Metal coordination carbon sphere material with molecular imprinting for removing boric acid in water body and preparation method of metal coordination carbon sphere material

Abstract

The invention discloses a metal coordination carbon sphere material with molecular imprinting for removing boric acid in a water body and a preparation method, and relates to the technical field of preparation of adsorption materials. The method comprises the following steps: preparing phenolic resin balls by taking formaldehyde and phenol as raw materials, and carbonizing the phenolic resin balls to obtain phenolic resin carbon balls; then tannic acid is introduced, and tannic acid modified phenolic resin carbon spheres are obtained; the tannic acid modified phenolic resin carbon spheres are dispersed in a metal salt solution, metal ions in the metal salt solution and oxygen atoms in tannic acid are subjected to a coordination reaction, and a metal-organic framework structure is formed; and finally, carrying out molecular imprinting treatment on the formed metal-coordinated phenolic resin carbon spheres by using boric acid as template molecules. The metal coordination carbon sphere material with molecular imprinting prepared by the invention has efficient adsorption performance and selectivity on boric acid, and is suitable for treatment of natural water samples and industrial wastewater containing boric acid.

Description

Technical Field

[0001] The present invention relates to the technical field of the preparation of adsorption materials, and particularly relates to a molecularly imprinted metal-coordinated carbon sphere material for removing boric acid in water and a preparation method thereof. Background Art

[0002] With the rapid development of industry, the pollution problem of boric acid in water is becoming increasingly serious. Boric acid is a toxic and harmful substance, posing a potential threat to the ecological environment and human health. Among many materials, carbon materials have broad application prospects in the fields of adsorption, separation, catalysis, etc. due to their unique physical and chemical properties, such as high specific surface area, good chemical stability and electrical conductivity. However, traditional carbon materials often lack the selective adsorption ability for specific target molecules, which limits their application in some application scenarios with high selectivity requirements.

[0003] In order to improve the selectivity of carbon sphere materials, molecular imprinting technology (MIT) is introduced into material design. Molecular imprinting technology can achieve efficient recognition and adsorption of specific molecules by constructing recognition sites on the material surface that match the shape, size and functional groups of the target molecules. However, traditional molecular imprinted materials usually rely on organic polymers as the matrix, and their mechanical strength and thermal stability are poor, which limits their application in high-temperature or harsh environments. Summary of the Invention

[0004] One of the purposes of the present invention is to provide a preparation method of a molecularly imprinted metal-coordinated carbon sphere material for removing boric acid in water. The formed metal-organic coordination structure not only enhances the stability of the carbon sphere material, but also provides rich active sites for subsequent molecular imprinting, improving the removal rate of boric acid in water.

[0005] In order to achieve the above purpose, the present invention adopts the following technical solutions:

[0006] A preparation method of a molecularly imprinted metal-coordinated carbon sphere material for removing boric acid in water successively includes the following steps:

[0007] a. Prepare phenolic resin spheres using formaldehyde and phenol as raw materials;

[0008] b. Carbonize the phenolic resin spheres under the condition of argon protection at a carbonization temperature of 700-900 °C to obtain phenolic resin carbon spheres;

[0009] c. Disperse the phenolic resin carbon spheres in an ethanol solution of tannic acid, and after reacting for a period of time, make tannic acid fully adsorbed on the surface of the phenolic resin carbon spheres to obtain tannic acid-modified phenolic resin carbon spheres;

[0010] d. Disperse the tannic acid-modified phenolic resin carbon spheres in a metal salt solution, adjust the pH value of the solution to 5 - 6, stir and react at room temperature for 20 - 25 h to cause the metal ions in the metal salt solution to undergo a coordination reaction with the oxygen atoms in tannic acid, forming a metal-organic framework-like structure. After the reaction, metal-coordinated phenolic resin carbon spheres are obtained;

[0011] e. Disperse the metal-coordinated phenolic resin carbon spheres in a boric acid solution so that boric acid exists in the form of B(OH) 4 - and undergoes an adsorption effect with the tannic acid and metal coordination sites of the metal-coordinated phenolic resin carbon spheres to obtain carbon spheres adsorbed with boric acid template molecules; Disperse the carbon spheres adsorbed with boric acid template molecules in an ethanol solution containing a crosslinking agent and an initiator, and carry out a polymerization reaction at a certain temperature to further fix the boric acid template molecules to obtain crosslinked and polymerized carbon spheres;

[0012] f. Disperse the crosslinked and polymerized carbon spheres in an acidic solution, elute the boric acid template molecules, and dry to obtain a metal-coordinated carbon sphere material with molecular imprinting.

[0013] For the preparation method of the above-mentioned metal-coordinated carbon sphere material with molecular imprinting for removing boric acid in water, the specific steps of step a are as follows: Mix and stir formaldehyde and phenol at a molar ratio of 1.2:1, heat up to 90 - 110 °C, add a dispersing agent and stir for 20 - 40 min, add a crosslinking agent and stir for 3 - 5 h; After the reaction, transfer the crosslinked product to a centrifuge tube, centrifuge to discard the supernatant, and collect the obtained prepolymer solution. After washing and drying, phenolic resin spheres are obtained.

[0014] For the preparation method of the above-mentioned metal-coordinated carbon sphere material with molecular imprinting for removing boric acid in water, the dispersing agent is polyvinyl alcohol, and the crosslinking agent is hexamethylenetetramine.

[0015] For the preparation method of the above-mentioned metal-coordinated carbon sphere material with molecular imprinting for removing boric acid in water, in step b, the carbonization heating rate is 4 - 6 °C / min, and the carbonization time is 1 - 3 h; After the carbonization is completed, naturally cool to room temperature, wash and dry the obtained carbon spheres with deionized water and ethanol to obtain phenolic resin carbon spheres.

