Preparation method of porous gallic acid modified chitosan-based composite aerogel material

Abstract

This invention discloses a method for preparing an amino-modified porous gallic acid-modified chitosan composite aerogel that efficiently and selectively adsorbs Cr(VI). The method uses ascorbic acid and H₂O₂ as initiators, and gallic acid and triethylenetetramine as modifiers to modify chitosan. The adsorbent is activated using plasma technology, and then freeze-dried under vacuum conditions to obtain a triethylenetetramine / gallic acid-modified chitosan-based composite aerogel that adsorbs Cr(VI). This invention uses triethylenetetramine / gallic acid-modified chitosan as raw material and employs dielectric barrier discharge plasma technology and vacuum freeze-drying technology to prepare a three-dimensional porous network structure aerogel. This aerogel can selectively treat Cr(VI) in chromium-containing wastewater at room temperature, exhibiting strong adsorption capacity and good anti-interference properties. The removal rate can reach over 95% at 30℃, and it is easily recyclable.

Description

Technical Field

[0001] This invention belongs to the field of adsorption material preparation technology, specifically relating to a method for preparing an amino-modified porous gallic acid-modified chitosan-based composite aerogel material for the efficient and selective removal of Cr(VI). This method can effectively alleviate the problem of Cr(VI) pollution, so as to achieve the goal of protecting human life and health and maintaining the balance of the ecological environment. Background Technology

[0002] Chromium and its compounds are widely used in industries such as leather tanning, electroplating, and metallurgy, resulting in large quantities of highly toxic and carcinogenic chromium-containing wastewater that seriously threatens human health and the balance of the ecological environment. In actual water bodies, chromium mainly exists in the forms of Cr(III) and Cr(VI), with Cr(VI) being 100-1000 times more toxic than Cr(III). Studies have reported that Cr(VI) can cause lung cancer and kidney cancer, and it has been classified as a Group A carcinogen. Currently, common methods for removing hexavalent chromium from water bodies include chemical precipitation, ion exchange, membrane separation, electrochemical methods, and adsorption. Among these, adsorption is widely used due to its low cost, simple operation, and lack of secondary pollution.

[0003] Chitosan (CS), as a natural biomass material, is inexpensive, readily available, and completely biodegradable, aligning with the development trend of adsorbents. The CS molecule contains abundant -NH2 and -OH groups, which form a high-charge-density cationic polyelectrolyte in acidic solutions, exhibiting strong electrostatic attraction to Cr(VI) anions. Simultaneously, these groups also possess reducing properties, reducing Cr(VI) to Cr(III), which can then be removed through complexation.

[0004] However, CS partially dissolves under acidic conditions. Furthermore, the -OH and -NH2 groups on its chains can extensively form hydrogen bonds between and within molecular chains, significantly reducing adsorption sites and limiting its adsorption capacity. In addition, its mechanical properties are poor. The reducing power of phenols is well-known; they have been successfully used for the chemical reduction of hexavalent chromium since 1990. Gallic acid (GA,3,4,5-trihydroxybenzoic acid) is a natural antioxidant, existing as a secondary metabolite in plants. Its molecules contain active groups such as hydroxyl and carboxyl groups, which can act as active sites for Cr(VI) adsorption. Triethylenetetramine (TEAE) is an inexpensive and high-density complexing agent containing nitrogen-containing active groups, possessing a strong metal ion complexing ability. Therefore, gallic acid and TEAE are used as modifiers to enhance the adsorption performance of chitosan. Simultaneously, the introduction of sodium alginate effectively solves the chitosan molding problem through the cross-linking effect between sodium alginate and cross-linking ions. SA and CS form a polyelectrolyte through electrostatic attraction, which is safe, non-toxic, and completely biodegradable. This effectively solves the problem of CS powder materials being easily lost and difficult to recycle. Therefore, the preparation of adsorbents using gallic acid and triethylenetetramine modified chitosan is a research topic worthy of attention. Summary of the Invention

[0005] The present invention aims to overcome the shortcomings of the prior art and provide a method for preparing an amino-based porous gallic acid-modified chitosan-based composite aerogel material with strong adsorption capacity, good anti-interference properties, simple preparation, low cost, easy recycling, and selective treatment of Cr(VI) in chromium-containing wastewater.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A method for preparing an amino-modified porous gallic acid-modified chitosan-based composite aerogel material that adsorbs Cr(VI) is described below:

[0008] (1) Dissolve sodium alginate powder in deionized water and disperse it by water bath heating and stirring.

