Acylhydrazone bond connected covalent organic framework material as well as preparation method and application thereof

Abstract

The invention relates to an acylhydrazone bond-connected covalent organic framework material, in particular to an acylhydrazone bond-connected covalent organic framework material as well as a preparation method and application thereof, and aims to overcome the defects of various materials for adsorbing Pd (II) in one aspect or the defects of poor stability and durability in high-acidity and high-radioactivity environments. Or the adsorption selectivity on Pd (II) is not strong. As an emerging crystalline organic porous polymer, the covalent organic framework is mainly formed by connecting pure organic structural units through dynamic covalent bonds, has the advantages of permanent high porosity, low density, high chemical stability, high thermal stability and the like, and is expected to realize Pd (II) adsorption in strong acid and ray irradiation environments.

Description

Technical Field

[0001] This invention relates to acylhydrazone-linked covalent organic framework materials, specifically to acylhydrazone-linked covalent organic framework materials, their preparation methods, and applications. Background Technology

[0002] Palladium has gained widespread attention due to its superior physicochemical properties, including high temperature resistance, oxidation resistance, corrosion resistance, high catalytic activity, and strong coordination ability, leading to its numerous applications in catalysis, energy storage, corrosion-resistant materials, electrical equipment, and biomedicine. Palladium is one of the fission products of spent nuclear fuel, and the content of platinum group metals in high-level radioactive waste generated during the spent fuel cycle is close to or reaches the level of natural minerals. Effectively separating platinum group metals from high-level radioactive waste has always been a hot and challenging issue in the international nuclear science and technology field. Separating palladium from high-level radioactive waste can effectively utilize rare and precious metal secondary resources, reduce the total amount of radioactive waste, and also help solve technical problems such as palladium clogging pipelines due to precipitation in spent fuel reprocessing.

[0003] Adsorption, as a "green extraction" technology, is widely used in the field of metal separation and enrichment due to its advantages such as simple operation, high separation efficiency, regenerable and recyclable adsorbents, and environmental friendliness. Regarding the adsorption of the noble metal palladium ions (Pd(II)), there have been numerous reports on various materials for the adsorption and recovery of palladium from water, such as nanofibers, ligand-supported silica, biopolymers, magnetic composites, functionalized graphene oxide, layered transition metal carbides, nitrides and carbon-nitrides (MXenes), metal-organic frameworks (MOFs), anion exchange resins, and porous organic polymers (POPs). However, high-level radioactive wastewater typically contains numerous metal ions and exhibits both high radioactivity and high acidity. The aforementioned materials lack stability and durability in high-acidity and high-radioactivity environments and show poor selectivity for Pd(II) adsorption. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of various materials used for adsorbing Pd(II), such as insufficient stability and durability in high acidity and high radioactivity environments, or weak adsorption selectivity for Pd(II), and to provide acylhydrazone-linked covalent organic framework materials, their preparation methods, and applications.

[0005] The concept of this invention is that covalent organic frameworks (COFs) have significant advantages in adsorbing Pd(II), especially their high specific surface area, structural tunability, and chemical stability, making them promising adsorbent materials. However, further research and optimization are needed to address the complexity of their synthesis and to verify their high efficiency and selectivity in practical applications. Acylhydrazone bonds have multiple conformations, and the interconversion between these conformations gives COFs a certain degree of flexibility. Simultaneously, the acylhydrazone bonds contain a large number of hydrogen bonds as acceptors, which is beneficial for the formation of intralayer or interlayer hydrogen bonds in COFs. The building blocks are based on benzene rings, and the planar structure of the framework enhances the interlayer π-π interactions. Hydrogen bonds and interlayer π-π interactions contribute to improving the crystallinity of COFs and their stability under acidic and irradiated environments. The sulfur atoms in the carbonyl (C=O), hydrazone (C=N-NH-) groups formed by acylhydrazone bonds, and the thioether-functionalized aldehyde units help provide coordination sites for palladium, thereby improving the selectivity of acylhydrazone covalent organic framework materials for Pd(II).

