A magnetically driven ultralight aerogel for efficient oil-water separation, preparation method and application thereof

Abstract

The present invention discloses a method for preparing a magnetically driven, high-efficiency, ultralight aerogel for oil-water separation, comprising the following steps: (1) adding bentonite stripped of negative magnetism to a prepared carboxylated nanocellulose solution, then adding a crosslinking agent under constant temperature stirring and continuing stirring, and cooling to room temperature to obtain a mixed solution; (2) subjecting the mixed solution to pre-freezing pretreatment and freeze drying to obtain an aerogel; (3) using an immersion method to hydrophobize the aerogel with a hydrophobic agent solution, then taking it out and drying it, thereby obtaining a magnetically driven, high-efficiency, ultralight aerogel for oil-water separation. The present invention solves the problems of powdered adsorbents being difficult to recycle and other block adsorbents having low oil absorption efficiency, being uncontrollable, and being non-recyclable. The preparation method is simple, and the obtained aerogel has high adsorption capacity and high adsorption capacity. It can remotely control the absorption of floating oil under the guidance of a magnetic field, can be recycled multiple times, and has high resource utilization.

Description

Technical Field

[0001] The present invention relates to the field of functional aerogel materials, and in particular to a magnetically driven, high-efficiency, oil-water separation, ultra-light aerogel, a preparation method and applications thereof. Background Art

[0002] In recent years, with the development of industrialization, oil spills have become an increasingly prominent problem, becoming a major source of marine pollution. Marine water pollution, one of the most serious environmental issues, has attracted widespread attention and action. Oil spills are primarily addressed through treatment methods such as physical filtration, extraction, adsorption, chemical degradation, combustion, and bioremediation. While filtration and extraction methods are simple to implement, they are time-consuming and labor-intensive, resulting in low efficiency. Chemical degradation, on the other hand, requires long cycles or often involves toxic additives, and is not always thorough. Adsorption, on the other hand, offers advantages such as ease of operation, low cost, high oil absorption efficiency, ease of recycling, and non-toxicity, offering promising applications. However, traditional physical adsorbents lack high hydrophobicity, resulting in low oil-water separation efficiency and difficulty in convenient handling and recycling at sea. Therefore, there is an urgent need to develop adsorbent materials with excellent oil-water selectivity and high adsorption capacity.

[0003] Each adsorption material has its own shortcomings. Traditional adsorption materials, such as natural organic adsorbents like kapok fiber and grain straw, have low oil absorption capacity and poor hydrophilicity; inorganic adsorbents like diatomaceous earth and zeolite exhibit poor floatability and slow kinetics; and synthetic organic adsorbents like oil-absorbing resins and polypropylene fibers are non-biodegradable and expensive. Natural bentonite, on the other hand, is abundant, inexpensive, richly porous, and negatively charged, with montmorillonite as its primary mineral component (approximately 85% to 90%). Montmorillonite, a typical layered silicate material, has advantages such as large specific surface area, low cost, abundant sources, and excellent mechanical properties, making it widely used in pollutant remediation. Magnetic bentonite loaded with magnetic nano-Fe₃O₄ has attracted widespread attention due to its excellent solid-liquid separation capabilities, ease of recycling, and its ability to respond to external magnetic fields, allowing for remote control and recovery.

[0004] Traditional powdered adsorbents suffer from drawbacks such as difficulty in solid-liquid separation and low adsorption efficiency. Therefore, shaped, solid oil-absorbing materials, owing to their advantages of solid-liquid separation and easy recyclability, have become a research hotspot. Aerogels are a class of excellent oil-absorbing materials characterized by a continuous three-dimensional nanoporous network structure, high surface area, high porosity, and low density. Cellulose is a highly abundant, renewable, and naturally degradable biomass. The entanglement of cellulose chains allows the preparation of cellulose-based aerogels via freeze-drying techniques. As a biodegradable material with a large surface area and high porosity, cellulose aerogels possess numerous adsorption sites and hold great promise for oil-water separation. However, due to the high number of hydroxyl groups on the surface of cellulose aerogels, which are highly hydrophilic, they readily absorb water while absorbing oil, and their mechanical properties are poor. Therefore, the use of bentonite as a reinforcing agent in cellulose modification improves the mechanical properties of carboxycellulose while also enhancing its adsorption performance and stability.

[0005] A Chinese patent document, "A Method for Preparing Super-Hydrophobic, Oil-Absorbing Nanocellulose Aerogel Material," has been published with application publication number CN107199020A. This invention produces a super-hydrophobic, oil-absorbent nanocellulose aerogel material through a process involving the preparation of a nanocellulose dispersion and composite nanocellulose, followed by dialysis and drying. However, like currently widely used adsorbents, the aerogel produced in this invention cannot be recycled multiple times and is a single-use, non-recyclable adsorbent, resulting in limited practicality. Furthermore, the oil absorption process of the aerogel is uncontrollable. Summary of the Invention

[0006] The present invention provides a magnetically driven, highly efficient, ultralight aerogel for oil-water separation, as well as a preparation method and application. These aerogels address the problems of existing oil-absorbing materials, such as poor hydrophobicity, low oil absorption efficiency, slow absorption rate, limited capacity, uncontrollable and non-recyclable properties, complex preparation processes, time-consuming and labor-intensive processes, and low resource utilization. By enabling remotely controlled oil-water separation and convenient recovery under the influence of an external magnetic field, multiple recycling methods contribute to resource conservation and cost reduction, demonstrating significant potential for marine oil spill cleanup and possessing significant application value.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A method for preparing a magnetically driven, high-efficiency, oil-water separation ultralight aerogel comprises the following steps:

[0009] (1) adding bentonite stripped of negative magnetism to the prepared carboxylated nanocellulose solution, then adding a crosslinking agent under constant temperature stirring and continuing to stir, cooling to room temperature and then ultrasonically removing bubbles, and pouring into a mold to obtain a mixed solution;

[0010] (2) subjecting the mixed solution obtained in step (1) to pre-freezing pretreatment and freeze-drying to obtain an aerogel;

[0011] (3) The aerogel prepared in step (2) is subjected to a hydrophobic treatment by an immersion method, and after being hydrophobized by a hydrophobic agent solution, the aerogel is taken out and dried to obtain an ultra-light aerogel with high efficiency in oil-water separation that can be driven magnetically.

