A chitosan-sodium alginate composite magnetic gel sphere modified with amino polycarboxylic acid, its preparation method and application

Abstract

This invention belongs to the field of environmental functional materials and wastewater treatment technology, and discloses an aminopolycarboxylic acid modified chitosan-sodium alginate composite magnetic gel sphere, its preparation method, and its application. Method: Chitosan, an aminopolycarboxylic acid compound, and water are mixed and stirred until homogeneous. The pH is adjusted to 5-6 with alkali to obtain a mixed solution. This solution is then mixed, stirred, and reacted with an aqueous solution of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide under ice-water bath conditions to obtain aminopolycarboxylic acid modified chitosan. This chitosan is then mixed with Fe3O4 magnetic nanoparticles and an aqueous solution of sodium alginate to obtain a suspension. This suspension is then added dropwise to a mixture of calcium chloride and polyacrylic acid to carry out a cross-linking and solidification reaction. After washing with water and magnetic separation, aminopolycarboxylic acid modified chitosan-sodium alginate composite magnetic gel spheres are obtained. The gel spheres of this invention not only have a large adsorption capacity and good selectivity, but also have a stable mechanical structure, are easy to separate and recover, and have good reusability.

Description

Technical Field

[0001] This invention belongs to the field of environmental functional materials and wastewater treatment technology, and more specifically, relates to an aminopolycarboxylic acid modified chitosan-sodium alginate composite magnetic gel ball, its preparation method, and its application. Background Technology

[0002] With rapid industrial development, the discharge of heavy metal-containing wastewater (such as lead, copper, and cadmium) from industries such as electroplating, mining, battery manufacturing, and fertilizer production is increasing year by year. This type of wastewater is characterized by high toxicity, poor biodegradability, and easy accumulation in organisms, posing a serious threat to the ecological environment and human health. Therefore, developing efficient and economical heavy metal wastewater treatment technologies is of significant practical importance.

[0003] Currently, heavy metal wastewater treatment technologies mainly include chemical precipitation, ion exchange, membrane separation, electrochemical methods, and adsorption. Among these, adsorption is widely used for the advanced treatment of low-concentration heavy metal wastewater due to its advantages such as simple operation, high treatment efficiency, wide applicability, and no secondary pollution. However, traditional adsorbents such as activated carbon, zeolite, and diatomaceous earth have limitations in their practical application due to their limited adsorption capacity, poor selectivity, difficulty in solid-liquid separation, and difficulty in recycling and regenerating them.

[0004] Chitosan is a low-cost, biodegradable, and non-toxic biopolymer that has attracted widespread attention in wastewater treatment due to its excellent adsorption properties for various pollutants. However, single-component chitosan materials suffer from drawbacks such as poor mechanical strength, easy solubility under acidic conditions, and insufficient adsorption capacity, making it difficult to meet practical application requirements.

[0005] To enhance the complexation capacity of chitosan for heavy metals, modification with amino polycarboxylic acids has become an important research direction. Amino polycarboxylic acid compounds such as diethylenetriaminepentaacetic acid (DTPA), ethylenediaminetetraacetic acid (EDTA), ethylene glycol bis(2-aminoethyl ether)tetraacetic acid (EGTA), and nitrilotriacetic acid (NTA) contain multiple amino and carboxyl groups, exhibiting extremely strong chelating and coordination abilities for heavy metal ions, which can significantly improve the adsorption capacity and selectivity of materials. However, amino polycarboxylic acid-modified chitosan still faces challenges such as small particle size, difficulty in solid-liquid separation, easy loss, and difficulty in reusing.

[0006] Therefore, there is an urgent need to develop a new composite material that can combine high-performance aminopolycarboxylic acid modified chitosan with a suitable gel carrier, so that it has the characteristics of high adsorption performance, excellent mechanical strength and easy separation and recovery. Summary of the Invention

[0007] The purpose of this invention is to address the shortcomings of existing technologies by proposing an aminopolycarboxylic acid-modified chitosan-sodium alginate composite magnetic gel sphere, its preparation method, and its applications. The gel spheres of this invention not only have a large adsorption capacity and good selectivity, but also possess a stable mechanical structure, are easy to separate and recover, and have good reusability.

