Tannic acid-iron surface modified cobalt-iron hydrotalcite nanofiber membrane as well as preparation method and application thereof

Abstract

The invention discloses a tannic acid-iron surface modified cobalt-iron hydrotalcite nanofiber membrane as well as a preparation method and application thereof, and relates to the technical field of fiber membrane materials. The invention provides a preparation method of a cobalt-iron hydrotalcite nanofiber membrane. According to the preparation method, adsorption and catalysis functions are simultaneously introduced to the nanofiber membrane to realize synergistic modification. Due to the synergistic effect, the removal efficiency of pollutants can be remarkably improved, and the problem of balancing between degradation efficiency and water flux increase in a traditional method can be effectively solved.

Description

Technical Field

[0001] The present invention relates to the technical field of fiber membrane materials, and in particular to a tannic acid-iron surface-modified cobalt-iron hydrotalcite nanofiber membrane and a preparation method and application thereof. Background Art

[0002] Pharmaceuticals and personal care products (PPCPs) are widely used in daily life and industry, but they are persistent and accumulative in the aquatic environment and are emerging new pollutants in recent years. These pollutants have been detected in many river basins, including antibiotics, hormones, and cosmetics, posing significant risks to the aquatic ecosystem and human health. Traditional wastewater treatment methods, such as flocculation and biological methods, often have high energy consumption, low efficiency, and low reaction kinetics for removal. The annual emissions of PPCPs are gradually increasing, and there is an urgent need to develop methods with low energy consumption, high reaction equilibrium constants, and high removal efficiencies to remove PPCPs. Catalytic membranes, by combining advanced oxidation processes (AOPs) with membrane filtration, represent an innovative approach. This method not only solves the problem of catalyst recovery but also improves the reaction kinetics by improving the contact between reactants and catalysts, thus being widely applied. Among them, nanofiber-based membranes are particularly favored due to their high porosity and large specific surface area, making them very suitable for the application of high-permeability catalytic membranes. It can effectively immobilize the catalyst in the pores, exposing more active sites, thus obtaining high-quality transport efficiency in the flow of catalytic nanofibers. In addition, using the ultrafiltration system of nanofiber membranes to convert the static catalytic process into a dynamic, multi-mechanism capture process, the degradation rate far exceeds traditional methods, and low-energy filtration is achieved under low hydraulic resistance.

[0003] Currently, existing membranes mostly adopt the method of simply depositing functional materials on the membrane surface, which often leads to low mass transfer efficiency between the membrane and pollutants and insufficient contact with pollutants. These problems not only reduce the water flux of the membrane but also weaken the pollutant removal effect.

[0004] In view of this, the present application is proposed. Summary of the Invention

[0005] Based on this, the purpose of the present invention is to overcome the deficiencies of the above-mentioned prior art and provide a tannic acid-iron surface-modified cobalt-iron hydrotalcite nanofiber membrane and a preparation method and application thereof.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is: A preparation method of a tannic acid-iron surface-modified cobalt-iron hydrotalcite nanofiber membrane, comprising the following steps:

[0007] (1) Prepare an aqueous solution of PDDA (poly(diallyldimethylammonium chloride)) - PVA (polyvinyl alcohol), prepare a membrane material by electrospinning, vacuum-dry the membrane material and then soak it in Solution 1, and obtain a PDDA-PVA nanofiber membrane after washing;

[0008] (2) Soak the PDDA-PVA nanofiber membrane in Solution 2, then carry out a hydrothermal reaction, wash and dry it, and then carry out alkali etching, and wash and dry to obtain the cobalt-iron hydrotalcite nanofiber membrane;

[0009] (3) Soak the cobalt-iron hydrotalcite nanofiber membrane in Solution 3, and transfer it to Solution 4 for soaking after a period of time to obtain the tannic acid-iron surface-modified cobalt-iron hydrotalcite nanofiber membrane.

[0010] In the present invention, the synergistic modification is achieved by simultaneously introducing adsorption and catalytic functions on the nanofiber membrane. This synergistic effect can not only significantly improve the removal efficiency of pollutants, but also effectively overcome the trade-off problem between the degradation efficiency and the increase in water flux in traditional methods.

[0011] Preferably, in the step (1), in the PDDA-PVA aqueous solution, the mass fraction of PVA is 4-8%, and the mass fraction of PDDA is 0.5-4%; further preferably, in the PDDA-PVA aqueous solution, the mass fraction of PVA is 8%, and the mass fraction of PDDA is 3%.

[0012] Preferably, in the step (1), heat the PDDA aqueous solution and the PVA aqueous solution in a constant temperature water bath at 60-100 °C for 4-10 h until completely dissolved, and then cool to eliminate all the bubbles in the solution. Further preferably, heat in a constant temperature water bath at 95 °C for 6 h.

