Electrospun photocatalytic nanofiber membrane, preparation method and application thereof

Abstract

The application belongs to the technical field of photocatalytic materials, and specifically discloses a static electrospinning photocatalytic nanofiber membrane and a preparation method and application thereof. The preparation method of the photocatalytic nanofiber membrane comprises the following steps: dissolving bismuth salt and polyurethane in a solvent, mixing, and forming a precursor liquid; then electrospinning the precursor liquid to obtain a precursor fiber membrane; and then soaking the precursor fiber membrane in an iodine salt solution, heating, and reacting to obtain the photocatalytic nanofiber membrane. The surface of the iodine bismuth oxide polyurethane membrane with polyurethane as a composite carrier is more hydrophilic, the contact with printing and dyeing wastewater can be enhanced, and thus the catalytic activity of the fiber membrane is improved; and the precursor fiber membrane and the low-temperature in-situ growth synthesis strategy realize the close combination of the precursor fiber membrane and BiOI, high-temperature calcination is not needed, the damage to the fiber membrane caused by high-temperature calcination is effectively avoided, the processing performance of the fiber membrane is improved, and the service life is prolonged.

Description

Technical Field

[0001] This invention belongs to the field of photocatalytic materials technology, specifically relating to an electrospun photocatalytic nanofiber membrane, its preparation method, and its application. Background Technology

[0002] Dyeing and printing wastewater is characterized by large volume, high organic pollutant content, high alkalinity, and significant water quality fluctuations, making it one of the most difficult types of industrial wastewater to treat. It contains dyes, sizing agents, auxiliaries, oils, acids and alkalis, fiber impurities, sand, and inorganic salts. Treatment methods for dyeing and printing wastewater mainly include physical, chemical, and biological methods. Among these, physical treatment primarily uses adsorption. This method involves mixing wastewater with powdered or granular porous materials such as activated carbon or clay, or passing the wastewater through a filter bed composed of these granular materials. The pollutants in the wastewater are adsorbed onto the surface of the porous materials or filtered out. This method is very effective in removing dissolved organic matter from water, but it cannot remove colloidal and hydrophobic dyes, and it only has good adsorption performance for water-soluble dyes such as cationic dyes, direct dyes, acid dyes, and reactive dyes. Biological treatment methods, primarily aerobic biological methods, are effective in removing biochemical oxygen demand (BOD), but their removal rates for color and chemical oxygen demand (COD) are not high. In particular, the widespread application of chemical sizing agents such as polyvinyl alcohol (PVA), surfactants, solvents, and alkali reduction technologies has not only brought the COD of dyeing and printing wastewater to 2000-3000 mg / L, but also reduced the BOD / COD ratio to below 0.2. Therefore, simple aerobic biological treatment is becoming increasingly difficult, and effluent often fails to meet standards. Chemical treatment methods are widely used due to their high decolorization efficiency in dyeing and printing wastewater, especially the use of photocatalysts for photocatalytic degradation.

[0003] Currently, photocatalysts used for wastewater treatment are mainly in powder form. However, powder has many problems such as difficulty in recycling and easy agglomeration in water, which prevents photocatalysts from being effectively applied in actual water treatment. Nanofiber membranes have the characteristics of large specific surface area, strong adsorption capacity, and stable mechanical properties, making them ideal functional materials for water treatment. Electrospinning can easily prepare nanofiber membranes, and the diameter of nanofibers, specific surface area, morphology, and physical properties of the membrane can be directionally controlled. Therefore, electrospun nanofiber membranes have attracted the attention of researchers. At present, they still have the following technical problems: (1) The exposure rate of active sites of photocatalysts is not high, and they are often encapsulated by polymer materials; (2) The unit photocatalytic efficiency is still lower than that of powder photocatalysts; (3) They cannot be reused and have a short service life. Summary of the Invention

[0004] This invention aims to solve at least one of the technical problems existing in the prior art. To this end, this invention proposes an electrospun photocatalytic nanofiber membrane, its preparation method, and its application. This invention employs a synthesis strategy of electrospun precursor membrane and low-temperature in-situ growth to prepare a photocatalytic nanofiber membrane, allowing BiOI to grow in situ on the surface of the fiber membrane substrate, thereby improving the catalytic activity of the fiber membrane and extending its service life.

