Method for preparing electrically conductive forward osmosis membrane, and electrically conductive forward osmosis membrane thereof

Abstract

A method for preparing an electrically conductive forward osmosis membrane, and an electrically conductive forward osmosis membrane thereof. Electrically conductive porous carbon paper (CP) is used as a base membrane; the base membrane is physically modified by means of the electrochemical deposition of polypyrrole (PPY), and then, the electrically conductive forward osmosis membrane (CPFO) is prepared on a polypyrrole intermediate layer by means of an interfacial polymerization (IP) reaction. The prepared electrically conductive forward osmosis membrane has good conductivity, antifouling properties and chemical stability, and can achieve the effects of efficiently separating pollutants and relieving membrane fouling in the field of the separation of algae from water.

Description

Method for preparing conductive forward osmosis membrane and its conductive forward osmosis membrane

[0001] Cross-references to related applications

[0002] This application claims priority to Chinese Patent Application No. 202410795442.3, filed in China on June 19, 2024, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This invention relates to a method for preparing a conductive forward osmosis membrane and the conductive forward osmosis membrane thereof, belonging to the field of water treatment technology. Background Technology

[0004] Compared to non-conductive forward osmosis membranes coupled with electrochemical coupling, electrochemically assisted conductive forward osmosis membranes can be directly used as cathodes or anodes. This not only makes the device compact and easy to handle and build, but also greatly reduces the mass transfer resistance between contaminants and electrodes. The preparation of conductive forward osmosis membranes can be broadly categorized into the following methods: One method involves modifying the conductivity of the skin layer. This is mostly done by coating a conductive material onto the polyamide layer. However, the biggest drawback of this coating method is limited uniformity, which significantly weakens the conductivity of the composite membrane. Another method involves modifying the conductivity of the support layer by coating it with a conductive material. However, this coating method also faces critical issues regarding uniformity and conductivity. For example, Chinese patent CN112473372B proposes a method of depositing a two-dimensional material MXene on a polymer membrane support layer and then preparing a conductive forward osmosis membrane through interfacial polymerization. However, because the support layer is a non-conductive material, it not only has a relatively high resistivity, but also experiences a gradual decline in membrane performance due to the loss of conductive additives during long-term operation.

[0005] Traditional methods for preparing conductive forward osmosis membranes mostly involve coating conductive materials onto the support layer or PA layer. However, because the support layer is a non-conductive material, it not only has a relatively high resistivity, but also its membrane performance gradually deteriorates over long-term operation due to the loss of conductive additives. Therefore, a method for preparing a forward osmosis membrane and a corresponding forward osmosis membrane that combines good conductivity and stability is needed.

[0006] Summary of the Invention

[0007] To address the aforementioned technical problems, this invention provides a method for preparing a conductive forward osmosis membrane and the same conductive forward osmosis membrane, which exhibits good conductivity and stability.

[0008] This invention is achieved through the following technical solution:

[0009] The first aspect of this application provides a method for preparing a conductive forward osmosis membrane, which includes the following steps:

[0010] a) Prepare a conductive intermediate layer on a conductive porous substrate to obtain a conductive base film;

[0011] b) An interfacial polymerization reaction is carried out on the conductive intermediate layer of the conductive base film to prepare a skin layer, thereby obtaining the conductive forward osmosis membrane.

[0012] Furthermore, the conductive porous substrate is conductive porous carbon paper; the conductive intermediate layer is a hydrophilic conductive material layer.

[0013] Furthermore, the conductive intermediate layer is polypyrrole; the conductive intermediate layer is prepared by electrochemically depositing a pyrrole-containing electrochemical polymer on the surface of conductive porous carbon paper as a substrate.

[0014] Furthermore, before step a), the following steps are included: pre-treating the conductive porous substrate; the pre-treatment of the conductive porous substrate is carried out in the following manner: obtaining a conductive porous substrate of appropriate size, immersing the conductive porous substrate of appropriate size in a petri dish, and then neutralizing the substrate.

[0015] Furthermore, the pretreatment of the conductive porous substrate is carried out in the following manner: the conductive porous substrate of appropriate size is immersed in a petri dish using a 0.2 mol / L sodium hydroxide (NaOH) solution for a period of time, and then immersed and rinsed with deionized water until neutral.

[0016] Furthermore, the electrochemical polymer is a mixture of pyrrole and sulfuric acid (H2SO4).

[0017] Furthermore, the method for preparing the skin layer is as follows: immerse the conductive base film in an aqueous solution of a certain concentration of polyamine compound, maintain complete immersion for a first specified time, remove excess aqueous solution to obtain a pretreated film; perform surface treatment on the pretreated film; pour an organic phase solution containing polyacrylamide compound onto the pretreated film to carry out an interfacial polymerization reaction, remove excess organic phase solution after a second specified time, and obtain a skin-layered conductive forward osmosis membrane with a polyamide layer.

[0018] Further, the method for preparing the polyamide layer is as follows: 25 ml of an aqueous solution containing m-phenylenediamine (MPD) is slowly poured onto the base membrane and immersed in it for 180 seconds; then the excess aqueous solution is poured off, and the aqueous solution is gently rolled over the membrane surface with a rubber roller to uniformly disperse the aqueous solution on the membrane surface, thus obtaining the pretreated membrane; then 25 ml of an organic solution of trimesoyl chloride (TMC) is poured onto the pretreated membrane, and after reacting for 90 seconds, the excess organic solution is poured off, thus obtaining the nascent forward osmosis membrane; the prepared nascent forward osmosis membrane is air-dried for 60 seconds and then cured by baking for 300 seconds, resulting in a selectively permeable skin layer on the membrane surface.

[0019] Furthermore, the aqueous phase solution is prepared as follows: a m-phenylenediamine compound solution with a concentration of 1.0wt%-6.0wt% is prepared and dissolved in an opaque or semi-transparent container using water as a solvent; the organic phase solution is prepared as follows: a pyromellitic trimethylol chloride compound with a concentration of 0.05wt%-0.5wt% is dissolved in a container using n-hexane as a solvent.

[0020] The second aspect of this application provides a conductive forward osmosis membrane, which is prepared by the preparation method described in the first aspect.

[0021] The beneficial effects of this invention are:

[0022] The present invention discloses a method for preparing a conductive forward osmosis membrane and the corresponding membrane. The method utilizes an integral conductive porous substrate as the support layer of the forward osmosis membrane. A conductive intermediate layer is obtained by electrochemically depositing a conductive polymer on the porous conductive substrate. The porous permeability, excellent conductivity, low contact resistance, and good mechanical strength enhance the water treatment capability of the conductive forward osmosis membrane. The conductive forward osmosis membrane prepared by this invention exhibits excellent conductivity, a smooth surface structure, and nanoscale filtration performance.

[0023] This application compensates for the defects of rough macropores in conductive porous carbon paper-based membranes by depositing an intermediate layer on a conductive porous substrate. A series of physicochemical properties of the membrane surface, such as hydrophilicity, roughness, pore size, and electrochemical characteristics, are changed, forming a completely new substrate morphology: high hydrophilicity, reasonable small pore size, and uniform roughness provide greater reactivity and contact area for interfacial polymerization reactions, thereby producing higher crosslinking degree and excellent forward osmosis performance. This improves the conductivity and stability of the conductive forward osmosis membrane, and enhances the antifouling effect of the membrane under applied voltage. Attached Figure Description

[0024] Figure 1a is a flowchart of the method for preparing a conductive forward osmosis membrane provided in this application;

[0025] Figure 1b is a flowchart of the preparation of a conductive forward osmosis membrane using conductive carbon paper as a substrate in an embodiment of this application;

[0026] Figures 2a-2o show scanning electron microscope (SEM) images of the surface of conductive porous carbon paper substrates obtained by depositing electrochemical polymer polypyrrole of different concentrations on pure conductive porous carbon paper substrates in different embodiments of this application at different deposition cycles (200, 400, 500, 600, 700).

[0027] Figure 3 is a schematic diagram of the permeation performance of the pure conductive porous carbon paper substrate and the conductive porous carbon paper substrate with different polypyrrole deposition concentrations in different embodiments of this application.

[0028] Figure 4 is an experimental schematic diagram showing the sheet resistance of a pure conductive porous carbon paper base film and conductive porous carbon paper base films with different polypyrrole deposition concentrations in different embodiments of this application.

[0029] Figure 5 is an experimental schematic diagram showing the contact angle of the comparative base film of pure conductive porous carbon paper substrate and the conductive porous carbon paper base film under different polypyrrole deposition cycles in different embodiments of this application.

[0030] Figure 6 is a schematic diagram of the Zeta potential of the comparative base film of pure conductive porous carbon paper substrate and the conductive porous carbon paper base film under different polypyrrole deposition cycles in different embodiments of this application.

[0031] Figures 7a-7f are atomic force microscopy (AFM) experimental schematic diagrams of the comparative base film of pure conductive porous carbon paper substrate and the conductive porous carbon paper base film under different polypyrrole deposition cycles in different embodiments of this application.

[0032] Figures 8a1-8a6 and 9b1-9b6 are scanning electron microscope (SEM) schematic diagrams of the surface of conductive forward osmosis membranes obtained after adding intermediate layers of polypyrrole with different concentrations in different embodiments of this application, forming a forward osmosis membrane on a pure conductive porous carbon paper substrate.

[0033] Figures 9c1-9c6 are cross-sectional scanning electron microscope (SEM) schematic diagrams of conductive forward osmosis membranes obtained in different embodiments of this application after adding intermediate layers of polypyrrole with different deposition layers on a pure conductive porous carbon paper substrate.

[0034] Figures 10a-10f show comparative atomic force microscopy (AFM) schematic diagrams of the forward osmosis membranes formed on pure conductive porous carbon paper substrates and the forward osmosis membranes obtained in different embodiments of this application after adding an intermediate layer of polypyrrole with the same concentration but different number of cycles.

[0035] Figure 11 shows a schematic diagram of the contact angle of the forward osmosis membrane formed on a pure conductive porous carbon paper substrate, compared with the contact angle of the forward osmosis membrane obtained in different embodiments of this application after adding polypyrrole intermediate layers of the same concentration but different number of cycles.

[0036] Figure 12 is a schematic diagram of X-ray photoelectron spectroscopy (XPS) of a comparative forward osmosis membrane formed on a pure conductive porous carbon paper substrate and a forward osmosis membrane obtained after adding an intermediate layer of polypyrrole with the same concentration but different number of cycles in different embodiments of this application.

[0037] Figure 13 is a cyclic voltammetry diagram of a forward osmosis membrane formed on a pure conductive porous carbon paper substrate and a forward osmosis membrane obtained in different embodiments of this application after adding a polypyrrole intermediate layer of the same concentration but different number of cycles.

[0038] Figure 14 shows a comparative electrochemical impedance diagram of a forward osmosis membrane formed on a pure conductive porous carbon paper substrate and a forward osmosis membrane obtained in different embodiments of this application after adding a polypyrrole intermediate layer of the same concentration but different number of cycles.

[0039] Figure 15 shows a cross-flow forward osmosis (FO) apparatus used to test the permeation selectivity of the forward osmosis membrane;

[0040] Figures 16a and 16b are schematic diagrams showing the performance of a comparative forward osmosis membrane formed on a pure conductive porous carbon paper substrate and a forward osmosis membrane obtained in different embodiments of this application after adding an intermediate layer of polypyrrole with the same concentration but different number of cycles deposited, in FO mode (polyamide layer facing feed solution) and PRO mode (polyamide layer facing draw solution).

[0041] Figure 17a is a schematic diagram showing the water permeability (A value) and salt permeability (B value) of a forward osmosis membrane formed on a pure conductive porous carbon paper base membrane and a forward osmosis membrane obtained after adding an intermediate layer of polypyrrole with the same concentration but different number of cycles in different embodiments of this application.

