A tocnf / pva / ga / pei aerogel and a preparation method and application thereof

Abstract

The present application relates to aerogel adsorption material technical field, especially to a kind of TOCNF / PVA / GA / PEI aerogel and its preparation method and application.The preparation method includes: TOCNF suspension and PVA solution are mixed, GA is added under acidic conditions to carry out pre-crosslinking, then adjust system to weak alkaline, again PEI solution is added, multiple crosslinking network is constructed by Schiff base reaction and hydrogen bond interaction, freeze-drying is obtained.Through the regulation and control of PEI concentration and system pH, the PEI rich in amino group is successfully introduced as structural component into aerogel skeleton, not only significantly increase the specific surface area and construct hierarchical porous structure, also greatly improve the mechanical strength and structural stability of material.The aerogel shows excellent adsorption capacity, fast adsorption rate to organic dye and heavy metal copper ion in water body, and has good cyclic regeneration capacity, has wide application prospect in the field of pollutant efficient removal in complex water environment.

Description

Technical Field

[0001] This invention relates to the field of aerogel adsorption materials technology, and in particular to a TOCNF / PVA / GA / PEI aerogel, its preparation method, and its applications. Background Technology

[0002] Aerogels are nanoporous materials with extremely high porosity and extremely low density, and have great potential applications in fields such as thermal insulation and adsorption. TOCNF / PVA / GA aerogel is one such environmentally friendly composite material. However, in practical applications, TOCNF / PVA / GA aerogel still has shortcomings in terms of recycling life and adsorption capacity, which creates a bottleneck in its application when dealing with industrial-grade, long-cycle, and highly complex wastewater.

[0003] Therefore, improving the recycling life and adsorption capacity of TOCNF / PVA / GA aerogels is an urgent problem to be solved. Summary of the Invention

[0004] In view of this, the present invention proposes a TOCNF / PVA / GA / PEI aerogel, its preparation method, and its applications. By introducing PEI (polyethyleneimine) into the TOCNF / PVA / GA system and controlling the concentration of PEI and the pH of the solution, the prepared TOCNF / PVA / GA / PEI aerogel exhibits increased specific surface area, a more compact pore structure, and enhanced mechanical properties, significantly improving the aerogel's recycling life and adsorption capacity.

[0005] The technical solution of this invention is implemented as follows: In a first aspect, the present invention provides a method for preparing TOCNF / PVA / GA / PEI aerogel, comprising the following steps: S1, add glutaraldehyde (GA) to mixture 1 and stir until homogeneous to obtain mixture 2; S2, add polyethyleneimine (PEI) solution to mixture 2, freeze dry to obtain TOCNF / PVA / GA / PEI aerogel.

[0006] This invention involves mixing the components in a sol state and forming a continuous network through chemical crosslinking. GA acts as a crosslinking agent, simultaneously crosslinking PVA and PEI to form a covalently bonded network framework. PVA serves as a connector, linking the rigid TOCNF and PEI, resulting in a more uniform and stable network structure. PEI is uniformly distributed within and on the surface of the aerogel framework, making it an integral part of the structure. This enhances the mechanical properties and structural integrity of the aerogel, making it suitable for repeated use.

[0007] Based on the above technical solutions, preferably, in step S2, the concentration of the polyethyleneimine solution is 0.5~2.5wt%.

[0008] Based on the above technical solution, a further preferred embodiment is that the concentration of the polyethyleneimine solution is 2.5 wt%.

[0009] At high PEI concentrations, the TOCNF / PVA / GA system will instantly agglomerate into clumps, separating the solution from the clump polymer and failing to form a homogeneous mixed gel system. At low PEI concentrations, insufficient cross-linking is likely to occur, resulting in a loose network that exists as a suspension or paste, failing to form a complete gel system.

[0010] Based on the above technical solution, preferably, in step S2, before adding the polyethyleneimine solution, the pH of the mixture 2 is adjusted to 7.5~8.5; Based on the above technical solutions, preferably, and even more preferably, the pH of the mixture 2 is adjusted to 8.0 before adding the polyethyleneimine solution.

[0011] Based on the above technical solutions, preferably, in step S1, the pH of the mixture 1 is 3.5~4.5.

[0012] Based on the above technical solution, in a further preferred embodiment, in step S1, the pH of the mixture 1 is 4.0.

[0013] When the solution pH is low (e.g., 3.0~7.0), PEI will be overprotonated, and the amino groups on PEI will react with H under low pH conditions. + Formed as -NH 3+ -NH 2+ The molecular chains are overstretched due to charge repulsion. At low solution pH, the carboxyl groups on the TOCNF surface are negatively charged, and the strongly positively charged PEI is instantaneously attracted to the fiber surface, forming flocculation or precipitation instead of uniform mixing. The Schiff base reaction between GA and amino groups is slow under weakly acidic or alkaline conditions, resulting in insufficient covalent cross-linking. At high solution pH (e.g., 9.0–11.0), the amino groups in PEI exist in the form of -NH2, with less net positive charge, resulting in weaker electrostatic attraction with TOCNF. PEI is not easily and firmly adsorbed onto the fiber surface, and may detach from the TOCNF / PVA network during mixing. The Schiff base reaction between GA and PEI is too rapid under these conditions, potentially resulting in rapid surface cross-linking and hindering PEI diffusion into the fiber.

[0014] Based on the above technical solutions, preferably, in step S1, the components of the mixture 1 include a polyvinyl alcohol (PVA) solution and a TOCNF suspension.