[0008] To achieve the above objectives, the first aspect of the present invention provides a method for preparing amino-polycarboxylic acid modified chitosan-sodium alginate composite magnetic gel spheres, the preparation method comprising the following steps: S1: Chitosan, aminopolycarboxylic acid compound and water are mixed and stirred evenly, and the pH is adjusted to 5-6 with alkali to obtain a mixed solution; 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDAC) aqueous solution is mixed with the mixed solution under ice water bath conditions, stirred and reacted (for cross-linking modification), and after filtration and washing, aminopolycarboxylic acid modified chitosan is obtained. S2: The amino-polycarboxylic acid modified chitosan, Fe3O4 magnetic nanoparticles and sodium alginate aqueous solution are mixed and uniformly dispersed to obtain a suspension (solid particles are uniformly dispersed in the liquid). S3: The suspension is added dropwise to a mixture of calcium chloride and polyacrylic acid (PAA) to carry out a cross-linking and curing reaction. After washing with water and magnetic separation, the amino-polycarboxylic acid modified chitosan-sodium alginate composite magnetic gel spheres are obtained.

[0009] According to the present invention, preferably, the aminopolycarboxylic acid compound is at least one selected from diethylenetriaminepentaacetic acid (DTPA), ethylenediaminetetraacetic acid (EDTA), ethylene glycol bis(2-aminoethyl ether)tetraacetic acid (EGTA), and nitrilotriacetic acid (NTA).

[0010] According to the present invention, preferably, the alkali is at least one of sodium hydroxide, potassium hydroxide and ammonia water.

[0011] According to the present invention, preferably, the mass ratio of chitosan to aminopolycarboxylic acid compound is 1:(1-5).

[0012] According to the present invention, preferably, the mass ratio of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide to chitosan is (1-5):1.

[0013] According to the present invention, preferably, in step S1, the temperature of the ice-water bath is 0-5°C, and the stirring and reaction time under ice-water bath conditions is 6-12 hours.

[0014] According to the present invention, preferably, the mass concentration of the sodium alginate aqueous solution is 1%-5%.

[0015] According to the present invention, preferably, the ratio of the amount of aminopolycarboxylic acid modified chitosan, Fe3O4 magnetic nanoparticles and sodium alginate aqueous solution is (1.5-2.5):(0.5-1.5):100g / g / mL.

[0016] According to the present invention, preferably, in the mixture of calcium chloride and polyacrylic acid, the concentration of calcium chloride is 0.3%-2% and the concentration of polyacrylic acid is 0.01-0.1 mol / L.

[0017] The second aspect of the present invention provides a method for preparing the aminopolycarboxylic acid modified chitosan-sodium alginate composite magnetic gel spheres.

[0018] The third aspect of this invention provides the application of the aforementioned aminopolycarboxylic acid modified chitosan-sodium alginate composite magnetic gel spheres as a magnetic adsorbent for removing heavy metal ions from water.

[0019] The beneficial effects of the technical solution of this invention are as follows: The aminopolycarboxylic acid modified chitosan-sodium alginate composite magnetic gel spheres of this invention not only have large adsorption capacity and good selectivity, but also have a stable mechanical structure, are easy to separate and recover, and have good reusability. Specifically: 1. Sodium alginate, as a natural polysaccharide, contains a large number of carboxyl groups, which can react with Ca... 2+ The rapid cross-linking of divalent metal ions to form a gel has advantages such as good sphericity, being green and non-toxic, and low cost. When combined with chitosan, it can improve its moldability and mechanical properties. The wet mechanical strength (using the pressing method) of the gel spheres of this invention is 1.5-2.0 N, exhibiting good mechanical strength and meeting the basic strength requirements of materials for practical applications.

