COF-based crown ether modified cellulose three-dimensional composite adsorption material

Abstract

The invention relates to the technical field of wastewater treatment, in particular to a COF-based crown ether modified cellulose three-dimensional composite adsorption material. Single TpPa-SO3H powder has weak adsorbability on Cs < + > in wastewater and is difficult to form. In order to solve the problems, the invention provides the COF-based crown ether modified cellulose three-dimensional composite adsorption material which is prepared by the following steps: firstly, adding CMC and a cross-linking agent into a TpPa-SO3H aqueous solution to form hydrogel, and freeze-drying to obtain TpPa-SO3H / CMC; and adding the CMC into a crown ether solution, stirring and soaking, washing and drying to obtain the Crown-TpPa-SO3H / CMC. The material takes TpPa-SO3H, CMC and 18-crown ether-6 as raw materials, the three components synergistically construct a'multi-stage adsorption 'mechanism, a sulfonic group of TpPa-SO3H preferentially captures Sr < 2 + >, 18-crown ether-6 is specifically complexed with Cs < + > and a CMC network to promote ion transmission, radioactive metal ions such as cesium or strontium in wastewater can be efficiently separated, and the material has efficient adsorption performance and practical applicability.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, specifically to a three-dimensional composite adsorbent material based on COF crown ether modified cellulose. Background Technology

[0002] The development of the nuclear energy industry has generated a large amount of wastewater containing radioactive nuclides. Among them, Cs and Sr, due to their long half-lives (about 30 years), high mobility, and serious harm to human health, have become key and challenging issues in wastewater treatment. Traditional separation methods, such as solvent extraction, precipitation, and ion exchange, usually suffer from problems such as complex operation, use of toxic solvents, and secondary pollution.

[0003] Solid-state adsorption is considered a promising alternative due to its simplicity, environmental friendliness, and high selectivity. Covalent organic framework (COF) materials, such as TpPa-SO3H, possess high specific surface area, ordered pores, and functionalizability. Their sulfonic acid groups (-SO3H) are particularly effective against Sr. 2+ It exhibits strong ion exchange capacity and selectivity. However, TpPa-SO3H shows resistance to Cs. + Its adsorption capacity is limited, and its powder form is easily lost and difficult to recycle in actual water treatment, which limits its large-scale application.

[0004] Crown ether compounds, such as 18-crown ether-6, have cavitation sizes similar to Cs. + Highly matched, Cs can be achieved through the "subject-object" interaction. + They exhibit specific recognition and complexation. However, small molecule crown ethers are easily dissolved and lost in the aqueous phase, making them unsuitable for direct use as adsorbents; therefore, they must be immobilized on a support.

[0005] Carboxymethyl cellulose (CMC) is a water-soluble biopolymer that can serve as an ideal material for constructing three-dimensional aerogels. Its molecular chains are rich in hydroxyl and carboxyl groups, which can both form stable macroporous structures through cross-linking and interact with functional components (such as COF and crown ethers) to achieve good dispersion and fixation.

[0006] The drawback of existing technology is that single TpPa-SO3H powder has a limited effect on Cs. + Cs exhibit weak adsorption and are difficult to form; small-molecule crown ethers, while highly selective, are prone to loss; and simple CMCs lack sufficient adsorption capacity and selectivity. Currently, there is a lack of a method that can integrate the advantages of all three while simultaneously achieving adsorption of Cs. + and Sr 2+ A composite adsorbent material that is highly efficient, synergistically removes pollutants, and is macroscopically shaped and easy to recycle. Summary of the Invention

[0007] The problem with existing technologies is that single TpPa-SO3H powder has a limited effect on Cs in wastewater.+ The adsorption capacity of cellulose is weak and it is difficult to form. To address these problems, this invention provides a three-dimensional composite adsorbent material of cellulose based on crown ether modified with COF, the preparation method of which includes the following steps: (1) Add CMC and crosslinking agent to TpPa-SO3H aqueous solution, stir the reaction so that CMC and crosslinking agent in the reaction system undergo covalent crosslinking reaction to form a three-dimensional network structure hydrogel that encapsulates TpPa-SO3H. After freeze-drying the hydrogel, TpPa-SO3H / CMC is obtained. (2) Add TpPa-SO3H / CMC to the crown ether solution, stir and soak at room temperature. After soaking, filter to collect the solid product and wash it with deionized water at least 3 times. Then freeze dry to obtain Crown-TpPa-SO3H / CMC.