[0015] The TOCNF suspension is a sunflower stalk cellulose nanofiber suspension, which is prepared as follows: using 40-60 mesh sunflower stalk powder as raw material, hemicellulose and lignin are removed by chemical treatment to obtain stalk cellulose. The cellulose is further oxidized by TEMPO at 12 mmol / g NaClO for 4 h, and then ultrasonically treated at 800 W for 1 h to obtain the TOCNF suspension.

[0016] Based on the above technical solutions, a further preferred embodiment is that the concentration of the PVA solution is 1~1.5wt%.

[0017] Based on the above technical solutions, and even more preferably, the concentration of the PVA solution is 1.5 wt%, the concentration of the TOCNF suspension is 1 wt%, and the concentration of the GA is 25 wt%.

[0018] Secondly, a TOCNF / PVA / GA / PEI aerogel is provided, which is prepared by the TOCNF / PVA / GA / PEI aerogel preparation method described above.

[0019] Thirdly, a method for adsorbing pollutants is provided, comprising the step of adding TOCNF / PVA / GA / PEI aerogel as described above to the pollutants.

[0020] Based on the above technical solutions, preferably, the pollutants include organic dyes and heavy metal ions.

[0021] Based on the above technical solutions, preferably, the organic dye includes MB (methylene blue) and CV (crystal violet); the heavy metal ions include Cu. 2+ .

[0022] Based on the above technical solutions, preferably, the initial pH of the pollutant is 3~11 or 1~5, and the initial concentration is 20~200mg / L.

[0023] Based on the above technical solutions, a further preferred embodiment is that the initial pH of the organic dye pollutant is 11, the initial pH of the heavy metal ions is 5, and the initial concentration of the pollutant is 100 mg / L.

[0024] The TOCNF / PVA / GA / PEI aerogel and its preparation method of the present invention have the following advantages over the prior art: 1. By covalently crosslinking PEI rich in primary and secondary amines onto the aerogel framework, the active sites on the material surface are greatly enriched. Experiments show that the optimized aerogel exhibits improved resistance to methylene blue (MB), crystal violet (CV), and Cu. 2+The theoretical maximum adsorption capacities can reach as high as 322.4 mg / g, 348.6 mg / g, and 358.1 mg / g, respectively, which is a significant leap compared to unmodified or low PEI content materials. At the same time, its rapid adsorption kinetics shorten the adsorption equilibrium time to 120 minutes.

[0025] 2. In-situ crosslinking of PEI constructs a dense dual-network structure based on Schiff bases and hydrogen bonds, endowing the aerogel with both rigidity and flexibility. The material not only exhibits excellent resilience (elastic modulus up to 159 kPa) under 80% high compressive strain, allowing it to be processed into various shapes to adapt to dynamic working conditions, but also completely solves the problem of swelling and collapse of traditional TOCNF / PVA / GA aerogels in the aqueous phase. After five adsorption-desorption cycles, the removal rate of the three target pollutants remains above 80%, significantly reducing long-term operating costs.