[0013] The inventors found in the actual experiment process that the concentration of PDDA has an important influence on the properties of the nanofiber membrane. As an adsorption material, PDDA can enhance the adsorption performance of the membrane after being added, so it is generally considered that the higher the concentration of PDDA, the better. However, PDDA also has significant hydrophilicity, and the increase in its concentration will increase the hydrophilicity of the membrane, thereby increasing the water flux, which may lead to a shortening of the residence time of pollutants on the membrane surface, and thus affect the removal effect. In addition, the water bath temperature and treatment time need to ensure that the molecular chains of PDDA and PVA are fully stretched, and PDDA is completely dissolved in the PVA aqueous solution to obtain a uniform spinning solution system.

[0014] Preferably, in the step (1), a 5 mL syringe is used. The nanofiber membrane is prepared by electrospinning technology, and the electrospinning parameters are set as follows: the applied voltage is 12 - 25 kV, the feeding rate is 0.2 - 1 mL / h, the receiving distance is 10 - 20 cm, and the receiving rotation speed is 50 - 200 rpm; preferably, the electrospinning parameters are set as follows: the applied voltage is 18 kV, the feeding rate is 0.4 mL / h, the receiving distance is 15 cm, and the receiving rotation speed is 100 rpm.

[0015] During the actual experiment, the inventors found that since both PDDA and PVA are macromolecular materials, the concentration of PDDA has a significant impact on parameter selection. When the concentration of PDDA is high, if the parameters are set too low, it may cause needle hole blockage; while if the parameters are too high, it will enhance the electrostatic effect, affecting the continuity and uniformity of electrospinning. Therefore, reasonable parameters need to be selected to ensure consistent electrospinning conditions at different PDDA concentrations.

[0016] Preferably, in the step (1), the temperature of vacuum drying is 40 - 80 °C, and the time of vacuum drying is 6 - 24 h; the solution 1 is a mixed solution of acetic acid, glutaraldehyde, and hydrochloric acid, and the volume ratio of acetic acid:glutaraldehyde:hydrochloric acid is acetic acid:glutaraldehyde:hydrochloric acid = 96:4:0.1, and the soaking time is 0.1 - 2 h; preferably, the temperature of vacuum drying is 60 °C, the time of vacuum drying is 12 h, and the soaking time is 0.5 h.

[0017] Preferably, in the step (1), the PDDA - PVA nanofiber membrane is obtained after washing and stored in deionized water for standby.

[0018] During the actual experiment, the inventors found that since the PDDA - PVA molecular chain contains a large number of hydroxyl groups, its excessive hydrophilicity will affect the stability of the membrane material in the aqueous environment. Cross - linking with glutaraldehyde can effectively improve this property, but the cross - linking time needs to be precisely controlled: insufficient cross - linking will cause the membrane material to swell or even dissolve in water, while excessive cross - linking will significantly reduce the hydrophilicity of the membrane, thereby affecting its permeation performance.

[0019] Preferably, in the step (2), the solution 2 is a mixed solution of urea, cobalt salt, and iron salt, and the molar ratio of urea:cobalt salt:iron salt is urea:cobalt salt:iron salt = 70 mmol:7.5 mmol:2.5 mmol; the cobalt salt is selected from at least one of cobalt chloride, cobalt sulfate, cobalt nitrate, and their hydrates, and the iron salt is selected from at least one of ferric chloride, ferric sulfate, and ferric nitrate;

[0020] and / or, the soaking time is 0.5 - 2 h;

[0021] and / or, the temperature of the hydrothermal reaction is 100 - 120 °C, and the reaction time is 8 - 15 h;

[0022] and / or, the drying temperature is 40 - 80 °C;

[0023] Further preferably, the soaking time is 1 h, the hydrothermal reaction temperature is 120 °C, the reaction time is 12 h, and the drying temperature is 60 °C.

[0024] The inventors found during the actual experiment that during the preparation of high-performance CoFe-LDHs nanofiber membranes (cobalt iron hydrotalcite nanofiber membranes), the regulation of the metal ratio can significantly change their crystal structure, lamellar charge density, and physical and chemical properties.

[0025] The inventors found during the actual experiment that the soaking time directly affects the loading effect of metal ions on the surface of nanofibers, and further provides sites for the nucleation of subsequent LDHs. When the soaking time is insufficient, the metal ion loading rate is low. After the time is too long, the loading rate tends to saturate, and it may cause fiber swelling, affecting the structural stability.

