Capacitive ion-exchanger and uses thereof

Abstract

The present invention relates to resin-free ion-exchange using an electrode capacitor assembly comprising an anode and a cathode which are both functionalized with negatively charged groups.

Description

CAPACITIVE ION-EXCHANGER AND USES THEREOFFIELD OF INVENTION

[0001] The present invention relates to an electrochemical cell and methods of use thereof for the selective exchange of cations having different valencies. The electrochemical cell comprises an electrode capacitor assembly comprising an anode and a cathode which are both functionalized with negatively charged groups.BACKGROUND

[0002] There is an increasing global need for potable water sources due to population growth and fresh water contamination. In a variety of locations facing water scarcity, water treatment and desalination are essential to maintain a secure water supply, and provide water for agriculture, energy production, industry, and livestock. Selective ion removal from feedwaters is necessary for a variety of applications, the most ubiquitous being water for agricultural uses. Agriculture accounts for about 70% of global water demand, mainly used for irrigation. Two important indicators for irrigation water quality are the sodium adsorption ratio (SAR), quantifying the ratio between the Na+content and the Mg2+and Ca2+contents, and water ionic conductivity, providing a representation of the total water salinity and acidity. The recommended upper limits for SAR and conductivity vary for different crops, where in many instances a SAR of < 10 mM1 / 2is recommended. In order to meet SAR limitations, monovalent cation water purification technologies which selectively remove Na+over Mg2+and Ca2+, or increase the concentrations of Mg2+and Ca2+without significantly raising ionic conductivity, are required.

[0003] Monovalent ion removal is challenging in traditional water desalination technologies. In reverse osmosis, the state-of-the-art desalination technique, the membrane rejects nearly all dissolved ions from feedwater, largely indiscriminately. In nanofiltration, another pressure-driven membrane-based technique, membrane rejection is not complete but rather selective based on ion size and charge, whereas for typical membranes, divalent ions are rejected preferentially due to their larger charge and hydrated volume. Ion-exchange techniques using ion-exchange membranes can exchange monovalent cations by bivalent ions. While this process does not significantly reduce ionic conductivity, it has a profoundeffect on the SAR. However, while utilized in specialized industry, the use of ion-exchange membranes is considered expensive rendering it impractical for large-scale water treatment.

[0004] In addition to the aforementioned techniques, electrochemical processes have been developed. In electrodialysis (ED), an ion exchange membrane-based electrochemical system is used to enable the selective permeation of monovalent ions over multivalent ions, often by layering multiple additional charged poly electrolyte layers onto the membranes. Such layers suffer from oxidation and adsorption of organic compounds, leading to challenges such as increased membrane ionic resistance, reduced monovalent ion permeation rate, and decreased membrane lifetime. An alternative technique termed capacitive deionization (CDI), is based on a membraneless electrochemical system. This technique enables water purification through direct ion electro sorption on the electrodes due to applied voltage (Suss et al., Energy Environ. Sci., vol. 8(8), 2015, 2296-2319). Multiple types of electrodes have been used in CDI, including microporous carbons that are functionalized with various types of chemical groups such as, negatively charged carboxylic and sulfonic groups, positively charged amine groups, and non-covalently adsorbed surfactants. Guyes et al. (npj Clean Water, vol. 4(1), 2021, 22) explored the selective removal of monovalent Na+over divalent Ca2+for irrigation water using CDI. Two flow-through electrode (FTE) CDI cells, namely a cell with two pristine electrodes (pristine-pristine cell) and a cell with a sulfonated cathode and a pristine anode (sulfonated-pristine cell) were investigated both experimentally and theoretically. It was experimentally shown that the sulfonated-pristine cell reduced SAR and feed conductivity more effectively than the pristine-pristine cell. Also, it was theoretically found that the sulfonated-pristine cell is monovalent cation selective for longer times after initiating charging (<236 s), relative to the pristine-pristine cell for which monovalent selectivity was predicted only for very short times (<24 s). Although the phenomenon was predicted by a theoretical model, a mechanistic explanation has not been suggested yet for the observed monovalent selectivity, preventing the broadening of this phenomenon towards a wider range of selective separations.

[0005] WO 2020 / 049559 is directed to a method for selective separation of ionic species from an ionic solution based on said species ionic hydrated size, the method comprising: (a) passing the ionic solution comprising at least a first ion and a second ion, said ions being of the same polarity and having distinct hydrated sizes, through an electrode capacitor assembly comprising: a first electrode and a second electrode, said electrodes comprising carbon having a pore structure comprising micropores, wherein the first electrode is a modifiedelectrode comprising carbon which is modified with negatively charged surface groups and / or the second electrode is a modified electrode comprising carbon which is modified with positively charged surface groups, and at least one flow channel for the passage of the solution; and (b) applying an electric potential or charge to the first and the second electrodes, thereby providing enhanced adsorption of the first ion in the first modified electrode or in the second modified electrode, as compared to the adsorption of the second ion.

[0006] U.S. 2022 / 0064029 is directed to a method for selective separation of positively charged monovalent ionic species from an ionic solution. The method comprises passing the ionic solution comprising a positively charged monovalent ion and a positively charged polyvalent ion through an electrode capacitor assembly comprising a first electrode and a second electrode, said electrodes comprising nanoporous carbon, wherein the first electrode is modified with sulfonate surface groups; and at least one flow channel for the passage of the solution. The method further comprises charging the electrode capacitor assembly (1) at a voltage of at least about 1.5 V; and / or (2) for scaled charging time of less than about 2.

[0007] There remains an unmet need for membraneless electrochemical ion-exchange techniques for brackish water treatment that do not require chemical treatment.SUMMARY

[0008] The present invention is directed to an ion exchange method comprising, inter alia, passing saline water comprising a plurality of cations having different valencies through an electrode capacitor assembly that does not include an ion-exchange resin, and charging the electrode capacitor assembly thereby achieving exchange between higher and lower valency cations on the anode. The method of the present invention can therefore be useful for various applications of ion exchange, advantageously providing ion swap without the requirement of chemicals regeneration or ion exchange resins.

[0009] The present invention is based on an unexpected finding that, when a cathode is functionalized with anionic functional groups in a dynamic CDI cell, it induces electric charge on the anode, even when the anode is not chemically functionalized and before the charging step initiates. Due to the induced electric charge, the anode is capable of electro sorbing cations that are desorbed therefrom when charging initiates. At early charging times, it was found that a higher repulsion of Ca2+relative to Na+from the anode occurs which is coupled to significant Na+storage at the cathode. The present invention is furtherbased on the surprising discovery that during charging, the CDI cell not only enhances monovalent cation selectivity but further acts as an ion exchanger. In this operational regime, Ca2+ions are desorbed from the anode and replaced by Na+ions thereby increasing the concentration of Ca2+in the effluent while Na+concentration in the effluent decreases. As the Cl" effluent concentration remains at approximately the feed value, no net charge removal (desalination) is obtained, but rather an ion exchange process.

[0010] Based on these findings, disclosed herein for the first time is an electrochemical cell and an ion-exchange method of use thereof, the electrochemical cell does not include an ion- exchange resin. The electrochemical cell of the present invention features an anode and a cathode comprising surfaces which are chemically modified with negatively charged groups, such as sulfonate or organo-phosphate functional groups.[Oi l] According to one aspect, there is provided a method for achieving ion-exchange in the absence of an ion-exchange resin, the method comprising the steps of:(a) passing saline water comprising a first cation having a first valency and a second cation having a second valency through an electrode capacitor assembly comprising a pair of electrodes comprising an anode and a cathode, wherein the anode and cathode are porous carbon electrodes each modified by negatively charged functional groups; and(b) applying an electrical potential between the cathode and the anode; thereby obtaining exchange between the first cation and the second cation on the anode in the absence of an ion-exchange resin.

[0012] In some embodiments, the first cation is a monovalent cation and the second cation is a divalent cation. In other embodiments, the first cation is a divalent cation and the second cation is a trivalent cation. In yet other embodiments, the first cation is a monovalent cation and the second cation is a polyvalent cation. In further embodiments, the first cation is a monovalent cation and the second cation is a polyvalent cation selected from a divalent cation, a trivalent cation, and a combination thereof. Each possibility represents a separate embodiment. In additional embodiments, the first cation is a monovalent cation selected from the group consisting of Na+, K+, Li+, and a mixture or combination thereof. Each possibility represents a separate embodiment. In particular embodiments, the first cation is a Na+ion. In other embodiments, the second cation is a divalent cation and / or a trivalent cation selected from the group consisting of Ca2+, Mg2+, Fe2+, Fe3+, Zn2+, Cu2+, Mn2+, and amixture or combination thereof. Each possibility represents a separate embodiment. In particular embodiments, the second cation is a Ca2+ion.

[0013] In further embodiments, the electrode capacitor assembly is in electrical communication with a power supply, wherein during operation, said power supply is configured to apply electrical potential or to supply electric charge to the electrodes.

[0014] In various embodiments, the porous carbon electrode is selected from the group consisting of activated carbon, carbon black, graphitic carbon, carbon fibers, carbon microfibers, carbon aerogel, fullerene carbon, carbon nanotubes (CNTs), graphene, carbide, carbon onions, carbon paper, and a mixture or combination thereof. Each possibility represents a separate embodiment.