[0026] 3. The introduction of PEI establishes a multi-layered adsorption mechanism (such as electrostatic attraction, chelate coordination, and hydrogen bonding), enabling the material to maintain high adsorption efficiency over a wide pH range. Simultaneously, it can effectively adsorb ions at high concentrations of coexisting Na+ ions. + Ca 2+ Cl - SO4 2- Under these conditions, relying on amino groups and Cu 2+ The strong coordination of heavy metals exhibits excellent anti-interference ability and selectivity. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is a flowchart illustrating the preparation process of the TOCNF / PVA / GA / PEI aerogel of the present invention. Figure 2 This invention is TOCNF / PVA 1.5% Chemical structure diagrams of / GA and TOCNF / PVA / GA / PEI aerogels, where (a) represents the FTIR diagram and (b) represents the XRD diagram; Figure 3 The diagram shows the microstructure of the TOCNF / PVA / GA / PEI aerogel of this invention, where figures (a) to (f) represent the TOCNF / PVA aerogel, respectively. 1.5% / GA、TOCNF / PVA / GA / PEI 0.5%TOCNF / PVA / GA / PEI 1% TOCNF / PVA / GA / PEI 1.5% TOCNF / PVA / GA / PEI 2% TOCNF / PVA / GA / PEI 2.5% ; Figure 4 This invention is TOCNF / PVA 1.5% Density and porosity analysis diagrams of / GA and TOCNF / PVA / GA / PEI aerogels; Figure 5 This invention is TOCNF / PVA 1.5% Thermogravimetric analysis (TGA) plots of / GA and TOCNF / PVA / GA / PEI aerogels, where (a) represents the TGA curve and (b) represents the DTG curve; Figure 6 This invention is TOCNF / PVA 1.5% XPS scan curves of GA / PVA / GA / PEI aerogels, where (a) shows the full spectrum of each sample and (b) shows the spectrum of TOCNF / PVA / GA / PEI aerogels. 2.5% aerogel C 1s peaks, (c) figure represents TOCNF / PVA / GA / PEI 2.5% Aerogel O 1s peaks, (d) figure represents TOCNF / PVA / GA / PEI 2.5% Aerogel N 1s peak fractionation; Figure 7 This invention is TOCNF / PVA 1.5% The compressibility of / GA and TOCNF / PVA / GA / PEI aerogels is shown in Figure (a), which represents the stress-strain curve, and Figure (b) represents the actual compressed object. Figure 8 These are actual images of TOCNF / PVA / GA / PEI aerogels of the present invention in different shapes; Figure 9 This invention is TOCNF / PVA 1.5% N2 adsorption-desorption isotherms and pore size distribution diagrams of / GA / PVA / GA / PEI aerogels, where (a) to (f) represent the N2 adsorption-desorption isotherms and pore size distribution diagrams of TOCNF / PVA / GA / PEI aerogels, respectively. 1.5% / GA、TOCNF / PVA / GA / PEI 0.5% TOCNF / PVA / GA / PEI 1% TOCNF / PVA / GA / PEI 1.5% TOCNF / PVA / GA / PEI 2% TOCNF / PVA / GA / PEI2.5% ; Figure 10 pH value for TOCNF / PVA / GA / PEI 2.5% The effect of aerogel adsorption is shown in Figure (a) for MB, Figure (b) for CV, and Figure (c) for Cu. 2+ ; Figure 11 Initial concentrations of TOCNF / PVA / GA / PEI 2.5% Aerogel adsorption of MB, CV and Cu 2+ Effect of adsorption capacity; Figure 12 MB, CV, and Cu are the components of the aerogel of this invention. 2+ The adsorption kinetic model is shown in (A) t figure, which represents the effect of reaction time on the adsorption amount of aerogel; (b) figure represents the pseudo-first-order kinetic model; (c) figure represents the pseudo-second-order kinetic model; and (d) figure represents the intraparticle diffusion model (C0=100mg / L, t=24h, V=100ml, dye pH=7, copper ion pH=5, T=25℃). Figure 13 The aerogel of this invention is effective against MB, CV and Cu. 2+ The adsorption isotherm model is shown in Figure (a), which represents the Langmuir model fit, and Figure (b) represents the Freundlich model fit. Figure 14 This invention is TOCNF / PVA / GA / PEI 2.5% The partition coefficients of aerogel adsorption, where (a) represents MB, (b) represents CV, and (c) represents Cu. 2+ (T=25℃, m=50mg, dye solution pH=7, copper ion solution pH=5, V=100mL); Figure 15 This invention is TOCNF / PVA / GA / PEI 2.5% Cyclic adsorption performance diagram of aerogel; Figure 16 For different concentrations of ions, TOCNF / PVA / GA / PEI 2.5% The effect of aerogel adsorption is shown in Figure (a) for MB, Figure (b) for CV, and Figure (c) for Cu. 2+ ; Figure 17 This invention is TOCNF / PVA / GA / PEI 2.5% FTIR image of aerogel after adsorption; Figure 18 This invention is TOCNF / PVA / GA / PEI 2.5%SEM-EDS images of aerogel after adsorption, where (a), (d), and (g) represent MB, (b), (e), and (h) represent CV, and (c), (f), and (i) represent Cu. 2+ ; Figure 19 This is a diagram illustrating the adsorption mechanism of the TOCNF / PVA / GA / PEI aerogel of this invention. Detailed Implementation

[0029] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0030] The PEI (analytical grade) used in this invention was purchased from Shanghai Ron Reagent Co., Ltd., and the other reagents were all commercially available products.

[0031] Example 1 Preparation of TOCNF / PVA / GA / PEI aerogel.

[0032] A 1.5 wt% PVA solution and a 1 wt% TOCNF suspension were mixed thoroughly. The pH was adjusted to approximately 4.0 with 0.1 M HCl. 5 ml of 25% GA was added to each mixture, and the mixture was stirred for 60 min to ensure homogeneity. 100 ml of each mixture was taken, and the pH was adjusted to 8.0 with 0.1 M NaOH. PEI solutions with concentrations of 0 wt%, 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, and 3 wt% were added respectively to prepare a series of TOCNF / PVA samples. 1.5% / GA、TOCNF / PVA / GA / PEI 0.5% TOCNF / PVA / GA / PEI 1% TOCNF / PVA / GA / PEI 1.5% TOCNF / PVA / GA / PEI 2% TOCNF / PVA / GA / PEI 2.5% and TOCNF / PVA / GA / PEI 3% All samples were freeze-dried at -70℃ and 1 Pa for 72 hours. The preparation process is as follows: Figure 1 As shown.

[0033] Example 2 Characterization: The TOCNF / PVA / GA / PEI aerogel in Example 1 was tested using conventional testing methods, including FTIR, XRD, SEM, BET, TG, XPS, density, porosity, and compressibility. The results are as follows.

[0034] 1. Crystal structure, functional groups, and structural changes of aerogels: FTIR and XRD tests were performed on the aerogels to characterize the changes in functional groups and crystal structure during the material preparation process. For example... Figure 2 As shown in Figure (a), the infrared spectra of the aerogel are at 3399 cm⁻¹. -1 2900cm -1 1432cm -1 and 1100cm -1 The presence of characteristic cellulose peaks indicates that PEI modification did not alter the structure of cellulose. (This is in contrast to TOCNF / PVA.) 1.5% Compared to GA aerogel, TOCNF / PVA / GA / PEI aerogels have different performance at 1612 cm⁻¹. -1 1460cm -1 A new absorption peak appears at 1720 cm⁻¹, due to the bending vibration of the NH bond and the stretching vibration of CN. The bending vibration of the NH bond is attributed to the characteristic peak absorption of primary or secondary amines in PEI, and the intensity of this peak gradually increases with increasing PEI concentration. -1 The weakening of the C=O peak and the 1640 cm⁻¹ -1 ~1690cm -1 The stretching vibrations of C=N bonds within the specified range, and the newly emerging characteristic peaks, prove the successful preparation of TOCNF / PVA / GA / PEI aerogel. Higher PEI concentrations result in more complete cross-linking reactions and more pronounced changes in chemical bonds. At 3399 cm⁻¹... -1 The broad absorption peak at that point represents the OH stretching vibration. As the PEI concentration increases, the OH stretching vibration peak shifts slightly towards lower wavenumbers, indicating that the introduction of PEI enhances the hydrogen bond interactions in the system, leading to a decrease in the vibrational frequency of the OH bond.

