Temperature-dependent cellulose nanofiber oil-water separation membrane and preparation method thereof

Abstract

The application discloses a temperature-dependent flux-controllable cellulose nanofiber oil-water separation membrane material and a preparation method thereof. A sulfobetaine segment (SB) is used to chemically modify cellulose nanofiber (CNF) to prepare modified nanocellulose (CNFS-x), then the modified nanocellulose is physically blended with polyvinyl alcohol (PVA) to obtain a CNFS-x / PVA dispersion, and finally, the dispersion is used to prepare an oil-water separation composite membrane. The influence of different SB grafting degrees on the oil-water separation performance of the composite membrane is studied in detail. The research shows that with the increase of the grafting degree, the flux (water) of the composite membrane CNFS-x / PVA presents an upward trend, wherein the flux of the composite membrane CNFS-3 / PVA can reach 1456m ‑2 h ‑1 . In addition, the flux (water) of the composite membrane under high temperature (35 DEG C) conditions is obviously higher than that under room temperature (25 DEG C). When the content of PVA in the CNFS-3 / PVA composite membrane is 10%, the breaking strength of the composite membrane can reach 61.42 MPa, and the breaking elongation can reach 10.9%.

Description

TECHNICAL FIELD

[0001] The present application relates to a cellulose-based oil-water separation membrane material, in particular a temperature-dependent cellulose nanofiber oil-water separation membrane material and a preparation method thereof, belonging to the technical field of new materials. BACKGROUND

[0002] During oil exploration and transportation, frequent oil spill events often have a disastrous impact on marine ecosystems. The materials currently used in oil-water separation membranes on the market are mainly synthetic polymers such as polysulfone, polyether, polyacrylonitrile, and polyvinylidene fluoride. The above-mentioned polymers usually have poor hydrophilicity, low separation efficiency, and are difficult to biodegrade. In contrast, biomass-based oil-water separation membrane materials have gained great social attention in recent years due to their advantages of good hydrophilic effect, easy access to raw materials, low preparation cost, green environmental protection, and excellent oil-water separation efficiency. Among them, cellulose is the most abundant natural biomass polymer in nature, and cellulose, especially cellulose nanofiber, has a large specific surface area, high porosity, and good separation efficiency, and is widely used in oil-water separation membrane materials.

[0003] Flux is an important indicator for measuring the separation performance of oil-water separation membrane materials, and pore volume is a key factor affecting the flux of membrane materials. Generally, increasing the pore volume of membrane materials can improve their flux, but at the same time, it will reduce their mechanical properties. Adjusting the flux of membrane materials according to external stimuli such as pH, gas, and temperature provides a new strategy for effectively treating oil-containing wastewater. pH-adjusted oil-water separation membrane materials can efficiently treat surfactant-stabilized oil-water mixed emulsions, but the solutions after separation of most membrane materials will also be acidic or basic, which will cause secondary pollution to some extent. Gas regulation of the wettability of membrane materials will not cause a large accumulation of surface chemical reactions, but it requires additional consumption of gas, and the separation effect of some emulsified oil-water mixtures is not good. In oil-water separation, hydrophilic modified cellulose membrane materials can give them higher water permeation flux and separation efficiency. For example, cellulose acetate (CA) is used as the basic material for membrane manufacturing, and graphene oxide (GO) is subjected to electrohydrodynamic atomization to enhance its hydrophilicity. The optimized GO-based CA membrane exhibits higher water permeation flux and separation efficiency than the CA membrane (see Fabrication and characterization of superhydrophilic graphene-based electrospun

[0004] membranes for efficient oil-water separation ,Journal of WaterProcess Engineering, 2023, 54:104066). In contrast, the use of grafting temperature-responsive hydrophilic thermosensitive compounds on the surface of membrane materials not only increases the water permeation flux and separation efficiency of the membrane materials, but also realizes the temperature-controlled switching of material wettability, which is a hot research direction of oil-water separation membrane materials. Compared with the lowest critical solution temperature response (LCST) temperature-regulated membrane materials, the highest critical solution temperature response (UCST) regulation is more operable and practical. However, there are few reports on UCST-responsive membrane materials. Studies have shown that the synthesis of sulfobetaine monomer (SPE) into its homopolymer (PSPE) by aqueous radical polymerization has UCST response. The polymer exhibits more hydrophilic characteristics at high temperatures than at low temperatures (see The synthesis of a UCST-type zwitterionic polymer for the efficient recycling of cellulase at room temperature, Green Chemistry, 2021, 23, 2738). Lignin itself does not have temperature response performance, and by grafting sulfobetaine fragments (SB) to lignin, it is endowed with temperature response performance (see Synthesis of temperature and pH responsive lignin-grafted sulfobetaine for efficiently recycling cellulase, Bioresource Technology, 2023, 369:128357). In summary, the use of SB to graft and modify cellulose nanofibers is expected to endow them with UCST response and hydrophilicity. SUMMARY

