Nanocellulose composite aerogel as well as preparation method and application thereof

Abstract

The invention discloses nanocellulose composite aerogel as well as a preparation method and application thereof. The preparation method comprises the following steps: 1) reacting cellulose, sodium periodate and sodium hydrogen sulfite in a first solvent to obtain modified cellulose; 2) dissolving the modified cellulose in a second solvent, and performing ultrasonic treatment; and 3) mixing the product obtained in the step 2) with a metal salt of the MOF material, then adding an organic ligand of the MOF material and a surfactant for reaction, dissolving the reaction product in a third solvent, and drying to obtain the composite aerogel. Modified cellulose is used as a supporting material, metal ions of an MOF material are adsorbed on cellulose in situ, then organic ligand liquid of the MOF material is added, and a surfactant is added for regulation and control to promote in-situ nucleation and ordered growth of MOF on cellulose, so that the effect of adsorbing methylene blue in the environment is comprehensively improved.

Description

Technical Field

[0001] This invention relates to the field of inorganic materials technology, specifically to a nanocellulose composite aerogel, its preparation method, and its applications. Background Technology

[0002] Metal-organic frameworks (MOFs) are porous crystalline materials with periodic networks formed by the self-assembly of metal ions or metal clusters with organic ligands through coordination bonds. They have high porosity and large specific surface area, and the pore size and specific surface area can be adjusted by different ligand compositions. They have wide applications in gas isolation storage, drug delivery, sensing and catalysis.

[0003] Cellulose is a natural, renewable polymer material that is readily functionalized. In particular, the abundant hydroxyl groups in cellulose molecules can graft other functional groups, and it readily combines with metal ions or ligands to form functionally stable composite materials.

[0004] There are two main methods for combining MOF materials with cellulose. One is the direct loading method, which involves pre-synthesizing the MOF material and adding it to a cellulose precursor solution. This method is simple to operate, but the MOF material is prone to aggregation. The second method is the in-situ growth method, which involves immersing cellulose in a solution containing organic ligands and metal ions to grow MOFs in situ on the cellulose. This method reduces the amount of synthesized MOF material and decreases the degree of MOF aggregation. However, MOFs are usually difficult to grow on a surface and are therefore often grown under high temperature and high pressure conditions.

[0005] CN119386835A discloses a method for in-situ synthesis of MOFs at low temperature by adding cellulose and MOF growth solution to water, resulting in a cellulose-based MOF composite aerogel. The method involves pretreating cellulose with TEMPO, NaBr, and NaClO, then adding organic ligands of MOFs, followed by a crosslinking reaction with a metal salt of MOF and polyethyleneimine (PEI) to obtain the cellulose-based MOF composite aerogel. However, the pretreatment of cellulose in this patent under an alkaline environment leads to a decrease in mechanical properties.

[0006] Nevertheless, the challenges of in-situ MOF construction on cellulose include: (1) cellulose has limited surface active sites due to lack of modification, making it difficult to form effective chemical bonds with MOFs, resulting in low grafting efficiency. (2) Existing grafting techniques often employ physical doping or post-modification grafting of pre-synthesized MOFs, but this method often leads to unstable performance due to physical aggregation of MOF particles or weak interfacial bonding, making it difficult to achieve precise structural control in the later stages. (3) In-situ growth of MOFs on nanocellulose often results in problems such as disordered nucleation and uncontrollable morphology. Summary of the Invention

[0007] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a nanocellulose composite aerogel, its preparation method and uses.

[0008] To achieve the above and other related objectives, the present invention is obtained through the following technical solution.

[0009] The first aspect of this invention protects a method for preparing a nanocellulose composite aerogel, comprising the following steps:

[0010] 1) Cellulose, sodium periodate, and sodium bisulfite are reacted in the first solvent to obtain modified cellulose;

[0011] 2) Dissolve the modified cellulose in a second solvent and treat with ultrasound;

[0012] 3) Mix the ultrasonically treated product obtained in step 2) with the metal salt of MOF material, then add the organic ligand and surfactant of MOF material to react, dissolve the reaction product in a third solvent, and dry to obtain the nanocellulose composite aerogel.

[0013] The second aspect of this invention protects nanocellulose composite aerogels prepared by the method described above.

[0014] A third aspect of this invention protects the use of the aforementioned nanocellulose composite aerogel as an adsorbent material in the treatment of methylene blue in the environment.

[0015] A fourth aspect of the present invention protects a method for treating methylene blue in the environment, comprising: adding nanocellulose composite aerogel as described above into the environment.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] 1) This invention utilizes sodium periodate to oxidize the hydroxyl groups at C2 and C3 of the glucose units in cellulose to aldehyde groups, generating highly reactive dialdehyde cellulose (i.e., oxidized cellulose). The aldehyde group (-CHO) of dialdehyde cellulose serves as the reactive site, and the sulfite ion (HSO3) generated by the dissociation of dialdehyde cellulose in water with sodium bisulfite... - Furthermore, stable sulfonic acid groups (-SO3H) are formed. The sulfonated cellulose has high acidity sulfonic acid groups, which significantly improves the surface activity of cellulose.

[0018] 2) This invention uses modified cellulose as a supporting material. Metal ions from the MOF material are adsorbed in situ onto the cellulose, and then an organic ligand solution of the MOF material is added. Surfactants are added to regulate the in-situ nucleation and orderly growth of the MOF on the cellulose. Compared with traditional physical doping or post-modification grafting, the composite aerogel of this invention exhibits stable performance due to the strong binding force between the MOF particles and cellulose.

[0019] 3) The nanocellulose composite aerogel of the present invention is obtained by in-situ growth of MOF on modified cellulose. The experimental method is simple and the reaction conditions are mild.