[0035] The crystal structure of aerogel is as follows Figure 2 As shown in Figure (b), with TOCNF / PVA 1.5% Compared to GA aerogels, the introduction of PEI did not alter the crystal structure of the aerogels. All five aerogels (TOCNF / PVA / GA / PEI) exhibited broadened diffraction peaks near 2θ=20°, a typical characteristic of amorphous crystallization. A distinct diffraction peak was observed near 2θ=33°, reflecting the partial crystalline structure retained by TOCNF in the composite aerogel. As the PEI concentration increased from 0.5wt% to 2.5wt%, the crystallinity of the aerogel decreased; the increase in amorphous regions provides more adsorption sites, thereby improving the adsorption performance of the aerogel.

[0036] Microstructure of aerogels: such as Figure 3 As shown, TOCNF / PVA 1.5% / GA aerogels have fewer micropores on their surface, resulting in poor pore penetration and stability. With the introduction of PEI, all five aerogels (TOCNF, PVA, GA, and PEI) exhibit a dense and stable three-dimensional porous network structure. PEI is uniformly loaded on the pore wall surface, directly affecting the pore structure of the aerogel. Its supporting effect prevents pore structure collapse and increases pore wall roughness. As the PEI concentration increases, the pore structure of the aerogel becomes more concentrated and uniform. When the PEI concentration is 2.5 wt%, the pores in the aerogel are interconnected, forming crisscrossing channels that ensure the stability of MB, CV, and Cu. 2+ Molecular diffusion and adsorption within pores enable efficient removal of dyes and heavy metals.

[0037] Density and Porosity: Density and porosity analysis diagrams of aerogels prepared with different concentrations of PEI, from... Figure 4 It can be seen that with the increase of PEI concentration, the density of the aerogel increases while the porosity decreases. (TOCNF / PVA) 1.5% / GA、TOCNF / PVA / GA / PEI 0.5% TOCNF / PVA / GA / PEI 1% TOCNF / PVA / GA / PEI 1.5% TOCNF / PVA / GA / PEI 2% and TOCNF / PVA / GA / PEI 2.5% The porosities of the aerogels were 95.24%, 94%, 92.5%, 91%, 90%, and 89%, respectively. This is because, on the one hand, the increased PEI concentration enhanced the cross-linking degree of the material, with a large number of amino groups serving as additional cross-linking sites. The original macropores were divided into many micropores, reducing the interpore spacing and making the overall structure more compact. On the other hand, PEI molecules could fill the original pore structure, further reducing the pore space. These results indicate that PEI concentration is an effective parameter for controlling the pore structure of aerogels.

[0038] Thermal stability analysis: Figure 5 For TOCNF / PVA 1.5% Comparison of TG and DTG curves of / GA / TOCNF / PVA / GA / PEI aerogels. Figure 5As shown in (a), under N2 atmosphere, the mass change of aerogel mainly stems from water evaporation and thermal decomposition of organic matter. The low-temperature weight loss stage (30℃~200℃) is primarily due to water evaporation. Aerogels possess a high specific surface area and abundant pore structure, enabling them to adsorb a certain amount of water. With increasing PEI concentration, the network structure of the aerogel becomes denser, absorbing less water and correspondingly reducing the weight loss rate. In the thermal decomposition stage (200℃~400℃), polymer chains such as TOCNF, PVA, and PEI break and degrade at high temperatures. As the PEI concentration increases from 0% to 2.5%, the Tg of the aerogel... initial The weight loss rate of the aerogel increased slightly. This is because the amino groups in PEI molecules can covalently cross-link with functional groups such as hydroxyl groups in TOCNF and PVA molecules, enhancing the stability of the aerogel's network structure and causing the polymer chains to break only at higher temperatures. During the high-temperature carbonization stage (400℃~800℃), the remaining organic components of the aerogel carbonize into char residue. The weight loss rate of the aerogel in this stage showed little difference at different PEI concentrations, but the final char residue content increased slightly with increasing PEI concentration. This is because the nitrogen element in PEI molecules can promote the carbonization process at high temperatures, forming nitrogen-containing carbon structures, thereby increasing the char residue content. Figure 5 As shown in (b), the main decomposition peaks of all samples appeared at 250℃~300℃. With the increase of PEI concentration, the position of the decomposition peaks shifted slightly towards higher temperatures, indicating that the addition of PEI improved the thermal stability of the aerogel.

