Hydrogen bond self-assembled bio-based aerogel as well as preparation method and application thereof

Abstract

The invention relates to the technical field of functional polymer materials and environmental pollution control, in particular to hydrogen bond self-assembled bio-based aerogel as well as a preparation method and application thereof. Quaternized chitosan and tannic acid are self-assembled in a water phase through hydrogen bonds and electrostatic interaction to form a three-dimensional network structure, no cross-linking agent or organic solvent is added, the specific surface area of the bio-based aerogel BET is 2-10 m / g, and through the strong electrostatic adsorption effect between cationic groups in the quaternized chitosan and anionic dye molecules (such as Congo red), the cationic groups in the quaternized chitosan and the anionic dye molecules (such as Congo red) are separated from the anionic dye molecules. The material shows excellent dye removal efficiency and adsorption capacity under the conditions of normal temperature and normal pressure and hydrogen bonds provided by rich phenolic hydroxyl groups in tannic acid molecules and a pi-pi accumulation effect, the aerogel can quickly adsorb anionic dye, the adsorption process is efficient, the selectivity is high, the structure is stable, and the aerogel is degradable and can be applied to the field of dye adsorption. And the method has good reproducibility and repeated use stability, and has wide practical application and popularization prospects.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of functional polymer materials and environmental pollution control technology, and particularly relates to a hydrogen-bond self-assembled bio-based aerogel and a preparation method and application thereof. BACKGROUND

[0002] Dye wastewater is one of the main pollution sources in the fields of printing and dyeing, papermaking, leather, electroplating, etc., and anionic dyes such as Congo red, reactive red, acid orange, etc. widely exist in the dye wastewater, which are structurally stable, high in color, and biologically difficult to degrade. These dye molecules have complex aromatic conjugated structures and strong polar substituents, which are difficult to be effectively removed by traditional water treatment processes such as photodegradation and biodegradation, and are prone to long-term accumulation in the environment, leading to water eutrophication, increased risk of carcinogenesis and mutagenesis, and serious ecological toxicity.

[0003] To address the above challenges, the physical adsorption method is widely used due to its simple operation, fast response speed, and no introduction of additional pollution. Traditional adsorbents such as activated carbon, resin, zeolite, and oxidized metal have certain specific surface area and adsorption capacity, but they generally have high preparation cost, are non-degradable, have poor adsorption selectivity, are difficult to regenerate after adsorption saturation, and may even cause secondary pollution risk during the treatment process.

[0004] In recent years, green adsorbent materials based on natural polymers have attracted much attention, especially natural polymers such as chitosan, tannic acid, alginate, and starch derivatives, which have shown great potential in the treatment of anionic dye wastewater due to their biocompatibility, renewability, and rich functional groups (such as hydroxyl, amino, and phenolic hydroxyl groups). However, most existing natural adsorbent materials need to rely on chemical cross-linking agents such as glutaraldehyde and epoxide compounds to improve their structural stability and service life in water, which not only increases the process complexity and environmental load, but also may introduce toxic residues, reducing their application safety in the environment and food fields.

[0005] Therefore, how to design and construct a bio-based adsorbent material without chemical cross-linking agents, which has stable structure, degradation-friendly, moderate specific surface area, and significant adsorption efficiency, has become a key scientific problem and technical difficulty in realizing practical transformation in this field. SUMMARY

[0006] The present application aims to provide a hydrogen-bond self-assembled bio-based aerogel, a green bio-based aerogel material without any cross-linking agent, with moderate specific surface area and excellent adsorption performance, which is suitable for the treatment of anionic dye wastewater such as Congo red.

[0007] The application forms a three-dimensional network structure by mixing quaternary amine chitosan and tannic acid in an aqueous phase through hydrogen bonds, electrostatic interaction and pi-pi stacking, and obtains aerogel with a porous structure after freeze drying. The constructed aerogel has the advantages of structural stability, green environmental protection, no crosslinking agent pollution, biodegradability and the like, and exhibits excellent selective adsorption capacity for anionic dyes.

