Reverse electroosmosis filtration system and its use

Abstract

The present invention relates to a purification / filtration system using reverse electroosmotic flow through a composite or hybrid membrane element. The present invention also relates to a method for purifying an electrolyte solution using such a system. The present invention also relates to a water purification system, a water desalination system and an implantable artificial kidney comprising a reverse electroosmotic filtration system according to the present invention.

Description

[0001] priority

[0002] This PCT application claims priority to European patent application EP 20305110.7 filed on February 6, 2020, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present invention relates to a purification / filtration system using reverse electroosmotic flow through a composite or hybrid membrane element and to a method of purifying an electrolyte solution using such a system. Background Art

[0004] Population growth and improved quality of life have made access to clean water a central issue in many parts of the world. Drinking water is being contaminated by a variety of pollutants from different sources, ranging from particles to small-sized molecules such as colorants and pesticides, drugs and hormones. In fact, hormones diffused into water through the primary industry are becoming one of the most common pollutants today and are difficult to remove. Only a small amount of these molecules (usually below the standard detection limit) can cause harm to the environment and human health. For example, the use of pregnancy procedures releases estradiol and other hormones related to decreased sperm quality into potential drinking water. These hormones present in agriculture, fine industry or directly excreted by humans further enter the soil, plants and animals. It must be taken into account that more than 70% of human breast cancers are estrogen-dependent and that their development and growth are not only affected by endogenous estrogens, but may also be affected by environmental estrogen-like endocrine disruptors. Among water purification methods, purification methods involving osmotic phenomena are known. Osmosis is a natural phenomenon based on the following principle: when two aqueous solutions with different concentrations of impurities (such as salt) are separated by a semipermeable membrane that is permeable to water but impermeable to impurities such as salt, pure water will pass from the solution with lower concentration into the solution with higher concentration.

[0005] Specifically, the semipermeable membrane prevents salts dissolved in water from passing therethrough, so that the transfer of pure water is the only means by which concentration equilibrium can be established on both sides of the membrane.

[0006] The direct result of the transfer of pure water to the compartment containing the concentrated solution is an increase in the pressure of the solution across the membrane. This pressure is called the osmotic pressure (P osm ).

[0007] Two water treatment technologies utilize the properties of semipermeable membranes and the osmosis phenomenon, one is the so-called reverse osmosis technology, and the other is the so-called direct (forward) osmosis technology.

[0008] Currently, the most developed technology is reverse osmosis, which involves applying a pressure much higher than the osmotic pressure to a concentrated solution to reverse the flux of water molecules through a semipermeable membrane.

[0009] Reverse osmosis technology can produce high-purity water, but it is a method of implementing a method that is much higher than the osmotic pressure P osm The technology of high pressure and its energy consumption is very large. For example, desalination of water by reverse osmosis is a known technology in the field of water treatment. However, reverse osmosis desalination involves artificial application of relatively high pressure and therefore requires very high energy consumption. Therefore, the investment cost and operating cost of reverse osmosis facilities are high.

[0010] In addition, these processes usually allow high water flow rates to be obtained with low selectivity (low rejection), especially when the goal is to remove contaminants in the nanometer size range. For example, the low concentration and small size of hormone molecules not only hinder their detection by conventional analytical methods in water contaminant determination, but also hinder the removal of such small organic molecules by general purification methods.

[0011] Current commercial seawater reverse osmosis (SWRO) desalination can achieve up to 50% desalination water recovery, but may result in a stream with 7% rejection at an associated osmotic pressure of 784 psi. Actual desalination operating pressures must account for inefficiencies in pumping and control systems, which may result in required pumping pressures in excess of 1000 psi.

[0012] Most semipermeable polymer membranes suitable for seawater desalination cannot sustain operation or maintain separation efficiency at pressures exceeding 1100 psi and eventually fail, a condition that may force system operators to run the desalination process at lower salt rejection recoveries (i.e., 40% or less) to maintain membrane life.

[0013] Although methods and systems known in the art aim to improve energy efficiency, a major disadvantage is that they still require relatively high energy consumption.

[0014] Therefore, there is a great need for further improvements in reverse osmosis water purification systems. The present invention satisfies these needs and provides further related advantages. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 An exemplary system according to the present invention is schematically shown, which includes a composite reverse osmosis membrane element (30).

[0016] Figure 2 An exemplary system according to the present invention is schematically shown and includes a hybrid reverse osmosis membrane element (30).

[0017] Figure 3An exemplary system according to the present invention is schematically shown and includes a composite reverse osmosis membrane element (30) having a porous support (33).

[0018] 4A to 4D Exemplary features of a system according to the invention are shown. Figure 4A : schematically shows an exemplary filtration system / experimental setup according to the present invention; Figure 4B : Schematically illustrates the filtration process of molecules in an exemplary filtration system according to the present invention. Figure 4C : A representative FE-SEM image of the GO surface of a GO / PC composite reverse osmosis membrane element according to the present invention (left) and a 90° cross-sectional view of highly stacked GO showing a thickness of 8.66 μm for the self-supporting GO (right). Figure 4D : In the X-ray diffraction pattern of the GO / PC composite reverse osmosis membrane element according to the present invention, the first peak is associated with the interlayer planes in the range of 0.7nm-1.4nm of GO, and the second peak is associated with the presence of PC in the composite membrane.

[0019] FIG. 5A to FIG. 5F Exemplary results using a system according to the invention (GO / PC composite membrane) are shown. Figure 5A : Evolution of the saturation voltage with time in the presence of 100 mM KCl in each container of the cell (the time to reach equilibrium was considered to be 2 hours); Figure 5B : Relationship between electroosmotic flow and salt concentration and intensity; Figure 5C : Relationship between intensity and electroosmotic flow rate; Figure 5D : The relationship between current and intensity; Figure 5E : Voltage measured as a function of applied ionic current. The asymmetric response is due to the charge asymmetry across the GO / PC composite membrane. This measurement demonstrates that the membrane is composed of two materials with different properties. Fig. 5F : Voltages obtained by applying constant intensity values ​​ranging from -1 mA to 1 mA and, after achieving voltage equilibrium, (inset) different electroosmotic flows generated by the device while varying the salt concentration (1 mM, 10 mM, 30 mM and 100 mM) over the two containers, showing faster flow with decreasing salt concentration and with increasing applied intensity.

[0020] FIG. 6A to FIG. 6D Exemplary rejection results using a system according to the invention (GO / PC composite membrane) are shown: Fig. 6A To retain the first result, Figure 6B For the second optimized dye, Figure 6C for hormone retention: comparison of the UV-Vis spectrum of the testosterone present in the solution feed for filtration ("initial testosterone") with the absorption spectrum obtained in the elution phase after filtration ("eluted testosterone"), Fig.6D is the range of intact retention under the operating electroosmotic conditions (1 mM KCl, 0.5 mA) for the molecule used as a model (Rubypy).

[0021] Figure 7 : Simulation method: Calculation of water flux across an asymmetric membrane under voltage drop (AV) in an exemplary system according to the present invention. Q = water flux through the membrane; Qosm = permeate flux of water through the membrane at ΔV=0.

[0022] Figure 8 : Optical microscope image of the surface of a GO / PC composite film according to the present invention (no cracks were detected in the long range).

[0023] Fig. 9 BET surface area (analysis of the average pore size of the GO membrane element of the GO / PC composite reverse osmosis membrane according to the present invention in the absence of a PC substrate).

[0024] Fig.10 The pore size distribution of the GO membrane element of the GO / PC composite reverse osmosis membrane according to the present invention shows a relatively wide distribution from 1.8 nm to 6 nm.

[0025] Fig.11 Nitrogen adsorption BET isotherm of the GO membrane element of the GO / PC composite reverse osmosis membrane according to the present invention.

[0026] Fig.12 Photograph of an exemplary embodiment of a filtration system according to the invention.

[0027] Fig.13 The relationship between electroosmotic flow rate and concentration and voltage using bare PC membrane (PC membrane only) as container separator and different concentrations of KCl electrolyte solution.

[0028] Fig.14 Calibration curve: relationship between Ru(biPy) concentration and absorbance at 283 nm.

[0029] Fig.15 Comparative electroosmotic flow rates were determined at lower test concentrations (1 mM KCI) and different intensity values ​​by using either PC alone as membrane (open circles) or GO / PC composite membranes according to the present invention (solid black circles) as container separators. The flux rectification of the composite membranes as a function of current demonstrates the charge asymmetry of the membranes.

[0030] Although the system and process of the present application are susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and described in detail herein. However, it should be understood that the description of specific embodiments herein is not intended to limit the present application to the specific embodiments disclosed, but on the contrary, the present invention will cover all modifications, equivalents and substitutes falling within the spirit and scope of the method of the present application defined by the appended claims. DETAILED DESCRIPTION

[0031] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by one of ordinary skill in the art to which the invention belongs. Generally, the nomenclature used herein and the experimental methods to be described below are those well known and commonly used in the art.

[0032] To facilitate understanding of this disclosure, a number of terms and phrases are defined below:

[0033] As used herein, except in the claims, the terms "a", "an", "the" and / or "said" refer to one or more. As used in the claims, when used in conjunction with the words "comprise", "comprises" and / or "comprising", the words "a", "an", "the" and / or "said" may refer to one or more than one. As used herein and in the claims, the terms "having", "has", "is", "have", "including", "includes" and / or "include" have the same meaning as "comprise", "comprises" and / or "comprising". As used herein and in the claims, "another" may refer to at least a second or more. As used herein and in the claims, "about" refers to any inherent measurement error or numerical rounding of a value (e.g., a measurement, a calculated value such as a ratio), and thus the term "about" may be used with any value and / or range.

[0034] The phrases "combinations thereof," "mixtures thereof," and the like after a list, use of "and / or" as part of a list, lists in tables, use of "etc." as part of a list, the phrases "such as," and / or parenthetical lists with "for example," or the like refer to any combination (e.g., any subset) of a group of listed components, as well as combinations and / or mixtures of related species and / or embodiments described herein, even though not directly placed in such lists, are contemplated. These related and / or similar genera, subgenera, species, and / or embodiments described herein include both the form of individual components that may be claimed, and the form of mixtures and / or combinations that may be described in the claims as "at least one selected from...", "mixtures thereof," and / or "combinations thereof."

[0035] As used herein, the term "and / or" means any one of the items, any combination of the items, or all of the items associated with the term.

[0036] As will be understood by those skilled in the art, all numbers, including those expressing amounts of ingredients, properties such as cavity / pore size and zeta potential, experimental conditions, etc., are approximate and are understood to be optionally modified in all instances by the term "about". These values ​​can vary depending on the desired properties that one skilled in the art seeks to obtain utilizing the teachings described herein. It is also understood that these values ​​inherently contain variability necessarily caused by the standard deviation found in their respective test measurements.

[0037] As used herein, the term "about" may refer to a variation of ±5% of a specified value. For example, "about 50%" may include a variation from 45% to 55% in some embodiments. For integer ranges, the term "about" may include one or two integers greater than and / or less than the integer. Unless otherwise specified herein, the term "about" is intended to include values ​​(e.g., concentration values) close to the range, which are equivalent in terms of the functionality of the individual components, compositions, or embodiments.

[0038] As will be appreciated by those skilled in the art, for any and all purposes, particularly in providing a written description, all ranges listed herein also encompass any and all possible subranges and combinations of subranges thereof, as well as individual values, particularly integer values, constituting the range. The ranges listed include each specific value, integer, decimal, or identity within the range. Any listed range can be easily considered to fully describe and allow the same range to be broken down into at least equal halves, thirds, quarters, fifths, or tenths, etc. As non-limiting examples, each range discussed herein can be easily broken down into a lower third, a middle third, and an upper third, etc.

[0039] DETAILED DESCRIPTION OF CERTAIN PREFERRED EMBODIMENTS OF THE INVENTION

[0040] Illustrative embodiments are described below. For the sake of clarity, not all features of actual implementations are described in this specification. Of course, it should be understood that in the development of any such actual implementation, implementation-specific decisions must be made to achieve the developer's specific goals, such as compliance with system-related and business-related constraints, which will vary from implementation to implementation. Moreover, it should be understood that such development efforts may be complex and time-consuming, but are routine tasks for those of ordinary skill in the art having the benefit of this disclosure.

[0041] In the specification, when depicting devices in the drawings, reference may be made to the spatial relationships between various components and the spatial orientation of various aspects of the components. However, as will be appreciated by those skilled in the art after reading this application in its entirety, the devices, components, apparatus, etc. described herein may be positioned in any desired orientation. Therefore, the use of terms describing the spatial relationships between various components or describing the spatial orientation of aspects of such components should be understood to describe the relative relationships between components or the spatial orientation of aspects of such components, respectively, as the devices described herein may be oriented in any desired direction.

[0042] The system and process according to the present application overcome one or more of the above-mentioned problems usually associated with conventional membrane technology and process. Specifically, the system of the present application uses a reverse electroosmosis filtration system. This and other unique features of the system are discussed below and shown in the accompanying drawings.

[0043] The structure and operation of the system and process can be understood from the accompanying drawings in conjunction with the accompanying description. Figures 1 to 15 Several embodiments of the system are presented in . It should be understood that the various components, parts and features of the different embodiments may be combined together and / or interchanged with each other, all of which are within the scope of the present application, even though not all variations and specific embodiments are shown in the drawings. It should also be understood that the mixing and matching of features, elements and / or functions between the various embodiments is expressly contemplated herein, so that one of ordinary skill in the art will understand from this disclosure that, unless otherwise described, features, elements and / or functions of one embodiment may be appropriately combined in another embodiment.

[0044] In one aspect, the present invention provides a reverse electroosmosis filtration system, the reverse electroosmosis filtration system comprising:

[0045] a) a first container (10A) for receiving an electrolyte solution (11A) enriched with a solute of interest and comprising a first electrode (20A) in contact with the electrolyte solution (11A) contained in the container (10A);

[0046] b) a second container (10B) for receiving a liquid substantially free of the same solute of interest or the same solute of interest Depletion an electrolyte solution (11B) contained in a container (10B), and includes a second electrode (20B) in contact with the electrolyte solution (11B) contained in the container (10B);

[0047] c) a reverse osmosis membrane element (30) which separates the two containers and combines the following:

[0048] (i) a semipermeable membrane element (31), and

[0049] (ii) a nanoporous membrane element (32) having a surface charge of |zeta potential| ≥ 5 mV, preferably > 20 mV, most preferably ≥ 50 mV;

[0050] The semipermeable membrane element (31) and the nanoporous membrane element (32) having a surface charge may be the same element or two different elements;

[0051] The semipermeable membrane element (31) is configured to contact the electrolyte solution (11A) of the first container (10A), and the nanoporous membrane element (32) having a surface charge is configured to contact the electrolyte solution (11B) of the second container (10B); the reverse osmosis membrane element (30) realizes the following two functions: (i) solute filtration function; and (ii) electrically inducing the flow of the solvent from the electrolyte solution (11A) from the container (10A) through the reverse osmosis membrane element (30) to the container (10B);

[0052] The electrolyte solutions (11A) and (11B) in the containers (10A) and (10B), respectively, contain the same polar solvent;

[0053] The first electrode (20A) and the second electrode (20B) are operatively coupled to a source of electrical energy (40);

[0054] An electric field is applied between a first electrode (20A) and a second electrode (20B) to induce reverse osmosis flow of a polar solvent of an electrolyte solution (11A) from a container (10A) through a reverse osmosis membrane element (30) to a container (10B).