[0016] For the preparation method of the above-mentioned metal-coordinated carbon sphere material with molecular imprinting for removing boric acid in water, in step c, the solid-liquid ratio of the phenolic resin carbon spheres to the tannic acid ethanol solution is 1:10 g / mL, that is, 1 g of phenolic resin carbon spheres are dispersed in 10 mL of tannic acid ethanol solution; The concentration of the tannic acid ethanol solution is 4 - 6 g / L; The two are stirred and reacted at 200 - 400 rpm for 10 - 15 h.

[0017] The above preparation method of a molecularly imprinted metal-coordinated carbon sphere material for removing boric acid from water body. In step d, the metal salt solution is ZrCl 4 solution or FeCl 3 solution.

[0018] The above preparation method of a molecularly imprinted metal-coordinated carbon sphere material for removing boric acid from water body. The solid-liquid ratio of tannic acid-modified phenolic resin carbon spheres to the metal salt solution is 1:100 g / mL, that is, 1 g of tannic acid-modified phenolic resin carbon spheres are dispersed in 100 mL of the metal salt solution; the metal salt solution is ZrCl 4 solution, and the concentration of the ZrCl 4 solution is 0.05 mol / L.

[0019] The above preparation method of a molecularly imprinted metal-coordinated carbon sphere material for removing boric acid from water body. In step e, the solid-liquid ratio of metal-coordinated phenolic resin carbon spheres to the boric acid solution is 1:30 g / mL, that is, 1 g of metal-coordinated phenolic resin carbon spheres are dispersed in 30 mL of the boric acid solution; the concentration of the boric acid solution is 0.1 mol / L; the cross-linking agent is 0.1 mol / L of ethylene glycol dimethacrylate, and the initiator is 0.02 mol / L of potassium persulfate. The above preparation method of a molecularly imprinted metal-coordinated carbon sphere material for removing boric acid from water body. In step f, the acidic solution is 0.1 mol / L hydrochloric acid solution, and the pH is adjusted to 2-3 by the hydrochloric acid solution.

[0020] Another object of the present invention is to provide a molecularly imprinted metal-coordinated carbon sphere material for removing boric acid from water body, which is prepared by using the above preparation method of a molecularly imprinted metal-coordinated carbon sphere material for removing boric acid from water body.

[0021] Compared with the prior art, the present invention brings the following beneficial technical effects:

[0022] (1) The present invention provides a preparation method of a molecularly imprinted metal-coordinated carbon sphere material for removing boric acid from water body. First, phenolic resin spheres are prepared from formaldehyde and phenol as raw materials, and the phenolic resin spheres are carbonized to obtain phenolic resin carbon spheres. The purpose is: carbonize first and then functionalize, so that the active sites of tannic acid on the carbon spheres can react with Zr 4+Metal coordination occurs, and the remaining uncoordinated sites can chelate with boric acid. Subsequently, phenolic resin carbon spheres are dispersed in tannic acid ethanol solution. The phenolic resin carbon spheres have excellent sphericity and thermal stability. The tannic acid ethanol solution is rich in polyphenolic hydroxyl structures, which can form stable coordination bonds with the subsequent metal ion solution, thereby constructing a metal-organic framework-like structure and adsorbing boric acid to form chelation bonds. Using phenolic resin and tannic acid as the main raw materials, it further realizes the high-value utilization of natural polyphenolic substances and provides a new idea for the preparation of molecular imprinting materials.

[0023] (2) In the present invention, the metal ions in the metal salt solution coordinate with the oxygen atoms in tannic acid to form a metal-organic coordination structure. This structure not only enhances the stability of the material but also provides abundant active sites for subsequent molecular imprinting. In addition, by eluting the boric acid template molecules, a porous structure is formed, improving the pore distribution and specific surface area of the carbon sphere material, and significantly enhancing the adsorption performance and molecular recognition ability of the material.

[0024] (3) The metal coordination carbon sphere material with molecular imprinting prepared in the present invention exhibits excellent selective adsorption performance in the application of boron removal. The molecular imprinting cavity on the material surface can accurately recognize and adsorb boron molecules, and at the same time, the coordination of Zr 4+ further enhances the adsorption capacity of the material. Compared with traditional adsorption materials, the material of the present invention not only has higher adsorption capacity and selectivity but also has good stability and regeneration performance, and can be widely applied in the fields of water treatment, environmental remediation, etc., providing a new solution for the efficient treatment of boron pollution. Description of the Drawings

[0025] The following further describes the present invention with reference to the accompanying drawings:

[0026] Figure 1 It is the scanning electron microscope image of the material in Example 1.

[0027] Figure 2 It is the comparison chart of the adsorption selectivity of the materials prepared in Examples 1-3 and Comparative Examples 1-4 for boric acid, oxalic acid, and citric acid.

[0028] Figure 3 It is the comparison chart of the stability of the materials prepared in Examples 1-3 and Comparative Examples 1-4 after multiple adsorption-desorption cycles. Detailed Embodiments

[0029] The following will clearly and completely describe the technical solutions in the embodiments of the present application with reference to the accompanying drawings in the embodiments of the present application.

[0030] All the raw materials required for the present invention can be obtained through commercial channels.

[0031] The main technical concept of the present invention lies in: by introducing metal coordination into phenolic resin carbon spheres, a metal-organic coordination structure is formed. This structure can not only enhance the mechanical properties and thermal stability of the material, but also further improve the selective recognition ability of the material through the synergistic effect of the metal and the organic ligand.

