Aerogel as well as preparation method and application thereof

Abstract

The invention relates to the field of waste utilization, in particular to aerogel as well as a preparation method and application thereof. The preparation method comprises the following steps: adding sodium hypochlorite into dispersion liquid containing lignin-removed coffee grounds, sodium bromide and TEMPO, adjusting the pH value to 10-10.5, and when the pH value of the dispersion liquid is kept at a constant value within a period of time, adding ethanol for quenching reaction; carrying out dialysis and dispersion treatment on the reaction system after the quenching reaction is finished; and mixing the CNF dispersion liquid and the chitosan solution, emulsifying, stirring, directionally freezing, freeze-drying and cross-linking. According to the preparation method, the waste coffee grounds are used as the raw material, and no toxic chemical cross-linking agent is used, so that the aerogel has a stable three-dimensional network structure and excellent mechanical properties; the prepared aerogel has extremely high adsorption capacity on iodine, especially radioactive iodine, and an efficient, low-cost and sustainable solution is provided for treatment of radioactive iodine.

Description

Technical Field

[0001] This invention relates to the field of waste utilization, and more specifically, to an aerogel, its preparation method, and its application. Background Technology

[0002] Nuclear energy, as a clean and efficient energy source, occupies an important position in the global energy structure. However, the nuclear fission process produces substances including radioactive iodine (such as...). 129 I and 131 Various radionuclides, including I), are involved. These radioactive iodine isotopes are highly volatile, have long half-lives, and readily accumulate in the thyroid glands of organisms, posing a serious threat to the environment and public health. Therefore, developing efficient and reliable radioactive iodine capture and fixation technologies is a crucial step in the safe utilization of nuclear energy and the treatment of nuclear waste.

[0003] Currently, adsorption is widely used for the removal of radioactive iodine due to its simplicity, relatively low cost, and high efficiency. Common adsorbents include: Traditional porous materials include activated carbon and silver-based zeolites. While activated carbon is inexpensive, its adsorption capacity for iodine is limited, and its adsorption performance significantly decreases under high temperature and humidity conditions, posing a flammability risk. Although silver-based zeolites exhibit excellent adsorption performance, the high cost of the silver element and its potential environmental toxicity limit their large-scale application.

[0004] Novel framework materials, such as metal-organic frameworks (MOFs) and covalent organic frameworks (COFs), exhibit high adsorption capacity due to their high specific surface area and tunable pore structure. However, their synthesis process is usually complex and requires harsh conditions (such as oxygen-free and high-temperature environments), the raw materials are expensive, and they are mostly in powder form, which leads to difficulties in recycling and poor mechanical strength, making them difficult to apply in practical engineering.

[0005] Biomass-derived materials: To overcome the shortcomings of the aforementioned materials, researchers have begun to turn to biomass materials that are widely available, renewable, and biodegradable. Among them, aerogel adsorbents prepared from cellulose and chitosan show promising application prospects. However, in existing technologies, the preparation of cellulose / chitosan aerogels typically relies on chemical cross-linking agents (such as glutaraldehyde, epichlorohydrin, etc.) to enhance their structural stability. The introduction of these cross-linking agents not only increases the preparation cost and process complexity, but their residues and leaching may also cause secondary environmental pollution, violating the original intention of green chemistry.

[0006] Furthermore, in the preparation of aerogels, how to construct stable and ordered porous structures to provide efficient mass transfer channels and abundant adsorption sites, while ensuring that the material has sufficient mechanical strength to meet the needs of practical applications, remains a challenge for current technology.

[0007] Therefore, there is an urgent need in this field to develop a novel aerogel material that has low raw material costs, a green and environmentally friendly preparation process, does not require toxic chemical cross-linking agents, and simultaneously possesses high adsorption capacity and excellent mechanical properties for the efficient adsorption of radioactive iodine.

[0008] In view of this, the present invention is hereby proposed. Summary of the Invention

[0009] This invention aims to solve a series of technical problems existing in radioactive iodine adsorbent materials, such as high cost, secondary pollution caused by the use of toxic chemical crosslinking agents in the preparation process, poor mechanical strength of the materials and easy collapse in humid environments. To this end, this invention provides a method for preparing aerogel and its application.

[0010] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: One aspect of the present invention relates to a method for preparing an aerogel, comprising the following steps: (a) Add sodium hypochlorite to a dispersion containing lignin-removed coffee grounds, sodium bromide and TEMPO, adjust the pH to 10-10.5, and when the pH of the dispersion remains constant for a period of time, add ethanol to quench the reaction. (b) The reaction system after the quenching reaction is completed is subjected to dialysis and dispersion treatment to obtain CNF dispersion; (c) The CNF dispersion and chitosan solution are mixed and then emulsified, stirred, directionally frozen, freeze-dried and cross-linked to obtain the aerogel.

[0011] The aforementioned aerogel preparation method successfully prepared nanocellulose / chitosan aerogel using waste coffee grounds as raw material through a green process. This preparation method does not require the use of toxic chemical cross-linking agents, avoiding secondary pollution. At the same time, the aerogel possesses a stable three-dimensional network structure and excellent mechanical properties through directional freezing and thermal cross-linking technology, and can remain intact without collapsing in water. The prepared aerogel exhibits extremely high adsorption capacity for iodine, especially for radioactive iodine, and combines excellent adsorption performance, environmental friendliness, and good recycling potential, providing an efficient, low-cost, and sustainable solution for the remediation of radioactive iodine.

