Preparation method and application of a durable lignin sulfonate sodium doped polypyrrole composite filter membrane

Abstract

The application discloses a preparation method and application of a durable sodium lignosulfonate doped polypyrrole composite filter membrane, and the method comprises the following steps: (1) determining the stable adsorption of a dopant sodium lignosulfonate to a polypyrrole chain in a doping process by simulating the binding energy and atomic spacing between polypyrrole chains in different states (oxidation state and reduction state) and doped anions (lignosulfonate) through a density functional theory; and (2) taking the calculation result as a guide to design an experimental scheme, and preparing the durable composite filter membrane by depositing the sodium lignosulfonate doped polypyrrole composite membrane on a stainless steel mesh through an electrochemical oxidation method. The sodium lignosulfonate doped polypyrrole composite filter membrane prepared by the application has super-hydrophilic / underwater super-oleophobic properties, and can realize the separation of oil / water and solvent / water; the stable adsorption of the dopant sodium lignosulfonate to the polypyrrole chain makes the composite filter membrane maintain durability in the use process, and the high flux and high efficiency are maintained after 70 cycles.

Description

Technical Field

[0001] This invention belongs to the field of functional membrane manufacturing technology, and particularly relates to a method for preparing and applying a durable sodium lignosulfonate-doped polypyrrole composite filter membrane. Background Technology

[0002] Water resource issues have long been a major concern. The increase in oily domestic sewage and the frequent occurrence of oil spills generate large amounts of oily wastewater, which not only harms the environment and human health but also has a severe impact on ecosystems. Therefore, the recycling and reuse of oily wastewater is urgently needed. Oil-water separation membranes have attracted much attention in oily wastewater treatment due to their high separation efficiency and simple operation, but they also suffer from problems such as high cost, high chemical requirements, instability, and lack of durability. Conductive polymers are widely used in the preparation of oil-water separation materials due to their environmental stability and low toxicity; however, their electrochemical reversibility often involves doping / dedoping of dopants during redox processes, leading to changes in surface composition and wettability, thus affecting the durability of oil-water separation materials. Summary of the Invention

[0003] To address the problems existing in the prior art, this invention proposes a method for preparing and applying a durable sodium lignosulfonate-doped polypyrrole composite filter membrane. Guided by theory and calculation, the preparation scheme of this composite filter membrane achieves stable adsorption of the dopant and polypyrrole during use, avoiding the problem of dopant ion dedoping during use, which alters surface wettability and affects oil-water separation performance. The filter membrane prepared by this invention maintains high-efficiency oil-water separation even after multiple uses, exhibiting excellent durability.

[0004] To achieve the above objectives, the present invention provides the following technical solution:

[0005] A method for preparing a durable sodium lignosulfonate-doped polypyrrole composite filter membrane, using a stainless steel mesh as the working electrode, a conductive metal as the counter electrode, a saturated calomel electrode as the reference electrode, and an ethanol / water solution containing pyrrole monomer and sodium lignosulfonate as the electrolyte solution, wherein the sodium lignosulfonate-doped polypyrrole composite membrane is deposited on the stainless steel mesh by an electrochemical method.

[0006] The concentration ratio of the pyrrole monomer to sodium lignosulfonate is (0.1-0.5):(0.1-1.0).

[0007] Furthermore, the electrochemical method is a constant current method or a constant potential method.

[0008] Furthermore, the current density of the constant current method is 3.0-10.0 mA / cm². 2 The reaction time is 20-90 minutes; the potential of the constant potential method is 0.7-1.2V, and the reaction time is 20-60 minutes.

[0009] Furthermore, the volume ratio of ethanol to water in the ethanol / water solution is 1:4.

[0010] Furthermore, the conductive metal is a platinum sheet or a stainless steel sheet.

[0011] The preparation method described in this invention specifically involves first determining the feasibility of a durable composite filter membrane through simulation calculations, then designing an experimental scheme, and obtaining a durable sodium lignosulfonate-doped polypyrrole composite filter membrane by adjusting the preparation parameters. The method includes the following steps:

[0012] (1) Based on density functional theory, the orbital energies of sodium lignosulfonate anion and polypyrrole chain in conjugated polymer were simulated, an interface model of polypyrrole and sodium lignosulfonate was constructed, the binding energy and interatomic distance between polypyrrole and lignosulfonate in different states were calculated, and sodium lignosulfonate was determined as the dopant.

[0013] The interface model is established based on an initial distance of 1 / 2 lignin sulfonate and polypyrrole. Based on this, to maintain the weak interaction between the two components, the electronic structures of the geometry of the six pyrrole oligomers and lignin sulfonate were optimized using the 6-31G* basis set under the B3LYP-D3(BJ) hybrid functional group, and the single-point energies were calculated at the same level. The electronic structure and energy of the interface were also calculated at the B3LYP-D3(BJ) / 6-31G* level.

