A polypyrrole / carbon nanotube / silver nanowire conductive microfiltration membrane, a preparation method and application thereof

Abstract

The application discloses a polypyrrole / carbon nanotube / silver nanowire conductive microfiltration membrane and a preparation method and application thereof, wherein polyvinylidene fluoride (PVDF) is used as a membrane matrix, polypyrrole and carbon nanotubes are used as conductive fillers, a polypyrrole / carbon nanotube conductive microfiltration membrane is prepared through a blending method, silver nanowires are self-assembled in situ on the basis, so that the electronic transmission capacity of the conductive membrane is improved, and the polypyrrole / carbon nanotube / silver nanowire conductive microfiltration membrane is obtained. The application also relates to an application of the polypyrrole / carbon nanotube / silver nanowire conductive microfiltration membrane in an MFC-MBR coupling system, polypyrrole, polypyrrole / carbon nanotube and polypyrrole / carbon nanotube / silver nanowire conductive microfiltration membranes are simultaneously used as AnMBR filter membranes and MFC anodes, the electricity generation performance of the system is optimized, the in-situ degradation of organic membrane pollutants by the anode bioelectrochemical action is promoted, and the membrane pollution is controlled.

Description

Technical Field

[0001] This invention belongs to the field of membrane bioreactor preparation technology, and relates to a polypyrrole / carbon nanotube / silver nanowire conductive microfiltration membrane, its preparation method and application. Background Technology

[0002] Microbial fuel cells (MFCs) utilize microorganisms as catalysts to directly convert chemical energy into electrical energy by oxidizing the organic substrate at the anode. Microorganisms first degrade the organic substrate at the MFC anode to generate electrons and protons. Electrons are transferred to the anode surface via direct or indirect transport, and then transferred from the anode to the cathode through an external circuit. Protons diffuse to the cathode through internal system pathways. MFCs are widely used because they can treat both recalcitrant and readily degradable pollutants and offer higher removal efficiency than traditional biological treatment processes.

[0003] To enhance water reuse potential, membrane bioreactors (MBRs) are widely used. The MBR process combines traditional activated sludge treatment with membrane separation. Through microfiltration or ultrafiltration membrane technology (pore size ranging from 0.05 μm to 0.4 μm), bacterial flocculants and almost all suspended solids are physically retained inside the reactor. This not only successfully achieves complete separation of hydraulic retention time (HRT) and solids retention time (SRT), but also significantly reduces reactor volume, improving treatment capacity and purification efficiency. Despite the widespread use of MBRs in wastewater treatment, membrane fouling remains one of the most challenging problems hindering their development.

[0004] Currently, membrane fouling control technologies mainly include improving the properties of sludge mixed liquor, membrane cleaning, membrane modification, and mitigating membrane fouling through an applied electric field. Although the electrostatic repulsion of an applied electric field can effectively alleviate membrane fouling, membrane fouling can rapidly worsen over time because remaining viable bacteria and macromolecular fouling on the membrane surface can act as additional adhesion sites, causing further fouling. In this situation, the electrochemical repulsion provided solely by the cathode direct current will gradually weaken due to the continuous deposition of pollutants and bacteria. Summary of the Invention

[0005] Objective: To overcome the shortcomings of existing technologies, this invention provides a polypyrrole / carbon nanotube / silver nanowire conductive microfiltration membrane, its preparation method, and its application. The membrane exhibits excellent conductivity and can promote electron transfer to control membrane fouling.

[0006] Technical solution: To solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0007] In a first aspect, the present invention provides a method for preparing a polypyrrole / carbon nanotube / silver nanowire conductive microfiltration membrane, comprising:

[0008] S1. Dissolve polypyrrole, carbon nanotubes and polyvinylpyrrolidone in the organic solvent N,N-dimethylacetamide to obtain a mixed solution;

[0009] S2. Add polyvinylidene fluoride (PVDF) to the mixture, mix evenly, let stand, and degas to form a casting solution. Coat the casting solution onto the plate surface, control the film thickness and scrape to form a film. After staying in the air for a period of time, immerse in a water bath to complete the phase transformation (liquid phase to solid phase) and obtain a conductive film (i.e., polypyrrole / carbon nanotube conductive microfiltration membrane).

[0010] S3. Place the prepared conductive film into an aqueous solution containing a cationic dispersant and irradiate it with an ultraviolet lamp to obtain an ultraviolet-grafted conductive film.