[0006] To address the shortcomings of the existing technology and realize the inventive concept, the present invention provides the following technical solution:

[0007] A covalent organic framework material linked by acylhydrazone bonds, characterized by having a structure as shown in Formula I:

[0008]

[0009] A method for preparing the above-mentioned acylhydrazone-linked covalent organic framework material is characterized by comprising the following steps:

[0010] Step 1: Add 2,5-dimethyl sulfide, terephthalaldehyde, 1,3,5-tris[(4-carbazide)phenyl]benzene, and solvent to a Schlenk reaction tube to obtain a solution; the molar concentrations of 2,5-dimethyl sulfide and 1,3,5-tris[(4-carbazide)phenyl]benzene in the solution are in the ranges of 0.0195M~0.0455M and 0.0130M~0.0303M, respectively.

[0011] The solvents include o-dichlorobenzene, n-butanol, and acetic acid;

[0012] Step 2: After sealing the Schlenk reaction tube, ultrasonically vibrate it for 20±10 minutes, then perform three to five rounds of freezing-evacuation-thawing operations, and then react at 120±10℃ for 2-5 days to obtain the product;

[0013] Step 3: Wash the product from Step 2 with THF, deionized water, and DMSO. After washing, dry the product in a vacuum environment at 65±5℃ for 6-12 hours. After drying, a covalent organic framework material with acylhydrazone bonds is obtained.

[0014] Alternatively, the product in step 2 can be washed with deionized water, ethanol, and dichloromethane, and then subjected to Soxhlet extraction with THF at a heating temperature of approximately 90±10℃ for 4-12 hours to obtain a covalent organic framework material with acylhydrazone bonds.

[0015] Further, in step 1, the molar ratio of 2,5-dimethyl sulfide and 1,3,5-tris[(4-carbazide)phenyl]benzene in the solution is 1.5:1, and the concentration of acetic acid is 4-8M.

[0016] Application of a covalent organic framework material with the above-mentioned acylhydrazone bond in the adsorption, separation or recovery of palladium.

[0017] Furthermore, the covalent organic framework material linked by the acylhydrazone bond is used to mix with an acidic aqueous solution containing Pd(II) to adsorb and recover Pd(II);

[0018] The acidic aqueous solution is an HNO3 solution with a concentration of 1-6 mol / L or an acidic solution with pH = 0.5-6, and the concentration range of Pd(II) in the acidic aqueous solution is 1 ng / L to 200 mg / L.

[0019] The mixing time is 6 hours to 24 hours;

[0020] The acidic aqueous solution also contains other metal ions, including one or more of the following: Li(I), Mg(II), Al(III), K(I), Ti(IV), Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II), Sr(II), Zr(IV), Nb(V), Mo(V), Ru(III), Rh(III), Cd(II), Te(IV), Cs(I), Ba(II), La(III), Ce(III), and Pb(II).

[0021] A covalent organic framework material linked by acylhydrazone bonds, characterized by having a structure as shown in Formula II:

[0022]

[0023] A method for preparing the above-mentioned acylhydrazone-linked covalent organic framework material is characterized by comprising the following steps:

[0024] Step 1: Add 2,5-dimethyl sulfide terephthalaldehyde, 1,3,5-benzenetricarboxylhydrazine, and solvent to a Schlenk reaction tube to obtain a solution; the molar concentrations of 2,5-dimethyl sulfide terephthalaldehyde and 1,3,5-benzenetricarboxylhydrazine in the solution are 0.0195M~0.0455M and 0.0195M~0.0455M, respectively.

[0025] The solvents include mesitylene, 1,4-dioxane, and acetic acid;

[0026] Step 2: After sealing the Schlenk reaction tube, ultrasonically vibrate it for 20±10 minutes, then perform three to five rounds of freezing-evacuation-thawing operations, and then react at 120±10℃ for 2-5 days to obtain the product;

[0027] Step 3: Wash the product from Step 2 with THF, deionized water, DMSO and acetone. After washing, dry the product in a vacuum environment at 65±5℃ for 6-12 hours. After drying, a covalent organic framework material with acylhydrazone bond is obtained.

