Gallium ion imprinted covalent organic framework adsorbent as well as preparation method and application thereof

Abstract

The invention relates to a gallium ion imprinted covalent organic framework adsorbent as well as a preparation method and application thereof, and belongs to the technical field of environmental functional materials and water pollution treatment. The preparation method comprises the following steps: taking Ga (III) as a template ion to form a template-ligand compound with pyrogallic acid, taking the template-ligand compound as a structure-directing agent, and guiding melamine to be subjected to polycondensation polymerization in the presence of formaldehyde, so as to obtain the high-molecular polymer. The invention relates to a gallium ion imprinted covalent organic framework adsorbent which is a gallium ion imprinted covalent organic framework adsorbent marked as Ga-IIP-PFCOF, and a melamine-pyrogallic acid covalent organic framework which is constructed in situ, has a regular porous structure and is rich in gallium ion specific recognition sites. Ion imprinting holes with matched spatial configuration and complementary chemical environment are formed on the framework of the gallium ion imprinting covalent organic framework adsorbent, and the gallium ion imprinting covalent organic framework adsorbent has ultrahigh adsorption capacity and excellent selectivity on gallium ions.

Description

Technical Field

[0001] This invention relates to a gallium ion-imprinted covalent organic framework adsorbent, its preparation method and application, belonging to the fields of environmental functional materials and water pollution control technology. Background Technology

[0002] Currently, commonly used gallium recovery methods both domestically and internationally mainly include solvent extraction, ion exchange, electrochemical methods, and adsorption methods. Among these, adsorption methods have become a research hotspot in the field of gallium recovery due to their outstanding advantages such as simple operation process, low equipment requirements, and controllable operating costs. However, traditional adsorption materials (such as ion exchange resins and activated carbon) generally suffer from defects such as poor selectivity for gallium ions, limited adsorption capacity, and poor regeneration performance, making it difficult to meet the actual needs of efficient gallium recovery in complex systems.

[0003] In recent years, covalent organic frameworks (COFs) have shown great potential in adsorption and separation due to their precisely designable pore structures, tunable surface chemistry, and ultra-high specific surface area. However, their specific recognition ability for gallium ions still needs improvement, and they cannot effectively solve the interference problem of coexisting ions in complex systems. Ion imprinting, as a highly efficient specific recognition technology, can construct recognition holes that are highly compatible with the target gallium ions in terms of shape, size, and functional group matching through molecular design, significantly improving the selectivity of materials for gallium ions. However, in practical applications, this technology often suffers from problems such as excessively deep embedding and uneven distribution of imprinted sites, resulting in low adsorption capacity and slow mass transfer rate, which limits its industrial application. Summary of the Invention

[0004] To address the technical problems of low selectivity, limited adsorption capacity, and uneven distribution of imprinted sites and limited mass transfer in traditional ion-imprinted porous material preparation methods for gallium ions, this invention proposes a gallium ion-imprinted covalent organic framework adsorbent, its preparation method, and its application. The gallium ion-imprinted covalent organic framework adsorbent is a gallium ion-imprinted melamine-pyrogallic acid covalent organic framework adsorbent based on a "one-step template-guided synergistic synthesis" strategy, targeting Ga... 3+ Using ions as templates, and utilizing the stable complexes pre-formed with specific functional ligands (pyrogallic acid) as structure-directing agents, followed by a condensation reaction with melamine, an ion-imprinted covalent organic framework material with both an ordered porous structure and precise gallium ion recognition holes is constructed in situ. Therefore, this invention forms spatially matched, chemically complementary ion-imprinted holes on the framework of a gallium ion-imprinted covalent organic framework adsorbent, exhibiting ultra-high adsorption capacity and excellent selectivity for gallium ions.

[0005] A gallium ion-imprinted covalent organic framework adsorbent, using Ga(III) as a template ion to form a template-ligand complex with pyrogallic acid, and using the template-ligand complex as a structure directing agent, guides the condensation polymerization of melamine in the presence of formaldehyde. The resulting melamine-pyrogallic acid covalent organic framework, with a regular pore structure and rich in gallium ion-specific recognition sites, is designated as the gallium ion-imprinted covalent organic framework adsorbent, denoted as Ga-IIP-PFCOF, and its structural formula is as follows: .

