Flexible carbon nanofiber membrane as well as preparation method and application thereof

Abstract

The invention provides a flexible carbon nanofiber membrane as well as a preparation method and application thereof. The flexible carbon nanofiber membrane comprises a carbon nanofiber matrix and a modified material loaded in the carbon nanofiber matrix, the carbon nanofiber matrix comprises polyacrylonitrile, and the modified material comprises at least one of fluorine and zirconium oxide. The fluorine and / or zirconium oxide modified material is introduced, so that the performance is remarkably improved on the basis of a carbon nanofiber matrix, and the key defects of the existing carbon nanofiber membrane are effectively overcome. The invention also provides a preparation method and application of the flexible carbon nanofiber membrane.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of perfluorooctane sulfonic acid treatment, and particularly relates to a flexible carbon nanofiber membrane and a preparation method and application thereof. BACKGROUND

[0002] Electrochemical membrane water treatment technology has attracted extensive attention due to its environmental friendliness and high efficiency. This technology removes pollutants through electrochemical adsorption or oxidation of a membrane electrode driven by electrical energy. Carbon nanofiber membranes exhibit great potential due to their excellent electrical conductivity, mechanical properties and pollutant removal capacity, and are particularly suitable for wastewater treatment containing persistent organic pollutants such as perfluorooctane sulfonic acid. However, traditional electrochemical water treatment technology often faces the challenge of insufficient efficiency in treating such highly stable pollutants.

[0003] Existing carbon nanofiber membranes have significant limitations in the treatment of wastewater containing perfluorooctane sulfonic acid. On the one hand, their dependence on physical adsorption mechanisms results in limited capture capacity and efficiency for perfluorooctane sulfonic acid. On the other hand, the stability, flexibility and strength of the membrane are insufficient, and it is prone to corrosion and pollution in complex wastewater environments, shortening the service life. In addition, the complex preparation process and insufficient electrochemical activity also restrict its practical application. It is particularly noteworthy that existing materials are difficult to simultaneously remove composite pollutants such as perfluorooctane sulfonic acid and heavy metals efficiently, and lack antibacterial and antiviral functions, limiting their application efficiency in comprehensive water treatment scenarios.

[0004] In view of the above technical bottlenecks, it is urgent to develop a new type of flexible carbon nanofiber membrane. The membrane material needs to be prepared through process innovation and structure optimization to simultaneously improve the adsorption capacity of perfluorooctane sulfonic acid, material mechanical strength, environmental stability and electrochemical activity, while also endowing it with multifunctional pollutant removal capacity and antibacterial properties to meet the high standard requirements of complex wastewater treatment. SUMMARY

[0005] The present application aims to at least solve one of the above technical problems in the prior art. To this end, the present application provides a flexible carbon nanofiber membrane, which realizes significant performance improvement on the basis of the carbon nanofiber matrix by introducing fluorine and / or zirconium oxide modified materials, effectively overcoming the key defects of existing carbon nanofiber membranes.

[0006] The present application also provides a preparation method of a flexible carbon nanofiber membrane.

[0007] The present application also provides the application of a flexible carbon nanofiber membrane in adsorbing wastewater containing perfluorooctane sulfonic acid.

[0008] The first aspect of the present application provides a flexible carbon nanofiber membrane, comprising a carbon nanofiber matrix and a modified material loaded in the carbon nanofiber matrix, the carbon nanofiber matrix comprising polyacrylonitrile, and the modified material comprising at least one of fluorine and zirconium oxide.

[0009] One of the technical solutions of the present application about the flexible carbon nanofiber membrane has at least the following beneficial effects:

[0010] The flexible carbon nanofiber membrane of the present application realizes significant performance improvement on the basis of the carbon nanofiber matrix by introducing fluorine and / or zirconium oxide modified materials, effectively overcoming the key defects of existing carbon nanofiber membranes. Specifically:

[0011] The traditional carbon nanofiber membrane mainly relies on physical adsorption, and has limited capture capacity for persistent organic pollutants such as perfluorooctane sulfonic acid. The present application introduces fluorine elements (which have strong interaction with the C-F bond of perfluorooctane sulfonic acid) and zirconium oxide (which has high affinity for oxygen-containing anion pollutants such as perfluorooctane sulfonic acid), significantly improving the chemical adsorption capacity of the membrane material, thereby realizing efficient and selective removal of perfluorooctane sulfonic acid. At the same time, the introduction of zirconium oxide can synergistically adsorb heavy metal ions, solving the problem of single function of traditional membrane materials and enhancing the adsorption capacity and pollutant removal efficiency of the fiber membrane.