[0009] (2) Add the chitosan powder slowly in batches to the solution obtained in step (1) and stir magnetically. After it is evenly dispersed, add a mixture of hydrochloric acid, nitric acid, sulfuric acid and glacial acetic acid to the solution and stir magnetically until it is completely dissolved.

[0010] (3) Add ascorbic acid and H2O2 to the solution obtained in step (2) and stir magnetically;

[0011] (4) Add gallic acid powder to anhydrous ethanol solution and stir magnetically to dissolve it completely, then add it to the solution obtained in step (3) and stir magnetically.

[0012] (5) Add triethylenetetramine dropwise to the solution obtained in step (4) and stir magnetically;

[0013] (6) The solution obtained in step (5) is added dropwise to the CaCl2 solution and magnetically stirred. After cross-linking, the initial hydrogel spheres are formed.

[0014] (7) After washing the initial hydrogel balls obtained in step (6), place them in a dielectric barrier discharge reactor for activation;

[0015] (8) After washing the hydrogel balls obtained in step (7), transfer them to a glutaraldehyde solution and stir slowly to carry out cross-linking;

[0016] (9) The hydrogel balls obtained in step (8) are placed back into the dielectric barrier discharge reactor for activation;

[0017] (10) The hydrogel spheres obtained in step (9) are repeatedly washed and then freeze-dried to obtain the target product, an amino-modified porous gallic acid-modified chitosan-based composite aerogel material that adsorbs Cr(VI).

[0018] Further, in step (1), 0.5-1.0 g of sodium alginate powder is dissolved in 60 mL of deionized water and heated and stirred in a water bath at 60 °C for 1 h until it is uniform and free of lumps.

[0019] Further, in step (2), 1-2g of chitosan powder with a degree of deacetylation of 80%-95% is weighed and slowly poured into the solution obtained in step (1) in batches for magnetic stirring. After it is evenly dispersed, a mixed solution of hydrochloric acid, nitric acid, sulfuric acid and glacial acetic acid is added dropwise to the solution. For every 1g of chitosan powder added, 8-10mL of the mixed solution is added dropwise. During the dropwise addition, magnetic stirring is performed at a speed of 150-200rpm at room temperature. After all the powder has been added, magnetic stirring is performed for another 1h to ensure that it is fully mixed.

[0020] Furthermore, in step (2), the volume fraction ratio of hydrochloric acid, nitric acid or sulfuric acid to glacial acetic acid in the mixed solution is 1:5 to 1.

[0021] Further, in step (3), 0.1-0.3g of ascorbic acid and 0.3-0.9ml of 30% H2O2 are added to the solution obtained in step (2) and the mixture is magnetically stirred for 1h.

[0022] Further, in step (4), gallic acid is added to 10 ml of anhydrous ethanol with a mass fraction of 99.7%, and the mass ratio of gallic acid to chitosan is 1:4. The mixture is then magnetically stirred for 30 min and poured into the solution obtained in step (3). The mixture is then magnetically stirred for 30 min at room temperature.

[0023] Furthermore, in step (5), the mass ratio of the added triethylenetetramine to gallic acid is 1-3:3-1, and the mixture is magnetically stirred for 30 minutes to ensure thorough and uniform mixing.

[0024] Further, in step (6), the solution obtained in step (5) is dripped into 100 ml of 3% CaCl2 solution using a peristaltic pump. During the dripping process, the solution is slowly stirred at a speed of 100-150 rpm using a magnetic stirrer. After the dripping is completed, stirring is continued at room temperature. After crosslinking for 2 hours, the initial hydrogel spheres are formed. The inner diameter of the silicone tube of the peristaltic pump is 3 mm, and the flow rate of the peristaltic pump is 4.5 d / s.

