A honeycomb-like nanofiber membrane for separating emulsified oil in water and a method for preparing the same

Abstract

The application discloses a kind of honeycomb-like nanofiber membrane for separating emulsified oil in water and a preparation method thereof, and belongs to the technical field of functional micro-nanofiber materials.The preparation of the honeycomb-like nanofiber membrane of the application is to first form a TiO2 nanofiber membrane, then immerse the TiO2 nanofiber membrane in a pyrrole solution, and then add a FeCl3 solution for reaction to obtain a TiO2 / PPy nanofiber membrane; finally, immerse the TiO2 / PPy nanofiber membrane in an aqueous solution of Bi(NO3)3·5H2O and an aqueous solution of KX for reaction, respectively, and after 2-6 SILAR cycles, obtain a honeycomb-like TiO2 / PPy / BiOX nanofiber membrane; the honeycomb-like nanofiber membrane not only has a high emulsion separation effect, but also solves the problems of low oil stain degradation efficiency and poor stain resistance of traditional membranes, significantly improving the service life of the nanofiber membrane.

Description

Technical Field

[0001] This invention relates to a honeycomb-like nanofiber membrane for separating emulsified oil in water and its preparation method, belonging to the field of functional micro and nanofiber materials technology. Background Technology

[0002] Frequent oil spills and large-scale discharges of oily wastewater caused by large-scale oil development and transportation have not only wasted petroleum resources but also caused serious damage to the natural ecological environment. Compared with floating oil (particle size > 150 μm) and dispersed oil (particle size 20 μm-150 μm) in water, emulsified oil in water has become a challenge in the field of water purification due to its small particle size and difficulty in settling.

[0003] Existing technologies include centrifugation and chemical methods for separating emulsified oils, but these generally suffer from high energy consumption and low processing efficiency. Membrane separation technology offers advantages such as high cost-effectiveness, simple operation, and low energy consumption, showing great promise in the field of oil-water separation. Electrospun fiber membranes have attracted widespread attention in the field of high-performance oil-water emulsion separation due to their advantages of fine fiber diameter, small pore size, and high porosity. However, traditional electrospun fiber membranes typically have an average pore size of over 2 μm, making them unable to separate emulsified oils with smaller particle sizes (<1 μm). Furthermore, electrospun nanofiber membranes are prone to fouling and have poor antifouling properties, severely limiting their application.

[0004] To improve the separation efficiency of nanofiber membranes, existing technologies involve refining the fiber diameter to prepare small-pore (<0.5μm) fiber membranes, utilizing their physical sieving effect to intercept small-sized emulsified oil in water. For example, Chinese patent CN 107557894B discloses a high-efficiency, high-throughput two-dimensional mesh ultrafine nanofiber oil-water separation material and its preparation method. Specifically, it discloses an ultrathin two-dimensional mesh nanofiber oil-water separation material that utilizes the sieving effect of the nano- or submicron-sized pores (average pore size 10–500 nm) of the fiber membrane to separate emulsified water. However, the diameter of the nanofibers in this two-dimensional mesh is too fine (<50 nm), resulting in poor membrane strength and easy breakage, limiting its practical application.

[0005] To improve the antifouling properties of nanofiber membranes, existing technologies involve modifying the surface of nanofibers with photocatalysts. For example, Chinese patent CN103641243A discloses a floating photocatalytic self-cleaning microbial carrier membrane for removing oil pollution from water and its preparation method. This method loads photocatalytic materials onto the membrane and utilizes photocatalytic degradation of oil pollution to improve the membrane's antifouling properties. However, the fiber skeleton in existing nanofiber membranes lacks catalytic degradation capabilities, resulting in unsatisfactory antifouling effects.

[0006] Therefore, there is a need to develop an oil-water separation membrane with high separation efficiency and the ability to efficiently photocatalytically degrade oil pollution. Summary of the Invention

[0007] To address the problems of low separation efficiency and poor antifouling properties of existing nanofiber membranes for emulsified oil separation, this invention provides a honeycomb-like nanofiber membrane for separating emulsified oil in water and its preparation method. The nanofiber membrane prepared by this invention has a honeycomb-like semi-closed cavity, which enables the membrane to aggregate emulsified oil. That is, the turbulence effect of the water flow in the cavity increases the collision probability between oil droplets, thereby increasing the droplet size and achieving a highly efficient emulsion separation effect. Moreover, all components of the nanofiber membrane are semiconductors with photodegradation function, which solves the problems of low photocatalytic oil degradation efficiency and poor antifouling properties of traditional membranes, and significantly improves the service life of nanofiber membranes.