[0039] X-ray photoelectron spectroscopy analysis: The full spectrum of the aerogel is shown below. Figure 6 As shown, by Figure 6 It was found that C, N, and O elements were present in all aerogel samples. As the PEI concentration increased from 0% to 2.5%, the N content in the aerogel continuously increased, indicating that PEI was successfully introduced into the aerogel framework. The abundant amino groups on the aerogel surface can effectively adsorb dyes or heavy metal ions through electrostatic interactions or coordination, thereby effectively increasing the adsorption performance of the aerogel. Figure 6 Figure (b) shows TOCNF / PVA / GA / PEI. 2.5% The aerogel exhibits high-resolution C 1s peaks, revealing three carbon chemical environments: CC, CO, and C=O, corresponding to the polymer's alkyl chain, hydroxyl / ether bond, and carbonyl structure. Figure 7 Figure (c) is TOCNF / PVA / GA / PEI 2.5% The aerogel exhibits a high-resolution O 1s peak, which reveals two oxidative environments: CO and C=O, corresponding to oxygen in hydroxyl groups, ether bonds, and carbonyl groups. Figure 7 (d) is TOCNF / PVA / GA / PEI 2.5%The aerogel exhibits a high-resolution N 1s peak and characteristic C=N (398.8 eV) bond positions, corresponding to the Schiff base structure formed by the reaction of PEI and the aldehyde group on GA. In summary, TOCNF / PVA / GA / PEI... 2.5% Aerogels form cross-linked structures through aldol condensation and Schiff base reactions, and the introduction of PEI increases amino functional groups, providing a structural basis for the regulation of aerogel adsorption performance.

[0040] Mechanical property analysis: A compression test was performed on the material under 80% compressive strain conditions, and stress-strain curves were plotted. Figure 7 As shown. By Figure 7 It can be seen that as the PEI concentration increases, the compressive modulus of the aerogel gradually increases, and the TOCNF / PVA ratio increases. 1.5% / GA、TOCNF / PVA / GA / PEI 0.5% TOCNF / PVA / GA / PEI 1% TOCNF / PVA / GA / PEI 1.5% TOCNF / PVA / GA / PEI 2% The compressive moduli are 20 kPa, 25 kPa, 28 kPa, 50 kPa, and 62 kPa, respectively. (TOCNF / PVA / GA / PEI) 2.5% Aerogels exhibit the highest elastic modulus, reaching 159 kPa. This is attributed to the fact that as the PEI concentration increases, its abundant amino groups form a dense chemical cross-linking and hydrogen bond network with the various components, increasing the interfacial bonding force of the material and constructing a more robust honeycomb structure. This structure allows the aerogel to transmit stress more evenly under load, thereby effectively improving the elastic modulus.

[0041] TOCNF / PVA / GA / PEI hydrogels prepared by the cross-linking effect of PEI can be freeze-dried to obtain aerogels of different shapes, all of which retain their good shape and structure, such as... Figure 8 As shown, materials with different shapes and structures are suitable for various wastewater treatment scenarios, such as inside dyeing and printing wastewater conveying pipelines. They can be adjusted according to different working conditions, exhibiting good environmental adaptability and shape controllability.

[0042] Specific surface area analysis: The pore structure of the aerogel samples was systematically characterized using nitrogen adsorption-desorption tests. For example... Figure 9 As shown, all samples exhibited typical Type IV isotherm characteristics, accompanied by a significant H3 hysteresis loop, indicating that the PEI-modified aerogel still retains mesoporous structures. BET surface area analysis showed that with increasing PEI concentration, the specific surface area gradually increased, and the pore structure became more uniform. The introduction of PEI increased its specific surface area, pore size range, and average pore size. (TOCNF / PVA) 1.5% / GA、TOCNF / PVA / GA / PEI 0.5% TOCNF / PVA / GA / PEI 1% TOCNF / PVA / GA / PEI 1.5% TOCNF / PVA / GA / PEI 2% and TOCNF / PVA / GA / PEI 2.5% The specific surface area of ​​the aerogel is 45.95 m². 2 / g, 52.42m 2 / g, 57.89m 2 / g、61.23m 2 / g, 64.75m 2 / g and 69.52m 2 / g. TOCNF / PVA / GA / PEI 2.5% The specific surface area is compared with TOCNF / PVA / GA / PEI 0.5% It increased by 17.1m 2 / g, compared to TOCNF / PVA 1.5% / GA aerogel increased by 23.57m 2 / g. As the PEI concentration increased from 0 wt% to 2.5 wt%, the average pore size increased from 12.69 nm to 20.41 nm. This indicates that the increased PEI concentration leads to the formation of more mesopores and a finer three-dimensional network structure, providing more active sites for subsequent adsorption applications. When the PEI concentration was further increased to 3 wt%, significant aggregation occurred in the system, leading to solid-liquid separation and the inability to form a homogeneous and stable composite aerogel; therefore, its performance was not tested. In summary, TOCNF / PVA / GA / PEI 2.5% Aerogels outperform TOCNF / PVA in terms of specific surface area, mechanical properties, and porosity. 1.5% / GA、TOCNF / PVA / GA / PEI 0.5% TOCNF / PVA / GA / PEI 1% TOCNF / PVA / GA / PEI 1.5% TOCNF / PVA / GA / PEI 2% Therefore, TOCNF / PVA / GA / PEI were selected. 2.5% The adsorption properties of straw nanocellulose-based composite aerogel were studied.

[0043] Example 3 Analysis of the adsorption properties of aerogels.

