Ion-selective composite membrane

Abstract

The present invention relates to an ion-selective composite membrane having a thickness between 4 μm and 100 μm, comprising at least one inner layer (2) arranged between two outer layers (1, 3), in which: - the outer layers (1, 3) are each made of a first material comprising a network of nanofibers and / or crosslinked microfibers and pores with a diameter between 10 nm and 10 μm; - the inner layer (2) is made of a second material comprising nanoparticles functionalized on their surface with charged groups and / or groups that become charged in the presence of water and having pores with a diameter between 1 and 100 nm.

Description

[Technical Field]

[0001] Ion-selective conductive membranes play a key role in many industrial processes. [Background technology]

[0002] Many of these methods are in fact based on the ion-selective conduction, depending on the sign of their charge, between two volumes separated by a membrane under the action of a stress on either side of this interface, for example under the action of a pressure gradient, a potential gradient or a concentration gradient.

[0003] The membranes currently most commonly used, which have ion-selective conductivity according to the sign of their charge, are known as ion exchange membranes (IEM). A distinction is made between cation exchange membranes (CEM), which allow the circulation of cations, and anion exchange membranes (AEM), which allow the circulation of anions. These IEMs are prepared from ion exchange resin particles dispersed in an inert polymer binder (homogeneous IEM), or by introducing functional groups directly into the structure of the polymer that makes up the membrane (heterogeneous IEM).

[0004] IEMs are used, for example, in the field of water treatment to extract undesirable substances from the fluid to be treated, for example to desalinate brackish water or seawater. + ions and Cl - The extraction is produced by the migration of ions through alternating membranes that allow selective passage of anions (AEM) or cations (CEM) under the action of an electric field. At the end of the treatment, fresh water is recovered on the one hand and brine on the other hand.

[0005] Membranes with selective conductivity for ions of these charge signs are also used in methods for storing electrical energy in the form of electrolytic hydrogen or, conversely, for using this hydrogen as a source of electrical energy (hydrogen fuel cells). These methods involve an electrochemical reaction, namely, the electrolysis of water. Water electrolysis occurs in an electrolytic cell, a device containing a series of electrolytic cells arranged side by side and connected to a source of electrical energy via electrodes. Each electrolytic cell is typically formed by contacting two metal plates, called electrodes, with a solid or liquid electrolytic medium. In the case of a liquid electrolytic medium, the electrolytic cell contains electrodes immersed in an aqueous solution containing both water and the electrolyte necessary for the reaction, soluble chemical compounds, and a current conductor, e.g., potassium carbonate (KOH) (alkaline electrolysis) or sulfuric acid (H2SO4) (acid electrolysis). The two electrodes are connected to a generator, where the difference in their potential is increased. When the latter exceeds a certain threshold, the passage of current through the circuit is observed, and molecular oxygen (O2) is formed on the anode (the electrode connected to the positive pole of the generator) and molecular hydrogen (H2) is formed on the cathode (the electrode connected to the negative pole of the generator). For example, in the case of acid hydrolysis, at the anode, water molecules are converted according to the equation H2O → 2H + +2e - At the cathode, protons are released according to the equation H + +1e - → 1 / 2H2, and a flux of hydronium ions is created between the anode and cathode. To prevent the spontaneous recombination of H2 and O2 into explosive gases, a separator membrane must be placed between the electrodes to allow the passage of protons but not H2 and O2. More recently, proton exchange membrane (PEM) electrolysis has used cells in which the electrolyte medium is a solid polymer electrolyte in the form of a cation exchange membrane. In these cells, a porous metal electrode (Ep) is in direct contact with the ECM (M), with Ep-M-Ep assemblies on either side in contact with the aqueous solution. In these cells, the membrane material acts as both the separator membrane and the solid electrolyte.

[0006] However, in general, ionic currents are weakly conducted by IEMs, with significant ohmic contributions in electrodialysis and electrodialysis reverse systems, which limits the current densities that can be applied to the electrodes in most cases to a few hundred mA.cm. -2 Therefore, the operating range of the technology using IEMs is limited. Furthermore, the preparation of these membranes is very expensive, and for this reason, the majority of the maintenance investment in membrane-based processes is dedicated to replenishing these membranes.

[0007] IEMs can also be used for the generation of electricity from electrolyte gradients, particularly salinity gradients.

[0008] Thus, the reverse electrodialysis (RED) process is based on the use of membranes whose fundamental property is the selective transport of ions according to the sign of their charge. RED devices typically consist of alternating AEMs and CEMs separated by spacer membranes that form channels that allow fluid flow. Alternating circulation of salt water and fresh water through these cells makes it possible to establish an ion flux in each of the IEMs of the device. At the end of this stack of membranes, electrodes collect the current generated by the total ion flux.

[0009] One of the problems encountered with devices for generating electricity from salinity gradients, such as current RED devices, is that the power generation capacity of these devices is very low, because the power generated per unit area of ​​the membrane (i.e., membrane power) by current IEM is only a few W / m 2 This is due to the fact that it is a membrane.

[0010] An approach to this problem is presented in the international application WO2014 / 060690 published on April 24, 2014. In this approach, nanoporous membranes are proposed, the inner surfaces of whose pores are covered with boron nitride or more generally with a mixture of elements such as boron, carbon and nitrogen. These nanoporous membranes utilize the diffusion-percolation phenomenon within the pores, and can achieve a high energy density of kW / m 2 More recently, the inner surfaces of the pores have been coated with titanium oxide, generating a membrane power of 5 kW / m 2Nanoporous membranes that allow membrane powers of this order to be reached are provided in the international application WO2017 / 037213 published on March 9, 2017. However, this approach involves the use of membranes based on boron nitride or titanium oxide, the preparation of which on a larger scale than laboratory scale is complex and prohibitively expensive, given the materials required. Furthermore, the materials used in these membranes are environmentally hazardous and pose a risk if released into the environment. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] WO2014 / 060690 issue [Patent Document 2] WO2017 / 037213 issue Summary of the Invention [Problem to be solved by the invention]

[0012] To date, there are no membranes with these ion-selective conductivities according to the sign of charge that are simple and economical to prepare, generate high membrane power under the action of a salinity gradient, while posing limited environmental hazards. [Means for solving the problem]

[0013] It is therefore an object of the present invention to provide membranes with ion-selective conductivities according to the sign of their charge that are economical and easy to produce while being capable of generating high membrane power when integrated into devices for generating electricity from electrolyte gradients, in particular salinity gradients, or in the reverse devices for water purification or desalination.

