Preparation method and application of super-hydrophilic-underwater super-oleophobic oil-water separation material

Abstract

The invention discloses a preparation method of a super-hydrophilic-underwater super-oleophobic oil-water separation material. The preparation method comprises the following steps: dissolving polyacrylonitrile and cellulose powder in an organic solvent, and mixing and stirring to obtain a spinning solution; standing the spinning solution, defoaming, carrying out electrostatic spinning on the defoamed spinning solution, and drying after spinning to obtain a polyacrylonitrile cellulose nano composite membrane; the preparation method comprises the following steps: preparing a chitosan cross-linking solution, dipping the polyacrylonitrile cellulose nano-composite membrane in the chitosan cross-linking solution, coating chitosan, cleaning and drying after dipping, and finally obtaining a super-hydrophilic-underwater super-oleophobic oil-water separation material, namely the polyacrylonitrile cellulose cross-linked chitosan composite membrane. The super-hydrophilic-underwater super-oleophobic oil-water separation material prepared by the invention has the advantages of long-acting stability, high flux, high separation efficiency, emulsified oil adaptability and simple and convenient process, and has relatively high flux and separation efficiency of 99% or above for various oil-water emulsions and oil-water emulsions with different concentrations.

Description

Technical Field

[0001] The present invention belongs to the technical field of membrane separation, and in particular relates to a preparation method and application of a super-hydrophilic-underwater super-oleophobic oil-water separation material. Background Art

[0002] With the surge in industrial oily wastewater discharge, efficient oil-water separation technology has become a key requirement for environmental governance. Traditional physical separation methods (such as gravity sedimentation and centrifugal separation) are inefficient for treating emulsified oils, while chemical demulsification methods are prone to secondary pollution and are costly. Membrane separation technology has become a research hotspot due to its advantages such as high efficiency, energy saving, and good selectivity. However, existing separation membranes still face significant bottlenecks in practical application. On the one hand, traditional polymer membranes (such as polyvinylidene fluoride and polysulfone membranes) are prone to membrane fouling and flux drops when treating nano / micron-sized oil-water emulsions due to insufficient surface energy. On the other hand, while recently developed superwetting modified membranes (such as superhydrophilic / underwater superoleophobic membranes) can improve fouling resistance, their surface modification layers often suffer from poor chemical stability (e.g., zinc oxide and titanium dioxide coatings are prone to detachment) and insufficient mechanical strength, resulting in a significant decline in separation performance after long-term use. Furthermore, complex emulsion systems (such as stabilized emulsions containing surfactants) place higher demands on membrane selectivity. Existing membrane materials struggle to achieve both high separation efficiency and high flux, and their preparation processes often involve expensive materials or complex post-processing, hindering their widespread application. Therefore, developing a new separation membrane with long-term stability, compatibility with emulsified oils, and simplified processing remains a challenging technical challenge in this field. Summary of the Invention

[0003] An object of the present invention is to solve at least the above problems and / or disadvantages and to provide at least the advantages which will be described hereinafter.

[0004] In order to achieve these objects and other advantages of the present invention, a method for preparing a super-hydrophilic-underwater super-oleophobic oil-water separation material is provided, characterized in that it comprises the following steps: Step 1: dissolving polyacrylonitrile (PAN) and cellulose powder (CE) in an organic solvent and mixing and stirring to obtain a spinning solution; Step 2: The spinning solution is allowed to stand and then degassed, and the degassed spinning solution is subjected to electrospinning. After the spinning is completed, the spinning solution is dried to obtain a polyacrylonitrile cellulose nanocomposite membrane (PAN / CE); Step 3: Prepare a chitosan (CS) cross-linking solution, then immerse the polyacrylonitrile cellulose nanocomposite membrane (PAN / CE) in the chitosan cross-linking solution to coat it with chitosan. After immersion, wash and dry it to finally obtain a superhydrophilic-underwater superoleophobic oil-water separation material, namely, a polyacrylonitrile cellulose cross-linked chitosan composite membrane (PAN / CE / CS).

[0005] Preferably, in step 1, the organic solvent is any one of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAC), and a mixed solvent of tetrahydrofuran and dimethylformamide.

[0006] Preferably, in step 1, the mass ratio of polyacrylonitrile (PAN) to cellulose (CE) is 4:1 to 1:1, and the stirring time is 12 to 24 hours.

[0007] Preferably, in the step 2, the degassing time of the spinning solution is 1 to 3 hours, and the electrospinning parameters are: the needle is 18 to 24 stainless steel needle; the voltage is 10 to 16 kV; the propulsion speed is 0.5 to 0.8 mL / h; the electrode distance is 10 to 30 cm; the ambient temperature is 10 to 40 ° C; the ambient humidity is 20-50%; and the receiver speed is 100 to 300 r / min.