[0020] 4) The nanocellulose composite aerogel of the present invention can be used to adsorb methylene blue with excellent adsorption effect and has broad application potential. Attached Figure Description

[0021] Figure 1A This is a photograph of the nanocellulose composite aerogel prepared in Example 1 of the present invention.

[0022] Figure 1B This is a scanning electron microscope image of the nanocellulose composite aerogel prepared in Example 1 of the present invention.

[0023] Figure 1C This is a scanning electron microscope image of the nanocellulose composite aerogel prepared in Example 1 of the present invention.

[0024] Figure 2 This is a scanning electron microscope image of the nanocellulose composite aerogel prepared in Comparative Example 1 of the present invention.

[0025] Figure 3 This is a scanning electron microscope image of the nanocellulose composite aerogel prepared in Comparative Example 2 of the present invention.

[0026] Figure 4 This is a scanning electron microscope image of the nanocellulose composite aerogel prepared in Comparative Example 3 of the present invention.

[0027] Figure 5 This is a scanning electron microscope image of the nanocellulose composite aerogel prepared in Comparative Example 4 of the present invention.

[0028] Figure 6 This is a scanning electron microscope image of the nanocellulose composite aerogel prepared in Comparative Example 5 of the present invention.

[0029] Figure 7 Line graphs showing the adsorption effect of the final products prepared in Example 1 and Comparative Examples 1-11 of the present invention on the adsorption of methylene blue in water. Detailed Implementation

[0030] The first aspect of this invention protects a method for preparing a nanocellulose composite aerogel, comprising the following steps:

[0031] 1) Cellulose, sodium periodate, and sodium bisulfite are reacted in the first solvent to obtain modified cellulose;

[0032] 2) Dissolve the modified cellulose in a second solvent and treat with ultrasound;

[0033] 3) The ultrasonically treated product obtained in step 2) is mixed with the metal salt of MOF material, and the reaction is carried out by adding organic ligands and surfactants of MOF material. The resulting reaction product is dissolved in a third solvent and dried to obtain the nanocellulose composite aerogel.

[0034] This invention utilizes sodium periodate to oxidize the hydroxyl groups at C2 and C3 of the glucose units in cellulose to aldehyde groups, generating highly reactive dialdehyde cellulose (i.e., oxidized cellulose). The aldehyde group (-CHO) of dialdehyde cellulose serves as the reactive site, oxidizing the sulfite ion (HSO3). - (It is generated by the dissociation of sodium bisulfite in water) further forms stable sulfonic acid groups (-SO3H). The sulfonated cellulose has high acidity sulfonic acid groups, which significantly improves the surface activity of cellulose. Then, by adding surfactants, the MOF is induced to nucleate and grow in situ on cellulose in an orderly manner, and can subsequently effectively adsorb methylene blue in the environment, reducing the color of wastewater.

[0035] In some embodiments, the mass ratio of cellulose, sodium periodate, and sodium bisulfite is 1:(2-8):(2-6). Preferably, it is 1:4.14:3.42.

[0036] In some embodiments, the first solvent is selected from water.

[0037] In some embodiments, the cellulose and sodium periodate are first oxidized and then sulfonated with sodium bisulfite.

[0038] In some embodiments, the oxidation reaction time is 10-26 h, or it can be 10-16 h, or it can be 15-22 h, or it can be 18-26 h, or it can be 10, 14, 16, 19, 20, 22, 23, 25, or 26 h.

[0039] In some embodiments, the temperature of the oxidation reaction is 20-55°C, or it can be 20-35°C, or it can be 30-45°C, or it can be 40-55°C, or it can be 20, 25, 28, 30, 35, 40, 45, 50, or 55°C.

[0040] In some embodiments, the sulfonation reaction time is 30-42 hours, or it can be 30-38 hours, or it can be 35-42 hours, or it can be 30, 35, 40, 41, or 42 hours.

[0041] In some embodiments, the sulfonation reaction temperature is 20-55°C, or it can be 20-35°C, or it can be 30-45°C, or it can be 40-55°C, or it can be 20, 25, 28, 30, 35, 40, 45, 50, or 55°C.

[0042] In some specific embodiments, the oxidation reaction and the sulfonation reaction may be at the same or different temperatures. Those skilled in the art can adjust them according to actual needs so that cellulose is completely oxidized to dialdehyde cellulose (i.e., oxidized cellulose).

[0043] In some embodiments, the sulfonation reaction is followed by centrifugation and washing.

[0044] In some embodiments, the second solvent is selected from methanol. Replacing the aqueous solution of modified cellulose with a methanol solution provides a milder environment for MOF growth, making the MOF material more stable and easier to nucleate in methanol.

[0045] In some embodiments, the ultrasonic treatment time is 5-10 min, or it can be 5-8 min, 7-10 min, or 5, 6, 7, 8, 9, or 10 min. This invention uses ultrasonic treatment to physically decellulose, exposing more hydroxyl groups on the cellulose surface for chemical modification and adsorption of more MOF materials.

[0046] In some embodiments, the organic ligand is selected from 1,3,5-benzenetricarboxylic acid or dimethylimidazole.

[0047] In some embodiments, the metal salt is selected from cobalt salts, zinc salts, or copper salts. The zinc ions (Zn) 2+ ZIF-8 is formed by the coordination and self-assembly of cobalt ions (Co) with 2-methylimidazole; 2+ ZIF-67 is formed by the coordination and self-assembly of copper ions (Cu) with 2-methylimidazole; 2+ HKUST-1 is formed by self-assembly of the organic ligand 1,3,5-benzenetricarboxylic acid (BTC) via coordination bonds.

[0048] In some embodiments, the cobalt salt is selected from one or more of cobalt nitrate, cobalt sulfate, and cobalt hydrochloride.