[0014] Another object of the present invention is to provide membranes with ion-selective conductivity according to the sign of these charges that are prepared from materials that pose little or no environmental hazard.

[0015] These objectives are achieved by the invention described below. DETAILED DESCRIPTION OF THE INVENTION

[0016] composite membrane The first subject of the present invention is an ion-selective conductive composite membrane having a thickness between 4 μm and 100 μm, comprising at least one inner layer (2) arranged between two outer layers (1), (3), - the outer layers (1, 3) are each formed from a first material comprising a network of crosslinked nanofibers and / or microfibers and pores with a diameter between 10 nm and 10 μm, an ion-selective conducting composite membrane, the inner layer (2) being formed from a second material containing nanoparticles whose surface is functionalized with charged groups and / or groups that become charged in the presence of water, and having pores with a diameter between 1 and 100 nm;

[0017] The inventors have unexpectedly found that the composite membrane of the present invention can withstand a current of several hundred W / m under the action of a salinity gradient. 2 (film) of the order of magnitude, preferably at least 300 W / m 2 , more preferably at least 500 W / m 2 It was found that the membrane generates very high power.

[0018] Without wishing to be bound by any particular theory, the inventors believe that this very high membrane power is determined by the surface charge of the materials used in the layers of the membrane of the present invention, together with the outer layers (1, 3) and inner layer (2) and the porosity of the composite membrane.

[0019] In particular, the inventors further show that this combination of porosity and surface charge confers nanofluidic properties to the composite membrane and influences the selective passage of ions through the membrane, but by a specific and unexpected mechanism, which would not have been observed if the material comprising the membrane had greater porosity.

[0020] Composite membrane structure The thickness of the composite membrane is advantageously between 4 μm and 75 μm.

[0021] The thickness of each of the outer layers (1, 3) is advantageously between 2 μm and 45 μm, preferably between 2 μm and 30 μm, more preferably between 2 μm and 25 μm. The outer layers advantageously have the same thickness.

[0022] In contrast, the thickness of the inner layer (2) is preferably between 10 nm and 10 μm, more advantageously between 10 nm and 2 μm, preferably between 10 nm and 1 μm, preferably between 10 nm and 800 nm, preferably between 10 nm and 400 nm, more preferably between 200 nm and 500 nm.

[0023] Preferably, the thickness of each of the outer layers (1, 3) is advantageously between 2 μm and 45 μm, and the thickness of the inner layer (2) is between 10 nm and 10 μm.

[0024] According to the inventors, the extremely small thickness of the inner layer allows for good permeability while still obtaining high ion-selective conductivity.

[0025] In the present invention, the thickness of the composite membrane and the thickness of the different layers are measured by scanning electron microscopy of cross-sections of the dry membrane.

[0026] The composite membrane preferably comprises less than 10 wt. % of the second material relative to the weight of the first material, preferably between 2 wt. % and 8 wt. % of the second material relative to the weight of the first material, more preferably between 3 wt. % and 5 wt. % of the second material relative to the weight of the first material.

[0027] The surface charge density of the inner walls of the pores of the composite membrane is advantageously between 0.001 and 3 C / m 2 Between 0.1 and 1 C / m 2 It is between.

[0028] The surface charge density of the composite film is measured dosimetry.

[0029] Inner layer (2) Second ingredient According to the present invention, the term "nanoparticle" means a three-dimensional object having at least one external dimension lying on the nanometer scale (ie at least one dimension ranging between 1 and 100 nm).

[0030] The second material advantageously comprises nanoparticles in the form of individual nanoparticles, ie not agglomerated, or in other words covalently bonded to one another.

[0031] The second material advantageously comprises at least 50% by weight nanoparticles, at least 95% by weight nanoparticles, more preferably at least 99% by weight nanoparticles, relative to the weight of the second material.

[0032] Advantageously, the nanoparticles are not in the form of nanotubes.

[0033] The nanoparticles are preferably lamellar nanoparticles.

[0034] According to the present invention, the term "lamellar nanoparticles" refers to nanoparticles comprising atoms in the form of a monolayer of atoms that are covalently bonded together. Lamellar nanoparticles can consist of a single monolayer of atoms (2D materials) or a stack of 2 to 5 monolayers of atoms that are held together by weak bonds, e.g., van der Waals forces.

[0035] In other words, a lamellar nanoparticle is a three-dimensional object with a first external dimension on the nanometer scale and two other dimensions significantly larger than the first, specifically varying between the nanometer and micrometer scales.

[0036] The lamellar nanoparticles preferably have a median diameter (also designated by the acronym "D50") comprised between 5 and 50 μm, preferably between 10 and 20 μm, more preferably 15 μm.

[0037] D50 means that 50% by weight of the particles have a smaller size.

[0038] According to the present invention, the terms "monolayer," "bilayer," and "few-layer" in reference to lamellar nanoparticles refer to lamellar nanoparticles consisting of a monolayer of atoms, two monolayers of atoms, and 3-5 monolayers of atoms, respectively. Bilayer and few-layer lamellar nanoparticles are typically stabilized by weak interactions between the monolayers of atoms, e.g., van der Waals interactions.

[0039] The lamellar nanoparticles are preferably lamellar nanoparticles of metal oxides, in particular lamellar nanoparticles of SnO2 or TiO2, lamellar nanoparticles of transition metal dichalcogenides, for example lamellar nanoparticles of molybdenum disulfide MoS2, lamellar nanoparticles of carbon, or mixtures thereof.

[0040] The lamellar carbon nanoparticles are preferably lamellar nanoparticles of single-layer graphene, lamellar nanoparticles of two-layer graphene, lamellar nanoparticles of few-layer graphene or mixtures thereof.