[0012] Furthermore, the mass concentration of the carboxylated nanocellulose (CNF-C) solution in step (1) is 0.5-5wt%, preferably 1.0wt%, and the mass is 50-100g, preferably 80g; the mass of the negatively magnetic bentonite stripped is 0.01-2.0g, preferably 0.1g; the cross-linking agent includes a compound containing one or more groups of epoxy groups, hydroxyl groups, carboxyl groups, and amino groups, such as epichlorohydrin, polyethyleneimine, polyethylene glycol, ethylenediamine, glutaraldehyde, butanetetracarboxylic acid, etc., preferably polyethyleneimine, and the mass concentration of the cross-linking agent is 30-80wt%; preferably 50wt%.

[0013] The basis for screening cross-linking agents in the present invention is that polyethyleneimine (PEI) is a high molecular weight polymer containing a large number of nitrogen-containing functional groups (i.e., -NH and -NH2), which can interconnect CNF-C and MBTex to form a ternary composite material. However, PEI is very soluble and needs to be loaded onto a solid support. The amino groups in PEI combine with the carboxyl groups in cellulose CNF-C through an amidation reaction to form a network structure, protecting the stability of Fe3O4. At the same time, the organic functional groups of PEI can effectively participate in the adsorption process, improving the adsorption and recovery performance of the aerogel, making it more practical in actual oil-water separation environments. On the other hand, due to the high positive charge density and isoelectric point of PEI, the charge distribution on the surface of the material can be adjusted. The synergistic effect of hydrogen bonds and chemical bonds gives the CPM aerogel good mechanical properties.

[0014] Furthermore, the preparation method of the stripped negative magnetic bentonite includes the following steps: completely dissolving FeCl2·4H2O and FeCl3·6H2O in a molar ratio of 1:1.5-2.2 in 40-80 mL of water, placing the solution in a three-necked flask, performing microwave heating reaction using a computer microwave solid-liquid phase synthesizer, cooling the solution to room temperature after the reaction stops, and obtaining a black Fe3O4 magnetic fluid; adding 1-5 g of the stripped bentonite to the Fe3O4 magnetic fluid, placing the solution in a computer microwave solid-liquid phase synthesizer and continuing the reaction for 0.5-3 h, cooling the solution to room temperature after the reaction ends, washing, drying, grinding and sieving, and thus obtaining the stripped negative magnetic bentonite.

[0015] Furthermore, the computer microwave solid-liquid phase synthesizer setting parameters and reaction conditions in the preparation method of the stripped negative magnetic bentonite are: 50-60°C, 500-600W, and a stirring rate of 200-600rpm; the reaction process is: a microwave preheating stage reaction for 2-10 minutes, adding an alkaline solution to adjust the pH value of the reaction system to 7-13 and then reacting for 0.5-1h, aging for 0.3-1h after the reaction is completed, and cooling to room temperature; the alkaline solution is one or more of ammonia water, sodium hydroxide, and potassium hydroxide.

[0016] Furthermore, the preparation method of the exfoliated bentonite comprises the following steps: using a liquid phase exfoliation method, weighing 1 to 10 g of purified bentonite, adding it to 300 to 800 mL of water, placing it in an ultrasonic cell crusher, ultrasonicating for 2 to 5 hours, and drying it to obtain the exfoliated bentonite.

[0017] The method for preparing exfoliated negatively magnetic bentonite (MBTex) is based on the fact that natural bentonite (BT) has limited adsorption properties. Exfoliated bentonite (BTex) exposes its inner surface through delamination, increasing the specific surface area and adsorption sites, thereby improving adsorption performance. Furthermore, the treatment of marine oil spills often requires targeted adsorption in specific areas. Therefore, by using negative magnetism, magnets are used to control the movement of CPM aerogels across the water surface to adsorb oil at different locations on the surface, solving the problems of targeted adsorption, solid-liquid separation, and rapid recovery. Furthermore, MBTex is incorporated into the cellulose backbone structure as a reinforcing agent through a blend, improving the mechanical properties, mechanical strength, and elasticity of the composite aerogel.

[0018] Furthermore, the stirring temperature of the mixed solution in step (1) is 40-100° C., preferably 70° C.; the stirring time is 1-6 h, preferably 4 h; the ultrasonic power is 300-800 W, preferably 600 W; and the ultrasonic time is 0.5-2 h.

[0019] Furthermore, the pre-freezing treatment in step (2) is performed by refrigerator freezing, the pre-freezing treatment temperature is -8 to -20°C, preferably -10°C, and the pre-freezing treatment time is 3 to 18 hours; the freeze-drying temperature is -50 to -80°C, preferably -70°C, and the freeze-drying time is 12 to 72 hours, preferably 24 to 36 hours;

[0020] Furthermore, the mass concentration of the hydrophobic agent solution in step (3) is 0.1 to 5 wt%, preferably 1 wt%;

[0021] The hydrophobization treatment temperature is 25-60°C, preferably 30°C; the treatment time is 2-12 hours, preferably 3-6 hours. The hydrophobization temperature must be strictly controlled within the range specified in the present invention. Too low a temperature will result in a slow reaction rate and a long reaction time; too high a temperature will cause chain scission and degradation of the cellulose nanofibers. The hydrophobization treatment time should not be too long, as it will lead to excessive crosslinking of the aerogel, affecting its recovery.

[0022] The drying temperature is 40-100°C, preferably 45°C; the drying time is 5-36 hours, preferably 6-12 hours. Vacuum drying is preferred.

[0023] The hydrophobic agent is a silane coupling agent or an isocyanate, such as heptafluorodecyltrimethoxysilane, tridecafluorooctyltrimethoxysilane, methyltrimethoxysilane, hexadecyltrimethoxysilane, octadecyltrichlorosilane, hexamethylene diisocyanate, diphenylmethane diisocyanate, etc., preferably octadecyltrichlorosilane (OTS).

[0024] The solvent of the hydrophobic agent solution includes one or more of esters, ketones, ethers, aromatic hydrocarbons, aliphatic hydrocarbons, and benzene, preferably n-hexane.

[0025] Therefore, the present invention has the following beneficial effects:

[0026] (1) The present invention uses bentonite as a reinforcing agent for the modification of nanocellulose, thereby improving the mechanical properties of carboxylated nanocellulose while also enhancing its adsorption performance and stability.