[0055] The filter system according to the invention may be a purification system.

[0056] In another aspect, the present invention provides a method for purifying an electrolyte solution in a polar solvent, the method comprising the following steps:

[0057] i) providing an electrolyte solution (11A) comprising an undesirable solute in a polar solvent;

[0058] ii) providing a second electrolyte solution (11B) in a solvent of the same or different polarity as in step i), the second electrolyte solution not containing undesirable solutes;

[0059] iii) providing a reverse electroosmosis filtration system, the reverse electroosmosis filtration system comprising:

[0060] a) a first container (10A) provided with a first electrode (20A);

[0061] b) a second container (10B) provided with a second electrode (20B); the first electrode (20A) and the second electrode (20B) are operatively coupled to a source of electrical energy (40);

[0062] c) a reverse osmosis membrane element (30) which separates the two containers (10A) and (10B) and combines the following:

[0063] (i) a semipermeable membrane element (31), and

[0064] (ii) a nanoporous membrane element (32) having a surface charge of |zeta potential| ≥ 5 mV, preferably ≥ 20 mV, most preferably ≥ 50 mV;

[0065] The semipermeable membrane element (31) and the nanoporous membrane element (32) having a surface charge may be the same element or two different elements;

[0066] wherein the semipermeable membrane element (31) is in contact with the electrolyte solution (11A) in the container (10A), and the nanoporous membrane element (32) having a surface charge is in contact with the electrolyte solution (11B) in the container (10B);

[0067] The reverse osmosis membrane element (30) realizes the following two functions: (i) solute filtering function; and (ii) electrically inducing the flow of the solvent of the electrolyte solution (11A) from the container (10A) through the reverse osmosis membrane element (30) to the container (10B);

[0068] The reverse osmosis membrane element (30) is adapted to selectively prevent undesirable solutes from diffusing through the reverse osmosis membrane element (30);

[0069] iv) placing an electrolyte solution (11A) to be purified in a container (10A) so that a first electrode (20A) provided in the container is in contact with the electrolyte solution (11A);

[0070] v) placing a sufficient amount of a second electrolyte solution (11B) in a container (10B) such that a second electrode (20B) provided in the container is in contact with the electrolyte solution (11B);

[0071] vi) applying an electric field between the first electrode (20A) and the second electrode (20B) to induce reverse osmosis flow of a polar solvent from the container (10A) to the container (10B) through the reverse osmosis membrane element (30), which separates the two containers (10A) and (10B);

[0072] thereby allowing solvent to flow from container (10A) to container (10B) while retaining undesirable solutes in container (10A); and

[0073] vii) collecting a purified electrolyte solution (11B) from the container (10B), the purified electrolyte solution being substantially free of or depleted of undesirable solutes.

[0074] Throughout the present disclosure, the first electrode (20A) and the second electrode (20B) can be operably coupled to an electrical energy source (40) such that an electric field is or can be applied between the first electrode (20A) and the second electrode (20B) (e.g., the electrical energy source (40) allows an electric field to be applied between the first electrode (20A) and the second electrode (20B)).

[0075] As used herein, the term "solute" refers to a liquid or solid substance dissolved in a polar solvent used in the electrolyte solution (11A) and / or (11B).

[0076] As used herein, the term "substantially free of solutes" means that ≥99%, preferably ≥99.5%, more preferably ≥99.8%, even more preferably ≥99.9%, and most preferably 100% of the solutes have been removed (meaning that a solute rejection of ≥99.0%, more preferably ≥99.5%, even more preferably ≥99.8%, even more preferably ≥99.9%, and most preferably 100% or about 100% is achieved). In other words, the reverse osmosis membrane element (30) separating the two containers (10A) and (10B) allows <1.0%, more preferably <0.5%, even more preferably <0.2%, even more preferably <0.1%, and most preferably 0% of the undesirable solutes to pass through the reverse osmosis membrane.

[0077] As used herein, the term "solute-rich" means that the feed electrolyte solution (11A) contains a higher concentration of solute than the eluent electrolyte solution (11B).

[0078] As used herein, the term "solute-depleted" means that the eluent (second) electrolyte solution (11B) contains a lower concentration of solutes than the feed (first) electrolyte solution (11A).

[0079] As used herein, the term "semipermeable membrane" does not deviate from the conventional meaning of the term in the field of filtration membranes and refers to a membrane that allows certain molecules or ions to pass through by diffusion or artificially generated flux. For example, it can be a size exclusion membrane, an ion exchange membrane or any other membrane that allows separation / filtration of specific molecules or ions from a given electrolyte solution (e.g., a semipermeable membrane based on separation by chemical affinity).

[0080] As used herein, the term "electrolyte solution" refers to a conductive solution containing mobile ions that induce electroosmosis.

[0081] As used herein, the term "nanoporous membrane" does not deviate from the conventional meaning of this term in the field of filtration membranes and refers to a membrane with an average pore size of <1 μm, preferably ≤500 nm.

[0082] As used herein, "zeta potential" does not deviate from the conventional meaning of the term in electrochemistry when referring to the membrane surface charge, and refers to the potential difference between the membrane surface and the fixed layer of fluid attached to the membrane surface. The zeta potential generally depends on the properties of the membrane surface and the characteristics of the electrolyte solution in contact with the membrane surface (e.g., pH, ion concentration, ionic forces, etc.). The zeta potential can be calculated using the Smoluchowski equation (see the formula below).

[0083] As used herein, |zeta potential| refers to the absolute value of the zeta potential (i.e., the numerical value of the zeta potential, regardless of its sign). It will be readily appreciated from this disclosure that the present invention can be practiced using nanoporous membrane elements with negative or positive surface charges: once the membrane is contacted with an electrolyte solution, the zeta potential can be negative or positive, respectively.

[0084] As used herein, the term "polar solvent" does not deviate from the conventional meaning and common knowledge / usage in the art. Generally speaking, polar solvents include, but are not limited to, aprotic solvents with a dielectric constant ≥ 6 and a dipole moment ≥ 1.50D, and protic solvents such as water, alcohols, formic acid, acetic acid, hydrogen fluoride and ammonia.

[0085] The underlying phenomenon behind the present invention is based on the reverse electroosmotic effect. It excludes other diffusion phenomena, such as electrophoresis and diffusion-osmotic effects.

[0086] The reverse osmosis membrane element (30) may be a composite membrane element or a hybrid membrane element.

[0087] The permeate from which the excluded solute has been removed will leave the reverse osmosis membrane element (30) as a permeate stream (50) and can be collected in a container (10B). Therefore, the present invention also relates to a method for separating a solvent and a solute from an electrolyte solution containing a solute using a filtration system or purification method according to the present invention.

[0088] 1. Composite membrane

[0089] Figure 1 An exemplary embodiment is shown in FIG.

[0090] In one variation, the reverse osmosis membrane element (30) may be a composite membrane element, and according to the reverse electroosmosis filtration system of the present invention, the semipermeable membrane element (31) and the nanoporous membrane element (32) having a surface charge are two different elements combined together to form a double-layer composite asymmetric membrane (30A). The composite asymmetric membrane (30A) may include a semipermeable membrane (31) superimposed with a charged nanoporous membrane (32). Advantageously, the composite asymmetric membrane (30A) may include a semipermeable membrane (31) superimposed with a charged nanoporous membrane (32), the nanoporous membrane having a surface charge of |zeta potential|≥5mV, preferably ≥20mV, and most preferably ≥50mV.

[0091] As described below, the semipermeable membrane element itself may incorporate a semipermeable membrane and a porous support layer.

[0092] 1.1. Semipermeable membrane

[0093] The semipermeable membrane that can be used in the context of the present invention can be any semipermeable membrane known in the art. For example, the semipermeable membrane element (31) can be a size exclusion membrane, an ion exchange membrane, or any other membrane that allows separation / filtration of specific molecules or ions from a given electrolyte solution (e.g., based on a semipermeable membrane separated by chemical affinity), preferably a size exclusion membrane or an ion exchange membrane. For example, it can be a semipermeable membrane that separates pure water molecules from salt and other impurities: the membrane has permeability to water and relative impermeability to various dissolved impurities (including dissolved salts, organic matter, bacteria and pyrogens and other small molecules). Therefore, it can be a semipermeable membrane conventionally used in water purification technology that uses a semipermeable membrane to remove ions, molecules and larger particles from contaminated water. It can be a semipermeable membrane used in water purification or desalination systems, reverse osmosis systems, such as a thin film composite membrane (TFC or TFM).

[0094] The membrane used in reverse osmosis is usually made of polyamide, which is mainly selected based on its permeability to water and relative impermeability to various dissolved impurities (including salt ions and other small molecules that cannot be filtered). In another example, the semipermeable membrane element (31) can be an anion exchange membrane (AEM) or a cation exchange membrane (CEM). For example, the semipermeable membrane element (31) can be a Nafion semipermeable membrane.

[0095] The average pore size of the semipermeable membrane will be suitable for filtering out the target solute (11A) from the electrolyte solution. Therefore, the average pore size of the membrane will be small enough to prevent the target solute (and any other solute having a particle size greater than the target solute) from passing through the semipermeable membrane (31), while allowing polar solvents and other smaller-sized solutes to pass through the semipermeable membrane (31). The average pore size of the semipermeable membrane will be adjusted according to the following expected application types: microfiltration (50nm-500nm), ultrafiltration (1nm-50nm) or nanofiltration (≤1nm). Advantageously, the semipermeable membrane element (31) can have an average pore size of <500nm, preferably <300nm, more preferably <100nm, most preferably <50. In a preferred variation, the filtration system is intended for ultrafiltration, and the semipermeable membrane element (31) can have an average pore size between 1nm-50nm. In another preferred variation, the filtration system is intended for nanofiltration, and the semipermeable membrane element (31) can have an average pore size of <1nm. Such nanofiltration systems can be used, for example, for desalination.

[0096] Advantageously, the semipermeable membrane can be a nanoporous carbon membrane. The nanoporous carbon membrane includes a carbon nanotube membrane, a nanoporous graphene membrane and a multilayer graphene oxide membrane. All of these materials can show similar selective permeability and can be used as molecular sieves in applications involving membrane separation (such as nanofiltration, desalination, etc.). The carbon nanotube membrane consists of two perforated graphene sheets connected by short carbon nanotubes of limited diameter. However, due to the complexity of its manufacture, their practical application is limited. The nanoporous graphene membrane consists of a single sheet of graphene with nanopores of limited size. However, it is still difficult to obtain a large graphene sheet with a predetermined pore size and a high pore density. Graphene oxide (GO) membranes are composed of stacked GO nanosheets, which are separated by interconnected nanochannels, which form holes that allow selective permeation through the membrane. They can be produced relatively easily and cheaply by depositing GO solutions on various supports by spraying, dip coating, spin coating, vacuum filtration, etc., and are currently the most commonly used.

[0097] Furthermore, GO sheets can be converted into graphene-like reduced GO (rGO) sheets, which possess similar electrical, thermal, mechanical, and surface properties to pristine graphene.

[0098] Therefore, in the context of the present invention, the semipermeable membrane may be a carbon nanotube membrane, a nanoporous graphene membrane or a multilayer GO or rGO membrane, preferably a multilayer GO or rGO membrane, most preferably a multilayer GO membrane.

[0099] Advantageously, the semipermeable membrane (31) can be a size exclusion selective membrane composed of stacked graphene oxide flakes. Advantageously, the stacked graphene oxide flakes can form a network of 2D nanochannels, wherein the interlayer spacing between the GO flakes is in the range of 0.7nm-1.4nm. The interlayer spacing between the stacked graphene oxide flakes can be measured by any suitable method known in the art. For example, XRD can be used to measure.

[0100] Advantageously, the nanoporous carbon film pore size can be in the range of 0.7nm to 1.5nm, preferably ≤1.4nm, more preferably ≤1.3nm, more preferably ≤1.1nm, and even more preferably ≤1.0nm. When it comes to carbon-containing semipermeable membranes, "pore size" refers to the pore diameter in the case of carbon nanotubes and nanoporous graphene membranes, and refers to the width of the interlayer gap in the case of multilayer GO or rGO membranes. Typically, in the case of carbon nanotube membranes, the nanoporous carbon film can be from 0.05μm to 1μm thick, preferably from 100nm to 500nm thick. In the case of multilayer GO or rGO membranes, the carbon film can contain at least 2, preferably at least 3, and up to 300 layers of GO or rGO sheets, and can be 0.05μm to 20μm thick, 0.05μm to 10μm thick, 0.05μm to 5μm thick, or 0.05μm to 1μm thick. For example, the carbon film can be about 0.1μm thick.

[0101] In another variation, the semipermeable membrane can be a stacked membrane of layered materials. Any layered material can be used. For example, MoS2, hexagonal NiB, clay, graphite systems.

[0102] For example, the semipermeable membrane can be a multilayer MoS2 membrane, a multilayer hexagonal NiB membrane or a multilayer GO or rGO membrane, preferably a multilayer GO or rGO membrane, and most preferably a multilayer GO membrane.

[0103] In another exemplary variation, the semipermeable membrane may be an ion exchange membrane, such as an anion exchange membrane (eg, OH-, Cl- transfer) or a cation exchange membrane (eg, H+, Na+, K+ transfer).

[0104] Semipermeable membrane can be directly placed on the nanoporous membrane element (32) with surface charge. This can be achieved by, for example, vacuum filtration, preferably under wet conditions (from a dispersion in water or an aqueous solvent). For example, a dispersion of a carbonaceous material (e.g., carbon nanotubes, graphene, GO or rGO) or a layered material (e.g., MoS2, hexagonal NiB, clay, graphite system) in water can be added dropwise to the top of the nanoporous membrane with surface charge under vacuum. For example, the nanoporous membrane with surface charge can be arranged on a Buchner funnel connected to a vacuum pump, and the dispersion of the carbonaceous material or layered material in water can be slowly added (e.g., dripped) to the nanoporous membrane with surface charge, to form a stacked membrane (semipermeable membrane element) of carbonaceous material or layered material. Alternatively, before being placed on the nanoporous membrane element (32) with surface charge, the semipermeable membrane can first be placed on another porous supporting layer (33) (e.g., for ease of manufacture and / or processing). The porous supporting layer (33) should have a much larger pore size to allow the polar solvent flow of the electrolyte solution (11A) to penetrate from the container (10A) through the reverse osmosis membrane element (30) to the container (10B). Therefore, when a porous supporting layer is used, its pore size is preferably at least 5 times, 10 times or more of the pore size of the semipermeable membrane element (32), and the thickness is 30 μm to 300 μm, more preferably 100 μm to 200 μm. The porous supporting layer (33) can be made of a neutral (no surface charge) non-reactive polymer material such as a fluoropolymer (such as polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE)) or a mixed cellulose ester or cellulose acetate. As a non-limiting example, it can also be made of a porous ceramic material such as alumina or a porous ceramic based on silica.

[0105] When the semipermeable membrane (31) is placed on the porous support layer (33), the resulting combined filter membrane can be used in any orientation, that is, the semipermeable membrane surface or the porous support surface can be in contact with the nanoporous membrane element (32) having a surface charge. It is also possible to use a combined filter membrane in which the semipermeable membrane (31) is placed on both sides of the porous support layer (33) or alternatively between two porous support layers, as well as a multilayer combined filter membrane that alternates two or more layers of semipermeable membrane (31) and two or more layers of porous support (33).