[0008] Preferably, TpPa-SO3H is a two-dimensional covalent organic framework (COF) formed by the aldehyde-amine condensation reaction between 2,4,6-tricarboxymethyl phloroglucinol and 2,5-diaminobenzenesulfonic acid, which are linked by β-ketoenamine chemical bonds.

[0009] Preferably, the mass ratio of 2,4,6-tricarboxymethyl phloroglucinol to 2,5-diaminobenzenesulfonic acid is 5.46:4.2.

[0010] Preferably, the crown ether solution is a solution of the crown ether formed in a solvent, wherein the crown ether is 18-crown ether-6, and the solvent is an aqueous ethanol solution.

[0011] Preferably, in step (1), the ratio of TpPa-SO3H to CMC and crosslinking agent is 0.125g:1.25g:5mL.

[0012] Preferably, the crosslinking agent is epichlorohydrin.

[0013] Preferably, the mass ratio of crown ether to TpPa-SO3H / CMC in the reaction system of step (2) is 0.25:0.9.

[0014] Preferably, the stirring and soaking time in step (2) is not less than 6 hours.

[0015] The present invention has the following beneficial effects: (1) The present invention uses TpPa-SO3H (for Sr) 2+ High selectivity), 18-crown ether-6 (for Cs + High selectivity) and CMC are integrated into one, forming a "sulfonic acid group to capture Sr" 2+ Crown ether complex Cs +The multi-level synergistic adsorption mechanism of "carboxyl-assisted adsorption of radioactive metal ions" enables efficient and simultaneous removal of two key radionuclides, cesium and strontium, from wastewater, solving the problem of single material adsorption effect. (2) This invention uses CMC as a flexible matrix and utilizes its three-dimensional network structure to firmly encapsulate and fix nano-sized TpPa-SO3H powder, successfully transforming the powder material into a macroscopic three-dimensional bulk material. This aerogel is easy to separate and recycle from treated wastewater, avoiding secondary pollution and greatly improving the practicality and ease of operation of the material; (3) This invention utilizes the three-dimensional porous network of CMC to provide abundant loading sites and confinement space for crown ether molecules. The oxygen atoms of the crown ether form weak interactions with the carboxyl / hydroxyl groups of CMC, thereby being physically anchored to the gel backbone. This immobilization method effectively inhibits the dissolution and loss of small molecule crown ethers in the aqueous phase; (4) In this invention, CMC is covalently cross-linked with two-dimensional TpPa-SO3H to form a three-dimensional interpenetrating network structure, which provides an ideal channel for the rapid diffusion of water molecules and the mass transfer of metal ions. At the same time, the high specific surface area of ​​TpPa-SO3H, the COF channels, the complexation sites of crown ethers, and the carboxyl groups of CMC are all fully exposed, providing a large number of accessible active sites, ensuring the high adsorption capacity of the material and effectively shortening the adsorption time. Attached Figure Description

[0016] Figure 1 Zeta potential diagrams of Crown-TpPa-SO3H / CMC-1 obtained in Example 1 and TpPa-SO3H / CMC obtained in Comparative Example 5.

[0017] Figure 2 Adsorption equilibrium capacity test curves of the adsorption materials obtained in Example 1 and Comparative Examples 1, 2, and 4 for cesium ions in aqueous solutions with different initial concentrations under the same test conditions.