[0042] Figure 17b is a schematic diagram showing the salt rejection rate of a comparative forward osmosis membrane formed on a pure conductive porous carbon paper base membrane and a forward osmosis membrane obtained after adding an intermediate layer of polypyrrole with the same concentration but different number of cycles in different embodiments of this application.

[0043] Figures 18a and 18b are schematic diagrams comparing the water flux and backsalinity flux of a conductive forward osmosis membrane with a polypyrrole deposition concentration of 600 circulation cycles under different draw solution concentrations.

[0044] Figures 19a and 19b show schematic diagrams of the membrane flux changes of the conductive forward osmosis membrane in the application embodiments of this application under different applied voltages;

[0045] Figures 20a-20g show schematic diagrams of the filter cake layer thickness of the conductive forward osmosis membrane cross-section in the application embodiments of this application under different applied voltages;

[0046] Figures 21a-21d show schematic diagrams illustrating the effects of different voltages on the performance of the conductive forward osmosis membrane in the application embodiments of this application under single and mixed algal water components.

[0047] Figures 22a, 22a1-22g1, 22a2-22g2, 22a1'-22g1', and 22a2'-22g2' show scanning electron microscope (SEM) schematic diagrams of the conductive forward osmosis membrane in the embodiments of this application under different algal water compositions under different applied voltages.

[0048] Figures 23a-23e show schematic diagrams illustrating the effect of different voltages on the performance of the conductive forward osmosis membrane in algal water with added Ca2+ in the application embodiments of this application.

[0049] Figures 24a-24e show the effect of different voltages on the performance of the conductive forward osmosis membrane in algae water containing HA.

[0050] Figures 25a-25e show schematic diagrams illustrating the effect of different voltages on the performance of the conductive forward osmosis membrane in algal water containing Kaolinite coexisting with the present application embodiment.

[0051] Figures 26a and 26b respectively show the membrane flux changes of the forward osmosis membrane CPFO and the stripped regenerated forward osmosis membrane CPFO-C in the embodiments of this application under long-term operation and the spectrum of the intermediate layer after stripping the CPFO membrane skin layer;

[0052] Figures 27a-27f are SEM images of the conductive forward osmosis membrane before and after stripping in the embodiments of this application. Detailed Implementation

[0053] To make the technical means, creative features, objectives and effects of this application easier to understand, the following description, in conjunction with specific illustrations and tables, further elaborates on this application.

[0054] In a first aspect, this application provides a conductive forward osmosis membrane, comprising a support layer, an intermediate layer, and a skin layer with filtration properties, wherein the support layer is composed of a conductive porous substrate, and the intermediate layer is a conductive intermediate layer composed of a conductive material.

[0055] Furthermore, the conductive porous substrate is conductive porous carbon paper or conductive carbon material, which is porous and conductive; preferably, it is conductive porous carbon paper.

[0056] Furthermore, the conductive intermediate layer is made of polypyrrole material; the skin layer is a polyamide layer.

[0057] Furthermore, the polypyrrole is deposited onto the conductive porous carbon paper by electrochemical deposition of a pyrrole-containing electrochemical polymer material.

[0058] Furthermore, the skin layer formed on the conductive intermediate layer has a smooth, ridge-like morphology; the sheet resistance of the forward osmosis membrane is 156.4 mΩ / sq to 300 mΩ / sq, preferably 156.4 mΩ / sq to 209.3 mΩ / sq.

[0059] Furthermore, the conductive forward osmosis membrane has an average water flux of 9.09–33.96 L / (m²h) and a salt return flux of 3.38–21.48 g / (m²h) in FO / PRO mode. More preferably, the average water flux is 9.09–22.09 L / (m²h) or 21.76–33.96 L / (m²h); the salt return flux is 3.38–11.40 g / (m²h) or 5.48–21.48 g / (m²h); and even more preferably, the average water flux is 21.09 / 33.96 L / (m²h) and the average salt return flux is 4.61 and 5.48 g / (m²h).

[0060] In a second aspect, this application provides a method for preparing a conductive forward osmosis membrane, as shown in Figure 1a, comprising the following steps:

[0061] a) Prepare a conductive intermediate layer on a conductive porous substrate to obtain a conductive base film;

[0062] b) An interfacial polymerization reaction is carried out on the conductive intermediate layer of the conductive base film to prepare a skin layer, thereby obtaining the conductive forward osmosis membrane.

[0063] Furthermore, the conductive porous substrate is conductive porous carbon paper; the conductive intermediate layer is polypyrrole.

[0064] Furthermore, the conductive intermediate layer is prepared by electrochemically depositing a pyrrole-containing electrochemical polymer on the surface of conductive porous carbon paper as a substrate.

[0065] Furthermore, prior to step a), the conductive porous substrate is pretreated.

[0066] Furthermore, the pretreatment of the conductive porous substrate is carried out in the following manner: obtaining a conductive porous substrate of appropriate size, immersing the conductive porous substrate of appropriate size in a petri dish, and then neutralizing the substrate.

[0067] Furthermore, the pretreatment of the conductive porous substrate is carried out in the following manner: the conductive porous substrate of appropriate size is immersed in a petri dish using a 0.2 mol / L sodium hydroxide (NaOH) solution for a period of time, and then immersed and rinsed with deionized water until neutral.

[0068] Furthermore, the electrochemical polymer is a mixture of pyrrole and sulfuric acid (H2SO4).

[0069] Furthermore, the method for preparing the skin layer is as follows: the conductive base film is immersed in an aqueous solution of a certain concentration of polyamine compound, and after complete immersion and maintenance for a certain period of time, the excess aqueous solution is removed to obtain a pretreated film; the pretreated film is subjected to surface treatment; an organic phase solution containing polyacrylamide compound is poured onto the pretreated film to carry out an interfacial polymerization reaction, and after a second specified time, the excess organic phase solution is removed to obtain a skin conductive forward osmosis membrane with a polyamide layer.

[0070] Further, the method for preparing the polyamide layer is as follows: 25 ml of an aqueous solution containing m-phenylenediamine (MPD) is slowly poured onto the base membrane and immersed in it for 180 seconds; then the excess aqueous solution is poured off, and the aqueous solution is gently rolled over the membrane surface with a rubber roller to uniformly disperse the aqueous solution on the membrane surface, thus obtaining the pretreated membrane; then 25 ml of an organic solution of trimesoyl chloride (TMC) is poured onto the pretreated membrane, and after reacting for 90 seconds, the excess organic solution is poured off, thus obtaining the nascent forward osmosis membrane; the prepared nascent forward osmosis membrane is air-dried for 60 seconds and then cured by baking for 300 seconds, resulting in a selectively permeable skin layer on the membrane surface.

[0071] Furthermore, the aqueous phase solution is prepared as follows: a m-phenylenediamine compound solution with a concentration of 1.0wt%-6.0wt% is prepared and dissolved in an opaque or semi-transparent container using water as a solvent; the organic phase solution is prepared as follows: a pyromellitic trimethylol chloride compound with a concentration of 0.05wt%-0.5wt% is dissolved in a container using n-hexane as a solvent.

[0072] Please also refer to Figure 1b. Regarding the conductive forward osmosis membranes and their preparation methods described in the first and second aspects above, an embodiment of this application provides a method for preparing the aforementioned conductive forward osmosis membrane using conductive porous carbon paper as a supporting substrate, specifically including:

[0073] S1: First, pre-treat the conductive porous carbon paper substrate;

[0074] S2: Electrochemically deposit a conductive intermediate layer on a conductive porous carbon paper substrate to obtain a conductive porous carbon paper base film (CP); further, deposit an electrochemical polymer on the conductive porous carbon paper to obtain the conductive intermediate layer; further, the conductive intermediate layer of the electrochemical polymer is a polypyrrole intermediate layer.

[0075] S3: The conductive porous carbon paper base film is placed on a flat plate with the conductive intermediate layer facing upward, and an interfacial polymerization reaction is carried out on the conductive intermediate layer on the base film to obtain a conductive forward osmosis membrane with selective permeability.

[0076] The preparation method of the conductive forward osmosis membrane provided in the embodiments of this application is further described in detail below:

[0077] In step S1: a conductive porous carbon paper substrate of a suitable size, such as 10×10cm, is cut to a suitable size, such as 5×10cm, using a utility knife. It is then soaked in a petri dish with a certain concentration of sodium hydroxide solution, such as 0.2mol / L NaOH solution, for a certain period of time, such as 2h, to enhance the bonding ability between the electrochemical polymer, such as polypyrrole interlayer, and the conductive porous carbon paper substrate. After soaking, it is then soaked and rinsed with deionized water until neutral.

[0078] In step S2: A conductive porous carbon paper-based membrane with a polypyrrole interlayer is prepared. This involves electrochemical polymerization of polypyrrole using a three-electrode system. First, an electrochemical polymerization solution, a mixture of pyrrole and H₂SO₄, is prepared. The two solutions are mixed in a reactor for polymerization. The reactor is placed in a magnetic stirrer, and the stirring speed and ambient temperature are set. The electrochemical polymerization mode is set to cyclic voltammetry, with a fixed voltage scan range, scan rate, and number of cycles. The CP membranes deposited with polypyrrole are named CP-n based on the number of cycles.

[0079] In step S3, the conductive forward osmosis membrane obtained by interfacial polymerization on the base membrane is a conductive forward osmosis membrane with a polyamide layer obtained by interfacial polymerization on the base membrane with the deposited intermediate layer, including the following steps:

[0080] S4: Immerse the base membrane in an aqueous solution containing a polyamine compound, and remove the excess aqueous solution from the base membrane after a first specified time to obtain a pretreated membrane;

[0081] S5: Perform surface treatment on the pretreated membrane;

[0082] S6: Pour the organic phase solution containing polyacrylamide compounds onto the pretreated membrane treated in step S5, carry out the interfacial polymerization reaction, and remove the excess organic phase solution after a second specified time to obtain a conductive forward osmosis membrane with a polyamide layer.

[0083] In step S3: the base film is placed flat on a smooth plate with the base film facing upwards. In this embodiment, the smooth plate is a smooth glass plate. It further includes a rubber ring of a custom size and a stainless steel frame. The rubber ring and the stainless steel frame are fixed on the glass plate. It further includes a mounting and fixing device and a leak-proof device.

[0084] This also includes the steps of preparing aqueous solutions and organic solutions separately.

[0085] Furthermore, the aqueous phase solution is a polyamine compound aqueous phase solution, and the organic phase solution is a polyacrylamide compound organic phase solution; in the embodiments of this application, the aqueous phase solution is a m-phenylenediamine aqueous phase solution, and the organic phase solution is a trimesoyl pyromellitic acid organic phase solution.

[0086] Furthermore, step S4 involves pouring an aqueous solution into the frame to soak the base membrane, removing the excess aqueous solution after a first specified time, and dismantling the fixing device and the leak-proof device to obtain a pretreated membrane with an aqueous solution of amine monomer on its surface.

[0087] Furthermore, step S5 involves using a collecting roller to roll over the surface of the pretreated membrane, thereby distributing the aqueous solution containing amine monomers evenly on the membrane surface and making the membrane smoother. In this embodiment, the collecting roller is made of rubber.

[0088] Furthermore, step S6 involves pouring an organic phase solution into the frame for reaction, and then pouring off the excess organic phase solution after a second specified time. Since the two phase solutions are immiscible, the amine monomers in the aqueous phase diffuse into the organic phase solution. The monomers in the two phase solutions can only contact and react at the interface between the two phases. In addition, the reaction rate between monomers is extremely fast, and a polyamide layer can be formed on the surface of the intermediate layer of the conductive porous base film in a very short time.

[0089] The process further includes the following step S7: After the prepared conductive forward osmosis membrane is naturally dried in the air, it is cured to obtain a conductive forward osmosis membrane with a polyamide layer after a third specified time.

