Composite aerogel and preparation method and application thereof

Abstract

The application discloses a composite aerogel and a preparation method and application thereof, and belongs to the technical field of functional materials and environmental treatment. In the application, delignified cotton stalk cellulose is compounded with MXene to prepare a suspension, directional freezing self-assembly is carried out by using n-heptane as a heat transfer medium, and after freezing drying and polydimethylsiloxane dip coating, a PDMS / CMNF / MXene composite aerogel is obtained. The aerogel has an ultra-fine scale, high-density vertically arranged pore channels and a multi-level pore structure, and the pore channel diameter is 20-40 mu m. Under the driving of solar energy, the surface temperature of the aerogel can reach above 120 DEG C, the rapid in-situ viscosity reduction and efficient adsorption of high-viscosity crude oil are realized, the adsorption capacity is more than 56 times of the weight of the aerogel, and the performance retention rate is greater than 90% after 10 cycles. The application provides an efficient, green and recyclable solution for the treatment of marine high-viscosity crude oil leakage.

Description

Technical Field

[0001] This invention belongs to the field of functional materials and environmental governance technology, specifically relating to a composite aerogel, its preparation method, and its application. Background Technology

[0002] Marine oil spills have catastrophic impacts on the ecological environment. High-viscosity crude oil (such as heavy crude oil and asphaltene crude oil) has extremely poor fluidity at room temperature, with viscosity typically exceeding 1000 mPa·s, making it difficult for traditional adsorption materials to effectively handle. Solar-driven photothermal materials offer a new approach to solving this problem, generating heat through photothermal conversion to reduce the viscosity of crude oil, thereby improving adsorption efficiency.

[0003] Currently, anisotropic porous materials prepared based on directional freezing technology have been applied in the field of oil-water separation. Traditional directional freezing technology often uses a low-temperature freezing stage to allow ice crystals to grow along the temperature gradient direction, forming an oriented pore structure. However, this water-based freezing system has the following inherent drawbacks: the ice crystal size formed by water freezing is usually tens to hundreds of micrometers, resulting in a relatively large final pore size, which limits the specific surface area and capillary force of the material; the pores formed by freezing stage are mostly regular layered or honeycomb-like, lacking multi-level structures, which is not conducive to rapid liquid transport; the large pore wall size leads to a long heat conduction path, limiting the efficiency of heat transfer from the material surface to the interior; in addition, the water-based environment accelerates the oxidation of MXene, reducing the photothermal stability and service life of the material.

[0004] Therefore, developing a novel photothermal aerogel with a finer pore structure, higher thermal conductivity, and faster liquid transport capability is of great significance for achieving efficient recovery of high-viscosity crude oil. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a composite aerogel, its preparation method and application. Based on the synergistic mechanism of rapid in-situ photothermal viscosity reduction and enhanced capillary adsorption, this invention achieves efficient, rapid and recyclable recovery of high-viscosity crude oil.

[0006] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a method for preparing composite aerogels, comprising the following steps: S1. A CMNF / MXene suspension was obtained by mixing delignified cotton stalk cellulose with an MXene suspension and then subjecting the mixture to ultrasonic treatment. S2. The CMNF / MXene suspension was subjected to directional cryogenic self-assembly using the ice template method, and then freeze-dried to obtain CMNF / MXene aerogel; S3. Immerse the CMNF / MXene aerogel in a polydimethylsiloxane elastomer solution, then remove and cure to obtain PDMS / CMNF / MXene aerogel.

[0007] Preferably, the preparation method of delignified cotton stalk cellulose in S1 is as follows: cotton stalk powder is mixed and reacted with a eutectic solvent, filtered and washed to obtain cotton stalk fiber; the cotton stalk fiber is placed in NaClO2 solution for delignification treatment to obtain delignified cotton stalk cellulose.

[0008] Furthermore, the mixing reaction temperature is 80-110℃, and the time is 1-3h.

[0009] Furthermore, the eutectic solvent is a mixture of choline chloride, oxalic acid, and ethylene glycol in a molar ratio of 1:1:6.

[0010] Furthermore, the NaClO2 solution concentration is 0.77% and the pH is 4.6; the treatment temperature is 80℃ and the time is 4h.