[0008] The first objective of this invention is to provide a method for preparing a honeycomb-like nanofiber membrane for separating emulsified oil in water, the method comprising the following steps:

[0009] (1) Preparation of TiO2 nanofiber membrane

[0010] A polyvinylpyrrolidone solution was prepared, and isopropyl titanate (TIP) and zirconium acetate (Zr(Ac)4) were added. After stirring evenly under ice bath conditions, a spinning solution was obtained. The spinning solution was electrospun to obtain a hybrid fiber membrane, and the hybrid fiber membrane was then calcined to obtain a TiO2 nanofiber membrane.

[0011] (2) Preparation of TiO2 / PPy nanofiber membrane

[0012] The TiO2 nanofiber membrane obtained in step (1) was immersed in a pyrrole solution, and then FeCl3 solution was added to the pyrrole solution to react. After the reaction was completed, a TiO2 / PPy nanofiber membrane was obtained.

[0013] (3) Preparation of TiO2 / PPy / BiOX nanofiber membrane

[0014] Prepare aqueous solutions of Bi(NO3)3·5H2O and KX, respectively; then, immerse the TiO2 / PPy nanofiber membrane obtained in step (2) in the Bi(NO3)3·5H2O aqueous solution to fully adsorb Bi. 3+ Subsequently, the adsorbed Bi 3+ The nanofiber membrane was then immersed in an aqueous solution of KX to react and generate BiOX nanosheets; this process is recorded as one SILAR cycle; after 2 to 6 SILAR cycles, a honeycomb-like TiO2 / PPy / BiOX nanofiber membrane was obtained; wherein, X in KX is Br, I or Cl.

[0015] In one embodiment, the preparation of the polyvinylpyrrolidone solution in step (1) specifically involves dissolving polyvinylpyrrolidone in a mixed solution of anhydrous ethanol and oxalic acid; wherein the mass concentration of polyvinylpyrrolidone in the polyvinylpyrrolidone solution is 2-10%.

[0016] In one embodiment, the mass concentration of isopropyl titanate (TIP) in step (1) is 1-50% based on the total mass of the spinning solution, and the mass concentration of Zr(Ac)4 is 0.5-10% based on the total mass of the spinning solution, with the molar ratio of Zr element to the total content of Zr and Ti being 1-30 mol.

[0017] In one embodiment, the electrospinning process parameters in step (1) are set as follows: injection speed 0.5~3 mL / h, applied voltage 10~30 kV, ambient temperature 10~30 ℃, and relative humidity 30~90%.

[0018] In one embodiment, the calcination temperature in step (1) is 500~1000℃ and the calcination time is 1~10 h.

[0019] In one implementation, step (3) is performed for 2 to 4 cycles; more preferably 4 cycles.

[0020] In one embodiment, the pyrrole solution in step (2) is prepared by dissolving pyrrole in an HCl solution with a concentration of 1~2 mol / L; wherein the concentration of pyrrole in the pyrrole solution is 0.001~1 g / mL.

[0021] In one embodiment, the preparation of the FeCl3 solution in step (2) is specifically to dissolve FeCl3 powder in an HCl solution with a concentration of 1~2 mol / L; wherein the concentration of FeCl3 in the FeCl3 solution is 0.01~1 g / mL.

[0022] In one embodiment, the reaction in step (2) is carried out at 0-4°C for 0.5-4 hours.

[0023] In one embodiment, the concentration of the Bi(NO3)3·5H2O aqueous solution in step (3) is 1~50 mmol / L; the concentration of the KX aqueous solution is 1~50 mmol / L.

[0024] In one embodiment, step (3) involves immersing the TiO2 / PPy nanofiber membrane in a Bi(NO3)3·5H2O aqueous solution for 10-180 seconds; adsorbing Bi 3+ The nanofiber membrane was then immersed in KX aqueous solution for 10-180 seconds.

[0025] In one embodiment, step (3) may further consist of: preparing aqueous solutions of Bi(NO3)3·5H2O and KBr and KCl respectively; then, immersing the TiO2 / PPy nanofiber membrane obtained in step (2) in the aqueous solution of Bi(NO3)3·5H2O to fully adsorb Bi. 3+ Then adsorb Bi 3+ The nanofiber membrane was then immersed in an aqueous solution of KBr to react and generate BiOBr nanosheets; subsequently, the nanofiber membrane was immersed in an aqueous solution of Bi(NO3)3·5H2O to fully adsorb Bi. 3+ Then adsorb Bi 3+ The nanofiber membrane was then immersed in an aqueous solution of KCl to react and generate BiOCl nanosheets; this process is recorded as one SILAR cycle; after 2 to 4 SILAR cycles, TiO2 / PPy / BiOBr / BiOCl nanofiber membranes were obtained.

