds have the particularity of being able to accommodate at the center of the crystal mesh a potassium atom which can then be exchanged with cesium. This ion exchange is very selective with respect to cesium. This is the reason why ferrocyanides are among the most effective cesium exchangers.

This mixture is generally carried out with ultrasonic stirring.

This mixing is generally carried out so as to preserve the molar ratio M: M ', for example Cu / Fe which is generally 4: 3.

During step b), a base is added to microemulsion C so that the pH of the aqueous phase of the water in oil microemulsion C is generally greater than or equal to 8, preferably is 8 to 10, provided that what, one obtains a microemulsion D which one can qualify as basified microemulsion.

The base can be for example NH4OH or NaOH.

One can for example add a given volume of a basic solution, such as NH4OH at a given concentration, to obtain the desired pH greater than or equal to 8.

Thus, it is possible to add a given volume of a 25% aqueous solution of NH4OH, diluted 10 times, this volume corresponding to 10% of the total volume of water of microemulsion C to obtain microemulsion D.

In step c), a precursor of the inorganic oxide is added to the microemulsion D obtained in step b), whereby the microemulsion E is obtained.

The inorganic oxide is generally chosen from oxides of metals and metalloids, and the precursor of this oxide is therefore generally chosen from alkoxides of metals or metalloids, salts of metals or metalloids, such as chlorides and nitrates of metals and metalloids, and mixtures thereof.

In the case where the inorganic oxide is silica, the silica precursor (s) can be chosen from tetramethoxyorthosilane (TMOS), tetraethoxyorthosilane (TEOS), dimethyldiethoxysilane (DMDES), and their mixtures.

Generally, the microemulsion is added to D, a given volume of the precursor, such as TEOS, the silica precursor, a molar ratio h = n _H 2o / n _pr écurseur, from 4.3 to 60, preferably 4, 3.

During step d), maturation, mineralization of the microemulsion E obtained in step e) is carried out, whereby the porous inorganic oxide shell is formed around the nanoparticles of [Alk ⁺ _x ] M ^{n +} y [ M '(CN) m] t ^z and the nanoparticles with a core-shell structure are formed.

This maturation can be carried out by allowing the microemulsion E to react with stirring for a period of 12 to 120 hours, preferably 48 hours.

Without wishing to be bound by a theory, during this stage, it would seem that the precursor, such as TEOS, is rather in the organic phase and that, as soon as it meets a water molecule at the interface between phases, it hydrolyzes and polymerizes in the droplets of aqueous phase to form inorganic oxide such as silica.

During step e), one or more organic solvent (s) are added to the mineralized microemulsion E obtained in step e), whereby the microemulsion E is broken, destabilized.

This or these organic solvent (s) can be chosen from ethanol, acetone, DMSO, diethyl ether, etc.

During step f), the nanoparticles with a shell-core structure are separated from the “broken” microemulsion E obtained in step f).

This separation can be carried out by any suitable liquid-solid separation technique, for example by filtration or centrifugation.

For example, the “broken” microemulsion E can be centrifuged, for example at 14,800 rpm for a period of time, for example 10 minutes, and the supernatant is removed.

During step g), the nanoparticles with a core-shell structure separated in step f) are washed with an organic solvent such as absolute ethanol.

This step g) can comprise several successive washes, for example from 1 to 3 washes, in particular 3 washes with an organic solvent, such as absolute ethanol, the organic solvent being removed from the mixture comprising the washing solvent and nanoparticles after each washing by a suitable liquid-solid separation technique, for example by filtration or centrifugation.

For example, the mixture of washing solvent and nanoparticles can be centrifuged, and the supernatant is removed.

The nanoparticles with a core-shell structure according to the invention and the metal cation exchange material according to the invention can be used in particular, but not exclusively, in a process for extracting, separating, at least one metal cation from a liquid medium containing it, in which said liquid medium is brought into contact with the shell-core nanoparticles according to the invention and / or the metal cation exchange material. The invention therefore also relates to such an extraction, separation process.

Nanoparticles with a shell core structure according to the invention and the metal cation exchange material according to the invention, because of their excellent properties such as excellent exchange capacity, excellent selectivity, high reaction speed, are suitable. particularly for such use.

This excellent efficiency is obtained with reduced amounts of hexacyanoferrate or octacyanoferrate.

In addition, the excellent mechanical strength and stability properties of the nanoparticles with a core-shell structure according to the invention resulting from their specific structures, and of the metal cation exchange material according to the invention, allow in particular the continuous implementation of the separation process, which can thus be easily integrated into an existing installation, for example in a chain or processing line comprising several stages.

Advantageously, said liquid medium can be an aqueous liquid medium, such as an aqueous solution, for example sea water or brackish water.

The solutions which can be treated with nanoparticles with a core-shell structure according to the invention and the metal cation exchange material according to the invention are very varied, and may even contain, for example, corrosive agents, or the like, due to the excellent chemical stability of the material according to the invention.

The nanoparticles with a core-shell structure according to the invention and the metal cation exchange material according to the invention can be used in particular over a very wide pH range, for example from 2 to 10. For example, acid solutions may be treated (for example nitric acid solutions), for example concentrations higher than 0.1 M, neutral, or basic up to a pH of 10.

Said liquid medium can be a process liquid or an industrial effluent.

Advantageously, said liquid medium can be a liquid medium such as an aqueous solution containing radionuclides. For example, the liquid medium can be chosen from liquids and effluents from the nuclear industry, nuclear installations and activities using radionuclides.