[0027] (2) The preparation method of the present invention is simple and can overcome the shortcomings of existing adsorption methods. The raw material used is bio-based cellulose nanofiber, a polysaccharide that is widely present in nature, has a wide source and is biodegradable, harmless to the environment, and is in line with the concept of green development.

[0028] (3) The aerogel prepared by the present invention has an ultra-light and low density (standing on a leaf), a three-dimensional network structure with rich pores (12.12nm), and an ultra-high specific surface area (10.89m 2 ·g -1 ) and super hydrophobicity (hydrophobic angle is 151.5°), high water-oil selective absorption, which helps to adsorb oil stains, and has fast and efficient adsorption ability and high adsorption capacity for a variety of oils (24 to 78 times higher than the original weight).

[0029] (4) In addition, due to the introduction of MBTex, the composite aerogel exhibits excellent magnetically drivable properties, good mechanical properties and elasticity, and can quickly restore its original shape after being compressed without any obvious plastic deformation. Therefore, the absorption of floating oil can be remotely controlled under the guidance of a magnetic field, and after the oil absorption is completed, it can be quickly separated by a magnet, and the adsorbed oil can be squeezed out by simple mechanical extrusion, making the recycling process of waste oil simple, and also helping to save adsorption materials and reduce the cost of oil-water separation. The regenerated aerogel can be recycled many times, with high resource utilization. The magnetic adsorbent that can respond to the external magnetic field has received widespread attention because it can be remotely controlled and recycled, showing great potential for application in marine oil spill cleanup. The present invention provides guidance for the synthesis of cost-effective oil-water separation materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a photograph of the CNF-C / PEI / MBTex hydrophobic aerogel prepared in Example 3 placed on a plant leaf (demonstrating the ultra-light performance of the aerogel);

[0031] Figure 2 (a) and Figure 2 (b) SEM images of CNF-C / PEI / MBTex hydrophobic aerogel prepared in Example 3 at 200 μm and 100 μm scales, respectively;

[0032] Figure 3 This is a water contact angle test graph of the CNF-C / PEI / MBTex hydrophobic aerogel prepared in Example 3;

[0033] Figure 4 These are photographs of the surface wettability of oil (dyed red with Sudan III) and water (dyed blue with methylene) dropped onto the hydrophobic and non-hydrophobic CNF-C / PEI / MBTex aerogels prepared in Example 3 and Comparative Example 2, respectively;

[0034] Figure 5 3. It is a photograph of the oil absorption performance test process of the CNF-C / PEI / MBTex hydrophobic aerogel prepared in Example 3;

[0035] Figure 6 hysteresis loops of the CNF-C / PEI / MBTex / OTS aerogel prepared in Example 3 and the CNF-C / MBTex / OTS aerogel prepared in Comparative Example 1 under the conditions of a magnetic field strength of -20 KOe to 20 KOe and a temperature of 25°C;

[0036] Figure 7 3 is a diagram of the magnetically driven oil absorption process of CNF-C / PEI / MBTex hydrophobic aerogel prepared in Example 3;

[0037] Figure 8 (a) is a photograph of the process of CNF-C / PEI / MBTex hydrophobic aerogel recovering its height (elasticity) by manual squeezing; Figure 8 (b) Comparative process diagram of aerogel height (elasticity) before and after extrusion;

[0038] Figure 9 are the XRD diffraction patterns of CNF-C, CNF-C / MBTex / OTS, CNF-C / PEI / MBTex, and CNF-C / PEI / MBTex / OTS;

[0039] Figure 10 These are the FT-IR infrared spectra of MBTex, CNF-C, CNF-C / MBTex / OTS, CNF-C / PEI / MBTex, and CNF-C / PEI / MBTex / OTS. DETAILED DESCRIPTION

[0040] The technical solution of the present invention will be further described in detail below through specific embodiments in conjunction with the accompanying drawings.

[0041] In the present invention, unless otherwise specified, all equipment and raw materials can be purchased from the market or are commonly used in the industry. The methods in the following embodiments, unless otherwise specified, are all conventional methods in the art.

[0042] Example 1

[0043] A method for preparing a magnetically driven, high-efficiency, oil-water separation ultralight aerogel comprises the following steps:

[0044] (1) First, prepare a carboxylated nanocellulose (CNF-C) solution with a mass concentration of 0.5%. Take 50 g of it and add 0.05 g of the exfoliated magnetic bentonite (MBTex) powder to the CNF-C solution under constant temperature stirring in a 40°C water bath. Then add a 30% crosslinker PEI solution and continue to stir at constant temperature for 1 hour until the mixture is evenly dispersed. After cooling to room temperature, the mixture is ultrasonically dispersed in a 300 W ultrasonic disperser for 0.5 hour to disperse tiny bubbles, and then poured into a mold to obtain a mixed solution.

[0045] The exfoliated bentonite was prepared by liquid phase exfoliation method, 3.0 g of purified bentonite was added into 500 mL of ultrapure water, placed in an ultrasonic cell crusher, ultrasonicated for 3 h, and dried to obtain the exfoliated bentonite BTex.

[0046] MBTex was obtained by the negative magnetic properties of the exfoliated bentonite. The preparation method was as follows: FeCl2·4H2O and FeCl3·6H2O in a molar ratio of 1:1.5 were completely dissolved in 50 mL of ultrapure water and placed in a three-necked flask. The mixture was preheated for 2 min using a computer microwave solid-liquid phase synthesizer at a temperature of 53°C and a power of 540 W. Then, NH3·H2O was added to adjust the pH value of the reaction system to 9. The mixture was stirred at 53°C for 0.6 h to generate a black Fe3O4 magnetic fluid. After aging for another 0.3 h, 1 g of the exfoliated bentonite was added to the Fe3O4 magnetic fluid, and the mixture was placed in a microwave solid-liquid phase synthesizer and the reaction was continued for 0.5 h. After the reaction was completed, the mixture was cooled to room temperature, washed three times with anhydrous ethanol and deionized water respectively, dried, and ground through a 200-mesh sieve to obtain the exfoliated magnetic bentonite MBTex.

[0047] (2) The mixed solution was placed in a refrigerator and pre-frozen at -8°C for 18 h. After the pre-freezing, it was freeze-dried at -50°C for 12 h to obtain dry CPM aerogel.