[0025] Further, in step (7), the activation conditions are as follows: under standard atmospheric pressure, oxygen is introduced into the dielectric barrier discharge reactor at a flow rate of 100-200 mL / min, plasma is generated by applying a voltage of 100-500 V and a current of 4-6 A, discharge activation is performed every 5 min, each activation lasts 30-50 s, and the activation reaction lasts for a total of 30-60 min.

[0026] Further, in step (8), the hydrogel balls obtained in step (7) are poured into 100 mL of 3% glutaraldehyde solution for further crosslinking; the mixture is slowly stirred for 2 hours at a speed of 100-150 rpm using a magnetic stirrer; in step (10), excess water in the hydrogel balls obtained in step (9) is filtered out using filter paper, and the mixture is pre-cooled in a vacuum freeze dryer. After the temperature of the cold trap is lowered to -40°C, the hydrogel balls are placed in the cold trap for pre-freezing for 20 minutes, and then freeze-dried under a vacuum of 1-10 Pa for 12 hours. The temperature of the cold trap is maintained at around -60°C. After drying, the target product, amino-modified porous gallic acid-modified chitosan composite aerogel material adsorbing Cr(VI), is obtained.

[0027] (1) The equation for gallic acid-modified chitosan is:

[0028]

[0029] This invention utilizes dielectric barrier discharge plasma technology and vacuum freeze-drying technology to fabricate a three-dimensional porous network aerogel, which exhibits excellent adsorption capacity for Cr(VI), achieving a removal rate of over 95% at 30°C. The invention uses gallic acid and triethylenetetramine as modifiers to modify chitosan as a raw material, and leverages the cross-linking effect between sodium alginate and calcium ions to form a gel. Ascorbic acid and H₂O₂ are used as initiators to graft gallic acid onto chitosan, and triethylenetetramine is introduced through the cross-linking effect of glutaraldehyde, resulting in a material rich in active functional groups such as hydroxyl, amino, and carboxyl groups. These functional groups exhibit electrostatic attraction and reduction interactions with Cr(VI). Plasma technology is used to activate the adsorbent, effectively stimulating the functional groups and enhancing the material's functionality. The aerogel of this invention possesses a rich porous structure, and its adsorption of Cr(VI) is unaffected by other metal ions in water, enabling selective treatment of Cr(VI) in wastewater. Vacuum freeze-drying technology facilitates the formation of the aerogel, making it easy to recycle. Adsorption experiments showed that the aerogel has excellent practical application performance for Cr(VI). Attached Figure Description

[0030] The present invention will now be described in detail through specific embodiments. These embodiments are provided to enable a more thorough understanding of the invention and to fully convey the scope of the invention to those skilled in the art. As used throughout the specification and claims, the terms "comprising" or "including" are open-ended and are interpreted as "comprising but not limited to". The following description is a preferred embodiment for carrying out the invention; however, this description is intended to illustrate the general principles of the specification and is not intended to limit the scope of the invention. The scope of protection of the invention is determined by the appended claims. Unless otherwise specified, all reagents and materials used in the present invention are commercially available.

[0031] Figure 1 Dissolution of SA / CS mixture using different methods

[0032] Figure 2 This is a physical image of the amino-modified porous gallic acid-modified chitosan composite aerogel material of the present invention;

[0033] Figure 3 This is a SEM image of the amino-modified porous gallic acid-modified chitosan composite aerogel material of the present invention.

[0034] Figure 4 This is an EDS image of the amino-modified porous gallic acid-modified chitosan composite aerogel material after adsorption in this invention.

[0035] Figure 5 This is an anti-interference diagram of the amino-modified porous gallic acid-modified chitosan composite aerogel material of the present invention. Detailed Implementation

[0036] Example 1

[0037] A method for preparing an amino-modified porous gallic acid-modified chitosan composite aerogel material with high efficiency and selective adsorption of Cr(VI) includes the following steps:

[0038] (1) Dissolve 0.5g of sodium alginate in 60mL of deionized water and heat and stir in a water bath at 60℃ for 1h to make it evenly mixed without lumps.