[0014] (2) Based on the stable adsorption of sodium ligninsulfonate dopant with polypyrrole chains in different states as calculated in step (1), a sodium ligninsulfonate-doped polypyrrole composite film was deposited on a stainless steel mesh as the working electrode, a conductive metal as the counter electrode, and a saturated calomel electrode as the reference electrode, using an ethanol / water solution containing pyrrole monomers and sodium ligninsulfonate as the electrolyte solution. The concentration of pyrrole monomers in the electrolyte solution was 0.1-0.5 mol / L, the concentration of sodium ligninsulfonate was 0.1-1.0 mol / L, and the volume ratio of ethanol to water in the ethanol / water solution was 1:4.

[0015] Furthermore, the stainless steel mesh needs to be cleaned with acetone, ethanol, and deionized water before use to remove surface oil stains.

[0016] The present invention also provides a method for preparing the durable sodium lignosulfonate-doped polypyrrole composite filter membrane. The durable sodium lignosulfonate-doped polypyrrole composite filter membrane is prepared by uniformly doping sodium lignosulfonate into floret-shaped polypyrrole particles, and the resulting durable sodium lignosulfonate-doped polypyrrole composite filter membrane has an underwater oil contact angle greater than 150°.

[0017] The present invention also provides an application of the aforementioned durable sodium lignin sulfonate-doped polypyrrole composite filter membrane in oil-water separation.

[0018] Compared with the prior art, the present invention has the following advantages and technical effects:

[0019] (1) The polypyrrole composite filter membrane obtained by the present invention has good hydrophilic / underwater superoleophobic properties, excellent self-cleaning and durability, and the preparation process is simple, low cost, and does not contain toxic substances, making it suitable for widespread application.

[0020] (2) The polypyrrole composite filter membrane obtained by the present invention can achieve efficient oil-water separation and maintain high efficiency after multiple cycles of use. The separated filtrate maintains high purity, and the polypyrrole composite filter membrane exhibits durability and stability.

[0021] (3) The design scheme of the polypyrrole composite filter membrane obtained in this invention is guided by calculation. Based on density functional theory, the orbital energies of the dopant sodium lignin sulfonate and the polypyrrole backbone in the composite filter membrane are simulated to construct an interface model of polypyrrole and sodium lignin sulfonate, thereby calculating the binding energy and interatomic spacing. Based on the determination that the dopant sodium lignin sulfonate and polypyrrole are effectively adsorbed throughout the redox process, the polypyrrole composite filter membrane is prepared by electrochemical doping of sodium lignin sulfonate. This avoids dedoping of the dopant during use, which would alter the structure, composition, and wettability of the composite filter membrane, thereby affecting its oil-water separation performance and maintaining its stability and durability. Attached Figure Description

[0022] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings:

[0023] Figure 1 The model diagram of the obtained durable polypyrrole composite filter membrane under redox conditions is calculated based on density functional theory.

[0024] Figure 2 The infrared spectrum of the durable polypyrrole composite filter membrane obtained in Example 1;

[0025] Figure 3 The images shown are scanning electron microscope images of the durable polypyrrole composite filter membrane obtained in Example 4, with images from left to right at different magnifications.

[0026] Figure 4 The static water contact angle and static underwater oil contact angle of the durable polypyrrole composite filter membrane obtained in Example 4;

[0027] Figure 5This is a photograph of the durable polypyrrole composite filter membrane obtained in Example 5 used for oil-water separation.

[0028] Figure 6 The efficiency and flux of the durable polypyrrole composite filter membrane obtained in Example 5 for oil-water separation at different times;

[0029] Figure 7 This is an interface model of sodium lignosulfonate and polypyrrole chains in the durable polypyrrole composite filter membrane under oxidized and reduced states in Example 1, as well as a schematic diagram of oil-water separation. Detailed Implementation

[0030] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0031] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0032] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0033] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be obvious to those skilled in the art. This application specification and embodiments are merely exemplary.

[0034] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0035] All raw materials used in the following embodiments of the present invention are commercially available. Pyrrole, sodium lignosulfonate, and dichloromethane were purchased from Shanghai Maclean Biochemical Technology Co., Ltd. Ethanol, acetone, petroleum ether, and xylene were purchased from Hangzhou Gaojing Chemical Co., Ltd., and peanut oil was purchased from Shandong Luhua Group Co., Ltd.