[0011] Preferably, the mass concentration of cellulose in the CMNF / MXene suspension in S1 is 1.2-2.4%.

[0012] Preferably, the concentration of MXene in S1 is 1-5 mg / mL.

[0013] Furthermore, the preparation method of the MXene suspension is as follows: LiF is added to HCl solution to make the concentration of LiF in the system 9 mol / L, and then the MXene precursor is added to make the concentration of MXene 1-5 mg / mL.

[0014] Furthermore, the MXene includes Ti3C2T x .

[0015] Furthermore, the ultrasonic treatment time in S1 is 30-90 minutes.

[0016] Preferably, the ice template method in S2 is as follows: the suspension is poured into a mold, and n-heptane and liquid nitrogen are placed on top of the suspension in sequence. The ice crystals are induced to grow in a vertical direction by conducting cold energy through n-heptane.

[0017] Preferably, the freeze-drying pressure in step S2 is 0.05-0.3 kPa, and the time is 30-60 h.

[0018] Preferably, the concentration of the polydimethylsiloxane solution in S3 is 0.5-1.5%.

[0019] Preferably, the curing temperature in S3 is 70-90℃ and the curing time is 0.5-2h.

[0020] The present invention also provides PDMS / CMNF / MXene aerogel prepared by the above preparation method.

[0021] This invention also provides the application of the above-mentioned PDMS / CMNF / MXene aerogel in solar-driven adsorption and recovery of high-viscosity crude oil.

[0022] It contains at least the following beneficial technical effects: This invention employs directional freezing technology using n-heptane as the heat transfer medium. Compared with traditional direct freezing or cold table contact freezing, the volatility of n-heptane helps to form a local supercooled zone at the freezing front, promoting the refinement and uniform growth of ice crystals, thereby preparing a composite aerogel with ultrafine scale (25μm level), high-density vertically arranged channels and multi-level pore structure.

[0023] The refined pore structure of this invention significantly enhances the capillary force of the material. According to the Young's LaPlace equation, a reduction of one order of magnitude in pore radius corresponds to a corresponding increase of one order of magnitude in capillary pressure, greatly promoting the initial absorption of high-viscosity crude oil.

[0024] The ultra-thin pore walls reduce the heat conduction path, while the high-density vertical channels form more continuous heat conduction pathways, optimizing the material's heat conduction efficiency. This allows heat to be quickly transferred from the surface to the interior and bottom, achieving rapid in-situ viscosity reduction of crude oil.

[0025] The PDMS coating of this invention uniformly coats the skeleton without clogging the pores, giving the material superhydrophobic / superoleophilic properties and excellent compression resilience, while effectively preventing salt water from corroding MXene and improving the material's cycle stability and salt resistance.

[0026] This invention proposes a synergistic mechanism based on rapid in-situ photothermal viscosity reduction and enhanced capillary adsorption, achieving efficient, rapid, and recyclable recovery of high-viscosity crude oil. The entire process utilizes only solar energy, requiring no chemical reagents or external heat sources, making it green and environmentally friendly. Attached Figure Description

[0027] Figure 1 This is a process flow diagram for preparing PCM aerogel in Example 1 of the present invention.

[0028] Figure 2 The images show the cross-section and longitudinal section of the PCM aerogels prepared in Example 1 and Comparative Example 1 of this invention, as shown in the SEM images.

[0029] Figure 3 The images show the compression recovery of the PCM aerogel obtained in Example 1, which is used to test the mechanical properties of the aerogels in Example 1 and Comparative Example 1 of this invention.

[0030] Figure 4 This is a wettability diagram of the PCM aerogel obtained in Example 1 of the present invention.

[0031] Figure 5 (a) Photothermal conversion performance test of the aerogels of Example 1 and Comparative Example 1 of the present invention, and (b) Comparison of infrared thermographic images of the temperature distribution of the two aerogels under illumination.

[0032] Figure 6 (a) Comparison of the adsorption kinetics curves of the aerogels of Example 1 and Comparative Example 1 on high-viscosity crude oil, and (b) Adsorption of heavy viscous oil by the PCM aerogel obtained in Example 1 of the present invention. Detailed Implementation

[0033] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0034] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0035] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0036] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be obvious to those skilled in the art. This application specification and embodiments are merely exemplary.

