A modified covalent organic framework material for simultaneous adsorption of multiple heavy metal ions, and its preparation method and application

Abstract

The present invention belongs to the field of environmentally friendly new materials and specifically relates to a modified covalent organic framework material for simultaneously adsorbing multiple heavy metal ions, as well as its preparation method and application. The material preparation steps include: dissolving 1,3,5-tris(4-aminophenyl)benzene and 2,5-dihydroxyterephthalaldehyde in a mixed solvent, allowing the mixture to react at room temperature to obtain a mixed solution; adding scandium trifluoromethanesulfonate to the obtained mixed solution, allowing the mixture to react at room temperature; after the reaction, separating the insoluble matter from the reaction solution, washing the insoluble matter, and drying it to obtain a covalent organic framework substrate; and ultrasonically modifying the covalent organic framework substrate prepared using a neutral solution, and then washing and drying the modified substrate to obtain the modified covalent organic framework material. The neutral solution-modified material exhibits excellent adsorption of multiple mixed heavy metal ions in water and has promising application prospects in the adsorption and removal of heavy metal ions in aqueous environments.

Description

Technical Field

[0001] The present invention belongs to the field of environmentally friendly new materials, and specifically relates to a modified covalent organic framework material for simultaneously adsorbing multiple heavy metal ions, and a preparation method and application thereof. Background Art

[0002] Heavy metal wastewater is one of the common pollutants discharged in industrial production. Large amounts of toxic heavy metal pollutants enter water bodies, causing serious pollution to the water environment. Heavy metal ions are difficult to be naturally degraded and have high biological activity, persistence and bioaccumulation. Even at very low exposure concentrations, they can produce strong biological effects and "three-hazard" effects, seriously endangering human health and ecological safety. At the same time, the combined exposure between multiple heavy metal ions in the environment and between heavy metal ions and coexisting organic pollutants can produce synergistic toxic effects on organisms. Studies have shown that existing sewage treatment plants cannot effectively remove heavy metal pollutants in urban sewage at a deep level, resulting in their frequent detection in sewage treatment plant effluent and related water bodies, and accumulation in various environmental media such as sediments and soils. Although the concentration of heavy metal ions in sewage treatment plant effluent is relatively low, due to their bioaccumulation, they can still cause serious harm to human health through enrichment in the food chain. Therefore, it is necessary to develop methods that can simultaneously and deeply remove multiple low-concentration heavy metal ions in slightly polluted water.

[0003] Adsorption is one of the most effective methods for removing heavy metal ions. However, although existing adsorbents have good removal effects on high-concentration heavy metal ions, their removal performance on low-concentration heavy metal ions is poor. The main reason is that the existing adsorbents have insufficient selective adsorption force for heavy metal ions, resulting in the adsorbent reaching adsorption-desorption equilibrium after adsorbing a small amount of low-concentration heavy metal ions, and thus being unable to further achieve deep removal of heavy metal ions. Compared with traditional adsorbents, covalent organic framework materials are organic porous materials with a periodic network structure formed by light elements connected by covalent bonds. They not only have the advantages of high specific surface area, regular and orderly pores, and easy functional modification, but also have good thermal stability and chemical stability. In order to improve the adsorption capacity of covalent organic framework materials for heavy metal ions, researchers usually use the chelation effect of active groups on heavy metal ions and adopt two methods to prepare functionalized covalent organic framework materials: one is to pre-design a precursor modified with a specific free group as an organic monomer to prepare a modified covalent organic framework material with a specific function; the other is a group re-modification strategy after the synthesis of the covalent organic framework material. It should be noted that, because different active groups produce varying degrees of chelation with different types of heavy metal ions, the modified covalent organic framework materials prepared in the above manner can enhance the adsorption capacity of specific heavy metal ions, but it is difficult to simultaneously achieve efficient adsorption and removal of multiple low-concentration heavy metal ions. In addition, modified covalent organic framework materials are mostly synthesized via solvothermal methods, which have high reaction temperatures, long reaction times, harsh reaction conditions, and high costs, limiting their application in water purification. Summary of the Invention

[0004] In view of the problems and shortcomings in the prior art, the object of the present invention is to provide a modified covalent organic framework material for the simultaneous adsorption of multiple heavy metal ions, and a preparation method and application thereof.