[0039] (2) Weigh 1g of chitosan with a degree of deacetylation of 80% to 95%, and slowly pour it into the solution obtained in step (1) in batches. At the same time, after the chitosan is evenly dispersed, continue to slowly add HCl:CH3COOH = 1:5 mixed acid solution to the solution. Add 8mL of mixed acid solution. During the whole process, magnetic stirring is carried out at 150rpm at room temperature. After all the solution is added, magnetic stirring is carried out for 1h to ensure that it is fully mixed.

[0040] (3) Add 0.1g ascorbic acid and 0.3ml of 30% hydrogen peroxide as free radical initiators to the solution obtained in step (2), and stir with a magnetic stirrer for 1h to mix them thoroughly.

[0041] (4) Add 0.25 g gallic acid to 10 ml of 99.7% anhydrous ethanol, stir with a magnetic stirrer for 30 min, then pour it into the solution obtained in step (3), and continue stirring at room temperature for 30 min.

[0042] (5) Add triethylenetetramine and gallic acid in step (5) in a mass ratio of 3:1 and stir magnetically for 30 minutes to ensure thorough mixing.

[0043] (6) The solution obtained in step (5) was added dropwise to 100 ml of 3% CaCl2 solution using a peristaltic pump. During the addition, the solution was slowly stirred at a speed of 100-150 rpm using a magnetic stirrer. After the addition was completed, stirring was continued at room temperature. After crosslinking for 2 hours, the initial hydrogel spheres were formed. The inner diameter of the silicone tube attached to the peristaltic pump was 3 mm, and the flow rate of the peristaltic pump was 4.5 d / s.

[0044] (7) The activation conditions in step (7) are as follows: under standard atmospheric pressure, oxygen is introduced into the dielectric barrier discharge reactor at a flow rate of 100 mL / min, and plasma is generated by applying a voltage of 100 V and a current of 4 A. Discharge activation is performed every 5 min, each activation lasts 30 s, and the activation reaction lasts for a total of 30 min.

[0045] (8) Pour the hydrogel balls obtained in step (7) into 100 mL of 3% glutaraldehyde solution to continue crosslinking. During this period, stir slowly with a magnetic stirrer at a speed of 100-150 rpm for 2 hours.

[0046] (9) Filter out excess water from the hydrogel balls obtained in step (8) using filter paper. Pre-cool the hydrogel balls in a vacuum freeze dryer. After the temperature of the cold trap drops to -40°C, place the hydrogel balls in the cold trap for pre-freezing for 20 minutes. Then freeze-dry them under vacuum conditions of 1 to 10 Pa for 12 hours. Keep the temperature of the cold trap at around -60°C. After drying, obtain the modified chitosan-based composite aerogel with Cr(VI) adsorbed by the target product.

[0047] Example 2

[0048] A method for preparing an amino-modified porous gallic acid-modified chitosan composite aerogel material with high efficiency and selective adsorption of Cr(VI) includes the following steps:

[0049] (1) Dissolve 0.75g of sodium alginate in 60mL of deionized water and heat and stir in a water bath at 60℃ for 1h to make it evenly mixed without lumps.

[0050] (2) Weigh 1.5g of chitosan with a degree of deacetylation of 80% to 95% and slowly pour it into the solution obtained in step (1) in batches. At the same time, after the chitosan is evenly dispersed, continue to slowly add the mixed acid solution to the solution. Add 9mL of HNO3:CH3COOH = 1:4 mixed acid solution. During the whole process, stir magnetically at 150rpm at room temperature. After all the chitosan is added, stir magnetically for 1h to make it fully mixed.

[0051] (3) Add 0.2g of ascorbic acid and 0.6ml of 30% hydrogen peroxide as free radical initiators to the solution obtained in step (2), and stir with a magnetic stirrer for 1h to mix them thoroughly.

[0052] (4) Add 0.25 g gallic acid to 10 ml of 99.7% anhydrous ethanol, stir with a magnetic stirrer for 30 min, then pour it into the solution obtained in step (3), and continue stirring at room temperature for 30 min.