[0048] (3) Finally, n-hexane was used to prepare a 0.1 wt% octadecyltrichlorosilane (OTS) solution, and the aerogel sample was immersed in the hydrophobic agent solution. The sample was taken out and dried in a vacuum drying oven at 40°C to obtain a hydrophobic CPM composite aerogel.

[0049] Example 2

[0050] A method for preparing a magnetically driven, high-efficiency, oil-water separation ultralight aerogel comprises the following steps:

[0051] (1) First, a carboxylated nanocellulose (CNF-C) solution with a mass concentration of 3% was prepared. 60 g of the solution was taken and added to the CNF-C solution under constant temperature stirring in a 60°C water bath. 0.15 g of the exfoliated magnetic bentonite (MBTex) powder was then added to the CNF-C solution. A 65% crosslinker PEI solution was then added and the mixture was stirred at constant temperature for 3 h until the mixture was uniformly dispersed. After cooling to room temperature, the mixture was ultrasonically dispersed in an 800 W ultrasonic disperser for 1.5 h to disperse the tiny bubbles. The mixture was then poured into a mold to obtain a mixed solution.

[0052] The liquid phase exfoliation method was used to prepare the exfoliated bentonite. 3.0 g of purified bentonite was added to 500 mL of ultrapure water, placed in an ultrasonic cell crusher, ultrasonicated for 3 h, and dried to obtain ultrasonically exfoliated bentonite BTex.

[0053] MBTex was obtained by the negative magnetic properties of the exfoliated bentonite. The preparation method was as follows: FeCl2·4H2O and FeCl3·6H2O in a molar ratio of 1:1.8 were completely dissolved in 50 mL of ultrapure water and placed in a three-necked flask. The mixture was preheated for 7 minutes using a computer microwave solid-liquid phase synthesizer at a temperature of 57°C and a power of 570 W. Then, NaOH was added to adjust the pH value of the reaction system to 11. The mixture was stirred at 57°C for 0.8 hours to generate a black Fe3O4 magnetic fluid. After aging for another 0.7 hours, 3 g of the exfoliated bentonite was added to the Fe3O4 magnetic fluid, and the mixture was placed in a microwave solid-liquid phase synthesizer and the reaction was continued for 1 hour. After the reaction was completed, the mixture was cooled to room temperature, washed three times with anhydrous ethanol and deionized water respectively, dried, and ground through a 200-mesh sieve to obtain the exfoliated magnetic bentonite MBTex.

[0054] (2) The mixed solution was placed in a refrigerator and pre-frozen at -15°C for 12 h. After the pre-freezing, it was freeze-dried at -60°C for 36 h to obtain dry CPM aerogel.

[0055] (3) Finally, a 3 wt% octadecyltrichlorosilane (OTS) solution was prepared using n-hexane, and the aerogel sample was immersed in the hydrophobic agent solution. The sample was taken out and dried in a vacuum drying oven at 80°C to obtain a hydrophobic CPM composite aerogel.

[0056] Example 3

[0057] A method for preparing a magnetically driven, high-efficiency, oil-water separation ultralight aerogel comprises the following steps:

[0058] (1) First, a carboxylated nanocellulose (CNF-C) solution with a mass concentration of 1.0% was prepared. 80 g of the solution was added to the CNF-C solution under constant temperature stirring in a 70°C water bath. 0.10 g of the exfoliated magnetic bentonite (MBTex) powder was then added to the CNF-C solution. A 50% crosslinker PEI solution was then added and the mixture was stirred at constant temperature for 4 h until the mixture was uniformly dispersed. After cooling to room temperature, the mixture was ultrasonically dispersed in a 600 W ultrasonic disperser for 1 h to disperse the tiny bubbles. The mixture was then poured into a mold to obtain a mixed solution.

[0059] The exfoliated bentonite was prepared by liquid phase exfoliation method, 3.0 g of purified bentonite was added into 500 mL of ultrapure water, placed in an ultrasonic cell crusher, ultrasonicated for 3 h, and dried to obtain the exfoliated bentonite BTex.

[0060] MBTex was obtained by the negative magnetic stripping of bentonite. The preparation method was as follows: FeCl2·4H2O and FeCl3·6H2O in a molar ratio of 1:2 were completely dissolved in 50 mL of ultrapure water and placed in a three-necked flask. The mixture was preheated for 3 min at 60°C and 600 W using a computer microwave solid-liquid phase synthesizer. Then, NH3·H2O was added to adjust the pH value of the reaction system to 7. The mixture was stirred at 60°C for 0.5 h to generate a black Fe3O4 magnetic fluid. After aging for 0.5 h, 2 g of ultrasonically stripped bentonite was added to the Fe3O4 magnetic fluid, and the mixture was placed in a microwave solid-liquid phase synthesizer and the reaction was continued for 2 h. After the reaction was completed, the mixture was cooled to room temperature, washed three times with anhydrous ethanol and deionized water respectively, dried, and ground through a 200-mesh sieve to obtain the stripped magnetic bentonite MBTex.

[0061] (2) The mixed solution was placed in a refrigerator and pre-frozen at -10°C for 6 h. After the pre-freezing, it was freeze-dried at -70°C for 24 h to obtain dry CPM aerogel.

[0062] (3) Finally, n-hexane was used to prepare a 1 wt% octadecyltrichlorosilane (OTS) solution, and the aerogel sample was immersed in the hydrophobic agent solution. The sample was taken out and dried in a vacuum drying oven at 60°C to obtain a hydrophobic CPM composite aerogel.

[0063] Example 4

[0064] A method for preparing a magnetically driven, high-efficiency, oil-water separation ultralight aerogel comprises the following steps:

[0065] (1) First, a carboxylated nanocellulose (CNF-C) solution with a mass concentration of 5 wt% was prepared. 100 g of the solution was taken and 0.30 g of the exfoliated magnetic bentonite (MBTex) powder was added to the CNF-C solution under constant temperature stirring in a 100 °C water bath. Then, a crosslinker PEI solution with a concentration of 80% was added and the mixture was stirred at constant temperature for 6 h until the mixture was uniformly dispersed. After cooling to room temperature, the mixture was ultrasonically dispersed in a 500 W ultrasonic disperser for 2 h to disperse the tiny bubbles, and then poured into a mold to obtain a mixed solution.