[0044] The effect of pH on adsorption efficiency: Figure 10 For different pH values, the effects of TOCNF / PVA / GA / PEI2.5% Effect of aerogel adsorption. At pH 3, the adsorption capacities of the aerogel for MB and CV were 157 mg / g and 164.8 mg / g, respectively, with removal rates of 78.5% and 82.4%. As the pH increased to 11, the adsorption capacities of the aerogel for MB and CV were 181.8 mg / g and 189.8 mg / g, respectively, with removal rates of 90.9% and 94.9%. This is because at pH 3, the H+ in the solution... + Increased concentration causes it to compete with positively charged dye molecules for adsorption active sites, hindering dye adsorption and resulting in lower adsorption capacity. Simultaneously, MB can be protonated to form a neutral substance (MBH). 2+ →MBH3 2+ At low pH values, this weakens the interaction between MB and aerogel anions. Under acidic conditions, the amino groups in the adsorbent are protonated, forming positively charged -NH groups. 3+ With MB, CV and Cu 2+ Mutual electrostatic repulsion limits removal efficiency to some extent. Under alkaline conditions, the amino groups on the adsorbent surface are deprotonated, enhancing electrostatic attraction and significantly increasing adsorption capacity. At pH 1, TOCNF / PVA / GA / PEI... 2.5% Aerogels for Cu 2+ The adsorption capacity was 173 mg / g, and the removal rate was 86.5%. At pH 5, the aerogel showed good adhesion to Cu. 2+ The adsorption capacity increased to 191.7 mg / g, with a removal rate of 95.35%. The adsorption capacity of the aerogel for heavy metal ions increased with increasing pH, because at pH 1, high concentrations of H+ ions... + Protonation intensifies H + With Cu 2+ Competition leads to a decrease in adsorption rate. With increasing pH, deprotonation and release of active sites occur, and Cu... 2+ Coordination occurs between the carboxyl and amino groups, increasing the adsorption capacity.

[0045] Effect of initial concentration on adsorption efficiency: Figure 11 The change in aerogel adsorption capacity under different initial concentrations of dyes or heavy metal solutions is shown. The adsorption capacity of TOCNF / PVA / GA / PEI increases with increasing initial concentration. 2.5% The adsorption capacity of the aerogel showed a trend of initially increasing rapidly and then increasing slowly. At an initial concentration of 20 mg / L, the aerogel exhibited high adsorption capacity for MB, CV, and Cu. 2+The adsorption capacities were 72.4 mg / g, 78.4 mg / g, and 77.5 mg / g, respectively, with removal rates of 80.4%, 82.4%, and 82.2%. At lower initial concentrations, the aerogel surface had numerous adsorption sites, not yet reaching saturation, resulting in a rapid increase in removal rate. When the initial concentration increased to 150 mg / L, the rate of increase in adsorption capacity slowed down; at this point, the aerogel's adsorption capacity for MB, CV, and Cu decreased. 2+ The maximum adsorption capacities reached were 298.1 mg / g, 318.76 mg / g, and 340.7 mg / g, respectively, with removal rates of 92.2%, 92.3%, and 93.6%. When the initial concentration increased to 200 mg / L, the aerogel showed good adsorption for MB, CV, and Cu. 2+ The maximum adsorption capacities reached were 322.4 mg / g, 348.6 mg / g, and 358.1 mg / g, respectively, with removal rates of 94.85%, 96.15%, and 96.5%. This is because as the initial concentration gradually increases, the number of active sites on the aerogel surface remains constant, the number of available sites gradually decreases, and the adsorption capacity increases slowly. When all sites are occupied, the adsorption capacity reaches its maximum value, and adsorption eventually tends to equilibrium. After reaching adsorption equilibrium, further increasing the initial concentration has little effect on the adsorption capacity.

[0046] 3. Adsorption kinetics analysis: By measuring the adsorption amount at different times, a kinetic model was used to study the effect of time on the adsorption of MB, CV, and Cu in aerogels. 2+ The impact, the results are as follows Figure 12 As shown. Figure 12 Figure (a) is TOCNF / PVA / GA / PEI 2.5% Aerogels at different contact times affect MB, CV and Cu 2+ The adsorption capacity is shown in the figure. In the first 60 minutes, the adsorption rate is relatively fast. This is because, on the one hand, the aerogel surface has abundant hydroxyl, amino, and carboxyl groups, which facilitate the adsorption of dyes and heavy metal ions through hydrogen bonding and electrostatic interactions. On the other hand, aerogels are mesoporous materials, and their large pore volume and size enable rapid mass transfer, allowing dye or heavy metal molecules to enter the molecular interior through the pores and be captured by the abundant active sites. As time progresses, adsorption gradually reaches equilibrium, mainly because the adsorption sites become saturated. At 120 minutes, the aerogel reaches adsorption equilibrium for MB, CV, and Cu. 2+ The adsorption capacities were 169.1 mg / g, 182.2 mg / g, and 191.7 mg / g, respectively. To further investigate the adsorption kinetics of the composite aerogel, quasi-first-order kinetic models, quasi-second-order kinetic models, and intraparticle diffusion models were used to analyze the adsorption of MB, CV, and Cu by the composite aerogel at different contact times. 2+ The adsorption effect, such as Figure 12As shown in Table 1. Figure 12 Figure (b) shows the simulated curve of the pseudo-first-order dynamics curve. Figure 12 Figure (c) shows the simulated pseudo-second-order kinetic curves. The R² values ​​obtained by fitting the pseudo-second-order kinetic curves are 0.993, 0.966, and 0.977, respectively, which are higher than the correlation coefficients of the pseudo-first-order kinetic model. The simulated adsorption capacities are 163.62 mg / g, 174.12 mg / g, and 187.42 mg / g, respectively, which are closer to the experimental adsorption capacities. This further proves that the pseudo-second-order kinetic curves are more suitable for describing the adsorption of MB, CV, and Cu by TOCNF / PVA / GA / PEI 2.5% aerogel. 2+ The adsorption process. Figure 12 Figure (d) is a model of intraparticle diffusion. From the figure, it can be seen that q t and t 1 / 2 The curve exhibits a two-segment linear characteristic, and neither segment passes through the origin. This indicates that intraparticle diffusion is not the only rate-determining step; boundary diffusion also affects the adsorption rate.