[0011] S4. The UV-grafted conductive membrane is immersed in a silver nanowire solution containing an anionic dispersant. Through electrostatic adsorption, the silver nanowires are spontaneously deposited to obtain a polypyrrole / carbon nanotube / silver nanowire conductive microfiltration membrane.

[0012] In some embodiments, in S1, the concentration of polypyrrole in the mixture is 8 wt% to 13 wt%, the concentration of carbon nanotubes is 5 wt% to 10 wt%, and the concentration of polyvinylpyrrolidone is 8 wt% to 12 wt%.

[0013] The concentration of polypyrrole can be 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, or 13 wt%, etc.; the concentration of carbon nanotubes can be 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, or 10 wt%, etc.; and the concentration of polyvinylpyrrolidone can be 8 wt%, 9 wt%, 10 wt%, 11 wt%, or 12 wt%, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0014] In some embodiments, in S2, the amount of polyvinylidene fluoride (PVDF) added is 12% to 25% of the mass of the mixture; wherein, the amount of PVDF added can be 12wt%, 13wt%, 14wt%, 15wt%, 16wt%, 17wt%, 18wt%, 19wt%, 20wt%, 21wt%, 22wt%, 23wt%, 24wt%, 25% of the mass of the mixture, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0015] In S2, the thickness of the scraped film is 300–500 micrometers;

[0016] In S2, the time spent in the air is 10 to 40 seconds, preferably 20 to 30 seconds;

[0017] In step S2, after the conductive film is prepared, the conductive film is further cleaned with alcohol and deionized water, respectively.

[0018] In some embodiments, in S3, the cationic dispersant is selected from quaternary ammonium salt cationic surfactants; wherein the quaternary ammonium salt cationic surfactant is selected from at least one of polyquaternary ammonium salt-11, benzyl dimethyl dodecyl ammonium bromide, and dimethyl aminoethyl methacrylate-bromododecane.

[0019] In step S3, after preparing the UV-grafted conductive film, the step also includes removing the UV-grafted conductive film and rinsing it with deionized water.

[0020] In some embodiments, in S4, the anionic dispersant is selected from phosphate anionic surfactants, wherein the phosphate anionic surfactant is selected from perfluorooctyl phosphate, octadecyl phosphate, etc. At least one of the FSPs;

[0021] In step S4, the concentration of silver nanowires in the silver nanowire solution is 1–4 mg / mL. The concentration of silver nanowires can be 1 mg / mL, 2 mg / mL, 3 mg / mL, 4 mg / mL, etc., but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0022] In some embodiments, the method for preparing polypyrrole includes: dissolving ammonium persulfate in deionized water, adding pyrrole monomer, and mixing and reacting to obtain polypyrrole.

[0023] Furthermore, the preparation process of polypyrrole includes filtration after the mixing reaction to separate the desired polypyrrole, drying it in a vacuum oven, and grinding it for later use.

[0024] In the preparation of polypyrrole, the molar ratio of ammonium persulfate to pyrrole monomer is 1:1 to 1:3. The molar ratio of ammonium persulfate to pyrrole monomer can be 1:1, 1:2, 1:3, etc., but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0025] Secondly, the present invention also provides a polypyrrole / carbon nanotube / silver nanowire conductive microfiltration membrane, which is prepared by the above-described preparation method.

[0026] Thirdly, the present invention also provides the application of the aforementioned polypyrrole / carbon nanotube / silver nanowire conductive microfiltration membrane in a bioelectrochemical membrane bioreactor.

[0027] Furthermore, the polypyrrole / carbon nanotube / silver nanowire conductive microfiltration membrane is applied to an MFC-MBR coupling system. The conductive microfiltration membrane serves as both the anode of the microbial fuel cell (MFC) and the filter membrane of the membrane bioreactor (MBR), promoting electron transfer on the anode membrane surface and thus mitigating membrane fouling.

[0028] This invention provides a polypyrrole / carbon nanotube / silver nanowire conductive microfiltration membrane and its preparation method. The reaction mechanism is as follows: polypyrrole and carbon nanotubes are used as conductive materials, polyvinylpyrrolidone is used as a pore-forming agent, N,N-dimethylacetamide is used as an organic solvent, and PVDF is used as the membrane matrix. First, the above five substances are mixed evenly, then allowed to stand to remove bubbles (avoiding air bubbles, otherwise the formed membrane will be uneven). A uniform and smooth membrane is then scraped out using a membrane scraper and left in the air for a certain period of time. During this process, solvent evaporation affects the surface density and thickness of the membrane, thus affecting its mechanical properties. (Appropriate air bath time is beneficial to improving the mechanical strength of the membrane.) Finally, the membrane is placed in a coagulation bath (ultrapure water used in this patent). During this process, the solvent and non-solvent are fully exchanged, allowing the membrane to solidify. Next, cations are grafted onto the membrane surface using an ultraviolet grafting method. Then, the membrane is immersed in a silver nanowire solution mixed with an anionic dispersant. Through the electrostatic adsorption of cations and anions, the silver nanowires will spontaneously deposit on the membrane surface.