[0018] Figure 3 Adsorption equilibrium capacity test curves of the adsorption materials obtained in Example 1 and Comparative Examples 1, 2, and 4 for strontium ions in aqueous solutions with different initial concentrations of strontium ions under the same test conditions.

[0019] Figure 4 Figure 1 shows the adsorption equilibrium capacity test results of Crown-TpPa-SO3H / CMC-1 obtained in Example 1, TpPa-SO3H / CMC and CMC obtained in Comparative Example 5 for cesium ions in aqueous solution with an initial concentration of 10 mg / L under different pH conditions.

[0020] Figure 5Figure 1 shows the adsorption equilibrium capacity test results of strontium ions in an aqueous solution with an initial concentration of 10 mg / L obtained by Crown-TpPa-SO3H / CMC-1 obtained in Example 1 and TpPa-SO3H / CMC and CMC obtained in Comparative Example 5 under different pH conditions.

[0021] Figure 6 SEM image of Crown-TpPa-SO3H / CMC-1 obtained in Example 1. Detailed Implementation

[0022] The present invention will be described in detail below with reference to embodiments. However, it should be understood that the following embodiments are merely illustrative examples of implementation of the present invention and are not intended to limit the scope of the present invention.

[0023] Example 1

[0024] A three-dimensional composite adsorbent material based on COF crown ether modified cellulose is prepared by the following method: (1) Weigh 5.46 g of 2,5-diaminobenzenesulfonic acid and add it to a mixed solution of 10 mL of deionized water and 40 mL of acetic acid. Disperse the mixture evenly by sonication. Then place the beaker on a magnetic stirrer and stir at 250 r / min until the powder dissolves. Then weigh 4.20 g of 2,4,6-tricarboxymethyl phloroglucinol and add it to the mixed solution. After sonication for 10 min, stir the reaction for 72 h (phenomenon: the solution is blood red). After the reaction is completed, wash the product twice by centrifugation with water, anhydrous ethanol and anhydrous acetone in sequence. Finally, transfer the obtained solid product to a vacuum drying oven and dry it at 40 °C to constant weight to obtain TpPa-SO3H powder. (2) Take 0.125 g of TpPa-SO3H powder, add it to 50 mL of deionized water and sonicate to dissolve it evenly. Then add 1.125 g of carboxymethyl cellulose and stir at 500 r / min for 3 h. Then add 5 mL of epichlorohydrin to the reaction system and stir for 30 min. Pour it into a round silicone mold and place it together with the mold in a freeze dryer. Freeze dry at -50℃ for 72 h to obtain TpPa-SO3H / CMC. (3) Weigh 0.25 g of 18-crown ether-6 powder, add it to 10 mL of anhydrous ethanol, sonicate for 10 min, add 40 mL of deionized water, stir until the 18-crown ether-6 powder is completely dissolved to obtain a crown ether solution, then add 0.9 g of TpPa-SO3H / CMC to the crown ether solution, stir and soak at room temperature for 6 h, after soaking, filter and collect the solid gel, wash it 3 times with deionized water, then transfer it to a freeze dryer and freeze dry at -50℃ for 72 h to obtain the crown ether-modified cellulose three-dimensional composite adsorbent material based on COF, denoted as Crown-TpPa-SO3H / CMC-1.

[0025] Comparative Example 1 is the same as Example 1, except that in step (2) of Comparative Example 1, the amount of TpPa-SO3H powder added is 0.125g and the amount of carboxymethyl cellulose added is 0.375g. The obtained adsorbent material is denoted as Crown-TpPa-SO3H / CMC-2.

[0026] Comparative Example 2 is the same as Example 1, except that in step (2) of Comparative Example 2, the amount of TpPa-SO3H powder added is 0.125g and the amount of carboxymethyl cellulose added is 0.75g. The obtained adsorbent material is denoted as Crown-TpPa-SO3H / CMC-3.