[0026] A second objective of this invention is to provide a TiO2 / PPy / BiOX nanofiber membrane prepared by the method described above.

[0027] In one embodiment, the TiO2 / PPy / BiOX nanofiber membrane has a three-layer core-shell structure, including a TiO2 nanofiber core layer, a polypyrrole PPy nanoparticle intermediate layer, and a two-dimensional nanosheet bismuth halide (BiOX) (X=Br or Cl) shell layer.

[0028] In one embodiment, the PPy layer is prepared by in-situ polymerization technology; the two-dimensional nanosheet shell layer, which is the core of the nanofiber membrane for emulsified oil, has the characteristics of semi-closed cavity and hydrophilic and oleophobic wettability, and can efficiently aggregate emulsified oil in water, which is the key to improving the separation efficiency of the nanofiber membrane. It is prepared by continuous ion layer adsorption reaction method; the core, middle and shell layers of the honeycomb-like nanofiber membrane constitute a visible light driven photocatalyst, ensuring effective improvement of antifouling performance.

[0029] In one embodiment, the average pore size of the TiO2 / PPy / BiOX nanofiber membrane is 1.4~2.0μm; in air, the water wetting time of the TiO2 / PPy / BiOX nanofiber membrane is less than 1s, and the underwater oil contact angle of the membrane can reach 159.9°~161.6°.

[0030] In one embodiment, the TiO2 / PPy / BiOX nanofiber membrane has the characteristics of high emulsified oil separation efficiency and good antifouling properties. It has a good separation effect on diesel, gasoline, edible oil and engine oil in water, with a separation efficiency of more than 99%. After the fiber membrane is contaminated by oil, after being irradiated with visible light (<2h), the water flux recovery rate is higher than 99.9%.

[0031] A third objective of this invention is to provide an application of the aforementioned TiO2 / PPy / BiOX nanofiber membrane in the separation of emulsified oil in water.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] (1) The nanofiber membrane prepared by the present invention has a honeycomb-like semi-closed cavity, which makes the membrane have a coalescence effect on emulsified oil. That is, the turbulence effect of water flow in the cavity increases the collision probability between oil droplets, thereby increasing the oil droplet size and achieving efficient emulsion separation.

[0034] (2) Unlike traditional catalyst-modified nanofiber membrane materials, the nanofiber membrane prepared in this invention is composed of all fibers of catalyst, which solves the problems of low efficiency of traditional membrane photocatalytic oil degradation and poor anti-fouling properties, and significantly improves the service life of fiber membrane. Attached Figure Description

[0035] Figure 1 SEM images of the nanofiber membranes prepared in Examples 1-3 and Comparative Examples 1-3 are shown below. (a) shows the TiO2 / PPy / BiOBr-4 nanofiber membrane of Example 1 (4 SILAR cycles); (b) shows the TiO2 / PPy / BiOCl-4 nanofiber membrane of Example 2 (4 SILAR cycles); (c) shows the TiO2 / PPy / BiOBr / BiOCl-2 nanofiber membrane of Example 3 (2 SILAR cycles); (d) shows the TiO2 / PPy nanofiber membrane of Comparative Example 1; (e) shows the TiO2 / PPy / BiOBr-1 nanofiber membrane of Comparative Example 2 (1 SILAR cycle); and (f) shows the PAN / PPy / BiOBr-4 nanofiber membrane of Comparative Example 3 (4 SILAR cycles). Detailed Implementation

[0036] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to examples. However, the present invention is not limited to the examples listed, but should also include any other known modifications within the scope of the claims of the present invention.

[0037] The testing method involved in this invention:

[0038] 1. Appearance

[0039] The morphology of the fiber membrane samples was characterized by scanning electron microscopy (SEM, SU-8010, Hitachi, Japan).

[0040] 2. Aperture

[0041] The pore size distribution of the membrane was determined using a capillary flow meter (CFP-1100A, PMI, USA).

[0042] 3. Contact angle

[0043] The water contact angle of the samples in air and the oil contact angle underwater were tested at room temperature using a contact angle meter (Powereach JC2000D1). The types of oils included diesel, gasoline, edible oil, engine oil, and 1,2-dichloroethane. Since the underwater oil contact angles of different types of oils do not differ significantly, this invention mainly uses 1,2-dichloroethane as an example for illustration.