[0029] Beneficial Effects: The polypyrrole / carbon nanotube / silver nanowire conductive microfiltration membrane, its preparation method, and its application provided by this invention have the following advantages: The polypyrrole / carbon nanotube / silver nanowire conductive microfiltration membrane of this invention possesses excellent conductivity, hydrophilicity, and mechanical properties. The blending modification combines the excellent hydrophilicity of polypyrrole with the excellent conductivity of carbon nanotubes. Through surface modification, silver nanowires are electrostatically adsorbed. The dendritic silver nanowires facilitate electron transfer on the membrane surface, thereby promoting the degradation of organic pollutants on the membrane surface and mitigating membrane fouling. Attached Figure Description

[0030] Figure 1 This is a schematic flowchart of a method for preparing a polypyrrole / carbon nanotube / silver nanowire conductive microfiltration membrane according to an embodiment of the present invention. Detailed Implementation

[0031] The present invention will be further described below with reference to embodiments.

[0032] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0033] For the purposes of this specification and the appended claims, unless otherwise stated, all expressions, percentages, or proportions, and other numerical values ​​used in this specification and the appended claims, are to be understood to be modified by the term "about" in all cases. Furthermore, all scopes disclosed herein include their endpoints and can be combined independently.

[0034] Example 1

[0035] A method for preparing a polypyrrole / carbon nanotube / silver nanowire conductive microfiltration membrane includes the following steps:

[0036] (1) Weigh 3.42g of ammonium persulfate and dissolve it in 140mL of deionized water. Sonicate for 10 minutes to mix it evenly. Add 1.1mL of pyrrole and stir at 310r / min for 5 to 8 hours. Filter to separate the required polypyrrole, put it in a vacuum oven to dry and grind it for later use.

[0037] (2) Dissolve 10 wt% polypyrrole powder, 8 wt% carbon nanotube powder, and 10 wt% polyvinylpyrrolidone in the organic solvent N,N-dimethylacetamide and ultrasonically disperse for 30 min at 20 °C. Add 20 wt% PVDF powder to the mixture and stir at 70 °C for 8 h to form a uniform casting solution. Let the casting solution stand at 25 °C for 24 h to remove bubbles. After the bubbles in the casting solution have completely disappeared, coat the casting solution onto the surface of a glass plate. Adjust the height of the doctor blade to 350 μm and scrape the film at a uniform speed. After standing in the air for 30 s, immerse it in a 25 °C ultrapure water bath for 24 h to complete the phase inversion and peel the conductive film off the surface of the glass plate. Clean the successfully prepared film with alcohol and deionized water, and then place it in an aqueous solution containing dimethylaminoethyl methacrylate-bromododecane and irradiate it with a UV lamp for 4 h. Remove the conductive film and rinse it with deionized water. Immerse the UV-grafted conductive film in a mixture of... In a 3 mg / mL solution of silver nanowires from FSP, silver nanowires spontaneously deposit through strong electrostatic adsorption.

[0038] Comparative Example 1: 10 wt% polypyrrole powder and 10 wt% polyvinylpyrrolidone were dissolved in the organic solvent N,N-dimethylacetamide and ultrasonically dispersed at 20°C for 30 min. 20 wt% PVDF powder was added to the mixture, and the mixture was stirred at 70°C for 8 h to form a uniform casting solution. The casting solution was allowed to stand at 25°C for 24 h to remove bubbles. After the bubbles in the casting solution completely disappeared, the casting solution was coated onto the surface of a glass plate. The doctor blade height was adjusted to 350 μm, and the membrane was uniformly coated. After being exposed to air for 30 s, the membrane was immersed in a 25°C ultrapure water bath for 24 h to complete the phase inversion. The conductive membrane was then peeled off from the surface of the glass plate to obtain a polypyrrole conductive microfiltration membrane.

