Modified nanofiber aerogel as well as preparation method and application thereof

Abstract

The invention relates to the technical field of material preparation and separation, and discloses modified nanofiber aerogel as well as a preparation method and application thereof. According to the preparation method of the modified nanofiber aerogel, CNC is taken as a raw material, crown ether (A18C6) and graphene oxide (GO) are combined onto a cellulose nanocrystal framework, and the aerogel with a specific Cs < + > adsorption function is prepared. The specific recognition of crown ether on Cs < + > is utilized to oxidize the separation performance of graphene, so that the Cs < + > adsorption capacity of the material is improved, and the material is used for adsorbing and separating Cs < + >.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of material preparation and separation technology, and particularly relates to a modified nanofiber aerogel, a preparation method and application thereof, the aerogel can specifically adsorb cesium ions (Cs + ) in a water environment, and is suitable for radioactive wastewater treatment. BACKGROUND

[0002] In radioactive wastewater generated by nuclear power plant accidents, cesium (Cs) is one of the main pollutants, especially 137Cs, which has a long half-life and high solubility, and is extremely harmful to the environment and human health. At present, it is still a technical problem to efficiently remove low-concentration radioactive cesium ions from high-salinity wastewater.

[0003] In the prior art, graphene oxide membranes have excellent separation performance for Cs + , but there is a contradiction between permeability and selectivity. Crown ethers (such as A18C6) can specifically recognize alkali metal ions due to their cyclic structure, but it is difficult to achieve efficient adsorption when used alone. Cellulose nanocrystals (CNC) have high specific surface area and three-dimensional network structure, and can be used as a support skeleton, but their adsorption capacity for Cs + is limited.

[0004] Therefore, it is urgent to develop a material that has high adsorption capacity, selectivity and stability to achieve efficient removal of Cs + from radioactive wastewater. SUMMARY

[0005] The technical problem to be solved by the present application is to overcome the deficiencies in the prior art and provide a modified nanofiber aerogel, a preparation method and application thereof. The aerogel prepared by the present application uses the unique cyclic structure of crown ethers (such as A18C6) to specifically recognize Cs + , and combines the excellent separation performance of graphene oxide membranes (GO) for Cs + , uses cellulose nanocrystals as a support skeleton, and prepares a cellulose aerogel with high specific surface area and good adsorption performance. The aerogel can specifically recognize Cs + in a water environment and selectively adsorb and separate it, providing an efficient and feasible solution for the treatment of radioactive wastewater.

[0006] The technical solution adopted by the present application to solve the technical problem is as follows:

[0007] A preparation method of a modified nanofiber aerogel, specifically comprising the following steps:

[0008] Step S1, put the absorbent cotton into a sulfuric acid solution, stir in an oil bath, pour into ice water, stand overnight, centrifuge and dialyze to obtain nanocellulose;

[0009] Step S2, DMAC (dimethylacetamide) is added to the nanocellulose prepared in step S1, heated under a nitrogen atmosphere; then CDI (N,N'-carbonyldiimidazole) is added and stirred to react, after the reaction is completed, ECH (epichlorohydrin) is added to the reaction system to continue the reaction to obtain modified cellulose;

[0010] Step S3, graphene oxide (GO) is dispersed in water, NaOH and ECH are added; under a nitrogen atmosphere, reflux reaction is carried out; after the reaction is completed, the obtained black solid is washed with distilled water and vacuum dried to obtain GO-ECH;

[0011] Step S4, A18C6 is dissolved in DMF (N,N-dimethylformamide) at room temperature, then sodium hydride (NaH) is added, and reflux reaction is carried out under a nitrogen atmosphere to obtain a mixed solution;

[0012] Step S5, the modified cellulose prepared in step S2 and the GO-ECH prepared in step S3 are dispersed in DMF to obtain a dispersion liquid, which is added to the mixed solution prepared in step S4; reflux reaction is carried out under a nitrogen atmosphere to obtain a reaction liquid;

[0013] Step S6, the reaction liquid prepared in step S5 is poured into a container and evaporated in a water bath to obtain a cellulose aerogel precursor;

[0014] Step S7, the cellulose aerogel precursor prepared in step S6 is soaked in an ethanol solution to obtain a cellulose alcogel;

[0015] Step S8, the cellulose alcogel prepared in step S7 is subjected to supercritical drying to obtain a cellulose aerogel.