[0032] Example 1:

[0033] A preparation method of a metal coordination carbon sphere material with molecular imprinting for removing boric acid in water body specifically includes the following steps:

[0034] Step 1: Weigh formaldehyde and phenol according to a molar ratio of 1.2:1 and add them to a 500 mL three-necked flask. Install a stirring device, a thermometer, and a reflux condenser. Turn on the magnetic stirrer and stir at a speed of 550 rpm. At the same time, raise the temperature to 100 °C, add 0.5 g of polyvinyl alcohol (PVA) as a dispersant, and continue stirring for 30 minutes. Then add 1.0 g of hexamethylenetetramine (HMTA) as a crosslinking agent and continue stirring for 4 hours to obtain a prepolymer solution; after the reaction is completed, transfer the product in the three-necked flask to a centrifuge tube, centrifuge at a speed of 4000 rpm for 10 minutes, and discard the supernatant. First, wash the precipitate with deionized water 3 times, adding 50 mL of deionized water each time, shaking evenly and then centrifuging; then wash with absolute ethanol 3 times, adding 50 mL of absolute ethanol each time, and also shaking evenly and then centrifuging. Transfer the washed precipitate to a petri dish and place it in a vacuum drying oven at 105 °C for 24 h to obtain dried phenolic resin spheres.

[0035] Step 2: Put the phenolic resin spheres obtained in Step 1 into a high-temperature carbonization furnace, raise the temperature to 800 °C at a heating rate of 5 °C / min, and carbonize for 2 hours under argon protection (argon flow rate is 50 mL / min) to obtain phenolic resin carbon spheres; naturally cool to room temperature, take out the phenolic resin carbon spheres, wash them 3 times with deionized water and ethanol respectively, and dry for standby.

[0036] Step 3: Disperse the phenolic resin carbon spheres obtained in Step 2 in a tannic acid ethanol solution with a concentration of 4 - 6 g / L; stir and react at room temperature with a magnetic stirrer at 300 rpm for 12 hours to allow tannic acid to be fully adsorbed on the surface of the phenolic resin carbon spheres; after the reaction is completed, wash 3 times with deionized water and ethanol respectively to remove unreacted tannic acid to obtain tannic acid-modified phenolic resin carbon spheres;

[0037] Step 4: Disperse the tannic acid-modified phenolic resin carbon spheres obtained in Step 3 in 100 mL of 0.05 mol / L ZrCl 4 solution; adjust the pH value of the solution to 5 - 6 with dilute hydrochloric acid, stir and react at room temperature with a magnetic stirrer at 300 rpm for 24 hours to allow Zr 4+Coordinate with the oxygen atoms in tannic acid to form a metal-organic framework (MOF)-like structure; after the reaction, wash three times with deionized water and ethanol respectively to remove the uncoordinated metal ions, and obtain metal-coordinated phenolic resin carbon spheres;

[0038] Step Five: Disperse the metal-coordinated phenolic resin carbon spheres obtained in Step Four in 100 mL of 0.1 mol / L boric acid aqueous solution; adjust the pH value to 9-10 with sodium hydroxide solution, and stir and react at room temperature for 24 hours to make boric acid exist in the form of B(OH) 4 - and undergo an adsorption reaction with the tannic acid and metal coordination sites on the surface of the carbon spheres; after the reaction, wash three times with deionized water to remove the unadsorbed boric acid; disperse the obtained carbon spheres adsorbed with boric acid template molecules in an ethanol solution containing 0.1 mol / L ethylene glycol dimethacrylate and 0.02 mol / L potassium persulfate; stir and react at 60 °C for 6 hours to make the cross-linking agent undergo a polymerization reaction under the action of the initiator to fix the boric acid template molecules on the surface of the carbon spheres; after the reaction is completed, wash three times with ethanol and deionized water respectively to remove the unreacted cross-linking agent and initiator;

[0039] Step Six: Disperse the cross-linked and polymerized carbon spheres obtained in Step Five in 100 mL of 0.1 mol / L hydrochloric acid solution; adjust the pH value of the solution to 2-3, and stir and react at room temperature for 2 hours to elute the boric acid template molecules from the surface of the carbon spheres; wash three times with deionized water and ethanol respectively to remove the residual acid solution, and obtain a metal-coordinated carbon sphere material with molecular imprinting after drying.

[0040] The scanning electron micrograph of the carbon sphere material prepared in this example is as Figure 1 shown.

[0041] Example 2:

[0042] A preparation method of a metal-coordinated carbon sphere material with molecular imprinting for removing boric acid in water bodies, specifically including the following steps:

[0043] Step 1: Weigh formaldehyde and phenol according to a molar ratio of 1.2:1 and add them to a 500 mL three-necked flask. Install a stirring device, a thermometer, and a reflux condenser. Turn on the magnetic stirrer and stir at a speed of 550 rpm. At the same time, heat up to 100 °C, add 0.5 g of polyvinyl alcohol (PVA) as a dispersant, and continue stirring for 30 minutes. Then add 1.0 g of hexamethylenetetramine (HMTA) as a crosslinking agent and continue stirring for 4 hours to obtain a prepolymer solution. After the reaction is completed, transfer the product in the three-necked flask to a centrifuge tube and centrifuge at a speed of 4000 rpm for 10 minutes. Discard the supernatant. First, wash the precipitate with deionized water 3 times, adding 50 mL of deionized water each time, shaking well and then centrifuging. Then wash with absolute ethanol 3 times, adding 50 mL of absolute ethanol each time, shaking well and then centrifuging. Transfer the washed precipitate to a petri dish and dry it in a vacuum drying oven at 105 °C for 24 h to obtain dry phenolic resin spheres.

[0044] Step 2: Put the phenolic resin spheres obtained in Step 1 into a high-temperature carbonization furnace and heat up to 700 °C at a heating rate of 5 °C / min, and carbonize for 2 hours under argon protection (argon flow rate is 50 mL / min) to obtain phenolic resin carbon spheres. Naturally cool to room temperature, take out the phenolic resin carbon spheres, wash them 3 times with deionized water and ethanol respectively, and dry for standby.

