Intelligent oil-water separation membrane with pH regulation and control function and preparation method

Abstract

The invention provides a pH regulation and control intelligent oil-water separation membrane which comprises a metal net-shaped framework, a lignosulfonate-doped polypyrrole membrane is arranged on the metal net-shaped framework, a fluorine-containing hydrophobic substance is grafted on the sodium lignosulfonate-doped polypyrrole membrane, and the fluorine-containing hydrophobic substance is grafted on the metal net-shaped framework. And the surface wettability can be reversibly converted between hydrophilicity and super-hydrophobicity under pH regulation and control. The preparation method comprises the following steps: S1, preparing by adopting an electrochemical oxidation method, and carrying out electrochemical polymerization in an ethanol / aqueous solution containing sodium lignin sulfonate and pyrrole to obtain a lignosulfonate doped polypyrrole film; and S2, pre-wetting the lignosulfonate-doped polypyrrole film, and placing the lignosulfonate-doped polypyrrole film and the fluorine-containing hydrophobic substance in a vacuum environment at the same time, so that the fluorine-containing hydrophobic substance is fully gasified and deposited on the surface of the polypyrrole film, and deposition and grafting of the polypyrrole film are completed. The surface wettability is reversibly converted between hydrophilicity and super-hydrophobicity under pH regulation, and on-demand separation of light oil / water and heavy oil / water type oil-water mixtures is realized.

Description

Technical Field

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

[0002] Oil pollution caused by industrial production and oil spills has become a serious environmental problem, causing significant impacts on human health and the ecological environment. To this end, various oil-water separation methods and materials have been developed. Among them, membrane separation materials with super-wettable surfaces have attracted much attention due to their advantages such as simple manufacturing, high separation efficiency, and flexible operation. Many super-hydrophobic / super-oleophilic membranes and super-hydrophilic / underwater super-oleophobic membranes have been developed for oil removal and water removal from oil-water mixtures, respectively. However, the oil wettability (super-oleophilicity or super-oleophobicity) of these surfaces is usually constant, and surfaces with adjustable oil wettability are particularly important.

[0003] Traditional membrane separation materials still face problems such as membrane pollution, poor stability, and low number of cycles during use. In addition, the application scenarios of single wettability materials are single, making it difficult to achieve on-demand and intelligent separation. Therefore, it is of great practical significance and value to develop an oil-water separation membrane material with high recovery rate, stable wettability, and intelligently regulated wettability. 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. The pH-regulated intelligent oil-water separation membrane is doped with a polyanion dopant, has good durability, and is grafted with a fluorinated hydrophobic substance. Through pH regulation, the surface wettability thereof undergoes a reversible transition between hydrophilic and super hydrophobic under pH regulation, thereby realizing on-demand separation of light oil / water and heavy oil / water type oil-water mixtures, and effectively solving the limitations of the applicable scenarios of single wettability materials.

[0005] The specific technical scheme is as follows: A pH-controlled intelligent oil-water separation membrane comprises a metal mesh skeleton, on which a lignin sulfonate-doped polypyrrole membrane is arranged, and a fluorinated hydrophobic substance is grafted onto the polypyrrole membrane doped with sodium lignin sulfonate, so that the surface wettability can be reversibly changed between hydrophilic and super-hydrophobic under pH control.

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

[0007] Preferably, the lignin sulfonate is sodium lignin sulfonate.

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

[0009] Another subject is a method for preparing a pH-controlled intelligent oil-water separation membrane, comprising the following steps: 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 sodium 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.

[0010] Preferably, the fluorine-containing hydrophobic substance in step S2 is 0.2 g of perfluorooctyltriethoxysilane.

[0011] Preferably, the volume ratio of ethanol to water in the ethanol / water solution in step S1 is 1:4.

[0012] Preferably, in step S1, during electrochemical polymerization, the constant current is 0.005 A cm -2 , the aggregation time is 1000 seconds.

[0013] Preferably, in step S2, the temperature of the vacuum environment is 40° C. and the standing time is 30 minutes.

[0014] Preferably, in step S2, the lignin sulfonate-doped polypyrrole membrane is pre-wetted with deionized water, and after the deposition and grafting of the polypyrrole membrane, 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. The beneficial effects of the present invention are as follows: the present invention provides a pH-regulated intelligent oil-water separation membrane, in which lignin sulfonate is doped on a polypyrrole membrane to improve the durability of the polypyrrole membrane, and after being combined with a hydrophobic substance, the membrane exhibits superhydrophobicity, and its wettability can be reversibly transformed between superhydrophobic / superoleophilic and hydrophilic / underwater superoleophobic states under pH regulation.