[0036] This invention designs a scheme based on computation to obtain a durable conductive polymer oil-water separation membrane. A model is constructed using density functional theory to calculate the binding energy and interatomic distance of the dopant to the polypyrrole chains. Based on the determination of the stable adsorption of the dopant to polypyrrole, an electrochemical oxidation method is used to prepare the polypyrrole composite filter membrane. This invention prepares a durable polypyrrole oil-water separation material by doping with the polyionic dopant sodium lignin sulfonate, achieving efficient and stable oil-water separation. The micro-nano structure of the polypyrrole composite filter membrane helps to construct a hydrophilic surface, achieving superhydrophilic / underwater superoleophobic properties. Conductive polymers are widely used in oil-water separation due to their inherent hydrophilicity, but instability and low reusability limit their development. This invention discloses a durable sodium lignin sulfonate-doped polypyrrole composite filter membrane, which, based on simulation calculations, preferentially uses sodium lignin sulfonate, which can stably adsorb with polypyrrole, as the dopant, effectively solving the durability problem of current conductive polymer oil-water separation membranes.

[0037] This invention provides a method for preparing a durable sodium lignosulfonate-doped polypyrrole composite filter membrane. The method uses a stainless steel mesh as the working electrode, a conductive metal as the counter electrode, and a saturated calomel electrode as the reference electrode. An ethanol / water solution containing pyrrole monomer and sodium lignosulfonate is used as the electrolyte solution. The sodium lignosulfonate-doped polypyrrole composite membrane is deposited on the stainless steel mesh by an electrochemical method.

[0038] The concentration ratio of the pyrrole monomer to sodium lignosulfonate is (0.1-0.5):(0.1-1.0).

[0039] The method for preparing the durable sodium lignosulfonate-doped polypyrrole composite filter membrane involves first determining the feasibility of the durable composite filter membrane through simulation calculations, then designing an experimental scheme, and obtaining the durable sodium lignosulfonate-doped polypyrrole composite filter membrane by adjusting the preparation parameters. The method includes the following steps:

[0040] (1) Based on density functional theory, the orbital energies of sodium lignosulfonate anion and polypyrrole chain in conjugated polymer were simulated, an interface model of polypyrrole and sodium lignosulfonate was constructed, the binding energy and interatomic distance between polypyrrole and lignosulfonate in different states were calculated, and sodium lignosulfonate was determined as the dopant.

[0041] (2) Based on the stable adsorption of sodium lignosulfonate dopant with polypyrrole chains in different states as calculated in step (1), a sodium lignosulfonate doped polypyrrole composite film is deposited on a stainless steel mesh as the working electrode, a conductive metal as the counter electrode, a saturated calomel electrode as the reference electrode, and an ethanol / water solution containing pyrrole monomer and sodium lignosulfonate as the electrolyte solution by electrochemical method.

[0042] In some preferred embodiments, the electrochemical method is a galvanostatic method or a potentiostatic method. The current density of the galvanostatic method is 3.0-10.0 mA / cm². 2 The reaction time is 20-90 minutes; the potential of the constant potential method is 0.7-1.2V, and the reaction time is 20-60 minutes.

[0043] In some preferred embodiments, the concentration of pyrrole monomer in the electrolyte solution is 0.1-0.5 mol / L, the concentration of sodium lignosulfonate is 0.1-1.0 mol / L, and the volume ratio of anhydrous ethanol to water is 1:4.

[0044] In some preferred embodiments, the conductive metal of the counter electrode is a platinum sheet or a stainless steel sheet.

[0045] Before use, the stainless steel mesh needs to be cleaned with acetone, ethanol, and deionized water to remove surface oil.

[0046] The present invention also provides a method for preparing the durable sodium lignosulfonate-doped polypyrrole composite filter membrane. The durable sodium lignosulfonate-doped polypyrrole composite filter membrane is prepared by uniformly doping sodium lignosulfonate into floret-shaped polypyrrole particles, and the resulting durable sodium lignosulfonate-doped polypyrrole composite filter membrane has an underwater oil contact angle greater than 150°.

[0047] The present invention also provides an application of the aforementioned durable sodium lignin sulfonate-doped polypyrrole composite filter membrane in oil-water separation.

[0048] In the following examples and comparative examples, the method used to calculate the binding energy and interatomic spacing between the dopant sodium lignosulfonate and the polypyrrole chain is as follows:

[0049] Based on density functional theory, the orbital energies of sodium lignosulfonate and polypyrrole chains in conjugated polymers were simulated. Six pyrrole unit oligomers were selected to construct the interface model between sodium lignosulfonate and polypyrrole chains, with an initial distance of [missing information]. To maintain the weak interaction between the two, the electronic structures of the geometry of the six pyrrole oligomers and the lignin sulfonate group were optimized using the 6-31G* basis set under the B3LYP-D3(BJ) hybrid functional group, and the single-point energies were calculated at the same level. The electronic structure and energy of the interface were also calculated at the B3LYP-D3(BJ) / 6-31G* level. Therefore, the binding energy and interatomic distance between the two in the redox state were calculated, as shown in Table 1.