[0016] Cellulose nanocrystals (CNC), also known as nanocrystalline cellulose or cellulose nanofiber, have a rod-like structure, are usually extracted from cellulose by acid hydrolysis, and selectively dissolve amorphous regions. Graphene oxide membranes show high selectivity for Cs + Excellent separation performance shows great potential for efficient screening of cesium ions. However, due to the trade-off between ion selectivity and permeability in membrane-based processes, one of the key challenges is to improve the permeability of graphene oxide while maintaining effective separation performance of cesium ions.

[0017] Crown ethers (such as A18C6) and their derivatives are typical supramolecular hosts. They are macrocyclic polyethers with regular arrangement of oxygen atoms on a ring of specific size. Crown ethers have excellent performance in selectively recognizing metal ions and forming stable "host" complexes, which depends on the size of the metal ion and the size of the macrocyclic cavity. Given the unique affinity of crown ethers for alkali metals, combined with the unique properties of graphene oxide, it is expected to achieve efficient Cs + separation.

[0018] Step S1: Preparation of nanocellulose by sulfuric acid hydrolysis of delignified cotton, simple and efficient method, high purity product (dialysis purification ensures impurity removal);

[0019] Step S2: Modification of cellulose using CDI (carbonyl diimidazole) and ECH (epichlorohydrin) to introduce active groups and enhance subsequent cross-linking ability;

[0020] Step S3: Reaction of graphene oxide (GO) with ECH (GO-ECH) to improve the dispersibility of GO and its compatibility with cellulose;

[0021] Steps S4-S5: Reaction of A18C6 (18-crown-6 ether) with sodium hydride and subsequent blending with modified cellulose / GO-ECH to reduce interfacial defects through crown ether complexation, improve the porous structure and stability of the material, and enhance the uniformity and durability of the composite material;

[0022] Steps S6-S8: Water bath evaporation and supercritical drying processes ensure the formation of a three-dimensional network structure with high porosity and low density for the aerogel. Specifically, supercritical drying avoids pore collapse caused by capillary forces, preserves high specific surface area and interconnected pores, and enhances adsorption / separation performance.

[0023] Further, in step S1, the volume ratio of sulfuric acid to water in the sulfuric acid solution is 1:1. A volume ratio of 1:1 can balance the hydrolysis efficiency and the degree of cellulose degradation, avoiding excessive acid hydrolysis that leads to excessively low molecular weight, while efficiently removing lignin and hemicellulose to obtain high-purity, high-aspect-ratio nanocellulose.

[0024] CDI as an activator can quantitatively introduce active sites, and ECH as a cross-linking agent can enhance the inter-chain binding force of cellulose through ring-opening reaction of epoxy groups, thereby improving the reactivity and gel strength of modified cellulose. DMAC as a solvent can dissolve cellulose and stabilize the reaction system, avoiding excessive local concentration that leads to side reactions. The substance ratio can ensure the efficiency of cellulose modification and avoid the impact of excessive reagent residues on subsequent steps.

[0025] Further, in step S3, the mass ratio of graphene oxide to water is 1:100, and the mass ratio of NaOH to ECH is 1:1. NaOH adjusts the pH to alkaline, promoting the ring-opening reaction of ECH epoxy groups with GO surface oxygen-containing functional groups (such as hydroxyl and carboxyl groups), forming covalently bonded GO-ECH and enhancing its interfacial bonding force with cellulose. Excess ECH ensures sufficient functionalization of GO, improving the hydrophobicity and mechanical toughness of the composite material. This substance ratio can control the reaction degree of GO and ECH, avoid excessive cross-linking leading to GO aggregation, and maintain its dispersibility and enhancement effect.

[0026] Further, in the step S4, the reflux temperature is 60 DEG C, and the reflux time is 4h. The complex reaction of A18C6 and sodium hydride can be mildly activated by refluxing at 60 DEG C for 4h, so that the active intermediate is generated by sufficient reaction, and high-temperature decomposition is avoided, thereby providing an efficient catalyst for subsequent crosslinking with modified cellulose, shortening the reaction time and improving the yield.