[0015] In particular embodiments, the porous carbon electrode comprises a plurality of nanopores, micropores, mesopores, or a mixture or combination thereof. Each possibility represents a separate embodiment. In one embodiment, the electrodes have a specific pore volume of at least about 0.25 mL / g. In another embodiment, the electrodes have a mean pore diameter ranging from about 0.5 to about 2 nm, including each value within the specified range.

[0016] In further embodiments, each of the porous carbon electrodes is independently modified with negatively charged functional groups selected from sulfonate, sulfate, phosphate, phosphonate, phosphinate, alkoxide, amide, carboxylate, and a mixture or combination thereof. Each possibility represents a separate embodiment. In particular embodiments, each of the porous carbon electrodes is independently modified with negatively charged sulfonate or phosphate functional groups.

[0017] In additional embodiments, the electrode capacitor assembly further comprises at least one additional anode or cathode, wherein the additional anode or cathode are each modified by negatively charged functional groups. In particular embodiments, the electrode capacitor assembly comprises an equal number of anodes and cathodes each modified by negatively charged functional groups.

[0018] In some embodiments, step (a) comprises passing the saline water through an electrode capacitor assembly at a flow rate of about 5 to about 500 L / m2hr, including each value within the specified range.

[0019] In other embodiments, step (b) comprises applying voltage that is above the voltage at the point of zero charge of the anode. In yet other embodiments, step (b) comprisesapplying voltage that is at or above 0.6 V. In further embodiments, step (b) comprises applying voltage that is at or above 1 V. In additional embodiments, step (b) comprises applying voltage that is at or above 1.2 V. In some embodiments, step (b) comprises applying voltage of from about 0.6 V to about 2.5 V, including each value within the specified range.

[0020] In several embodiments, the electrode capacitor assembly is adjacent to an agricultural irrigation system, a wastewater treatment system, a brackish water desalination system or a chemical reactor. Each possibility represents a separate embodiment.

[0021] In additional embodiments, the method provides product water having reduced concentration of the first cation as compared to its concentration in the feed saline water. In some embodiments, the product water has at least 2% reduction in the concentration of the first cation as compared to the feed saline water. In further embodiments, the first cation is a Na+ion, and the method provides product water with a sodium adsorption ratio (SAR) of less than about 10.0 mM1 / 2.

[0022] According to another aspect, the present invention provides a method of achieving at least one of reducing sodium adsorption ratio (SAR) and water conductivity of saline water, the method comprising the steps of:(a) passing saline water comprising a monovalent cation comprising sodium and a polyvalent cation through an electrode capacitor assembly comprising a pair of electrodes comprising an anode and a cathode, wherein the anode and cathode are porous carbon electrodes each modified by negatively charged functional groups; and(b) applying an electrical potential between the cathode and the anode; thereby obtaining product water having least one of reduced sodium adsorption ratio (SAR) and water conductivity.

[0023] In some embodiments, the obtained product water is characterized by a SAR of less than about 10.0 mM1 / 2. In other embodiments, the obtained product water is characterized by a SAR in the range of about 1 to about 10 mM1 / 2, including each value within the specified range. In yet other embodiments, the obtained product water is characterized by water conductivity of less than about 5.0 mS / cm. In further embodiments, the obtained product water is characterized by water conductivity in the range of about 0.1 to about 5 mS / cm, including each value within the specified range.

[0024] According to yet another aspect, there is provided an electrochemical cell that is devoid of an ion-exchange resin, the cell comprising an electrode capacitor assembly comprising a pair of electrodes comprising an anode and a cathode, wherein the anode and cathode are porous carbon electrodes each modified by negatively charged functional groups. In some embodiments, the electrode capacitor assembly further comprises at least one additional anode or cathode which are modified by negatively charged functional groups. In particular embodiments, the electrode capacitor assembly comprises an equal number of anodes and cathodes each modified by negatively charged functional groups. In one embodiment, the cell is configured to provide ion exchange between a first cation having a first valency and a second cation having a second valency on the anode upon the application of an electrical potential between the cathode and the anode.

[0025] Further embodiments and the full scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.BRIEF DESCRIPTION OF THE FIGURES

[0026] Figures 1A-1C show model calculations for a cell with a functionalized cathode and a pristine anode. (1A) Anode’s ionic charge, σionic,A,as a function of the cell voltage, Vcellfor electrode mass ratio, mA / mc= 0.2 (dotted line), 1.0 (solid line), and 5.0 (dashed line). (IB) Each electrode’s PZC, Vpzc ,as a function of cathode chemical charge, σChem,Cand for electrode mass ratio, mA / mc= 0.2 (dotted line), 1.0 (solid line), and 5.0 (dashed line). (1C) σionic, Aas a function of σChem,C(bottom x-axis) and as a function of mA / mc(top x-axis) for Vcell= 0.

[0027] Figures 2A-2D show model calculations for an electrode capacitor assembly with a functionalized cathode and a pristine anode. (2A) The scaled effluent concentration,for Vch= 1. 2 V (lefty-axis) of Ca2+and Na+, and the separation factor, (righty-axis),all as a function of scaled time,Inset shows as a function of for Vch= 1. 2 V and Vch= 0.4 V. (2B) Equilibrium results for anode and cathode micropore ionic charge concentration, σionic,as a function of Vcell. (2C) Equilibrium model calculations for Vcell=0 including anode micropore ion concentration (lefty-axis) of Ca2+and Na+, and the anode’s ionic charge concentration, σionic, A(right y-axis), all as a function of σChem,C. (2D) Comparison between model results (lines) and experimental results (markers) of ion electrosorption, (left y-axis, solid lower line, and squares), (left y-axis, dashedupper line, and circles), and (right y-axis, solid middle line, and triangles), all as afunction of Vch. Inset shows the calculated and measured scaled conductivity at the conductivity sensor,as a function offor Vch= 0.8 V .

[0028] Figures 3A-3G show the model results for a sulfonated- sulfonated cell. (3A) Ion dynamics for Vch= 1. 2 V, showing scaled effluent concentration of Ca2+, Na+, and C1-, as a function of scaled time,(3B) Equilibrium results of ionic charge density, σionic, of cathode and anode micropores, as a function of Vcell. (3C) Equilibrium values for zero cell voltage, including the anode’s micropore concentrations of Ca2+(lefty-axis) and Na+(lefty- axis), as well as σionic, A(right y-axis), all as a function of the anode’s chemical charge, σChem,A. (3D) Time-dependent model results for Vch= 1.2 V showing average micropore concentration in the anode (left y-axis) of Ca2+, Na+, and C1-, and Donnan potential (right y- axis, DP), as a function of (3E) Ion electrosorption, (left y-axis), (left y-axis),and (right y-axis), all as a function of Vch. (3F) A schematic illustration of an anodemicropore during charging forA schematic illustration of an anode micropore during charging for

[0029] Figures 4A-4D show scanning electron microscopy (SEM) images of pristine carbon sheet. (4A-4B) Before phosphorylation. (4C-4D) After phosphorylation.

[0030] Figure 5 shows infra-red (IR) spectra of pristine sheet before (upper spectrum) and after (lower spectrum) phosphorylation.

[0031] Figures 6A-6B show results of model-to-data fitting. (6A) Experimental titration data (Data) and micropore EDL theory results (Model) for unused phosphorylated material. Blank titration without any carbon material is shown as well (Blank). (6B) Chemical surface charge concentration, σchemof phosphorylated material, obtained from model-to-titration data fitting.

[0032] Figure 7 shows ion electro sorption at varying charging voltages.

[0033] Figure 8A-8B show results of a two-step process. (8A) SAR at initial, first run and second run. (8B) Final concentration of Na+at initial, first run and second run.

[0034] Figure 9 shows the effect of charging and discharging time durations on Ceff Na+ y-axis, squares), and final SAR (right y-axis, circles).

[0035] Figure 10 shows the effect of using multiples electrodes on SAR (left y-axis) and water conductivity (right y-axis).

[0036] Figures 11A-11B show the effect of the number of cycles in a batch mode configuration on the product water. (11A) SAR (left y-axis, squares) and water conductivity (right y-axis, circles). (11B) (left y-axis, squares) and (right y-axis, circles).

[0037] Figures 12A-12B show the effect of the number of cycles in a single pass mode on the product water. (12A) SAR (left y-axis, squares) and water conductivity (right y-axis, circles). (12B) CNa+ (left y-axis, squares) and CCa2+ (right y-axis, circles).DETAILED DESCRIPTION

[0038] The present invention is directed to an electrochemical cell and method of achieving cation exchange between cations having different valencies. The electrochemical cell features at least two electrodes which are functionalized with negatively charged groups. The cell and method of the present invention obviate the need for expensive chemicals and ion exchange resins and membranes thereby also being environmentally friendly.

[0039] Disclosed herein for the first time is an electrochemical cell which operates as a capacitive ion-exchanger in the absence of ion-exchange resins and methods of obtaining product water with reduced SAR and water conductivity using the electrochemical cell. The cell, according to the principles of the present invention, comprises at least a pair of porous carbon electrodes which are functionalized with negatively charged groups such as sulfonate or organo-phosphate groups.

