Systems and methods for making electroactive mixed matrix membranes

Abstract

Described herein are techniques for the scalable production of electroactive mixed matrix membranes. The disclosed membranes may be produced via spray coating using suspensions of active particles such as carbon nanotubes. These membranes offer stable, effective separation capabilities while being derived from highly flexible and industrially applicable spray coating technologies that have as yet been ill suited to the generation of the electroactive mixed matrix membranes disclosed herein.

Description

SYSTEMS AND METHODS FOR MAKING ELECTRO ACTIVE MIXED MATRIXMEMBRANESCROSS REFERENCE TO OTHER APPLICATIONS

[0001] This application claims benefit of U.S. Provisional Application No. 63 / 554,859, filed February 16, 2024, and U.S. Provisional Application No. 63 / 736,525, filed December 19, 2024, each of which are incorporated herein in their entirety.BACKGROUND OF THE INVENTION

[0002] Separation membranes are used to remove solutes from feed solutions. One example of this is desalination, where membranes are used to remove salts from a water source. Such membranes are prone to fouling or reduced flux over time due to scaling. Scalable membrane fabrication technologies for the production of stable and durable semi-permeable electroactive membranes is an outstanding problem in the art.SUMMARY OF THE INVENTION

[0003] In one aspect disclosed herein is a method of coating a substrate with a suspension to produce an electroactive semi-permeable membrane comprising: providing the suspension, wherein the suspension comprises a plurality of active particles; disposing the suspension into a sprayer; dispensing the suspension onto the substrate at a rate of at least 5 in2 / min, wherein the substrate is supported by a conveyor system in fluidic communication with the sprayer, and wherein a rate of dispensing is at least 2 ml / min, and heating the substrate comprising the suspension to obtain the electroactive semi-permeable membrane, wherein a retentate of a leaching test of the electroactive semi -permeable membrane has an NTU within 10% of a feed solution of the leaching test. In some embodiments, the method further comprises: repeating each of the abovementioned operations. In some embodiments, the method further comprises: coating the substrate with a polyamide layer In some embodiments, the method further comprises washing the electroactive semi-permeable membrane. In some embodiments, a pH of the feed solution is about 2 to about 13. In some embodiments, the NTU is within 5% of the feed solution of the leaching test. In further embodiments, a pH of the feed solution is about 4 to about 11. In further embodiments, a composition of the suspension changes for at least one iteration of the repeating operation. In some embodiments, the suspension has a viscosity of at least 0.8 cP. In some embodiments, a length of an active particle of the plurality of active particles is at least 10 pm. In some embodiments, an average normalized flux of the electroactive semi-permeable membrane is at least 0.6 for a recovery percent of about 50%. In some embodiments, an average sheet resistance of the electroactive semi-permeable membraneis at most 2000 Q / n. In some embodiments, a standard deviation of a measured surface resistivity of the electroactive semi -permeable membrane is at most 10% of the measured surface resistivity. In some embodiments, a mass loading of active particles on the substrate is at least 0.5 g / m2. In some embodiments, the sprayer comprises one or more spraying components. In further embodiments, at least one of the one or more spraying components is configured to aerosolize the suspension. In further embodiments, the sprayer comprises one or more of an inkjet, an electrospray, or a conventional sprayer. In some embodiments, the conveyor system completes one or more revolutions during the dispensing operation. In some embodiments, the substrate is heated to at least 35 °C. In some embodiments, the substrate comprises an ultrafiltration membrane. In further embodiments, the ultrafiltration membrane comprises one or more of polysulfone, poly-ether sulfone, or a non-woven polyester. In further embodiments, a permeability of the ultrafiltration membrane is substantially similar to a permeability of the electroactive semi-permeable membrane. In some embodiments, the suspension further comprises a binder, a viscosity modifier, or a dispersant. In further embodiments, the binder is a crosslinked polymer binder, wherein the plurality of active particles are encapsulated by the crosslinked polymer binder. In further embodiments, the dispersant comprises one or more of an aqueous or organic solvent. In some embodiments, the plurality of active particles comprises a one-dimensional nanomaterial. In further embodiments, the one-dimensional nanomaterial comprises a nanotube, a nanowire, or a nanorod. In further embodiments, the plurality of active particles further comprises nanoparticles. In some embodiments, the substrate has dimensions comprising a width of about 5 inches to about 42 inches and a length of about 12 inches to about 108 inches.

[0004] In another aspect disclosed herein is a method of coating a substrate with a suspension to produce an electroactive semi-permeable membrane comprising: providing the suspension, wherein the suspension comprises a plurality of active particles; disposing the suspension into a sprayer; dispensing the suspension onto the substrate at a rate of at least 5 in2 / min, wherein the substrate is supported by a conveyor system in fluidic communication with the sprayer, and wherein a rate of dispensing is at least 2 ml / min, and heating the substrate comprising the suspension to obtain the electroactive semi-permeable membrane, wherein a permeability of the substrate is substantially similar to a permeability of the electroactive semi-permeable membrane. In some embodiments, the method further comprises: repeating each of the operations abovementioned operations. In some embodiments, the method further comprises: coating the substrate with a polyamide layer In some embodiments, the method further comprises washing the electroactive semi-permeable membrane. In further embodiments, a composition of the suspension changes for at least one iteration of the repeating operation. Insome embodiments, the suspension has a viscosity of at least 0.8 cP. In some embodiments, a length of an active particle of the plurality of active particles is at least 10 pm. In some embodiments, an average normalized flux of the electroactive semi-permeable membrane is at least 0.6 for a recovery percent of about 50%. In some embodiments, an average sheet resistance of the electroactive semi-permeable membrane is at most 2000 Q / n. In some embodiments, a standard deviation of a measured surface resistivity of the electroactive semi-permeable membrane is at most 10% of the measured surface resistivity. In some embodiments, a mass loading of active particles on the substrate is at least 0.5 g / m2. In some embodiments, the sprayer comprises one or more spraying components. In further embodiments, at least one of the one or more spraying components is configured to aerosolize the suspension. In further embodiments, the sprayer comprises one or more of an inkjet, an electrospray, or a conventional sprayer. In some embodiments, the conveyor system completes one or more revolutions during the dispensing operation. In some embodiments, the substrate is heated to at least 35 °C. In some embodiments, the substrate comprises an ultrafiltration membrane. In further embodiments, the ultrafiltration membrane comprises one or more of polysulfone, poly-ether sulfone, or a nonwoven polyester. In some embodiments, a permeability of the ultrafiltration membrane is substantially similar to a permeability of the electroactive semi-permeable membrane. In some embodiments, the suspension further comprises a binder, a viscosity modifier, or a dispersant. In further embodiments, the binder is a crosslinked polymer binder, wherein the plurality of active particles are encapsulated by the crosslinked polymer binder. In further embodiments, the dispersant comprises one or more of an aqueous or organic solvent. In some embodiments, the plurality of active particles comprises a one-dimensional nanomaterial. In further embodiments, the one-dimensional nanomaterial comprises a nanotube, a nanowire, or a nanorod. In some embodiments, the plurality of active particles further comprises nanoparticles. In some embodiments, the substrate has dimensions comprising a width of about 5 inches to about 42 inches and a length of about 12 inches to about 108 inches. In some embodiments, a retentate of a leaching test of the electroactive semi-permeable membrane has an NTU within 10% of a feed solution of the leaching test. In further embodiments, a pH of the feed solution is about 2 to about 13. In some embodiments, a retentate of a leaching test of the electroactive semi- permeable membrane has an NTU within 5% of a feed solution of the leaching test. In further embodiments, a pH of the feed solution is about 2 to about 13.

[0005] In another aspect disclosed herein is a method for removing a boron species from a water source, comprising: (a) filtering the water source through an electroactive membrane, wherein the water source comprises at least boric acid and at least one scaling species, wherein the electroactive membrane comprises a surface configured to receive an applied voltage, andwherein the water source is provided to the surface of the electroactive membrane; (b) applying a first voltage to the electroactive membrane, thereby generating borate ions from the boron species; and (c) applying a second voltage to the electroactive membrane, thereby removing at least a portion of the at least one scaling species from the surface of the electroactive membrane, wherein at least a portion of the borate ions are rejected from the electroactive membrane. In some embodiments, the first voltage and the second voltage are applied via an alternating waveform. In some embodiments, the alternating waveform comprises a square waveform. In some embodiments, the alternating waveform comprises a sinusoidal waveform. In some embodiments, the alternating waveform comprises a duty cycle of from about 20% to about 80%. In some embodiments, the alternating waveform comprises a duty cycle of from about 20% to about 50%. In some embodiments, the alternating waveform comprises a peak to peak voltage of about 4 V to about 6 V. In some embodiments, the frequency of the alternating waveform is from about 1 Hz to about 500 Hz. In some embodiments, the frequency of the alternating waveform is from about 1 Hz to about 5Hz. In some embodiments, the first voltage is configured to raise the pH of the water source to at least about 9. In some embodiments, the pH of the water source is at least about 9 within at least about 5 pm from the surface of the electroactive membrane. In some embodiments, (b) and (c) occur during (a). In some embodiments, (b) and (c) occur repeatedly during (a) by applying an alternating voltage waveform comprising the first voltage and the second voltage. In some embodiments, the scaling species comprises a metal or a silicate. In some embodiments, the metal comprises an alkali metal or an alkaline earth metal. In some embodiments, the water source has a TDS level of at least about 35,000 ppm. In some embodiments, the filtering comprises delivering the water source to the surface of the electroactive membrane at a pressure of about 100 psi to about 800 psi. In some embodiments, (a)-(c) are performed in at least a first stage and a second stage. In some embodiments, the pressure of the water source is about 300 psi to about 1,000 psi in the first stage. In some embodiments, the pressure of the water source is about 100 psi to about 300 psi in the second stage. In some embodiments, at least about 80% of the boron species is rejected from the electroactive membrane. In some embodiments, the electroactive membrane comprises a layered structure. In some embodiments, the layered structure comprises at least a polyamide layer and an electroactive layer. In some embodiments, the electroactive layer comprises a carbon nanomaterial or a conductive nanoparticle.INCORPORATION BY REFERENCE

[0006] All publications, patents, and patent applications mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication, patent, or patent application was specifically and individually indicated to be incorporated by reference.BRIEF DESCRIPTION OF THE DRAWINGS

[0007] The novel features of the invention are set forth with particularity in the appended claims. A better understanding of the features and advantages of the present invention will be obtained by reference to the following detailed description that sets forth illustrative embodiments, in which the principles of the invention are utilized, and the accompanying drawings of which:

[0008] FIG. 1 depicts a non-limiting embodiment of a semi-continuous drum-based spraycoating system.

[0009] FIG. 2 depicts a non-limiting embodiment of a semi -continuous conveyor-based spraycoating system with one sprayer.

[0010] FIG. 3 depicts a non-limiting embodiment of a semi -continuous conveyor-based spraycoating system with two sprayers.

[0011] FIG. 4 depicts non-limiting embodiments of electroactive mixed matrix membranes.

[0012] FIG. 5 depicts borate rejection at a surface of a reverse osmosis membrane.

[0013] FIG. 6A depicts a sinusoidal alternating waveform.

[0014] FIG. 6B depicts a square wave alternating waveform with a duty cycle of 20%.

[0015] FIG. 6C depicts a square wave alternating waveform with a duty cycle of 50%.

[0016] FIG. 6D depicts a square wave alternating waveform with a duty cycle of 80%.

[0017] FIG. 7 depicts an experimental setup for a drum-based semi-continuous coating system.

[0018] FIG. 8 depicts a photograph of the surface texture of an unwashed versus washed coated membrane.

[0019] FIG. 9 depicts a low-resolution SEM micrograph showing the surface texture of three membrane samples prepared using carbon nanotubes and different coating methodologies.

[0020] FIG. 10 depicts a high-resolution SEM micrographs showing the surface texture and details of carbon nanotube films on the membranes prepared using different coating methodologies.

[0021] FIG. 11A depicts observed flux decline profiles for all passive vs hybrid trains.

[0022] FIG. 11B depicts normalized flux decline profiles for all passive vs hybrid trains.

[0023] FIG. 12A depicts observed flux decline profiles for passive RO vs active RO.

[0024] FIG. 12B depicts normalized flux decline profiles for passive vs active RO.

[0025] FIG. 13A depicts observed salt rejection profiles for all passive vs hybrid trains.

[0026] FIG. 13B depicts normalized salt rejection profiles for all passive vs hybrid trains.

[0027] FIG. 14A depicts observed salt rejection profiles for passive RO vs active RO.

[0028] FIG. 14B depicts normalized salt rejection profiles for passive RO vs active RO.

[0029] FIG. 15A depicts FIB-SEM images and their EDS elemental surface analysis for the first membrane from the all-passive train.

[0030] FIG. 15B depicts FIB-SEM images and their EDS elemental surface analysis for the first membrane from the hybrid train.

[0031] FIG. 16A depicts FIB-SEM images and their EDS elemental surface analysis for the passive RO membrane.

[0032] FIG. 16B depicts FIB-SEM images and their EDS elemental surface analysis for the active RO Membrane.

[0033] FIG. 17 depicts a one-stage reverse osmosis system.

[0034] FIG. 18 depicts a two-stage reverse osmosis process.

[0035] FIG. 19 depicts the effect of Eppon boron rejection.

[0036] FIG. 20A depicts the effect of frequency on boron rejection at 4 Fpp.

[0037] FIG. 20B depicts the effect of frequency on boron rejection at 5 Fpp.

[0038] FIG. 20C depicts the effect of frequency on boron rejection at 6 Epp.

[0039] FIG. 21 depicts the effect of waveform configuration on boron rejection.

[0040] FIG. 22A depicts permeability versus recovery percent for a plurality of active modules at different FPPversus a passive module.

[0041] FIG. 22B depicts rejection versus recovery percent for a plurality of active modules at different FPPversus a passive module.

[0042] FIG. 23A depicts permeability versus recovery percent for a plurality of active modules at different frequencies versus a passive module.

[0043] FIG. 23B depicts rejection versus recovery percent for a plurality of active modules at different frequencies versus a passive module.

[0044] FIG. 24A depicts reproducibility in permeability versus recovery percent.

[0045] FIG. 24B depicts reproducibility in permeability versus recovery percent.

[0046] FIG. 25A depicts permeability decline profiles of an active module and a passive module.

[0047] FIG. 25B depicts permeability decline profiles of an active module and a passive module.

[0048] FIG. 26A depicts permeability decline profiles of an active module and a passive module.

[0049] FIG. 26B depicts permeability decline profiles of an active module and a passive module.

[0050] FIG. 27 depicts a table of rejection values for a plurality of active modules and one passive module and a rejection profile comparison for an active module versus a passive module.

[0051] FIG. 28A depicts permeability versus recovery percent for a non-electrified active module versus a passive module.

[0052] FIG. 28B depicts rejection versus recovery percent for a non-electrified active module versus a passive module.DETAILED DESCRIPTION

[0053] While various embodiments of the invention have been shown and described herein, it will be obvious to those skilled in the art that such embodiments are provided by way of example only. Numerous variations, changes, and substitutions may occur to those skilled in the art without departing from the invention. It should be understood that various alternatives to the embodiments of the invention described herein may be employed.

[0054] Membranes are permselective barriers to specific components of a fluid mixture. When a liquid mixture is filtered through such membranes by applying a pressure driving force, entities in the mixture larger than the membrane pores are retained (typically solutes in a solution), while other components smaller than the pore size, including the liquid solvent, permeate through the filter. Membrane filtration processes can be classified based on the membrane pore sizes as microfiltration (MF; with pores larger than 0.2 microns), ultrafiltration (UF; with pores in the range of 10 - 200 nanometers), nanofiltration (NF; pores in the range of 1 - 10 nm), and reverse osmosis (RO; pores less than 1 nm, usually in the range of 0.4 - 0.8 nm). These membranes are commonly made from polymers and in some cases ceramics. At the two extremes of the membrane filtration spectrum, MF is commonly used for removing suspended particles, such as microbes from water, whereas RO has become a staple technology for desalination, or removal of salt from water. UF and NF processes encompass separation ofvarious intermediate sizes of entities from the solvent and contribute to a vast array of separation processes. The membranes and methods and systems for making membranes disclosed herein may be applied to a diverse array of aqueous media separation, water purification, and water treatment processes.

[0055] Some membranes may employ passive separation techniques, where the separation is due to size-based exclusion of solutes, preordained by the pore sizes of the membrane. Depending on the material properties of the polymeric or ceramic constituents of these membranes, for instance, presence of bound or interfacial charges on the membrane surface or in the pores, there can also be charge exclusion, or hydrophobic / hydrophilic exclusion phenomena contributing to the separation process. Furthermore, many classes of ion-exchange membranes that exhibit electrode characteristics (electron donor / acceptor) and form the membrane electrode assembly in proton exchange membrane systems fall under these classes of materials. The membranes accessible by the systems and methods disclosed herein may enhance the functionality of such membranes. In some embodiments, the membranes disclosed herein may provide said functionality via the conductivity of membrane constituents. In some embodiments, said functionality may be tunable by an external electric field. In some embodiments, the functionality may include the ability to prevent scaling and fouling of the membrane surface. In some embodiments, the prevention of scaling may be performed by applying an alternating voltage to an electroactive membrane.

[0056] The membranes disclosed herein may draw inspiration from characteristics of biological membranes which have the ability to actively transport particular components (e.g., ions) between extracellular fluids and their cytoplasm. One well known example of this is the active transport of potassium through selective potassium ion channels. The systems and methods disclosed herein may provide analogous benefits and address limitations in the art of existing filtration technologies such as reverse osmosis membranes used for desalination. For instance, in some embodiments, the membranes herein may provide functional characteristics that can be modulated via an external electric field. This modulation may reduce dependence of the membranes on their initial distribution of functional components and enable greater operational freedom. In some embodiments, multiple layers a membrane may comprise multiple electroactive layers and provide flexibility in generated membrane architectures. In some embodiments, the organization and modularity of these layers may facilitate highly selective, robust separation of solutes from solutions, including the purification of solvents. In some cases, the membranes herein may be configured for reverse osmosis.