[0012] The polyacrylonitrile (PAN) based carbon nanofiber membrane itself has good flexibility and mechanical properties, and the introduction of fluorine can enhance the hydrophobicity and chemical inertness of the material, reduce membrane pollution and corrosion; the loading of zirconium oxide nanoparticles further improves the mechanical strength and thermal stability of the membrane, so that it can maintain structural integrity in complex wastewater environment for a long time, prolonging the service life. The mechanical strength and environmental stability of the fiber membrane are improved.

[0013] The addition of zirconium oxide not only improves the electrocatalytic activity of the membrane and promotes the electrochemical oxidation reaction, but also activates the pollutant degradation process through the surface hydroxyl site, thereby improving the decomposition efficiency of perfluorooctane sulfonic acid. In addition, the synergistic effect of fluorine and zirconium oxide endows the membrane material with antibacterial properties, effectively inhibiting biological pollution and solving the problem of easy attachment of microorganisms to traditional membranes. The electrochemical activity and multifunctionality are optimized.

[0014] Based on electrospinning and carbonization technology, the present application introduces a modified material (fluorine or zirconium oxide) in one step, avoiding complex post-processing steps, reducing preparation cost and environmental risk, while ensuring the structural uniformity and performance stability of the membrane material.

[0015] In conclusion, the flexible carbon nanofiber membrane of the present application realizes the synergistic optimization of adsorption performance, mechanical strength, electrochemical activity and anti-pollution ability through material modification, provides a reliable technical solution for efficient removal of PFOS and composite pollutants, and has significant environmental protection and economic value.

[0016] According to some embodiments of the present application, the molecular weight of the polyacrylonitrile is MW=85000-150000.

[0017] According to some embodiments of the present application, the carbon nanofiber matrix is distributed with a pore structure, and the pore diameter of the pore structure is 80-120 nm.

[0018] According to some embodiments of the present application, the carbon nanofiber matrix is distributed with a pore structure, and the pore diameter of the pore structure is 80-120 nm.

[0019] According to some embodiments of the present application, the content of the modified material in the carbon nanofiber matrix is 1-20%.

[0020] According to some embodiments of the present application, the thickness of the flexible carbon nanofiber membrane is 0.1-30 mm.

[0021] The second aspect of the present application provides a method for preparing the flexible carbon nanofiber membrane of the first aspect of the present application, comprising the following steps:

[0022] S1: dissolving polyacrylonitrile and modified material in a solvent to obtain a spinning solution, and electrospinning the spinning solution to obtain a pre-fabricated fiber membrane;

[0023] S2: sequentially performing freeze-drying, pre-oxidation treatment and carbonization treatment on the pre-fabricated fiber membrane to obtain the flexible carbon nanofiber membrane.

[0024] The flexible carbon nanofiber membrane preparation method (electrospinning combined with freeze-drying-pre-oxidation-carbonization process) of the present application has the following significant beneficial effects compared with traditional carbon nanofiber membrane preparation technology:

[0025] 1. Simple and efficient process, realizing uniform loading. One-step blending electrospinning: after blending and dissolving polyacrylonitrile (PAN) and modified material (fluorine / zirconium oxide), electrospinning is carried out, which avoids the complex process of traditional multi-step modification (such as post-impregnation, gas phase deposition), simplifies the process and reduces the cost. Further, the modified material is dispersed at the molecular level in the spinning solution, and is directly embedded into the fiber interior through electrospinning, which avoids the agglomeration or uneven distribution problem caused by traditional loading methods (such as surface coating), and improves the performance consistency of the membrane.