[0047] Table 1. Adsorption of MB, CV, and Cu by aerogels 2+ kinetic parameters

[0048] 4. Adsorption isotherm analysis: For TOCNF / PVA / GA / PEI 2.5% The adsorption results of the aerogel were linearly fitted, and the fitting results of the Langmuir isotherm and Freundlich isotherm models are as follows: Figure 13 As shown in Figures (a) and (b), the fitting parameters are shown in Table 2.

[0049] Table 2. Isotherm Fitting Data

[0050] The results show that both isotherm models fit the adsorption results well. However, the normalization coefficient R of the Langumir model is lower. 2 The R values ​​were 0.984, 0.983, and 0.984, respectively, all higher than Freundlich's model fit R. 2 The values ​​are 0.976, 0.971, and 0.975, respectively. This indicates that the Langumir model better describes TOCNF / PVA / GA / PEI. 2.5% Aerogel adsorption of MB, CV and Cu 2+The process is monolayer adsorption, with uniform distribution of adsorption sites on the surface and the same ability of adsorption active centers. The maximum monolayer adsorption amounts on the aerogel are 169.1 mg / g, 182.2 mg / g, and 191.7 mg / g respectively. As shown in Table 2, 0 < RL < 1 indicates easy adsorption. At the same time, the parameter 0.1 < 1 / n < 0.5 obtained by fitting with the Freundlich model further demonstrates the 2.5% characteristic of easy adsorption of the TOCNF / PVA / GA / PEI

[0051] 5. Adsorption thermodynamics analysis: To further study the 2.5% energy change and spontaneity during the adsorption of MB, CV, and Cu by the TOCNF / PVA / GA / PEI 2+ aerogel. The adsorption processes at three temperature gradients of 25 °C, 35 °C, and 45 °C were studied respectively. The corresponding calculation data are shown in Table 3.

[0052] Table 3 Reaction thermodynamic parameters

[0053] Figure 14 represents the energy change of the aerogel. As the temperature increases, ΔG gradually decreases, indicating that increasing the temperature is beneficial to the adsorption of MB, CV, and Cu by the aerogel. 2+ During the adsorption process, ΔG are all negative values, indicating that the entire adsorption process is spontaneous. ΔH and ΔS are both positive values, indicating that increasing the temperature is beneficial to the adsorption of MB, CV, and Cu by the aerogel, and the adsorption process is endothermic and can be controlled by the change of entropy. 2+

[0054] 6. Recycling performance analysis: The recycling ability of the adsorbent is an important indicator for evaluating the performance of the adsorption material itself. Figure 15 For the TOCNF / PVA / GA / PEI 2.5% aerogel after five adsorption-desorption cycles for MB, CV, and Cu 2+The adsorption capacity was [not specified]. During the fifth adsorption cycle, the adsorption capacity of the aerogel remained at 95.7 mg / g, 97.89 mg / g, and 105.5 mg / g, respectively, with removal rates of 80.2%, 84.3%, and 85.1%. The decrease in adsorption efficiency was mainly due to the reduction in the number of functional groups on the aerogel surface during the desorption cycle, or the continued occupation of adsorption sites by metal complexes, while pores partially collapsed. The TOCNF / PVA / GA / PEI 2.5% aerogel exhibits good adsorption-desorption effects on pollutants, has high reusability, and shows promising application prospects in water treatment.

[0055] Ion interference analysis: Na + Ca 2+ Cl - and SO4 2- These are all common ions found in daily life. The study investigated the effects of the presence of these ions on TOCNF / PVA / GA / PEI. 2.5% Aerogels for MB, CV and Cu 2+ The adsorption effect is affected. Figure 16 The adsorption capacity of the aerogel in NaCl, CaCl2, and Na2SO4 solutions of different concentrations was shown. The results indicate that the adsorption capacity of the aerogel in low concentrations of NaCl, CaCl2, and Na2SO4 solutions is [not specified]. + and Cl - The aerogel exhibits some interference with adsorption performance; however, the adsorption effect decreases less with increasing concentration, and the adsorption capacity shows minimal change. When the NaCl concentration is 0.02 mol / L, the aerogel shows good adsorption performance for MB, CV, and Cu. 2+ The adsorption capacities were 163.45 mg / g, 169.20 mg / g, and 164.72 mg / g, respectively. When the NaCl concentration was 0.06 mol / L, the aerogel exhibited good adsorption for MB, CV, and Cu. 2+ The adsorption capacities of the three compounds were 161.13 mg / g, 167.42 mg / g, and 161.72 mg / g, respectively, while the adsorption capacities of CaCl2 at the same concentration were 157.13 mg / g, 156.72 mg / g, and 148.75 mg / g, respectively. 2+ Than Na + This further weakens the adsorption performance of aerogels. With the increase of SO4... 2- As the concentration of atom increases, the adsorption capacity of the aerogel decreases more significantly. Simultaneously, the charge shielding effect of high-concentration anions weakens the TOCNF / PVA / GA / PEI combination. 2.5% Aerogels with MB, CV and Cu 2+ Electrostatic attraction.

