Multi-site COF-COF adsorbent as well as preparation method and application thereof

Abstract

The invention relates to a multi-site COF-COF adsorbent as well as a preparation method and application thereof, and belongs to the technical field of composite adsorption materials. According to the invention, pyrogallol and diaminomaleonitrile are used to construct a primary COF skeleton, the primary COF skeleton is expanded by 2, 5-dithiourea to prepare the multi-site COF-COF adsorbent DPDA, and the structural formula of the multi-site COF-COF adsorbent DPDA is shown in the specification; the multi-site COF-COF adsorbent disclosed by the invention can be used for efficiently and selectively adsorbing gallium ions from a solution, and the multi-site COF-COF adsorbent has relatively high cyclic regeneration capacity.

Description

Technical Field

[0001] This invention relates to a multi-site COF-COF adsorbent, its preparation method and application, belonging to the field of composite adsorption material technology. Background Technology

[0002] Gallium is an important rare metal with an irreplaceable role in industries such as information technology, communications, electronic devices, and new energy. However, due to its low abundance and extremely dispersed distribution in the Earth's crust, gallium rarely exists as an independent mineral and is mostly found as an associated mineral in ores such as aluminum and zinc, making gallium extraction difficult and costly.

[0003] Gallium enrichment and extraction methods mainly include amalgamation, stepwise precipitation, solvent extraction, and adsorption. Among these, adsorption has become an important technical route for gallium extraction due to its advantages such as short process flow, high separation selectivity, and high recovery efficiency. However, the performance of existing adsorption materials still has shortcomings. Traditional adsorbents such as activated carbon and ion exchange resins generally suffer from poor chemical stability, poor selectivity for gallium ions, and limited adsorption capacity, making it difficult to meet the requirements for efficient and stable gallium extraction in complex systems. Especially in industrial applications, when adsorbents adsorb gallium, vanadium adsorption is often accompanied by significant vanadium adsorption, which is difficult to elute, leading to vanadium accumulation in the adsorbent and affecting the adsorption capacity and recycling of gallium.

[0004] Covalent organic frameworks (COFs) possess high specific surface area and designability, making them suitable for metal ion adsorption processes. However, most COFs rely on Schiff base bonding, which is prone to breakage under acidic or alkaline conditions; they also suffer from insufficient framework strength and stability, making them unsuitable for long-term use in complex environments. Many COFs use only two monomers linked in a single repeating manner, a synthetic strategy that fails to fully utilize the designability advantages of COFs, limiting the complexity and flexibility of the frameworks. Furthermore, while existing COFs possess certain adsorption capacities, their selectivity for gallium ions is insufficient, especially in complex solutions containing competing metal ions such as vanadium, where efficient separation is difficult to achieve.

[0005] Therefore, although existing gallium adsorbents have been improved in terms of long-term and selective gallium adsorption, they still have problems such as low gallium adsorption capacity and poor reusability, and have not solved the major problem of vanadium co-adsorption in industrial production. Summary of the Invention

[0006] To address the problems of low gallium adsorption capacity, poor reusability, and unavoidable vanadium co-adsorption in existing adsorbents, as well as the defects of unstable bonding, insufficient framework extension, and poor structural stability in existing COF adsorbents, this invention provides a method for preparing a multi-site COF-COF adsorbent. The method involves constructing a primary COF framework using pyrogallol and diaminomaleitrile, followed by framework extension with 2,5-dithiourea to obtain the adsorbent DPDA (multi-site COF-COF adsorbent). The multi-site COF-COF comprises a primary COF framework formed by a polyhydroxy polyphenol matrix linked by amino groups, further constructed through -C(=S)-NH- linkages, achieving multi-directional extension and expansion of the framework. It possesses various coordination functional units such as -OH, -NH / -NH2, and -C(=S)-NH-, enabling the construction of a heteroatom network containing oxygen, nitrogen, and sulfur coordination centers. Based on this unique structure, the multi-site COF-COF can achieve efficient adsorption of gallium ions in complex solutions, exhibiting high gallium ion selectivity and adsorption capacity, and can be recycled multiple times.