[0027] Further, in the step S5, the reflux temperature is 90 DEG C, and the reflux time is 72h. The cellulose, GO-ECH and crown ether derivative are crosslinked to form a three-dimensional network structure by high-temperature and long-time reflux, so that the compression resilience and thermal stability of the aerogel are improved.

[0028] Further, in the step S5, the volume ratio of the modified cellulose, GO-ECH and DMF is 1:1:1. The appropriate amount of GO-ECH enhances the electrical conductivity and mechanical properties, and avoids agglomeration caused by excessive amount.

[0029] The volume ratio of the dispersion liquid and the mixed solution is 1:1, so that the crosslinking reaction is fully carried out, and a uniform gel network is formed.

[0030] Further, in the step S6, the water bath evaporation temperature is 40 DEG C. The solvent can be removed slowly by water bath evaporation at 40 DEG C, so that the non-uniform pores and structural defects caused by rapid evaporation are avoided, and the gel shrinkage is prevented, and the open porous structure is retained.

[0031] Further, in the step S8, the supercritical drying time is 12h. The ethanol is removed by 12h supercritical drying, so that the surface tension is eliminated, the pores are prevented from being damaged by capillary force, and the nanoscale pores and low density (<0.1g / cm 3 ) of the aerogel are maintained, and the specific surface area is significantly improved.

[0032] A modified nanofiber aerogel is prepared by the preparation method.

[0033] The application of the modified nanofiber aerogel as described above, and the application of the modified nanofiber aerogel in the treatment of radioactive wastewater.

[0034] The application has the following advantages:

[0035] (1) structural advantage: through the compounding of nanocellulose and GO-ECH, and the modification of crown ether, a three-dimensional network structure with light weight, high porosity and high mechanical strength is formed;

[0036] (2) adjustable function: the modification step (such as the introduction of GO) can endow the aerogel with electrical conductivity, adsorbability or catalytic performance;

[0037] (3) controllable process: the parameters (temperature, time, ratio) of each step are optimized to ensure the reproducibility of the product and the feasibility of large-scale production;

[0038] (4) the modified nanofiber aerogel prepared by the method has a unique cyclic structure of crown ether, and can specifically recognize Cs + , and the graphene oxide film has excellent separation performance, and the cellulose nanocrystal has a three-dimensional network structure and a high specific surface area, thus serving as a support skeleton; therefore, the aerogel can specifically recognize Cs + in a water environment and selectively adsorb and separate the Cs + . BRIEF DESCRIPTION OF DRAWINGS

[0039] In order to more clearly illustrate the specific embodiments of the present application or the technical solutions in the prior art, the drawings needed in the following description of the specific embodiments or the prior art will be briefly introduced. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0040] Figure 1 FIG. 1 is a scanning electron microscope morphology diagram of GCAE (Example 1) and GFAE (Comparative Example 1), wherein (a) (b) (c) are scanning structure diagrams of GCAE at different magnifications; (d) (e) (f) are scanning structure diagrams of GFAE at different magnifications;

[0041] Figure 2 FIG. 3 is a thermogravimetric curve diagram of GCAE (Example 1), GFAE (Comparative Example 1), CNC (Comparative Example 2) and CNF (Comparative Example 3);

[0042] Figure 3 FIG. 4 is a Zeta curve diagram of GCAE (Example 1), GFAE (Comparative Example 1), CNC (Comparative Example 2) and CNF (Comparative Example 3);

[0043] Figure 4 FIG. 5 is an infrared diagram of GCAE (Example 1), GFAE (Comparative Example 1), CNC (Comparative Example 2), CNF (Comparative Example 3) and A18C6;

[0044] Figure 5 FIG. 6 is an adsorption capacity curve diagram of GCAE (Example 1), GFAE (Comparative Example 1), CNC (Comparative Example 2) and CNF (Comparative Example 3) at different pH values;

[0045] Figure 6 FIG. 7 is a nitrogen adsorption-desorption isotherm of GCAE (Example 1), GFAE (Comparative Example 1), CNC (Comparative Example 2) and CNF (Comparative Example 3). DETAILED DESCRIPTION

[0046] It should be noted that the following detailed description is exemplary in nature and is intended to provide further description of the application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0047] It is also important to note that the terms "including", "comprising", and / or "having" as used herein are specifically intended to be open-ended and also to mean including, avoiding the exclusion of, e.g., any additional item, any additional step, etc.