[0027] Comparative Example 3

[0028] Take 0.125 g of TpPa-SO3H powder obtained in Example 1 and 0.25 g of 18-crown ether-6 powder, add them to 50 mL of deionized water and sonicate until homogeneous. Then add 1.125 g of carboxymethyl cellulose and stir at 500 r / min for 3 h. Then add 5 mL of epichlorohydrin to the reaction system and stir for 30 min. Pour the mixture into a circular silicone mold and place it together with the mold in a freeze dryer. Freeze dry at -50℃ for 72 h to obtain Crown-TpPa-SO3H / CMC-4.

[0029] Comparative Example 4 is the TpPa-SO3H powder obtained in Example 1.

[0030] Comparative Example 5 is the TpPa-SO3H / CMC obtained in Example 1.

[0031] Performance testing

[0032] The adsorbent materials obtained in the embodiments and comparative examples of this invention were added to 20 mL of radioactive solution, respectively. 0.5 M hydrochloric acid was added dropwise to adjust the pH to 6.8. The solutions were stirred and adsorbed for 12 h at 200 rpm on a shaker. After adsorption was complete, the adsorbent material was removed by filtration, and the remaining Sr in the filtrate was determined by atomic absorption spectrometry (AAS). 2+ Cs + mass concentration C 末 ,according to The adsorption capacity is calculated using the formula, where C0 (mg / L) is the Cs value. + or Sr 2+ The initial concentration, C e (mg / L) represents the equilibrium concentration; V(L) is the volume of the radioactive solution, and m(g) is the mass of the adsorbent. The radioactive solution is formed by thoroughly dissolving cesium chloride and strontium chloride in deionized water, with an initial concentration (C0) of 32 mg / L for both cesium and strontium ions. Specific test results are shown in Table 1.

[0033] Table 1

[0034] The Zeta potential diagrams of Crown-TpPa-SO3H / CMC-1 obtained in Example 1 and TpPa-SO3H / CMC obtained in Comparative Example 5 are shown in the appendix to the specification. Figure 1 As shown in the image, the Zeta potentials of both TpPa-SO3H / CMC and Crown-TpPa-SO3H / CMC significantly shifted negatively as the pH increased from 2 to 8, indicating that the surface negative charge increased with increasing pH, providing stronger electrostatic attraction for cation adsorption. Simultaneously, at the same pH, the crown ether modified Crown-TpPa-SO3H / CMC had a more negative potential than TpPa-SO3H / CMC, indicating that crown ether modification significantly increased the surface negative charge density of the material. Combined with the adsorption data in Table 1, Example 1 (crown ether modified material) showed a significant increase in the adsorption potential of Cs... + The adsorption capacity (70.38 mg / g) was higher than that of Comparative Example 5 (unmodified TpPa-SO3H / CMC, 58.41 mg / g), and the adsorption capacity for Sr was also higher. 2+ The adsorption of Cs was also enhanced accordingly, which reflects both the electrostatic adsorption mechanism that "the stronger the surface negative charge, the greater the driving force for cation adsorption" and the effect of crown ethers on Cs. + Its specific complexing effect makes it effective against Cs + The adsorption enhancement effect is more prominent, ultimately achieving efficient adsorption of cesium and strontium cations.

[0035] The adsorption equilibrium capacity test curves of the adsorbent materials obtained in Example 1 and Comparative Examples 1, 2, and 4 for cesium ions in aqueous solutions with different initial concentrations under the same test conditions are shown in the appendix to the instruction manual. Figure 2 As shown.

[0036] The adsorption equilibrium capacity test curves of the adsorbent materials obtained in Example 1 and Comparative Examples 1, 2, and 4 for cesium ions in aqueous solutions with different initial concentrations of strontium ions under the same test conditions are shown in the appendix to the instruction manual. Figure 3 As shown.