[0056] Example 4: Study on the adsorption mechanism of aerogel.

[0057] FTIR analysis of aerogel before and after adsorption TOCNF / PVA / GA / PEI 2.5% Aerogel adsorption of MB, CV and Cu 2+ The FTIR spectrum of the molecule is as follows Figure 17 As shown, after the aerogel adsorbs MB and CV, at 1580 cm⁻¹ -1 The appearance of a new absorption peak indicates the C=C vibration of the benzene ring skeleton, proving that all dye molecules were successfully adsorbed. Aerogel adsorption of Cu 2+ Subsequently, the -OH peak ranged from 3200 to 3450 cm⁻¹. -1 Move to 3189~3650cm -1 At this point, the peak broadens, hydrogen bonding strengthens, and the hydrogen bond environment becomes more ordered and stable. The -COOH peak widens from 1715 cm⁻¹. -1 Move to 1725cm -1 At this point, the copper ion coordinates with the carbonyl oxygen, and the positions of NH and CN change, proving that MB, CV, and Cu... 2+ It was successfully adsorbed onto the aerogel.

[0058] 2. SEM-EDS analysis of aerogels before and after adsorption TOCNF / PVA / GA / PEI 2.5% Aerogel adsorption of MB, CV and Cu 2+ SEM-EDS images after molecularization are shown below Figure 18 As shown in the figure, TOCNF / PVA / GA / PEI 2.5% The aerogel surface is rough, and the pore channels are blocked, allowing most of the adsorption sites to be effectively occupied. The aerogel successfully adsorbed MB, CV, and Cu. 2+ Comparing the results before and after adsorption, the nitrogen content in the aerogel increased significantly, indicating that MB and CV were successfully adsorbed. Furthermore, Cu was detected in the aerogel after adsorption. 2+ And the content is as high as 14.2%.

[0059] 3. Removal Mechanism Analysis TOCNF / PVA / GA / PEI 2.5% Aerogels for MB, CV and Cu 2+ The efficient adsorption mechanism can be attributed to the synergistic effect of physical adsorption, hydrogen bonding, electrostatic attraction, and coordination. The adsorption mechanism is as follows: Figure 19 As shown. TOCNF / PVA / GA / PEI 2.5%Aerogels offer a high specific surface area and abundant pores, allowing them to trap pollutant molecules through their channels. The abundant amino, hydroxyl, and carboxyl functional groups on the aerogel surface can form hydrogen bonds with aromatic rings or nitrogen-containing groups in MB and CV dyes, promoting dye adsorption. The charged functional groups on the aerogel surface can also interact with cationic dyes such as MB, CV, and Cu. 2+ Electrostatic attraction is generated between them, thereby improving the removal rate of positively charged pollutants. The abundant amino groups in PEI can react with Cu... 2+ Stable metal coordination complexes are formed, enabling highly selective adsorption of heavy metal ions.

[0060] Comparative Example 1 This comparative example is basically the same as Example 1, except that the pH was not adjusted to 8.0 before adding the 2.5wt% PEI solution. As a result, a large amount of precipitate appeared after adding the PEI solution, and a uniform gel system could not be formed.

[0061] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing TOCNF / PVA / GA / PEI aerogel, characterized in that, Includes the following steps: S1, Add glutaraldehyde to mixture 1 and stir until homogeneous to obtain mixture 2; S2, add polyethyleneimine solution to mixture 2, freeze dry to obtain TOCNF / PVA / GA / PEI aerogel.

2. The method for preparing TOCNF / PVA / GA / PEI aerogel as described in claim 1, characterized in that: In step S2, the concentration of the polyethyleneimine solution is 0.5~2.5wt%.

3. The method for preparing TOCNF / PVA / GA / PEI aerogel as described in claim 1, characterized in that: In step S2, before adding the polyethyleneimine solution, the pH of the mixture 2 is adjusted to 7.5~8.

5.

4. The method for preparing TOCNF / PVA / GA / PEI aerogel as described in claim 1, characterized in that: In step S1, the pH of the mixture 1 is 3.5~4.

5.

5. The method for preparing TOCNF / PVA / GA / PEI aerogel as described in claim 1, characterized in that: In step S1, the components of the mixture 1 include a polyvinyl alcohol solution and a TOCNF suspension.

6. The method for preparing TOCNF / PVA / GA / PEI aerogel as described in claim 5, characterized in that: The concentration of the polyvinyl alcohol solution is 1~1.5wt%.

7. A TOCNF / PVA / GA / PEI aerogel, characterized in that: It is prepared by the method for preparing TOCNF / PVA / GA / PEI aerogel according to any one of claims 1 to 6.

8. A method for adsorbing pollutants, characterized in that: The step includes adding the TOCNF / PVA / GA / PEI aerogel of claim 7 to the contaminant.

9. The method for adsorbing pollutants as described in claim 8, characterized in that: The pollutants include organic dyes and heavy metal ions.

10. The method for adsorbing pollutants as described in claim 8, characterized in that: The initial pH of the pollutant is 3-11 or 1-5, and the initial concentration is 20-200 mg / L.

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