[0053] (5) Add triethylenetetramine and gallic acid in step (5) in a mass ratio of 2:1, and stir magnetically for 30 minutes to ensure thorough mixing.

[0054] (6) The solution obtained in step (5) was added dropwise to 100 ml of 3% CaCl2 solution using a peristaltic pump. During the addition, the solution was slowly stirred at a speed of 100-150 rpm using a magnetic stirrer. After the addition was completed, stirring was continued at room temperature. After crosslinking for 2 hours, the initial hydrogel spheres were formed. The inner diameter of the silicone tube attached to the peristaltic pump was 3 mm, and the flow rate of the peristaltic pump was 4.5 d / s.

[0055] (7) The activation conditions in step (7) are as follows: under standard atmospheric pressure, oxygen is introduced into the dielectric barrier discharge reactor at a flow rate of 150 mL / min, and plasma is generated by applying a voltage of 100 V and a current of 4 A. Discharge activation is performed every 5 min, each activation lasts for 40 s, and the activation reaction lasts for a total of 40 min.

[0056] (8) Pour the hydrogel balls obtained in step (7) into 100 mL of 3% glutaraldehyde solution to continue crosslinking. During this period, stir slowly with a magnetic stirrer at a speed of 100-150 rpm for 2 hours.

[0057] (9) Filter out excess water from the hydrogel balls obtained in step (8) using filter paper. Pre-cool the hydrogel balls in a vacuum freeze dryer. After the temperature of the cold trap drops to -40°C, place the hydrogel balls in the cold trap for pre-freezing for 20 minutes. Then freeze-dry them under vacuum conditions of 1 to 10 Pa for 12 hours. Keep the temperature of the cold trap at around -60°C. After drying, obtain the modified chitosan-based composite aerogel with Cr(VI) adsorbed by the target product.

[0058] Example 3

[0059] A method for preparing an amino-modified porous gallic acid-modified chitosan composite aerogel material with high efficiency and selective adsorption of Cr(VI) includes the following steps:

[0060] (1) Dissolve 1g of sodium alginate in 60mL of deionized water and heat and stir in a water bath at 60℃ for 1h to make it evenly mixed without lumps.

[0061] (2) Weigh 1g of chitosan with a degree of deacetylation of 80% to 95%, and slowly pour it into the solution obtained in step (1) in batches. At the same time, after the chitosan is evenly dispersed, continue to slowly add the mixed acid solution to the solution. Add 10mL of H2SO4:CH3COOH = 1:3 mixed acid solution. During the whole process, stir magnetically at 150rpm at room temperature. After all the chitosan is added, stir magnetically for 1h to make it fully mixed.

[0062] (3) Add 0.2g of ascorbic acid and 0.6ml of 30% hydrogen peroxide as free radical initiators to the solution obtained in step (2), and stir with a magnetic stirrer for 1h to mix them thoroughly.

[0063] (4) Add 0.25 g gallic acid to 10 ml of 99.7% anhydrous ethanol, stir with a magnetic stirrer for 30 min, then pour it into the solution obtained in step (3), and continue stirring at room temperature for 30 min.

[0064] (5) Add triethylenetetramine and gallic acid to step (5) in a mass ratio of 1:1 and stir magnetically for 30 minutes to ensure thorough mixing.

[0065] (6) The solution obtained in step (5) was added dropwise to 100 ml of 3% CaCl2 solution using a peristaltic pump. During the addition, the solution was slowly stirred at a speed of 100-150 rpm using a magnetic stirrer. After the addition was completed, stirring was continued at room temperature. After crosslinking for 2 hours, the initial hydrogel spheres were formed. The inner diameter of the silicone tube attached to the peristaltic pump was 3 mm, and the flow rate of the peristaltic pump was 4.5 d / s.

[0066] (7) The activation conditions in step (7) are as follows: under standard atmospheric pressure, oxygen is introduced into the dielectric barrier discharge reactor at a flow rate of 200 mL / min, and plasma is generated by applying a voltage of 100 V and a current of 4 A. Discharge activation is performed every 5 min, each activation lasts 50 s, and the activation reaction lasts for a total of 50 min.