These include, for example, cooling water and radioactive effluents from the operation or remediation / dismantling of nuclear power plants, aqueous solutions and radioactive effluents from operation or remediation / dismantling of nuclear fuel cycle factories, from the mine to the dismantling of end-of-life facilities, or aqueous solutions and radioactive effluents from laboratories, research centers or other industries using radionuclides.

It is however obvious that the nanoparticles with a core-shell structure according to the invention and the metal cation exchange material according to the invention can also be used in other non-nuclear, industrial or other fields of activity.

Thus, hexacyanoferrates selectively fix thallium and this property could be used in the purification of effluents from cement works to reduce or eliminate the discharges and emissions of this element which is a violent poison.

The liquid medium, preferably an aqueous solution, may, in addition to said metal cation to be separated, contain other salts in solution such as NaNCh or LiNO3 or also AlfNChh or any other soluble salt of alkali or alkaline earth metal, for example at a concentration up to 2 moles / L. The solution may also contain, as indicated above, acids, bases, and even organic compounds.

Thus, the liquid medium can be an aqueous solution containing, in addition to said metal cation, salts (of course different from the salts of said metal cation) such as NaCl, for example at a concentration greater than 30 g / L.

The process according to the invention makes it possible, surprisingly, to efficiently and selectively separate a metal cation such as a cesium cation, even from liquid media, such as aqueous solutions, highly charged with salts, in particular with NaCl . Such media highly charged with NaCI are, for example, sea water and brackish water.

Generally, said metal cation can be present at a concentration of 0.1 picogram at 100 mg / L, preferably 0.1 picogram at 10 mg / L.

The term “metal” also covers isotopes and in particular the radioactive isotopes of said metal.

Preferably, the cation is a cation of an element selected from Cs, Co, Ag, Ru, Fe and Tl and isotopes including radioactive thereof among which one can cite ⁵⁸ Co, ⁶⁰ Co, ^55-59 Fe , ¹³⁴ Cs, ¹³⁷ Cs, and io3, io5, io5, io7 _Ru .

The metal cation is in particular the cesium Cs cation.

More preferably, the cation is a cation of ¹³⁴ Cs, or ¹³⁷ Cs.

A preferred use of nanoparticles with a core-shell structure according to the invention and of the metal cation exchange material according to the invention is in fact the fixation of cesium which contributes to a large part of the gamma activity of liquids from the nuclear industry. and which is selectively fixed by hexacyanoferrates.

The process according to the invention can advantageously be carried out with a liquid medium which is an aqueous solution, containing as metal cation a cation of ¹³⁴ Cs or ¹³⁷ Cs, and containing, in addition, salts, such as NaCI, preferably at a high concentration, for example greater than 30 g / L.

The method according to the invention makes it possible to efficiently and selectively separate these metal cations of radioactive cesium from such liquid media highly charged with salts such as NaCl. This effective and selective separation is possible thanks to the selectivity of nanoparticles with a core-shell structure according to the invention and of the metal cation exchange material according to the invention with respect to Cs in the presence of a competing ion such as Na .

This process has all the advantages intrinsically linked to nanoparticles with a shell-core structure according to the invention and to the metal cation exchange material according to the invention, implemented in this process, and which have already been described above.

We have seen that the separation process which uses the nanoparticles with a core-shell structure according to the invention and / or the metal cation exchange material according to the invention is preferably implemented continuously, the nanoparticles with structure- core-shell according to the invention and / or the metal cation exchange material according to the invention, preferably in the form of particles, then being packaged for example in the form of a column, the nanoparticles having a core-shell structure according to the invention and / or the metal cation exchanger material according to the invention preferably forming a fluidized bed, the fluidization of which is ensured by the solution to be treated, but the fixing process can also be implemented batchwise, in "batch" mode, the bringing nanoparticles with a shell-core structure according to the invention and / or the metal cation exchange material according to the invention into contact with the solution iter then being preferably carried out with stirring. Column packaging makes it possible to continuously process large quantities of solution, with a high flow rate thereof.

The contact time of the solution to be treated with the nanoparticles with a core-shell structure according to the invention and / or the metal cation exchange material according to the invention is variable and can range, for example, from 1 minute to 1 hour for continuous operation and, for example from 10 minutes to approximately 24 hours, for "batch" operation.

At the end of the fixing process, the pollutants present in the solution, such as cations, are immobilized in the nanoparticles with shell-core structure according to the invention and / or the exchanger, fixing material, of metal cations according to the invention. invention by sorption, that is to say by ion exchange or adsorption within the nanoparticles, within the structure of the nanoparticles.

The invention will now be described in more detail in what follows in connection in particular with particular embodiments thereof which are the subject of examples.

This description is made in relation to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is an image taken in transmission electron microscopy MET ("Transmission Electron Microscopy", "TEM" in English) in the clear field of silica nanoparticles alone synthesized with the surfactant Na (AOT) unmodified, and wa = 20 in Example 1.

The scale shown in this figure represents 20 nm.

Figure 2 is an image taken in transmission electron microscopy MET ("Transmission Electron Microscopy", "TEM" in English) in the clear field of silica nanoparticles with copper oxide particles in their center (it is therefore of shell core nanoparticles with a core consisting of copper oxide and a silica shell) synthesized, prepared, with the modified surfactant Na (AOT) / Cu (AOT) 2 and wc = 15 in Example 2.

The scale shown in this figure represents 20 nm.

Figure 3 is an image taken in “STEM-HAADF” mode (“Scanning Transmission Electron Microscopy-High Angle Annular Dark Field” in dark field) of silica nanoparticles with copper oxide particles in their center (it these are therefore shell core nanoparticles with a core consisting of copper oxide and a silica shell) synthesized with the modified surfactant Na (AOT) / Cu (AOT) 2, and wc = 15 in Example 2.