[0049] In some embodiments, the zinc salt is selected from one or more of zinc nitrate, zinc sulfate, and zinc hydrochloride.

[0050] In some embodiments, the copper salt is selected from one or more of copper nitrate, copper sulfate, and copper hydrochloride.

[0051] In some embodiments, the mass ratio of the modified cellulose to the metal salt is 1:(1-8). Preferably, it is 1:5.8.

[0052] In some embodiments, the molar ratio of the metal salt to the organic ligand is 1:(1-8). Preferably, it is 1:2.

[0053] In some embodiments, the surfactant is selected from one or both of CTAB and triethylamine. The addition of CTAB in this invention is beneficial for controlling the morphology of MOFs and forming smaller MOF particles. For example, different crystal faces of ZIF-67 crystals have different surface energies and exposed atoms. The addition of CTAB preferentially adsorbs on high-energy crystal faces, reducing their growth rate, while low-energy crystal faces grow faster, leading to a morphology change. Furthermore, the cationic head group of CTAB (CTA)... + Co is adsorbed onto the crystal surface through electrostatic attraction or coordination, occupying growth sites and hindering growth. 2+ The ions and 2-methylimidazole ligands further coordinate polymerization. This leads to a slower growth rate and a significant reduction in particle size after nucleation.

[0054] In some embodiments, the molar ratio of the metal salt to the surfactant is (5–40):1. Preferably, it is 10:0.57.

[0055] In some embodiments, the third solvent is selected from tert-butanol. After the MOF material is grown in situ on modified cellulose in a methanol system, it needs to be freeze-dried (water-treated) to form a uniformly dispersed aerogel with abundant pores. Tert-butanol is suitable as a displacement solvent to form an aqueous system. The nonpolar effect of tert-butanol disrupts the formation of hydrogen bonds between water molecules and cellulose hydroxyl groups, thereby effectively avoiding the formation of large ice crystals. It also has a high freezing temperature of 25°C and a higher saturated vapor pressure than water, which can accelerate the sublimation rate and shorten the drying time. Therefore, the addition of tert-butanol helps the gel drying process.

[0056] In some embodiments, the drying is selected from freeze-drying or supercritical drying. The freeze-drying pressure is 20-30 Pa. Freeze-drying is widely used in the preparation of cellulose aerogels due to its advantages such as safety, economy, and simple operation. It achieves drying by freezing and sublimating the solvent in the pores of the cellulose gel. However, the growth of large ice crystals during the drying process can damage the three-dimensional porous structure of the aerogel; therefore, the addition of tert-butanol can play a protective role.

[0057] In some embodiments, the freeze-drying temperature is -60 to -50°C, or it can be -60, -58, -55, -53, -52, or -50°C.

[0058] In some embodiments, the freeze-drying time is 36 to 48 hours, or it can be 36, 37, 38, 40, 42, 44, 46, or 48 hours.

[0059] In some embodiments, the drying process also includes a pre-cooling treatment.

[0060] In some embodiments, the temperature of the cold treatment is -30 to -20°C, or it can be -30, -28, -25, -23, -22, or -20°C.

[0061] In some embodiments, the cold treatment time is 8-12 hours, or it can be 8, 9, 10, 11, or 12 hours.

[0062] In some embodiments, the cellulose is obtained by extracting sawdust powder selected from poplar wood. The sawdust powder is passed through a 60-mesh sieve.

[0063] In some embodiments, the extraction of sawdust powder includes the following steps: 1) extracting sawdust powder in phenylethanol to obtain an extract; 2) treating the extract with sodium chlorite to remove hemicellulose to obtain substance A; 3) treating substance A with sodium hydroxide to obtain substance B; 4) treating substance B with sodium chlorite, and then adding sodium hydroxide for further treatment to obtain alkali-treated cellulose; 5) mixing the alkali-treated cellulose with water and ultrasonically treating it to obtain nanofibers.

[0064] In some specific embodiments, the power of the ultrasonic treatment is 1200W.

[0065] In some specific embodiments, the ultrasonic treatment time is 30 minutes.

[0066] The second aspect of this invention protects nanocellulose composite aerogels prepared by the method described above.

[0067] Compared to natural cellulose, the nanocellulose composite aerogel of this invention exhibits stronger adsorption capacity. Compared to common porous adsorption materials such as activated carbon, the nanocellulose composite aerogel of this invention is lower in cost and more reproducible.

[0068] A third aspect of this invention protects the use of the nanocellulose composite aerogel as described above as an adsorbent material for treating methylene blue in the environment.

[0069] A fourth aspect of the present invention protects a method for treating methylene blue in the environment, comprising: adding nanocellulose composite aerogel as described above into the environment.

[0070] In some embodiments, the environment includes one or more of water, soil, and aquatic sediments.

[0071] In some embodiments, the amount of nanocellulose composite aerogel added is 10-40 mg / mL, 10-22 mg / mL, 21-32 mg / mL, or 30-40 mg / mL, based on the volume of water.

[0072] In summary, the nanocellulose composite aerogel of the present invention, through pre-modification followed by loading of MOF materials, and synergistic treatment with ultrasonication and the addition of surfactants, exposes more active sites in cellulose and grows more MOF materials in situ, thereby improving the adsorption efficiency of methylene blue.

[0073] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0074] Before further describing specific embodiments of the present invention, it should be understood that the scope of protection of the present invention is not limited to the specific embodiments described below; it should also be understood that the terminology used in the embodiments of the present invention is for describing specific embodiments and not for limiting the scope of protection of the present invention; in the specification and claims of the present invention, unless otherwise expressly stated in the text, the singular forms "a", "an" and "this" include the plural forms.