[0005] The technical problem to be solved by the present application is to provide a temperature-dependent cellulose nanofiber oil-water separation membrane and a preparation method thereof, which utilizes the temperature response performance of the membrane material to realize a water flux that is significantly higher at high temperatures than at low temperatures, and endows the nanofiber membrane material with temperature response characteristics.

[0006] To achieve the above technical problems, the present application first discloses a temperature-dependent cellulose nanofiber oil-water separation membrane, which is obtained by pouring the mixture of modified cellulose nanofiber and polyvinyl alcohol into a mold,

[0007] 。

[0008] Further, the mass ratio of the modified cellulose nanofiber and polyvinyl alcohol is 3-19:1.

[0009] Further, the mass ratio of the sulfobetaine fragment represented by formula (I) to cellulose nanofiber is 1-60:1.

[0010] The present application also discloses a preparation method of the temperature-dependent cellulose nanofiber oil-water separation membrane as described above,

[0011] (1) grafting the sulfobetaine fragment represented by formula (I) to cellulose nanofiber under alkaline conditions at 40-60 ℃ and pH=11-12 for 0.5-6 h to obtain modified cellulose nanofiber, and the pH can be adjusted by 1 mol / L sodium hydroxide alkaline solution;

[0012] (2) physically blending the modified cellulose nanofiber and polyvinyl alcohol solution at 20-30 ℃ for 0.5-2 h to obtain a suspension, and then pouring the suspension into a mold to prepare the temperature-dependent cellulose nanofiber oil-water separation membrane.

[0013] Further, the drying temperature during the pouring into the mold in step (2) is 30-40 ℃, and the drying time is 6-9 h.

[0014] Further, the sulfobetaine fragment represented by formula (I) is prepared by the following steps,

[0015] (1) adding a certain amount of N,N-dimethyl ethanolamine and 3-bromopropane sulfonic acid sodium into N,N-dimethyl acetamide, mixing uniformly, heating the system to 60-80 ℃, and stirring at constant temperature for 10-16 h, then filtering under reduced pressure to obtain HSB (hydroxyl replaces chlorine in the SB molecule represented by formula (I)) crude product, and then refining the HSB by beating with tetrahydrofuran, wherein the amount of tetrahydrofuran used for beating is sufficient to meet the beating requirement, and generally the mass-volume ratio of HSB crude product to tetrahydrofuran is 0.5-1.5 g:3 mL;

[0016] (2) The refined HSB obtained in step (1) is added into thionyl chloride, and constant temperature stirring is carried out at-10-10 DEG C for 4-8 h, after the reaction is completed, the crude product is obtained by reduced pressure distillation, then the crude product is further treated by thiofurfuryl alcohol beating, and then the target product is precipitated by adding tetrahydrofuran, and finally the refined sulfobetaine fragment is obtained by freeze drying.

[0017] Further, in step (1) of the sulfobetaine fragment preparation, the mass-volume ratio of 3-bromopropyl sodium sulfonate and N,N-dimethyl ethanolamine is 0.5-1.5 g:2 mL.

[0018] Further, in step (1) of the sulfobetaine fragment preparation, the mass-volume ratio of 3-bromopropyl sodium sulfonate and N,N-dimethyl ethanolamine is 0.5-1.5 g:2 mL.

[0019] Further, in step (2) of the sulfobetaine fragment preparation, the mass-volume ratio of HSB and thionyl chloride is 0.5-1.5 g:9 mL.

[0020] Further, in step (2) of the sulfobetaine fragment preparation, the mass-volume ratio of refined HSB and thiofurfuryl alcohol is 0.5-1.5 g:3 mL, and the mass-volume ratio of refined HSB and tetrahydrofuran is 0.5-1.5 g:3 mL.