[0106] Advantageously, the semipermeable membrane may preferably be adapted to achieve a solute rejection of 98.0% or more, preferably ≥98.5%, more preferably ≥99.0%, still more preferably ≥99.5%, and most preferably 100% or about 100%.

[0107] Naturally, the average pore size of the semipermeable membrane will be appropriate to the solutes to be filtered out.

[0108] 1.2. Nanoporous membranes with surface charges

[0109] The nanoporous membranes available in the context of the present invention can be any membrane made nanoporous with a surface charge known in the art, or any nanoporous membrane in which at least a portion of the inner surface of the nanochannel of the membrane is substantially formed of at least one material having a suitable surface charge. As used in the present disclosure, unless otherwise specified, the term "substantially formed of a material" means "made of a material". The term also includes the possibility that the material is optionally chemically modified (e.g., on the surface and / or on the surface of the pore wall) to adjust its physicochemical properties to suit the intended use. Chemical modification can include doping (e.g., adding a metal element to the surface or core of a material network); coating (e.g., with a thin layer of a material having a suitable surface charge); covalent functionalization; physical adsorption or chemical adsorption of a compound / substance, such as by chemical vapor deposition, atomic layer deposition, sol-gel coating or dip coating or electrochemical deposition; or ionization of ionizable functional groups on the surface of the material by pH changes.

[0110] In a preferred embodiment, at least a portion of the inner surface of the nanochannel is substantially formed of or coated with at least one material having a suitable surface charge. Advantageously, the nanochannel may preferably be completely formed of or coated with at least one material having a suitable surface charge.

[0111] As used herein, "at least a portion of the inner surface of a nanochannel" means that the inner surface of the nanochannel may include one or more segments substantially formed of a material having a suitable surface charge, or the entire inner surface is substantially formed of at least one material having a suitable surface charge. The segments may be regular or irregular, intermittent or non-intermittent and / or in the form of a single layer or multiple layers. Preferably, the entire inner surface of the nanochannel is substantially formed of at least one material having a suitable surface charge.

[0112] Nanoporous membranes useful in the context of the present invention may have a positive or negative surface charge.

[0113] When the nanoporous membrane carries a positive surface charge, applying an electric field between the electrodes (20A) and (20B) will induce anions in the electrolyte solution (11B) to flow from the positively charged pore surface of the nanoporous membrane element (32) to the electrode (20B), wherein the electrode (20B) in contact with the electrolyte solution (11B) in the second container (10B) is positively charged. This anion flow concomitantly induces the polar solvent to flow from the first container (10A) through the reverse osmosis membrane element (30) to the second container (10B).

[0114] On the contrary, when the nanoporous membrane carries a negative surface charge, applying an electric field between the electrodes (20A) and (20B) will induce cations in the electrolyte solution (11B) to flow from the negatively charged pore surface of the nanoporous membrane element (32) to the electrode (20B), wherein the electrode (20B) in contact with the electrolyte solution (11B) in the second container (10B) is negatively charged. This cation flow concomitantly induces the polar solvent to flow from the first container (10A) through the reverse osmosis membrane element (30) to the second container (10B).

[0115] Advantageously, the nanoporous membrane with a positive or negative surface charge may have a surface charge with a |zeta potential| ≥ 5 mV, preferably ≥ 20 mV, most preferably ≥ 50 mV.

[0116] Examples of materials with surface charges suitable for use in nanoporous membrane elements according to the present invention include titanium oxide, boron nitride, SiO2, polyethersulfone, polycarbonate, anodized aluminum oxide (anodized aluminum oxide), hydrotalcite, Ni-Fe layered double hydroxide, Ni2dobdc, Mg2dobdc (dobdc = 1,4-dioxo-2,5-phthalate), cellulose or a polyelectrolyte layer polymer membrane, which is a nanoporous membrane such as obtained by successively dip-coating a cationic polyethyleneimine layer and an anionic polyacrylic acid layer onto a polycarbonate membrane. Ni2dobdc and Mg2dobdc are known metal organic frameworks having dobdc ligands and Ni or Mg metal sites, respectively. Advantageously, materials with surface charges suitable for use in nanoporous membrane elements according to the present invention include materials substantially formed of titanium oxide, boron nitride, SiO2, polyethersulfone, polycarbonate, anodized aluminum oxide; preferably titanium oxide, boron nitride, SiO2, polycarbonate and anodized aluminum oxide; most preferably titanium oxide, polycarbonate and anodized aluminum oxide.

[0117] Titanium oxide refers to any type of titanium oxide, for example titanium (IV) oxide or titanium dioxide, and mixtures of two or more thereof. These titanium oxides may be in different solid polymorphic forms, in particular amorphous or crystalline forms. With respect to titanium dioxide (TiO2), mainly rutile or anatase crystal types are used, preferably anatase.

[0118] As used herein, “substantially formed of titanium oxide, boron nitride, or the like” refers to a material formed of titanium oxide, boron nitride, or the like, which may include a minority element such as an impurity.

[0119] The physicochemical properties of materials (such as titanium oxide, boron nitride, anodized aluminum oxide, SiO2) can often be adjusted and amplified by doping or functionalization, that is, by inserting metallic chemical elements such as iron, silver, vanadium, gold, platinum, niobium, tungsten, or non-metallic elements such as nitrogen, sulfur, carbon, hydrogen, boron, phosphorus, or silanes, amines or other different chemical compounds of the organic group, preferably in small quantities, on the surface or in the core of the material network.

[0120] For example, the nanoporous membrane material can be titanium oxide, which can be doped on the surface or in the core of its crystalline network by inserting metallic chemical elements such as iron, silver, vanadium, gold, platinum, niobium, tungsten or non-metallic elements such as nitrogen, sulfur, carbon, hydrogen, boron, phosphorus or different chemical compounds such as silanes or amines, preferably in an amount of 0.5 wt% to 10 wt% and more preferably 1 wt% to 5 wt%.

[0121] Nanoporous membranes useful in the context of the present invention can be supported by a nanoporous or perforated mechanical base morphology, on which at least one material with a suitable surface charge is deposited. For example, the nanoporous membrane can be composed of a flexible polymer film, on which a layer of at least one material with a suitable surface charge (such as TiO2) is deposited.

[0122] Membranes containing nanochannels (having an inner surface substantially formed of or coated with at least one material having a suitable surface charge) such as ceramic membranes (e.g., titanium oxide, anodized aluminum oxide, SiO2) can be directly obtained by anodizing metal foils (e.g., Ti, Al or Si) (see Progress on free-standing and flow-through TiO2 nanotubes membranes, Guohua Lin, Kaiying Wang, Nils Hoivik, Henrik Jakobsen, Solar Energy Materials & Solar Cells, 98, 2012, pp. 24 to 38; TiO2 nanotubes synthesis and applications, Poulomi Roy, Steffen Berger, Patrick Schmuki, Angewandte Chemistry Int. Ed, 50, 2011, pp. 2904 to 2939). Other techniques such as sol-gel techniques in the presence of block copolymers or graft copolymers also allow the synthesis of ceramic films such as TiO2 films with regular oriented nanochannels (see Jung Tae Park, Won Seok Chi, Sang Jin Kim, Daeyeon Lee & Jong Hak Kim, Scientific Reports 4: 5505, Nature, 2014). Using this method, the morphological parameters, length, width and asymmetry of the nanochannels can also be adjusted. In addition, very thin ceramic films such as titanium oxide films with regular controlled nanochannels can be obtained using powder and sintering techniques. The film can be obtained, for example, on a nanoporous substrate with a preformed morphology using different deposition techniques via CVD (chemical vapor deposition), ALD (atomic layer deposition) or HiPIMS (high power pulsed magnetron sputtering).

[0123] Alternatively, the surface of the negatively or positively charged material can be chemically modified to enhance the negative or positive charge naturally present on the material after contacting the material with an electrolyte solution at a given pH, respectively. In other words, the surface of the charged nanoporous membrane (32) can be chemically modified to enhance the surface charge of the nanoporous membrane. The chemical modification can be achieved by chemical vapor deposition, atomic layer deposition, sol-gel coating or dip coating. Advantageously, the chemical modification can be achieved on the surface of the pore wall of the nanoporous membrane. For example, the charged nanoporous membrane (32) can be obtained from a polycarbonate membrane having an average pore size of <500nm, preferably <300nm, and more preferably <200nm; the inner pore wall of the nanoporous membrane has been chemically modified by dip coating the polycarbonate membrane in an aqueous solution of polydopamine. At pH=7, polycarbonate has a negative surface charge, and the negative surface charge is enhanced when the polycarbonate surface is coated with a polyamine.

[0124] In another alternative, when the surface of the membrane material carries ionizable functional groups, pH can be used to adjust the surface charge of the membrane. For example, for membrane materials such as TiO2, SiO2, Al2O3 that carry -OH groups on the surface, driving the pH of the electrolyte solution in contact with the membrane to an alkaline value (pH = 8-14) will deprotonate the -OH groups, thereby enhancing the negatively charged surface. Therefore, changes in pH can be used to adjust / control the zeta potential of the membrane surface. In fact, depending on the pH of the electrolyte solution to which the nanoporous membrane element (32) is in contact, the surface charge of the same membrane can be positive or negative. For example, a nanoporous membrane element (32) substantially formed of TiO2 carries -OH groups at pH ≥ 9. burden surface charge, and carries just Surface charge.

[0125] Without wishing to be bound by any particular theory, it is proposed that the nanochannels of materials with negative surface charges, taking into account their type, size and physicochemical properties, in particular their surface charge density, are of the following order of magnitude: Titanium dioxide: ~ -100 mC / m 2 (pH≥9)

[0126] Boron nitride: ~-1C / m 2 (pH≥10)

[0127] Silicon dioxide: ~-10mC / m 2 (pH ≥ 6)

[0128] Polycarbonate: ~-10mC / m 2 (pH≥5)

[0129] The electroosmotic nanofluid phenomenon generated by applying an electric field promotes the passage of cations (i.e., ions with a charge opposite to the surface charge of the material). The flow of cations from the Debye layer at the interface of the negatively charged membrane surface (because it contains anions and cations that are unbalanced under the action of the surface charge, so it is charged as a whole) then induces the flow of polar solvent in the same direction as the flow of cations. Therefore, under the application of a suitable electric field, the polar solvent flows from the container (10A) to the container (10B) through the reverse osmosis membrane element (30). Since the reverse osmosis membrane element (30) includes a semipermeable membrane element (31), which is selective for one or more specific solutes present in the electrolyte solution (11A), the flow of cations (32) generated in the pores of the nanoporous membrane induces the flow of the electrolyte solution (11A) from the container (10A) to the container (10B), while preventing the solute from passing (the solute is filtered out and stays in the container (10A)).

[0130] In contrast, nanochannels of materials with positive surface charges are proposed to facilitate the passage of anions (ie, ions having a charge opposite to the surface charge of the material) via an electroosmotic nanofluidic phenomenon generated by the application of an electric field.

[0131] In both cases (cation flow or anion flow), the flow of polar solvent is induced in the same direction as the cation / anion flow that occurs when a suitable electric field is applied between electrodes (20A) and (20B).

[0132] The membrane surface charge can be measured using any suitable method known in the art. For example, the zeta potential of a nanoporous membrane can be calculated using an electrokinetic analyzer.

[0133] The following formula can be implemented to estimate the zeta potential value of the membrane surface:

[0134]

[0135] in:

[0136] ε is the dielectric constant of the solvent (e.g., water),

[0137] ζ is the zeta potential,

[0138] η is the viscosity of the solvent (e.g., water),

[0139] A p is the total cross-sectional surface area of ​​all pores in the membrane exposed to the electrolyte solution,

[0140] ΔP is the pressure drop over the length L of the hole, and

[0141] I 流 It is the current flowing current.

[0142] When using a nanoporous membrane with pores of low tortuosity (e.g., nanoporous anodized aluminum with mostly cylindrical pores), the length of the pores, L, can correspond to the thickness of the nanoporous membrane. For nanoporous membranes with pores of significant tortuosity, calculations of the permeability relative to applied pressure allow the total pore length to be determined by applying the relevant tortuosity factor.

[0143] By changing the pH of the electrolyte solution using appropriate concentrations of a suitable acid (e.g., HCl) or base (e.g., KOH, NaOH, etc.), the zeta potential of the membrane surface can be measured at different pH values ​​(acidic, neutral and alkaline conditions). Preferably, the acid / base is selected to be compatible with the ions present in the electrolyte solution used in the process / system of the present invention. For example, when a KCI electrolyte solution is used, KOH can be used as a base to adjust the pH.

[0144] For example, if a |zeta potential| of minimum 5 mV is desired at the membrane surface, a membrane material may be chosen that carries a high surface charge, which allows a high zeta potential to be maintained at the surface when the membrane is in contact with an electrolyte solution.

[0145] Average pore size-nanoporous membrane

[0146] The nanoporous membrane element (32) preferably has a larger average pore size than the semipermeable membrane element (31): the solute filtration function is performed by the semipermeable element (31), while the function of the nanoporous membrane element (32) is to promote the reverse osmosis flow of the solvent when an appropriate electric field is applied between electrodes (20A) and (20B).

[0147] Advantageously, the nanoporous membrane element (32) with a positive or negative surface charge may have an average pore size of <500 nm, preferably <300 nm, more preferably <100 nm, and most preferably <50. Preferably, in the context of the present invention, the average diameter of the nanochannels of the nanoporous membrane element (32) may be between 1 nm and 500 nm, preferably between 1 nm and 300 nm, more preferably between 10 nm and 100 nm, and most preferably between 10 nm and 50 nm.

[0148] As used herein, the term "average diameter" refers to the internal average diameter of a nanochannel. The nanochannel may have a nanotubular, conical asymmetric, neck-shaped or perforated basic morphology. If the nanochannel has a nanotubular morphology, i.e., a circular cross section, the average diameter corresponds to the inner diameter of the circular cross section. If the nanochannel has a conical asymmetric, neck-shaped or perforated basic morphology, or an elliptical or irregular cross section, the average diameter corresponds to the average value of the minimum inner diameter and the maximum inner diameter. The average diameter of the nanochannel can be measured using methods known to those skilled in the art. For example, the average diameter can be measured by scanning electron microscopy or transmission electron microscopy. Advantageously, the nanochannels (32) contained in the nanoporous membrane element can have a uniform diameter. If on the same membrane, the nanochannels do not all have a uniform diameter, the average diameter will correspond to the average value of the average diameters of all nanochannels.

[0149] Advantageously, in the context of the present invention, the nanochannel has a nanotubular, tapered asymmetric, necked or perforated base morphology, preferably the nanochannel has a tapered asymmetric morphology.

[0150] The morphological parameters of the nanoporous membranes useful in the context of the present invention can be evaluated using conventional techniques, including scanning electron microscopy (SEM), atomic force microscopy (AFM), confocal scanning laser microscopy (CSLM) and transmission electron microscopy (TEM). Alternatively or in addition, X-ray micro-computed tomography (micro-CT), nuclear magnetic resonance (NMR), spin echo small angle neutron scattering (SESANS) and / or magnetic small angle neutron scattering (MSANS) can be used (these techniques are generally faster and more complete techniques because they can give 3D (volume) analysis). Using these techniques, the morphological parameters of the nanoporous membranes according to the present invention, such as pore size, pore size distribution, surface roughness, molecular weight cut-off and thickness, can be evaluated.