[0026] The inventors found during the actual experiment that during the growth of PDDA-PVA nanofibers, since the PVA molecule contains abundant hydroxyl groups, and the LDHs surface also has a large number of hydroxyl groups, this provides a large number of natural nucleation sites for the growth of LDHs on PDDA-PVA nanofibers. This characteristic enables LDHs to directly grow on PDDA-PVA nanofibers without any chemical modification or pretreatment of the substrate membrane, thus achieving one-step reaction completion. Therefore, by selecting the hydrothermal method and slow crystallization, LDHs are uniformly nucleated and grown, with simple and controllable operation.

[0027] Preferably, in the step (2), the conditions for alkali etching are as follows: the concentration of urea used is 0.5 - 5 mmol / L, the alkali etching temperature is 30 - 50 °C, and the alkali etching time is 0.5 - 3 h; preferably, the concentration of urea used is 2.5 mmol / L, the alkali etching temperature is 40 °C, and the alkali etching time is 2 h.

[0028] Constructive defect engineering is an effective strategy to improve the performance of catalysts by enhancing the synergistic effect. By introducing defects at the atomic scale, the distribution of active sites in the material is improved. Therefore, by etching the Co(II) or Fe(III) sites in LDHs, a large number of defects are generated, thus significantly enhancing the catalytic activity. It should be noted that the etching conditions have a significant impact on the results. The increase in time will exacerbate the etching degree of the metal, resulting in the generation of a large number of defects, which may significantly reduce the crystallinity of LDHs, and further weaken its binding strength on the membrane, ultimately affecting the loading amount of LDHs on the membrane.

[0029] Preferably, in the step (3), Solution 3 is an FeCl3·6H2O solution with a volume molar concentration of 1 - 10 mM, and the soaking time in Solution 3 is 3 - 30 min; Solution 4 is a tannic acid solution with a volume molar concentration of 1 - 5 mM, and the soaking time in Solution 4 is 10 - 60 s; Further preferably, Solution 3 is an FeCl3·6H2O solution with a volume molar concentration of 7.2 mM, and the soaking time in Solution 3 is 30 min; Solution 4 is a tannic acid (TA) solution with a volume molar concentration of 2.4 mM, and the soaking time in Solution 4 is 30 s.

[0030] The inventors found during the actual experiment that by adjusting the complexation times of TA and Fe 3+ (i.e., the number of repetitions of step (3)) and performing a drying treatment after each operation, precise regulation of the adsorption performance of the LDH composite membrane can be achieved. The phenolic hydroxyl groups in TA react with Fe 3+ to undergo a complexation reaction, and one complexation process of TA and Fe 3+ (TA-Fe) attaches to the membrane surface. This step can be repeated multiple times as needed until the desired amount of TA-Fe complex is formed on the membrane surface. The TA-Fe complex structure shows a significant positive charge on its surface and can efficiently adsorb negatively charged pollutants through strong electrostatic interactions.

[0031] In addition, the present invention provides a tannic acid-iron surface-modified cobalt-iron layered double hydroxide nanofiber membrane prepared by the preparation method of the tannic acid-iron surface-modified cobalt-iron layered double hydroxide nanofiber membrane.

[0032] Furthermore, the present invention provides the application of the tannic acid-iron surface-modified cobalt-iron layered double hydroxide nanofiber membrane in the field of water treatment.

[0033] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention realizes synergistic modification by simultaneously introducing adsorption and catalytic functions on the nanofiber membrane. This synergistic effect can significantly improve the removal efficiency of pollutants. That is, by optimizing the combination of the adsorption material and the catalytic material (cobalt-iron layered double hydroxide) and regulating process parameters (such as PDDA concentration, etching conditions, etc.), high-efficiency pollutant degradation can be achieved while ensuring a high water flux, thereby providing an efficient and sustainable solution for the field of water treatment. Description of the Drawings

[0034] Figure 1 SEM image of the pure PVA fiber membrane prepared in Test Example 1;

[0035] Figure 2 SEM image of the PDDA-3-PVA nanofiber membrane prepared in Test Example 4;

[0036] Figure 3SEM image of the unetched cobalt-iron hydrotalcite nanofiber membrane prepared in Test Example 4';

[0037] Figure 4 SEM image of the cobalt-iron hydrotalcite nanofiber membrane prepared in Test Example 4'';

[0038] Figure 5 SEM image of the tannic acid-iron surface-modified cobalt-iron hydrotalcite nanofiber membrane prepared in Test Example 4''';

[0039] Figure 6 Schematic diagram of the filtration device;

[0040] Figure 7 Performance diagrams of the nanofiber membranes prepared in Test Examples 1 - 5;

[0041] Figure 8 Performance diagrams of the cobalt-iron hydrotalcite nanofiber membranes prepared in Test Examples 21'' - 23'' and Test Example 4'';

[0042] Figure 9 Adsorption / catalysis comparative performance diagrams of Test Example 4, Test Example 1', Test Example 4', and Test Example 4'';