The scale shown in this figure represents 20 nm.

Figures 4A and 4B are images taken in “STEMHAADF” mode silica nanoparticles with copper oxide particles in their center (these are therefore shell core nanoparticles with a core consisting of copper oxide and a shell silica) synthesized, prepared in Example 2, with wc = 15.

The scales shown in these figures represent 20 nm.

Figures 5A and 5B show the spectra "EELS" ("Electron Energy Loss Spectroscopy" in English) associated with images (a) and (b) respectively of Figures 4A and 4B.

On the abscissa is the energy loss ("Energy Loss") in eV, and on the ordinate is the number of strokes ("Counts").

FIG. 6 is an image taken in “STEM-HAADF” mode in the dark field of the core nanoparticles of K2CuFe (CN) 6-shell of S1O2, designated K2CuFe (CN) 6 @ SiO2, prepared in Example 3, with wc = 15 .

The scale shown in this figure represents 20 nm.

Figure 7 is an image taken in “STEM-HAADF” mode of the core nanoparticles of K2CuFe (CN) 6-shell of S1O2, designated K2CuFe (CN) 6 @ SiO2, prepared in Example 4, with wc = 7.5.

The scale shown in this figure represents 10 nm.

Figure 8 shows the "EELS" spectrum of the bright particle in the image of Figure 7.

On the abscissa is the energy loss ("Energy Loss") in eV, and on the ordinate is the number of strokes ("Counts").

FIG. 9 is an X-ray powder diffractogram (DRX) of the nanoparticles made of copper ferrocyanide and silica shell K2CuFe (CN) 6 @ SiO2 prepared in Example 4 with wc = 7.5 (Spectrum A), and copper ferrocyanide nanoparticles without silica shell K2CuFe (CN) 6 (spectrum B).

The abscissa is plotted 20 (in °).

Figure 10 is an infrared spectrum of the nanoparticles copper ferrocyanide core and silica shell K2CuFe (CN) 6 @ SiO2 prepared in Example 4 with wc = 7.5 (Spectrum A), and nanoparticles of copper ferrocyanide without shell silica K2CuFe (CN) 6 (spectrum B).

The number of waves (in cm ^-1 ) is plotted on the abscissa.

FIG. 11 is an image taken in electronic transmission electron microscopy (“Transmission Electron Microscopy”, “TEM” in English) of the core-shell nanoparticles, K2CuFe (CN) 6 @ SiO2, prepared in Example 4, with wc = 7.5.

The scale shown in this figure represents 200 nm.

FIG. 12 is a “HRTEM” image in a dark field in “STEM-HAADF” mode of the core-shell nanoparticles, K2CuFe (CN) 6 @ SiO2, prepared in Example 4, with wc = 7.5.

The scale shown in this figure represents 10 nm.

Figure 13 is the EDX spectrum of core-shell nanoparticles K2CuFe (CN) 6 @ SiO2 prepared in Example 4, before sorption of Cs.

Figure 14 is the EDX spectrum of the core-shell nanoparticles K2CuFe (CN) 6 @ SiO2 prepared in Example 4, after sorption of Cs (see Example 6).

DETAILED PRESENTATION OF PARTICULAR EMBODIMENTS

The invention will now be described with reference to the following examples given by way of illustration and not limitation.

In the examples which follow, the following preparation protocol, which comprises 7 steps, is used to prepare the core-shell nanoparticles according to the invention in Examples 3 and 4.

Also prepared, in Example 1 which follows, nanoparticles "core" in silica, that is to say which comprise only a core comprising silica and which do not comprise a shell.

In addition, in Example 2 which follows, nanoparticles of silica are prepared with copper oxide particles at their center. They are therefore shell core nanoparticles, with a core consisting of copper oxide and a silica shell. Preparation protocol.

This preparation protocol is based on the publications by S. Vaucher et al. [3], and of J. Eastoe et al. [2], The Eastoe document simply describes the modification of ΓΑΟΤ with the exchange occurring between the initial Na and the transition metal of interest.

Vaucher's document, for its part, simply describes the synthesis of nanoparticles of cobalt ferrocyanide without a shell, in particular without a silica shell.

1. Preparation of the modified surfactant based on AOT (sodium dioctyl sulfosuccinate, “dioctylsulfosuccinate sodium knows” sold by Sigma-Aldrich®).

A given volume of AOT at 1 mol / L in absolute ethanol is mixed with a saturated solution of metal nitrate M ²⁺ (NO3h. (In Examples 2, 3 and 4 which follow, M is Cu). addition of diethyl ether separates the mixture into two phases, the aqueous phase is eliminated and the organic phase is washed several times with water until the nitrates are completely eliminated.

The solvent of the organic phase containing the modified surfactant is evaporated to give a paste, then the paste is dried at 35 ° C under vacuum for 48 hours.

The unmodified AOT surfactant is called Na (AOT) while the copper-modified AOT surfactant is called Cu (AOT) 2.

• Heart-shell type nanoparticles are prepared using two microemulsions, called microemulsions A and B respectively.

2. Preparation of microemulsion A.

Microemulsion A is prepared, with ultrasonic stirring, from unmodified AOT at a concentration of 0.1 M in isooctane, and water (Example 1, Fig. 1) or an aqueous solution of K4Fe ( CN) 6 at a concentration [K4Fe (CN) e] = x M, with x between 0.005 M and 0.5 M, and ideally taken at 0.05 M. The volume of K4Fe (CN) 6 solution is adapted according to wa = [H ₂ O] / [AOT], wa can be between 5 and 30, and is ideally chosen such that wa = 10.

