Nano-cellulose composite aerogel, preparation method thereof and application of nano-cellulose composite aerogel in wastewater dye adsorption

Abstract

The invention discloses a nanocellulose composite aerogel, a preparation method thereof and application of the nanocellulose composite aerogel in wastewater dye adsorption, and belongs to the technical field of water treatment. The preparation method comprises the following steps: blending nano cellulose, a cross-linked polymer and a nano reinforcing material under the assistance of ultrasonic waves to form stably dispersed composite sol; injecting the composite sol into a mold, carrying out pre-freezing, and then carrying out vacuum freeze drying; and immersing the aerogel obtained after freeze drying into a cross-linking agent solution for post-crosslinking treatment, and drying to obtain the nano-cellulose composite aerogel. The nano-cellulose composite aerogel provided by the invention has the beneficial effects that efficient adsorption of cationic dyes and anionic dyes is realized at the same time, and the nano-cellulose composite aerogel is suitable for advanced treatment of printing and dyeing wastewater.

Description

Technical Field

[0001] The invention belongs to the technical field of water treatment, and particularly relates to a nano-cellulose composite aerogel, a preparation method thereof, and application thereof in wastewater dye adsorption. Background Art

[0002] Industrial dye wastewater discharge is a major source of water pollution. Dyes have stable molecular structures, are highly toxic, and have high chromaticity. Some dyes are carcinogenic, teratogenic, and mutagenic. If discharged directly into the environment without effective treatment, they not only severely damage aquatic ecosystems, hinder photosynthesis in aquatic organisms, deplete dissolved oxygen in the water, threaten human health, and cause bioaccumulation through the food chain. Current methods for treating dye wastewater include flocculation and sedimentation, biodegradation, membrane separation, and adsorption. Adsorption has attracted considerable attention due to its ease of operation and high efficiency. However, while widely used, traditional adsorbents such as activated carbon suffer from limited adsorption capacity, difficulty in regeneration, high cost, and poor selectivity. Some newer adsorbent materials (such as polymeric adsorbents and mineral materials) also suffer from limitations such as slow adsorption rates, weak adsorption capacity for specific dye types (only for cations or anions), poor mechanical strength, and difficulty in recycling and reuse, making them difficult to meet the demand for efficient, broad-spectrum, economical, and environmentally friendly dye wastewater treatment.

[0003] Aerogels, nanoporous materials with a three-dimensional network structure, high porosity, high surface area, and low density, have shown great potential in the field of adsorption. Their rich pore structure facilitates the rapid diffusion and accommodation of dye molecules, and their large specific surface area provides ample adsorption sites. However, the practical application of aerogels still faces many challenges. Aerogels (especially those based on biomass or polymers) have poor mechanical strength and are prone to swelling, collapse, or disintegration in a wet state, making them difficult to withstand the stresses of actual water treatment operations (such as stirring, filtration, and regeneration cycles). Furthermore, their adsorption performance is highly dependent on surface chemistry. Single modified aerogels are generally effective only for dyes of specific charge types (e.g., only cationic or only anionic) and lack broad-spectrum adsorption capacity for complex wastewaters containing mixed-charge dyes. Furthermore, the cross-linked networks and functional groups of some aerogels are insufficiently stable in complex aqueous environments, affecting the durability of adsorption performance and regeneration. Summary of the Invention

[0004] In response to the problems of poor mechanical strength and adsorption capacity of aerogel adsorption materials in the prior art, the present invention provides a nanocellulose composite aerogel, a preparation method thereof, and its application in wastewater dye adsorption. By cross-linking nanocellulose with a cross-linked polymer and a nano-reinforcement material, a high-strength composite aerogel with high-efficiency and broad-spectrum dye adsorption capacity is prepared, which is used for dye adsorption in wastewater.

[0005] Specifically, the technical solution of the present invention is as follows.

[0006] The present invention discloses a method for preparing a nanocellulose composite aerogel, comprising the following steps: (1) Nanocellulose, cross-linked polymer, nanoreinforcement material and water are blended under ultrasound assistance to form a stably dispersed composite sol; (2) injecting the composite sol into a mold, pre-freezing it, and then vacuum freeze-drying it; (3) The aerogel obtained after vacuum freeze drying is immersed in a crosslinker solution for post-crosslinking treatment, and the nanocellulose composite aerogel is obtained after drying.