[0008] To solve the above technical problems, the technical scheme adopted by the application is as follows: a hydrogen bond self-assembly bio-based aerogel is formed by self-assembly of quaternary amine chitosan and tannic acid in an aqueous phase through hydrogen bonds and electrostatic interaction without adding any crosslinking agent or organic solvent, the bio-based aerogel has a BET specific surface area of 2-10 m² / g, and the adsorption mechanism is mainly ion combination and molecular force.

[0009] Although the specific surface area of the aerogel material obtained by the application is relatively low (2-10 m² / g), the intermolecular binding capacity provided by the surface functional groups (quaternary amine cation groups and phenolic hydroxyl groups) realizes an adsorption capacity far exceeding that of similar materials.

[0010] The application further provides a preparation method of the hydrogen bond self-assembly bio-based aerogel. S1, dissolving quaternary amine chitosan in an aqueous solution; S2, adding a tannic acid aqueous solution to the quaternary amine chitosan solution of step S1, and stirring for 30 min until the mixture is uniform; S3, freezing the mixed solution at -40 ℃, and then freeze-drying the solution in a freeze-drying box to form an aerogel.

[0011] As a further limitation of the technical scheme of the application, the raw materials are dried at 60 ℃ for more than 12 h before use.

[0012] As a further limitation of the technical scheme of the application, the concentration of the quaternary amine chitosan solution in step S1 is 3wt%.

[0013] As a further limitation of the technical scheme of the application, the concentration of the tannic acid aqueous solution in step S2 is 10wt%.

[0014] As a further limitation of the technical scheme of the application, the volume ratio of the quaternary amine chitosan solution to the tannic acid aqueous solution in step S2 is 1:1.

[0015] As a further limitation of the technical scheme of the application, the freezing method in step S3 is liquid nitrogen freezing, the temperature of the freeze-drying box is -60 ℃, and the pressure is 0.1 pa.

[0016] The application further provides an application of the hydrogen bond self-assembly bio-based aerogel in preparing an organic dye adsorption material.

[0017] The application also provides application of the hydrogen-bond self-assembled bio-based aerogel in resource recycling and wastewater treatment.

[0018] Preferably, the wastewater is anionic dye wastewater.

[0019] Compared with the prior art, the application has the following beneficial effects: The aerogel material provided by the application is based on natural polymers such as chitosan and tannic acid, has a wide source of raw materials and low cost, and belongs to renewable bio-based resources. The material does not depend on petroleum chemical derivatives, conforms to the current national policy guidance of the “double carbon” strategy and green and sustainable development, has good ecological safety and promotion value. In the preparation process of the aerogel, no toxic and harmful organic solvents, crosslinking agents or heavy metal catalysts are used, avoiding problems such as chemical crosslinking residues and volatile organic compound (VOC) emissions commonly found in traditional materials. The entire synthesis process is simple to operate and has low energy consumption, has the advantages of being green, low-carbon and scalable, and ensures that it is non-toxic to the human body and does not pollute the environment.

[0020] Unlike traditional aerogels that rely on high specific surface area adsorption, the adsorption performance of the aerogel of the application mainly comes from the electrostatic adsorption between the cationic groups (such as quaternary ammonium groups) in the material and the anionic dyes, and the hydrogen bonding and π-π stacking provided by the polyphenols such as tannic acid. This makes the material still exhibit excellent adsorption capacity and adsorption rate even in the case of limited specific surface area, and is particularly suitable for the treatment of anionic dye wastewater such as Congo red and reactive red, which has stable structure and high color.

[0021] The aerogel prepared by the application has a dense structure and good water phase stability, and is not easy to collapse or break during use, and has strong reusability. At the same time, the main components can be biodegraded in the natural environment, avoiding the problem of secondary pollution after use, and having good environmental friendliness and terminal treatment convenience. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 The figure is the FTIR test result graph of the aerogel without adsorbing dyes (a), the aerogel after adsorbing Congo red dye (b), the aerogel after adsorbing rhodamine B dye (c), quaternary ammonium chitosan (d) and tannic acid (e).