[0043] Figure 10 Comparative performance diagrams of Test Example 4''', Test Examples 25''' - 27''' of the complexed TA-Fe membranes with different numbers of times and uncomplexed Test Example 4'; Detailed implementation manners

[0044] To better illustrate the purpose, technical solutions, and advantages of the present invention, the present invention will be further described below in conjunction with the accompanying drawings and specific embodiments. The purpose is to understand the content of the present invention in detail, rather than to limit the present invention. All other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the protection scope of the present invention. The experimental reagents and instruments designed in the embodiments and comparative examples of the present invention are all common ordinary reagents and instruments, unless otherwise specified, and can be obtained from commercial channels. In the embodiments and comparative examples, the experimental methods used are all conventional methods unless otherwise specified; and unless otherwise specified, the raw materials used in parallel experiments are from the same batch of raw materials.

[0045] The following is an explanation of all the raw materials in the process of the specific implementation manner of the present application, but is not limited to the following raw materials:

[0046] PDDA: (C2H4O)n, Mw = 7000, Macklin Reagent Co., Ltd.;

[0047] PVA: (C8H 16 CIN)n, Mw = 200000, Aladdin Reagent Co., Ltd.;

[0048] All the other raw materials are conventional commercially available products.

[0049] Test Example A - Preparation of PDDA-PVA nanofiber membrane

[0050] Test Examples 1-5

[0051] The present invention provides a method for preparing a PDDA-PVA nanofiber membrane, which includes the following steps: preparing an aqueous solution of PDDA (polydiallyldimethylammonium chloride)-PVA (polyvinyl alcohol), preparing a membrane material by electrospinning, vacuum-drying the membrane material and then soaking it in Solution 1, and washing to obtain a PDDA-PVA nanofiber membrane.

[0052] Specifically, in the PDDA-PVA aqueous solution, the mass fraction of PVA is 8wt%, and the mass fractions of PDDA are 0, 1, 2, 3, 4wt%. After being completely dissolved by heating in a water bath at 95°C for 6h and then cooled until the bubbles disappear, it is injected into a 5 mL syringe. The electrospinning technique is used to prepare a nanofiber membrane, and the parameter settings are: applied voltage 18 kV, propulsion rate 0.4 mL / h, receiving distance 15 cm, and receiving rotation speed 100 rpm. The obtained fiber membrane is vacuum-dried at 60°C for 12h and then immersed in Solution 1 (96 mL acetic acid, 4 mL glutaraldehyde, and 0.1 mL hydrochloric acid) for 0.5h. After cross-linking, the membrane material is thoroughly rinsed with deionized water and stored in deionized water for standby.

[0053] Test Examples 1-5 are named PDDA-0 (mass fraction of PDDA 0wt%, i.e., without PDDA), PDDA-1 (mass fraction of PDDA 1wt%), PDDA-2 (mass fraction of PDDA 2wt%), PDDA-3 (mass fraction of PDDA 3wt%), PDDA-4 (mass fraction of PDDA 4wt%) according to different mass fractions of PDDA; that is, Test Example 1 prepares a PDDA-0-PVA nanofiber membrane, Test Example 2 prepares a PDDA-1-PVA nanofiber membrane, Test Example 3 prepares a PDDA-2-PVA nanofiber membrane, Test Example 4 prepares a PDDA-3-PVA nanofiber membrane, and Test Example 5 prepares a PDDA-4-PVA nanofiber membrane.

[0054] Test Examples 6-9

[0055] Compared with the PDDA-3-PVA nanofiber membrane prepared in Test Example 4, only the water bath temperature and time of the PDDA and PVA aqueous solutions are different during the preparation process. Specifically:

[0056] Test Example 6 - Heating in a water bath at 60°C for 10h.

[0057] Test Example 7 - Heating in a water bath at 100°C for 4h.

[0058] Test Example 8 - Heated in a 50°C water bath for 12 h.

[0059] Test Example 9 - Heated in a 120°C water bath for 2 h.

[0060] Test Examples 10 - 11

[0061] Compared with the PDDA-3-PVA nanofiber membrane prepared in Test Example 4, only the electrospinning technique was used to prepare the nanofiber membrane during the preparation process, and the parameter settings were different.

[0062] Test Example 10 - Electrospinning parameter settings: applied voltage 15 kV, advancing rate 0.8 mL / h, receiving distance 10 cm, receiving rotation speed 150 rpm.

[0063] Test Example 11 - Electrospinning parameter settings: applied voltage 25 kV, advancing rate 0.2 mL / h, receiving distance 20 cm, receiving rotation speed 50 rpm.