[0045] Step 3: Disperse the phenolic resin carbon spheres obtained in Step 2 in a tannic acid ethanol solution with a concentration of 4 - 6 g / L; stir and react at room temperature with a magnetic stirrer at 300 rpm for 12 hours to allow tannic acid to be fully adsorbed on the surface of the phenolic resin carbon spheres; after the reaction is completed, wash 3 times with deionized water and ethanol respectively to remove the unreacted tannic acid, and obtain tannic acid-modified phenolic resin carbon spheres;

[0046] Step 4: Disperse the tannic acid-modified phenolic resin carbon spheres obtained in Step 3 in 100 mL of 0.05 mol / L ZrCl 4 solution; adjust the pH value of the solution to 5 - 6 with dilute hydrochloric acid, and stir and react at room temperature with a magnetic stirrer at 300 rpm for 24 hours to allow Zr 4+ to undergo a coordination reaction with the oxygen atoms in tannic acid to form a metal-organic framework (MOF)-like structure; after the reaction is completed, wash 3 times with deionized water and ethanol respectively to remove the uncoordinated metal ions, and obtain metal-coordinated phenolic resin carbon spheres;

[0047] Step 5: Disperse the metal-coordinated phenolic resin carbon spheres obtained in Step 4 in 100 mL of 0.1 mol / L boric acid aqueous solution; adjust the pH value to 9 - 10 with sodium hydroxide solution, and stir and react at room temperature for 24 hours to allow boric acid to be in the form of B(OH) 4 -It exists in the form of and adsorbs with tannic acid and metal coordination sites on the surface of carbon spheres; after the reaction, it is washed 3 times with deionized water to remove unadsorbed boric acid; the carbon spheres adsorbed with boric acid template molecules are dispersed in an ethanol solution containing 0.1 mol / L ethylene glycol dimethacrylate and 0.02 mol / L potassium persulfate; the reaction is stirred at 60 °C for 6 hours to polymerize the crosslinking agent under the action of the initiator and fix the boric acid template molecules on the surface of the carbon spheres; after the reaction is completed, it is washed 3 times with ethanol and deionized water respectively to remove unreacted crosslinking agent and initiator;

[0048] Step 6: Disperse the crosslinked and polymerized carbon spheres obtained in Step 5 in 100 mL of 0.1 mol / L hydrochloric acid solution; adjust the pH value of the solution to 2-3, and stir and react at room temperature for 2 hours to elute the boric acid template molecules from the surface of the carbon spheres; wash 3 times with deionized water and ethanol respectively to remove the residual acid solution, and obtain a metal-coordinated carbon sphere material with molecular imprinting after drying.

[0049] Example 3:

[0050] The difference from Example 1 is:

[0051] In Step 4, the tannic acid-modified phenolic resin carbon spheres obtained in Step 3 are dispersed in 100 mL of 0.05 mol / L FeCl 3 solution; the pH value of the solution is adjusted to 5-6 with dilute hydrochloric acid or sodium hydroxide solution, and the reaction is stirred at a speed of 300 rpm at room temperature for 24 h to make Fe 3+ coordinate with the oxygen atoms in tannic acid. After the reaction is completed, it is washed 3 times with deionized water and absolute ethanol respectively to remove uncoordinated metal ions.

[0052] Comparative Example 1:

[0053] A preparation method of a carbon sphere material for removing boric acid in water body specifically includes the following steps:

[0054] Step 1: Weigh formaldehyde and phenol according to a molar ratio of 1.2:1 and add them to a 500 mL three-necked flask. Install a stirring device, a thermometer, and a reflux condenser. Turn on the magnetic stirrer and stir at a speed of 550 rpm. At the same time, heat up to 100 °C, add 0.5 g of polyvinyl alcohol (PVA) as a dispersant, and continue stirring for 30 minutes. Then add 1.0 g of hexamethylenetetramine (HMTA) as a crosslinking agent and continue stirring for 4 hours to obtain a prepolymer solution. After the reaction is completed, transfer the product in the three-necked flask to a centrifuge tube and centrifuge at a speed of 4000 rpm for 10 minutes. Discard the supernatant. First, wash the precipitate with deionized water 3 times, adding 50 mL of deionized water each time, shaking well and then centrifuging. Then wash with absolute ethanol 3 times, adding 50 mL of absolute ethanol each time, and also shaking well and centrifuging. Transfer the washed precipitate to a petri dish and place it in a vacuum drying oven at 105 °C for drying for 24 h to obtain dried phenolic resin spheres.

[0055] Step 2: Put the phenolic resin spheres obtained in Step 1 into a high-temperature carbonization furnace and heat up to 800 °C at a heating rate of 5 °C / min, and carbonize for 2 hours under argon protection (argon flow rate is 50 mL / min) to obtain phenolic resin carbon spheres. Naturally cool to room temperature, take out the phenolic resin carbon spheres, wash them 3 times with deionized water and ethanol respectively, and dry for standby.