[0090] S8: The conductive forward osmosis membrane with the polyamide layer is stored in deionized water until testing; further, it is stored in deionized water at a temperature of 4°C.

[0091] In a further embodiment, the process for preparing the aqueous solution is as follows: dissolve m-phenylenediamine in deionized water in an opaque container such as a brown container, and then sonicate for 10-50 minutes.

[0092] In a further embodiment, the process for preparing the organic phase solution is as follows: 1,3,5-benzenetricarboxylic chloride (TMC) is dissolved in n-hexane solvent, and then sonicated for 10-50 minutes. In a further embodiment of this application, 0.15 wt% 1,3,5-benzenetricarboxylic chloride (TMC) is dissolved in 50 ml of n-hexane solution and sonicated for 30 minutes to completely dissolve it.

[0093] In a further embodiment, the aqueous solution contains 1.0 wt% to 6.0 wt% of intermediate-phenylenediamine, more preferably 3 wt%; and the organic solution contains 0.05 wt% to 0.5 wt% of trimesoyl chloride, more preferably 0.15 wt%.

[0094] In a further embodiment, the first specified time is 3-7 minutes, more preferably 5 minutes; the second specified time is 1-6 minutes, more preferably 2 minutes; and the third specified time is 30-90 seconds, more preferably 60 seconds.

[0095] In the embodiments described in this application, including the accompanying drawings, the following terms are used as they appear: Conductive porous carbon paper membrane (CP) refers to a conductive porous carbon paper membrane electrochemically deposited on a conductive porous carbon paper substrate; conductive forward osmosis membrane is a conductive forward osmosis membrane prepared by interfacial polymerization on a conductive porous carbon paper membrane. Conductive forward osmosis membranes prepared by interfacial polymerization of conductive porous carbon paper membranes CP-0, CP-200, CP-400, CP-500, CP-600, and CP-700, based on the number of polypyrrole deposition cycles, are respectively named CPFO0 membrane, CPFO200 membrane, CPFO400 membrane, CPFO500 membrane, CPFO600 membrane, and CPFO700 membrane. Any corresponding descriptions of experiments, tests, and parameters in the embodiments described herein refer to the aforementioned substrate. The skin layer is a polyamide layer; draw concentration represents the draw solution concentration; water flux represents the water flux; and reverse salt flux represents the reverse salt flux.

[0096] In the embodiments of this application, the electrochemical polymer polypyrrole deposition concentration is 0.1 mol / L-0.2 mol / L, and the number of cycles is 200-700, particularly 200, 400, 500, 600, and 700 cycles; preferably, a further embodiment of this application has an electrochemical polymer polypyrrole deposition concentration of 0.15 mol / L and a number of cycles of 600.

[0097] Preferably, the preparation process of the polypyrrole interlayer in step S2 is as follows: 10.35 mL (0.1-0.2 mol / L) of pyrrole solution, 3.0 mL of ethylene glycol, 3.0 mL of oxalic acid, and 13.40 g of sodium dodecyl sulfate are fully dissolved in 500 mL of deionized water. Separately, 16.1 mL of concentrated sulfuric acid (98%) is measured using a graduated cylinder and completely dissolved in 500 mL of deionized water. Finally, the two solutions are mixed in a reactor, and polymerization is immediately carried out. The reactor is placed in a magnetic stirrer, and the stirring speed and ambient temperature are set. The electrochemical polymerization mode is set to cyclic voltammetry (CV), with a fixed voltage scan range, scan rate, and number of cycles. The CP films deposited with polypyrrole are named CP-n according to the number of cycles.

[0098] Preferably, the optimal pyrrole solution concentration is 0.15 mol / L.

[0099] Preferably, a three-electrode system is used in step S2. The working electrode is the treated conductive porous carbon paper film, the auxiliary electrodes are two titanium meshes with the same area as the conductive porous carbon paper film, the working electrode is placed between the two auxiliary electrodes as polypyrrole, and the reference electrode is a saturated calomel electrode (SCE).

[0100] Preferably, the distance between electrodes is 1.5 cm, the stirring speed is 50 RPM, and the reactor temperature is maintained at around 5°C; the system voltage scanning range is -0.2-0.9V, the scanning rate is 0.03-0.06V / S, and the number of cycles is set to 0, 200, 400, 500, 600, and 700 cycles, respectively.

[0101] Preferably, the process for preparing the aqueous solution is as follows: dissolve m-phenylenediamine in deionized water and then sonicate for 10-50 minutes; the process for preparing the organic solution is as follows: dissolve trimesoyl chloride in n-hexane solvent and then sonicate for 10-50 minutes.

[0102] Preferably, the mass percentage of intermediate-phenylenediamine (m-phenylenediamine) in the aqueous phase solution is 1.0 wt% to 6.0 wt%, and the mass percentage of pyromellitic acid chloride in the organic phase solution is 0.05 wt% to 0.5 wt%.

[0103] Preferably, the first specified time is 3-7 minutes, the second specified time is 1-6 minutes, and more preferably 2 minutes;

[0104] Furthermore, after obtaining the polyamide skin in step (c-3), the process further includes step (d): the prepared membrane is naturally dried in the air and then cured to obtain a conductive forward osmosis membrane with a polyamide layer after a third specified time.

[0105] Preferably, the third specified time is 30-90 seconds.

[0106] Figures 2a-2o show scanning electron microscope (SEM) images of conductive porous carbon paper-based films with different concentrations of electrochemical polymer polypyrrole at different deposition cycles (200, 400, 500, 600, 700). Figures 2a-2e show a polypyrrole deposition concentration of 0.1 mol / L, Figures 2f-2j show a concentration of 0.15 mol / L, and Figures 2k-2o show a concentration of 0.2 mol / L. The SEM images show that the lower polypyrrole concentration (0.1 mol / L) results in a conductive porous carbon paper-based film with larger pore sizes, while the higher concentration (0.2 mol / L) results in a conductive porous carbon paper-based film with smaller pore sizes. Figures 2f-2j show that the conductive porous carbon paper substrate film formed after the deposition of polypyrrole at a concentration of 0.15 mol / L has a relatively uniform pore size. Polypyrrole can effectively cover the macroporous structure on the bottom surface of the conductive porous carbon paper substrate and has a relatively smooth surface structure.

[0107] Table 1 shows the porosity and average pore size of conductive porous carbon paper-based films obtained under different deposition concentrations of electrochemical polymer polypyrrole (0.15 mol / L) in the CP-0, CP-200, CP-400, CP-500, CP-600, and CP-700 layers. CP-0, the original conductive porous carbon paper substrate, has high porosity and a large pore structure, with a porosity and average pore size of 41.1% and 280 μm, respectively. As the number of polypyrrole intermediate layer cycles increases, the porosity and average pore size of CP-200, CP-400, CP-500, CP-600, and CP-700 all decrease, reaching 30.4% and 0.93 μm, respectively. This is because the intermediate layer formed by the deposition and coverage of polypyrrole leads to a decrease in porosity and average pore size. The skin layer generated by the interfacial polymerization reaction on the base membrane containing the intermediate layer in the embodiments of this application floats on the surface of the conductive porous carbon paper base membrane, and will not penetrate into the base membrane or greatly reduce the penetration of the skin layer into the base membrane, thereby improving the performance of the forward osmosis membrane.

[0108] Table 1. Porosity and average pore size of the base film

[0109] The permeation performance of conductive porous carbon paper-based membranes obtained with different initial deposition concentrations is shown in Figure 3. The permeation performance of the conductive porous carbon paper-based membrane can be adjusted by changing the number of circulation cycles, so that it can achieve a filter with a nanoscale pore size.

[0110] Figure 4 shows the resistance of conductive porous carbon paper-based films obtained with different pyrrole deposition concentrations and different numbers of deposition cycles. As an important standard for evaluating conductivity, resistance is inversely proportional to the conductivity of a material. The figure shows that at a low initial concentration (0.1 mol / L), the resistance of the conductive porous carbon paper-based film gradually decreases with increasing number of cycles. This is because the macroporous structure of the original conductive porous carbon paper-based film is not conducive to electron transfer. The deposition of polypyrrole increases the specific surface area, reducing the ion insertion distance to the nanometer range, promoting charge transfer and reducing resistance. A deposition concentration of 0.15 mol / L shows an excellent trend of enhanced conductivity. Further in this embodiment, the preferred deposition concentration of polypyrrole on the conductive porous carbon paper-based film is 0.15 mol / L. At this concentration, the conductive porous carbon paper-based film exhibits excellent conductivity, and its scanning electron microscopy (SEM) image and permeability also show excellent performance. The contact angle of a substrate is an indicator used to characterize the hydrophilicity or hydrophobicity of a surface structure or coating. It represents the magnitude of the interaction force between solid and liquid molecules, that is, the surface tension of a water droplet covering the substrate surface or coating. Figure 5 shows a schematic diagram characterizing the hydrophilicity and hydrophobicity of conductive porous carbon paper films (CP-0, CP-200, CP-400, CP-500, CP-600, CP-700 conductive porous carbon paper films) obtained with different deposition layers corresponding to a polypyrrole concentration of 0.15 mol / L. The figure shows that the substrate becomes increasingly hydrophilic as the polypyrrole interlayer is deposited. This is because the polypyrrole chains contain a large number of nitrogen atoms, and the addition of sodium dodecylbenzenesulfonate (SDBS) dopant during deposition further enhances the hydrophilicity by increasing the -SO3 groups. A more hydrophilic substrate makes it easier to form a more cross-linked and complete polyamide layer.

[0111] Zeta potential reflects the positive and negative charge and quantity of the solid film surface. Figure 6 shows the Zeta potential of conductive porous carbon paper films (CP-0, CP-200, CP-400, CP-500, CP-600, CP-700 conductive porous carbon paper films) obtained with different deposition layers corresponding to a polypyrrole concentration of 0.15 mol / L. It can be seen that the CP-0 film exhibits a stable positive charge characteristic. With the deposition of the polypyrrole intermediate layer, the conductive porous carbon paper film surface exhibits a negative charge characteristic. At the same time, the introduction of the dopant sodium dodecylbenzenesulfonate (SDBS) increases the -SO3 content, which further strengthens the negative charge of the film surface.

[0112] The surface roughness of the base film not only plays a crucial role in the surface structure composition but also significantly influences the formation of the polyamide layer during interfacial polymerization, thereby affecting the separation and permeation performance of the composite membrane. Figures 7a-7f show atomic force microscopy images of conductive porous carbon paper base films (CP-0, CP-200, CP-400, CP-500, CP-600, and CP-700 conductive porous carbon paper base films) obtained with different deposition layers corresponding to a polypyrrole concentration of 0.15 mol / L. Table 2 shows the specific parameters of the surface roughness of these base films. It can be seen that as the number of polypyrrole deposition layers increases, the roughness of the base film first decreases and then increases. This is because the uniform deposition of polypyrrole covers the rough macropores of the conductive porous carbon paper base film, reducing the pore size fluctuation and thus lowering the roughness.

[0113] Table 2. Roughness parameters of the base film surface

[0114] Ra represents the average surface roughness, and Rq represents the root mean square roughness.