[0007] Furthermore, in the composite sol of step (1), the mass concentration of nanocellulose is 0.5-2.0%, the mass concentration of the cross-linked polymer is 0.1-1.0%, and the mass concentration of the nano-reinforcement material is 0.05-1.0%.

[0008] Furthermore, the nanocellulose in step (1) is TEMPO-oxidized nanocellulose, and the carboxyl content is 0.8-1.8 mmol / g.

[0009] Furthermore, the cross-linked polymer in step (1) is one of chitosan, sodium alginate or polyethyleneimine; and the nano-reinforcement material is one of graphene oxide, MXene and montmorillonite.

[0010] Furthermore, the ultrasonic-assisted conditions in step (1) are 400-800W and 20-40min.

[0011] Furthermore, the pre-freezing conditions in step (2) are -15~-40°C, 12-36h, and the vacuum freeze-drying time is 24-48h. Furthermore, the cross-linking agent solution in step (3) is glutaraldehyde, epichlorohydrin or genipin solution, and the mass concentration of the cross-linking agent solution is 0.1-2.0%.

[0012] Furthermore, the post-crosslinking treatment in step (3) is carried out at a crosslinking temperature of 30-60° C. and for 2-4 hours. In the present invention, the nanocellulose composite aerogel is prepared by the preparation method.

[0013] In the present invention, the rice cellulose composite aerogel is used for wastewater dye adsorption.

[0014] Compared with the prior art, the present invention has at least the following beneficial technical effects: The nanocellulose composite aerogel provided by the present invention simultaneously achieves efficient and broad-spectrum adsorption of cationic dyes and anionic dyes. This is due to its unique design: based on carboxylated nanocellulose as the skeleton, a cross-linked polymer with rich amino groups (such as chitosan, polyethyleneimine) or hydroxyl groups (such as sodium alginate) is synergistically introduced, and nano-reinforced materials (such as graphene oxide, MXene, montmorillonite) are compounded. The synergistic effect of multiple functional groups and nanomaterials enables it to effectively capture dye molecules with different charge properties through various mechanisms such as electrostatic attraction, hydrogen bonding, and π-π stacking, significantly overcoming the defect of the narrow adsorption range of single modified aerogels. At the same time, through the introduction of cross-linked polymers and nano-reinforced materials, combined with post-crosslinking treatment, the crosslinking density, mechanical strength and wet structural stability of the aerogel are greatly improved, making it less likely to swell, collapse or disintegrate in actual water treatment operations (such as stirring and filtration), ensuring its good operability and recycling potential. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The accompanying drawings, which constitute part of the present invention, are provided to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are provided to explain the present invention and do not constitute undue limitations thereon. The embodiments of the present invention will be described in detail below with reference to the accompanying drawings, wherein: Figure 1 This is a scanning electron microscope image of the nanocellulose composite aerogel prepared in Example 1. DETAILED DESCRIPTION

[0016] The present invention will be further described below in conjunction with specific examples. It should be understood that these examples are intended to illustrate the present invention only and are not intended to limit the scope of the invention. The experimental methods in the following examples, for which specific conditions are not specified, are generally performed under conventional conditions or as recommended by the manufacturer.

[0017] Unless otherwise defined, all professional and scientific terms used herein have the same meanings as those familiar to those skilled in the art. The reagents and raw materials used in the present invention can be purchased through conventional channels. Unless otherwise specified, the reagents and raw materials used in the present invention are used in accordance with conventional methods in the art or in accordance with the product instructions.

[0018] The present invention will now be further described with reference to the accompanying drawings and specific implementation methods.