[0066] The exfoliated bentonite was prepared by liquid phase exfoliation method, wherein 3.0 g of purified bentonite was added to 500 mL of ultrapure water, placed in an ultrasonic cell crusher, sonicated for 3 hours, and dried to obtain the exfoliated bentonite BTex.

[0067] MBTex was obtained by the negative magnetic stripping of bentonite. The preparation method was as follows: FeCl2·4H2O and FeCl3·6H2O in a molar ratio of 1:2.2 were completely dissolved in 50 mL of ultrapure water and placed in a three-necked flask. The mixture was preheated for 10 min using a computer microwave solid-liquid phase synthesizer at a temperature of 50°C and a power of 500 W. KOH was then added to adjust the pH value of the reaction system to 13. The mixture was stirred at 50°C for 1 h to generate a black Fe3O4 magnetic fluid. After aging for another 1 h, 5 g of ultrasonically stripped bentonite was added to the Fe3O4 magnetic fluid, and the mixture was placed in a microwave solid-liquid phase synthesizer and the reaction was continued for 3 h. After the reaction was completed, the mixture was cooled to room temperature, washed three times with anhydrous ethanol and deionized water respectively, dried, and ground through a 200-mesh sieve to obtain the stripped magnetic bentonite MBTex.

[0068] (2) The mixed solution was placed in a refrigerator and pre-frozen at -20°C for 3 h. After the pre-freezing, it was freeze-dried at -80°C for 72 h to obtain dry CPM aerogel.

[0069] (3) Finally, n-hexane was used to prepare a 5 wt% octadecyltrichlorosilane (OTS) solution, the aerogel sample was immersed in the hydrophobic agent solution, and then taken out and dried in a vacuum drying oven at 100 °C to obtain a hydrophobic CPM composite aerogel.

[0070] Comparative Example 1 (no crosslinking agent added)

[0071] The difference between Comparative Example 1 and Example 3 is that the cross-linking agent polyethyleneimine (cross-linking agent PEI) is not added in step (1), and the remaining steps and process conditions are exactly the same.

[0072] Comparative Example 2 (without hydrophobic treatment)

[0073] The difference between Comparative Example 2 and Example 3 is that step (3) is omitted, and the remaining steps and process conditions are exactly the same.

[0074] With certain parameters in Example 3 kept unchanged, multiple groups of single-factor experiments were designed to optimize the optimal preparation process parameters of the aerogel prepared by the present invention.

[0075] (1) Effect of different CNF-C solution concentrations on the adsorption performance of waste oil

[0076] CNF-C solution concentration (%) Waste oil adsorption capacity (g / g) 0.5 38.9 1.0 59.8 2.0 43.3 3.0 38.6 4.0 32.2 5.0 30.7

[0077] In this set of experiments, a series of aerogels were prepared to explore the effect of varying CNF-C concentration on waste oil adsorption. The preparation process conditions varied only the CNF-C solution concentration, remaining consistent with those in Example 3. The experimental data in the table show that with increasing CNF-C concentration, the aerogels' oil absorption rate initially increased and then decreased. When the CNF-C solution concentration was 1%, the aerogels exhibited the highest adsorption of waste oil, reaching an average of 59.8 g of waste oil per gram. This result is due to the high dispersibility of carboxylated nanocellulose (CNF-C) in water and its abundant carboxyl and hydroxyl groups. Aerogels prepared using a 1.0% cellulose precursor via freeze-drying exhibited advantages such as a three-dimensional porous structure, low density, and high specific surface area. However, at high concentrations, the cellulose chains readily entangle and cross-link, forming a dense network structure, which reduces porosity and, in turn, decreases oil adsorption. At lower concentrations, the resulting network structure is too loose and inadequate, resulting in limited oil encapsulation. Therefore, under the experimental conditions, the optimal CNF-C solution concentration was determined to be 1.0%.

[0078] (2) Effect of different PEI concentrations on the adsorption performance of waste oil

[0079] PEI solution concentration (%) Waste oil adsorption capacity (g / g) 30 20.3 40 44.6 50 59.8 60 31.7 70 28.4 80 22.6

[0080] In this experimental group, the optimal crosslinker PEI concentration was determined by varying only the PEI solution concentration, while maintaining all other parameters consistent with those in Example 3. The experimental data in the table show that as PEI concentration increases, the aerogel's adsorption of waste oil initially increases and then decreases, reaching its highest adsorption capacity at a PEI concentration of 50%. This is attributed to the fact that carboxylated nanocellulose contains functional groups such as hydroxyl and carboxyl groups, which react more vigorously with amino groups and result in a high degree of crosslinking. When the PEI concentration exceeds 50%, excessive crosslinking is likely to occur, increasing the density of the aerogel and reducing its oil absorption relative to its own weight. Furthermore, excessive crosslinking reduces its resilience, making it less reusable. When the PEI concentration is below 50%, the insufficient degree of crosslinking prevents the resulting network from encapsulating more of the solution, resulting in reduced oil absorption. Therefore, under these experimental conditions, a PEI concentration of 50% was determined to be optimal.

[0081] (3) Effect of different MBTex contents on the adsorption performance of waste oil

[0082] MBTex content (g) Waste oil adsorption capacity (g / g) 0.025 22.4 0.050 30.8 0.100 59.8 0.125 31.7 0.150 28.4 0.175 23.6

[0083] In this set of experiments, a series of aerogels were prepared to explore the effect of MBTex content on the adsorption performance of waste oil. Among them, the process conditions for preparation were to change only the MBTex content, and the rest were consistent with the conditions in Example 3. It can be seen from the experimental data in the table that with the increase of MBTex content, the oil absorption rate of the aerogel showed a trend of first increasing and then decreasing. When the MBTex content was 0.100g, the aerogel had the highest adsorption capacity for waste oil. The reason for the analysis is: due to the limited adsorption performance of natural bentonite (BT), the stripped bentonite (BTex) exposes the inner surface to the outside through stratification, increasing the specific surface area and adsorption sites, thereby improving the adsorption performance. At the same time, MBTex is incorporated into the cellulose skeleton structure as a reinforcing agent in a blended manner to improve the mechanical properties, mechanical strength and elasticity of the composite aerogel. When the MBTex content is lower than 0.100g, the adsorption amount decreases due to the reduction of adsorption sites on the aerogel surface. However, if the content is higher than 0.100g, the excess MBTex powder will become oversaturated and dissolve during the preparation of the mixed solution, resulting in an inhomogeneous mixed solution and reduced oil absorption. Therefore, under the experimental conditions, an MBTex content of 0.100g was determined to be the optimal content.