[0057] The systems and methods disclosed herein may provide electroactive membranes that may have behavior dependent on an external stimuli. In some embodiments, the external stimuli may comprise an electric field. Such electroactive membranes may provide more robust, selective, or efficient membranes. In some embodiments, a robust membrane may be resistant to scaling. In some embodiments, a selective membrane may remove particular species from a feed solution. In some embodiments, an efficient membrane may have improved flux with improved or stable salt rejection with respect to a passive membrane. These advantages may not be accessible via passive membranes that have behavior defined entirely by their static composition. In some embodiments disclosed herein are electroactive membranes comprising a class of mixed matrix membranes which contain layers of conductive structures on the membrane, which can be activated using externally applied electric fields. In some embodiments, conducting nanomaterials such as graphene oxides, carbon nanotubes, nanowires, or conducting polymers like polyaniline, or their combinations may be used to impart conductivity to electroactive membranes.

[0058] In some embodiments, the length of 1 -dimensional nanomaterials used as conducting nanomaterials herein may be about 5 pm to about 60 pm, about 5 pm to about 10 pm, about 5 pm to about 15 pm, about 5 pm to about 20 pm, about 5 pm to about 25 pm, about 5 pm to about 30 pm, about 5 pm to about 35 pm, about 5 pm to about 40 pm, about 5 pm to about 45 pm, about 5 pm to about 50 pm, about 5 pm to about 55 pm, about 5 pm to about 60 pm, about 10 pm to about 15 pm, about 10 pm to about 20 pm, about 10 pm to about 25 pm, about 10 pm to about 30 pm, about 10 pm to about 35 pm, about 10 pm to about 40 pm, about 10 pm to about 45 pm, about 10 pm to about 50 pm, about 10 pm to about 55 pm, about 10 pm to about 60 pm, about 15 pm to about 20 pm, about 15 pm to about 25 pm, about 15 pm to about 30 pm, about 15 pm to about 35 pm, about 15 pm to about 40 pm, about 15 pm to about 45 pm, about 15 pm to about 50 pm, about 15 pm to about 55 pm, about 15 pm to about 60 pm, about 20 pm to about 25 pm, about 20 pm to about 30 pm, about 20 pm to about 35 pm, about 20 pm to about 40 pm, about 20 pm to about 45 pm, about 20 pm to about 50 pm, about 20 pm to about 55 pm, about 20 pm to about 60 pm, about 25 pm to about 30 pm, about 25 pm to about 35 pm, about 25 pm to about 40 pm, about 25 pm to about 45 pm, about 25 pm to about 50 pm, about 25 pm to about 55 pm, about 25 pm to about 60 pm, about 30 pm to about 35 pm, about 30 pm to about 40 pm, about 30 pm to about 45 pm, about 30 pm to about 50 pm, about 30 pm to about 55 pm, about 30 pm to about 60 pm, about 35 pm to about 40 pm, about 35 pm to about 45 pm, about 35 pm to about 50 pm, about 35 pm to about 55 pm, about 35 pm to about 60 pm, about 40 pm to about 45 pm, about 40 pm to about 50 pm, about 40 pm to about 55 pm, about 40 pm to about 60 pm, about 45 pm to about 50 pm, about 45 pm to about 55 pm, about 45 pmto about 60 pm, about 50 pm to about 55 pm, about 50 pm to about 60 pm, or about 55 pm to about 60 pm. In some embodiments, the length may be about 5 gm, about 10 gm, about 15 gm, about 20 gm, about 25 gm, about 30 gm, about 35 gm, about 40 gm, about 45 gm, about 50 gm, about 55 gm, or about 60 gm. In some embodiments, the length may be at least about 5 gm, about 10 gm, about 15 gm, about 20 gm, about 25 gm, about 30 gm, about 35 gm, about 40 gm, about 45 gm, about 50 gm, or about 55 gm.

[0059] In some embodiments disclosed herein, mixed matrix membranes for electroactive membrane separation are described, including approaches of making such mixed matrix electroactive membranes targeting specific functionalities and applications. Disclosed are examples and embodiments of large-scale deposition approaches configured for consistently and rapidly creating mixed matrix membranes on common non-woven polymeric substrates. For example, mixed matrix membranes may be formed on a polysulfone substrate. These approaches may facilitate large volume processing of flat sheet membranes with compositional and performance characteristics not accessible by other methods. In some cases, the mixed matrix membranes may be referred to as electroactive membranes.Methods of membrane production

[0060] Conventional approaches of membrane production often require a continuous process that necessitates a single deposition step, whereby the entire film is deposited onto the substrate in a single pass. This typically requires conditioning and fixing the composition of the coating fluid to be pre-engineered to ensure that the entire desired amount of material can be deposited in one single application step. The fixing of the coating film can be done in subsequent processing steps, which may include heating, dipping the coated substrate in a sequence of chemical baths to achieve the desired chemical bonding, rinsing, removal of additives, and curing. Following each chemical bath, the substrate is passed through air-knives to dry out excess fluids. In some applications, the substrate may require substantial post-treatment to ensure the stability of the produced membrane. Additionally, due to the mentioned constraints, the architectures and functionalities of the membranes accessible by said approaches are substantially limited by what properties may be imparted using a single pre-engineered composition.

[0061] Unlike polymer solutions used in conventional membrane casting, the mixed matrix membranes produced by the systems and methods disclosed herein provide techniques to embed electroactive solid-like active particles (e.g., nanorods, nanowires, or nanotubes) in the membrane. These solid-like particulate substances may provide benefits including rendering the final membrane active, selective for ion separation, or less prone to scaling or biofouling. Theincorporation of such particles can be challenging for conventional membrane coating sprayers or applicators. Larger forms of active particles (e.g., 30 pm carbon nanotubes) may hinder a spray of the sprayer as the openings of conventional sprayer nozzles may be narrow and subject to build-up of an advancing particles of the advancing suspension. Build-up of advancing particles may result in defects (e.g., streaks) on the resulting film. The systems and methods disclosed herein address this and other long-standing issues in the art, providing spray-coating of substrates with functional (e.g., so as to retain uniform conductivity) loadings of active particles.

[0062] In addition to the benefits offered over conventional membrane fabrication techniques, the systems and methods disclosed herein may provide solutions to problems of non-scalable mixed matrix membrane fabrication techniques. Said non-scalable techniques may require a transverse pressure drop across a porous substrate to be coated, and a dispersion of the coating suspension containing the active particles may be applied to the high-pressure side of the substrate. The pressure drop draws a suspension containing the active particles across the porous substrate, causing the drag force to build up a film of the retained active particles on the surface of the substrate. Such techniques, however, have been shown to produce non-uniform mixed matrix membranes which may substantially limit their performance, compounding issues with the general scalability of pressure-drop based techniques. Further, existing techniques to produce mixed matrix membranes may suffer from a low adhesion of active materials due to the inherent challenges of coating hydrophobic materials (e.g., carbon nanomaterials) on hydrophilic materials (e.g., a polyamide or polysulfone material). Still further, existing processes may also be ill-suited to producing tight mixed matrix membranes, such as reverse osmosis membranes. With techniques relying on a pressure differential to produce mixed matrix membranes, the pressure drop required to achieve an adequate force for the nanoparticles to deposit on the membrane is quite substantial owing to the low porosity of substrates used. In addition to the pressure considerations, the active materials may not be well adhered to the surface due to their reliance on non-bonding interactions to retain surface contact. The systems and methods disclosed herein provide techniques to coat hydrophilic porous substrates with hydrophobic active particles in a manner that increases both active particle coating density and adhesion.Manufacturing Scaling considerations for mixed matrix membrane productionPre-treatment

[0063] A substrate for coating by the systems and methods disclosed herein may have filtration characteristics such as solvent permeability, rejection selectivity of specific solute components, and a surface amenable to coating with an electroactive material. In some embodiments, the electroactive material may comprise one-dimensional nanomaterials. In some embodiments, theone-dimensional nanomaterials comprise active particles. In some embodiments, the active particles comprise one or more of nanorods, nanowires, nanotubes. In some embodiments, nanoparticles may comprise a portion of the active particles. Substrates suitable for coating may include polymeric ultrafiltration membranes made with polysulfone (PS), polyether sulfone (PES), poly acrylo nitrile (PAN), or poly-aniline (PANi). These substrates may be amenable to binding suitably functionalized active particles with an appropriate binder or cross-linker added to an active particle dispersion.Active particles

[0064] The active particles to be selected for electroactive membrane coating may be electrically conductive. In some embodiments, a dispersion comprising the active particles may comprise a concentration sufficient to ensure that the final deposited material retains electrical continuity across the entire active surface of the membrane. The active particles for making conductive films may comprise 1 -dimensional materials like carbon nanotubes , nanowires, or nanorods. In some embodiments, a carbon nanotube may be single walled or multi-walled. In some embodiments, a nanowire may comprise a metal. In some embodiments, a nanowire may comprise silver, platinum, gold, or other conductive metal. Conductive and doped polymers including polyaniline or polypyrroles may also be suitable candidates in some applications. In some embodiments, 2D or 3D nanomaterials comprising graphene flakes, graphene oxides, or conducting nanoparticles, may also be used for preparation of conductive films. In some embodiments, a conductive nanoparticle may comprise indium tin oxide. In some embodiments, graphenes, graphene oxides, or nanoparticles can sometimes be added to these mixtures as joiners or fillers. In some embodiments, a joiner or filler may facilitate homogeneous electrical properties of the film.Suspension Composition

[0065] To be dispersed, active particles may be suspended in a liquid matrix. With increased focus on green chemistry approaches conducive to good manufacturing practices, it is often desirable to prepare aqueous dispersions. However, owing to the extraordinarily strong van der Waals interactions between some types of the active particles disclosed herein (e.g., carbon nanotubes), aggregation may occur rendering dispersal of an aqueous solution comprising the active particles extremely difficult. To address this issue, the stability of the dispersion may be enhanced by adding one or more of a suitable surfactant, a co-solvent, or a dispersant. In some embodiments, the ultimate objective of the mixed matrix membrane manufacturing is to deposit the nanoparticles to the membrane substrate permanently. In such instances, a binder may be introduced to the dispersion. The function of the binder may be to attach to or wrap around thenanoparticles, as well as to attach to the membrane substrate, preferentially through chemical bonding, such that the nanoparticles may be permanently adhered to the membrane surface. Finally, to make the dispersion flow, spread, and produce uniform films on the substrate, its viscosity, surface tension, and spreading characteristics need to be tuned through addition of components such as viscosity modifiers and interfacial tension modifiers. In some embodiments, the binder used herein may comprise a cross-linked polymeric material. In some embodiments, the cross-linked polymeric material may comprise polyvinyl alcohol. In some embodiments, the cross-linked polymeric material may confer improved membrane robustness and active particle adhesion by providing a means to chemically bond encapsulated, hydrophobic active materials on a hydrophilic porous substrate.

[0066] In some embodiments, a viscosity of a suspension herein may be at least about 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0 or more cP. In some embodiments, a viscosity of a suspension herein may be about 0.5 cP to about 2 cP. In some embodiments, a viscosity of a suspension herein may be about 0.5 cP to about 0.75 cP, about 0.5 cP to about 1 cP, about 0.5 cP to about 1.25 cP, about 0.5 cP to about 1.5 cP, about 0.5 cP to about 1.75 cP, about 0.5 cP to about 2 cP, about 0.75 cP to about 1 cP, about 0.75 cP to about 1.25 cP, about 0.75 cP to about 1.5 cP, about 0.75 cP to about 1.75 cP, about 0.75 cP to about 2 cP, about 1 cP to about 1.25 cP, about 1 cP to about 1.5 cP, about 1 cP to about 1.75 cP, about 1 cP to about 2 cP, about 1.25 cP to about 1.5 cP, about 1.25 cP to about 1.75 cP, about 1.25 cP to about 2 cP, about 1.5 cP to about 1.75 cP, about 1.5 cP to about 2 cP, or about 1.75 cP to about 2 cP. In some embodiments, a viscosity of a suspension herein may be about 0.5 cP, about 0.75 cP, about 1 cP, about 1.25 cP, about 1.5 cP, about 1.75 cP, or about 2 cP.Sprayer

[0067] A continuous coating mechanism may include film extrusion, film deposition, film or pattern transfer, or spray coating. In some embodiments, film extrusion may comprise a knife over roller technique. In some embodiments, film deposition may comprise a slot die technique. In some embodiments, a film or pattern transfer may comprise use of a gravure or roller. In some embodiments, spray coating may comprise conventional spray, HVLP, inkjet, or electrospray. Selection of the appropriate coating method depends on the characteristics of the coating dispersion, the substrate, the micro- and nanostructure of the coating intended, as well as the needs for post-treatment of the coated film. In some embodiments, a sprayer is used to coat a substrate with a suspension of active particles. In some embodiments, the sprayer may comprise a conventional spray, an inkjet, an HVLP, or an electrospray.

[0068] One embodiment of a semi-continuous coating system for producing electroactive mixed matrix membrane is shown in FIG. 1. The membrane substrate to be coated (6) may be wrapped on a support drum (5) which may be rotating. The spray system comprises a feed tank (1) containing a dispersion of one or more dispersions to be dispensed through a mixer (2) and a spray nozzle / atomizer (3). The atomizer may use compressed air supplied by a compressor (4) to nebulize the liquid for spraying on the rotating drum. A heater (7) on the opposite end of the drum may allow for in-situ evaporation of the excess liquid dispersant after each pass through the sprayer.

[0069] In some embodiments disclosed herein, the number of active and non-active layers may be at least about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or more. In some embodiments, the number of active and non-active layers may be about 1 to about 10, about 1 to about 2, about 1 to about 3, about 1 to about 4, about 1 to about 5, about 1 to about 6, about 1 to about 7, about 1 to about 8, about 1 to about 9, about 1 to about 10, about 2 to about 3, about 2 to about 4, about 2 to about 5, about 2 to about 6, about 2 to about 7, about 2 to about 8, about 2 to about 9, about 2 to about 10, about 3 to about 4, about 3 to about 5, about 3 to about 6, about 3 to about 7, about 3 to about 8, about 3 to about 9, about 3 to about 10, about 4 to about 5, about 4 to about 6, about 4 to about 7, about 4 to about 8, about 4 to about 9, about 4 to about 10, about 5 to about 6, about 5 to about 7, about 5 to about 8, about 5 to about 9, about 5 to about 10, about 6 to about 7, about 6 to about 8, about 6 to about 9, about 6 to about 10, about 7 to about 8, about 7 to about 9, about 7 to about 10, about 8 to about 9, about 8 to about 10, or about 9 to about 10.

[0070] In some embodiments disclosed herein, a suspension may be applied layer-by-layer to obtain a single layer of a plurality of layers of an electroactive mixed matrix membrane. In some embodiments, a layer-by-layer deposition of the suspension may comprise coating a substrate using at least about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, or more passes of a spray for depositing said suspension. In some embodiments, a layer-by-layer deposition of the suspension may comprise coating a substrate using about 1 pass to about 20 passes. In some embodiments, a layer-by-layer deposition of the suspension may comprise coating a substrate using about 1 pass to about 2 passes, about 1 pass to about 3 passes, about 1 pass to about 4 passes, about 1 pass to about 5 passes, about 1 pass to about 6 passes, about 1 pass to about 8 passes, about 1 pass to about 10 passes, about 1 pass to about 15 passes, about 1 pass to about 20 passes, about 2 passes to about 3 passes, about 2 passes to about 4 passes, about 2 passes to about 5 passes, about 2 passes to about 6 passes, about 2 passes to about 8 passes, about 2 passes to about 10 passes, about 2 passes to about 15 passes, about 2 passes to about 20 passes, about 3 passes to about 4 passes, about 3 passes to about 5 passes, about 3 passes to about 6 passes, about 3 passes to about 8 passes, about 3 passes to about 10 passes, about 3passes to about 15 passes, about 3 passes to about 20 passes, about 4 passes to about 5 passes, about 4 passes to about 6 passes, about 4 passes to about 8 passes, about 4 passes to about 10 passes, about 4 passes to about 15 passes, about 4 passes to about 20 passes, about 5 passes to about 6 passes, about 5 passes to about 8 passes, about 5 passes to about 10 passes, about 5 passes to about 15 passes, about 5 passes to about 20 passes, about 6 passes to about 8 passes, about 6 passes to about 10 passes, about 6 passes to about 15 passes, about 6 passes to about 20 passes, about 8 passes to about 10 passes, about 8 passes to about 15 passes, about 8 passes to about 20 passes, about 10 passes to about 15 passes, about 10 passes to about 20 passes, or about 15 passes to about 20 passes of a spray for depositing said suspension. In some embodiments, a layer-by-layer deposition of the suspension may comprise coating a substrate using about 1 pass, about 2 passes, about 3 passes, about 4 passes, about 5 passes, about 6 passes, about 8 passes, about 10 passes, about 15 passes, or about 20 passes of a spray for depositing said suspension.