[0008] Preferably, in step 2, the drying temperature is 70-100° C. and the drying time is 10-14 hours.

[0009] Preferably, in step 3, the chitosan cross-linking solution is prepared by mixing chitosan, acetic acid, and a cross-linking agent in a mass volume ratio of 0.1 g to 0.2 g: 30 to 50 mL: 0.1 to 0.2 mL and stirring uniformly with ultrasonic stirring, wherein the cross-linking agent is one or more of glutaraldehyde, formaldehyde, glyoxal, polyethylene glycol diglycidyl ether, citric acid, sulfate, and natural polyphenols.

[0010] Preferably, in step three, the dipping and cross-linking time is 15-60 seconds, the drying temperature is 70-90° C., and the drying time is 0.5-1 hour.

[0011] Preferably, in step 3, the chitosan cross-linking solution is prepared by: S1, chitosan is added to water, and the pH is adjusted to 5-6 with acetic acid, and the chitosan is stirred to dissolve completely, and then maleic acid is added, heated to react, and freeze-dried after the reaction is completed to obtain modified chitosan, and then the modified chitosan, acetic acid, and a cross-linking agent are mixed in a mass volume ratio of 0.1g-0.2g:30-50mL:0.1-0.2mL and ultrasonically stirred to obtain a modified chitosan cross-linked solution; the cross-linking agent is one or more of glutaraldehyde, formaldehyde, glyoxal, polyethylene glycol diglycidyl ether, citric acid, sulfate, and natural polyphenols; S2. Add carbon nanotubes into water and disperse them by ultrasonication to obtain a carbon nanotube dispersion, which is then added into the modified chitosan cross-linking solution and stirred to obtain a mixed solution.

[0012] Preferably, in S1, the mass ratio of chitosan, water and maleic acid is 0.1:20-30:0.02-0.03, the reaction is heated to 70-80°C for 1-2 hours, and the freeze-drying temperature is -10--20°C, and the freeze-drying is carried out for 4-8 hours.

[0013] Preferably, in S2, the ultrasonic dispersion frequency is 20-40 kHz, the ultrasonic dispersion time is 10-20 min, the concentration of the carbon nanotube dispersion is 3-5 wt %, and the volume ratio of the modified chitosan cross-linking solution to the carbon nanotube dispersion is 1:0.2-0.4.

[0014] The present invention also provides an application of a polyacrylonitrile-cellulose-crosslinked chitosan composite membrane, and the polyacrylonitrile-cellulose-crosslinked chitosan composite membrane is applied to the separation of different oil-water emulsions.

[0015] The present invention also provides an application of a polyacrylonitrile-cellulose-crosslinked chitosan composite membrane, and the polyacrylonitrile-cellulose-crosslinked chitosan composite membrane is applied to the separation of high-concentration oil-water emulsions.

[0016] The present invention has at least the following beneficial effects: the super-hydrophilic-underwater super-oleophobic oil-water separation material prepared by the present invention has the characteristics of long-term stability, high flux, high separation efficiency, compatibility with emulsified oil and simple process. The polyacrylonitrile cellulose nanocomposite membrane is prepared by electrospinning. The cellulose membrane gives the composite membrane super-hydrophilicity by virtue of its natural hydrophilicity, which can effectively reduce the adsorption of oil and increase water flux; and then the membrane surface is cross-linked and modified by impregnation with chitosan cross-linking solution, giving the membrane surface the following key characteristics: 1. Super-hydrophilicity / underwater super-oleophobicity, cross-linking 1. The chitosan coating is rich in hydroxyl / amino groups, which enhance the hydration layer through hydrogen bonding to achieve efficient oil-water separation; 2. Anti-pollution and self-cleaning ability, the cross-linked network inhibits oil droplet penetration and reduces membrane pore clogging; 3. Environmental friendliness, compared with synthetic polymers, the chitosan cross-linked coating is biodegradable; the present invention also modifies chitosan by maleic acid, which can play a demulsification role in the oil-water separation process and improve the oleophobicity of the composite membrane; at the same time, carbon nanotubes are introduced to further enhance the hydrophilicity of the composite membrane to improve the separation flux of the composite membrane.