[0041] According to the present invention, the term "monolayer graphene" refers to a two-dimensional crystalline material consisting of a specific allotropic form of carbon, which can be represented as a flat honeycomb. More specifically, monolayer graphene is a material consisting of a single sp 2 It is a sheet of hybridized carbon atoms in a plane, and therefore can be described as a monolayer.

[0042] According to the present invention, the term "bilayer graphene (or BLG)" refers to a material consisting of a stack of two monolayers of graphene stabilized by van der Waals interactions between the two monolayers of graphene. BLG can be obtained by exfoliation of graphite or by chemical vapor deposition (CVD).

[0043] According to the present invention, the term "few-layer graphene (or FLG)" means a material consisting of a stack of 3 to 5 sheets of graphene stabilized by van der Waals type interactions between the different graphene planes.

[0044] Single-layer graphene lamellar nanoparticles are preferred.

[0045] According to a preferred embodiment, the second material advantageously comprises at least 50% by weight of monolayer graphene, more preferably at least 95% by weight of monolayer graphene. The lamellar monolayer graphene nanoparticles preferably have a median diameter (also designated by the acronym "D50") of between 5 and 50 μm, preferably between 10 and 20 μm, more preferably 15 μm.

[0046] The lamellar nanoparticles of molybdenum disulfide are preferably single-layered lamellar nanoparticles of molybdenum disulfide, double-layered lamellar nanoparticles of molybdenum disulfide, few-layered lamellar nanoparticles of molybdenum disulfide or mixtures thereof.

[0047] Depending on the sign of these charges, the charged groups or groups that become charged in the presence of water will impart a negative or positive surface charge on the inner layer (2) of the composite membrane when placed in the presence of water.

[0048] Any charged group known to those skilled in the art or a group that becomes charged in the presence of water and that allows an increase in the surface charge of the graphene particles can be used in the context of the present invention.

[0049] In one embodiment, the nanoparticles are surface functionalized with negatively charged groups and / or groups that become negatively charged in the presence of water.

[0050] Negatively charged groups and / or groups that become negatively charged in the presence of water include epoxide groups, hydroxyl groups, carbonyl groups, carboxyl groups, sulfonate groups -SO3 - , carboxyalkyl group R-CO2 - (R is C1-C4 alkyl, preferably C1 alkyl), an aminodiacetate group -N(CH2CO2 - )2, phosphonate group PO3 2- Amidoxime group -C(=NH2)(NOH), aminophosphonate group -CH2-NH-CH2-PO3 2- , a thiol group -SH, and mixtures thereof.

[0051] Preferably, the nanoparticles whose surfaces are functionalized with negatively charged groups or groups that become negatively charged in the presence of water are lamellar nanoparticles of graphene oxide (or GO).

[0052] The lamellar graphene oxide nanoparticles have negatively charged groups or groups that become negatively charged in the presence of water, which groups are advantageously selected from epoxide groups, hydroxyl groups, carbonyl groups, carboxyl groups, and mixtures thereof.

[0053] In one embodiment, the nanoparticles are surface functionalized with positively charged groups and / or groups that become positively charged in the presence of water.

[0054] Advantageously, the positively charged groups and / or groups that become positively charged in the presence of water are quaternary ammonium groups -N(R)3 + (wherein R is a C1-C4 alkyl), a tertiary ammonium group -N(H)R)2 + (R is a C1-C4 alkyl, preferably a C1 alkyl), a dimethylhydroxyethylammonium group -N(C2H4OH)CH3)2 + and mixtures thereof.

[0055] Outer layer (1, 3) First ingredient According to the present invention, the expression "nanofiber" refers to a cellulose-based three-dimensional object having two of its three external dimensions in the nanometer scale (i.e., two of the three dimensions in the range of 1 to 100 nm) and a third external dimension that is significantly larger than the other two, but not necessarily in the nanometer scale.

[0056] The nanofibers thus have a diameter in the range of 1 to 100 nm, preferably in the range of 1 to 70 nm, more preferably in the range of 4 to 30 nm, in particular in the range of 4 to 20 nm, and their length is advantageously between 0.5 and 100 μm, in particular between 0.5 and 50 μm, for example between 0.5 and 10 μm, for example further between 0.5 and 2 μm.

[0057] According to the present invention, the expression "microfiber" means a three-dimensional object having two of its three external dimensions in the micrometer scale (i.e., two of the three dimensions in the range of 0.1 to 10 μm) and having a third external dimension significantly larger than the other two dimensions.

[0058] Thus, the microfibers have a diameter in the range of 0.1 μm to 10 μm, advantageously in the range of 0.1 μm to 5 μm, even more advantageously in the range of 0.1 μm to 2 μm, in particular in the range of 0.1 μm to 1 μm, 0.1 μm to 7 μm, or 0.1 μm to 0.2 μm.

[0059] Furthermore, their length is advantageously between 0.5 μm and 100 μm, in particular between 1 μm and 50 μm, for example between 1 μm and 10 μm, for example further between 1 μm and 5 μm.

[0060] The nanofibers and / or microfibers advantageously have a shape factor of greater than 10, preferably greater than 100.

[0061] According to the present invention, the expression "shape factor" in relation to nanofibers and / or microfibers means the ratio of their length L to their diameter d (L / d).

[0062] The diameter of the nanofibers and / or microfibers can be measured by TEM or SEM.

[0063] According to the present invention, the term "crosslinked" in reference to nanofibers and / or microfibers means that the fibers are linked together by covalent chemical bonds (sometimes called "bridges") to form a three-dimensional network, in other words, they are not merely aggregated or self-assembled through weak bonds.

[0064] The first material plays a structuring role in the composite membrane, in particular in the sense that it makes it possible to maintain the functionalized nanoparticles described above in the form of a second layer (2) arranged between the outer layers (1, 3).

[0065] Furthermore, the first material of the outer layers (1, 3) ensures the integrity of the inner layer (2), especially during its use, when the latter is subjected to stresses such as pressure gradients on either side of the membrane.