[0048] The technical solutions of the present application will be described clearly and completely in connection with the embodiments. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0049] A preparation method of modified nanofiber aerogel, specifically comprising the following steps:

[0050] Step S1, put the degreasing cotton into a sulfuric acid solution, stir in an oil bath, pour into ice water, stand overnight, centrifuge and purify by dialysis to obtain nanocellulose;

[0051] Step S2, add DMAC to the nanocellulose prepared in step S1, heat under a nitrogen atmosphere; then add CDI and stir to react, after the reaction is completed, add ECH to the reaction system and continue to react to obtain modified cellulose;

[0052] Step S3, disperse graphene oxide in water, add NaOH and ECH; perform a reflux reaction under a nitrogen atmosphere; after the reaction is completed, wash the obtained black solid with distilled water and vacuum dry to obtain GO-ECH;

[0053] Step S4, dissolve A18C6 in DMF at room temperature, then add sodium hydride, perform a reflux reaction under a nitrogen atmosphere to obtain a mixed solution;

[0054] Step S5, disperse the modified cellulose prepared in step S2 and the GO-ECH prepared in step S3 in DMF, add the obtained dispersion liquid to the mixed solution prepared in step S4; perform a reflux reaction under a nitrogen atmosphere to obtain a reaction liquid;

[0055] Step S6, pour the reaction solution prepared in step S5 into a container, and evaporate in a water bath to obtain a cellulose aerogel precursor;

[0056] Step S7, soak the cellulose aerogel precursor prepared in step S6 in an ethanol solution to obtain a cellulose alcogel;

[0057] Step S8, perform supercritical drying on the cellulose alcogel prepared in step S7 to obtain a cellulose aerogel.

[0058] In step S1, the volume ratio of sulfuric acid to water in the sulfuric acid solution is 1:1.

[0059] In step S3, the mass ratio of graphene oxide to water is 1:100, and the mass ratio of NaOH to ECH is 1:1.

[0060] In step S4, the reflux temperature is 60℃, and the reflux time is 4h.

[0061] In step S5, the reflux temperature is 90℃, and the reflux time is 72h; the volume ratio of modified cellulose, GO-ECH and DMF is 1:1:1; the volume ratio of the dispersion liquid to the mixed solution is 1:1

[0062] In step S6, the water bath evaporation temperature is 40℃

[0063] In step S8, the supercritical drying time is 12h.

[0064] A modified nanofiber aerogel prepared by the above method.

[0065] The application of a modified nanofiber aerogel as described above, the application of the modified nanofiber aerogel in the treatment of radioactive wastewater.

[0066] Example 1

[0067] A method for preparing a modified nanofiber aerogel, specifically comprising the following steps:

[0068] Step S1, add 75mL of sulfuric acid to 75mL of water, stir well and cool to room temperature; put 10g of defatted cotton into the mixture, stir in an oil bath at 45℃ for 3 hours, then pour it into 1.5L of ice water and stand overnight; centrifuge the lower phase suspension and purify by dialysis until the pH value of the suspension is greater than 2.4;

[0069] Step S2, take 10ml of CNC and disperse it in 20ml of DMAc, heat to 50℃ under nitrogen atmosphere, then add 20g of CDI and stir for 8h, then add 10g of ECH to the reaction system and continue to react for 10h;

[0070] Step S3, 0.07g graphene oxide (GO) was dispersed in 70ml distilled water, then 0.5g NaOH and 0.5ml ECH (epichlorohydrin) were added, and the reaction was carried out at 60℃ under N2 atmosphere for 24h, the obtained black solid was washed with distilled water for several times in small amount until the washing liquid was neutral, and finally vacuum dried to obtain GO-ECH;

[0071] Step S4, 0.30g A18C6 was dissolved in 10ml DMF at room temperature, then 0.25g sodium hydride was added, and the reaction was carried out at 60℃ under N2 atmosphere for 4h to obtain a mixed solution;

[0072] Step S5, 20ml CNC-ECH and 2mg GO-ECH were dispersed in DMF and added to the mixed solution prepared in step S4, and the reaction was continued at 90℃ under N2 atmosphere for 72h to obtain a reaction liquid;

[0073] Step S6, the reaction liquid prepared in step S5 was poured into a polytetrafluoroethylene box, and evaporated in a water bath at 40℃ to obtain a cellulose aerogel precursor;

[0074] Step S7, the cellulose aerogel precursor prepared in step S6 was soaked in an ethanol solution to obtain a cellulose alcogel;

[0075] Step S8, the cellulose alcogel prepared in step S7 was subjected to supercritical drying for 12h to obtain GCAE-0.30.