[0012] Another aspect of the present invention relates to aerogels prepared by the aforementioned method.

[0013] The aerogel described above possesses a stable three-dimensional network structure and excellent mechanical properties, allowing it to remain intact and not collapse in water, greatly enhancing its convenience and recyclability in practical aquatic environments. Simultaneously, this product exhibits extremely high adsorption capacity for radioactive iodine vapor, outperforming many traditional materials. Furthermore, due to its composition as natural biomass, it is environmentally friendly and non-toxic, providing a highly efficient, stable, and safe green adsorption material solution for nuclear waste treatment.

[0014] Another aspect of the present invention relates to a method for adsorbing iodine, wherein an aerogel prepared by the aforementioned aerogel preparation method or the aforementioned aerogel is used to adsorb iodine.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. Green from the source, turning waste into treasure, low cost This invention utilizes waste coffee grounds as the initial raw material, achieving high-value resource utilization of solid waste. This not only significantly reduces the raw material cost of nanocellulose aerogels but also provides an effective way to address the environmental pressure caused by coffee grounds, aligning with the requirements of a circular economy and sustainable development.

[0016] 2. The preparation process is environmentally friendly, avoiding secondary pollution. This invention eliminates the need for any toxic chemical crosslinking agents during the aerogel molding and crosslinking process. Instead, it utilizes a simple thermal crosslinking technique to induce a condensation reaction between the carboxyl groups on nanocellulose and the amino groups on chitosan, forming stable amide bonds. This method fundamentally eliminates the risks of residue and leaching that may arise from traditional chemical crosslinking agents, avoids secondary environmental pollution, and makes the process greener and safer.

[0017] 3. The product has an excellent structure, outstanding mechanical properties, and stability. Through the synergistic effect of directional freezing and thermal cross-linking processes, the prepared aerogel possesses a highly ordered three-dimensional network and a multi-level porous structure with both layered structures. This structure endows the material with excellent mechanical strength, enabling it to maintain structural integrity without collapsing in water. This solves the problems of poor mechanical strength and easy collapse in water in traditional biomass aerogels, greatly facilitating the recycling and reuse of the material.

[0018] 4. Excellent adsorption performance and broad application prospects. The aerogel prepared in this invention exhibits an extremely high adsorption capacity for iodine, outperforming many traditional activated carbon, zeolites, and even some MOF materials. This is mainly attributed to: Abundant active sites: Chitosan provides a large number of amino groups, which, together with the carboxyl and hydroxyl groups of nanocellulose, constitute multiple adsorption sites for iodine molecules.

[0019] Ideal porous structure: The through-channels formed by directional freezing provide an ideal path for the rapid diffusion of iodine vapor, and the huge specific surface area greatly increases the contact area with iodine.

[0020] Multiple adsorption mechanisms: Physical adsorption (pore trapping, van der Waals forces) and chemical adsorption (complex formation, charge transfer, etc.) occur simultaneously between the material and iodine, and the synergistic effect ensures high adsorption performance.

[0021] 5. The process parameters are clearly defined, making it easy to scale up for industrial production. This invention provides clear and optimized parameter ranges for key preparation steps (such as the determination of the TEMPO oxidation endpoint, component ratio, freezing and crosslinking temperature and time, etc.), with a clear process flow and strong operability, laying a solid technical foundation for large-scale industrial production.

[0022] In summary, this invention successfully transforms waste biomass into a high-performance, high-value-added environmental functional material. Its preparation method is green and economical, and the final product shows great application potential in the field of iodine adsorption, combining both environmental and economic benefits. Attached Figure Description

[0023] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0024] Figure 1 Infrared spectra of CNF, CNF1 / CS1, CNF1 / CS2, CNF1 / CS3, CNF1 / CS4, CNF1 / CS5 and CS; Figure 2 SEM images and water stability images (h) of CNF aerogel (a), CNF1 / CS1 aerogel (b), CNF1 / CS2 aerogel (c), CNF1 / CS3 aerogel (d), CNF1 / CS4 aerogel (e), CNF1 / CS5 aerogel (f) and CS aerogel are shown for structural morphology characterization. Figure 3 Compressive strength (50%) of CNF, CNF1 / CS1, CNF1 / CS2, CNF1 / CS3, CNF1 / CS4, CNF1 / CS5 and CS aerogel; Figure 4 TG plots for CNF, CNF1 / CS1, CNF1 / CS2, CNF1 / CS3, CNF1 / CS4, CNF1 / CS5 aerogels and CS aerogels; Figure 5 XRD patterns of CNF, CNF1 / CS1, CNF1 / CS2, CNF1 / CS3, CNF1 / CS4, CNF1 / CS5 and CS aerogels; Figure 6 Porosity (a), density (b), and water absorption (g) of CNF1 / CS1 aerogel, CNF1 / CS2 aerogel, CNF1 / CS3 aerogel, CNF1 / CS4 aerogel, and CNF1 / CS5 aerogel. Figure 7 Comparison of the adsorption capacities of CNF, CNF1 / CS1, CNF1 / CS2, CNF1 / CS3, CNF1 / CS4, CNF1 / CS5 and CS aerogel; Figure 8 The effects of CNF1 / CS5 aerogel adsorption concentration on iodine adsorption (a) and adsorption time on iodine adsorption (b); Figure 9 The first-order kinetic linear fitting curve (a) and the second-order kinetic linear fitting curve (b) of iodine adsorption by CNF1 / CS5 aerogel are shown. Figure 10 The effect of CNF1 / CS5 aerogel adsorption time on iodine adsorption (a) and the amount of adsorption after recovery (b). Detailed Implementation