[0006] The preparation method of the gallium ion-imprinted covalent organic framework adsorbent includes the following specific steps: (1) Gallium chloride and pyrogallol were added to a methanol-deionized water mixed solvent and stirred to dissolve them to obtain a mixed solution. The pH of the mixed solution was adjusted to 2.8-3.2, and the pre-assembly reaction was carried out at a temperature of 45-55℃ for 1.5-2.5 h to obtain a template-ligand complex solution. The reaction formula is as follows: ; (2) Melamine was completely dissolved in N,N-dimethylformamide solvent to obtain a melamine solution. At a temperature of 25~35℃, the melamine solution was added dropwise to the template-ligand complex solution, followed by the dropwise addition of formaldehyde. The temperature was raised to 60~80℃ and polycondensation was carried out for 20~28h to obtain a polymer solution system. The reaction formula is as follows: ; (3) The polymer solution system was washed with a mixture of N,N-dimethylformamide and methanol, and then washed with sulfuric acid solution until no Ga ions were detected in the eluent. It was then washed with deionized water more than 3 times, dried, and ground to obtain a gallium ion imprinted covalent organic framework adsorbent. The reaction formula for removing template ions Ga(III) by washing with sulfuric acid solution is as follows: ; Preferably, in step (1), the molar ratio of gallium chloride to pyrogallol is 1:2~4.

[0007] Preferably, in step (1), the volume ratio of methanol to deionized water in the methanol-deionized water mixed solvent is 2.5~3.5:1, and the concentration of gallium chloride in the mixed solution is 0.2~0.4mol / L.

[0008] Preferably, in step (2), the molar concentration of the melamine solution is 0.8~1 mol / L, the volume ratio of the melamine solution to the template-ligand complex solution is 1.5~2.5:5, and the dropping rate of the melamine solution is 0.2~0.4 ml / min.

[0009] More preferably, in step (2), the molar ratio of melamine to formaldehyde is 2~4:20~28, and the formaldehyde dropping rate is 1.5~1.7 ml / min.

[0010] Preferably, in step (3) the volume ratio of N,N-dimethylformamide to methanol in the N,N-dimethylformamide-methanol mixture is 1:0.5~1.5.

[0011] Preferably, the concentration of the sulfuric acid solution in step (3) is 0.8~1.2 mol / L.

[0012] The principle of selective adsorption of Ga(III) ions by the gallium ion-imprinted covalent organic framework adsorbent of this invention: 1. Mesoporous structure and pore characteristics 1) The adsorbent Ga-IIP-PFCOF is a typical mesoporous material. BET characterization confirmed that its average pore size is 18.51 nm, and the pore volume is mainly concentrated in the mesoporous range of 0-50 nm, with a significant pore volume peak in the 2-20 nm range. This mesoporous structure provides sufficient space to accommodate Ga(III) and related species, reduces the diffusion resistance of Ga(III) inside the material, and ensures the high efficiency of mass transfer during adsorption. 2) The material exhibits an amorphous or low-crystallinity structure, with strong and broad diffuse diffraction peaks appearing only around 2θ=23° in XRD tests. This structural characteristic facilitates the formation of abundant and easily accessible imprinted sites, avoiding the site shading problem that may exist in crystalline materials, and providing a structural basis for the specific recognition and binding of Ga(Ⅲ). 3) The material consists of a continuous cluster structure formed by the aggregation of a large number of smooth, uniformly sized spherical particles. The aggregates are loose and porous, with obvious pores between the particles. This morphological feature increases the contact area between the material and Ga-containing wastewater, and at the same time provides a convenient channel for the diffusion of Ga(III) from the solution to the material surface and internal sites, thereby enhancing the adsorption kinetics.

[0013] 2. Specific effects of ion-imprinted holes 1) Through a "one-step template-guided collaborative synthesis" strategy, using Ga 3+ Using a template, guided by the complex formed between the template and pyrogallol, the polycondensation reaction between the template and melamine was regulated to construct a Ga-rich COF framework in situ. After template elution, imprinted cavities with geometric shape memory and chemical recognition functions were formed in the material. 2) The spatial size of the imprinted cavity is related to Ga(Ⅲ) and its main species formed in solution (such as Ga(OH)4). - The high degree of matching enables the specific recognition of Ga(Ⅲ) through steric hindrance, effectively excluding other metal ions (such as V) in the solution. 3+ Interference from (etc.) significantly improves adsorption selectivity.