[0071] In some embodiments, a conveyor system supporting a substrate may rotate the substrate so as to permit repeated spray-coating of the same substrate with one or more suspensions. In some embodiments, the conveyor system comprises a drum. In some embodiments, the drum has a rotation rate of at least about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 25, 30, 35, 40, 45, 50, or more revolutions per minute (rpm). In some embodiments, the drum has a rotation rate of about 1 rpm to about 50 rpms. In some embodiments, the drum has a rotation rate of about 1 rpm to about 5 rpms, about 1 rpm to about 10 rpms, about 1 rpm to about 15 rpms, about 1 rpm to about 20 rpms, about 1 rpm to about 25 rpms, about 1 rpm to about 30 rpms, about 1 rpm to about 35 rpms, about 1 rpm to about 40 rpms, about 1 rpm to about 45 rpms, about 1 rpm to about 50 rpms, about 5 rpms to about 10 rpms, about 5 rpms to about 15 rpms, about 5 rpms to about 20 rpms, about 5 rpms to about 25 rpms, about 5 rpms to about 30 rpms, about 5 rpms to about 35 rpms, about 5 rpms to about 40 rpms, about 5 rpms to about 45 rpms, about 5 rpms to about 50 rpms, about 10 rpms to about 15 rpms, about 10 rpms to about 20 rpms, about 10 rpms to about 25 rpms, about 10 rpms to about 30 rpms, about 10 rpms to about 35 rpms, about 10 rpms to about 40 rpms, about 10 rpms to about 45 rpms, about 10 rpms to about 50 rpms, about 15 rpms to about 20 rpms, about 15 rpms to about 25 rpms, about 15 rpms to about 30 rpms, about 15 rpms to about 35 rpms, about 15 rpms to about 40 rpms, about 15 rpms to about 45 rpms, about 15 rpms to about 50 rpms, about 20 rpms to about 25 rpms, about 20 rpms to about 30 rpms, about 20 rpms to about 35 rpms, about 20 rpms to about 40 rpms, about 20 rpms to about 45 rpms, about 20 rpms to about 50 rpms, about 25 rpms to about 30 rpms, about 25 rpms to about 35 rpms, about 25 rpms to about 40 rpms, about 25 rpms to about 45 rpms, about 25 rpms to about 50 rpms, about 30 rpms to about 35 rpms, about 30 rpms to about 40 rpms, about 30 rpms to about 45 rpms, about 30 rpms to about 50 rpms, about 35rpms to about 40 rpms, about 35 rpms to about 45 rpms, about 35 rpms to about 50 rpms, about 40 rpms to about 45 rpms, about 40 rpms to about 50 rpms, or about 45 rpms to about 50 rpms. In some embodiments, the drum has a rotation rate of about 1 rpm, about 5 rpms, about 10 rpms, about 15 rpms, about 20 rpms, about 25 rpms, about 30 rpms, about 35 rpms, about 40 rpms, about 45 rpms, or about 50 rpms.

[0072] In some embodiments, a sprayer used for dispersing one or more suspension onto a substrate may have a dispersal rate of at least about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, or more ml / min. In some embodiments, the drum has a rotation rate of about1 ml / min to about 20 ml / min. In some embodiments, the drum has a rotation rate of about 1 ml / min to about 2 ml / min, about 1 ml / min to about 3 ml / min, about 1 ml / min to about 4 ml / min, about 1 ml / min to about 5 ml / min, about 1 ml / min to about 6 ml / min, about 1 ml / min to about 7 ml / min, about 1 ml / min to about 8 ml / min, about 1 ml / min to about 9 ml / min, about 1 ml / min to about 10 ml / min, about 1 ml / min to about 15 ml / min, about 1 ml / min to about 20 ml / min, about2 ml / min to about 3 ml / min, about 2 ml / min to about 4 ml / min, about 2 ml / min to about 5 ml / min, about 2 ml / min to about 6 ml / min, about 2 ml / min to about 7 ml / min, about 2 ml / min to about 8 ml / min, about 2 ml / min to about 9 ml / min, about 2 ml / min to about 10 ml / min, about 2 ml / min to about 15 ml / min, about 2 ml / min to about 20 ml / min, about 3 ml / min to about 4 ml / min, about 3 ml / min to about 5 ml / min, about 3 ml / min to about 6 ml / min, about 3 ml / min to about 7 ml / min, about 3 ml / min to about 8 ml / min, about 3 ml / min to about 9 ml / min, about 3 ml / min to about 10 ml / min, about 3 ml / min to about 15 ml / min, about 3 ml / min to about 20 ml / min, about 4 ml / min to about 5 ml / min, about 4 ml / min to about 6 ml / min, about 4 ml / min to about 7 ml / min, about 4 ml / min to about 8 ml / min, about 4 ml / min to about 9 ml / min, about 4 ml / min to about 10 ml / min, about 4 ml / min to about 15 ml / min, about 4 ml / min to about 20 ml / min, about 5 ml / min to about 6 ml / min, about 5 ml / min to about 7 ml / min, about 5 ml / min to about 8 ml / min, about 5 ml / min to about 9 ml / min, about 5 ml / min to about 10 ml / min, about 5 ml / min to about 15 ml / min, about 5 ml / min to about 20 ml / min, about 6 ml / min to about 7 ml / min, about 6 ml / min to about 8 ml / min, about 6 ml / min to about 9 ml / min, about 6 ml / min to about 10 ml / min, about 6 ml / min to about 15 ml / min, about 6 ml / min to about 20 ml / min, about 7 ml / min to about 8 ml / min, about 7 ml / min to about 9 ml / min, about 7 ml / min to about 10 ml / min, about 7 ml / min to about 15 ml / min, about 7 ml / min to about 20 ml / min, about 8 ml / min to about 9 ml / min, about 8 ml / min to about 10 ml / min, about 8 ml / min to about 15 ml / min, about 8 ml / min to about 20 ml / min, about 9 ml / min to about 10 ml / min, about 9 ml / min to about 15 ml / min, about 9 ml / min to about 20 ml / min, about 10 ml / min to about 15 ml / min, about 10 ml / min to about 20 ml / min, or about 15 ml / min to about 20 ml / min.

[0073] In some embodiments, the rate of area of substrate that may be processed by said sprayer is at least about 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 20, 25, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, or more in2 / min. In some embodiments, the rate of area of substrate that may be processed by said sprayer is about 5 in2 / min to about 150 in2 / min. In some embodiments, the rate of area of substrate that may be processed by said sprayer is about 5 in2 / min to about 10 in2 / min, about 5 in2 / min to about 15 in2 / min, about 5 in2 / min to about 20 in2 / min, about 5 in2 / min to about 25 in2 / min, about 5 in2 / min to about 50 in2 / min, about 5 in2 / min to about 75 in2 / min, about 5 in2 / min to about 100 in2 / min, about 5 in2 / min to about 125 in2 / min, about 5 in2 / min to about 150 in2 / min, about 10 in2 / min to about 15 in2 / min, about 10 in2 / min to about 20 in2 / min, about 10 in2 / min to about 25 in2 / min, about 10 in2 / min to about 50 in2 / min, about 10 in2 / min to about 75 in2 / min, about 10 in2 / min to about 100 in2 / min, about 10 in2 / min to about 125 in2 / min, about 10 in2 / min to about 150 in2 / min, about 15 in2 / min to about 20 in2 / min, about 15 in2 / min to about 25 in2 / min, about 15 in2 / min to about 50 in2 / min, about 15 in2 / min to about 75 in2 / min, about 15 in2 / min to about 100 in2 / min, about 15 in2 / min to about 125 in2 / min, about 15 in2 / min to about 150 in2 / min, about 20 in2 / min to about 25 in2 / min, about 20 in2 / min to about 50 in2 / min, about 20 in2 / min to about 75 in2 / min, about 20 in2 / min to about 100 in2 / min, about 20 in2 / min to about 125 in2 / min, about 20 in2 / min to about 150 in2 / min, about 25 in2 / min to about 50 in2 / min, about 25 in2 / min to about 75 in2 / min, about 25 in2 / min to about 100 in2 / min, about 25 in2 / min to about 125 in2 / min, about 25 in2 / min to about 150 in2 / min, about 50 in2 / min to about 75 in2 / min, about 50 in2 / min to about 100 in2 / min, about 50 in2 / min to about 125 in2 / min, about 50 in2 / min to about 150 in2 / min, about 75 in2 / min to about 100 in2 / min, about 75 in2 / min to about 125 in2 / min, about 75 in2 / min to about 150 in2 / min, about 100 in2 / min to about 125 in2 / min, about 100 in2 / min to about 150 in2 / min, or about 125 in2 / min to about 150 in2 / min.

[0074] In some embodiments, the substrate may be held at a temperature during deposition of one or more suspension. In some embodiments, the temperature may be at least about 5, 10, 15, 20, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, or more °C. In some embodiments, the temperature may be about 5 °C to about 100 °C. In some embodiments, the temperature may be about 5 °C to about 10 °C, about 5 °C to about 15 °C, about 5 °C to about 20 °C, about 5 °C to about 25 °C, about 5 °C to about 50 °C, about 5 °C to about 75 °C, about 5 °C to about 100 °C, about 10 °C to about 15 °C, about 10 °C to about 20 °C, about 10 °C to about 25 °C, about 10 °C to about 50 °C, about 10 °C to about 75 °C, about 10 °C to about 100 °C, about 15 °C to about 20 °C, about 15 °C to about 25 °C, about 15 °C to about 50 °C, about 15 °C to about 75 °C, about 15 °C to about 100 °C, about 20 °C to about 25 °C, about 20 °C to about 50 °C, about 20 °C to about 75 °C, about 20 °C to about 100 °C, about 25 °C to about 50 °C, about 25 °C toabout 75 °C, about 25 °C to about 100 °C, about 50 °C to about 75 °C, about 50 °C to about 100 °C, or about 75 °C to about 100 °C.

[0075] In some embodiments, a system or method herein may be configurable to provide a continuous coated product with desired functional characteristics. For example, a system herein may comprise adjustable sprayer or conveyor settings. The selection of a specific approach to produce a membrane using the systems and methods disclosed herein starts with defining the functional characteristics of the mixed matrix membrane desired, the substrate and coating architectures that will enable the functional characteristics of the coated membrane product, and then tune the coating methodology, processing conditions, as well as the coating formulation in a synergistic manner. Examples of this are provided in the examples section of this disclosure. Conventional approaches of designing membranes and manufacturing these membranes may be piecemeal, and often sequential manner, with no well-defined coordination between the different optimization approaches. Accordingly, the systems and methods described herein provide particular advantage in their configurability and amenability to a diverse array of membranes.Processes for Making Electroactive Mixed Matrix Membranes

[0076] The dispersal of a pre-determined amount of active particles in a single pass membrane coating operation may not be accessible using existing techniques due to at least the poor dispersion characteristics of the active particle containing suspensions used. In some embodiments, a pre-determined amount of active particles may comprise a fixed mass loading of active particles in grams per square meter of a substrate surface. Poor dispersion characteristics of active particles may in existing techniques may restrict the volume fraction or mass of active particles that can be dispersed in the dispersant before agglomeration of the active particles becomes an issue. In some embodiments, a dispersant may comprise aqueous, organic, or mixed solvents. Further, the low particle loading in the dispersions compatible with existing coating techniques often results in a lower viscosity of the dispersion - rendering such suspensions outside the range of operation of many types of coating techniques. The systems and methods disclosed herein overcome these difficulties and provide an aerosolized spray coating method whereby the substrate may be repeatedly coated with an appropriate type of sprayer.

[0077] In some embodiments, the fixed mass loading of particles may be at least about 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2 or more g / m2. In some embodiments, the fixed mass loading of particles may be about 0.1 g / m2to about 2 g / m2. In some embodiments, the fixed mass loading of particles may be about 0.1 g / m2to about 0.25 g / m2, about 0.1 g / m2to about 0.75 g / m2, about 0.1 g / m2to about 1 g / m2, about 0.1 g / m2to about 1.25 g / m2, about 0.1 g / m2to about 1.5 g / m2, about 0.1 g / m2to about 1.75 g / m2, about 0.1 g / m2toabout 2 g / m2, about 0.25 g / m2to about 0.75 g / m2, about 0.25 g / m2to about 1 g / m2, about 0.25 g / m2to about 1.25 g / m2, about 0.25 g / m2to about 1.5 g / m2, about 0.25 g / m2to about 1.75 g / m2, about 0.25 g / m2to about 2 g / m2, about 0.75 g / m2to about 1 g / m2, about 0.75 g / m2to about 1.25 g / m2, about 0.75 g / m2to about 1.5 g / m2, about 0.75 g / m2to about 1.75 g / m2, about 0.75 g / m2to about 2 g / m2, about 1 g / m2to about 1.25 g / m2, about 1 g / m2to about 1.5 g / m2, about 1 g / m2to about 1.75 g / m2, about 1 g / m2to about 2 g / m2, about 1.25 g / m2to about 1.5 g / m2, about 1.25 g / m2to about 1.75 g / m2, about 1.25 g / m2to about 2 g / m2, about 1.5 g / m2to about 1.75 g / m2, about 1.5 g / m2to about 2 g / m2, or about 1.75 g / m2to about 2 g / m2.

[0078] To achieve such a coating process, the systems and methods disclosed herein may be used with pre-cut flat sheet substrates of a desired size. This approach may be suitable for existing manufacturing infrastructure that are not compatible with other, less scalable techniques for producing electroactive mixed matrix membranes. For example, the systems and methods taught herein may be suitable for any manufacturing facility using spiral wound module configurations.

[0079] In some embodiments, spiral wound modules may be made with cut-sheets of substrates with a standard width ranging between 5.0 inch to 42.0 inch. In some embodiments, the leaf length of membrane cut for these membranes can range from 12.0 inch to 108.0 inch. In some embodiments, such pre-cut sheets may be wrapped around a drum (FIG. 1) or a pair of rollers (FIGs. 2 or 3) of different widths such that a given area of the sheet can be repeatedly passed under a spray nozzle. In some embodiments, non-standard widths and lengths may be used for a custom module.

[0080] In some embodiments, the cut-sheets may comprise a length of at least about 10, 12, 14, 16, 18, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 108, 110, 115, 120, 125, 130, 135, 140, 145, 150, or more inches. In some embodiments, the cut-sheets may comprise a length of about 10 in to about 150 in. In some embodiments, the cut-sheets may comprise a length of about 10 in to about 25 in, about 10 in to about 50 in, about 10 in to about 75 in, about 10 in to about 100 in, about 10 in to about 125 in, about 10 in to about 150 in, about 25 in to about 50 in, about 25 in to about 75 in, about 25 in to about 100 in, about 25 in to about 125 in, about 25 in to about 150 in, about 50 in to about 75 in, about 50 in to about 100 in, about 50 in to about 125 in, about 50 in to about 150 in, about 75 in to about 100 in, about 75 in to about 125 in, about 75 in to about 150 in, about 100 in to about 125 in, about 100 in to about 150 in, or about 125 in to about 150 in. In some embodiments, the cut-sheets may comprise a length of about 10 in, about 25 in, about 50 in, about 75 in, about 100 in, about 125 in, or about 150 in.

[0081] In some embodiments, the cut-sheets may comprise a width of about 5, 10, 15, 20, 25, 30, 35, 40, 42, 45, 50, 55, 60, 65, 70, 75, 80, 90, 95, 100, 105, 110, 115, 120, 125, 130, 135, 140, 145, 150, or more inches. In some embodiments, the cut-sheets may comprise a width of about 10 in to about 150 in. In some embodiments, the cut-sheets may comprise a width of about 10 in to about 25 in, about 10 in to about 50 in, about 10 in to about 75 in, about 10 in to about 100 in, about 10 in to about 125 in, about 10 in to about 150 in, about 25 in to about 50 in, about 25 in to about 75 in, about 25 in to about 100 in, about 25 in to about 125 in, about 25 in to about 150 in, about 50 in to about 75 in, about 50 in to about 100 in, about 50 in to about 125 in, about 50 in to about 150 in, about 75 in to about 100 in, about 75 in to about 125 in, about 75 in to about 150 in, about 100 in to about 125 in, about 100 in to about 150 in, or about 125 in to about 150 in.

[0082] The sheets can be fed to the membrane coating system using a roll feeder, which can cut the sheets and attach these to the roller drum (FIG. 1) or a conveyor system consisting of two rollers. The conveyor systems of FIGs. 2 or 3 may be designed to accommodate different lengths of the sheets.

[0083] In some embodiments, a mechanism of attaching and stretching the flat sheet substrate to a conveyor system may involve utilizing glues through an in-line applicator at the edges of the substrate. The glue may attach the sheet to the drum or the conveyor. For the conveyor system, a tensioner device may maintain the web stretch to a desired level of tension. In some embodiments, examples of which are depicted in FIGs. 2 and 3, it may be possible to use either a single feed tank for the suspension, or the suspension and the binder can be pre-mixed in-situ during spray coating (e.g., FIG. 2), or different sets of spray coaters can be used (e.g., FIG. 3). The heating system may be positioned at different locations. In some embodiments, the heating may remove solvent (dispersant) through evaporation.

[0084] In some embodiments, a combination of measurements such as rpm of the rollers, a linear speed of the substrate, a temperature of the coated film during processing, or a tension of the substrate may be monitored during the coating process.

[0085] The spray coating process may involve delivering the dispersion through a stirring mechanism into the fluid manifold of the sprayer. In some embodiments the dispersion may be a single pre-mixed dispersion. In some embodiments, the single pre-mixed dispersion may comprise active particles, a binder, a viscosity modifier, a dispersant, or a combination thereof. In some embodiments, this may be achieved using a positive displacement or metering pump that can be set to a desired rate of liquid loading to the sprayer. The air flow to the sprayer nozzle may need to be adjusted to the desired level that allows suitable nebulization of thedroplets. In some embodiments, the air flow may be configured to change a width or area of coating. In some embodiments, a sprayer distance from the substrate may be adjusted to ensure uniform coating of the substrate.

[0086] In some embodiments, after spray coating a substrate to a desired mass loading of active particles, coated substrate may be cut at the glued sections. A postprocessing operation may be used to remove excess unused materials from the coated substrate. In some embodiments, the membranes are extracted from the rinse bath and allowed to dry. In some embodiments, the membranes are dried using an air-knife. In some embodiments, the membranes may be heated as post-treatment operation. The pre-cut and coated sheets may then be ready for processing into modules.