[0044] 4. Separation performance

[0045] Preparation of oil-in-water emulsion: Mix oil and water at a volume ratio of 1:99, and sonicate at 560 W for 30 min to prepare the oil-in-water emulsion. Use 0.5 g L... 1 The oil can be diesel, gasoline, edible oil, or engine oil, and the particle size of the emulsified oil in the resulting oil-in-water emulsion is less than 1 μm.

[0046] Emulsion separation experiments were conducted by placing the membrane in a dead-end filtration device. The membrane permeation flux (J, Lm) was measured. 2 h 1 Calculate according to formula (1):

[0047] (1)

[0048] After emulsion separation, the filtrate was collected and its total organic carbon content (TOC content, mg / L) was tested. 1 ), calculate the membrane separation efficiency (%) according to formula (2):

[0049] (2)

[0050] 5. Stain resistance

[0051] The antifouling performance was evaluated by testing the membrane water flux recovery rate. First, the flux of pure water through the membrane was named J. 纯水 The oil-in-water emulsion was then separated using a fiber membrane, followed by irradiation of the contaminated fiber membrane with a xenon lamp (λ: 400~1000 nm) for 2 hours. The water flux J of the fiber membrane was then measured. 可见光照射 The separation flux recovery rate (FRR, %) of the fiber membrane is calculated according to formula (3):

[0052] (3)

[0053] Example 1

[0054] A method for preparing a TiO2 / PPy / BiOBr nanofiber membrane includes the following steps:

[0055] (1) Dissolve 0.25 g of polyvinylpyrrolidone (PVP) in a mixed solution of 3 g of anhydrous ethanol and 1.5 g of oxalic acid, and stir for 30 min to obtain a PVP solution; then, slowly add 1 g of isopropyl titanate (TIP) and 0.15 g of zirconium acetate (Zr(Ac)4) to the PVP solution, wherein the molar ratio of Zr element to the total metal content is 11.6%; after stirring evenly in an ice-water bath, a spinning solution is obtained; then the spinning solution is spun at a pouring rate of 1.5 mL / h and an applied voltage of 15 kV, and the ambient temperature and humidity during the electrospinning process are 25±3℃ and 50±5%, respectively. After spinning, a hybrid fiber membrane is obtained; finally, the hybrid fiber membrane is heated to 600℃ at a heating rate of 2℃ / min and calcined in air for 1 h to obtain a TiO2 nanofiber membrane;

[0056] (2) Prepare an HCl solution with a concentration of 1 mol / L, dissolve 0.2 g of pyrrole in 50 mL of HCl solution, and immerse the TiO2 nanofiber membrane prepared in step (1) in the HCl solution containing pyrrole for 1 h under ice bath conditions; then, dissolve 1 g of FeCl3 powder in 15 mL of HCl solution with a concentration of 1 mol / L, and slowly add it dropwise to the solution in which the TiO2 nanofiber membrane is immersed, stir slowly at 0℃ and soak for 2 h to obtain TiO2 / PPy nanofiber membrane;

[0057] (3) The TiO2 / PPy nanofiber membrane prepared in step (2) was immersed in a 5 mmol / L Bi(NO3)3·5H2O aqueous solution for 120 s to adsorb Bi 3+ Ions are removed, and the fiber membrane is then immersed in a 5 mmol / L KBr solution for 120 s to generate BiOBr nanosheets, followed by rinsing with deionized water; the above steps are considered as one complete SILAR cycle. After 4 cycles, a TiO2 / PPy / BiOBr-4 nanofiber membrane with a honeycomb-like structure is obtained.

[0058] Example 2

[0059] A method for preparing a TiO2 / PPy / BiOCl nanofiber membrane includes the following steps:

[0060] (1) Dissolve 0.5 g PVP in a mixed solution of 3 g anhydrous ethanol and 1.5 g oxalic acid and stir for 30 min to obtain a PVP solution; then, slowly add 1 g isopropyl titanate (TIP) and 0.15 g zirconium acetate (Zr(Ac)4) to the PVP solution, wherein the molar ratio of Zr element to total metal content is 11.6%; after stirring evenly in an ice-water bath, a spinning solution is obtained; then the spinning solution is spun at a pouring rate of 1.5 mL / h and an applied voltage of 20 kV. During the spinning process, the ambient temperature and humidity are controlled at 25±3℃ and 50±5%, respectively. After spinning, a hybrid fiber membrane is obtained; finally, the hybrid fiber membrane is heated to 600℃ at a heating rate of 2℃ / min and calcined in air for 1 h to obtain a TiO2 nanofiber membrane;