3. Preparation of microemulsion B.

Microemulsion B is produced, under ultrasound, from the modified surfactant (prepared in step 1) at a concentration of 0.044 mol / L in isooctane and from different quantities of water, wb. wb is between 2.5 and 15, ideally wb is chosen equal to 5.

4. Preparation of a microemulsion C.

Microemulsions A (wa) and B (wb = wa / 2) are mixed under ultrasound while preserving the molar ratio (M ²⁺ : Fe) = (4: 3), thus giving a microemulsion C containing the ferrocyanide nanoparticles of transition metal (Cu in the examples, except in Example 1). The wc ratio here is generally equal to 7.5.

In Example 2, there is no transition metal ferrocyanide.

The procedure for this step is followed in full in Examples 3 and 4.

5. Preparation of a microemulsion D.

A given volume of NH4OH (25%) diluted 10 times is added, generally 10% of the total volume of water of microemulsion C to obtain a microemulsion D.

6. Preparation of a microemulsion E.

Is added to microemulsion D, a given volume of tetraethylorthosilicate (TEOS), silica precursor, according to the molar ratio h = nH2o / nTEos, between 4.3 and 60, ideally h = 4.3. A microemulsion is thus obtained.

This last microemulsion (microemulsion E) is left to react for 48 hours with stirring.

7. Washing of the particles is carried out by adding one or more organic solvent (s) to microemulsion E, such as ethanol, acetone, DMSO, diethyl ether, etc. The whole is then centrifuged at 14,800 rpm (rpm) for 10 min and the supernatant is removed. The nanoparticles thus recovered are then washed three times with absolute ethanol by repeating the centrifugation-elimination cycles of the supernatant.

This protocol makes it possible to prepare core-shell nanoparticles according to the invention with a core of transition metal ferrocyanide and a shell of porous silica.

Example 1.

In this example, nanoparticles "core" in silica are prepared, that is to say which comprise only a core constituted by silica, and which do not comprise a shell.

These nanoparticles are synthesized from a single microemulsion A as prepared in step 2 of the protocol but comprising only the unmodified AOT surfactant (also called Na (AOT)).

This microemulsion contains unmodified ΙΆ0Τ at a concentration of 0.1 M in isooctane and the amount of water added (only water, without K4Fe (CN) e) wa is equal to 20.

Steps 5 to 7 of the protocol are then carried out with the transition to a basic pH and then the addition of the silica precursor, the microemulsion A previously prepared playing the role of the microemulsion (C).

Finally, we can consider that in this example, steps 2, 5, 6, 7 of the protocol described above are carried out.

Figure 1 shows the silica nanoparticles obtained in this example. The nanoparticles measure 18.6 nm and seem fairly homogeneous in size, with no darker particles inside. The nanoparticles are probably porous.

Example 2.

In this example, nanoparticles of "core" made of copper oxide and shell of silica are prepared.

These nanoparticles are synthesized from a microemulsion A as prepared in step 2 of the protocol, but comprising only pure water and unmodified ΙΆ0Τ at wa = 20.

In other words, in emulsion A, the solution of K4Fe (CN) 6 is not added but only water.

A microemulsion B is also prepared containing modified ΓΑΟΤ (prepared as in step 1 of the protocol) at a concentration of 0.044 mol / L in isooctane and the amount of water added wb is equal to 10.

Step 4 of the protocol is then carried out by mixing microemulsions A and B to form microemulsion C with wc = 15. Steps 5 to 7 of the protocol are then carried out, with the microemulsion (C).

In other words, in this example 2, the entire protocol is followed with the unmodified (microemulsion A) and modified (microemulsion B) surfactant. The only difference comes from the fact that the K4Fe (CN) 6 solution is not added to microemulsion A but just water. Then, microemulsion A is mixed with microemulsion B (Cu (AOT) 2 + water) to form microemulsion C. Then the protocol continues.

Figures 2 and 3 show the silica nanoparticles obtained in this example 2. The nanoparticles thus obtained measure 28.9 nm and have darker spots at their center (in bright field), or brighter, lighter, in dark field 2.4 nm.

Figures 4A and 4B also show the silica nanoparticles obtained in this Example 2 which have copper oxide particles in their center.

It has been possible to demonstrate with the aid of EELS spectroscopy (see FIGS. 5A and 5B) that the lighter, brighter zones exhibited by the nanoparticles of FIGS. 3, 4A, and 4B are particles of copper oxide due copper present in the modified surfactant.

Indeed, the spectrum shown in Figure 5A shows the presence of the electronic transitions L2 (951 eV) and L ₃ (931 eV) characteristic of copper and the spectrum shown in Figure 5B clearly highlights the electronic transitions of silica: L ₂ , ₃ at 99 eV and Li at 149 eV.

All of these elements allow us to affirm that the bright points (Figure 3, and also Figures 4A and 4B) correspond to copper oxide and that the shell all around these points is indeed silica.

So, in this example, we are preparing many core-shell nanoparticles.

Example 3.

In this example, nanoparticles heart-shell is prepared according to the invention in heart K ₂ CuFe (CN) 6 and shell silica, which are denoted by K ₂ CuFe (CN) ₆ @SiO _2.

These nanoparticles are prepared by observing the protocol described above with wa = 20, wb = 10 and wc = 15.

Figure 6 shows the core-shell nanoparticles with a copper ferrocyanide core and a silica shell obtained in this example.

These nanoparticles have the same type of bright spots but in fewer numbers than the “core” nanoparticles of copper oxide and silica shell of example 2, presented in FIG. 3, FIG. 4A, and FIG. 4B.

The sizes of the nanoparticles are homogeneous, they are indeed 22.9 nm +/- 3.2 nm.

Example 4.