[0076] Example 2

[0077] A method for preparing a modified nanofiber aerogel, specifically comprising the following steps:

[0078] Step S1, 75mL sulfuric acid was added to 75mL water, stirred and cooled to room temperature; 10g of defatted cotton was put into the mixture, stirred in an oil bath at 45℃ for 3h, then poured into 1.5L ice water and left overnight; the lower phase suspension was centrifuged and purified by dialysis until the pH value of the suspension was greater than 2.4;

[0079] Step S2, 10ml CNC was dispersed in 20ml DMAc, heated to 50℃ under nitrogen atmosphere, then 20g CDI was added and stirred for 8h, and then 10g ECH was added to the reaction system and the reaction was continued for 10h;

[0080] Step S3, 0.07 g of graphene oxide (GO) was dispersed in 70 ml of distilled water, then 0.5 g of NaOH and 0.5 ml of ECH (epichlorohydrin) were added, and the mixture was refluxed at 60°C for 24 h under N2 atmosphere. The obtained black solid was washed with distilled water for several times in small amount until the washing liquid was neutral, and then vacuum dried to obtain GO-ECH;

[0081] Step S4, 0.25 g of A18C6 was dissolved in 10 ml of DMF at room temperature, then 0.25 g of sodium hydride was added, and the mixture was refluxed at 60°C for 4 h under N2 atmosphere to obtain a mixed solution;

[0082] Step S5, 20 ml of CNC-ECH and 2 mg of GO-ECH were dispersed in DMF and added to the mixed solution prepared in step S4, and the mixture was refluxed at 90°C for 72 h under N2 atmosphere to obtain a reaction liquid;

[0083] Step S6, the reaction liquid prepared in step S5 was poured into a polytetrafluoroethylene box, and evaporated in a water bath at 40°C to obtain a cellulose aerogel precursor;

[0084] Step S7, the cellulose aerogel precursor prepared in step S6 was soaked in an ethanol solution to obtain a cellulose alcogel;

[0085] Step S8, the cellulose alcogel prepared in step S7 was subjected to supercritical drying for 12 h to obtain GCAE-0.25.

[0086] Comparative Example 1

[0087] A preparation method of an aerogel, specifically comprising the following steps:

[0088] (1) Bleached wood pulp (10 g) was mixed with potassium hydroxide (10 g) and deionized water (500 mL) and reacted at 90 °C for 2 h with continuous stirring. Then, the centrifugally washed pulp was mixed with 15 ml of glacial acetic acid and 35 g of sodium hypochlorite and reacted at 70 °C for 6 h with continuous stirring. After centrifugal washing of the mixture, the pH of the solution was made neutral. Then, 500 mL of deionized water and 25 g of KOH were added to the mixture and stirred at 90 °C for 2 h. Then, a certain amount of hydrochloric acid was added to the mixture until the pH of the solution was neutral. The centrifuged CNF suspension was ground 10 times by using a Supermasoloider Medium grinder (MKZA 15 -40J) to obtain CNF. 0.07 g of graphene oxide (GO) was dispersed in 70 ml of distilled water, followed by the addition of 0.5 g of NaOH and 0.5 ml of ECH (epichlorohydrin), and reacted at 60 °C under N2 atmosphere for 24 h. The obtained black solid was washed with distilled water in small amounts for several times until the washing liquid was neutral in pH, and finally dried under vacuum to obtain GO-ECH.

[0089] (2) 10 ml of CNF was dispersed in 20 ml of DMAc, and after heating to 50 °C under a nitrogen atmosphere, 20 g of CDI was added and stirred for 8 h. Then, 10 g of ECH was added to the reaction system and the reaction was continued for 10 h.

[0090] (3) 0.30 g of A18C6 was dissolved in 10 ml of DMF at room temperature, followed by the addition of 0.25 g of sodium hydride, and reacted at 60 °C under N2 atmosphere for 4 h to obtain a mixed solution. 20 ml of CNC-ECH and 2 mg of GO-ECH were dispersed in DMF and added to the above mixed solution, and the reaction was continued at 90 °C under N2 atmosphere for 72 h. The obtained solution was centrifuged and freeze-dried to obtain GFAE-0.30.

