A surface-modified silicone rubber composite membrane and its preparation method

Abstract

The present invention provides a surface-modified silicone rubber composite membrane and a preparation method thereof, belonging to the technical field of composite membrane preparation; in the present invention, polydimethylsiloxane is used as a flexible matrix, providing excellent gas permeability, and the reaction activity is enhanced by introducing vinyl functional groups, enabling it to graft thermosensitive monomers and photo-responsive monomers, endowing the membrane material with temperature and photo-responsive capabilities; cellulose nanocrystals are modified by MOF, which improves the specific surface area and pore structure of the filler, enhances the mechanical properties and molecular sieve effect of the membrane, and at the same time ensures the uniform dispersion of the filler in the matrix; graphene oxide is modified by crown ether, further enhancing the ion recognition ability, mechanical enhancement and separation selectivity of the membrane; the combination of the three realizes the high efficiency and multi-functional adaptability of the surface-modified silicone rubber composite membrane in complex separation tasks.

Description

Technical Field

[0001] The present invention belongs to the technical field of composite film preparation, and relates to a surface-modified silicone rubber composite film and a preparation method thereof. Background Art

[0002] Polydimethylsiloxane is a widely used silicone polymer, which is favored for its excellent biocompatibility, good flexibility and low surface energy. This material has good heat resistance and chemical stability. However, although polydimethylsiloxane performs well in many applications, there are still some deficiencies in its mechanical properties and separation efficiency.

[0003] Firstly, the mechanical properties of polydimethylsiloxane are weak, especially under high load or high impact conditions. Due to its high flexibility, polydimethylsiloxane is prone to deformation when subjected to tensile and compressive forces, resulting in its tensile strength and tear strength being lower than those of other high-performance materials. This makes polydimethylsiloxane perform poorly in some engineering applications with higher requirements, especially in cases where long-term load or dynamic stress needs to be borne.

[0004] Secondly, in terms of the separation efficiency for organic hydrocarbon gases, the hydrophobicity and molecular selectivity of polydimethylsiloxane are insufficient, making it ineffective in gas separation applications. Especially in the separation of organic hydrocarbon gases such as gasoline vapor, the gas permeability and selective permeability of traditional polydimethylsiloxane membranes are low, and different types of hydrocarbon molecules cannot be effectively separated, resulting in unsatisfactory performance in high-efficiency separation applications. Summary of the Invention

[0005] In view of the above problems, the purpose of the present invention is to provide a surface-modified silicone rubber composite film and a preparation method thereof. In the present invention, polydimethylsiloxane is used as a flexible matrix to provide excellent gas permeability, and by introducing vinyl functional groups, the reaction activity is significantly improved, enabling it to graft thermosensitive monomers and photo-responsive monomers, endowing the membrane material with temperature and photo-responsive capabilities; cellulose nanocrystals are modified by MOF, significantly improving the specific surface area and pore structure of the filler, enhancing the mechanical properties and molecular sieve effect of the membrane, and at the same time ensuring the uniform dispersion of the filler in the matrix; graphene oxide is modified by crown ether, further enhancing the ion recognition ability, mechanical strengthening effect and separation selectivity of the membrane. The combination of the three realizes the high efficiency and multi-functional adaptability of the composite film in complex separation tasks.

[0006] To achieve this purpose, the present invention adopts the following technical solutions:

[0007] In the first aspect, the present invention provides a preparation method of a surface-modified silicone rubber composite film, and the preparation method of the surface-modified silicone rubber composite film includes:

[0008] S1: React N-isopropylacrylamide with vinyltrimethoxysilane to obtain a thermosensitive monomer;

[0009] S2: React p-aminoazobenzene with 3-isocyanatopropyltrimethoxysilane to obtain a photo-responsive monomer;

[0010] S3: React polydimethylsiloxane with vinyltrimethoxysilane under the catalysis of dibutyltin dilaurate to obtain vinyl-modified polydimethylsiloxane; Disperse it in hydrochloric acid solution for treatment to obtain pre-hydrolyzed vinyl-modified polydimethylsiloxane; Mix and react the pre-hydrolyzed vinyl-modified polydimethylsiloxane with tetramethylammonium hydroxide, the thermosensitive monomer and the photo-responsive monomer to obtain a multi-modified polydimethylsiloxane;

[0011] S21: Disperse cellulose nanocrystals in deionized water, add copper nitrate and trimesic acid after ultrasonic dispersion to obtain a fifth reaction solution, and after reaction, centrifuge, wash and dry to obtain MOF-modified cellulose nanocrystals;

[0012] S22: Under nitrogen protection, disperse 18-crown-6 and potassium carbonate in N,N-dimethylformamide, and then add an N,N-dimethylformamide solution of N-(3-chloropropyl)phthalimide to react to obtain phthalimide-modified crown ether; Mix the phthalimide-modified crown ether with hydrazine hydrate and react to obtain amino crown ether;

[0013] S23: Disperse graphene oxide in an N,N-dimethylformamide solution, add 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide to obtain a seventh reaction solution, stir at room temperature and then add amino crown ether, continue to react, centrifuge, wash and vacuum dry to obtain crown ether-modified graphene oxide;

[0014] S4: Disperse the multi-modified polydimethylsiloxane, MOF-modified cellulose nanocrystals and crown ether-modified graphene oxide in tetrahydrofuran, add a crosslinking agent and a catalyst after ultrasonic dispersion to obtain a casting solution, coat it on the surface of a support substrate membrane, and obtain a surface-modified silicone rubber composite membrane after heat treatment.

[0015] Specifically, S1: Disperse N-isopropylacrylamide and vinyltrimethoxysilane in anhydrous methanol to obtain a first reaction solution, react under nitrogen protection and benzoyl peroxide catalysis, then rotary evaporate, wash and dry to obtain a thermosensitive monomer;

[0016] S2: Disperse p-aminoazobenzene in dichloromethane, dropwise add a dichloromethane solution of 3-isocyanatopropyltrimethoxysilane to obtain a second reaction solution, react at room temperature under nitrogen protection, then filter, concentrate under reduced pressure and recrystallize to obtain a photo-responsive monomer;

[0017] S3: Dissolve polydimethylsiloxane in tetrahydrofuran, add vinyltrimethoxysilane and dibutyltin dilaurate to obtain a third reaction solution. After reaction, perform vacuum distillation to obtain vinyl-modified polydimethylsiloxane; disperse it in a hydrochloric acid solution for treatment to obtain pre-hydrolyzed vinyl-modified polydimethylsiloxane; prepare a tetrahydrofuran solution of pre-hydrolyzed vinyl-modified polydimethylsiloxane, add tetramethylammonium hydroxide, a thermosensitive monomer and a photo-responsive monomer to obtain a fourth reaction solution. After reaction, adjust the pH with a sodium bicarbonate solution, stir, filter, wash, and perform rotary evaporation to obtain multi-modified polydimethylsiloxane.

[0018] S21: Disperse cellulose nanocrystals in deionized water. After ultrasonic dispersion, add copper nitrate and trimesic acid to obtain a fifth reaction solution. After reaction, centrifuge, wash, and dry to obtain MOF-modified cellulose nanocrystals;

[0019] S22: Disperse 18-crown-6 in N,N-dimethylformamide (DMF). Under nitrogen protection, add potassium carbonate and stir, then dropwise add a DMF solution of N-(3-chloropropyl)phthalimide to obtain a sixth reaction solution. Stir and react at a constant temperature; filter, perform rotary evaporation, and column chromatography to obtain phthalimide-modified crown ether; prepare a methanol solution of phthalimide-modified crown ether, add hydrazine hydrate under stirring and then carry out a reflux reaction, perform rotary evaporation and purification to obtain amino crown ether;

[0020] S23: Disperse graphene oxide in DMF. After uniform dispersion, add 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide to obtain a seventh reaction solution. Stir at room temperature and then add amino crown ether, continue the reaction, centrifuge, wash, and perform vacuum drying to obtain crown ether-modified graphene oxide;

[0021] S4: Disperse multi-modified polydimethylsiloxane, MOF-modified cellulose nanocrystals and crown ether-modified graphene oxide in tetrahydrofuran, perform ultrasonic dispersion to obtain a dispersion liquid, then add a cross-linking agent and a catalyst, and continue to disperse, perform vacuum degassing to obtain a casting solution; uniformly coat it on the surface of a support base film, and obtain a surface-modified silicone rubber composite film after heat treatment.