[0075] When numerical ranges are given in the embodiments, it should be understood that, unless otherwise stated in the present invention, both endpoints of each numerical range and any value between the two endpoints may be selected. Unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art. In addition to the specific methods, apparatus, and materials used in the embodiments, based on the knowledge of the prior art possessed by one of ordinary skill in the art and the description of this invention, any prior art methods, apparatus, and materials similar to or equivalent to those described, apparatus, and materials in the embodiments of this invention may be used to implement the present invention.

[0076] In the following examples and comparative examples, cellulose was extracted from poplar powder. Before use, it underwent ultrasonic treatment for 30 minutes, repeated every 10 minutes for a total of three treatments. The cell disruptor was operated at approximately 80% power.

[0077] Example 1

[0078] Example 1 provides a nanocellulose composite aerogel, in which ZIF-67 is grown in situ on modified cellulose; the preparation method includes the following steps:

[0079] 1.1 A 0.25 wt% (solid content) cellulose suspension was prepared by mixing 100 g of 1 wt% (solid content 1 wt%) cellulose suspension with 300 g of 1.38 wt% (solid content 1.38 wt%) sodium periodate suspension. The suspension was stirred at 700 r / min for 18 h under light-protected conditions. After centrifugation at 8000 r / min, the precipitate was washed three times with deionized water to obtain oxidized cellulose. The oxidized cellulose was then dispersed in deionized water to obtain an oxidized cellulose aqueous solution. 3.42 g of sodium bisulfite was dissolved in deionized water and added to the oxidized cellulose aqueous solution to prepare an oxidized cellulose suspension with a solid content of 1 wt%. The suspension was then continuously stirred at 700 r / min for 36 h for sulfonation. After centrifugation at 8000 r / min, the precipitate was washed four times with deionized water and redispersed in deionized water to obtain an aqueous solution of modified cellulose.

[0080] 1.2 The modified cellulose aqueous solution was replaced with methanol solution to prepare a modified cellulose methanol suspension with a solid content of 0.5 wt%, and then ultrasonically dispersed in an ultrasonic cleaner for 30 min.

[0081] 1.3 Then, add a methanol solution of cobalt nitrate, sonicate for 5 minutes, and stir to react for 6 hours. After the reaction is complete, wash the solution with methanol by centrifugation to remove excess Co. 2+ The cellulose was reconstituted into a methanol suspension with a solid content of 0.5 wt%, yielding mixed solution A. A methanol solution of dimethylimidazole was added to mixed solution A in three batches, with a 1-hour interval between each batch. After thorough mixing with the ligand solution, a methanol solution of CTAB was added, and the mixture was stirred continuously at 700 rpm for 24 hours. After the reaction was complete, the solution was washed three times with methanol to obtain the reaction product.

[0082] The methanol solution of dimethylimidazole was obtained by dissolving 20 mmol of dimethylimidazole in 100 mL of methanol; the aqueous solution of cobalt nitrate was obtained by dissolving 10 mmol of cobalt nitrate hexahydrate in 100 mL of methanol; the methanol solution of CTAB was obtained by dissolving 0.57 mmol of hexadecyltrimethylammonium bromide in 50 mL of methanol; and the mass ratio between modified cellulose and cobalt nitrate was 1:5.8.

[0083] 1.4. The reaction product obtained in step 1.3 was redispersed in 50 mL of tert-butanol, stirred thoroughly, and centrifuged twice to completely replace the solvent with tert-butanol, thus preparing a tert-butanol suspension with a solid content of 1 wt%. Then, it was pre-treated by freezing at -20°C for 10 h, followed by freeze-drying at a pressure of 25 Pa and a cold trap temperature of -53°C for 40 h to obtain the final product, nanocellulose composite aerogel.

[0084] Figure 1A This is a photograph of the aerogel obtained after freeze-drying in Example 1.

[0085] Figure 1B and 1C This is a scanning electron microscope image of the nanocellulose composite aerogel prepared in Example 1.

[0086] from Figure 1A-1C It can be seen that after 24 hours of growth, more MOF particles grew in situ. Figure 1B , 1C The box represents MOF particles on the surface of modified cellulose, while the integrity of the porous structure of the nanocellulose composite aerogel is well maintained, which is beneficial for the subsequent adsorption of pollutants in the environment.

[0087] Example 2

[0088] Example 2 provides a nanocellulose composite aerogel, in which ZIF-8 is grown in situ on modified cellulose; the preparation method includes the following steps:

[0089] 1.1 A cellulose suspension with a solid content of 1 wt% was mixed with 300 g of sodium periodate solution with a solid content of 1.38 wt% to form a cellulose suspension with a solid content of 0.25 wt%. The suspension was stirred at 700 r / min for 18 h under light-protected conditions. After the reaction, the cellulose was washed three times by centrifugation at 8000 r / min with deionized water. The precipitate was oxidized cellulose, which was dispersed in deionized water to obtain an oxidized cellulose aqueous solution. 3.42 g of sodium bisulfite was dissolved in deionized water and added to the oxidized cellulose aqueous solution to prepare a cellulose suspension with a solid content of 1 wt%. The suspension was stirred continuously at 700 r / min for sulfonation reaction for 36 h. After the reaction, the cellulose was washed four times by centrifugation at 8000 r / min with deionized water and redispersed in deionized water to obtain an aqueous solution of modified cellulose.

[0090] 1.2 The modified cellulose aqueous solution was replaced with methanol solution to prepare a modified cellulose methanol suspension with a solid content of 0.5 wt%, and then ultrasonically dispersed in an ultrasonic cleaner for 30 min.