[0005] To address the aforementioned technical problems, a first aspect of the present invention provides a method for preparing a photocatalytic nanofiber membrane, comprising the following steps:

[0006] (1) Dissolve bismuth salt and polyurethane in a solvent and mix them to form a precursor liquid;

[0007] (2) Electrospinning the precursor liquid to obtain a precursor fiber membrane;

[0008] (3) The precursor fiber membrane is immersed in an iodine salt solution, heated, and reacted to obtain the photocatalytic nanofiber membrane.

[0009] Specifically, this invention uses polyurethane (TPU) as one of the precursor raw materials. Polyurethane has high plasticity and chemical corrosion resistance, as well as good mechanical properties and thermal stability. In addition, the surface of polyurethane has a lot of functional groups, which makes the surface of the iodine oxybismuth polyurethane membrane with polyurethane as the composite carrier more hydrophilic, which is conducive to enhancing the contact with dyeing and printing wastewater, thereby improving the catalytic activity of the fiber membrane.

[0010] Meanwhile, traditional fiber membranes often employ calcination processes during preparation, but calcination carbonizes and embrittles the membrane material, significantly reducing its mechanical properties and plasticity, thus hindering further processing. This invention utilizes a synthesis strategy of precursor fiber membranes and low-temperature in-situ growth, reducing damage to the membrane material caused by high-temperature calcination and facilitating subsequent processing. Furthermore, the in-situ growth method allows for tight bonding between the precursor fiber membrane and the catalytically active substance BiOI at low temperatures, enabling the membrane material to be recycled during application.

[0011] Preferably, the bismuth salt is a bismuth salt soluble in organic solvents; more preferably, the bismuth salt is selected from at least one of bismuth nitrate, bismuth chloride, bismuth citrate, bismuth salicylate, bismuth acetate, and bismuth oxalate; even more preferably, the bismuth salt is bismuth nitrate.

[0012] Preferably, the solvent is a polar organic solvent; more preferably, the solvent is selected from at least one of N,N-dimethylformamide (DMF), acetone, ethanol, and water; even more preferably, the solvent is N,N-dimethylformamide.

[0013] Preferably, the iodized salt solution is a solution of a compound that is soluble in an organic solvent and ionizes to release iodide ions; more preferably, the iodized salt solution is a potassium iodide solution and / or a sodium iodide solution.

[0014] Preferably, the mass ratio of the bismuth salt to the polyurethane is (1-3):1.

[0015] Preferably, the mass-to-volume ratio of the bismuth salt to the solvent is 0.1-0.2 g: 1 mL.

[0016] Preferably, in step (1), the mixing is performed by stirring at room temperature for 3-6 hours.

[0017] Preferably, in step (2), the parameters of electrospinning are: spinning voltage 25-35KV, spinning speed 1-1.5mL / h.

[0018] Preferably, in step (3), the concentration of the iodized salt solution is 15-25 g / L.

[0019] Preferably, the heating temperature is 80-120°C.

[0020] Preferably, the reaction time is 10-15 hours.

[0021] A second aspect of the present invention provides a photocatalytic nanofiber membrane, which is prepared according to the above preparation method, and the photocatalytic nanofiber membrane includes a fiber membrane substrate and BiOI, wherein the BiOI is grown in situ on the surface of the fiber membrane substrate.

[0022] Specifically, the photocatalytic active material BiOI is grown in situ on the surface of the fiber membrane substrate, which not only helps to increase the exposure rate of active sites and improve the photocatalytic performance of the fiber membrane, but also enables the recycling of the fiber membrane and extends its service life.

[0023] A third aspect of the present invention provides the application of the above-described photocatalytic nanofiber membrane in wastewater treatment.

[0024] Preferably, the wastewater is dyeing and printing wastewater.

[0025] Compared with the prior art, the above-described technical solution of the present invention has at least the following technical effects or advantages:

[0026] (1) This invention uses bismuth salt and polyurethane as precursors, and prepares a precursor fiber membrane by electrospinning. The precursor fiber membrane is then immersed in an iodine salt solution, and BiOI is grown in situ on the fiber membrane substrate at low temperature. On the one hand, the bismuth oxyiodine polyurethane membrane with polyurethane as the composite carrier has a more hydrophilic surface, which enhances its contact with dyeing and printing wastewater, thereby improving the catalytic activity of the fiber membrane. On the other hand, the synthesis strategy of combining the precursor fiber membrane with low-temperature in-situ growth allows for a tight bond between the precursor fiber membrane and BiOI, eliminating the need for high-temperature calcination and effectively avoiding damage to the fiber membrane caused by high-temperature calcination, thus improving the processing performance of the fiber membrane. Furthermore, the photocatalytic nanofiber membrane prepared by this invention can be repeatedly recycled, thereby greatly improving its service life.