[0028] Alternatively, the product in step 2 can be washed with deionized water, ethanol, and dichloromethane, and then subjected to Soxhlet extraction with THF at a heating temperature of approximately 90±10℃ for 4-12 hours to obtain a covalent organic framework material with acylhydrazone bonds.

[0029] Further, in step 1, the molar concentration ratio of 2,5-dimethyl sulfide and 1,3,5-tris[(4-carbazide)phenyl]benzene is 1.5:1, and the concentration of acetic acid is 4-8M.

[0030] Applications of the aforementioned covalent organic framework materials linked by acylhydrazone bonds in the adsorption, separation, or recovery of palladium.

[0031] Furthermore, the covalent organic framework material linked by the acylhydrazone bond is mixed with an acidic aqueous solution containing Pd(II) to adsorb and recover Pd(II);

[0032] The acidic aqueous solution is an HNO3 solution with a concentration of 1-6 mol / L or an acidic solution with pH = 0.5-6, and the concentration range of Pd(II) in the acidic aqueous solution is 1 ng / L to 200 mg / L.

[0033] The mixing time is 0.5h to 4h;

[0034] The acidic aqueous solution also contains other metal ions, including one or more of the following: Li(I), Mg(II), Al(III), K(I), Ti(IV), Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II), Sr(II), Zr(IV), Nb(V), Mo(V), Ru(III), Rh(III), Cd(II), Te(IV), Cs(I), Ba(II), La(III), Ce(III), and Pb(II).

[0035] Compared with the prior art, the beneficial effects of the present invention are:

[0036] This invention, as a novel crystalline organic porous polymer, uses a covalent organic framework mainly composed of pure organic structural units connected by dynamic covalent bonds. It possesses advantages such as permanent high porosity, low density, high chemical stability, and high thermal stability, and is expected to achieve Pd(II) adsorption under strong acid and radiation irradiation environments. Attached Figure Description

[0037] Figure 1 This is a preparation route diagram of an embodiment of the preparation method for HzMt-1, a covalent organic framework material linked by acylhydrazone bonds according to the present invention;

[0038] Figure 2 This is a preparation route diagram of an embodiment of the preparation method for HzMt-2, a covalent organic framework material linked by acylhydrazone bonds according to the present invention;

[0039] Figure 3 Infrared characterization of HzMt-1, the covalent organic framework material with acylhydrazone linkages of the present invention;

[0040] Figure 4 Infrared characterization of HzMt-2, the covalent organic framework material with acylhydrazone linkages of the present invention;

[0041] Figure 5 Powder X-ray diffraction patterns of HzMt-1 and HzMt-2, covalent organic framework materials linked by acylhydrazone bonds, as shown in this invention.

[0042] Figure 6 The N2 adsorption-desorption curves and BJH desorption pore size distribution diagrams of HzMt-1, a covalent organic framework material with acylhydrazone linkages according to the present invention, are shown below.

[0043] Figure 7 The N2 adsorption-desorption curves and BJH desorption pore size distribution diagrams of HzMt-2, a covalent organic framework material with acylhydrazone linkages according to the present invention, are shown below.

[0044] Figure 8The adsorption capacity diagrams of Pd(II) for the acylhydrazone-linked covalent organic framework materials HzMt-1 and HzMt-2 under different acidic conditions are shown.

[0045] Figure 9 The diagram shows the Pd(II) adsorption capacity of the covalent organic framework materials HzMt-1 and HzMt-2, which are acylhydrazone-linked covalent organic framework materials of the present invention, before and after irradiation.

[0046] Figure 10 The adsorption isotherms of HzMt-1 and HzMt-2, covalent organic framework materials linked by acylhydrazone bonds, are shown in the present invention.

[0047] Figure 11 This is a Pd(II) adsorption selectivity diagram of the acylhydrazone-linked covalent organic framework materials HzMt-1 and HzMt-2 of the present invention. Detailed Implementation

[0048] The present invention will be further described below with reference to the accompanying drawings and exemplary embodiments.