[0026] 2. Freeze-drying protects the porous structure and enhances the adsorption performance. Freeze-drying technology avoids the fiber structure collapse caused by conventional thermal drying through low-temperature sublimation of the solvent, preserving the high specific surface area and porous structure, and providing more active sites for pollutant adsorption. The fiber network has no shrinkage stress accumulation during the drying process, so the final carbonized membrane still has excellent flexibility and mechanical strength.

[0027] 3. Optimizing the pre-oxidation and carbonization process improves the material performance. The trapezoidal polymer structure of PAN fibers is formed by pre-oxidation, avoiding fiber fusion and adhesion during carbonization, and ensuring the independent fiber morphology and flexibility of the final carbon nanofiber membrane. Controllable carbonization temperature achieves high electrical conductivity while preserving the active sites of fluorine / zirconium oxide (such as C-F bonds or Zr-O bonds), balancing electrochemical activity and mechanical performance.

[0028] 4. Environmentally friendly and suitable for large-scale production. Reduces the use of chemical reagents and eliminates the need for subsequent modification steps (such as acid treatment or chemical vapor deposition), reducing waste liquid discharge and energy consumption. Electrospinning is compatible with continuous carbonization equipment, making it easy to achieve roll-to-roll production and meet industrialization needs.

[0029] In summary, the method of the present application solves the problems of complex preparation process, high cost, and insufficient membrane performance in the background art through material-process collaborative design. The prepared flexible carbon nanofiber membrane has high adsorption capacity (for perfluorooctane sulfonic acid and other pollutants), excellent mechanical strength, stable electrochemical activity, and antibacterial function, providing a feasible industrial production path for efficient water treatment.

[0030] According to some embodiments of the present application, the voltage during the electrospinning process is 12-18 kV.

[0031] According to some embodiments of the present application, the voltage during the electrospinning process is any one of 12 kV, 13 kV, 14 kV, 15 kV, 16 kV, 17 kV, 18 kV or a range value formed by any two of them, such as 14 kV-16 kV.

[0032] According to some embodiments of the present application, the flow rate of the spinning solution during the electrospinning process is 0.2-1.0 mL / h.

[0033] According to some embodiments of the present application, the flow rate of the spinning solution during the electrospinning process is any one of 0.2 mL / h, 0.3 mL / h, 0.4 mL / h, 0.5 mL / h, 0.6 mL / h, 0.7 mL / h, 0.8 mL / h, 0.9 mL / h, 1.0 mL / h or a range value formed by any two of them, such as 0.4 mL / h-0.6 mL / h.

[0034] According to some embodiments of the present application, the distance between the needle and the collector in the electrospinning process is 5-25 cm.

[0035] According to some embodiments of the present application, the temperature of the freeze-drying is -20--40℃.

[0036] According to some embodiments of the present application, the time of the freeze-drying is 20-30 h.

[0037] According to some embodiments of the present application, the temperature of the pre-oxidation treatment is 200℃-300℃.

[0038] According to some embodiments of the present application, the temperature of the pre-oxidation treatment is any one of 200℃, 210℃, 220℃, 230℃, 240℃, 250℃, 260℃, 270℃, 280℃, 290℃, 300℃ or a range value formed by any two of them, such as 240℃-260℃.

[0039] According to some embodiments of the present application, the time of the pre-oxidation treatment is 1-3 h.

[0040] According to some embodiments of the present application, the method of the carbonization treatment comprises: under a protective atmosphere, increasing the temperature to 700-1000℃ at a temperature increasing rate of 1-3℃ / min, and keeping the temperature for 1-3 h.

[0041] The third aspect of the present application provides the application of the flexible carbon nanofiber membrane in adsorbing wastewater containing perfluorooctane sulfonic acid.

[0042] The flexible carbon nanofiber membrane provided by the present application has the following remarkable advantages in the adsorption treatment of wastewater containing perfluorooctane sulfonic acid.

[0043] Beneficial effects:

[0044] 1. High efficient and selective adsorption of PFOS. The fluorine-modified carbon nanofiber produces strong interaction with perfluorooctane sulfonic acid molecules through C-F bond, and the zirconium oxide selectively captures the sulfonic acid group of PFOS through Lewis acid-base interaction, which significantly improves the adsorption capacity (3-5 times higher than traditional activated carbon). The three-dimensional network structure and open pores of the nanofiber (specific surface area > 800 m 2 / g) shorten the diffusion path of perfluorooctane sulfonic acid, and more than 90% adsorption rate can be achieved within 30 minutes.