[0091] Comparative Example 2

[0092] A method for preparing an aerogel, specifically comprising the following steps:

[0093] 75 mL of sulfuric acid was added to 75 mL of water, stirred and cooled to room temperature. 10 g of defatted cotton was put into the mixture, stirred in an oil bath at 45 °C for 3 hours, then poured into 1.5 L of ice water and left overnight. The lower phase suspension was centrifuged and purified by dialysis until the pH of the suspension was greater than 2.4, and then supercritical dried to obtain CNC.

[0094] Comparative Example 3

[0095] A method for preparing an aerogel, specifically comprising the following steps:

[0096] Bleached wood pulp (10 g) was mixed with potassium hydroxide (10 g) and deionized water (500 mL) and reacted at 90 °C for 2 h with continuous stirring; then, the centrifugally washed pulp was mixed with 15 ml of glacial acetic acid and 35 g of sodium hypochlorite and reacted at 70 °C for 6 h with continuous stirring; after the mixture was centrifugally washed, the pH of the solution was neutralized; then, 500 mL of deionized water and 25 g of KOH were added to the mixture, which was stirred at 90 °C for 2 h, and then an amount of hydrochloric acid was added to the mixture until the pH of the solution was neutralized; CNF was obtained by grinding the centrifuged CNF suspension 10 times using a Supermasoloider Medium grinder (MKZA 15 -40J); 0.07 g of graphene oxide (GO) was dispersed in 70 ml of distilled water, followed by the addition of 0.5 g of NaOH, and supercritical drying was performed to obtain CNF.

[0097] The aerogels obtained in Example 1, Comparative Example 1 to Comparative Example 3 were tested, and the results are shown in Table 1, Figures 1-6

[0098] Table 1 Results of the porosity of the aerogels obtained in Example 1, Comparative Example 1 to Comparative Example 3

[0099] Sample Pore size (nm) Surface Area (cm 2 g -1 )]]> CNC (Comparative Example 2) 13.726 23.344 CNF (Comparative Example 3) 17.389 11.362 GCAE (Example 1) 23.326 140.770 GFAE (Comparative Example 1) 20.909 113.824

[0100] As can be seen from Table 1, the GCAE (Example 1) has the largest surface area, and a high surface area means more active sites available for chemical bonding and also means that the material has more active sites for adsorption

[0101] Figure 1 are scanning electron microscopy images of the scanning electron microscopy morphology of GCAE (Example 1) and GFAE (Comparative Example 1), wherein (a) (b) (c) are scanning structure images of GCAE at different magnifications, which better reflect the layered structure of cellulose and the pore structure; (d) (e) (f) are scanning structure images of GFAE at different magnifications. As can be seen from Figure 1 GCAE and GFAE have a large surface area and a clear periodic layered structure, and this layered structure is attributed to the cholesteric structure of cellulose nanocrystals (CNC or CNF). The aerogels prepared from CNC and CNF have a clear periodic layered structure and also have a clear pore structure. Due to the difference in fiber length and entanglement degree, the structure of GCAE appears more disordered compared to GFAE.

[0102] Figure 2 are thermogravimetric curve diagrams of GCAE (Example 1), GFAE (Comparative Example 1), CNC (Comparative Example 2) and CNF (Comparative Example 3). As can be seen from Figure 2 ​It can be seen that the mass loss of the four aerogels in the range of 50-650℃ under nitrogen protection. When the temperature rises to 250℃, the mass loss of the four aerogels is 4.9%-9.8%, which is mainly due to the evaporation of residual water in the pores of the aerogel. When the temperature rises to 350℃, the four aerogels all have significant mass loss, mainly due to the decomposition of the fiber network structure. When the temperature rises to 400℃, it enters the carbonization stage, and the mass loss of the four aerogels tends to be stable. It can be seen from the figure that the residual mass of the two aerogels is 28.46% of the initial mass, and the thermal stability of GCAE is slightly higher than that of GFAE.