[0091] 1.3 Add an aqueous solution of zinc nitrate to the product after ultrasonic treatment in step 1.2, ultrasonically disperse for 5 min, and then stir and react for 6 h. After the reaction is complete, wash the excess Zn in the solution with methanol by centrifugation. 2+ The mixture was reconstituted into a methanol suspension with a solid content of 0.5 wt%, yielding a mixed solution D. A methanol solution of dimethylimidazole was added to solution D in three batches, with a 1-hour interval between each batch. After thorough mixing with the ligand solution, a methanol solution of CTAB was added, and the mixture was stirred continuously at 700 rpm for 24 hours. After the reaction was complete, the solution was washed three times with methanol to obtain the reaction product.

[0092] The methanol solution of dimethylimidazole was obtained by dissolving 20 mmol of dimethylimidazole in 100 mL of methanol; the aqueous solution of zinc nitrate was obtained by dissolving 10 mmol of zinc nitrate hexahydrate in 100 mL of methanol; the methanol solution of CTAB was obtained by dissolving 0.57 mmol of cetyltrimethylammonium bromide in 50 mL of methanol; and the mass ratio between modified cellulose and zinc nitrate was 1:5.8.

[0093] 1.4. The reaction product obtained in step 1.3 was redispersed in 50 mL of tert-butanol, stirred thoroughly, and centrifuged twice. The solvent was then replaced with tert-butanol to prepare a tert-butanol suspension with a solid content of 1 wt%. Next, it was pre-treated by freezing at -20°C for 10 h, and then freeze-dried for 40 h at a freeze-drying pressure of 25 Pa and a cold trap temperature of -53°C to obtain the final product, nanocellulose composite aerogel.

[0094] When using the nanocellulose composite aerogel of Example 3 to adsorb methylene blue in water (using the same method as in the application example), the C... t / C0 is 0.45%.

[0095] Example 3

[0096] Example 3 provides a nanocellulose composite aerogel, on which HKUST-1 is grown in situ on modified cellulose; the preparation method includes the following steps:

[0097] 1.1 100g of a cellulose suspension with a solid content of 1wt% and 300g of a sodium periodate suspension with a solid content of 1.38wt% were mixed to form a cellulose suspension with a solid content of 0.25wt%. The suspension was stirred at 700r / min for 18h under light-protected conditions. After the reaction, the cellulose was washed three times by centrifugation at 8000r / min with deionized water. The precipitate was oxidized cellulose, which was dispersed in deionized water to obtain an oxidized cellulose aqueous solution. 3.42g of sodium bisulfite was dissolved in deionized water and added to the oxidized cellulose aqueous solution to prepare a modified cellulose suspension with a solid content of 1wt%. The suspension was stirred continuously at 700r / min for sulfonation reaction for 36h. After the reaction, the cellulose was washed four times by centrifugation at 8000r / min with deionized water and redispersed in deionized water to obtain a modified cellulose aqueous solution.

[0098] 1.2 The modified cellulose aqueous solution was replaced with methanol solution to prepare a modified cellulose methanol suspension with a solid content of 0.5 wt%, and then ultrasonically dispersed in an ultrasonic cleaner for 30 min.

[0099] 1.3. Add the product from step 1.2, after ultrasonic treatment, to an aqueous solution of copper nitrate. After ultrasonic dispersion for 5 minutes, stir and react for 6 hours. After the reaction is complete, wash the solution with methanol by centrifugation to remove excess Cu. 2+ The cellulose was reconstituted into a methanol suspension with a solid content of 0.5 wt%, yielding a mixed solution D. A methanol solution of 1,3,5-benzenetricarboxylic acid (BTC) was added to solution D in three batches, with a 1-hour interval between each batch. After thorough mixing with the ligand solution, a methanol solution of CTAB was added, and the mixture was stirred continuously at 700 rpm for 24 hours. After the reaction was complete, the solution was washed three times with methanol to obtain the reaction product.

[0100] The methanol solution of 1,3,5-benzenetricarboxylic acid was obtained by dissolving 20 mmol of 1,3,5-benzenetricarboxylic acid in 100 mL of methanol; the aqueous solution of copper nitrate was obtained by dissolving 10 mmol of copper nitrate in 100 mL of methanol; the methanol solution of CTAB was obtained by dissolving 0.57 mmol of hexadecyltrimethylammonium bromide in 50 mL of methanol; the mass ratio of cellulose to copper nitrate was 1:5.8.

[0101] 1.4. The reaction product obtained in step 1.3 was redispersed in 50 mL of tert-butanol, stirred thoroughly, and centrifuged twice. The solvent was then replaced with tert-butanol to prepare a tert-butanol suspension with a solid content of 1 wt%. Next, it was pre-treated by freezing at -20°C for 10 h, and then freeze-dried for 40 h at a freeze-drying pressure of 25 Pa and a cold trap temperature of -53°C to obtain the final product, nanocellulose composite aerogel.

[0102] When using the nanocellulose composite aerogel of Example 3 to adsorb methylene blue in water (using the same method as in the application example), the C... t / C0 is 0.46%.

[0103] Comparative Example 1

[0104] The difference between Comparative Example 1 and Example 1 is that modified cellulose was not used; instead, natural nanocellulose was used directly to grow MOF materials. The process includes the following steps:

[0105] 1) 100g of cellulose suspension with a solid content of 1wt% was prepared into a cellulose methanol suspension with a solid content of 0.5wt% by solvent replacement with methanol solution, and then ultrasonically dispersed in an ultrasonic cleaner for 30min.

[0106] 2) Then add a methanol solution of cobalt nitrate, sonicate for 5 minutes, and stir for 6 hours. After the reaction is complete, wash the solution with methanol by centrifugation to remove excess Co. 2+ The cellulose was reconstituted into a methanol suspension with a solid content of 0.5 wt%, yielding mixed solution A. A methanol solution of dimethylimidazole was added to mixed solution A in three batches, with a 1-hour interval between each batch. After thorough mixing with the ligand solution, a methanol solution of CTAB was added, and the mixture was stirred continuously at 700 rpm for 24 hours. After the reaction was complete, the solution was washed three times with methanol to obtain the reaction product.