[0050] Table 1. Binding energy and interatomic spacing between sodium lignosulfonate and polypyrrole chains

[0051]

[0052] The calculated binding energies between lignin sulfonate and polypyrrole chains in different states (oxidized and reduced) were -0.33 eV and -0.29 eV, respectively. In both oxidized and reduced states, the binding energies between lignin sulfonate and polypyrrole chains were close to and much less than 0 eV, indicating strong adsorption between lignin sulfonate and polypyrrole chains in different states. Furthermore, comparison of atomic spacing revealed that while the configuration of lignin sulfonate varied in different states, the change in atomic spacing between lignin sulfonate and polypyrrole chains was minimal, indicating a stable and robust adsorption between lignin sulfonate and polypyrrole.

[0053] Guided by this result, sodium lignosulfonate-doped polypyrrole composite filter membranes were prepared via electrochemical oxidation. The model diagram of the obtained durable polypyrrole composite filter membrane under redox conditions, based on density functional theory calculations, is shown below. Figure 1 As shown, it can be seen that the interatomic distance between sodium lignosulfonate and polypyrrole chains is small and changes little during the redox process. Sodium lignosulfonate is stably adsorbed into the polypyrrole chains, which will not be described again below.

[0054] The following embodiments are further illustrations of the technical solution of the present invention.

[0055] Example 1

[0056] Pretreatment of a 2.0×1.5cm stainless steel mesh: immersion in acetone followed by ultrasonication, and cleaning with ethanol and deionized water to remove oil stains. A three-electrode system with constant current deposition was used to deposit a polypyrrole composite film doped with sodium lignosulfonate onto the clean stainless steel mesh. The deposition process was carried out in a water / ethanol solution containing 0.1 mol / L pyrrole monomer and 0.1 mol / L sodium lignosulfonate (ethanol to water volume ratio 1:4), with a constant current density of 3.0 mA / cm². 2The deposition time was 90 minutes. A clean stainless steel mesh and a saturated calomel electrode were used as the working electrode and reference electrode, respectively, and a 3.0 × 4.0 cm stainless steel sheet was used as the counter electrode. The prepared polypyrrole composite filter membrane was washed with deionized water and dried to obtain a durable sodium lignosulfonate-doped polypyrrole composite filter membrane.

[0057] The infrared spectrum of the durable sodium lignosulfonate-doped polypyrrole composite filter membrane obtained in this embodiment is as follows: Figure 2 As shown, by Figure 2 It can be seen that: 1442cm -1 The position corresponds to the tensile vibration of CN in the pyrrole ring, 1013 cm. -1 The vibration occurs at 1278 cm⁻¹ within the CH and NH planes. -1 The peak at 961 cm⁻¹ is attributed to the CN-C bond stretching vibrations and the in-plane vibrations of the CH bonds in polypyrrole. -1 and 1132cm -1 The peak at the specified position is attributed to the S=O stretching vibration of the sulfonate anion. These results indicate that the pyrrole monomer polymerizes, and sodium lignin sulfonate is successfully doped into the polypyrrole membrane. The durable polypyrrole composite filter membrane prepared in this example has a uniform and smooth surface and exhibits superhydrophilic / underwater superoleophobic properties, with a water contact angle of 0° and an underwater oil contact angle of 152°. This lignin-doped polypyrrole composite filter membrane demonstrates high throughput and high efficiency for separating peanut oil / water mixtures (volume ratio of peanut oil to water 3:5), with a throughput of 68.9 L·m⁻¹. -2 ·h -1 The separation efficiency was 97.12%.

[0058] Example 2

[0059] Pretreatment of a 2.0×1.5cm stainless steel mesh: immersion in acetone followed by ultrasonication, and cleaning with ethanol and deionized water to remove oil stains. A three-electrode system with constant current deposition was used to deposit a polypyrrole composite film doped with sodium lignosulfonate onto the clean stainless steel mesh. The deposition process was carried out in a water / ethanol solution containing 0.1 mol / L pyrrole and 1.0 mol / L sodium lignosulfonate (ethanol to water volume ratio 1:4), with a constant current density of 5.0 mA / cm². 2 The deposition time was 20 minutes. A clean stainless steel mesh and a saturated calomel electrode were used as the working electrode and reference electrode, respectively, and a 3.0 × 4.0 cm stainless steel sheet was used as the counter electrode. The prepared polypyrrole composite filter membrane was washed with deionized water and dried.