[0023] Figure 2 The figure is the potential value graph of the aerogel at different pH values.

[0024] Figure 3 The figure is the result graph of the influence of different pH on the adsorption effect of the aerogel on Congo red solution.

[0025] Figure 4 Effect of different adsorbent dosage on the adsorption of aerogel. DETAILED DESCRIPTION

[0026] The application will be further described in conjunction with specific examples. EXAMPLE

[0027] A preparation method of a hydrogen-bond self-assembled bio-based aerogel: (1) Dissolve 0.3 g of quaternary amine chitosan in 10 mL of deionized water, and magnetically stir until the solution is clear.

[0028] (2) Dissolve 1 g of tannic acid in 10 mL of aqueous solution, and magnetically stir until completely dissolved.

[0029] (3) Blend 10 mL of the quaternary amine chitosan solution and 10 mL of the tannic acid solution, continue to stir for 30 min, and observe that the solution gradually changes from a liquid state to a gel state; (3) After injecting the blended solution (gel state) into a mold, place it in liquid nitrogen for freezing for 2 hours.

[0030] (4) Freeze dry the solution at -50°C and 0.1 Pa for 48 hours using a freeze dryer to obtain a light brown aerogel.

[0031] Material characterization: The FTIR spectrum shows that by comparing the spectra a, d, and e, it can be found that the curves a, d, and e exhibit a wide peak shape near the wave number 3300 cm -1 , and the peak value of the curves d and e is significantly lower than that of the curve a. This is because hydrogen bonds are formed between hydroxyl groups, resulting in a decrease in the number of free hydroxyl groups. It can be inferred that the formation mechanism of the bio-based aerogel is based on physical crosslinking. The components are tightly connected through the formation of hydrogen bonds, thereby constructing the overall structure of the bio-based aerogel. At the same time, by comparing the spectra a, b, and c, it can be found that the spectrum b detects a vibration peak of sulfonic acid group (-SO3 - ) near the wave number 1064.9 cm -1 . The appearance of this characteristic peak clearly indicates that Congo red molecules have been successfully adsorbed to the surface or internal structure of the bio-based aerogel. Looking at the curve (c), an absorption peak appears in the wave number range 1700-1750 cm -1 . This absorption peak corresponds to the stretching vibration of C=O in the ester group. At the same time, symmetric and asymmetric stretching vibration double peaks of carboxylate (-COO - ) appear near the wave numbers 1400 cm -1 and 1550 cm -1 , respectively. The spacing between the two peaks is about 150 cm -1This distance feature is a typical signature of carboxylate salt, which can confirm that Rhodamine B has been adsorbed onto the bio-based aerogel, and the adsorption process may involve specific interactions with the surface functional groups of the bio-based aerogel, resulting in the appearance of the above characteristic absorption peak, which also indicates that the bio-based aerogel has adsorption effect on both anionic and cationic dyes.

[0032] From the data in Table 1, the BET specific surface area is 2.31 m² / g, and the t-plot micropore specific surface area is 2.93 cm³ / g; it can be seen that the specific surface area of the bio-based aerogel is relatively small, and thus the adsorption of the dye by the aerogel is not dependent on the specific surface area. In combination with the FTIR data, it can also be known that the adsorption of the dye by the bio-based aerogel is mainly through hydrogen bonding and the action of anions and cations.

[0033] Table 1 BET data

[0034] The initial concentration of Congo Red in the simulated wastewater is 150 mg / L.

[0035] According to Figure 2 It can be seen from the results that as the pH value increases, the Zeta potential value of the bio-based aerogel gradually decreases, and when pH > 5, the Zeta potential value starts to become negative. This indicates that the surface charge of the particles changes from positive to negative, which changes the electrostatic repulsion between particles, thereby affecting the stability of the dispersion system, so the stability of the aerogel adsorption system can be optimized by adjusting the pH.