[0040] Porous carbon electrodes composed of macropores for electrolyte and ion transport and micropores for ion storage in overlapped electric double layers (EDLs) are used. A one- dimensional transient model that includes multiple competing ions, micropore chemical charge, and charging dynamics was applied in order to study the mechanisms that govern monovalent electro sorption selectivity. When a sulfonated-pristine model cell was examined and the point of zero charge (PZC) of each electrode was analyzed, it was surprisingly found that the anode’s PZC shifted positively, even though it was not chemically functionalized. When the results were investigated using analytical expressions for electrode PZC, it was determined that the anode was connected electrically to the chemically-modified cathode. Itwas also shown that the shift in PZC leads to cation storage by the anode even when no voltage was applied and the cell was fully discharged. It was further found that at certain operational conditions, the cell achieves cation exchange at the anode with net charge of the feed water remaining unchanged. The present invention therefore provides a new concept of electrochemical cell operation that has not been previously realized or utilized. This new concept can be implemented in a variety of applications, in particular, in providing water with desirable SAR and water conductivity that can be utilized as irrigation water.

[0041] Guyes et al., (npj Clean Water, vol. 4(1), 2021, 22) used a CDI cell with a sulfonated cathode and a pristine anode for selective monovalent cations separation. U.S. 2022 / 0064029 disclosed a method for selective separation of monovalent ionic species from an ionic solution utilizing an electrode capacitor assembly comprising a first nanoporous carbon electrode which is modified with sulfonate surface groups (i.e., the cathode) and a second nanoporous carbon electrode (i.e., the anode) which can be either pristine (i.e., not chemically modified) or can be modified, for example, by positively charged surface groups. It was not previously realized that by functionalizing both the cathode and the anode with negatively charged functional groups, a new mode of operation of the electrode capacitor assembly can be obtained which affords exchange between cations with different valencies instead of conventional desalination.

[0042] In particular, Guyes et al., (npj Clean Water, vol. 4(1), 2021, 22) showed that an FTE CDI cell with a sulfonated cathode and a pristine anode presents elongated monovalent selectivity window and improved removal of monovalent cations relative to a pristine- pristine cell.

[0043] In order to explore the tendency of electrodes to either electrosorb or desorb ions during charging, an analysis of the electrode PZC was performed. Figure 1A shows the anode's calculated micropore ionic charge concentration, σionic, A’for a functionalized- pristine cell with electrode mass ratio of mAl =0.2 (dotted line), 1.0 (solid line), and 5.0 (dashed line), all as a function of the cell voltage, Vcell. The Vcellvalue for which σionic, A= 0 is the anode's PZC, VPZC,A. Although the anode is pristine, it was surprisingly found that VPZC,A> 0 , namely the electrodes’ PZC, in the absence of any chemical charge, is not zero and the electrode shows an induced electric charge at Vcell= 0 (which balances the ioniccharge). Without being bound by any theory or mechanism of action, it is contemplated that the cathode's charged chemical groups induce electric charge in the pristine anode through the system’s charge balance (equation (4) hereinbelow). It was further surprisingly found that Vpzc Adoes not depend on mAI mC, although the magnitude of the induced electric charge at the anode, σionic, A, at Vcell= 0 strongly depends on the mass ratio (equation (6) hereinbelow).

[0044] It can further be inferred from these results that at a state where Vcell< VPZC,A, the cationic species are in excess in the anode micropores due to electrosorption, σionic, A>0. Therefore, for a charging process that initiates at the discharged state with a cell voltage which is smaller than the anode's PZC, < VPZC,A, the anode has excess cations at the onset of charging. As charging initiates, the anode initially desorbs these excess cations, leading to a so-called “inversion peak”.

[0045] Figure IB presents VPZC,Aand Vpzc,c, for mAI mC=0.2 (dotted lines), 1.0 (solid lines) and 5.0 (dashed lines), all as a function of the cathode's chemical charge , σChem,Cwhere the VPZC,Acurves are identical for all mass ratios. It can be seen that VPZC C< 0 for σChem,C< 0, and strongly decreases with decreasing mAI as depicted by equation (7) hereinbelow. However, VPZC,Aincreases slightly as σChem,Cbecomes more negative. Overall, the cathode’s micropore chemical group concentration affects the PZC of both the anode and the cathode, while electrode mass ratio only affects the PZC of the chemically- treated electrode alone.

[0046] It was further surprisingly found that when the cell is short circuited, =0, the pristine anode is electrically charged. Figure 1C depicts a plot of ^aioA as a function of σChem,C(bottom x-axis), as well as σionic, Aa function of mAI mCfor σChem,C= — 2M (top x-axis). When σChem,C=0 there is no induced electric charge at the anode as σionic, A= 0. As σChem,Cbecomes more negative, σionic, Aincreases, demonstrating the importance of the cathode chemical charge to induced electric charge at the anode.

[0047] To understand the monovalent selectivity mechanism and the elongation of its time window for a sulfonated-pristine cell, the sulfonated cathode was modeled with micropore chemical charge concentration of -2M. Figure 2A presents the results at Vch=1.2V where at early times, a significant rise of both cations’ concentrations occurs, indicating significant cation desorption, which is followed by complete monovalent selectivity, then partial selectivity, and eventually ion-exchange where Ca2+is significantly electrosorbed due to its higher valence, while Na+is repelled. The inset of Figure 2A presents a closer view of the early time dynamics emphasizing that the peak concentration for each ion only weakly depends on the cell voltage and that most of the cations in the anodes’ micropores are desorbed. For , a desorption of cationic species from the anode occurs atthe beginning of the charging step. Figure 2B shows that during cell charging from 0 V to 1.2 V, cationic species are electrosorbed into the cathode and the vast majority of cations present in the anode when at 0 V are desorbed. Figure 2C shows the theoretical model correlations between decreases,there is an increase in has a largermagnitude and increases faster relative to Without being bound by theory ormechanism of action, this is attributed to the mechanism of valence-based selectivity, where divalent ions are preferred by charged micropore EDLs over monovalent ions. Figure 2D presents model results (lines) and experimental results (markers) for the sulfonated-pristine cell indicating good correlation between the two. The inset of Figure 2D presents dynamic model and experimental results of the conductivity scaled by the feed conductivity at the conductivity sensor,, as a function offor three full cycles at

[0048] Hence, it was unexpectedly found that a cathode having strong negatively charged chemical groups on its surface can improve the cell's monovalent cation selectivity because, before charging initiates, there is a significant excess of Ca2+in the anode micropores due to induced negative electric charge at the anode, resulting in strong Ca2+desorption during charging. It was further unexpectedly found that when both the cathode and the anode are functionalized with negatively charged groups, enhanced Ca2+storage in the anode micropores occurs in the discharged state, thereby leading to superior monovalent cation selectivity compared to the hitherto known pristine-anode cell. The electrochemical cellaccording to the principles of the present invention affords an ion exchange mode of operation which is advantageous as an alternative to ion exchange resins and chemicals.

[0049] According to some aspects and embodiments, the present invention provides a method for obtaining ion exchange in the absence of an ion-exchange resin by utilizing an electrochemical cell comprising a pair of porous carbon electrodes, said electrodes are functionalized with negatively charged groups.

[0050] According to some aspects and embodiments, the present invention provides a method for obtaining ion exchange in the absence of an ion-exchange resin by utilizing an electrochemical cell comprising a pair of porous carbon electrodes, wherein the cathode is functionalized with negatively charged groups and the anode is either pristine (non- functionalized) or functionalized with negatively charged groups, preferably organo- phosphate groups.

[0051] It is to be understood that when both cathode and anode are functionalized with negatively charged groups, the negatively charged groups may be the same or different with each possibility representing a separate embodiment.

[0052] Within the scope of the present invention is the use of porous carbon electrodes. The term “carbon” as used herein refers to different types of carbonaceous materials, including inter alia, activated carbon, carbon black, graphitic carbon, carbon fibers, carbon microfibers, carbon aerogel, carbon nanotubes (CNTs), graphene, carbide, carbon-based nanostructures such as fullerenic carbons or carbon onions, carbon paper and any combination thereof. Each possibility represents a separate embodiment. The carbon fibers and / or microfibers can be woven into larger carbon filaments, fabrics, cloth, or sheets. Each possibility represents a separate embodiment. The carbon paper can comprise carbon microfibers woven into flat sheets. In certain embodiments, the cathode and the anode comprise activated carbon. In further embodiments, the cathode and the anode comprise activated carbon fibers. In still further embodiments, the cathode and the anode are in a form of an activated carbon cloth.

[0053] According to some embodiments, the cathode, the anode, or both have a thickness ranging from about 10 pm to about 10 mm, including each value within the specified range. In further embodiments, the cathode, the anode, or both have a thickness ranging from about 100 pm to about 1 mm, including each value within the specified range. In still further embodiments, the cathode, the anode, or both have a thickness ranging from about 250 pmto about 750 μm, including each value within the specified range. In certain embodiments, the cathode, the anode, or both have a thickness ranging from about 500 pm to about 700 pm, including each value within the specified range.