[0060] After completion of this embodiment, a uniform and dense polypyrrole composite membrane was deposited on a stainless steel mesh, forming a superhydrophilic surface with a micro-nano structure. The water contact angle of the polypyrrole composite filter membrane was 0°, and the underwater oil contact angle was 153°. This sodium lignosulfonate-doped polypyrrole composite filter membrane was used to separate xylene / water mixtures (xylene to water volume ratio of 3:5), achieving an oil-water separation flux and efficiency of 69.2 L·m⁻¹. -2 ·h -1 And 96.38%.

[0061] Example 3

[0062] Pretreatment of a 2.0×1.5cm stainless steel mesh: immersion in acetone followed by ultrasonication, and cleaning with ethanol and deionized water to remove oil stains. A three-electrode system with constant current deposition was used to deposit a polypyrrole composite film doped with sodium lignosulfonate onto the clean stainless steel mesh. The deposition process was carried out in a water / ethanol solution containing 0.3 mol / L pyrrole and 0.1 mol / L sodium lignosulfonate (ethanol to water volume ratio 1:4), with a constant current density of 10.0 mA / cm². 2 The deposition time was 20 minutes. A clean stainless steel mesh and a saturated calomel electrode were used as the working electrode and reference electrode, respectively, and a 3.0 × 4.0 cm stainless steel sheet was used as the counter electrode. The prepared polypyrrole composite filter membrane was washed with deionized water and dried.

[0063] The durable sodium lignosulfonate-doped polypyrrole composite filter membrane obtained in this embodiment has a uniform and dense surface and exhibits superhydrophilic / underwater superoleophobic properties, with a water contact angle of 0° and an underwater oil contact angle of 154°. This composite filter membrane was used to separate oil-water mixtures such as xylene / water and peanut oil / water (both with a volume ratio of 3:5 for xylene and water, and 3:5 for peanut oil and water), achieving separation fluxes of 70.32 L·m⁻¹ for both. -2 ·h -1 69.72 L·m -2 ·h -1 The separation efficiencies were 99.39% and 99.26%, respectively.

[0064] Example 4

[0065] Pretreatment of a 2.0×1.5cm stainless steel mesh: immersion in acetone followed by sonication, and cleaning with ethanol and deionized water to remove oil stains. A three-electrode system with constant current deposition was used to deposit a polypyrrole composite film doped with sodium lignosulfonate onto the clean stainless steel mesh. The deposition process was carried out in a water / ethanol solution containing 0.5 mol / L pyrrole and 1.0 mol / L sodium lignosulfonate (ethanol to water volume ratio 1:4), with a constant current density of 5.0 mA / cm². 2The deposition time was 40 minutes. A clean stainless steel mesh and a saturated calomel electrode were used as the working electrode and reference electrode, respectively, and a 2.0 × 3.0 cm platinum sheet was used as the counter electrode. The prepared polypyrrole composite filter membrane was washed with deionized water and dried.

[0066] The scanning electron microscope (SEM) of the durable sodium lignosulfonate-doped polypyrrole composite filter membrane obtained in this embodiment is as follows: Figure 3 As shown. By Figure 3 As can be seen, the polypyrrole composite filter membrane obtained in this embodiment is flat and dense, and the stainless steel mesh is completely covered by the black polypyrrole composite membrane. The scanning electron microscope image at a higher magnification shows the nanostructure of the membrane layer, and the formed floret-shaped polypyrrole particles help to construct a hydrophilic surface.

[0067] The water static contact angle and underwater oil static contact angle of the durable sodium lignosulfonate-doped polypyrrole composite filter membrane obtained in this embodiment are as follows: Figure 4 As shown. By Figure 4 It is found that the sodium lignosulfonate-doped polypyrrole composite filter membrane exhibits superhydrophilic / underwater superoleophobic properties, with water contact angles of 0° and underwater oil contact angles of 156°. This sodium lignosulfonate-doped polypyrrole composite filter membrane can achieve rapid oil-water separation, with a flux and efficiency of 69.6 L·m⁻¹ for separating peanut oil / water (volume ratio of peanut oil to water 3:5). -2 ·h -1 And 98.2%.