[0039] Comparative Example 2: 10 wt% polypyrrole powder, 8 wt% carbon nanotube powder, and 10 wt% polyvinylpyrrolidone were dissolved in the organic solvent N,N-dimethylacetamide and ultrasonically dispersed at 20°C for 30 min. 20 wt% PVDF powder was added to the mixture, and the mixture was stirred at 70°C for 8 h to form a uniform casting solution. The casting solution was allowed to stand at 25°C for 24 h to remove bubbles. After the bubbles in the casting solution completely disappeared, the casting solution was coated onto the surface of a glass plate. The height of the doctor blade was adjusted to 350 μm, and the film was uniformly coated. After being exposed to air for 30 s, the film was immersed in a 25°C ultrapure water bath for 24 h to complete the phase inversion. The conductive film was then peeled off from the surface of the glass plate to obtain a polypyrrole / carbon nanotube conductive microfiltration membrane.

[0040] Example 2

[0041] The application of a polypyrrole / carbon nanotube / silver nanowire conductive microfiltration membrane includes the following steps:

[0042] A custom-designed stainless steel mold and conductive microfiltration membrane were assembled and placed in an MFC-MBR coupling system. The membrane module, acting as the anode, was positioned below the liquid level in the device. The carbon felt served as the air cathode, contacting air above and water below. A 100Ω external resistor connected the anode and cathode, and a peristaltic pump enabled continuous inflow and outflow of water. The total volume of the device was 18.2L, and the effective area of ​​the anode membrane was 12.5cm². 2 The concentration of the sludge mixed liquor was 8032 mg / L.

[0043] The apparatus operates at a constant flux, maintaining an effluent flux of 0.7 mL / min. A pressure sensor monitors the transmembrane pressure difference in real time. The experiment is stopped when the transmembrane pressure difference increases to more than 30 kPa. Before operation, the pure water flux of the membrane module is measured. Upon stopping the experiment, the transmembrane pressure difference and flux are measured. Then, deionized water is used to flush away loosely bound contaminants from the membrane surface, and the transmembrane pressure difference and flux are measured again. Darcy's law is used to determine the proportion of reversible and irreversible fouling.

[0044] Based on the polypyrrole / carbon nanotube / silver nanowire conductive microfiltration membrane prepared in Example 1 and the polypyrrole and polypyrrole / carbon nanotube conductive microfiltration membranes of Comparative Examples 1-2, three types of anodes were constructed in the MFC-AnMBR system: polypyrrole, polypyrrole / carbon nanotube, and polypyrrole / carbon nanotube / silver nanowire conductive microfiltration membranes. The polypyrrole and polypyrrole / carbon nanotube conductive microfiltration membranes served as control groups, while the polypyrrole / carbon nanotube / silver nanowire conductive microfiltration membrane served as the experimental group. All anodes were placed in the same sludge mixed liquor system to ensure that the membrane material was the only factor affecting membrane fouling. The experimental data are shown in Table 1.

[0045]

[0046]

[0047] Experimental results show that the polypyrrole / carbon nanotube / silver nanowire conductive microfiltration membrane not only achieves excellent COD removal efficiency, but also improves its power generation performance by 35.67% to 91.67%, increases the operating time by 1.28 to 1.85 times, and reduces the total membrane fouling resistance by 35.82% to 55.47%.

[0048] Various contaminants accumulate on the surface of MBR membranes. Microorganisms attached to the surface oxidize and decompose readily degradable organic membrane contaminants as substrates, and the generated electrons can be further used for the reductive degradation of recalcitrant organic contaminants. When the contaminant deposition rate and decomposition rate reach equilibrium, contaminants will not accumulate on the membrane surface. Polypyrrole, carbon nanotubes, and silver nanowires, which have excellent conductivity, not only promote the redox process of electroactive microorganisms on the electrode surface, but also play a significant role in promoting interfacial electron transfer between microorganisms and electrodes, as well as the generation and accumulation of extracellular electron-mediated substances.

[0049] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a polypyrrole / carbon nanotube / silver nanowire conductive microfiltration membrane, characterized in that, The method comprises the following steps: S1, dissolving polypyrrole, carbon nanotubes and polyvinylpyrrolidone in an organic solvent N, N-dimethylacetamide to obtain a mixed solution; S2, adding polyvinylidene fluoride PVDF to the mixed solution, uniformly mixing, standing, defoaming to form a casting solution, coating the casting solution on the surface of a plate, controlling the thickness of the blade to prepare a film, immersing the film in a water bath after staying in the air for a period of time to complete phase inversion, and obtaining a conductive film; S3, placing the prepared conductive film into an aqueous solution containing a cationic dispersant, and irradiating with an ultraviolet lamp to obtain an ultraviolet grafted conductive film; S4, immersing the ultraviolet grafted conductive film into a silver nanowire solution containing an anionic dispersant, and depositing silver nanowires spontaneously through electrostatic adsorption to obtain a polypyrrole / carbon nanotube / silver nanowire conductive microfiltration membrane.