[0017] The superhydrophilic-underwater superoleophobic oil-water separation material prepared by the present invention has a high flux and a separation efficiency of more than 99% for a variety of oil-water emulsions and oil-water emulsions of different concentrations. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The SEM images of the composite membrane materials prepared in Example 1 and Comparative Example 1 are shown; Figure 2 The infrared images of the film materials prepared in Example 1, Comparative Example 1 and Comparative Example 2 are shown; Figure 3This is the performance diagram of the emulsion flux and separation efficiency of four different oil-water emulsions after the PAN / CE / CS composite membrane in Application Example 1 was treated with 1M acid, alkali and salt solutions; Figure 4 This is the performance diagram of the separation flux and separation efficiency of the PAN / CE / CS composite membrane for high-concentration oil-water emulsion in Application Example 1; Figure 5 Graph showing the separation flux and separation efficiency of kerosene emulsion in Example 1 and Examples 3-5; Figure 6 This is the performance diagram of emulsion flux and separation efficiency of four different oil-water emulsions in comparative example 3. DETAILED DESCRIPTION

[0019] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments so that those skilled in the art can implement the invention with reference to the description. It should be understood that terms such as "having", "including" and "comprising" used herein do not exclude the presence or addition of one or more other elements or their combinations.

[0020] Example 1 A method for preparing a super-hydrophilic-underwater super-oleophobic oil-water separation material comprises the following steps: Step 1: Dissolve 0.852 g of PAN powder and 0.852 g of cellulose powder in 10 mL of DMF and stir at room temperature for 12 h to obtain a spinning solution; Step 2: The spinning solution was allowed to stand and deaerated for 3 hours. After deaeration, the spinning solution was placed in a plastic syringe, and the syringe was placed in a syringe pump. A 22-gauge stainless steel needle was used during the spinning process; the voltage was 10 KV; the propulsion speed was 0.6 mL / h; the electrode distance was 20 cm; the receiver speed was 200 r / min. After spinning for 8 hours, the aluminum foil loaded with the fiber film was removed and dried in an 80°C oven for 12 hours to obtain a PAN / CE composite film; Step 3: 50 mL of acetic acid, 0.1 g of chitosan, and 0.1 mL of glutaraldehyde were mixed and ultrasonically stirred to obtain a chitosan cross-linking solution. The PAN / CE composite membrane was then immersed in the chitosan cross-linking solution for 15 s to coat the chitosan. The impregnated composite membrane was rinsed with deionized water and dried in an oven at 80 ° C for 0.5 h to obtain a superhydrophilic-underwater superoleophobic oil-water separation material, i.e., a PAN / CE / CS composite membrane. The SEM image of the composite membrane is shown in FIG. Figure 1As shown in Figures b1-b3 (SEM images at different magnifications), the chitosan coating significantly alters the appearance and fiber diameter of the PAN / CE membrane. The fiber morphology becomes rougher, and a clear, defined chitosan coating is visible on the fiber surface. Compared to the PAN / CE fiber membrane, the coating is significantly larger and evenly permeates the entire width of the PAN / CE nanofiber membrane. This process significantly enhances the distribution and permeability of the PAN and CS nanofibers.

[0021] like Figure 2 As shown, at 2240 cm -1 The nitrile stretching vibration observed at 3683 cm is due to the presence of nitrile groups in polyacrylonitrile-based films. -1 The characteristic peak at 3590 cm was identified as the stretching vibration of hydroxyl group, while the peak at 3590 cm -1 and 1546 cm -1 The NH stretching vibration at 1628 cm is related to the amide II group of chitosan. These unique peaks confirm the presence of chitosan coating on the film surface. -1 The characteristic peak at is attributed to the vibration of chitosan amide I group (C=O).

[0022] Example 2 A method for preparing a super-hydrophilic-underwater super-oleophobic oil-water separation material comprises the following steps: Step 1: Dissolve 0.852 g of PAN powder and 0.639 g of cellulose powder in 10 mL of DMF and stir at room temperature for 12 h to obtain a spinning solution; Step 2: The spinning solution was allowed to stand and deaerated for 3 hours. After deaeration, the spinning solution was placed in a plastic syringe, and the syringe was placed in a syringe pump. A 22-gauge stainless steel needle was used during the spinning process; the voltage was 10 KV; the propulsion speed was 0.6 mL / h; the electrode distance was 20 cm; the receiver speed was 200 r / min. After spinning for 8 hours, the aluminum foil loaded with the fiber film was removed and dried in an 80°C oven for 12 hours to obtain a PAN / CE composite film; Step 3: 40 mL of acetic acid, 0.1 g of chitosan, and 0.1 mL of glutaraldehyde were mixed and ultrasonically stirred to obtain a chitosan cross-linking solution. The PAN / CE composite membrane was then immersed in the chitosan cross-linking solution for 15 s to coat the chitosan. The impregnated composite membrane was rinsed with deionized water and dried in an oven at 80 ° C for 0.5 h to finally obtain a superhydrophilic-underwater superoleophobic oil-water separation material, i.e., a PAN / CE / CS composite membrane.