[0068] Example 5

[0069] Pretreatment of a 2.0×1.5cm stainless steel mesh: immersion in acetone followed by ultrasonication, and cleaning with ethanol and deionized water to remove oil stains. A three-electrode system with constant current deposition was used to deposit a polypyrrole composite film doped with sodium lignosulfonate onto the clean stainless steel mesh. The deposition process was carried out in a water / ethanol solution containing 0.3 mol / L pyrrole and 0.1 mol / L sodium lignosulfonate (ethanol to water volume ratio 1:4), with a constant current density of 5.0 mA / cm². 2 The deposition time was 20 minutes. A clean stainless steel mesh and a saturated calomel electrode were used as the working electrode and reference electrode, respectively, and a 3.0 × 4.0 cm stainless steel sheet was used as the counter electrode. The prepared polypyrrole composite filter membrane was washed with deionized water and dried.

[0070] The durable sodium lignosulfonate-doped polypyrrole composite filter membrane prepared in this embodiment is used for oil-water separation. (See attached image for a physical example.) Figure 5 As shown. The efficiency and flux for separating peanut oil / water mixtures (volume ratio of peanut oil to water 3:5) at different times are shown in the figure. Figure 6 As shown. By Figure 6It can be seen that the polypyrrole composite filter membrane doped with sodium lignosulfonate still maintains a high oil-water separation flux and efficiency of 70.14 L·m⁻¹ after 70 cycles. -2 ·h -1 and 97.18% (first-pass flux and efficiency were 78.83 L·m). -2 ·h -1 (and 99.26%). Even after 70 cycles, the water / oil after oil-water separation still maintained high purity. This is because, according to calculations, sodium lignosulfonate can effectively adsorb onto the polypyrrole chains during use, enhancing the durability of the polypyrrole composite filter membrane. The average roughness of the polypyrrole composite filter membrane in the oxidized, reduced, and intrinsic states are 225 nm, 181 nm, and 217 nm, respectively, with minimal roughness variation. This is due to the rigid substrate, which also ensures the stability of the polypyrrole composite filter membrane in terms of roughness.

[0071] Example 6

[0072] Pretreatment of a 2.0 × 1.5 cm stainless steel mesh: immersion in acetone followed by sonication, and cleaning with ethanol and deionized water to remove oil stains. A three-electrode potentiostatic method was used to deposit a polypyrrole composite membrane doped with sodium lignosulfonate onto the clean stainless steel mesh. The deposition process was carried out in a water / ethanol solution containing 0.3 mol / L pyrrole and 0.1 mol / L sodium lignosulfonate (ethanol to water volume ratio 1:4), with a constant potential of 0.7 V and a deposition time of 60 minutes. The clean stainless steel mesh and a saturated calomel electrode served as the working electrode and reference electrode, respectively, and a 3.0 × 4.0 cm stainless steel sheet served as the counter electrode. The prepared polypyrrole composite filter membrane was washed with deionized water and dried.

[0073] The durable sodium lignin sulfonate-doped polypyrrole composite filter membrane obtained in this embodiment is used to separate oil-water mixtures such as dichloromethane / water, petroleum ether / water, and xylene / water. After deposition on a stainless steel mesh for 60 minutes under constant potential, a dense black lignin-doped polypyrrole composite membrane is formed on the surface of the stainless steel mesh. This composite filter membrane achieves superhydrophilic / underwater superoleophobic properties, with a water contact angle of 0° and an underwater oil contact angle of 150°. This composite filter membrane can be used to separate dichloromethane / water oil-water mixtures (dichloromethane to water volume ratio of 3:5), with a separation flux and efficiency of 71.2 L·m⁻¹. -2 ·h -1 And 98.6%.

[0074] Example 7

[0075] Pretreatment of a 2.0 × 1.5 cm stainless steel mesh: immersion in acetone followed by sonication, and cleaning with ethanol and deionized water to remove oil stains. A three-electrode potentiostatic method was used to deposit a polypyrrole composite membrane doped with sodium lignosulfonate onto the clean stainless steel mesh. The deposition process was carried out in a water / ethanol solution containing 0.3 mol / L pyrrole and 0.1 mol / L sodium lignosulfonate (ethanol to water volume ratio 1:4), with a constant potential of 1.2 V and a deposition time of 60 minutes. The clean stainless steel mesh and a saturated calomel electrode served as the working electrode and reference electrode, respectively, and a 2.0 × 3.0 cm platinum sheet served as the counter electrode. The prepared polypyrrole composite filter membrane was washed with deionized water and dried.

[0076] The durable sodium lignosulfonate-doped polypyrrole composite filter membrane obtained in this embodiment has a uniform and dense surface and exhibits superhydrophilic / underwater superoleophobic properties, with a water contact angle of 0° and an underwater oil contact angle of 150°. This sodium lignosulfonate-doped polypyrrole composite filter membrane was used to separate peanut oil / water mixtures (peanut oil to water volume ratio of 3:5). After 70 oil-water separation cycles, it maintained high flux and high efficiency, with a flux of 68.7 L·m³. -2 ·h -1 The efficiency is 96.82%. Furthermore, the separated water and oil retain high purity. This polypyrrole composite membrane exhibits good durability and stability.