[0061] (2) Prepare an HCl solution with a concentration of 1 mol / L, dissolve 0.2 g of pyrrole in 50 mL of HCl solution, and immerse the TiO2 nanofiber membrane prepared in step (1) in the HCl solution containing pyrrole for 1 h under ice bath conditions; then, dissolve 1 g of FeCl3 powder in 15 mL of HCl solution with a concentration of 1 mol / L, and slowly add it dropwise to the solution in which the fiber membrane is immersed, stir slowly at 0℃ and soak for 1 h to obtain TiO2 / PPy nanofiber membrane;

[0062] (3) The TiO2 / PPy nanofiber membrane prepared in step (2) was immersed in a 5 mmol / L Bi(NO3)3·5H2O aqueous solution for 90 s to adsorb Bi. 3+ Ions were removed, and the fiber membrane was then immersed in a 5 mmol / L KCl solution for 90 s to generate BiOCl nanosheets, followed by rinsing with deionized water; the above steps are considered as one complete SILAR cycle. After 4 cycles, TiO2 / PPy / BiOCl-4 nanofiber membranes were obtained.

[0063] Example 3

[0064] A method for preparing a TiO2 / PPy / BiOBr / BiOCl nanofiber membrane includes the following steps:

[0065] (1) Dissolve 0.3 g PVP in a mixed solution of 4 g anhydrous ethanol and 2 g oxalic acid, stir for 30 min to obtain a PVP solution; then, slowly add 1 g isopropyl titanate (TIP) and 0.15 g zirconium acetate (Zr(Ac)4) to the PVP solution, wherein the molar ratio of Zr element to total metal content is 11.6%; after stirring evenly in an ice-water bath, a spinning solution is obtained; then the spinning solution is spun at a pouring rate of 1.5 mL / h and an applied voltage of 18 kV, and the ambient temperature and humidity are controlled at 23±3℃ and 45±5% during the spinning process, respectively. After spinning, a hybrid fiber membrane is obtained; finally, the hybrid fiber membrane is heated to 600℃ at a heating rate of 3℃ / min and calcined in air for 1 h to obtain a TiO2 nanofiber membrane;

[0066] (2) Prepare a 1 mol / L HCl solution, dissolve 0.2 g of pyrrole in 50 mL of HCl solution, and immerse the TiO2 nanofiber membrane prepared in step (1) in the HCl solution containing pyrrole for 1.5 h under ice bath conditions; then, dissolve 1 g of FeCl3 powder in 15 mL of 1 mol / L HCl solution and slowly add it dropwise to the solution in which the fiber membrane is immersed, stir slowly at 0℃ and soak for 0.5 h to obtain TiO2 / PPy nanofiber membrane;

[0067] (3) The TiO2 / PPy nanofiber membrane prepared in step (2) was immersed in a 5 mmol / L Bi(NO3)3·5H2O aqueous solution for 150 s to adsorb Bi. 3+ The ions were then removed, and the fiber membrane was immersed in a 5 mmol / L KBr solution for 150 s to react and generate BiOBr nanosheets; subsequently, the fiber membrane was immersed in a 5 mmol / L Bi(NO3)3·5H2O aqueous solution for 150 s to adsorb Bi. 3+ Ions were extracted, and then the fiber membrane was immersed in 5 mmol / L KCl solution for 150 s to react and generate BiOBr / BiOCl nanosheets, which constituted one cycle; after 2 SILAR cycles, TiO2 / PPy / BiOBr / BiOCl-2 nanofiber membrane was obtained.

[0068] Comparative Example 1

[0069] A method for preparing a TiO2 / PPy nanofiber membrane includes the following steps:

[0070] (1) Dissolve 0.25 g PVP in a mixed solution of 3 g anhydrous ethanol and 1.5 g oxalic acid and stir for 30 min to obtain a PVP solution; then, slowly add 1 g isopropyl titanate (TIP) and 0.15 g zirconium acetate (Zr(Ac)4) to the PVP solution, wherein the molar ratio of Zr element to total metal content is 11.6%; after stirring evenly in an ice-water bath, a spinning solution is obtained; spinning is carried out under the conditions of a pouring rate of 1.5 mL / h and an applied voltage of 15 kV, and the ambient temperature and humidity are controlled at 25±3℃ and 50±5% during the spinning process; finally, the hybrid fiber membrane is heated to 600℃ at a heating rate of 2℃ / min and calcined in air for 1 h to obtain a TiO2 nanofiber membrane;