[0023] Example 3 A method for preparing a super-hydrophilic-underwater super-oleophobic oil-water separation material comprises the following steps: Step 1: Dissolve 0.852 g of PAN powder and 0.852 g of cellulose powder in 10 mL of DMF and stir at room temperature for 12 h to obtain a spinning solution; Step 2: The spinning solution was allowed to stand and deaerated for 3 hours. After deaeration, the spinning solution was placed in a plastic syringe, and the syringe was placed in a syringe pump. A 22-gauge stainless steel needle was used during the spinning process; the voltage was 10 KV; the propulsion speed was 0.6 mL / h; the electrode distance was 20 cm; the receiver speed was 200 r / min. After spinning for 8 hours, the aluminum foil loaded with the fiber film was removed and dried in an 80°C oven for 12 hours to obtain a PAN / CE composite film; Step 3: Add 1 g of chitosan to 300 mL of water, adjust the pH to 5 with acetic acid, stir to completely dissolve the chitosan, then add 0.3 g of maleic acid, heat to 70°C for 2 h, and freeze-dry at -20°C for 6 h to obtain modified chitosan; 50 mL of acetic acid, 0.1 g of modified chitosan, and 0.1 mL of glutaraldehyde were mixed and ultrasonically stirred to obtain a modified chitosan cross-linking solution. The PAN / CE composite membrane was then immersed in the modified chitosan cross-linking solution for 15 seconds to coat the chitosan. The immersed composite membrane was rinsed with deionized water and dried in an oven at 80°C for 0.5 hours to finally obtain a superhydrophilic-underwater superoleophobic oil-water separation material, namely, the PAN / CE / CS-1 composite membrane.

[0024] Example 4 A method for preparing a super-hydrophilic-underwater super-oleophobic oil-water separation material comprises the following steps: Step 1: Dissolve 0.852 g of PAN powder and 0.852 g of cellulose powder in 10 mL of DMF and stir at room temperature for 12 h to obtain a spinning solution; Step 2: The spinning solution was allowed to stand and deaerated for 3 hours. After deaeration, the spinning solution was placed in a plastic syringe, and the syringe was placed in a syringe pump. A 22-gauge stainless steel needle was used during the spinning process; the voltage was 10 KV; the propulsion speed was 0.6 mL / h; the electrode distance was 20 cm; the receiver speed was 200 r / min. After spinning for 8 hours, the aluminum foil loaded with the fiber film was removed and dried in an 80°C oven for 12 hours to obtain a PAN / CE composite film; Step 3: Add 0.05 g of carbon nanotubes to 10 mL of water and ultrasonically disperse them at 20 kHz for 10 min to obtain a 5 wt% carbon nanotube dispersion. Mix 50 mL of acetic acid, 0.1 g of chitosan, and 0.1 mL of glutaraldehyde and ultrasonically stir to obtain a chitosan cross-linked solution. Then, add the carbon nanotube dispersion to the chitosan cross-linked solution and mix well to obtain a mixed solution. The PAN / CE composite membrane was immersed in the mixed solution for 15 seconds to coat the chitosan. The immersed composite membrane was rinsed with deionized water and then dried in an oven at 80°C for 0.5 hours to obtain a superhydrophilic-underwater superoleophobic oil-water separation material, namely, the PAN / CE / CS-2 composite membrane.

