An organically covalently cross-linked alginate fiber, its preparation method and application

Abstract

This invention belongs to the field of valuable metal recovery and water purification technology, and more specifically, relates to an organically covalently cross-linked alginate fiber, its preparation method, and its applications. This invention prepares alginate fibers with good water resistance through organic covalent cross-linking technology, which can be used for the recovery of valuable metals from aqueous solutions, the removal of heavy metals, the softening of drinking water, and the removal of cationic organic pollutants. It can solve the problem of calcium content in existing alginate fibers. 2+ The alginate adsorbent material prepared by ion crosslinking technology suffers from a large number of sacrificed adsorption sites, resulting in low adsorption capacity and limiting its widespread application. The organic covalently crosslinked alginate fiber designed and synthesized in this invention has the characteristics of fast adsorption rate, excellent adsorption performance, and easy solid-liquid separation. Moreover, the organic covalently crosslinked alginate fiber can be regenerated and reused.

Description

Technical Field

[0001] This invention belongs to the field of valuable metal recycling and water purification technology, and more specifically, relates to an organically covalently cross-linked alginate fiber, its preparation method and application. Background Technology

[0002] Alginic acid has attracted widespread attention for its advantages such as wide availability, low cost, and environmental friendliness, making its recovery from valuable resources and removal of pollutants in aqueous solutions a key focus. However, the water solubility of alginic acid significantly limits its application in aquatic environments. Therefore, improving the water resistance of alginic acid-based materials is of great research value for broadening their application in water treatment.

[0003] Currently, overcoming the water solubility of alginate is mainly achieved through the interaction of alginate molecules with calcium ions (Ca). 2+ Ionic crosslinking between ions can improve the water resistance of alginate-based materials (e.g., Figure 1 (As shown). However, Ca 2+ The introduction of ions will compete with cationic pollutants for adsorption, which will greatly reduce the performance of alginate-based adsorbents in recovering valuable cationic metals and removing cationic pollutants. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide an organically covalently cross-linked alginate fiber, its preparation method, and its applications in the fields of resource recovery and water treatment in aqueous solutions, thereby solving the problem of the Ca content of existing alginate fibers. 2+ The alginate adsorbent materials prepared by ion crosslinking technology suffer from technical problems that limit their widespread application, such as sacrificing adsorption sites and having small adsorption capacity.

[0005] To achieve the above objectives, the present invention provides a method for preparing organically covalently crosslinked alginate fibers, comprising the following steps:

[0006] (1) Sodium alginate and water are mixed to obtain alginate hydrogel;

[0007] (2) The alginate hydrogel described in step (1) is extruded into an acidic aqueous solution or an organic solution to form fibers in the solution. The alginate fibers are obtained by solid-liquid separation. The alginate fibers are insoluble in the acidic aqueous solution or the organic solution.

[0008] (3) After drying the alginate fiber described in step (2), soak it in an acidic aqueous solution or organic solution of an organic covalent crosslinking agent to undergo an organic covalent crosslinking reaction. After the reaction is completed, wash and dry the fiber to obtain organically covalently crosslinked alginate fiber; and the alginate fiber is insoluble in the acidic aqueous solution or organic solution of the organic covalent crosslinking agent.

[0009] The acidic aqueous solutions in steps (2) and (3) may be the same or different, and the organic solutions in steps (2) and (3) may be the same or different.

[0010] Preferably, in step (1), the sodium alginate and water are mixed, and the mass ratio of sodium alginate to water is (2-6):100.

[0011] Preferably, the acidic aqueous solutions in steps (2) and (3) are each independently one or more acidic aqueous solutions with a pH less than 2;

[0012] The organic solutions described in steps (2) and (3) are each independently one or more of methanol, ethanol, and N,N-dimethylformamide.

[0013] Preferably, the organic covalent crosslinking agent in step (3) is one or more of epichlorohydrin, ethylene glycol diglycidyl ether, and glutaraldehyde.

[0014] Preferably, the volume percentage concentration of the organic covalent crosslinking agent in the acidic aqueous solution or organic solution is 0.5-25%, more preferably 0.5-10%.

[0015] Preferably, the reaction temperature during the organic covalent crosslinking reaction is 70-100℃ and the reaction time is 6-12h.