[0115] Figures 8a1-9c6 show the surface and cross-sectional schematic diagrams of the conductive forward osmosis membranes formed on a pure CP base membrane, comparing the results with those obtained in different embodiments of this application after adding intermediate layers of polypyrrole with different concentrations; Figures 8a1-8a6 and 9b1-9b6 show the surface images of the conductive forward osmosis membranes CPFO0, CPFO200, CPFO400, CPFO500, CPFO600, and CPFO700 formed on base membranes with different concentrations and deposition rings of polypyrrole after deposition; Figures 8a1-8a6 show the surface images of the conductive forward osmosis membranes formed on base membranes with different deposition rings and a polypyrrole deposition concentration of 0.1 mol / L; Figures 9b1-9b6 show the surface images of the conductive forward osmosis membranes formed on base membranes with different deposition rings and a polypyrrole deposition concentration of 0.15 mol / L. As shown in the figure, the polyamide layer formed on the CP-0 base membrane without a deposited polypyrrole interlayer exhibits a smooth morphology rather than a ridge-like structure due to the macropores and hydrophobic properties of the conductive porous carbon paper base membrane. This is mainly because the macropores and hydrophobic properties of the conductive porous carbon paper base membrane slow down the diffusion rate of the m-phenylenediamine aqueous phase stored in the membrane pores, and the amount of amine monomers adsorbed on the base membrane surface is limited. After the deposition of the polypyrrole interlayer, a continuous, defect-free polyamide layer with a distinct ridge-like structure is formed on the conductive porous carbon paper base membrane, exhibiting increasingly larger leaf-like structures. This is partly because the successful deposition of polypyrrole reduces the macropores of the base membrane, compensating for the macropore defects and making the surface morphology of the base membrane more flat and uniform, resulting in a perfect, defect-free polyamide layer. On the other hand, the deposition of the polypyrrole interlayer changes the surface physicochemical properties of the base membrane—the increased hydrophilicity of the substrate allows for the adsorption of more amine monomers, which is beneficial for interfacial polymerization reactions, resulting in a more pronounced ridge-like structure. Figures 9c1-9c6 show the cross-sectional morphology of the conductive forward osmosis membrane provided in this application. Figure 9c1 shows that without the deposited polypyrrole interlayer, the formed polyamide layer is discontinuous and exhibits a collapsed morphology. Figures 9c2-9c6 show that after depositing polypyrrole on the conductive porous carbon paper substrate, continuous polyamide layers are formed on CPFO200, CPFO400, CPFO500, CPFO600, and CPFO700 membranes, with the thickness increasing from 260 nm to 560 nm. This is because the increased hydrophilicity of the deposited polypyrrole interlayer with increasing deposition time gives m-phenylenediamine a stronger adsorption force on the substrate, thereby increasing the availability of m-phenylenediamine during interfacial polymerization and forming a thicker polyamide layer. On the other hand, the gradual decrease in the roughness and pore size of the substrate membrane as the interlayer is deposited allows for a more continuous and uniform distribution of m-phenylenediamine on the substrate, resulting in an increased polyamide layer thickness.

[0116] Figures 10a-10f show atomic force microscopy images of conductive forward osmosis membranes CPFO0, CPFO200, CPFO400, CPFO500, CPFO600 and CPFO700 formed on a base film with different deposition cycles at a polypyrrole deposition concentration of 0.15 mol / L. In this embodiment, atomic force microscopy was used to measure the roughness of the prepared polypyrrole conductive forward osmosis membranes with the same deposition time. As shown in the figure and Table 3, the average surface roughness Ra (nm) of CPFO0, CPFO200, CPFO400, CPFO500, CPFO600, and CPFO700 membranes are 380.6±16.8, 257.4±10.4, 209.5±11.3, 171.4±6.9, 107.8±7.4, and 164.8±6.5 nm, respectively, and the root mean square roughness Rq (nm) are 452.4±26.7, 354.8±24.6, 269.9±20.3, 269.0±16.2, 134.0±19.0, and 205.8±20.3 nm, respectively. The roughness of the conductive forward osmosis membrane shows a trend of first decreasing and then increasing. Because the deposited polypyrrole cannot completely cover the rough carbon fiber surface of the conductive porous carbon paper-based film, the CPFO0 film has the highest surface roughness. In contrast, the surface roughness of the CPFO200, CPFO400, CPFO500, CPFO600, and CPFO700 films deposited with different layers of conductive polypyrrole in this application is significantly lower than that of CPFO0. The surface roughness of the films formed by different layers varies. With the deposition of the polypyrrole interlayer, the rough carbon fiber surface is completely covered. The roughness of the CPFO600 and CPFO700 films shows an increasing trend because the formed polypyrrole interlayer has high hydrophilicity, which is sufficient to enhance the reactivity of m-phenylenediamine and trimesoyl chloride, thus increasing the roughness.

[0117] Table 3. Surface roughness of conductive forward osmosis membrane

[0118] Ra represents the average surface roughness, and Rq represents the root mean square roughness.

[0119] Figure 11 shows the contact angle of the forward osmosis membranes formed on a pure conductive porous carbon paper substrate, compared with the forward osmosis membranes obtained in different embodiments of this application after adding polypyrrole interlayers of the same concentration but different number of cycles. It can be seen that the forward osmosis membranes prepared on the base membrane exhibit increasingly hydrophilic properties as the deposited polypyrrole interlayer is deposited. This is because the strong hydrophilicity of the deposited polypyrrole interlayer adsorbs more m-phenylenediamine and reacts with trimesoyl chloride to generate more polyamide layers. The polyamide layers contain hydrophilic amino groups, thus the conductive forward osmosis membrane also exhibits an enhanced hydrophilicity effect.

[0120] X-ray spectroscopy was used to analyze the comparative forward osmosis membrane formed on a pure conductive porous carbon paper substrate and the forward osmosis membranes obtained in different embodiments of this application after adding a polypyrrole interlayer with the same concentration but different number of cycles deposited (Figure 12). Table 4 shows the composition and ratio of each element on the surface of the prepared conductive forward osmosis membrane. Combining Figure 12 and Table 4, it can be seen that oxygen atom peak O1s, nitrogen atom peak N1s, and carbon atom peak C1s were found in the conductive forward osmosis membranes prepared under different conditions, which proves that a polyamide layer was successfully formed on the base membrane. The degree of crosslinking of the polyamide layer formed on the base membrane without the deposition of the polypyrrole interlayer was 46.24%. At this time, the polyamide layer structure was loose, the degree of crosslinking with the substrate was very low, and it had poor selectivity. The increase in N1s content with the increase of polypyrrole deposition time also indicates the increase of the degree of crosslinking of the polyamide layer to a certain extent. The experimental results of this application's embodiments show that this is closely related to the deposited polypyrrole intermediate layer. The increase in the amount of polypyrrole deposition causes the substrate to aggregate and adsorb more aqueous-amine monomers. The results indicate that the high hydrophilicity of the substrate provides a concave liquid surface and continuous small surface pore size, which provides a larger reaction area for interfacial polymerization, thereby forming a continuous and highly selective active layer and producing a higher degree of local crosslinking.

[0121] Table 4. Percentage of different elements and degree of crosslinking in conductive forward osmosis membranes

[0122] Electrochemical characterization is a fundamental and important indicator of the conductivity of conductive composite membranes. This includes scanning the cyclic voltammetry (CVT) curves of the conductive composite membrane (Figure 13) and electrochemical impedance spectroscopy (EIS) testing (Figure 14). The figures show that the original base membrane exhibits very stable current across a scanning voltage range of -2V to +2V, with a narrow and thin shape, and almost no redox tendency within this range, demonstrating excellent redox stability. The CVT curve of the conductive forward osmosis membrane with a deposited polypyrrole interlayer shows a higher current density than the CPFO0 membrane in the -2V to +2V range, and this current density increases with the number of deposition cycles. This is because the electron transfer rate in the conductive membrane is very high after polypyrrole deposition, and the polypyrrole can tightly wrap the carbon fibers to form a bridging effect. This result is consistent with the electrochemical impedance spectroscopy test results, which show that the impedance of the conductive forward osmosis membrane gradually decreases with the number of deposition cycles, further confirming the excellent conductivity of the conductive forward osmosis membrane.

[0123] The performance of the conductive forward osmosis membrane of this application was tested below. Figure 15 shows the conductive cross-flow FO device used in this application to test the permeation selectivity of the forward osmosis membrane. No voltage was applied during the test. The effective membrane area of ​​the conductive forward osmosis membrane 100 in the membrane tank was 15 cm². Deionized water was placed on the stirring device 200 as the feed solution, and sodium chloride solution was placed on the balance 300 as the draw solution. Two peristaltic pumps 400 and 500 were used to circulate the feed solution and draw solution, respectively. During operation, the temperature of the feed solution and draw solution was controlled at 25°C, and the speed of the peristaltic pumps was 9.8 cm / s.

[0124] Figures 16a and 16b show the performance of forward osmosis membranes formed on pure conductive porous carbon paper substrates in FO mode and PRO mode, respectively, in different embodiments of this application after adding interlayers of polypyrrole with the same concentration but different number of cycles. The figures show that the forward osmosis membrane prepared using the original conductive porous carbon paper substrate has poor forward osmosis performance. The conductive forward osmosis membrane after depositing the polypyrrole interlayer exhibits excellent forward osmosis performance. The forward osmosis performance of the conductive forward osmosis membrane reaches its optimal level when the number of deposition cycles is 600, with water flux of 21.09 / 33.96 L / (m²h) and salt return flux of 4.61 / 5.48 g / (m²h) in FO / PRO modes, respectively. When the number of polypyrrole deposition cycles is 700, the flux is 9.9 / 21.7 L / (m²h) and the salt return is 7.71 / 3.38 g / (m²h). This is because: the higher hydrophilicity of the polyamide layer provides a larger pathway for water passage, resulting in higher water flux. Increased hydrophilicity also strengthens the adsorption of amine monomers onto the base membrane, allowing it to store more amine monomers for interfacial polymerization to generate more amide bonds, thus improving the degree of crosslinking. A higher degree of crosslinking means more amide bonds are formed in the polyamide layer, making it denser and resulting in lower salt return flux. The improved performance is partly due to the deposition of the polypyrrole interlayer, which fills the rough surface of the carbon fibers, improving the hydrophobic interfacial properties, compensating for macropore defects, and reducing porosity. The reduced roughness of the interlayer allows the m-phenylenediamine aqueous solution to uniformly cover the interlayer during interfacial polymerization, making the resulting polyamide layer more continuous and less prone to detachment. The improvement in macropore defects prevents the collapse of the polyamide layer, and the small pore size structure enables the formation of a continuous, defect-free polyamide layer with a distinct leaf-like structure. A forward osmosis membrane with its active layer (polyamide) facing the feed solution and its porous support layer (base membrane) facing the draw solution is referred to as the AL-FS mode (also known as the FO mode). A forward osmosis membrane with its active layer (polyamide layer) facing the draw solution and its porous support layer (base membrane) facing the feed solution is referred to as the AL-DS mode (also known as the PRO mode).

[0125] Figures 17a and 17b show the pure water flux (A) and salt permeability coefficient (B) of forward osmosis membranes formed on pure conductive porous carbon paper substrates, comparing the results in different embodiments of this application after adding polypyrrole interlayers of the same concentration but different cycle numbers. The figures show that the pure water flux (A) and salt permeability coefficient (B) of CPFO200, CPFO400, CPFO500, CPFO600, and CPFO700 membranes initially decrease and then increase. As the polypyrrole interlayer is deposited on the CP membrane, the polyamide layer structure becomes more complete and the cross-linking degree is higher. The increased cross-linking degree of the polyamide layer has a positive impact on the retention rate. This is because a high degree of cross-linking means that the formed polyamide layer has more amide bonds, resulting in a higher retention rate and salt permeability coefficient. As can be seen from the above, the conductive forward osmosis membrane with a polypyrrole interlayer has better forward osmosis filtration performance.

[0126] Figures 18a and 18b show schematic diagrams of water flux (18a) and reverse salt flux (18b) of a membrane with a polypyrrole deposition concentration of 600 circulation cycles under different draw solution concentrations. In both operating modes of the forward osmosis membrane, the water flux increases with increasing NaCl draw solution concentration. Simultaneously, the reverse salt flux also increases. This is mainly because for the same salt solution, a higher salt concentration leads to a higher osmotic pressure, which in turn increases the flux. A higher draw solution concentration gradient allows more salt to permeate into the feed solution, resulting in an increase in reverse salt flux. In the figures, draw concentration represents draw solution concentration, water flux represents water flux, and reverse salt flux represents reverse salt flux.