[0022] As a preferred technical solution of the present invention, in step S1, the molar ratio of N-isopropylacrylamide to vinyltrimethoxysilane is (4.0 - 4.5):1. For example, it can be 4.00:1, 4.05:1, 4.10:1, 4.15:1, 4.20:1, 4.25:1, 4.30:1, 4.35:1, 4.40:1, 4.45:1 or 4.50:1, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0023] In some alternative embodiments, the total concentration of N-isopropylacrylamide and vinyltrimethoxysilane in methanol is 10-15 wt.%, for example, it can be 10.0 wt.%, 10.5 wt.%, 11.0 wt.%, 11.5 wt.%, 12.0 wt.%, 12.5 wt.%, 13.0 wt.%, 13.5 wt.%, 14.0 wt.%, 14.5 wt.% or 15.0 wt.%, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0024] In some alternative embodiments, the temperature at which the first reaction solution reacts under nitrogen protection is 65-70 °C, for example, it can be 65.0 °C, 65.5 °C, 66.0 °C, 66.5 °C, 67.0 °C, 67.5 °C, 68.0 °C, 68.5 °C, 69.0 °C, 69.5 °C or 70.0 °C, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0025] In some alternative embodiments, the reaction time of the first reaction solution under nitrogen protection is 5-6 h, for example, it can be 5.0 h, 5.1 h, 5.2 h, 5.3 h, 5.4 h, 5.5 h, 5.6 h, 5.7 h, 5.8 h, 5.9 h or 6.0 h, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0026] As a preferred technical solution of the present invention, in step S2, the concentration of p-aminoazobenzene in dichloromethane is 5-8 wt.%, for example, it can be 5.0 wt.%, 5.3 wt.%, 5.6 wt.%, 5.9 wt.%, 6.2 wt.%, 6.5 wt.%, 6.8 wt.%, 7.1 wt.%, 7.4 wt.%, 7.7 wt.% or 8.0 wt.%, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0027] In some alternative embodiments, the concentration of the dichloromethane solution of 3-isocyanatopropyltrimethoxysilane is 3-5 wt%, for example, it can be 3.0 wt.%, 3.2 wt.%, 3.4 wt.%, 3.6 wt.%, 3.8 wt.%, 4.0 wt.%, 4.2 wt.%, 4.4 wt.%, 4.6 wt.%, 4.8 wt.% or 5.0 wt.%, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0028] In some alternative embodiments, the molar ratio of 3-isocyanatopropyltrimethoxysilane to p-aminoazobenzene is (1.1 - 1.2):1. For example, it can be 1.10:1, 1.11:1, 1.12:1, 1.13:1, 1.14:1, 1.15:1, 1.16:1, 1.17:1, 1.18:1, 1.19:1 or 1.20:1. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0029] In some alternative embodiments, the dropping rate of the dichloromethane solution of 3-isocyanatopropyltrimethoxysilane is 3 - 4 mL / min. For example, it can be 3.0 mL / min, 3.1 mL / min, 3.2 mL / min, 3.3 mL / min, 3.4 mL / min, 3.5 mL / min, 3.6 mL / min, 3.7 mL / min, 3.8 mL / min, 3.9 mL / min or 4.0 mL / min. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0030] In some alternative embodiments, the reaction time of the second reaction solution at room temperature under nitrogen protection is 18 - 20 h. For example, it can be 18.0 h, 18.2 h, 18.4 h, 18.6 h, 18.8 h, 19.0 h, 19.2 h, 19.4 h, 19.6 h, 19.8 h or 20.0 h. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0031] As a preferred technical solution of the present invention, in step S3, the mass ratio of polydimethylsiloxane to tetrahydrofuran is 1:(5 - 8). For example, it can be 1:5.0, 1:5.3, 1:5.6, 1:5.9, 1:6.2, 1:6.5, 1:6.8, 1:7.1, 1:7.4, 1:7.7 or 1:8.0. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0032] In some alternative embodiments, the molar ratio of vinyltrimethoxysilane to polydimethylsiloxane is (1.2 - 1.5):1. For example, it can be 1.20:1, 1.23:1, 1.26:1, 1.29:1, 1.32:1, 1.35:1, 1.38:1, 1.41:1, 1.44:1, 1.47:1 or 1.50:1. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0033] In some alternative embodiments, the feeding amount of dibutyltin dilaurate is 200 - 500 ppm of the mass of polydimethylsiloxane. For example, it can be 200 ppm, 230 ppm, 260 ppm, 290 ppm, 320 ppm, 350 ppm, 380 ppm, 410 ppm, 440 ppm, 470 ppm or 500 ppm. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0034] In some alternative embodiments, the reaction temperature of the third reaction solution is 70 - 75 °C. For example, it can be 70.0 °C, 70.5 °C, 71.0 °C, 71.5 °C, 72.0 °C, 72.5 °C, 73.0 °C, 73.5 °C, 74.0 °C, 74.5 °C or 75.0 °C. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0035] In some alternative embodiments, the reaction time of the third reaction solution is 4 - 6 h. For example, it can be 4.0 h, 4.2 h, 4.4 h, 4.6 h, 4.8 h, 5.0 h, 5.2 h, 5.4 h, 5.6 h, 5.8 h or 6.0 h. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0036] In some alternative embodiments, the mass fraction of the tetrahydrofuran solution of vinyl-modified polydimethylsiloxane is 20 - 25 wt.%. For example, it can be 20.0 wt.%, 20.5 wt.%, 21.0 wt.%, 21.5 wt.%, 22.0 wt.%, 22.5 wt.%, 23.0 wt.%, 23.5 wt.%, 24.0 wt.%, 24.5 wt.% or 25.0 wt.%. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0037] In some alternative embodiments, the molar ratio of vinyl-modified polydimethylsiloxane to the thermosensitive monomer and the photo-responsive monomer is (70 - 80):(15 - 10):(15 - 10). For example, it can be 70:15:15, 71:14.5:14.5, 72:14:14, 73:13.5:13.5, 74:13:13, 75:12.5:12.5, 76:12:12, 77:11.5:11.5, 78:11:11, 79:10.5:10.5 or 80:10:10. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0038] In some alternative embodiments, the feeding amount of tetramethylammonium hydroxide accounts for 0.1-0.2% of the total mass of the thermosensitive monomer and the photo-responsive monomer. For example, it can be 0.10%, 0.11%, 0.12%, 0.13%, 0.14%, 0.15%, 0.16%, 0.17%, 0.18%, 0.19% or 0.20%, but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0039] In some alternative embodiments, the temperature for the reaction of the fourth reaction solution is 75-80 °C. For example, it can be 75.0 °C, 75.5 °C, 76.0 °C, 76.5 °C, 77.0 °C, 77.5 °C, 78.0 °C, 78.5 °C, 79.0 °C, 79.5 °C or 80.0 °C, but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0040] In some alternative embodiments, the reaction time of the fourth reaction solution is 6-8 h. For example, it can be 6.0 h, 6.2 h, 6.4 h, 6.6 h, 6.8 h, 7.0 h, 7.2 h, 7.4 h, 7.6 h, 7.8 h or 8.0 h, but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0041] In some alternative embodiments, the concentration of the sodium bicarbonate solution is 1-2 mol / L. For example, it can be 1.0 mol / L, 1.2 mol / L, 1.4 mol / L, 1.6 mol / L, 1.8 mol / L or 2.0 mol / L, but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0042] In some alternative embodiments, the pH is adjusted to 7-7.5 using the sodium bicarbonate solution. For example, it can be 7.00, 7.05, 7.10, 7.15, 7.20, 7.25, 7.30, 7.35, 7.40, 7.45 or 7.50, but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0043] As a preferred technical solution of the present invention, in S4, the cross-linking agent is any one of HMS-301, PMHS or D4H;

[0044] The catalyst is any one of Karstedt catalyst or chloroplatinic acid;

[0045] The support base film is any one of polypropylene, polyvinylidene fluoride or polysulfone;