[0084] (4) Effects of different hydrophobic agents on the adsorption performance of waste oil

[0085] Different hydrophobic agents Water contact angle (°) Waste oil adsorption capacity (g / g) Methyltrimethoxysilane 130.8 49.7 Hexadecyltrimethoxysilane 148.6 56.2 Octadecyltrichlorosilane 151.5 59.8 No hydrophobic agent added 0 33.6

[0086] A hydrophobic agent is an additive modifier that gives a material a certain hydrophobic function. After hydrophobic modification, the aerogel changes from hydrophilic to hydrophobic, showing excellent water-oil selective absorption properties. Fluorine-based hydrophobic agents with fluorine groups are known. Such fluorine-based hydrophobic agents are generally manufactured by polymerizing or copolymerizing monomers with fluoroalkyl groups. When such fluorine-based hydrophobic agents are used to treat materials, although excellent hydrophobicity is exerted, since monomers with fluoroalkyl groups are difficult to decompose, there are environmental problems. Therefore, this experiment mainly explores the effects of different silane coupling agents, methyltrimethoxysilane, hexadecyltrimethoxysilane, and octadecyltrichlorosilane, on the hydrophobicity and oil absorption properties of CPM aerogel materials. The aerogel prepared in Example 3 is compared with the aerogel prepared under the same process conditions as those prepared by changing only the hydrophobic agent or not adding the hydrophobic agent. The results showed that different silane coupling agents had varying effects on the hydrophobic properties of the material, with water contact angles ranging from 130° to 152°. Aerogels without hydrophobic agents exhibited excellent hydrophilicity, with a water contact angle of 0°. This is primarily due to the different types and quantities of functional groups introduced into the aerogels by different hydrophobic agents, which altered the surface energy of the material. These differences in hydrophobic angles, in turn, led to differences in the oil absorption rates of the aerogels. Consequently, octadecyltrichlorosilane, with its excellent hydrophobic properties, exhibited the highest adsorption capacity for oil. Furthermore, CPM aerogels treated with hydrophobic agents exhibited high water-oil selectivity, facilitating the adsorption of oil contaminants. Finally, under these experimental conditions, octadecyltrichlorosilane was selected as the optimal hydrophobic modifier.

[0087] The ultralight elastic hydrophobic aerogel prepared in Example 3 was tested for performance, and the results were as follows:

[0088] Figure 1 This is a macroscopic photograph of the magnetically driven, highly efficient, ultralight aerogel for oil-water separation obtained in Example 3. The aerogel is cylindrical and has a regular shape, demonstrating good formability. The ultralight aerogel, obtained through freeze-drying, slightly bends at the tip of a leaf when placed on it, as shown in the photo, demonstrating its exceptional lightness.

[0089] Figure 2The SEM images of the aerogel obtained in Example 3, taken at 200 μm and 100 μm scales, show that the CPM hydrophobic aerogel prepared in Example 3 possesses a dense, continuous, and stable three-dimensional honeycomb network structure. The unique fiber structure and properties of CNF-C give the CPM hydrophobic aerogel a uniform three-dimensional texture, with thin layers tightly connected to form a 3D skeleton with high porosity. The carbon skeleton surface is relatively rough, and a large number of interconnected macropores are evenly distributed across the CPM aerogel surface, facilitating the storage of oils and the removal of pollutants, indicating that the material has excellent oil absorption capacity. This is primarily due to the entanglement between the crosslinker PEI and the cellulose CNF-C, which affects the growth of ice crystals, thereby forming a pore structure of varying regularity and size. This increases the number of mesopores and macropores with adsorption capacity, further facilitating the removal of organic pollutants. Furthermore, the average distance between PEI and cellulose promotes the further formation of the aerogel membrane, allowing more ice crystals to agglomerate and form larger pore channels. On the other hand, the amount of crosslinker PEI added affects the dispersion of MBTex in the cellulose matrix, while the strong hydrogen bonding between MBTex and cellulose affects the aerogel network structure. These results indicate that CPM aerogels with a three-dimensional network structure have been successfully prepared.

[0090] Figure 3 This is a graph of the water contact angle of the aerogel prepared in Example 3. It can be seen that the water contact angle of the aerogel after hydrophobic modification with octadecyltrichlorosilane / n-hexane solution reaches 151.5°, which has good hydrophobic properties and is beneficial to improving water-oil selectivity. Figure 4 This is a macroscopic diagram of the hydrophobic effect, illustrating the surface wettability of CPM aerogels before and after modification. For better identification, water is dyed blue with methylene blue and motor oil is dyed red with Sudan III. Once blue water droplets and red oil droplets are placed on the surface of the hydrophobically modified CPM aerogel, only the oil droplets can easily and quickly penetrate the CPM aerogel, while the water droplets remain on the surface of the aerogel in a stable spherical shape ( Figure 4 Left). In contrast, when water droplets and oil droplets are placed on the surface of CPM aerogel without hydrophobic modification, both water droplets and oil droplets can easily penetrate into the interior of the aerogel ( Figure 4 The above results confirm that the CPM aerogel has excellent superhydrophobic and oleophilic properties after hydrophobic modification.

[0091] Figure 5The complete process of CPM hydrophobic aerogel adsorbing waste motor oil (dyed red by Sudan III) from water is shown. It can be clearly recorded that when the CPM hydrophobic aerogel comes into contact with the oil-water mixture, it completely absorbs the waste motor oil floating on the water surface within 5 seconds. These results indicate that CPM aerogel has high porosity, good mechanical stability, and superhydrophobic lipophilicity, resulting in excellent oil absorption capacity, fast adsorption rate, and good adsorption performance, making it an ideal adsorbent for efficient oil-water separation and removal of other organic pollutants from water.