[0025] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0026] One aspect of the present invention relates to a method for preparing an aerogel, comprising the following steps: (a) Add sodium hypochlorite to a dispersion containing lignin-removed coffee grounds, sodium bromide, and TEMPO, and adjust the pH to 10-10.5 (e.g., a point value or a range between any two of 10, 10.1, 10.2, 10.3, 10.4, or 10.5, for example). When the pH of the dispersion remains constant for a period of time, add ethanol to quench the reaction. (b) The reaction system after the quenching reaction is completed is subjected to dialysis and dispersion treatment to obtain CNF dispersion; (c) The CNF dispersion and chitosan solution are mixed and then emulsified, stirred, directionally frozen, freeze-dried and cross-linked to obtain the aerogel.

[0027] The aforementioned aerogel preparation method uses waste coffee grounds as raw material and successfully prepares nanocellulose / chitosan aerogel through a green process. This preparation method does not require the use of toxic chemical cross-linking agents, avoiding secondary pollution. At the same time, through directional freezing and thermal cross-linking technology, the aerogel has a stable three-dimensional network structure and excellent mechanical properties, and can remain intact without collapsing in water. The prepared aerogel exhibits extremely high adsorption capacity for iodine (including radioactive iodine), and has excellent adsorption performance, environmental friendliness, and good recycling potential, providing an efficient, low-cost, and sustainable solution for the treatment of radioactive iodine.

[0028] Further, in step (a), the mass ratio of the coffee grounds, the sodium bromide, and the TEMPO is 20:2~4:0.4~0.8, including but not limited to 20:2:0.8, 20:3:0.6, or 20:4:0.4. This ratio ensures the optimal catalytic efficiency of the TEMPO oxidation system, guaranteeing a high degree of carboxylation of the nanocellulose while avoiding reagent waste and side reactions.

[0029] Further, in step (a), the sodium hypochlorite is added in solution form, and the mass ratio of the coffee grounds to the sodium hypochlorite solution is 20:56~60, including but not limited to 20:56, 20:57, 20:58, 20:57 or 20:60. This ratio provides a suitable amount of oxidant to ensure that the primary hydroxyl groups of cellulose are fully oxidized to carboxyl groups, thereby laying a solid foundation for subsequent cross-linking with chitosan. The available chlorine content in the sodium hypochlorite solution is ≥10wt%.

[0030] Furthermore, the time period is 10-12 minutes, including but not limited to a point value of any one of 10 minutes, 11 minutes, or 12 minutes, or a range between any two. Using pH stability for 10-12 minutes as the reaction endpoint criterion allows for precise control of the oxidation degree, preventing excessive oxidation that could lead to cellulose chain degradation, and ensuring the integrity and yield of nanocellulose.

[0031] Furthermore, the setpoint is 10~10.5, including but not limited to a point value or a range between any two of 10, 10.1, 10.2, 10.3, 10.4, or 10.5. Precisely maintaining the pH of the reaction system within this weakly alkaline range provides an optimal reaction environment for the TEMPO oxidation reaction, ensuring the high efficiency and selectivity of the oxidation process.

[0032] Further, in step (a), the ratio of coffee grounds to ethanol is 20g:20~25mL, including but not limited to 20g:20mL, 20g:21mL, 20g:24mL, or 20g:25mL. This amount of ethanol can quickly and completely terminate the oxidation reaction, fix the reaction product, and prevent uncontrollable changes in the properties of the product during subsequent processing.

[0033] Further, in step (c), the mass ratio of the CNF dispersion to the chitosan solution is 1:1 to 5, including but not limited to 1:1, 1:2, 1:3, 1:4, or 1:5. This ratio range is key to forming a stable three-dimensional network structure, which can significantly improve the adsorption capacity for iodine and the mechanical strength of the material by increasing the chitosan content while ensuring the porosity of the material.

[0034] Furthermore, the concentration of the CNF dispersion is 1.8wt% to 2.2wt%, including but not limited to any one of 1.8wt%, 1.9wt%, 2.0wt%, 2.1wt%, or 2.2wt%, or a range between any two. This concentration range ensures that the dispersion has a suitable viscosity, which facilitates processing and allows for uniform mixing with the chitosan solution to form a uniform aerogel framework.

[0035] Furthermore, the concentration of the chitosan solution is 1.8 wt% to 2.2 wt%, including but not limited to any one of 1.8 wt%, 1.9 wt%, 2.0 wt%, 2.1 wt%, or 2.2 wt%, or a range between any two. This concentration gives the chitosan solution suitable rheological properties, facilitates thorough compounding with the CNF dispersion, and ensures that the final aerogel product has ideal pore structure and mechanical properties.