[0005] Based on the above purpose, the present invention adopts the following technical solutions:

[0006] A first aspect of the present invention provides a method for preparing a modified covalent organic framework material for simultaneously adsorbing multiple heavy metal ions, comprising the following steps:

[0007] (1) dissolving 1,3,5-tris(4-aminophenyl)benzene and 2,5-dihydroxyterephthalaldehyde in a mixed solvent, and allowing to react at room temperature to obtain a mixed solution;

[0008] (2) adding scandium trifluoromethanesulfonate to the mixed solution obtained in step (1), allowing the mixture to react at room temperature, separating insoluble matter from the reaction solution after the reaction is completed, washing the insoluble matter, and drying the insoluble matter to obtain a covalent organic framework substrate;

[0009] (3) Using a neutral solution to perform ultrasonic modification on the covalent organic framework substrate prepared in step (2), and then washing and drying the modified substrate to obtain a modified covalent organic framework material.

[0010] Preferably, the neutral solution in step (3) is any one of a magnesium chloride aqueous solution, a sodium chloride aqueous solution, and a potassium chloride aqueous solution; and the concentration of the neutral solution is 0.5 to 3 mol / L.

[0011] More preferably, the neutral solution is a magnesium chloride aqueous solution, and the concentration of the magnesium chloride aqueous solution is 0.5 to 3 mol / L.

[0012] More preferably, the concentration of the magnesium chloride aqueous solution is 1 mol / L.

[0013] Preferably, the molar ratio of 1,3,5-tris(4-aminophenyl)benzene to 2,5-dihydroxyterephthalaldehyde in step (1) is 2:3.

[0014] Preferably, the mixed solvent in step (1) is a mixed solvent of 1,4-dioxane and 1,3,5-trimethylbenzene.

[0015] Preferably, the volume ratio of 1,4-dioxane to 1,3,5-trimethylbenzene in the mixed solvent is (1-5):1.

[0016] More preferably, the volume ratio of 1,4-dioxane to 1,3,5-trimethylbenzene in the mixed solvent is 4:1.

[0017] Preferably, the molar ratio of p-phenylenediamine to scandium trifluoromethanesulfonate in step (2) is (10-150):1.

[0018] More preferably, the molar ratio of p-phenylenediamine to scandium trifluoromethanesulfonate is 16:1.

[0019] Preferably, the standing reaction time in step (1) and step (2) is 10 to 60 minutes.

[0020] Preferably, the detergent for washing the insoluble matter in step (2) is at least one of methanol, ethanol and acetone.

[0021] Preferably, the washing method in step (3) is washing with water and methanol in sequence.

[0022] Preferably, the drying temperature in step (2) and step (3) is 50-100° C., and the drying time is 10-24 h.

[0023] The second aspect of the present invention provides a modified covalent organic framework material prepared by the method of the first aspect and capable of being used for the simultaneous adsorption of multiple heavy metal ions.

[0024] The third aspect of the present invention provides the use of the modified covalent organic framework material described in the second aspect in the removal and purification of multiple heavy metal ions in water.

[0025] Preferably, the modified covalent organic framework material is used to adsorb and remove lead ions, chromium ions (trivalent), cobalt ions, nickel ions, manganese ions and copper ions in water.

[0026] Preferably, when the modified covalent organic framework material is used as a water adsorbent, 0.05 g to 10 g of the modified covalent organic framework material can be added per liter of water with a heavy metal ion concentration of 0.01 mg / L to 20 mg / L.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] (1) Compared with the traditional preparation method of covalent organic framework materials (high temperature and high pressure hydrothermal method combined with chemical synthesis method), this application adopts a simple room temperature synthesis method and a neutral solution rapid ultrasonic modification strategy to prepare modified covalent organic framework materials. The operation method is simple and the preparation time is short. The modification strategy is easy to operate, the conditions are mild, the time consumption is short, the yield is high, and the performance is stable and reproducible. This modification technology can greatly improve the adsorption capacity of covalent organic framework materials for heavy metal ions and has good application potential. In particular, when magnesium chloride solution is used as a modifier, it shows good adsorption effect on the six heavy metal ions in the mixed multi-component system.