[0037] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0038] Unless otherwise specified, "room temperature" and "normal temperature" in this invention refer to 25±2℃.

[0039] Unless otherwise specified, all raw materials or instruments used in the following embodiments of the present invention are commercially available.

[0040] Example 1 S1. Preparation of delignified cotton stalk cellulose: Cotton stalk powder was mixed with a eutectic solvent (choline chloride, oxalic acid, and ethylene glycol in a molar ratio of 1:1:6) in a container and reacted in an oil bath at 100°C for 3 hours. The reaction solution was filtered, and the resulting solid was washed to obtain cotton stalk fibers. The cotton stalk fibers were placed in a 0.77% NaClO2 solution, and the pH was adjusted to 4.6 with acetic acid. The solution was reacted at 80°C for 4 hours, filtered, washed until neutral, and dried to obtain delignified cotton stalk cellulose.

[0041] Preparation of S2 and MXene colloidal suspensions: 1 g of LiF was added to 20 mL of HCl solution (9 mol / L) and stirred until completely dissolved. 1 g of Ti3AlC2 powder was slowly added to prevent overheating, and the mixture was magnetically stirred at 35 °C for 24 h. The resulting suspension was centrifuged at 6000 rpm and washed repeatedly with deionized water until the pH of the supernatant was close to neutral, yielding a multilayer Ti3C2T... x Precipitation. Subsequently, multilayer Ti3C2T... x The MXene was dispersed in deionized water and ultrasonically exfoliated for 2 hours under an argon atmosphere in an ice-water bath. Finally, it was centrifuged at 3500 rpm for 5 minutes, and the upper dark green supernatant was collected to obtain a colloidal suspension with a concentration of 5 mg / mL.

[0042] Preparation of S3, CMNF / MXene composite suspension: The delignified cotton stalk cellulose obtained in step S1 was added to deionized water and dispersed using a high-speed disperser to obtain a cellulose micro / nanofiber dispersion. This dispersion was then mixed with the MXene suspension obtained in step S2 in a specific ratio to prepare a mixed suspension with a cellulose mass concentration of 1.2% and an MXene concentration of 3 mg / mL. The mixed suspension was ultrasonically treated in an ice-water bath for 60 min to obtain a homogeneous CMNF / MXene suspension.

[0043] S4, n-Heptane-conducted directional freezing and PDMS coating: The CMNF / MXene suspension obtained in step S3 was poured into a polytetrafluoroethylene mold (2 cm inner diameter, 3 cm height). Directional freezing was performed using an ice template method protected by n-heptane: a layer of n-heptane (analytical grade, 2 mm thick) was slowly added above the suspension, and then a liquid nitrogen container was placed above the n-heptane. The evaporation of the n-heptane conducted the cooling, causing ice crystals to grow vertically from bottom to top. After the sample was completely frozen, it was quickly transferred to a freeze dryer and freeze-dried at 0.1 kPa for 48 h to obtain unmodified CMNF / MXene aerogel. This aerogel was immersed in a 1% (w / w) polydimethylsiloxane (PDMS) n-hexane solution, allowed to stand for 10 min, then removed, excess solution drained, and cured in an oven at 80°C for 1 h to obtain a PDMS / CMNF / MXene composite aerogel, denoted as PCM-C.

[0044] Example 2 S1. Preparation of delignified cotton stalk cellulose: Cotton stalk powder was mixed with a eutectic solvent (choline chloride, oxalic acid, and ethylene glycol in a molar ratio of 1:1:6) in a container and reacted in an oil bath at 80°C for 1 hour. The reaction solution was filtered while hot, and the resulting solid was washed three times with deionized water to obtain cotton stalk fibers. The cotton stalk fibers were placed in a 0.77% NaClO2 solution, and the pH was adjusted to 4.6 with acetic acid. The solution was reacted at 80°C for 4 hours. After the reaction was completed, the solution was filtered, washed with deionized water until neutral, and dried in an oven at 60°C to constant weight to obtain delignified cotton stalk cellulose.