[0066] The nanofibers and / or microfibers advantageously carry charged groups or groups that become charged in the presence of water.

[0067] In a first embodiment, the charged groups and / or groups that become charged in the presence of water in the outer layer (1) have the opposite sign to the charged groups and / or groups that become charged in the presence of water in the outer layer (3). In this embodiment, the composite membrane is a bipolar composite membrane.

[0068] In a second embodiment, the charged groups and / or groups that become charged in the presence of water of the two outer layers (1, 3) have the same sign, advantageously the same sign as the charged groups or groups that become charged in the presence of water of the functionalized nanoparticles described above.

[0069] This has the advantage of increasing the overall surface charge of the composite membrane of the present invention.

[0070] According to the inventors, the presence of these charged groups with the same sign in the inner (2) and outer (1, 3) layers of the composite membrane, or groups that become charged in the presence of water, makes it possible to obtain a synergistic effect, i.e., an unexpected improvement in the ion-selective conductance through the composite membrane.

[0071] Thus, in this embodiment, the first material plays a role in the structure of the composite membrane and its ability to ensure ion-selective conductivity.

[0072] Furthermore, the covalent chemical bonds involved in cross-linking the nanofibers and / or microfibers can also carry charged groups and / or groups that become charged in the presence of water, such as when the cross-linking agent used is citric acid, in which case the cross-linking chemical bonds play a role in both the structure and surface charge of the nanoporous material.

[0073] In one embodiment, the nanofibers and / or microfibers are comprised of an electrically conductive material, such as activated carbon, as described below.

[0074] In this embodiment, the outer layers (1, 3) are capable of conducting electrons and therefore act as capacitive electrodes when the composite membrane is introduced into membrane electrolysis or reverse electrolysis processes, preferably electrodialysis or reverse electrodialysis processes. In other words, the outer layers conduct the current necessary to carry out the electrolysis or electrodialysis reactions, or collect the current generated by the electrolysis or reverse electrodialysis reactions.

[0075] According to this embodiment, when the composite membrane is introduced into an electrodialysis reverse process, fluid can flow through the porosity of the outer layers (1, 3), and the electrical energy generated by electrodialysis reverse is directly collected by the nanofibers and / or microfibers of the outer layers (1, 3).

[0076] Thus, the composite membranes according to this embodiment allow for the fabrication of electrodialysis reversal devices without the need to use spacer devices to form passageways that allow fluid to flow between membranes, as is the case with the RED-type devices presented above.

[0077] This has the advantage of greatly reducing the resistance ("bulk") associated with the spacing between membranes, commonly referred to as bulk resistance, thus resulting in a system that generates higher membrane power.

[0078] organic matter The first material of the outer layers (1, 3) advantageously comprises nanofibers and / or microfibers of organic material.

[0079] According to the present invention, organic substances are materials that essentially contain carbon, oxygen and hydrogen.

[0080] The organic material consists essentially of carbon, oxygen and hydrogen, i.e., the organic material consists of at least 90 mole % carbon, oxygen and hydrogen, preferably at least 95 mole % carbon, oxygen and hydrogen, more preferably at least 97 mole % carbon, oxygen and hydrogen.

[0081] According to a preferred embodiment, the organic material comprises 70-100 mol % carbon, 0-30 mol % hydrogen and 0-15 mol % oxygen.

[0082] The organic material also advantageously does not contain fluorine, an element commonly found in ion exchange membranes (IEMs).

[0083] The organic material is advantageously chosen from cellulose, activated carbon, or mixtures thereof.

[0084] cellulose matrix In one embodiment, the first material is a cellulose matrix comprising crosslinked cellulose nanofibers and / or microfibers.

[0085] According to the present invention, the term "crosslinked" in reference to cellulose nanofibers and / or microfibers means that the fibers are connected to each other with covalent chemical bonds (sometimes called "bridges") to form a three-dimensional network in the cellulose matrix form, in other words, they are not merely aggregated or self-assembled through weak bonds.

[0086] The network of cellulose nanofibers and / or microfibers advantageously has pores with diameters between 10 and 1000 nm.

[0087] The cellulose nanofibers advantageously have a diameter in the range of 1 to 100 nm, preferably in the range of 1 to 70 nm, more preferably in the range of 4 to 30 nm, in particular in the range of 4 to 20 nm, and their length is advantageously between 0.5 and 100 μm, in particular between 0.5 and 50 μm, for example between 0.5 and 10 μm, for example further between 0.5 and 2 μm.

[0088] The cellulose microfibers advantageously have a diameter in the range of 100 nm to 1000 nm, preferably in the range of 100 nm to 700 nm, more preferably in the range of 100 to 200 nm, and their length is advantageously between 0.5 μm and 100 μm, in particular between 1 μm and 50 μm, for example between 1 μm and 10 μm, and even more preferably between 1 μm and 5 μm.

[0089] The cellulose nanofibers and / or microfibers advantageously have a shape factor of greater than 30, preferably greater than 100.

[0090] Advantageously, the cellulose matrix comprises at least 90% by weight of cellulose nanofibers and / or microfibers, at least 95% by weight of cellulose nanofibers and / or microfibers, more preferably even at least 99% by weight of nanofibers and / or cellulose microfibers, relative to the weight of the cellulose matrix.

[0091] Cellulose nanofibers and / or microfibers can be obtained by techniques known to those skilled in the art, in particular by mechanical, enzymatic or chemical treatment of lignocellulosic materials of natural origin, such as wood.

[0092] In the case of wood, these treatments have the specific effect of separating cellulose from other wood constituents, such as lignin and hemicellulose. To this end, natural cellulose fibers are pre- or post-treated chemically, especially enzymatically, and / or mechanically to initiate structural disruption before mechanical treatment in a homogenizer. It is known that the size and especially the diameter of the cellulose fibers of such materials can be modulated depending on the treatments applied to the natural cellulose source.