[0127] In this embodiment, a conductive composite forward osmosis membrane is prepared by depositing a conductive polymer, such as a polypyrrole interlayer, on a hydrophobic, macroporous porous conductive substrate and then performing an interfacial polymerization reaction. The conductive porous substrate membrane has excellent conductivity, a smooth surface structure, and nanoscale filter performance, providing a good foundation for the preparation of a perfect skin layer.

[0128] In this embodiment, the deposition concentration of the polypyrrole interlayer is preferably 0.1-0.2 mol / L, more preferably 0.15 mol / L. At this concentration, the polypyrrole interlayer exhibits excellent conductivity (minimum sheet resistance of 156.4 mΩ / sq), a smooth surface structure, and nanoscale filter performance. When using pyrrole with an initial concentration of 0.15 mol / L, the deposition cycle number is preferably 600. The prepared CPFO600 membrane exhibits excellent performance, with water flux and salt return of 33.96 / 21.09 L / (m2h) and 5.48 / 4.61 g / (m2h) respectively in FO / PRO operation mode. It also has excellent electrochemical reactivity and minimal impedance.

[0129] When a conductive intermediate layer is deposited using pyrrole at an initial concentration of 0.15 mol / L, the thickness and integrity of the skin layer gradually increase with the increase of the number of deposition layers, while the degree of crosslinking shows a trend of first increasing and then decreasing.

[0130] The conductive forward osmosis membrane of this application has good conductivity, strong filtration and fouling resistance, and strong stability.

[0131] In this application, the conductive porous substrate may also be one of conductive carbon fiber or conductive paper.

[0132] In this application, the conductive material of the conductive intermediate layer can also be a negatively charged, hydrophilic conductive material such as polyaniline.

[0133] The polyamide layer forms a smooth morphology on the original conductive porous substrate, but not a spine-like morphology. After the deposition of the intermediate layer, the defects of the rough macropores in the conductive porous carbon paper-based membrane are compensated for. A series of physicochemical properties, such as the hydrophilicity, roughness, pore size, and electrochemical characteristics of the membrane surface, are altered, forming a completely new substrate morphology that affects the morphology and performance of the polyamide layer. High hydrophilicity, reasonable small pore size, and uniform roughness provide greater reactivity and contact area for the interfacial polymerization reaction, resulting in higher crosslinking degree and excellent forward osmosis performance.

[0134] The present application will be further described in detail below through specific embodiments.

[0135] Example 1

[0136] A conductive forward osmosis membrane is prepared according to the following steps:

[0137] (1) Cut the purchased 10×10cm conductive porous carbon paper substrate to a size of 5×10cm, and soak it in a petri dish with 0.2mol / L NaOH solution for 2h to enhance the bonding ability between the polypyrrole intermediate layer and the CP film. After soaking, rinse it with deionized water until neutral.

[0138] (2) Dissolve 10.35 mL (0.15 mol / L) of pyrrole solution, 3.0 mL of ethylene glycol, 3.0 mL of oxalic acid, and 13.40 g of sodium dodecylbenzenesulfonate in 500 mL of deionized water. Separately, measure 16.1 mL of concentrated sulfuric acid (98%) using a graduated cylinder and dissolve it completely in 500 mL of deionized water. Finally, mix the two solutions in the reactor and immediately proceed with polymerization using a three-electrode system. The working electrode is a pretreated conductive porous carbon paper-based membrane, and the auxiliary electrodes are two titanium meshes with the same area as the CP membrane. The working electrode is placed between the two auxiliary electrodes, and the reference electrode is a saturated calomel electrode (SCE). The distance between them is 1.5 cm. All four electrodes are completely immersed in the electrochemical polymerization solution. The reactor is placed in a stainless steel basin on a magnetic stirrer at a stirring speed of 50 RPM. Ice packs are placed around the reactor to maintain the temperature at around 5°C. The electrochemical polymerization was performed using cyclic voltammetry (CV), with a voltage scan range of -0.2V to 0.9V, a scan rate of 0.05V / s, and a cycle count of 200.

[0139] (3) Dissolve m-phenylenediamine (MPD) in 3.0 wt% of deionized water in a 50 ml brown bottle and sonicate for 30 min to obtain an aqueous m-phenylenediamine solution; dissolve pyromellitic chloride (1,3,5-phenyltricarboxylic chloride (TMC)) in 0.15 wt% of n-hexane solvent in 50 ml and sonicate for 30 min to completely dissolve it to obtain an organic pyromellitic chloride solution.

[0140] (4) The modified conductive porous carbon paper base film is placed flat on a clean glass plate and fixed and leak-proof using a stainless steel frame and rubber ring; the conductive porous carbon paper base film after deposition of the intermediate layer is placed on the glass plate with the top facing up.

[0141] (5) Pour 50 ml of the prepared m-phenylenediamine aqueous solution into the frame to soak the conductive porous carbon paper base membrane for 5 minutes, then pour off the excess aqueous solution and remove the stainless steel plate frame and rubber ring to obtain the pretreated membrane.

[0142] (6) Roll the pretreated membrane surface with a rubber roller.

[0143] (7) Pour 50 ml of the prepared pyromellitic chloride organic phase solution into the frame and react for 2 minutes. Then pour off the excess organic solution to obtain a preliminary forward osmosis membrane with an interfacial polymerization reaction skin.

[0144] (8) After the obtained preliminary forward osmosis membrane is air-dried in the air for 60 seconds, it is placed in an oven to cure for 5 minutes to obtain a conductive forward osmosis membrane with a selective permeable polyamide layer.

[0145] (9) The prepared conductive forward osmosis membrane with polyamide layer was stored in deionized water at 4°C until testing.

[0146] The pore diameters of the base membrane in the forward osmosis membrane prepared in the above embodiments are shown in Figure 2f and Table 1, with the average pore diameter mostly distributed at 110 μm. As shown in Figures 16a and 16b and Table 4, deionized water was used as the feed solution, and NaCl aqueous solution was used as the draw solution. The cross-flow rate and temperature of the feed solution and draw solution were controlled at 9.8 cm / s and 25 °C, respectively. The cross-linking degree of the forward osmosis membrane prepared in the above embodiments was tested to be 65.53%, the water contact angle was approximately 67°, the water flux was 83.4 L / m²h, the reverse salt flux was 82.7 g / m²h, the water permeability coefficient A was 5.51 L / m²h / bar, the salt permeability coefficient B was 2.82 L / m²h, and the salt rejection rate was 68%.

[0147] The resulting forward osmosis membrane is referred to as CPFO200 membrane.

[0148] Example 2

[0149] The difference between Example 2 and Example 1 is that the number of cycles during the polymerization of polypyrrole when depositing polypyrrole on a conductive porous carbon paper substrate was set to 400 cycles, while other conditions were the same as in Example 1. The resulting forward osmosis membrane is designated as CPFO400 membrane.

[0150] The pore diameters of the base membrane in the forward osmosis membrane prepared in the above embodiments are shown in Figure 2g and Table 1, with the average pore diameter mostly distributed at 50.6 μm. As shown in Figures 16a and 16b and Table 4, deionized water was used as the feed solution, and NaCl aqueous solution was used as the draw solution. The cross-flow rate and temperature of the feed solution and draw solution were controlled at 9.8 cm / s and 25 °C, respectively. The cross-linking degree of the forward osmosis membrane prepared in the above embodiments was tested to be 76.05%, the water contact angle was approximately 63°, the water flux was 64.7 L / m²h, the reverse salt flux was 58.2 g / m²h, the water permeability coefficient A was 4.1 L / m²h / bar, the salt permeability coefficient B was 1.9 L / m²h, and the salt rejection rate was 82.56%.

[0151] Example 3

[0152] The difference between Example 3 and Example 1 is that the number of cycles during the polymerization of polypyrrole when depositing polypyrrole on a conductive porous carbon paper substrate was set to 500, while other conditions were the same as in Example 1. The resulting forward osmosis membrane is designated as a CPFO500 membrane.

[0153] The pore diameters of the base membrane in the forward osmosis membrane prepared in the above embodiments are shown in Figure 2h and Table 1, with the average pore diameter mostly distributed at 14.97 μm. As shown in Figures 16a and 16b and Table 4, deionized water was used as the feed solution, and NaCl aqueous solution was used as the draw solution. The cross-flow rate and temperature of the feed solution and draw solution were controlled at 9.8 cm / s and 25 °C, respectively. The cross-linking degree of the forward osmosis membrane prepared in the above embodiments was tested to be 80.60%, the water contact angle was approximately 58°, the water flux was 14.21 L / m²h, the reverse salt flux was 12.07 g / m²h, the water permeability coefficient A was 2.74 L / m²h / bar, the salt permeability coefficient B was 0.81 L / m²h, and the salt rejection rate was 88.09%.

[0154] Example 4

[0155] The difference between Example 4 and Example 1 is that the number of cycles during the polymerization of polypyrrole when depositing polypyrrole on the conductive porous carbon paper substrate was set to 600, while other conditions were the same as in Example 1. The resulting forward osmosis membrane is designated as CPFO600 membrane.

[0156] The pore diameters of the base membrane in the forward osmosis membrane prepared in the above embodiments are shown in Figure 2i and Table 1, with the average pore diameter mostly distributed at 1.08 μm. As shown in Figures 16a and 16b and Table 4, deionized water was used as the feed solution, and NaCl aqueous solution was used as the draw solution. The cross-flow rate and temperature of the feed solution and draw solution were controlled at 9.8 cm / s and 25 °C, respectively. The cross-linking degree of the forward osmosis membrane prepared in the above embodiments was tested to be 85.26%, the water contact angle was approximately 52°, the water flux was 21.09 L / m²h, the reverse salt flux was 4.61 g / m²h, the water permeability coefficient A was 2.85 L / m²h / bar, the salt permeability coefficient B was 0.26 L / m²h, and the salt rejection rate was 98.61%.

[0157] Example 5

[0158] The difference between Example 5 and Example 1 is that the number of cycles during the polymerization of polypyrrole when depositing polypyrrole on the conductive porous carbon paper substrate was set to 700, while other conditions were the same as in Example 1. The resulting forward osmosis membrane is designated as CPFO700 membrane.

[0159] The pore diameters of the base membrane in the forward osmosis membrane prepared in the above embodiments are shown in Figure 2j and Table 1, with the average pore diameter mostly distributed at 0.93 μm. As shown in Figures 16a and 16b and Table 4, deionized water was used as the feed solution, and NaCl aqueous solution was used as the draw solution. The cross-flow rate and temperature of the feed solution and draw solution were controlled at 9.8 cm / s and 25 °C, respectively. The cross-linking degree of the forward osmosis membrane prepared in the above embodiments was tested to be 85.48%, the water contact angle was approximately 46°, the water flux was 9.9 L / m²h, the reverse salt flux was 7.71 g / m²h, the water permeability coefficient A was 2.23 L / m²h / bar, the salt permeability coefficient B was 0.31 L / m²h, and the salt rejection rate was 97.53%.

[0160] This application utilizes electrochemical deposition of a polypyrrole interlayer to control the pore size and hydrophilicity / hydrophobicity of a conductive porous carbon paper-based membrane. Following interfacial polymerization (IP), a non-collapsed and continuous polyamide layer is formed, thus preparing a conductive forward osmosis membrane. Its algae-water separation performance is then tested. The conductive forward osmosis membrane was characterized and analyzed using scanning electron microscopy, solid-state surface zeta potential analysis, and X-ray photoelectron spectroscopy. The conductive forward osmosis membrane provided in this application has the following main properties and structure: a skin layer thickness of 260 nm-560 nm; a crosslinking degree of 46.24%-85.48%; a water contact angle of 46°-74°, with the base membrane portion having a water contact angle of 29°-88°; a zeta potential of -25 mV-5 mV; in FO mode, the conductive forward osmosis membrane achieves a maximum water flux of 92 L / m²h and a minimum reverse salt flux of 4.61 g / m²h; in PRO mode, the conductive forward osmosis membrane achieves a maximum water flux of 135.08 L / m²h and a minimum reverse salt flux of 0.58 g / m²h; and a salt rejection rate of 97%-98.6%. The results indicate that a polypyrrole interlayer with an optimal concentration and suitable number of cycles can effectively control the conductive porous carbon paper base membrane and prepare a conductive forward osmosis membrane with excellent separation performance.