[0056] Step 3: Disperse the phenolic resin carbon spheres obtained in Step 2 in a tannic acid ethanol solution with a concentration of 4 - 6 g / L; stir and react at room temperature with a magnetic stirrer at 300 rpm for 12 hours to allow tannic acid to be fully adsorbed on the surface of the phenolic resin carbon spheres; after the reaction is completed, wash 3 times with deionized water and ethanol respectively to remove the unreacted tannic acid, and obtain tannic acid-modified phenolic resin carbon spheres;

[0057] Step 4: Disperse the tannic acid-modified phenolic resin carbon spheres obtained in Step 3 in 100 mL of 0.05 mol / L ZrCl 4 solution; adjust the pH value of the solution to 5 - 6 with dilute hydrochloric acid, and stir and react at room temperature with a magnetic stirrer at 300 rpm for 24 hours to allow Zr 4+ to undergo a coordination reaction with the oxygen atoms in tannic acid to form a metal-organic framework (MOF)-like structure; after the reaction is completed, wash 3 times with deionized water and ethanol respectively to remove the uncoordinated metal ions, and obtain metal-coordinated phenolic resin carbon spheres;

[0058] Step 5: Disperse the metal-coordinated phenolic resin carbon spheres obtained in Step 4 in 100 mL of 0.1 mol / L boric acid aqueous solution; adjust the pH value to 9 - 10 with sodium hydroxide solution, and stir and react at room temperature for 24 hours to allow boric acid to be in the form of B(OH) 4 -exists in the form of and adsorbs on the tannic acid and metal coordination sites on the surface of the carbon spheres; after the reaction, wash with deionized water three times to remove the unadsorbed boric acid;

[0059] Step Six: Disperse the carbon spheres obtained in Step Five in 100 mL of 0.1 mol / L hydrochloric acid solution; adjust the pH value of the solution to 2 - 3, stir and react at room temperature for 2 hours to elute the boric acid template molecules from the surface of the carbon spheres; wash with deionized water and ethanol three times respectively to remove the residual acid solution, and obtain the metal coordination carbon sphere material with molecular imprinting after drying.

[0060] In this comparative example, the carbon spheres adsorbed with boric acid molecules did not undergo the cross - linking polymerization step, but directly eluted the template molecules. The finally obtained metal coordination carbon sphere material with molecular imprinting has the boric acid template molecules only physically adsorbed on the surface of the carbon spheres and not firmly fixed. During subsequent use, such as when eluting the template molecules and adsorbing again, the boric acid molecules are likely to detach from the surface of the carbon spheres, unable to form stable molecular imprinting cavities, resulting in a significant decline in the selective adsorption performance of the material for boric acid.

[0061] Comparative Example 2:

[0062] A preparation method of a carbon sphere material for removing boric acid in water bodies specifically includes the following steps:

[0063] Step One: Weigh formaldehyde and phenol according to a molar ratio of 1.2:1 and add them to a 500 mL three - necked flask, install a stirring device, a thermometer and a reflux condenser. Turn on the magnetic stirrer, stir at a speed of 550 rpm, and at the same time heat up to 100 °C, add 0.5 g of polyvinyl alcohol (PVA) as a dispersant, and continue stirring for 30 minutes. Then add 1.0 g of hexamethylenetetramine (HMTA) as a cross - linker and continue stirring for 4 hours to obtain a prepolymer solution; after the reaction, transfer the product in the three - necked flask to a centrifuge tube, centrifuge at a speed of 4000 rpm for 10 min, and discard the supernatant. First, wash the precipitate with deionized water three times, adding 50 mL of deionized water each time, shake well and then centrifuge; then wash with absolute ethanol three times, adding 50 mL of absolute ethanol each time, and also shake well and centrifuge. Transfer the washed precipitate to a petri dish and dry it in a vacuum drying oven at 105 °C for 24 h to obtain dry phenolic resin spheres.

[0064] Step Two: Put the phenolic resin spheres obtained in Step One into a high - temperature carbonization furnace, heat up to 800 °C at a heating rate of 5 °C / min, carbonize for 2 hours under argon protection (argon flow rate is 50 mL / min) to obtain phenolic resin carbon spheres; naturally cool to room temperature, take out the phenolic resin carbon spheres, wash with deionized water and ethanol three times respectively, and dry for standby.

[0065] Step 3: Disperse the phenolic resin carbon spheres obtained in Step 2 in a tannic acid ethanol solution with a concentration of 4 - 6 g / L; at room temperature, stir and react for 12 hours with a magnetic stirrer at 300 rpm to allow tannic acid to be fully adsorbed on the surface of the phenolic resin carbon spheres; after the reaction, wash 3 times with deionized water and ethanol respectively to remove the unreacted tannic acid, and obtain tannic acid-modified phenolic resin carbon spheres;

[0066] Step 4: Disperse the tannic acid-modified phenolic resin carbon spheres obtained in Step 3 in 100 mL of a 0.1 mol / L boric acid aqueous solution; adjust the pH value to 9 - 10 with a sodium hydroxide solution, and stir and react at room temperature for 24 hours to allow boric acid to exist in the form of B(OH) 4 - and undergo an adsorption interaction with the tannic acid and metal coordination sites on the surface of the carbon spheres; after the reaction, wash 3 times with deionized water to remove the unadsorbed boric acid; disperse the obtained carbon spheres adsorbed with boric acid template molecules in an ethanol solution containing 0.1 mol / L ethylene glycol dimethacrylate and 0.02 mol / L potassium persulfate; stir and react at 60 °C for 6 hours to allow the cross-linking agent to undergo a polymerization reaction under the action of the initiator, and fix the boric acid template molecules on the surface of the carbon spheres; after the reaction is completed, wash 3 times with ethanol and deionized water respectively to remove the unreacted cross-linking agent and initiator;

[0067] Step 5: Disperse the cross-linked and polymerized carbon spheres obtained in Step 4 in 100 mL of a 0.1 mol / L hydrochloric acid solution; adjust the pH value of the solution to 2 - 3, and stir and react at room temperature for 2 hours to elute the boric acid template molecules from the surface of the carbon spheres; wash 3 times with deionized water and ethanol respectively to remove the residual acid solution, and obtain a metal coordination carbon sphere material with molecular imprinting after drying.