[0107] The dimethylimidazole methanol solution was obtained by dissolving 20 mmol of dimethylimidazole in 100 mL of methanol; the zinc nitrate aqueous solution was obtained by dissolving 10 mmol of zinc nitrate hexahydrate in 100 mL of methanol; the CTAB methanol solution was obtained by dissolving 0.57 mmol of cetyltrimethylammonium bromide in 50 mL of methanol; and the mass ratio between cellulose and cobalt nitrate was 1:5.8.

[0108] 3) The reaction product obtained in step 2) was redispersed in 50 mL of tert-butanol, stirred evenly, and centrifuged twice to completely replace the solvent with tert-butanol to prepare a tert-butanol suspension with a solid content of 1 wt%. Then, it was pre-treated by freezing at -20°C for 10 h, followed by freeze-drying at a pressure of 25 Pa and a cold trap temperature of -53°C for 40 h to obtain the final product.

[0109] The final product obtained in Comparative Example 1 was observed using a scanning electron microscope, and the results are shown in the figure. Figure 2 .

[0110] from Figure 2It can be seen that after 24 hours of growth, although MOF particles can grow in situ on the surface of natural nanocellulose, due to the lack of modification by sodium periodate and sodium bisulfite, the interaction between hydrogen bonds and van der Waals forces between natural nanocellulose particles results in incomplete defibrination of nanocellulose, with fewer exposed metal adsorption sites. Consequently, the amount of MOFs growing in situ on nanocellulose is relatively small, and the subsequent adsorption efficiency for pollutants is reduced.

[0111] Comparative Example 2

[0112] The difference between Comparative Example 2 and Example 1 is that the MOF was pre-synthesized, and then the pre-synthesized MOF was physically mixed with the modified cellulose aerogel. The specific steps are as follows:

[0113] 1) MOF presynthesis

[0114] 10 mmol of cobalt nitrate hexahydrate and 20 mmol of dimethylimidazole were dissolved separately in 100 mL of methanol, and then stirred at room temperature. The dimethylimidazole methanol solution was added to the cobalt nitrate methanol solution, and after thorough mixing with the ligand solution, the CTAB methanol solution was added, and the mixture was aged at room temperature for 24 h. The CTAB methanol solution was obtained by dissolving 0.57 mmol of hexadecyltrimethylammonium bromide in 50 mL of methanol.

[0115] 2) Synthesis of sulfonated cellulose aerogel

[0116] 100g of a cellulose suspension with a solid content of 1wt% and 300g of a sodium periodate suspension with a solid content of 1.38wt% were mixed to form a cellulose suspension with a solid content of 0.25wt%. The suspension was subjected to oxidation reaction for 18 hours under light-protected conditions with stirring at 700 rpm. After centrifugation at 8000 rpm, the precipitate was washed three times with deionized water to obtain oxidized cellulose. The oxidized cellulose was dispersed in deionized water to obtain an oxidized cellulose aqueous solution. 3.42g of sodium bisulfite was dissolved in deionized water and added to the oxidized cellulose aqueous solution to prepare an oxidized cellulose suspension with a solid content of 1wt%. The suspension was subjected to sulfonation reaction for 36 hours with continuous stirring at 700 rpm. After centrifugation at 8000 rpm, the precipitate was washed four times with deionized water.

[0117] The obtained reaction product was redispersed in 50 mL of tert-butanol, stirred thoroughly, and centrifuged twice to replace the solvent with tert-butanol. Then, it was pre-treated by freezing at -20 °C for 10 h, followed by freeze-drying at a pressure of 25 Pa and a cold trap temperature of -53 °C for 40 h to obtain sulfonated cellulose aerogel.

[0118] 3) Physical mixing of sulfonated cellulose aerogel and MOF particles

[0119] The sulfonated cellulose aerogel from step 2) was added to the MOF methanol solution from step 1), and after aging for 24 hours, the final product was obtained through physical adsorption.

[0120] The final product obtained in Comparative Example 2 was observed using a scanning electron microscope, and the results are shown in the figure. Figure 3 .

[0121] from Figure 3 It can be seen that after 24 hours of physical adsorption, MOF particles accumulated on the surface of the modified cellulose aerogel. Because this composite method involves physical mixing, the accumulation of MOF particles on the aerogel surface greatly restricts the porosity of the nanocellulose.

[0122] Comparative Example 3

[0123] The difference between Comparative Example 3 and Example 1 is that the modified cellulose was not dissolved in the second solvent and ultrasonically treated. All other aspects are the same as in Example 1.

[0124] The final product obtained in Comparative Example 3 was observed using a scanning electron microscope, and the results are shown in the figure. Figure 4 .

[0125] from Figure 4 It can be seen that the modified cellulose without ultrasonic treatment becomes too coarse after 24 hours of growth, with fewer exposed active sites, resulting in a smaller amount of organometallic framework growing in situ on the cellulose and a reduced adsorption efficiency for pollutants.

[0126] Comparative Example 4

[0127] The difference between Comparative Example 4 and Experimental Example 1 is that cellulose was modified with aminosulfonic acid and then loaded with MOF. All other steps are the same as in Example 1. The specific steps are as follows:

[0128] A 0.5 g aqueous solution of nanocellulose with a solid content of 1 wt% was prepared into a 0.5 wt% nanocellulose DMF solution by multiple displacements with DMF. 2.66 g of aminosulfonic acid was dissolved in 40 mL of DMF. After complete dissolution, it was mixed with the 0.5 wt% nanocellulose DMF solution and placed in an oil bath at 80°C with continuous stirring for 1.5 h. After the reaction was completed, the mixture was centrifuged at 8000 r / min. The precipitate was washed four times with deionized water and redispersed in deionized water to obtain an aqueous solution of modified cellulose. Then, steps 1.2, 1.3, and 1.4 in Example 1 were performed in the same manner.