[0045] Preparation of S2 and MXene colloidal suspensions: 1 g of LiF was added to 20 mL of HCl solution (9 mol / L), and the mixture was magnetically stirred until the LiF was completely dissolved. 1 g of Ti3AlC2 powder was slowly added, controlling the addition rate to prevent overheating. After the addition was complete, the mixture was magnetically stirred at 35 °C for 24 h. The resulting suspension was centrifuged at 6000 rpm for 5 min, the supernatant was discarded, and the precipitate was repeatedly washed with deionized water and centrifuged until the pH of the supernatant was close to neutral, yielding multilayer Ti3C2T. x Precipitation. Subsequently, multilayer Ti3C2T... x Dispersed in 50 mL of deionized water, the mixture was ultrasonically exfoliated for 2 h under an argon atmosphere in an ice-water bath. Finally, it was centrifuged at 3500 rpm for 5 min, and the upper dark green supernatant was collected to obtain a colloidal suspension with a concentration of 5 mg / mL.

[0046] Preparation of S3, CMNF / MXene composite suspension: The delignified cotton stalk cellulose obtained in step S1 was added to deionized water and dispersed using a high-speed disperser at 10,000 rpm for 5 min to obtain a cellulose micro / nanofiber dispersion. This dispersion was then mixed with the MXene suspension obtained in step S2 in a specific ratio to prepare a mixed suspension with a cellulose mass concentration of 1.2% and an MXene concentration of 1 mg / mL. The mixed suspension was ultrasonically treated in an ice-water bath for 30 min to obtain a homogeneous CMNF / MXene suspension.

[0047] S4, n-Heptane-conducted directional freezing and PDMS coating: The CMNF / MXene suspension obtained in step S3 was poured into a polytetrafluoroethylene mold (2 cm inner diameter, 3 cm height). Directional freezing was performed using an ice template method protected by n-heptane: a layer of n-heptane (analytical grade, 2 mm thick) was slowly added above the suspension, and then a liquid nitrogen container was placed above the n-heptane. The evaporation of the n-heptane conducted the cooling, causing ice crystals to grow vertically from bottom to top. After the sample was completely frozen, it was quickly transferred to a freeze dryer and freeze-dried at 0.05 kPa for 30 h to obtain unmodified CMNF / MXene aerogel. This aerogel was then immersed in a 0.5% (w / w) polydimethylsiloxane (PDMS) n-hexane solution, allowed to stand for 10 min, removed, excess solution drained, and cured in an oven at 70°C for 0.5 h to obtain a PDMS / CMNF / MXene composite aerogel.

[0048] Example 3 S1. Preparation of delignified cotton stalk cellulose: Cotton stalk powder was mixed with a eutectic solvent (choline chloride, oxalic acid, and ethylene glycol in a molar ratio of 1:1:6) in a container and reacted in an oil bath at 95°C for 2 hours. The reaction solution was filtered while hot, and the resulting solid was washed three times with deionized water to obtain cotton stalk fibers. The cotton stalk fibers were placed in a 0.77% NaClO2 solution, the pH was adjusted to 4.6 with acetic acid, and the reaction was carried out at 80°C for 4 hours. After the reaction was completed, the solution was filtered, washed with deionized water until neutral, and dried in an oven at 60°C to constant weight to obtain delignified cotton stalk cellulose.

[0049] Preparation of S2 and MXene colloidal suspensions: 1 g of LiF was added to 20 mL of HCl solution (9 mol / L), and the mixture was magnetically stirred until the LiF was completely dissolved. 1 g of Ti3AlC2 powder was slowly added, controlling the addition rate to prevent overheating. After the addition was complete, the mixture was magnetically stirred at 35 °C for 24 h. The resulting suspension was centrifuged at 6000 rpm for 5 min, the supernatant was discarded, and the precipitate was repeatedly washed with deionized water and centrifuged until the pH of the supernatant was close to neutral, yielding multilayer Ti3C2T. x Precipitation. Subsequently, multilayer Ti3C2T... x Dispersed in 50 mL of deionized water, the mixture was ultrasonically exfoliated for 2 h under an argon atmosphere in an ice-water bath. Finally, it was centrifuged at 3500 rpm for 5 min, and the upper dark green supernatant was collected to obtain a colloidal suspension with a concentration of 5 mg / mL.