[0027] (2) The photocatalytic nanofiber membrane prepared by the present invention has good degradation performance for organic dyes. After 240 minutes of light irradiation, the degradation efficiency of methylene blue can reach 85%. Attached Figure Description

[0028] Figure 1 A photograph of the photocatalytic nanofiber membrane prepared in Example 1;

[0029] Figure 2 SEM images of the photocatalytic nanofiber membrane prepared in Example 1 at different magnifications;

[0030] Figure 3 SEM image of the photocatalytic nanofiber membrane prepared in Comparative Example 2;

[0031] Figure 4 The image shows the color change of the photocatalytic nanofiber membrane prepared in Example 1 during the degradation of methylene blue.

[0032] Figure 5 The remaining amount of methylene blue after degradation by the photocatalytic nanofiber membrane prepared in Example 1;

[0033] Figure 6 The remaining amount of methylene blue degraded by the photocatalytic nanofiber membrane prepared in Comparative Example 1;

[0034] Figure 7 The remaining amount of methylene blue degraded by the photocatalytic nanofiber membrane prepared in Comparative Example 2. Detailed Implementation

[0035] The present invention will now be described in detail with reference to embodiments to facilitate understanding of the invention by those skilled in the art. It is particularly important to note that the embodiments are merely illustrative of the invention and should not be construed as limiting the scope of protection of the invention. Non-essential improvements and adjustments made to the invention by those skilled in the art based on the above description should still fall within the scope of protection of the invention. Furthermore, all raw materials mentioned below, unless otherwise specified, are commercially available products; all process steps or preparation methods not mentioned in detail are process steps or preparation methods known to those skilled in the art.

[0036] Example 1

[0037] A method for preparing a photocatalytic nanofiber membrane, characterized by comprising the following steps:

[0038] (1) Dissolve 5g of bismuth nitrate in 10mL of ethylene glycol (EG), sonicate until completely dissolved, and then add 40mL of DMF to form a bismuth nitrate solution;

[0039] (2) Dissolve 5g of TPU in 50mL of DMF to form a TPU solution;

[0040] (3) The bismuth nitrate solution obtained in step (1) and the TPU solution obtained in step (2) are mixed at a volume ratio of 1:1 and stirred at room temperature for 4 hours to form a precursor fluid.

[0041] (4) The precursor liquid obtained in step (3) is electrospun to obtain a precursor fiber membrane; wherein: the electrospinning parameters are: spinning voltage 30KV, feed speed 1.5mL / h.

[0042] (5) The precursor fiber membrane obtained in step (4) is immersed in a potassium iodide solution with a concentration of 20 g / L, heated to 100°C, and reacted for 12 hours to obtain the photocatalytic nanofiber membrane of this embodiment.

[0043] Example 2

[0044] A method for preparing a photocatalytic nanofiber membrane, characterized by comprising the following steps:

[0045] (1) Dissolve 8g of bismuth nitrate in 10mL of ethylene glycol (EG), sonicate until completely dissolved, and then add 40mL of DMF to form a bismuth nitrate solution;

[0046] (2) Dissolve 10g of TPU in 50mL of DMF to form a TPU solution;

[0047] (3) The bismuth nitrate solution obtained in step (1) and the TPU solution obtained in step (2) are mixed at a volume ratio of 1:1 and stirred at room temperature for 4 hours to form a precursor fluid.

[0048] (4) The precursor liquid obtained in step (3) is electrospun to obtain a precursor fiber membrane; wherein: the electrospinning parameters are: spinning voltage 25KV, feed speed 1mL / h.

[0049] (5) The precursor fiber membrane obtained in step (4) is immersed in a potassium iodide solution with a concentration of 15 g / L, heated to 80°C, and reacted for 10 hours to obtain the photocatalytic nanofiber membrane of this embodiment.