[0016] Preferably, the ratio of the amount of alginate fiber to the acidic aqueous solution or organic solution of the organic covalent crosslinking agent in step (3) is 1g:50-200mL.

[0017] According to another aspect of the present invention, an organically covalently cross-linked alginate fiber prepared by the preparation method described above is provided.

[0018] According to another aspect of the invention, the application of the organically covalently cross-linked alginate fiber described above in the adsorption, removal or recovery of heavy metals in aqueous solutions, or in softening drinking water, is provided.

[0019] According to another aspect of the invention, the application of the aforementioned organically covalently crosslinked alginate fiber in the removal of cationic organic pollutants in an aqueous solution is provided.

[0020] In summary, compared with the prior art, the above-described technical solutions conceived by this invention mainly possess the following technical advantages:

[0021] This invention provides an organically covalently cross-linked alginate fiber. The alginate fiber is prepared by immersing it in an acidic aqueous solution of an organic covalently cross-linking agent or an organic solution in which alginate is insoluble, thereby undergoing an organic covalently cross-linking reaction. This process produces water-insoluble alginate fiber. When applied to the fields of resource recovery and water treatment agents in aqueous solutions, it can solve the problem of calcium content in existing alginate solutions. 2+ The ion crosslinking technique for preparing alginate adsorbents suffers from limitations in its widespread application due to the sacrifice of adsorption sites, resulting in low adsorption capacity. This method, however, offers simple and mild preparation conditions. The resulting organically covalently crosslinked alginate fibers can be used for the recovery / removal of heavy metals from aqueous solutions, softening of drinking water, and removal of cationic organic pollutants from aqueous solutions. They exhibit characteristics such as fast adsorption rate, high adsorption performance, and easy solid-liquid separation. Furthermore, the organically covalently crosslinked alginate fibers are regenerable and reusable. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the traditional synthesis mechanism of water-resistant alginate crosslinking using the electrostatic interaction of calcium ions;

[0023] Figure 2 This is a schematic diagram of the preparation method of organic covalently crosslinked alginate fiber according to the present invention;

[0024] Figure 3 This is an evaluation of the adsorption performance of organic covalently crosslinked alginate fibers prepared with different crosslinking agent concentrations in Comparative Example 3 on Sn(II) in acidic aqueous solution (adsorption conditions: pH≈1, adsorbent dosage = 0.5 g / L);

[0025] Figure 4 This invention provides an evaluation of the adsorption performance of organic covalently cross-linked alginate fibers for Pb(II), Cd(II), and Zn(II) (adsorption conditions: pH≈5, adsorbent dosage = 0.5g / L).

[0026] Figure 5 This is a study on the regeneration performance of organic covalently crosslinked alginate fibers provided in the embodiments of the present invention;

[0027] Figure 6 This invention provides an evaluation of the adsorption performance of organic covalently cross-linked alginate fibers for Ca(II) and Mg(II) (adsorption conditions: pH≈7, adsorbent dosage = 0.5g / L).

[0028] Figure 7 These are digital photos of organic covalently cross-linked alginate fibers before and after adsorption of methylene blue, provided in an embodiment of the present invention (adsorption conditions: pH≈7, adsorbent dosage = 0.4g / L). Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings and embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the invention and should not be considered as specific limitations thereof. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0030] The embodiments of the present invention are implemented under the premise of the technical solution of the present invention, and detailed implementation methods and processes are given. However, the protection scope of the present invention is not limited to the following embodiments. The process parameters in the following embodiments that do not specify specific conditions are generally in accordance with conventional conditions.

[0031] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0032] The process parameters in the following examples, unless otherwise specified, are generally performed under conventional conditions.

[0033] This invention provides a method for preparing organically covalently crosslinked alginate fibers, such as... Figure 2 As shown, it includes the following steps:

[0034] (1) Sodium alginate and water are mixed to obtain alginate hydrogel;

[0035] (2) The alginate hydrogel described in step (1) is squeezed into an acidic aqueous solution or an organic solution to form alginate fibers in the solution. The alginate fibers are obtained by solid-liquid separation. The alginate fibers are insoluble in the acidic aqueous solution or the organic solution. Here, solid-liquid separation can be done by directly scooping out the solution or by other conventional solid-liquid separation methods to remove the solution portion.