[0021] The present application first endows the cellulose-based membrane material with UCST response, realizes that the water flux in a high-temperature environment is obviously higher than that in a low-temperature environment by using the temperature response performance of the membrane material, endows the nanofiber membrane material with the temperature response characteristic, so that excellent separation performance is achieved, and the long-term cycle stability of the membrane material is also endowed. Moreover, the present application can control the flux by controlling the feeding amount of the intermediate SB. When the mass ratio of PVA in the CNFS-3 / PVA composite membrane is 10%, the breaking strength of the composite membrane can reach 61.42 MPa, and the breaking elongation can reach 10.9%. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 The figure is the oil-water separation performance test result of the oil-water separation membrane of the present application;

[0023] Figure 2 The figure is the oil-water separation performance test result of the oil-water separation membrane of the present application; DETAILED DESCRIPTION

[0024] The present application will be further explained in combination with the following examples. The following examples are only used to illustrate the present application, but not used to limit the implementation range of the present application.

[0025] The reagents used in the following examples can be purchased from the market. The oil-water separation flux is measured by a micro filter.

[0026] Preparation of sulfobetaine fragment (SB) shown in formula (I):

[0027]

[0028] (I)

[0029] (1) At room temperature, 44 mL of N, N-dimethyl ethanolamine and 24 g of 3-bromopropane sulfonate sodium were added into 480 mL of N, N-dimethylacetamide, mixed uniformly, then the system was heated to 70 ℃, and constant temperature stirring was carried out for 12 h. After the reaction was completed, the crude product of intermediate HSB was obtained by vacuum filtration, and finally the refined HSB was obtained by four hydrogenated furan beating.

[0030] (2) At room temperature, 15 g of refined HSB obtained in step (1) was added into 126 mL of thionyl chloride, and constant temperature stirring was carried out at 5 ℃ for 5.5 h. After the reaction was completed, the crude product of sulfobetaine fragment (SB) was obtained by vacuum distillation, and then 40 mL of trifluoroethanol was added for beating, and 40 mL of tetrahydrofuran was added to precipitate the target product. Finally, the refined sulfobetaine fragment (SB) was obtained by freeze-drying.

[0031] Preparation of temperature-dependent cellulose nanofiber oil-water separation membrane:

[0032] (1) Under the conditions of 60 ℃ and alkaline (pH=11~12 adjusted by 20wt% sodium hydroxide solution), cellulose nanofiber and sulfobetaine fragment (SB) monomer were grafted on the hydroxyl sites of cellulose nanofiber to synthesize CNFS-x (x is a natural number, representing different batches, corresponding to different grafting degrees of SB and CNF). The grafting reaction was carried out for 5 h. After the reaction was completed, the fiber was washed with distilled water until the pH value reached about 7.

[0033] (2) Preparation of PVA (polyvinyl alcohol) solution: 5 g of PVA was added to 95 mL of distilled water at room temperature, and placed in a 70 ℃ constant temperature water bath for 40 min, then gradually heated to 90 ℃, and stirred for 1 h to obtain a PVA solution;

[0034] A certain amount of CNFS-x was taken in a beaker and ultrasonically dispersed for 30 min for standby, and a certain amount of prepared PVA solution was taken in a beaker to obtain a CNFS-x / PVA mixed solution. The mixed solution was uniformly stirred on a magnetic stirrer for 2 h, and finally a composite membrane was prepared by casting method, which was poured into a casting mold and dried at 40 ℃ for 9 h. After drying, the CNFS-x / PVA composite film was obtained, which was the temperature-dependent cellulose nanofiber oil-water separation membrane of the application.

[0035] Comparative Example 1

[0036] Preparation of CNF / PVA composite film

[0037] The specific experimental steps of the CNF / PVA composite film are as follows: 5 g of PVA and 95 g of deionized water are mixed and placed in a constant temperature water bath at 70 °C for 40 min, then gradually heated to 90 °C, stirred for 1 h, and a PVA solution is obtained. Take 9 mL of CNF in a beaker and ultrasonically disperse for 30 min for standby, then take 1 mL of PVA solution in a beaker to obtain a CNF / PVA mixed solution, and uniformly stir the mixed solution on a magnetic stirrer for 2 h. Finally, the composite film is prepared by the method of casting into a film, which is poured into a film casting mold and dried at 40 °C for 9 h to obtain a CNF / PVA composite film.