[0019] Example 1 (1) TEMPO-oxidized nanocellulose (carboxyl content 1.2 mmol / g) was prepared into an aqueous solution with a mass concentration of 1.0 wt%, and chitosan and graphene oxide were added and blended under ultrasonic assistance (power 600 W, 30 min) to form a stably dispersed composite sol. The concentration of chitosan was 0.5 wt%, and the concentration of graphene oxide was 0.5 wt%. (2) The composite sol was injected into a mold, pre-frozen at -25 °C for 24 h, and then transferred to a freeze dryer for vacuum freeze drying for 36 h to obtain a dry composite aerogel; (3) The aerogel obtained after freeze-drying was immersed in a 1.0 wt% glutaraldehyde aqueous solution and cross-linked at 45 °C for 3 h. After being taken out, it was washed with deionized water three times and dried at 60 °C for 6 h to obtain a nanocellulose composite aerogel.

[0020] Example 2 (1) TEMPO-oxidized nanocellulose (carboxyl content 0.8 mmol / g) was prepared into an aqueous solution with a mass concentration of 0.5 wt%, and sodium alginate and MXene were added and blended under ultrasound assistance (power 400 W, 40 min) to form a stably dispersed composite sol. The concentration of sodium alginate was 0.2 wt%, and the concentration of MXene was 0.1 wt%. (2) The composite sol was injected into a mold, pre-frozen at -15 °C for 36 h, and then transferred to a freeze dryer for vacuum freeze drying for 48 h to obtain a dry composite aerogel; (3) The aerogel obtained after freeze-drying was immersed in a 1.0 wt% epichlorohydrin solution and cross-linked at 30 °C for 4 h. After being taken out, it was washed with deionized water three times and dried at 45 °C for 12 h to obtain a nanocellulose composite aerogel.

[0021] Example 3 (1) TEMPO-oxidized nanocellulose (carboxyl content 1.8 mmol / g) was prepared into an aqueous solution with a mass concentration of 2.0 wt%, and polyethyleneimine and montmorillonite were added and blended under ultrasound assistance (power 800 W, 20 min) to form a stably dispersed composite sol. The concentration of polyethyleneimine was 1.0 wt%, and the concentration of montmorillonite was 1.0 wt%. (2) The composite sol was injected into a mold, pre-frozen at -40 °C for 12 h, and then transferred to a freeze dryer for vacuum freeze drying for 24 h to obtain a dry composite aerogel; (3) The aerogel obtained after freeze-drying was immersed in a 1.0 wt% genipin solution (the solvent was PBS buffer), cross-linked at 60 °C for 2 h, washed with water three times, and vacuum dried at -60 °C for 48 h to obtain a nanocellulose composite aerogel.

[0022] Comparative Example 1 Compared with Example 1, Comparative Example 1 does not perform the cross-linking treatment in step (3), specifically: (1) TEMPO-oxidized nanocellulose (carboxyl content 1.2 mmol / g) was prepared into an aqueous solution with a mass concentration of 1.0 wt%, and chitosan and graphene oxide were added and blended under ultrasonic assistance (power 600 W, 30 min) to form a stably dispersed composite sol. The concentration of chitosan was 0.5 wt%, and the concentration of graphene oxide was 0.5 wt%. (2) The composite sol was injected into the mold, pre-frozen at -25 °C for 24 h, and then transferred to a freeze dryer for vacuum freeze drying for 36 h to obtain a dry composite aerogel.

[0023] Comparative Example 2 Compared with Example 1, chitosan and graphene oxide were not added in step (1) of Comparative Example 2, specifically: (1) TEMPO-oxidized nanocellulose (carboxyl content 1.2 mmol / g) was prepared into an aqueous solution with a mass concentration of 1.0 wt%; (2) The aqueous solution was injected into the mold, pre-frozen at -25 °C for 24 h, and then transferred to a freeze dryer for vacuum freeze drying for 36 h to obtain a dry composite aerogel; (3) The aerogel obtained after freeze-drying was immersed in a 1.0 wt% glutaraldehyde aqueous solution and cross-linked at 45 °C for 3 h. After being taken out, it was washed with deionized water three times and dried at 60 °C for 6 h to obtain a nanocellulose composite aerogel.