[0037] The adsorption equilibrium capacity tests of the Crown-TpPa-SO3H / CMC-1 obtained in Example 1, the TpPa-SO3H / CMC obtained in Comparative Example 5, and the CMC under different pH conditions for cesium ions in an aqueous solution (a solution formed by dissolving cesium chloride in deionized water) with an initial concentration of 10 mg / L are shown in the attached specification. Figure 4 As shown.

[0038] The adsorption equilibrium capacity tests of the Crown-TpPa-SO3H / CMC-1 obtained in Example 1, the TpPa-SO3H / CMC obtained in Comparative Example 5, and the CMC under different pH conditions for strontium ions in an aqueous solution with an initial concentration of 10 mg / L (a solution formed by dissolving strontium chloride in deionized water) are shown in the appendix to the instruction manual. Figure 5 As shown.

[0039] The SEM image of Crown-TpPa-SO3H / CMC-1 obtained in Example 1 is shown in the attached instruction manual. Figure 6 As shown in the image, the obtained adsorbent material has a porous three-dimensional network structure.

[0040] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A three-dimensional composite adsorbent material of cellulose based on COF crown ether modification, characterized in that, The preparation method includes the following steps: (1) Add CMC and crosslinking agent to TpPa-SO3H aqueous solution, stir the reaction so that CMC and crosslinking agent in the reaction system undergo covalent crosslinking reaction to form a three-dimensional network structure hydrogel that encapsulates TpPa-SO3H. After freeze-drying the hydrogel, TpPa-SO3H / CMC is obtained. (2) Add TpPa-SO3H / CMC to the crown ether solution, stir and soak at room temperature. After soaking, filter to collect the solid product and wash it with deionized water at least 3 times. Then freeze dry to obtain Crown-TpPa-SO3H / CMC.

2. The three-dimensional composite adsorbent material of cellulose based on crown ether modified with COF according to claim 1, characterized in that, TpPa-SO3H is a two-dimensional covalent organic framework (COF) formed by the aldehyde-amine condensation reaction between 2,4,6-tricarboxymethyl phloroglucinol and 2,5-diaminobenzenesulfonic acid, which are linked by β-ketoenamine chemical bonds.

3. The three-dimensional composite adsorbent material of cellulose based on crown ether modified with COF according to claim 2, characterized in that, The mass ratio of 2,4,6-tricarboxymethyl phloroglucinol to 2,5-diaminobenzenesulfonic acid is 5.46:4.

2.

4. The three-dimensional composite adsorbent material of cellulose based on COF crown ether modification according to claim 1, characterized in that, The crown ether solution is a solution of a crown ether formed in a solvent, wherein the crown ether is 18-crown ether-6 and the solvent is an aqueous ethanol solution.

5. The three-dimensional composite adsorbent material of crown ether modified cellulose based on COF according to claim 1, characterized in that, In step (1), the ratio of TpPa-SO3H to CMC and crosslinking agent is 0.125g:1.25g:5mL.

6. The three-dimensional composite adsorbent material of cellulose based on COF crown ether modification according to claim 4, characterized in that, The crosslinking agent is epichlorohydrin.

7. The three-dimensional composite adsorbent material of crown ether modified cellulose based on COF according to claim 1, characterized in that, In step (2), the mass ratio of crown ether to TpPa-SO3H / CMC in the reaction system is 0.25:0.

9.

8. The three-dimensional composite adsorbent material of crown ether modified cellulose based on COF according to claim 1, characterized in that, The stirring and soaking time in step (2) shall not be less than 6 hours.

9. A method for removing radioactive metal ions from wastewater, characterized in that, The COF-based crown ether modified cellulose three-dimensional composite adsorbent material described in any one of claims 1-8 is used as an adsorbent additive for wastewater.

10. A method for removing radioactive metal ions from wastewater according to claim 9, characterized in that, The radioactive metal ion is one or both of cesium and strontium.

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