[0029] (2) In addition, the simple ultrasonic modification of the covalent organic framework material using a neutral magnesium chloride solution did not affect the surface morphology of the covalent organic framework material. Although the specific surface area of ​​the covalent organic framework material decreased, the adsorption capacity of various heavy metal ions was greatly improved. The modified covalent organic framework material prepared by the room temperature synthesis method and the magnesium chloride ultrasonic strategy proposed in the present invention can be effectively applied to the removal of various heavy metal ions in water, and the existing modified covalent organic framework material can only achieve the adsorption of specific heavy metal ions, but cannot achieve efficient adsorption and removal of multiple heavy metal ions in water at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 X-ray diffraction (XRD) patterns of the modified covalent organic framework material in Example 1 of the present invention and the unmodified covalent organic framework material prepared in Comparative Example 1;

[0031] Figure 2 a is a scanning electron microscope (SEM) image of the unmodified covalent organic framework material in Comparative Example 1 of the present invention, Figure 2b is a scanning electron microscope (SEM) image of the modified covalent organic framework material in Example 1 of the present invention;

[0032] Figure 3 Graph showing the adsorption rates of various heavy metal ions by the modified covalent organic framework material in Example 1 of the present invention under different solution pH conditions in a single system;

[0033] Figure 4 : is a thermodynamic adsorption curve of heavy metal ions by the modified covalent organic framework material in Example 1 of the present invention in a mixed multi-component system;

[0034] Figure 5 1 is a graph showing the kinetic adsorption of heavy metal ions by the modified covalent organic framework material in Example 1 of the present invention in a mixed multi-component system;

[0035] Figure 6 This is a graph showing the adsorption rates of the modified covalent organic framework material in Example 1 of the present invention in a mixed multi-component system when simultaneously adsorbing 0.01, 0.05, and 0.1 mg / L of six mixed heavy metal ions. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below through embodiments in conjunction with the accompanying drawings. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0037] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0038] (1) Preparation of modified covalent organic framework materials for simultaneous adsorption and removal of multiple heavy metal ions

[0039] Example 1

[0040] A method for preparing a modified covalent organic framework material for simultaneously adsorbing multiple heavy metal ions comprises the following steps:

[0041] (1) Weigh 210.8 mg of 1,3,5-tris(4-aminophenyl)benzene and 149.5 mg of 2,5-dihydroxyterephthalaldehyde into a 50 mL conical flask, add 19.2 mL of 1,4-dioxane and 4.8 mL of 1,3,5-trimethylbenzene, sonicate to dissolve them, and allow to react at room temperature for 20 min to obtain a mixed solution;

[0042] (2) adding 18 mg of scandium trifluoromethanesulfonate to the mixed solution obtained in step (1), dissolving it by ultrasonication, and allowing it to react at room temperature for 20 minutes. After the reaction is completed, the insoluble matter is separated from the reaction solution by centrifugation, and the insoluble matter is washed three times by centrifugation with methanol and vacuum-dried at 70° C. for 12 hours. The obtained material is called a covalent organic framework substrate;

[0043] (3) Weigh 300 mg of the covalent organic framework substrate obtained in step (2) and disperse it in 300 mL of a 1 mol / L neutral magnesium chloride aqueous solution. Ultrasonicate for 30 min, centrifuge, wash with water and methanol three times each, and vacuum dry at 70°C for 12 h to obtain a modified covalent organic framework material.

[0044] Example 2

[0045] A method for preparing a modified covalent organic framework material for simultaneously adsorbing multiple heavy metal ions. The preparation method is basically the same as that of Example 1, except that the concentration of the magnesium chloride aqueous solution in step (3) is 0.5 mol / L.

[0046] Example 3

[0047] A method for preparing a modified covalent organic framework material for simultaneously adsorbing multiple heavy metal ions. The preparation method is basically the same as that of Example 1, except that the concentration of the magnesium chloride aqueous solution in step (3) is 2 mol / L.

[0048] Example 4

[0049] A method for preparing a modified covalent organic framework material for simultaneously adsorbing multiple heavy metal ions. The preparation method is basically the same as that of Example 1, except that the concentration of the magnesium chloride aqueous solution in step (3) is 3 mol / L.

[0050] Example 5

[0051] A method for preparing a modified covalent organic framework material for simultaneously adsorbing multiple heavy metal ions is provided. The preparation method is substantially the same as that of Example 1, except that the neutral solution in step (3) is sodium chloride.

[0052] Example 6

[0053] A method for preparing a modified covalent organic framework material for simultaneously adsorbing multiple heavy metal ions is provided. The preparation method is substantially the same as that of Example 1, except that the neutral solution in step (3) is potassium chloride.

[0054] Comparative Example 1

[0055] A method for preparing a covalent organic framework substrate (i.e., an unmodified covalent organic framework material) for simultaneously adsorbing and removing multiple heavy metal ions. The preparation method is basically the same as that of Example 1, except that there is no modification treatment in step (3).

