Ion-Selective Composite Membrane

Abstract

The present invention relates to an ion-selective composite membrane having a thickness of between 4 μm and 100 μm, comprising at least one inner layer disposed between two outer layers, wherein: —the outer layers are each formed of a first material comprising a network of nanofibres and/or crosslinked microfibres and pores with a diameter of between 10 nm and 10 μm, —the inner layer is formed of a second material comprising nanoparticles functionalized at the surface by charged groups and/or groups which become charged in the presence of water and having pores with a diameter of between 1 and 100 nm.

Claims

1. An ion-selective conduction composite membrane having a thickness of between 4 μm and 100 μm comprising at least one inner layer, disposed between two outer layers, in which: the outer layers are each formed of a first material comprising a network of crosslinked nanofibers and/or microfibers and pores with a diameter of between 10 nm and 10 μm, the inner layer is formed of a second material comprising nanoparticles functionalized at the surface by charged groups and/or groups which become charged in the presence of water and having pores with a diameter of between 1 and 100 nm.

2. The membrane according to claim 1, wherein the thickness of each of the outer layers is advantageously between 2 μm and 45 μm, and the thickness of the inner layer is between 10 nm and 10 μm.

3. The membrane according to claim 1, wherein the nanoparticles are lamellar nanoparticles.

4. The membrane according to claim 1, wherein the ionized groups, the charged groups and/or groups which become charged in the presence of water have a negative electric charge.

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

6. The membrane according to claim 1, wherein the crosslinked nanofibers and/or microfibers are nanofibers and/or microfibers of an organic material.

7. The membrane according to claim 1, wherein the crosslinked nanofibers and/or the microfibers carry at their surface charged groups and/or groups which become charged in the presence of water, said groups having a charge of the same sign as that of the charged groups and/or groups which become charged in the presence of water of the functionalized nanoparticles of the inner layer.

8. A method for manufacturing a composite membrane according to claim 1 comprising the steps of: i) filtering a solution comprising nanofibers and/or microfibers on a filtration support so as to form a first inner layer comprising nanofibers and/or microfibers; ii) filtering a solution of particles of nanoparticles functionalized at the surface by charged groups and/or groups which become charged in the presence of water on the first layer obtained at the end of step i) so as to form an inner layer on said first outer layer; iii) filtering a solution of nanofibers and/or microfibers so as to form a second outer layer comprising nanofibers and/or microfibers on the inner layer obtained at the end of step ii); iv) filtering a crosslinking solution capable of crosslinking the nanofibers and/or the microfibers of the outer layers; v) drying the product of step iv); vi) removing the filtration support, so as to obtain a composite membrane.

9. A method comprising utilizing the composite membrane according to claim 1 as an ion-selective conduction membrane.

10. The method according to claim 9 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 implementation of an electrolysis reaction or for the implementation of a reverse electrodialysis reaction.

11. The membrane according to claim 3, wherein the lamellar nanoparticles are lamellar nanoparticles of a metal oxide, of a dichalcogenide of a transition metal, of carbon, or a mixture thereof.

12. The membrane according to claim 3, wherein the lamellar nanoparticles are lamellar nanoparticles of graphene oxide.

13. The membrane according to claim 11, wherein the lamellar nanoparticles of the dichalcogenide of a transition metal are lamellar nanoparticles of molybdenum disulfide.

14. The membrane according to claim 4, wherein the groups are selected from the epoxide group, the hydroxyl group, the carbonyl group, the carboxyl group, the sulfonate group —SO.sub.3.sup.−, the carboxyalkyl group R—CO.sub.2 with R being a C1-C4 alkyl, the aminodiacetate group —N(CH.sub.2CO.sub.2.sup.−).sub.2, the phosphonate group PO.sub.3.sup.2−; the amidoxine group —C(═NH.sub.2)(NOH), the aminophosphonate group —CH.sub.2—NH—CH.sub.2—PO.sub.3.sup.2−, the thiol group —SH, and mixtures thereof.

