A polyacrylonitrile-polyimide-montmorillonite double super-hydrophobic nanocomposite aerogel, a preparation method and application thereof

Abstract

The application provides acrylonitrile-polyimide-montmorillonite double super-hydrophobic nanocomposite aerogel, a preparation method and application thereof. The application uses polyamide acid as a bonding agent and a crosslinking agent, mixes with acrylonitrile nanofibers (PAN), layered montmorillonite (MMT) and deionized water, and directional freeze-drying is carried out to obtain a large pore orientation structure, and then imidization is carried out to obtain PAN / PI-MMT double super-hydrophobic nanofiber composite aerogel with certain strength. After directional freezing and imidization treatment, the montmorillonite is uniformly distributed on the nanofiber, and a multiple concave structure is formed. The aerogel has underwater super-hydrophobicity and underwater super-hydrophobicity due to the multiple concave structure, and can separate oil and water as needed. The composite aerogel with oriented large pores and secondary pores can maintain high separation filtration efficiency and high flux during the oil-water separation process.

Description

Technical Field

[0001] This invention belongs to the field of aerogel technology, and particularly relates to a method for preparing and applying a polyacrylonitrile-polyimide-montmorillonite dual superhydrophobic nanocomposite aerogel. Background Technology

[0002] Superwetting materials have been extensively studied due to their high separation efficiency, ease of use, and recyclability. However, most current superwetting materials only possess single-property wettability, making them less convenient to use. Dual superhydrophobic materials can avoid the problem of limited application scenarios, achieving on-demand oil-water separation with a single material, thus significantly reducing usage costs.

[0003] Theoretically, it is impossible for the same solid surface to simultaneously exhibit both superhydrophobicity under oil and superoleophobicity under water. In the same oil-water-solid three-phase system, the underwater oil contact angle and the underwater water contact angle are complementary; that is, the underwater oleophobic interface behaves as hydrophilic in oil, and the oil-hydrophobic interface behaves as oleophilic in water. Due to this thermodynamic contradiction, it is difficult to endow a single surface with dual superhydrophobic properties.

[0004] Given that current technology makes it difficult to prepare dual superhydrophobic materials, it is necessary to improve this approach. Summary of the Invention

[0005] In view of this, the present invention proposes a polyacrylonitrile-polyimide-montmorillonite dual superhydrophobic nanocomposite aerogel, its preparation method and application, in order to solve the technical problems existing in the prior art.

[0006] In a first aspect, the present invention provides a method for preparing a polyacrylonitrile-polyimide-montmorillonite dual superhydrophobic nanocomposite aerogel, comprising the following steps:

[0007] A mixed dispersion was obtained by mixing polyacrylonitrile nanofiber dispersion, water-soluble polyamic acid fiber, and sheet montmorillonite.

[0008] The mixed dispersion was subjected to directional freezing and freeze-drying in sequence to obtain a macroporous oriented nanofiber composite aerogel of polyacrylonitrile / polyamic acid-montmorillonite.

[0009] The polyacrylonitrile / polyamic acid-montmorillonite macroporous oriented nanofiber composite aerogel was subjected to imidization treatment to obtain polyacrylonitrile-polyimide-montmorillonite dual superhydrophobic nanocomposite aerogel.

[0010] The mass of the laminated montmorillonite is 5-10% of the mass of the polyacrylonitrile nanofibers in the polyacrylonitrile nanofiber dispersion.

[0011] Preferably, the concentration of the polyacrylonitrile nanofiber dispersion is 6-16 wt%.

[0012] The mass of the water-soluble polyamic acid fiber is 5-15% of the mass of the polyacrylonitrile nanofibers in the polyacrylonitrile nanofiber dispersion.

[0013] Preferably, the imidization treatment comprises, in sequence:

[0014] The temperature is increased to a first temperature at a first heating rate to perform a first imidization treatment;

[0015] The temperature is increased to a second temperature at a second heating rate to carry out a second imidization treatment;

[0016] The temperature is increased to a third temperature at a third heating rate to carry out a third imidization treatment;

[0017] Wherein, the first temperature is 85-115℃ and the first imidization treatment time is 50-80 min;

[0018] The second temperature is 185–215°C, and the second imidization treatment time is 50–80 min;

[0019] The third temperature is 285–315°C, and the third imidization treatment time is 50–80 min;

[0020] The first heating rate, the second heating rate, and the third heating rate are each independently 3–7 °C / min. -1 .

[0021] Preferably, the directional freezing specifically includes:

[0022] The mixed dispersion is placed in a mold, and the bottom of the mold is placed in a cold source for directional freezing;

[0023] The mold is made of thermally conductive metal, the cold source is liquid nitrogen, and the directional freezing time is 5 to 15 minutes.

[0024] Before placing the mixed dispersion in the mold, the process also includes placing the mold in a cold source for pre-cooling, with a pre-cooling time of 5 to 8 minutes.

[0025] Preferably, the freeze-drying temperature is -30 to -65°C and the time is 24 to 72 hours.

[0026] Preferably, the preparation method of the polyacrylonitrile nanofiber dispersion includes the following steps:

[0027] Polyacrylonitrile solution was spun into polyacrylonitrile nanofibers by electrospinning.

[0028] Polyacrylonitrile nanofibers were dispersed in water and homogenized and broken down to shorten the polyacrylonitrile nanofibers, resulting in a polyacrylonitrile nanofiber dispersion.

[0029] Among them, the diameter of the polyacrylonitrile nanofibers is 500-680 nm and the length is 45-60 μm.