[0056] Comparative Example 2

[0057] A method for preparing a modified covalent organic framework material for simultaneously adsorbing multiple heavy metal ions is provided. The preparation method is substantially the same as that of Example 1, except that in step (3), an alkaline solution of sodium hydroxide is used to modify the material.

[0058] Comparative Example 3

[0059] A method for preparing a modified covalent organic framework material for simultaneously adsorbing multiple heavy metal ions is provided. The preparation method is substantially the same as that of Example 1, except that in step (3), an alkaline solution of potassium hydroxide is used to modify the material.

[0060] Comparative Example 4

[0061] A method for preparing a modified covalent organic framework material for simultaneously adsorbing multiple heavy metal ions is provided. The preparation method is substantially the same as that of Example 1, except that in step (3), an alkaline solution of ammonia is used to modify the material.

[0062] (II) Structural characterization of modified covalent organic framework materials

[0063] The crystal structures of the modified covalent organic framework materials and the unmodified covalent organic framework materials prepared in Example 1 and Comparative Example 1 were characterized by X-ray diffractometer (XRD). Figure 1 ,from Figure 1 It can be seen that a high-intensity peak is observed at 2.9° for both materials, which is caused by the

[100] crystal plane reflection of the covalent organic framework material, indicating that the modification of magnesium chloride does not affect the crystal structure of the covalent organic framework matrix material.

[0064] The morphology and structure of the modified covalent organic framework material and the unmodified covalent organic framework material prepared in Example 1 and Comparative Example 1 were observed by SEM electron microscope. Figure 2 As shown in the figure, the morphology of both materials is a spherical structure with a relatively dense surface, and the particle size is about 1 μm. The modification of magnesium chloride does not cause obvious changes in the particle size and basic morphology of the materials.

[0065] (III) Study on the adsorption properties of modified covalent organic framework materials prepared under different conditions for various heavy metal ions

[0066] In the mixed multi-component system, the modified covalent organic framework materials prepared in Examples 1 to 6 and Comparative Examples 2 to 4 and the unmodified covalent organic framework substrate prepared in Comparative Example 1 were subjected to 6 kinds of heavy metal ions (Pb 2+ Cr 3+ 、Co 2+ 、Cu 2+ 、Ni 2+ 、Mn 2+ )’s adsorption performance evaluation.

[0067] The specific experimental process is as follows: a certain amount of metal salts (lead nitrate (Pb(NO3)2, chromium trichloride (CrCl3), cobalt chloride hexahydrate (CoCl2·6H2O), copper chloride (CuCl2), nickel chloride (NiCl2) and manganese chloride (MnCl2)) were weighed and dissolved in water at pH=2, and heavy metal ion aqueous solutions with concentrations of 1000 mg / L were prepared as stock solutions. The stock solutions of single heavy metal ions were then diluted with pure water to prepare mixed solutions of six heavy metal ions with a concentration of 0.1 mg / L and a pH of 6 as working solutions; 3 mg of the modified covalent organic framework materials prepared in Examples 1 to 6 and Comparative Examples 2 to 4 and the unmodified covalent organic framework substrate prepared in Comparative Example 1 were weighed and placed in 50 mL centrifuge tubes, and 30 mL of the solution was added thereto. A 0.1 mg / L aqueous solution of mixed heavy metal ions was shaken at room temperature for 12 hours, and then the centrifuge tube was centrifuged at 10,000 rpm for 5 minutes. The supernatant was taken and the content of heavy metal ions in the supernatant was determined by ICP-MS, and the equilibrium adsorption rate of heavy metal ions was calculated respectively.

[0068] The calculation formula of equilibrium adsorption rate is as follows:

[0069] Adsorption rate % = (c0-c t / c0)×100%

[0070] Among them, c0 (mg / L) and c t (mg / L) refers to the initial concentration of heavy metal ions and the concentration of heavy metal ions in the system solution at time t, respectively.

[0071] The specific adsorption results are shown in Table 1:

[0072] Table 1 Adsorption rate of 6 mixed heavy metal ions in water by materials prepared from Examples 1 to 6 and Comparative Examples 1 to 4

[0073]

[0074] As can be seen from Table 1, compared to the unmodified covalent organic framework substrate prepared in Comparative Example 1, the modified covalent organic framework materials prepared in Examples 1-4 all exhibited superior adsorption properties for the six heavy metal ions in the mixed multicomponent system. When the concentration of the magnesium chloride modifier was 1 mol / L, the modified covalent organic framework material prepared in Example 1 exhibited adsorption rates of 89% to 100% for the six heavy metal ions.