[0093] Thus, cellulose nanofibers and / or microfibers can be obtained by mechanical treatment of wood fibers, which provides sufficient mechanical energy to burst the fibers of native cellulose by at least partially breaking the hydrogen bonds that hold the microfibrils together. Mechanical treatment is often followed by a chemical or enzymatic treatment step. For example, this treatment step can be an oxidation treatment, particularly an oxidation treatment using an oxidizing agent such as TEMPO (2,2,6,6-tetramethylpiperidin-1-yl)oxy). The resulting product is often referred to in the literature as "nanofibrillated cellulose" (abbreviated as "NFC"), "cellulose nanofiber" (abbreviated as "CNF"), or "microfibrillated cellulose" (abbreviated as "MFC").

[0094] Generally, MFC materials are prepared from mechanical and / or chemical processes on a smaller scale than those used to obtain NFC, and thus MFC has fibers with larger diameters than those typically observed in NFC. However, there are no clear definitions of MFC and NFC / CNF, and therefore these terms are often used interchangeably in the literature.

[0095] The cellulose nanofibers and / or microfibers are preferably nanocellulose nanofibers and / or microfibers.

[0096] Cellulose nanofibers and / or microfibers may contain impurities from their preparation process, which may in particular be hemicellulose or lignin.

[0097] Thus, the cellulose matrix may in particular comprise at most 5% by weight hemicellulose, more preferably at most 3% by weight hemicellulose, or else at most 1% by weight hemicellulose.

[0098] The cellulose matrix may in particular comprise up to 5% by weight of lignin, more preferably up to 3% by weight of lignin, otherwise up to 1% by weight of lignin.

[0099] Due to the fact that cellulose monomers naturally carry alcohol groups at their C2, C3 or C6 carbon atoms, the cellulose nanofibers and / or microfibers of the present invention inherently carry a negative surface charge.

[0100] In one embodiment, the intrinsic negative surface charge of the cellulose nanofibers and / or microfibers of the present invention can be increased by functionalizing them with negatively charged groups and / or groups that become negatively charged in the presence of water. This embodiment is particularly advantageous when the charged groups and / or groups that become negatively charged in the presence of water of the functionalized nanoparticles of the second layer (2) have a negative sign. In fact, this has the advantage of increasing the surface charge of the entire composite membrane of the present invention.

[0101] The charged groups carried by the microfibers and / or nanofibers and / or groups that become charged in the presence of water are advantageously chemically bound in a covalent manner to the surface of said cellulose microfibers and / or nanofibers.

[0102] Any charged group known to those skilled in the art that allows an increase in the charge density of the microfibers and / or cellulose nanofibers of the present invention and / or groups of the latter that become charged in the presence of water can be used within the scope of the present invention.

[0103] Advantageously, the negatively charged groups and / or groups that become negatively charged in the presence of water carried by the cellulose nanofibers and / or microfibers are sulfonate groups -SO3 - , carboxyl group -CO2 - , carboxyalkyl group R-CO2 - (R is C1-C4 alkyl, preferably C1 alkyl), an aminodiacetate group -N(CH2CO2 - )2, phosphonate group PO3 2- Amidoxime group -C(=NH2)(NOH), aminophosphonate group -CH2-NH-CH2-PO3 2- , a thiol group -SH, and mixtures thereof.

[0104] Carboxyl group - CO2 - and carboxyalkyl groups R-CO2 - (R is C1 to C4 alkyl, preferably C1 alkyl).

[0105] Therefore, -CO2 - Cellulose nanofibers and / or microfibers bearing carboxyl groups (i.e., oxidized cellulose nanofibers and / or microfibers) can be obtained, for example, by oxidation of cellulose nanofibers and / or microfibers, for example, by TEMPO oxidation, where oxidation occurs preferentially on the primary alcohol groups carried by the C6 carbon atoms of the cellulose nanofiber and / or microfiber monomers.

[0106] Carboxyalkylate group R-CO2 - Cellulose nanofibers and / or microfibers bearing the formula (i.e., carboxyl-alkylated cellulose nanofibers and / or microfibers) can be obtained, for example, by etherification of cellulose nanofibers and / or microfibers. The etherification occurs preferentially on alcohol groups carried by the C2, C3, or C6 carbon atoms of the monomers of the cellulose nanofibers and / or microfibers.

[0107] In another embodiment, the intrinsic negative surface charge of the cellulose nanofibers and / or microfibers of the present invention can be reversed by functionalizing them with positively charged groups and / or groups that become charged in the presence of water.

[0108] This embodiment is preferred if the charged groups of the functionalized nanoparticles of the second layer (2) and / or the groups that become charged in the presence of water have a positive sign.

[0109] Any charged group and / or group that becomes charged in the presence of water and that is known to those skilled in the art and that makes it possible to impart a positive surface charge onto the cellulose nanofibers and / or microfibers can be used in the context of the present invention.

[0110] Advantageously, the positively charged groups and / or groups that become positively charged in the presence of negatively charged water are quaternary ammonium groups -N(R)3 + (wherein R is a C1-C4 alkyl), a tertiary ammonium group -N(H)R)2 + (R is a C1-C4 alkyl, preferably a C1 alkyl), a dimethylhydroxyethylammonium group -N(C2H4OH)CH3)2 + and mixtures thereof.

[0111] Quaternary ammonium groups are preferred.

[0112] In certain embodiments, the nanofibers and / or microfibers of the outer layers (1, 3) advantageously carry charged groups or groups that become charged in the presence of water, and the charged groups and / or groups that become charged in the presence of water from the outer layer (1) have the opposite sign to the charged groups and / or groups that become charged in the presence of water from the other outer layer (3). In this embodiment, the composite membrane is a bipolar composite membrane.

[0113] activated carbon material In one embodiment, the first material is an activated carbon felt comprising crosslinked activated carbon nanofibers and / or microfibers.

[0114] According to the present invention, the term "crosslinked" in reference to activated carbon nanofibers and / or microfibers means that the fibers are connected to one another by covalent chemical bonds (sometimes called "bridges") to form a three-dimensional network in the form of an activated carbon felt. In other words, they are not merely aggregated or self-assembled through weak bonds.

[0115] The activated carbon felt advantageously has a thickness between 5 and 60 μm, preferably between 5 and 50 μm, more preferably between 5 and 45 μm.