[0020] 2. The present invention introduces Fe3O4 magnetic nanoparticles to endow the gel ball material with magnetic responsiveness, realizing rapid separation under an external magnetic field (that is, after adsorption is completed, the adsorbent can be rapidly separated by an external magnetic field), effectively solving the solid-liquid separation problem, making the gel ball material of the present invention easy to separate and recycle, simple to operate, and reducing the risk of loss of the gel ball material of the present invention.

[0021] 3. The preparation method of the gel spheres of the present invention is simple, easy to operate, mild, environmentally friendly and low in cost; the main raw materials of the present invention are natural polymers (chitosan, sodium alginate) and biodegradable components. The preparation process is mild and does not introduce toxic organic solvents. It conforms to the concept of green chemistry and the raw materials are widely available, making it suitable for large-scale preparation. It has broad application prospects in the field of heavy metal wastewater treatment.

[0022] 4. This invention utilizes amino polycarboxylic acid compounds (such as EDTA, DTPA, etc.) to covalently modify chitosan, which significantly increases the density of coordinating groups on the surface of the gel sphere material, exhibiting high adsorption capacity and good selectivity for various heavy metal ions such as Pb(II) and Cu(II).

[0023] 5. The gel ball material of the present invention can be regenerated by a suitable eluent after adsorption saturation. It still maintains a high adsorption capacity after multiple adsorption-desorption cycles, and has good economic benefits and practical prospects.

[0024] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0025] The above and other objects, features and advantages of the present invention will become more apparent from the more detailed description of exemplary embodiments of the invention in conjunction with the accompanying drawings.

[0026] Figure 1 The diagram shows a process flow diagram of a method for preparing an aminopolycarboxylic acid modified chitosan-sodium alginate composite magnetic gel ball provided by the present invention.

[0027] Figure 2 A physical image of the EDTA-modified chitosan-sodium alginate composite magnetic gel spheres obtained in Example 1 of the present invention is shown.

[0028] Figure 3 The magnetic hysteresis curve of the EDTA-modified chitosan-sodium alginate composite magnetic gel ball obtained in Example 1 of the present invention is shown ("M" is the magnetization intensity, "Field (Oe)" is the applied magnetic field intensity (Oe).

[0029] Figure 4 The graphs showing the effect of different pH values ​​on the removal of Pb(II) and Cu(II) ions by the EDTA-modified chitosan-sodium alginate composite magnetic gel balls obtained in Example 1 of the present invention are shown ("Removal efficiency", "initial pH value", "Pb(II) concentration", "Cu(II) concentration", "Temperature", "dose", and "Contact time" are all data points).

[0030] Figure 5The diagram shows the regeneration efficiency of the EDTA-modified chitosan-sodium alginate composite magnetic gel spheres obtained in Example 1 of the present invention (“Regeneration efficiency” and “Cycles” represent the number of cycles). Detailed Implementation

[0031] Preferred embodiments of the invention will now be described in more detail. While preferred embodiments of the invention are described below, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that the invention will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0032] Example 1

[0033] This embodiment provides a method for preparing amino-polycarboxylic acid modified chitosan-sodium alginate composite magnetic gel spheres, the preparation method comprising the following steps: S1: Disperse 2.0g chitosan and 3.6g EDTA in 100mL of deionized water, adjust the pH to 5-6 with sodium hydroxide aqueous solution, and stir continuously until completely dissolved to obtain a mixed solution; under ice-water bath (0-5℃) conditions, add an aqueous solution containing 4.75g EDAC dropwise to the mixed solution (60mL), and mechanically stir the reaction for 12 hours; after the reaction is completed, wash with disodium hydrogen phosphate (0.2M) aqueous solution, filter, and rinse repeatedly with deionized water until neutral to obtain aminopolycarboxylic acid modified chitosan.