[0036] Furthermore, the emulsification time is 1 to 3 minutes, including but not limited to a point value of 1 minute, 2 minutes, or 3 minutes, or a range between any two. Sufficient emulsification ensures uniform mixing of CNF and CS at the nano / micro scale, providing a guarantee for the formation of a homogeneous and stable composite gel precursor.

[0037] Furthermore, the stirring temperature is 38–42°C (e.g., any value or range between any two of 38°C, 39°C, 40°C, 41°C, or 42°C), and the stirring time is 4–4.5 h (e.g., any value or range between any two of 4 h, 4.1 h, 4.2 h, 4.3 h, 4.4 h, or 4.5 h). These mild heating and stirring conditions promote the initial interaction between CNF and CS molecular chains, laying the foundation for the formation of a uniform and stable gel network in the subsequent thermal crosslinking steps.

[0038] Furthermore, the cold source temperature for the directional freezing is -65 to -60°C (for example, it can be any one of -65°C, -64°C, -63°C, -61°C, or -60°C, or a range between any two), and the time is 1 to 1.5 hours (for example, it can be any one of 1 hour, 1.1 hours, 1.2 hours, 1.3 hours, 1.4 hours, or 1.5 hours, or a range between any two). This rapid, deep-cold directional freezing condition ensures that ice crystals grow in an orderly and uniform manner along the temperature gradient, thereby replicating a regular, interconnected layered porous structure in the aerogel, which is key to achieving efficient adsorption and excellent mechanical properties.

[0039] Furthermore, the crosslinking is performed under vacuum conditions at a temperature of 105–115°C (e.g., any value or range between any two of 105°C, 107°C, 109°C, 111°C, 113°C, or 115°C), for a time of 1–1.5 h (e.g., any value or range between any two of 1 h, 1.1 h, 1.2 h, 1.3 h, 1.4 h, or 1.5 h). The vacuum environment prevents oxidative degradation of the material at high temperatures, while this combination of temperature and time effectively drives the amidation condensation reaction between the carboxyl groups of CNF and the amino groups of CS, forming a stable covalent crosslinked network, significantly enhancing the water stability and mechanical strength of the aerogel.

[0040] Furthermore, the lignin removal includes the following steps: The mixture containing coffee grounds is heated and boiled continuously for 0.8 to 1.2 hours (for example, it can be any point value or any range between 0.8 hours, 0.9 hours, 1.0 hours, 1.1 hours or 1.2 hours, or any value between any two), and then washed, filtered and dried. The dried coffee grounds are subjected to alkaline washing in a 3wt% to 5wt% sodium hydroxide aqueous solution (e.g., any value of 3wt%, 4wt%, or 5wt%, or any range between two of these values) at a temperature of 90 to 95°C (e.g., any value of 90°C, 91°C, 92°C, 93°C, or 95°C, or any range between two of these values) for a time of 0.8 to 1.2 hours (e.g., any value of 0.8 hours, 0.9 hours, 1.0 hours, 1.1 hours, or 1.2 hours, or any range between two of these values). The alkali-washed coffee grounds are bleached, washed, and dried in a 3wt% to 5wt% sodium chlorite aqueous solution (e.g., any value of 3wt%, 4wt%, or 5wt%, or any range between two of these values). The bleaching pH is 4.2 to 4.4 (e.g., any value of 4.2, 4.3, or 4.4, or any range between two of these values), the bleaching temperature is 90 to 95°C (e.g., any value of 90°C, 91°C, 92°C, 93°C, or 95°C, or any range between two of these values), and the bleaching time is 1.8 to 2.2 hours (e.g., any value of 1.8 hours, 1.9 hours, 2.0 hours, 2.1 hours, or 2.2 hours, or any range between two of these values).

[0041] Another aspect of the present invention relates to aerogels prepared by the aforementioned method.

[0042] The aerogel described above possesses a stable three-dimensional network structure and excellent mechanical properties, allowing it to remain intact and not collapse in water, greatly enhancing its convenience and recyclability in practical aquatic environments. Simultaneously, this product exhibits an extremely high adsorption capacity for iodine vapor (up to 1642 mg / g), outperforming many traditional materials. Furthermore, due to its composition as natural biomass, it is environmentally friendly and non-toxic, providing a highly efficient, stable, and safe green adsorption material solution for nuclear waste treatment.

[0043] Another aspect of the present invention relates to a method for adsorbing iodine, wherein an aerogel prepared by the aforementioned aerogel preparation method or the aforementioned aerogel is used to adsorb iodine.