[0014] 3. Interaction mechanism between functional groups and Ga(Ⅲ) 1) Coordination binding: Both the N atom on the triazine ring and the O atom in the phenolic hydroxyl group of pyrogallic acid have lone pairs of electrons, which can form coordinate bonds (N-Ga bond, O-Ga bond) with Ga(III). XPS characterization showed that after adsorption, the N-Ga characteristic peak at 396.34 eV and the O-Ga characteristic peak at 531.03 eV appeared, confirming the occurrence of coordination binding; DFT calculations further showed that the N site of the triazine ring (IIP-MFCOF9) had the strongest coordination binding ability with Ga(III) due to its optimal negative charge concentration. 2) Electrostatic attraction: Within a suitable pH range (9-11), the material surface maintains a positive charge, while Ga(III) mainly exists as the negatively charged Ga(OH)4. - In its existing form, the two act as gallium ion-imprinted melamine-pyrogallic acid covalent organic framework adsorbents through electrostatic attraction to promote the enrichment and binding of Ga(III) to the material surface; the nitrogen atoms (C-NH) on the triazine ring can undergo protonation to form -NH2. + Further enhance the effect on Ga(OH)4 - The electrostatic trapping ability; Zeta potential tests confirmed that the surface positive charge of the material is related to Ga(OH)4 within this pH range. - The negative charge of the electronegativity creates a strong electrostatic attraction, resulting in an adsorption efficiency of over 95%. 3) Multi-site synergistic effect: Ion-imprinted sites (-OH) achieve Ga(OH)4 synergistic effect by leveraging spatial matching advantages. - The specific recognition of Ga(III) by the triazine ring N site and the phenolic hydroxyl O site, through coordination binding and electrostatic attraction, jointly completes the capture and fixation of Ga(III). DFT calculations show that the binding energy of all adsorption sites is negative, indicating that the interaction between each site and Ga(III) is thermodynamically spontaneous and stable, and the synergistic effect of multiple sites significantly improves the adsorption capacity and selectivity.

[0015] The beneficial effects of this invention are: (1) This invention utilizes a "one-step template-guided collaborative synthesis" strategy to achieve Ga 3+ Using a template, a template-ligand complex is formed with pyrogallol. Under the guidance of the template-ligand complex, a condensation reaction is then carried out with melamine to construct a COF backbone rich in Ga recognition units in situ. After the template is eluted, imprinted cavities with geometric shape memory and chemical recognition functions are formed in the material. (2) The gallium ion-imprinted melamine-pyrogallic acid covalent organic framework adsorbent Ga-IIP-PFCOF of the present invention has an extremely high adsorption capacity (525.75 mg / g) for Ga(III) and excellent selective adsorption ability, with a high partition coefficient, and is suitable for complex aquatic environments. (3) The gallium ion imprinted melamine-pyrogallic acid covalent organic framework adsorbent Ga-IIP-PFCOF of the present invention has excellent chemical and thermal stability. It can be efficiently regenerated through simple desorption treatment. Its performance decays little after multiple cycles, which reduces the cost of use. (4) In the adsorption process of the gallium ion imprinted melamine-pyrogallic acid covalent organic framework adsorbent Ga-IIP-PFCOF of the present invention, not only Ga(III) is physically adsorbed through electrostatic interaction, but the triazine ring N site and phenolic hydroxyl O site also work together through coordination and electrostatic attraction to capture and fix Ga(III). Attached Figure Description

[0016] Figure 1 This is a SEM image of the gallium ion-imprinted melamine-pyrogallic acid covalent organic framework adsorbent Ga-IIP-PFCOF from Example 1. Figure 2 EDS image of Ga-IIP-PFCOF, the gallium ion-imprinted melamine-pyrogallic acid covalent organic framework adsorbent in Example 1; Figure 3 The FT-IR image of the gallium ion-imprinted melamine-pyrogallic acid covalent organic framework adsorbent Ga-IIP-PFCOF in Example 1 is shown. Figure 4 The XPS total spectra of Ga(III) before and after adsorption by the gallium ion-imprinted melamine-pyrogallic acid covalent organic framework adsorbent Ga-IIP-PFCOF in Example 1 are shown. Figure 5 This is a SEM image of Ga(III) adsorbed by the gallium ion-imprinted melamine-pyrogallic acid covalent organic framework adsorbent Ga-IIP-PFCOF in Example 1. Figure 6 The image shows the EDS diagram of Ga(III) after adsorption by the gallium ion-imprinted melamine-pyrogallic acid covalent organic framework adsorbent Ga-IIP-PFCOF in Example 1. Detailed Implementation

[0017] The present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the content described.

[0018] In this embodiment of the invention, the gallium ion-imprinted covalent organic framework adsorbent uses Ga(III) as the template ion to form a template-ligand complex with pyrogallic acid. This template-ligand complex then acts as a structure directing agent, guiding the condensation polymerization of melamine in the presence of formaldehyde. The resulting in-situ constructed melamine-pyrogallic acid covalent organic framework, characterized by a regular pore structure and rich in gallium ion-specific recognition sites, is designated as the gallium ion-imprinted covalent organic framework adsorbent, denoted as Ga-IIP-PFCOF, with the following structural formula: .