[0077] Comparative Example 1

[0078] Pretreatment of a 2.0 × 1.5 cm stainless steel mesh: immersion in acetone followed by sonication, and cleaning with ethanol and deionized water to remove oil stains. A three-electrode potentiostatic method was used to deposit a polypyrrole composite membrane doped with sodium lignosulfonate onto the clean stainless steel mesh. The deposition process was carried out in a water / ethanol solution containing 0.05 mol / L pyrrole and 0.05 mol / L sodium lignosulfonate (ethanol to water volume ratio 1:4), with a constant potential of 0.7 V and a deposition time of 20 minutes. The clean stainless steel mesh and a saturated calomel electrode served as the working electrode and reference electrode, respectively, and a 2.0 × 3.0 cm platinum sheet served as the counter electrode. The prepared polypyrrole composite filter membrane was washed with deionized water and dried.

[0079] After this comparative example was completed, the color of the stainless steel mesh remained unchanged, and its surface was not covered by the black polypyrrole composite membrane. In the oil-water separation experiment, the composite filter membrane prepared in this comparative example failed to separate the oil-water mixture; both oil and water passed through the filter membrane smoothly.

[0080] Comparative Example 2

[0081] Pretreatment of a 2.0×1.5cm stainless steel mesh: immersion in acetone followed by ultrasonication, and cleaning with ethanol and deionized water to remove oil stains. A three-electrode system with constant current deposition was used to deposit a polypyrrole composite film doped with sodium lignosulfonate onto the clean stainless steel mesh. The deposition process was carried out in a water / ethanol solution containing 0.3 mol / L pyrrole and 0.1 mol / L sodium lignosulfonate (ethanol to water volume ratio 1:4), with a constant current of 20 mA / cm². 2 The deposition time was 20 minutes. A clean stainless steel mesh and a saturated calomel electrode were used as the working electrode and reference electrode, respectively, and a 2.0 × 3.0 cm platinum sheet was used as the counter electrode. The prepared polypyrrole composite filter membrane was washed with deionized water and dried.

[0082] After this comparative example was completed, an uneven striped black polypyrrole composite membrane was deposited on the surface of the stainless steel mesh. The composite filter membrane prepared in this comparative example only exhibits superhydrophilic properties in certain areas, and cannot efficiently separate oil-water mixtures, resulting in low purity of water and oil after separation.

[0083] Comparative Example 3

[0084] Pretreatment of a 2.0 × 1.5 cm stainless steel mesh: immersion in acetone followed by sonication, and cleaning with ethanol and deionized water to remove oil stains. A three-electrode potentiostatic method was used to deposit a polypyrrole composite membrane doped with sodium lignosulfonate onto the clean stainless steel mesh. The deposition process was carried out in a water / ethanol solution containing 0.3 mol / L pyrrole and 0.1 mol / L sodium lignosulfonate (ethanol to water volume ratio 1:4), with a constant potential of 2 V and a deposition time of 20 minutes. The clean stainless steel mesh and a saturated calomel electrode served as the working electrode and reference electrode, respectively, and a 2.0 × 3.0 cm platinum sheet served as the counter electrode. The prepared polypyrrole composite filter membrane was washed with deionized water and dried.

[0085] The polypyrrole composite filter membrane prepared in this comparative example has a rough surface and cannot achieve superhydrophilic / underwater superoleophobic properties, with a water contact angle of 30°. In oil-water separation experiments, the composite filter membrane prepared in this comparative example failed to intercept oil and solvent, and thus could not achieve the purpose of separating oil-water mixtures.

[0086] Figure 7 This diagram illustrates the interface model of sodium lignosulfonate and polypyrrole chains in a durable polypyrrole composite filter membrane under oxidized and reduced states, and the schematic diagram of oil-water separation. Figure 7As can be seen, sodium ions move in and out of the polypyrrole composite filter membrane as it transitions between oxidative and reduced states. However, the interface model between sodium lignosulfonate and the polypyrrole chains changes very little in both oxidative and reduced states, indicating the stability of sodium lignosulfonate doping in the polypyrrole membrane. Therefore, the resulting polypyrrole composite filter membrane can effectively retain oil droplets and allow water droplets to pass through in both oxidative and reduced states, achieving rapid oil-water separation. The structural stability of sodium lignosulfonate and the polypyrrole chains in the polypyrrole composite filter membrane ensures its durability.