[0034] S2: Disperse the above-mentioned aminopolycarboxylic acid modified chitosan (2.0g) and Fe3O4 magnetic nanoparticles (1.0g) in 100mL of sodium alginate aqueous solution (2%, w / v) and stir thoroughly to form a uniformly dispersed suspension.

[0035] S3: Dissolve 1.25g CaCl2 in 300mL of solution containing 0.05mol·L⁻¹ -1 A mixture of calcium chloride and polyacrylic acid (i.e., curing solution) was prepared in an aqueous solution of PAA; the suspension was dripped into the curing solution through a syringe and allowed to react fully for 12 hours; finally, it was washed multiple times with deionized water and magnetically separated to obtain EDTA-modified chitosan-sodium alginate composite magnetic gel spheres.

[0036] Figure 2 This is a photograph of the EDTA-modified chitosan-sodium alginate composite magnetic gel spheres obtained in Example 1. From... Figure 2 As can be seen, the gel spheres obtained in Example 1 are black spherical particles that can be attracted by a magnet, thereby achieving solid-liquid separation.

[0037] Figure 3The magnetic hysteresis curve of the EDTA-modified chitosan-sodium alginate composite magnetic gel spheres obtained in Example 1 shows a saturation magnetization of 34.7 emu / g.

[0038] Pb(II) ion solutions and Cu(II) ion solutions with an initial concentration of 1 mmol / L were prepared, and their pH values ​​were adjusted to 1-6 respectively. 10 mL of the above heavy metal ion solutions were placed in a screw-top centrifuge tube, and 10 mg of the gel beads prepared in Example 1 was added. The centrifuge tube was sealed and placed in a constant temperature water bath shaker. After shaking for 24 hours at 25°C and 175 rpm, the concentration of remaining heavy metal ions was determined by atomic absorption spectrometry. The effect of solution pH on the removal efficiency of Pb(II) and Cu(II) ions by the gel beads was obtained. Figure 4 As shown, it can be seen that as the solution pH increases, the efficiency of the gel balls in removing Pb(II) and Cu(II) ions gradually increases, reaching equilibrium at pH 4-6, and also showing good removal effect under low pH conditions (pH 2-3). This indicates that the gel balls prepared in Example 1 can be used in strongly acidic environments.

[0039] Figure 5 The graph shows the reusability of the EDTA-modified chitosan-sodium alginate composite magnetic gel spheres obtained in Example 1. Figure 5 It can be seen that after five consecutive adsorption-desorption cycles, the removal rate of the gel balls did not decrease significantly and remained above 80% of the initial adsorption capacity, indicating that the gel balls prepared in Example 1 have good reusability.

[0040] Example 2

[0041] The only difference between this embodiment and Embodiment 1 is that: Use diethylenetriaminepentaacetic acid (DTPA) instead of EDTA; The mass ratio of chitosan to DTPA is 1:3; The mass ratio of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide to chitosan is 3:1; The mass concentration of the sodium alginate aqueous solution is 3%; In the mixture of calcium chloride and polyacrylic acid, the concentration of calcium chloride is 1%, and the concentration of polyacrylic acid is 0.08 mol·L⁻¹. -1 .

[0042] The resulting gel spheres also exhibited good adsorption performance and magnetic separation effect for Pb(II) and Cu(II) ions.

[0043] Example 3

[0044] The only difference between this embodiment and Embodiment 1 is that: Use NTA instead of EDTA; The mass ratio of chitosan to NTA is 1:1.5; The mass ratio of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide to chitosan is 2:1; The mass concentration of the sodium alginate aqueous solution is 4%; In the mixture of calcium chloride and polyacrylic acid, the concentration of calcium chloride is 1.5% and the concentration of polyacrylic acid is 0.03 mol·L⁻¹. -1 .

[0045] The resulting gel spheres also exhibited good adsorption performance and magnetic separation effect for Pb(II) and Cu(II) ions.

