A pH-Regulated Intelligent Oil-Water Separation Membrane and Preparation Method

Abstract

The present invention provides a pH-regulated intelligent oil-water separation membrane, which includes a metal mesh framework. A lignosulfonate-doped polypyrrole membrane is disposed on the metal mesh framework. A fluorine-containing hydrophobic substance is grafted onto the sodium lignosulfonate-doped polypyrrole membrane, and the surface wettability can be reversibly transformed between hydrophilic and superhydrophobic under pH regulation. Its preparation method includes: S1 using an electrochemical oxidation method to prepare, electrochemically polymerizing in an ethanol / water solution containing sodium lignosulfonate and pyrrole to obtain a lignosulfonate-doped polypyrrole membrane; S2 pre-wetting the lignosulfonate-doped polypyrrole membrane and placing it in a vacuum environment together with the fluorine-containing hydrophobic substance, so that the fluorine-containing hydrophobic substance is fully vaporized and deposited on the surface of the polypyrrole membrane, completing the deposition and grafting of the polypyrrole membrane. Its surface wettability can be reversibly transformed between hydrophilic and superhydrophobic under pH regulation, realizing the on-demand separation of light oil / water and heavy oil / water type oil-water mixtures.

Description

Technical Field

[0001] The present invention relates to the technical field of oil-water separation membranes, and particularly to a pH-regulated intelligent oil-water separation membrane and a preparation method thereof. Background Art

[0002] Oil pollution caused by industrial production and oil spill accidents has become a serious environmental problem, having a significant impact on human health and the ecological environment. For this reason, various oil-water separation methods and materials have been developed. Among them, membrane separation materials with superwetting surfaces have attracted much attention due to advantages such as simple manufacturing, high separation efficiency, and flexible operation. Many superhydrophobic / superoleophilic membranes and superhydrophilic / underwater superoleophobic membranes have been developed, which are used for oil removal and water removal in oil-water mixtures respectively. However, the oil wettability (superoleophilicity or superoleophobicity) of these surfaces is usually constant, and a surface with adjustable oil wettability is particularly important.

[0003] Traditional membrane separation materials still face problems such as membrane fouling, poor stability, and low number of recycling times during use. Moreover, the application scenarios of single-wettability materials are single, and it is difficult to achieve on-demand and intelligent separation. Therefore, developing an oil-water separation membrane material with high recovery rate, stable wetting performance, and the ability to intelligently regulate wettability has important practical significance and value. Summary of the Invention

[0004] In order to solve the above technical problems, the present invention provides a pH-regulated intelligent oil-water separation membrane and a preparation method thereof. The pH-regulated intelligent oil-water separation membrane is doped with a polyanion dopant, has good durability, and is grafted with a fluorine-containing hydrophobic substance. Through pH regulation, its surface wettability can reversibly transform between hydrophilic and superhydrophobic, realizing on-demand separation of light oil / water and heavy oil / water type oil-water mixtures, and effectively solving the limitation of the applicable scenarios of single-wettability materials.

[0005] The specific technical solution is as follows: A pH-regulated intelligent oil-water separation membrane includes a metal mesh skeleton, on which a lignosulfonate-doped polypyrrole membrane is provided. The lignosulfonate-doped polypyrrole membrane is grafted with a fluorine-containing hydrophobic substance, and its surface wettability can reversibly transform between hydrophilic and superhydrophobic under pH regulation.

[0006] Preferably, the metal mesh skeleton is a stainless steel mesh.

[0007] Preferably, the lignosulfonate is sodium lignosulfonate.

[0008] Preferably, the fluorine-containing hydrophobic substance is perfluorooctyltriethoxysilane.

[0009] Another subject is a preparation method of a pH-regulated intelligent oil-water separation membrane, including the following steps,

[0010] Preparation of polypyrrole film substrate S1

[0011] Prepared by electrochemical oxidation method using a two-electrode DC power supply. In the two-electrode system, a metal mesh is used as the working electrode and a metal sheet is used as the counter electrode. Electrochemical polymerization is carried out in an ethanol / water solution containing sodium lignosulfonate and pyrrole, with a constant current of 0.003 - 0.007 A cm -2 , and the polymerization time is 800 - 1200 seconds to obtain a sodium lignosulfonate-doped polypyrrole film, which is washed and reserved for use;

[0012] Preparation of composite film S2

[0013] The sodium lignosulfonate-doped polypyrrole film is pre-wetted and then placed in a vacuum environment together with a fluorine-containing hydrophobic substance, so that the fluorine-containing hydrophobic substance is fully vaporized and deposited on the surface of the polypyrrole film. The temperature of the vacuum environment is 35 - 45 °C, and the placement time is 25 - 35 minutes. The deposition and grafting of the polypyrrole film are completed, and after washing and drying, a pH-regulated intelligent oil-water separation membrane is obtained.