[0050] Example 3

[0051] A method for preparing a photocatalytic nanofiber membrane, characterized by comprising the following steps:

[0052] (1) Dissolve 10g of bismuth nitrate in 10mL of ethylene glycol (EG), sonicate until completely dissolved, and then add 40mL of DMF to form a bismuth nitrate solution;

[0053] (2) Dissolve 10g of TPU in 40mL of DMF to form a TPU solution;

[0054] (3) The bismuth nitrate solution obtained in step (1) and the TPU solution obtained in step (2) are mixed at a volume ratio of 1:1 and stirred at room temperature for 4 hours to form a precursor fluid.

[0055] (4) The precursor liquid obtained in step (3) is electrospun to obtain a precursor fiber membrane; wherein: the electrospinning parameters are: spinning voltage 35KV, feed speed 1.5mL / h.

[0056] (5) The precursor fiber membrane obtained in step (4) is immersed in a potassium iodide solution with a concentration of 25 g / L, heated to 120°C, and reacted for 15 hours to obtain the photocatalytic nanofiber membrane of this embodiment.

[0057] Comparative Example 1

[0058] A method for preparing a photocatalytic nanofiber membrane, characterized by comprising the following steps:

[0059] (1) Dissolve 5g of bismuth nitrate in 10mL of ethylene glycol (EG), sonicate until completely dissolved, and then add 40mL of DMF to form a bismuth nitrate solution;

[0060] (2) Dissolve 5g of polyacrylonitrile (PAN) in 50mL of DMF to form a PAN solution;

[0061] (3) Mix the bismuth nitrate solution obtained in step (1) with the PAN solution obtained in step (2) at a volume ratio of 1:1 and stir at room temperature for 4 hours to form a precursor fluid.

[0062] (4) The precursor liquid obtained in step (3) is electrospun to obtain a precursor fiber membrane; wherein: the electrospinning parameters are: spinning voltage 30KV, feed speed 1.5mL / h.

[0063] (5) The precursor fiber membrane obtained in step (4) is immersed in a potassium iodide solution with a concentration of 20 g / L, heated to 100 °C, and reacted for 12 hours to obtain the photocatalytic nanofiber membrane of this comparative example.

[0064] Comparative Example 2

[0065] (1) Dissolve 5g of bismuth nitrate in 10mL of ethylene glycol (EG), sonicate until completely dissolved, and then add 40mL of DMF to form a bismuth nitrate solution;

[0066] (2) Dissolve 5g of TPU in 50mL of DMF to form a TPU solution;

[0067] (3) The bismuth nitrate solution obtained in step (1) and the TPU solution obtained in step (2) are mixed at a volume ratio of 1:1 and stirred at room temperature for 4 hours to form a precursor fluid.

[0068] (4) The precursor liquid obtained in step (3) is electrospun to obtain a precursor fiber membrane; wherein: the electrospinning parameters are: spinning voltage 30KV, feed speed 1.5mL / h.

[0069] (5) The precursor fiber membrane obtained in step (4) is immersed in a potassium iodide solution with a concentration of 20 g / L, then pre-oxidized at 150 °C for 20 min in an air atmosphere, and then carbonized at 350 °C for 4 hours in a nitrogen atmosphere to obtain the photocatalytic nanofiber membrane of this comparative example.

[0070] Performance testing

[0071] 1. Structural Analysis

[0072] The appearance of the photocatalytic nanofiber membrane prepared in Example 1 was observed with the naked eye, and its microstructure was observed by scanning electron microscopy. The results are as follows: Figure 1-2 As shown.

[0073] Figure 1 Here is a photograph of the photocatalytic nanofiber membrane prepared in Example 1. Figure 1 As can be seen, the photocatalytic nanofiber membrane is orange-yellow, mainly because BiOI material is generated on the surface of the fiber membrane after soaking in potassium iodide solution. This material has a certain visible light sensing ability.

[0074] Figure 2 SEM images of the photocatalytic nanofiber membrane prepared in Example 1 at different magnifications, from Figure 2It can be seen that the photocatalytic nanofiber membrane is mainly composed of interwoven fiber threads, and the thickness of each fiber thread is relatively uniform.