2. The method for preparing the polypyrrole / carbon nanotube / silver nanowire conductive microfiltration membrane according to claim 1, characterized in that, In S1, the concentration of polypyrrole in the mixed solution is 8 wt % to 13 wt %, the concentration of carbon nanotubes is 5 wt % to 10 wt %, and the concentration of polyvinylpyrrolidone is 8 wt % to 12 wt %.

3. The method for preparing the polypyrrole / carbon nanotube / silver nanowire conductive microfiltration membrane according to claim 1, characterized in that, In S2, the amount of polyvinylidene fluoride PVDF added is 12% to 25% of the mass of the mixed solution.

4. The method for preparing the polypyrrole / carbon nanotube / silver nanowire conductive microfiltration membrane according to claim 1, characterized in that, In S2, the thickness of the blade is 300 to 500 microns.

5. The method for preparing the polypyrrole / carbon nanotube / silver nanowire conductive microfiltration membrane according to claim 1, characterized in that, In S2, the time of staying in the air is 10 to 40 seconds.

6. The method for preparing the polypyrrole / carbon nanotube / silver nanowire conductive microfiltration membrane according to claim 1, characterized in that, In S2, the time of staying in the air is 20 to 30 seconds.

7. The method for preparing the polypyrrole / carbon nanotube / silver nanowire conductive microfiltration membrane according to claim 1, characterized in that, In S2, after the conductive film is prepared, it further comprises cleaning the conductive film with alcohol and deionized water respectively.

8. The method for preparing the polypyrrole / carbon nanotube / silver nanowire conductive microfiltration membrane according to claim 1, characterized in that, In S3, the cationic dispersant is selected from quaternary ammonium salt cationic surfactants; wherein the quaternary ammonium salt cationic surfactant is selected from at least one of polyquaternium-11, benzyl dimethyl dodecyl ammonium bromide, and dimethylaminoethyl methacrylate bromododecane.

9. The method for preparing the polypyrrole / carbon nanotube / silver nanowire conductive microfiltration membrane according to claim 1, characterized in that, In S3, after the ultraviolet grafted conductive film is prepared, it further comprises taking out the ultraviolet grafted conductive film and rinsing it with deionized water.

10. The method for preparing the polypyrrole / carbon nanotube / silver nanowire conductive microfiltration membrane according to claim 1, characterized in that, In S4, the anionic dispersant is selected from phosphate anionic surfactants, wherein the phosphate anionic surfactant is selected from at least one of perfluorooctyl phosphate, octadecyl phosphate, and Zonyl FSP.

11. The method for preparing the polypyrrole / carbon nanotube / silver nanowire conductive microfiltration membrane according to claim 1, characterized in that, In S4, the concentration of silver nanowires in the silver nanowire solution is 1 to 4 mg / mL.

12. The method for preparing the polypyrrole / carbon nanotube / silver nanowire conductive microfiltration membrane according to claim 1, characterized in that, The preparation method of the polypyrrole comprises: dissolving ammonium persulfate in deionized water, adding pyrrole monomer, and mixing to obtain polypyrrole.

13. The method for preparing the polypyrrole / carbon nanotube / silver nanowire conductive microfiltration membrane according to claim 12, characterized in that, In the preparation process of polypyrrole, after the mixing reaction, it further comprises suction filtration to separate the required polypyrrole, drying in a vacuum oven, and grinding for standby use.

14. The method for preparing the polypyrrole / carbon nanotube / silver nanowire conductive microfiltration membrane according to claim 12, characterized in that, In the preparation process of polypyrrole, the molar ratio of ammonium persulfate and pyrrole monomer added is 1:1 to 1:

3.

15. A polypyrrole / carbon nanotube / silver nanowire conductive microfiltration membrane prepared by the preparation method of any one of claims 1-14.

16. The use of the polypyrrole / carbon nanotube / silver nanowire conductive microfiltration membrane of claim 15 in a bioelectrochemical membrane bioreactor.

17. Use according to claim 16, characterized in that, The polypyrrole / carbon nanotube / silver nanowire conductive microfiltration membrane is applied to a MFC-MBR coupling system, the conductive microfiltration membrane is used as a microbial fuel cell MFC anode and a membrane bioreactor MBR filtration membrane, electron transfer on the surface of the anode membrane is promoted, and thus membrane pollution is slowed down.

Images