[0151] The pore size represents the size of the hole, and the hole is a channel with a variable cross section. The distance between two relative pore walls is used as the pore size of a simple geometry (usually: the diameter of a cylindrical hole with a pore size>2nm, the width of a slit-shaped hole with a pore size<2nm). If the hole has an irregular shape, some averages are performed to report the average pore size. The methods for measuring the pore size, average pore size and pore size distribution of porous materials are well known in the art (e.g., see ISO 15901 specification), including some statistical analyses using models, e.g., nonlinear optimization and Monte Carlo integration for materials where the pores do not all have the same size and / or geometry. Given the chemical and physical properties of the nanoporous membrane element (32) and the range of the average pore size (preferably, the average diameter of the nanochannels of the nanoporous membrane element (32) can be between 1 nm and 500 nm, preferably between 1 nm and 300 nm, more preferably between 10 nm and 100 nm, and most preferably between 10 nm and 50 nm), according to ISO 15901 specifications, the average pore size can be measured by nitrogen adsorption at -196°C (liquid nitrogen temperature).

[0152] Nanoporous membranes usable in the context of the present invention can be symmetrical or asymmetrical. As used herein, when referring to nanoporous membranes according to the present invention, "asymmetric" means that the pore size distribution of the nanoporous membrane is uneven throughout the membrane thickness. In contrast, symmetric membranes have a uniform pore size distribution throughout the membrane thickness. Typically, for asymmetric membranes, there is a very thin dense surface layer that acts as a functional layer on top of a porous sublayer with a specific pore diameter. Asymmetric membranes consist of, for example, a 0.1 μm-1 μm thick surface layer (selective barrier) on a highly porous 100 μm-200 μm thick substructure. The pore size of the porous sublayer can be as low as ≤1 nm and as high as 500 nm, and the pore size range defines the type of application that asymmetric membranes can be used for: microfiltration (50 nm-500 nm), ultrafiltration (1 nm-50 nm) and nanofiltration (≤1 nm). The pore size and its distribution can be determined by numerical analysis of the pore size observed in electron micrographs of membrane cross sections. The above pore size values ​​represent the arithmetic mean of the pore size distribution observed on the membrane cross section by scanning electron microscopy (SEM).

[0153] Advantageously, the average cross-section of the nanoporous membrane nanochannels and their specific regular through-morphology promote good diffusion of solutions through the membrane. Thus, the nanoporous membrane element (32) is clearly separated from the semipermeable membrane element (31) via its nanochannels that potentially allow both water molecules and ions to circulate, since each of the nanochannels advantageously has a cross-section greater than the size of these molecules.

[0154] Therefore, in one aspect, the reverse electroosmosis filtration system according to the present invention combines a semipermeable membrane (31) and a charged nanoporous membrane (32) with a surface charge, wherein the semipermeable membrane (31) is preferably superimposed with the charged nanoporous membrane (32). Therefore, the present invention is achieved to overcome technical biases, especially in surface chemistry, which may negatively affect the performance of the charged membrane in terms of its function of electrically inducing the flow of solvent from the electrolyte solution (11A) from the container (10A). For example, it is expected that under certain conditions, the combination of GO and 2D material membranes with oxide-type membranes (e.g., aluminum oxide, silicon oxide, titanium oxide) may form chemical bonds between the two surfaces (via hydroxyl condensation), making the composite membrane element more difficult to peel off and possibly impairing the stability and overall performance of the composite membrane element. Contrary to the prior art bias, the inventors have achieved a highly stable and high-performance composite membrane that combines a semipermeable membrane (31) and a charged nanoporous membrane (32) with a surface charge.

[0155] 1.3. Exemplary Features of Composite Membrane Filtration Systems

[0156] In an exemplary embodiment, the reverse electroosmotic filtration system according to the present invention can combine a semipermeable membrane (31), a charged nanoporous membrane (32) with a surface charge of |zeta potential| ≥ 5 mV, and a particularly advantageous selection of electrodes (20A) and (20B).

[0157] The semipermeable membrane (31) can be selected from a nanoporous carbon film or a stacked membrane of a layered material. The nanoporous carbon film or the stacked membrane of a layered material can be as described above. The pore size of the nanoporous carbon film can be in the range of 0.7nm to 1.5nm, preferably ≤1.4nm, more preferably ≤1.3nm, more preferably ≤1.1nm, and even more preferably ≤1.0nm. For example, the semipermeable membrane can be a multilayer MoS2 membrane, a multilayer hexagonal NiB membrane, or a multilayer GO or rGO membrane, preferably a multilayer GO or rGO membrane, and most preferably a multilayer GO membrane. Advantageously, the semipermeable membrane (31) can be a size exclusion selective membrane composed of stacked graphene oxide flakes.

[0158] The charged nanoporous membrane (32) with a surface charge of |zeta potential| ≥ 5 mV can be made of titanium oxide, boron nitride, SiO2, polyethersulfone, polycarbonate, anodized aluminum oxide; preferably titanium oxide, boron nitride, SiO2, polycarbonate and anodized aluminum oxide; most preferably titanium oxide, polycarbonate and anodized aluminum oxide.

[0159] The semipermeable membrane (31) is preferably superimposed with a charged nanoporous membrane (32). The semipermeable membrane can be placed directly on the nanoporous membrane element (32) with a surface charge, or can be placed on another porous support layer (33) before being placed on the nanoporous membrane element (32) with a surface charge (e.g., for ease of manufacturing and / or handling), as described above.

[0160] The first electrode (20A) and the second electrode (20B) can be any metal or carbon electrode that can have a capacitive effect. Suitable metal electrodes include Zn, Fe, Pt and Au electrodes. Suitable carbon electrodes include carbon paste electrodes, glassy carbon electrodes, graphite or graphite carbon electrodes or any carbon electrode used in salt batteries. Advantageously, the first electrode (20A) and the second electrode (20B) can be platinum electrodes. Preferably, the first electrode (20A) and the second electrode (20B) can be carbon electrodes (the advantage is that it allows the filtration system according to the present invention to be operated at very low voltages (on the order of 1V-2V)).

[0161] 2. Hybrid Film

[0162] Figure 2 An exemplary embodiment is shown in FIG.

[0163] In another variation, the reverse osmosis membrane element (30) can be a hybrid membrane element, wherein the semipermeable membrane element (31) and the nanoporous membrane element (32) having a surface charge are the same element to form a single hybrid membrane (30). Advantageously, the hybrid membrane (30B) can have a predetermined pore size and zeta potential suitable for the target solute to be concentrated / depleted or eliminated / filtered out. Advantageously, the single hybrid membrane (30B) can have an average pore size (11A) suitable for filtering out the target solute from the electrolyte solution, and a surface charge on the pore wall surface of the hybrid membrane of |zeta potential|≥5mV, preferably ≥20mV, and most preferably ≥50mV.

[0164] For example, the average pore size of the hybrid membrane will be small enough to prevent the target solute (and any other solute having a particle size greater than the target solute) from passing through the hybrid membrane (30B), while allowing polar solvents and other smaller sized solutes to pass through the hybrid membrane (30B). The average pore size of the hybrid membrane (30B) will be adjusted according to the following intended application types: microfiltration (50nm-500nm), ultrafiltration (1nm-50nm) or nanofiltration (≤1nm). Advantageously, the pore size of the hybrid membrane (30) (i.e., the average pore size measured according to ISO 15901 specification) is <500nm, preferably <300nm, more preferably <100nm, and most preferably <50nm. In a preferred variation, the filtration system is intended for ultrafiltration, and the hybrid membrane (30B) can have a pore size with an average pore size between 1nm-50nm.

[0165] The hybrid membrane element may be a nanoporous membrane having a suitable (positive or negative) surface charge, as generally described above and in any of the variants including preferred and advantageous variants, with an average pore size suitable for eliminating / filtering the target solute from the electrolyte solution (11A), as described in the paragraph above. For the sake of brevity, the description of the nanoporous membrane is not repeated here, but it should be understood that it applies to the hybrid membrane element after making necessary modifications in detail.

[0166] Advantageously, the hybrid membrane (30B) may be a nanoporous membrane substantially formed of a material having a positive or negative surface charge (|zeta potential| ≥ 5 mV, preferably ≥ 20 mV, most preferably ≥ 50 mV), such as TiO2, boron nitride, SiO2, polyethersulfone, polycarbonate, anodized aluminum, hydrotalcite, Ni-Fe layered

[0167] Double hydroxide, Ni2dobdc, Mg2dobdc (dobdc = 1,4-dioxo-2,5-phthalate), cellulose or polyelectrolyte layer polymer membrane, which polyelectrolyte layer polymer membrane is a nanoporous membrane such as obtained by successively dip-coating a cationic polyethyleneimine layer and an anionic polyacrylic acid layer onto a polycarbonate membrane; preferably TiO2, BN, SiO2, polycarbonate, anodized aluminum oxide, hydrotalcite, Ni-Fe layered double hydroxide, Ni2dobdc, Mg2dobdc, cellulose or polyelectrolyte layer polymer membrane; most preferably TiO2, BN, anodized aluminum oxide, SiO2 or polycarbonate.

[0168] Advantageously, the hybrid membrane (30B) can be a size exclusion selective membrane coated on its inner pore walls with a material having a positive or negative surface charge of |zeta potential| ≥5 mV, preferably ≥20 mV, most preferably ≥50 mV, such as TiO2, boron nitride, SiO2, polyethersulfone, polycarbonate, anodized aluminum, hydrotalcite, Ni-Fe layered double hydroxide, Ni2dobdc, Mg2dobdc (dobdc = 1,4-dioxo-2,5-benzenediol Acid), cellulose or polyelectrolyte layer polymer membrane, the polyelectrolyte layer polymer membrane is a nanoporous membrane such as obtained by successively dip-coating a cationic polyethyleneimine layer and an anionic polyacrylic acid layer onto a polycarbonate membrane; preferably TiO2, BN, SiO2, polycarbonate, anodized aluminum oxide, hydrotalcite, Ni-Fe layered double hydroxide, Ni2dobdc, Mg2dobdc, cellulose or polyelectrolyte layer polymer membrane; most preferably TiO2, BN, anodized aluminum oxide, SiO2 or polycarbonate.

[0169] Containers (10A) and (10B)

[0170] In the present disclosure, any reverse osmosis membrane element (30) of the separation container (10A) and (10B) can be used without any particular limitation, as long as the reverse osmosis membrane element does not allow solute permeation and mainly allows solvent permeation. Advantageously, the reverse osmosis membrane element (30) can be preferably adapted to achieve a solute rejection rate of 98.0% or higher, preferably ≥98.5%, more preferably ≥99.0%, still more preferably ≥99.5%, and most preferably 100% or about 100%.

[0171] For the implementation of the method of the present invention, any separation device / system comprising two compartments separated by a reverse osmosis membrane element (30) can be used. The mixture to be separated is placed in the first compartment (container (10A)), and the extracted organic compound is recovered in the second compartment (container (10B)).

[0172] In the present disclosure, the reverse electroosmosis filtration / purification system can be performed in a batch or continuous manner to maximize its effect. For example, the reverse electroosmosis filtration / purification system according to the present invention can be configured in multiples. In other words, the unit "container (10A)-reverse osmosis membrane element (30)-container (10B)" can be configured in multiple stages.

[0173] In an exemplary variation, it can be configured such that the reverse electroosmosis filtration / purification system includes N containers (10) and N-1 reverse osmosis membrane elements (30), where N is an integer. For example, N can range between 3 and 100, more specifically between 3 and 50. In such a multi-container device, the containers and reverse osmosis membrane elements can be as described above. Thus, the assembly can be formed by alternating containers (10) that alternately contain electrolyte solutions enriched with the solute of interest and less concentrated electrolyte solutions, and are separated from each other by reverse osmosis membrane elements (30).

[0174] Polar solvents

[0175] The polar solvent may advantageously be a solvent capable of generating acidic ions. For example, the polar solvent may be water, an alcohol such as methanol or ethanol, a water-alcohol mixture, ammonia, acetone or acetonitrile.

[0176] Electrolyte solution (11A) and (11B) and solute

[0177] An electrolyte solution useful in the context of the present invention may be any electrolyte solution containing at least one solute of interest / undesirable solute in a polar solvent as defined herein.

[0178] For example, the solvent may be water or an aqueous solution.

[0179] In a preferred variation, the electrolyte solution may be an aqueous solution containing electrolytes. The electrolytes may be of any chemical type, as long as they dissolve in the solution in the form of charged ions. Preferably, these ions are derived from dissolved salts, such as NaCl, KCl, CaCl2 and MgCl2. The electrolyte solution may be a synthetic solution; a natural solution, such as fresh water from a lake or river, groundwater, brackish water, seawater, industrial process water, oil production water, or a biological solution / fluid.

[0180] Examples of solute-containing aqueous solutions used as electrolyte solutions according to the present invention include seawater, brackish water, cellular metabolites, reaction products, biological fluids, etc., wherein cellular metabolites are intended to include cultures of animal cells, plant cells or microorganisms, their primary metabolites, secondary metabolites, proteins secreted in vitro, biotransformation products, etc.

[0181] Examples of the reaction solution include chemical reaction products and enzymatic reaction products.

[0182] Examples of microbial primary metabolites include organic acids (e.g., acetic acid, propionic acid, butyric acid, lactic acid, succinic acid, etc.), alcohols (e.g., ethanol, butanol, etc.), hexane, amino acids (e.g., lysine, tryptophan, etc.), vitamins, polysaccharides, etc., but are not limited thereto.

[0183] Examples of microbial secondary metabolites include antibiotics (e.g., penicillin, etc.), enzyme inhibitors, physiologically active substances (e.g., paclitaxel, etc.), etc., and examples of microbial in vitro secretory proteins include enzymes such as amylase, cellulase, etc., insulin, interferon, monoclonal antibodies, etc. In addition, microbial biotransformation products are substances produced by using microorganisms or enzymes, and examples thereof include steroids, etc., but are not limited thereto.

[0184] Examples of biological fluids include blood, serum, plasma, urine, saliva, tears, dialysate, intestinal contents, parenteral nutrition solutions, seminal plasma, and cerebrospinal fluid.

[0185] Preferably, the electrolyte solution may be an aqueous solution comprising a solute selected from alkali metal halides or alkaline earth metal halides, preferably selected from NaCl, KCl, CaCl2 and MgCl2, more preferably the solute is NaCl.

[0186] The solute may be selected from solid particles, organic or inorganic small molecules such as dye complexes (e.g., tris(2,2'-bipyridyl)dichlororuthenium(II) hexahydrate), biomolecules such as hormones (e.g., testosterone), proteins, polysaccharides, polynucleotides, polypeptides, enzymes or antibodies, pollutants (e.g., from wastewater, industrial process water or landfill leachate), metabolic waste or salts / ions. When the solute of interest to be concentrated is a solid, it is preferably a material that is easily crystallized depending on temperature and pH and is not highly viscous even at high concentrations.