[0046] As a preferred technical solution of the present invention, in step S21, the mass fraction of the cellulose nanocrystals dispersed in deionized water is 1-2 wt.%, for example, it can be 1.0 wt.%, 1.1 wt.%, 1.2 wt.%, 1.3 wt.%, 1.4 wt.%, 1.5 wt.%, 1.6 wt.%, 1.7 wt.%, 1.8 wt.%, 1.9 wt.% or 2.0 wt.%, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0047] In some alternative embodiments, the power of the ultrasonic dispersion is 300-400 W, for example, it can be 300 W, 310 W, 320 W, 330 W, 340 W, 350 W, 360 W, 370 W, 380 W, 390 W or 400 W, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0048] In some alternative embodiments, the time of the ultrasonic dispersion is 30-40 min, for example, it can be 30 min, 31 min, 32 min, 33 min, 34 min, 35 min, 36 min, 37 min, 38 min, 39 min or 40 min, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0049] In some alternative embodiments, the mass ratio of copper nitrate to cellulose nanocrystals is (0.3-0.5):1, for example, it can be 0.30:1, 0.32:1, 0.34:1, 0.36:1, 0.38:1, 0.40:1, 0.42:1, 0.44:1, 0.46:1, 0.48:1 or 0.50:1, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0050] In some alternative embodiments, the molar ratio of trimesic acid to copper nitrate is (2-3):1, for example, it can be 2.0:1, 2.2:1, 2.4:1, 2.6:1, 2.8:1 or 3.0:1, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0051] In some alternative embodiments, the reaction time of the fifth reaction solution is 4-6 h, for example, it can be 4.0 h, 4.2 h, 4.4 h, 4.6 h, 4.8 h, 5.0 h, 5.2 h, 5.4 h, 5.6 h, 5.8 h or 6.0 h, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0052] As a preferred technical solution of the present invention, in step S22, the concentration of 18-crown-6 dispersed in N,N-dimethylformamide is 0.2-0.4M. For example, it can be 0.20M, 0.22M, 0.24M, 0.26M, 0.28M, 0.30M, 0.32M, 0.34M, 0.36M, 0.38M or 0.40M, but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0053] In some alternative embodiments, the temperature for adding potassium carbonate is 0-5°C. For example, it can be 0.0°C, 0.5°C, 1.0°C, 1.5°C, 2.0°C, 2.5°C, 3.0°C, 3.5°C, 4.0°C, 4.5°C or 5.0°C, but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0054] In some alternative embodiments, the molar ratio of potassium carbonate to 18-crown-6 is (1.2-1.5):1. For example, it can be 1.20:1, 1.23:1, 1.26:1, 1.29:1, 1.32:1, 1.35:1, 1.38:1, 1.41:1, 1.44:1, 1.47:1 or 1.50:1, but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0055] In some alternative embodiments, the molar ratio of N-(3-chloropropyl)phthalimide to 18-crown-6 is (1.2-1.5):1. For example, it can be 1.20:1, 1.23:1, 1.26:1, 1.29:1, 1.32:1, 1.35:1, 1.38:1, 1.41:1, 1.44:1, 1.47:1 or 1.50:1, but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0056] In some alternative embodiments, the concentration of the N,N-dimethylformamide solution of N-(3-chloropropyl)phthalimide is 0.3-0.5M. For example, it can be 0.30M, 0.32M, 0.34M, 0.36M, 0.38M, 0.40M, 0.42M, 0.44M, 0.46M, 0.48M or 0.50M, but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0057] In some alternative embodiments, the temperature of the sixth reaction solution during the stirring reaction under constant temperature is 50 - 60 °C. For example, it can be 50.0 °C, 51.0 °C, 52.0 °C, 53.0 °C, 54.0 °C, 55.0 °C, 56.0 °C, 57.0 °C, 58.0 °C, 59.0 °C or 60.0 °C. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0058] In some alternative embodiments, the time of the sixth reaction solution during the stirring reaction under constant temperature is 10 - 14 h. For example, it can be 10.0 h, 10.4 h, 10.8 h, 11.2 h, 11.6 h, 12.0 h, 12.4 h, 12.8 h, 13.2 h, 13.6 h or 14.0 h. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0059] In some alternative embodiments, the concentration of the methanol solution of phthalimide - modified crown ether is 0.1 - 0.2 g / mL. For example, it can be 0.10 g / mL, 0.11 g / mL, 0.12 g / mL, 0.13 g / mL, 0.14 g / mL, 0.15 g / mL, 0.16 g / mL, 0.17 g / mL, 0.18 g / mL, 0.19 g / mL or 0.20 g / mL. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0060] In some alternative embodiments, the molar ratio of hydrazine hydrate to phthalimide - modified crown ether is (3 - 4):1. For example, it can be 3.0:1, 3.2:1, 3.4:1, 3.6:1, 3.8:1 or 4.0:1. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0061] In some alternative embodiments, the temperature of the reflux reaction is 60 - 70 °C. For example, it can be 60.0 °C, 61.0 °C, 62.0 °C, 63.0 °C, 64.0 °C, 65.0 °C, 66.0 °C, 67.0 °C, 68.0 °C, 69.0 °C or 70.0 °C. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0062] In some alternative embodiments, the time of the reflux reaction is 4 - 8 h. For example, it can be 4.0 h, 4.4 h, 4.8 h, 5.2 h, 5.6 h, 6.0 h, 6.4 h, 6.8 h, 7.2 h, 7.6 h or 8.0 h. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0063] As a preferred technical solution of the present invention, in step S23, the mass fraction of graphene oxide dispersed in N,N-dimethylformamide is 0.1-0.2 wt.%, for example, it can be 0.10 wt.%, 0.11 wt.%, 0.12 wt.%, 0.13 wt.%, 0.14 wt.%, 0.15 wt.%, 0.16 wt.%, 0.17 wt.%, 0.18 wt.%, 0.19 wt.% or 0.20 wt.%, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0064] In some alternative embodiments, the mass ratio of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride, N-hydroxysuccinimide and graphene oxide is (2-3):2:1, for example, it can be 2:2:1, 2.1:2:1, 2.2:2:1, 2.3:2:1, 2.4:2:1, 2.5:2:1, 2.6:2:1, 2.7:2:1, 2.8:2:1, 2.9:2:1 or 3:2:1, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0065] In some alternative embodiments, the seventh reaction solution is stirred at room temperature for 2-3 h, for example, it can be 2.0 h, 2.2 h, 2.4 h, 2.6 h, 2.8 h or 3.0 h, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0066] In some alternative embodiments, the mass ratio of amino crown ether and graphene oxide is (2-3):1, for example, it can be 2.0:1, 2.2:1, 2.4:1, 2.6:1, 2.8:1 or 3.0:1, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0067] In some alternative embodiments, the time for the continued reaction is 20-24 h, for example, it can be 20.0 h, 20.4 h, 20.8 h, 21.2 h, 21.6 h, 22.0 h, 22.4 h, 22.8 h, 23.2 h, 23.6 h or 24.0 h, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0068] As a preferred technical solution of the present invention, in step S4, the mass ratio of the multi-modified polydimethylsiloxane to tetrahydrofuran is 1:(3-4), for example, it can be 1:3.0, 1:3.2, 1:3.4, 1:3.6, 1:3.8 or 1:4.0, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0069] In some alternative embodiments, the temperature of the heat treatment is 60 - 70 °C. For example, it can be 60.0 °C, 61.0 °C, 62.0 °C, 63.0 °C, 64.0 °C, 65.0 °C, 66.0 °C, 67.0 °C, 68.0 °C, 69.0 °C, or 70.0 °C. However, it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0070] In some alternative embodiments, the time of the heat treatment is 4 - 5 h. For example, it can be 4.0 h, 4.2 h, 4.4 h, 4.6 h, 4.8 h, or 5.0 h. However, it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0071] In a second aspect, the present invention provides a surface - modified silicone rubber composite film. The surface - modified silicone rubber composite film comprises multi - modified polydimethylsiloxane, MOF - modified cellulose nanocrystals, crown - ether - modified graphene oxide, a cross - linker, and a catalyst. The mass ratio of the multi - modified polydimethylsiloxane, MOF - modified cellulose nanocrystals, crown - ether - modified graphene oxide, cross - linker, and catalyst is: 100:(1 - 3):(1.5 - 3):(4 - 6):(0.1 - 0.2).

[0072] In the present invention, first, polydimethylsiloxane is selected as the matrix, and vinyl functional groups are introduced through chemical modification to improve the reactivity of the material and lay a foundation for subsequent functionalization reactions. In specific operations, vinyltrimethoxysilane is used as the modification reagent, and vinyl groups are introduced to the molecular chain ends of polydimethylsiloxane through a silanization reaction. To promote the efficient progress of this reaction and ensure the quality stability of the product, dibutyltin dilaurate is introduced as a homogeneous catalyst. Dibutyltin dilaurate is a typical organotin catalyst. By reducing the reaction activation energy, it significantly increases the condensation reaction rate between siloxane groups and trimethoxysilane, while avoiding the occurrence of side reactions.

[0073] Through this reaction, vinyl - modified polydimethylsiloxane is successfully prepared. The vinyl functional groups at the molecular chain ends of vinyl - modified polydimethylsiloxane have high reactivity and can chemically graft with a variety of functional monomers. The core of this modification step lies in that by introducing vinyl, not only is the efficient participation of polydimethylsiloxane in the functionalization reaction realized, but also its chemical binding ability with subsequent thermosensitive monomers and photo - responsive monomers is significantly improved. The presence of vinyl enables these functional monomers to be stably grafted onto the molecular chain of polydimethylsiloxane through chemical bonds, avoiding problems such as phase separation or uneven distribution that may occur in traditional physical mixing.

[0074] In addition, the introduction of vinyl groups also endows polydimethylsiloxane with a higher degree of freedom in molecular design, enabling it to further participate in cross-linking reactions to form a multifunctional silicone rubber matrix with a network structure. This matrix not only retains the inherent flexibility and excellent gas permeability of polydimethylsiloxane but also enhances its dynamic regulation ability under external stimuli such as temperature response and light response through subsequent functionalization, laying a solid foundation for the multifunctionality and high-efficiency separation performance of the composite membrane.

[0075] In the present invention, in order to endow the material with temperature-responsive properties, a thermosensitive monomer is specifically introduced to functionalize and modify polydimethylsiloxane. The selected thermosensitive monomer is N-isopropylacrylamide, which is a typical thermosensitive monomer and is widely used in the design of temperature-responsive materials due to its unique lower critical solution temperature property. The molecular structure of N-isopropylacrylamide contains a hydrophilic amide group and a hydrophobic isopropyl group, and its thermosensitive behavior stems from the competitive effect of these two groups at a specific temperature. Specifically, at temperatures below the critical solution temperature, the amide group exhibits hydrophilicity by forming hydrogen bonds with water molecules; while at temperatures above the critical solution temperature, the hydrogen bonds break, and the hydrophobic isopropyl group dominates, causing the N-isopropylacrylamide group to exhibit hydrophobicity. This reversible hydrophilic-hydrophobic transition makes N-isopropylacrylamide an ideal thermosensitive functional monomer.

[0076] In order to stably introduce the thermosensitive characteristics of N-isopropylacrylamide into the silicone rubber matrix, the present invention combines N-isopropylacrylamide with vinyltrimethoxysilane through a free radical copolymerization reaction to generate a thermosensitive copolymer containing a siloxane side chain. Specifically, the acryloyl double bond of N-isopropylacrylamide and the vinyl group of vinyltrimethoxysilane undergo copolymerization under the action of an initiator to form a polymer chain with siloxane functional groups. Subsequently, through a siloxane condensation reaction, the siloxane groups of the thermosensitive copolymer form covalent bonds with the silanol groups of the pre-hydrolyzed vinyl-modified polydimethylsiloxane, achieving the stable grafting of the thermosensitive monomer. This method not only retains the thermosensitive characteristics of N-isopropylacrylamide but also ensures the uniform distribution of functional groups in the matrix through chemical bonding, significantly enhancing the stability and functional controllability of the material.

[0077] The temperature-responsive characteristics brought about by the modification of this thermosensitive monomer endow the membrane material with the ability to dynamically regulate its performance during use. Specifically, the modified polydimethylsiloxane matrix exhibits significant hydrophilic-hydrophobic changes when the temperature rises or falls. This change directly affects the adsorption behavior and transport ability of the membrane towards different molecules. For example, during pervaporation, when the temperature is higher than the critical solution temperature, the membrane surface becomes more hydrophobic, enabling more effective selective permeation and separation of organic vapors; while at temperatures below the critical solution temperature, the membrane surface becomes hydrophilic, which may be more suitable for the permeation and separation of water molecules. Therefore, through this modification with the thermosensitive monomer, not only is the membrane material endowed with the intelligent response ability to external temperature changes, but also the separation efficiency and applicable range of the membrane in different application scenarios are significantly increased.