[0071] (2) Prepare a 1 mol / L HCl solution, dissolve 0.2 g of pyrrole in 50 mL of HCl solution, and immerse the TiO2 nanofiber membrane prepared in step (1) in the HCl solution containing pyrrole for 1 h under ice bath conditions; then, dissolve 1 g of FeCl3 powder in 15 mL of 1 mol / L HCl solution and slowly add it dropwise to the solution in which the TiO2 nanofiber membrane is immersed, stir slowly at 0℃ and soak for 2 h to obtain TiO2 / PPy nanofiber membrane.

[0072] Comparative Example 2

[0073] A method for preparing a TiO2 / PPy / BiOBr nanofiber membrane includes the following steps:

[0074] (1) Dissolve 0.25 g of polyvinylpyrrolidone (PVP) in a mixed solution of 3 g of anhydrous ethanol and 1.5 g of oxalic acid, and stir for 30 min to obtain a PVP solution; then, slowly add 1 g of isopropyl titanate (TIP) and 0.15 g of zirconium acetate (Zr(Ac)4) to the PVP solution, wherein the molar ratio of Zr element to the total metal content is 11.6%; after stirring evenly in an ice-water bath, a spinning solution is obtained; then the spinning solution is spun at a pouring rate of 1.5 mL / h and an applied voltage of 15 kV, and the ambient temperature and humidity during the electrospinning process are 25±3℃ and 50±5%, respectively. After spinning, a hybrid fiber membrane is obtained; finally, the hybrid fiber membrane is calcined in air at 600℃ for 1 h at a heating rate of 2℃ / min to obtain a TiO2 nanofiber membrane;

[0075] (2) Prepare a 1 mol / L HCl solution, dissolve 0.2 g of pyrrole in 50 mL of HCl solution, and immerse the TiO2 nanofiber membrane prepared in step (1) in the HCl solution containing pyrrole for 1 h under ice bath conditions; then, dissolve 1 g of FeCl3 powder in 15 mL of 1 mol / L HCl solution and slowly add it dropwise to the solution in which the TiO2 nanofiber membrane is immersed, stir slowly at 0℃ and soak for 2 h to obtain TiO2 / PPy nanofiber membrane;

[0076] (3) The TiO2 / PPy nanofiber membrane prepared in step (2) was immersed in a 5 mmol / L Bi(NO3)3·5H2O aqueous solution for 120 s to adsorb Bi 3+ Ions were removed, and the fiber membrane was then immersed in a 5 mmol / L KBr solution for 120 s to generate BiOBr nanosheets, followed by rinsing with deionized water; thus, a TiO2 / PPy / BiOBr-1 nanofiber membrane with a honeycomb-like structure was obtained.

[0077] Comparative Example 3

[0078] A method for preparing a PAN / PPy / BiOBr nanofiber membrane includes the following steps:

[0079] (1) Dissolve 1 g PAN in 9 g DMF solution to obtain PAN spinning solution; spin the PAN nanofiber membrane under the conditions of 1.5 mL / h injection rate and 25 kV applied voltage. During the spinning process, the ambient temperature and humidity are controlled at 23±3℃ and 50±5%, respectively.

[0080] (2) Prepare a 1 mol / L HCl solution, dissolve 0.2 g of pyrrole in 50 mL of HCl solution, and immerse the PAN nanofiber membrane prepared in step (1) in the HCl solution containing pyrrole for 1 h under ice bath conditions; then, dissolve 1 g of FeCl3 powder in 15 mL of 1 mol / L HCl solution and slowly add it dropwise to the solution in which the PAN nanofiber membrane is immersed, stir slowly at 0℃ and soak for 2 h to obtain PAN / PPy nanofiber membrane;

[0081] (3) The PAN / PPy nanofiber membrane prepared in step (2) was immersed in a 5 mmol / L Bi(NO3)3·5H2O aqueous solution for 120 s to adsorb Bi 3+Ions are removed, and the fiber membrane is then immersed in a 5 mmol / L KBr solution for 120 s to generate BiOBr nanosheets, followed by rinsing with deionized water; the above steps are considered as one complete SILAR cycle. After 4 cycles, a PAN / PPy / BiOBr-4 nanofiber membrane with a honeycomb-like structure is obtained.