[0187] In the present disclosure, the solute may be a salt (or liquid), and the solvent may be water. For example, the electrolyte solution (11A) may be seawater, the solute is NaCl, and the process is water desalination. Therefore, the present invention also relates to a water desalination system, comprising a reverse electroosmosis filtration system according to the present invention in any variant form described herein. Therefore, in one aspect, the present invention relates to a process for desalination of seawater, comprising the following steps: i) providing a reverse electroosmosis filtration system, the reverse electroosmosis filtration system comprising:

[0188] a) a first container (10A) equipped with a first electrode (20A), the first container containing seawater, such that the first electrode (20A) equipped with the first container is in contact with the seawater contained in the first container (10A);

[0189] b) a second container (10B) equipped with a second electrode (20B), the second container containing water, such that the second electrode (20B) equipped with the second container is in contact with the water contained in the second container (10B); the first electrode (20A) and the second electrode (20B) are operatively coupled to an electrical energy source (40);

[0190] c) a reverse osmosis membrane element (30) that separates the first container (10A) and the second container (10B) and combines the following:

[0191] (i) a semipermeable membrane element (31) having an average pore size of <1 nm, and

[0192] (ii) a nanoporous membrane element (32) having a surface charge of |zeta potential| ≥ 5 mV, preferably ≥ 20 mV, most preferably ≥ 50 mV, as measured using an electrokinetic analyzer; the nanoporous membrane having an average pore size of < 1 μm, preferably < 500 nm, as measured according to ISO 15901 specifications;

[0193] wherein the semipermeable membrane element (31) and the nanoporous membrane element (32) having a surface charge are two different elements and are preferably stacked on each other;

[0194] wherein the semipermeable membrane element (31) is in contact with seawater contained in a first container (10A), and the nanoporous membrane element (32) having a surface charge is in contact with water contained in a second container (10B);

[0195] The reverse osmosis membrane element (30) realizes the following two functions: (i) solute filtering function; and (ii) electrically inducing the flow of water from the first container (10A) through the reverse osmosis membrane element (30) to the second container (10B);

[0196] The reverse osmosis membrane element (30) is adapted to selectively prevent Na+ and Cl- from diffusing through the reverse osmosis membrane element (30); ii) applying an electric field between the first electrode (20A) and the second electrode (20B) to induce reverse osmosis flow of water from the first container (10A) through the reverse osmosis membrane element (30) to the second container (10B), the reverse osmosis membrane element separating the first container (10A) and the second container (10B);

[0197] thereby allowing water to flow from the first container (10A) to the second container (10B) while retaining the Na+ and Cl- solutes in the first container (10A); and

[0198] iii) collecting desalted water (10B) from the second container, the desalted water being substantially free of Na+ and Cl- solutes; wherein ≥99%, preferably ≥99.5%, more preferably ≥99.8%, still more preferably ≥99.9%, and most preferably 100% of the Na+ and Cl- solutes remain in the seawater contained in the first container (10A). Through this process, the water (10A) contained in the first container becomes more concentrated in NaCl than the seawater (11A) placed in the first container at the beginning of the process. Conversely, through this process, fresh water ("eau douce" in French) can be collected in the second container (11B). The semipermeable membrane element (31) can be any semipermeable membrane used in water purification or desalination systems, reverse osmosis systems, such as a thin film composite membrane (TFC or TFM). The semipermeable membrane element (31) can be any nanofiltration semipermeable membrane. For example, the nanoporous carbon membrane described in the present disclosure can be suitable for the desalination process according to the present invention, and the pore size of the nanoporous carbon membrane can be 0.7nm to 1.5nm, preferably ≤1.4nm, more preferably ≤1.3nm, still more preferably ≤1.1nm, and even more preferably ≤1.0nm. For example, the semipermeable membrane (31) can be a size exclusion selective membrane composed of stacked graphene oxide or reduced graphene oxide flakes, preferably a size exclusion selective membrane composed of stacked graphene oxide flakes. The salinity in the ocean varies from place to place, but the relative proportions of most major dissolved components remain virtually constant. Although there are small amounts of other ions in seawater (e.g., K+, Mg2+, S042-), sodium (Na+) and chloride (CI-) ions still account for about 91% of all seawater ions. Advantageously, the process for desalination of seawater according to the present invention can produce a retained stream having a salinity of ≤5% (≤50 ppt), preferably ≤3% (≤30 ppt), more preferably ≤1% (≤10 ppt), and most preferably ≤0.5% (≤5 ppt). Salinity is usually derived from electrical conductivity (EC) measurements. EC is measured by passing an electric current between two metal plates or electrodes in a water sample and measuring the ease with which the current flows between the plates. The use of EC measurements to estimate the ionic content of seawater led to the development of the Practical Salinity Standard 1978 (PSS-78, which has been considered by the Joint Expert Panel on Oceanographic Tables and Standards and is recommended by all oceanographic organizations as a scale for reporting future salinity data). The practical salinity of a seawater sample is defined as the ratio of the conductivity of the seawater sample at a temperature of 15°C and a pressure of 1 standard atmosphere to the conductivity of a potassium chloride (KCI) solution containing 32.4356 g KCI in 1 kg of solution at the same temperature and pressure. A ratio of 1 corresponds to a true salinity of 35 (standard sea water). Since the definition is a ratio, the true salinity is expressed as a dimensionless number.

[0199] The invention also relates to a water purification system comprising a reverse electroosmosis filtration system according to the invention in any of the variants described herein. For example, water contaminants to be filtered may include endocrine disruptors, hormones, pesticides and / or dyes.

[0200] More precisely, in one aspect, the present invention relates to a method for purifying a liquid comprising water and impurities, the method implementing the technique of electro-reverse osmosis. Purifying water, water purification, generally refers to any operation involving the treatment of water containing an initial content of impurities, so that at the end of the operation, the final content of impurities is lower than the initial content. Impurities are elements other than those constituting pure water (i.e. H2O, OH - and H + ) any element, molecule, ion or other. This purification method can be, for example, a method for desalinating seawater, a method for treating industrial process water, or a method for treating landfill leachate.

[0201] Thus, in one aspect, the present patent application proposes a method for recovering potable water from a large number of saline sources, in particular surface water containing various concentrations of sodium chloride. The application range is from less than 1% to 20% salinity, for example in the following salinity water applications: brackish water of 0.5%-3.5% salinity, seawater of 3.5%-4.5% salinity, and salt water of 5%-20% salinity.

[0202] In the present disclosure, the electrolyte solution containing the solute may be a biological fluid, preferably a dialysate. Therefore, the present invention also relates to an implantable artificial kidney comprising a reverse electroosmotic filtration system according to the present invention in any of the variants described herein.

[0203] The basic principle of the present invention is that the reverse osmosis membrane element (30) (single hybrid membrane) or at least a portion thereof (composite membrane comprising a semipermeable membrane element (31) and a nanoporous membrane element (32)) carries sufficient surface charge (which can be positive or negative) to induce a zeta potential at the membrane / electrolyte solution interface, which zeta potential is high enough to induce anions or cations to flow through the nanochannels of the nanoporous membrane when a suitable electric field is applied between electrodes (20A) and (20B), respectively.

[0204] This phenomenon is governed by the same principles that apply to the zeta potential of colloidal particle suspensions.

[0205] In the case of colloidal suspensions, the fact that many organic and inorganic colloidal particles have a negative charge in an aqueous environment causes them to repel each other and maintain a stable state that characterizes their dispersion. The electrochemical dispersion of colloidal particles has been studied for many years. Several models such as the double layer and DLVO theory have been developed to explain the stability of colloids. The double layer model predicts that when suspended particles are present in a liquid phase, the inner dense layer at the surface of each particle (composed of ions in the solution attracted by the charge of the particles) presents a charge of opposite polarity to the natural charge of the particles themselves under the physical and chemical conditions of the suspension. The outer layer of opposite polarity, also composed of ions in the solution, diffuses within a given distance from the surface of the particles. The net potential between the two layers (commonly referred to as zeta potential in the art) produces repulsion, which counteracts the van der Waals attraction between the particles. If the outer layer diffuses over a sufficiently wide radius, thereby increasing the influence of the zeta potential, the particles remain separated and will remain in a stable suspension. On the other hand, if the diffusion radius of the outer layer is reduced to the extent that van der Waals forces dominate, the particles are attracted to form agglomerates, which tend to separate from the liquid phase.

[0206] This principle is extended to the present invention: the dense layer at the surface of the inner pore wall of the nanoporous membrane (composed of ions in the electrolyte solution attracted by the surface charge present at the surface of the inner pore wall of the nanoporous membrane) presents a charge opposite to the natural charge polarity of the nanoporous membrane itself under the physical and chemical conditions of the electrolyte solution. The outer layer of opposite polarity (also composed of ions in the solution) diffuses within a given distance from the surface of the nanoporous membrane. The net potential between the two layers is called the zeta potential. The zeta potential is the potential difference between the Stern dense layer and the liquid. Therefore, it characterizes the charge distribution on the surface of the inner pore wall of the nanoporous membrane.

[0207] Therefore, the zeta potential depends on the ionic force of the electrolyte solution and the ion concentration in the solution around the membrane surface.

[0208] In order to increase the zeta potential and improve the reverse osmosis flow generated on either side of the reverse osmosis membrane element, the pH of the electrolyte solutions (11A) and (11B) can be adjusted according to the isoelectric point of the inner surface of the nanochannel of the nanoporous membrane (32) (composite membrane element) or (32A) (hybrid membrane element) with surface charge.

[0209] The effect of pH on the surface charge of the membrane can be studied by measuring the zeta potential of nanoporous membrane samples at different pH values ​​of the electrolyte solution. As the pH value of the electrolyte solution increases, the zeta potential of the nanoporous membrane may be pushed toward negative values. For example, one mechanism by which the increase in pH drives the zeta potential toward negative values ​​includes the deprotonation of substances on the surface of the pore wall of the membrane (e.g., deprotonation of OH to O -, for example on the surface of a TiO2 or SiO2 film).

[0210] For example, when using a ceramic nanoporous membrane such as TiO2 or BN nanoporous membrane to obtain a negative charge on the inner surface of the nanochannel, the pH of the solution can be adjusted to a value between (pHiso+1) and 14, more advantageously to a value between (pHiso+2) and 12. In order to obtain a positive charge on the inner surface of the nanochannel, the pH of the solution can be adjusted to a value between 0 and (pHiso-1), more advantageously to a value between 1 and (pHiso-2). The increase in the negative zeta potential value of the nanoporous membrane and the increase in the pH value may be due to, for example, the deprotonation of functional groups on the membrane surface.

[0211] As used herein, "pHiso" refers to the pH value of the isoelectric point of the constituent material of the inner surface of the nanochannel. pHiso is measured using methods known to the skilled artisan, specifically using potentiometric acid-base titration methods.

[0212] When the electrolyte solution containing the solute is an aqueous solution, the aqueous solution may have a pH of 2 to 13, depending on the nature of the nanoporous membrane and the surface charge naturally present thereon, and the temperature at which the water remains liquid, for example, 0° C. to 100° C., preferably 15° C. to 50° C., more preferably 20° C. to 40° C. The temperature may be higher or lower than the above temperature. For example, other solute / solvent mixtures may have a temperature that deviates from the above temperature.

[0213] Electrodes (20A) and (20B)

[0214] As discussed previously, each of the containers (10A) and (10B) of the purification / filtration system according to the present invention comprises electrodes (20A and 20B, respectively) arranged so that the electrodes are in contact with the electrolyte solution (11A and 11B, respectively). Different types of electrodes may be used in the context of the present invention.

[0215] A cation or anion collector (e.g., Na + or Cl - All types of electrodes for ion flow, preferably made of silver and silver chloride (Ag / AgCl), carbon and platinum (C / Pt-), carbon (C-), graphite or [Fe(CN)6] 4- / [Fe(CN)6] 3-type iron complex. The first electrode (20A) and the second electrode (20B) can be any metal or carbon electrode that can have a capacitive effect. Suitable metal electrodes include Zn, Fe, Pt and Au electrodes. Suitable carbon electrodes include carbon paste electrodes, glassy carbon electrodes, graphite or graphite carbon electrodes or any carbon electrodes used in salt batteries. Advantageously, the first electrode (20A) and the second electrode (20B) can be platinum electrodes. Advantageously, the first electrode (20A) and the second electrode (20B) can be carbon electrodes. The advantage of using a carbon electrode is that it allows the filtration system according to the present invention to be operated at very low voltages (on the order of 1V-2V).

[0216] The electrodes (20A) and (20B) may be partially or completely immersed in the electrolyte solutions (11A) and (11B), respectively. It may also be provided that the electrodes (20A) and / or (20B) may be at least a portion of the wall of the container (10A) and / or (10B).

[0217] These electrodes (20A) and (20B) are both connected to a power source (40), allowing an electric field to be generated between the two electrodes. These electrodes may be connected to the power source (40) only via a cable.

[0218] Electrical Energy Components(40)

[0219] In the system and process according to the present invention, the electric energy source element (40) can be any suitable power source known in the art. For example, it can be a generator, a battery, a photovoltaic panel or any other form of power source. In the present disclosure, the purpose of the energy source element (40) is to generate an electric field between the electrodes (20A) and (20B). In this regard, the electrodes (20A) and (20B) connected to the energy source element (40) are not used to collect the ion current generated by the membrane element (e.g., by the diffusion-osmosis effect).

[0220] Advantageously, the electrical energy element (40) may include one or more batteries. Thus, the reverse electroosmosis filtration system according to the present invention may be a portable / mobile system. For example, the electrical energy element (40) may be configured to be charged by light, wherein in particular, the electrical energy element includes a solar cell or a photodiode.

[0221] Advantageously, the electrical energy source element (40) may be configured to be charged by utilizing the reverse electroosmotic effect of pumping an electrolyte solution through the reverse osmosis membrane element (30).

[0222] To this end, the electrical energy source element (40) may include a hydraulic turbine element operatively connected to the reverse electroosmosis membrane element (30).

[0223] Flow Control(50)

[0224] The reverse electro-induced flux through the composite or hybrid membrane element according to the invention can be controlled using the following different parameters:

[0225] (i) Surface charge of nanoporous membranes: The flow rate over the membrane element can be increased by using membranes with higher surface charge. The surface charge can be adjusted by the choice of materials, any chemical modification that can be applied to modify the membrane surface charge, the pH of the electrolyte solution in contact with the membrane surface carrying the surface charge. Advantageously, a minimum surface charge of |zeta potential| ≥ 5 mV, more preferably ≥ 20 mV, most preferably ≥ 50 mV is preferred. As previously mentioned, the membrane surface charge can be adjusted based on the choice of materials constituting the membrane and / or based on the ionic force / concentration of the electrolyte solution in contact with the membrane.

[0226] (ii) Pore size: With respect to semipermeable membranes (eg when composite membranes are used), the pore size will naturally depend on the size and / or chemical nature of the solutes to be filtered / separated.

[0227] With regard to the nanoporous membrane element (which implements the "pumping function" in the system), there are no special constraints on the pore size, except when the nanoporous membrane element also implements the role of a size-exclusion semipermeable membrane (for example, this is the case with the hybrid membrane element described herein, where the average pore size of the nanoporous membrane should be suitable for the size of the solute to be separated / filtered out). In other words, electroosmosis has no or almost no dependence on the pore size of the nanoporous membrane element. The nanoporous membrane pore size only needs to be sufficient to induce electroosmotic flow of polar solvents through the membrane. This is true for variants using composite membranes as well as for variants using hybrid membranes (i.e., when using dual semipermeable / nanoporous membrane elements, such as Figure 2 ) is correct. Advantageously, the average pore size of the nanoporous membrane element (which realizes the function of the flow of polar solvents in the electrically induced system) can be <500nm, preferably <300nm, more preferably <100nm, most preferably <50nm. In a preferred variant, the filtration system is intended for ultrafiltration, and the average pore size of the nanoporous membrane element can be between 1nm-50nm.