[0045] 2. Anti-interference and synergistic purification ability. The amphoteric property of zirconium oxide makes the membrane maintain stable adsorption performance in the pH range of 3-11, overcoming the problem of sharp decrease in efficiency of traditional materials under acidic / alkaline conditions, and having wide pH adaptability. Heavy metals (such as Pb 2+ , Cd 2+, by zirconium oxide ion exchange) and organic pollutants (by carbon fiber electrochemical oxidation), achieving one-stop treatment of composite pollution.

[0046] 3. Long-term stability and easy regeneration characteristics. Fluorine modification endows the membrane with superhydrophobicity (contact angle > 150°), effectively inhibiting the attachment of organic dirt and biofilm, and still maintaining 90% of the initial flux in oil-containing wastewater or high-COD environment. Perfluorooctane sulfonate can be desorbed using a 0.1M NaOH / ethanol mixture (desorption rate > 95%), and after 10 cycles, the adsorption capacity only decreases by 8%, greatly reducing the operation and maintenance cost.

[0047] 4. Safety and environmental friendliness. Zero secondary pollution: the carbon fiber skeleton and pre-oxidation modified material (ZrO2) do not dissolve out during the adsorption process, avoiding the risk of nanomaterial leakage and achieving zero secondary pollution. The flexible membrane can be directly used as an electrode for an electrosorption-degradation coupling system, and the perfluorooctane sulfonate degradation rate can reach 85% at a voltage of 2V, mineralized into harmless small molecules. BRIEF DESCRIPTION OF DRAWINGS

[0048] Figure 1 is a preparation process flow chart of the flexible carbon nanofiber membrane of Example 1.

[0049] Figure 2 is a micro-morphology diagram of the flexible carbon nanofiber membrane of Example 1.

[0050] Figure 3 is an element distribution diagram of the flexible carbon nanofiber membrane of Example 1.

[0051] Figure 4 is a transmission electron microscope element distribution diagram of the flexible carbon nanofiber membrane of Example 1.

[0052] Figure 5 is a fluorine doping schematic diagram of the flexible carbon nanofiber membrane of Example 1.

[0053] Figure 6 is a preparation process flow chart of the flexible carbon nanofiber membrane of Example 2.

[0054] Figure 7 is a micro-morphology diagram of the flexible carbon nanofiber membrane and the blank membrane of Example 2.

[0055] Figure 8 is an element distribution diagram of the flexible carbon nanofiber membrane and the blank membrane of Example 2.

[0056] Figure 9 is a flexible and high-strength real object diagram of the flexible carbon nanofiber membrane of Example 2. DETAILED DESCRIPTION

[0057] The concept and the technical effects of the present application will be described clearly and completely in combination with the embodiments, so that the purpose, features and effects of the present application can be fully understood. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments of the present application, other embodiments obtained by those skilled in the art without creative labor are within the protection scope of the present application.

[0058] In the description of the present application, the description of the terms "one embodiment", "some embodiments", "illustrative embodiment", "example", "specific example" or "some examples" means that the specific features, structures, materials or characteristics described in combination with the embodiment or example are contained in at least one embodiment or example of the present application. In the present specification, the illustrative description of the above terms does not necessarily mean the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0059] Unless otherwise specified, "room temperature" in the present application means 25℃±5℃.

[0060] Unless otherwise specified, "about" in the present application means that the allowable error is within ±2%.

[0061] Unless otherwise specified, the specific conditions in the embodiments are carried out according to the conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments used are not marked with the manufacturer, which are all conventional products that can be purchased on the market.

[0062] Example 1

[0063] A flexible carbon nanofiber membrane is prepared, the carbon nanofiber matrix is polyacrylonitrile, and a modified material is loaded in the matrix, and the modified material is fluorine.

[0064] The process flow is as follows: raw material preparation → electrospinning → freeze drying → pre-oxidation → carbonization treatment → fluorine-doped flexible carbon nanofiber aerogel, as shown in Figure 1 The specific method is as follows:

[0065] Dissolve 1g of PAN and 0.05g of ammonium fluoride in 10g of DMF to form a spinning solution by electrospinning technology.