[0087] The spraying operation may be repeated to deposit multiple types of thin film architectures including single layer, multi-layer, or alternating conductive and dielectric layers, allowing for deposition of complex structures. Furthermore, the approach of spray coating can be modified easily to allow coating using high pressure spray, electroacoustic sprays, HVLP, air brush, inkjet, and electrospray systems. The dispersion may be rendered amenable each type of spraying physics through modification of the dispersion characteristics and modifying the viscosity using additives such as ethylene glycol, poly-vinyl pyrrolidone, ethyl cellulose, etc. With inkjet printing, it is also possible to develop patterns of the electroactive material deposits on the membranes.

[0088] The methods described herein may be applied for different types of dispersants. While it is applied here with water, the efficiency of the coating and in-situ evaporative drying of the film can be rendered more efficient if a suitable dispersant with low boiling point is used. This can be achieved using solvents including alcohols or methyl-ethyl ketones.

[0089] In some embodiments, a systems and methods comprise a semi-continuous approach of coating electroactive and conducting films onto large aspect ratio flat sheet membranes using spray coating. This process is depicted in FIG. 2. In the depicted, non-limiting embodiment, an electroactive dispersion (1) and a binder (2) formulation(s) are fed from their respective tanks to a mixer (5) through two pumps (3, 4), where the injection rate of each pump can be adjusted to provide the intended ratio of active particles and the binder. The in-line mixer may be an ultrasonic mixer or a high-shear mixer. The mixed formulation then passes through an atomizer / spray nozzle (6), assisted by a compressed air source (7), which assists in nebulizing the mixture into the spray of desired characteristics (droplet size, coverage, and rate of deposition). The substrate (13) may be wrapped on a conveyor system consisting of a motorized driving roller (9), a follower roller (11), and a tensioning system (12) that maintains the properweb-tension of the sheet. The roller speed may be adjusted by a variable speed motor (10) to control the deposition rate, as well as the subsequent heating rate. The heating system (8) comprises infra-red heating elements with adjustable intensity to allow evaporative drying of the carrier fluid (dispersant), after each pass of the spray coater. The coating system may repeatedly spray on the sheet for a pre-determined number of passes, allowing the mass deposition of the active ingredient of the film to the desired limit. In some embodiments, the limit may be a percolation threshold.

[0090] In some embodiments, a spray coating system with two different formulations may be deposited simultaneously. In one non-limiting depicted embodiment shown in FIG. 3, the simultaneous deposition may allow variations in the coating formulation between a first set of coating dispersion (la, 2a) and a second set of dispersion (lb, 2b), variations in coating rate (through changes in pump speeds of pumps 3 a, 4a, and 3b, 4b), as well as nature of the spray delivered by the two spray nozzles (6a, 6b). The option of multiple tandem spray coaters in this manner may allow for creating a surface coating to a higher level of precision with respect to mass deposition, structure of the deposit. This can also reduce the number of passes of the substrate needed to achieve a desired level of mass deposition of the active material.Membranes

[0091] The methods and systems disclosed herein may be used to produce membranes with varying layers of electroactive layers. In some cases, the membranes produced may be referred to as electroactive membranes or electroactive mixed matrix membranes. In some embodiments, a polyamide or non-electroactive layer may be coated on a substrate prior to or between electroactive layers. The electroactive membrane architectures described in this disclosure may exemplified by the membranes depicted in FIG. 4. Embodiment A shows an electroactive architecture with the base ultrafiltration membrane (e.g., polysulfone, PS, or poly-ether sulfone, PES, on a non-woven polyester substrate) (1), a thin film polyamide layer (2) in the middle, and a top-coating of the electroactive or conducting layer (3). Embodiment B shows a multi-layer architecture, where the underlying support membrane may comprise of a PS or PES backing (7) and a polyamide layer (8). The electroactive coating on this substrate comprises of four additional layers 9, 10, 11, and 12 which may be deposited sequentially and bound to the substrate. These layers can have different conductive and dielectric characteristics, forming a sandwiched structure that can provide the required impedance characteristics of the electroactive membranes. Embodiment C is yet another possible embodiment where the base may comprise of a PS / PES membrane (13) and has a coating of a first layer of electroactive material (14). On top of this layer, a polyamide layer (15) may be deposited using interfacial polymerization. On topof this polyamide layer, two additional layers of conductive / dielectric materials are shown (16, 17). Various combinations of these deposited and interfacially polymerized architectures can be developed through the systems and methods described herein.

[0092] The adhesion of membranes may be evaluated using leaching tests, where adhesion correlates to a turbidity of a solution represented by relative nephelometric turbidity units (NTU). In some embodiments, the membranes accessible by the systems and methods disclosed herein may show pH dependent NTUs of leaching solutions to be highly similar to NTUs of a feed solution. In some embodiments, this similarity may indicate that few active particles of the membrane were released into the solution, indicating strong adhesion. The adhesion of the active particles may be modulated by a crosslinking polymer. In some embodiments, the crosslinking polymer may be polyvinyl alcohol (PVA). In some embodiments, the adhesion may be controlled by one or more of the degree of PVA crosslinking, concentration of PVA, ratio of active particles to PVA, mass deposition, spray-solution velocity or spray rate. The PVA may provide a means to adhere hydrophobic active particles to a hydrophilic surface. In some embodiments, the adherence may be a function of encapsulation, where the hydrophobic active particles are encapsulated by a hydrophilic polymer. In some embodiments, the hydrophilic polymer may form stronger non-bonding or bonding interactions with a substrate. This may provide significant adhesion benefits over other techniques that rely on non-bonding or physical interactions between hydrophobic and hydrophilic materials.

[0093] In some embodiments, for a pH of 2-13 of a feed solution of a leaching test, a deviation of an NTU of a retentate as compared to the feed solution of the leaching test may be 15%, 14%, 13%, 12%, 11%, 10%, 9%, 8%, 7%, 6%, 5%, or less. In some embodiments, for a pH 4-11 of a feed solution of a leaching test, a deviation of an NTU of a retentate as compared to the feed solution of the leaching test may be 15%, 14%, 13%, 12%, 11%, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, or less.

[0094] In some embodiments, the membranes disclosed herein may be used as reverse osmosis membranes. Reverse osmosis membranes may comprise materials with extremely small pores. In some embodiments, reverse osmosis membranes may comprise pores of about 0.1 nm to about 1.0 nm. Existing techniques may not be able to produce functionalized membranes for reverse osmosis as disclosed herein with conventional pressure deposition techniques due to the tight matrix of materials of standard reverse osmosis membranes. Additionally, pressure deposition techniques would not be compatible with the polyamide layers disclosed herein. In some embodiments, the polyamide layers may comprise primary (e.g., m-phenylenediamine) or secondary amine (e.g., piperazine) monomers. The active particles relevant to the electroactivemixed matrix membranes discussed herein may be too large to pass through a polyamide layer and would not therefore be able to be pressure deposited onto a substrate material. In some embodiments, the systems and methods disclosed herein may facilitate the deposition of electroactive materials onto ultrafiltration membranes. In some embodiments, the deposition of electroactive materials may modify membranes with pore sizes suitable for reverse osmosis. In some embodiments, the systems and methods disclosed herein may confer the active, functional benefits of electroactive layers. Additionally, these benefits may be accessible via the scalable technologies disclosed herein.

[0095] In some embodiments, a measured average surface resistance of a membrane produced by the systems and methods disclosed herein is at most 100, 200, 300, 400, 500, 600, 700, 800, 900, 1,000, 1,100, 1,200, 1,300, 1,400, 1,500, 1,600, 1,700, 1,800, 1,900, 2,000, 2,100, 2,200, 2,300, 2,400, 2,500, or less Q / n. In some embodiments, the average standard deviation of surface resistance is at most 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, or less percent (%) of the measured average surface resistance.

[0096] In some embodiments, a membrane herein may be activated using alternating waveform. In some embodiments, the alternating waveform may comprise a sinusoidal or a square waveform. In some embodiments, a sinusoidal waveform may be described by a peak to peak voltage (FpP), a frequency, or both. In some embodiments, a square waveform may be described by a peak to peak voltage (VPP), a frequency, a duty cycle, or any combination thereof.

[0097] In some embodiments, a Vppof an alternating waveform herein may be about 2 V to about 8 V. In some embodiments, a Vppof an alternating waveform herein may be about 2 V to about 3 V, about 2 V to about 4 V, about 2 V to about 5 V, about 2 V to about 6 V, about 2 V to about 7 V, about 2 V to about 8 V, about 3 V to about 4 V, about 3 V to about 5 V, about 3 V to about 6 V, about 3 V to about 7 V, about 3 V to about 8 V, about 4 V to about 5 V, about 4 V to about 6 V, about 4 V to about 7 V, about 4 V to about 8 V, about 5 V to about 6 V, about 5 V to about 7 V, about 5 V to about 8 V, about 6 V to about 7 V, about 6 V to about 8 V, or about 7 V to about 8 V. In some embodiments, a Vppof an alternating waveform herein may be about 2 V, about 3 V, about 4 V, about 5 V, about 6 V, about 7 V, or about 8 V. In some embodiments, a FpPof an alternating waveform herein may be at least about 2 V, about 3 V, about 4 V, about 5 V, about 6 V, or about 7 V. In some embodiments, a Vppof an alternating waveform herein may be at most about 3 V, about 4 V, about 5 V, about 6 V, about 7 V, or about 8 V.

[0098] In some embodiments, a frequency of an alternating waveform herein may be about 0.1 Hz to about 10,000 Hz. In some embodiments, a frequency of an alternating waveform herein may be about 0.1 Hz to about 0.5 Hz, about 0.1 Hz to about 1 Hz, about 0.1 Hz to about 5 Hz,about 0.1 Hz to about 10 Hz, about 0.1 Hz to about 50 Hz, about 0.1 Hz to about 100 Hz, about 0.1 Hz to about 500 Hz, about 0.1 Hz to about 1,000 Hz, about 0.1 Hz to about 5,000 Hz, about 0.1 Hz to about 10,000 Hz, about 0.5 Hz to about 1 Hz, about 0.5 Hz to about 5 Hz, about 0.5 Hz to about 10 Hz, about 0.5 Hz to about 50 Hz, about 0.5 Hz to about 100 Hz, about 0.5 Hz to about 500 Hz, about 0.5 Hz to about 1,000 Hz, about 0.5 Hz to about 5,000 Hz, about 0.5 Hz to about 10,000 Hz, about 1 Hz to about 5 Hz, about 1 Hz to about 10 Hz, about 1 Hz to about 50 Hz, about 1 Hz to about 100 Hz, about 1 Hz to about 500 Hz, about 1 Hz to about 1,000 Hz, about 1 Hz to about 5,000 Hz, about 1 Hz to about 10,000 Hz, about 5 Hz to about 10 Hz, about 5 Hz to about 50 Hz, about 5 Hz to about 100 Hz, about 5 Hz to about 500 Hz, about 5 Hz to about 1,000 Hz, about 5 Hz to about 5,000 Hz, about 5 Hz to about 10,000 Hz, about 10 Hz to about 50 Hz, about 10 Hz to about 100 Hz, about 10 Hz to about 500 Hz, about 10 Hz to about 1,000 Hz, about 10 Hz to about 5,000 Hz, about 10 Hz to about 10,000 Hz, about 50 Hz to about 100 Hz, about 50 Hz to about 500 Hz, about 50 Hz to about 1,000 Hz, about 50 Hz to about 5,000 Hz, about 50 Hz to about 10,000 Hz, about 100 Hz to about 500 Hz, about 100 Hz to about 1,000 Hz, about 100 Hz to about 5,000 Hz, about 100 Hz to about 10,000 Hz, about 500 Hz to about 1,000 Hz, about 500 Hz to about 5,000 Hz, about 500 Hz to about 10,000 Hz, about 1,000 Hz to about 5,000 Hz, about 1,000 Hz to about 10,000 Hz, or about 5,000 Hz to about 10,000 Hz. In some embodiments, a frequency of an alternating waveform herein may be about 0.1 Hz, about 0.5 Hz, about 1 Hz, about 5 Hz, about 10 Hz, about 50 Hz, about 100 Hz, about 500 Hz, about 1,000 Hz, about 5,000 Hz, or about 10,000 Hz. In some embodiments, a frequency of an alternating waveform herein may be at least about 0.1 Hz, about 0.5 Hz, about 1 Hz, about 5 Hz, about 10 Hz, about 50 Hz, about 100 Hz, about 500 Hz, about 1,000 Hz, or about 5,000 Hz. In some embodiments, a frequency of an alternating waveform herein may be at most about 0.5 Hz, about 1 Hz, about 5 Hz, about 10 Hz, about 50 Hz, about 100 Hz, about 500 Hz, about 1,000 Hz, about 5,000 Hz, or about 10,000 Hz.

[0099] In some embodiments, a duty cycle of an alternating waveform herein may be about 5 % to about 95 %. In some embodiments, a duty cycle of an alternating waveform herein may be about 5 % to about 10 %, about 5 % to about 20 %, about 5 % to about 30 %, about 5 % to about 40 %, about 5 % to about 50 %, about 5 % to about 60 %, about 5 % to about 70 %, about 5 % to about 80 %, about 5 % to about 90 %, about 5 % to about 95 %, about 10 % to about 20 %, about 10 % to about 30 %, about 10 % to about 40 %, about 10 % to about 50 %, about 10 % to about 60 %, about 10 % to about 70 %, about 10 % to about 80 %, about 10 % to about 90 %, about 10 % to about 95 %, about 20 % to about 30 %, about 20 % to about 40 %, about 20 % to about 50 %, about 20 % to about 60 %, about 20 % to about 70 %, about 20 % to about 80 %, about 20 % to about 90 %, about 20 % to about 95 %, about 30 % to about 40 %, about 30 % toabout 50 %, about 30 % to about 60 %, about 30 % to about 70 %, about 30 % to about 80 %, about 30 % to about 90 %, about 30 % to about 95 %, about 40 % to about 50 %, about 40 % to about 60 %, about 40 % to about 70 %, about 40 % to about 80 %, about 40 % to about 90 %, about 40 % to about 95 %, about 50 % to about 60 %, about 50 % to about 70 %, about 50 % to about 80 %, about 50 % to about 90 %, about 50 % to about 95 %, about 60 % to about 70 %, about 60 % to about 80 %, about 60 % to about 90 %, about 60 % to about 95 %, about 70 % to about 80 %, about 70 % to about 90 %, about 70 % to about 95 %, about 80 % to about 90 %, about 80 % to about 95 %, or about 90 % to about 95 %. In some embodiments, a duty cycle of an alternating waveform herein may be about 5 %, about 10 %, about 20 %, about 30 %, about 40 %, about 50 %, about 60 %, about 70 %, about 80 %, about 90 %, or about 95 %. In some embodiments, a duty cycle of an alternating waveform herein may be at least about 5 %, about 10 %, about 20 %, about 30 %, about 40 %, about 50 %, about 60 %, about 70 %, about 80 %, or about 90 %. In some embodiments, a duty cycle of an alternating waveform herein may be at most about 10 %, about 20 %, about 30 %, about 40 %, about 50 %, about 60 %, about 70 %, about 80 %, about 90 %, or about 95 %.

[0100] In some embodiments, a voltage applied to a membrane herein may be configured to generate a pH of at least about 9 to about 10.5. In some embodiments, a voltage applied to a membrane herein may be configured to generate a pH of at least about 9 to about 9.2, about 9 to about 9.4, about 9 to about 9.6, about 9 to about 9.8, about 9 to about 10, about 9 to about 10.2, about 9 to about 10.4, about 9 to about 10.5, about 9.2 to about 9.4, about 9.2 to about 9.6, about 9.2 to about 9.8, about 9.2 to about 10, about 9.2 to about 10.2, about 9.2 to about 10.4, about 9.2 to about 10.5, about 9.4 to about 9.6, about 9.4 to about 9.8, about 9.4 to about 10, about 9.4 to about 10.2, about 9.4 to about 10.4, about 9.4 to about 10.5, about 9.6 to about 9.8, about 9.6 to about 10, about 9.6 to about 10.2, about 9.6 to about 10.4, about 9.6 to about 10.5, about 9.8 to about 10, about 9.8 to about 10.2, about 9.8 to about 10.4, about 9.8 to about 10.5, about 10 to about 10.2, about 10 to about 10.4, about 10 to about 10.5, about 10.2 to about 10.4, about 10.2 to about 10.5, or about 10.4 to about 10.5. In some embodiments, a voltage applied to a membrane herein may be configured to generate a pH of at least about 9, about 9.2, about 9.4, about 9.6, about 9.8, about 10, about 10.2, about 10.4, or about 10.5. In some embodiments, a voltage applied to a membrane herein may be configured to generate a pH of at least about at least about 9, about 9.2, about 9.4, about 9.6, about 9.8, about 10, about 10.2, or about 10.4. In some embodiments, the generated pH may describe the solution within about 5 pm to about 50 pm from a surface of a membrane. In some embodiments, the generated pH may describe the solution within about 5 pm to about 10 pm, about 5 pm to about 15 pm, about 5 pm to about 20 pm, about 5 pm to about 25 pm, about 5 pm to about 30 pm, about 5 pm to about 35 pm, about5 pm to about 40 pm, about 5 pm to about 45 pm, about 5 pm to about 50 pm, about 10 pm to about 15 pm, about 10 pm to about 20 pm, about 10 pm to about 25 pm, about 10 pm to about 30 pm, about 10 pm to about 35 pm, about 10 pm to about 40 pm, about 10 pm to about 45 pm, about 10 pm to about 50 pm, about 15 pm to about 20 pm, about 15 pm to about 25 pm, about 15 pm to about 30 pm, about 15 pm to about 35 pm, about 15 pm to about 40 pm, about 15 pm to about 45 pm, about 15 pm to about 50 pm, about 20 pm to about 25 pm, about 20 pm to about 30 pm, about 20 pm to about 35 pm, about 20 pm to about 40 pm, about 20 pm to about 45 pm, about 20 pm to about 50 pm, about 25 pm to about 30 pm, about 25 pm to about 35 pm, about 25 pm to about 40 pm, about 25 pm to about 45 pm, about 25 pm to about 50 pm, about 30 pm to about 35 pm, about 30 pm to about 40 pm, about 30 pm to about 45 pm, about 30 pm to about 50 pm, about 35 pm to about 40 pm, about 35 pm to about 45 pm, about 35 pm to about 50 pm, about 40 pm to about 45 pm, about 40 pm to about 50 pm, or about 45 pm to about 50 pm from a surface of a membrane. In some embodiments, the generated pH may describe the solution within about 5 pm, about 10 pm, about 15 pm, about 20 pm, about 25 pm, about 30 pm, about 35 pm, about 40 pm, about 45 pm, or about 50 pm from a surface of a membrane. In some embodiments, the generated pH may describe the solution within at most about 10 pm, about 15 pm, about 20 pm, about 25 pm, about 30 pm, about 35 pm, about 40 pm, about 45 pm, or about 50 pm from a surface of a membrane.