[0067] (8) Pour the hydrogel balls obtained in step (7) into 100 mL of 3% glutaraldehyde solution to continue crosslinking. During this period, stir slowly with a magnetic stirrer at a speed of 100-150 rpm for 2 hours.

[0068] (9) Filter out excess water from the hydrogel balls obtained in step (8) using filter paper. Pre-cool the hydrogel balls in a vacuum freeze dryer. After the temperature of the cold trap drops to -40°C, place the hydrogel balls in the cold trap for pre-freezing for 20 minutes. Then freeze-dry them under vacuum conditions of 1 to 10 Pa for 12 hours. Keep the temperature of the cold trap at around -60°C. After drying, the amino-modified porous gallic acid-modified chitosan composite aerogel with adsorbed Cr(VI) is obtained.

[0069] Example 4

[0070] A method for preparing an amino-modified porous gallic acid-modified chitosan composite aerogel material with high efficiency and selective adsorption of Cr(VI) includes the following steps:

[0071] (1) Dissolve 1g of sodium alginate in 60mL of deionized water and heat and stir in a water bath at 60℃ for 1h to make it evenly mixed without lumps.

[0072] (2) Weigh 2g of chitosan with a degree of deacetylation of 80% to 95% and slowly pour it into the solution obtained in step (1) in batches. At the same time, after the chitosan is evenly dispersed, continue to slowly add the mixed acid solution to the solution. Add 8mL of H2SO4:CH3COOH = 1:2 mixed acid solution. During the whole process, use magnetic stirring at 150rpm at room temperature. After all the chitosan is added, continue magnetic stirring for 1h to make it fully mixed.

[0073] (3) Add 0.3g ascorbic acid and 0.6ml of 30% hydrogen peroxide as free radical initiators to the solution obtained in step (2), and stir with a magnetic stirrer for 1h to make it fully mixed.

[0074] (4) Add 0.5g gallic acid to 10ml of 99.7% anhydrous ethanol, stir with a magnetic stirrer for 30min, then pour it into the solution obtained in step (3), and continue stirring at room temperature for 30min.

[0075] (5) Add triethylenetetramine and gallic acid in step (5) in a mass ratio of 1:3 and stir magnetically for 30 minutes to ensure they are fully mixed.

[0076] (6) The solution obtained in step (5) was added dropwise to 100 ml of 3% CaCl2 solution using a peristaltic pump. During the addition, the solution was slowly stirred at a speed of 100-150 rpm using a magnetic stirrer. After the addition was completed, stirring was continued at room temperature. After crosslinking for 2 hours, the initial hydrogel spheres were formed. The inner diameter of the silicone tube attached to the peristaltic pump was 3 mm, and the flow rate of the peristaltic pump was 4.5 d / s.

[0077] (7) The activation conditions in step (7) are as follows: under standard atmospheric pressure, oxygen is introduced into the dielectric barrier discharge reactor at a flow rate of 150 mL / min, and plasma is generated by applying a voltage of 100 V and a current of 4 A. Discharge activation is performed every 5 min, each activation lasts for 40 s, and the activation reaction lasts for a total of 60 min.

[0078] (8) Pour the hydrogel balls obtained in step (7) into 100 mL of 3% glutaraldehyde solution to continue crosslinking. During this period, stir slowly with a magnetic stirrer at a speed of 100-150 rpm for 2 hours.

[0079] (9) Filter out excess water from the hydrogel balls obtained in step (8) using filter paper. Pre-cool the hydrogel balls in a vacuum freeze dryer. After the temperature of the cold trap drops to -40°C, place the hydrogel balls in the cold trap for pre-freezing for 20 minutes. Then freeze-dry them under vacuum conditions of 1 to 10 Pa for 12 hours. Keep the temperature of the cold trap at around -60°C. After drying, obtain the modified chitosan-based composite aerogel with Cr(VI) adsorbed by the target product.