[0025] Example 5 A method for preparing a super-hydrophilic-underwater super-oleophobic oil-water separation material comprises the following steps: Step 1: Dissolve 0.852 g of PAN powder and 0.852 g of cellulose powder in 10 mL of DMF and stir at room temperature for 12 h to obtain a spinning solution; Step 2: The spinning solution was allowed to stand and deaerated for 3 hours. After deaeration, the spinning solution was placed in a plastic syringe, and the syringe was placed in a syringe pump. A 22-gauge stainless steel needle was used during the spinning process; the voltage was 10 KV; the propulsion speed was 0.6 mL / h; the electrode distance was 20 cm; the receiver speed was 200 r / min. After spinning for 8 hours, the aluminum foil loaded with the fiber film was removed and dried in an 80°C oven for 12 hours to obtain a PAN / CE composite film; Step 3: First prepare a chitosan cross-linking solution, specifically comprising: S1. Add 1 g of chitosan to 300 mL of water, adjust the pH to 5 with acetic acid, stir to completely dissolve the chitosan, then add 0.3 g of maleic acid, heat to 70 ° C for 2 h, and freeze-dry at -20 ° C for 6 h to obtain modified chitosan; 50 mL of acetic acid, 0.1 g of modified chitosan, and 0.1 mL of glutaraldehyde are mixed and ultrasonically stirred to obtain a modified chitosan cross-linking solution. S2, adding 0.05 g of carbon nanotubes to 10 mL of water, and ultrasonically dispersing them at 20 kHz for 10 min to obtain a 5 wt% carbon nanotube dispersion; adding 0.05 g of carbon nanotubes to 10 mL of water, and ultrasonically dispersing them at 20 kHz for 10 min to obtain a 5 wt% carbon nanotube dispersion, and then adding the carbon nanotube dispersion to the modified chitosan cross-linking solution, mixing them evenly, to obtain a mixed solution; The PAN / CE composite membrane was then immersed in the mixed solution for 15 seconds to coat the chitosan. The immersed composite membrane was rinsed with deionized water and dried in an oven at 80°C for 0.5 hours to finally obtain a superhydrophilic-underwater superoleophobic oil-water separation material, namely, the PAN / CE / CS-3 composite membrane.

[0026] Comparative Example 1 Step 1: Dissolve 0.852 g of PAN powder and 0.852 g of cellulose powder in 10 mL of DMF and stir at room temperature for 12 h to obtain a spinning solution; Step 2: The spinning solution was allowed to stand and deaerated for 3 hours. After deaeration, the spinning solution was placed in a plastic syringe, and the syringe was placed in a syringe pump. A 22-gauge stainless steel needle was used during the spinning process; the voltage was 10 KV; the propulsion speed was 0.6 mL / h; the electrode distance was 20 cm; the receiver speed was 200 r / min. After spinning for 8 hours, the aluminum foil loaded with the fiber film was removed and dried in an oven at 80°C for 12 hours to obtain a PAN / CE composite membrane (the SEM image of which is shown in FIG. Figure 1 As shown in a1-a3, where a1-a3 are SEM images at different magnifications).

[0027] Comparative Example 2 A method for preparing a polyacrylonitrile fiber membrane comprises the following steps: 0.852 g of polyacrylonitrile powder (PAN) was dissolved in 10 mL of DMF solution, and then stirred at room temperature for 12 hours to obtain a spinning solution after dissolution. Electrospinning was then performed, and the spinning solution was placed in a plastic syringe, and the syringe was placed in a syringe pump. A 22-gauge metal needle was used during the spinning process, the speed was maintained at 0.6 mL / h, the voltage was set to 10KV, and a metal drum collector wrapped with aluminum foil was used. The speed was set to 120 r / min. After spinning for 8 hours, the aluminum foil loaded with the fiber film was removed and dried in an oven at 80°C for 12 hours to obtain a polyacrylonitrile fiber membrane, recorded as a PAN fiber membrane.

[0028] Comparative Example 3 A method for preparing a super-hydrophilic-underwater super-oleophobic oil-water separation material comprises the following steps: Step 1: Dissolve 0.852 g of PAN powder and 0.852 g of cellulose powder in 10 mL of DMF and stir at room temperature for 12 h to obtain a spinning solution; Step 2: The spinning solution was allowed to stand and deaerated for 3 hours. After deaeration, the spinning solution was placed in a plastic syringe, and the syringe was placed in a syringe pump. A 22-gauge stainless steel needle was used during the spinning process; the voltage was 10 KV; the propulsion speed was 0.6 mL / h; the electrode distance was 20 cm; the receiver speed was 200 r / min. After spinning for 8 hours, the aluminum foil loaded with the fiber film was removed and dried in an 80°C oven for 12 hours to obtain a PAN / CE composite film; Step 3: Dissolve 0.1g chitosan in 40mL of a mixed solution of water and acetic acid (water / acetic acid volume ratio is 7 / 3) and stir for 4 hours to obtain a uniform solution. The role of acetic acid is to help dissolve chitosan. Add 0.1mL of glutaraldehyde to the mixed solution and ultrasonically stir for 20min to perform a cross-linking reaction to obtain a chitosan cross-linked solution. Glutaraldehyde undergoes a cross-linking reaction with the amino group (-NH2) in chitosan to form a cross-linked chitosan layer. The cross-linked chitosan solution is poured onto the PAN / CE nanofiber membrane and kept for 20 minutes to ensure that the cross-linking reaction is fully carried out. Finally, remove the excess cross-linked chitosan solution and dry it thoroughly at room temperature. The chitosan cross-linked composite membrane is obtained.