[0050] Preparation of S3, CMNF / MXene composite suspension: The delignified cotton stalk cellulose obtained in step S1 was added to deionized water and dispersed using a high-speed disperser at 10,000 rpm for 5 min to obtain a cellulose micro / nanofiber dispersion. This dispersion was then mixed with the MXene suspension obtained in step S2 in a specific ratio to prepare a mixed suspension with a cellulose mass concentration of 1.8% and an MXene concentration of 3 mg / mL. The mixed suspension was ultrasonically treated in an ice-water bath for 60 min to obtain a homogeneous CMNF / MXene suspension.

[0051] S4, n-Heptane-conducted directional freezing and PDMS coating: The CMNF / MXene suspension obtained in step S3 was poured into a polytetrafluoroethylene mold (2 cm inner diameter, 3 cm height). Directional freezing was performed using an ice template method protected by n-heptane: a layer of n-heptane (analytical grade, 2 mm thick) was slowly added above the suspension, and then a liquid nitrogen container was placed above the n-heptane. The evaporation of the n-heptane conducted the cooling, causing ice crystals to grow vertically from bottom to top. After the sample was completely frozen, it was quickly transferred to a freeze dryer and freeze-dried at 0.15 kPa for 45 h to obtain unmodified CMNF / MXene aerogel. This aerogel was immersed in a 1.0% (w / w) polydimethylsiloxane (PDMS) n-hexane solution, allowed to stand for 10 min, then removed, excess solution drained, and cured in an oven at 80°C for 1 h to obtain a PDMS / CMNF / MXene composite aerogel.

[0052] Example 4 S1. Preparation of delignified cotton stalk cellulose: Cotton stalk powder was mixed with a eutectic solvent (choline chloride, oxalic acid, and ethylene glycol in a molar ratio of 1:1:6) in a container and reacted in an oil bath at 110°C for 3 hours. The reaction solution was filtered while hot, and the resulting solid was washed three times with deionized water to obtain cotton stalk fibers. The cotton stalk fibers were placed in a 0.77% NaClO2 solution, the pH was adjusted to 4.6 with acetic acid, and the reaction was carried out at 80°C for 4 hours. After the reaction was completed, the solution was filtered, washed with deionized water until neutral, and dried in an oven at 60°C to constant weight to obtain delignified cotton stalk cellulose.

[0053] Preparation of S2 and MXene colloidal suspensions: 1 g of LiF was added to 20 mL of HCl solution (9 mol / L), and the mixture was magnetically stirred until the LiF was completely dissolved. 1 g of Ti3AlC2 powder was slowly added, controlling the addition rate to prevent overheating. After the addition was complete, the mixture was magnetically stirred at 35 °C for 24 h. The resulting suspension was centrifuged at 6000 rpm for 5 min, the supernatant was discarded, and the precipitate was repeatedly washed with deionized water and centrifuged until the pH of the supernatant was close to neutral, yielding multilayer Ti3C2T. x Precipitation. Subsequently, multilayer Ti3C2T... x Dispersed in 50 mL of deionized water, the mixture was ultrasonically exfoliated for 2 h under an argon atmosphere in an ice-water bath. Finally, it was centrifuged at 3500 rpm for 5 min, and the upper dark green supernatant was collected to obtain a colloidal suspension with a concentration of 5 mg / mL.

[0054] Preparation of S3, CMNF / MXene composite suspension: The delignified cotton stalk cellulose obtained in step S1 was added to deionized water and dispersed using a high-speed disperser at 10,000 rpm for 5 min to obtain a cellulose micro / nanofiber dispersion. This dispersion was then mixed with the MXene suspension obtained in step S2 in a specific ratio to prepare a mixed suspension with a cellulose mass concentration of 2.4% and an MXene concentration of 5 mg / mL. The mixed suspension was ultrasonically treated in an ice-water bath for 90 min to obtain a homogeneous CMNF / MXene suspension.