[0030] Preferably, the method for preparing the water-soluble polyamic acid fiber includes the following steps:

[0031] 4,4'-diaminodiphenyl ether and pyromellitic dianhydride were added to N,N-dimethylacetamide to carry out a polycondensation reaction, thereby obtaining a water-insoluble polyamic acid.

[0032] Triethylamine was mixed with the insoluble polyamic acid and modified to obtain a water-soluble polyamic acid solution.

[0033] The water-soluble polyamic acid solution was subjected to ice-water precipitation and then freeze-dried to obtain water-soluble polyamic acid fibers.

[0034] Preferably, polyacrylonitrile powder is dissolved in an organic solvent to obtain a polyacrylonitrile solution; wherein the concentration of the polyacrylonitrile solution is 5-15 wt%; and the organic solvent includes amide solvents.

[0035] The operating parameters for electrospinning control include: extrusion speed of 0.06–0.10 mm / min. -1 The spinning voltage is 10–14 kV;

[0036] The process parameters for homogenization crushing control include: temperature of 10-30℃, rotation speed of 10000-16000rpm, and time of 30-60min.

[0037] Preferably, 4,4'-diaminodiphenyl ether and pyromellitic dianhydride are added to N,N-dimethylacetamide, and a polycondensation reaction is carried out at -10 to 0°C for 4 to 8 hours under an inert atmosphere to obtain a water-insoluble polyamic acid; wherein the molar ratio of 4,4'-diaminodiphenyl ether, pyromellitic dianhydride, and N,N-dimethylacetamide is (0.8 to 1.2):(0.8 to 1.2):(25 to 30);

[0038] Triethylamine is mixed with the insoluble polyamic acid and reacted at -10 to 0°C for 4 to 8 hours to obtain a water-soluble polyamic acid solution; wherein the molar ratio of 4,4'-diaminodiphenyl ether to triethylamine is 1:(0.6 to 1);

[0039] Water was added to the obtained water-soluble polyamic acid solution to allow precipitation. The resulting solid product was then freeze-dried to obtain water-soluble polyamic acid fibers. The freeze-drying temperature was -30 to -65°C and the time was 24 to 72 hours.

[0040] Secondly, the present invention also provides a polyacrylonitrile-polyimide-montmorillonite dual superhydrophobic nanocomposite aerogel, which is prepared by the aforementioned preparation method.

[0041] Thirdly, the present invention also provides an application of the polyacrylonitrile-polyimide-montmorillonite dual superhydrophobic nanocomposite aerogel prepared by the preparation method described above, or the polyacrylonitrile-polyimide-montmorillonite dual superhydrophobic nanocomposite aerogel described above, as an oil-water separation material or an air filtration material.

[0042] The polyacrylonitrile-polyimide-montmorillonite dual superhydrophobic nanocomposite aerogel of the present invention, its preparation method, and its application have the following advantages over the prior art:

[0043] 1. The preparation method of the polyacrylonitrile-polyimide-montmorillonite dual superhydrophobic nanocomposite aerogel of the present invention uses polyamic acid as a binder and crosslinking agent, mixes it with polyacrylonitrile nanofibers, sheet montmorillonite, and deionized water, and then directionally freeze-dries it to obtain a macroporous oriented structure. Subsequently, it undergoes imidization to obtain a PAN / PI-MMT dual superhydrophobic nanofiber composite aerogel with a certain strength. After directional freezing and imidization, MMT (sheet montmorillonite) is uniformly distributed on the nanofibers, forming a multi-concave structure. This aerogel, due to its multi-concave structure, exhibits both underwater superoleophobicity and oil-water superhydrophobicity, allowing for oil-water separation as needed. The composite aerogel with oriented macropores and secondary pores maintains high separation and filtration efficiency and high throughput during oil-water separation.

[0044] 2. The preparation method of the polyacrylonitrile-polyimide-montmorillonite dual superhydrophobic nanocomposite aerogel of the present invention is simple to operate, the raw materials are low in toxicity, easy to obtain, green and environmentally friendly, and have low production costs, making it suitable for industrial production.

[0045] 3. The polyacrylonitrile / polyimide-montmorillonite dual-superhydrophobic nanofiber composite aerogel prepared by the method provided in this invention has a hierarchical porous structure, including macropores, mesopores, and micropores. The aerogel provided by this invention possesses macropore orientation, a hierarchical porous structure, and a multi-concave micro / nano structure, endowing it with excellent separation efficiency, separation flux, mechanical properties, and dual-superhydrophobic properties. The aerogel shows great promise for applications in marine oil spill treatment, domestic oily wastewater separation, and sensors.

[0046] 4. The polyacrylonitrile-polyimide-montmorillonite dual superhydrophobic nanocomposite aerogel prepared by this invention exhibits double superhydrophobic properties. Its contact angle with water or oil in air is 0°, and its contact angle with oil underwater and water underwater are both greater than 150°. The oil flux of the polyacrylonitrile-polyimide-montmorillonite dual superhydrophobic nanocomposite aerogel prepared by this invention is (2.63±0.08~5.83±0.20)×10⁻¹⁰. 4 L m-2 h -1 It exhibits excellent resilience of aerogels, with a compression resilience of 81.43 ± 0.84% ​​at 40% strain. Attached Figure Description

[0047] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0048] Figure 1 Scanning electron microscope images of the composite aerogels prepared in Example 1 and Comparative Examples 1-2;

[0049] Figure 2 The figures show the contact angle test results of the composite aerogels prepared in Example 1 and Comparative Examples 1-2;

[0050] Figure 3 The separation efficiency of the composite aerogels prepared in Example 1 and Comparative Examples 1-2 for filtering different oils;

[0051] Figure 4 The flux of the composite aerogels prepared in Example 1 and Comparative Examples 1-2 for filtering different oils;

[0052] Figure 5 The image shows the resilience test results of the composite aerogel prepared in Comparative Example 2.