[0024] Adsorption performance test The equilibrium adsorption capacity of the nanocellulose composite aerogels prepared in Examples 1-3, the composite aerogel prepared in Comparative Example 1, and the nanocellulose composite aerogel prepared in Comparative Example 2 was tested. The equilibrium adsorption capacity was tested at a temperature of 25°C, and 1 g of aerogel was added to a Congo red solution (CR) and a methylene blue (MB) solution with an initial concentration of 500 mg / L. The test results are shown in Table 1.

[0025] Table 1 Equilibrium adsorption capacity of dyes by aerogels As shown in Table 1, the composite aerogels (Examples 1-3) significantly improved the adsorption performance of anionic / cationic dyes by introducing cross-linked polymers and reinforcing materials (such as graphene oxide, MXene, montmorillonite, and polyethyleneimine) and supplemented by a cross-linking process. This confirms that composite design and chemical cross-linking can construct an efficient multi-level adsorption network to achieve efficient adsorption of dyes.

[0026] Compression performance test The compression properties of the aerogels prepared in Examples 1, 2, and 3, Comparative Example 1, and 2 were tested. Cylindrical aerogel compression specimens with a diameter of 25 mm and a height of 20 mm were prepared. The aerogels were compressed to 80% at a rate of 0.5 mm / min. The load was removed, returning the specimen to its initial position, and the stress value at 80% strain was recorded. The stress change and performance stability of the aerogel specimens were evaluated. The test results are shown in Table 2.

[0027] Table 2 Aerogel compression properties According to the data in Table 2, Examples 1-3 significantly enhanced the aerogel network structure by adding chitosan / graphene oxide, sodium alginate / MXene, polyethyleneimine / montmorillonite and supplemented with crosslinking (glutaraldehyde / epichlorohydrin / genipin), making its compressive stress higher than that of Comparative Example 1 without crosslinking and Comparative Example 2 without adding reinforcing materials.

[0028] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art will be able to repair the technical solutions described in the aforementioned embodiments or replace some of the technical features therein with equivalents. Any repairs, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for preparing a nanocellulose composite aerogel, characterized in that: The following steps are involved: (1) Nanocellulose, cross-linked polymer, nanoreinforcement material and water are blended under ultrasound assistance to form a stably dispersed composite sol; (2) injecting the composite sol into a mold, pre-freezing it, and then vacuum freeze-drying it; (3) The aerogel obtained after freeze-drying is immersed in a cross-linking agent solution for post-cross-linking treatment, and the nanocellulose composite aerogel is obtained after drying.

2. The method for preparing the nanocellulose composite aerogel according to claim 1, wherein: In the composite sol of step (1), the mass concentration of nanocellulose is 0.5-2.0%, the mass concentration of the cross-linked polymer is 0.1-1.0%, and the mass concentration of the nano-reinforcement material is 0.05-1.0%.

3. The method for preparing the nanocellulose composite aerogel according to claim 1, wherein: The nanocellulose described in step (1) is TEMPO-oxidized nanocellulose with a carboxyl content of 0.8-1.8 mmol / g.

4. The method for preparing the nanocellulose composite aerogel according to claim 1, characterized in that: The cross-linked polymer in step (1) is one of chitosan, sodium alginate or polyethyleneimine; and the nano-reinforcement material is one of graphene oxide, MXene or montmorillonite.

5. The method for preparing the nanocellulose composite aerogel according to claim 1, characterized in that: The ultrasonic-assisted conditions in step (1) are 400-800W and 20-40min.

6. The method for preparing the nanocellulose composite aerogel according to claim 1, characterized in that: The pre-freezing conditions described in step (2) are -15~-40℃, 12-36h, and the vacuum freeze-drying time is 24-48h.

7. The method for preparing the nanocellulose composite aerogel according to claim 1, characterized in that: The cross-linking agent solution described in step (3) is glutaraldehyde, epichlorohydrin or genipin solution, and the mass concentration of the cross-linking agent solution is 0.1-2.0%.

8. The method for preparing the nanocellulose composite aerogel according to claim 1, characterized in that: The post-crosslinking treatment conditions in step (3) are a crosslinking temperature of 30-60°C and a time of 2-4 hours.

9. A nanocellulose composite aerogel prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the rice cellulose composite aerogel according to claim 9 in wastewater dye adsorption.

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