[0044] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0045] Example 1 (CNF1 / CS1) The aerogel preparation method provided in this embodiment includes the following steps: 1. Add 2000mL of deionized water to a beaker, then add 500g of coffee grounds, heat and stir until boiling for 1 hour, wash with deionized water, filter, and then put it in an 80℃ drying oven to dry for 24 hours. 2. Wash the coffee grounds three times with alkali. Take 250g of the washed and dried coffee grounds and wash them with 1000mL of 3wt% sodium hydroxide solution at 90℃ for 1 hour to remove the lignin from the coffee grounds. 3. The coffee grounds were bleached three times and mixed with 1000 mL of 3wt% sodium chlorite aqueous solution at a pH of 4.3 and a temperature of 90℃ for 2 hours to further extract the delignified sample. 4. Wash the bleached sample carefully with deionized water until neutral, and dry it in a 50℃ forced-air drying oven for 12 hours to obtain delignin-free coffee grounds (DSCG). 5. Take 20g of dried DSCG and disperse it in 300mL of deionized water. Add 2g of sodium bromide and 0.4g of TEMPO to the dispersion and mix evenly with mechanical stirring at 500r / min. 6. Slowly add 56g of sodium hypochlorite solution to the DSCG dispersion, and then adjust the pH of the system to 10-10.5 by adding 0.1M hydrochloric acid solution and 5wt% sodium hydroxide solution; 7. Continue the reaction at room temperature. When the pH of the dispersion remains constant between 10 and 10.05 for 10 minutes, add 20 mL of ethanol to quench the reaction. 8. Pour the above dispersion into a dialysis bag, dialyze it in deionized water until neutral, and then store it in a refrigerator at 4°C. After sonicating the dispersion for 10 minutes using a cell powder analyzer, CNF dispersion was successfully prepared. 9. Dilute the CNF dispersion to 2.0 wt%, dissolve the high-viscosity chitosan in 1% acetic acid solution to obtain a 2.0 wt% chitosan solution; mix the nanocellulose solution and chitosan solution uniformly at different mass ratios of 1:1, emulsify the mixture for 1 min using a high shear average emulsifier, and then stir at 40℃ for 4 h to ensure uniform dispersion. 10. Pour the above solution into a self-made cylindrical template with a copper plate at the bottom and a 3D-printed PLA mold on the side. The mold has a diameter of 3.2 cm and a height of 1 cm. Place the template on a cold source at -60℃ and freeze it directionally for 1 hour. 11. After complete directional freezing, place the product in a freeze dryer for 48 hours to freeze dry and obtain an uncrosslinked precursor; 12. The uncrosslinked precursor was placed in a vacuum oven at 110°C for 1 hour to thermally crosslink it, thus obtaining CNF / CS aerogel.

[0046] Example 2 (CNF1 / CS2) The only difference from Example 1 is step 9, where the mass ratio of nanocellulose solution to chitosan solution is 1:2.

[0047] Example 3 (CNF1 / CS3) The only difference from Example 1 is step 9, where the mass ratio of nanocellulose solution to chitosan solution is 1:3.

[0048] Example 4 (CNF1 / CS4) The only difference from Example 1 is step 9, where the mass ratio of nanocellulose solution to chitosan solution is 1:4.

[0049] Example 5 (CNF1 / CS5) The only difference from Example 1 is step 9, where the mass ratio of nanocellulose solution to chitosan solution is 1:5.

[0050] Comparative Example 1 The difference from Example 1 is that in step 9, chitosan solution was not added.

[0051] Comparative Example 2 Using only chitosan solution and without adding CNF dispersion, continue to prepare aerogels according to steps 9-12 of Example 1.

[0052] Experimental Example 1 The testing method is as follows: (1) Mechanical property testing The mechanical properties of aerogels were tested using a universal electronic testing machine (DWD-10H, Jinan Huaxing Experimental Equipment Co., Ltd.). The aerogel sample was placed in the center of the compression plate of the universal electronic testing machine. After adjusting the distance of the compression plate, the load, displacement, and strain on the display screen were zeroed. The sample was compressed at a rate of 1 mm / min to test its performance. The average value of the data from three samples in each group was taken.

[0053] (2) Determination of water absorption performance Immerse the aerogel thoroughly in 50 mL of water, then remove the aerogel and let it stand for a while until it stops dripping. Weigh the immersed aerogel again. Measure and calculate the water absorption of the aerogel using the following formula. W (g / g): ; in W 2 and W 1 represents the mass of a fully water-saturated aerogel and a dried aerogel, respectively.

[0054] (3) Determination of porosity Porosity was measured using anhydrous ethanol as the medium. The initial weight of the aerogel was measured. W 0, the weight of the sample after soaking in anhydrous ethanol for 24 hours is recorded as . W t The porosity was calculated using the following formula, repeated three times for each sample.

[0055] ; in P Porosity W 0 represents the initial weight of the aerogel. W t This represents the weight of the expanded aerogel. V 0 represents the initial volume of the aerogel, and ρ0 represents the density of the dehydrated alcohol (0.79 g / mL).

[0056] Fourier Infrared Characterization The amide condensation reaction between the carboxyl groups on nanocellulose and the amino groups in chitosan is beneficial for improving the mechanical stability of CNF / CS aerogel. Infrared spectroscopy analysis revealed that the characteristic diffraction pattern of the chitosan aerogel is mainly amide II bands, with the largest band at 1589 cm⁻¹. -1 The band at 1381 cm⁻¹ is an amide II band, mainly caused by in-plane bending vibrations of the N–H plane. -1 This corresponds to the stretching vibration of –CN, 1666cm. -1 The peak at 3480 cm⁻¹ is the stretching vibration peak of C–O. -1 The peaks at 3437 and 1560 cm⁻¹ represent the –OH stretching vibration. -1 The absorption peaks are for N–H tensile vibrations, at 1654 and 1315 cm⁻¹. -1 This is due to the C–N stretching vibration, indicating the formation of amide bonds between nanocellulose and chitosan, as shown in the following results. Figure 1 As shown.