[0101] In some embodiments, a pressure applied to a membrane herein during a reverse osmosis process may about 100 psi to about 1,200 psi. In some embodiments, a pressure applied to a membrane herein during a reverse osmosis process may about 100 psi to about 200 psi, about 100 psi to about 300 psi, about 100 psi to about 400 psi, about 100 psi to about 500 psi, about 100 psi to about 600 psi, about 100 psi to about 700 psi, about 100 psi to about 800 psi, about 100 psi to about 900 psi, about 100 psi to about 1,000 psi, about 100 psi to about 1,100 psi, about 100 psi to about 1,200 psi, about 200 psi to about 300 psi, about 200 psi to about 400 psi, about 200 psi to about 500 psi, about 200 psi to about 600 psi, about 200 psi to about 700 psi, about 200 psi to about 800 psi, about 200 psi to about 900 psi, about 200 psi to about 1,000 psi, about 200 psi to about 1,100 psi, about 200 psi to about 1,200 psi, about 300 psi to about 400 psi, about 300 psi to about 500 psi, about 300 psi to about 600 psi, about 300 psi to about 700 psi, about 300 psi to about 800 psi, about 300 psi to about 900 psi, about 300 psi to about 1,000 psi, about 300 psi to about 1,100 psi, about 300 psi to about 1,200 psi, about 400 psi to about 500 psi, about 400 psi to about 600 psi, about 400 psi to about 700 psi, about 400 psi to about 800 psi, about 400 psi to about 900 psi, about 400 psi to about 1,000 psi, about 400 psi to about 1,100 psi, about 400 psi to about 1,200 psi, about 500 psi to about 600 psi, about 500 psi to about 700 psi, about 500 psi to about 800 psi, about 500 psi to about 900 psi, about 500 psi toabout 1,000 psi, about 500 psi to about 1,100 psi, about 500 psi to about 1,200 psi, about 600 psi to about 700 psi, about 600 psi to about 800 psi, about 600 psi to about 900 psi, about 600 psi to about 1,000 psi, about 600 psi to about 1,100 psi, about 600 psi to about 1,200 psi, about 700 psi to about 800 psi, about 700 psi to about 900 psi, about 700 psi to about 1,000 psi, about 700 psi to about 1,100 psi, about 700 psi to about 1,200 psi, about 800 psi to about 900 psi, about 800 psi to about 1,000 psi, about 800 psi to about 1,100 psi, about 800 psi to about 1,200 psi, about 900 psi to about 1,000 psi, about 900 psi to about 1,100 psi, about 900 psi to about 1,200 psi, about 1,000 psi to about 1,100 psi, about 1,000 psi to about 1,200 psi, or about 1,100 psi to about 1,200 psi. In some embodiments, a pressure applied to a membrane herein during a reverse osmosis process may about 100 psi, about 200 psi, about 300 psi, about 400 psi, about 500 psi, about 600 psi, about 700 psi, about 800 psi, about 900 psi, about 1,000 psi, about 1,100 psi, or about 1,200 psi. In some embodiments, a pressure applied to a membrane herein during a reverse osmosis process may about at least about 100 psi, about 200 psi, about 300 psi, about 400 psi, about 500 psi, about 600 psi, about 700 psi, about 800 psi, about 900 psi, about 1,000 psi, or about 1,100 psi.

[0102] In some embodiments, a reverse osmosis process may be performed in a plurality of stages. In some embodiments, a pressure applied to the membrane in a first stage may be about 300 psi to about 1,200 psi. In some embodiments, a reverse osmosis process may be performed in a plurality of stages. In some embodiments, a pressure applied to the membrane in a first stage may be about 300 psi to about 400 psi, about 300 psi to about 500 psi, about 300 psi to about 600 psi, about 300 psi to about 700 psi, about 300 psi to about 800 psi, about 300 psi to about 900 psi, about 300 psi to about 1,000 psi, about 300 psi to about 1,100 psi, about 300 psi to about 1,200 psi, about 400 psi to about 500 psi, about 400 psi to about 600 psi, about 400 psi to about 700 psi, about 400 psi to about 800 psi, about 400 psi to about 900 psi, about 400 psi to about 1,000 psi, about 400 psi to about 1,100 psi, about 400 psi to about 1,200 psi, about 500 psi to about 600 psi, about 500 psi to about 700 psi, about 500 psi to about 800 psi, about 500 psi to about 900 psi, about 500 psi to about 1,000 psi, about 500 psi to about 1,100 psi, about 500 psi to about 1,200 psi, about 600 psi to about 700 psi, about 600 psi to about 800 psi, about 600 psi to about 900 psi, about 600 psi to about 1,000 psi, about 600 psi to about 1,100 psi, about 600 psi to about 1,200 psi, about 700 psi to about 800 psi, about 700 psi to about 900 psi, about 700 psi to about 1,000 psi, about 700 psi to about 1,100 psi, about 700 psi to about 1,200 psi, about 800 psi to about 900 psi, about 800 psi to about 1,000 psi, about 800 psi to about 1,100 psi, about 800 psi to about 1,200 psi, about 900 psi to about 1,000 psi, about 900 psi to about 1,100 psi, about 900 psi to about 1,200 psi, about 1,000 psi to about 1,100 psi, about 1,000 psi to about 1,200 psi, or about 1,100 psi to about 1,200 psi. In some embodiments, a reverse osmosisprocess may be performed in a plurality of stages. In some embodiments, a pressure applied to the membrane in a first stage may be about 300 psi, about 400 psi, about 500 psi, about 600 psi, about 700 psi, about 800 psi, about 900 psi, about 1,000 psi, about 1,100 psi, or about 1,200 psi. In some embodiments, a reverse osmosis process may be performed in a plurality of stages. In some embodiments, a pressure applied to the membrane in a first stage may be about at least about 300 psi, about 400 psi, about 500 psi, about 600 psi, about 700 psi, about 800 psi, about 900 psi, about 1,000 psi, or about 1,100 psi. In some embodiments, a reverse osmosis process may be performed in a plurality of stages.

[0103] In some embodiments, a reverse osmosis process using a membrane as described herein may be performed in a plurality of stages. In some embodiments, a pressure applied to the membrane in a second stage may be about 100 psi to about 500 psi. In some embodiments, a reverse osmosis process may be performed in a plurality of stages. In some embodiments, a pressure applied to the membrane in a second stage may be about 100 psi to about 200 psi, about 100 psi to about 300 psi, about 100 psi to about 400 psi, about 100 psi to about 500 psi, about 200 psi to about 300 psi, about 200 psi to about 400 psi, about 200 psi to about 500 psi, about 300 psi to about 400 psi, about 300 psi to about 500 psi, or about 400 psi to about 500 psi. In some embodiments, a reverse osmosis process may be performed in a plurality of stages. In some embodiments, a pressure applied to the membrane in a second stage may be about 100 psi, about 200 psi, about 300 psi, about 400 psi, or about 500 psi. In some embodiments, a reverse osmosis process may be performed in a plurality of stages. In some embodiments, a pressure applied to the membrane in a second stage may be at least about 100 psi, about 200 psi, about 300 psi, or about 400 psi. In some embodiments, a reverse osmosis process may be performed in a plurality of stages.

[0104] In some embodiments, a feed solution for a membrane configured for reverse osmosis herein may comprise a high salinity solution. For example, the membranes herein may provide particular utility in desalination of seawater. In some embodiments, the feed solution may comprise a total dissolved solids (TDS) value of about 20,000 ppm to about 70,000 ppm. In some embodiments, the feed solution may comprise a total dissolved solids (TDS) value of about 20,000 ppm to about 25,000 ppm, about 20,000 ppm to about 30,000 ppm, about 20,000 ppm to about 35,000 ppm, about 20,000 ppm to about 40,000 ppm, about 20,000 ppm to about 45,000 ppm, about 20,000 ppm to about 50,000 ppm, about 20,000 ppm to about 55,000 ppm, about 20,000 ppm to about 60,000 ppm, about 20,000 ppm to about 65,000 ppm, about 20,000 ppm to about 70,000 ppm, about 25,000 ppm to about 30,000 ppm, about 25,000 ppm to about 35,000 ppm, about 25,000 ppm to about 40,000 ppm, about 25,000 ppm to about 45,000 ppm, about 25,000 ppm to about 50,000 ppm, about 25,000 ppm to about 55,000 ppm, about 25,000ppm to about 60,000 ppm, about 25,000 ppm to about 65,000 ppm, about 25,000 ppm to about 70,000 ppm, about 30,000 ppm to about 35,000 ppm, about 30,000 ppm to about 40,000 ppm, about 30,000 ppm to about 45,000 ppm, about 30,000 ppm to about 50,000 ppm, about 30,000 ppm to about 55,000 ppm, about 30,000 ppm to about 60,000 ppm, about 30,000 ppm to about 65,000 ppm, about 30,000 ppm to about 70,000 ppm, about 35,000 ppm to about 40,000 ppm, about 35,000 ppm to about 45,000 ppm, about 35,000 ppm to about 50,000 ppm, about 35,000 ppm to about 55,000 ppm, about 35,000 ppm to about 60,000 ppm, about 35,000 ppm to about 65,000 ppm, about 35,000 ppm to about 70,000 ppm, about 40,000 ppm to about 45,000 ppm, about 40,000 ppm to about 50,000 ppm, about 40,000 ppm to about 55,000 ppm, about 40,000 ppm to about 60,000 ppm, about 40,000 ppm to about 65,000 ppm, about 40,000 ppm to about 70,000 ppm, about 45,000 ppm to about 50,000 ppm, about 45,000 ppm to about 55,000 ppm, about 45,000 ppm to about 60,000 ppm, about 45,000 ppm to about 65,000 ppm, about 45,000 ppm to about 70,000 ppm, about 50,000 ppm to about 55,000 ppm, about 50,000 ppm to about 60,000 ppm, about 50,000 ppm to about 65,000 ppm, about 50,000 ppm to about 70,000 ppm, about 55,000 ppm to about 60,000 ppm, about 55,000 ppm to about 65,000 ppm, about 55,000 ppm to about 70,000 ppm, about 60,000 ppm to about 65,000 ppm, about 60,000 ppm to about 70,000 ppm, or about 65,000 ppm to about 70,000 ppm. In some embodiments, the feed solution may comprise a total dissolved solids (TDS) value of about 20,000 ppm, about 25,000 ppm, about 30,000 ppm, about 35,000 ppm, about 40,000 ppm, about 45,000 ppm, about 50,000 ppm, about 55,000 ppm, about 60,000 ppm, about 65,000 ppm, or about 70,000 ppm. In some embodiments, the feed solution may comprise a total dissolved solids (TDS) value of at least about 20,000 ppm, about 25,000 ppm, about 30,000 ppm, about 35,000 ppm, about 40,000 ppm, about 45,000 ppm, about 50,000 ppm, about 55,000 ppm, about 60,000 ppm, or about 65,000 ppm.

[0105] In some embodiments a scaling species herein may comprise a metal, alkali metal, or an alkali earth metal. In some cases, a scaling species herein may comprise a carbonate, a sulfate, a silicate, or a hydroxide. In some embodiments, a scaling species may be an inorganic species that fouls or scales onto a surface of a membrane herein. Generally, a scaling species may be any species present in seawater, ocean water, or brackish water that fouls a surface of a reverse osmosis membrane, optionally when a cathodic potential is applied to the membrane.

[0106] In some embodiments, a passive or non-active membrane may provide a greater decrease in permeability with respect to increasing recovery rate versus a membrane with an electroactive layer. In some embodiments, a membrane herein may retain at least about 65% of its permeability up to a recovery % of about 30%, optionally wherein the salt rejection of the membrane is at least about 97% up to the recovery % of about 30%. In some embodiments, amembrane herein may retain at least about 55% of its permeability up to a recovery % of about 40%, optionally wherein the salt rejection of the membrane is at least about 97% up to the recovery % of about 40%. In some embodiments, a membrane herein may retain at least about 15% of its permeability up to a recovery % of about 60%, optionally wherein the salt rejection of the membrane is at least about 92% up to the recovery % of about 60%.Boron removal via alternating waveforms

[0107] Membranes accessible by the systems and methods described herein may provide particular utility for removal of species through modulation of pH near a surface of a membrane. For example, some chemical species may exist largely as a neutral or charged species depending on the pH of a solution comprising the species. Generally, reverse osmosis membranes may more efficiently remove charged species from a feed solution. Accordingly, electroactive membranes as described herein may be used to modulate local pH to shift equilibria of species from neutral to charged states, thereby facilitating rejection of some chemical species by reverse osmosis membranes.

[0108] The above phenomenon may be used to remove boron species from water sources enriched with boron. For example, as shown in FIG. 5, charged species on or near the electrode surface may electrostatically repel borate, thereby rejecting boron during reverse osmosis. Boron removal from seawater is critical for agricultural irrigation and industrial applications. In some embodiments, agricultural or industrial applications may require boron concentrations below 0.1 ppm. For example, though boron is an essential nutrient for plant growth, its optimal concentration range for several agricultural applications is narrow. Boron concentrations below the range of optimal concentrations may result in nutrient deficiencies while concentrations above this range may result in toxicities. An important source of water for agricultural or industrial uses may be seawater, where boron is typically present as boric acid (H3BO3) at concentrations around 5 ppm.

[0109] Seawater, which typically has a pH well below the pKa of boric acid, greatly favors the neutral boric acid species. For example, the pKa of boric acid at 25 °C is about 9.24, while the pH of seawater is typically ~8. This frustrates attempts at boric acid removal from seawater using reverse osmosis membranes. Existing techniques leverage chemical additives, such as NaOH, to raise the pH to remove the boron . Accordingly, the membranes herein may be used to generate a locally elevated pH via the application of cathodic potentials to the membranes. This elevated pH may shift the boric acid / borate equilibrium (H3BO3 + H2O B(OH)4 +H+) to favor the borate species. Further, the membranes described herein may be configured for the application of alternating voltage waveforms. The alternation of cathodic and anodic potentialsmay facilitate both the elevation of local pH near the membrane surface and mitigation of membrane fouling via scaling that may occur during the application of cathodic potentials. Further, the described systems and methods may forego chemical additives to raise pH, thereby providing a sustainable solution to a significant industrial and agricultural problem.Membrane activation

[0110] Described herein is an electrochemical approach to modulate pH near a membrane surface. Generally, the membranes used for boron removal herein may be accessible by the systems and methods for making membranes described above. By applying an external electrical field to a membrane described herein, the membrane may be rendered a cathode, an anode, or alternately as a cathode or anode. Generally, alternating waveforms introduce periodic shifts in the electric field, which may modulate the membrane surface pH while intermittently reversing or reducing the field strength. This pulsed approach facilitates cathodic generation of hydroxide ions (OH-) to sustain high pH for boron rejection while also periodically mitigating or reducing scale formation. In some embodiments a cathodic potential applied to a membrane herein in aqueous solution may generate OH species via the reduction of water, thereby raising local pH. As described above, elevated pH may favor borate species in the acid-based equilibrium of boric acid and borate.[OHl] In some embodiments, the use of a membrane herein as for reverse osmosis may result in scaling of species in a feed solution on the membrane. In some embodiments, the scaling may be exacerbated by the application of cathodic potentials. In some embodiments, ions in solution such as Ca2+or Mg2+may scale on the surface of the electrode. Accordingly, the application of anodic potentials may be used to remove scaled species from the surface of the electrode. In some embodiments, a cathodic potential and an anodic potential may be applied iteratively to switch between pH elevating and anti-scaling conditions. In some embodiments, scaling may be referred to as fouling. In some embodiments, the anodic potential and cathodic potential may be applied via an alternating waveform.