[0014] Preferably, in step S2, the fluorine-containing hydrophobic substance is 0.2 g of perfluorooctyltriethoxysilane.

[0015] Preferably, in step S1, the volume ratio of ethanol to water in the ethanol / water solution is 1:4.

[0016] Preferably, in step S1, during electrochemical polymerization, the constant current is 0.005 A cm -2 , and the polymerization time is 1000 seconds.

[0017] Preferably, in step S2, the temperature of the vacuum environment is 40 °C, and the placement time is 30 minutes.

[0018] Preferably, in step S2, the sodium lignosulfonate-doped polypyrrole film is pre-wetted with deionized water. After the deposition and grafting of the polypyrrole film are completed, it is washed twice with ethanol, once with deionized water, and dried in an oven at 45 °C to obtain a pH-regulated intelligent oil-water separation membrane. Polypyrrole film

[0019] The beneficial effects of the present invention are as follows: A pH-regulated intelligent oil-water separation membrane provided by the present invention dopes sodium lignosulfonate on the polypyrrole film, improving the durability of the polypyrrole film. After combining with a hydrophobic substance, it exhibits superhydrophobicity, and its wettability can be reversibly transformed between superhydrophobic / superoleophilic and hydrophilic / underwater superoleophobic states under pH regulation.

[0020] Using a metal mesh skeleton as the substrate, which has a rigid structure and its overall structure will not change; at the same time, polypyrrole also has a conjugated rigid structure and its structure is difficult to change. Under the action of different pH values, the protonation / deprotonation of polypyrrole changes the surface potential of polypyrrole, and the long-chain fluorinated groups are negatively charged due to the strong electronegativity of fluorine elements, thus affecting the arrangement state of fluorine chains on the surface of polypyrrole, further affecting the elemental composition of the membrane surface, and finally affecting the wettability of the membrane, realizing the regulation from superhydrophilic to superhydrophobic. Thus, the reversible switching between superhydrophobic and hydrophilic is achieved, and the on-demand separation of light oil / water and heavy oil / water type oil-water mixtures is realized. The composite membranes after acid and base regulation have oil-water separation efficiencies of 98.6% and 93.4% respectively, and can be stably cycled 50 times and 30 times respectively. The pH-regulated intelligent oil-water separation membrane prepared by the present invention shows good application prospects in the fields of sewage treatment and oil exploitation, etc. Brief Description of the Drawings

[0021] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for description in the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings. Among them:

[0022] Figure 1 It is the SEM morphology diagram and Mapping diagram of Example 1, where a is the SEM morphology diagram of the stainless steel mesh, b is the SEM morphology diagram of the PPy-NaLS membrane, c is the SEM morphology diagram of the PFOTs / PPy-NaLS membrane, and d is the Mapping diagram of the intrinsic PFOTs / PPy-NaLS membrane;

[0023] Figure 2 It is the infrared spectrum diagram of the PPy-NaLS membrane and the PFOTs / PPy-NaLS membrane in Example 1;

[0024] Figure 3 It is the SEM morphology diagram and Mapping diagram after acid and base regulation in Example 1, where a is the SEM morphology diagram of the PFOTs / PPy-NaLS membrane after acid regulation, b is the SEM morphology diagram of the PFOTs / PPy-NaLS membrane after base regulation, c is the Mapping diagram of the PFOTs / PPy-NaLS membrane after acid regulation, and d is the Mapping diagram of the PFOTs / PPy-NaLS membrane after base regulation;

[0025] Figure 4Schematic diagram of the change in the wettability of the PFOTs / PPy-NaLS membrane during the acid-base regulation process in Example 1, where a is the water contact angle of the intrinsic PFOTs / PPy-NaLS membrane, b is the water contact angle of the PFOTs / PPy-NaLS membrane after acid regulation, and c is the water contact angle of the PFOTs / PPy-NaLS membrane after base regulation;

[0026] Figure 5 Contact angle change diagram of the PFOTs / PPy-NaLS composite membrane in Example 1 during 5 times of acid-base reversible regulation;

[0027] Figure 6 Flux diagram of the PFOTs / PPy-NaLS composite membrane in Example 1 during acid-base reversible regulation, where a is the flux of the PFOTs / PPy-NaLS composite membrane after 30 times of base regulation, and b is the flux of the PFOTs / PPy-NaLS composite membrane after 50 times of acid regulation. Detailed implementation manners

[0028] To make the above objects, features, and advantages of the present invention more obvious and understandable, the following will describe the detailed implementation manners of the present invention with reference to the accompanying drawings of the specification. Many specific details are set forth in the following description to fully understand the present invention, but the present invention can also be implemented in other ways different from those described herein. Those skilled in the art can make similar generalizations without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below.