[0054] In some embodiments, the cathode, the anode, or both can comprise intercalation and / or redox-active materials blended with carbon. As used herein, the term “intercalation” refers to a reversible insertion of cations or anions into sites within the solid electrode material. A non-limiting example of a suitable intercalation-active material is graphite, which allows intercalation of potassium ions and / or lithium ions. Non-carbonaceous intercalation materials can be selected from sodium manganese oxide (NMO), transition metal hexacyanoferrates (MHCFs), two-dimensional (2D) transition metal carbides, carbonitrides and nitrides (MXenes), or molybdenum sulfide. Each possibility represents a separate embodiment. Non-limiting examples of redox-active electrode materials include silver metal (for the Ag / AgCl redox reaction), sodium iron phosphate, two-dimensional layered titanium disulfide, bismuth-BiOCl, and metal oxychlorides such as VOC1 and FeOCl. Each possibility represents a separate embodiment. Additional information on the redox active materials suitable for use as intercalation materials of carbon-based electrodes can be found in Suss et al. Joule 2.1, 2018, 10-15, hereby incorporated by reference in its entirety.

[0055] As disclosed hereinabove, the cathode and anode within the scope of the present invention comprise porous carbon comprising a plurality of pores. In certain embodiments, the pores are selected from nanopores, micropores, mesopores or a combination thereof. Each possibility represents a separate embodiment. Within the scope of the present invention are pores in the range of about 0.5 to about 200 nm, including each value within the specified range. Exemplary pore sizes include, but are not limited to, pores with mean pore diameters ranging from about 0.5 to about 2 nm, about 2 to about 10 nm, about 10 to about 50 nm, or about 50 to about 100 nm, including each value within the specified ranges. The pores can have a shape selected from spherical, non-spherical, slit-shaped, polygon shapes, and combinations thereof. Each possibility represents a separate embodiment.

[0056] According to some embodiments, the cathode and / or the anode have a specific pore volume of at least about 0.1 mL / g. According to further embodiments, the cathode and / or the anode have a specific pore volume of at least about 0.25 mL / g. According to still further embodiments, the cathode and / or the anode have a specific pore volume of at least about 0.5 mL / g. In some embodiments, the cathode and / or the anode have a specific pore volumeranging from about 0.1 mL / g to about 1 mL / g, including each value within the specified range. In further embodiments, the cathode and / or the anode have a specific pore volume ranging from about 0.25 mL / g to about 0.75 mL / g, including each value within the specified range. In some related embodiments, the specific pore volume is determined based on nitrogen absorption measurements.

[0057] In some embodiments, the cathode and / or the anode have a surface area of above about 500 m2 / g, based on nitrogen absorption measurements. In further embodiments, the cathode and / or the anode have a surface area of above about 1000 m2 / g, based on nitrogen absorption measurements.

[0058] According to the principles of the present invention, the cathode and anode comprise activated carbon which is chemically modified with negatively charged groups.

[0059] The term “negatively charged groups” as used herein refers to groups bearing a negative charge, for example, sulfate, sulfonate, phosphate, phosphonate, phosphinate, alkoxide, amide, carboxylate, and combinations thereof. Each possibility represents a separate embodiment. It is to be understood that the modification by the negatively charged groups according to the principles of the present invention refers to chemical modification of the surface of the electrodes.

[0060] In some currently preferred embodiments, both the cathode and the anode are modified with sulfonate groups. The term “sulfonate” (also termed herein a “sulfonic” group) refers to the group -O-S(=O)2-R, where R can be selected from C, C-O, S, N, P, H, substituted or unsubstituted alkyl, aryl, alkenyl, alkynyl, and / or alkoxy moieties which may be linear, branched, or cyclic, and substituted or unsubstituted aryl and / or heteroaryl moieties. Each possibility represents a separate embodiment.

[0061] The term “sulfonate surface group” refers to a sulfonate group present on the surface of the cathode and / or the anode, more particularly on the surface of the porous carbon of the cathode and / or the anode or on the porous carbon sites, which are accessible to the saline water. The sulfonate groups can be bound to the surface of the cathode and / or the anode via atoms present on the porous carbon surface, such as, but not limited to, carbon atoms (C), and oxidized carbon atoms (C-O). It is to be understood that when sulfonate groups are bound via oxidized carbon atoms (i.e., wherein R is C-O), the cathode and / or the anode are modified by sulfate groups (-O-S(=O)2-O-C). The term “sulfonate surface groups”, as used herein, is therefore also meant to encompass sulfate surface groups. The atoms throughwhich the sulfonate surface groups are attached to the electrode surface may depend on the purity levels of the porous carbon. Preferably, the sulfonate groups are bound to the atoms, which are present on the porous carbon surface, via covalent bonds.

[0062] According to some embodiments, the cathode and / or the anode may be sulfonated as is known in the art. For example, the cathode and / or the anode can be sulfonated by exposing the porous carbon to concentrated sulfuric acid (H2SO4). In some embodiments, the cathode and / or the anode are modified by sulfonate surface groups by immersing the porous carbon into 20% fuming sulfuric acid for about 12-36 hours, including each value within the specified range. In some embodiments, the modification process further includes exposing the treated carbon to an organic solvent, e.g., hexane, followed by exposing the carbon to deionized water. The temperature of the deionized water can range from about 0°C to about 50°C, including each value within the specified range. In some embodiments, the treated carbon is exposed to at least one portion of water, which has a temperature of about 0°C and to at least one portion of water which has a temperature of about 25°C. The treated carbon can be exposed to each portion of the deionized water for any time duration between about 1 minute and about 5 hours, including each value within the specified range.

[0063] According to some embodiments, the cathode and / or the anode are sulfonated by immersing the electrodes in nitric acid at a temperature ranging from about 20°C to about 100°C, including each value within the specified range, and then immersing them in fuming sulfuric acid. In some embodiments, the temperature of nitric acid ranges from about 50°C to about 100°C, including each value within the specified range.

[0064] According to some embodiments, the cathode and / or the anode are sulfonated with diazonium salt of sulfanilic acid, as detailed, for example, in U.S. 7,294,185, which is incorporated by reference herein in its entirety.

[0065] In some currently preferred embodiments, both the cathode and the anode are modified with organophosphate groups. The term “phosphate” as used herein refers to the group PO43', which further encompasses a phosphate group attached to the surface of the porous carbon via organic moieties including, but not limited to, substituted or unsubstituted alkyl, aryl, alkenyl, alkynyl, carboxyl and / or alkoxy moieties which may be linear, branched, or cyclic, and substituted or unsubstituted aryl and / or heteroaryl moieties with each possibility representing a separate embodiment. The phosphate group further attached to an organic moiety is hereby referred to as an “organophosphate group”.

[0066] As detailed above for the sulfonate group modifications, the organophosphate groups may also be attached to the surface of the cathode and / or the anode, more particularly the groups may be present on the surface of the porous carbon of the cathode and / or the anode or on the porous carbon sites, which are accessible to the saline water.

[0067] According to some embodiments, the cathode and / or the anode may be phosphorylated using a phosphorylating agent as is known in the art. For example, the cathode and / or the anode are phosphorylated by first oxidizing the surface of the porous carbon followed by hydrogeneration using a reducing agent such as LiAlH4. Finally, the surface is phosphorylated using a phosphorylating agent e.g., triethylphosphite or phosphoryl chloride (POCI3). According to some embodiments, hydrogenation is performed at a temperature ranging from about -78°C to about 100°C, including each value within the specified range, preferably at a temperature ranging from about 50°C to about 70°C, including each value within the specified range. In some embodiments, the temperature at which phosphorylation is performed ranges from about 0°C to about 150°C, including each value within the specified range.

[0068] As contemplated by the present invention, the modification of the electrodes with negatively charged groups renders their surface strongly negatively charged. According to the principles of the present invention, it is contemplated that the negative charge on the surface of the electrodes affords enhanced efficiency of the selective lower valent cationic removal and ion exchange.

[0069] Within the scope of the present invention is the degree of surface coverage by the negatively charged groups of at least 0.1% of the total weight of the electrodes. In other embodiments, the surface coverage by the negatively charged groups is at least 1% of the total weight of the electrodes. In yet other embodiments, the surface coverage by the negatively charged groups is at least 2% of the total weight of the electrodes. In further embodiments, the surface coverage by the negatively charged groups is from about 0.1% to about 20% of the total weight of the electrodes, including each value within the specified range. In some related embodiments, the surface coverage by the negatively charged groups is determined based on ICP measurements.

[0070] While the electrode capacitor assembly of the invention can operate with a single pair of electrodes (a cathode and an anode as disclosed herein), a plurality of electrodes comprising two or more anodes and / or two or more cathodes are encompassed by the presentinvention. The number of additional anodes and / or cathodes can be tailored according to the operation mode, saline water utilized, and desired product water. When more than one anode and / or cathode are used, they are preferably used such that there is an equal number of anodes and cathodes in the electrode capacitor assembly thereby enabling a symmetric setup.

[0071] According to the principles of the present invention, the method comprises step (a) of passing the saline water through an electrode capacitor assembly. In some embodiments, passing the saline water through the electrode capacitor assembly is performed at a flow rate of about 5 to about 500 L / m2hr, including each value within the specified range. Exemplary flow rates include, but are not limited to, from about 10 to about 400 L / m2hr, from about 10 to about 300 L / m2hr, from about 10 to about 250 L / m2hr, from about 10 to about 150 L / m2hr, and from about 10 to about 100 L / m2hr, including each value within the specified ranges. It is to be understood that the flow rate as used herein refers to the flow rate of the saline water divided by the cross-sectional electrode area through which it passes.