[0068] In this comparative example, ZrCl is not added to the tannic acid-modified phenolic resin carbon spheres 4 solution, that is, the metal coordination reaction is not carried out. It is found in the experiment that during the high-temperature carbonization process, due to the lack of the support of the MOF structure, the structural stability of the carbon spheres is poor. When adsorbing the boric acid template molecules, the specific binding sites provided by the MOF structure cannot be utilized, resulting in a decrease in the adsorption capacity and selectivity of boric acid. Moreover, during multiple adsorption-desorption cycles, the material is more likely to undergo structural damage.

[0069] Comparative Example 3:

[0070] A preparation method of a carbon sphere material for removing boric acid in water body, specifically including the following steps:

[0071] Step 1: Weigh formaldehyde and phenol according to a molar ratio of 1.2:1 and add them to a 500 mL three-necked flask. Install a stirring device, a thermometer, and a reflux condenser. Turn on the magnetic stirrer and stir at a speed of 550 rpm. At the same time, heat up to 100 °C, add 0.5 g of polyvinyl alcohol (PVA) as a dispersant, and continue stirring for 30 minutes. Then add 1.0 g of hexamethylenetetramine (HMTA) as a crosslinking agent and continue stirring for 4 hours to obtain a prepolymer solution. After the reaction is completed, transfer the product in the three-necked flask to a centrifuge tube and centrifuge at a speed of 4000 rpm for 10 min. Discard the supernatant. First, wash the precipitate with deionized water 3 times, adding 50 mL of deionized water each time. After shaking evenly, centrifuge. Then wash with absolute ethanol 3 times, adding 50 mL of absolute ethanol each time. Similarly, after shaking evenly, centrifuge. Transfer the washed precipitate to a petri dish and dry it in a vacuum drying oven at 105 °C for 24 h to obtain dry phenolic resin spheres.

[0072] Step 2: Put the phenolic resin spheres obtained in Step 1 into a high-temperature carbonization furnace and heat up to 800 °C at a heating rate of 5 °C / min. Carbonize for 2 hours under argon protection (argon flow rate is 50 mL / min) to obtain phenolic resin carbon spheres. Naturally cool to room temperature, take out the phenolic resin carbon spheres, wash them 3 times with deionized water and ethanol respectively, and dry for standby.

[0073] Step 3: Disperse the phenolic resin carbon spheres obtained in Step 2 in a tannic acid ethanol solution with a concentration of 4 - 6 g / L. Stir and react at room temperature with a magnetic stirrer at 300 rpm for 12 hours to allow tannic acid to be fully adsorbed on the surface of the phenolic resin carbon spheres. After the reaction is completed, wash 3 times with deionized water and ethanol respectively to remove the unreacted tannic acid and obtain tannic acid-modified phenolic resin carbon spheres.

[0074] Step 4: Disperse the tannic acid-modified phenolic resin carbon spheres obtained in Step 3 in 100 mL of 0.05 mol / L ZrCl 4 solution. Adjust the pH value of the solution to 5 - 6 with dilute hydrochloric acid. Stir and react at room temperature with a magnetic stirrer at 300 rpm for 24 hours to allow Zr 4+ to undergo a coordination reaction with the oxygen atoms in tannic acid to form a metal-organic framework (MOF)-like structure. After the reaction is completed, wash 3 times with deionized water and ethanol respectively to remove the uncoordinated metal ions and obtain metal-coordinated phenolic resin carbon spheres.

[0075] In this comparative example, the prepared metal-coordinated phenolic resin carbon spheres directly adsorbed boric acid without subsequent operations such as molecular imprinting. Due to the absence of molecular imprinting cavities, the material lacked specific recognition ability for boric acid adsorption and only relied on some physical and chemical adsorption effects on the surface of the carbon spheres. The adsorption discrimination between boric acid and other interfering substances (such as oxalic acid and citric acid) was not significant, resulting in significantly lower boric acid adsorption capacity and selectivity coefficient compared to Example 1.

[0076] Comparative Example 4:

[0077] A preparation method of a molecularly imprinted metal-coordinated carbon sphere material for removing boric acid from water bodies specifically includes the following steps:

[0078] Step 1: Weigh formaldehyde and phenol according to a molar ratio of 1.2:1 and add them to a 500 mL three-necked flask. Install a stirring device, a thermometer, and a reflux condenser. Turn on the magnetic stirrer and stir at a speed of 550 rpm while heating to 100 °C. Add 0.5 g of polyvinyl alcohol (PVA) as a dispersant and continue stirring for 30 minutes. Then add 1.0 g of hexamethylenetetramine (HMTA) as a crosslinking agent and continue stirring for 4 hours to obtain a prepolymer solution. After the reaction, transfer the product in the three-necked flask to a centrifuge tube and centrifuge at a speed of 4000 rpm for 10 minutes. Discard the supernatant. First, wash the precipitate with deionized water 3 times, adding 50 mL of deionized water each time, shaking well and then centrifuging. Then wash with absolute ethanol 3 times, adding 50 mL of absolute ethanol each time, and also shaking well and centrifuging. Transfer the washed precipitate to a petri dish and place it in a vacuum drying oven at 105 °C for 24 hours to obtain dried phenolic resin spheres.

[0079] Step 2: Disperse the dried phenolic resin spheres in a tannic acid ethanol solution with a concentration of 4 - 6 g / L. Stir and react at room temperature with a magnetic stirrer at 300 rpm for 12 hours to allow tannic acid to be fully adsorbed on the surface of the phenolic resin spheres. After the reaction, wash with deionized water and ethanol 3 times respectively to remove unreacted tannic acid and obtain tannic acid-modified phenolic resin spheres.

[0080] Step 3: Disperse the tannic acid-modified phenolic resin spheres in 100 mL of a 0.05 mol / L ZrCl 4 solution. Adjust the pH value of the solution to 5 - 6 with dilute hydrochloric acid and stir and react at room temperature with a magnetic stirrer at 300 rpm for 24 hours to allow Zr 4+ to coordinate with the oxygen atoms in tannic acid to form a metal-organic framework (MOF)-like structure. After the reaction, wash with deionized water and ethanol 3 times respectively to remove uncoordinated metal ions and obtain metal-coordinated phenolic resin spheres.