[0029] Application Example 1 The PAN / CE / CS composite membrane prepared in Example 1 was used to separate the oil-water emulsion as follows: First, prepare four different oil-water emulsion systems: (1) 1 mL of kerosene and 99 mL of deionized water were mixed to prepare a surfactant-free emulsion, which was stirred at 500 r / min for 5 h. The mixture was then ultrasonically treated to produce a stable oil-in-water emulsion (kerosene-water emulsion). (2) 1 mL of toluene and 99 mL of deionized water were mixed to prepare a surfactant-free emulsion, which was stirred at 500 r / min for 5 h and then ultrasonically treated to produce a stable oil-in-water emulsion (toluene oil-water emulsion). (3) Prepare a surfactant-free emulsion by mixing 1 mL of n-hexane with 99 mL of deionized water, stirring at 500 r / min for 5 hours, and ultrasonically treating the mixture to produce a stable oil-in-water emulsion (n-hexane oil-water emulsion). (4) 1 mL of tributyl phosphate mixed oil (wherein the volume ratio of tributyl phosphate oil to n-dodecane is 7 / 3) was mixed with 2 M nitric acid emulsion (99 mL of nitric acid emulsion) to prepare a surfactant-free emulsion to simulate nuclear industry oily wastewater. The mixture was stirred at 500 r / min for 5 hours and ultrasonically treated to produce a stable oil-in-water emulsion. The effective filtration area was 12.56 cm 2 The filtration device separates all the oil-in-water emulsions (tributyl n-dodecyl phosphate mixed oil nitric acid emulsions).

[0030] The effective filtration area is 12.56 cm 2 A filtration device (the filtration membrane in the device is the PAN / CE / CS composite membrane prepared in Example 1) is used to separate all the oil-in-water emulsions. The separation flux and separation efficiency are calculated according to the following formula: Separation flux = (emulsion volume) / time × filtration area Separation efficiency = (1-(concentration before separation / concentration after separation)) × 100 In practical applications, oil-water separation membrane materials are exposed to a variety of oil-water mixtures with varying pH values ​​and salt concentrations. For example, industrial wastewater may contain oily, acidic, or alkaline substances, while seawater contains high concentrations of salt. Membrane instability in acidic, alkaline, and saline environments can alter its performance, rendering it unsuitable for practical use. Therefore, to evaluate the stability of PAN / CE / CS composite membranes under acidic, alkaline, and saline conditions, the membranes were immersed in 1 M hydrochloric acid, sodium hydroxide, and sodium chloride for 6 hours. Subsequently, the separation flux and efficiency were evaluated in four emulsion systems to assess their stability.

[0031] After being treated with acid, alkali and salt solutions, the PAN / CE / CS composite membrane was tested for separation of kerosene emulsion. Figure 3 As shown in Figure a, the flux of separating kerosene emulsion did not decrease significantly, and the separation efficiency remained above 99%. After being treated with acidic solution, the membrane flux decreased the most, from the original 3628 L·m -1 ·h -1 Down to 2783 L·m -1 ·h -1 , the separation efficiency dropped from 99.68% to 99.07%. Although the membrane flux decreased after treatment with acid, alkali and salt solutions, the separation efficiency remained at a high level, which still shows that the PAN / CE / CS composite membrane has high efficiency, stability and potential for water treatment applications.

[0032] After being treated with acid, alkali and salt solutions, the PAN / CE / CS composite membrane was tested for separation of toluene emulsion. Figure 3 As shown in Figure b, there is no significant change in the separation of toluene emulsion after acid, alkali and salt treatment, and the flux remains basically the same, at 3077 L·m -1 ·h -1 The separation efficiency was still above 99%, which showed that the PAN / CE / CS composite membrane had high efficiency, stability and potential for water treatment applications.

[0033] After being treated with acid, alkali and salt solutions, the PAN / CE / CS composite membrane was tested for separation of n-hexane emulsion. Figure 3 As shown in c, after acid, alkali and salt treatment, the separation flux of n-hexane emulsion decreased slightly. After hydrochloric acid treatment, it increased from the original 3956 L·m -1 ·h -1 Reduced to 3022 L·m -1 ·h -1 The separation efficiency dropped from 99% to 98.16%, indicating that the PAN / CE / CS composite membrane has high efficiency, stability and potential for water treatment applications.