[0036] (3) After drying the alginate fiber described in step (2), soak it in an acidic aqueous solution or organic solution of an organic covalent crosslinking agent to undergo an organic covalent crosslinking reaction. After the reaction is completed, wash and dry the fiber to obtain organically covalently crosslinked alginate fiber. The alginate fiber is insoluble in the acidic aqueous solution or organic solution of the organic covalent crosslinking agent. The acidic aqueous solution described in steps (2) and (3) may be the same or different. The organic solution described in steps (2) and (3) may be the same or different.

[0037] The term "insoluble" in this invention refers to the fact that alginate fibers maintain good fiber morphology even in acidic aqueous solutions or organic solutions.

[0038] In some embodiments, step (1) involves mixing the sodium alginate and water, wherein the mass ratio of sodium alginate to water is (2-6):100. The acidic aqueous solutions in steps (2) and (3) are each independently one or more acidic aqueous solutions with a pH less than 2, including but not limited to aqueous solutions with a pH less than 2 such as hydrochloric acid, sulfuric acid, and nitric acid; the organic solutions in steps (2) and (3) are each independently one or more liquid organic solvents such as methanol, ethanol, and N,N-dimethylformamide.

[0039] In some embodiments, the alginate hydrogel described in step (2) is extruded into an acidic aqueous solution or organic solution, and alginate fiber is obtained by extruding the alginate hydrogel into an acidic aqueous solution or organic solution through compressed air extrusion or mechanical extrusion.

[0040] In some embodiments, the organic covalent crosslinking agent in step (3) is one or more of epichlorohydrin (ECH), ethylene glycol diglycidyl ether (EGDE), and glutaraldehyde (GA), with ECH being preferred.

[0041] In some embodiments, the volume percentage concentration of the organic covalent crosslinking agent in the acidic aqueous solution or organic solution is 0.5-25%, preferably 0.5-10%, and more preferably 0.5-8%. The reaction temperature during the organic covalent crosslinking reaction is 70-100℃, and the reaction time is 6-12 hours. In step (3), the ratio of the alginate fiber to the acidic aqueous solution or organic solution of the organic covalent crosslinking agent is 1 g: 50-200 mL.

[0042] The alginate fiber prepared by the method of this invention has been experimentally proven to be useful for adsorbing, removing, or recovering heavy metals from aqueous solutions, or for softening drinking water. The aqueous solution can be various types of wastewater (including but not limited to simulated steel cold rolling wastewater, electroplating wastewater, etc.). In some embodiments, the alginate fiber after adsorbing heavy metals or softening drinking water can be regenerated and reused using acidic aqueous solutions such as nitric acid or hydrochloric acid.

[0043] The alginate fiber prepared by the method of this invention has been experimentally verified to be used for the removal of cationic organic pollutants in aqueous solutions. In some embodiments, the cationic organic pollutants are one or more of methylene blue, crystal violet, malachite green, etc.

[0044] This invention prepares water-resistant alginate fibers through non-ionic crosslinking, specifically organic covalent crosslinking technology, for the recovery / removal of heavy metals in aqueous solutions, softening of drinking water, and removal of cationic organic pollutants. Experiments demonstrate that, compared to existing calcium-ion-crosslinked alginate fibers, the organically covalently crosslinked alginate fibers of this invention significantly increase the adsorption capacity of alginate adsorbent materials.

[0045] The following is an example:

[0046] Example 1

[0047] A method for preparing organically covalently crosslinked alginate fibers includes the following steps:

[0048] (1) Mix 3.75g of sodium alginate and 96.25g of water to obtain alginate hydrogel;

[0049] (2) The alginate hydrogel described in step (1) is extruded into anhydrous ethanol solution under a pressure of 0.2-0.4 MPa using an air compressor to obtain alginate fiber, which is then taken out and freeze-dried.

[0050] (3) Immerse 0.05g of the alginate fiber prepared in step (2) in 10mL of ECH N,N-dimethylformamide solution (ECH concentration 1% (v / v)) and allow it to undergo an organic covalent crosslinking reaction at 80℃ for 12h. Then wash with deionized water and dry to obtain organically covalently crosslinked alginate fiber. The ratio of alginate fiber to ECH N,N-dimethylformamide solution is 1g:200mL.