In this example, core-shell nanoparticles according to the invention are prepared with a K2CuFe (CN) 6 core and a silica shell which are designated by K ₂ CuFe (CN) ₆ @SiO ₂ .

These nanoparticles are prepared by observing the protocol described above, but with wa equal to 10, wb equal to 5, and therefore wc equal to 7.5.

If we observe the macroscopic appearance of the copper ferrocyanide nanoparticles obtained at the end of step 4 of the protocol and of the nanoparticles with a core structure of copper ferrocyanide-silica shell obtained in this example, at the end of the protocol, we see that the powders of copper ferrocyanide nanoparticles are purple in color and that after the silica growth stage, these powders (nanoparticles with a copper ferrocyanide core-silica shell structure) become pale pink .

Figure 7 shows the core-shell nanoparticles with a copper ferrocyanide core and a silica shell obtained in this example with wc equal to 7.5.

These nanoparticles have the same type of bright spots but in fewer numbers than the “core” nanoparticles of copper oxide and silica shell (example 2), presented in FIG. 3, FIG. 4A and FIG. 4B.

The sizes of the nanoparticles are 15.1 nm +/- 3.4 nm.

An EELS spectrum was also produced on the nanoparticles prepared in this example and shown in Figure 7. This spectrum is represented in Figure 8 where it appears that the core of the nanoparticles contains Fe thanks to the electronic transitions L ₂ to 721 eV and L3 at 708 eV.

On this basis, we can say that the bright points in Figure 7 probably correspond to copper which is in excess compared to K4Fe (CN) 6 (cf. protocol point 4) and that the presence of iron, attested by the EELS spectrum of Figure 8 is a good indication of the presence of K ₂ CuFe (CN) 6 within the silica.

Figures 11 and 12 also show the core-shell nanoparticles with a copper ferrocyanide core and a silica shell obtained in this example with wc equal to 7.5.

This example shows that even by varying the amount of water in the system (w going from 15 in example 3 to 7.5 in this example), core-shell nanoparticles according to the invention are still obtained.

This is verified by carrying out different characterizations using techniques such as X-ray diffraction (XRD) (Figure 9) and infrared spectroscopy in ATR mode (“Attenuated Total Reflectance” in English) (Figure 10).

These characterizations are carried out on the copper ferrocyanide nanoparticles obtained at the end of step 4 of the protocol and on the nanoparticles with a core structure of copper ferrocyanide-silica shell obtained in this example, at the end of the protocol.

These characterizations make it possible to confirm that the copper ferrocyanide nanoparticles have been well synthesized, as attested by the different diffraction peaks (see indexing on the diffractogram using the pattern 01-075-0023: this corresponds to a diffractogram from the literature allowing us to identify the Bragg peaks).

More precisely, the reference diffractogram was calculated from the ICSD database using the software POWD-12 ++ (1997), and from the publication by Rigamonti R., Gazz. Chim. Ital., Volume 67, p. 137 (1937), as well as the vibration of elongation (vcïn) in the infrared spectrum which is present at 2100 cm ^-1 .

Note that ICSD designates the Inorganic Cristal Structure Database of the FIZ, Karlsruhe, Germany.

Note also that POWD-12 ++ is software for the analysis of X-ray diffraction.

Thus, it is a diffractogram calculated using the software and available in the ICSD database.

In addition, when we study the core-shell nanoparticles, which therefore contain silica, we note the presence of the amorphous silica bump for 20 = 25 ° in XRD as well as characteristic bands in infrared.

The vibration bands are all shown in Table I below.

Note that for the infrared spectrum of copper ferrocyanide nanoparticles alone, many bands are visible, no doubt due to the surfactant residues (AOT). All of these elements, characterizations, observations and analyzes allow us to conclude that the core nanoparticles of copper ferrocyanide and silica shell according to the invention have indeed been successfully prepared.

Wave number (cm ⁴ ) Attributions Yes ice 450 50-Si-0 590 vSi-O, SiO ₂ faults 790 VsSi-O, Si-O-Si (symmetrical) 955 v Si-O, Si-OH 1060 Vas Si-O-Si (asymmetric) 3660 vSÎO-H ABP 2100 vCeN Organic 2900-2980 vCH 1380-1400 6CH ₂ and CH ₃ Water 1600 δΗ-Ο-H bound water 3060-3580 vO-H

Table I.

Characteristic bands liable to appear in the infrared spectra relating to the various nanoparticles NPs synthesized in the examples, in particular nanoparticles according to the invention, prepared in example 4, and also particles of ferrocyanide alone and particles of silica alone (v : elongation, δ: deformation).

Thus, in FIG. 10, on spectrum B, corresponding to ferrocyanide alone, the presence of ABP and of organics is noted.

In FIG. 10, on spectrum A, corresponding to the core-shell nanoparticles NPs according to the invention, the presence of both silica, ABP and organics is noted.

Finally, on the spectra of the nanoparticles of Examples 1 and 2, we will find the bands corresponding to silica and of organics, while on the spectra of the nanoparticles of Examples 3 and 4, we will find both the bands corresponding to ΙΆΒΡ, with silica and organic.

In order to refine the composition of the core-shell nanoparticles, SEM-EDX analyzes were carried out on the core-shell nanoparticles prepared in Example 3 with wc = 15.

The EDX spectra, presented in Figures 13 and 14, show the presence of the right elements, Cu, Fe, K, C, N, Si and O in the proportions expected for this type of copper ferrocyanide nanoparticles (see Table III more low).

From these results, we were able to determine the formula of the synthesized copper ferrocyanide (example 3, wc = 15) is K i.6Cui.2Fe (CN) 6, and we could notice that we had a mixture of two types of cubic copper ferrocyanides, KzCuFe (CN) 6 and Cu2Fe (CN) 6 in 80/20 proportions.