[0038] Oil-water mixture separation test 1: 10 mL of oil phase (toluene, petroleum ether, n-heptane and n-hexane) and 10 mL of water phase are mixed and poured into a separator. During the oil-water separation process, the effective contact area of the CNF / PVA composite film with the oil-water mixture is 7.06 cm 2 . Test its oil-water separation performance at 25 °C environment. The oil-water mixture separation is carried out under the action of gravity without any other external force. The results are shown in Table 1.

[0039] Oil-water mixture separation test 2: 10 mL of oil phase (toluene, petroleum ether, n-heptane and n-hexane) and 10 mL of water phase are mixed and poured into a separator. During the oil-water separation process, the effective contact area of the CNF / PVA composite film with the oil-water mixture is 7.06 cm 2 . Test its oil-water separation performance at 35 °C environment. The oil-water mixture separation is carried out under the action of gravity without any other external force. The results are shown in Table 1.

[0040] Oil-water emulsion separation test: four kinds of emulsions are prepared with toluene, petroleum ether, n-heptane and n-hexane as oil phase, water as continuous phase and Tween 80 as surfactant. Respectively, toluene / water, petroleum ether / water, n-heptane / water and n-hexane / water four different emulsions, the effective contact area of CNF / PVA composite film with oil-water emulsion is 7.06 cm 2 . Test its emulsion separation performance at 25 °C environment. The oil-water emulsion is carried out under pressure environment, the pressure is ΔP = 0.095 bar. The results are shown in Table 1.

[0041] Example 1

[0042] The specific experimental steps of the CNFS-1 / PVA (modified according to CNF: 0.1 g, SB: 0.36 g, mass ratio 1:3.6) composite film are as follows: 5 g of PVA and 95 g of deionized water are mixed and placed in a 70 °C constant temperature water bath for 40 min, then gradually heated to 90 °C, stirred for 1 h, and a PVA solution is obtained. Take 9 mL of CNFS-1 (about 0.09 g) in a beaker and ultrasonic dispersion for 30 min, then take 1 mL of PVA solution (about 0.01 g of PVA) in a beaker to obtain a CNFS-1 / PVA mixed solution, and uniformly stir the mixed solution on a magnetic stirrer for 2 h. Finally, the composite film is prepared by the method of casting into a film, which is poured into a film casting mold and dried at 40 °C for 9 h to obtain a composite film.

[0043] Oil-water mixture separation test 1: 10 mL of oil phase (toluene, petroleum ether, n-heptane and n-hexane) and 10 mL of water phase are mixed and poured into a separator. During the oil-water separation process, the effective contact area of the CNFS-1 / PVA composite film with the oil-water mixture is 7.06 cm 2 . Test its oil-water separation performance at 25 °C environment. The oil-water mixture separation is carried out under the action of gravity without any other external force. The results are shown in Table 1.

[0044] Oil-water mixture separation test 2: 10 mL of oil phase (toluene, petroleum ether, n-heptane and n-hexane) and 10 mL of water phase are mixed and poured into a separator. During the oil-water separation process, the effective contact area of the CNFS-1 / PVA composite film with the oil-water mixture is 7.06 cm 2 . Test its oil-water separation performance at 35 °C environment. The oil-water mixture separation is carried out under the action of gravity without any other external force. The results are shown in Table 1.

[0045] Oil-water emulsion separation test: Toluene, petroleum ether, n-heptane and n-hexane are used as oil phase, water as continuous phase, and Tween 80 as surfactant to prepare four kinds of emulsions. Respectively, toluene / water, petroleum ether / water, n-heptane / water and n-hexane / water four different emulsions, the effective contact area of CNFS-1 / PVA composite film with oil-water emulsion is 7.06 cm 2 . Test its emulsion separation performance at 25 °C environment. The oil-water emulsion is carried out under pressure environment, the pressure is ΔP = 0.095 bar. The results are shown in Table 1.

[0046] Example 2

[0047] The specific experimental steps of the CNFS-2 / PVA (modified according to CNF: 0.1 g, SB: 2.84 g, mass ratio 1:28.4) composite film are as follows: 5 g of PVA and 95 g of deionized water are mixed and placed in a 70 °C constant temperature water bath for 40 min, then gradually heated to 90 °C, stirred for 1 h, and a PVA solution is obtained. Take 9 mL of CNFS-2 (about 0.09 g) in a beaker and ultrasonic disperse for 30 min, then take 1 mL of PVA solution (about 0.01 g of PVA) in a beaker to obtain a CNFS-2 / PVA mixed solution, and uniformly stir the mixed solution on a magnetic stirrer for 2 h. Finally, the composite film is prepared by the method of casting into a film, which is poured into a film casting mold and dried at 40 °C for 9 h to obtain a composite film.