[0078] In addition, the introduction of the thermosensitive monomer also forms a synergistic effect with other functional modifications (such as the introduction of photo-responsive monomers), enabling the finally prepared composite membrane material to simultaneously respond to multiple external stimulus conditions. This multi-functional response characteristic endows the membrane material with higher adaptability in complex operating environments, providing more possibilities for its applications in fields such as oxygen enrichment separation, organic vapor recovery, and pervaporation.

[0079] In the present invention, in order to endow the membrane material with photo-responsive characteristics, a photo-responsive monomer was specifically introduced to functionalize the polydimethylsiloxane. The selected photo-responsive molecule is p-aminoazobenzene, which is a classic photo-responsive compound, and its core characteristic stems from the cis-trans isomerization behavior of the azobenzene group in the molecule. Under ultraviolet light irradiation, the structure of the azobenzene molecule changes from the thermodynamically stable trans state to the cis state; while under visible light or in the dark, the cis state gradually reverts to the trans state. This photo-induced reversible isomerization process leads to significant changes in the molecular configuration and geometric structure, accompanied by changes in the intermolecular spatial arrangement and intermolecular forces. Therefore, azobenzene is an ideal photo-responsive functional monomer and is widely used in the development of photo-controlled switches, intelligent materials, and photo-responsive separation membranes.

[0080] To introduce the photo-responsive characteristics of p-aminoazobenzene into the polydimethylsiloxane matrix, the present invention achieved the binding of p-aminoazobenzene to the siloxane group through a chemical reaction. Specifically, the amino group in p-aminoazobenzene reacts with 3-isocyanatopropyltrimethoxysilane to generate a silylated photo-responsive monomer. In this reaction, the isocyanate group and the amino group undergo an addition reaction to form a stable urea bond, while firmly connecting the azobenzene group to the siloxane molecule. Subsequently, the photo-responsive monomer is grafted onto the molecular chain of polydimethylsiloxane by means of a covalent bond, enabling it to be embedded in the silicone rubber matrix. This chemical modification method not only ensures the efficient binding of the photo-responsive group in the matrix, but also significantly improves its dispersion uniformity and long-term stability in the matrix.

[0081] The introduction of photo-responsive monomers endows the membrane material with sensitivity to light stimuli. Under ultraviolet light irradiation, the azobenzene group transforms from the trans structure to the cis structure. This isomerization process leads to changes in molecular size and intermolecular arrangement, thereby triggering the adjustment of the internal microstructure of the membrane material. For example, the cis structure of azobenzene has a greater steric occupancy effect than the trans structure, and this configurational change may cause dynamic regulation of membrane pores, thus altering the permeability of the membrane to different molecules or ions. In addition, the isomerization of the azobenzene group may also affect the hydrophilic-hydrophobic distribution on the membrane surface, further regulating its separation performance. Therefore, by introducing photo-responsive monomers, the membrane material can not only achieve the selective separation of specific molecules under external light stimuli but also realize the dynamic regulation of separation behavior when switching between ultraviolet light and visible light.

[0082] This photo-responsive property has significant advantages in various application scenarios. For example, in the pervaporation process, the selective separation of volatile organic compounds and water molecules by the membrane can be dynamically adjusted by changing the light irradiation conditions; in the gas separation process, the photo-responsive property can be used to optimize the permeation rate of the membrane to specific gases, thereby improving the separation efficiency. In addition, the combination of photo-responsive monomers and the membrane matrix is achieved through covalent bonds, and this stable chemical bonding method ensures the long-term durability of the photo-responsive function, maintaining its performance advantages even in complex operating environments.

[0083] In the present invention, cellulose nanocrystals are introduced into the composite membrane as a functional filler to enhance the mechanical properties and separation efficiency of the membrane. Cellulose nanocrystals are nanoscale crystals prepared from natural cellulose by methods such as acid hydrolysis, and they have unique structural characteristics and performance advantages. Their molecular backbone consists of β-1,4-glucose units, with a highly ordered crystal structure, thus exhibiting extremely high crystallinity. Compared with traditional inorganic or synthetic fillers, cellulose nanocrystals have a series of excellent properties, including light weight, high strength, good biocompatibility, high thermal stability, and renewability, and are thus considered a highly potential environmentally friendly nanomaterial.

[0084] The surface of cellulose nanocrystals is rich in a large number of hydroxyl groups, and these active groups provide great possibilities for surface chemical modification. Through appropriate chemical modification, functional groups can be introduced onto the surface of cellulose nanocrystals, thereby achieving directional reinforcement and functionalization in composite materials. In the present invention, in order to further enhance the performance and functionality of cellulose nanocrystals, a MOF modification technique is adopted. MOF is a class of porous materials formed by metal ions or metal clusters and organic ligands through coordination bonds, which have an extremely high specific surface area, adjustable pore structure, and excellent molecular sieve effect. Through MOF modification, cellulose nanocrystals not only possess the ability to enhance the mechanical properties of the membrane but also increase the separation selectivity and adsorption capacity of the material.

[0085] Specifically, the present invention realizes the preparation of MOF-modified cellulose nanocrystals through the following steps: First, the cellulose nanocrystals are dispersed in deionized water. Utilizing the high reactivity of the hydroxyl groups on their surface, copper nitrate and trimesic acid are introduced during the reaction. These chemical reagents form an MOF layer on the surface of the cellulose nanocrystals through a coordination reaction. Copper nitrate provides the metal center, while trimesic acid, as a tridentate ligand, coordinates with the metal center, ultimately forming a stable MOF structure. This MOF layer uniformly coats the surface of the cellulose nanocrystals, endowing them with the unique properties of MOF.

[0086] The introduction of MOF significantly enhances the functionality of cellulose nanocrystals. As a highly porous material, the MOF layer provides an extremely high specific surface area and a large number of adjustable pores. These pores can not only efficiently adsorb specific molecules but also play the role of a molecular sieve effect, enabling the material to have higher selectivity for the separation of different molecules. In addition, the introduction of the MOF layer does not significantly increase the mass of the cellulose nanocrystals because MOF itself has a low density, which also ensures that the overall lightweight characteristics of the material are retained.

[0087] In the composite membrane system, the role of MOF-modified cellulose nanocrystals is multiple. On the one hand, the high strength and high crystallinity of cellulose nanocrystals significantly enhance the mechanical properties of the membrane, making the composite membrane have higher tensile strength and anti-deformation ability, thereby improving the stability and durability of the membrane under complex operating conditions. On the other hand, the porous structure of the MOF layer endows the composite membrane with excellent selective separation performance. During the pervaporation or gas separation process, MOF-modified cellulose nanocrystals can achieve efficient separation of specific molecules or gases through the molecular sieve effect and adsorption selectivity. For example, MOF can preferentially adsorb or screen organic vapor molecules through its pore structure while blocking larger unwanted molecules, thus significantly improving the separation efficiency.

[0088] In addition, MOF-modified cellulose nanocrystals also exhibit good interfacial compatibility. Due to the rich hydroxyl groups on the surface of cellulose nanocrystals and the porous characteristics of the MOF layer, their dispersibility in the composite membrane matrix is relatively good, effectively avoiding structural defects caused by filler agglomeration. This uniform dispersibility not only ensures the integrity of the composite membrane but also further improves the separation performance and mechanical properties of the membrane material.

[0089] In the present invention, graphene oxide is introduced as a filler into the composite membrane to enhance the mechanical properties, separation efficiency, and selectivity of the membrane. Graphene oxide is an oxidized derivative of graphene, and its surface is rich in various oxygen-containing functional groups, which endow it with unique chemical activity and good hydrophilicity. This enables graphene oxide to have good dispersion stability in solution and provides abundant reaction sites for surface functional modification. In addition, the two-dimensional layered structure of graphene oxide gives it an extremely high specific surface area, providing sufficient active sites for molecular adsorption and transport.

[0090] Graphene oxide also has excellent mechanical properties. The carbon-carbon bonds in its single-layer structure have extremely high strength and rigidity, enabling it to play a significant strengthening role in the composite membrane. Especially in the separation membrane, the interlayer channels of graphene oxide have a molecular sieve effect, which can selectively permeate molecules according to their size, shape, or polarity. This molecular sieve effect endows the composite membrane with high separation performance and can block larger or unwanted molecules from passing through the membrane, thereby achieving the preferential separation of target molecules.

[0091] To further improve the dispersibility and functionality of graphene oxide in the composite membrane, the present invention conducts chemical modification of it with amino crown ether. Specifically, amino crown ether is covalently bonded to the carboxyl group on the surface of graphene oxide through an amidation reaction to prepare crown ether-modified graphene oxide. The core of the amidation reaction is the dehydration condensation reaction between the carboxyl group and the amino group, which generates stable amide bonds under appropriate catalysts or reaction conditions. This chemical modification not only ensures the stable binding of crown ether molecules on the surface of graphene oxide but also significantly improves the surface characteristics of graphene oxide.

[0092] Crown ether molecules are a class of typical cyclic compounds, and their molecular structure contains multiple oxygen atoms. These oxygen atoms can form complexes with specific cations or small molecules through lone pairs of electrons. By introducing crown ether molecules onto the surface of graphene oxide, its unique ion recognition ability and complexation effect are successfully imparted to the composite membrane. Crown ether-modified graphene oxide can selectively adsorb and transport specific ions or small molecules, thereby significantly improving the separation selectivity of the membrane.

[0093] The introduction of crown ether molecules improves the dispersibility of graphene oxide in the silicone rubber matrix. Since the oxygen atoms in the crown ether molecules can form strong interactions with the silicon-oxygen groups in the silicone rubber matrix, crown ether-modified graphene oxide can be more uniformly distributed in the matrix, avoiding the agglomeration phenomenon that may occur with traditional graphene oxide. This uniform dispersibility ensures the uniformity and stability of the composite membrane performance.