15. The membrane according to claim 14, wherein the carboxyalkyl group is R—CO.sub.2.sup.− with R being a C1 alkyl.

16. The membrane according to claim 5, wherein the groups are selected from the quaternary ammonium group —N(R).sub.3.sup.+ with R being a C1-C4 alkyl, the tertiary ammonium group —N(HR).sub.2.sup.+ with R being a C1-C4 alkyl, the dimethylhydroxyethylammonium group —N(C.sub.2H.sub.4OH)CH.sub.2.sup.+, and mixtures thereof.

17. The membrane according to claim 16, wherein the tertiary ammonium group is —N(H)R).sub.2.sup.+ with R being a C1 alkyl.

18. The membrane according to claim 6, wherein the crosslinked nanofibers and/or microfibers are nanofibers and/or microfibers of cellulose or activated carbon.

19. The method according to claim 8, wherein step v) is performed in an oven.

20. The method according to claim 10 for the production of electricity.

21. The method according to claim 20 for the production of electricity from a salinity gradient.

Description

DESCRIPTION OF FIGURES

[0172] FIG. 1 is a schematic sectional view of a membrane according to the invention, in which the outer layers (1,3) are formed of a cellulose matrix comprising crosslinked cellulose nanofibers and/or microfibers and the inner layer (2) is formed of a material comprising nanoparticles functionalized at the surface by charged groups and/or groups which become charged in the presence of water.

EXAMPLES

[0173] The present invention will be better understood upon reading the following examples which illustrate the invention without limitation.

Example 1: Preparation of a Composite Membrane in Accordance with the Invention

Equipment and Raw Materials

[0174] The material used in this example is listed below: [0175] A Buchner filter [0176] A 1 bar vacuum pump [0177] 0.1 μm PVDF filter paper [0178] A proofing oven
The raw materials used in this example are listed below: [0179] Cellulose nanofibers negatively charged by carboxymethylation or TEMPO oxidation; [0180] Citric acid, 99% by volume; [0181] Graphene oxide marketed by the company Sigma Aldrich under the reference n° 777676.

Preparation of the Composite Membrane

[0182] The preparation method implemented in this example is detailed below: [0183] 1.75 ml of nanocellulose solution is filtered on the buchner filter with a PVD filter. The vacuum pump is set to 1 bar vacuum; [0184] Once all the solution has been filtered, 5 ml of citric acid solution is filtered thereon (which will act as a crosslinking agent between the nanofibers); [0185] .square-solid.Once the citric acid has been filtered, 7 ml of graphene oxide solution is filtered; [0186] Once the graphene oxide solution has been filtered, 1.75 ml of nanocellulose solution is filtered; [0187] Once all the solution has been filtered, 5 ml of citric acid solution is filtered thereon (which will act as a crosslinking agent between the nanofibers); [0188] .square-solid.Once all the filtered citric acid solution stops the pump, the Buchner device is opened and the filter paper with its filtrate is removed.
The filter paper/filtrate combination is then placed in a study oven at 85° C. for 15 minutes (drying and crosslinking reaction).
Finally, the membrane is detached from its filtration medium, to make things easier, it may possibly be soaked beforehand in an isopropanol solution.
The membranes thus obtained are composed of 17.5 g/m.sup.2 of nanocellulose.
The nanocellulose contents and the mass contents of graphene oxide were varied.
Nanocellulose contents below 10 mg/m.sup.2 do not allow to obtain membranes with sufficient mechanical strength.
For reasons of mechanical strength and ionic resistance, these values of 17 g/m.sup.2 of cellulose and 4% by weight of graphene oxide seem optimal.
These membranes have an inner layer of graphene oxide having a thickness of about 100 nm, and outer layers of cellulose each having a thickness of about 10 μm.