[0019] Example 1: A method for preparing a gallium ion-imprinted covalent organic framework adsorbent, the specific steps of which are as follows: (1) Gallium chloride and pyrogallic acid (molar ratio of gallium chloride to pyrogallic acid is 1:3) were added to a methanol-deionized water mixed solvent (volume ratio of methanol to deionized water is 3:1) and stirred to dissolve to obtain a mixed solution (the concentration of gallium chloride in the mixed solution is 0.313 mol / L). The pH of the mixed solution was adjusted to 3, and the pre-assembly reaction was carried out at 50℃ for 2 h to obtain a template-ligand complex solution; the reaction formula is as follows: ; (2) Melamine was completely dissolved in N,N-dimethylformamide solvent to obtain a melamine solution with a concentration of 0.94 mol / L. At a temperature of 30°C, the melamine solution was added dropwise to the template-ligand complex solution at a rate of 0.3 ml / min (the volume ratio of melamine solution to template-ligand complex solution was 2:5). Then, formaldehyde was added dropwise at a rate of 1.6 ml / min (the molar ratio of melamine to formaldehyde was 3:24). The temperature was raised to 70°C and the polycondensation reaction was carried out for 24 h to obtain a polymer solution system. The reaction formula is as follows: ; (3) The polymer solution system was washed with a mixture of N,N-dimethylformamide and methanol (the volume ratio of N,N-dimethylformamide to methanol was 1:1), then washed with a 1 mol / L sulfuric acid solution until no Ga ions were detected in the eluent. It was then washed more than three times with deionized water, dried, and ground to obtain the gallium ion-imprinted melamine-pyrogallic acid covalent organic framework adsorbent, namely the gallium ion-imprinted covalent organic framework adsorbent Ga-IIP-PFCOF. The reaction formula for removing the template ion Ga(III) by washing with sulfuric acid solution is as follows: ; The SEM image of the gallium ion-imprinted covalent organic framework adsorbent Ga-IIP-PFCOF in this embodiment is shown below. Figure 1 ,from Figure 1 It can be seen that the material is composed of a large number of spherical particles with smooth surfaces and relatively uniform size. These particles aggregate into a continuous cluster structure; the aggregate as a whole presents a fluffy and porous morphology, and obvious gaps can be seen between the particles. The EDS diagram of the gallium ion-imprinted covalent organic framework adsorbent Ga-IIP-PFCOF in this embodiment is shown below. Figure 2 The main elements of the gallium ion-imprinted covalent organic framework adsorbent Ga-IIP-PFCOF are C, N, and O, with mass percentages of C, N, and O being 49.99%, 35.36%, and 14.66%, respectively. The FT-IR spectrum of the gallium ion-imprinted covalent organic framework adsorbent Ga-IIP-PFCOF in this embodiment is shown below. Figure 3 The chemical bonds and functional groups of Ga-IIP-PFCOF with the precursor pyrogallic acid and melamine exhibit the following patterns: Ga-IIP-PFCOF at 3409 cm⁻¹... -1 A broad absorption peak appears at 3534 cm⁻¹, which originates from the phenolic hydroxyl group of pyrogallic acid. -1 The stretching vibration at 3466 cm⁻¹ corresponds to the melamine-NH group at 3466 cm⁻¹. -1 and 3422cm -1 The superposition of symmetric and asymmetric stretching vibrations at the position of the peak, and the significant redshift, directly indicate that the phenolic hydroxyl group interacts with Ga during the pre-assembly stage. 3+ Coordination occurred, which also proves that the -NH structure of melamine was retained after copolymerization, confirming the dual role of metal coordination and covalent crosslinking in material preparation; at 1634 cm⁻¹ -1 The absorption peak at 1617 cm⁻¹ corresponds to the aromatic ring of pyrogallol at 1617 cm⁻¹. -1 1524cm -1 1486cm -1 The skeletal stretching vibrations at the location, and the C=N bonds in the melamine triazine ring at 1652 cm⁻¹ -1 1538cm -1 The superimposed displacement of stretching vibrations indicates that both the aromatic ring and triazine ring skeletons are intact within the polymer network, consistent with the design of the copolymerization reaction; 1344 cm -1 The absorption peak at 1091 cm⁻¹ is attributed to the redshift of the stretching vibration of the CN bond connecting the amino group and the triazine ring in melamine at 1436 cm⁻¹. This shift reflects the crosslinking of melamine with formaldehyde and pre-assembled units during copolymerization, leading to changes in the electron cloud density and chemical environment of the CN bond; -1 The absorption peak at 1004 cm⁻¹ originates from the CO bond connecting the phenolic hydroxyl group to the benzene ring in pyrogallic acid. -1 The blue shift of the stretching vibration further indicates that the phenolic hydroxyl group maintains its connection with the benzene ring after participating in metal coordination. 