[0051] The other steps are the same as in Example 1, but the preparation conditions are changed to obtain the organic covalently crosslinked alginate fibers of Examples 2 to 13. The preparation conditions and water solubility of the alginate fibers are listed in Table 1.

[0052] Table 1. Stability of organic covalently cross-linked alginate fibers prepared under different conditions in water.

[0053]

[0054]

[0055] As can be seen from Table 1, the organic covalently cross-linked alginate fibers prepared under the conditions of each embodiment have good water resistance.

[0056] Comparative Example 1

[0057] The uncrosslinked alginate fiber obtained in step (2) of Example 1 was dried and a small amount was mixed with water. It was found that it dissolved in water.

[0058] Comparative Example 2

[0059] The other steps are the same as in Example 1, except that the concentration of the organic covalent crosslinking agent in step (3) is replaced with 0% to obtain alginate fiber. After drying, a small amount is mixed with water and it is found that it dissolves in water. This indicates that in the synthesis process of the alginate fiber with good water resistance prepared in Examples 1-13, the crosslinking agent (ECH, EGDE, GA) plays a major role, and the solvent used (N,N-dimethylformamide, pH=1 hydrochloric acid aqueous solution) does not participate in the reaction.

[0060] Comparative Example 3

[0061] The other steps are the same as in Example 1, except that the concentration of the organic covalent crosslinking agent in step (3) is replaced with 8%, 10%, 15%, and 20%, respectively, and organic covalent crosslinked alginate fibers are obtained respectively.

[0062] Alginic acid fibers obtained by crosslinking with different concentrations of organic covalent crosslinking agents were used to recover Sn(II) from simulated acidic steel cold rolling wastewater. The initial Sn(II) concentration was approximately 800 mg / L, and the dosage of organically covalently crosslinked alginate fibers was 0.5 g / L. The adsorption pH was 1, the temperature was 25℃, and the adsorption time was 3 h. Experiments showed that when the ECH concentration increased from 8% to 20% during the preparation of the organically covalently crosslinked alginate fibers, their adsorption capacity for Sn(II) decreased from 341.1 mg / g to 7.8 mg / g (see...). Figure 3 This may be because during the material preparation process, an excessively high concentration of crosslinking agent consumes a large number of adsorption sites (carboxyl groups, -COOH), thus significantly reducing its adsorption capacity for Sn(II).

[0063] Example 14

[0064] The covalently cross-linked alginate fibers prepared in Examples 1, 4, 5, and 6 were used to adsorb Pb(II), Cd(II), and Zn(II) from simulated aqueous solutions. The initial concentration of Pb(II), Cd(II), or Zn(II) was 200 mg / L, the dosage of organic covalently cross-linked alginate fibers was 0.5 g / L, the adsorption pH was 5, the temperature was 25 °C, and the adsorption time was 3 hours. The adsorption capacities for Pb(II), Cd(II), and Zn(II) were measured to be 313.3–348.9 mg / g, 217.2–240.2 mg / g, and 122.9–149.0 mg / g, respectively (see [link to example]). Figure 4 Its concentration is higher than that of most adsorbents currently reported (Table 2).

[0065] Furthermore, the heavy metal-loaded organically covalently cross-linked alginate fibers obtained after adsorption in Example 14 were separated and recovered from the aqueous solution, and then regenerated by soaking in a 1M HNO3, HCl acidic solution for 1 hour. The regenerated adsorbent was rinsed with deionized water until neutral. The adsorption performance of the regenerated adsorbent for metal ions was then further evaluated under the above adsorption conditions. Figure 5 As shown, after three adsorption-desorption cycles, its adsorption performance for heavy metal ions did not decrease significantly. This indicates that the heavy metal-loaded organically covalently cross-linked alginate fiber can be completely regenerated using acidic solutions such as HNO3 and HCl.