[0075] Similarly, the present invention also uses neutral solutions such as sodium chloride and potassium chloride and alkaline solutions such as sodium hydroxide, potassium hydroxide and ammonia as modifiers to prepare a series of modified covalent organic framework materials (see Example 4, Example 5 and Comparative Examples 2 to 4). The adsorption test results show that compared with the unmodified covalent organic framework substrate in Comparative Example 1, the modification treatment of the substrate with sodium chloride and potassium chloride significantly improves the material's adsorption of Pb 2+ The adsorption effect of the modified substrate by sodium hydroxide, potassium hydroxide and ammonia water was partially enhanced, and the adsorption effect of copper ions was also partially improved, but the adsorption effect of the other four heavy metal ions in the mixed system was still poor; while the modification treatment of the substrate by sodium hydroxide, potassium hydroxide and ammonia water had some effect on the adsorption of copper ions, but the adsorption effect of the other five heavy metal ions in the mixed system was still poor.

[0076] The above results fully demonstrate that the modification of magnesium chloride is better than the treatment of other modifiers. The modification of magnesium chloride significantly enhances the adsorption capacity of the covalent organic framework material for a variety of mixed heavy metal ions, confirming that the technology proposed in the present invention can prepare a modified covalent organic framework material that has a good adsorption effect on a variety of heavy metal ions in water in a relatively short period of time. Comparing the chemical structure of the covalent organic framework before and after modification, we found that the covalent organic framework substrate structure has free hydroxyl or carbonyl groups, and the ultrasonic treatment of magnesium chloride does not affect the original free hydroxyl or carbonyl groups on the surface of the substrate, and the modification of magnesium chloride instead causes a decrease in the specific surface area of ​​the covalent organic framework material (the BET specific surface areas of the unmodified and modified covalent organic framework materials are 123.3 m 2 / g and 93.5m 2 This indicates that the enhanced adsorption capacity of the modified material for various heavy metal ions is not due to chelation or the material's specific surface area. Furthermore, we found that while the modified covalent organic framework rapidly adsorbs heavy metal ions, it also gradually releases a large amount of magnesium ions into the adsorption solution. Therefore, the enhanced adsorption of heavy metal ions is likely due to the modification of magnesium chloride, which creates magnesium ionization channels in the covalent organic framework material, enabling rapid and efficient adsorption of heavy metal ions through ion exchange.

[0077] (IV) Study on the adsorption process of various heavy metal ions by covalent organic framework materials

[0078] The modified covalent organic framework material prepared in Example 1 is used as the experimental material to study the effects of the material of the present invention on six heavy metal ions (Pb 2+ Cr 3+ 、Co 2+ 、Cu 2+ 、Ni 2+ 、Mn 2+ ) adsorption process.

[0079] 1. Study on the influence of adsorption solution pH

[0080] (1) Experimental methods

[0081] A certain amount of metal salts (lead nitrate (Pb(NO3)2), chromium trichloride (CrCl3), cobalt chloride hexahydrate (CoCl2·6H2O), copper chloride (CuCl2), nickel chloride (NiCl2) and manganese chloride (MnCl2)) were weighed and dissolved in water at pH = 2. A 1000 mg / L heavy metal ion aqueous solution was prepared as a stock solution. The stock solution was then diluted with pure water to prepare a single heavy metal ion solution with a concentration of 0.1 mg / L as a working solution, and 0.1 mol / L hydrochloric acid or sodium hydroxide was added to adjust the pH of the working solution to obtain 0.1 mg / L single heavy metal ion working solutions with different pH values ​​(4, 5, 6, 7, 8); 3 mg of the modified covalent organic framework material was accurately weighed and placed in a 50 mL centrifuge tube, and then 30 mL of 0.1 mg / L single heavy metal ion aqueous solution with different pH values ​​was added thereto, and the mixture was shaken and adsorbed at room temperature for 12 hours; the centrifuge tube was centrifuged at 10,000 rpm for 5 minutes, and the supernatant was taken and the metal ion content was determined by ICP-MS.