781 cm⁻¹ -1 The absorption peak at 709 cm⁻¹ is due to the CH bond of the benzene ring in pyrogallic acid. -1 765cm -1Out-of-plane bending vibration at [specific location], and the superimposed peak of the stretching vibration of the melamine triazine ring skeleton at 811 cm -1 confirmed the coexistence of the two cyclic structures in Ga-IIP-PFCOF; XPS analysis of the gallium ion-imprinted covalent organic framework adsorbent Ga-IIP-PFCOF (see Figure 4 ). In the spectrum of the gallium ion-imprinted covalent organic framework adsorbent Ga-IIP-PFCOF, the peaks mainly come from C1s, N1s, and O1s; Adsorption performance test of the gallium ion-imprinted covalent organic framework adsorbent Ga-IIP-PFCOF for Ga(Ⅲ): Prepare Ga(Ⅲ) solutions with different initial concentrations (50 - 400 mg / L), adjust the pH to 10 < pH < 11 with HCl or NaOH. Add 30 mL of the Ga(Ⅲ) solution to several 15 mL centrifuge tubes, and respectively add 10 mg of the gallium ion-imprinted melamine-pyrogallic acid covalent organic framework adsorbent Ga-IIP-PFCOF prepared in this example. Oscillate in a constant temperature oscillator at 298 K, 308 K, and 318 K at 200 rpm until adsorption equilibrium (48 hours); in addition, according to different times (5 min - 1380 min), operate a set of kinetics at 298 K according to the above steps, sample and filter, measure the residual Ga(Ⅲ) concentration in the filtrate, and calculate the adsorption capacity; the results show that its maximum adsorption capacity reaches 525.75 mg / g, and the adsorption behavior conforms to the R-P isothermal model and the pseudo-second-order kinetic model, indicating that the gallium ion-imprinted melamine-pyrogallic acid covalent organic framework adsorbent Ga-IIP-PFCOF is mainly monolayer chemical adsorption; Selective adsorption performance of the gallium ion-imprinted covalent organic framework adsorbent Ga-IIP-PFCOF for Ga(Ⅲ) in the presence of competing ions: At a temperature of 298 K, add the gallium ion-imprinted melamine-pyrogallic acid covalent organic framework adsorbent Ga-IIP-PFCOF (40 mg) to the simulated adsorption solution (Ga(Ⅲ) 93.33 mg / L, As(Ⅲ) 303.77 g / L, V(Ⅲ) 95.22 mg / L) respectively, oscillate at an oscillation speed of 200 rpm for 24 h, centrifuge to separate the adsorbent and obtain the supernatant, and measure the residual concentration of the remaining metal ions in the supernatant by ICP-OES; the removal rate of Ga(Ⅲ) in the simulated adsorption solution is 29.52%, the removal rate of As(Ⅲ) is 1%, and the removal rate of V(Ⅲ) is 3%; thus, it can be seen that the gallium ion-imprinted melamine-pyrogallic acid covalent organic framework adsorbent Ga-IIP-PFCOF has good selectivity for Ga(Ⅲ); Desorption and recycling performance of the gallium ion-imprinted covalent organic framework adsorbent Ga-IIP-PFCOF: At room temperature, 40 mg of gallium ion-imprinted melamine-pyrogallic acid covalent organic framework adsorbent Ga-IIP-PFCOF and Ga(III) solutions (pH=3, 40 mL, 92.3647 mg / L) were added to 50 mL centrifuge tubes and shaken at 200 rpm for 24 h. The gallium ion-imprinted melamine-pyrogallic acid covalent organic framework adsorbent Ga-IIP-PFCOF was separated by centrifugation, and the supernatant was obtained. ICP-OES analysis showed that the remaining Ga(III) concentration in the supernatant was 0.0906 mg / L, and the adsorption capacity of Ga(III) by the gallium ion-imprinted melamine-pyrogallic acid covalent organic framework adsorbent Ga-IIP-PFCOF was 92.2741 mg / g, with an adsorption efficiency of 99.9%. After adsorption of Ga(III), the gallium ion-imprinted melamine-pyrogallic acid covalent organic framework adsorbent Ga-IIP-PFCOF was eluted with potassium thiocyanate desorption solution (40 mL) for 24 h. After centrifugation, the gallium ion-imprinted melamine-pyrogallic acid covalent organic framework adsorbent Ga-IIP-PFCOF was washed with distilled water until the solution was neutral, thus completing the regeneration of the gallium ion-imprinted melamine-pyrogallic acid covalent organic framework adsorbent Ga-IIP-PFCOF. After 5 repeatability experiments, the adsorption efficiency of Ga(III) in the 5th adsorption was still above 99%. In addition, the gallium ion-imprinted melamine-pyrogallic acid covalent organic framework adsorbent Ga-IIP-PFCOF after adsorption of Ga(III) was analyzed by XPS, SEM, and EDS (see [link to analysis]). Figures 4-6 ),from Figure 4 Characteristic peaks of Ga were found in the XPS plot. Figure 5 The SEM images show that Ga is uniformly distributed on the gallium ion-imprinted melamine-pyrogallic acid covalent organic framework adsorbent Ga-IIP-PFCOF. Figure 6 EDS analysis showed that the Ga content reached 6.72%.