[0075] Figure 3 SEM images of the photocatalytic nanofiber membrane prepared in Comparative Example 2 are shown below. Figure 3 It can be seen that the conventional heat treatment (pre-oxidation + carbonization) of the precursor fiber membrane damages the prepared photocatalytic fiber membrane and causes the fibers to clump.

[0076] 2. Photocatalytic performance

[0077] The photocatalytic nanofiber membrane prepared according to this invention was subjected to photocatalytic performance testing using 40 mg / L methylene blue organic dye under visible light irradiation. The specific testing procedure was as follows: 100 mg of bismuth oxyiodide membrane material was placed in 100 mL of 40 mg / L methylene blue solution and allowed to adsorb in the dark for 1 hour. 5 mL of the dark-adsorbed methylene blue solution (A0) was then collected and filtered. A photocatalytic degradation process was then carried out using simulated sunlight. At irradiation times of 30 min, 60 min, 120 min, and 240 min, 5 mL of methylene blue solution was collected and filtered, and these were labeled A1, A2, A3, and A4, respectively. The absorbance of samples A0-A4 was measured using a UV spectrophotometer at a wavelength of 292 nm.

[0078] Figure 4 This is a color change diagram of the photocatalytic nanofiber membrane prepared in Example 1 during the degradation of methylene blue. Figure 4 It can be seen that the color of methylene blue becomes lighter and lighter with increasing illumination time. Meanwhile, the remaining amount of methylene blue in the sample solution after 240 min of light irradiation was detected using UV-Vis spectrophotometry, and the results are as follows. Figure 5 As shown. From Figure 4 It can be seen that after 240 minutes of light irradiation, the photocatalytic nanofiber membrane prepared in Example 1 can achieve a degradation efficiency of 87% for methylene blue.

[0079] The degradation of methylene blue by the photocatalytic nanofiber membranes prepared in Comparative Example 1 and Comparative Example 2 was detected using the same method, and the detection results are as follows: Figure 6 and Figure 7 As shown. From Figure 6-7 It can be seen that after 240 min of light irradiation, the degradation efficiencies of the photocatalytic nanofiber membranes prepared in Comparative Example 1 and Comparative Example 2 for methylene blue were 35% and 5%, respectively.

[0080] For those skilled in the art, several simple deductions or substitutions can be made without departing from the inventive concept, without requiring creative effort. Therefore, any simple improvements made to this invention by those skilled in the art based on the disclosure of this invention should be within the scope of protection of this invention. The above embodiments are preferred embodiments of this invention, and all processes similar to this invention and equivalent changes should fall within the scope of protection of this invention.

Claims

1. An application of a photocatalytic nanofiber membrane in wastewater treatment, characterized in that, The preparation method of the photocatalytic nanofiber membrane includes the following steps: (1) Dissolve bismuth salt and polyurethane in a solvent and mix to form a precursor liquid; the mass ratio of bismuth salt to polyurethane is (1-3):1; the mixing is carried out by stirring at room temperature for 3-6 hours. (2) Electrospinning the precursor liquid to obtain a precursor fiber membrane; (3) The precursor fiber membrane is immersed in an iodized salt solution, heated, and reacted to obtain the photocatalytic nanofiber membrane; the concentration of the iodized salt solution is 15-25 g / L; the heating temperature is 80-120℃; and the reaction time is 10-15 hours. The preparation method does not include the calcination step.

2. The application according to claim 1, characterized in that, The bismuth salt is selected from at least one of bismuth nitrate, bismuth chloride, bismuth citrate, bismuth salicylate, bismuth acetate, and bismuth oxalate.

3. The application according to claim 1, characterized in that, The solvent is selected from at least one of N,N-dimethylformamide, acetone, ethanol, and water.

4. The application according to claim 1, characterized in that, The iodized salt solution is a potassium iodide solution and / or a sodium iodide solution.

5. The application according to claim 1, characterized in that, The mass-to-volume ratio of the bismuth salt to the solvent is 0.1-0.2 g: 1 mL.

6. The application according to claim 1, characterized in that, In step (2), the parameters for electrospinning are: spinning voltage 25-35KV, spinning speed 1-1.5mL / h.

7. The application according to claim 1, characterized in that, The photocatalytic nanofiber membrane comprises a fiber membrane substrate and BiOI, wherein the BiOI is grown in situ on the surface of the fiber membrane substrate.

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