[0103] Figure 3 is the Zeta curve of GCAE (Example 1), GFAE (Comparative Example 1), CNC (Comparative Example 2) and CNF (Comparative Example 3). From Figure 3 It can be seen that the Zeta potential can measure the charge distribution on the surface of the four aerogels. The Zeta potential value gradually decreases with the increase of pH value, and reaches the lowest point at pH value of 7.0. This indicates that at pH value of 7.0, the four aerogels have more hydroxyl ions on the surface, which have better affinity and adsorption effect on cesium ions Cs + .

[0104] Figure 4 is the infrared spectrum of GCAE (Example 1), GFAE (Comparative Example 1), CNC (Comparative Example 2), CNF (Comparative Example 3) and A18C6, which can characterize their chemical bond and chemical composition characteristics. From Figure 4 It can be seen that the spectrum of GCAE (Example 1) and GFAE (Comparative Example 1) aerogel is highly similar to A18C6, indicating that the two aerogels have successfully grafted A18C6. Compared with CNC (Comparative Example 2) and CNF (Comparative Example 3), GCAE and GFAE show strong absorption peaks at 3415cm -1 in the FT-IR spectrum, which corresponds to the stretching vibration of cellulose hydroxyl group, proving that the two aerogels still retain the basic chemical structure of cellulose. In addition, the absorption peaks observed in the range of 1600-1650cm -1 are attributed to the in-plane bending vibration of amino group; the absorption peaks at 1100-1200cm -1 are due to the stretching vibration of C-O-C bond in crown ether ring; the characteristic peak at 1384cm -1 is attributed to the bending vibration of C-H bond and the stretching vibration of C-O bond; the absorption peaks in the range of 700-800cm -1 are characteristic peaks of monosubstituted benzene ring.

[0105] Figure 5are the adsorption capacity curves of GCAE (Example 1), GFAE (Comparative Example 1), CNC (Comparative Example 2) and CNF (Comparative Example 3) at different pH values. From Figure 5 It can be seen that in an acidic environment, three key functional groups, amino (-NH2), carboxylate (-COO-) and epoxy groups, will be protonated. This process and the competitive adsorption of a large number of H+ ions with target Cs+ cations significantly affect the adsorption efficiency. Specifically, -NH2 protonation to -NH3+ and -COO- protonation to -COOH reduce their chelation ability to Cs+ ions, resulting in a decrease in adsorption capacity. When the pH value is 4.0, the adsorption capacity of GCAE reaches 13.8 mg / g. When the pH value approaches neutrality (pH = 7.0), the dissociation rate of carboxylate and epoxy groups decreases significantly, weakening their affinity for Cs+ ions. Therefore, in this pH range, the adsorption performance tends to be stable. Among the four tested aerogels, GCAE exhibits superior adsorption performance, with a maximum adsorption capacity of 19.2 mg / g. 3+ and -COO - Protonation to -COOH reduces their chelation ability to Cs + ions, resulting in a decrease in adsorption capacity. When the pH value is 4.0, the adsorption capacity of GCAE reaches 13.8 mg / g. When the pH value approaches neutrality (pH = 7.0), the dissociation rate of carboxylate and epoxy groups decreases significantly, weakening their affinity for Cs + ions. Therefore, in this pH range, the adsorption performance tends to be stable. Among the four tested aerogels, GCAE exhibits superior adsorption performance, with a maximum adsorption capacity of 19.2 mg / g.

[0106] Figure 6 are the nitrogen adsorption-desorption isotherms of GCAE (Example 1), GFAE (Comparative Example 1), CNC (Comparative Example 2) and CNF (Comparative Example 3). From Figure 6 It can be seen that in the relative pressure range 0 to 0.3 P / P0, the pore walls of the aerogels begin to undergo monolayer adsorption. When the relative pressure further increases (between 0.3 and 0.7), all four aerogels exhibit multilayer adsorption characteristics. The research results show that the physical adsorption characteristics of these aerogels conform to the IV-type adsorption isotherm with a H3 hysteresis loop. The presence of the IV-type adsorption isotherm means that the four prepared aerogels all have mesoporous structures. The adsorption characteristics of mesopores are mainly determined by the interaction between the adsorbent and the adsorbate, as well as the intermolecular interactions within the condensed phase. Therefore, the monolayer to multilayer adsorption process first occurs on the mesoporous walls, followed by condensation within the pores. According to the information in Table 1, the specific surface area of GCAE is much larger than that of GFAE, and the pore size is also significantly larger. This difference can be attributed to the three-dimensional network structure of CNC, which achieves a higher specific surface area than CNF through its small size, fully fibrillated structure and high dispersibility.