[0057] Structural morphology characterization A mixture of nanocellulose and chitosan was sublimated and dehydrated at 110℃ to form an ultralight composite aerogel, the morphology of which was studied by SEM images. Figure 2 It was observed that oxidized cellulose can form molecules such as cellulose through intermolecular and intramolecular hydrogen bonds. Figure 2 The hollow structure shown in figure a. The resulting CNF aerogel is easily broken in water after freeze-drying. Figure 2h). Firstly, this is because nanocellulose itself possesses a hydrophilic carboxyl group. Secondly, when CNF comes into contact with water, it collapses due to the hydrogen bonding between the surface hydroxyl groups and water molecules. The crosslinking of CNF and CS is beneficial for improving mechanical strength and water absorption capacity, and it is extremely stable in water, maintaining its original structure without collapsing. Figure 2 h). Therefore, oxidation treatment of cellulose is necessary to achieve better bonding between cellulose and chitosan. CNF / CS aerogel exhibits both fibrous network and lamellar structures. Figure 2 (bf). Aerogels possess both fibrous network and sheet-like structures, with numerous honeycomb structures forming within the sheet-like structures. These network structures significantly enhance the stress transfer and energy dissipation properties of aerogels, thereby effectively strengthening their resistance to damage under external forces. CS aerogels have a layered structure ( Figure 2 g), is unstable in water, exhibits swelling, cannot maintain its original structure, is easily broken under pressure, and is not conducive to recycling. Figure 2 h). This shows that without CNFs, there can be no cross-linking between CNFs and CSs to construct the network structure. Therefore, CNFs play a crucial role in building and maintaining the integrity of the cellular network framework.

[0058] Mechanical property characterization The applicability of aerogels in practical engineering applications is greatly influenced by their mechanical properties, which are in turn related to their pore structure. This study systematically investigated the impact of porous structure characteristics on the mechanical properties of aerogels using compression testing. Compressive strength is an important indicator of an aerogel's resistance to failure under compressive loads; higher compressive strength indicates a more robust pore structure, enabling it to withstand greater external forces without damage. Figure 3 As shown, at 50% deformation, the compressive strengths of CNF, CNF1 / CS1, CNF1 / CS2, CNF1 / CS3, CNF1 / CS4, CNF1 / CS5, and CS aerogels are 26.96, 44.54, 56.75, 64.45, 70.15, 73.81, and 30.93 kPa, respectively. This indicates that CNF / CS aerogel has a higher compressive strength than CNF and CS aerogels, and the amide bonds formed by their combination greatly contribute to the improvement of the aerogel's mechanical properties.

[0059] Thermal stability performance characterization Thermogravimetric analysis (TGA) can provide some understanding of a material's thermal stability. For example... Figure 4 These are the thermogravimetric analyses (TGAs) of seven aerogels: CNF, CNF1 / CS1, CNF1 / CS2, CNF1 / CS3, CNF1 / CS4, CNF1 / CS5, and CS. Figure 4It can be seen that CS aerogel experiences an initial weight loss of 22% at around 100°C, with the maximum weight loss occurring at around 290°C. CNF aerogel experiences an initial weight loss of 14% at around 100°C, with the maximum weight loss occurring at around 255°C. CNF / CS aerogels both experience an initial weight loss of 19% at around 100°C, with the maximum weight loss occurring at around 280°C. The initial weight loss and maximum decomposition temperature of CNF / CS aerogel fall between those of CS and CNF aerogels. The initial weight loss may be due to the reduction of hydrophilic groups caused by the cross-linking of amino and carboxyl groups. However, the thermal stability of CNF / CS aerogel is lower than that of CS aerogel because the introduction of cellulose carboxyl groups disrupts the tight packing of some chitosan molecular chains, weakening the hydrogen bond network.

[0060] X-ray diffraction spectroscopy characterization Figure 5 XRD patterns of seven aerogels (CNF, CNF1 / CS1, CNF1 / CS2, CNF1 / CS3, CNF1 / CS4, CNF1 / CS5, and CS) are shown. XRD analysis revealed that the cellulose aerogel exhibited characteristic diffraction peaks at 11.83° (101 crystal plane), 19.89° (110 crystal plane), and 21.28° (020 crystal plane), confirming its typical cellulose type I crystal structure. The chitosan diffraction pattern showed broadened diffraction peaks at 19.51° (120 crystal plane) and 19.81° (110 crystal plane), indicating that it mainly exists in an amorphous form. Notably, after cross-linking, the diffraction peak positions remained largely unchanged, but the intensity of the crystalline peaks decreased. This phenomenon is attributed to the amide bonds formed during cross-linking disrupting the ordered arrangement of the molecular chains, leading to the disordering of some crystalline regions.