[0066] Table 2. Comparison of adsorption performance of biomass adsorbents for Zn(II), Cd(II) and Pb(II)

[0067]

[0068] Example 15

[0069] The organically covalently cross-linked alginate fibers prepared in Examples 1, 4, 5, and 6 were used to remove Ca(II) and Mg(II) ions from a neutral (pH≈7) simulated aqueous solution. The initial concentrations of Ca(II) and Mg(II) ions were approximately 200 mg / L. The dosage of the organically covalently cross-linked alginate fibers was 0.5 g / L, the temperature was 25 °C, and the adsorption time was 3 hours. The relevant results are as follows: Figure 6 As shown in the figure. The results indicate that the prepared adsorbent material can be effectively used for the removal of Ca(II) and Mg(II) ions in a neutral (pH≈7) environment, which means that the prepared organically covalently cross-linked alginate fiber can be used for water softening.

[0070] Example 16

[0071] The adsorption performance of the organic covalently cross-linked alginate fiber prepared in Example 2 for the cationic dye methylene blue is as follows: Figure 7 As shown, organic covalently cross-linked alginate fibers have a significant removal effect on methylene blue in solution. After adsorption, the color of the methylene blue solution is significantly reduced. Under the conditions of initial concentration of 10 mg / L and 100 mg / L, solution pH≈7, and adsorbent dosage = 0.4 g / L, the removal rate of methylene blue is higher than 95%.

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[0094] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. The application of an organically covalently cross-linked water-resistant alginate fiber in the adsorption, removal, or recovery of heavy metals from aqueous solutions, or in the softening of drinking water, characterized in that... The method for preparing the organically covalently crosslinked water-resistant alginate fiber includes the following steps: (1) Sodium alginate and water are mixed to obtain alginate hydrogel; (2) The alginate hydrogel described in step (1) is extruded into an organic solution to form fibers in the solution, and the alginate fibers are obtained by solid-liquid separation; and the alginate fibers are insoluble in the organic solution; the organic solution is one or more of methanol, ethanol, and N,N-dimethylformamide; (3) After freeze-drying the alginate fiber described in step (2), it is immersed in an organic solution of an organic covalent crosslinking agent to undergo an organic covalent crosslinking reaction. After the reaction is completed, the fiber is washed and dried to obtain organically covalently crosslinked alginate fiber. The alginate fiber is insoluble in the organic solution of the organic covalent crosslinking agent. The organic covalent crosslinking agent is one or more of epichlorohydrin, ethylene glycol diglycidyl ether, and glutaraldehyde. The reaction temperature during the organic covalent crosslinking reaction is 70-100 ℃, and the reaction time is 6-12 h. The organic solutions mentioned in steps (2) and (3) may be the same or different.

2. The application of an organically covalently cross-linked, water-resistant alginate fiber in the removal of cationic organic pollutants in aqueous solution, characterized in that... The method for preparing the organically covalently crosslinked water-resistant alginate fiber includes the following steps: (1) Sodium alginate and water are mixed to obtain alginate hydrogel; (2) The alginate hydrogel described in step (1) is extruded into an organic solution to form fibers in the solution, and the alginate fibers are obtained by solid-liquid separation; and the alginate fibers are insoluble in the organic solution; the organic solution is one or more of methanol, ethanol, and N,N-dimethylformamide; (3) After freeze-drying the alginate fiber described in step (2), it is soaked in an organic solution of an organic covalent crosslinking agent to undergo an organic covalent crosslinking reaction. After the reaction is completed, the fiber is washed and dried to obtain organically covalently crosslinked alginate fiber. The alginate fiber is insoluble in the organic solution of the organic covalent crosslinking agent. The organic covalent crosslinking agent is one or more of epichlorohydrin, ethylene glycol diglycidyl ether, and glutaraldehyde. The reaction temperature during the organic covalent crosslinking reaction is 70-100 ℃, and the reaction time is 6-12 h. The organic solutions mentioned in steps (2) and (3) may be the same or different.

3. The application as described in claim 1 or 2, characterized in that, Step (1) Mix the sodium alginate and water, wherein the mass ratio of sodium alginate to water is (2-6):

100.

4. The application as described in claim 1 or 2, characterized in that, The volume percentage concentration of the organic covalent crosslinking agent in the organic solution is 0.5-25%.

5. The application as described in claim 1 or 2, characterized in that, In step (3), the ratio of the amount of alginate fiber to the organic solution of the organic covalent crosslinking agent is 1 g: 50-200 mL.

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