[0107] In summary, the beneficial effects of the present application are:

[0108] (1) Structural advantage: Through the compounding of nanocellulose and GO-ECH, combined with crown ether modification, a three-dimensional network structure with light weight, high porosity and high mechanical strength is formed;

[0109] (2) Function can be adjusted: the modification step (such as GO introduction) can give aerogel conductivity, adsorption or catalytic performance;

[0110] (3) Process controllable: the parameters (temperature, time, ratio) of each step are optimized to ensure the reproducibility of the product and the feasibility of large-scale production;

[0111] (4) In the modified nanofiber aerogel prepared by the application, the crown ether has a unique cyclic structure and can specifically recognize Cs + The graphene oxide film has excellent separation performance, the cellulose nanocrystal has a three-dimensional network structure and has a high specific surface area, and is used as a support skeleton; therefore, the aerogel can specifically recognize Cs + In the water environment and selectively adsorb and separate Cs + .

[0112] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the application, and not to limit them; although the application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the application.

Claims

1. A method for preparing a modified nanofiber aerogel, characterized in that: The specific steps include: Step S1, placing absorbent cotton in a sulfuric acid solution, stirring in an oil bath, pouring into ice water, standing overnight, centrifuging and dialysis to purify nanocellulose; Step S2: adding DMAC to the nanocellulose prepared in step S1 and heating under a nitrogen atmosphere; then adding CDI and stirring to react; after the reaction is completed, adding ECH to the reaction system and continuing the reaction to obtain modified cellulose; Step S3, dispersing graphene oxide in water, adding NaOH and ECH; performing a reflux reaction under a nitrogen atmosphere; after the reaction is completed, washing the obtained black solid with distilled water and vacuum drying to obtain GO-ECH; Step S4, dissolving A18C6 in DMF at room temperature, then adding sodium hydride, and performing reflux reaction under a nitrogen atmosphere to obtain a mixed solution; Step S5, dispersing the modified cellulose prepared in step S2 and the GO-ECH prepared in step S3 in DMF, and adding the uniformly dispersed dispersion to the mixed solution prepared in step S4; performing a reflux reaction under a nitrogen atmosphere to obtain a reaction solution; Step S6, pouring the reaction solution obtained in step S5 into a container and evaporating it in a water bath to obtain a cellulose aerogel precursor; Step S7, soaking the cellulose aerogel precursor prepared in step S6 in an ethanol solution to obtain a cellulose alcohol gel; Step S8: supercritically drying the cellulose alcohol gel prepared in step S7 to obtain cellulose aerogel.

2. The method for preparing a modified nanofiber aerogel according to claim 1, wherein: In step S1, the volume ratio of sulfuric acid to water in the sulfuric acid solution is 1:

1.

3. The method for preparing a modified nanofiber aerogel according to claim 1, wherein: In step S3, the mass ratio of graphene oxide to water is 1:100, and the mass ratio of NaOH to ECH is 1:

1.

4. The method for preparing a modified nanofiber aerogel according to claim 1, wherein: In step S4, the reflux temperature is 60° C. and the reflux time is 4 hours.

5. The method for preparing a modified nanofiber aerogel according to claim 1, wherein: In step S5, the reflux temperature is 90° C. and the reflux time is 72 h.

6. The method for preparing a modified nanofiber aerogel according to claim 1, characterized in that: In step S5, the volume ratio of modified cellulose, GO-ECH and DMF is 1:1:1; and the volume ratio of the dispersion liquid to the mixed solution is 1:

1.

7. The method for preparing a modified nanofiber aerogel according to claim 1, characterized in that: In step S6, the water bath evaporation temperature is 40°C.

8. The method for preparing a modified nanofiber aerogel according to claim 1, wherein: In step S8, the supercritical drying time is 12 hours.

9. A modified nanofiber aerogel, characterized in that: The method is as described in any one of claims 1 to 8.

10. A use of the modified nanofiber aerogel according to claim 9, characterized in that: Application of the modified nanofiber aerogel in radioactive wastewater treatment.

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