[0228] (iii) Pore geometry: In general, a semipermeable membrane may not have a well-defined pore geometry (e.g., it may be "spaghetti-shaped"). With respect to nanoporous membrane elements, there are no particular constraints on pore geometry: the system can operate at any pore geometry (provided that the nanoporous membrane material carries a suitable surface charge, as described in further detail herein), ranging from materials with symmetrical pore shapes (such as anodized aluminum, characterized by cylindrical pores) to materials with highly tortuous pores (such as polycarbonate). For example, pores with nanotubular morphology, i.e., cylindrical pores of circular cross-section, conical asymmetric pore shapes, honeycomb pore geometries, hourglass-shaped pores, etc., may be used. The electroosmotic flow through a nanoporous membrane may be optimized by adjusting the pore geometry of the membrane. This can be achieved empirically by varying the pore geometry of a given nanoporous membrane using methods well known in the art.

[0229] Generally, flow can be optimized if the geometry of the membrane pores is preferably symmetrical and has little or no tortuosity. Thus, a nanotubular morphology (i.e., a circular cross section) will have the effect of increasing flow through the membrane, as opposed to, for example, a conical asymmetric pore shape.

[0230] (iv) Electric field strength: For a given nanoporous membrane (32) and membrane surface area exposed to the electrolyte solution in the system according to the invention, the flow rate increases as the current (and hence the electric field) applied between the electrodes increases (see e.g. Figure 4B and Fig.12 The choice of applied current will depend in part on the type of filtration application (microfiltration (50 nm-500 nm), ultrafiltration (1 nm-50 nm), or nanofiltration (≤ 1 nm). The intensity and electric field are selected to maximize flow. It also depends on the number of pores through which electroosmotic flow can be induced, and therefore on the surface area of ​​the nanoporous membrane in contact with the electrolyte solution and the surface pore density of the nanoporous membrane. Typically, for given conditions of pH, concentration, etc. in the electrolyte solution, a curve of flow rate versus intensity (or current) is plotted to determine the optimal range of electric field strength. For ultrafiltration purposes, the applied current is 2.5-3.0 relative to the membrane size. Preferably in the range of 0.5 mA to 20 mA, e.g. 0.5 mA to 15 mA, 0.5 mA to 10 mA, preferably 0.5 mA to 5 mA, more preferably 0.5 mA to 2 mA. The electric field strength will preferably be adjusted depending on the electrodes and / or membrane used: care should be taken so that there are no secondary redox reactions that would damage, for example, the electrodes and / or the membrane. For example, when using platinum electrodes, there is no limit per se to the voltage that can be applied (the electrodes can withstand any voltage): the voltage limit will be at the voltage threshold at which the electrolysis of the solvent starts (e.g. when water is used as solvent, the applied voltage should not exceed 5 V to avoid water electrolysis).

[0231] In contrast, when using Ag / AgCI electrodes, the applied voltage should not exceed 1 V to avoid secondary redox reactions at the electrode level (in this case, the properties of the electrodes will limit the applied voltage).

[0232] (v) Ionic force / concentration of electrolyte solution: The flow rate is inversely proportional to the salt concentration in the electrolyte solution (see e.g. Figure 4B and Fig.12 ).

[0233] The choice of salt concentration in the electrolyte solution will depend on the flow rate to be achieved. For ultrafiltration purposes, the salt concentration in the electrolyte solution preferably ranges from 0.1 mM to 100 mM, preferably from 0.1 mM to 50 mM, more preferably from 0.1 mM to 10 mM, most preferably from 1 mM to 10 mM.

[0234] In summary, we have developed a filtration method based on the application of an electric field using a composite membrane with a nanometer average pore size (<500nm) (which has a significant surface charge). When the membrane separates two reservoirs / containers containing water (or other polar solvents) and mobile electrolytes (e.g., salts), an electric field is applied between the two reservoirs / containers of the unit to produce an electroosmotic flow (water / solvent moves from one unit to another in the direction opposite to the normal osmotic flow). It has been demonstrated herein that this reverse osmosis flow can be used for filtration / purification applications by an unexpected combination of a nanoporous membrane with a surface charge and a selective membrane. Therefore, water with electrolytes can be used as a separation carrier for uncharged molecules (hormones, dyes, drugs, etc.). It is not necessary to have an electrolyte concentration difference between the two reservoirs / containers of the unit, nor is it necessary to apply a pressure difference to obtain flow. The flow can be controlled by different parameters, such as the surface charge of the membrane, the diameter of the pores and their geometry (tortuousness, asymmetry, etc.) and the electric field.

[0235] As discussed above, the shortage of drinking water resources is a major international problem. On the one hand, certain industrial wastes, especially pharmaceutical and chemical wastes, pose major problems for treatment plants. On the other hand, some arid countries make extensive use of reverse osmosis desalination processes to obtain drinking water. However, the energy costs of these processes significantly increase the price of water and also the price of facilities.

[0236] Electric field filtration makes it possible to save the application of high pressure in traditional water treatment processes. For example, in order to desalinate, it is necessary to apply a pressure (>30 bar) that exceeds the osmotic pressure. These processes are expensive and complicated to implement. Even for larger molecules (hormones, drugs, etc.) that are sometimes difficult to eliminate, the application of electric fields also reduces water treatment costs. The use of 2D nanomaterials (such as graphene oxide or boron nitride) combined with this filtration method also makes it possible to work with thinner membranes, thereby improving the permeability for the same selectivity.

[0237] Contrary to the standard methods (usually of the reverse osmosis type) based on the application of mechanical forces through pressure differences, the present invention implements the use of electric fields to induce separation and filtration. Therefore, the present invention provides a filtration method that is not based on concentration differences (such as direct osmosis) or pressure differences (reverse osmosis), but on the application of electric fields. This offers huge economic advantages: lower facility costs, applying electricity is cheaper than applying pressure, and processes of mechanical stress are avoided (which usually use pressures of the order of 50 bars on the membrane, which does not occur here). This also has significant ecological advantages, since it can provide an upstream solution for filtering complex molecules to be eliminated in purification plants. For example, the electric field filtration system according to the present invention can be installed in factories of the pharmaceutical or textile industries for wastewater pretreatment.

[0238] Thus, the present invention provides a very valuable alternative to filtration / purification processes and water treatment processes that overcomes the shortcomings of existing processes.

[0239] Equivalent

[0240] The following representative embodiments and drawings are intended to help illustrate the present invention and are not intended to, and should not be construed as, limiting the scope of the present invention. Indeed, various modifications of the present invention and many further embodiments thereof, in addition to those shown and described herein, will become apparent to those skilled in the art from the entire contents of this document, including the following examples and references to the scientific and patent literature cited herein.

[0241] It should also be understood that the contents of these cited references are incorporated herein by reference to help illustrate the state of the art.

[0242] The following examples contain important additional information, exemplification and guidance that are applicable to the practice of the various embodiments of the present invention and their equivalents.

[0243] Example

[0244] Process and system according to the present invention and their simplification in practice can be further understood by illustrating the embodiments of how some processes are performed. However, it should be understood that these embodiments should not be construed as limiting the present invention. Modifications of the present invention known now or further developed are considered to fall within the scope of the present invention described herein and claimed hereinafter.

[0245] abbreviation

[0246] GO: graphene oxide

[0247] PC: Polycarbonate

[0248] PMMA: Polymethacrylate

[0249] Materials and methods

[0250] A commercial aqueous dispersion of graphene oxide at a concentration of 0.4 wt% was purchased from Graphenea SA. Polycarbonate track-etched membranes were provided by Sterlitech Corporation. Potassium chloride (>99%), tris(2,2'-bipyridyl)dichlororuthenium(II) hexahydrate (>99.95%), and testosterone (>99.9%) were purchased from Sigma-Aldrich. All experiments were performed at room temperature (25±3°C) and neutral pH.

[0251] Example 1 - Composite membrane preparation and characterization

[0252] GO / PC membranes were prepared by vacuum filtration. In a typical preparation, a diluted dispersion of graphene oxide (GO) was prepared by first centrifuging a commercial dispersion provided by Graphenea SA at low speed (2000 rpm, ALLEGRA64-R). The precipitated solid was discarded until the density of the dispersion was adjusted to 1.003 mg L-1, typically for four cycles. The dispersion was then filtered using a 100 μl / min (Millipore) system (A100). Water dilutes 1.5mL of this suspension to a total volume of 15mL. This diluted GO dispersion is added dropwise to the top of a 25mm polycarbonate (PC) substrate disk, which has a thickness of 24±1μm and a porosity of 4.7%, which is provided by a 100nm track-etched hole (Nuclepore track-etched membrane, 25mm, 0.1μm) arranged on a Buchner funnel sealed at one end and connected to a vacuum pump at the other end. When the vacuum filtration process ends (usually less than 16 hours), the composite GO / PC membrane disk is divided into two fragments. One part is inserted into a purification device, while the other part is retained for characterization.

[0253] The surface charge of the PC film was measured using the conductivity equation [1] and was determined to be approximately 0.2 mC / m 2 .

[0254] The pore size of the GO membrane was measured using XRD and determined to be 0.8 nanometers on average (the average interlayer distance between stacked GO sheets). The XRD diffraction pattern showed a broad distribution of interlayer distances (from 0.7 nm to 1.4 nm).

[0255] Material characterization

[0256] The surface morphology of the GO / PC films was observed by optical microscopy in transmission mode and field emission scanning electron microscopy (FE-SEM) in a Thermo-FischerTM Quattro S instrument. Figure 4C ). After tilting the sample holder by 90°, the cross section of the GO layer was observed. The X-ray diffraction patterns of the films were collected in refraction mode ( Figure 4D ). Nitrogen adsorption and desorption isotherms were collected in a volumetric instrument at 77 K. The average void space between the GO layers of the GO / PC membrane was determined by applying the Bragg law to the 001 peak of the recorded diffraction pattern, while the pore size distribution of the membrane and its specific surface area were determined by applying the DFT model and the BET equation, respectively, to the typical nitrogen adsorption isotherms.

[0257] Example 2 - Filtration of Dye Complex

[0258] Evaluation of the electroosmotic purification system according to the present invention was performed using a custom electrokinetics set-up, in which the composite GO / PC membrane prepared as in Example 1 separated two reservoirs of 6 mL volume each ( Figure 1 During the flow determination, each reservoir (10A) and (10B) was filled with water and a solution of the same salt concentration (KCi). For the retention experiments, 1 μM to 200 μM of tris(2,2'-bipyridyl)dichlororuthenium(II) hexahydrate (99.95%) (Ru-bypi) was added to the reservoir (10A) as a test contaminant.

[0259] A platinum electrode (Sigma-Aldrich) was placed in each reservoir (10A) and (10B) and connected to a Keithley 2410 Sourcemeter via wires to ensure a constant tension between -1 mA and 1 mA.

[0260] The gap between the two reservoirs is equipped with a PMMA disk with a circular hole of 0.5 cm in diameter in the middle. For this reason, glue (Staycast 1266, Aldrich) is applied around the GO / PC composite membrane, leaving the middle part facing the hole on the PMMA disk unapplied. After the glue cures (usually 24 hours), the PMMA disk with the GO / PC composite membrane covering the hole is placed between the reservoirs, resting on each O-ring, then pressed and mechanically sealed.

[0261] After closing the circuit, the flow from reservoir (10A) to reservoir (10B) was measured by coupling the outlet tube of the reservoir to a flow meter (comprising a capillary calibrated in millimeters): Briefly, each reservoir was independently connected to a flow meter (glass capillary of known diameter, with a ruler next to it so that the volume could be known). The quantitative determination of Ru-bypi was performed by UV-Vis spectroscopy in a NanoDrop (Thermo Fisher Scientific). The external calibration curve of the instrument and the interception measurement were performed by preparing solutions of Ru(bypi) ranging from 0.5 μM to 100 μM and determining their absorbance at 283 nm.

[0262] Example 3 - Filtration of hormones

[0263] Example 2 was repeated using 10 mg mL-1 testosterone as the contaminant instead of the Ru(bypi) dye.

[0264] Quantitative determination of testosterone was performed by UV-Vis spectroscopy in a NanoDrop (Thermo Fisher Scientific). External calibration curves and inhibition measurements of the instrument were performed by preparing 0.9 μM and 9 μM solutions of testosterone and determining their absorbance at 283 nm (see Figure 5A ).

[0265] Results and discussion

[0266] By way of the preceding examples, an ultrafiltration process and system is achieved through a thin composite semipermeable membrane (~8 μm-9 μm) consisting of graphene oxide (semipermeable membrane) in combination with a polycarbonate nanoporous membrane presenting a suitable surface charge, wherein flow is obtained by applying a low energy electromotive force. The examples illustrate an assembly consisting of two reservoirs (10A) and (10B) separated by a composite membrane according to the invention, wherein a voltage drop can be applied between the faces of the membrane. The system is tested in terms of flux and retention, initially with probe molecules to optimize operating conditions, and finally with testosterone, a pollutant that commonly contaminates drinking water.

[0267] Without wishing to be bound by any particular theory, it is proposed that at a certain voltage drop, electroosmotic flow of water occurs within the nanopores of the PC membrane due to the formation of a Debye layer in close contact with the charged surface of the PC material. The overall asymmetry of membranes made of nanoporous materials that exhibit surface charges [2] results in an asymmetric response of the water flow rate to the voltage drop. The water flow rate is expressed by the following expression:

[0268] Q = Qosm + Qs*(exp(V / V0)-1)(Formula 2)

[0269] where Qosm = K_hydro*kT Dc*2 is the contribution of permeate to the flux and the second term originates from the rectified electroosmotic flow in the asymmetric membrane; Qs is the saturation value of the flux and depends on the properties of the membrane pores.

[0270] Due to the semipermeability of GO membrane, ions cannot be carried and only water is allowed to pass through the GO / PC membrane. At the same time, the high cohesion of layer-by-layer GO membrane provides high selectivity during the purification process.

[0271] First, the water flux across the asymmetric membrane under the voltage drop (AV) is calculated ( Figure 7 ). Interestingly, for ΔV>0, the flow increases exponentially with the voltage drop and overcomes the permeate contribution to the flow. This suggests that the permeate flow can be balanced above a threshold voltage. In this case, flow can be generated from the positive to the negative electrode of the membrane.

[0272] At this stage, it is worth noting that the above formula shows that the characteristic voltage in Equation 2 is fixed by ΔV0.