[0046] Example 4

[0047] The only difference between this embodiment and Embodiment 1 is that: Use ethylene glycol bis(2-aminoethyl ether)tetraacetic acid (EGTA) instead of EDTA; The mass ratio of chitosan to EGTA is 1:2; The mass ratio of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide to chitosan is 2.5:1; In step S1, the reaction is mechanically stirred for 15 hours to ensure sufficient grafting; The mass concentration of the sodium alginate aqueous solution is 2%; In the mixture of calcium chloride and polyacrylic acid, the concentration of calcium chloride is 1%, and the concentration of polyacrylic acid is 0.05 mol·L⁻¹. -1 .

[0048] The resulting gel spheres also exhibited good adsorption performance and magnetic separation effect for Pb(II) and Cu(II) ions.

[0049] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A method for preparing amino-polycarboxylic acid modified chitosan-sodium alginate composite magnetic gel spheres, characterized in that, The preparation method includes the following steps: S1: Chitosan, aminopolycarboxylic acid compound and water are mixed and stirred evenly, and the pH is adjusted to 5-6 with alkali to obtain a mixed solution; 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide aqueous solution is mixed with the mixed solution under ice water bath conditions, stirred and reacted, filtered and washed to obtain aminopolycarboxylic acid modified chitosan. S2: The amino-polycarboxylic acid modified chitosan, Fe3O4 magnetic nanoparticles and sodium alginate aqueous solution are mixed and uniformly dispersed to obtain a suspension; S3: The suspension is added dropwise to a mixture of calcium chloride and polyacrylic acid to carry out a cross-linking and curing reaction. After washing with water and magnetic separation, the amino polycarboxylic acid modified chitosan-sodium alginate composite magnetic gel spheres are obtained.

2. The preparation method of aminopolycarboxylic acid modified chitosan-sodium alginate composite magnetic gel spheres according to claim 1, wherein, The aminopolycarboxylic acid compound is at least one of diethylenetriaminepentaacetic acid, ethylenediaminetetraacetic acid, ethylene glycol bis(2-aminoethyl ether)tetraacetic acid, and hymenotriacetic acid.

3. The preparation method of aminopolycarboxylic acid modified chitosan-sodium alginate composite magnetic gel spheres according to claim 1, wherein, The mass ratio of chitosan to amino polycarboxylic acid compound is 1:(1-5).

4. The preparation method of aminopolycarboxylic acid modified chitosan-sodium alginate composite magnetic gel spheres according to claim 1, wherein, The mass ratio of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide to chitosan is (1-5):

1.

5. The preparation method of aminopolycarboxylic acid modified chitosan-sodium alginate composite magnetic gel spheres according to claim 1, wherein, In step S1, the temperature of the ice-water bath is 0-5℃, and the stirring and reaction time under ice-water bath conditions is 6-12h.

6. The preparation method of aminopolycarboxylic acid modified chitosan-sodium alginate composite magnetic gel spheres according to claim 1, wherein, The mass concentration of the sodium alginate aqueous solution is 1%-5%.

7. The preparation method of aminopolycarboxylic acid modified chitosan-sodium alginate composite magnetic gel spheres according to claim 1, wherein, The ratio of aminopolycarboxylic acid modified chitosan, Fe3O4 magnetic nanoparticles and sodium alginate aqueous solution is (1.5-2.5):(0.5-1.5):100g / g / mL.

8. The method for preparing amino-polycarboxylic acid modified chitosan-sodium alginate composite magnetic gel spheres according to claim 1, wherein, In the mixture of calcium chloride and polyacrylic acid, the concentration of calcium chloride is 0.3%-2%, and the concentration of polyacrylic acid is 0.01-0.1 mol / L.

9. The aminopolycarboxylic acid modified chitosan-sodium alginate composite magnetic gel spheres prepared by the method according to any one of claims 1-8.

10. The application of the aminopolycarboxylic acid modified chitosan-sodium alginate composite magnetic gel spheres according to claim 9 as a magnetic adsorbent for removing heavy metal ions from water.

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