[0053] Figure 6 The graph shows the resilience test results of the composite aerogel prepared in Example 1.

[0054] Figure 7 The image shows the resilience test results of the composite aerogel prepared for Comparative Example 1. Detailed Implementation

[0055] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0056] To better understand the invention and not to limit its scope, all figures indicating amounts, percentages, and other numerical values ​​used in this application should, in all cases, be understood to be modified by the word "approximately." Therefore, unless specifically stated otherwise, the numerical parameters listed in the specification and appended claims are approximate values ​​and may vary depending on the desired properties being sought. Each numerical parameter should at least be considered as obtained based on reported significant figures and through conventional rounding methods.

[0057] It should be noted that the order of description of the following embodiments is not intended to limit the preferred order of embodiments. Furthermore, in the description of this application, the term "comprising" means "including but not limited to". Various embodiments of the present invention may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a rigid limitation on the scope of the invention; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single digits within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Additionally, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the referred range.

[0058] This invention provides a method for preparing polyacrylonitrile-polyimide-montmorillonite dual superhydrophobic nanocomposite aerogel, comprising the following steps:

[0059] S1. Mix the polyacrylonitrile nanofiber dispersion, water-soluble polyamic acid fiber, and laminated montmorillonite to obtain a mixed dispersion.

[0060] S2. The mixed dispersion was subjected to directional freezing and freeze-drying in sequence to obtain polyacrylonitrile / polyamic acid-montmorillonite macroporous oriented nanofiber composite aerogel.

[0061] S3. The polyacrylonitrile / polyamic acid-montmorillonite macroporous oriented nanofiber composite aerogel was subjected to imidization treatment to obtain polyacrylonitrile-polyimide-montmorillonite double superhydrophobic nanocomposite aerogel.

[0062] The mass of the lamellae montmorillonite is 5 to 10% of the mass of the polyacrylonitrile nanofibers in the polyacrylonitrile nanofiber dispersion.

[0063] The preparation method of the polyacrylonitrile-polyimide-montmorillonite dual superhydrophobic nanocomposite aerogel of the present invention involves mixing a polyacrylonitrile nanofiber dispersion, water-soluble polyamic acid fibers, and sheet-like montmorillonite to obtain a mixed dispersion; then directionally freezing and freeze-drying the mixed dispersion to obtain a polyacrylonitrile / polyamic acid-montmorillonite macroporous oriented nanofiber composite aerogel; and then subjecting the polyacrylonitrile / polyamic acid-montmorillonite macroporous oriented nanofiber composite aerogel to an imidization treatment to obtain a polyacrylonitrile-polyimide-montmorillonite dual superhydrophobic nanocomposite aerogel.

[0064] This invention introduces multiple concave structures on the material surface, combining polar-nonpolar theory and liquid injection theory, to allow water or oil to enter the multiple concave micro / nano structures and form a liquid film. The multiple concave structures on the solid surface can trap air, creating a negative Laplace pressure difference at the gas-liquid interface, thus transforming the gas-liquid interface from a concave surface to a convex surface at the liquid-liquid interface, preventing the wetting of another phase. Therefore, the multiple concave structures can effectively maintain the oil-water interface. This material can be wetted by oil as an "oil-removing" separation material or by water as a "water-removing" separation material, enabling on-demand separation of oil-water mixtures.

[0065] Specifically, the layered montmorillonite and polyacrylonitrile nanofibers of this invention are hydrophilic materials, while polyimide is a hydrophobic material. Adjusting the ratio of these three materials controls the hydrophilicity and oleophilicity of the material in air. Due to hydrogen bonding, the montmorillonite is uniformly distributed on the surface of the polyacrylonitrile nanofibers, forming a multi-concave structure, thereby achieving dual superhydrophobic properties.

[0066] This invention uses polyamic acid as a binder and crosslinking agent, mixing it with polyacrylonitrile nanofibers, layered montmorillonite, and deionized water, followed by directional freeze-drying to obtain a macroporous oriented structure. Subsequent imidization yields a PAN / PI-MMT dual superhydrophobic nanofiber composite aerogel with a certain strength. After directional freeze-drying and imidization, MMT (montmorillonite) is uniformly distributed on the nanofibers, forming a multi-concave structure. This aerogel exhibits both underwater superoleophobicity and oil-water superhydrophobicity due to its multi-concave structure, enabling on-demand oil-water separation. The composite aerogel with oriented macropores and secondary pores maintains high separation and filtration efficiency and high throughput during oil-water separation.

[0067] In some embodiments, the lamellae montmorillonite specifically employs lamellae sodium-based montmorillonite.

[0068] In some embodiments, the concentration of the polyacrylonitrile nanofiber dispersion is 6–16 wt% (mass concentration); preferably, the concentration is 9–12 wt%.

[0069] In some embodiments, the mass of the water-soluble polyamic acid fiber is 5-15% of the mass of the polyacrylonitrile nanofibers in the polyacrylonitrile nanofiber dispersion, preferably, the mass of the water-soluble polyamic acid fiber is 10% of the mass of the polyacrylonitrile nanofibers in the polyacrylonitrile nanofiber dispersion.