[0049] In this invention, a covalent organic framework material (Formula I) with acylhydrazone linkages was obtained by condensation of 2,5-dimethyl sulfide terephthalaldehyde (2,5-Bis(methylthio)terephthalaldehyde) and 1,3,5-tris[(4-hydrazinecarbonyl)phenyl]benzene (1,3,5-tris[(4-hydrazinecarbonyl)phenylbenzene), defined as HzMt-1;

[0050] A covalent organic framework material (Formula II) with acylhydrazone linkages was obtained by condensation of 2,5-dimethyl sulfide-terephthalaldehyde and 1,3,5-benzene-1,3,5-tricarbohydrazide, and defined as HzMt-2.

[0051] The synthesis of 1,3,5-tris[(4-carbazide)phenyl]benzene and 1,3,5-benzenetricarbazide followed the synthetic method of terephthalic acid hydrazide (Journal of the American Chemical Society., 2020, 142(42), 18138-18149). The synthesis of 2,5-dimethyl sulfide terephthalaldehyde followed the synthetic method in previous literature (Journal of Hazardous Materials., 2022, 429, 128303).

[0052] Reference Figure 1 The preparation method of the above-mentioned HzMt-1 includes the following steps:

[0053] Step 1: Take 34.0 mg (0.15 mmol) of 2,5-dimethyl sulfide terephthalaldehyde, 48.1 mg (0.10 mmol) of 1,3,5-tris[(4-carbazide)phenyl]benzene, and solvent and add them to a Schlenk reaction tube to obtain a solution; the molar ratio of 2,5-dimethyl sulfide and 1,3,5-tris[(4-carbazide)phenyl]benzene in the solution is 1.5:1;

[0054] The solvent is 1.5-3.5 mL of o-dichlorobenzene, 1.5-3.5 mL of n-butanol, and 0.3-0.7 mL of 4-8 M acetic acid aqueous solution; alternatively, one of combinations 1, 2, and 3 can be used, as shown in Table 1:

[0055] Table 1

[0056]

[0057] Step 2: After sealing the Schlenk reaction tube, ultrasonically vibrate it for 20±10 minutes, then perform three to five rounds of freezing-evacuation-thawing operations, and then react at 120±10℃ for 3±1 days to obtain the product;

[0058] The freezing-evacuation-thawing operation is used to remove gases from the solvent to reduce interference from oxidation and hydrolysis reactions;

[0059] Step 3: Wash the product from Step 2 with THF (tetrahydrofuran), deionized water, and DMSO (dimethyl sulfoxide). After washing, dry the product in a vacuum environment at 65±5℃ for 6-12 hours. After drying, HzMt-1 is obtained, which is a yellow powder solid with a mass of 50.1 mg (yield: 65.3%).

[0060] The washing is used to remove unreacted starters, byproducts, and catalysts, etc.; the drying is used to further remove the solvent and obtain a dried product.

[0061] In another embodiment, step 3 may also be:

[0062] The product from step 2 was washed with deionized water, ethanol, and dichloromethane, and then subjected to Soxhlet extraction with THF at a heating temperature of approximately 90±10℃ for 4-12 hours to obtain HzMt-1.

[0063] This invention discloses the application of HzMt-1 in the adsorption, separation, or recovery of palladium. Specifically, HzMt-1 is mixed with an acidic aqueous solution containing Pd(II) for 6-24 hours to adsorb and recover Pd(II). The acidic aqueous solution is an HNO3 solution with a concentration of 1-6 mol / L or an acidic solution with pH = 0.5-6. The concentration of Pd(II) in the acidic aqueous solution ranges from 1 ng / L to 200 mg / L. The acidic aqueous solution also contains other metal ions, including one or more of Li(I), Mg(II), Al(III), K(I), Ti(IV), Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II), Sr(II), Zr(IV), Nb(V), Mo(V), Ru(III), Rh(III), Cd(II), Te(IV), Cs(I), Ba(II), La(III), Ce(III), and Pb(II).