[0072] The saline water can be stored in a suitable reservoir, such as, for example, feedwater tank (also termed herein “feed tank”) from which is can be transferred and passed into the electrode capacitor assembly. In some embodiments, the saline water is flown into the electrode capacitor assembly from a reservoir in which the saline water to be treated is naturally present (e.g., seawater). In some embodiments, the electrode capacitor assembly has an inlet and an outlet. In further embodiments, the saline water enters the electrode capacitor assembly at the inlet and exits the electrode capacitor assembly at the outlet thereof.

[0073] According to some aspects and embodiments, the method comprises step (b), which comprises applying an electrical potential between the cathode and the anode. In certain embodiments, applying an electric potential between the cathode and the anode induces charging of the electrode capacitor assembly.

[0074] According to the various aspects and embodiments of the present invention, step (b) comprises applying voltage which is above the voltage at the point of zero charge of the anode. The term “point of zero charge” as used herein, refers to the cell potential for which an electrode stores zero net ionic charge. Accordingly, the point of zero charge of the anode may be defined by the following equationwherein VT is the thermal potential defined by VT=RT I F , where R is the ideal gas constant, T is the absolute temperature, and F is Faraday’s constant;is the chemical charge concentration in the micropores of the cathode, and CmA is the ion macropore concentration.

[0075] According to some embodiments, the application of an electrical potential is performed by applying voltage of at least 0.6 V. Exemplary voltages include, but are not limited to, from about 0.6 to about 2.5 V, including each value within the specified range. According to some embodiments, step (b) comprises applying a voltage of at least about 0.8 V. According to further embodiments, step (b) comprises applying a voltage of at least about 1.0 V. According to still further embodiments, step (b) comprises applying a voltage of at least about 1.2 V. According to yet further embodiments, step (b) comprises applying a voltage of at least about 1.5 V. According to still further embodiments, step (b) comprises applying a voltage of at least about 1.8 V. According to yet further embodiments, step (b) comprises applying a voltage of at least about 2 V.

[0076] According to some embodiments, the electrode capacitor assembly is charged for a duration of time to afford the product water with desirable attributes. Exemplary time durations are typically normalized by cell diffusion timescale. The term “cell diffusion timescale”, as used herein refers to D / lj, where D is diffusivity of the lower valent ion at infinite dilution and leis the thickness of the cathode.

[0077] Accordingly, scaled charging time, t can be calculated by the following equation: t = tD / lg, where t is the charging time.

[0078] Scaled charging time is a universal parameter, which accounts for the specific parameters of the electrode capacitor assembly and of the saline water. According to some embodiments, step (b) comprises applying an electrical potential for a scaled charging time of less than about 1.5. According to further embodiments, step (b) comprises charging the electrode capacitor assembly for a scaled charging time of less than about 1. According to further embodiments, step (b) comprises applying an electrical potential for a scaled charging time of less than about 0.5.

[0079] According to some embodiments, step (b) comprises applying an electrical potential for less than about 7.5 min. According to further embodiments, step (b) comprises applying an electrical potential for less than about 6 min. According to still further embodiments, step (b) comprises applying an electrical potential for less than about 5 min. According to yetfurther embodiments, step (b) comprises applying an electrical potential for less than about 4 min. According to still further embodiments, step (b) comprises applying an electrical potential for less than about 3 min. According to yet further embodiments, step (b) comprises applying an electrical potential for less than about 2 min.

[0080] It should be understood that unless otherwise specified, the values of potentials or voltage indicated throughout the specification and in the claims refer to the potential of the cathode measured versus the potential of the anode, or to the potential of the anode measured versus the potential of the cathode, for a single electrode capacitor assembly. If the electrode capacitor assembly is configured in a stack configuration, having multiple cells connected in series or in parallel, the indicated potential or voltage values refer to a single cell. The overall potential applied to the entire stack can be calculated as known in the art depending on the manner in which the cells are connected. The term “cell” as used herein, refers to the electrode capacitor assembly comprising a pair of electrodes.

[0081] According to some embodiments, steps (a) and (b) are performed simultaneously such that the saline water is passed through the electrode capacitor assembly during the charging step. Typically, the method comprises continuous passing of the saline water through the electrode capacitor assembly while the electric potential is applied to the electrode capacitor assembly. The term “continuous” as used herein, refers in some embodiments to a constant flow rate at which the saline water is passed into the electrode capacitor assembly. In additional embodiments, the term “continuous” refers to recirculation of the saline water into the ionic solution reservoir, following its flow from the electrode capacitor assembly. The saline water can be recirculated two, three, four, five, six, seven, eight, nine, ten or more times. Each possibility represents a separate embodiment.

[0082] According to some embodiments, the electrode capacitor assembly is configured in a form of a Capacitive Deionization (CDI) system. In some embodiments, the system is a membraneless CDI, i.e., it is not configured as a “Membrane Capacitive Deionization” or “MCDI”. In some embodiments, the electrode capacitor assembly is configured in a form of a flow-through electrode Capacitive Deionization (FTE-CDI) system. An FTE-CDI typically operates in a mode whereby the saline water flows directly through the electrodes, wherein the flow is configured substantially orthogonal to the electrode surface planes. In some embodiments, the FTE-CDI comprises a cathode which is configured as the upstream electrode and an anode which is configured as the downstream electrode, i.e., the flow first passes through the cathode and then through the anode. In such mode of operation, theelectrode capacitor assembly typically further comprises a porous separator configured to isolate the cathode from the anode. In accordance with these embodiments, the porous separator enables the flow through the interconnected pores of the porous carbon electrodes and separator. As used herein, the term “interconnected pores” refers to a porous material having an open porosity, wherein the pores of the material are connected, thus enabling the passage of a fluid from the bulk to the internal volume of the pores within the material.

[0083] In further embodiments, the electrode capacitor assembly is in electrical communication with a power supply, wherein during operation said power supply is configured to apply electrical potential or to supply electric charge to the electrodes.

[0084] According to the principles of the present invention, the system may also comprise two current collectors which contact the posterior side of each electrode. In further embodiments, the current collectors are designed to allow passage of the saline water therethrough, e.g., by containing pores. The electrode capacitor assembly can be enclosed within an electrically insulating casing having an inlet and an outlet for the flow of the saline, being in fluid flow connection with the current collectors. The electrode capacitor assembly can further include one or more gaskets in order to provide sealing. The system can further include a feed tank, a feed pump, treated water tank, and / or a waste tank. Each possibility represents a separate embodiment. The pump is configured to induce the flow of the saline water from the feed tank into the electrode capacitor assembly, and from the electrode capacitor assembly into the treated water tank or the feed tank.

[0085] The electrode capacitor assembly of the present invention can be configured in various cell geometries, as known in the art. In some embodiments, the electrode capacitor assembly is operated in a flow-by mode, wherein the electrode capacitor assembly is configured in a stack configuration, having a spacer separating the electrodes, wherein the saline water flows through the spacer in a horizontal manner, parallel to the electrodes. In some embodiments, the electrode capacitor assembly is operated in a flow-by mode utilizing flow-electrodes. In such embodiments, the electrode capacitor assembly comprises at least two electrode channels, wherein each electrode channel comprises a flowable carbon electrode in the form of a suspension (slurry) and / or a fluidized bed electrode. The at least two electrode channels are in ionic contact with at least two ion-permeable membranes, which separate the carbon electrodes from the saline water flowing through a flow channel. Each flowable carbon electrode flows through the electrode channel, which separates the membranes from the respective current collectors.

[0086] According to the principles of the present invention, the saline water comprises a plurality of cations with different valencies. Thus, the saline water has at least a first cation having a first valency and second cation having a second valency. As used herein, the term “first cation having a first valency” refers to a cation having a valency of one, two, three, or more provided that it is lower than the valency of the second cation. Accordingly, the term “second cation having a second valency” refers to a cation having a valency of two, three, four or more provided that it is higher than the valency of the first cation. In some embodiments, the first cation comprises a monovalent ion. In other embodiments, the first cation comprises a polyvalent ion having a lower valency than the second cation. In further embodiments, the second cation is a polyvalent cation which can be a divalent cation, a trivalent cation or a mixture of divalent and trivalent cations. Each possibility represents a separate embodiment. In some embodiments, the saline water comprises cations selected from Li+, Na+, K+, Mg2+, Ca2+, Fe2+, Fe3+, Pb2+, Hg2+, Cd2+, In3+, Ru3+, Ru4+, Zn2+, Co2+, Co3+, Pt2+, Pt4+, Au+, AU3+, Ag+, Sn4+, Sn2+, Cu2+, and combinations thereof. Each possibility represents a separate embodiment.

[0087] According to some embodiments, the monovalent cations are selected from the group consisting of: Na+, Ei+, K+, Au+, Ag+, and combinations thereof. Each possibility represents a separate embodiment. According to some embodiments, the polyvalent cations are selected from the group consisting of: Ca2+, Mg2+, Mn2+, Fe2+, Fe3+, Al3+, Pb2+, Hg2+, Cd2+, Ni2+, In3+, RU3+, RU4+, Zn2+, Co2+, Co3+, Pt2+, Pt4+, Au3+, Sn4+, Sn2+, Cu2+, and combinations thereof. Each possibility represents a separate embodiment. According to certain embodiments, the monovalent cations are sodium ions (Na+) and the polyvalent cations are calcium ions (Ca2+) or calcium and magnesium ions (Ca2++ Mg2+).