[0070] In some embodiments, the imidization treatment is preferably a programmed imidization treatment, which preferably includes sequentially performing a first heating, a first imidization, a second heating, a second imidization, a third heating, and a third imidization; specifically, the imidization treatment sequentially includes:

[0071] The temperature is increased to a first temperature at a first heating rate to perform a first imidization treatment;

[0072] The temperature is increased to a second temperature at a second heating rate to carry out a second imidization treatment;

[0073] The temperature is increased to a third temperature at a third heating rate to carry out a third imidization treatment;

[0074] The first temperature is 85–115°C and the first imide treatment time is 50–80 min; preferably, the first temperature is 95–105°C and the first imide treatment time is 60–70 min.

[0075] The second temperature is 185–215°C and the second imide treatment time is 50–80 min; preferably, the second temperature is 195–205°C and the second imide treatment time is 60–70 min.

[0076] The third temperature is 285–315°C and the third imide treatment time is 50–80 min; preferably, the third temperature is 295–305°C and the third imide treatment time is 60–70 min.

[0077] The first, second, and third heating rates were each set independently for 3–7 °C / min. -1 Preferably 4-6℃ min -1 .

[0078] In some embodiments, directional freezing is preferably directional freezing using a unidirectional orientation ice crystal template.

[0079] In some embodiments, directional freezing specifically includes:

[0080] Place the mixed dispersion in a mold, and place the bottom of the mold in a cold source for directional freezing;

[0081] The mold is made of thermally conductive metal, the cold source is liquid nitrogen, and the directional freezing time is 5 to 15 minutes.

[0082] Specifically, the mixed dispersion is placed in a mold, preferably made of a thermally conductive metal, more preferably copper or iron; the cold source preferably includes liquid nitrogen; the directional freezing time is preferably 5 to 15 minutes, more preferably 7 to 13 minutes; and the bottom surface of the mold is placed in the cold source for directional freezing.

[0083] In some embodiments, before placing the mixed dispersion in the mold, the process further includes placing the mold in a cold source for pre-cooling for 5 to 8 minutes.

[0084] In some embodiments, in step S2, the freeze-drying temperature is -30 to -65°C, preferably -40 to 60°C; the freeze-drying time is 24 to 72 hours, preferably 52 to 60 hours.

[0085] In some embodiments, the preparation method of polyacrylonitrile nanofiber dispersion includes the following steps:

[0086] S11. Polyacrylonitrile solution is spun into polyacrylonitrile nanofibers by electrospinning.

[0087] S12. Disperse polyacrylonitrile nanofibers in water and perform homogenization and crushing treatment to shorten the polyacrylonitrile nanofibers to obtain a polyacrylonitrile nanofiber dispersion.

[0088] Among them, the diameter of the polyacrylonitrile nanofibers is 500-680 nm and the length is 45-60 μm.

[0089] In some embodiments, the method for preparing water-soluble polyamic acid fibers includes the following steps:

[0090] S21. Add 4,4'-diaminodiphenyl ether and pyromellitic dianhydride to N,N-dimethylacetamide to carry out a polycondensation reaction to obtain water-insoluble polyamic acid.

[0091] S22. Triethylamine is mixed with non-water-soluble polyamic acid and modified to obtain a water-soluble polyamic acid solution.

[0092] S23. The water-soluble polyamic acid solution is subjected to ice-water precipitation and then freeze-dried to obtain water-soluble polyamic acid fiber.

[0093] In some embodiments, the polyacrylonitrile solution is obtained by dissolving polyacrylonitrile powder in an organic solvent, preferably an amide solvent, more preferably including N,N'-dimethylformamide (DMF); the dissolution temperature is preferably room temperature, and the dissolution time is preferably 8-12 h, more preferably 10 h; the concentration of the polyacrylonitrile solution is 5-15 wt%; the electrospinning process includes: an extrusion speed preferably of 0.06-0.10 mm / min. -1More preferably, it is 0.07–0.09 mm min. -1 The distance between the syringe and the roller is preferably 15-25 cm, more preferably 18-22 cm; the voltage is preferably 10-14 kV, more preferably 11-13 kV; the process parameters for controlling the homogenization crushing treatment include: the homogenization crushing temperature is preferably 10-30℃, more preferably 20-25℃; the homogenization crushing speed is preferably 10000-16000 rpm, more preferably 15000 rpm; the homogenization crushing time is preferably 30-60 min, more preferably 40-50 min.

[0094] It is understood that polyacrylonitrile nanofibers are homogenized and crushed to form polyacrylonitrile nanofibers. The diameter of the polyacrylonitrile nanofibers is preferably 500-680 nm, more preferably 530-660 nm, and the length is preferably 45-60 μm.

[0095] In some embodiments, 4,4'-diaminodiphenyl ether (ODA) and pyromellitic dianhydride (PMDA) are added to N,N-dimethylacetamide and subjected to a polycondensation reaction at -10 to 0°C for 4 to 8 hours under an inert atmosphere to obtain a water-insoluble polyamic acid; wherein the molar ratio of 4,4'-diaminodiphenyl ether, pyromellitic dianhydride, and N,N-dimethylacetamide is (0.8 to 1.2):(0.8 to 1.2):(25 to 30);

[0096] Triethylamine was mixed with insoluble polyamic acid and reacted at -10 to 0°C for 4 to 8 hours to obtain a water-soluble polyamic acid solution; wherein the molar ratio of 4,4'-diaminodiphenyl ether to triethylamine was 1:(0.6 to 1);

[0097] The solid product obtained by water precipitation is freeze-dried to obtain water-soluble polyamic acid fiber; wherein the freeze-drying temperature is -30 to -65℃ and the time is 24 to 72 hours.

[0098] In the above embodiments, water was added to the obtained water-soluble polyamic acid solution for precipitation, and the resulting solid product was freeze-dried to obtain water-soluble polyamic acid fiber; wherein, there is no special limitation on the amount of water, and the amount of water is determined by the fact that the precipitation product no longer increases.