[0020] Example 2: A method for preparing a gallium ion-imprinted covalent organic framework adsorbent, the specific steps of which are as follows: (1) Gallium chloride and pyrogallic acid (the molar ratio of gallium chloride to pyrogallic acid is 1:3) were added to a methanol-deionized water mixed solvent (the volume ratio of methanol to deionized water is 2.5:1) and stirred to dissolve to obtain a mixed solution (the molar concentration of gallium chloride in the mixed solution is 0.2 mol / L). The pH value of the mixed solution was adjusted to 2.8, and the pre-assembly reaction was carried out at a temperature of 45℃ for 1.5 h to obtain a template-ligand complex solution. (2)Completely dissolve melamine in N,N-dimethylformamide solvent to obtain a melamine solution with a concentration of 0.8 mol / L. At a temperature of 25 °C, drop the melamine solution into the template-ligand complex solution at a rate of 0.2 ml / min (the volume ratio of the melamine solution to the template-ligand complex solution is 1.5:5), and then drop formaldehyde at a rate of 1.5 ml / min (the molar ratio of melamine to formaldehyde is 3:20). Raise the temperature to 60 °C and carry out a polycondensation polymerization reaction for 20 h to obtain a polymer solution system; (3)Wash the polymer solution system with a mixed solution of N,N-dimethylformamide-methanol (the volume ratio of N,N-dimethylformamide to methanol is 1:0.5), then wash it with a sulfuric acid solution with a concentration of 0.8 mol / L until no Ga ions can be detected in the eluate, and then wash it with deionized water more than 3 times, dry and grind it to obtain a gallium ion-imprinted melamine-pyrogallic acid covalent organic framework adsorbent, that is, a gallium ion-imprinted covalent organic framework adsorbent Ga-IIP-PFCOF; Adsorption performance test of gallium ion-imprinted covalent organic framework adsorbent Ga-IIP-PFCOF for Ga(Ⅲ): Prepare Ga(Ⅲ) solutions with different initial concentrations (50 - 400 mg / L), adjust 10 < pH < 11 with HCl or NaOH. Add 30 mL of Ga(Ⅲ) solution to several 15 mL centrifuge tubes, and respectively add 10 mg of the gallium ion-imprinted melamine-pyrogallic acid covalent organic framework adsorbent Ga-IIP-PFCOF prepared in this example. Oscillate in a constant temperature oscillator at 298 K, 308 K and 318 K at 200 rpm until adsorption equilibrium (48 hours); in addition, according to different times (5 min - 1380 min), operate a set of kinetics at 298 K according to the above steps, take samples and filter, measure the residual Ga(Ⅲ) concentration in the filtrate, and calculate the adsorption capacity; the results show that its maximum adsorption capacity reaches 460.85 mg / g, and the adsorption behavior conforms to the R-P isothermal model and the pseudo-second-order kinetic model, indicating that the gallium ion-imprinted melamine-pyrogallic acid covalent organic framework adsorbent Ga-IIP-PFCOF is mainly monolayer chemical adsorption; Selective adsorption performance of gallium ion-imprinted covalent organic framework adsorbent Ga-IIP-PFCOF for Ga(Ⅲ) in the presence of competitive ions: At 298 K, 40 mg of gallium ion-imprinted melamine-pyrogallic acid covalent organic framework adsorbent Ga-IIP-PFCOF was added to simulated adsorption solutions (Ga(III) 93.33 mg / L, As(III) 303.77 g / L, V(III) 95.22 mg / L). The adsorbent was centrifuged at 200 rpm for 24 h, and the supernatant was obtained. The residual concentration of metal ions in the supernatant was determined by ICP-OES. The removal rates of Ga(III) in the simulated adsorption solutions were 25.42%, As(III) 0.08%, and V(III) 2.65%. This shows that the gallium ion-imprinted melamine-pyrogallic acid covalent organic framework adsorbent Ga-IIP-PFCOF has good selectivity for Ga(III). Desorption and cycling performance of Ga-IIP-PFCOF, a gallium ion-imprinted covalent organic framework adsorbent: At room temperature, 40 mg of gallium ion-imprinted melamine-pyrogallic acid covalent organic framework adsorbent Ga-IIP-PFCOF and Ga(III) solutions (pH=3, 40 mL, 92.3647 mg / L) were added to 50 mL centrifuge tubes and shaken at 200 rpm for 24 h. The gallium ion-imprinted melamine-pyrogallic acid covalent organic framework adsorbent Ga-IIP-PFCOF was separated by centrifugation, and the supernatant was obtained. The residual Ga(III) concentration in the supernatant was determined to be 4.1926 mg / L by ICP-OES. The gallium ion-imprinted melamine-pyrogallic acid covalent organic framework adsorbent Ga-IIP-PFCOF effectively adsorbs Ga(III)... The adsorption capacity was 88.1721 mg / g, and the adsorption efficiency was 95.46%. After adsorbing Ga(III), the gallium ion-imprinted melamine-pyrogallic acid covalent organic framework adsorbent Ga-IIP-PFCOF was eluted with potassium thiocyanate desorption solution (40 mL) for 24 h. After centrifugation, the gallium ion-imprinted melamine-pyrogallic acid covalent organic framework adsorbent Ga-IIP-PFCOF was washed with distilled water until the solution was neutral to complete the regeneration of the gallium ion-imprinted melamine-pyrogallic acid covalent organic framework adsorbent Ga-IIP-PFCOF. After 5 repeatability experiments, the adsorption efficiency of Ga(III) in the 5th adsorption was still above 90%.