[0064] Reference Figure 2 The preparation method of the above-mentioned HzMt-2 includes the following steps:

[0065] Step 1: Take 34.0 mg (0.15 mmol) of 2,5-dimethyl sulfide terephthalaldehyde, 25.2 mg (0.15 mmol) of 1,3,5-benzenetricarboxyhydrazide, and solvent and add them to a Schlenk reaction tube to obtain a solution; the molar ratio of 2,5-dimethyl sulfide terephthalaldehyde to 1,3,5-benzenetricarboxyhydrazide in the solution is 1.5:1;

[0066] The solvent is 1.5-3.5 mL of mesitylene, 1.5-3.5 mL of 1,4-dioxane, and 0.3-0.7 mL of 4-8 M acetic acid aqueous solution;

[0067] Alternatively, one of combinations 1, 2, and 3 can be used, as shown in Table 2:

[0068] Table 2

[0069]

[0070] Step 2: After sealing the Schleenk reaction tube, ultrasonically vibrate it for 20±10 minutes, then perform three to five rounds of freezing-evacuation-thawing operations, and then react at 120±10℃ for 3±1 days to obtain the product;

[0071] Step 3: Wash the product with THF, deionized water, DMSO and acetone. After washing, dry the product in a vacuum environment at 65±5℃ for 6-12 hours. After drying, the covalent organic framework material HzMt-2 is obtained, which is a yellow powder solid with a mass of 35.8 mg (yield: 66.5%).

[0072] In another embodiment, step 3 may also be:

[0073] The product was washed with deionized water, ethanol, and dichloromethane, and then subjected to Soxhlet extraction with THF. The extraction temperature was approximately 90±10℃, and the extraction time was approximately 4-12 hours.

[0074] This invention discloses the application of HzMt-2 in the adsorption, separation, or recovery of palladium. Specifically, HzMt-2 is mixed with an acidic aqueous solution containing Pd(II) for 0.5 h to 4 h to adsorb and recover Pd(II). The acidic aqueous solution is an HNO3 solution with a concentration of 1-6 mol / L or an acidic solution with pH = 0.5-6. The concentration of Pd(II) in the acidic aqueous solution ranges from 1 ng / L to 200 mg / L. The acidic aqueous solution also contains other metal ions, including one or more of Li(I), Mg(II), Al(III), K(I), Ti(IV), Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II), Sr(II), Zr(IV), Nb(V), Mo(V), Ru(III), Rh(III), Cd(II), Te(IV), Cs(I), Ba(II), La(III), Ce(III), and Pb(II).

[0075] Experimental verification

[0076] 1. Structure

[0077] HzMt-1 and HzMt-2 were characterized by infrared spectroscopy, X-ray powder diffraction, and N2 adsorption-desorption curves. Figure 3 Here is the infrared characterization image of HzMt-1. Figure 4 Here is the infrared characterization image of HzMt-2. Figure 5 The powder X-ray diffraction patterns are for HzMt-1 and HzMt-2. Figure 6 The N2 adsorption-desorption curves and BJH desorption pore size distribution diagrams for HzMt-1 are shown. Figure 7 The N2 adsorption-desorption curves and BJH desorption pore size distribution diagrams for HzMt-2 are shown. Figures 3 to 7 Both studies indicate that HzMt-1 and HzMt-2 are crystalline porous covalent organic framework structures.

[0078] 2. Adsorption

[0079] Reference Figure 8 , Figure 9Both HzMt-1 and HzMt-2 can adsorb Pd(II) under both strongly acidic and radioactive environments. Under strongly acidic conditions, the maximum adsorption capacity reached 248.15 mg / g and 439.60 mg / g, respectively. After irradiation with a dose of 100 kGy, HzMt-2 retained 99.4% of its original adsorption capacity.

[0080] Reference Figure 11 Under the condition of coexistence of 25 metal ions including Li(I), Mg(II), Al(III), K(I), Ti(IV), Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II), Sr(II), Zr(IV), Nb(V), Mo(V), Ru(III), Rh(III), Cd(II), Te(IV), Cs(I), Ba(II), La(III), Ce(III), Pb(II), and Pd(II), both HzMt-1 and HzMt-2 can achieve an adsorption efficiency of over 98% for Pd(II), while exhibiting extremely poor adsorption capacity for the remaining 24 ions, with adsorption efficiencies of less than 5%, which can be almost ignored.