[0092] In order to quantitatively analyze the adsorption performance of CPM hydrophobic aerogels for different oils and organic solvents, waste engine oil was used as a simulated pollutant to study the adsorption capacity of CPM aerogels. The aerogels prepared in Examples 1 to 4 and Comparative Examples 1 and 2 were subjected to the following procedures: Each 2×2×3 cm 3 The mass of the small piece of aerogel is recorded as m0. Each small piece of aerogel is immersed in various oils and organic solvents (n-hexane, cyclohexane, chloroform, peanut oil, rapeseed oil and waste engine oil) until it reaches adsorption saturation. Then, the soaked aerogel pieces are taken out and the organic oil overflowing from the surface of each small piece of aerogel is adsorbed with filter paper. After the mass stabilizes, it is quickly weighed and recorded as m1.

[0093] The adsorption performance is constant using the mass oil absorption rate: Q = (m1-m0) / m0, where Q is the adsorption capacity per unit mass of aerogel, m0 is the initial mass of aerogel, and m1 is the final mass after adsorption saturation.

[0094] The oil absorption performance indicators of the hydrophobic oil-absorbing aerogels of Examples 1 to 4 and the aerogels of Comparative Examples 1 and 2 were tested, and the results are shown in the following table:

[0095]

[0096] As shown in the table above, CPM hydrophobic aerogels can effectively and selectively adsorb various organic solvents and oils (n-hexane, cyclohexane, chloroform, peanut oil, rapeseed oil, and engine oil) at room temperature, with an adsorption capacity of 24 to 78 times their own mass. Non-hydrophobic aerogels absorb water in addition to oil. In summary, the adsorption properties of aerogels are related to their porous structure and porosity, as well as the viscosity of different oils. CPM aerogels treated with a hydrophobic agent exhibit a high degree of water- and oil-selective absorption, which facilitates the adsorption of oil stains and achieves significant oil absorption.

[0097] Figure 6The following are the hysteresis loops for MBTex, CNF-C / MBTex / OTS, and CNF-C / PEI / MBTex / OTS under magnetic field strengths of -20kOe to 20kOe and a temperature of 25°C. As can be seen from the curves in the figure, the hysteresis loops for MBTex, CNF-C / MBTex / OTS, and CNF-C / PEI / MBTex / OTS all resemble S-shaped curves with no hysteresis, indicating that the prepared aerogels possess excellent superparamagnetic properties. The saturation magnetization of MBTex is significantly higher than that of CNF-C / MBTex / OTS and CNF-C / PEI / MBTex / OTS. The lower saturation magnetic intensity of CNF-C / PEI / MBTex / OTS compared to MBTex is due to the co-modification and attachment of the organic molecules CNF-C and PEI to MBTex, which reduces its magnetic content. Furthermore, the magnetic saturation intensity of the CNF-C / PEI / MBTex / OTS aerogel was slightly higher than that of the CNF / MBTex / OTS aerogel, indicating that simply modifying MBTex with CNF-C does not effectively protect the chemical stability of the magnetic Fe₃O₄. This is because the magnetic Fe₃O₄ is prone to oxidation aggregation and loss of magnetism when in contact with air, and can even cause secondary environmental pollution. In summary, the introduction of the CNF-C / PEI dual network structure into the aerogel has a certain protective effect on the magnetic core, effectively preventing the oxidation of Fe₃O₄, improving the stability and cyclability of the CNF-C / PEI / MBTex / OTS aerogel, and enabling more effective controllable directional adsorption under the control of a magnetic field, thereby improving adsorption efficiency.

[0098] Figure 7 This diagram illustrates the process of using magnets to control the movement of CPM aerogels on the water surface for targeted oil absorption. As shown, due to the aerogel's ultra-lightweight, low-density, and highly hydrophobic properties, it can float on the water surface. Using an external magnet for magnetic traction, the ultra-light magnetic aerogel is directed to the oily area. Its rapid movement and selective adsorption remove the floating oil (dyed with Sudan III) in the water, playing a crucial role in the practical application of aerogel adsorbents for efficient oil-water separation. As can be seen in the figure, the CPM aerogel is quickly attracted by the magnet, completely absorbing the floating oil on the water surface, demonstrating its high magnetic sensitivity. The water surface remains very clear after adsorption, and the aerogel can be rapidly recovered and recycled by the magnet after oil absorption.

[0099] Reusability is a key parameter for the practical application of oil absorbents. Figure 8 This demonstrates the compressible regeneration and recycling of CPM hydrophobic aerogel, thereby achieving the performance of repeated use. Figure 8As shown in (a), the adsorbed waste oil can be easily discharged by simple manual squeezing, and the squeezed aerogel can quickly recover to its original shape after release. Figure 8 (b) Records the height change of the CPM hydrophobic aerogel before and after extrusion and release of waste oil. The height of the aerogel after oil extrusion remains essentially unchanged compared to before extrusion, with no noticeable plastic deformation. These results demonstrate that the CPM hydrophobic aerogel has excellent compressive resistance and elasticity, making it cost-effective to recycle multiple times through simple mechanical extrusion.

[0100] The overall crystallinity and crystalline phase of CNF-C, CNF-C / MBTex / OTS, CNF-C / PEI / MBTex, and CNF-C / PEI / MBTex / OTS aerogels were evaluated by XRD. Figure 9 The XRD patterns of CNF-C reveal a semicrystalline structure, with a broad peak within the 2θ range of 10° to 30°, confirming the presence of an amorphous phase. CNF-C exhibits only one diffraction peak at 22.6°, corresponding to the (002) crystal plane, a characteristic peak of type I cellulose. Compared to CNF-C, CNF-C / MBTex / OTS exhibits distinct diffraction peaks, indicating exposure of different crystalline surfaces due to composite aerogel formation and morphological changes in CNF-C. The XRD patterns of CNF-C / PEI / MBTex and CNF-C / PEI / MBTex / OTS exhibit diffraction peaks similar to those of CNF-C, but with significantly reduced intensities, attributed to successful silanization and the reaction between the organic molecules CNF-C and PEI. The XRD pattern of CNF-C / PEI / MBTex / OTS aerogel showed almost no impurity peaks, indicating that the crystal purity of CNF-C was high after modification with MBTex and PEI. The above results all indicate that MBTex and PEI loading was successful.