[0021] Example 3: A method for preparing a gallium ion-imprinted covalent organic framework adsorbent, the specific steps of which are as follows: (1) Gallium chloride and pyrogallic acid (the molar ratio of gallium chloride to pyrogallic acid is 1:4) were added to a methanol-deionized water mixed solvent (the volume ratio of methanol to deionized water is 3.5:1) and stirred to dissolve to obtain a mixed solution (the concentration of gallium chloride in the mixed solution is 0.4 mol / L). The pH value of the mixed solution was adjusted to 3.2, and pre-assembly reaction was carried out at 55 °C for 2.5 h to obtain a template-ligand complex solution; (2) Melamine was completely dissolved in N,N-dimethylformamide solvent to obtain a melamine solution with a concentration of 1 mol / L. At 35 °C, the melamine solution was dropped into the template-ligand complex solution at a rate of 0.4 ml / min (the volume ratio of the melamine solution to the template-ligand complex solution is 2.5:5), and then formaldehyde was dropped in at a rate of 1.7 ml / min (the molar ratio of melamine to formaldehyde is 3:28). The temperature was raised to 80 °C and polycondensation polymerization reaction was carried out for 28 h to obtain a polymer solution system; (3) The polymer solution system was washed with a N,N-dimethylformamide-methanol mixed solution (the volume ratio of N,N-dimethylformamide to methanol is 1:1.5), then washed with a sulfuric acid solution with a concentration of 1.2 mol / L until no Ga ions could be detected in the eluate, and then washed with deionized water more than 3 times, dried and ground to obtain a gallium ion-imprinted melamine-pyrogallic acid covalent organic framework adsorbent, that is, a gallium ion-imprinted covalent organic framework adsorbent Ga-IIP-PFCOF; Adsorption performance test of gallium ion-imprinted covalent organic framework adsorbent Ga-IIP-PFCOF for Ga(Ⅲ): Ga(Ⅲ) solutions with different initial concentrations (50 - 400 mg / L) were prepared, and 10 < pH < 11 was adjusted with HCl or NaOH. 30 mL of Ga(Ⅲ) solution was added to several 15 mL centrifuge tubes, and 10 mg of the gallium ion-imprinted melamine-pyrogallic acid covalent organic framework adsorbent Ga-IIP-PFCOF prepared in this example was added respectively. It was oscillated at 200 rpm in a constant temperature oscillator at 298 K, 308 K and 318 K until adsorption equilibrium (48 hours); in addition, according to different times (5 min - 1380 min), a set of kinetics was operated at 298 K according to the above steps, sampled and filtered, the residual Ga(Ⅲ) concentration in the filtrate was measured, and the adsorption capacity was calculated; the results showed that its maximum adsorption capacity reached 496.15 mg / g, and the adsorption behavior conforms to the R-P isothermal model and the pseudo-second-order kinetic model, indicating that the gallium ion-imprinted melamine-pyrogallic acid covalent organic framework adsorbent Ga-IIP-PFCOF is mainly monolayer chemical adsorption; Selective adsorption performance of gallium ion-imprinted covalent organic framework adsorbent Ga-IIP-PFCOF for Ga(Ⅲ) in the presence of competitive ions: At 298 K, 40 mg of gallium ion-imprinted melamine-pyrogallic acid covalent organic framework adsorbent Ga-IIP-PFCOF was added to simulated adsorption solutions (Ga(III) 93.33 mg / L, As(III) 303.77 g / L, V(III) 95.22 mg / L). The adsorbent was centrifuged at 200 rpm for 24 h, and the supernatant was obtained. The residual concentration of metal ions in the supernatant was determined by ICP-OES. The removal rates of Ga(III) in the simulated adsorption solutions were 25.63%, As(III) 0.72%, and V(III) 1.83%. This shows that the gallium ion-imprinted melamine-pyrogallic acid covalent organic framework adsorbent Ga-IIP-PFCOF has good selectivity for Ga(III). Desorption and cycling performance of Ga-IIP-PFCOF, a gallium ion-imprinted covalent organic framework adsorbent: At room temperature, 40 mg of gallium ion-imprinted melamine-pyrogallic acid covalent organic framework adsorbent Ga-IIP-PFCOF and Ga(III) solutions (pH=3, 40 mL, 92.3647 mg / L) were added to 50 mL centrifuge tubes and shaken at 200 rpm for 24 h. The gallium ion-imprinted melamine-pyrogallic acid covalent organic framework adsorbent Ga-IIP-PFCOF was separated by centrifugation, and the supernatant was obtained. The residual Ga(III) concentration in the supernatant was determined to be 9.2461 mg / L by ICP-OES. The gallium ion-imprinted melamine-pyrogallic acid covalent organic framework adsorbent Ga-IIP-PFCOF effectively adsorbs Ga(III)... The adsorption capacity was 83.1186 mg / g, and the adsorption efficiency was 89.99%. After adsorbing Ga(III), the gallium ion-imprinted melamine-pyrogallic acid covalent organic framework adsorbent Ga-IIP-PFCOF was eluted with potassium thiocyanate desorption solution (40 mL) for 24 h. After centrifugation, the gallium ion-imprinted melamine-pyrogallic acid covalent organic framework adsorbent Ga-IIP-PFCOF was washed with distilled water until the solution was neutral to complete the regeneration of the gallium ion-imprinted melamine-pyrogallic acid covalent organic framework adsorbent Ga-IIP-PFCOF. After 5 repeatability experiments, the adsorption efficiency of Ga(III) in the 5th adsorption was still above 85%.