[0034] After being treated with acid, alkali and salt solutions, the PAN / CE / CS composite membrane was tested for separation of tributyl n-dodecyl phosphate mixed oil and nitric acid emulsion. Figure 3 As shown in Figure d, in the emulsion system containing 2 M nitric acid solution, the flux of the n-dodecyl tributyl phosphate mixture showed a more significant decrease compared to the other three emulsion systems. This is not only due to the depletion of hydrophilic chitosan, but also related to the molecular properties of n-dodecane and tributyl phosphate. n-dodecane is a straight-chain alkane, while tributyl phosphate has a large molecular structure with branches and polar groups. After mixing, the differences in molecular size and shape lead to a more complex spatial arrangement of molecules in the mixture. In contrast, the molecular size of the main components of kerosene is relatively uniform, while the molecular structures of toluene and n-hexane are simple and regular. During membrane separation, these molecules are more easily repelled by the membrane pores or surface. In contrast, the n-dodecane and tributyl phosphate mixture exhibits relatively high viscosity and poor flowability. During membrane separation, high-viscosity oil mixtures often form a thick boundary layer on the membrane surface, reducing membrane flux.

[0035] In summary, if Figure 3 As shown, the PAN / CE / CS membrane achieves a separation efficiency exceeding 99% under harsh environmental conditions. This is attributed to the tight cross-linking of chitosan (CS) on the PAN / CE membrane surface. The introduction of the chitosan coating not only enhances the hydrophilicity of the composite membrane but also plays a key role in regulating its microstructure. The construction of micro- and nanostructures contributes to an overall improvement in the separation flux and efficiency of oil-water emulsions. The separation efficiency of the composite membrane remains over 99% in conventional emulsions and after acid-, base-, and salt-treatment. The separation flux decreases only slightly after acid-, base-, and salt-treatment, demonstrating the excellent durability of the PAN / CE / CS membrane under harsh environmental conditions. Its water flux and oil displacement properties remain consistent, allowing it to effectively separate emulsions.

[0036] The composite membranes prepared in Examples 3-5 were used to separate kerosene emulsion according to the above test method. The separation flux and separation efficiency are shown in the figure below. Figure 5 As shown. Figure 5 It can be seen that Example 3 modifies chitosan by using maleic acid, which can play a role in demulsification during the oil-water separation process, improve the oleophobicity of the composite membrane, and improve the separation flux; Example 4 introduces carbon nanotubes to further enhance the hydrophilicity of the composite membrane and improve the water flux of the composite membrane. Example 5 modifies chitosan while also introducing carbon nanotubes, and its separation flux is the largest and highest.

[0037] The composite membrane prepared in Comparative Example 3 was used to test the separation performance of kerosene, toluene, n-hexane and n-dodecane (TBP) mixed oil emulsion according to the above test method. The separation flux and separation efficiency results are shown in Figure 2. Figure 6As shown. Comparative Examples 1 and 2 failed to complete the emulsion separation test due to insufficient hydrophilicity. As can be seen from Figure 6, by modifying and coating the polyacrylonitrile / cellulose nanofiber membrane, the hydrophilicity and underwater oleophobicity of the composite membrane are improved. In the oil-water separation process, the composite membrane can achieve efficient demulsification with a separation efficiency of more than 99%. However, since Comparative Example 3 uses a chitosan cross-linking solution poured on the composite membrane to achieve cross-linking, its modification effect is not as good as the dipping method used in Example 1 to coat the chitosan cross-linking solution. Therefore, the separation flux of the composite membrane prepared in Comparative Example 3 for oil-water emulsion is not as good as that of Example 1.

[0038] The present invention also evaluated the separation performance of PAN / CE / CS membrane at oil concentrations of 20%, 30%, 40%, and 50%; Figure 4 The separation of 40% n-dodecane and TBP in 2 M nitric acid was demonstrated. Under gravity-driven conditions, the flow rate of the 20% emulsion was stable at 1910 L·m -1 ·h -1 The separation efficiency was about 99.7%. As the concentration increased to 30%, 40%, and 50%, the flux gradually decreased. The flux of the 50% concentration emulsion was 1549 L·m -1 ·h -1 , while the separation efficiency remained at 99.4%. During the gravity-driven separation of highly concentrated oil-water emulsions, the membrane surface remained intact. The PAN / CE / CS membrane demonstrated high flux and excellent separation efficiency when processing highly concentrated, high-viscosity oil-water emulsions. This demonstrates that the PAN / CE / CS membrane can effectively separate highly concentrated, complex oil-water emulsions with high flux and separation efficiencies exceeding 99%.

[0039] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the description and implementation methods. They can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present invention is not limited to the specific details and examples shown and described herein.