[0007] A multi-site COF-COF adsorbent is prepared by constructing a primary COF framework using pyrogallol and diaminomaleitrile, followed by modification and expansion of the primary COF framework with 2,5-dithiourea. The structural formula of the multi-site COF-COF adsorbent is as follows: .

[0008] The preparation method of the multi-site COF-COF adsorbent includes the following specific steps: (1) Add pyrogallol and diaminomaleitrile to ethanol, stir to dissolve and obtain solution A. Reflux solution A at 60-80℃ for 67-77 h, cool to room temperature, separate solid and liquid, wash the solid with ethanol, and vacuum dry to obtain the primary COF skeleton, denoted as PDA; the synthesis steps are as follows: ; (2) The primary COF framework and 2,5-dithiourea were added to ethanol and stirred until homogeneous to obtain mixture B. Mixture B was refluxed at 50-70℃ for 1-3 h, and then SnCl4 was added and refluxed for another 2-4 h. After cooling to room temperature, the solid and liquid were separated. The solid was washed with ethanol and deionized water and dried under vacuum to obtain the multi-site COF-COF adsorbent, denoted as DPDA. The synthesis steps are as follows: .

[0009] Preferably, in step (1), the molar ratio of pyrogallol to diaminomaleitrile is 2:2~4, and the concentration of pyrogallol in solution A is 0.15~0.25mol / L.

[0010] Preferably, in step (2), the molar ratio of 2,5-dithiourea to the primary COF skeleton is 1:1~3, and the concentration of 2,5-dithiourea in mixture B is 0.2~0.4 mol / L.

[0011] Preferably, the amount of SnCl4 added in step (2) is 0.03~0.06 mol / L.

[0012] The multi-site COF-COF adsorbent described in this invention can be used to selectively capture gallium ions in solution.

[0013] The mechanism of efficient gallium ion adsorption by multi-site COF-COF adsorbents: The multi-site COF-COF adsorbent DPDA introduces a large number of nitrogen, sulfur, and oxygen functional groups, providing sufficient binding sites for gallium ion adsorption; the hydroxyl and amino groups in the DPDA adsorbent successfully capture gallium ions, and electrostatic attraction and chelation occur between them; the distribution coefficient of the multi-site DPDA adsorbent for gallium ions is 3.46 L / g, which is significantly higher than that for other metal ions, indicating that DPDA has selective adsorption capacity for gallium ions; the Ga-N and Ga-O can be broken by using a combination solution of thiourea and hydrochloric acid, enabling the DPDA adsorbent to be recycled.

[0014] The beneficial effects of this invention are: (1) The multi-site COF-COF adsorbent of the present invention maintains the covalent organic framework structure and has hydroxyl and amino functional groups; it can efficiently and selectively adsorb gallium ions from gallium-containing solutions, and the multi-site COF-COF adsorbent has a strong recycling capacity. (2) The preparation method of the multi-site COF-COF adsorbent of the present invention is simple, flexible and low cost; and it is non-toxic, high-performance, easy to separate, has good selectivity and recycling ability, and will not cause secondary pollution to the environment. Attached Figure Description

[0015] Figure 1 A schematic diagram of the three-dimensional structure of the primary COF framework PDA of the multi-site COF-COF adsorbent; Figure 2 This is a schematic diagram of the three-dimensional structure of a multi-site COF-COF adsorbent. Figure 3 This is a SEM image of the multi-site COF-COF adsorbent from Example 1; Figure 4 EDS diagram of the multi-site COF-COF adsorbent in Example 1; Figure 5 The image shows the FT-IR spectrum of the multi-site COF-COF adsorbent in Example 1. Figure 6The effect of coexisting ions on the adsorption of gallium ions by the multi-site COF-COF adsorbent prepared in Example 1; Figure 7 This is a SEM image of gallium ions adsorbed by the multi-site COF-COF adsorbent in Example 1. Figure 8 The image shows the XPS image of gallium ions after adsorption by the multi-site COF-COF adsorbent in Example 1. Detailed Implementation

[0016] 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.

[0017] In this invention, a multi-site COF-COF adsorbent is constructed using pyrogallol and diaminomaleitrile to form a primary COF framework (see...). Figure 1 Multi-site COF-COF adsorbents were prepared by expanding the primary COF framework with 2,5-dithiourea (see...). Figure 2 Its structural formula is: ; The nitrogen-oxygen co-doped COF adsorbent maintains a covalent organic framework structure and has hydroxyl and amino functional groups.