[0080] Example 5

[0081] A method for preparing an amino-modified porous gallic acid-modified chitosan composite aerogel material with high efficiency and selective adsorption of Cr(VI) includes the following steps:

[0082] (1) Dissolve 1g of sodium alginate in 60mL of deionized water and heat and stir in a water bath at 60℃ for 1h to make it evenly mixed without lumps.

[0083] (2) Weigh 2g of chitosan with a degree of deacetylation of 80% to 95% and slowly pour it into the solution obtained in step (1) in batches. At the same time, after the chitosan is evenly dispersed, continue to slowly add the mixed acid solution to the solution. Add 9mL of H2SO4:CH3COOH = 1:1 mixed acid solution. During the whole process, use magnetic stirring at 150rpm at room temperature. After all the chitosan is added, use magnetic stirring for 1h to make it fully mixed.

[0084] (3) Add 0.3g ascorbic acid and 0.9ml of 30% hydrogen peroxide as free radical initiators to the solution obtained in step (2), and stir with a magnetic stirrer for 1h to mix them thoroughly.

[0085] (4) Add 0.5g gallic acid to 10ml of 99.7% anhydrous ethanol, stir with a magnetic stirrer for 30min, then pour it into the solution obtained in step (3), and continue stirring at room temperature for 30min.

[0086] (5) Add triethylenetetramine and gallic acid in step (5) in a mass ratio of 1:3 and stir magnetically for 30 minutes to ensure they are fully mixed.

[0087] (6) The solution obtained in step (5) was added dropwise to 100 ml of 3% CaCl2 solution using a peristaltic pump. During the addition, the solution was slowly stirred at a speed of 100-150 rpm using a magnetic stirrer. After the addition was completed, stirring was continued at room temperature. After crosslinking for 2 hours, the initial hydrogel spheres were formed. The inner diameter of the silicone tube attached to the peristaltic pump was 3 mm, and the flow rate of the peristaltic pump was 4.5 d / s.

[0088] (7) The activation conditions in step (7) are as follows: under standard atmospheric pressure, oxygen is introduced into the dielectric barrier discharge reactor at a flow rate of 200 mL / min, and plasma is generated by applying a voltage of 100 V and a current of 4 A. Discharge activation is performed every 5 min, each activation lasts 50 s, and the activation reaction lasts for a total of 60 min.

[0089] (8) Pour the hydrogel balls obtained in step (7) into 100 mL of 3% glutaraldehyde solution to continue crosslinking. During this period, stir slowly with a magnetic stirrer at a speed of 100-150 rpm for 2 hours.

[0090] (9) Filter out excess water from the hydrogel balls obtained in step (8) using filter paper. Pre-cool the hydrogel balls in a vacuum freeze dryer. After the temperature of the cold trap drops to -40°C, place the hydrogel balls in the cold trap for pre-freezing for 20 minutes. Then freeze-dry them under vacuum conditions of 1 to 10 Pa for 12 hours. Keep the temperature of the cold trap at around -60°C. After drying, the amino-modified porous gallic acid-modified chitosan composite aerogel with adsorbed Cr(VI) is obtained.

[0091] Experimental results

[0092] Chitosan and sodium alginate were mixed using different methods: Figure 1 a is a mixture of CS-mixed acid solution and SA-mixed acid solution; Figure 1 b is a mixture of CS-mixed acid solution and SA-aqueous solution; Figure 1 c represents the experimental method used in this study, which involves adding CS to the SA-water solution, and after it is evenly dispersed, adding 8 ml of mixed acid solution. Figure 1 d and e are solutions with an excess of mixed acid solution added. It can be clearly seen that substances precipitate in the first two methods, indicating that CS and SA solutions are immiscible. However, using the method in this experiment, CS and SA can form a homogeneous solution and are well miscible. But if an excess of mixed acid solution is added, the solution becomes viscous and does not drip when the beaker is inverted.