[0022] The specific embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A gallium ion-imprinted covalent organic framework adsorbent, characterized in that: Using Ga(III) as a template ion to form a template-ligand complex with pyrogallic acid, and using the template-ligand complex as a structure directing agent, melamine undergoes condensation polymerization in the presence of formaldehyde. This results in the in-situ construction of a melamine-pyrogallic acid covalent organic framework (Ga-IIP-PFCOF) with a regular pore structure and rich in gallium ion-specific recognition sites, denoted as Ga-IIP-PFCOF. Its structural formula is as follows: .

2. The method for preparing the gallium ion-imprinted covalent organic framework adsorbent according to claim 1, characterized in that, The specific steps are as follows: (1) Add gallium chloride and pyrogallol to a methanol-deionized water mixed solvent and stir to dissolve to obtain a mixed solution. Adjust the pH of the mixed solution to 2.8~3.2 and pre-assemble at 45~55℃ for 1.5~2.5h to obtain a template-ligand complex solution. (2) Melamine is completely dissolved in N,N-dimethylformamide solvent to obtain melamine solution. At a temperature of 25~35℃, the melamine solution is added dropwise to the template-ligand complex solution, and then formaldehyde is added dropwise. The temperature is raised to 60~80℃ and polycondensation reaction is carried out for 20~28h to obtain polymer solution system. (3) The polymer solution system is washed with N,N-dimethylformamide-methanol mixture, then washed with sulfuric acid solution until no Ga ions are detected in the eluent, and then washed with deionized water more than 3 times, dried and ground to obtain gallium ion imprinted covalent organic framework adsorbent.

3. The method for preparing the gallium ion-imprinted covalent organic framework adsorbent according to claim 2, characterized in that: Step (1) The molar ratio of gallium chloride to pyrogallol is 1:2~4.

4. The method for preparing the gallium ion-imprinted covalent organic framework adsorbent according to claim 2, characterized in that: In step (1), the volume ratio of methanol to deionized water in the methanol-deionized water mixed solvent is 2.5~3.5:1, and the molar concentration of gallium chloride in the mixed solution is 0.2~0.4mol / L.

5. The method for preparing the gallium ion-imprinted covalent organic framework adsorbent according to claim 2, characterized in that: Step (2) The molar concentration of the melamine solution is 0.8~1mol / L, the volume ratio of the melamine solution to the template-ligand complex solution is 1.5~2.5:5, and the dropping rate of the melamine solution is 0.2~0.4ml / min.

6. The method for preparing the gallium ion-imprinted covalent organic framework adsorbent according to claim 5, characterized in that: Step (2) The molar ratio of melamine to formaldehyde is 2~4:20~28, and the dropping rate of formaldehyde is 1.5~1.7 ml / min.

7. The method for preparing the gallium ion-imprinted covalent organic framework adsorbent according to claim 2, characterized in that: In step (3), the volume ratio of N,N-dimethylformamide to methanol in the N,N-dimethylformamide-methanol mixture is 1:0.5~1.

5.

8. The method for preparing the gallium ion-imprinted covalent organic framework adsorbent according to claim 2, characterized in that: Step (3) The concentration of sulfuric acid solution is 0.8~1.2 mol / L.

9. The application of the gallium ion-imprinted covalent organic framework adsorbent of claim 1 in the selective adsorption of Ga(III) ions in gallium-containing wastewater.

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