[0064] Test Examples 12 - 15

[0065] Compared with the PDDA-3-PVA nanofiber membrane prepared in Test Example 4, only the immersion time in Solution 1 (96 mL acetic acid, 4 mL glutaraldehyde, and 0.1 mL hydrochloric acid) was different during the preparation process.

[0066] Test Example 12 - Immersion for 0.1 h.

[0067] Test Example 13 - Immersion for 1.5 h.

[0068] Test Example 14 - Immersion for 1 min.

[0069] Test Example 15 - Immersion for 2.5 h.

[0070] Test Example B - Prepared an unetched cobalt-iron hydrotalcite nanofiber membrane.

[0071] Test Examples 1' - 15'

[0072] The PDDA-PVA nanofiber membranes prepared in Test Examples 1 - 15 were respectively used to prepare unetched cobalt-iron hydrotalcite nanofiber membranes by the following method.

[0073] Weigh 4.2 g (70 mmol) of urea, 2.182 g (7.5 mmol) of cobalt nitrate hexahydrate, and 1.010 g (2.5 mmol) of iron nitrate nonahydrate and pour them into a beaker. Add 100 mL of deionized water to form Solution 2, and stir magnetically for 30 minutes. Immerse the PDDA-PVA nanofiber membranes prepared in Test Examples 1-15 in Solution 2 for 1 h respectively, and transfer them together to the inner liner of a hydrothermal reaction kettle. Hydrothermally react in an oven at 120 °C for 12 hours. After the reaction is completed, wash the surface of the nanofiber membrane with deionized water to remove the excess cobalt-iron hydrotalcite, and place it in a vacuum drying oven at 60 °C for 8 hours for standby to obtain the unetched cobalt-iron hydrotalcite nanofiber membrane.

[0074] Specifically, the unetched cobalt-iron hydrotalcite nanofiber membrane prepared in Test Example 1’ is obtained by the above method using the PDDA-PVA nanofiber membrane of Test Example 1.

[0075] The unetched cobalt-iron hydrotalcite nanofiber membrane prepared in Test Example 15’ is obtained by the above method using the PDDA-PVA nanofiber membrane of Test Example 15.

[0076] And so on, not listed one by one.

[0077] Test Examples 16’ - 19’

[0078] Compared with the unetched cobalt-iron hydrotalcite nanofiber membranes prepared in Test Example 16’ and Test Example 4’, only the immersion time in Solution 2 is different during the preparation process.

[0079] Test Example 16’ - Immersion in Solution 2 for 0 h.

[0080] Test Example 17’ - Immersion in Solution 2 for 0.5 h.

[0081] Test Example 18’ - Immersion in Solution 2 for 2 h.

[0082] Test Example 19’ - Immersion in Solution 2 for 3 h.

[0083] Test Example C - Obtain the cobalt-iron hydrotalcite nanofiber membrane

[0084] Test Examples 1” - 19”

[0085] Respectively, use the following method to prepare the cobalt-iron hydrotalcite nanofiber membranes from the unetched cobalt-iron hydrotalcite nanofiber membranes prepared in Test Examples 1’ - 19’.

[0086] Put the prepared cobalt-iron hydrotalcite nanofiber membrane into an aqueous sodium hydroxide solution with a concentration of 2.5 mmol / L and heat it in a water bath. The temperature of alkali etching is 40 °C, and the time of alkali etching is 2 h. Then wash it with deionized water and dry it.

[0087] Specifically, the cobalt-iron hydrotalcite nanofiber membrane prepared in Test Example 1 was obtained by using the unetched cobalt-iron hydrotalcite nanofiber membrane of Test Example 1' and preparing it through the above method.

[0088] Test Examples 20'' - 24''

[0089] Compared with the cobalt-iron hydrotalcite nanofiber membrane prepared in Test Example 20'' and Test Example 4'', only the alkali etching time is different during the preparation process.

[0090] Test Example 20'' - The alkali etching time is 0 h.

[0091] Test Example 21'' - The alkali etching time is 0.5 h.

[0092] Test Example 22'' - The alkali etching time is 1 h.

[0093] Test Example 23'' - The alkali etching time is 3 h.

[0094] Test Example 24'' - The alkali etching time is 4 h.

[0095] Test Example D - Preparation of tannic acid-iron surface-modified cobalt-iron hydrotalcite nanofiber membrane

[0096] Test Examples 1''' - 24'''

[0097] The cobalt-iron hydrotalcite nanofiber membranes prepared in Test Examples 1'' - 24'' were respectively prepared into tannic acid-iron surface-modified cobalt-iron hydrotalcite nanofiber membranes by the following method.