[0082] (2) Result analysis

[0083] like Figure 3 As shown in the figure, when the pH of the adsorption solution is 4, the modified covalent organic framework material has an adsorption effect on all six heavy metals, especially Pb 2+ Cr 3+ 、Co 2+ 、Cu 2+ 、Ni 2+ 、Mn 2+ The adsorption rates of the modified covalent organic framework material were 83%, 93%, 36%, 98%, 76% and 27% respectively. After further increasing the pH of the solution, the adsorption effects of the six heavy metal ions increased significantly at first and then showed a slight downward trend. When the pH was 6, the adsorption capacity of the modified covalent organic framework material was the highest, and the adsorption capacity of Pb 2+ Cr 3+ 、Co 2+ 、Cu 2+ 、Ni 2+ 、Mn 2+The adsorption rates were 90%, 98%, 87%, 99%, 97% and 98% respectively. The above results show that the modified covalent organic framework material exhibits good adsorption effect on the six heavy metal ions in water within a relatively wide solution pH range (4-8), and is suitable for the removal and purification of heavy metal ions in water.

[0084] 2. Study on thermodynamic adsorption properties

[0085] (1) Experimental methods

[0086] A certain amount of metal salts (lead nitrate (Pb(NO3)2), chromium trichloride (CrCl3), cobalt chloride hexahydrate (CoCl2·6H2O), copper chloride (CuCl2), nickel chloride (NiCl2), and manganese chloride (MnCl2)) were weighed and dissolved in water at pH = 2. Aqueous solutions of heavy metal ions with a concentration of 1000 mg / L were prepared as stock solutions. The stock solutions were then diluted with pure water to prepare mixed heavy metal ion aqueous solutions (pH = 6) with concentrations of 0.01, 0.05, 0.1, 0.5, 1, 5, and 10 mg / L as working solutions. 3 mg of the modified covalent organic framework material was accurately weighed and placed in a 50 mL centrifuge tube. 30 mL of mixed heavy metal ion aqueous solutions with different initial concentrations were then added to the tubes, and the mixtures were shaken and adsorbed at room temperature for 12 h. The tubes were centrifuged at 10,000 rpm for 5 min. The supernatant was taken and the metal ion content was determined by ICP-MS. The equilibrium adsorption capacity for the six heavy metal ions was calculated. The calculation formula of equilibrium adsorption capacity is as follows:

[0087] Q=(c0-c t )v / m

[0088] Among them, Q (mg / g) refers to the adsorption capacity of the adsorbent material, c0 (mg / mL) and c t (mg / mL) refers to the initial concentration of heavy metal ions and the concentration of ions in the system solution at time t, v (mL) refers to the volume of the adsorption solution, and m (g) refers to the mass of the adsorption material.

[0089] (2) Result analysis

[0090] like Figure 4 As shown in the figure, in the mixed multi-component system, within the heavy metal ion concentration range of 0.01 to 10 mg / L, the adsorption capacity of the modified covalent organic framework material for the six heavy metal ions continued to increase with the increase of the initial concentration of heavy metal ions. When the initial concentration of the mixed heavy metal ions was 10 mg / L, the modified covalent organic framework material had a high adsorption capacity for Pb 2+ Cr 3+ 、Co 2+ 、Cu 2+ 、Ni 2+ 、Mn2+ The adsorption capacities of the six heavy metals were 61 mg / g, 71 mg / g, 32 mg / g, 71 mg / g, 21 mg / g and 10 mg / g, respectively. The order of adsorption capacities of the six heavy metals was Cr, 3+ ≈Cu 2+ >Pb 2+ >Co 2+ >Ni 2+ >Mn 2+ This indicates that the adsorption of the six heavy metal ions on the surface of the modified covalent organic framework material in the mixed system has a competitive effect. The modified covalent organic framework material exhibits different degrees of affinity for the six heavy metals in the mixed system, and has a strong affinity for Cr. 3+ and Cu 2+ The adsorption capacity of the modified covalent organic framework material is relatively strong, while the adsorption capacity for cobalt ions, nickel ions, and manganese ions is relatively weak. However, whether for low or high concentrations of heavy metal ions, good adsorption and removal effects of the six heavy metal ions can be achieved by adjusting the concentration of the modified covalent organic framework material.

[0091] 3. Kinetic adsorption performance study

[0092] (1) Experimental methods

[0093] The kinetic adsorption and removal effect of the modified covalent organic framework material prepared in Example 1 on heavy metal ions was studied, and the results were as follows: Figure 5 shown.