[0094] Disperse the multi-modified polydimethylsiloxane, MOF-modified cellulose nanocrystals, and crown ether-modified graphene oxide in tetrahydrofuran. After adding the crosslinking agent and catalyst, chemical bonding between the matrix material and the filler can be achieved. The role of the crosslinking agent is to connect the functional groups between the PDMS molecular chains through chemical reactions to form a three-dimensional crosslinked network structure. The formation of this network structure not only enhances the mechanical properties of the composite membrane but also significantly improves its stability under complex operating conditions. At the same time, the crosslinking agent reacts with the active functional groups on the surface of the filler, causing the filler to be further embedded in the crosslinked network, strengthening the interfacial bonding between the matrix and the filler. The introduction of the catalyst accelerates the crosslinking reaction by reducing the activation energy of the crosslinking reaction, ensuring the complete formation of the network structure during the film-forming process.

[0095] Coat the obtained casting solution on the surface of the base film, and the coated film is heat-treated under specific temperature conditions. The heat treatment process plays two roles: on the one hand, the heat energy provided by the heat treatment further promotes the complete progress of the crosslinking reaction, ensuring the integrity of the three-dimensional crosslinked network; on the other hand, as the solvent gradually volatilizes and the chemical reaction deepens, the film surface gradually becomes dense and flat, forming a uniform ultra-thin film structure.

[0096] There is also a synergistic enhancement effect in the whole system: MOF-modified cellulose nanocrystals and crown ether-modified graphene oxide not only play their respective roles in enhancing and functionalizing, but their interaction also significantly optimizes the performance of the membrane. MOF-modified cellulose nanocrystals have a highly regular porous structure and a high specific surface area, while crown ether-modified graphene oxide is characterized by a two-dimensional layered structure. The two can form a multi-scale separation channel network in the composite membrane. The micropores of MOF and the interlayer channels of crown ether-modified graphene oxide work together to enable the membrane to achieve efficient separation of molecules with different sizes and different properties simultaneously. For example, the microporous structure of MOF can screen out smaller molecules, while the two-dimensional channels of crown ether-modified graphene oxide can selectively adsorb and transport larger molecules or specific ions. The synergistic effect of this multi-scale separation mechanism enables the membrane to exhibit superior performance in more complex mixture separation tasks.

[0097] MOF-modified cellulose nanocrystals and crown ether-modified graphene oxide surfaces contain abundant active functional groups, which can form strong interfacial bonding with the reactive groups in the multi-modified polydimethylsiloxane matrix through chemical bonds or hydrogen bonds. This interfacial bonding not only enhances the dispersion stability of the filler in the matrix but also optimizes the stress transfer ability between the filler and the matrix, thereby further improving the mechanical strength and long-term stability of the membrane. In addition, this interfacial synergistic effect effectively prevents the possible migration or shedding of the filler during operation, ensuring the durability of the membrane's separation performance during long-term use.

[0098] Secondly, the porous structure of MOF-modified cellulose nanocrystals provides a more unobstructed path for molecular diffusion in the matrix material. At the same time, the good compatibility between the MOF layer on its surface and polydimethylsiloxane reduces the interfacial resistance, further enhancing the permeation flux of the membrane. The two-dimensional structure of crown ether-modified graphene oxide provides additional molecular selective sieving ability through its interlayer channels, complementing the high permeability of polydimethylsiloxane. These interfacial synergistic effects ensure that the composite membrane maintains a high permeation efficiency while achieving high-selectivity separation.

[0099] Multi-modified polydimethylsiloxane as the matrix material provides good processability and ductility for the composite membrane with its flexible molecular chains. However, flexible materials usually have deficiencies in mechanical strength and dimensional stability. The introduction of MOF-modified cellulose nanocrystals and crown ether-modified graphene oxide forms an effective mechanical reinforcement for the matrix material through their rigid structures. The high crystallinity of MOF-modified cellulose nanocrystals and the high Young's modulus of crown ether-modified graphene oxide enable the composite membrane to achieve high-strength structural stability while maintaining flexibility. This synergistic balance between flexibility and rigidity enables the composite membrane to withstand higher mechanical stresses in complex operating environments while maintaining excellent separation performance.

[0100] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0101] In the present invention, polydimethylsiloxane as a flexible matrix material provides excellent flexibility and gas permeability in the composite membrane, and at the same time provides a structural basis for functional modification and intelligent response characteristics. By introducing vinyl functional groups, the reaction activity of hydroxy polydimethylsiloxane is significantly improved, enabling it to efficiently combine with a variety of functional monomers. The grafting of thermosensitive monomers endows the membrane material with temperature-responsive characteristics, regulating the hydrophilicity and hydrophobicity of the membrane at different temperatures, thereby optimizing the separation performance; the introduction of photo-responsive monomers endows the membrane with photo-responsive ability, regulating the pore structure and separation behavior of the membrane through the switching of ultraviolet light and visible light.

[0102] In the present invention, cellulose nanocrystals as functional fillers provide high mechanical strength and separation selectivity in the composite membrane. By modifying cellulose nanocrystals with MOF, a uniform porous MOF structure is introduced on its surface, significantly increasing the specific surface area and pore number of cellulose nanocrystals, enabling it to have molecular sieve effect and adsorption selectivity. Secondly, it improves the mechanical properties and selective separation ability of the composite membrane, and at the same time its good dispersibility ensures the integrity of the membrane structure, providing an important support for an efficient and stable separation process.

[0103] In the present invention, graphene oxide is introduced as a functional filler with a two-dimensional structure, providing mechanical reinforcement and molecular sieve effects in the composite membrane. By introducing crown ether molecules on the surface of graphene oxide, the ion recognition ability and dispersion stability of graphene oxide are significantly enhanced. The crown ether-modified graphene oxide combines mechanical reinforcement, ion selectivity, and molecular sieve effects in the composite membrane system, forming a good synergistic effect with the matrix material and providing excellent performance support for complex separation tasks. Brief Description of the Drawings

[0104] Figure 1 It is a flowchart of the preparation method of the surface-modified silicone rubber composite membrane provided by the embodiment of the present invention. Detailed Embodiments

[0105] The technical solutions of the present invention will be described in detail below with reference to specific embodiments and their accompanying drawings. The embodiments described herein are specific specific embodiments of the present invention for illustrating the concept of the present invention; these descriptions are all explanatory and exemplary, and should not be construed as limiting the embodiments of the present invention and the protection scope of the present invention. Except for the embodiments described herein, those skilled in the art can also adopt other obvious technical solutions based on the content disclosed in the claims and the specification of this application. These technical solutions include technical solutions that make any obvious substitutions and modifications to the embodiments described herein.

[0106] The chemical reagents used in the embodiments and comparative examples of the present invention are all commercially available products without further purification or treatment.

[0107] Example 1

[0108] This example provides a surface-modified silicone rubber composite membrane and its preparation method. Refer to Figure 1 , the preparation method of the surface-modified silicone rubber composite membrane specifically includes the following steps:

[0109] S1: Disperse N-isopropylacrylamide and vinyltrimethoxysilane in anhydrous methanol at a molar ratio of 4:1 to obtain a first reaction solution, where the total concentration of N-isopropylacrylamide and vinyltrimethoxysilane in the first reaction solution is 12 wt%. React at 67 °C for 5.8 h under the catalysis of benzoyl peroxide and nitrogen protection, then perform rotary evaporation, washing, and drying to obtain a thermosensitive monomer;

[0110] S2: Disperse p-aminoazobenzene at a concentration of 6 wt.% in dichloromethane, and dropwise add a dichloromethane solution of 3-isocyanatopropyltrimethoxysilane with a dropping rate of 4 mL / min and a dropping concentration of 4.5 wt% to obtain a second reaction solution, where the molar ratio of 3-isocyanatopropyltrimethoxysilane to p-aminoazobenzene is 1.16:1. After reacting at room temperature for 18 h under nitrogen protection, filter, concentrate under reduced pressure, and recrystallize to obtain a photo-responsive monomer;

[0111] S3: Dissolve polydimethylsiloxane in tetrahydrofuran at a mass ratio of 1:7, add vinyltrimethoxysilane and dibutyltin dilaurate to obtain a third reaction solution, where the molar ratio of vinyltrimethoxysilane to polydimethylsiloxane is 1.42:1 and the feeding amount of dibutyltin dilaurate is 400 ppm relative to the mass of polydimethylsiloxane. React at 72 °C for 4.6 h, and distill under reduced pressure to obtain vinyl-modified polydimethylsiloxane; Disperse it in a hydrochloric acid solution for treatment to obtain pre-hydrolyzed vinyl-modified polydimethylsiloxane; Prepare a tetrahydrofuran solution of pre-hydrolyzed vinyl-modified polydimethylsiloxane with a mass fraction of 22 wt.%, add tetramethylammonium hydroxide, a thermosensitive monomer, and a photo-responsive monomer to obtain a fourth reaction solution, where the molar ratio of vinyl-modified polydimethylsiloxane to the thermosensitive monomer and the photo-responsive monomer is 76:12:12, and the feeding amount of tetramethylammonium hydroxide accounts for 0.16% of the total mass of the monomers. React at 76 °C for 7 h, then adjust the pH to 7 with a 1.5 mol / L sodium bicarbonate solution, stir, filter, wash, and rotary evaporate to obtain multi-modified polydimethylsiloxane.