[0061] Characterization of porosity, density, and water absorption properties Since both CNF and CS aerogels are unstable in water and cannot maintain their original structural state, it is essential to crosslink them to prepare stable CNF / CS aerogels. Next, the density, porosity, and water absorption of CNF1 / CS1, CNF1 / CS2, CNF1 / CS3, CNF1 / CS4, and CNF1 / CS5 aerogels were tested. Figure 6 As the chitosan content increased, the porosity of the CNF / CS aerogel decreased from 92.28% to 87.52%. Figure 6 a). However, the density of the aerogel pore structure is gradually increasing, with its apparent density increasing from 30.91 mg / cm³ for CNF1 / CS1 aerogel. 3 Increased to 39.12 mg / cm³ of CNF1 / CS5 aerogel. 3 ( Figure 6(b) This dense structure enhances the mechanical properties of the aerogel, giving it greater load-bearing capacity. Simultaneously, as the amount of chitosan covering the pores increases, the material's hydrophilicity also improves. Figure 6 c).

[0062] Experiment Example 2 Because radioactive iodine poses certain hazards to the human body and the environment, this experimental example uses iodine with the same number of protons to replace radioactive iodine to avoid the harm of pollutants. The aerogel's adsorption capacity for ordinary iodine is equivalent to that of radioactive iodine.

[0063] Adsorption behavior of gaseous iodine (I2) Gravimetric analysis is a common method for evaluating the iodine vapor capture efficiency of adsorbents. The iodine capture capacity of CNF / CS aerogel was estimated using gravimetric measurements. Iodine vapor adsorption experiments were conducted at atmospheric pressure and 80°C. Before adsorption, the sample and vials were vacuum-dried at 80°C for 24 hours to remove moisture and residual solvent. 20 mg samples were weighed on a balance with an accuracy of 0.01 mg and placed in pre-weighed glass vials (10 mL). The vials were then placed in a larger, sealed vial (30 mL) containing more than 10 times the molecular weight of iodine and stored in a forced-air drying oven at 80°C. At regular intervals, the vials were removed, cooled to room temperature, and weighed. To minimize error, three parallel experiments were performed, and the average value was used to calculate the iodine absorption. q (mg / g) is calculated using the following formula: ; in m 0 and m 1 represents the mass of the sample before and after iodine capture, respectively.

[0064] Study on the adsorption performance of iodine in solution The following steps were used to determine the iodine adsorption performance of CNF1 / CS5 aerogel in solvent: First, iodine crystals were accurately weighed and dissolved in cyclohexane solution to prepare a 0.5 mg / mL standard iodine solution. 20 mg of CNF1 / CS5 aerogel was placed in a 10 mL glass reaction flask, and 3 mL of the above iodine solution was added. The adsorption experiment was conducted at a constant temperature of (25 ± 0.5) ℃. After the predetermined time, the reaction solution was filtered. The absorbance of the filtrate was measured at a characteristic wavelength of 522 nm using a UV-Vis spectrophotometer. Based on the pre-established iodine standard curve (concentration-absorbance relationship), the residual iodine concentration in the solution was calculated. The iodine adsorption capacity of CNF1 / CS5 aerogel was determined by material balance (initial iodine content - residual iodine content) using the following formula: ; in, C0 (mg / mL) is the initial concentration (0.5 mg / mL) and C t (mg / mL) represents the concentration at time t; V (mL) is the volume of the solution; m This represents the amount of adsorbent (mg).

[0065] Plotting absorption curves and standard curves The absorption spectra of iodine / cyclohexane solutions were determined using ultraviolet-visible spectrophotometry. First, a series of iodine / cyclohexane standard solutions with concentration gradients of 0.2, 0.4, 0.6, 0.8, and 1.0 mg / mL were precisely prepared. Using a UV-Vis spectrophotometer, with pure cyclohexane as a blank reference, and a 1 cm path length quartz cuvette, the absorbance of each concentration solution was measured within the wavelength range of 200–800 nm. Finally, the UV-Vis absorption spectra of the standard solutions were plotted with wavelength on the x-axis and absorbance on the y-axis for subsequent analysis.

[0066] UV-Vis absorption spectroscopy revealed a characteristic absorption peak (λmax = 522 nm) in the iodine / cyclohexane solution. According to the Lambert-Beer law, the absorbance at this wavelength exhibits a good linear relationship with the iodine concentration. A standard working curve was established by measuring the absorbance of a series of standard solutions at λmax, demonstrating excellent linear correlation (R0). 2 >0.99), laying a reliable foundation for subsequent quantitative analysis.

[0067] Determination of iodine concentration in solution The experiment used ultraviolet-visible spectrophotometry to determine the iodine concentration. First, using pure cyclohexane as a blank reference, the wavelength range of 250–800 nm was scanned to obtain the ultraviolet-visible absorption spectrum of the test solution. The absorbance value y at this characteristic wavelength was recorded and substituted into a pre-established absorbance-concentration standard curve for quantitative analysis. Based on the linear relationship of Lambert-Beer's law, the corresponding iodine concentration x in the test solution can be accurately obtained by back-calculating from the absorbance value y. This value is the iodine concentration in the test solution.