[0116] The pores of the activated carbon felt advantageously have a diameter between 1 and 10 μm.

[0117] The activated carbon microfibers advantageously have a diameter in the range of 0.1 to 10 μm, preferably in the range of 1 to 10 μm, more preferably in the range of 2 to 10 μm, and their length is advantageously between 10 and 500 μm, in particular between 20 and 400 μm, for example between 20 and 300 μm, and even for example between 1 and 200 μm.

[0118] The activated carbon felt preferably comprises activated carbon microfibers.

[0119] The activated carbon nanofibers and / or microfibers advantageously have a shape factor of greater than 10, preferably greater than 50.

[0120] Advantageously, the activated carbon felt comprises at least 90% by weight of activated carbon nanofibers and / or microfibers, at least 95% by weight of activated carbon nanofibers and / or microfibers, more preferably even at least 99% by weight of activated carbon nanofibers and / or microfibers, based on the weight of the activated carbon felt.

[0121] Activated carbon nanofibers and / or microfibers can be obtained by techniques known to those skilled in the art, in particular by partial combustion and pyrolysis of fibrous carbon precursors.

[0122] They are usually obtained by a method that consists in carbonizing fibers of organic resins (wood, fruit, stone, nutshells) or mineral (peat, coal, lignite) carbon precursors and then activating them using an activator. The carbon atoms then appear in the form of a plane of randomly assembled aromatic rings in a shape comparable to that of crumpled paper.

[0123] The activated carbon nanofibers and / or microfibers consist essentially of carbon, i.e., they consist of at least 60 mol% carbon, preferably at least 70 mol% carbon, and more preferably at least 80 mol% carbon, with the remainder being elements such as oxygen and hydrogen.

[0124] According to a preferred embodiment, the activated carbon nanofibers and / or microfibers contain 60-100 mol % carbon, 0-30 mol % hydrogen and 0-15 mol % oxygen.

[0125] Furthermore, activated carbon nanofibers and / or microfibers inherently carry a negative surface charge due to the fact that the ends of the polycyclic aromatic units that make up activated carbon carry oxygen and hydrogen atoms in the form of hydroxyls, carboxylic acids, lactones, phenols, chromenes, and pyrones.

[0126] The activated carbon nanofibers and / or microfibers conduct electricity.

[0127] method A second object of the present invention is a method for producing a composite membrane according to the first object of the present invention, comprising the steps of: i) filtering a solution containing nanofibers and / or microfibers on a filtering support to form a first inner layer (1) containing nanofibers and / or microfibers; ii) filtering a solution of nanoparticles whose surface is functionalized with charged groups and / or groups that become charged in the presence of water onto the first layer (1) obtained at the end of step i) to form an inner layer (2) on said first outer layer (1); iii) filtering the solution of nanofibers and / or microfibers to form a second outer layer (3) comprising nanofibers and / or microfibers on the inner layer (2) obtained at the end of step ii); iv) filtering a crosslinking solution capable of crosslinking the nanofibers and / or microfibers of the outer layer (1, 3); v) drying the product of step iv), preferably in an oven; vi) removing the filtration support to obtain a composite membrane The method is characterized by comprising the steps of:

[0128] Nanofibers and / or microfibers and functionalized nanoparticles are as defined in the first object of the present invention.

[0129] The method is simple, easy to implement, economical, and allows for control of the thickness of each layer of the composite membrane.

[0130] The filtrations of steps i), ii), iii) and iv) are advantageously carried out using a vacuum pump, preferably under a vacuum of 1 bar.

[0131] The filtration of step i) may optionally be followed by a step i1) consisting of filtering the crosslinking solution on the outer layer (1) obtained at the end of step i).

[0132] The filtration of step ii) may optionally be followed by step ii1) consisting of filtering the crosslinking solution on the second layer obtained at the end of step ii).

[0133] The solution of nanofibers and / or microfibers introduced in steps i) and iii) contains 0.1% to 1% by weight of cellulose nanofibers and / or microfibers, preferably 0.3% to 0.6% by weight of cellulose nanofibers and / or microfibers.

[0134] The nanofibers and / or microfibers of the solutions of steps i) and iv) can be functionalized as detailed in the first object of the present invention.

[0135] The solution of functionalized nanoparticles introduced in step ii) contains 0.001% to 0.01% by weight of functionalized nanoparticles, preferably 0.003% to 0.006% by weight of functionalized nanoparticles.

[0136] The cross-linking solution introduced in step v) advantageously comprises between 0.005M and 0.02M of one or more cross-linking agents, preferably between 0.008M and 0.012M of one or more cross-linking agents.

[0137] The drying of step v) is advantageously carried out at a temperature that allows the crosslinking reaction to occur and below a temperature that would damage the fibers and / or nanofibers. Preferably, the drying is carried out at a temperature comprised between 80°C and 150°C, in particular between 80°C and 120°C, more preferably still between 80°C and 100°C.

[0138] As detailed above, the cross-linking agent preferentially retains charged groups and / or groups that become charged in the presence of water.

[0139] Citric acid is preferred.

[0140] At the end of step vi), the composite membrane is in the form of a dry material.

[0141] The method may further comprise a step vii) consisting in mechanically strengthening said ion-selective conductive membrane by applying a pressure between 3 and 4 bar to the composite membrane obtained at the end of step vi), at a temperature in the range of 60°C to 95°C, preferably in the range of 80°C to 90°C, for a period of at least 5 minutes.

[0142] The application of pressure in step vii) can be carried out using a press, in particular a heat press.

[0143] Any other technique known to those skilled in the art, whether discontinuous (i.e., batchwise) or continuous, may be considered, for example the so-called "roll-to-roll" technique, in which the membrane is produced continuously and then stored in the form of a roll.

[0144] use A third object of the present invention is the use of a composite membrane prepared according to the first object of the present invention or by the method defined in the second object of the present invention as an ion-selective membrane.

[0145] This conductivity advantageously occurs under the action of a stress, preferably a potential gradient or a concentration gradient, acting on either side of the composite membrane.