[0112] S21: Disperse cellulose nanocrystals at a mass fraction of 1.7 wt.% in deionized water, ultrasonically disperse for 40 min at a power of 370 W, then add copper nitrate and trimesic acid to obtain a fifth reaction solution, where the mass ratio of copper nitrate to cellulose nanocrystals is 0.4:1 and the molar ratio of trimesic acid to copper nitrate is 2.7:1. After reacting for 5.4 h, centrifuge, wash, and dry to obtain MOF-modified cellulose nanocrystals;

[0113] S22: Disperse 18-crown-6 at a concentration of 0.3 M in DMF. Under nitrogen protection, add potassium carbonate at 3 °C and stir. The molar ratio of potassium carbonate to 18-crown-6 is 1.3:1. Subsequently, dropwise add a DMF solution of N-(3-chloropropyl)phthalimide with a concentration of 0.43 M to obtain a sixth reaction solution. The molar ratio of N-(3-chloropropyl)phthalimide to 18-crown-6 is 1.35:1. Stir and react at a constant temperature of 56 °C for 12 h; filter, rotary evaporate, and perform column chromatography to obtain phthalimide-modified crown ether; prepare a methanol solution of phthalimide-modified crown ether with a concentration of 0.1 g / mL, add hydrazine hydrate under stirring and then carry out a reflux reaction. The molar ratio of hydrazine hydrate to phthalimide-modified crown ether is 3.8:1, the reflux reaction temperature is 68 °C, and the time is 6 h. Rotary evaporate and purify to obtain amino crown ether;

[0114] S23: Disperse graphene oxide at a mass fraction of 0.18 wt.% in DMF. After uniform dispersion, add 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide to obtain a seventh reaction solution. The mass ratio of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide to graphene oxide is 2.3:2:1. Stir at room temperature for 2.8 h, then add amino crown ether with a mass ratio of 2.5:1 to graphene oxide, and continue to react for 22 h. Centrifuge, wash, and vacuum dry to obtain crown ether-modified graphene oxide;

[0115] S4: Disperse multi-modified polydimethylsiloxane, MOF-modified cellulose nanocrystals, and crown ether-modified graphene oxide in tetrahydrofuran. The mass ratio of multi-modified polydimethylsiloxane to tetrahydrofuran is 1:3.5. Ultrasonically disperse to obtain a dispersion. Subsequently, add crosslinking agent HMS-301 and catalyst Karstedt, and continue to disperse. Perform vacuum degassing to obtain a casting solution. The mass ratio of multi-modified polydimethylsiloxane, MOF-modified cellulose nanocrystals, crown ether-modified graphene oxide, crosslinking agent, and catalyst is: 100:2:2.5:5.4:0.15; uniformly coat it on the surface of a polypropylene support membrane, and heat-treat at 67 °C for 4.5 h to obtain a surface-modified silicone rubber composite membrane.

[0116] Example 2

[0117] This example provides a surface-modified silicone rubber composite membrane and a preparation method thereof. The preparation method of the surface-modified silicone rubber composite membrane specifically includes the following steps:

[0118] S1: Disperse N-isopropylacrylamide and vinyltrimethoxysilane at a molar ratio of 4.5:1 in anhydrous methanol to obtain a first reaction solution, where the total concentration of N-isopropylacrylamide and vinyltrimethoxysilane in the first reaction solution is 10 wt%. After reacting at 68 °C for 6 h under the catalysis of benzoyl peroxide and under nitrogen protection, rotary evaporation, washing, and drying are carried out to obtain a thermosensitive monomer;

[0119] S2: Disperse p-aminoazobenzene at a concentration of 7.2 wt% in dichloromethane, and add a dichloromethane solution of 3-isocyanatopropyltrimethoxysilane with a dropping rate of 3.4 mL / min and a dropping concentration of 3 wt% to obtain a second reaction solution, where the molar ratio of 3-isocyanatopropyltrimethoxysilane to p-aminoazobenzene is 1.2:1. After reacting at room temperature for 20 h under nitrogen protection, filtration, concentration under reduced pressure, and recrystallization are carried out to obtain a photo-responsive monomer;

[0120] S3: Dissolve polydimethylsiloxane at a mass ratio of 1:6 in tetrahydrofuran, add vinyltrimethoxysilane and dibutyltin dilaurate to obtain a third reaction solution, where the molar ratio of vinyltrimethoxysilane to polydimethylsiloxane is 1.5:1 and the feeding amount of dibutyltin dilaurate is 500 ppm relative to the mass of polydimethylsiloxane. React at 73 °C for 5.6 h, and carry out vacuum distillation to obtain vinyl-modified polydimethylsiloxane; Disperse it in a hydrochloric acid solution for treatment to obtain pre-hydrolyzed vinyl-modified polydimethylsiloxane; Prepare a tetrahydrofuran solution of pre-hydrolyzed vinyl-modified polydimethylsiloxane with a mass fraction of 25 wt.%, add tetramethylammonium hydroxide, thermosensitive monomer, and photo-responsive monomer to obtain a fourth reaction solution, where the molar ratio of vinyl-modified polydimethylsiloxane to thermosensitive monomer and photo-responsive monomer is 74:13:13, and the feeding amount of tetramethylammonium hydroxide accounts for 0.18% of the total mass of the monomers. React at 78 °C for 8 h, and then adjust the pH to 7.2 with a 2 mol / L sodium bicarbonate solution, stir, filter, wash, and rotary evaporate to obtain multi-modified polydimethylsiloxane.

[0121] S21: Disperse cellulose nanocrystals at a mass fraction of 2 wt% in deionized water, ultrasonically disperse for 34 min at a power of 350 W, and then add copper nitrate and trimesic acid to obtain a fifth reaction solution, where the mass ratio of copper nitrate to cellulose nanocrystals is 0.3:1 and the molar ratio of trimesic acid to copper nitrate is 2.3:1. After reacting for 6 h, centrifuge, wash, and dry to obtain MOF-modified cellulose nanocrystals;

[0122] S22: Disperse 18-crown-6 at a concentration of 0.4 M in DMF. Under nitrogen protection, add potassium carbonate at 5 °C and stir. The molar ratio of potassium carbonate to 18-crown-6 is 1.2:1. Subsequently, dropwise add a DMF solution of N-(3-chloropropyl)phthalimide with a concentration of 0.5 M to obtain a sixth reaction solution. The molar ratio of N-(3-chloropropyl)phthalimide to 18-crown-6 is 1.42:1. Stir and react at a constant temperature of 60 °C for 14 h; filter, rotary evaporate, and perform column chromatography to obtain phthalimide-modified crown ether; prepare a methanol solution of phthalimide-modified crown ether with a concentration of 0.2 g / mL, add hydrazine hydrate under stirring and then carry out a reflux reaction. The molar ratio of hydrazine hydrate to phthalimide-modified crown ether is 3:1, the reflux reaction temperature is 70 °C, and the time is 8 h. Rotary evaporate and purify to obtain amino crown ether;

[0123] S23: Disperse graphene oxide at a mass fraction of 0.12 wt% in DMF. After uniform dispersion, add 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide to obtain a seventh reaction solution. The mass ratio of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide to graphene oxide is 2.5:2:1. Stir at room temperature for 2.3 h, then add amino crown ether with a mass ratio to graphene oxide of 2.8:1, and continue to react for 23 h. Centrifuge, wash, and vacuum dry to obtain crown ether-modified graphene oxide;

[0124] S4: Disperse multi-modified polydimethylsiloxane, MOF-modified cellulose nanocrystals, and crown ether-modified graphene oxide in tetrahydrofuran. The mass ratio of multi-modified polydimethylsiloxane to tetrahydrofuran is 1:3.7. Ultrasonically disperse to obtain a dispersion, then add a crosslinking agent and a catalyst, and continue to disperse. Remove air bubbles under vacuum to obtain a casting solution. The mass ratio of multi-modified polydimethylsiloxane, MOF-modified cellulose nanocrystals, crown ether-modified graphene oxide, crosslinking agent PMHS, and catalyst chloroplatinic acid is: 100:3:3:4.6:0.2; uniformly coat it on the surface of a polyvinylidene fluoride support membrane, and heat-treat at 70 °C for 4.8 h to obtain a surface-modified silicone rubber composite membrane.

[0125] Example 3

[0126] This example provides a surface-modified silicone rubber composite membrane and a preparation method thereof. The preparation method of the surface-modified silicone rubber composite membrane specifically includes the following steps:

[0127] S1: Disperse N-isopropylacrylamide and vinyltrimethoxysilane at a molar ratio of 4.2:1 in anhydrous methanol to obtain a first reaction solution, where the total concentration of N-isopropylacrylamide and vinyltrimethoxysilane in the first reaction solution is 14 wt%. After reacting at 65 °C for 5 h under the catalysis of benzoyl peroxide and under nitrogen protection, rotary evaporation, washing, and drying are carried out to obtain a thermosensitive monomer;

[0128] S2: Disperse p-aminoazobenzene at a concentration of 5 wt.% in dichloromethane, and add a dichloromethane solution of 3-isocyanatopropyltrimethoxysilane with a dropping rate of 3 mL / min and a dropping concentration of 5 wt% to obtain a second reaction solution, where the molar ratio of 3-isocyanatopropyltrimethoxysilane to p-aminoazobenzene is 1.1:1. After reacting at room temperature for 19.8 h under nitrogen protection, filtration, concentration under reduced pressure, and recrystallization are carried out to obtain a photo-responsive monomer;

[0129] S3: Dissolve polydimethylsiloxane in tetrahydrofuran at a mass ratio of 1:5, add vinyltrimethoxysilane and dibutyltin dilaurate to obtain a third reaction solution, where the molar ratio of vinyltrimethoxysilane to polydimethylsiloxane is 1.3:1 and the feeding amount of dibutyltin dilaurate is 200 ppm relative to the mass of polydimethylsiloxane. React at 70 °C for 4 h, and carry out vacuum distillation to obtain vinyl-modified polydimethylsiloxane; Disperse it in a hydrochloric acid solution for treatment to obtain pre-hydrolyzed vinyl-modified polydimethylsiloxane; Prepare a tetrahydrofuran solution of pre-hydrolyzed vinyl-modified polydimethylsiloxane with a mass fraction of 20 wt.%, add tetramethylammonium hydroxide, the thermosensitive monomer, and the photo-responsive monomer to obtain a fourth reaction solution, where the molar ratio of vinyl-modified polydimethylsiloxane to the thermosensitive monomer and the photo-responsive monomer is 70:15:15, and the feeding amount of tetramethylammonium hydroxide accounts for 0.1% of the total mass of the monomers. React at 75 °C for 6 h, then adjust the pH to 7.4 with a 1.8 mol / L sodium bicarbonate solution, stir, filter, wash, and rotary evaporate to obtain a multi-modified polydimethylsiloxane.