[0015] Using a metal mesh skeleton as a substrate, it has a rigid structure, and its overall structure will not change; at the same time, polypyrrole is also a conjugated rigid structure, and its structure is difficult to change. Under different ph effects, the protonation / deprotonation of polypyrrole changes the surface potential of polypyrrole, and the long-chain fluorinated group is negatively charged because of the strong electronegativity of the fluorine element, thereby affecting the arrangement state of the fluorine chain on the surface of polypyrrole, further affecting the element composition of the membrane surface, and finally affecting the wettability, and realizing the regulation from super-hydrophilic to super-hydrophobic. Thus, the reversible switching between super-hydrophobic / hydrophilic is realized, so as to realize the on-demand separation of light oil / water and heavy oil / water type oil-water mixtures. The composite membrane after acid and alkali regulation has an oil-water separation efficiency of 98.6% and 93.4%, respectively, and can be stably circulated 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 production. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative labor. Among them: Figure 1 The SEM morphology images and mapping images of Example 1, wherein a is the SEM morphology image of the stainless steel mesh, b is the SEM morphology image of the PPy-NaLS film, c is the SEM morphology image of the PFOTs / PPy-NaLS film, and d is the mapping image of the intrinsic state PFOTs / PPy-NaLS film; Figure 2 IR spectra of the PPy-NaLS film and the PFOTs / PPy-NaLS film in Example 1; Figure 3 The SEM morphology images and Mapping images of Example 1 after acid and alkali regulation, wherein a is the SEM morphology image of the PFOTs / PPy-NaLS membrane after acid regulation, b is the SEM morphology image of the PFOTs / PPy-NaLS membrane after alkali regulation, c is the Mapping image of the PFOTs / PPy-NaLS membrane after acid regulation, and d is the Mapping image of the PFOTs / PPy-NaLS membrane after alkali regulation; Figure 4Schematic diagram of the wettability change of the PFOTs / PPy-NaLS membrane surface during acid-base regulation in Example 1, wherein a is the water contact angle of the PFOTs / PPy-NaLS membrane in the intrinsic state, 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 alkali regulation; Figure 5 The contact angle variation diagram of the PFOTs / PPy-NaLS composite film of Example 1 during 5 times of acid-base reversible regulation; Figure 6 This is the flux diagram of the PFOTs / PPy-NaLS composite membrane of Example 1 under acid-base reversible regulation, where a is the flux of the PFOTs / PPy-NaLS composite membrane regulated 30 times by base, and b is the flux of the PFOTs / PPy-NaLS composite membrane regulated 50 times by acid. DETAILED DESCRIPTION

[0017] In order to make the above-mentioned purposes, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the drawings of the specification. In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention can also be implemented in other ways different from this description, and those skilled in the art can make similar generalizations without violating the connotation of the present invention, so the present invention is not limited by the specific embodiments disclosed below.

[0018] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The term "in one embodiment" that appears in different places in this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive with other embodiments.

[0019] Example 1 like Figure 1-2 As shown, a pH-controlled intelligent oil-water separation membrane includes a metal mesh skeleton (a stainless steel mesh is used in this embodiment), a polypyrrole membrane doped with lignin sulfonate (sodium lignin sulfonate is used in this embodiment) is arranged on the metal mesh skeleton, and a fluorine-containing hydrophobic substance (perfluorooctyltriethoxysilane is used in this embodiment) is grafted onto the polypyrrole membrane doped with sodium lignin sulfonate, and the surface wettability can be reversibly changed between hydrophilic and super-hydrophobic under pH control.

[0020] like Figure 3 The SEM morphology and mapping images of the pH-regulated smart oil-water separation membrane shown in the figure change after acid-base regulation, so that its surface wettability undergoes a reversible transition between hydrophilic and superhydrophobic.

[0021] A method for preparing a pH-controlled intelligent oil-water separation membrane comprises the following steps: Preparation of S1 polypyrrole film substrate The polypyrrole film substrate was prepared by electrochemical oxidation with a two-electrode DC power supply. In the two-electrode system, a clean stainless steel mesh was used as the working electrode and a stainless steel sheet was used as the counter electrode. The electrochemical polymerization process was carried out in an ethanol / water solution containing 0.1 M sodium lignin sulfonate and 0.3 M pyrrole, where the volume ratio of ethanol / water solution was 1:4, and the constant current was 0.005 A cm -2 , the polymerization time is 1000 seconds. Finally, the prepared polypyrrole film substrate is washed twice with ethanol and water in sequence to obtain a PPy-NaLS film.