[0094] A certain amount of metal salts (lead nitrate (Pb(NO3)2), chromium trichloride (CrCl3), cobalt chloride hexahydrate (CoCl2·6H2O), copper chloride (CuCl2), nickel chloride (NiCl2) and manganese chloride (MnCl2)) were weighed and dissolved in water at pH = 2. A 1000 mg / L heavy metal ion aqueous solution was prepared as a stock solution. The stock solution was then diluted with pure water to prepare a 0.10 mg / L mixed heavy metal ion aqueous solution (pH = 6) as a working solution. In the mixed multicomponent system of the six heavy metal ions, 3 mg of the modified covalent organic framework material was accurately weighed and placed in a 50 mL centrifuge tube, and then 30 mL of the solution was added. A 0.1 mg / L aqueous solution of mixed heavy metal ions was oscillated and adsorbed at room temperature for different reaction times (10s, 20s, 30s, 1min, 5min, 10min, 20min, 30min, 60min, 90min, 120min, 180min, 240min, 300min); the centrifuge tube was centrifuged at 10000rpm for 5min, and the supernatant was used to determine the content of heavy metal ions by ICP-MS. The equilibrium adsorption capacity of the modified covalent organic framework material for the six heavy metal ions was calculated respectively, and the adsorption and removal ability of the modified covalent organic framework material for the six heavy metal ions was evaluated.

[0095] (2) Result analysis

[0096] Figure 5 This is the kinetic adsorption curve of 0.1 mg / L of 6 heavy metal ions by the modified covalent organic framework material in the mixed multi-element system. It can be seen from the figure that within the first 30 minutes, the modified covalent organic framework material has a strong adsorption capacity for Cr in the mixed system. 3 + 、Cu 2+ and Pb 2+ The adsorption rate of the three heavy metal ions was 78% to 94%, and the adsorption of the three heavy metal ions reached equilibrium after 90 minutes of adsorption. 2+ 、Ni 2+ and Mn 2+ The adsorption of Co 2+ 、Ni 2+ and Mn 2+ The adsorption rate can reach 72-77%, which indicates that the modified covalent organic framework material has a good adsorption effect on Cr in the mixed system. 3+ 、Cu 2+ and Pb 2+ The adsorption capacity is much greater than that of Cr 3+ 、Cu 2+ and Pb 2+This is consistent with the thermodynamic adsorption law of the six heavy metal ions in the mixed system. In any case, by extending the adsorption time or increasing the amount of adsorbent, the modified covalent organic framework material can achieve efficient adsorption and removal of the six heavy metal mixed ions at the same time.

[0097] 4. Adsorption and removal experiments of mixed heavy metal ions with different initial concentrations

[0098] (1) Experimental methods

[0099] A certain amount of metal salts (lead nitrate (Pb(NO3)2), chromium trichloride (CrCl3), cobalt chloride hexahydrate (CoCl2·6H2O), copper chloride (CuCl2), nickel chloride (NiCl2) and manganese chloride (MnCl2)) were weighed and dissolved in water at pH = 2. A 1000 mg / L heavy metal ion aqueous solution was prepared as a stock solution. The stock solution was then diluted with pure water to prepare six heavy metal ion mixed standard solutions (pH = 6) with concentrations of 0.01, 0.05 and 0.1 mg / L as working solutions. In the mixed multicomponent system of the six heavy metal ions, 3 mg of the modified covalent organic framework material was accurately weighed and placed in a 50 mL centrifuge tube, and then 30 mL of the solution was added to each of the six heavy metal ion mixed standard solutions. The mixed standard solutions of heavy metal ions at 0.01, 0.05, and 0.1 mg / L were shaken and adsorbed at room temperature for 12 hours. The centrifuge tube was centrifuged at 10,000 rpm for 5 minutes, and the supernatant was taken and the content of heavy metal ions was determined by ICP-MS. The adsorption rates of the modified covalent organic framework material for the six heavy metal ions were calculated respectively, and the simultaneous removal effect of the modified covalent organic framework material on the six heavy metal ion mixture was evaluated. The results are as follows: Figure 6 shown.