These measurements also made it possible to estimate the proportions of transition metal ferrocyanides and of silica in the nanoparticles according to the invention while keeping in mind that these values can be distorted by matrix effects intrinsic to the measurement and nanoparticles. Thus, the CuABP @ SiO2 nanoparticles consist of 12% CuABP and 88% silica (Table IV).

Example 5.

In this example, in order to prove the effectiveness of core-shell nanoparticles with respect to the decontamination of aqueous effluents contaminated with radioactive Cs, tests, tests, sorption of Cs were carried out.

These tests are carried out with 5 mg of nanoparticles, and 10 mL of an aqueous solution containing the Cs ⁺ and Na ⁺ ions with a cesium concentration: [Cs] = 0.077 mmol / L, and a sodium concentration: [Na] = 0.751 mmol / L.

The nanoparticles are brought into contact with the aqueous solution for a total of 48 hours.

The concentrations of the Na-ι-, K +, and CS + ions are determined (if the measurement applies) by ion chromatography in the initial solution or stock solution and in the solution brought into contact with the nanoparticles, after a contact time of 24 hours and a contact time of 48 hours.

Different types of nanoparticles could be tested, namely:

core-shell nanoparticles according to the invention comprising a core based on copper ferrocyanide and a silica shell (these are the nanoparticles of Example 3, with wc = 15). These nanoparticles are designated CuABP @ SiO2. Nanoparticles contacted for 24 hours are designated CuABP @ SiO2-24h, and nanoparticles contacted for 48 hours are designated CuABP @ SiO2-48h.

“core” nanoparticles of copper oxide and silica shell SiO2 (these are core nanoparticles of copper oxide and silica shell of example 2 and not nanoparticles of example 1), as a reference. The nanoparticles contacted for 24 hours are designated SiO2-24h, and the nanoparticles contacted for 48 hours are designated SiO2-48h.

The results of the assays of the Na-ι-, K +, and CS + ions are collated in Table II below.

Samples Na (mmol / L) K (mmol / L) Cs (mmol / L) Stock solution 0.751 ± 0.001 n / A. 0.077 ± 0.001 CuABP @ SiO ₂ -24h 0.994 ± 0.003 0.124 ± 0.001 n / A. CuABP @ SiO ₂ -48h 1.004 ± 0.001 0.130 ± 0.001 n / A. SiO ₂ -24h 0.778 ± 0.001 n / A. 0.075 ± 0.001 SiO ₂ -48h 0.777 ± 0.003 n / A. 0.076 ± 0.001

Table II.

Determination of ions in solution (Na ⁺ , K ⁺ and Cs ⁺ ) by ion chromatography during the contacting of the nanoparticles with a solution containing the ions Cs ⁺ and Na ⁺ .

These results show that the core-shell nanoparticles based on copper ferrocyanide according to the invention completely capture the Cs contained in the starting solution by exchanging it with the potassium already present in the structure, and this after 24 hours of setting up. contact.

We can then calculate Q, the mass of Cs adsorbed (in mg) per g of core-shell nanoparticles. It is found that Qci which is the value of Q determined by ion chromatography is equal to 20.5 mg / g of nanoparticles.

We also note the increase in the amount of sodium in the solution in contact with the nanoparticles compared to the initial stock solution. This sodium probably comes from unmodified ΙΆ0Τ trapped in the nanoparticles and which passes into the solution in the presence of water.

Thus, several phenomena occur when the nanoparticles are brought into contact with the solution, in fact there is a passage of sodium into the solution by leaching, but also a passage of potassium into the solution by ion exchange with cesium.

These exchanges would not be possible without a porous structure, which therefore makes it possible to affirm that the core-shell nanoparticles according to the invention are porous, or more exactly that the shell of the nanoparticles according to the invention is porous.

In order to check whether the sorptions are due to the transition metal ferrocyanides, sorption tests are carried out, as already mentioned above with nanoparticles made of copper oxide core and silica shell S1O2 (these are nanoparticles made of copper oxide and silica shell of example 2 and not nanoparticles of example 1).

The results of the assays of the Na-ι-, K +, and CS + ions are also given in Table II above.

In this case, after 24 and 48 hours of bringing the nanoparticles of copper oxide core and silica shell into contact with the solution containing Cs, there is no decrease in the amount of Cs, proof that the silica does not absorb not this item of interest.

The differences between the two measurements made at 24h and 48h respectively may be due to the dosing method (these are fluctuations due to the measurement itself), or to the evaporation of the solution, which is certainly weak , but which nevertheless exists.

These tests therefore made it possible to demonstrate the effectiveness of the nanoparticles according to the invention for the decontamination in Cs of a solution.

Example 6.

In this example, the core-shell nanoparticles (nanoparticles synthesized in Example 3, wc = 15) are analyzed by Dispersive X-ray Energy Spectrometry (“Energy dispersive X-ray spectrometry” or “EDX” in English) before and after sorption of Cs.

The EDX spectra of the shell core nanoparticles according to the invention, with a KzCuFe (CN) 6 core and a shell in S1O2, before and after sorption of Cs are given in FIGS. 13 and 14. The nanoparticles before sorption of cesium are designated by K2CuFe (CN) 6 @ SiO2 or CuABP @ SiO2, and the nanoparticles after sorption of cesium are designated by K2CuFe (CN) 6 @ SiO2 + Cs or CuABP @ SiO2 + Cs.

Table III below gives the atomic percentage, obtained by EDX analysis of the elements Si, K, Fe, Cu, and Cs in the nanoparticles before sorption CuABP @ SiO2, and after sorption CuABP @ SiO2 + Cs, for the nanoparticles prepared in Example 3.