[0098] The cobalt-iron hydrotalcite nanofiber membranes prepared in Test Examples 1'' - 24'' were immersed in a 7.2 mM FeCl3·6H2O solution. After 30 min, the membrane was thoroughly rinsed with deionized water to remove the unreacted Fe 3+ ions, and it was transferred to a 2.4 mM tannic acid solution and immersed for 30 s to obtain the tannic acid-iron surface-modified cobalt-iron hydrotalcite nanofiber membrane. (The complexation times of TA and Fe 3+ are 4, that is, after 30 min in a 7.2 mM FeCl3·6H2O solution, the membrane was thoroughly rinsed with deionized water and repeated 4 times)

[0099] Specifically, the tannic acid-iron surface-modified cobalt-iron hydrotalcite nanofiber membrane prepared in Test Example 1''' was obtained by using the cobalt-iron hydrotalcite nanofiber membrane of Test Example 1'' and preparing it through the above method.

[0100] Test Examples 25''' - 27'''

[0101] In comparison with the tannic acid-iron surface-modified cobalt-iron hydrotalcite nanofiber membrane prepared in Test Example 4''', only the complexation times of TA and Fe 3+ are different. By successively performing TA-Fe 3+ complexation and drying treatment, the subsequent complexation reacts on the basis of the film formed in the previous time, thereby preparing composite membranes with different complexation times.

[0102] Test Example 25''' —— The complexation times of TA and Fe 3+ is 1. (That is, in a FeCl3·6H2O solution with a volume molar concentration of 7.2 mM, after 30 min, the membrane was rinsed thoroughly with deionized water once)

[0103] Test Example 26''' —— The complexation times of TA and Fe 3+ is 2. (That is, in a FeCl_{3}·6H_{2}O solution with a volume molar concentration of 7.2 mM, after 30 min, the membrane was repeatedly rinsed with deionized water 2 times)

[0104] Test Example 27''' —— The complexation times of TA and Fe 3+ is 3. (That is, in a FeCl_{3}·6H_{2}O solution with a volume molar concentration of 7.2 mM, after 30 min, the membrane was repeatedly rinsed with deionized water 3 times)

[0105] The surface morphology of the nanofiber membrane was analyzed using a Hitachi Regulus 8100 scanning electron microscope from Shimadzu Corporation, Japan.

[0106] Morphology analysis was respectively performed on the PDDA-0-PVA nanofiber membrane (pure PVA fiber membrane) prepared in Test Example 1, the PDDA-3-PVA nanofiber membrane prepared in Test Example 4, the unetched cobalt-iron hydrotalcite nanofiber membrane prepared in Test Example 4', the cobalt-iron hydrotalcite nanofiber membrane prepared in Test Example 4'', and the tannic acid-iron surface-modified cobalt-iron hydrotalcite nanofiber membrane prepared in Test Example 4'''. The results are as Figure 1-5 shown.

[0107] As Figure 1 can be seen, the scanning electron microscope images show that the pure PVA fiber membrane prepared in Test Example 1 exhibits a smooth and porous structure ( Figure 1 ). When PDDA modification is added (the PDDA-3-PVA nanofiber membrane prepared in Test Example 4), the morphology of the PVA membrane does not change significantly ( Figure 2 ). However, after modifying with cobalt-iron hydrotalcite (the unetched cobalt-iron hydrotalcite nanofiber membrane prepared in Test Example 4', Figure 3), when the Co / Fe precursor ratio is 3:1, the LDHs nanosheets are uniformly wound around the fiber surface, forming well-dispersed active sites. At the same time, the stacking of large-sized LDHs sheet structures is observed. After alkali etching treatment (the cobalt-iron hydrotalcite nanofiber membrane prepared in "Experimental Example 4"), the small LDHs structures on the nanofiber surface remain stable and do not change significantly( Figure 4 ), but it can be observed that the number of large LDHs decreases. There is no obvious change in the nanofiber membrane complexed 4 times( Figure 5 ).

[0108] Performance Test - 2

[0109] The determination of water flux and removal effect was completed through a gravity-driven flow filtration experiment. The specific operation is to place the nanofiber membrane in the filtration device (the effective filtration area is 3.5 cm 2 ), and the water level height is controlled by adjusting the inlet water speed of the pump, thereby realizing the filtration process relying on gravity. The schematic diagram of the filtration device is as Figure 6 shown.

[0110] Tetracycline (TC) was selected to represent PPCPs pollutants. After preparing 200 mL of TC aqueous solution (5 mg / L, 10 mg / L, or 15 mg / L), 4 mg of peroxymonosulfate (PMS) was added to carry out the oxidation reaction. The flow filtration experiment was driven by gravity, and all membranes were controlled to have the same flux (by changing the water column height). Samples were taken every once in a while and detected and calculated by ultraviolet spectrophotometry (the maximum absorption peak of TC is 360 nm) to obtain the removal rate.