[0066] Inject the spinning solution into a syringe and spin by electrospinning technology.

[0067] Apply a voltage of 15kV between the needle and the aluminum foil collector, and the flow rate of the solution is 0.8mL / h.

[0068] After electrospinning, freeze-dry for 24h, and then pre-oxidize at 250℃ in air for 2h.

[0069] Carbonization treatment: the temperature was raised to 900℃ at a rate of 2℃ / min under argon atmosphere, and the temperature was kept for 2 hours to obtain the fluorine-doped flexible carbon nanofiber membrane.

[0070] The carbon nanofiber matrix is distributed with a pore structure, and the pore size of the pore structure is 1000 nm.

[0071] The content of the modified material in the carbon nanofiber matrix is 1%.

[0072] The thickness of the flexible carbon nanofiber membrane is 30 mm.

[0073] The microstructure of the prepared fiber membrane is shown in Figure 2 It can be seen from Figure 2 that the fluorine-doped carbon nanofibers inside the fiber membrane are uniformly and continuously dispersed.

[0074] The element distribution map of the prepared fiber membrane is shown in Figure 3 It can be seen from Figure 3 that the fluorine element is uniformly distributed on the surface of the carbon nanofiber, proving the uniformity of fluorine modification.

[0075] The transmission electron microscope element distribution map of the prepared fiber membrane is shown in Figure 4 It can be seen from Figure 4 that the surface of a single carbon nanofiber realizes uniform fluorine modification.

[0076] The fluorine-doped schematic diagram of the prepared fiber membrane is shown in Figure 5 It can be seen from Figure 5 that the fluorine element is uniformly distributed on the surface of the carbon layer.

[0077] The flexible carbon nanofiber membrane prepared in this embodiment is used to remove perfluorooctane sulfonic acid in wastewater.

[0078] The comparative sample is a flexible carbon nanofiber membrane without F doping.

[0079] The test method is high performance liquid chromatography-mass spectrometry.

[0080] The test found that the maximum adsorption capacity of the flexible carbon nanofiber membrane doped with F for perfluorooctane sulfonic acid and perfluorooctane carboxylic acid was 45 mg / g and 36 mg / g, respectively, and the adsorption kinetics was better than that of the flexible carbon nanofiber membrane without doping.

[0081] The contact angle of the flexible carbon nanofiber membrane doped with F is 176°, which is significantly higher than that of the flexible carbon nanofiber membrane without doping, which is 81°.

[0082] The water permeation flux of the flexible carbon nanofiber membrane doped with F is higher than that of the flexible carbon nanofiber membrane without doping. 2 / h) is higher than that of the flexible carbon nanofiber membrane without doping (~120±2L / m2 / h), which exhibits good hydrophobicity and high adsorption capacity, and can effectively remove perfluoroalkyl and polyfluoroalkyl substances in water.

[0083] Example 2

[0084] A flexible carbon nanofiber membrane is prepared, the carbon nanofiber substrate is polyacrylonitrile, and a modified material is loaded in the substrate, and the modified material is ZrO2.

[0085] The preparation process is as follows: raw material preparation→ electrospinning→ drying→ pre-oxidation→ carbonization→ obtaining a zirconium oxide doped flexible carbon nanofiber membrane, as shown in Figure 6 The specific method is as follows:

[0086] 1g of PAN and 0.2g of zirconium acetate are dissolved in 10g of DMF to form a spinning solution, and the spinning solution is injected into a syringe for spinning by electrospinning technology.

[0087] A voltage of 15kV is applied between the needle and the aluminum foil collector, and the flow rate of the solution is 0.4mL / h.

[0088] Drying and pretreatment: the collected electrospun fibers are dried in a vacuum drying oven at 60℃ for 12 hours, and then pretreated at 250℃ in air for 2 hours.

[0089] Carbonization treatment: under a nitrogen atmosphere, the temperature is raised to 800℃ at a rate of 2℃ / min, and the temperature is kept for 2 hours to obtain a zirconium oxide doped flexible carbon nanofiber membrane.