[0129] The final product obtained in Comparative Example 4 was observed using a scanning electron microscope, and the results are shown in the figure. Figure 5 .

[0130] from Figure 5It can be seen that when nanocellulose is modified with aminosulfonic acid, the MOF particles on the surface of the nanocellulose have uneven morphology and the adsorption efficiency for pollutants is reduced.

[0131] Comparative Example 5

[0132] The difference between Comparative Example 5 and Experimental Example 1 is that cellulose was modified using Tempo, NaBr, and sodium hypochlorite. All other steps are the same as in Example 1. The specific steps are as follows:

[0133] 1) Add 0.02g Tempo and 0.14g solid NaBr to 100g of a 1wt% cellulose suspension. Cover the mouth of the beaker with aluminum foil to protect it from light. Stir continuously at room temperature. Use a syringe to draw 2.1mL of sodium hypochlorite solution and add it dropwise slowly to the suspension. Use a pH meter to measure the pH value of the mixture.

[0134] 2) Prepare a 0.5M NaOH aqueous solution and add it dropwise to the mixture. Measure the pH value of the solution every 1 hour until the pH of the mixture is about 10-10.5, at which point the reaction is terminated.

[0135] 3) Add the reacted solution to the Buchner funnel, wash with distilled water and filter several times until the solution is neutral.

[0136] 4) Take the filtered precipitate into a beaker, add water to 100g, and sonicate for 5-10 minutes.

[0137] 5) Pour the sonicated suspension into a large beaker, add water to 500 mL, stir well and centrifuge. Centrifuge at 7000 r / min for 5 min, take the supernatant to obtain the Tempo oxidized cellulose solution, and then proceed as in steps 1.2, 1.3 and 1.4 of Example 1.

[0138] The final product obtained in Comparative Example 5 was observed using a scanning electron microscope, and the results are shown in the figure. Figure 6 .

[0139] from Figure 6 It is known that after modifying cellulose with Tempo, NaBr, and sodium hypochlorite, there is insufficient cross-linking between fibers, resulting in nanocomposites lacking mechanical properties.

[0140] Comparative Example 6

[0141] The difference between Comparative Example 6 and Example 1 is that the surfactant CTAB was not added; otherwise, they are the same as in Example 1.

[0142] Comparative Example 7

[0143] The difference between Comparative Example 7 and Comparative Example 1 is that the surfactant CTAB was not added; otherwise, they are the same as Comparative Example 1.

[0144] Comparative Example 8

[0145] The difference between Comparative Example 8 and Comparative Example 2 is that the surfactant CTAB was not added; otherwise, they are the same as Comparative Example 2.

[0146] Comparative Example 9

[0147] The difference between Comparative Example 9 and Comparative Example 3 is that the surfactant CTAB was not added; otherwise, they are the same as Comparative Example 3.

[0148] Comparative Example 10

[0149] The difference between Comparative Example 10 and Comparative Example 4 is that the surfactant CTAB was not added; otherwise, they are the same as Comparative Example 4.

[0150] Comparative Example 11

[0151] The difference between Comparative Example 11 and Comparative Example 5 is that the surfactant CTAB was not added; otherwise, they are the same as Comparative Example 5.

[0152] Application examples

[0153] The products prepared in Example 1 and Comparative Examples 1-11 were subjected to methylene blue adsorption experiments.

[0154] 1) Preparation of pollutant solution.

[0155] Weigh an appropriate amount of methylene blue powder, dissolve it in deionized water, and prepare a stock solution with a concentration of methylene blue C0 = 20 mg / L.

[0156] 2) Adsorption experiment.

[0157] Take 40 mL of a contaminant solution with C0 = 20 mg / L and place it in a centrifuge tube. Add 20 mg of the products from Example 1 and Comparative Examples 1-11, respectively. Shake at 150 rpm in a constant temperature shaker at time points of 0, 30, 60, 90, 120, 150, and 180 min. Separate by centrifugation (8000 rpm, 5 min), collect the supernatant, and determine the residual concentration C of the contaminant in the supernatant using UV-Vis. t (mg / L), via (1-C) t / C0)*100% represents its adsorption efficiency.

[0158] The specific experimental steps for UV-Vis determination of methylene blue are as follows:

[0159] The supernatant was collected by centrifugation and quantitatively diluted. A certain amount of the diluted solution was added to a cuvette, and UV-Vis spectrophotometry was performed. The maximum absorption wavelength of methylene blue was 664 nm. The ratio of the absorbance corresponding to the maximum absorption wavelength at each time period to the absorbance of the initial concentration of methylene blue before the reaction indicates the trend of contaminant concentration change in the supernatant at each time period.

[0160] C t A smaller / C0 value indicates higher adsorption efficiency, C t The larger the / C0 value, the lower the adsorption efficiency.

[0161] The adsorption effects of the products of Example 1 and Comparative Examples 1-11 on methylene blue are shown in the curves. Figure 7 .

[0162] from Figure 7 It can be seen that during the adsorption process from 0 to 180 minutes, the adsorption effect of the nanocellulose composite aerogel prepared in Example 1 on the pollutant methylene blue is much greater than that in Comparative Examples 1-11. After 30 minutes of adsorption, the concentration C of methylene blue in Example 1 and Comparative Examples 1-11 is significantly lower. t The ratios to the initial concentration C0 were 0.47, 0.9, 0.915, 0.99, 0.53, 0.61, 0.526, 0.95, 0.965, 0.99, 0.58, and 0.66, respectively.