[0111] The test results are as Figure 7-10 shown in Table 1.

[0112] As Figure 7 shown (selecting a TC concentration of 5 mg / L and no PMS), by changing the mass percentage content of PDDA, the change in the pollutant adsorption effect can be observed (i.e., testing the nanofiber membranes prepared in Experimental Examples 1 - 5). As the PDDA content increases, its adsorption effect gradually enhances, and the removal effect also improves accordingly. However, when the PDDA content exceeds 4 wt%, the removal effect begins to decline. This may be attributed to the strong hydrophilicity of PDDA, resulting in an increase in the water permeability of the membrane, thereby shortening the residence time of pollutants in the membrane and affecting the removal efficiency.

[0113] As Figure 8As shown (selecting a TC concentration of 10 mg / L with PMS), by adjusting the alkali etching time, its effect on the removal efficiency was studied (i.e., testing the cobalt-iron layered double hydroxide nanofiber membranes prepared in Test Examples 20”-23” and Test Example 4”). The results showed that alkali etching could significantly improve the removal efficiency, which was mainly attributed to the structural defects introduced during the alkali etching process, increasing the active sites in the material, thereby enhancing the catalytic performance. It was found that the removal rate of the cobalt-iron layered double hydroxide nanofiber membrane prepared by alkali etching for 2 hours remained above 99%. However, when the etching time exceeded 3 hours, the removal effect began to decline. Excessive etching time may lead to the generation of a large number of defects, reducing the crystallinity of LDHs, and then weakening its binding strength on the membrane, ultimately affecting the loading amount of LDHs.

[0114] As Figure 9 shown (selecting a TC concentration of 10 mg / L), the unetched cobalt-iron layered double hydroxide nanofiber membranes prepared in Test Example 1’ and Test Example 4’ were tested.

[0115] From Membrane Test Examples 1’ and 4’, it can be seen that there is a large gap between without adsorption and with adsorption. While having an adsorption effect, by enhancing the catalytic performance, the removal efficiency of pollutants can be significantly improved. This is mainly due to the fact that the adsorption effect enables pollutants to be rapidly enriched on the membrane surface, thus accelerating the contact between the catalyst and pollutants and promoting the catalytic reaction. Then, by etching the LDHs to form structural defects, the catalysis is accelerated. This synergistic effect of adsorption and catalysis can efficiently and rapidly remove pollutants.

[0116] As Figure 10 shown (selecting a TC concentration of 15 mg / L), as the number of complexation times increases, the removal efficiency of the membrane for pollutants significantly improves, which is mainly attributed to the enhanced adsorption ability brought by the TA-Fe complexation structure. When the number of complexation times reaches 3 - 4 times, the removal effect gradually tends to be saturated, because the number of TA-Fe sites available for complexation on the membrane surface is limited, resulting in the adsorption capacity approaching the maximum value. This synergistic mechanism of adsorption-catalysis not only realizes the efficient enrichment of pollutants but also promotes rapid degradation through surface catalytic reactions, thus significantly improving the overall removal efficiency.

[0117] Table 1

[0118] Case Flux (L·m-2·h-1·bar-1) Test Example 4 79900 Test Example 1’ 24100 Test Example 4’ 30495 Test Example 4” 35620 Experimental Example 4”’ 32850

[0119] Table 1 shows that the water flux of the fiber membrane in Test Example 4’ after LDHs modification decreased from 79900 to 30495 L·m -2 ·h -1 ·bar -1, the increase in pore channel resistance is caused by the increased coverage of LDHs nanosheets. The hydrophilicity of PDDA results in Test Example 1’ < Test Example 4’. The slight detachment of LDHs caused by alkali etching leads to Test Example 4’ < Test Example 4”. The membrane flux experimental example 4”’ complexed with TA-Fe is not much different from the modified strong one. All of the above are consistent with SEM.

[0120] In summary, the PVA nanofibers modified by adsorption exhibit excellent pollutant adsorption performance. On this basis, cobalt-iron layered double hydroxides are further grown to introduce catalytic functions, and the hydrotalcite is etched to enhance its active defects, thus significantly improving the catalytic effect. This synergistic effect of adsorption and catalysis can not only efficiently and rapidly remove pollutants, but also maintain excellent high permeability. These dual advantages in terms of pollutant removal and water flux highlight the great potential and application prospects of this material in the field of efficient water treatment.