[0081] The adsorption experiment is as follows:

[0082] HzMt-1 and HzMt-2 were mixed with acidic aqueous solutions containing Pd(II) to adsorb Pd(II). The acidic aqueous solution was either a 1-3 mol / L HNO3 solution or an acidic aqueous solution with pH = 1-5. The differences in adsorption performance of HzMt-1 and HzMt-2 under different acidic conditions were studied.

[0083] The adsorption capacities of HzMt-1 and HzMt-2 are calculated using the following formula:

[0084]

[0085] Where C0 is the initial concentration (mg / L), C e Let V be the concentration at a certain moment (mg / L), V be the solution volume (L), m be the material mass (g), and Q be the adsorption capacity (mg / g).

[0086] The concentration range of Pd(II) in acidic aqueous solutions is 1 ng / L to 200 mg / L; in this example, the concentration of Pd(II) is 50 mg / L. The adsorption results are as follows: Figure 8As shown, both HzMt-1 and HzMt-2 exhibited better adsorption capacity under strongly acidic conditions, with the adsorption capacity decreasing as the acidity decreased. Both showed the highest adsorption capacity at pH=1, reaching 170.83 mg / g and 273.5 mg / g, respectively. Under strongly acidic conditions, the adsorption capacity of HzMt-1 showed little difference, while HzMt-2 showed the highest adsorption capacity in a 1 mol / L HNO3 solution, reaching 243.35 mg / g. In a 3 mol / L HNO3 environment, both still had adsorption capacities of 150.64 mg / g and 174.55 mg / g, respectively. Figure 9 As shown, after irradiation with a dose of 100 kGy, adsorption was carried out under strongly acidic conditions of 1 mol / L HNO3 and c(Pd(II)) = 100 mg / L. The adsorption performance of HzMt-1 decreased from 240.23 mg / g without irradiation to 105.35 mg / g after irradiation, retaining only 43.9% of the original adsorption capacity. The adsorption performance of HzMt-2 decreased only slightly from 401.05 mg / g without irradiation to 398.73 mg / g after irradiation, retaining 99.4% of the original adsorption capacity. Figure 10 As shown, under strongly acidic conditions of 1 mol / L HNO3, and with c(Pd(II)) = 10-150 mg / L, the maximum adsorption capacities of the two at a concentration of c(Pd(II)) = 150 mg / L were calculated to be 248.15 mg / g and 439.60 mg / g, respectively.

Claims

1. A covalent organic framework material linked by acylhydrazone bonds, characterized in that: It has the structure shown in Equation I:

2. A method for preparing a covalent organic framework material linked by acylhydrazone bonds as described in claim 1, characterized in that, Includes the following steps: Step 1: Add 2,5-dimethyl sulfide, terephthalaldehyde, 1,3,5-tris[(4-carbazide)phenyl]benzene, and solvent to a Schlenk reaction tube to obtain a solution; the molar concentrations of 2,5-dimethyl sulfide and 1,3,5-tris[(4-carbazide)phenyl]benzene in the solution are in the ranges of 0.0195M to 0.0455M and 0.0130M to 0.0303M, respectively. The solvents include o-dichlorobenzene, n-butanol, and acetic acid; Step 2: After sealing the Schlenk reaction tube, ultrasonically vibrate it for 20±10 minutes, then perform three to five rounds of freezing-evacuation-thawing operations, and then react at 120±10℃ for 2-5 days to obtain the product; Step 3: Wash the product from Step 2 with THF, deionized water, and DMSO. After washing, dry the product in a vacuum environment at 65±5℃ for 6-12 hours. After drying, a covalent organic framework material with acylhydrazone bonds is obtained. Alternatively, the product in step 2 can be washed with deionized water, ethanol, and dichloromethane, and then subjected to Soxhlet extraction with THF at a heating temperature of approximately 90±10℃ for 4-12 hours to obtain a covalent organic framework material with acylhydrazone bonds.