[0036] According to Figure 3 It can be seen from the results that when 3 mg of aerogel is added to 50 mL of solution, and the adsorption capacity reaches 1840 mg / L under the conditions of 30°C and pH 5.5 for 30 minutes.

[0037] According to Figure 4 It can be seen from the results that when the dosage of the bio-based aerogel increases from 3 mg to 18 mg, the CR removal efficiency shows a significant upward trend, from 55.68% to 93.36%, while the adsorption capacity shows a downward trend, from 1190.6 mg / g to 334 mg / g. This phenomenon can be attributed to the interaction between the availability of the adsorbent and the mass limitation of the pollutants. Under the condition of lower dosage, the limited adsorption sites on the bio-based aerogel are quickly saturated by CR molecules, and the adsorption capacity approaches the theoretical maximum value; while under the condition of higher dosage, compared with the fixed CR concentration, the active sites provided by the adsorbent are excessive, resulting in a decrease in the utilization rate of the adsorbent, and thus the unit mass adsorption capacity decreases.

[0038] Adsorption mechanism analysis: Strong electrostatic adsorption between quaternary amine cation and Congo red sulfonic group; Tannic acid provides phenolic hydroxyl groups to form hydrogen bonds and π-π stacking with dye molecules, enhancing the selective recognition ability; Three-dimensional structure provides physical support, ensuring swelling stability and liquid exchange rate.

Claims

1. A hydrogen-bonded self-assembled bio-based aerogel, characterized in that, The bio-based aerogel, consisting of quaternary ammonium chitosan and tannic acid, self-assembles in an aqueous phase through hydrogen bonding and electrostatic interactions to form a three-dimensional network structure without the addition of any crosslinking agents or organic solvents. The specific surface area of ​​the bio-based aerogel is 2-10 m² / g, and the adsorption mechanism is mainly based on ion bonding and molecular interactions.

2. The method for preparing a hydrogen-bonded self-assembled bio-based aerogel according to claim 1, characterized in that, Includes the following steps: S1. Dissolve quaternary ammonium chitosan in an aqueous solution; S2. Add tannic acid aqueous solution to the quaternary ammonium chitosan solution in step S1 and stir for 30 min until the mixture is uniform. S3. After freezing the mixed solution at -40 ℃, freeze-dry it in a freeze dryer to form an aerogel.

3. The method for preparing a hydrogen-bonded self-assembled bio-based aerogel according to claim 1, characterized in that, The raw materials used are dried at 60 ℃ for more than 12 hours before use.

4. The method for preparing a hydrogen-bonded self-assembled bio-based aerogel according to claim 1, characterized in that, The concentration of the quaternary ammonium chitosan solution in step S1 is 3 wt%.

5. The method for preparing a hydrogen-bonded self-assembled bio-based aerogel according to claim 1, characterized in that, The concentration of the tannic acid aqueous solution in step S2 is 10 wt%.

6. The method for preparing a hydrogen-bonded self-assembled bio-based aerogel according to claim 1, characterized in that, In step S2, the volume ratio of the quaternary ammonium chitosan solution to the tannic acid aqueous solution is 1:

1.

7. A method for preparing a hydrogen-bonded self-assembled bio-based aerogel according to claim 1, characterized in that, The freezing method in step S3 is liquid nitrogen freezing, and the temperature of the freeze dryer is -60 ℃ and the pressure is 0.1 Pa.

8. The application of the hydrogen-bonded self-assembled bio-based aerogel according to claim 1 in the preparation of organic dye adsorption materials.

9. The application of the hydrogen-bonded self-assembled bio-based aerogel according to claim 1 in resource recycling and wastewater treatment.

10. The application according to claim 9, characterized in that, The wastewater is anionic dye wastewater.

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