[0068] Study on the adsorption properties of composite aerogels Using the CS aerogel, CNF aerogel, and CNF / CS aerogel prepared above as adsorbents, the adsorption results for a constant amount of iodine vapor in a simulated gaseous environment showed that... Figure 7As can be seen, CNF aerogel has a weak adsorption capacity for iodine, with an adsorption capacity of only 58.5 mg / g. With the increase of CS content in the aerogel, the adsorption capacity rapidly increases from 1068 mg / g for CNF1 / CS1 to 1514 mg / g for CNF1 / CS4, and reaches 1642 mg / g for CNF1 / CS5, comparable to the adsorption capacity of CS aerogel (1645 mg / g). This indicates that constructing composite aerogels is feasible. Compared with the other six aerogels, it not only exhibits excellent adsorption capacity but also superior performance. The superior iodine adsorption performance of CNF1 / CS5 may be due to the increased amount of available chitosan, which provides a sufficient number of amino groups on the aerogel surface, thus providing more adsorption sites. On the other hand, this is also related to the three-dimensional honeycomb network of CNF1 / CS5, which increases the contact area between the aerogel and iodine.

[0069] Study on the adsorption performance of iodine in solution First, find the optimal concentration for adsorption by this suitable material, from... Figure 8 As shown in Figure a, the adsorption rate increases rapidly from 0.1 mg / mL to 0.5 mg / mL. However, adsorption slows down when the concentration exceeds 0.5 mg / mL. Therefore, a concentration of 0.5 mg / mL was chosen for subsequent adsorption experiments. Further analysis of the adsorption kinetic curves (…) Figure 8 (b) It was found that the adsorption process of CNF1 / CS5 aerogel can be divided into two distinct stages. In the first 48 hours, the adsorption capacity increases over time, eventually reaching an equilibrium adsorption capacity of 104 mg / g (maximum adsorption capacity 107 mg / g). This kinetic behavior is likely mainly due to the abundant active sites on the material surface in the initial stage, which promotes rapid adsorption. As the adsorption sites are gradually occupied, the number of available active sites decreases, leading to a significant decrease in the adsorption rate in the later stage, eventually reaching a dynamic equilibrium.

[0070] To further elucidate the iodine adsorption mechanism of CNF1 / CS5 aerogel, this study employed pseudo-first-order and pseudo-second-order kinetic models for nonlinear fitting analysis of the experimental data. Specifically, the high correlation of the pseudo-first-order kinetics reflects the contribution of physisorption, while the good fit of the pseudo-second-order kinetics confirms the important role of chemisorption. For example... Figure 9 As shown, both dynamic models exhibit good fit (R²). 2 The coefficients of determination (>0.95) are similar. This phenomenon indicates that the adsorption process follows both pseudo-first-order and pseudo-second-order kinetics, confirming that the adsorption of iodine by CNF1 / CS5 aerogel is the result of the synergistic effect of physical and chemical adsorption.

[0071] Cyclic performance study of CNF1 / CS5 composite aerogel The iodine-containing CNF1 / CS5 aerogel was immersed twice in 20 mL of ethanol at room temperature for 6 hours each time, then vacuum dried at 80 °C, and the experiment was repeated. The analytical results for material reuse are as follows: Figure 10 As shown, after the third cycle, the CNF1 / CS5 aerogel weight gain ratio still increased by 63%.

[0072] Although the present invention has been illustrated and described with specific embodiments, it should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, without departing from the spirit and scope of the present invention; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing an aerogel, characterized in that, Includes the following steps: (a) Add sodium hypochlorite to a dispersion containing lignin-removed coffee grounds, sodium bromide and TEMPO, adjust the pH to 10-10.5, and when the pH of the dispersion remains constant for a period of time, add ethanol to quench the reaction. (b) The reaction system after the quenching reaction is completed is subjected to dialysis and dispersion treatment to obtain CNF dispersion; (c) The CNF dispersion and chitosan solution are mixed and then emulsified, stirred, directionally frozen, freeze-dried and cross-linked to obtain the aerogel.

2. The method for preparing aerogel according to claim 1, characterized in that, In step (a), the mass ratio of the coffee grounds, the sodium bromide, and the TEMPO is 20:2~4:0.4~0.8; And / or, in step (a), the sodium hypochlorite is added in the form of a solution, and the mass ratio of the coffee grounds to the sodium hypochlorite solution is 20:56~60.

3. The method for preparing aerogel according to claim 1, characterized in that, The time period is 10-12 minutes; And / or, the set value is 10~10.

5.

4. The method for preparing aerogel according to claim 1, characterized in that, In step (a), the ratio of coffee grounds to ethanol is 20g: 20~25mL; And / or, in step (c), the mass ratio of the CNF dispersion to the chitosan solution is 1:1~5.

5. The method for preparing aerogel according to claim 1, characterized in that, The concentration of the CNF dispersion is 1.8wt%~2.2wt%; And / or, the concentration of the chitosan solution is 1.8wt%~2.2wt%.

6. The method for preparing aerogel according to claim 1, characterized in that, The emulsification time is 1-3 minutes; And / or, the stirring temperature is 38~42℃, and the stirring time is 4~4.5h.

7. The method for preparing aerogel according to claim 1, characterized in that, The cold source temperature for the directional freezing is -65 to -60°C, and the time is 1 to 1.5 hours.

8. The method for preparing aerogel according to claim 1, characterized in that, The crosslinking is carried out under vacuum conditions at a temperature of 105~115℃ for 1~1.5h.

9. The aerogel prepared by the method of any one of claims 1 to 8.

10. A method for adsorbing iodine, characterized in that, The aerogel prepared by the method of any one of claims 1 to 8 or the aerogel of claim 9 adsorbs iodine.

Images