[0029] Secondly, the so-called "one embodiment" or "embodiment" herein refers to a specific feature, structure, or characteristic that can be included in at least one implementation manner of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment that is mutually exclusive with other embodiments.

[0030] Example 1

[0031] As Figure 1-2 shown, a pH-regulated intelligent oil-water separation membrane includes a metal mesh skeleton (stainless steel mesh is used in this embodiment). A polypyrrole membrane doped with lignosulfonate (sodium lignosulfonate is used in this embodiment) is provided on the metal mesh skeleton. A fluorine-containing hydrophobic substance (perfluorooctyltriethoxysilane is used in this embodiment) is grafted on the polypyrrole membrane doped with sodium lignosulfonate, and the surface wettability can be reversibly changed between hydrophilic and superhydrophobic under pH regulation.

[0032] As Figure 3 shown, the SEM morphology diagram and Mapping diagram of the pH-regulated intelligent oil-water separation membrane change after acid-base regulation, making its surface wettability reversibly change between hydrophilic and superhydrophobic.

[0033] A preparation method of a pH-regulated intelligent oil-water separation membrane comprises the following steps

[0034] S1 Preparation of polypyrrole membrane substrate

[0035] The polypyrrole membrane substrate is prepared by an electrochemical oxidation method using a two-electrode DC power supply. In the two-electrode system, a clean stainless steel mesh serves as the working electrode, and a stainless steel sheet serves as the counter electrode. The electrochemical polymerization process is carried out in an ethanol / water solution containing 0.1 M sodium lignosulfonate and 0.3 M pyrrole, where the volume ratio of the ethanol / water solution is 1:4, with a constant current of 0.005 A cm -2 , and the polymerization time is 1000 seconds. Finally, the prepared polypyrrole membrane substrate is washed twice with ethanol and water in sequence to obtain the PPy-NaLS membrane.

[0036] S2 Preparation of PFOTs grafted PFOTs / PPy-NaLS composite membrane

[0037] The prepared polypyrrole membrane is pre-wetted with deionized water and placed in a vacuum environment at 40 °C for 30 minutes together with a petri dish containing 0.2 g of PFOTs, so that PFOTs is fully vaporized and deposited on the surface of the polypyrrole membrane to complete the deposition and grafting of the polypyrrole membrane. Finally, the obtained PFOTs / PPy-NaLS composite membrane is washed twice with ethanol and once with deionized water, and dried in an oven at 45 °C to obtain the PFOTs / PPy-NaLS composite membrane, which is the pH-regulated intelligent oil-water separation membrane.

[0038] pH regulation process of PFOTs / PPy-NaLS composite membrane

[0039] The wettability of the PFOTs / PPy-NaLS composite membrane in different pH environments is tested, and the water contact angle of the composite membrane under different pH aqueous solutions and different time conditions is measured. An alkaline aqueous solution with pH = 13 and an acidic aqueous solution with pH = 3 are respectively prepared using sodium hydroxide and hydrochloric acid, and the PFOTs / PPy-NaLS composite membrane is immersed therein for 30 minutes, 3 hours, 6 hours, and 9 hours respectively, and then its water contact angle is measured.

[0040] The results are as Figure 4 shown. The as-prepared PFOTs / PPy-NaLS composite membrane has superhydrophobicity, and even when a certain pressure is applied to the water droplet, the water droplet can still completely detach from the membrane surface (as Figure 4 shown in a). Subsequently, the PFOTs / PPy-NaLS composite membrane is immersed in a hydrochloric acid aqueous solution with pH = 3 for 30 minutes, 3 hours, 6 hours, and 9 hours respectively. The composite membrane still maintains superhydrophobicity, and the water contact angle is greater than 156° (as Figure 3as shown in Fig. b). After the PFOTs / PPy-NaLS composite film was immersed in an alkaline aqueous solution of sodium hydroxide with pH = 13 for 3 hours, the water contact angle began to decrease; after 6 hours of immersion, the water contact angle decreased to 46°, indicating that with the prolongation of time, the hydrophobicity of the composite film was gradually destroyed and transformed into hydrophilicity. Further experiments showed that after the hydrophilic composite film was re-immersed in an acidic aqueous solution with pH = 3 for 6 hours, its surface property changed from hydrophilic to hydrophobic (as Figure 4 shown in Fig. c).