[0088] In some embodiments, the method of the present invention affords the reduction in the first cation concentration as compared to the initial concentration of the first cation in the feed saline water. Currently preferred is the reduction in the first cation concentration of at least 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or even more of the initial concentration. Each possibility represents a separate embodiment. Thus, for example, when Na+constitutes as the first cation and a mixture of Ca2+and Mg2+constitutes as the second cation, the obtained SAR of the product water is less than about 10.0, about 9.0, about 8.0, about 7.0, about 6.0, about 5.0, about 4.0, about 3.0, about 2.0, or about 1.0 mM1 / 2, with each possibility representing a separate embodiment.

[0089] In some embodiments, the process of the present invention affords the reduction water conductivity as compared to the initial water conductivity of the feed saline water. Currently preferred is the reduction in water conductivity of at least 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or even more of the initial conductivity. Each possibility represents a separate embodiment. Thus, for example, the obtained water conductivity of the product water is less than about 5.0, about 4.5, about 4.0, about 3.5, about 3.0, about 2.5, about 2.0, about 1.5, about 1.0, about 0.5, or about 0.1 mS / cm, with each possibility representing a separate embodiment.

[0090] In order to obtain the desired reduction in the concentration of the first cation or in water conductivity, steps (a) and (b) can be repeated as needed.

[0091] Thus, in some embodiments, the electrode capacitor assembly operates in a single- pass charge mode, wherein the saline water stream which exits the electrode capacitor assembly is stored in a separate container and not recycled back to the feed tank. In other embodiments, the electrode capacitor assembly operates in a batch mode, wherein the saline water stream which exits the electrode capacitor assembly is recycled back to the feed tank. In yet other embodiments, the electrode capacitor assembly operates in multiple passes mode, wherein the saline water stream which exits the electrode capacitor assembly is recycled back to the cell and steps (a) and (b) are repeated. Suitable repetitions include, but are not limited to, 2 to 50 cycles, including each integer within the specified range. It is to be understood that the method of the present invention further comprises a step of regenerating the electrodes and discharging the cell. In accordance with these embodiments, the method comprises step (c) of applying a reverse electrical potential or no electrical potential between the cathode and the anode thereby obtaining exchange between the second cation and the first cation on the anode. In additional embodiments, the saline stream which exits the electrode capacitor assembly is recycled back to the cell at the end of step (b), so that discharging is repeated into the same saline solution.

[0092] The method of the present invention is particularly suitable for the treatment of agricultural water designated for irrigation, as it allows to reduce the concentration of the monovalent cations such as sodium ions, while maintaining the desired concentration of the polyvalent ions such as calcium and magnesium ions.

[0093] Without being bound by any theory or mechanism of action, obtaining product water with reduced concentration of the first cation is achieved by at least one of enhancedadsorption of the first cation on the cathode, enhanced desorption of the second cation from the anode, and ion exchange of the second cation with the first cation in the anode. Each possibility represents a separate embodiment.

[0094] According to the principles of the present invention, the cell and method disclosed herein are devoid of cation-exchange resins and membranes. Cations exchange resins typically include polymers having acidic functional groups such as styrene / divinyl benzene cation exchange resins having sulfonic functionality. Exemplary cation exchange resins include, for example, Amberlite 200, Amberlite 252 and Duolite C26, Amberlite IR-120, Amberlite IR-122, Amberlite IR-132, Duolite C20, Duolite C206, Amberlite XE-501, and Amberlite DPI.

[0095] Where a range of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit unless the context clearly dictates otherwise, between the upper and lower limit of that range and any other stated or intervening value in that stated range, is encompassed within the invention. The upper and lower limits of these smaller ranges may independently be included in the smaller ranges, and are also encompassed within the invention, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included in the invention.

[0096] As used herein, the term “about” when combined with a value refers to ± 10% of the reference value.

[0097] It is noted that as used herein and in the appended claims, the singular forms “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a cation” includes a plurality of cations, and so forth. It is further noted that the claims may be drafted to exclude any optional element. As such, this statement is intended to serve as antecedent basis for use of such exclusive terminology as “solely”, “only” and the like in connection with the recitation of claim elements or use of a “negative” limitation.

[0098] In those instances where a convention analogous to “at least one of A, B, and C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a complex comprising at least one of A, B, and C” would include but not be limited to complexes that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and / or A, B, and C together, etc.). It will befurther understood by those within the art that virtually any disjunctive word and / or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase “A or B” will be understood to include the possibilities of “A” or “B” or “A and B”.

[0099] It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination. All combinations of the embodiments pertaining to the invention are specifically embraced by the present invention and are disclosed herein just as if each and every combination was individually and explicitly disclosed. In addition, all sub- combinations of the various embodiments and elements thereof are also specifically embraced by the present invention and are disclosed herein just as if each and every such sub-combination was individually and explicitly disclosed herein.

[0100] Additional objects, advantages, and novel features of the present invention will become apparent to one ordinarily skilled in the art upon examination of the following examples, which are not intended to be limiting. Additionally, each of the various embodiments and aspects of the present invention as delineated hereinabove and as claimed in the claims section below finds experimental support in the following examples.EXAMPLESEXAMPLE 1 - THEORETICAL MODEL

[0101] In order to develop the theoretical model suitable for studying the electrochemical cell of the present invention, an FTE CDI cell, as presented by Guyes et al., (npj Clean Water, vol. 4(1), 2021, 22) was analyzed using the modified-Donnan (mD) model (Biesheuvel et al. Russian J. Electrochem. vol. 48, 2012, 580-592; Guyes et al., Desalination, vol. 415, 2017, 8-13; Wang et al., J. Colloid Interface Sci., vol. 512, 2018, 522-528; and Biesheuvel et al., J. Colloid Interface Sci., vol. 360(1), 2011, 239-248) with a fixed amount of surface charged chemical groups (Biesheuvel et al., Colloids Interface Sci. Commun., vol. 9, 2015, 1-5), accounting for ion volume exclusion (Suss, J. Electrochem. Soc., vol. 164(9), 2017, E270- E275; Mansoori et al., J. Chem. Phys., vol. 54(4), 1971, 1523-1526; and Boublik, J. Chem.Phys., vol. 53(1), 1970, 471-472) and for a feed containing Ca2+, Na+, and Cl". The equations, were solved using COMSOL Multiphysics®.

[0102] To explore the PZC of a cell that contained two porous electrodes and a separator, an expression for a simplified case of a monovalent binary electrolyte neglecting nonideal effects (i.e., ion size) was developed. First, the local potential balance across the micropores for each electrode was applied

[0103]

[0104] whereis the electrode potential scaled by the thermal potentialand where similar scaling applies to all electrostatic potentials in this model. R is the ideal gas constant, T is the absolute temperature, and F is Faraday’s constant. Furthermore,is the macropore potential,is the Donnan potential drop, andis the Stern potential, defined by , where Csis the Stern capacitance and is the microporeelectronic charge concentration, calculated by applying a micropore charge balance for each electrode's micropores,

[0105] (2)

[0106] Here,is the chemical charge concentration in the micropores, and is the net ionic charge concentration, where is theion valenceand is the micropore concentration of the ion, given by the mD model (neglectingion size effects),

[0107] (3)

[0108] Here is theion macropore concentration. Assuming the electroneutralitycondition holds in the macropore, for a binary monovalent electrolytewas obtained. To connect between the electrodes, zero net charge in the cell was assumed, and the total charge balance of the system was solved,

[0109] (4)

[0110] where mAand mcare the mass of the anode and the cathode, respectively, andVmi,AVmi,Care the specific micropore volume of the anode and cathode, respectively.Using the equations presented above, an expression relating to the cell voltage, was developed, and the ionic charge of the electrodes, orσionic, C, at equilibrium was calculated according to the following equations,

[0111] (5)

[0112] where σionic, Cis related to σionic, Aby the expression Using equation (5) for thesulfonated-pristine cell described in Guyes et al., (npj Clean Water, vol. 4(1), 2021, 22), i.e., σChem,A=0 the expression for the anode's PZC was found by setting σionic, A= 0 ,

[0113] (6),

[0114] and the cathode's PZC,

[0115] (7).

[0116] The first metric is the electro sorption of ion i per unit electrode mass, given by

[0117] (8)

[0118] where fcollis the collection time, A is the cross-section area of the cell, Cfeed,iis the i-thion feed concentration, and is the concentration at the downstream conductivity sensor. The latter parameter was calculated using the mass balance over the outflow tubing between the cell effluent and conductivity sensor (Guyes et al., Desalination, vol. 415, 2017, 8-13).