[0081] Step 4: Put the metal-coordinated phenolic resin spheres into a high-temperature carbonization furnace, heat them up to 800 °C at a heating rate of 5 °C / min, and carbonize them for 2 hours under argon protection (argon flow rate is 50 mL / min) to obtain metal-coordinated phenolic resin carbon spheres; naturally cool them to room temperature, take out the metal-coordinated phenolic resin carbon spheres, wash them 3 times with deionized water and ethanol respectively, and dry them for standby.

[0082] Step 5: Disperse the metal-coordinated phenolic resin carbon spheres obtained in Step 4 in 100 mL of 0.1 mol / L boric acid aqueous solution; adjust the pH value to 9 - 10 with sodium hydroxide solution, and stir and react at room temperature for 24 hours to make boric acid exist in the form of B(OH) 4 - and have an adsorption effect with tannic acid and metal coordination sites on the surface of the carbon spheres; after the reaction, wash them 3 times with deionized water to remove the unadsorbed boric acid; disperse the obtained carbon spheres adsorbed with boric acid template molecules in an ethanol solution containing 0.1 mol / L ethylene glycol dimethacrylate and 0.02 mol / L potassium persulfate; stir and react at 60 °C for 6 hours to make the cross-linking agent polymerize under the action of the initiator and fix the boric acid template molecules on the surface of the carbon spheres; after the reaction is completed, wash them 3 times with ethanol and deionized water respectively to remove the unreacted cross-linking agent and initiator;

[0083] Step 6: Disperse the cross-linked and polymerized carbon spheres obtained in Step 5 in 100 mL of 0.1 mol / L hydrochloric acid solution; adjust the pH value of the solution to 2 - 3, and stir and react at room temperature for 2 hours to elute the boric acid template molecules from the surface of the carbon spheres; wash them 3 times with deionized water and ethanol respectively to remove the residual acid solution, and dry to obtain a metal-coordinated carbon sphere material with molecular imprinting.

[0084] Test the carbon sphere materials prepared in the above Examples 1 - 3 and Comparative Examples 1 - 4, and the test results are shown in Table 1.

[0085] Table 1

[0086]

[0087]

[0088] Figure 2 It is a comparative chart of the adsorption selectivity of the materials prepared in Examples 1 - 3 and Comparative Examples 1 - 4 for boric acid, oxalic acid, and citric acid. Figure 3 It is a comparative chart of the stability after multiple adsorption - desorption cycles of the materials prepared in Examples 1 - 3 and Comparative Examples 1 - 4. In terms of the comparison of the examples, the comparison between Example 1 and Example 2 reflects the influence of the carbonization temperature. When the carbonization temperature drops from 800 °C to 700 °C, the specific surface area of the material decreases from 580 m 2 / g decreased to 450 m 2 / g, and the average pore size increased from 2.8 nm to 3.2 nm. This is because the lower carbonization temperature leads to incomplete carbonization, low graphitization degree of carbon spheres, and poor development of internal pore structure. In terms of adsorption performance, the boric acid adsorption capacity decreased from 48.6 mg / g to 35.2 mg / g, the adsorption capacities for oxalic acid and citric acid increased, and the selectivity coefficient decreased from 9.8 to 7.2, indicating that the decrease in carbonization temperature resulted in a reduction in effective molecularly imprinted cavities and a decline in the specific recognition ability of boric acid. The comparison between Example 1 and Example 3 shows the role of metal ion types. In Example 3, FeCl 3 was used to replace ZrCl 4 , the specific surface area decreased to 520 m 2 / g, and the pore size increased to 4.5 nm. The different MOF structures formed by different metal ions led to a loose pore structure. The boric acid adsorption capacity was 42.5 mg / g, and the selectivity coefficient decreased to 8.5, indicating that Zr 4+ is more excellent in forming a structure conducive to the selective adsorption of boric acid.

[0089] In terms of comparative examples, in Comparative Example 1, the cross-linking polymerization step was not carried out, and the boric acid adsorption capacity was only 12.3 mg / g, and the selectivity coefficient was 1.2, which was much lower than that of Example 1. In Example 1, cross-linking polymerization formed a three-dimensional network structure through ethylene glycol dimethacrylate under the initiation of potassium persulfate to fix the boric acid template molecule, while in Comparative Example 1, boric acid was only physically adsorbed, and no effective molecularly imprinted cavities could be formed, resulting in a significant decline in the specific adsorption ability. Comparative Example 2 did not form a metal-organic framework (MOF)-like structure, with poor stability. After multiple cycles, some carbon spheres were broken, the boric acid adsorption capacity was 18.7 mg / g, and the selectivity coefficient was 2.5. In Example 1, the MOF structure formed by Zr 4+ and tannic acid enhanced the stability and provided a specific adsorption environment. The lack of this structure in Comparative Example 2 led to a decrease in adsorption capacity and selectivity. In Comparative Example 3, molecular imprinting was not introduced. The specific surface area and pore size were similar to those of Example 3, but the boric acid adsorption capacity was 25.8 mg / g, and the selectivity coefficient was 1.8, which was significantly lower than that of Example 1, indicating that molecular imprinting endows the material with the specific recognition ability for boric acid.