[0112] In some embodiments, the alternating waveform may be a square waveform or a sinusoidal waveform as shown in FIGs. 6A-6D. A sinusoidal waveform as shown in FIG. 6A may be generally described by its peak to peak voltage separation (Vpp) and its frequency. A square waveform as shown in FIGs. 6B-6D may be generally described by its peak to peak voltage separation (Vpp), its frequency, and its duty cycle. Generally, a duty cycle may indicate a percentage of time of which the working potential is applied to an electrode. In some embodiments, the working potential may be the potential applied to a membrane herein to generate a locally elevated pH. In some embodiments, the working potential may be a cathodicor reducing potential. For example, as shown in FIG. 6B, a 20% duty cycle square wave may be used to apply a cathodic potential to a membrane herein during 20% of an oscillation of a square waveform. In some embodiments, the cathodic potential, the anodic potential, or both may be pulsed. For example, a waveform may comprise an anodic portion, a cathodic portion, a null potential portion, or a combination thereof. In some embodiments, an alternating waveform may be optimized or configured for a particular feed solution by adjusting a frequency of the waveform, a duty cycle of the waveform, an amplitude of the waveform, or any combination thereof. In some embodiments, an alternating waveform may provide precise, dynamic control of the electrochemical environment of the membrane surface.Method of boron removal

[0113] In some embodiments, a method for removing a boron species from a water source may comprise (a) filtering the water source through an electroactive membrane, wherein the water source comprises at least boric acid and at least one scaling species, wherein the electroactive membrane comprises a surface configured to receive an applied voltage, and wherein the water source is provided to the surface of the electroactive membrane, (b) applying a first voltage to the electroactive membrane, thereby generating borate ions from the boron species, and (c) applying a second voltage to the electroactive membrane, thereby repelling the borate ions from the surface of the electroactive membrane and removing at least a portion of the at least one scaling species from the surface of the electroactive membrane. In some embodiments, (b) and (c) may occur during (a). In some embodiments, (b) and (c) may occur iteratively during (a). For example, In some embodiments, the first voltage and the second voltage are applied via an alternating waveform. In some embodiments, the alternating waveform comprises a sinusoidal or square waveform.

[0114] In some embodiments, an alternating waveform comprises a duty cycle of from about 20% to about 80%. In some embodiments, an alternating waveform comprises a duty cycle of from about 20% to about 50%. In some embodiments, the alternating waveform comprises a peak to peak voltage of about 4 V to about 6 V. In some embodiments, the frequency of the alternating waveform is from about 1 Hz to about 500 Hz. In some embodiments, the frequency of the alternating waveform is from about 1 Hz to about 5Hz.

[0115] In some embodiments, the first voltage is configured to raise the pH of the water source to at least about 9. In some embodiments, the pH of the water source is at least about 9 within at least about 5 pm from the surface of the electroactive membrane. In some embodiments, the scaling species comprises a metal or a silicate. In some embodiments, the metal comprises analkali metal or an alkaline earth metal. In some embodiments, the water source has a TDS level of at least about 35,000 ppm .

[0116] In some embodiments, filtering comprises delivering the water source to the surface of the electroactive membrane at a pressure of about 100 psi to about 800 psi. In some embodiments, (a)-(c) are performed at least two times in a first stage and a second stage. In some embodiments, the pressure of the water source is about 300 psi to about 1,000 psi in the first stage. In some embodiments, the pressure of the water source is about 100 psi to about 300 psi in the second stage. In some embodiments, at least about 80% of the boron species is rejected by the electroactive membrane during (c).

[0117] In some embodiments, the electroactive membrane comprises a layered structure as described elsewhere herein. In some embodiments, the layered structure comprises at least a polyamide layer and an electroactive layer. In some embodiments, the electroactive layer comprises a carbon nanomaterial or a conductive nanoparticle.

[0118] Specific exemplary membranes, their methods of making, and their performance characteristics may be seen in the non-limiting examples section.

[0119] Although certain embodiments and examples are disclosed below, inventive subject matter extends beyond the specifically disclosed embodiments to other alternative embodiments, uses, and to modifications and equivalents thereof. Thus, the scope of the claims appended hereto is not limited by any of the particular embodiments described below. For example, in any method or process disclosed herein, the acts or operations of the method or process may be performed in any suitable sequence and are not necessarily limited to any particular disclosed sequence. Various operations may be described as multiple discrete operations in turn, in a manner that may be helpful in understanding certain embodiments, however, the order of description should not be construed to imply that these operations are order dependent. Additionally, the structures, systems, devices, methods, or combinations thereof described herein may be embodied as integrated components or as separate components.

[0120] As used herein, the singular forms "a", "an", and "the" include plural references unless the context clearly dictates otherwise.

[0121] Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising" means various components can be co jointly employed in the methods and articles (e.g., compositions and apparatuses including device and methods). For example, the term "comprising" will beunderstood to imply the inclusion of any stated elements, operations, or steps but not the exclusion of any other elements or steps.EXAMPLES

[0122] The following examples are intended to illustrate but not limit the disclosed embodiments.Example 1Electroactive Reverse Osmosis MembranesMembrane Substrate for Coating and Pre-Treatment

[0123] Brackish water reverse osmosis BWRO-HF or BWRO-HR flat sheet products were used as substrates for coating to make electroactive RO membranes. These membranes may be readily obtained from any commercial flat sheet manufacturer as long as it is of a thin film composite (TFC) variant, with a thin film polyamide layer on top of a conventional polysulfone UF backbone cast on non-woven polyester. The TFC membrane should ideally be cast using interfacial polymerization at the interface of MPD and TMC liquid films.

[0124] The membranes should be freshly prepared prior to coating and should not have any type of coating (the polyamide layer should be exposed). A fresh membrane should be white in color, and an aging membrane will be brownish owing to oxidization. The coating film adhesion to the RO membrane will be adversely affected if the polyamide layer is oxidized.

[0125] Aged or aging sheet can still be used but requires rinsing. Washing the sheet in 2 g / 1 NaOH solution at 50°C for 10 minutes changing the batch of NaOH two to three times will condition the membrane for coating. Following the caustic rinse, washing the sheet in DI water at 50°C for 10 minutes is recommended. Rinsing should be continued with fresh batches of DI water till the rinse bath water pH is similar to that of DI water.

[0126] Some commercial TFC RO membranes are preserved with a coating of polyvinyl alcohol PVA for preservation. These membranes should also be pretreated by soaking in an acidic (pH 2.0 medium for 30 minutes), followed by rinsing with DI water to ensure that no acid remains on the membrane. After pre-treatment, the membranes should be air-dried and prepared for coating.Formulation of Coating Dispersion

[0127] Multiwalled Carbon Nanotubes (MWCNTs) were used as purchased from a bulk CNT manufacturer. The MWCNTs were functionalized with carboxylic surface groups (approximately 5 - 8 % surface functionalization). The typical sizes of the MWCNTs areexpected to be in the range of 5 - 15 nm in diameter, and 10 - 20 micrometers in length. The purity of the MWCNTs is > 95% (as specified by the manufacturer).

[0128] The binder selected was Poly Vinyl Alcohol (PVA) with MW of 67 kDa. A 10 wt% stock solution of the PVA was prepared separately by dissolving in the DI water.

[0129] A complexing agent was used. In this formulation it was Succinic Acid (CAS Number: 110-15-6).

[0130] The surfactant used was Sodium dodecyl sulfate (SDS) with a purity of > 99%. The powdered surfactant was added to the MWCNT dispersion as needed.

[0131] Sulfuric Acid was used to titrate the MWCNT dispersion by adding the acid to render the final pH of the dispersion between 1.8 - 2.2.Preparation of the Dispersion

[0132] A 10 wt.% stock aqueous solution of PVA was obtained by dissolving 10 g of PVA in 90 ml of DI water. The PVA was stirred for at least 5 hours to fully dissolve at 90 °C with stirring at 500 rpm.

[0133] Separately, 1 g of CNTs and 10 g SDS were dispersed in 989 g of DI water to make a 1000 g CNT suspension.

[0134] The CNT suspension was sonicated for 30 minutes made up of 15 minutes pulse on and 15 minutes pulse off. The sonication power is set at 40% and temperature at 40°C.

[0135] The sonicated CNT suspension was centrifuged for 30 minutes at 4000 rpm. After this stage, the supernatant was skimmed 90% of the suspension was decanted and the bottom 10 v / v% solution discarded. Fill the decanted suspension into a second batch of centrifuge tubes, and centrifuge this for another 20 minutes. The centrifuge was set to 4000 rpm.

[0136] To make a 500 g PVA / CNT solution at a ratio of 1 : 1, 2.5 g of room temperature PVA solution was added into 497.5 g CNT suspension.

[0137] The solution was stirred at room temperature for 5 minutes to mix thoroughly.

[0138] 0.0010 g of succinic acid was added to the solution.

[0139] After 10 minutes, the solution was titrated with strong sulfuric acid until the pH was between 1.8 and 2.2.

[0140] An additional amount of SDS was added to the solution, 10% of the initial amount of SDS used.

[0141] The solution was left stirring overnight.

[0142] The prepared coating dispersion can have a pot life of approximately 3 days. Note that the PVA in the acidic medium will start hydrolyzing, and the kinetics of degradation can be monitored by monitoring the pH of the dispersion. If the pH is above 2.2, the suspension should be considered degraded.Coating Process (Spray Coating)

[0143] The substrate membrane was wrapped around a drum (FIG. 1 and FIG. 7) inside a fume hood. The polyamide layer side of the membrane was left exposed (not facing the drum).

[0144] Infrared (IR) lamps were positioned for heat treatment (e.g., FIG. 1) such that the full width of the membrane received a constant heat flux, and was maintained at the same temperature, 80-90°C..

[0145] The drum was rotated at a fixed speed to allow the membrane surface temperature to reach ~85 °C.

[0146] The coating dispersion was fed into the dispenser (e.g., FIG. 1). The spraying operation was started and the air flow of the spray nozzle was adjusted to ensure a uniform spray pattern is being formed. The distance of spray nozzle from the surface was adjusted such that full width of the substrate was coated.

[0147] The spray was held at a fixed distance from the substrate. The spray nozzle can be translated axially in a periodic manner if a larger width of the membrane sheet needs to be coated using a single spray nozzle. Alternatively, multiple spray nozzles can be used in parallel to attain the desired width coverage on the substrate.

[0148] The rotational rpm of the drum was adjusted to ensure that the heating rate is sufficient to ensure complete evaporation of the dispersant from the surface of the substrate, and the membrane temperature was at least 80 °C immediately before the spray was applied.

[0149] The spray coating process was continued to obtain the desired number of layers and the coated substrate was allowed to dry for about 180 seconds.

[0150] The rotation of the drum was stopped and the heater turned off.

[0151] The coated substrate was removed from the drum.Post-treatment

[0152] The membrane was dried at 110°C for 2 minutes.

[0153] The membrane was washed with DI water at room temperature by spraying 5000 ml DI water using a water bottle. The washing removed excess dispersants, surfactants and othermaterials that were accumulated during the coating processes. The membrane will appear dark after a proper washing sequence (FIG. 8).

[0154] The washed membrane was dried at 90°C for 1 min to preserve the sheet for further testing or to measure sheet resistance.Example 2Multiple Layer Electroactive Reverse Osmosis MembranesPreparation of the Dispersions

[0155] In this formulation, the MWCNT dispersion and the PVA binder were prepared separately and stored. Methods of preparation of the CNT dispersion and the PVA binder solution were described earlier in Example 1. First a 1 : 1 PVA / CNT suspension was prepared by mixing the CNT suspension with the PVA suspension as described in Example 1. This primary suspension was then diluted by adding different proportions of pure CNT dispersion (without PVA in the suspension) as shown in Table 1.

[0156] Table 1 : Different coating suspensions prepared by varying the proportions of PVA and CNT.Table 1: Different coating suspensions prepared by varying the proportions of PVA and CNT.Coat # 1 :0 (PVA / CNT: CNT) 1 : 1 (PVA / CNT: CNT) 1 :3 (PVA / CNT: CNT)1 50 ml2 100 ml3 200 ml4 50 ml

[0157] Three coating suspensions were prepared. The base suspension was the 1 : 1 PVA / CNT mixture (denoted as 1 :0). The second suspension was prepared by adding 1 part of pure CNT suspension to 1 part of the PVA / CNT base suspension. The third suspensions was prepared by adding 3 parts of the pure CNT suspension to 1 part of the base PVA / CNT suspension. These three suspensions were stabilized separately, with each suspension designated as the designer fluid to be sprayed as separate layers on the substrate.

[0158] The mixtures were stirred in an ultrasonicator for 45 minutes prior to their use in the spray coating.Layer by Layer Spray Coating Approach

[0159] The substrate used was a standard BWRO membrane. After mounting the membrane on the roller drum, and setting up the heater, the first layer of coating was applied using the suspension formulation 1 (base formulation). This layer was deposited using a spray coater, applying 50 mL of the dispersion (approximately 6 consecutive coatings).

[0160] The second layer was applied using the suspension formulation 2. Approximately 100 mL of the suspension was deposited on the membrane as a second coat using the spray coater.

[0161] The third layer was applied using the suspension formulation 3. Approximately 200 mL of the suspension was coated on the membrane using this formulation.

[0162] The final layer was again applied with the suspension formulation 1 (base formulation). Approximately 50 mL of the coating suspension was applied in this pass.

[0163] The heat curing settings, the sprayer settings, and the speed of the rotation of the drum were maintained fixed during the process. All these settings were kept similar to those described in Example 1.

[0164] In another example, the spray coating was performed using an airbrush instead of the spray gun. The results indicate that the coating integrity is not affected by the spraying method (as long at the dispersions and spray formulations can be spray coated).Post Treatment

[0165] The post treatment method for this example is similar to the approach described in Example 1.Example 3Characterization of the Coated Membranes

[0166] A very important property of the electroactive membranes is the sheet resistance. The sheet resistance of the membranes prepared were measured using a four-probe sheet resistance measurement instrument. Note that a lower sheet resistance reflects a higher conductivity of the coated film. The methodology involves: (i) ensuring the membrane is dry, (ii) switching on the resistivity meter (4 pin Loresta GP, MCP-T610, Mitsubishi Chemical Analytech), (iii) placing the 4-pin probe on the surface of the membrane and record the reading.

[0167] The results are presented in Table 2 below. It is important to take into consideration that sheet resistance is a function of resistivity and thickness. The thickness of the coating layer in the membranes presented in this work is dependent on the mass deposition. Therefore, it is not surprising that the sheet resistance of the 0.6 g / m2single layer method membrane has the highest sheet resistance. At 1.2 g / m2mass deposition, this membrane is expected to be thicker than the0.6 g / m24-layer method membrane. Therefore, the fact that the 1.2 g / m2membrane has lower sheet resistance can be attributed to the mass deposition of CNTs on the substrate. The 4-layer membrane of Example 2 has a lower mass deposit (0.6 g / m2) than the membrane of Example 1 (1.2 g / m2), yet it has the lowest sheet resistance. This is owing to the layer by layer construction of the coated membrane in Example 2, whereby less PVA was deposited on the composite membranes.Table 2: Sheet resistance, permeability and rejection of the membranes prepared in Examples 1 and 2. The control represents the BWRO substrate prior to coating.

[0168] The water treatment data of the membranes are also presented in Table 2. Due to the reduction in PVA use and lower mass deposition, the 4-layer method membrane has higher water permeability than the 1.2 g / m2single layer membrane. The higher rejection observed for this membrane is resultant from the smooth, homogenous surface morphology. The 0.6 g / m2single layer membrane is ignored because the layer washed off, the membrane was deemed not fit for use.Scanning Electron Micrographs

[0169] SEM was used to image the surface of the membranes. FIG. 9 shows SEM images taken at different magnifications. The aim was to illustrate the effect of the single layer coating and the 4-layer coating methods on the morphology of the CNT layer. The images provide a few key insights, (i) At lower magnification, the images show that at any of the mass depositions used in this work, membranes fabricated with the single layer coating method have defects on the surface, (ii) The defects might have been caused by agglomerated CNT particles that detached when the membrane was washed. This conclusion is motivated by the observation that the membrane with higher mass deposition has a higher density of the defects. Coating the membrane with high mass disposition using the single layer method at a flow rate of 3 ml / min takes 4 hours and 45 minutes. This is a long time, so the CNTs are anticipated to aggregate throughout the period. Coating the low mass deposition membrane using the one-layer method takes half the time, (iii) The SEM of the membrane made from the 4-layer method indicates that the surface is smooth, with no visible defects. The defect-free surface may be explained in termsof the chemistry of the coating solutions and the velocity of the spray solution. The fourth layer in the 4-layer method was made using a high-volume low pressure (HVLP) spray gun which achieves high velocity solution deposition on a substrate, (iv) At higher magnification (FIG. 10), the SEM images show that the single layer method produces a coarse morphology, (v) Both at 0.6 and 1.2 g / m2mass deposition, the morphology shows some large voids, (vi) On the other hand, the membrane from the 4-layer method has a uniform morphology made of a homogenous pore-network in the CNT deposit.Coating layer stability

[0170] One of the important quality controls used for this membrane is adhesion. The CNT layer is required to stick on the substrate so that it does not leach into water systems when the membranes are in use. In this work, the stability of the coating was evaluated by turbidity measurements and surface imaging. To investigate the leaching of the CNTs, the membranes were used to treat 2 g / 1 NaCl aqueous solution using a crossflow system. Turbidity of the feed, retentate and permeate streams was measured. The results are shown below. The turbidity of the retentate was monitored more closely to indicate any potential increase due to break-off and leaching of the CNT from the membrane surface. The permeate is less likely to be affected by leaching CNTs because their particle size is too large to pass through the polyamide layer in the substrate.Table 3: Leaching tests indicating the stability of the membranes

[0171] There was no leaching from the 1.2 g / m2and the 4-layer 0.6 g / m2membranes as indicated by the turbidity monitoring results in Table 3. The test shows that when the adhesion is poor (for instance in the 0.6 g / m2single layer membrane) the concentrate turbidity increases, which indicates removal of the CNT particles from the membrane surface. That is the membrane made from single layer coating at a mass deposition of 0.6 g / m2. The adhesion in this membrane was very poor. The CNT layer was very loose. The adhesion in the other two membranes was very strong. The adhesion is controlled by the degree of PVA crosslinking, concentration of PVA, ratio of CNT to PVA, mass deposition, spray-solution velocity and spray rate.Example 4Performance of Electroactive Membranes in Desalination of Brackish Water

[0172] Over the course of two weeks, membrane desalination field tests were performed using an oil and gas produced water as the feed water source. The feed water was characterized with the following contaminants of concern: colloids, dissolved organics, hydrocarbons and mineral scale forming ions and inorganic substances including calcite, silica, and iron. Standard Passive RO membrane modules as well as Active RO membrane modules were tested in a series of configurations and comparative data was collected.