[0146] A fourth object of the invention is also the use of a composite membrane according to the first object of the invention or prepared by the method defined in the second object of the invention for the extraction of ionic or ionizable substances from water to be treated, for the extraction of organic compounds from water to be treated, for carrying out electrolytic reactions or for carrying out electrodialysis reversal reactions, in particular for the generation of electricity, in particular for the generation of electricity from a salinity gradient.

[0147] The composite membranes can be used for the extraction of ionic or ionizable substances from water to be treated. The composite membranes can be used in particular in methods for extracting ionic or ionizable substances from water to be treated, for example, in desalination and deionization processes. The composite membranes can include, for example, the treatment of polluted water with elements selected from ionized forms of manganese and ionized forms of iron, and / or with substances such as nitrate ions, ammonium ions, carbonate ions, or organic compounds in ionic form.

[0148] This treatment can be carried out especially under the action of a concentration gradient (filtration) or an electric potential (electrodialysis) on either side of the composite membrane.

[0149] In other words, the composite membrane can be used in any kind of ion separation process in aqueous media under the action of an electrical potential on either side of the composite membrane.

[0150] Electrodeionation (commonly referred to as "desalination") is an electrodialysis technique aimed at extracting ions, especially sodium and chloride ions, contained in seawater. Electrodialysis aims to remove all types of ions from relatively concentrated solutions, especially industrial wastewater. Electrodeionization is an electrodialysis technique used to extract solutions with low ion concentrations, usually solutions that have already been treated by reverse osmosis, especially solutions useful for obtaining ultrapure water. Electrodeionization is particularly used in the pharmaceutical industry.

[0151] When the composite membrane is bipolar, it can be used in a bipolar electrolysis process, preferably bipolar electrodialysis. The composite membrane can also be used to extract one or more organic compounds, preferably alcohols or alkanes, preferably C1 to C12, such as methanol, ethanol, propanol, butanol, ethylene glycol, propylene glycol, glycerol, methane, ethane, propane, butane, and mixtures thereof, from the water to be treated.

[0152] The composite membrane can also be used for carrying out electrolytic reactions, in which the migration of ions through the composite membrane under the action of a potential gradient is accompanied by oxidation and reduction reactions at the electrodes. This can be, for example, a water electrolysis reaction for the production of hydrogen under the action of a potential on either side of the composite membrane.

[0153] The composite membranes can also be used for carrying out reverse electrolysis reactions, particularly for generating electricity.

[0154] The composite membrane is preferably used for the manufacture of a device intended to generate an electric current by reverse electrodialysis under the action of an electrolyte concentration gradient, preferably a salinity gradient, acting on either side of the composite membrane. [Brief explanation of the drawings]

[0155] [Figure 1] 1 is a schematic cross-sectional view of a membrane according to the invention, in which the outer layer (1, 3) is formed of a cellulose matrix comprising cross-linked cellulose nanofibers and / or microfibers, and the inner layer (2) is formed of a material comprising nanoparticles whose surface is functionalized with charged groups and / or groups that become charged in the presence of water. [Example]

[0156] The invention will be better understood on reading the following examples which illustrate the invention without limiting it.

[0157] Example 1 Preparation of composite membranes according to the present invention Equipment and raw materials The materials used in this example are listed below: - Buchner filter - 1 bar vacuum pump - 0.1μm PVDF filter paper - Reinforced oven

[0158] The raw materials used in this example are listed below: - cellulose nanofibers negatively charged by carboxymethylation or TEMPO oxidation; - Citric acid, 99% by volume; - Graphene oxide sold by the company Sigma Aldrich under the reference n°777676.

[0159] Preparation of composite membranes The preparation method introduced in this example is detailed below: · 1.75 ml of nanocellulose solution is filtered on a Buchner filter with a PVD filter. The vacuum pump is set to a vacuum of 1 bar; · Once all the solution has been filtered, filter 5 ml of citric acid solution over it (acts as a cross-linking agent between the nanofibers); Once the citric acid is filtered, filter 7ml of graphene oxide solution; Once the graphene oxide solution is filtered, filter 1.75 ml of nanocellulose solution; Once all the solution has been filtered, filter 5 ml of citric acid solution over it (to act as a cross-linking agent between the nanofibers); Once all the filtered citric acid solution has been pumped, open the Büchner device and remove the filter paper with the filtrate.

[0160] The filter paper / filtrate combination is then placed in a laboratory oven at 85° C. for 15 minutes (drying and cross-linking reaction).

[0161] Finally, the membrane is separated from its filtration medium, possibly having been soaked beforehand in an isopropanol solution for easier handling.

[0162] The membrane thus obtained was 17.5 g / m 2 It is composed of nanocellulose.

[0163] The nanocellulose content and the mass content of graphene oxide were varied. 2With a nanocellulose content below this, it is not possible to obtain a film with sufficient mechanical strength.

[0164] For reasons of mechanical strength and ionic resistance, these 17 g / m 2 Values ​​of cellulose and 4 wt.% graphene oxide appear to be optimal.

[0165] These films have an inner layer of graphene oxide with a thickness of about 100 nm and outer layers of cellulose with a thickness of about 10 μm each.

[0166] Membrane power measurement Tests were carried out using a device made of two independent reservoirs, each containing a sodium chloride (NaCl) solution dissolved at 1 M in the concentrated solution, then 0.1 M, 0.01 M and 0.001 M in the diluent, making it possible to set Rc gradients of 10, 100 and 1000 between the two reservoirs.

[0167] The two reservoirs are separated by a composite membrane according to the invention, obtained as detailed in Example 1.

[0168] Silver grid Ag / AgCl electrodes are immersed in each of the reservoirs on either side of the membrane to measure the current generated across the membrane.

[0169] The results of these measurements are shown in Table 1.