[0090] In summary, for the molecularly imprinted metal coordination carbon sphere material prepared by the present invention, factors such as the introduction of molecular imprinting, cross-linking polymerization, the formation of metal coordination structure, and carbonization temperature in the preparation process have a significant impact on the material properties. In Comparative Example 4, tannic acid modification and metal coordination were carried out before carbonization, and its specific surface area was 400 m 2 / g, the boric acid adsorption capacity was 22.4 mg / g, and the selectivity coefficient was 2.3, both of which were lower than those in Examples 1 to 3. This indicates that performing tannic acid modification and metal coordination after carbonization is more conducive to forming a stable MOF structure, thereby improving the adsorption performance and selectivity of the material. The stability of Comparative Example 4 was 78%, which was also lower than those in Examples 1 to 3, indicating that modification and coordination before carbonization may cause the material to be more prone to structural damage during multiple cycles.

[0091] Those parts not described in the present invention can be achieved by referring to the prior art.

[0092] Those of ordinary skill in the art should recognize that the above embodiments are only used to illustrate the present application and are not intended to limit the present application. As long as appropriate changes and variations made to the above embodiments fall within the scope of the spirit of the present application, they fall within the scope of protection required by the present application.

Claims

1. A method for preparing a molecularly imprinted metal-coordinated carbon sphere material for removing boric acid from water, characterized in that: The following steps are included in sequence: a. Prepare phenolic resin balls using formaldehyde and phenol as raw materials; b. carbonizing the phenolic resin balls at a carbonization temperature of 700 to 900° C. under argon protection to obtain phenolic resin carbon balls; c. dispersing the phenolic resin carbon spheres in a tannic acid ethanol solution, and reacting for a period of time so that the tannic acid is fully adsorbed on the surface of the phenolic resin carbon spheres to obtain tannic acid-modified phenolic resin carbon spheres; d. Dispersing the phenolic resin carbon spheres modified with tannic acid in a metal salt solution, adjusting the pH value of the solution to 5-6, and stirring the solution at room temperature for 20-25 hours to allow the metal ions in the metal salt solution to react with the oxygen atoms in the tannic acid to form a metal-organic framework structure, and obtaining metal-coordinated phenolic resin carbon spheres after the reaction is completed; e. Disperse the metal-coordinated phenolic resin carbon spheres in a boric acid solution so that the boric acid reacts with B(OH)4 - The tannic acid and metal coordination sites of the phenolic resin carbon spheres that exist in the form of and coordinate with the metal are adsorbed to obtain carbon spheres adsorbed with boric acid template molecules; the carbon spheres adsorbed with the boric acid template molecules are dispersed in an ethanol solution containing a crosslinking agent and an initiator, and a polymerization reaction occurs at a certain temperature to further fix the boric acid template molecules to obtain crosslinked polymerized carbon spheres; f. Dispersing the cross-linked polymerized carbon spheres in an acidic solution, eluting the boric acid template molecules, and drying to obtain metal-coordinated carbon sphere materials with molecular imprinting.

2. The method for preparing a molecularly imprinted metal coordinated carbon sphere material for removing boric acid in water according to claim 1, characterized in that: The specific steps of step a are: mixing and stirring formaldehyde and phenol at a molar ratio of 1.2:1, heating to 90-110° C., adding a dispersant and stirring for 20-40 minutes, adding a crosslinking agent and stirring for 3-5 hours; after the reaction is completed, transferring the crosslinked product to a centrifuge tube, centrifuging and discarding the supernatant, collecting the obtained prepolymer solution, washing, and drying, and obtaining phenolic resin balls.

3. The method for preparing a molecularly imprinted metal coordinated carbon sphere material for removing boric acid from water according to claim 2, characterized in that: The dispersant is polyvinyl alcohol, and the cross-linking agent is hexamethylenetetramine.

4. The method for preparing a molecularly imprinted metal coordinated carbon sphere material for removing boric acid from water according to claim 1, characterized in that: In step b, the carbonization heating rate is 4-6°C / min, and the carbonization time is 1-3h; after the carbonization is completed, the carbon balls are naturally cooled to room temperature, and the obtained carbon balls are washed and dried with deionized water and ethanol to obtain phenolic resin carbon balls.

5. The method for preparing a molecularly imprinted metal coordinated carbon sphere material for removing boric acid from water according to claim 1, characterized in that: In step c, the solid-liquid ratio of the phenolic resin carbon spheres to the tannic acid ethanol solution is 1:10 g / mL; the concentration of the tannic acid ethanol solution is 4-6 g / L; and the two are stirred and reacted at 200-400 rpm for 10-15 hours.

6. The method for preparing a molecularly imprinted metal coordinated carbon sphere material for removing boric acid from water according to claim 1, characterized in that: In step d, the metal salt solution is a ZrCl4 solution or a FeCl3 solution.

7. The method for preparing a molecularly imprinted metal coordinated carbon sphere material for removing boric acid from water according to claim 6, characterized in that: The solid-liquid ratio of the tannic acid-modified phenolic resin carbon spheres to the metal salt solution is 1:100 g / mL; the metal salt solution is a ZrCl4 solution, and the concentration of the ZrCl4 solution is 0.05 mol / L.

8. The method for preparing a molecularly imprinted metal coordinated carbon sphere material for removing boric acid in water according to claim 1, characterized in that: In step e, the solid-liquid ratio of the metal-coordinated phenolic resin carbon spheres to the boric acid solution is 1:30 g / mL; the concentration of the boric acid solution is 0.1 mol / L; the cross-linking agent is 0.1 mol / L of ethylene glycol dimethacrylate, and the initiator is 0.02 mol / L of potassium persulfate.

9. The method for preparing a molecularly imprinted metal coordinated carbon sphere material for removing boric acid from water according to claim 1, characterized in that: In step f, the acidic solution is a 0.1 mol / L hydrochloric acid solution, and the pH is adjusted to 2-3 by the hydrochloric acid solution.

10. A molecularly imprinted metal coordinated carbon sphere material for removing boric acid from water, characterized in that: The compound is prepared by the preparation method according to any one of claims 1 to 9.

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