CuABP @ SiO2 CuABP @ SiO2 + Cs Element Atom. [%] Atom. [%] Yes 40.6 38.2 K 1.6 0.4 Fe 1 1 Cu 1.2 1.1 Cs 0 0.7

Table III.

Atomic percentage of the elements Si, K, Fe, Cu, Cs, for the nanoparticles prepared in Example 3 (before and after contacting with a solution of Cs).

Table IV below gives the atomic percentage of the elements CuHCF, SiO2, and Cs obtained by EDX analysis in the nanoparticles before sorption CuABP @ SiO2, and after sorption CuABP @ SiO2 + Cs, for the nanoparticles prepared in Example 3 .

CuABP @ SiO2 CuABP @ SiO2 + Cs Mass. [%] Mass. [%] CuHCF 12.6 11.1 SiO ₂ 87.4 85.4 Cs n / A. 3.5

Mass percentage of CuABP, S1O2 and Cs elements for the nanoparticles prepared in Example 3.

Table IV.

It is noted that the element Cs could not be detected by the analysis before sorption, but the analysis of the particles after sorption showed the presence of Cs up to 3.5% by mass.

We can therefore consider that the core-shell nanoparticles according to the invention are capable of adsorbing at least 35 mg of Cs / g of core-shell nanoparticles, namely Qedx = 35 mg of Cs / g, where Qedx is the value of Q determined. by X-ray Dispersive Energy Spectrometry.

It can be noted that a fairly large difference is obtained between the measurement made by ion chromatography and the analysis by EDX. These differences are probably due to the approximations inherent in EDX for such low elementary dosages (3.5% by mass for cesium). Thus, the values acquired by ion chromatography are more reliable than those from the EDX analysis with Qci = 20.5 mg / g.

Finally, it can be considered that the nanoparticles according to the invention are capable of exchanging at least 20.5 mg of Cs per g of nanoparticles with a core-shell structure according to the invention.

This sorption capacity value alone shows that the nanoparticles according to the invention have excellent cesium adsorption properties.

However, this value of the sorption capacity of the nanoparticles according to the invention is to be compared with the values of the sorption capacity given in the existing literature on this subject.

For example, Delchet et al. [4] have shown that mesoporous silicas or porous glass beads post-functionalized with ferrocyanides had sorption capacities of 17 mg / g and 5 mg / g, respectively, without competing ions.

Furthermore, Causse et al. [5], by synthesizing silica monoliths functionalized with a high level of copper ferrocyanide nanoparticles, found cesium sorption capacities of up to 10.6 mg / g.

This shows that the nanoparticles with a core-shell structure according to the invention have a cesium adsorption capacity which is greater, or even significantly greater, than the adsorption capacities of analogous materials of the prior art which are the subject of documents [4 ] and [5],

REFERENCES [1] WO-A1-2015 / 091677.

[2] Eastoe, J., et al., Variation of surfactant counterion and its effect on the structure and properties of Aerosol-OT-based water-in-oil microemulsions, Journal of the Chemical Society, Faraday Transactions, 1992, 88 ( 3), p. 461-471.

[3] Vaucher, S., et al., “Molecule-based Magnetic nanoparticles: Synthesis of Cobalt

Hexacyanoferrate, Cobalt Pentacyanonitrosylferrate and Chromium Hexacyanochromate Coordination Polymers in Water in OU Microemulsion ”, N a no Letters, 2002, 2 (3), p. 225-229.

[4] Delchet, C. et al., Extraction of radioactive cesium using innovative functionalized porous materials, RSC Advances, 2012, 2 (13): p. 5707-5716.

[5] Causse, J., et al., Facile one-pot synthesis of copper hexacyanoferrate nanoparticle functionalised silica monoliths for the selective entrapment of 137Cs, Journal of Materials Chemistry A, 2014, 2 (25): p. 9461-9464.

Claims (22)