[0048] Oil-water mixture separation test: 10 mL of oil phase (toluene, petroleum ether, n-heptane and n-hexane) and 10 mL of water phase are mixed and poured into a separator. The effective contact area of the CNFS-2 / PVA composite film with the oil-water mixture is 7.06 cm 2 during oil-water separation. Test its oil-water separation performance at 35 °C environment. Oil-water separation is carried out under the action of gravity without any other external force. The results are shown in Table 1.

[0049] Oil-water emulsion separation test: Toluene, petroleum ether, n-heptane and n-hexane are used as oil phase, water as continuous phase, and Tween 80 as surfactant to prepare four kinds of emulsions. The effective contact area of the CNFS-2 / PVA composite film with the oil-water emulsion is 7.06 cm 2 . Test its emulsion separation performance at 25 °C environment. Oil-water emulsion is carried out under pressure environment, the pressure is ΔP = 0.095 bar. The results are shown in Table 1.

[0050] Example 3

[0051] The specific experimental steps for preparing CNFS-3 / PVA composite films (modified with 0.1g CNF and 5.68g SB, mass ratio 1:56.8) are as follows: 5g PVA and 95g deionized water were mixed and placed in a 70°C water bath for 40 minutes. The temperature was then gradually raised to 90°C and stirred for 1 hour to obtain a PVA solution. 9mL of CNFS-3 (approximately 0.09g) was placed in a beaker and ultrasonically dispersed for 30 minutes. 1mL of the PVA solution (containing approximately 0.01g PVA) was then added to the beaker to obtain a CNFS-3 / PVA mixed solution. The mixed solution was stirred at a constant speed on a magnetic stirrer for 2 hours. Finally, the composite film was prepared by casting. The film was poured into a casting mold and dried at 40°C for 9 hours to obtain the composite film.

[0052] Oil-water mixture separation test: 10 mL of oil phase (toluene, petroleum ether, n-heptane, and n-hexane) and 10 mL of water phase were mixed and poured into the separator. During the oil-water separation process, the effective contact area between the CNFS-3 / PVA composite film and the oil-water mixture was 7.06 cm 2 The oil-water separation performance was tested at 35°C. The oil-water mixture was separated under gravity, without any other external forces. The results are shown in Table 1.

[0053] Oil-water emulsion separation test: Four types of emulsions were prepared using toluene, petroleum ether, n-heptane, and n-hexane as the oil phase, water as the continuous phase, and Tween 80 as the surfactant. The effective contact area between the CNFS-3 / PVA composite film and the oil-water emulsion was 7.06 cm 2 The emulsion separation performance was tested at 25°C. The oil-water emulsion separation was performed under pressure, with a pressure of ΔP = 0.095 bar. The results are shown in Table 1.

[0054] Table 1 Oil-water separation performance of different CNFS-x / PVA composite films

[0055] Examples Oil water mixture flux (L m -2 h -1 )]]> Oil-water mixture separation efficiency (%) Oil water emulsion flux (L m -2 h -1 )]]> Oil-water emulsion separation efficiency (%) Comparative Example 1 (25°C) 25 96.3 86 95.8 Comparative Example 1 (35°C) 25 96.9 / / Example 1 (25°C) 295 98.6 368 96.3 Example 1 (35°C) 442 98.4 / / Example 2 (25°C) / / 1122 95.9 Example 2 (35°C) 1429 98.4 / / Example 3 (25°C) / / 1160 96.5 Example 3 (35°C) 1456 98.8 / /

[0056] As can be seen from Table 1, the higher the SB segments grafted onto the cellulose nanofibers (i.e., the higher the SB grafting rate), the better the separation performance of the oil-water mixture and the oil-water emulsion. This may be attributed to the fact that the hydrophilicity of the composite film is further enhanced with the increase of the grafting degree, as shown in the fluxes of CNFS-3 / PVA being 1456 and 1160 L m, respectively. -2 h -1 The separation efficiencies were 98.8% and 96.5%, respectively; while the flux of unmodified CNF / PVA under the same conditions was only 25 L m-2 h -1 and 86 L m -2 h -1 From Example 1, it can be seen that the flux (water) of the composite film under high temperature (35℃) conditions is significantly higher than that at room temperature (25℃). In summary, the above cellulose-based oil-water separation film material can realize flux regulation relying on temperature.