[0041] As Figure 5 shown, the water contact angle change diagram of the PFOTs / PPy-NaLS composite film after 5 reversible regulations of pH between acid and base indicates that the pH regulation of the PFOTs / PPy-NaLS composite film has good stability.

[0042] As Figure 6 shown, the oil-water separation performance of the PFOTs / PPy-NaLS film is stable and good after alkali regulation or acid regulation. As Figure 6 shown in Fig. a, its flux was greater than 94% in the first 30 regulations with pH = 13, and as Figure 6 shown in Fig. b, its flux was greater than 98% in the first 50 regulations with pH = 3.

[0043] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not restrictive. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention, and they should all be covered within the scope of the claims of the present invention.

Claims

1. A pH-controlled intelligent oil-water separation membrane, characterized in that: It comprises a metal mesh skeleton, on which a polypyrrole membrane doped with sodium lignin sulfonate is arranged, and on which perfluorooctyl triethoxysilane is grafted, so that the surface wettability can be reversibly changed between hydrophilic and superhydrophobic under pH control; The polypyrrole film doped with lignin sulfonate is prepared by electrochemical oxidation; The fluorine-containing hydrophobic substance is grafted onto the polypyrrole membrane doped with lignin sulfonate, and the fluorine-containing hydrophobic substance is gasified in a vacuum environment and deposited on the surface of the polypyrrole membrane, wherein the temperature of the vacuum environment is 35-45° C. and the placement time is 25-35 minutes.

2. According to claim 1, a pH-controlled intelligent oil-water separation membrane is characterized in that: The metal mesh skeleton is a stainless steel mesh.

3. A method for preparing a pH-controlled intelligent oil-water separation membrane according to any one of claims 1 to 2, characterized in that: The following steps are included: Preparation of S1 polypyrrole film substrate The samples were prepared by electrochemical oxidation with a two-electrode DC power supply. In the two-electrode system, a metal mesh was used as the working electrode and a metal sheet was used as the counter electrode. Electrochemical polymerization was carried out in an ethanol / water solution containing lignin sulfonate and pyrrole. The constant current was 0.003-0.007 A cm -2 , the polymerization time is 800-1200 seconds, and a polypyrrole membrane doped with lignin sulfonate is obtained, which is washed and set aside; Preparation of S2 composite membrane The lignin sulfonate-doped polypyrrole membrane is pre-wetted and placed in a vacuum environment together with a fluorinated hydrophobic substance to fully vaporize the fluorinated hydrophobic substance and deposit on the surface of the polypyrrole membrane. The temperature of the vacuum environment is 35-45°C and the placement time is 25-35 minutes. The deposition and grafting of the polypyrrole membrane are completed. The pH-controlled intelligent oil-water separation membrane is obtained after cleaning and drying.

4. The method for preparing a pH-controlled intelligent oil-water separation membrane according to claim 3, characterized in that: In step S2, the fluorinated hydrophobic substance is 0.2 g of perfluorooctyltriethoxysilane.

5. The method for preparing a pH-controlled intelligent oil-water separation membrane according to claim 3, characterized in that: In step S1, the volume ratio of ethanol to water in the ethanol / water solution is 1:

4.

6. The method for preparing a pH-controlled intelligent oil-water separation membrane according to claim 3, characterized in that: In step S1, during electrochemical polymerization, the constant current was 0.005 A cm -2 , the aggregation time is 1000 seconds.

7. The method for preparing a pH-controlled intelligent oil-water separation membrane according to claim 3, characterized in that: In step S2, the temperature of the vacuum environment is 40°C and the placement time is 30 minutes.

8. The method for preparing a pH-controlled intelligent oil-water separation membrane according to claim 3, characterized in that: In step S2, the lignin sulfonate-doped polypyrrole membrane is pre-wetted with deionized water. After the deposition and grafting of the polypyrrole membrane are completed, it is washed twice with ethanol and once with deionized water, and then dried in an oven at 45°C to obtain a pH-controlled intelligent oil-water separation membrane.

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