1. Nanoparticles with a core-shell structure, in which: the core of each of said nanoparticles is constituted by a 5 nanoparticle in a metal hexacyanometallate or octacyanometallate, corresponding to the formula [Alk ⁺ x] M ^{n +} y [M '(CN) m] t ^z ·, where Alk ⁺ is a monovalent cation chosen from alkali metal cations and the ammonium cation NH4 ⁺ , x is 0, 1 or 2, M is a transition metal, n is 2 or 3, y is 1, 2 or 3, M 'is a transition metal, m is equal to 6 or 8, z is equal to 3 or 4, and t is equal to 1 or 2; 10 - the shell of said nanoparticles, which surrounds the heart, is made of at least one porous inorganic oxide. 2. Nanoparticles according to claim 1, in which the inorganic oxide of the shell is chosen from the oxides of at least one metal or metalloid, Such as Si, Ti, Zr, Th, Nb, Ta, V, W, Y, Ca, Mg and Al, and mixtures thereof; preferably, the inorganic oxide of the shell is silica. 3. Nanoparticles according to any one of the preceding claims, in which M ^{n +} is Fe ²⁺ , Ni ²⁺ , Fe ³⁺ , Co ²⁺ , Cu ²⁺ , or Zn ²⁺ . 4. Nanoparticles according to any one of the preceding claims, in which M 'is Fe ²⁺ or Fe ³⁺ or Co ³⁺ and m is 6; or M 'is Mo ⁵⁺ and m is 8. 5. Nanoparticles according to any one of the preceding claims, in which [M '(CN) m] ^z_ is [FefCNk] ³ ', [FefCNk] ^{4 5} ', [Co (CN) 6] ³ or [Mo (CN ) ₈ ] ³ -. 6. Nanoparticles according to any one of the preceding claims, in which the metal hexacyanometallate or octacyanometallate 30 corresponds to the formula K2M Fe (CN) 6, for example IÇCu Fe (CN) 6, IÇZnFefCNk, or K2C0 Fe (CN) 6. 7. Nanoparticles according to any one of the preceding claims, in which the metal hexacyanometallate or octacyanometallate nanoparticles have a sphere or spheroid shape. 8. Nanoparticles according to any one of the preceding claims, which have a sphere or spheroid shape. 9. Nanoparticles according to any one of the preceding claims, in which the metal hexacyanometallate or octacyanometallate nanoparticles have an average size, such as a diameter, of 2 to 20 nm, preferably 2 to 10 nm, preferably another 2 to 5 nm. 10. Nanoparticles according to any one of the preceding claims, in which the shell has a thickness of 2 to 100 nm, preferably from 5 to 20 nm. 11. Nanoparticles according to any one of the preceding claims, which have an average size, such as a diameter, from 4 to 120 nm, preferably from 4 to 50 nm, more preferably from 4 to 20 nm. 12. Method for preparing nanoparticles with a core-shell structure according to any one of claims 1 to 11, which comprises at least the following successive steps: a) a water-in-oil microemulsion C is prepared, formed of droplets of an aqueous phase constituted by a suspension of nanoparticles of [Alk ⁺ _x ] M ^{n +} y [M '(CN) m] t ^z , said droplets being dispersed in a continuous oily phase; b) adding a base to the microemulsion C obtained in step a) so that the pH of the aqueous phase of the water-in-oil microemulsion C is greater than or equal to 8, preferably is 8 to 10, provided that what, we get a microemulsion D; c) adding a precursor of the inorganic oxide to the microemulsion D obtained in step b), whereby a microemulsion E is obtained; d) maturation, mineralization of the microemulsion E obtained in step c) is carried out, whereby the porous inorganic oxide shell is formed around the nanoparticles of [Alk \] M ^{n +} _y [M '(CN) _m ] t ^z and the core-shell nanoparticles are formed; e) adding one or more organic solvent (s) to the mineralized microemulsion E obtained in step d), whereby the microemulsion E is broken; f) the nanoparticles with a shell-core structure are separated from the broken microemulsion E obtained in step e); g) washing the nanoparticles with a core-shell structure separated in step f). 13. The method of claim 12, wherein the microemulsion water in oil C, formed of droplets of an aqueous phase consisting of a suspension of nanoparticles of [Alk \] M ^{n +} _y [M '(CN) _m ] t ^z , said droplets being dispersed in a continuous oily phase is prepared by the following steps: al) reacting an anionic organic surfactant with cations M ^{n +} , whereby an anionic surfactant modified by the cations M ^{n +} is obtained; bl) a water-in-oil microemulsion A is prepared, stabilized by the organic surfactant, and formed of droplets of an aqueous phase containing [Alk ⁺ _X ] [M '(CN) m] t ^z ', for example kUFefCNk, dispersed in a continuous oily phase; cl) preparing a water-in-oil microemulsion B, stabilized by the modified organic surfactant prepared in step a1), and formed of droplets of an aqueous phase consisting of water, dispersed in a continuous oily phase; dl) mixing the microemulsion A and the microemulsion B, whereby the water-in-oil microemulsion C is obtained, formed of droplets of an aqueous phase constituted by a suspension of nanoparticles of [Alk ⁺ x] M ^{n +} y [ M '(CN) m] t ^z , said droplets being dispersed in a continuous oily phase. 14. A metal cation exchanger material comprising nanoparticles with a core-shell structure according to any one of claims 1 to 11, and a solid or liquid matrix. 15. Solid metal cation exchange material according to claim 14, which is in the form of a cellular monolith constituted by a matrix of an inorganic oxide with hierarchical and open porosity comprising macropores, mesopores, and micropores, said said macropores, mesopores and micropores being interconnected, and the nanoparticles with a core-shell structure being distributed in said porosity. 16. Method for extracting at least one metal cation from a liquid medium containing it, in which said liquid medium is brought into contact with nanoparticles having a shell-core structure according to any one of claims 1 to 11 and / or the metal cation exchange material according to any one of claims 14 and 15. 17. The method of claim 16, wherein said liquid medium is an aqueous liquid medium, such as an aqueous solution, for example sea water or brackish water. 18. Method according to any one of claims 16 to 17, wherein said liquid medium is a liquid medium containing radionuclides, in particular the liquid medium is chosen from liquids and effluents from the nuclear industry, nuclear installations and activities using radionuclides. 19. Method according to any one of claims 16 to 18, in which the liquid medium is an aqueous solution containing, in addition to said metal cation, salts such as NaCl, for example at a concentration greater than 30 g / L. 20. A method according to any one of claims 16 to 19, wherein said metal cation is present at a concentration of 0.1 picogram at 100 mg / L, preferably 0.1 picogram at 10 mg / L. 5 21. Method according to any one of claims 16 to 20, in which the metal cation is a cation of an element chosen from Cs, Co, Ag, Ru, Fe and Tl and the isotopes, in particular radioactive thereof, preferably, the cation is a cation of ¹³⁴ Cs, or of ¹³⁷ Cs. 10 22. Method according to any one of claims 16 to 21, in which the liquid medium is an aqueous solution, containing as metal cation a cation of ¹³⁴ Cs, or ¹³⁷ Cs, and containing, in addition, salts such than NaCI, for example at a concentration greater than 30 g / L. 1/7 S.61702 III 2d || g | B H III Μ »j MM I rnSmi · WbîwBk