[0273] Then, a device that is easily scalable and able to work under these premises to exploit this phenomenon in water purification, which represents pollutants that are about to cause harm to the environment and human health, was prepared. The device consists of two reservoirs (10A) and (10B), separated by a semipermeable GO / PC membrane prepared in Example 1, each of which is further filled with a solution of water and salt (KCi), and then coupled to a power source ( Figure 4A The selectively permeable graphene oxide layer on top of the polycarbonate was formed by stacking GO sheets layer by layer with the help of pressure difference and water penetration. The prepared membrane GO / PC was formed by stacking GO sheets layer by layer with the help of pressure difference and water penetration, and the membrane GO / PC is suitable for purification because no cracks were detected in the long range ( Figure 8 ). FE-SEM image of the membrane surface ( Figure 4C ) confirmed their previously observed cohesion, while cross-sections of the membrane revealed a dense interlaminar structure with a thickness of approximately 9 μm ( Figure 4C ).

[0274] The film showed a PXRD diffraction pattern ( Figure 4D ) obtained an average interlayer distance of 0.8 nm, which is in good agreement with previously reported GO membranes prepared in the presence of water. The broad peak recorded in the diffraction pattern indicates a wide distribution of interlayer distances (0.7 nm to 1.4 nm). [2] The presence of the PC substrate was also confirmed in the diffraction pattern, corresponding to a second diffraction peak centered at 17 degrees. [3] Further analysis of the average pore size of the GO layers of the composite membranes was performed in the absence of the PC substrate and revealed an average pore size of 18 nm. 2 g-1 The apparent surface area ( Fig. 9 ), which is consistent with the previously reported GO membranes prepared by a similar method. [4] The pore size distribution of the GO layer was also obtained from the collected data of nitrogen adsorption isotherms, showing a broad distribution from 1.8 nm to 6 nm ( Fig.10 ), except for the fact that the isotherm trend will reach a plateau around 0.6P / P0 indicating that there are no larger pores in the membrane.

[0275] Once the GO film was attached, the GO / PC membrane was placed between the reservoirs of the system. The contents of reservoir (10A) were in contact with the GO side of the composite GO / PC membrane, while the contents of reservoir (10B) were in contact with the PC side of the composite GO / PC membrane. The electrokinetics unit was mechanically closed and several experiments were measured to demonstrate its feasibility for the phenomenon and the intended application.

[0276] Each reservoir was independently filled with 6 mL of water to first confirm that there were no leaks in the system and then to confirm the stability of the flux if no electric driving force was applied ( Fig.12 ). A voltage was then applied by fixing 1A to the electrodes. As expected, after 2 hours, no changes in the system were detected, since the driving force is given only by the movement of ions balancing the surface charge of GO close to the surface. [5]

[0277] Once a second agent capable of producing these ionic imbalances was included (KOI at 100 μM), water flux was measured after application of a driving force ( Figure 5A ). As predicted by our theoretical model, the boundary condition of this phenomenon is estimated to be ΔV = 0. Then, by using GO / PC membrane ( Figure 5B ) or by using a bare PC substrate as a reservoir separator ( Fig.13 ) to estimate the flux obtained at different salt concentrations and apply the intensity. Figure 5B A clear trend was revealed, with the flux of the whole system increasing as the salt concentration decreased. This was observed in both membranes (bare PC and GO / PC membranes) for a range of salt concentrations from 100 mM to 1 mM and intensities between 1 mA and 0.5 mA. Therefore, the operating condition of 1 mM KCI was fixed. Since no additional pressure is required to drive the flux through the membrane, the use of thin films is preferred in terms of cost, as less starting material is required.

[0278] Apply variable intensity ranging from -1A to 1A to the electrodes ( Figure 5C ). In the case of no flux and 1.3 mLs -1The water flux carried out between is exponentially related to the applied intensity above the threshold and in the absence of flux below this value, again in good agreement with the model predictions. Interestingly, when ΔV<0, the negative nature of the GO surface also does not hold due to the lack of this flux. Under these conditions44, no interface close to the surface is formed and therefore no flux is facilitated. It is also important to note that the resilience of the membrane to the process is confirmed, since no flux changes are obtained if the determination is made by keeping the same membrane and changing the feed solution or by switching to a fresh solution. Once the basis of the phenomenon is established, the voltage drop at the interface during the process is denominated ( Figure 5D ). The values ​​obtained indicate a low-cost high-energy process comparable to the pressure-driven method. If we extrapolate the values ​​at laboratory scale and consider the linear dependence without further optimization, we estimate that for 1 m 2 The membrane window is 238 L / h.

[0279] In Figure 5, the electrokinetic response of the composite membrane under electrical forcing is shown. The GO / PC membrane was placed between two macroscopic reservoirs filled with water and a solution of 100mM KCI. Initially, a constant voltage drop was applied to the electrodes and the induced ionic current was recorded. As shown in Figure 5, the system takes a relatively long time to stabilize at the equilibrium value. After about 2h of constant 4V potential, a constant current of ~2mA was measured. We believe that only when this constant current state is reached is the membrane in equilibrium and all faces of GO are filled with solution. The salt concentration was then reduced to the actual conditions of fresh water, Cs=1mM. In Figure 5E In , we present the voltage-current recorded here for a complete characterization of the membrane response. The curve exhibits a clear asymmetric response, where the voltage caused by a positive current is larger than the voltage caused by a negative current, where the magnitudes are equal. Such an asymmetric response is common for nanofluidic systems presenting geometric or charge asymmetries. In the system studied, we infer that the asymmetry arises from the charge contrast between the neutral GO and the negatively charged polycarbonate. Most importantly, the measurements confirm the presence of surface charges at the fluid-solid interface: this mode of surface conduction is crucial for electroosmotic flow. In Fig. 5F In this paper, we finally study the water flux through the membrane induced by electrical actuation. We present the water flux as a function of current intensity for different salt concentrations of Cs 1mM-100mM: the induced flux is linear with the current and it depends strongly on the salt concentration, where low concentrations lead to larger electroosmotic fluxes. The electroosmotic velocity can be quantified by A for the effective surface, ζ for the so-called zeta potential proportional to the interfacial charge, η for the fluid viscosity, RM for the ionic resistance of the membrane, I for the applied current, and L for the membrane thickness.

[0280]

[0281] We recover linearity using applied electrical drive; moreover, in the case of materials with constant surface charge at the interface, the zeta potential has been shown to decrease with concentration, in good agreement with experimental results. Fig. 5F In the inset, we compare the electroosmotic flow induced in the composite GO / PC membrane and bare PC. The responses of the two systems are very similar, indicating that the core of the process lies in the charged polycarbonate material. Although polycarbonate exhibits approximately 0.2 mC / m 2 The tiny surface charge of the membrane does not simply act as a passive substrate, but is in fact the active phase of the membrane in the process. Electroosmosis originating from the first nanometers of the surface can then generate a macroscopic water flow through the membrane. Fig. 5F , we can calculate that the flow rate is Ф~250Lh - 1 m -2 Of particular interest is the comparison of the pressure driving the ow with the electroosmotic flow: for the membranes studied here, the electrodes were positioned 1 cm from the membrane and we obtained a flux induced by a pressure of 1 bar corresponding to the flow induced by a constant potential of 40 V. This value can be greatly reduced by increasing the surface charge of the active part of the membrane and / or by reducing the separation between the electrode and the membrane.

[0282] Description of the apparatus for purification under electroosmotic conditions

[0283] Under the above conditions, when a voltage drop is applied, only water molecules flow, while the interlayer stacking of the GO membrane acts as a molecular sieve for molecules with a hydrodynamic diameter higher than the average pore size of the membrane, thereby providing the selectivity of the membrane. If the PC membrane acts as an engine for water flow, the thin layer of GO plays the role of a selective filter. The perfectly stacked GO with 2D sheets exhibits a very organized structure with an interlayer distance of -0.8nm, which can even be reduced in the presence of liquid water. Any particle in the fluid that is larger than this critical distance cannot pass through the composite membrane.

[0284] For the retention experiments, a small molecule (Ru-bipy) was selected, whose expected hydrodynamic radius was 0.6 nm. [6] The retention of the molecule was determined after 2 h of electroosmosis (Equation 3, Fig.14 ).

[0285] Retention = 1-(Cperm / Cfeed) (Formula 3)

[0286] where Cperm represents the solute concentration in the permeate, and Cfeed represents the solute concentration in the feed solution (the electrolyte solution filtered using the system).

[0287] In the first assay, Ru-bipy filtration was performed at 9 μM feed (Ru-bipy concentration) and 1 mA constant intensity. The elution phase presented only a concentration of 0.9 μM Ru(bypi), corresponding to a 90% rejection ( Fig. 6A ). This experiment has demonstrated the use of the system according to the invention for purifying water containing small molecules under reverse electroosmosis conditions.

[0288] Total retention assay

[0289] The applied intensity was reduced to 0.5 mA, thereby reducing the applied driving force and, therefore, the probability of the molecule to penetrate the nanodefects of the GO membrane. Under these conditions, complete retention was obtained with Ru-bipy up to 150 μM concentration, when feeding 200 μM Ru-bipy solution, respectively, where the retention decreased to 0.99 and finally to 0.84 ( Figure 6B ). This complete retention can be achieved at low energy cost.

[0290] Hormone retention

[0291] Once we have demonstrated with the probe molecule that 3 ) to obtain complete retention, we fed the reservoir with an aqueous solution of the hormone testosterone (10 mg / mL): the choice of hormone is of particular interest as it is above the value normally present in water. This molecule, commonly present in several water sources, is difficult to detect and filter due to its small hydrodynamic radius. The reservoir (10A) containing the electrolyte solution in contact with the GO side of the composite GO / PC membrane was filled with an aqueous solution of the hormone testosterone (10 mg mL), which represents 100 times more than the value expected in a real water sample. [7] This molecule, commonly present in several water sources, is difficult to detect and filter due to its small ratio. Applying optimized conditions (for the membrane used in the examples, the applied intensity was reduced to 0.5 mA, ~78 mm 2 Surface area, corresponding to the surface of the gap between the two reservoirs (10A) and (10B): 0.5 cm diameter disk) and the hormone present in the feed solution ( Figure 6C ), showing the great potential of this new method for water purification.

[0292] In summary, we have developed an experimental assembly for water purification by reverse osmosis, which consists of a feed reservoir (10A), a semipermeable graphene oxide-based membrane, an elution reservoir (10B) and two electrodes for inducing a voltage drop between the two faces of the membrane. The experimental assembly is able to achieve a water flux of 4.7 ml / h. Voltage-induced reverse osmosis purification with GO-based membranes produces ow liquids above the threshold voltage, a flux per bar at 40 V, and has been optimized for complete retention of small molecules of 0.6 nm operating at 0.5 mA, which means 0.32 kWh / m 3 energy consumption. Taking into account its small size and the expectation that this phenomenon is linearly extrapolated, we believe that a larger membrane cross-section will improve the flux comparable to conventional filtration methods, but with the advantage of high selectivity according to the method of the present invention. Reverse osmosis purification with GO-based membranes has been optimized in terms of energy consumption and retention, estimating a threshold voltage V>0 to generate flow and complete retention of a test molecule (Ru-bipy) with a hydrodynamic radius of 0.6 nm when 0.5 mA is applied.

[0293] Finally, the device was also tested for use in filtering a hormone (testosterone) exceeding common concentrations currently detected in drinking water, with high retention rates estimated (75%) without significant flow losses being detected.

[0294] References

[0295] 1.Bocquet,L.&Charlaix,E.Nanofluidics,from bulk to interfaces.Chem.Soc.Rev.,2010,39,1073-1095.

[0296] 2.Zhang et al.JACS,2015,137,46,14765-14772.

[0297] 3.Vijayalakkshmi et at.International Journal of Polymer Science,2011,1687.

[0298] 4.Wei etal.International journal of hydrogen energy,2016,41,11692-11699

[0299] 5.Kirby,2009,Cambridge University press.Micro-nanoscale fluidmechanics:Transport in microfluidic devices.

[0300] 6.Joshi et al.Science,2014,343,752-754.

[0301] 7.US geological survey(USGS),2008,www.epa.gov

[0302] 8.A.Siria,P.Poncharal,A.-L.Biance,R.Fulcrand,X.Blase,S.Purcell,L.Bocquet,“Giant osmotic energy conversion measured in a single transmembraneboron-nitride nanotube”Nature 494 455-458(2013)

Claims

1. A reverse electroosmosis filtration system, comprising: a) a first container (10A), the first container being used to receive a first electrolyte solution (11A) enriched with a solute of interest, and comprising a first electrode (20A) in contact with the first electrolyte solution (11A) contained in the first container (10A); b) a second container (10B), the second container being used to receive a second electrolyte solution (11B) substantially free of the same solute of interest or depleted in the same solute of interest, and comprising a second electrode (20B) in contact with the second electrolyte solution (11B) contained in the second container (10B); wherein the first electrolyte solution (11A) contains a higher concentration of solute than the second electrolyte solution (11B); or wherein, compared to the first electrolyte solution (11A), ≥ 99% of the solute of interest has been removed in the second electrolyte solution (11B) received in the second container (10B); c) a reverse osmosis membrane element (30), which separates the first container and the second container and combines the following: (i) a semipermeable membrane element (31), and (ii) a nanoporous membrane element (32), the nanoporous membrane element having a surface charge of |zeta potential| ≥ 5 mV as measured using an electrokinetic analyzer; the nanoporous membrane element having an average pore size of < 1 µm as measured according to ISO 15901 specification; wherein the semipermeable membrane element (31) and the nanoporous membrane element (32) having a surface charge are two different elements; The semipermeable membrane element (31) is configured to be in contact with the first electrolyte solution (11A) of the first container (10A), and the reverse osmosis membrane element (30) realizes the following two functions: (i) solute filtration function; and (ii) electrically inducing the flow of solvent from the first container (10A) through the reverse osmosis membrane element (30) to the second container (10B); The first electrolyte solution (11A) in the first container (10A) and the second electrolyte solution (11B) in the second container (10B) respectively contain the same polar solvent; wherein the polar solvent includes an aprotic solvent with a dielectric constant ≥ 6 and a dipole moment ≥ 1.50D, and a protic solvent; The first electrode (20A) and the second electrode (20B) are operatively coupled to an electrical energy source element (40); The reverse electroosmosis filtration system is configured to apply an electric field between the first electrode (20A) and the second electrode (20B) and induce reverse osmosis flow of the polar solvent of the first electrolyte solution (11A) from the first container (10A) through the reverse osmosis membrane element (30) to the second container (10B).

2. The reverse electroosmosis filtration system according to claim 1, wherein the semipermeable membrane element (31) and the nanoporous membrane element (32) having a surface charge are two different elements combined together to form a double-layer composite asymmetric membrane (30A), the composite asymmetric membrane (30A) comprising a semipermeable membrane element (31) superimposed with a charged nanoporous membrane element (32), the charged nanoporous membrane element having a surface charge with a |zeta potential| ≥ 5 mV.

3. The reverse electroosmosis filtration system according to claim 2, wherein the semipermeable membrane element (31) is a size exclusion membrane, an ion exchange membrane or any other membrane that allows separation / filtration of specific molecules or ions from a given electrolyte solution.

4. The reverse electroosmosis filtration system according to claim 3, wherein the semipermeable membrane element (31) is a size exclusion selective membrane composed of stacked graphene oxide sheets.

5. The reverse electroosmosis filtration system according to claim 2, wherein the charged nanoporous membrane element (32) has an average pore size of < 500 nm and is essentially formed of a material selected from TiO2, boron nitride, SiO2, polyethersulfone, polycarbonate, anodized aluminum, hydrotalcite, Ni-Fe layered double hydroxide, Ni2dobdc, Mg2dobdc (dobdc = 1,4-dioxo-2,5-phthalate), cellulose or a polyelectrolyte layer polymer membrane.