[0161] Application Example 1:

[0162] On the other hand, this application provides an application of a conductive forward osmosis membrane. This conductive forward osmosis membrane can be used to treat algal solutions and algal water, as well as other wastewater. The following is a description of the application of the conductive forward osmosis membrane in this application. Membrane fouling has always been a difficult challenge to completely solve in the application of forward osmosis membrane technology. Other researchers have conducted many studies on anti-fouling, such as modifying the surface charge of the PA layer, modifying the support layer of the composite membrane, and pretreating pollutants. However, these methods are relatively complex in preparation and introduce new sources of pollution. This application proposes to separate algal solutions using a conductive composite forward osmosis membrane with an applied voltage. The following describes the application implementation of the forward osmosis algal solution treatment method and system in this application by selecting the PRO mode with relatively high membrane flux for algal solution separation, and the effects of electric field strength, individual / mixed algal water components, coexisting substances in the water on membrane fouling, and the removal efficiency of undesirable metabolites (MC-LR, GSM, 2-MIB) in algal-containing water. The stability of the conductive composite FO membrane during long-term, multi-cycle operation is also explained.

[0163] The conductive forward osmosis membrane provided in this application is used in a forward osmosis method and system for treating algae-water separation. The system includes a conductive forward osmosis membrane, and a negative voltage is applied during the treatment process or system. Further, the conductive forward osmosis membrane is the forward osmosis membrane provided in this application, and the negative voltage is -4.0V to 0V (excluding 0V), further specifically -0.5V, -1.0V, -1.5V, -2.0V, -2.5V, -3.0V, or -4.0V.

[0164] Figures 19a and 19b illustrate the changes in membrane flux of the conductive forward osmosis membrane in the application embodiments of this application under different applied voltages. Figure 19a shows the applied negative voltage, and Figure 19b shows the applied positive voltage. As can be seen from Figure 19a, without an external electric field, the flux decreased by 64% after 8 hours of continuous treatment of algae-containing water. This is mainly because during the algae-containing water treatment process, a large number of algal cells and extracellular polymers deposited and adhered to the surface of the conductive forward osmosis membrane and entered the membrane pores, thus clogging the surface pores and causing severe membrane fouling, leading to a decrease in flux. When a negative voltage was applied to the conductive forward osmosis membrane, the membrane flux for treating algae-containing water decreased by 56%, 46%, and 34% respectively as the magnitude of the applied negative voltage increased. Applying a -2V voltage increased the membrane flux by 34% compared to no voltage applied, because the applied negative voltage caused electrostatic repulsion with the negatively charged pollutants in the algae water, alleviating the process of pollutant adhesion to the conductive forward osmosis membrane surface, thereby reducing membrane fouling during the algae-containing water treatment process.

[0165] Figure 19b shows a schematic diagram of membrane flux when a positive voltage is applied to the conductive forward osmosis membrane. The figure shows that applying a positive voltage to the CPFO membrane alleviates the declining trend in membrane flux for treating algae-containing water. When +1.0V, +1.5V, and +2.0V voltages are applied to the composite membrane, the membrane flux for treating algae-containing water decreases by 64%, 72%, and 80%, respectively. In comparison, the flux decreases by 16% when +2.0V is applied compared to when there is no voltage. This is because algal cells and extracellular organic matter in the algae-containing water carry a large number of negative charges. When a positive voltage is applied to the membrane, electrostatic attraction occurs, causing more pollutants to adhere to the membrane surface, forming a thicker filter cake layer. This results in more severe membrane fouling when a positive voltage is applied compared to when there is no voltage.

[0166] Figures 20a-20g show schematic diagrams of the filter cake layer thickness of the conductive forward osmosis membrane cross-section in this embodiment of the application under different applied voltages. The voltages applied in the figures are 0V, -1.0V, -1.5V, -2.0V, +1.0V, +1.5V, and +2V, respectively. As can be seen from the figures, when a negative voltage is applied, the filter cake layer thickness gradually decreases from 12.56 μm when no voltage is applied to 5.71 μm when a -2V voltage is applied. This indicates that applying a negative voltage generates electrostatic repulsion of pollutants, mitigating membrane fouling during the treatment of algae-containing water. However, after applying a positive voltage, the filter cake layer thickness gradually increases with increasing applied voltage. This is because applying a positive voltage generates electrostatic attraction of pollutants, causing more pollutants to adhere to the membrane surface, thus exacerbating membrane fouling during the treatment of algae-containing water.

[0167] Figures 21a-21d illustrate the effects of different voltages on the performance of the conductive forward osmosis membrane in the application embodiments of this application under single and mixed algal water components. Figures 21a and 21b show flux changes, 21c shows flux recovery rate, and 21d shows membrane resistance. In Figure 21a, with only algal water components, the flux of intracellular organic matter (IOM) is reduced more than that of extracellular organic matter (EOM) when no voltage is applied. The final specific fluxes after 8 hours of operation for intracellular and extracellular organic matter are 0.31 and 0.36, respectively. This is related to the composition of the two substances. Because intracellular organic matter carries less negative potential than extracellular organic matter, and at the same soluble organic carbon (DOC) concentration, intracellular organic matter contains more small molecules and particles, it is more likely to adhere to the membrane surface and clog the pores, resulting in a more severe flux reduction. After applying an electric field of -2V, the flux decline is slowed down due to the inherent charge of both extracellular and intracellular organic matter. After 8 hours of operation, the final specific fluxes of live and dead algal cells were 0.17 and 0.13, respectively. This is because the zeta potential of the dead algal cell solution is lower than that of the live algal cell solution, making it easier for dead algal cells to aggregate and precipitate in the solution and adhere to the composite membrane surface. Another reason is that the broken cell structure of dead algal cells has a smaller molecular structure, making it easier to enter the membrane pores and cause pore blockage, resulting in more severe membrane fouling. The reason why the flux decline of live and dead algal cells is faster than that of extracellular and intracellular organic matter is that under long-term operating conditions, algal cells are compressible. The pressure on the filter cake layer formed by algal cells gradually increases, thus compressing the filter cake layer and reducing its porosity, resulting in rapid flux decline. When a voltage of -2V was applied, the flux of live and dead algal cells increased by 42% and 34%, respectively, compared to when no voltage was applied. This is because the large amount of negative charge carried by the live and dead algal cells caused electrostatic repulsion with the applied negative voltage, slowing down the adhesion of algal cells to the positive osmosis membrane and reducing the accumulation of pollutants on the membrane surface, thus alleviating the decline in membrane flux. The flux decline of extracellular and intracellular organic matter did not improve significantly after applying voltage because their inherently low negative potential mitigated the electrostatic repulsion effect (flux increases of 6% and 4%, respectively, compared to when voltage was applied).

[0168] As shown in Figure 21b, which illustrates the flux changes of the mixed algal water components, without the application of voltage, the flux of the live algal cell + extracellular organic matter mixture decreased the fastest among the three mixed algal water components, ultimately reaching a specific flux of 0.08. This is because of the synergistic effect between live algal cells and extracellular organic matter; the compressible, thick filter cake layer formed by algal cells, combined with the extracellular organic matter filling the gaps between algal cells, creates severe compound pollution. In the presence of dead algal cells, the filter cake layer formed by the incompressibility of broken algal cells is thinner than that formed by live algal cells. Although the same amount of organic matter fills the gaps in the filter cake layer, the final specific flux is slightly higher than that of the live algal cell + extracellular organic matter mixture. When an electric field of -2V is applied, it can be seen from the figure that compared with no voltage applied, the flux attenuation of the three mixed algal water components (live algal cells + extracellular organic matter, dead algal cells + extracellular organic matter + intracellular organic matter, and dead algal cells + intracellular organic matter) is alleviated, increasing by 37%, 27%, and 29%, respectively. This is because the live algal cells + extracellular organic matter have the most negative charge and therefore have a stronger electrostatic repulsion to reduce the adhesion of pollutants. Therefore, when a negative voltage is applied, it shows a higher membrane flux mitigation effect than the other two mixed components.

[0169] Figures 21c and 21d illustrate flux recovery rate and membrane resistance, respectively. The figures show an increase in flux recovery rate and a decrease in reversible and irreversible resistance after voltage application. The flux recovery rates after hydraulic washing for membranes fouled by extracellular and intracellular organic matter are 89.5% and 86.2%, respectively. This indicates that some organic matter from both types of organic matter adheres to the membrane surface and clogs the pores, resulting in irreversible fouling. Due to their inherent characteristics, intracellular organic matter causes more severe irreversible fouling than extracellular organic matter. The flux recovery rates for live and dead algal cells after hydraulic washing are 97% and 90%, respectively. This indicates that organic fouling is the main component of irreversible fouling in forward osmosis membranes, while live and dead algal cell fouling alone can be removed by hydraulic washing, resulting in reversible fouling. Among the three mixed algal water components, the highest flux recovery rate (92%) was achieved for live algal cells + extracellular organic matter after hydraulic washing, and the highest reversible resistance was observed in algal-containing water. The flux recovery rates after hydraulic flushing were 80.3% and 82.1% for dead algal cells + extracellular organic matter + intracellular organic matter, and for dead algal cells + intracellular organic matter, respectively. This indicates that irreversible fouling is aggravated, as both dead algal cells and intracellular organic matter contribute to increased irreversible fouling. Therefore, irreversible fouling is most severe when dead algal cells, intracellular organic matter, and extracellular organic matter are present simultaneously. Thus, the reversibility of fouling in mixed algal components is worse than that observed in single algal components. The above application demonstrates that the forward osmosis membrane of this application exhibits strong antifouling and stability. Furthermore, it can be seen that membrane fouling is reduced after applying a negative voltage, and the amount of contaminants adhering to the membrane surface is significantly reduced.

[0170] Figures 22a, 22a1-22g1, 22a2-22g2, 22a1'-22g1', and 22a2'-22g2' show scanning electron microscope (SEM) images of the conductive forward osmosis membrane in this embodiment of the application under different algal water compositions under different applied voltages. Figure 22a is the original membrane surface SEM image. Figures 22a1-22g1 are the membrane surface SEM images after contamination with extracellular organic matter, intracellular organic matter, live algal cells, dead algal cells, live algal cells + extracellular organic matter, dead algal cells + intracellular organic matter, and dead algal cells + extracellular organic matter + intracellular organic matter, respectively, without applied voltage. Figures 22a2-22g2 are the membrane surface SEM images after contamination with extracellular organic matter, intracellular organic matter, live algal cells, dead algal cells, live algal cells + extracellular organic matter, dead algal cells + intracellular organic matter, and dead algal cells + extracellular organic matter + intracellular organic matter, respectively, under an applied voltage of -2V. Scanning electron microscopy (SEM) images: Figures 22a1'-22g1' show cross-sectional SEM images of membranes after contamination with extracellular organic matter, intracellular organic matter, live algal cells, dead algal cells, live algal cells + extracellular organic matter, dead algal cells + intracellular organic matter, and dead algal cells + extracellular organic matter + intracellular organic matter, respectively, without applied voltage; Figures 22a2'-22g2' show cross-sectional SEM images of membranes after contamination with extracellular organic matter, intracellular organic matter, live algal cells, dead algal cells, live algal cells + extracellular organic matter, dead algal cells + intracellular organic matter, and dead algal cells + extracellular organic matter + intracellular organic matter, respectively, under a -2V voltage. The figures show that applying a negative voltage reduces membrane contamination, significantly decreasing the amount of contaminants adhering to the membrane surface. The thickness of the filter cake layer on the membrane surface of the three mixed algal components decreases, mitigating flux decline and reducing both reversible and irreversible membrane contamination. The thickness of the uppermost layer in each cross-sectional image represents the thickness of the contaminants under different voltages.