[0130] S21: Disperse cellulose nanocrystals at a mass fraction of 1 wt% in deionized water, ultrasonically disperse for 30 min at a power of 300 W, and then add copper nitrate and trimesic acid to obtain a fifth reaction solution, where the mass ratio of copper nitrate to cellulose nanocrystals is 0.5:1 and the molar ratio of trimesic acid to copper nitrate is 2:1. After reacting for 4 h, centrifuge, wash, and dry to obtain MOF-modified cellulose nanocrystals;

[0131] S22: Disperse 18-crown-6 at a concentration of 0.2 M in DMF. Under nitrogen protection, add potassium carbonate at 0 °C and stir. The molar ratio of potassium carbonate to 18-crown-6 is 1.5:1. Subsequently, dropwise add a DMF solution of N-(3-chloropropyl)phthalimide with a concentration of 0.3 M to obtain a sixth reaction solution. The molar ratio of N-(3-chloropropyl)phthalimide to 18-crown-6 is 1.3:1. Stir and react at a constant temperature of 55 °C for 10 h; filter, rotary evaporate, and perform column chromatography to obtain phthalimide-modified crown ether; prepare a methanol solution of phthalimide-modified crown ether with a concentration of 0.15 g / mL, add hydrazine hydrate under stirring and then carry out a reflux reaction. The molar ratio of hydrazine hydrate to phthalimide-modified crown ether is 4:1, the reflux reaction temperature is 60 °C, and the time is 5 h. Rotary evaporate and purify to obtain amino crown ether;

[0132] S23: Disperse graphene oxide at a mass fraction of 0.1 wt.% in DMF. After uniform dispersion, add 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide to obtain a seventh reaction solution. The mass ratio of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide to graphene oxide is 2:2:1. Stir at room temperature for 2 h, then add amino crown ether with a mass ratio of 2:1 to graphene oxide, and continue to react for 20 h. Centrifuge, wash, and vacuum dry to obtain crown ether-modified graphene oxide;

[0133] S4: Disperse multi-modified polydimethylsiloxane, MOF-modified cellulose nanocrystals, and crown ether-modified graphene oxide in tetrahydrofuran. The mass ratio of multi-modified polydimethylsiloxane to tetrahydrofuran is 1:3. Ultrasonically disperse to obtain a dispersion liquid. Subsequently, add a crosslinking agent and a catalyst, and continue to disperse. Vacuum degas to obtain a casting solution. The mass ratio of multi-modified polydimethylsiloxane, MOF-modified cellulose nanocrystals, crown ether-modified graphene oxide, crosslinking agent D4H, and catalyst chloroplatinic acid is: 100:1:1.5:4:0.18; uniformly coat it on the surface of a polysulfone support membrane, and heat-treat at 60 °C for 4 h to obtain a surface-modified silicone rubber composite membrane.

[0134] Example 4

[0135] This example provides a surface-modified silicone rubber composite membrane and a preparation method thereof. The preparation method of the surface-modified silicone rubber composite membrane specifically includes the following steps:

[0136] S1: Disperse N-isopropylacrylamide and vinyltrimethoxysilane at a molar ratio of 4.4:1 in anhydrous methanol to obtain a first reaction solution, where the total concentration of N-isopropylacrylamide and vinyltrimethoxysilane in the first reaction solution is 15 wt%. React at 70 °C for 5.4 h under the catalysis of benzoyl peroxide and under nitrogen protection, then perform rotary evaporation, washing, and drying to obtain a thermosensitive monomer;

[0137] S2: Disperse p-aminoazobenzene at a concentration of 8 wt% in dichloromethane, and dropwise add a dichloromethane solution of 3-isocyanatopropyltrimethoxysilane with a dropping rate of 3.7 mL / min and a dropping concentration of 4.2 wt% to obtain a second reaction solution, where the molar ratio of 3-isocyanatopropyltrimethoxysilane to p-aminoazobenzene is 1.12:1. React at room temperature for 19 h under nitrogen protection, then filter, concentrate under reduced pressure, and recrystallize to obtain a photo-responsive monomer;

[0138] S3: Dissolve polydimethylsiloxane at a mass ratio of 1:8 in tetrahydrofuran, add vinyltrimethoxysilane and dibutyltin dilaurate to obtain a third reaction solution, where the molar ratio of vinyltrimethoxysilane to polydimethylsiloxane is 1.2:1 and the feeding amount of dibutyltin dilaurate is 300 ppm relative to the mass of polydimethylsiloxane. React at 75 °C for 6 h, and perform vacuum distillation to obtain vinyl-modified polydimethylsiloxane; Disperse it in a hydrochloric acid solution for treatment to obtain pre-hydrolyzed vinyl-modified polydimethylsiloxane; Prepare a tetrahydrofuran solution of pre-hydrolyzed vinyl-modified polydimethylsiloxane with a mass fraction of 23 wt.%, add tetramethylammonium hydroxide, thermosensitive monomer, and photo-responsive monomer to obtain a fourth reaction solution, where the molar ratio of vinyl-modified polydimethylsiloxane to thermosensitive monomer and photo-responsive monomer is 80:10:10, and the feeding amount of tetramethylammonium hydroxide accounts for 0.2% of the total mass of the monomers. React at 80 °C for 7.8 h, then adjust the pH to 7.5 with a 1 mol / L sodium bicarbonate solution, stir, filter, wash, and perform rotary evaporation to obtain multi-modified polydimethylsiloxane.

[0139] S21: Disperse cellulose nanocrystals at a mass fraction of 1.2 wt% in deionized water, ultrasonically disperse for 38 min at a power of 400 W, then add copper nitrate and trimesic acid to obtain a fifth reaction solution, where the mass ratio of copper nitrate to cellulose nanocrystals is 0.43:1 and the molar ratio of trimesic acid to copper nitrate is 3:1. React for 4.6 h, then centrifuge, wash, and dry to obtain MOF-modified cellulose nanocrystals;

[0140] S22: Disperse 18-crown-6 at a concentration of 0.34 M in DMF. Under nitrogen protection, add potassium carbonate at 4 °C and stir. The molar ratio of potassium carbonate to 18-crown-6 is 1.4:1. Subsequently, dropwise add a DMF solution of N-(3-chloropropyl)phthalimide with a concentration of 0.4 M to obtain the sixth reaction solution. The molar ratio of N-(3-chloropropyl)phthalimide to 18-crown-6 is 1.5:1. Stir and react at a constant temperature of 50 °C for 13 h; filter, rotary evaporate, and perform column chromatography to obtain phthalimide-modified crown ether; prepare a methanol solution of phthalimide-modified crown ether with a concentration of 0.18 g / mL, add hydrazine hydrate under stirring and then carry out a reflux reaction. The molar ratio of hydrazine hydrate to phthalimide-modified crown ether is 3.6:1, the reflux reaction temperature is 65 °C, and the time is 4 h. Rotary evaporate and purify to obtain amino crown ether;

[0141] S23: Disperse graphene oxide at a mass fraction of 0.2 wt% in DMF. After uniform dispersion, add 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide to obtain the seventh reaction solution. The mass ratio of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide to graphene oxide is 3:2:1. Stir at room temperature for 3 h, then add amino crown ether with a mass ratio to graphene oxide of 3:1, and continue to react for 24 h. Centrifuge, wash, and vacuum dry to obtain crown ether-modified graphene oxide;

[0142] S4: Disperse multi-modified polydimethylsiloxane, MOF-modified cellulose nanocrystals, and crown ether-modified graphene oxide in tetrahydrofuran. The mass ratio of multi-modified polydimethylsiloxane to tetrahydrofuran is 1:4. Ultrasonically disperse to obtain a dispersion, then add crosslinking agent PMHS and catalyst Karstedt, and continue to disperse. Vacuum degas to obtain a casting solution. The mass ratio of multi-modified polydimethylsiloxane, MOF-modified cellulose nanocrystals, crown ether-modified graphene oxide, crosslinking agent, and catalyst is: 100:2.5:2.3:6:0.1; Uniformly coat it on the surface of a polyvinylidene fluoride support membrane, and heat-treat at 62 °C for 5 h to obtain a surface-modified silicone rubber composite membrane.

[0143] Comparative Example 1

[0144] This comparative example provides a surface-modified silicone rubber composite membrane. The difference from Example 1 is that in S3, the molar ratio of vinyltrimethoxysilane to polydimethylsiloxane is changed to 2:1, and other operation steps and process parameters are exactly the same as those in Example 1.

[0145] Comparative Example 2

[0146] This comparative example provides a surface-modified silicone rubber composite membrane, which is different from Example 1 in that in S3, the molar ratio of vinyltrimethoxysilane to polydimethylsiloxane is changed to 1:1, and other operation steps and process parameters are exactly the same as those in Example 1.

[0147] Comparative Example 3

[0148] This comparative example provides a surface-modified silicone rubber composite membrane, which is different from Example 1 in that in S4, the mass ratio of multi-modified polydimethylsiloxane, MOF-modified cellulose nanocrystals, crown ether-modified graphene oxide, cross-linking agent and catalyst is: 100:5:2.5:5.4:0.15, and other operation steps and process parameters are exactly the same as those in Example 1.