Claims

1. A method for preparing a super-hydrophilic-underwater super-oleophobic oil-water separation material, characterized in that: The following steps are involved: Step 1: dissolving polyacrylonitrile and cellulose powder in an organic solvent and mixing and stirring to obtain a spinning solution; Step 2: The spinning solution is allowed to stand and then degassed, and the degassed spinning solution is subjected to electrostatic spinning, and then dried after spinning to obtain a polyacrylonitrile cellulose nanocomposite film; Step 3: prepare a chitosan cross-linking solution, and then immerse the polyacrylonitrile cellulose nanocomposite membrane in the chitosan cross-linking solution to coat the chitosan. After the immersion is completed, wash and dry to finally obtain a super hydrophilic-underwater super oleophobic oil-water separation material, namely, a polyacrylonitrile cellulose cross-linked chitosan composite membrane.

2. The method for preparing a super hydrophilic-underwater super oleophobic oil-water separation material according to claim 1, wherein In the step 1, the organic solvent is any one of N,N-dimethylformamide, N,N-dimethylacetamide, and a mixed solvent of tetrahydrofuran and dimethylformamide.

3. The method for preparing a super hydrophilic-underwater super oleophobic oil-water separation material according to claim 1, wherein In the step 1, the mass ratio of polyacrylonitrile to cellulose is 4:1 to 1:1, and the stirring time is 12 to 24 hours.

4. The method for preparing a super hydrophilic-underwater super oleophobic oil-water separation material according to claim 1, wherein In the step 2, the degassing time of the spinning solution is 1 to 3 hours, and the electrospinning parameters are: the needle is an 18-24 stainless steel needle; the voltage is 10 to 16 kV; the propulsion speed is 0.5 to 0.8 mL / h; the electrode distance is 10 to 30 cm; the ambient temperature is 10 to 40° C.; the ambient humidity is 20-50%; and the receiver speed is 100 to 300 r / min.

5. The method for preparing a super hydrophilic-underwater super oleophobic oil-water separation material according to claim 1, wherein In the step 2, the drying temperature is 70-100° C. and the drying time is 10-14 hours.

6. The method for preparing a super hydrophilic-underwater super oleophobic oil-water separation material according to claim 1, wherein In the step 3, the chitosan cross-linking solution is prepared by mixing chitosan, acetic acid, and a cross-linking agent in a mass volume ratio of 0.1 g to 0.2 g: 30 to 50 mL: 0.1 to 0.2 mL and stirring uniformly by ultrasonication, wherein the cross-linking agent is one or more of glutaraldehyde, formaldehyde, glyoxal, polyethylene glycol diglycidyl ether, citric acid, sulfate, and natural polyphenols.

7. The method for preparing a super-hydrophilic-underwater super-oleophobic oil-water separation material according to claim 1, wherein In the step 3, the preparation method of the chitosan cross-linking solution is: S1, chitosan is added to water, and the pH is adjusted to 5-6 with acetic acid, and the chitosan is stirred to dissolve completely, and then maleic acid is added, heated to react, and freeze-dried after the reaction is completed to obtain modified chitosan, and then the modified chitosan, acetic acid, and a cross-linking agent are mixed in a mass volume ratio of 0.1g-0.2g:30-50mL:0.1-0.2mL and ultrasonically stirred to obtain a modified chitosan cross-linked solution; the cross-linking agent is one or more of glutaraldehyde, formaldehyde, glyoxal, polyethylene glycol diglycidyl ether, citric acid, sulfate, and natural polyphenols; S2. Add carbon nanotubes into water and disperse them by ultrasonication to obtain a carbon nanotube dispersion, which is then added into the modified chitosan cross-linking solution and stirred to obtain a mixed solution.

8. The method for preparing a super hydrophilic-underwater super oleophobic oil-water separation material according to claim 1, wherein In the step 3, the dipping and cross-linking time is 15-60 seconds, the drying temperature is 70-90° C., and the drying time is 0.5-1 hour.

9. An application of a polyacrylonitrile-cellulose cross-linked chitosan composite membrane prepared by the preparation method according to any one of claims 1 to 8, characterized in that: Polyacrylonitrile-cellulose cross-linked chitosan composite membranes were applied to the separation of different oil-water emulsions.

10. An application of a polyacrylonitrile-cellulose cross-linked chitosan composite membrane prepared by the preparation method according to any one of claims 1 to 8, characterized in that: Polyacrylonitrile-cellulose cross-linked chitosan composite membrane was applied to the separation of high-concentration oil-water emulsions.

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