[0101] The chemical structures of MBTex, CNF-C, CNF-C / MBTex / OTS, CNF-C / PEI / MBTex, and CNF-C / PEI / MBTex / OTS aerogels were studied by FT-IR analysis. The results of infrared spectroscopy analysis are shown in Figure 4. Figure 10 As shown. The infrared absorption spectrum of CNF-C shows that in the range of 3600-3000cm -1 3000-2800cm -1 and 1100-1000cm -1 The absorption peaks appearing at 1670-1600 cm represent the stretching vibrations of -OH, CH and CO in cellulose. -1 and 1400cm -1The absorption peaks at 2922 cm-1 are the symmetric and asymmetric stretching vibrations of carboxylates. -1 and 2852cm -1 The peaks at 3448 cm are attributed to the stretching vibration of -CH3 and -CH2, respectively. -1 and 1628cm -1 The absorption peak of 1106cm is related to the stretching vibration of water molecules between layers. -1 The prominent characteristic peak at 2582 cm was assigned to Si-O stretching vibration, and the same characteristic absorption peak can be seen in the infrared spectrum of CNF-C / PEI / MBTex / OTS aerogel, indicating that MBTex was successfully introduced into the structure of CNF-C / PEI / MBTex / OTS aerogel. -1 The absorption peak at 1327 cm corresponds to the stretching vibration of -COOH. -1 The new peak at 521 cm is due to the stretching mode of -CONH-, indicating that the -OH in CNF-C successfully connects with the -NH2 in PEI to form an amide bond. At the same time, the cross-linking of PEI enhances the cross-linking density between cellulose molecules, indicating the existence of hydrogen bonds between CNF, MBTex and PEI. -1 The typical absorption peak at is the Fe-O stretching vibration, confirming that Fe3O4 is successfully loaded on the surface of CNF-C / PEI / MBTe aerogel. The above FT-IR analysis shows that PEI and MBTex have successfully modified the structure of CNF-C / PEI / MBTex aerogel, forming a network structure.

[0102] The scope of protection of the present invention is not limited to the above-mentioned embodiments. All technical solutions based on the concept of the present invention are within the scope of protection of the present invention. It should be noted that for those skilled in the art, various improvements and modifications that do not depart from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a magnetically driven ultralight aerogel for efficient oil-water separation, characterized in that: The following steps are involved: (1) adding bentonite stripped of negative magnetism to the prepared carboxylated nanocellulose solution, then adding a crosslinking agent while stirring at a constant temperature and continuing to stir, cooling to room temperature and removing bubbles by ultrasonication, and pouring into a mold to obtain a mixed solution, wherein the crosslinking agent is polyethyleneimine; (2) pre-freezing and freeze-drying the mixed solution obtained in step (1) to obtain an aerogel; (3) The aerogel prepared in step (2) is subjected to a hydrophobic treatment by an impregnation method, and after being hydrophobized by a hydrophobic agent solution, the aerogel is taken out and dried to obtain an ultra-light aerogel with high efficiency in oil-water separation that can be driven magnetically; The method for preparing stripped negatively magnetic bentonite comprises the following steps: completely dissolving FeCl2·4H2O and FeCl3·6H2O at a molar ratio of 1:1.5-2.2 in 40-80 mL of water, placing the mixture in a three-necked flask, performing microwave heating reaction using a computer microwave solid-liquid phase synthesizer, and cooling the mixture to room temperature after the reaction stops to obtain a black Fe3O4 magnetic fluid; adding 1-5 g of stripped bentonite to the Fe3O4 magnetic fluid, placing the mixture in the computer microwave solid-liquid phase synthesizer and continuing the reaction for 0.5-3 h, cooling the mixture to room temperature after the reaction ends, washing, drying, grinding, and sieving to obtain the stripped negatively magnetic bentonite; The stirring temperature of the mixed solution in step (1) is 40-100° C., the stirring time is 1-6 h, the ultrasonic power is 300-800 W, and the ultrasonic time is 0.5-2 h; The pre-freezing treatment temperature in step (2) is -8 to -20°C, and the pre-freezing treatment time is 3 to 18 hours; the freeze-drying temperature is -50 to -80°C, and the freeze-drying time is 12 to 72 hours; The mass concentration of the hydrophobic agent solution in step (3) is 0.1~5 wt%; The temperature of the hydrophobic treatment is 25~60℃; the time of the hydrophobic treatment is 2~12 hours; Drying temperature is 40~100℃; drying time is 5~36 hours; The hydrophobic agent is alkoxysilane or isocyanate; The solvent of the hydrophobic agent solution includes one or more of esters, ketones, ethers, aromatic hydrocarbons, and aliphatic hydrocarbons.

2. The method for preparing the magnetically driven, high-efficiency, oil-water separation ultralight aerogel according to claim 1, characterized in that: The mass concentration of the carboxylated nanocellulose solution in step (1) is 0.5-5 wt%, and the mass is 50-100 g; the mass of the stripped negative magnetic bentonite is 0.01-2.0 g; and the mass concentration of the cross-linking agent is 30-80 wt%.

3. The method for preparing the magnetically driven high-efficiency oil-water separation ultra-light aerogel according to claim 1, characterized in that: In the method for preparing the negatively magnetic bentonite stripped, the computer microwave solid-liquid phase synthesizer setting parameters and reaction conditions are: 50-60°C, 500-600 W, and a stirring rate of 200-600 rpm. The reaction process is: a microwave preheating stage for 2-10 minutes, adding an alkaline solution to adjust the pH value of the reaction system to 7-13 and then reacting for 0.5-1 hour. After the reaction is completed, the reaction is aged for 0.3-1 hour and cooled to room temperature. The alkaline solution is one or more of ammonia water, sodium hydroxide, and potassium hydroxide.

4. The method for preparing a magnetically driven, high-efficiency, oil-water separation ultralight aerogel according to claim 1, characterized in that: The method for preparing the exfoliated bentonite comprises the following steps: using a liquid phase exfoliation method, weighing 1-10 g of purified bentonite, adding the mixture to 300-800 mL of water, placing the mixture in an ultrasonic cell pulverizer, ultrasonicating the mixture for 2-5 hours, and drying the mixture to obtain the exfoliated bentonite.

5. A magnetically driven, highly efficient, ultralight aerogel for oil-water separation prepared according to the method of any one of claims 1 to 4.

6. Use of the magnetically driven, efficient, oil-water separation ultralight aerogel according to claim 5 as an adsorption material.

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