[0099] Specifically, in some embodiments, the preparation method of water-soluble polyamic acid preferably includes the following steps: adding 4,4'-diaminodiphenyl ether and pyromellitic dianhydride to a polar solvent (denoted as the first mixture) to carry out a polycondensation reaction to obtain insoluble polyamic acid; mixing triethylamine with the insoluble polyamic acid (denoted as the second mixture) to modify it to obtain a water-soluble polyamic acid solution; subjecting the water-soluble polyamic acid solution to ice-water precipitation and then freeze-drying to obtain water-soluble polyamic acid fibers. In this invention, the molar ratio of 4,4'-diaminodiphenyl ether (ODA) and pyromellitic dianhydride (PMDA) is preferably 1:1; the polar solvent is preferably an amide solvent: N,N'-dimethylacetamide (DMAc); this invention does not have a special limitation on the amount of polar solvent used, as long as it can ensure the smooth progress of the polycondensation reaction. In this invention, the temperatures for the first mixing, condensation reaction, modification, and second mixing are preferably -10 to 0°C, more preferably -5 to 0°C; the condensation reaction is preferably carried out under a protective atmosphere, preferably an inert gas, more preferably including argon or helium; this invention does not have a special limitation on the time for the first mixing and the second mixing, as long as the raw materials are mixed evenly. In this invention, the molar ratio of 4,4'-diaminodiphenyl ether to triethylamine is preferably 1:(0.6 to 1), more preferably 1:(0.9 to 1). This invention does not have a special limitation on the amount of ice water used, as long as the amount of ice water precipitation product no longer increases. After completing the ice water precipitation, this invention preferably further includes freeze-drying the obtained ice water precipitation product to obtain water-soluble polyamic acid nanofibers; the freeze-drying temperature is preferably -30 to -65°C, more preferably -40 to -60°C; the freeze-drying time is preferably 24 to 72 hours, more preferably 52 to 60 hours.

[0100] In some embodiments, a polyacrylonitrile nanofiber dispersion, water-soluble polyamic acid fiber, and sheet montmorillonite are mixed to obtain a mixed dispersion. Specifically, the polyacrylonitrile nanofiber dispersion and sheet montmorillonite are first mixed and then homogenized. The homogenization speed is preferably 15,000 rpm and the homogenization time is preferably 10 to 15 min. The resulting dispersion of polyacrylonitrile nanofiber and montmorillonite is then mixed with water-soluble polyamic acid fiber to obtain the mixed dispersion.

[0101] This invention utilizes directional freezing technology to obtain a macroporous oriented structure. During the freezing process, polyacrylonitrile nanofibers, polyamic acid, and montmorillonite are compressed by growing ice crystals to form fiber walls. After the ice crystals sublimate, macropores are formed. The fiber walls, due to the intertwining of nanoscale polyacrylonitrile nanofibers, form mesopores and micropores. Montmorillonite, through hydrogen bonding, is uniformly distributed on the polyacrylonitrile nanofibers, constructing a multi-concave structure. Polyamic acid is compressed to the nodes of the polyacrylonitrile nanofibers. After imamidation, the polyamic acid firmly encapsulates the polyacrylonitrile nanofibers and undergoes chemical cross-linking. Furthermore, the polyacrylonitrile itself undergoes cyclization at the nodes upon heating, resulting in chemical cross-linking. When the aerogel is subjected to external pressure, stress initially concentrates at the nodes. Due to the strong cross-linking at the nodes, pressure can be effectively released, giving the aerogel excellent resilience. This invention utilizes hydrophilic polyacrylonitrile nanofibers, hydrophilic lamellar montmorillonite, and hydrophobic polyamic acid to regulate the hydrophilicity / phobicity and surface energy of the aerogel, constructing a multi-concave structure that enables the aerogel to exhibit superoleophobicity underwater and superhydrophobicity in oil. The preparation method provided by this invention is simple to operate, uses low-toxicity and readily available raw materials, is environmentally friendly, has low production costs, and is suitable for industrial production.

[0102] The polyacrylonitrile / polyimide-montmorillonite dual-superhydrophobic nanofiber composite aerogel prepared by the method provided in this invention has a hierarchical porous structure, including macropores, mesopores, and micropores. The aerogel provided by this invention possesses macropore orientation, a hierarchical porous structure, and a multi-concave micro / nano structure, endowing it with excellent separation efficiency, separation flux, mechanical properties, and dual-superhydrophobic properties. The aerogel shows great promise for applications in marine oil spill treatment, domestic oily wastewater separation, and sensors.

[0103] Based on the same inventive concept, the present invention also provides a polyacrylonitrile-polyimide-montmorillonite dual superhydrophobic nanocomposite aerogel, which is prepared by the above-described preparation method.

[0104] The polyacrylonitrile-polyimide-montmorillonite dual superhydrophobic nanocomposite aerogel prepared by this invention has a multi-concave structure, which is a micro-nano structure composed of polyacrylonitrile nanofibers and two-dimensional sheet montmorillonite.

[0105] The polyacrylonitrile-polyimide-montmorillonite dual superhydrophobic nanocomposite aerogel prepared by this invention exhibits dual superhydrophobic properties. Its contact angle with water or oil in air is 0°, while its contact angle with oil underwater and with water underwater are both greater than 150°. The oil flux of the polyacrylonitrile-polyimide-montmorillonite dual superhydrophobic nanocomposite aerogel prepared by this invention is (2.63±0.08~5.83±0.20)×10⁻⁶. 4 L m -2 h -1It exhibits excellent resilience of aerogels, with a compression resilience of 81.43 ± 0.84% ​​at 40% strain.