[0173] Specifically, a hybrid train of Passive and Active RO membranes were compared to an equivalent all Passive train. Separately, an Active RO was operated in a head-to-head comparative run against a Passive RO. Both observed and normalized flux and salt rejection data suggests that with minimal pre-treatment and specifically no chemical pre-treatment, and despite having operated for a longer time, Active RO outperforms Passive RO potentially enabling 25% higher recovery rate with 30-60% reduction in membrane cleaning equipment.

[0174] Similarly, when used in a Hybrid train along with Passive membrane modules, Active RO membranes improve the entire train performance and potentially enable a 25% increase in train recovery while cutting the membrane cleaning requirements by half. Microscopic imagery and elemental analysis of the membrane surfaces confirm that Active RO membranes incur significantly less scaling of supersaturated mineral salts than Passive membranes. They also show that in hybrid train where an Active RO membrane is used along with Passive RO membranes, the former reduces the scaling of Passive membranes in that train. Possible mechanism is through a formation of larger mineral agglomerates that are easier to discharge through the concentrate stream and are much less stable and easier to clean than numerous tiny scaling nucleation sites that are common characteristics of Passive membrane scaling.Table 4: Feed produced water qualityParameter Unit Minimum Maximum Average AnalysisSourceTDS mg / L 5,369 7,624 6,571 OnsiteIron mg / L 0.31 1.28 0.75 OnsiteSilica mg / L 26 66 48 OnsiteTotal Alkalinity mgCaCO3 / L 2,260 2,300 2,280 OffsiteTotal Hardness mgCaCOs / L 53 247 106 OnsiteSulfate mg / L 5 10 7.5 Onsite / OffsiteTurbidity NTU 3.21 50.00 8.25 OnsiteTPH mg / L 13 16 14.5 OffsiteCOD mg / L 610 610 610 Offsite pH - 8.30 8.70 8.50 OffsiteGRO mg / L 1.48 1.48 1.48 OffsiteDRO mg / L 5.41 5.41 5.41 OffsiteBTEX mg / L 0.61 0.61 0.61 Offsite

[0175] The key contaminants of concern include: (i) dissolved organics and hydrocarbons, (ii) iron, silica, and calcium carbonate (even at low RO recoveries), and (iii) colloids.Testing

[0176] Phase 1 (Baseline): where three standard 2514 (2.5” in diameter and 14” long) spiral wound brackish water reverse osmosis modules (Passive RO) were put in series. The object was to establish a comparison baseline. The length of the test was 5 batches, or the equivalent of 10 operating hours.

[0177] Phase 2 (Hybrid): similar to Phase 1, consisting of three modules in series; two Passive RO modules in series followed by a spiral wound 2514 Active BWRO module (Active RO) as the last element. The objective of the test can be stated as follows: The last element in a series always experiences the most scaling potential as it sees the most concentrated water. Here the goal was to examine how a single Active RO element can impact the scaling potential of the entire train. The length of the test was eight (8) batches, equivalent to sixteen (16) operating hours. This was to illustrate the hybrid train’s superior performance at a longer exposure to the feed water.

[0178] Phase 3 (head-to-head): here the last Passive RO module from Phase 1 was run in a head-to-head comparative test against the Active RO module from Phase 2. The objective of the test was to generate direct comparative data between the two modules. Each module was operated for eight (8) batches, equivalent to sixteen (16) hours of operation. At the end each of the Active RO and Passive RO modules were operated for a total sixteen (16) and thirteen (13) batches, respectively (32 and 26 hours).

[0179] Active RO module flatsheets had the same base membrane as the passive RO modules. The applied electrical conditions were 4 Volts AC (sine wave) at 30-240 mA applied current, alternating at a 1 Hz frequency. Each phase was operated at a constant pressure mode at a starting flux of 15 GFD (26 LMH). Constant pressure mode allowed the flux to decline as the feed water became more concentrated and membranes scaled or fouled.

[0180] For each phase, the following operating parameters were reported, (i) Rate of flux decline (J / Jo) for both observed and normalized operating fluxes, (ii) Salt rejection, both observed and normalized.

[0181] Normalization of flux and salt rejection was performed using the following formula:In this formula, Pf= feed pressure, — = one half of feed to concentrate pressure drop, Pp= product pressure, 7ifc= osmotic pressure of feed-concentrate mixture, TCF = temperature correction factor, Q = product flow, Subscript s = standard conditions, Subscript o = operating conditions.

[0182] The temperature correction factor follows the formula, where T = temperature in °C:

[0183] TCF = EXP [2640 x { 1 / 298 - 1 / (273 + T)}]; T > 25°C

[0184] TCF = EXP [3020 x { 1 / 298 - 1 / (273 + T)}]; T < 25°C

[0185] As standard conditions, we take the initial performance for each recovery set point for the first batch of each test phase.

[0186] For the osmotic pressure, different formulas are available in the literature. A valid and practical short approximation is, for Cfc<20,000 mg / L:

[0187] Where C& is the concentration of feed-concentrate and calculated using the following formula, where Y is the actual recovery each element (or the trains sees) and Cf is the feed TDS in mg / L.:

[0188] Normalized salt rejection is calculated by first calculating the normalized product concentration using the following formula:

[0189] Terms not yet defined under A are (i) Cp(product concentration as ion in mg / L) and (ii) 7tp(osmotic pressure of the permeate in bar). Once these values are calculated, the following formula is used to calculate the normalized salt rejection (NSR):

[0190] Similar to normalized flux, as standard conditions, the initial performance for each recovery set point are taken for the first batch of each pilot phase.Flux Decline Profiles

[0191] Average observed and normalized flux decline profiles for Phase 1 (All Passive) vs Phase 2 (Hybrid) are shown in FIGs. HA and 11B, respectively.

[0192] Key observations are as follows, (i) Hybrid Train shows 24% less flux decline for the observed values and no decline for normalized values up to 50% recovery, (ii) This, at minimum, translates to 50% reduction in membrane cleaning requirements and potentially 25% more recovery. This assumes the threshold for membrane cleaning to be 10-15% flux decline as per most membrane manufacturer recommendations.

[0193] Observed and normalized flux decline profiles for phase 3 (Passive RO vs Active RO) are shown in FIGs. 12A and 12B, respectively. Key observations are as follows, (i) Active RO shows 12% less flux decline for the observed values and 34% less flux decline for normalized values up to 50% recovery, (ii) This translates to 30-60% reduction in cleaning requirements and potentially 25% more recovery. This assumes the threshold for membrane cleaning to be 10- 15% flux decline as per most membrane manufacturer recommendations.Salt Rejection Profiles

[0194] Observed and normalized membrane salt rejection profiles for Phase 1 (All Passive) vs Phase 2 (Hybrid) are shown in FIGs. 13A and 13B, respectively. Key observations are as follows, (i) for both observed and normalized values, the Hybrid train shows better salt rejection. This is due to lower flux decline because of the Active RO membrane in that train.

[0195] Observed and normalized membrane salt rejection profiles for phase 3 (Passive RO vs Active RO) are shown in FIGs. 14A and 14B, respectively. Key observations are as follows, (i) For both observed and normalized values, Active RO salt rejection is initially on-par with Passive RO, but it gets better at higher recoveries (Lower flux decline)Membrane Autopsy Results

[0196] Membrane modules from the tests were subjected to autopsy studies with the following objectives, (i) Visual inspection of the quality of module and flatsheet post-filtration, (ii) Identify the nature of scaling and fouling species on the flatsheet surfaces, (iii) Examine and identify the mechanisms and patterns of scaling and fouling for Passive vs electroactive membranes

[0197] Four modules were used for this study: First module from All Passive Train (Phase 1, Passive RO-A), First Module from Hybrid Train (Phase 2, Passive RO-A), Passive RO and Active RO modules from Phase 3.

[0198] The modules were cut open and flatsheet and feed spacers were visually examined for signs of mechanical damage and scaling and fouling. Key observations are as follows, (i) No signs of mechanical damage (telescoping, flatsheet or module damage) were observed in any of the modules, (ii) Surface of all Passive RO membrane flatsheets were covered with orange-red layers indicating presence of Iron, (iii) Surface of Active RO membrane flatsheet seemed visibly much cleaner and the conductive layer was fully intact confirming the robustness of the electrically conducting coating film.

[0199] X-Ray Diffraction (XRD) (Bruker eco D8 Advance) was used to identify the nature of mineral scale species on membrane flatsheets. This is a technique used in materials science to determine the crystallographic structure of a material. XRD works by irradiating a material with incident X-rays and then measuring the intensities and scattering angles of the X-rays that leave the material. Key minerals on all membranes identified were: (i) Fayalite (Fe2SiO4), (ii) Calcite (CaCOs), (iii) Hematite (Fe20s), and (iv) Quartz (SiO2).

[0200] Focus Ion Beam - Scanning electron microscopy (FIB-SEM, Fera3 Tescan) was used to take microscopic images of the membrane flatsheet. The FIB component adds a second beam, the ion-beam, to cut into the material while the SEM carries out high-resolution imaging.

[0201] Membrane samples are sputter coated by beryllium to reduce the electric charging of SEM samples and attain the highest quality of imaging possible.

[0202] Images taken by FIB-SEM were then subjected to another technique; electron dispersive spectroscopy (EDS, Oxford Instruments). EDS produces elemental analysis and distribution ofvarious material seen on the membrane image taken by the FIB-SEM. Together, FIB-SEM and EDS provide a definitive imaging and analytic overview of the state of the membrane flatsheet, elements covering the membrane surface, and the extent and patterns at which these materials cover the membrane surface.

[0203] FIGs. 15A and 15B provides a head-to-head comparison of the surfaces of the Passive membranes used in All Passive (Phase 1, FIG. 15A) and Hybrid (Phase 2, FIG. 15B) phases of the pilot test. Key observations are as follows. Although both membranes are Passive RO membranes, situated in the same position in the pilot train, their images and surface elemental analysis, each shows a distinct scaling profile, (i) The membrane from the All-Passive train (Phase 1) shows a classical pattern of scaling, numerous tiny nucleation sites indiscriminately and uniformly distributed over its surface, while the membrane from the Hybrid train (Phase 2) shows significantly less nucleation sites with areas of larger scale conglomerates. This means that Active RO as the last module in the Hybrid train changes the scaling mechanism of the entire train by conglomerating the sealants. These larger conglomerates are then easier to discharge through the concentrate stream and also much easier to clean from the membrane surface. This significantly reduces the nucleation sites on the membrane surface leading to lower rate of flux decline, (ii) This means replacing only 30% of a train with electroactive membranes leads to significantly less scaling, cleaning needs, and overall higher plant uptime and recovery and maintenance costs.

[0204] FIGs. 16A and 16B provides a head-to-head comparison of the surfaces of the Passive (FIG. 16A) and Active (FIG. 16B) RO membranes from Phase 3. Key observations are as follows. Similar to the contrast between Phases 1 and 2 Membranes, we observe two distinctly different scaling profiles here as well with Passive RO membrane uniformly covered with tiny nucleation sites, Active RO membrane has considerably fewer nucleation sites with some areas covered with conglomerates. Once formed, these mineral conglomerates are easier to discharge through the concentrate stream and are also much easier to clean from the membrane surface. This behavior justifies the lower rate of flux decline.

[0205] A comparative two-week testing of active RO membranes (Active-RO) vs passive RO (standard-RO) membrane modules was performed treating Oil & Gas Produced Water. The produced water was characterized with varying quality, containing high levels of alkalinity, Iron, silica, and dissolved organics and hydrocarbons, and Turbidity, posing high potential for various types of membrane scaling and fouling. The feed water feeding the test unit primarily passed through a multimedia filtration unit, upstream of which was an intermittently operating volatile organic carbon stripping unit.

[0206] The tests were performed in three phases. Phase 1 : using three conventional 2514 RO modules (Passive RO) in series to create a comparative baseline. Phase 2: replacing the last RO in Phase 1 configuration with an Active 2514 RO module (Active RO). The last module in series always experiences the highest concentration and as a result has the highest tendency for scaling of sparingly soluble mineral salts. The objective here was if and how the Active RO module could impact the scaling profile of the entire train. Phase 3: head-to-head comparison of the Passive RO module from Phase 1 and Active RO Module from Phase 2. All phases were performed at feed-and-bleed mode at constant pressure and starting flux of 15 GFD / 25 LMH. In this mode of operation, a batch of feed water is run through the pilot system and the permeate is discarded while the concentrate is returned to the feed tank. This results in ever increasing concentration of feed water in the feed tank, simulating various concentration factors (recoveries). Pressure, flow, and water quality data was collected for each phase and individual membrane modules throughout the operation.

[0207] Both absolute and normalized field flux profiles and membrane autopsy results suggest that with minimal pre-treatment and specifically no chemical pre-treatment, Active-RO membranes outperform Passive-RO that in terms flux stability while producing equivalent and at times better quality of desalinated water. This can enable a potential 25% higher recovery, 30- 60% less cleaning membrane cleaning requirement (more plant uptime).

[0208] Active RO membranes seem to encourage formation of large conglomerates of mineral scale that are much easier to remove through the concentrate stream leading to significantly less nucleation sites on the surface of the membrane.Example 5Evaluation of electroactive membranes versus passive membranesMaterials and Methods

[0209] Solution preparation: To evaluate the electroactive membranes described herein, active reverse osmosis (RO) modules comprising the electroactive membranes described herein were evaluated using a synthetic seawater prepared using Instant Ocean, simulating seawater with a TDS level of -42,000 ppm. Below, active RO modules are compared to passive RO modules.

[0210] Reverse osmosis modules: Cross-flow spiral-wound seawater RO (SWRO) elements with 4 inch diameter and 40 inch (1 m) length were used for the tests. The passive module used SWRO membranes procured from LG-Nano, which were high rejection Seawater TFC membranes. The active RO modules were prepared using the same specifications (membrane area, spacer dimensions, etc.) as the passive modules, except for the surface coating treatment onthe membranes, making them electroactive. The active RO modules, furthermore, had electrical connections facilitating delivery of electrical power of prescribed waveform to these modules.

[0211] Electrochemical Setup: RIGOL DG822 was used as a signal generator, for applying sinusoidal and square waveforms with varying amplitudes, frequencies, and duty cycles. An oscilloscope (RIGOL DS 1054) was used for monitoring the applied waveform and any changes in the waveform owing to the load. The current passage through the active filtration system was additionally monitored using an ammeter (BK Instruments).

[0212] Boron concentration, pH, and conductivity measurements: Inductively Coupled Plasma Mass Spectrometry (ICP-MS) was utilized for boron detection, ensuring high sensitivity and accuracy. pH and conductivity were measured using a calibrated Oakton pH meter and conductivity meter, respectively.Experimental System Description

[0213] First stage RO process: As shown in FIG. 17, the synthetic seawater was passed through a SWRO module and the permeate was collected as the feed for the second stage of RO, while the concentrate was recirculated back to the feed tank, simulating various recovery rates under constant feed pressure mode. Table 5 below shows bleeding permeate volume (L) and approximate feed tank solution electrical conductivity (EC) versus various recovery percentages. The data collected in the first stage RO process is used to calculate membrane permeabilities presented elsewhere below.Table 5: Various simulated recoveries in constant feed pressure mode.

[0214] As presented herein, permeability (or A-value) may be given by:

[0215] In some embodiments, the denominator of the permeability equation above may be referred to as the trans membrane pressure.

[0216] As presented herein, a rejection % may be given by:

[0217] In the above, Cpis a total dissolved solids (TDS) of the permeate in mg / L, and the is the TDS of the feed solution in mg / L. As shown herein, permeability “A-values” for each run are normalized to the initial permeability of the membranes (Ao).

[0218] Two stage RO process: As shown in FIG. 18, The permeate collected from the first- stage RO, with an average TDS of 1500 ppm and 3 ppm of boron, was utilized as the feed water for the second-stage RO. The following test configurations were applied for the passive and active RO modules, respectively: (i) Conventional - passive module: RO with pH elevated above 10.5 through the addition of NaOH. (ii) Electrochemical - active RO module: use of an electroactive membrane to generate localized high pH.Results and Discussion

[0219] Results from conventional (passive) RO system: The passive module demonstrated average salt and boron rejection rates of 97.35% and 66%, respectively, at 40% recovery for the first stage. The average boron concentration in permeate was 3 ppm. By adjusting pH >10, boron rejection improved significantly, with permeate concentrations nearing 0.41 ppm. Table 6 demonstrates the salt and boron rejection when passive RO modules were tested.Table 6: Salt and boron rejection for passive RO module

[0220] Results from electrochemical second stage RO: The active RO module achieved average rejection rates of 97.00% for salt and 67.68% for boron at 40% recovery for the first stage. The average boron concentration in permeate was 3 ppm. Electrifying the Active module increases the pH on the membrane surface, significantly enhancing boron rejection. As a result, permeate concentrations were reduced to approximately 0.43 ppm.

[0221] The amplitude and frequency effects of the alternating waveform used with the active RO module is shown in FIG. 19. FIG. 19 illustrates the effect of the amplitude of a sinusoidalAC signal on boron rejection. As shown, increasing the amplitude from 4 Cppto 5 FpPsignificantly enhanced pH elevation and boron rejection. However, further increasing the amplitude from 5 FpPto 6 Fppresulted in negligible additional improvement.

[0222] FIGs. 20A-C demonstrates the impact of the frequency of a sinusoidal AC signal on boron rejection. At a low amplitude (4 FpP) as shown in FIG. 20A, increasing the frequency enhances boron rejection due to the associated rise in pH. However, at higher amplitudes as shown in FIGs. 20B and 20C (5 Fppand 6 FpP), the effect of frequency becomes negligible.Table 7: effect of amplitude and frequency of sinusoidal AC signal on Boron rejection.