[0087] Effect verification

[0088] The polypyrrole composite filter membranes obtained in Examples 1-7 were all successfully doped with sodium lignosulfonate, forming micro-nano structures on their surface. The sodium lignosulfonate-doped polypyrrole composite filter membranes possess superhydrophilic and underwater superoleophobic properties, enabling efficient separation of oil-water mixtures and maintaining stability even after multiple cycles.

[0089] Example 5 is a preferred embodiment. The prepared polypyrrole composite filter membrane is flat and dense, with a nanostructure, a static water contact angle of 0° (superhydrophilic), and an underwater oil contact angle of 156°. This lignin-doped polypyrrole composite filter membrane was used in oil-water separation experiments on mixtures of peanut oil, cyclohexane, dichloromethane, xylene, and petroleum ether. The polypyrrole composite filter membrane effectively intercepted oil, achieving oil-water separation and exhibiting high oil-water separation efficiency. The polypyrrole composite filter membrane obtained in Example 5 maintained high flux and oil separation efficiency after 70 oil-water separation cycles, reaching 70.14 L·m⁻¹, respectively. -2 ·h -1 With a strength of 97.18%, it demonstrates excellent durability and stability during repeated use.

[0090] The polypyrrole composite filter membranes obtained in Comparative Examples 1 to 3 could not form a smooth, dense, and uniform membrane surface and polypyrrole micro-nano structure, resulting in poor hydrophilicity and difficulty in achieving efficient and stable oil-water separation.

[0091] Comparative Example 4

[0092] Same as Example 5, except that sodium lignosulfonate is replaced with sodium perfluorooctanoate.

[0093] The results showed that the flux and efficiency when used for oil-water separation were 51.2 L·m⁻². -2 ·h -1 and 85.4%.

[0094] Comparative Example 5

[0095] Same as Example 5, except that the concentration of sodium lignosulfonate is 2 mol / L.

[0096] The results showed that the flux and efficiency when used for oil-water separation were 60.9 L·m⁻².-2 ·h -1 and 82.6%.

[0097] The above are merely preferred embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for preparing a durable sodium lignosulfonate-doped polypyrrole composite filter membrane, characterized in that, Includes the following steps: (1) Based on density functional theory, the orbital energies of sodium lignosulfonate anion and polypyrrole chain in conjugated polymer were simulated, an interface model of polypyrrole and sodium lignosulfonate was constructed, the binding energy and interatomic distance between polypyrrole and lignosulfonate in different states were calculated, and sodium lignosulfonate was determined as the dopant. (2) Based on the stable adsorption of sodium lignosulfonate dopant and polypyrrole chains in different states calculated in step (1), a stainless steel mesh is used as the working electrode, a conductive metal is used as the counter electrode, a saturated calomel electrode is used as the reference electrode, and an ethanol / water solution containing pyrrole monomer and sodium lignosulfonate is used as the electrolyte solution. A sodium lignosulfonate-doped polypyrrole composite film is deposited on the stainless steel mesh by electrochemical method. The molar ratio of the pyrrole monomer to sodium lignosulfonate is (0.1-0.5):(0.1-1.0).

2. The method for preparing the durable sodium lignosulfonate-doped polypyrrole composite filter membrane according to claim 1, characterized in that, The electrochemical method is either a constant current method or a constant potential method.

3. The method for preparing the durable sodium lignosulfonate-doped polypyrrole composite filter membrane according to claim 2, characterized in that, The current density of the constant current method is 3.0-10.0 mA / cm². 2 The reaction time is 20-90 minutes; the potential of the constant potential method is 0.7-1.2V, and the reaction time is 20-60 minutes.

4. The method for preparing the durable sodium lignosulfonate-doped polypyrrole composite filter membrane according to claim 1, characterized in that, The volume ratio of ethanol to water in the ethanol / water solution is 1:

4.

5. The method for preparing the durable sodium lignosulfonate-doped polypyrrole composite filter membrane according to claim 1, characterized in that, The conductive metal is a platinum sheet or a stainless steel sheet.

6. A durable sodium lignosulfonate-doped polypyrrole composite filter membrane prepared by the method for preparing a durable sodium lignosulfonate-doped polypyrrole composite filter membrane according to any one of claims 1-5, characterized in that, Sodium lignosulfonate is uniformly doped into floret-shaped polypyrrole particles, resulting in a durable sodium lignosulfonate-doped polypyrrole composite filter membrane with an underwater oil contact angle greater than 150°.

7. The application of the durable sodium lignosulfonate-doped polypyrrole composite filter membrane as described in claim 6 in oil-water separation.

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