[0106] Based on the same inventive concept, the present invention also provides an application of the polyacrylonitrile-polyimide-montmorillonite dual superhydrophobic nanocomposite aerogel prepared by the above-mentioned preparation method as an oil-water separation material.

[0107] The present invention relates to the application of polyacrylonitrile-polyimide-montmorillonite dual superhydrophobic nanocomposite aerogel as an oil-water separation material or air filtration material. The polyacrylonitrile-polyimide-montmorillonite dual superhydrophobic nanocomposite aerogel provided by the present invention possesses advantages such as switchable dual superhydrophobicity, high recyclability, macroporous orientation, hierarchical pore structure, high specific surface area, and stable physicochemical properties. It is an ideal high-performance oil-water separation material, and the aerogel shows great promise for applications in marine oil spill treatment, domestic oil and wastewater separation, and sensors.

[0108] The following specific embodiments further illustrate the polyacrylonitrile-polyimide-montmorillonite dual superhydrophobic nanocomposite aerogel of this application, its preparation method, and its application. This section further illustrates the content of the present invention with reference to specific embodiments, but should not be construed as limiting the present invention. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in the art.

[0109] Example 1

[0110] This application provides a method for preparing a polyacrylonitrile-polyimide-montmorillonite dual superhydrophobic nanocomposite aerogel, comprising the following steps:

[0111] S1. Add polyacrylonitrile powder to N,N'-dimethylformamide and stir and mix at room temperature (25℃) for 10 h to obtain a polyacrylonitrile solution with a concentration of 10 wt%.

[0112] The polyacrylonitrile solution was transferred to a 10 mL syringe for electrospinning to obtain polyacrylonitrile nanofibers (diameter 530–660 nm). The electrospinning process conditions were as follows: extrusion speed 0.08 mm / min, needle-to-roll distance 21 cm, and voltage 12 kV.

[0113] Polyacrylonitrile nanofibers were dispersed in deionized water and homogenized at room temperature and 15,000 rpm for 45 min using a homogenizer to obtain a polyacrylonitrile nanofiber dispersion (concentration of 7.5 wt%, short fiber length of 45-60 μm).

[0114] S2. Dissolve 4.31g of 4,4'-diaminodiphenyl ether in 51g of N,N'-dimethylacetamide, then add 4.69g of pyromellitic dianhydride, place in an ice-water bath (0℃), and perform polycondensation reaction under argon atmosphere for 5.5h; then add 2.18g of triethylamine, continue the reaction for 5.5h, add 3L of deionized water to the resulting water-soluble polyamic acid solution for precipitation, wash the obtained solid component with water, and freeze-dry at -55℃ to constant weight to obtain water-soluble polyamic acid fiber;

[0115] S3. Place the lamellae montmorillonite in a polyacrylonitrile nanofiber dispersion and homogenize it for 15 min at room temperature and a rotation speed of 15000 rpm to obtain a stable dispersion containing polyacrylonitrile nanofibers and lamellae montmorillonite; wherein, the mass of the lamellae montmorillonite (lamellae montmorillonite purchased from Guzhang County Shanlin Shiyu Mineral Products Co., Ltd., its model is CAS[1318-93-0]) added is 10 wt% of the mass of polyacrylonitrile nanofibers in the polyacrylonitrile nanofiber dispersion.

[0116] S4. Place the water-soluble polyamic acid fiber in the dispersion in S3, and stir at room temperature until the water-soluble polyamic acid fiber is completely dissolved to obtain a mixed dispersion; wherein, the mass of the water-soluble polyamic acid fiber is 10% of the mass of the polyacrylonitrile nanofibers in the polyacrylonitrile nanofiber dispersion.

[0117] S5. Contact the bottom of the iron mold with liquid nitrogen to pre-cool the mold for 10 min; then transfer the mixed dispersion in S4 into the iron mold and freeze it in an oriented manner for 10 min; then freeze-dry it at -55℃ for 48 h to obtain polyacrylonitrile / polyamic acid-montmorillonite macroporous oriented nanofiber composite aerogel (denoted as PAN / PAA-MMT-10).

[0118] S6. The polyacrylonitrile / polyamic acid-montmorillonite macroporous oriented nanofiber composite aerogel was placed in a tube furnace and subjected to programmed imidization treatment in air to obtain a polyacrylonitrile-polyimide-montmorillonite dual superhydrophobic nanocomposite aerogel (denoted as PAN / PI-MMT-10); wherein, the imidization treatment process is as follows: at 5℃ min -1 The heating rate starts from room temperature, increases to 100°C, holds for 1 hour, and then increases by 5°C / min. -1 The temperature was increased to 200℃ at a rate of [missing information] and held for 1 hour, then increased at 5℃ / min [missing information]. -1 The temperature was increased to 300℃ and then held for 1 hour.

[0119] Comparative Example 1

[0120] This comparative example provides a method for preparing a composite aerogel, which is the same as in Example 1, except that in step S3, the mass of the added lamellar montmorillonite is 15 wt% of the mass of the polyacrylonitrile nanofibers in the polyacrylonitrile nanofiber dispersion, and the remaining process parameters are the same as in Example 1; the prepared composite aerogel is denoted as PAN / PI-MMT-15.

[0121] Comparative Example 2

[0122] This comparative example provides a method for preparing a composite aerogel, which is the same as in Example 1, except that in step S3, no sheet montmorillonite is added, and the other process parameters are the same as in Example 1; the prepared composite aerogel is denoted as PAN / PI.