[0057] The above only lists specific embodiments of the present application. The present application is not limited to the above embodiments, and there can be many variations. All variations that can be directly derived or inferred from the disclosure of the present application by those of ordinary skill in the art should be considered within the scope of the present application.

Claims

1. A temperature-dependent cellulose nanofiber oil-water separation membrane, characterized by: The oil-water separation membrane is obtained by mixing modified cellulose nanofibers and polyvinyl alcohol and then forming a membrane through a casting method. The modified cellulose nanofibers are obtained by grafting a sulfobetaine segment represented by formula (I) onto the hydroxyl site of the cellulose nanofibers under alkaline conditions. 。 2. The temperature-dependent cellulose nanofiber oil-water separation membrane according to claim 1, characterized in that: The mass ratio of the modified cellulose nanofibers to polyvinyl alcohol is 3-19:

1.

3. The temperature-dependent cellulose nanofiber oil-water separation membrane according to claim 1, characterized in that: The mass ratio of the sulfobetaine fragment represented by formula (I) to the cellulose nanofibers is 1 to 60:

1.

4. A method for preparing the temperature-dependent cellulose nanofiber oil-water separation membrane according to any one of claims 1 to 3, characterized in that: (1) Grafting the sulfobetaine fragment represented by formula (I) onto cellulose nanofibers at an alkaline temperature of 40-60°C and pH 11-12 for 0.5-6 hours to obtain modified cellulose nanofibers; (2) The modified cellulose nanofibers and polyvinyl alcohol solution were physically mixed at 20-30 °C for 0.5-2 h to obtain a suspension, and the suspension was then cast into a membrane to prepare a temperature-dependent cellulose nanofiber oil-water separation membrane.

5. The method for preparing the temperature-dependent cellulose nanofiber oil-water separation membrane according to claim 4, characterized in that: The drying temperature during the casting and film formation in step (2) is 30-40°C, and the drying and film formation time is 6-9h.

6. The method for preparing the temperature-dependent cellulose nanofiber oil-water separation membrane according to claim 4, characterized in that: The sulfobetaine fragment represented by formula (I) is prepared by the following steps: (1) Add a certain amount of N,N-dimethylethanolamine and sodium 3-bromopropane sulfonate to N,N-dimethylacetamide, mix well, heat the system to 60-80 °C, and stir at constant temperature for 10-16 hours. After the reaction is completed, vacuum filter to obtain crude HSB, and then beat with tetrahydrofuran to obtain refined HSB; (2) The purified HSB obtained in step (1) is added to thionyl chloride, and the mixture is stirred at a constant temperature of -10 to 10°C for 4 to 8 hours. After the reaction is completed, the crude product is obtained by vacuum distillation, and the crude product is further slurried with trifluoroethanol. Then, tetrahydrofuran is added to precipitate the target product, and finally, the purified sulfobetaine fragment is obtained by freeze drying.

7. The method for preparing the temperature-dependent cellulose nanofiber oil-water separation membrane according to claim 6, characterized in that: In step (1) of preparing the sulfobetaine fragment, the mass volume ratio of sodium 3-bromopropanesulfonate and N,N-dimethylethanolamine is 0.5-1.5 g:2 mL.

8. The method for preparing the temperature-dependent cellulose nanofiber oil-water separation membrane according to claim 6, characterized in that: In step (1) of preparing the sulfobetaine fragment, the mass volume ratio of sodium 3-bromopropanesulfonate and N,N-dimethylacetamide is 0.5-1.5 g:20 mL.

9. The method for preparing the temperature-dependent cellulose nanofiber oil-water separation membrane according to claim 6, characterized in that: In step (2) of preparing the sulfobetaine fragment, the mass volume ratio of HSB and thionyl chloride is 0.5-1.5 g:9 mL.

10. The method for preparing the temperature-dependent cellulose nanofiber oil-water separation membrane according to claim 6, characterized in that: In step (2) of preparing the sulfobetaine fragment, the mass volume ratio of the refined HSB to trifluoroethanol is 0.5-1.5 g:3 mL, and the mass volume ratio of the refined HSB to tetrahydrofuran is 0.5-1.5 g:3 mL.

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