[0163] After 30 minutes of adsorption, compared with the unmodified Comparative Example 1, the nanocellulose composite aerogel of Example 1 showed a higher C1 value for the pollutant methylene blue. t / C0 was reduced by 47.8%; compared with Comparative Example 4 which used aminosulfonic acid, the nanocellulose composite aerogel of Example 1 showed a lower C0 value for the pollutant methylene blue. t / C0 was reduced by 11.3%; compared with Comparative Example 5, which used Tempo-modified cellulose, the nanocellulose composite aerogel of Example 1 showed a lower C0 value for the pollutant methylene blue. t / CO decreased by 23.0%. In summary, the modification of cellulose with sodium periodate and sodium bisulfite in this invention is more conducive to the adsorption of methylene blue.

[0164] After 30 minutes of adsorption, compared with Comparative Example 6 without CTAB, the nanocellulose composite aerogel of Example 1 showed a higher C1 concentration for the pollutant methylene blue. t / C0 was reduced by 10.6%; compared with Comparative Example 2, which is a composite material formed by physical mixing, the nanocellulose composite aerogel of Example 1 showed a lower C0 value for the pollutant methylene blue. t / C0 was reduced by 48.6%; compared with Comparative Example 3 without ultrasonic treatment, the nanocellulose composite aerogel of Example 1 showed a significant reduction in C of the pollutant methylene blue.t / CO was reduced by 52.5%. In summary, the nanocellulose composite aerogel of the present invention, through pre-modification followed by loading of MOF material and ultrasonic treatment, exposes more active sites in the cellulose, which is conducive to the orderly growth of MOF material and thus improves the adsorption efficiency of methylene blue.

[0165] Comparative Examples 1-5, compared to their counterparts 7-11, involved the addition of CTAB. The results showed that the addition of CTAB increased the C30 at 30 minutes. t / C0 decreased by 5.56%, 5.46%, 0%, 9.43%, and 8.20%, respectively. In summary, the addition of CTAB is more beneficial for the adsorption of methylene blue.

[0166] The above embodiments are for illustrating the implementation schemes disclosed in this invention and should not be construed as limiting the invention. Furthermore, various modifications listed herein, as well as variations in the methods and compositions of the invention, will be apparent to those skilled in the art without departing from the scope and spirit of the invention. Although the invention has been specifically described in conjunction with various specific preferred embodiments, it should be understood that the invention should not be limited to these specific embodiments. In fact, various modifications as described above that are obvious to those skilled in the art to obtain the invention should be included within the scope of this invention.

Claims

1. A method for preparing a nanocellulose composite aerogel, characterized in that, Includes the following steps: 1) Cellulose, sodium periodate, and sodium bisulfite are reacted in the first solvent to obtain modified cellulose; 2) Dissolve the modified cellulose in a second solvent and treat with ultrasound; 3) Mix the ultrasonically treated product obtained in step 2) with the metal salt of MOF material, then add the organic ligand and surfactant of MOF material to react, dissolve the reaction product in a third solvent, and dry to obtain the nanocellulose composite aerogel.

2. The preparation method according to claim 1, characterized in that, The first solvent is selected from water; And / or, the second solvent is selected from methanol; And / or, the metal salt is selected from cobalt salts, zinc salts, or copper salts; And / or, the organic ligand is selected from 1,3,5-benzenetricarboxylic acid or dimethylimidazole; And / or, the surfactant is selected from one or both of CTAB and triethylamine; And / or, the third solvent is selected from tert-butanol.

3. The preparation method according to claim 2, characterized in that, The mass ratio of cellulose, sodium periodate and sodium bisulfite is 1:(2-8):(2-6); And / or, the mass ratio of the modified cellulose to the metal salt is 1:(1-8); And / or, the molar ratio of the metal salt to the organic ligand is 1:(1-8); And / or, the molar ratio of the metal salt to the surfactant is (5-40):1; And / or, the cobalt salt is selected from one or more of cobalt nitrate, cobalt sulfate, and cobalt hydrochloride; And / or, the zinc salt is selected from one or more of zinc nitrate, zinc sulfate, and zinc hydrochloride; And / or, the copper salt is selected from one or more of copper nitrate, copper sulfate, and copper hydrochloride.

4. The preparation method according to claim 1, characterized in that, The cellulose and sodium periodate are first oxidized, and then sulfonated with sodium bisulfite.

5. The preparation method according to claim 4, characterized in that, The oxidation reaction takes 10-26 hours; And / or, the oxidation reaction is carried out at a temperature of 20-55°C; And / or, the sulfonation reaction takes 30-42 hours; And / or, the sulfonation reaction is carried out at a temperature of 20-55°C.

6. The preparation method according to claim 1, characterized in that, The ultrasonic treatment time is 5-10 minutes; And / or, the drying is selected from freeze drying or supercritical drying; And / or, the drying process may further include a pre-cooling treatment.

7. The preparation method according to claim 6, characterized in that, The pressure for freeze drying is 20–30 Pa; And / or, the freeze-drying temperature is -60 to -50°C; And / or, the freeze-drying time is 36–48 h; And / or, the temperature of the pre-cooling treatment is -30 to -20°C; And / or, the precooling treatment time is 8-12 hours.

8. The nanocellulose composite aerogel obtained by the preparation method according to any one of claims 1-7.

9. The use of the nanocellulose composite aerogel as an adsorbent material in treating methylene blue in the environment, as described in claim 8.

10. A method for treating methylene blue in the environment, characterized in that, include: Add the nanocellulose composite aerogel as described in claim 8 to the environment.

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