3. The method for preparing the acylhydrazone-linked covalent organic framework material according to claim 2, characterized in that: In step 1, the molar ratio of 2,5-dimethyl sulfide and 1,3,5-tris[(4-carbazide)phenyl]benzene in the solution is 1.5:1, and the concentration of acetic acid is 4-8M.

4. The application of the acylhydrazone-linked covalent organic framework material of claim 1 in the adsorption, separation or recovery of palladium.

5. The application of the acylhydrazone-linked covalent organic framework material according to claim 4 in the adsorption, separation, or recovery of palladium, characterized in that: The covalent organic framework material linked by the acylhydrazone bond was mixed with an acidic aqueous solution containing Pd(II) to adsorb and recover Pd(II); The acidic aqueous solution is an HNO3 solution with a concentration of 1-6 mol / L or an acidic solution with pH = 0.5-6, and the concentration range of Pd(II) in the acidic aqueous solution is 1 ng / L to 200 mg / L. The mixing time is 6h~24h; The acidic aqueous solution also contains other metal ions, including one or more of the following: Li(I), Mg(II), Al(III), K(I), Ti(IV), Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II), Sr(II), Zr(IV), Nb(V), Mo(V), Ru(III), Rh(III), Cd(II), Te(IV), Cs(I), Ba(II), La(III), Ce(III), and Pb(II).

6. A covalent organic framework material linked by acylhydrazone bonds, characterized in that: It has the structure shown in Equation II:

7. A method for preparing a covalent organic framework material linked by acylhydrazone bonds as described in claim 6, characterized in that, Includes the following steps: Step 1: Add 2,5-dimethyl sulfide terephthalaldehyde, 1,3,5-benzenetricarboxyhydrazide, and solvent to a Schlenk reaction tube to obtain a solution; the molar concentrations of 2,5-dimethyl sulfide terephthalaldehyde and 1,3,5-benzenetricarboxyhydrazide in the solution are in the ranges of 0.0195M~0.0455M and 0.0195M~0.0455M, respectively. The solvents include mesitylene, 1,4-dioxane, and acetic acid; Step 2: After sealing the Schlenk reaction tube, ultrasonically vibrate it for 20±10 minutes, then perform three to five rounds of freezing-evacuation-thawing operations, and then react at 120±10℃ for 2-5 days to obtain the product; Step 3: Wash the product from Step 2 with THF, deionized water, DMSO and acetone. After washing, dry the product in a vacuum environment at 65±5℃ for 6-12 hours. After drying, a covalent organic framework material with acylhydrazone bond is obtained. Alternatively, the product in step 2 can be washed with deionized water, ethanol, and dichloromethane, and then subjected to Soxhlet extraction with THF at a heating temperature of approximately 90±10℃ for 4-12 hours to obtain a covalent organic framework material with acylhydrazone bonds.

8. The method for preparing the acylhydrazone-linked covalent organic framework material according to claim 6, characterized in that: In step 1, the molar ratio of 2,5-dimethyl sulfide and 1,3,5-tris[(4-carbazide)phenyl]benzene is 1.5:1, and the concentration of acetic acid is 4-8M.

9. The application of the acylhydrazone-linked covalent organic framework material according to claim 6 in the adsorption, separation or recovery of palladium.

10. The application of the acylhydrazone-linked covalent organic framework material according to claim 9 in the adsorption and recovery of palladium, characterized in that: The covalent organic framework material linked by the acylhydrazone bond is mixed with an acidic aqueous solution containing Pd(II) to adsorb and recover Pd(II); The acidic aqueous solution is an HNO3 solution with a concentration of 1-6 mol / L or an acidic solution with pH = 0.5-6, and the concentration range of Pd(II) in the acidic aqueous solution is 1 ng / L to 200 mg / L. The mixing time is 0.5h to 4h; The acidic aqueous solution also contains other metal ions, including one or more of the following: Li(I), Mg(II), Al(III), K(I), Ti(IV), Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II), Sr(II), Zr(IV), Nb(V), Mo(V), Ru(III), Rh(III), Cd(II), Te(IV), Cs(I), Ba(II), La(III), Ce(III), and Pb(II).

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