[0170] [Table 1]

[0171] U Osmo is the membrane potential from which the Nernst potential of the electrode is estimated (U Nernst) I Osmo is the membrane-bound current and is calculated by measuring the membrane's electrical resistance according to Ohm's law I=U / R. P Osmo Max is calculated using the formula Pmax=(UxI) / 4. Membrane power is 1cm of composite membrane 2 Multiplying the value obtained above by 10 000 gives W / m 2 It is expressed as:

[0172] It has also been observed that applying a pressure of 3-4 bar to the membrane between two metal plates while heating at 85°C improves the mechanical stability of the membrane by 10-20%.

[0173] (Comparative Example 2) A film that does not contain graphene oxide and is not a film of the present invention Preparation of graphene oxide-free, non-inventive membranes The materials used are those detailed in Example 1.

[0174] The preparation method introduced in this comparative example is as follows: Filter 3.5 ml of the nanocellulose solution on a Buchner filter with a PVDF filter. Set the vacuum pump to 1 bar vacuum. Once all the solution has been filtered, 10 ml of citric acid solution is filtered again on top (to act as a cross-linking agent between the nanofibers). Once all the filtered citric acid solution has been pumped off, open the Buchner device and remove the filter paper with the filtrate.

[0175] The assembly of filtrate and filter paper is then placed in a laboratory oven at 85°C for 15 minutes (drying and cross-linking reaction).

[0176] Finally, the membrane is separated from its filtration medium, possibly having been soaked beforehand in an isopropanol solution for easier handling.

[0177] The membrane thus obtained had a density of 17.5 g / m 2 Nanocellulose In It is composed.

[0178] Power of membranes other than the membrane of the present invention The device used is in all respects the same as that detailed in Example 1, except that in this comparative example the film does not contain graphene oxide.

[0179] The results of these measurements are shown in Table 2.

[0180] [Table 2]

[0181] U Osmo is the membrane-bound potential from which the Nernst potential of the electrode is estimated (U Nernst) I Osmo is the membrane-bound current and is calculated by measuring the membrane's electrical resistance according to Ohm's law I=U / R. P Osm oMax is calculated by the formula Pmax=(UxI) / 4. The membrane power is 2 Multiplying the value obtained above by 10,000 gives W / m 2 It is expressed as: [Explanation of symbols]

[0182] (1) First outer layer (2) Inner layer (3) Second outer layer

Claims

1. An ion-selective conductive composite membrane having a thickness of 4 μm to 100 μm, comprising at least one inner layer (2) disposed between two outer layers (1, 3), - the outer layers (1, 3) are each made of a first material comprising crosslinked nanofibers and / or crosslinked microfibers of cellulose forming a network and having pores with a diameter between 10 nm and 10 μm, - the inner layer (2) is formed of a second material comprising lamellar nanoparticles of graphene oxide functionalized on the surface with charged groups and / or groups that become charged in the presence of water, and having pores with a diameter between 1 and 100 nm, An ion-selective conducting composite membrane, wherein the thickness of each of the outer layers (1, 3) is between 2 μm and 45 μm, and the thickness of the inner layer (2) is between 10 nm and 10 μm.

2. The membrane of claim 1 , wherein the ionized groups, charged groups and / or groups that become charged in the presence of water have a negative charge.

3. The group may be an epoxide group, a hydroxyl group, a carbonyl group, a carboxyl group, a sulfonate group -SO 3 - , carboxyalkyl group R-CO 2 - (R is C1-C4 alkyl), an aminodiacetate group -N(CH 2 CO 2 - ) 2 , phosphonate group PO 3 2- Amidoxime group -C(=NH 2 )(NOH), aminophosphonate group -CH 2 -NH-CH 2 -PO 3 2- 3. The membrane of claim 2, wherein the thiol group is selected from the group consisting of -SH, -SH- ...

4. The carboxyalkyl group is R—CO 2 - (R is C1 alkyl).

5. The membrane of claim 1, wherein the charged groups and / or groups that become charged in the presence of water have a positive charge.

6. The group is a quaternary ammonium group -N(R) 3 + (wherein R is a C1-C4 alkyl), a tertiary ammonium group -N(H)R) 2 + (R is C1-C4 alkyl), a dimethylhydroxyethylammonium group -N(C 2 H 4 OH)CH 3 ) 2 + 10. The membrane of claim 1, wherein the polyisoprene is selected from the group consisting of methyl methyl acrylate, methyl meth ...

7. The tertiary ammonium group is —N(H)R) 2 + (R is C1 alkyl).

8. A membrane as described in claim 1, in which the crosslinked nanofibers and / or crosslinked microfibers of cellulose carry charged groups and / or groups that become charged in the presence of water on their surface.

9. 9. The membrane according to claim 8, wherein said groups have a charge of the same sign as the charged groups of the functionalized nanoparticles of the inner layer (2) and / or the groups that become charged in the presence of water.

10. 10. A method for producing the composite membrane of claim 1, comprising: i) filtering a solution containing cellulose nanofibers and / or microfibers on a filtering support to form a first outer layer (1) containing cellulose nanofibers and / or microfibers; ii) filtering a solution of lamellar nanoparticles of graphene oxide functionalized on the surface with charged groups and / or groups that become charged in the presence of water onto the first outer layer (1) obtained at the end of step i) to form an inner layer (2) on said first outer layer (1); iii) filtering the solution of cellulose nanofibers and / or microfibers to form a second outer layer (3) comprising cellulose nanofibers and / or microfibers on the inner layer (2) obtained at the end of step ii); iv) filtering a crosslinking solution capable of crosslinking the cellulose nanofibers and / or microfibers of the outer layers (1, 3); v) drying the product of step iv); vi) removing the filtration support to obtain a composite membrane A method comprising:

11. 11. The method of claim 10, wherein step v) is carried out in an oven.

12. 11. Use of the composite membrane of claim 1 or prepared according to the method of claim 10 as an ion-selective conducting membrane.

13. 11. Use of a composite membrane according to claim 1 or prepared according to the method according to claim 10 for the extraction of ionic or ionizable substances from water to be treated, for the extraction of organic compounds from water to be treated, for the performance of electrolysis reactions, or for the performance of electrodialysis reversal reactions.

14. 14. Use according to claim 13 for the generation of electricity.

15. 15. Use according to claim 14 for the generation of electricity from a salinity gradient.

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