[0100] (2) Result analysis

[0101] Figure 6 The adsorption effect of modified covalent organic framework materials on six heavy metal ions with different initial concentrations in the mixed system is shown in Figure 2. Figure 6 It can be seen that when the initial concentrations of the six heavy metal ions in the mixed system are 0.01 mg / L, the removal rates of the modified covalent organic framework materials for the six heavy metal ions are all 100%; when the initial concentrations of the six heavy metal ions in the mixed system are 0.05 mg / L, the removal rates of the modified covalent organic framework materials for the six heavy metal ions are all 96-100%, Pb 2+ Cr 3+ 、Co 2+ 、Cu 2+ 、Ni 2+ 、Mn 2+The residual concentrations of the six heavy metal ions were 0.3 μg / L, 0, 2.0 μg / L, 0, 1.1 μg / L and 0, respectively, which were far lower than the limit values ​​of these heavy metal ions in my country's national standard GB 5749-2022 "Sanitary Standard for Drinking Water". When the initial concentrations of the six heavy metal ions in the mixed system were 0.1 mg / L, the removal rates of the modified covalent organic framework materials for the six heavy metal ions were all 94-100%, and Pb 2+ Cr 3+ 、Co 2+ 、Cu 2+ 、Ni 2+ 、Mn 2+ The residual concentrations were 5.5 μg / L, 0.09 μg / L, 2.4 μg / L, 0, 1.2 μg / L, and 0, respectively, all far below the limit values ​​for these heavy metal ions in my country's national standard GB 5749-2022, "Sanitary Standard for Drinking Water." This indicates that the modified covalent organic framework material synthesized in the present invention exhibits good removal effects on multiple heavy metal ions in a mixed multi-component coexisting system and has good practical application value.

[0102] In summary, the present invention effectively overcomes the deficiencies in the prior art and has a high industrial application value. The above embodiments serve to illustrate the substantial content of the present invention, but are not intended to limit the scope of protection of the present invention. Those skilled in the art will appreciate that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the essence and scope of protection of the technical solutions of the present invention.

Claims

1. A method for preparing a modified covalent organic framework material for simultaneously adsorbing multiple heavy metal ions, characterized in that: The steps include: (1) dissolving 1,3,5-tris(4-aminophenyl)benzene and 2,5-dihydroxyterephthalaldehyde in a mixed solvent and allowing to react at room temperature to obtain a mixed solution; (2) adding scandium trifluoromethanesulfonate to the mixed solution obtained in step (1), allowing the mixture to react at room temperature, and after the reaction is completed, separating insoluble matter from the reaction solution, washing the insoluble matter, and drying the insoluble matter to obtain a covalent organic framework substrate; (3) using a neutral solution to perform ultrasonic modification on the covalent organic framework substrate prepared in step (2), and then washing and drying the modified substrate to obtain a modified covalent organic framework material; The neutral solution in step (3) is any one of a magnesium chloride aqueous solution, a sodium chloride aqueous solution, and a potassium chloride aqueous solution; the concentration of the neutral solution is 0.5 to 3 mol / L.

2. The method for preparing a modified covalent organic framework material for simultaneously adsorbing multiple heavy metal ions according to claim 1, characterized in that: The neutral solution in step (3) is an aqueous solution of magnesium chloride.

3. The method for preparing a modified covalent organic framework material for simultaneously adsorbing multiple heavy metal ions according to claim 2, characterized in that: The molar ratio of 1,3,5-tris(4-aminophenyl)benzene to 2,5-dihydroxyterephthalaldehyde in step (1) is 2:

3.

4. The method for preparing a modified covalent organic framework material for simultaneously adsorbing multiple heavy metal ions according to claim 3, characterized in that: The mixed solvent in step (1) is a mixed solvent of 1,4-dioxane and 1,3,5-trimethylbenzene; the volume ratio of the 1,4-dioxane to 1,3,5-trimethylbenzene is (1-5):

1.

5. The method for preparing a modified covalent organic framework material for simultaneously adsorbing multiple heavy metal ions according to claim 4, characterized in that: The molar ratio of the 1,3,5-tris(4-aminophenyl)benzene to scandium trifluoromethanesulfonate is (10-150):

1.

6. The method for preparing a modified covalent organic framework material for simultaneously adsorbing multiple heavy metal ions according to claim 1, characterized in that: The standing reaction time in step (1) and step (2) is 10 to 60 minutes.

7. The method for preparing a modified covalent organic framework material for simultaneously adsorbing multiple heavy metal ions according to claim 1, characterized in that: The detergent for washing the insoluble matter in step (2) is at least one of methanol, ethanol and acetone.

8. A modified covalent organic framework material prepared by the method according to any one of claims 1 to 7 and capable of simultaneously adsorbing multiple heavy metal ions.

9. Use of the modified covalent organic framework material according to claim 8 in removing and purifying multiple heavy metal ions in water.

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