[0121] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A preparation method of a tannic acid-iron surface-modified cobalt-iron hydrotalcite nanofiber membrane, characterized in that, It includes the following steps: (1) Prepare a PDDA-PVA aqueous solution, prepare a membrane material by electrospinning, vacuum dry the membrane material and then soak it in Solution 1, and wash it to obtain a PDDA-PVA nanofiber membrane; (2) Soak the PDDA-PVA nanofiber membrane in Solution 2, then carry out a hydrothermal reaction, wash and dry it, and then carry out alkali etching, and wash and dry to obtain the cobalt-iron hydrotalcite nanofiber membrane; (3) Soak the cobalt-iron hydrotalcite nanofiber membrane in Solution 3, and transfer it to Solution 4 for soaking after a period of time to obtain the tannic acid-iron surface-modified cobalt-iron hydrotalcite nanofiber membrane.

2. The preparation method of the tannic acid-iron surface-modified cobalt-iron hydrotalcite nanofiber membrane according to claim 1, characterized in that, In the step (1), in the PDDA-PVA aqueous solution, the mass fraction of PVA is 4-8%, and the mass fraction of PDDA is 0.5-4%; Preferably, in the PDDA-PVA aqueous solution, the mass fraction of the PVA is 8%, and the mass fraction of the PDDA is 3%.

3. The preparation method of the tannic acid-iron surface-modified cobalt-iron hydrotalcite nanofiber membrane according to claim 1, characterized in that, In the step (1), the electrospinning setting parameters are as follows: the applied voltage is 12-25 kV, the advancing rate is 0.2-1 mL / h, the receiving distance is 10-20 cm, and the receiving rotation speed is 50-200 rpm; preferably, the electrospinning setting parameters are as follows: the applied voltage is 18 kV, the advancing rate is 0.4 mL / h, the receiving distance is 15 cm, and the receiving rotation speed is 100 rpm.

4. The method for preparing the tannic acid-iron surface-modified cobalt-iron hydrotalcite nanofiber membrane according to claim 1, wherein: In the step (1), the temperature of the vacuum drying is 40-80 °C, and the time of the vacuum drying is 6-24 h; Solution 1 is a mixed solution of acetic acid, glutaraldehyde, and hydrochloric acid, and the volume ratio of acetic acid: glutaraldehyde: hydrochloric acid = acetic acid: glutaraldehyde: hydrochloric acid = 96:4:0.1, and the soaking time is 0.1-2 h; preferably, the temperature of the vacuum drying is 60 °C, the time of the vacuum drying is 12 h, and the soaking time is 0.5 h.

5. The preparation method of the tannic acid-iron surface-modified cobalt-iron hydrotalcite nanofiber membrane according to claim 1, characterized in that, In the step (2), Solution 2 is a mixed solution of urea, cobalt salt, and iron salt, and the molar ratio of urea: cobalt salt: iron salt = 70 mmol: 7.5 mmol: 2.5 mmol; the cobalt salt is selected from at least one of cobalt chloride, cobalt sulfate, cobalt nitrate, and their hydrates, and the iron salt is selected from at least one of ferric chloride, ferric sulfate, and ferric nitrate; and / or, the soaking time is 0.5-2 h; and / or, the temperature of the hydrothermal reaction is 100-120 °C, and the reaction time is 8-15 h; and / or, the drying temperature is 40-80 °C; Preferably, the soaking time is 1 h, the temperature of the hydrothermal reaction is 120 °C, the reaction time is 12 h, and the drying temperature is 60 °C.

6. The preparation method of the tannic acid-iron surface-modified cobalt-iron hydrotalcite nanofiber membrane according to claim 1, wherein, In the step (2), the conditions of the alkali etching are as follows: the concentration of the used urea is 0.5-5 mmol / L, the temperature of the alkali etching is 30-50 °C, and the time of the alkali etching is 0.5-3 h; preferably, the concentration of the used urea is 2.5 mmol / L, the temperature of the alkali etching is 40 °C, and the time of the alkali etching is 2 h.

7. The preparation method of the tannic acid-iron surface-modified cobalt-iron hydrotalcite nanofiber membrane according to claim 1, characterized in that, In step (3), solution 3 is an FeCl3·6H2O solution with a volume molar concentration of 1-10 mM, and the soaking time in solution 3 is 3-30 min; solution 4 is a tannic acid solution with a volume molar concentration of 1-5 mM, and the soaking time in solution 4 is 10-60 s; preferably, solution 3 is an FeCl3·6H2O solution with a volume molar concentration of 7.2 mM, and the soaking time in solution 3 is 30 min; solution 4 is a tannic acid solution with a volume molar concentration of 2.4 mM, and the soaking time in solution 4 is 30 s.

8. A tannic acid-iron surface-modified cobalt-iron hydrotalcite nanofiber membrane prepared by the preparation method of the tannic acid-iron surface-modified cobalt-iron hydrotalcite nanofiber membrane according to any one of claims 1-7.

9. An application of the tannic acid-iron surface-modified cobalt-iron hydrotalcite nanofiber membrane according to claim 8 in the field of water treatment.

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