Membrane Power Measurement

[0189] The tests were carried out with a device made up of two independent reservoirs each containing a solution of sodium chloride (NaCl) dissolved at 1 M for the concentrated solution, then 0.1 M, 0.01 M and 0.001 M in dilute solution allowing to set the Rc gradient of 10, 100 and 1000 between the two reservoirs.
The two reservoirs are separated by a composite membrane in accordance with the invention obtained as detailed in Example 1.
Silver grid Ag/AgCl electrodes are immersed in each of the reservoirs on either side of the membrane to measure the electric current produced through the membranes.
The results of these measurements are shown in Table 1.

TABLE-US-00001 TABLE 1 NFC cellulose membrane + 2% graphene oxide Concentration gradient 1000 100 10 U (mV) 330 250 151 R (Ohm .Math. cm.sup.2) 0.16 0.16 0.145 I (mA) 2063 1563 1041 Pmax W/m.sup.2 1702 977 393 U Nernst (mV) 140 90 45 U Osmo (mV) 190 160 106 I Nernst (mA) 875 563 310 I Osmo (mA) 1188 1000 731 P Osmo Max(W/m.sup.2) 564 400 194

With:

[0190] U Osmo the membrane potential from which the Nernst potential of the electrodes is deduced (U Nernst)
I Osmo the current linked to the membrane, calculated by measuring the electrical resistance of the membrane according to Ohm's law I=U/R
P Osmo Max is calculated by the formula Pmax=(U×1)/4
The membrane powers are expressed in W/m.sup.2 by multiplying by 10 000 the values obtained on 1 cm.sup.2 of composite membrane.
It has also been observed that by applying a pressure of 3 to 4 bars to the membrane between two metal plates during heating at 85° C., the mechanical stability of the membrane is improved by 10 to 20%.

Comparative Example 2: Membrane not in Accordance with the Invention not Comprising Graphene Oxide

[0191] Preparation of Membranes not in Accordance with the Invention not Comprising Graphene Oxide

[0192] The materials used are those detailed in Example 1.

The preparation method implemented in this comparative example is as follows:
3.5 ml of nanocellulose solution are filtered on the buchner filter with a PVDF filter. The vacuum pump is set to 1 bar vacuum.
Once all the solution has been filtered, 10 ml of citric acid solution is filtered again thereon (which acts as a crosslinking agent between the nanofibers).
Once all the filtered citric acid solution stops the pump, the buchner device is opened and the filter paper with its filtrate is removed.
The filtrate filter paper assembly is then placed in a study oven at 85° C. for 15 minutes (drying and crosslinking reaction).
Finally, the membrane is detached from its filtration medium, to make things easier, it may possibly be soaked beforehand in an isopropanol solution.
The membranes thus obtained are composed of 17.5 g/m.sup.2 of nanocellulose.
Membrane Power of Membranes not in Accordance with the Invention
The device used is in all respects similar to that detailed in Example 1 with the exception of the membrane which in this comparative example does not comprise graphene oxide.
The results of these measurements are shown in Table 2.

TABLE-US-00002 TABLE 2 Cellulose NFC membrane Concentration gradient 1000 100 10 U (mV) 220 150 95 R (Ohm .Math. cm.sup.2) 0.08 0.08 0.0725 I (mA) 2750 1875 1310 Pmax W/m.sup.2 1513 703 311 U Nernst (mV) 140 90 45 U Osmo (mV) 80 60 150 I Nernst (mA) 1750 1125 621 I Osmo (mA) 1000 750 690 P Osmo Max (W/m.sup.2) 200 113 86

With:

[0193] U Osmo the potential linked to the membrane from which the Nernst potential of the electrodes is deduced (U Nernst)
I Osmo the current linked to the membrane, calculated by measuring the electrical resistance of the membrane according to Ohm's law I=U/R
P Osmo Max is calculated by the formula Pmax=(U×I)/4
The membrane powers are expressed in W/m.sup.2 by multiplying by 10 000 the values obtained on 1 cm.sup.2 of membrane.