[0093] Meanwhile, a comparison of the adsorption properties of the composite aerogels prepared in Examples 1-5 revealed that the composite aerogel prepared under the experimental conditions in Example 4 (see physical image) showed the best adsorption performance. Figure 1 a) It showed the best removal effect on Cr(VI). Its SEM image is shown below. Figure 1 As shown in Figure b, the composite aerogel clearly exhibits a three-dimensional porous network structure, which creates favorable conditions for the adsorption of Cr(VI). The aerogel prepared in Example 3 achieved a Cr(VI) removal rate of over 95%, and the EDS diagram after adsorption is shown below. Figure 1 As shown in c. From Figure 1 As can be seen from d, compared to common anions (Cl... - SO4 2- H2PO4 - CO3 2- NO3 - ) and cations (K) + Na + Mg 2+ Ca 2+Aerogel materials have excellent anti-interference ability against Cr(VI).

[0094] It is understood that the above specific description of the present invention is only for illustrating the present invention and is not limited to the technical solutions described in the embodiments of the present invention. Those skilled in the art should understand that modifications or equivalent substitutions can still be made to the present invention to achieve the same technical effect; as long as the use needs are met, they are all within the protection scope of the present invention.

Claims

1. A method for preparing an amino-modified porous gallic acid-modified chitosan-based composite aerogel material for highly efficient selective adsorption of Cr(VI), characterized in that, Includes the following steps: (1) Dissolve 1g of sodium alginate in 60mL of deionized water and heat and stir in a water bath at 60℃ for 1h to make it evenly mixed without lumps; (2) Weigh 2g of chitosan with a degree of deacetylation of 80% to 95%, and slowly pour it into the solution obtained in step (1) in batches. At the same time, after the chitosan is evenly dispersed, continue to slowly add the mixed acid solution to the solution. Add 8mL of H2SO4:CH3COOH = 1:2 mixed acid solution. During the whole process, stir magnetically at 150rpm at room temperature. After all the chitosan is added, stir magnetically for 1h to make it fully mixed. (3) Add 0.3g ascorbic acid and 0.6mL of 30% hydrogen peroxide as free radical initiators to the solution obtained in step (2), and stir with a magnetic stirrer for 1h to mix them thoroughly. (4) Add 0.5 g gallic acid to 10 mL of 99.7% anhydrous ethanol, stir with a magnetic stirrer for 30 min, then pour it into the solution obtained in step (3), and continue stirring at room temperature for 30 min. (5) Add triethylenetetramine dropwise to the solution obtained in step (4). The mass ratio of triethylenetetramine to gallic acid is 1:

3. Stir magnetically for 30 minutes to ensure that the mixture is fully and evenly mixed. (6) The solution obtained in step (5) is added dropwise to 100 mL of 3% CaCl2 solution using a peristaltic pump. During the addition, the solution is slowly stirred at a speed of 100-150 rpm using a magnetic stirrer. After the addition is completed, stirring is continued at room temperature. After crosslinking for 2 hours, the initial hydrogel spheres are formed. The inner diameter of the silicone tube of the peristaltic pump is 3 mm, and the flow rate of the peristaltic pump is 4.5 d / s. (7) After washing the initial hydrogel balls obtained in step (6), place them in a dielectric barrier discharge reactor for activation. The activation conditions are as follows: under standard atmospheric pressure, oxygen is introduced into the dielectric barrier discharge reactor at a flow rate of 150 mL / min, and plasma is generated by applying a voltage of 100 V and a current of 4 A. Discharge activation is performed every 5 min, each activation lasts for 40 s, and the activation reaction lasts for a total of 60 min. (8) Pour the hydrogel balls obtained in step (7) into 100 mL of 3% glutaraldehyde solution to continue cross-linking. During this period, stir slowly with a magnetic stirrer at a speed of 100-150 rpm for 2 hours. (9) Filter out excess water from the hydrogel balls obtained in step (8) using filter paper. Pre-cool the hydrogel balls in a vacuum freeze dryer. After the temperature of the cold trap drops to -40°C, place the hydrogel balls in the cold trap for pre-freezing for 20 minutes. Then freeze-dry them under vacuum conditions of 1 to 10 Pa for 12 hours. Keep the temperature of the cold trap at around -60°C. After drying, obtain the amino-modified porous gallic acid-modified chitosan-based composite aerogel material that efficiently and selectively adsorbs Cr(VI).

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