[0149] Comparative Example 4

[0150] This comparative example provides a surface-modified silicone rubber composite membrane, which is different from Example 1 in that in S4, the mass ratio of multi-modified polydimethylsiloxane, MOF-modified cellulose nanocrystals, crown ether-modified graphene oxide, cross-linking agent and catalyst is: 100:0.1:2.5:5.4:0.15, and other operation steps and process parameters are exactly the same as those in Example 1.

[0151] Comparative Example 5

[0152] This comparative example provides a surface-modified silicone rubber composite membrane, which is different from Example 1 in that in S4, the mass ratio of multi-modified polydimethylsiloxane, MOF-modified cellulose nanocrystals, crown ether-modified graphene oxide, cross-linking agent and catalyst is: 100:2:6:5.4:0.15, and other operation steps and process parameters are exactly the same as those in Example 1.

[0153] Comparative Example 6

[0154] This comparative example provides a surface-modified silicone rubber composite membrane, which is different from Example 1 in that in S4, the mass ratio of multi-modified polydimethylsiloxane, MOF-modified cellulose nanocrystals, crown ether-modified graphene oxide, cross-linking agent and catalyst is: 100:2:0.5:5.4:0.15, and other operation steps and process parameters are exactly the same as those in Example 1.

[0155] Perform performance tests on the surface-modified silicone rubber composite membranes of the above Examples 1-4 and Comparative Examples 1-6, and the specific process is as follows:

[0156] Test the tensile strength of the sample according to GB / T 528-2009;

[0157] Test the gas permeation flux and the separation performance of oxygen and nitrogen of the ultra-thin silicone rubber composite membrane.

[0158] The test results are shown in Table 1.

[0159] Table 1: Test Results of the Performance of the Surface-Modified Silicone Rubber Composite Membrane

[0160]

[0161] From the test results of Example 1, Comparative Example 1, and Comparative Example 2, it can be seen that when the feeding amount of vinyltrimethoxysilane is too large, the residual unreacted groups will reduce the integrity of the crosslinked network, causing local stress concentration, thereby reducing the mechanical properties of the ultra-thin silicone rubber composite membrane. At the same time, too many unreacted groups form microscopic defects, resulting in a decrease in the selectivity of the ultra-thin silicone rubber composite membrane; when its feeding amount is too low, it will lead to insufficient modification sites of polydimethylsiloxane, low grafting amount of subsequent functional groups, resulting in uneven crosslinking density of the ultra-thin silicone rubber composite membrane and a decrease in mechanical properties. At the same time, it will also lead to insufficient functionalization degree of polydimethylsiloxane, incomplete construction of mass transfer channels, low selective gas transmission efficiency, and poor overall separation performance of the ultra-thin silicone rubber composite membrane.

[0162] From the test results of Example 1, Comparative Example 3, and Comparative Example 4, it can be seen that when the content of MOF-modified cellulose nanocrystals is too high, it is easy to agglomerate to form stress concentration points, thereby destroying the continuity of the polymer chains and significantly reducing the mechanical properties of the ultra-thin silicone rubber composite membrane. At the same time, the agglomeration will form non-selective channels, resulting in a decrease in the gas selectivity of the ultra-thin silicone rubber composite membrane and a reduction in the overall separation efficiency; when the content of MOF-modified cellulose nanocrystals is too low, it has little effect on the mechanical properties of the ultra-thin silicone rubber composite membrane and can maintain basic mechanical properties, but the selective adsorption sites provided by MOF will be insufficient, resulting in a decrease in separation performance.

[0163] From the test results of Example 1, Comparative Example 5, and Comparative Example 6, it can be seen that when the content of crown ether-modified graphene oxide is too high, the stacking of graphene oxide sheets leads to uneven stress, thereby reducing the mechanical properties of the ultra-thin silicone rubber composite membrane. At the same time, too many mass transfer channels destroy the denseness of the ultra-thin silicone rubber composite membrane, and its selectivity decreases significantly; when the content of crown ether-modified graphene oxide is too low, it has little effect on the mechanical properties of the matrix and basically maintains the original mechanical properties, but the selective transmission channels are insufficient, and the improvement of separation performance is limited.

[0164] The above is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A method for preparing a surface-modified silicone rubber composite membrane, characterized in that, The preparation method includes: S1: React N-isopropylacrylamide with vinyltrimethoxysilane to obtain a thermosensitive monomer; S2: React p-aminoazobenzene with 3-isocyanatopropyltrimethoxysilane to obtain a light-responsive monomer; S3: React polydimethylsiloxane with vinyltrimethoxysilane under the catalysis of dibutyltin dilaurate to obtain vinyl-modified polydimethylsiloxane, where the molar ratio of vinyltrimethoxysilane to polydimethylsiloxane is (1.2 - 1.5):1; Disperse it in a hydrochloric acid solution for treatment to obtain pre-hydrolyzed vinyl-modified polydimethylsiloxane; Mix and react the pre-hydrolyzed vinyl-modified polydimethylsiloxane with tetramethylammonium hydroxide, the thermosensitive monomer and the light-responsive monomer to obtain a multi-modified polydimethylsiloxane; S4: Disperse the multi-modified polydimethylsiloxane, MOF-modified cellulose nanocrystals, and crown ether-modified graphene oxide in tetrahydrofuran, where the mass ratio of the multi-modified polydimethylsiloxane to tetrahydrofuran is 1:(3 - 4). After uniform dispersion, add a crosslinking agent and a catalyst to obtain a casting solution, and coat it on the surface of a support base film. After heat treatment, a surface-modified silicone rubber composite film is obtained, where the mass ratio of the multi-modified polydimethylsiloxane, MOF-modified cellulose nanocrystals, crown ether-modified graphene oxide, crosslinking agent, and catalyst is: 100:(1 - 3):(1.5 - 3):(4 - 6):(0.1 - 0.2); Among them, the MOF-modified cellulose nanocrystals are obtained by dispersing cellulose nanocrystals in deionized water, adding copper nitrate and trimesic acid after ultrasonic dispersion to obtain a fifth reaction solution, and centrifuging, washing, and drying after the reaction; The crosslinking agent is any one of HMS-301, PMHS, or D4H; The catalyst is any one of Karstedt catalyst or chloroplatinic acid; The support base film is any one of polypropylene, polyvinylidene fluoride, or polysulfone; The preparation method of the crown ether-modified graphene oxide is as follows: Under nitrogen protection, disperse 18-crown-6 and potassium carbonate in N,N-dimethylformamide, and then add an N,N-dimethylformamide solution of N-(3-chloropropyl)phthalimide to react to obtain phthalimide-modified crown ether; Mix the phthalimide-modified crown ether with hydrazine hydrate and react to obtain amino crown ether; Disperse graphene oxide in N,N-dimethylformamide, add 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide to obtain a seventh reaction solution. After stirring at room temperature, add amino crown ether and continue to react, and centrifuge, wash, and vacuum dry to obtain crown ether-modified graphene oxide.

2. The preparation method of a surface-modified silicone rubber composite membrane according to claim 1, characterized in that, In S1: The molar ratio of N-isopropylacrylamide to vinyltrimethoxysilane is (4.0 - 4.5):

1.

3. The preparation method of a surface-modified silicone rubber composite membrane according to claim 1, wherein, In S2: The molar ratio of 3-isocyanatopropyltrimethoxysilane to p-aminoazobenzene is (1.1 - 1.2):

1.

4. The preparation method of a surface-modified silicone rubber composite membrane according to claim 1, characterized in that, In S3: The feeding amount of dibutyltin dilaurate is 200 - 500 ppm of the mass of polydimethylsiloxane; The molar ratio of the vinyl-modified polydimethylsiloxane to the thermosensitive monomer and the photo-responsive monomer is (70 - 80):(15 - 10):(15 - 10); The feeding amount of the tetramethylammonium hydroxide accounts for 0.1 - 0.2% of the total mass of the thermosensitive monomer and the photo-responsive monomer.

5. The preparation method of a surface-modified silicone rubber composite membrane according to claim 1, characterized in that, In S4: The temperature of the heat treatment is 60 - 70 °C; The time of the heat treatment is 4 - 5 h.

6. The preparation method of a surface-modified silicone rubber composite membrane according to claim 1, characterized in that, In the preparation of the MOF-modified cellulose nanocrystals: The mass fraction of the cellulose nanocrystals dispersed in deionized water is 1 - 2 wt.%; The power of the ultrasonic dispersion is 300 - 400 W; The time of the ultrasonic dispersion is 30 - 40 min; The mass ratio of the copper nitrate to the cellulose nanocrystals is (0.3 - 0.5):1; The molar ratio of the trimesic acid to the copper nitrate is (2 - 3):1; The reaction time of the fifth reaction solution is 4 - 6 h.

7. The preparation method of a surface-modified silicone rubber composite membrane according to claim 1, wherein In the preparation method of the crown ether-modified graphene oxide: The concentration of the 18-crown-6 dispersed in N,N-dimethylformamide is 0.2 - 0.4 M; The molar ratio of the potassium carbonate to the 18-crown-6 is (1.2 - 1.5):1; The molar ratio of the N-(3-chloropropyl)phthalimide to the 18-crown-6 is (1.2 - 1.5):1; The molar ratio of the hydrazine hydrate to the phthalimide-modified crown ether is (3 - 4):

1.

8. The preparation method of a surface-modified silicone rubber composite membrane according to claim 1, characterized in that, In the preparation method of the crown ether-modified graphene oxide: The mass fraction of the graphene oxide dispersed in N,N-dimethylformamide is 0.1 - 0.2 wt.%; The mass ratio of the 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride, N-hydroxysuccinimide and the graphene oxide is (2 - 3):2:1; The mass ratio of the amino crown ether to the graphene oxide is (2 - 3):

1.

9. A surface-modified silicone rubber composite membrane prepared by using the preparation method of a surface-modified silicone rubber composite membrane according to any one of claims 1 - 8.

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