[0082] Results Measurement

[0083] 1. Morphological and structural characteristics of nanofiber membranes

[0084] The morphologies of the nanofiber membranes obtained in Examples 1-3 and Comparative Examples 1-3 are as follows: Figure 1 As shown. Figure 1 (a) is the TiO2 / PPy / BiOBr-4 nanofiber membrane of Example 1 (4 SILAR cycles); Figure 1 (b) is the TiO2 / PPy / BiOCl-4 nanofiber membrane of Example 2 (4 SILAR cycles); Figure 1 (c) is the TiO2 / PPy / BiOBr / BiOCl-2 nanofiber membrane of Example 3 (2 SILAR cycles); Figure 1 (d) is the TiO2 / PPy nanofiber membrane of Comparative Example 1; Figure 1 (e) is the TiO2 / PPy / BiOBr-1 nanofiber membrane of Comparative Example 2 (1 SILAR cycle); Figure 1 (f) is the PAN / PPy / BiOBr-4 nanofiber membrane of Comparative Example 3 (4 SILAR cycles).

[0085] As can be seen from the figure, TiO2 / PPy / BiOBr-4, TiO2 / PPy / BiOCl-4, TiO2 / PPy / BiOBr / BiOCl-2, and PAN / PPy / BiOBr-4 nanofiber membranes all have honeycomb-like semi-closed cavities; the surface of TiO2 / PPy nanofiber membrane is relatively smooth and has no two-dimensional nanosheets; the surface of TiO2 / PPy / BiOBr-1 has sparse two-dimensional nanosheets and no semi-closed cavities.

[0086] 2. Analysis of pore structure and wettability of nanofiber membranes

[0087] The pore structure and wettability of the nanofiber membranes obtained in Examples 1-3 and Comparative Examples 1-3 are shown in Table 1. The obtained nanofiber membranes exhibit hydrophilicity and underwater superoleophobicity, with a water wetting time of less than 1 s and an underwater oil contact angle of 159.9-161.6°. Furthermore, the average pore size of each nanofiber membrane is approximately 1.51-1.61 μm, and the pore connectivity is good.

[0088] Table 1. Pore structure and wettability of different fiber membranes

[0089]

[0090] 3. Separation performance and antifouling properties of nanofiber membranes in separating emulsified oil from water.

[0091] The separation performance of the nanofiber membranes obtained in Examples 1-3 and Comparative Examples 1-3 for water-in-diesel emulsions is shown in Table 2. The TiO2 / PPy / BiOBr-4, TiO2 / PPy / BiOCl-4, TiO2 / PPy / BiOBr / BiOCl-2, and PAN / PPy / BiOBr-4 nanofiber membranes exhibited high separation flux (>6500 L / m³). -2 h -1 Simultaneously, the PAN / PPy / BiOBr-4 nanofiber membrane exhibited high separation efficiency (>99.9%) for emulsified oil with a particle size smaller than 1 μm. This is because the turbulent effect of water flow in the semi-closed honeycomb cavities of the fiber membrane increases the collision probability between oil droplets, resulting in larger oil droplet size and thus efficient separation of emulsified oil droplets in water. In contrast, the TiO2 / PPy nanofiber membrane in Comparative Example 1 and the TiO2 / PPy / BiOBr-1 nanofiber membrane in Comparative Example 2 were unable to efficiently separate emulsified oil droplets (separation efficiency <84%). This is because the fiber surfaces of these two types of fiber membranes lack nanosheets or have very few nanosheets, resulting in the absence of semi-closed honeycomb cavities on the fiber surface, making it difficult to generate agglomeration of emulsified oil. In addition, the PAN / PPy / BiOBr-4 nanofiber membrane had poor antifouling properties (flux recovery rate <80%), because the PAN component in the fiber membrane has no catalytic activity, leading to poor antifouling performance.

[0092] Table 2. Oil-water separation performance and flux recovery rate of different fiber membranes

[0093]

[0094] The embodiments provided above are not intended to limit the scope of the invention, nor are the described steps intended to limit the order of execution. Any obvious modifications made to the invention by those skilled in the art based on existing common knowledge also fall within the scope of protection defined by the claims.