[0119] (9)

[0120] Here, is the total volume in the tubing between the cell and the conductivity sensor,Vwis the superficial flow velocity, andiis the effluent concentration of the i-thion. To imitate the experimental procedure, the collection of water starts 20s after the conductivity of the water at the conductivity sensor decreases below the feed value, and lasts for 120s. The next metric is the separation factor, , which quantifies the selective removal ofNa+over Ca2+, defined as

[0121] (10)

[0122] is defined to be positive for the electro sorption of both Na+and Ca2+whilewas not defined when both andMoreover, for brevity, a parameterwas defined that describes the i-thion concentration scaled by the i-thfeed concentration,

[0123] (11).EXAMPLE 2 - ELECTRODE CAPACITOR ASSEMBLY CELL FUNCTIONS AS AN ION-EXCHANGER

[0124] In order to test the performance of an electrode capacitor assembly that contains an anode and a cathode that are both functionalized with strong acid groups, the theoretical model of Example 1 was applied when using a micropore concentration of -2M.

[0125] Figure 3A presents model results for all as a functionof and forAccording to the model, at short times ofthere is a significant rise in , although to a much higher value of compared toin Figure 2A. At longer times, a decrease in both cations’ concentration untilis observed. Unlike the system described in Figure 2A, here a second subsequent rise in is observed, reaching a local maximum ofThen, decreases again, but does not reach below unity, and increases forthe remaining duration of the charging step. Consequently, since calcium is desorbed and sodium adsorbed, and remains infinite for the entire chargingstep, as indicating a perfect Na+selectivity. It can also be seenthat during most of the charging step. Accordingly, it is shown that the overallprocess is essentially an ion exchange process, as Na+is removed from the feed and replaced with Ca2+. Meanwhile, there is almost no CT removal from the feed, and so therefore the feed's net charge remains unchanged. This represents a novel operational mode as all hitherto known cells operate in desalination mode resulting in net charge removal during charging.

[0126] Figure 3B shows the plot ofas a function of . It can be seenthat during the entire charging step, are positive, for anyreasonable. Additionally, increases linearly with whiledecreaseslinearly. Figure 3C depicts calculated values ofinthe anode at equilibrium (left y-axis) and the (right y-axis), both as a function offor zero applied cell voltage. Asthe magnitude ofA increases. increases as well but relatively slowly, with amaximum value of However, increasesstrongly, to a value of and does not reach a maximumvalue in the range analyzed here. Also, increases with and is alsosignificantly higher than that of the sulfonated-pristine cell due to the presence of chemical charge. Divalent cation selectivity in the anode as at the discharged stateis observed. This result indicates that when the charging step initiates, there is stronger Ca2+desorption than Na+from the anode to the effluent stream.

[0127] The results of Figure 3C elucidate the initial rise in cations concentration shown in Figure 3 A. However, it does not explain the development of the second peak seenin Figure 3A, occurring while decreases and maintains approximately thesame value. It is contemplated that this occurs due to ion swapping in anode micropores, where Ca2+is desorbed while Na+is electrosorbed. To examine the latter, the left y-axis (logarithmic scale) of Figure 3D shows the anode’s spatial-averaged micropore concentration, (solid line), Na+(dashed line), and C1- (dotted line), and theright y-axis shows the spatial-averaged Donnan potential (DP) in the anode, as afunction ofA decrease in both is observed untilFromthis time, begins to increase, while continues decreasing, indicating thatNa+is electrosorbed into the anode while Ca2+is desorbed from the anode. Also, for the entire charging step due to the negatively charged functional groups,and further in the anode, so that no C1- electro sorption occurs. Overall, the modeltogether with the experimental results show that the positive electronic charge injected into the anode during charging is compensated not by C1- electro sorption but by swapping divalent Ca2+cations for monovalent Na+cations.

[0128] Figure 3E shows (solid line) and (dashed line) on the left y-axis, whilethe right y-axis plots all as a function of Vch. A monotonic rise in is observedwith VchfromHowever, barely changes, between at V andAs a result of these trends, is infinite for theentire cell voltage range considered here.

[0129] The schematic illustration shown in Figure 3F presents the desorption of Ca2+and Na+during the charging step from a functionalized anode and Figure 3G presents the ion swapping of Ca2+and Na+during the charging step from a functionalized anode.

[0130] Overall, the results show that sulfonated- sulfonated electrode capacitor assembly provides higher Ca2+storage in the anode micropores in the discharged state, and thus improved monovalent cation selectivity compared to the pristine-anode cell. The cell not only enhances monovalent cation selectivity but further acts as an ion exchanger. In this operational regime, the Ca2+effluent concentration increases while Na+decreases and the Cl" effluent concentration remains at approximately the feed value. Such mode of operation has not yet been previously described.EXAMPLE 3 - ELECTRODE CAPACITOR ASSEMBLY CONTAINING ORGANO PHOSPHATE FUNCTIONALIZED ELECTRODES

[0131] In order to substantiate the robustness of an electrode capacitor assembly containing two negatively functionalized electrodes to selectively remove monovalent cations from feedwater and perform ion exchange, additional functionalization of activated carbon cloth electrode with organo-phosphate groups has been performed.

[0132] In particular, an activated carbon cloth (ACC-5092-15; Kynol Europa GmbH, Germany) having a thickness of -600 pm and a surface area of -1400 m2 / g was used. This material was initially oxidized and after washing with deionized water, the carbon sheets were dried under high vacuum at 50 °C overnight and then moved to a flask containing anhydrous tetrahydrofuran (THF). Excess LiAlHi (3 times the weight of the sheet) was added carefully under N2 atmosphere at 0 °C. The mixture was then warmed to 60-65°C for 48 h. The mixture was quenched with ice-water, before removing the carbon sheets andsoaking them in concentrated HC1 solution (32 vol%) twice, to remove aluminum salts. The carbon sheets were washed with water three times and dried under high vacuum.

[0133] The hydrogenated carbon sheet was then phosphorylated. Iodine (1.5 g, 1.1 equivalents) was added to a solution of the triethylphosphite (1 ml, 1.2 equivalents) in anhydrous CH2CI2 (5.0 ml) at 0 °C. After 5 minutes, the clear, colorless solution was allowed to warm to 25 °C. The phosphorylating agent was then added dropwise, over a period of 10- 15 minutes, to a flask containing the carbon sheets (0.26 g) and pyridine (2.5 ml, 4.0 equivalents) in anhydrous CH2CI2 (25.0 ml). The mixture was lightly stirred under reflux for 48 h. Then, the carbon sheets were removed, soaked in deionized water for 15 min three times, and dried under high vacuum.

[0134] The functionalized electrode was analyzed using ICP, which showed a 1.65 mass weight percent of phosphorous thereby indicating that a good surface coverage by the functional groups was obtained. The pore volume, measured by nitrogen adsorption using BET, showed a significant reduction, which could be a consequence of the crowding with the large phosphoric acid groups (Table 1). The electrode was then viewed in a scanning electron microscope (SEM) that showed no significant changes in the carbon material morphology, although a few black spots were evident which may represent residual organic material (Figures 4A-4D).

[0135] To further confirm the chemical functionalization, infrared (IR) spectroscopy was performed (Figure 5). When compared to a pristine activated carbon cloth electrode, which is mainly composed of carbon-carbon single and double bonds, multiple new peaks appeared, including peaks representative of P-0 and P=O bonds.

[0136] To quantify the concentration of functional groups on the carbon material’s surface, titration was carried out (Figures 6A-6B).

[0137] Table 1.

[0138] A CDI setup was prepared using a feedwater reservoir containing 2.1 mM CaCh and 17.4 mM NaCl. The cell voltage applied during charging was 1.2 V and during discharging 0 V. The charging and discharging time durations were 3 minutes each.

[0139] The results are presented in Table 2 where Repl, Rep2, and Rep3 represent repetitions with different batches of phosphorylated electrodes.

[0140] Table 2.

[0141] It can be seen that the electrode capacitor assembly containing two negatively charged electrodes provides enhanced monovalent removal and improved SAR values.

[0142] To substantiate the robustness of the electrode capacitor assembly containing negatively functionalized electrodes to selectively remove monovalent cations from feedwater and perform ion exchange, a CDI setup was prepared using a feedwater reservoir containing 2.1 mM CaC12and 17.4 mM NaCl. The cell voltage applied during charging varied from 0.6 to 2.0 V and the discharging voltage was fixed at -0.6 V. The charging and discharging time durations were 3 minutes each. Figure 7 shows the electro sorption of Na+and Ca2+with varying charging voltages. At all charging voltages, electrodesorption of Ca2+was observed indicating perfect monovalent cation selectivity. At these charging- discharging voltages, the electrodes exclusively removed Na+from the feedwater, thereby releasing more Ca2+from the micropores than its absorption.

[0143] A two-step process was also performed to achieve monovalent selectivity and lower SAR value in the effluent. The first step involved performing charging-discharging at 1.2 V and -0.2 V, respectively, for 24 cycles with 3 minutes each, and collecting the effluent from all charging cycles. The collected effluent was introduced into the electrode capacitor assembly again in the second run as the feed, and additional charging- discharging at 1.2 V and -0.2 V, respectively, were performed for 7 continuous cycles, 3 minutes each. Figure 8A shows the reduction in SAR from 12 to 6 after the second run, and Figure 8B shows the reduction in the final concentration of Na+from 16.54 mM to 6.81 mM after the second run. Negligible reduction in Ca2+concentration was also observed from 2.01 mM to 1.40 mM after the second run (Figure 8B), indicating that the cell is monovalent cation selective.