[0171] The following application examples illustrate the influence of coexisting substances in water on conductive forward osmosis membranes in algae-water separation.

[0172] Natural algal water has a complex composition, containing a large amount of inorganic matter, organic matter, and inorganic particles. Existing research techniques indicate that in ultrafiltration, algal cells and soluble algal products, in the presence of natural organic matter and inorganic particles, have a synergistic effect on membrane fouling, thus affecting membrane fouling. The following application examples of this application illustrate the impact of adding Ca2+, HA, and kaolin to algal water on the fouling and contaminant removal of the conductive forward osmosis membrane during the algal water separation process.

[0173] Application Example 2: The effect of algal water containing Ca2+ coexisting substances on forward osmosis membranes:

[0174] First, Ca2+ was added to the algae-containing water to illustrate the impact of CPFO membrane fouling. After each fouling experiment cycle, the membrane was physically cleaned and the draw solution and feed solution were replaced. Figures 23a, 23b, 23c, 23d, and 23e show that during continuous multi-cycle operation, when Ca2+ was absent in the algae-containing water, the initial flux of the 2nd, 3rd, and 4th cycles decreased by 9%, 20%, and 25%, respectively, with increasing operating cycles. After applying voltage, the initial flux of the 2nd, 3rd, and 4th cycles decreased by 2%, 7%, and 12%, respectively. This indicates that prolonged multi-cycle operation under negative voltage slowed the flux decline because the electrostatic repulsion between the CPFO membrane and the algae-containing water reduced the adhesion of algal contaminants. When the coexisting substance Ca2+ was added to the algae-containing water, the initial flux in the 2nd, 3rd, and 4th cycles decreased by 15%, 25%, and 37%, respectively, with the increase of the operating cycle and without applied voltage. This is because Ca2+ promotes its binding with oxygen-containing functional groups in the algae-containing water and the surface of the algae-containing water membrane. Studies have shown that the average porosity of the gel filter cake layer formed by Ca2+ and algae shows a linear decreasing trend with increasing Ca2+ concentration when the critical calcium ion concentration exceeds 6 mm / L (the value of Ca2+ in this experiment was 8 mmol / L). Therefore, the combination of Ca2+ and algae-containing water becomes more tightly cross-linked and denser, unlike the flocculent filter cake layer formed in algae-containing water. As can be seen from Figures 23a and 23b, the particle size in the algae-containing water gradually increases when Ca2+ is added, thus forming a stable and dense cross-linked gel network, leading to increased membrane fouling and irreversible fouling. When Ca2+ was added and a negative voltage was applied simultaneously, the initial flux at the CPFO membrane surface decreased by 5%, 10%, and 14% in the 2nd, 3rd, and 4th cycles, respectively, indicating that applying a negative voltage can effectively mitigate membrane fouling. This suggests that, under the same conditions, applying a negative voltage resulted in greater membrane fouling resistance and stability, and a smaller decrease in water flux compared to not applying a negative voltage.

[0175] Next, we explain the removal of pollutants. With voltage applied, the CPFO membrane achieved a removal rate of over 99.5% for algal toxins in all four cycles. This is because the mutual repulsion between algal toxin molecules and the CPFO membrane surface hinders the migration of pollutants to the membrane surface, thus increasing the removal rate. Without voltage, Figures 23a, 23b, 23c, 23d, and 23e show that the CPFO membrane's removal rate for algal toxins was lower, around 95.5% in all four cycles. However, when Ca2+ was added to the solution, the CPFO membrane's removal rate for algal toxins exceeded 99.5%. This is because adsorption kinetics and isothermal experiments showed that the presence of K+ or Ca2+ in the solution enhances the adsorption sites for microcystin toxins, promoting the adsorption of MC-LR in the filter cake layer and achieving a high rejection rate >99.5%. Regarding the removal rates of 2-MIB and GSM, Figures 23d and 23e show that in the first cycle, only without voltage applied and with the addition of Ca2+ did the removal rate reach over 99.5%; under other conditions, the removal rate was over 95%. In the second, third, and fourth cycles, the removal efficiency of 2-MIB and GSM reached over 99.5%. This is because these two pollutants are not electrically charged. Under heavy pollution conditions, they can achieve ideal removal by sieving through the pore size of the filter cake layer with small porosity formed by the dense cross-linking of Ca2+ and algal water on the membrane surface, thus improving the removal rate from about 95% to over 99%.

[0176] This application example demonstrates that, in water containing coexisting substances, when Ca2+ is present in algae-containing water, membrane fouling is more severe over prolonged operation without applied voltage compared to when Ca2+ is absent. This is because the combination of Ca2+ and oxygen-containing functional groups in the algae water forms a dense, cross-linked fouling layer on the membrane surface, intensifying membrane fouling. However, when a negative voltage is applied, membrane fouling is reduced in algae-containing water after the addition of Ca2+, resulting in less flux decline. When Ca2+ is added to the solution, the removal rates of MC-LR, 2-MIB, and GSM reach over 99.5%. Adsorption kinetics and isothermal experiments show that the presence of K+ or Ca2+ in the solution enhances the adsorption sites for microcystin, promoting MC-LR adsorption in the filter cake layer and achieving a high MC-LR rejection rate. 2-MIB and GSM are electrically neutral pollutants, and the dense, cross-linked filter cake layer formed by Ca2+ and algae water on the membrane surface achieves ideal removal efficiency through pore sieving. Overall, under the same conditions, membrane fouling is lower when a negative voltage is applied.

[0177] Application Example 3: The effect of algal water containing HA coexisting substances on conductive forward osmosis membranes:

[0178] Figures 24a-24e show the effect of HA addition on the specific flux of the CPFO membrane. Figure 24a shows the effect of HA on membrane flux; Figure 24b shows the effect of HA on particle size in algae-containing water; Figures 24c-24e are schematic diagrams of pollutant removal rates. It can be seen that in continuous multi-cycle operation, firstly, when there is no HA in the algae-containing water, as the number of operating cycles increases, the initial flux of the 2nd, 3rd, and 4th cycles decreases by 9%, 20%, and 25%, respectively. After applying voltage, the decrease in the initial flux of the 2nd, 3rd, and 4th cycles slows down by 6%, 11%, and 10%, respectively. The reason is that long-term multi-cycle operation under applied voltage slows down the decrease in flux because the electrostatic repulsion between the CPFO membrane and the algae-containing water reduces the adhesion of algal pollutants. When the coexisting substance HA is added to algae-containing water, it is equivalent to increasing the concentration of organic matter in the algae-containing water. With the increase of the operating cycle, the initial flux of the 2nd, 3rd, and 4th cycles decreased by 15%, 25%, and 37%, respectively. This is because HA can be adsorbed on the EOM surface through hydrophobic interactions, enhancing the hydrophobicity of the EOM and thus increasing the irreversibility of membrane fouling. Correspondingly, as shown in Figures 24a, 24b, 24c, 24d, and 24e, the particle size in the algae-containing water gradually increases over time when HA is added. When a voltage is applied to the CPFO membrane surface, the initial flux of the 2nd, 3rd, and 4th cycles decreased by 5%, 10%, and 14%, respectively, indicating that applying a negative voltage can effectively mitigate membrane fouling. However, when a voltage is applied to the CPFO membrane surface, Figure 24a shows that the flux decline is reduced when HA is added compared to when no HA is added. This is because the addition of HA makes the algae-containing polluted water slightly acidic. Studies have shown that current density and slightly acidic pH are conducive to the rapid formation of large flocs and porous structures, effectively reducing membrane pore blockage. This also corresponds to Figure 24b, where the addition of HA gradually increases the particle size in the algae water when the voltage is applied. This porous filter cake layer structure effectively alleviates membrane fouling.

[0179] In studies on pollutant removal from algae-containing water, the CPFO membrane achieved a removal rate of over 99.5% for MC-LR in all four cycles when a -2V voltage was applied, which was significantly higher than when no voltage was applied. This is because the electrostatic repulsion between the negatively charged MC-LR molecules and the negative voltage applied to the membrane increased the removal rate. However, in the absence of voltage and HA, although the CPFO membrane also exhibited electronegativity, the weak negative charge on the membrane surface, as shown in the application examples, was insufficient to completely remove MC-LR from algae-containing water. But when HA was added to the solution, the CPFO membrane still achieved a removal rate of over 99.5% for MC-LR in all four cycles, due to the background effect of HA. Some studies have demonstrated that humic substances increased the negative charge on the membrane surface, thereby strengthening the electrostatic repulsion between MC-LR molecules and the CPFO membrane, resulting in a high removal rate. The removal rates of 2-MIB and GSM showed different results. As shown in Figures 24d and 24e, in the absence of HA, the removal rates of both 2-MIB and GSM were around 95% in all four cycles, which was relatively low. This may be because these two pollutants are not electrically charged and are only retained by the highly selective PA layer of the CPFO membrane. However, when HA was present in the algae-containing water, the removal rates of both 2-MIB and GSM were found to be above 99.5% in all four cycles. This is because 2-MIB and GSM readily combine with coexisting humic substances in the water (the interaction between humic substances and 2-MIB is mainly van der Waals forces and hydrogen bonds, consistent with the fact that HA is mainly composed of proteins, amino acids, and peptides), leading to changes in the physicochemical properties of 2-MIB and altering its migration and removal behavior, thus enhancing the removal rate.

[0180] The above application examples illustrate that when HA coexists in algae-containing water, the reason why membrane fouling is more severe with HA than without HA is that HA can adsorb onto the EOM surface through hydrophobic interactions, enhancing the hydrophobicity of the EOM and thus increasing the irreversibility of membrane fouling. When a voltage is applied to the CPFO membrane surface, the flux decline is reduced (membrane flux reduction is 9%) with HA compared to without it. This is because adding HA makes the algae-containing polluted solution weakly acidic, and the weak current density and weakly acidic pH generated by the applied voltage are conducive to the rapid formation of large flocs and porous structures, effectively reducing membrane pore blockage. When HA is added to the solution, the removal rates of MC-LR, 2-MIB, and GSM reach over 99.5% because the background effect of HA increases the negative charge on the membrane surface, thereby strengthening the electrostatic repulsion between MC-LR molecules and the CPFO membrane, achieving a high removal rate. 2-MIB and GSM readily combine with humus coexisting in the water (the interaction between humus and 2-MIB is mainly van der Waals forces and hydrogen bonds), causing changes in the physicochemical properties of 2-MIB to achieve a high removal rate.

[0181] Application Example 4: The effect of algal water containing kaolinite coexisting with conductive forward osmosis membranes:

[0182] Figures 25a-25e illustrate the effect of the presence of Kaolinite coexisting substances on the specific flux of the CPFO membrane. It can be seen that during continuous multi-cycle operation, initially, when Kaolinite was absent in the algae-containing water, the flux decrease was mitigated by 5%, 13%, and 17% respectively with increasing operating cycles when voltage was applied compared to when no voltage was applied. This is also due to the electrostatic repulsion on the CPFO membrane surface reducing the adhesion of algal contaminants. When Kaolinite was present in the algae-containing water, the initial flux decreased by 10%, 18%, and 27% in the 2nd, 3rd, and 4th cycles, respectively. This is because the presence of Kaolinite inorganic particles increases the fouling layer thickness with each longer cycle, increasing hydraulic resistance and exacerbating external concentration polarization during FO, thus worsening membrane fouling and reducing water flux. When a voltage is applied, Figure 25a shows that the flux decay is less severe with the addition of kaolinite compared to the absence of kaolinite. This is because the current density generated by the applied voltage causes kaolinite to produce aluminum coagulants per unit time, thereby enhancing the aggregation of pollutants in algae-containing water and forming large-particle flocs (as can be seen from the data in Figure 25b), thus reducing membrane fouling.