[0123] Performance testing

[0124] (1) Scanning electron microscopy test

[0125] Figure 1 The images shown are scanning electron microscope (SEM) images of the composite aerogels prepared in Example 1 and Comparative Examples 1-2; where (a1) and (a2) are PAN / PI prepared in Comparative Example 2, (b1) and (b2) are PAN / PI-MMT-10 prepared in Example 1, and (c1) and (c2) are SEM images of PAN / PI-MMT-15 prepared in Comparative Example 1 at different magnifications.

[0126] Depend on Figure 1 It is known that the polyacrylonitrile-polyimide-montmorillonite dual superhydrophobic nanocomposite aerogel prepared by the present invention has a macroporous skeleton structure. The composite aerogel wall is composed of secondary pores formed by polyacrylonitrile nanofibers. Laminar montmorillonite is distributed on the fiber surface to form a multi-concave structure. Polyimide acts as a binder and crosslinking agent to connect polyacrylonitrile nanofibers to construct a dual superhydrophobic aerogel with a multi-level porous structure.

[0127] Figure 2 The figures show the contact angle test results of the composite aerogels prepared in Example 1 and Comparative Examples 1-2; where (a1) and (a2) are PAN / PI prepared in Comparative Example 2, (b1) and (b2) are PAN / PI-MMT-10 prepared in Example 1, and (c1) and (c2) are PAN / PI-MMT-15 prepared in Comparative Example 1. Figure 2 In China, CA O / W CA represents the underwater oil contact angle of different nanocomposite aerogels. W / O This indicates the contact angle between oil and water for different nanocomposite aerogels.

[0128] Specifically, the contact angle test method is as follows:

[0129] The procedure for testing the oil-water contact angle is as follows: Immerse the aerogel in 30 mL of n-hexane for 1 hour. At this point, the aerogel will completely sink to the bottom of the solvent without any bubbles emerging, thus obtaining the oil-water test sample. Then, place it in a glass container filled with n-hexane, drop 3 μL of water onto the aerogel surface, and record the oil-water contact angle.

[0130] Underwater oil contact angle: The aerogel was soaked in ethanol and water for 1 hour in sequence to completely fill the aerogel with water. Then the aerogel was placed in an optical glass box filled with water, and 5 μl of n-hexane was dropped on the sample surface to observe the n-hexane contact angle.

[0131] Depend on Figure 2 It can be seen that the PAN / PI-MMT-10 prepared in Example 1 has an underwater oil contact angle and an oil-to-water contact angle both greater than 150°, exhibiting dual superhydrophobic properties; while the PAN / PI-MMT-15 prepared in Comparative Example 1 has an underwater oil contact angle less than 150°; the PAN / PI prepared in Comparative Example 2 has an underwater oil contact angle and an oil-to-water contact angle both less than 150°; the aerogels prepared in Comparative Examples 1 and 2 can only achieve dual superhydrophobic properties. The PAN / PI-MMT-10 prepared in Example 1 has a contact angle of 0° with water or oil in air.

[0132] (3) Oil-water separation performance test

[0133] Test Method: Oil-water separation was performed under gravity, using various oily organic solvents (including dichloromethane and n-hexane) and oils (vegetable oil and pump oil). Mixtures were prepared with a heavy oil (specifically dichloromethane) to water mass ratio of 4:1 and a light oil (n-hexane, vegetable oil, and pump oil) to water mass ratio of 1:4. Both mixtures were homogenized using a high-speed homogenizer at 10,000 rpm for 5 minutes. Filtration efficiency was calculated based on the oil mass before and after filtration.

[0134]

[0135] In the formula, m0 and m1 represent the masses of oil before and after separation, respectively. The oil flux of the aerogel can be calculated using Equation 2.

[0136]

[0137] In the formula, V is the volume of the filtered liquid; A is the filtration area; and t is the time required to filter a certain volume of liquid.

[0138] Figures 3-4 The graph shows the oil-water separation test results of the composite aerogels prepared in Example 1 and Comparative Examples 1-2; Figure 3 It can be seen that the composite aerogel prepared in Example 1 has an average filtration efficiency of 95.43%–99.31% for different oils, which is greater than that of Comparative Examples 1–2. Figure 4It can be seen that the average flux of the composite aerogel prepared in Example 1 of the present invention for filtering different oils is 2.534 to 5.358 × 10⁻⁶. 4 L m -2 h -1 .

[0139] (4) Rebound performance test

[0140] Test method: The compressive resilience of the composite aerogels prepared in Example 1 and Comparative Examples 1 and 2 was tested using a high and low temperature universal testing machine. A 50N pressure sensor was used, and the compression rate was 1.0 mm / min. -1 The test results are as follows: Figures 5-7 As shown.

[0141] Depend on Figures 5-7 It can be seen that the polyacrylonitrile / polyimide-montmorillonite dual superhydrophobic nanofiber composite aerogel PAN / PI-MMT-10 prepared in Example 1 has a resilience of 81.43% at 40% strain, which is greater than that of the aerogels PAN / PI-MMT-15 and PAN / PI prepared in Comparative Examples 1 and 2, and has excellent compressive resilience.

[0142] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a polyacrylonitrile-polyimide-montmorillonite dual superhydrophobic nanocomposite aerogel, characterized in that, Includes the following steps: A mixed dispersion was obtained by mixing polyacrylonitrile nanofiber dispersion, water-soluble polyamic acid fiber, and sheet montmorillonite. The mixed dispersion was subjected to directional freezing and freeze-drying in sequence to obtain a macroporous oriented nanofiber composite aerogel of polyacrylonitrile / polyamic acid-montmorillonite. The polyacrylonitrile / polyamic acid-montmorillonite macroporous oriented nanofiber composite aerogel was subjected to imidization treatment to obtain polyacrylonitrile-polyimide-montmorillonite dual superhydrophobic nanocomposite aerogel. The mass of the laminated montmorillonite is 10% of the mass of the polyacrylonitrile nanofibers in the polyacrylonitrile nanofiber dispersion; The polyacrylonitrile nanofibers have a diameter of 500~680 nm and a length of 45~60 μm.