[0223] Signal Type Comparison: FIG. 21 and Table 8 show the effect of wave form on boron rejection. Sinusoidal signals yielded consistent boron rejection at moderate amplitudes. At different duty cycles, the amount of local OH ions remain the same since the power condition doesn’t change, keeping the pH at 9. With a 20% duty cycle, the membrane acts as the anode for 80% of the whole period, leading to more boron rejection due to charge repulsion compared to an 80% duty cycle. Consequently, square wave signals with 20% duty cycle performed best in boron rejection.Table 8: effect of wave form on Boron rejection.Example 6Illustrative salt rejection and permeability versus recovery percent experimentsVoltage dependence

[0224] Shown in FIG. 22A and FIG. 22B is a comparison between several active reverse osmosis (RO) modules and a passive RO module. A 1Hz waveform was applied to the active RO modules at various applied voltages. As shown, at various recoveries, the active RO modules hold a permeability of a 10-15% higher than the passive RO module while retaining similar salt rejection percentages. In this example, increasing voltage was shown to increase permeability in the active modules and generally promote salt rejection.Frequency dependence

[0225] Shown in FIG. 23A and 23B is a comparison between several active RO modules and a passive RO module. Waveforms of varying frequency were applied to the active RO modules at 4 pP. As shown, the active modules were shown higher rejection at higher recovery rates as compared to a passive module while retaining similar salt rejection percentages.Reproducibility

[0226] Shown in FIG. 24A and 24B are reproducibility results from two active RO modules operated under different conditions. In FIG. 24A, two active RO modules operated at 4 Vppand 500 Hz were shown to have similar permeability behavior as a function of recovery %.Similarly, in FIG. 24B, two active RO modules operated at 6ppand 1 Hz were shown to have similar permeability behavior as a function of recovery %.Permeability comparison, active versus passive modules

[0227] Shown in FIG. 25A and 25B are comparisons between the permeabilities of active versus passive RO modules. The active RO module of FIG. 25A was operated at 4 Fppand 500 Hz. The active RO module of FIG. 25B was operated at 4 Fppand 1 Hz. In FIG. 25A, three points are highlighted on the active RO module curve highlighting increased permeability at 30%, 40%, and 60% recovery. Points, 1, 2, and 3, show a retention of permeability of 7.17%, 6.39%, and 7.27% greater than the passive RO module, respectively, at various recovery percentages. Similarly, in FIG. 25B, three points are highlighted on the active RO module curve highlighting increased permeability at 30%, 40%, and 60% recovery. Points, 1, 2, and 3, show a retention of permeability of 3.49%, 7.03%, and 5.34% greater than the passive RO module, respectively, at various recovery percentages.

[0228] Shown in FIG. 26A and 26B are comparisons between the permeabilities of active versus passive membranes. The active RO module of FIG. 26A was operated at 8 Fppand 1 Hz. The active RO module of FIG. 26B was operated at 6 Fppand 1 Hz. In FIG. 26A, three points are highlighted on the active RO module curve highlighting increased permeability at 30%, 40%, and 60% recovery. Points, 1, 2, and 3, show a retention of permeability of 10.54%, 11.27%, and 4.58% greater than the passive RO module, respectively, at various recovery percentages. Similarly, in FIG. 26B, three points are highlighted on the active RO module curve highlighting increased permeability at 30%, 40%, and 60% recovery. Points, 1, 2, and 3, show a retention of permeability of 6.76%, 3.40%, and 4.52% greater than the passive RO module, respectively, at various recovery percentages.Rejection profile comparison, active versus passive modules

[0229] Shown in FIG. 27 is a table illustrating active power conditions versus salt rejection and a graph visually showing a comparison between an active RO module operated at 4 Fppand 500 Hz and a passive module at various recovery percentages. As shown, in the table and illustrative graph, active RO module salt rejection is comparable to passive modules. This demonstrates that the addition of electroactive layers to passive reverse osmosis membranes does not force a tradeoff between salt rejection and functionalization for advantages described elsewhere herein including anti-scaling / anti-fouling.Active RO module without applied potential versus passive module

[0230] Shown in FIG. 28A is a comparison of permeability between an active RO module and a passive RO module at various recovery percentages. Shown in FIG. 28B is a comparison of permeability between an active RO module and a passive RO module at various salt rejectionpercentages versus recovery percentages. In both FIG. 28A and FIG. 28B, no potential was applied to the active RO module. As shown, functionalization of a RO membrane with electroactive layers does not significantly hinder passive filtration in membranes with electroactive layers.Summary table of various boron rejection testsTable 9: Boron rejection testsExample 7Theoretical modeling of boron rejection systems and methodsWaveforms

[0231] A sinusoidal waveform as applied herein may be represented by the equation below for V(t), where Kamp is the amplitude of the voltage, / is the frequency of the waveform in Hz, and t is time in seconds.

[0232] A square waveform as applied herein may be represented by the equation below for V(t), where Kamp is the amplitude of the voltage, D is the duty cycle (fraction of time voltage is “on”, 0 < D < 1), and T is the period of the waveform (T=l / f).0 < t < D. T7(t) -VAmpD.T < t < TRMS Voltage and Current

[0233] The root mean square (RMS) voltage value for a sinusoidal waveform is given by:

[0234] For a square waveform, the RMS voltage value is given by:

[0235] For an equivalent circuit comprising a resistance (R) and a capacitance (C) in parallel, the current (I(t)) is:

[0236] The RMS current is then:^RMS —

[0237] where (o = 27if) is the angular frequency.Electrical Double Layer Relaxation

[0238] For a charged electrode, the electrical double layer capacitance (CEDL) introduces a timedependent relaxation described by: q(t) = CEDLV(t)Force Balance on an Ion

[0239] A charged particle in solution experiences forces due to the electric field, hydrodynamic drag, and other body forces (e.g., gravity). The force balance is given by: qE — 6irqr v — m g = 0

[0240] In the equation above, q is charge of the particle, E is electric field (E = V / d), with d as the distance between electrodes, r| is dynamic viscosity of the fluid, r is particle radius, v is drift velocity, m is particle mass, and g is gravitational acceleration. Neglecting gravity for very small particles, the steady-state drift velocity is given by:Electrochemical Reactions at the Electrode

[0241] Above the threshold potential Vth, water electrolysis generates hydroxyl ions:2H2O + 2e~ H2+ 2OH~

[0242] The rate of hydroxyl ion production / ?0H- is:

[0243] In above, i is current density, n is the number of electrons transferred per reaction, and F is Faraday's constant. The borate formation equilibrium is given by:

[0244] The equilibrium constant Keqfor this reaction governs the extent of borate ion formation. pH Increase and Borate Formation

[0245] The local pH near the membrane is: pH = - log10[H+]

[0246] Assuming OH dominates:

[0247] In the equation above, Vflowis volumetric flow rate and A is membrane surface area.General Formula for pH and Borate Formation

[0248] Combining the equations of above, the extent of borate formation (XB) is given by:

[0249] The local increase in pH near the electrode is:

[0250] The drift velocity of ions away from the electrode, reducing fouling, is:

[0251] The enhanced boron rejection at higher frequencies aligns with electrochemical kinetics governed by the Butler-Volmer equation:

[0252] Increased amplitudes likely generate higher local OH concentrations, supporting the hypothesis of electrochemical pH enhancement.

[0253] While preferred embodiments of the present invention have been shown and described herein, it will be obvious to those skilled in the art that such embodiments are provided by way of example only. Numerous variations, changes, and substitutions will now occur to those skilled in the art without departing from the invention. It should be understood that various alternatives to the embodiments of the invention described herein may be employed in practicing the invention. It is intended that the following claims define the scope of the invention and that methods and structures within the scope of these claims and their equivalents be covered thereby.

Claims

CLAIMSWHAT IS CLAIMED IS:

1. A method of coating a substrate with a suspension to produce an electroactive semi- permeable membrane comprising: a) providing the suspension, wherein the suspension comprises a plurality of active particles; b) disposing the suspension into a sprayer; c) dispensing the suspension onto the substrate at a rate of at least 5 in2 / min, wherein the substrate is supported by a conveyor system in fluidic communication with the sprayer, and wherein a volumetric rate of dispensing is at least 2 ml / min, and d) heating the substrate comprising the suspension to obtain the electroactive semi- permeable membrane, wherein a retentate of a leaching test of the electroactive semi-permeable membrane has an NTU within 10% of a feed solution of the leaching test.

2. The method of claim 1, further comprising repeating each of the operations (a)-(d).

3. The method of claims 1 or 2, further comprising coating the substrate with a polyamide layer4. The method of claim 1, further comprising washing the electroactive semi -permeable membrane.

5. The method of claim 1, wherein a pH of the feed solution is about 2 to about 13.

6. The method of claim 1, wherein the NTU is within 5% of the feed solution of the leaching test.

7. The method of claim 6, wherein a pH of the feed solution is about 4 to about 11.

8. The method of claim 2, wherein a composition of the suspension changes for at least one iteration of the repeating operation.

9. The method of claim 1, wherein the suspension has a viscosity of at least 0.8 cP.

10. The method of claim 1, wherein a length of an active particle of the plurality of active particles is at least 10 pm.

11. The method of claim 1, wherein an average normalized flux of the electroactive semi- permeable membrane is at least 0.6 for a recovery percent of about 50%.

12. The method of claim 1, wherein an average sheet resistance of the electroactive semi- permeable membrane is at most 2000 Q / n.

13. The method of claim 1, wherein a standard deviation of a measured surface resistivity of the electroactive semi-permeable membrane is at most 10% of the measured surface resistivity.

14. The method of claim 1, wherein a mass loading of active particles on the substrate is at least 0.5 g / m2.

15. The method of claim 1, wherein the sprayer comprises one or more spraying components.

16. The method of claim 15, wherein at least one of the one or more spraying components is configured to aerosolize the suspension.

17. The method of claim 15, wherein the sprayer comprises one or more of an inkjet, an electrospray, or a conventional sprayer.

18. The method of claim 1, wherein the conveyor system completes one or more revolutions during the dispensing operation.

19. The method of claim 1, wherein the substrate is heated to at least 35 °C.

20. The method of claim 1, wherein the substrate comprises an ultrafiltration membrane.

21. The method of claim 20, wherein the ultrafiltration membrane comprises one or more of polysulfone, poly-ether sulfone, or a non-woven polyester.

22. The method of claims 20 or 21, wherein a permeability of the ultrafiltration membrane is substantially similar to a permeability of the electroactive semi-permeable membrane.

23. The method of claim 1, wherein the suspension further comprises a binder, a viscosity modifier, or a dispersant.

24. The method of claim 23, wherein the binder is a crosslinked polymer binder, wherein the plurality of active particles are encapsulated by the crosslinked polymer binder.

25. The method of claim 23, wherein the dispersant comprises one or more of an aqueous or organic solvent.

26. The method of claim 1, wherein the plurality of active particles comprises a onedimensional nanomaterial.

27. The method of claim 26, wherein the one-dimensional nanomaterial comprises a nanotube, a nanowire, or a nanorod.

28. The method of claims 1, wherein the plurality of active particles further comprises nanoparticles.

29. The method of claim 1, wherein the substrate has dimensions comprising a width of about 5 inches to about 42 inches and a length of about 12 inches to about 108 inches.

30. A method of coating a substrate with a suspension to produce an electroactive semi- permeable membrane comprising: a) providing the suspension, wherein the suspension comprises a plurality of active particles; b) disposing the suspension into a sprayer; c) dispensing the suspension onto the substrate at a rate of at least 5 in2 / min, wherein the substrate is supported by a conveyor system in fluidic communication with the sprayer, and wherein a volumetric rate of dispensing is at least 2 ml / min, and d) heating the substrate comprising the suspension to obtain the electroactive semi- permeable membrane, wherein a permeability of the substrate is substantially similar to a permeability of the electroactive semi-permeable membrane.

31. The method of claim 30, further comprising repeating each of the operations (a)-(d).

32. The method of claims 30 or 31, further comprising coating the substrate with a polyamide layer33. The method of claim 30, further comprising washing the electroactive semi -permeable membrane.

34. The method of claim 31, wherein a composition of the suspension changes for at least one iteration of the repeating operation.

35. The method of claim 30, wherein the suspension has a viscosity of at least 0.8 cP.

36. The method of claim 30, wherein a length of an active particle of the plurality of active particles is at least 10 pm.

37. The method of claim 30, wherein an average normalized flux of the electroactive semi- permeable membrane is at least 0.6 for a recovery percent of about 50%.

38. The method of claim 30, wherein an average sheet resistance of the electroactive semi- permeable membrane is at most 2000 Q / n.

39. The method of claim 30, wherein a standard deviation of a measured surface resistivity of the electroactive semi-permeable membrane is at most 10% of the measured surface resistivity.

40. The method of claim 30, wherein a mass loading of active particles on the substrate is at least 0.5 g / m2.

41. The method of claim 30, wherein the sprayer comprises one or more spraying components.

42. The method of claim 41, wherein at least one of the one or more spraying components is configured to aerosolize the suspension.

43. The method of claim 41, wherein the sprayer comprises one or more of an inkjet, an electrospray, or a conventional sprayer.

44. The method of claim 30, wherein the conveyor system completes one or more revolutions during the dispensing operation.

45. The method of claim 30, wherein the substrate is heated to at least 35 °C.

46. The method of claim 30, wherein the substrate comprises an ultrafiltration membrane.

47. The method of claim 46, wherein the ultrafiltration membrane comprises one or more of polysulfone, poly-ether sulfone, or a non-woven polyester.

48. The method of claims 46 or 47, wherein a permeability of the ultrafiltration membrane is substantially similar to a permeability of the electroactive semi-permeable membrane.

49. The method of claim 30, wherein the suspension further comprises a binder, a viscosity modifier, or a dispersant.

50. The method of claim 49, wherein the binder is a crosslinked polymer binder, wherein the plurality of active particles are encapsulated by the crosslinked polymer binder.

51. The method of claim 49, wherein the dispersant comprises one or more of an aqueous or organic solvent.

52. The method of claim 30, wherein the plurality of active particles comprises a onedimensional nanomaterial.

53. The method of claim 52, wherein the one-dimensional nanomaterial comprises a nanotube, a nanowire, or a nanorod.

54. The method of claims 30, wherein the plurality of active particles further comprises nanoparticles.

55. The method of claim 30, wherein the substrate has dimensions comprising a width of about 5 inches to about 42 inches and a length of about 12 inches to about 108 inches.

56. The method of claim 30, wherein a retentate of a leaching test of the electroactive semi- permeable membrane has an NTU within 10% of a feed solution of the leaching test.

57. The method of claim 56, wherein a pH of the feed solution is about 2 to about 13.

58. The method of claim 30, wherein a retentate of a leaching test of the electroactive semi- permeable membrane has an NTU within 5% of a feed solution of the leaching test.

59. The method of claim 58, wherein a pH of the feed solution is about 2 to about 13.

60. A method for removing a boron species from a water source, comprising: a) filtering the water source through an electroactive membrane, wherein the water source comprises at least boric acid and at least one scaling species, wherein the electroactive membrane comprises a surface configured to receive an applied voltage, and wherein the water source is provided to the surface of the electroactive membrane; b) applying a first voltage to the electroactive membrane, thereby generating borate ions from the boron species; and c) applying a second voltage to the electroactive membrane, thereby removing at least a portion of the at least one scaling species from the surface of the electroactive membrane, wherein at least a portion of the borate ions are rejected from the electroactive membrane.

61. The method of claim 60, wherein the first voltage and the second voltage are applied via an alternating waveform.

62. The method of claim 61, wherein the alternating waveform comprises a square waveform.

63. The method of claim 61, wherein the alternating waveform comprises a sinusoidal waveform.

64. The method of claim 61, wherein the alternating waveform comprises a duty cycle of from about 20% to about 80%.

65. The method of claim 64, wherein the alternating waveform comprises a duty cycle of from about 20% to about 50%.

66. The method of any one of claims 61 to 65, wherein the alternating waveform comprises a peak to peak voltage of about 4 V to about 6 V.

67. The method of any one of claims 61 to 66, wherein the frequency of the alternating waveform is from about 1 Hz to about 500 Hz.

68. The method of claim 67, wherein the frequency of the alternating waveform is from about 1 Hz to about 5Hz.

69. The method of claim 60, wherein the first voltage is configured to raise the pH of the water source to at least about 9.

70. The method of claim 69, wherein the pH of the water source is at least about 9 within at least about 5 pm from the surface of the electroactive membrane.

71. The method of claim 60, wherein (b) and (c) occur during (a).

72. The method of claim 71, wherein (b) and (c) occur repeatedly during (a) by applying an alternating voltage waveform comprising the first voltage and the second voltage.

73. The method of claim 60, wherein the scaling species comprises a metal or a silicate.

74. The method of claim 73, wherein the metal comprises an alkali metal or an alkaline earth metal.

75. The method of claim 60, wherein the water source has a TDS level of at least about 35,000 ppm.

76. The method of claim 60, wherein the filtering comprises delivering the water source to the surface of the electroactive membrane at a pressure of about 100 psi to about 800 psi.

77. The method of claim 60, wherein (a)-(c) are performed in at least a first stage and a second stage.

78. The method of claim 77, wherein the pressure of the water source is about 300 psi to about 1,000 psi in the first stage.

79. The method of claim 78, wherein the pressure of the water source is about 100 psi to about 300 psi in the second stage.

80. The method of claim 60, wherein at least about 80% of the boron species is rejected from the electroactive membrane.

81. The method of claim 60, wherein the electroactive membrane comprises a layered structure.

82. The method of claim 81, wherein the layered structure comprises at least a polyamide layer and an electroactive layer.

83. The method of claim 82, wherein the electroactive layer comprises a carbon nanomaterial or a conductive nanoparticle.

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