[0022] S2 Preparation of PFOTs grafted PFOTs / PPy-NaLS composite membrane The prepared polypyrrole membrane was pre-wetted with deionized water and placed in a vacuum environment at 40°C for 30 minutes together with a culture dish containing 0.2 g of PFOTs to fully vaporize and deposit on the surface of the polypyrrole membrane, completing the deposition and grafting of the polypyrrole membrane. Finally, the obtained PFOTs / PPy-NaLS composite membrane was washed twice with ethanol and once with deionized water, and dried in an oven at 45°C to obtain a PFOTs / PPy-NaLS composite membrane, which is a pH-controlled intelligent oil-water separation membrane.

[0023] pH regulation process of PFOTs / PPy-NaLS composite membrane The wettability test of PFOTs / PPy-NaLS composite film in different pH environments measured the water contact angle of the composite film under different pH aqueous solutions and different time conditions. Sodium hydroxide and hydrochloric acid were used to prepare pH=13 alkaline aqueous solution and pH=3 acidic aqueous solution, and the PFOTs / PPy-NaLS composite film was immersed in them for 30 minutes, 3 hours, 6 hours and 9 hours, respectively, and then its water contact angle was measured.

[0024] The results are as follows Figure 4 As shown in Figure 2, the intrinsic PFOTs / PPy-NaLS composite film has superhydrophobicity. Even if a certain pressure is applied to the water droplet, the water droplet can still completely detach from the membrane surface (e.g. Figure 4 Subsequently, the PFOTs / PPy-NaLS composite film was immersed in a hydrochloric acid aqueous solution with a pH of 3 for 30 minutes, 3 hours, 6 hours, and 9 hours, respectively. The composite film still maintained superhydrophobicity, and the water contact angle was greater than 156° (as shown in Fig. Figure 3b). When the PFOTs / PPy-NaLS composite film was immersed in an alkaline aqueous solution of sodium hydroxide at pH = 13 for 3 hours, the water contact angle began to decrease; after immersion for 6 hours, the water contact angle dropped to 46°, indicating that with the extension of time, the hydrophobicity of the composite film was gradually destroyed and turned into hydrophilicity. Further experiments showed that when the hydrophilic composite film was immersed in an acidic aqueous solution at pH = 3 for 6 hours, its surface properties changed from hydrophilic to hydrophobic (as shown in Figure 2). Figure 4 c).

[0025] like Figure 5 As shown in the figure, the water contact angle change of the PFOTs / PPy-NaLS composite membrane after the pH was reversibly adjusted between acid and base five times, indicating that the pH regulation of the PFOTs / PPy-NaLS composite membrane has good stability.

[0026] like Figure 6 As shown in Figure 2, the oil-water separation performance of PFOTs / PPy-NaLS membrane is stable and good after alkali or acid regulation. Figure 6 As shown in a, in the first 30 times of alkaline regulation at pH 13, the flux was greater than 94%. Figure 6 As shown in b, the flux was greater than 98% in the first 50 times of alkaline regulation at pH 3.

[0027] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A pH-controlled intelligent oil-water separation membrane, characterized in that: The invention comprises a metal mesh skeleton, on which a polypyrrole membrane doped with sodium lignin sulfonate is arranged, and a fluorine-containing hydrophobic substance is grafted onto the polypyrrole membrane doped with sodium lignin sulfonate, so that the surface wettability can be reversibly changed between hydrophilic and super hydrophobic under pH control.

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. The pH-controlled intelligent oil-water separation membrane according to claim 1, characterized in that: The lignin sulfonate is sodium lignin sulfonate.

4. The pH-controlled intelligent oil-water separation membrane according to claim 1, characterized in that: The fluorine-containing hydrophobic substance is perfluorooctyltriethoxysilane.

5. A method for preparing a pH-controlled intelligent oil-water separation membrane according to any one of claims 1 to 4, 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 sodium 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.

6. The method for preparing a pH-controlled intelligent oil-water separation membrane according to claim 5, characterized in that: In step S2, the fluorinated hydrophobic substance is 0.2 g of perfluorooctyltriethoxysilane.

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

4.

8. The method for preparing a pH-controlled intelligent oil-water separation membrane according to claim 5, characterized in that: In step S1, during electrochemical polymerization, the constant current was 0.005 A cm -2 , the aggregation time is 1000 seconds.

9. The method for preparing a pH-controlled intelligent oil-water separation membrane according to claim 5, characterized in that: In step S2, the temperature of the vacuum environment is 40°C and the placement time is 30 minutes.

10. The method for preparing a pH-controlled intelligent oil-water separation membrane according to claim 5, 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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