[0055] S4, n-Heptane-conducted directional freezing and PDMS coating: The CMNF / MXene suspension obtained in step S3 was poured into a polytetrafluoroethylene mold (2 cm inner diameter, 3 cm height). Directional freezing was performed using an ice template method protected by n-heptane: a layer of n-heptane (analytical grade, 2 mm thick) was slowly added above the suspension, and then a liquid nitrogen container was placed above the n-heptane. The evaporation of the n-heptane conducted the cooling, causing ice crystals to grow vertically from bottom to top. After the sample was completely frozen, it was quickly transferred to a freeze dryer and freeze-dried at 0.3 kPa for 60 h to obtain unmodified CMNF / MXene aerogel. This aerogel was immersed in a 1.5% (w / w) polydimethylsiloxane (PDMS) n-hexane solution, allowed to stand for 10 min, then removed, excess solution drained, and cured in an oven at 90°C for 2 h to obtain a PDMS / CMNF / MXene composite aerogel.

[0056] Comparative Example 1 The preparation method for this comparative example is the same as that of Example 1, except that conventional copper plate contact directional freezing is used: the CMNF / MXene suspension obtained in step S3 is poured into a polytetrafluoroethylene mold of the same specifications. The mold is placed on a pre-cooled copper plate, with one side of the copper plate partially immersed in liquid nitrogen. The high thermal conductivity of the copper plate creates a temperature gradient from bottom to top at the bottom of the suspension, inducing vertical growth of ice crystals. After the sample is completely frozen, it is quickly transferred to a freeze dryer and freeze-dried at 0.1 kPa for 48 h to obtain an unmodified aerogel. Subsequently, PDMS coating is performed under the exact same conditions as in Example 1 to obtain a PDMS / CMNF / MXene composite aerogel, denoted as PCM-R.

[0057] Experimental Example 1 Channel structure characterization The aerogels prepared in Example 1 and Comparative Example 1 were observed using scanning electron microscopy (SEM). Figure 2 As shown (where a is the cross-section and longitudinal section of the PCM aerogel prepared in Example 1 and Comparative Example 1, respectively), both exhibit a honeycomb-like porous structure in cross-section. The pore diameter of the conventional copper-based cryogenic aerogel PCM-R is 40-80 μm, and the pore wall thickness is 1.5 μm. The pore diameter of the n-heptane conductive cryogenic aerogel PCM-C is 20-40 μm, and the pore wall thickness is 1 μm. The ice crystal size formed by n-heptane conductive cryogenics is significantly smaller than that of conventional copper-based cryogenics, and the pore density is significantly increased: the number of vertical pores per unit area increases. In the vertical section, a highly ordered vertically arranged pore structure is displayed, and the surface exhibits nanoscale roughness. MXene nanosheets uniformly cover the surface of the CMNF framework, forming a continuous photothermal network; the PDMS coating uniformly coats the framework without blocking the pores.

[0058] Experimental Example 2 Mechanical property testing like Figure 3 As shown, the mechanical properties were determined by compression testing. Using an Instron 5967 (China) universal testing machine material testing system and a 50 N pressure sensor, a square aerogel (length: 15 × 15 mm, height: 10 mm) was compressed at a pressure of 10 mm·min⁻¹. - The displacement rate is compressed until the compressive strain reaches 50%. The vertically aligned layered structure endows PCM-C and PCM-R aerogels with excellent compressive resilience. PCM-C aerogel exhibits anisotropy in both the axial and radial directions, and can withstand 50% compressive strain in the radial direction and fully rebound.

[0059] Experimental Example 3 Wettability test like Figure 4 As shown, the water contact angle (WCA) was measured using a contact angle analyzer (JJ2000B, Zhongchen, Shanghai, China): 3 μL of water was placed on the aerogel surface using a microsyringe. The aerogel exhibits superhydrophobic / superoleophilic properties; various liquids exhibit hydrophobicity on the aerogel surface, and it is hydrophobic both inside and outside the aerogel. The aerogel displays a distinct silver mirror effect underwater.

[0060] Experiment Example 4 Photothermal performance test Under natural or artificial light, MXene on the aerogel surface rapidly absorbs light energy and converts it into heat energy. Due to its unique vertical pore structure, heat is quickly conducted along the pore walls to the interior and bottom of the material. The temperature at the bottom of the material can rise to 120°C within 1-2 minutes, causing the viscosity of high-viscosity crude oil in the contact area to decrease by 2-3 orders of magnitude. The crude oil with reduced viscosity is then rapidly transported upward along the vertical pores under the enhanced capillary force.