6. The reverse electroosmosis filtration system according to claim 2 or 4, wherein the surface of the charged nanoporous membrane element (32) is chemically modified to enhance the surface charge of the nanoporous membrane.

7. The reverse electroosmosis filtration system according to claim 6, wherein the chemical modification is achieved on the surface of the pore walls of the nanoporous membrane.

8. The reverse electroosmosis filtration system according to claim 5, wherein the charged nanoporous membrane element (32) is obtained from a polycarbonate membrane with an average pore size of <500nm; the inner pore wall of the charged nanoporous membrane has been chemically modified by immersing the polycarbonate membrane in an aqueous solution of polydopamine.

9. The reverse electroosmosis filtration system according to any one of claims 1 to 5, wherein the electrical energy element (40) is a battery.

10. The reverse electroosmosis filtration system according to claim 9, wherein the electrical energy element (40) is configured to be charged by at least one of the following means: light, wherein specifically, the electrical energy element comprises a solar cell or a photodiode; or using the reverse electroosmosis effect of pumping an electrolyte solution through the reverse osmosis membrane element (30), wherein specifically, the electrical energy element (40) comprises a hydraulic turbine element operatively connected to the reverse osmosis membrane element (30).

11. The reverse electroosmosis filtration system according to claim 1, wherein the polar solvent comprises water, alcohol, formic acid, acetic acid, hydrogen fluoride and ammonia.

12. The reverse electroosmosis filtration system according to claim 3, wherein the semipermeable membrane element (31) is a semipermeable membrane based on separation by chemical affinity.

13. The reverse electroosmosis filtration system according to claim 5, wherein the polyelectrolyte layer polymer membrane is a nanoporous membrane obtained by sequentially dip-coating a cationic polyethyleneimine layer and an anionic polyacrylic acid layer onto a polycarbonate membrane.

14. The reverse electroosmosis filtration system according to claim 1, wherein ≥ 99.5% of the solute of interest has been removed in the second electrolyte solution (11B) for receiving in the second container (10B) compared to the first electrolyte solution (11A).

15. The reverse electroosmosis filtration system according to claim 1, wherein ≥ 99.8% of the solute of interest has been removed in the second electrolyte solution (11B) for receiving in the second container (10B) compared to the first electrolyte solution (11A).

16. The reverse electroosmosis filtration system according to claim 1, wherein ≥ 99.9% of the solute of interest has been removed in the second electrolyte solution (11B) for receiving in the second container (10B) compared to the first electrolyte solution (11A).

17. The reverse electroosmosis filtration system according to claim 1, wherein 100% of the solute of interest has been removed in the second electrolyte solution (11B) for receiving in the second container (10B) compared to the first electrolyte solution (11A).

18. The reverse electroosmosis filtration system according to claim 1, wherein the nanoporous membrane element has a surface charge of |zeta potential| ≥ 20 mV.

19. The reverse electroosmosis filtration system according to claim 1, wherein the nanoporous membrane element has a surface charge of |zeta potential| ≥ 50 mV.

20. The reverse electroosmosis filtration system according to claim 1, wherein the nanoporous membrane element has an average pore size of ≤ 500 nm.

21. The reverse electroosmosis filtration system of claim 2, wherein the charged nanoporous membrane element has a surface charge with a |zeta potential| ≥ 20 mV.

22. The reverse electroosmosis filtration system of claim 2, wherein the charged nanoporous membrane element has a surface charge with a |zeta potential| ≥ 50 mV.

23. The reverse electroosmosis filtration system of claim 5, wherein the charged nanoporous membrane element has an average pore size of <300 nm.

24. The reverse electroosmosis filtration system of claim 5, wherein the charged nanoporous membrane element has an average pore size of <100 nm.

25. The reverse electroosmosis filtration system of claim 5, wherein the charged nanoporous membrane element has an average pore size of <50 nm.

26. A reverse electroosmosis filtration system according to claim 8, wherein the charged nanoporous membrane element is obtained from a polycarbonate membrane with an average pore size of < 300 nm.

27. A reverse electroosmosis filtration system according to claim 8, wherein the charged nanoporous membrane element is obtained from a polycarbonate membrane with an average pore size of < 200 nm.

28. A method for purifying an electrolyte solution in a polar solvent, comprising the steps of: i) providing a first electrolyte solution (11A), the first electrolyte solution comprising an undesirable solute in a polar solvent; wherein the polar solvent comprises an aprotic solvent having a dielectric constant ≥ 6 and a dipole moment ≥ 1.50D, and a protic solvent; ii) providing a second electrolyte solution (11B) in a solvent of the same or different polarity as in step i), wherein the second electrolyte solution does not contain the undesirable solute; iii) providing a reverse electroosmosis filtration system, the reverse electroosmosis filtration system comprising: a) a first container (10A), the first container being equipped with a first electrode (20A); b) a second container (10B), the second container being provided with a second electrode (20B); the first electrode (20A) and the second electrode (20B) being operatively coupled to a source of electrical energy (40); c) a reverse osmosis membrane element (30) that separates the first container (10A) and the second container (10B) and combines the following: (i) a semipermeable membrane element (31), and (ii) a nanoporous membrane element (32), the nanoporous membrane element having a surface charge of |zeta potential| ≥ 5 mV as measured using an electrokinetic analyzer; the nanoporous membrane element having an average pore size of < 1 µm as measured according to ISO 15901 specification; wherein the semipermeable membrane element (31) and the nanoporous membrane element (32) having a surface charge are two different elements; wherein the semipermeable membrane element (31) is in contact with the first electrolyte solution (11A) in the first container (10A), and the nanoporous membrane element (32) having a surface charge is in contact with the second electrolyte solution (11B) in the second container (10B); The reverse osmosis membrane element (30) realizes the following two functions: (i) a solute filtering function; and (ii) a function of electrically inducing the flow of the solvent of the first electrolyte solution (11A) from the first container (10A) through the reverse osmosis membrane element (30) to the second container (10B); The reverse osmosis membrane element (30) is adapted to selectively prevent the undesirable solute from diffusing through the reverse osmosis membrane element (30); iv) placing the first electrolyte solution (11A) to be purified in the first container (10A), so that the first electrode (20A) provided in the first container is in contact with the first electrolyte solution (11A); v) placing a sufficient amount of the second electrolyte solution (11B) in the second container (10B) so that the second electrode (20B) provided in the second container is in contact with the second electrolyte solution (11B); vi) applying an electric field between the first electrode (20A) and the second electrode (20B) to induce reverse osmosis flow of the polar solvent from the first container (10A) to the second container (10B) through the reverse osmosis membrane element (30), the reverse osmosis membrane element separating the first container (10A) and the second container (10B); thereby allowing the solvent to flow from the first container (10A) to the second container (10B) while retaining the undesirable solute in the first container (10A); and vii) collecting a purified second electrolyte solution (11B) from the second container (10B), the purified second electrolyte solution being substantially free of undesirable solutes or depleted of undesirable solutes; wherein the first electrolyte solution (11A) contains a higher concentration of solutes than the second electrolyte solution (11B); or wherein ≥ 99% of the solute of interest remains in the first electrolyte solution (11A).

29. The method according to claim 28, wherein the polar solvent is a solvent capable of generating acidic ions.

30. The method of claim 28, wherein the undesirable solute is selected from solid particles, organic or inorganic small molecules, biomolecules, pollutants, metabolic waste products, or salts / ions.

31. The method of claim 28, wherein the polar solvent comprises water, alcohol, formic acid, acetic acid, a water-alcohol mixture, hydrogen fluoride, ammonia, acetone, or acetonitrile.

32. The method according to claim 30, wherein the organic or inorganic small molecule is a dye complex; or the biomolecule is a hormone, protein, polysaccharide, polynucleotide, polypeptide, enzyme or antibody.

33. The method of claim 28, wherein the nanoporous membrane element has a surface charge of |zeta potential| ≥ 20 mV.

34. The method of claim 28, wherein the nanoporous membrane element has a surface charge of |zeta potential| ≥ 50 mV.

35. The method of claim 28, wherein the nanoporous membrane element has an average pore size of ≤ 500 nm.

36. The method of claim 28, wherein ≥ 99.5% of the solute of interest is retained in the first electrolyte solution (11A).

37. The method of claim 28, wherein ≥ 99.8% of the solute of interest is retained in the first electrolyte solution (11A).

38. The method of claim 28, wherein ≥ 99.9% of the solute of interest is retained in the first electrolyte solution (11A).

39. The method of claim 28, wherein 100% of the solute of interest is retained in the first electrolyte solution (11A).

40. A water purification system comprising the reverse electroosmosis filtration system according to any one of claims 1 to 27.

41. A water desalination system comprising the reverse electroosmosis filtration system according to any one of claims 1 to 27.

42. An implantable artificial kidney comprising the reverse electroosmotic filtration system according to any one of claims 1 to 27.

43. A method for desalinating seawater, comprising the following steps: i) providing a reverse electroosmosis filtration system, the reverse electroosmosis filtration system comprising: a) a first container (10A), the first container being equipped with a first electrode (20A), the first container containing seawater, such that the first electrode (20A) equipped with the first container is in contact with the seawater contained in the first container (10A); b) a second container (10B), the second container being equipped with a second electrode (20B), the second container containing water, such that the second electrode (20B) equipped with the second container is in contact with the water contained in the second container (10B); the first electrode (20A) and the second electrode (20B) are operatively coupled to an electric energy element (40); c) a reverse osmosis membrane element (30) that separates the first container (10A) and the second container (10B) and combines the following: (i) a semipermeable membrane element (31) having an average pore size of < 1 nm, and (ii) a nanoporous membrane element (32), the nanoporous membrane element having a surface charge of |zeta potential| ≥ 5 mV as measured using an electrokinetic analyzer; the nanoporous membrane element having an average pore size of < 1 µm as measured according to ISO 15901 specification; The semi-permeable membrane element (31) and the nanoporous membrane element (32) having a surface charge are two different elements and are stacked on top of each other; wherein the semipermeable membrane element (31) is in contact with the seawater contained in the first container (10A), and the nanoporous membrane element (32) having a surface charge is in contact with water contained in the second container (10B); The reverse osmosis membrane element (30) realizes the following two functions: (i) solute filtering function; and (ii) electrically inducing the flow of water from the first container (10A) through the reverse osmosis membrane element (30) to the second container (10B); The reverse osmosis membrane element (30) is suitable for selectively preventing Na+ and Cl- from diffusing through the reverse osmosis membrane element (30); ii) applying an electric field between the first electrode (20A) and the second electrode (20B) to induce reverse osmosis flow of water from the first container (10A) to the second container (10B) through the reverse osmosis membrane element (30), the reverse osmosis membrane element separating the first container (10A) and the second container (10B); thereby allowing water to flow from the first container (10A) to the second container (10B) while retaining Na+ and Cl- solutes in the first container (10A); and iii) collecting desalinated water from the second container (10B), the desalinated water being substantially free of Na+ and Cl- solutes; wherein ≥ 99% of the Na+ and Cl- solutes are retained in the brine contained in the first container (10A).

44. A method according to claim 43, wherein the semipermeable membrane element (31) and the nanoporous membrane element (32) having a surface charge are two different elements combined together to form a double-layer composite asymmetric membrane (30A), the composite asymmetric membrane (30A) comprising a semipermeable membrane element (31) superimposed with a charged nanoporous membrane element (32), the charged nanoporous membrane element having a surface charge with a |zeta potential| ≥5 mV.

45. The method according to claim 44, wherein the semipermeable membrane element (31) is a size exclusion membrane, an ion exchange membrane or any other membrane allowing separation / filtration of specific molecules or ions from a given electrolyte solution.

46. ​​The method according to claim 45, wherein the semipermeable membrane element (31) is a size exclusion selective membrane composed of stacked graphene oxide sheets.

47. A method according to claim 44, wherein the charged nanoporous membrane element (32) has an average pore size of <500nm and is essentially formed of a material selected from TiO2, boron nitride, SiO2, polyethersulfone, polycarbonate, anodized aluminum, hydrotalcite, Ni-Fe layered double hydroxide, Ni2dobdc, Mg2dobdc (dobdc = 1,4-dioxo-2,5-phthalate), cellulose or a polyelectrolyte layer polymer membrane.

48. The method of claim 44 or 46, wherein the surface of the charged nanoporous membrane element (32) is chemically modified to enhance the nanoporous membrane surface charge.

49. The method of claim 48, wherein the chemical modification is effected on the surface of the nanoporous membrane pore walls.

50. A method according to claim 47, wherein the charged nanoporous membrane element (32) is obtained from a polycarbonate membrane with an average pore size of < 500 nm; the inner pore walls of the charged nanoporous membrane have been chemically modified by immersing the polycarbonate membrane in an aqueous solution of polydopamine.

51. The method according to any one of claims 43 to 47, wherein the electrical energy element (40) is a battery.

52. A method according to claim 51, wherein the electrical energy element (40) is configured to be charged by at least one of the following means: light, wherein specifically, the electrical energy element includes a solar cell or a photodiode; or using the reverse electroosmosis effect of pumping an electrolyte solution through the reverse osmosis membrane element (30), wherein specifically, the electrical energy element (40) includes a hydraulic turbine element operatively connected to the reverse osmosis membrane element (30).

53. The method according to claim 45, wherein the semipermeable membrane element (31) is a semipermeable membrane based on separation by chemical affinity.

54. The method of claim 47, wherein the polyelectrolyte layer polymer membrane is a nanoporous membrane obtained by sequentially dip-coating a cationic polyethyleneimine layer and an anionic polyacrylic acid layer onto a polycarbonate membrane.

55. The method of claim 43, wherein the nanoporous membrane element has a surface charge of |zeta potential| ≥ 20 mV.

56. The method of claim 43, wherein the nanoporous membrane element has a surface charge of |zeta potential| ≥ 50 mV.

57. The method of claim 43, wherein the nanoporous membrane element has an average pore size of ≤ 500 nm.

58. The method of claim 43, wherein ≥ 99.5% of Na+ and Cl- solutes are retained in the brine contained in the first container (10A).

59. The method of claim 43, wherein ≥ 99.8% of Na+ and Cl- solutes are retained in the brine contained in the first container (10A).

60. The method of claim 43, wherein ≥ 99.9% of Na+ and Cl- solutes are retained in the brine contained in the first container (10A).

61. The method of claim 43, wherein 100% of the Na+ and Cl- solutes are retained in the brine contained in the first container (10A).

62. The method of claim 44, wherein the charged nanoporous membrane element has a surface charge with a |zeta potential| ≥ 20 mV.

63. The method of claim 44, wherein the charged nanoporous membrane element has a surface charge with a |zeta potential| ≥ 50 mV.

64. The method of claim 47, wherein the charged nanoporous membrane elements have an average pore size of < 300 nm.

65. The method of claim 47, wherein the charged nanoporous membrane elements have an average pore size of < 100 nm.

66. A method according to claim 47, wherein the charged nanoporous membrane element has an average pore size of < 50nm.

67. The method of claim 50, wherein the charged nanoporous membrane element is obtained from a polycarbonate membrane having an average pore size of <300 nm.

68. The method of claim 50, wherein the charged nanoporous membrane element is obtained from a polycarbonate membrane having an average pore size of <200 nm.

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