2. The preparation method of the polyacrylonitrile-polyimide-montmorillonite dual superhydrophobic nanocomposite aerogel as described in claim 1, characterized in that, The concentration of the polyacrylonitrile nanofiber dispersion is 6~16 wt%; The mass of the water-soluble polyamic acid fiber is 5-15% of the mass of the polyacrylonitrile nanofibers in the polyacrylonitrile nanofiber dispersion.

3. The preparation method of the polyacrylonitrile-polyimide-montmorillonite dual superhydrophobic nanocomposite aerogel as described in claim 1, characterized in that, The imidization process includes, in sequence: The temperature is increased to a first temperature at a first heating rate to perform a first imidization treatment; The temperature is increased to a second temperature at a second heating rate to carry out a second imidization treatment; The temperature is increased to a third temperature at a third heating rate to carry out a third imidization treatment; Wherein, the first temperature is 85~115 ℃ and the first imidization treatment time is 50~80 min; The second temperature is 185~215 ℃, and the second imidization treatment time is 50~80 min; The third temperature is 285~315 ℃, and the third imidization treatment time is 50~80 min; The first heating rate, the second heating rate, and the third heating rate are each independently 3~7 °C·min. -1 ; And / or, the directional freezing specifically includes: The mixed dispersion is placed in a mold, and the bottom of the mold is placed in a cold source for directional freezing; The mold is made of thermally conductive metal, the cold source is liquid nitrogen, and the directional freezing time is 5-15 minutes.

4. The preparation method of the polyacrylonitrile-polyimide-montmorillonite dual superhydrophobic nanocomposite aerogel as described in claim 1, characterized in that, The freeze-drying temperature is -30 to -65 ℃ and the time is 24 to 72 h.

5. The preparation method of the polyacrylonitrile-polyimide-montmorillonite dual superhydrophobic nanocomposite aerogel as described in claim 1, characterized in that, The preparation method of the polyacrylonitrile nanofiber dispersion includes the following steps: Polyacrylonitrile solution was spun into polyacrylonitrile nanofibers by electrospinning. Polyacrylonitrile nanofibers were dispersed in water and subjected to homogenization and crushing to shorten the polyacrylonitrile nanofibers, resulting in a polyacrylonitrile nanofiber dispersion.

6. The preparation method of the polyacrylonitrile-polyimide-montmorillonite dual superhydrophobic nanocomposite aerogel as described in claim 1, characterized in that, The method for preparing the water-soluble polyamic acid fiber includes the following steps: 4,4'-diaminodiphenyl ether and pyromellitic dianhydride were added to N,N'-dimethylacetamide to carry out a polycondensation reaction, thereby obtaining a water-insoluble polyamic acid. Triethylamine was mixed with the insoluble polyamic acid and modified to obtain a water-soluble polyamic acid solution. The water-soluble polyamic acid solution was subjected to ice-water precipitation and then freeze-dried to obtain water-soluble polyamic acid fibers.

7. The preparation method of the polyacrylonitrile-polyimide-montmorillonite dual superhydrophobic nanocomposite aerogel as described in claim 5, characterized in that, Polyacrylonitrile powder is dissolved in an organic solvent to obtain a polyacrylonitrile solution; wherein the concentration of the polyacrylonitrile solution is 5-15 wt%; the organic solvent includes amide solvents; The operating parameters for electrospinning control include: extrusion speed of 0.06~0.10 mm·min. -1 The spinning voltage is 10~14kV; The process parameters for homogenization crushing control include: temperature of 10~30 ℃, rotation speed of 10000~16000 rpm, and time of 30~60 min.

8. The preparation method of the polyacrylonitrile-polyimide-montmorillonite dual superhydrophobic nanocomposite aerogel as described in claim 6, characterized in that, 4,4'-diaminodiphenyl ether and pyromellitic dianhydride were added to N,N'-dimethylacetamide and subjected to a polycondensation reaction at -10 to 0 °C for 4 to 8 h under an inert atmosphere to obtain a water-insoluble polyamic acid; wherein the molar ratio of 4,4'-diaminodiphenyl ether, pyromellitic dianhydride and N,N'-dimethylacetamide was (0.8 to 1.2):(0.8 to 1.2):(25 to 30); Triethylamine was mixed with the insoluble polyamic acid and reacted at -10 to 0 °C for 4 to 8 h to obtain a water-soluble polyamic acid solution; wherein the molar ratio of 4,4'-diaminodiphenyl ether to triethylamine was 1:(0.6 to 1); Water was added to the obtained water-soluble polyamic acid solution to induce precipitation, and the resulting solid product was freeze-dried to obtain water-soluble polyamic acid fibers; wherein the freeze-drying temperature was -30 to -65 ℃ and the time was 24 to 72 h.

9. A polyacrylonitrile-polyimide-montmorillonite dual superhydrophobic nanocomposite aerogel, characterized in that, It is prepared by any one of the preparation methods described in claims 1 to 8.

10. The application of a polyacrylonitrile-polyimide-montmorillonite dual superhydrophobic nanocomposite aerogel prepared by any of the preparation methods described in claims 1 to 8, or the polyacrylonitrile-polyimide-montmorillonite dual superhydrophobic nanocomposite aerogel described in claim 9, as an oil-water separation material or an air filtration material.

Images