[0061] A solar simulation testing system (AM 1.5G, 1 kW / m²) was set up, and an aerogel PCM-C sample (3 cm in diameter and 1 cm in thickness) was placed on an insulating substrate; an infrared thermal imager was used to monitor the temperature distribution. like Figure 5 As shown, in Example 1, the surface center point of the material rises to 95°C in 30 seconds and reaches the equilibrium temperature of 122°C in 60 seconds; in Comparative Example 1, the same component aerogel PCM-R prepared by conventional water-based directional freezing has a surface equilibrium temperature of 101.6°C. Experimental Example 5 High viscosity crude oil adsorption performance Prepare a simulated high-viscosity crude oil with a viscosity of 12500 mPa·s at 25℃.

[0062] Place the aerogel sample (2×2×1 cm) on the surface of the oil film (5 mm thick); turn on the sunlight simulator; record the adsorption weight in real time; Aerogel of Example 1: Adsorption capacity of 46.67 g / g in 3 minutes, reaching equilibrium of 55.67 g / g in 7 minutes; Comparative Example 1 aerogel: 39 g / g at 3 minutes, reaching equilibrium at 46.21 g / g at 9 minutes; Under no-light conditions, the aerogel in Example 1 adsorbed 19.64 g / g in 10 minutes, demonstrating the key role of photothermal viscosity reduction. Thanks to its high-density pore structure, the adsorption rate is 3-5 times higher than that of traditional materials; when the aerogel adsorption reaches saturation (the adsorption amount can reach 50-60 times its own weight), it is collected.

[0063] Experimental Example 6 Actual seawater environment test High-viscosity crude oil was laid on the surface of simulated seawater (3.5% NaCl, pH 8.1) for field testing. PCM aerogel was cut into appropriate sizes and directly placed into the high-viscosity crude oil contaminated area. The material automatically floated at the oil-water interface and cleaned up the floating oil.

[0064] PCM-C aerogel exhibits excellent salt resistance and chemical stability; its adsorption performance decreases by only 7% compared to freshwater environments. After continuous floating on the water surface for 72 hours, the material's performance showed no significant change, and the PDMS coating effectively prevented the corrosion of MXene by salt water.

[0065] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several improvements and modifications without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method of preparing a composite aerogel, characterized by, Includes the following steps: S1. A CMNF / MXene suspension was obtained by mixing delignified cotton stalk cellulose with an MXene suspension and then subjecting the mixture to ultrasonic treatment. S2. The CMNF / MXene suspension was subjected to directional cryogenic self-assembly using the ice template method, and then freeze-dried to obtain CMNF / MXene aerogel; S3. Immerse the CMNF / MXene aerogel in a polydimethylsiloxane elastomer solution, then remove and cure to obtain PDMS / CMNF / MXene aerogel.

2. The preparation method according to claim 1, characterized in that, The preparation method of delignified cotton stalk cellulose in S1 is as follows: cotton stalk powder is mixed and reacted with a eutectic solvent, filtered and washed to obtain cotton stalk fiber; the cotton stalk fiber is placed in NaClO2 solution for delignification treatment to obtain delignified cotton stalk cellulose.

3. The preparation method according to claim 1, characterized in that, The mass concentration of cellulose in the CMNF / MXene suspension in S1 is 1.2-2.4%.

4. The preparation method according to claim 1, characterized in that, The concentration of MXene in S1 is 1-5 mg / mL.

5. The preparation method according to claim 1, characterized in that, The ice template method in S2 specifically involves pouring the suspension into a mold, placing n-heptane and liquid nitrogen sequentially above the suspension, and inducing ice crystals to grow in a vertical direction by conducting cold energy through n-heptane.

6. The preparation method according to claim 1, characterized in that, The freeze-drying process in S2 is carried out at a pressure of 0.05-0.3 kPa for 30-60 hours.

7. The preparation method according to claim 1, characterized in that, The concentration of the polydimethylsiloxane solution in S3 is 0.5-1.5%.

8. The preparation method according to claim 1, characterized in that, The curing temperature in S3 is 70-90℃, and the curing time is 0.5-2h.

9. The PDMS / CMNF / MXene aerogel prepared by the preparation method according to any one of claims 1-8.

10. The application of the PDMS / CMNF / MXene aerogel according to claim 9 in solar-driven adsorption and recovery of high-viscosity crude oil.

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