Claims

1. A method for preparing a honeycomb-like nanofiber membrane for separating emulsified oil in water, characterized in that, The method includes the following steps: (1) Preparation of TiO2 nanofiber membrane A polyvinylpyrrolidone solution was prepared, and isopropyl titanate (TIP) and zirconium acetate (Zr(Ac)4) were added. After stirring evenly under ice bath conditions, a spinning solution was obtained. The spinning solution was electrospun to obtain a hybrid fiber membrane, and the hybrid fiber membrane was then calcined to obtain a TiO2 nanofiber membrane. The polyvinylpyrrolidone solution is prepared by dissolving polyvinylpyrrolidone in a mixed solution of anhydrous ethanol and oxalic acid. (2) Preparation of TiO2 / PPy nanofiber membrane The TiO2 nanofiber membrane obtained in step (1) was immersed in a pyrrole solution, and then FeCl3 solution was added to the pyrrole solution to react. After the reaction was completed, a TiO2 / PPy nanofiber membrane was obtained. The pyrrole solution is prepared by dissolving pyrrole in an HCl solution with a concentration of 1-2 mol / L. The FeCl3 solution is specifically prepared by dissolving FeCl3 powder in an HCl solution with a concentration of 1-2 mol / L. (3) Preparation of TiO2 / PPy / BiOX nanofiber membrane Prepare aqueous solutions of Bi(NO3)3·5H2O and KX respectively; then, immerse the TiO2 / PPy nanofiber membrane obtained in step (2) in the aqueous solution of Bi(NO3)3·5H2O to fully adsorb Bi. 3+ ; Then, adsorbed Bi 3+ The nanofiber membrane was then immersed in an aqueous solution of KX to react and generate BiOX nanosheets; This process is recorded as 1 SILAR cycle; after 2 to 6 SILAR cycles, a honeycomb-like TiO2 / PPy / BiOX nanofiber membrane is obtained; where X in KX is Br, I or Cl.

2. The method according to claim 1, characterized in that, The polyvinylpyrrolidone mass concentration in the polyvinylpyrrolidone solution in step (1) is 2-10%.

3. The method according to claim 1, characterized in that, In step (1), the mass concentration of isopropyl titanate (TIP) is 1-50% based on the total mass of the spinning solution, and the mass concentration of Zr(Ac)4 is 0.5-10% based on the total mass of the spinning solution. The molar ratio of Zr element to the total content of Zr and Ti is 1-30 mol.

4. The method according to claim 1, characterized in that, The electrospinning process parameters in step (1) are set as follows: injection speed 0.5~3 mL / h, applied voltage 10~30 kV, ambient temperature 10~30 ℃, and relative humidity 30~90%.

5. The method according to claim 1, characterized in that, In step (3), the time for immersing the TiO2 / PPy nanofiber membrane in Bi(NO3)3·5H2O aqueous solution for one SILAR cycle is 10~180s; adsorption of Bi 3+ The nanofiber membrane was then immersed in KX aqueous solution for 10-180 seconds.

6. The method according to claim 1, characterized in that, Step (3) can also be: preparing aqueous solutions of Bi(NO3)3·5H2O and KBr and KCl respectively; then, immersing the TiO2 / PPy nanofiber membrane obtained in step (2) in the aqueous solution of Bi(NO3)3·5H2O to fully adsorb Bi. 3+ Then adsorb Bi 3+ The nanofiber membrane was then immersed in an aqueous solution of KBr to react and generate BiOBr nanosheets; subsequently, the nanofiber membrane was immersed in an aqueous solution of Bi(NO3)3·5H2O to fully adsorb Bi. 3+ Then adsorb Bi 3+ The nanofiber membrane was then immersed in an aqueous solution of KCl to react and generate BiOCl nanosheets. This process is recorded as one SILAR cycle; after 2 to 4 SILAR cycles, TiO2 / PPy / BiOBr / BiOCl nanofiber membranes are obtained.

7. A TiO2 / PPy / BiOX nanofiber membrane, characterized in that, Prepared by the method described in any one of claims 1 to 6.

8. The TiO2 / PPy / BiOX nanofiber membrane according to claim 7, characterized in that, The TiO2 / PPy / BiOX nanofiber membrane has a three-layer core-shell structure, including a TiO2 nanofiber core layer, a polypyrrole (PPy) nanoparticle intermediate layer, and a two-dimensional nanosheet bismuth oxide (BiOX) shell layer.

9. The TiO2 / PPy / BiOX nanofiber membrane according to claim 7, characterized in that, The average pore size of the TiO2 / PPy / BiOX nanofiber membrane is 1.4~2.0 μm; in air, the water wetting time of the TiO2 / PPy / BiOX nanofiber membrane is less than 1s, and the underwater oil contact angle of the membrane can reach 159.9°~161.6°.

10. The application of the TiO2 / PPy / BiOX nanofiber membrane according to any one of claims 7 to 9 in the separation of emulsified oil in water.

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