[0144] The charging and discharging time durations were varied from 3 to 4 to 5 minutes each in order to obtain maximum water recovery while keeping the charging and discharging voltages at 1.2 V and -0.2 V, respectively. Figure 9 shows that the lowest Na+concentration in the effluent and the lowest SAR value were obtained at each cycle duration of 8 minutes (4 charging, 4 discharging). This corresponds to 75% maximum water recovery. Accordingly, subsequent experiments were performed by utilizing a duration of 4 minutes for water recovery.

[0145] The number of layers of both cathode and anode electrodes in the electrode capacitor assembly was varied in order to determine its effect on the water quality obtained. An equal number of electrode layers provides a symmetric setup, whereas an unequal number provides an asymmetric cell. The cell was explored in a batch mode operation, in which a fixed volume of saline feed is flown through the cell. The effluent is collected after each charging cycle and analyzed. The effluent after each discharging cycle is added to the saline reservoirand re-introduced into the CDI cell. Figure 10 shows the SAR and conductivity of the feed after applying charging and discharging voltages of 1.2 V and -0.2 V, respectively, for 3 minutes each. The symmetric cell with a greater number of electrode layers displayed a lower SAR and a lower conductivity as compared to the asymmetric cell or a symmetric cell with a lower number of electrodes on each side (Figure 10). It is contemplated that more layers of electrodes provide a higher concentration of micropores thereby enhancing the electro sorption of the ions in the micropores.

[0146] Single layer of electrodes in a batch mode configuration was further tested at charging and discharging voltages of 1.6 V and -0.2 V, respectively, with a duration of 4 minutes each. The effluent after the charging cycles was collected and analyzed. The effluent after the discharging cycles was re-introduced into the cell as feed. Figure 11A shows the SAR and conductivity of the effluent and Figure 1 IB shows the concentrations of the sodium and calcium ions in the effluent. The salinity of the feed is shown to increase with each cycle. Therefore, with subsequent cycles, SAR and conductivity of the effluent increased (Figure 11 A) with the lowest SAR (ca. 6) observed after 4 cycles in this mode of operation.

[0147] The performance of single layers of electrodes was also explored in a repeated single pass mode, at charging and discharging voltages of 1.6 V and -0.2 V, respectively, with a duration of 4 minutes each. Figure 12A-12B show that in this mode of operation, SAR values decreased from 12 to around 6, and the final concentration of Na+in the effluent decreased from 17.51 mM to 7.62 mM. The values show repeatability in their nature. The SAR, conductivity and final Na+ion concentration remain constant after the 10thcycle up to the 40thcycle. The calcium concentration decreased from 2.1 mM to a minimum of 1.35 mM, indicating monovalent cation selectivity.

[0148] To further substantiate the repeatability of the electrode preparation process, different batches of phosphorylated electrodes were prepared and tested under similar conditions. Table 3 shows the characteristic properties of the electrodes where Repl, Rep2, and Rep3 represent repetitions with different batches of phosphorylated electrodes.

[0149] Table 3.

[0150] Although the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims.

Claims

CLAIMS1. A method for achieving ion-exchange in the absence of an ion-exchange resin, the method comprising the steps of:(a) passing saline water comprising a first cation having a first valency and a second cation having a second valency through an electrode capacitor assembly comprising a pair of electrodes comprising an anode and a cathode, wherein the anode and cathode are porous carbon electrodes each modified by negatively charged functional groups; and(b) applying an electrical potential between the cathode and the anode, thereby obtaining exchange between the first cation and the second cation on the anode in the absence of an ion-exchange resin.

2. The method of claim 1, wherein the first cation is a monovalent cation and the second cation is a polyvalent cation selected from a divalent cation, a trivalent cation, and a mixture or combination thereof.

3. The method of claim 2, wherein the monovalent cation is selected from the group consisting of Na+, K+, Li+, and a mixture or combination thereof.

4. The method of claim 2, wherein the monovalent cation is a Na+ion.

5. The method of claim 2, wherein the polyvalent cation is selected from the group consisting of Ca2+, Mg2+, Fe2+, Fe3+, Zn2+, Cu2+, Mn2+, and a mixture or combination thereof.

6. The method of claim 5, wherein the polyvalent cation is a Ca2+ion.

7. The method of claim 1, wherein the first cation is a divalent cation and the second cation is a trivalent cation.

8. The method of any one of claims 1 to 7, wherein the electrode capacitor assembly is in electrical communication with a power supply, wherein during operation, said power supply is configured to apply electrical potential or to supply electric charge to the electrodes.

9. The method of any one of claims 1 to 8, wherein the porous carbon electrode is selected from the group consisting of activated carbon, carbon black, graphitic carbon, carbon fibers,carbon microfibers, carbon aerogel, fullerene carbon, carbon nanotubes (CNTs), graphene, carbide, carbon onions, carbon paper, and a mixture or combination thereof.

10. The method of any one of claims 1 to 9, wherein the porous carbon electrode comprises a plurality of nanopores, micropores, mesopores, or a mixture or combination thereof.

11. The method of any one of claims 1 to 10, wherein each of the porous carbon electrodes is independently modified with negatively charged functional groups selected from sulfonate, sulfate, phosphate, phosphonate, phosphinate, alkoxide, amide, carboxylate, and a mixture or combination thereof.

12. The method of claim 11, wherein each of the porous carbon electrodes is independently modified with negatively charged sulfonate or phosphate functional groups.

13. The method of any one of claims 1 to 12, wherein the electrode capacitor assembly further comprises at least one additional anode or cathode, wherein the additional anode or cathode are each modified by negatively charged functional groups.

14. The method of claim 13, wherein the electrode capacitor assembly comprises an equal number of anodes and cathodes each modified by negatively charged functional groups.

15. The method of any one of claims 1 to 14, wherein step (a) comprises passing the saline water through an electrode capacitor assembly at a flow rate of about 5 to about 500 L / m2hr.

16. The method of any one of claims 1 to 15, wherein step (b) comprises applying voltage that is above the voltage at the point of zero charge of the anode.

17. The method of any one of claims 1 to 16, wherein step (b) comprises applying voltage of from about 0.6 V to about 2.5 V.

18. The method of any one of claims 1 to 17, wherein the electrode capacitor assembly is adjacent to an agricultural irrigation system, a wastewater treatment system, a brackish water desalination system or a chemical reactor.

19. The method of any one of claims 1 to 18, comprising obtaining product water with reduced concentration of the first cation as compared to the feed saline water.

20. The method of claim 19, wherein the product water has at least 2% reduction in the concentration of the first cation as compared to the feed saline water.

21. The method of any one of claims 1 to 20, wherein the first cation is a Na+ion, and wherein the method further comprises obtaining product water with a sodium adsorption ratio (SAR) of less than about 10.0 mM1 / 2.

22. An electrochemical cell that is devoid of an ion-exchange resin, the cell comprising an electrode capacitor assembly comprising a pair of electrodes comprising an anode and a cathode, wherein the anode and cathode are porous carbon electrodes each modified by negatively charged functional groups.

23. The cell of claim 22, wherein the electrode capacitor assembly is in electrical communication with a power supply, wherein during operation, said power supply is configured to apply electrical potential or to supply electric charge to the electrodes.

24. The cell of claim 22 or 23, wherein the porous carbon electrode is selected from the group consisting of activated carbon, carbon black, graphitic carbon, carbon fibers, carbon microfibers, carbon aerogel, fullerene carbon, carbon nanotubes (CNTs), graphene, carbide, carbon onions, carbon paper, and a mixture or combination thereof.

25. The cell of any one of claims 22 to 24, wherein the porous carbon electrode comprises a plurality of nanopores, micropores, mesopores, or a mixture or combination thereof.

26. The cell of any one of claims 22 to 25, wherein each of the porous carbon electrodes is independently modified with negatively charged functional groups selected from sulfonate, sulfate, phosphate, phosphonate, phosphinate, alkoxide, amide, carboxylate, and a mixture or combination thereof.

27. The cell of claim 26, wherein each of the porous carbon electrodes is independently modified with negatively charged sulfonate or phosphate functional groups.

28. The cell of any one of claims 22 to 27, wherein the electrode capacitor assembly further comprises at least one additional anode or cathode, wherein the additional anode or cathode are each modified by negatively charged functional groups.

29. The cell of claim 28, wherein the electrode capacitor assembly comprises an equal number of anodes and cathodes each modified by negatively charged functional groups.

30. The cell of any one of claims 22 to 29 which is configured to provide ion exchange between a first cation having a first valency and a second cation having a second valency on the anode upon the application of an electrical potential between the cathode and the anode.

31. A method of achieving at least one of reducing sodium adsorption ratio (SAR) and water conductivity of saline water, the method comprising the steps of:(a) passing saline water comprising a monovalent cation comprising sodium and a polyvalent cation through an electrode capacitor assembly comprising a pair of electrodes comprising an anode and a cathode, wherein the anode and cathode are porous carbon electrodes each modified by negatively charged functional groups; and(b) applying an electrical potential between the cathode and the anode, thereby obtaining product water having least one of reduced sodium adsorption ratio (SAR) and water conductivity.

32. The method of claim 31, wherein the product water has a SAR of less than about 10.0 mM1 / 2.

33. The method of claim 31, wherein the product water has water conductivity of less than about 5.0 mS / cm.

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