[0090] The carbon nanofiber substrate has a pore structure, and the pore size of the pore structure is 100nm.

[0091] The content of the modified material in the carbon nanofiber substrate is 5%.

[0092] The thickness of the flexible carbon nanofiber membrane is 0.2mm.

[0093] The microstructure of the prepared fiber membrane is shown in Figure 7 From Figure 7 it can be seen that the modified carbon nanofiber membrane is composed of uniform and continuous carbon nanofibers, and the pore size is smaller than that of the original sample.

[0094] The element distribution map of the prepared fiber membrane is shown in Figure 8 From Figure 8 it can be seen that the surface of the modified membrane uniformly and massively loads zirconium elements.

[0095] The actual picture of the prepared fiber membrane is shown in Figure 9 From Figure 9 it can be seen that the modified membrane material has excellent softness and high strength.

[0096] The flexible carbon nanofiber membrane prepared in the example was used to remove PFOS in wastewater containing 10 mM NaCl and humic acid.

[0097] The comparative sample was a non-doped flexible carbon nanofiber membrane.

[0098] The test method was high performance liquid chromatography-mass spectrometry.

[0099] The test found that the adsorption capacity of the flexible carbon nanofiber membrane for PFOS reached 120 mg / g, and was not affected by impurities in the environment water body, that is, in the presence of 10 mM NaCl and humic acid, the removal efficiency of PFOS could be maintained at 90%. Under the condition of 1.2 V, the electrochemical stability current density was 12 mA / cm 2 , and only attenuated by 10% within 160 hours, showing good electrochemical stability and high removal efficiency for perfluoro and polyfluoro alkyl substances.

[0100] The above has made a detailed description of the present application in combination with the examples, but the present application is not limited to the above examples, and various changes can be made within the knowledge range possessed by those skilled in the art without departing from the purpose of the present application.

Claims

1. A flexible carbon nanofiber membrane, characterized in that: The invention comprises a carbon nanofiber matrix and a modified material loaded in the carbon nanofiber matrix, wherein the carbon nanofiber matrix comprises polyacrylonitrile, and the modified material comprises at least one of fluorine and zirconium oxide.

2. The flexible carbon nanofiber membrane according to claim 1, characterized in that A pore structure is distributed in the carbon nanofiber matrix, and the pore diameter of the pore structure is 80-120 nm.

3. The flexible carbon nanofiber membrane according to claim 1, characterized in that The content of the modified material in the carbon nanofiber matrix is ​​1-20%.

4. The flexible carbon nanofiber membrane according to claim 1, characterized in that The thickness of the flexible carbon nanofiber membrane is 0.1 to 30 mm.

5. A method for preparing the flexible carbon nanofiber membrane according to any one of claims 1 to 4, characterized in that: The following steps are involved: S1: dissolving polyacrylonitrile and a modified material in a solvent to obtain a spinning solution, and electrospinning the spinning solution to obtain a prefabricated fiber membrane; S2: subjecting the prefabricated fiber membrane to freeze-drying, pre-oxidation treatment and carbonization treatment in sequence to obtain the flexible carbon nanofiber membrane.

6. The method according to claim 5, characterized in that During the electrospinning process, the voltage is 12 to 18 kV; and / or, during the electrospinning process, the flow rate of the spinning solution is 0.2 to 1.0 mL / h; and / or, during the electrospinning process, the distance between the needle and the collector is 5 to 25 cm.

7. The method according to claim 5, characterized in that The freeze-drying temperature is -20 to -40°C; and / or the freeze-drying time is 20 to 30 hours.

8. The method according to claim 5, characterized in that The temperature of the pre-oxidation treatment is 200° C. to 300° C.; and / or the time of the pre-oxidation treatment is 1 to 3 hours.

9. The method according to claim 5, characterized in that The carbonization treatment method comprises: heating the temperature to 700-1000° C. at a heating rate of 1-3° C. / min under a protective atmosphere, and keeping the temperature for 1-3 hours.

10. Use of the flexible carbon nanofiber membrane according to any one of claims 1 to 4 in adsorbing wastewater containing perfluorooctane sulfonic acid.

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