[0183] In the study of pollutant removal from algae-containing water, Figure 25c shows that under applied voltage, the CPFO membrane achieved a removal rate of over 99.5% for MC-LR in all four cycles. However, when no voltage was applied, the removal rate of MC-LR in algae-containing water with the addition of kaolinite particles (>99.5%) was higher than that without the addition of kaolinite particles (<95%). This is because MC-LR can be enhanced by the removal of particles with fine textures on the surface of high-viscosity clay minerals such as kaolinite, thereby improving retention and filtration. Regarding the removal rates of 2-MIB and GSM, Figures 25c, 25d, and 25e show that with the addition of kaolinite, the removal rates of 2-MIB and GSM were over 99.5% in all four cycles. This is because the layered structure of kaolinite itself has strong adsorption properties, enhancing the retention rate of 2-MIB and GSM by the CPFO membrane.

[0184] When Kaolinite coexists in algae-containing water, membrane fouling is more severe in the presence of Kaolinite than in the absence of Kaolinite without applied voltage. This is because the addition of Kaolinite masks the negative charge on the surface of algal cells, thus weakening the electrostatic repulsion with the CPFO membrane surface and exacerbating membrane fouling. When a negative voltage is applied to the membrane surface, membrane fouling is reduced in the presence of Kaolinite compared to its absence (membrane flux reduction of 7%). This is because the current generated by the applied negative voltage causes the kaolinite to produce aluminum coagulants per unit time, thereby enhancing pollutant aggregation and forming large-particle flocs that reduce membrane fouling. When Kaolinite is added to the solution, the removal rates of MC-LR, 2-MIB, and GSM reach over 99.5% because MC-LR can enhance the retention and filtration of high-viscosity clay minerals such as kaolinite with finely textured particles on the surface, thus enhancing the removal rate. 2-MIB and GSM are enhanced by the strong adsorption of organic matter by the layered structure of Kaolinite itself.

[0185] The conductive forward osmosis membrane provided in this application maintains stronger fouling resistance and stability during long-term, multi-cycle operation.

[0186] The conductive forward osmosis membrane prepared in this application maintained strong performance in algae-water separation stability and pollutant removal capacity under long-term operation. In the embodiments of this application, the prepared conductive forward osmosis membrane underwent a long-term operation experiment for six consecutive cycles. To further verify the continuous and reusable value of the prepared composite membrane, after six cycles, the PA layer of the composite membrane was peeled off, and a new PA layer was generated on the original conductive substrate using interfacial polymerization. This regenerated conductive composite membrane was named CPFO-C. The long-term algae-water separation stability and pollutant removal capacity of CPFO-C were further investigated. Furthermore, some physicochemical properties of the CPFO and CPFO-C membranes were analyzed and characterized.

[0187] To better illustrate the stability of the CPFO membrane under long-term operating conditions, the PA layer on the surface was peeled off after the CPFO membrane had been running continuously for 6 cycles (8 hours per cycle) and then interfacial polymerization was performed again. The conductive FO membrane at this time was named CPFO-C membrane. Next, we will explain the flux stability and pollutant removal capacity of the CPFO membrane in algae-water separation after running continuously for 6 cycles (8 hours per cycle).

[0188] Figures 26a and 26b show the membrane flux changes of CPFO and CPFO-C membranes under long-term operation, and the FT-IR spectra of the ppy interlayer after peeling off the PA layer of the CPFO membrane, respectively. It can be seen that, compared with the CPFO membrane before peeling, the CPFO-C membrane after peeling maintained operational stability after six consecutive cycles of long-term operation, except for a decrease in flux caused by irreversible membrane fouling due to algae-containing water in the CPFO membrane. The infrared spectrum in Figure 26b shows that continuous use of the CP-based membrane did not change the chemical composition of the ppy interlayer, and no new functional group peaks appeared. The stable properties of the base film allow for interfacial polymerization reactions, resulting in a well-morphologically optimized PA layer structure after the original PA layer is peeled off (Figures 27a-27f show SEM images of the CPFO film before and after peeling, where Figures 27a and 27d are SEM schematic diagrams of the PA layer of the CPFO film; Figures 27b and 27e are SEM schematic diagrams of the exposed Ppy intermediate layer after peeling off the PA layer; and Figures 27c and 27f are SEM schematic diagrams of the PA layer of the CPFO-C film).

[0189] Table 4-2 Pollutant removal efficiency (Remove ratio) of CPFO membrane and CPFO-C membrane

[0190] Under prolonged operation, it was found that while the flux of the CPFO membrane decreased slightly before and after the PA layer was peeled off, the removal efficiency of the three pollutants remained very high. This was mainly due to SEM, pollutant removal efficiency, and Fourier transform infrared spectroscopy tests, which showed that the CP-based membrane maintained stable chemical properties and the performance of the composite FO membrane even after long-term operation. Therefore, long-term operation will not damage the physicochemical properties and performance of the CPFO membrane, and it exhibits strong chemical practicality and durability.

[0191] Furthermore, the conductive forward osmosis membrane provided in this application is prepared by electrochemically depositing a polypyrrole interlayer on a conductive porous carbon paper substrate. The deposition of the polypyrrole interlayer compensates for the rough macropores of the conductive porous carbon paper substrate, thereby altering a series of physicochemical properties of the substrate surface, such as hydrophilicity, roughness, pore size, and electrochemical characteristics. The new morphology of the interlayer also affects the morphology and properties of the polyamide layer. With the increase in the number of polypyrrole interlayer deposition layers, the conductive porous carbon paper substrate forms a completely new substrate morphology. High hydrophilicity, a suitable small pore size, and uniform roughness provide greater reactivity and contact area for the reaction of m-phenylenediamine and trimesoyl chloride, resulting in higher crosslinking degree and excellent forward osmosis performance.

[0192] Furthermore, the forward osmosis membrane provided in this application, under the preferred conditions of a pyrrole concentration of 0.15 mol / L and a further preferred number of turns of 600, exhibits a substrate surface pore size of 1.08 ± 3.4 μm, a porosity of 34.6 ± 1.7%, and a hydrophilic contact angle of 32.4 ± 2.31°. The conductive forward osmosis membrane prepared under these conditions demonstrates optimal electrochemical activity and the lowest impedance, achieving the best forward osmosis performance: water flux and salt return flux in FO / PRO operation mode are 33.96 / 21.09 L / (m²h) and 5.48 / 4.61 g / (m²h), respectively.

[0193] Furthermore, the forward osmosis membrane provided in this application exhibits high removal rates for undesirable metabolites in algae-containing water, such as algal toxins (MC-LR), geosmin (GSM), and dimethylisocyanate (2-MIB). Under the influence of electric field strength, applying a negative voltage can significantly alleviate membrane fouling; applying a -2V voltage increases the flux by 34% compared to not applying voltage. Regardless of whether voltage is applied, the conductive forward osmosis membrane achieves a removal rate of over 95% for all three pollutants. Specifically, when a negative voltage is applied, the removal rate for MC-LR reaches over 99.5%, and the removal rates for GSM and 2-MIB are over 95%.

[0194] In addition, the positive osmosis membrane provided in this application has the best membrane flux for live algae cells and extracellular organic matter in mixed algae water components after applying a negative voltage, with an improvement effect of about 37%.

[0195] Furthermore, even when the polyamide layer is peeled off and repolymerized to obtain a new forward osmosis membrane under long-term operation, the forward osmosis membrane provided in this application still maintains a high removal rate of algal toxins, geosmin, and dimethylisocyanate, except for a slight decrease in flux. It does not damage the physicochemical properties and performance of the conductive forward osmosis membrane, and has strong chemical practicality and durability.

[0196] The conductive base membrane provided in this application has the advantage of being reusable, which saves costs and reduces environmental pollution for the overall filtration and separation system.

[0197] The above provides a detailed description of the conductive forward osmosis membrane preparation method, the forward osmosis membrane itself, and the algae-water separation system and method applied thereto. For those skilled in the art, based on the ideas of the embodiments of this application, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A method of making a conductive forward osmosis membrane, characterized by, The method comprises the following steps: a) preparing a conductive intermediate layer on a conductive porous substrate to obtain a conductive base film; b) preparing a skin layer on the conductive intermediate layer of the conductive base film by interfacial polymerization to obtain the conductive forward osmosis membrane.

2. The method of claim 1, wherein the method is performed in the presence of a solvent. The conductive porous substrate is a conductive porous carbon paper; and the conductive intermediate layer is a layer of hydrophilic conductive material.

3. The method of claim 2, wherein the method is carried out by the steps of: The conductive intermediate layer is polypyrrole, and the conductive intermediate layer is prepared by an electrochemical polymerization method of electrochemically depositing a pyrrole-containing electrochemical polymer on the surface of the conductive porous carbon paper.

4. The method of claim 3, wherein the method is carried out by the steps of: Before step a), the method further comprises the following step: pretreating the conductive porous substrate; and the pretreatment is performed by obtaining a conductive porous substrate of a suitable size, soaking the conductive porous substrate of the suitable size in a culture dish, and then performing neutral treatment on the substrate.

5. The method of claim 4, wherein the method is carried out by the steps of: The pretreatment is performed by soaking the conductive porous substrate of the suitable size in a culture dish using a 0.2 mol / L sodium hydroxide (NaOH) solution for a period of time, and then soaking and rinsing the substrate with deionized water until neutral.

6. The method of claim 5, wherein the method is carried out by: The electrochemical polymer is a mixture of pyrrole and sulfuric acid (H2SO4).

7. The method of claim 1, wherein the method is carried out at a temperature of about 20 °C to about 100 °C. The skin layer is prepared by soaking the conductive base film in an aqueous solution of a polyamine compound at a certain concentration, completely soaking the film for a first specified time, removing the excess aqueous solution, and obtaining a pretreated film; performing surface treatment on the pretreated film; pouring an organic phase solution containing a polyacyl chloride compound onto the treated pretreated film, performing interfacial polymerization, removing the excess organic phase solution after a second specified time, and obtaining a skin layer conductive forward osmosis membrane with a polyamide layer.

8. The method of claim 7, wherein the method is carried out by, The polyamide layer is prepared by slowly pouring 25 ml of an aqueous solution containing a meta-phenylenediamine compound (MPD) onto the base film and soaking the film therein, completely soaking the film for 180 s; then pouring off the excess aqueous solution, gently rolling the film surface with a rubber roller to uniformly disperse the aqueous solution on the film surface, and obtaining the pretreated film; and then pouring 25 ml of an organic phase solution of trimesoyl chloride compound (TMC) onto the pretreated film, reacting for 90 s, pouring off the excess organic solution, and obtaining a nascent forward osmosis membrane; and air-drying the prepared nascent forward osmosis membrane for 60 s and oven-drying and solidifying the membrane for 300 s to obtain a skin layer with selective permeability on the membrane surface.

9. The method of claim 8, wherein the method is carried out at a temperature of about 20°C to about 100°C. The aqueous solution is prepared as follows: dissolving a meta-phenylenediamine compound solution with a concentration of 1.0 wt%-6.0 wt% in a lightproof or semi-lightproof container using water as the solvent; and the organic phase solution is prepared as follows: dissolving a trimesoyl chloride compound with a concentration of 0.05 wt%-0.5 wt% in a container using n-hexane as the solvent.

10. An electrically conductive forward osmosis membrane, characterized in that, The conductive forward osmosis membrane is prepared by the method of any one of claims 1-9.

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