[0018] Example 1: A method for preparing a multi-site COF-COF adsorbent, the specific steps of which are as follows: (1) Add pyrogallol and diaminomaleitrile to ethanol, stir to dissolve and obtain solution A. Reflux solution A at 70°C for 72 h, cool to room temperature, separate the solid and liquid, wash the solid with ethanol, and vacuum dry to obtain the primary COF framework, denoted as PDA (see [link to product description]). Figure 1 The molar ratio of pyrogallol to diaminomaleitrile is 2:3, and the concentration of pyrogallol in solution A is 0.2 mol / L; the synthesis steps are as follows: ; (2) The primary COF framework and 2,5-dithiourea were added to ethanol and stirred until homogeneous to obtain mixture B. Mixture B was refluxed at 60°C for 1.5 h, and then SnCl4 was added and refluxed for another 3 h. After cooling to room temperature, the solid and liquid were separated. The solid was washed with ethanol and deionized water and dried under vacuum to obtain the multi-site COF-COF adsorbent, denoted as DPDA. In step (2), the molar ratio of 2,5-dithiourea to the primary COF framework was 1:2, and the concentration of 2,5-dithiourea in mixture B was 0.3 mol / L. The amount of SnCl4 added was 0.05 mol / L. The synthesis steps are as follows: ; SEM, EDS, and FT-IR images of the multi-site COF-COF adsorbent DPDA in this embodiment are shown below. Figures 3-5 As shown in the figure, the multi-site COF-COF adsorbent is mainly composed of C, N, O, and S, with weight percentages of 52.08%, 27.51%, 14.96%, and 5.45%, respectively. In the FT-IR spectrum, the stretching vibration peaks of OH and NH appear in the range of 3662.1–3319.3 cm⁻¹. -1 Within this range, it indicates that -OH, -NH and other groups are retained; 1508.6 and 1466.3 cm -1 The presence of NC(=S)-N signal indicates the formation of the expected amidine group structure. The appearance of the above groups confirms the successful synthesis of the multi-site COF-COF adsorbent. The selective adsorption performance of the multi-site COF-COF adsorbent DPDA for Ga(III) in this embodiment was determined: At room temperature, DPDA (40 mg) and the adsorption solution (pH = 9, 40 mL) were added to a 50 mL centrifuge tube. The adsorption solution contained Ga(III) 65.31 mg / L, As(V) 130.59 mg / L, Ca(II) 51.48 mg / L, V(V) 51.54 mg / L, and Ge(IV) 40.34 mg / L. The tube was shaken at 230 rpm for 24 h. The adsorbent was separated by centrifugation, and the supernatant was obtained. The residual concentration of the remaining metal ions in the supernatant was determined by ICP-OES. The effect of coexisting ions on the adsorption of gallium ions by the multi-site COF-COF adsorbent prepared in this embodiment is shown in the figure. Figure 6 The adsorption rates were calculated to be 77.60% for Ga(III), 6.57% for As(V), 14.84% for Ca(II), 15.21% for V(V), and 8.21% for Ge(IV). This shows that the multi-site COF-COF adsorbent DPDA in this embodiment has strong selectivity for Ga(III). This embodiment measures the adsorption performance of the multi-site COF-COF adsorbent DPDA on Ga(III) alone: At room temperature, DPDA (10 mg) and Ga(III) solution (pH = 9, 10 mL, 51.43 mg / L) were added to a 15 mL centrifuge tube and shaken at 230 rpm for 24 h; the adsorbent was separated by centrifugation and the supernatant was obtained. SEM, EDS, and XPS analyses were performed on the multi-site COF-COF adsorbent DPDA after gallium ion adsorption. Figures 7-8It was found that Ga was uniformly distributed on DPDA; the Ga(3d) peak appeared in the XPS spectrum after Ga ions were adsorbed on DPDA, confirming that the multi-site COF-COF adsorbent successfully adsorbed gallium ions. The residual gallium ion concentration in the supernatant was determined to be 1.85 mg / L by ICP-OES. The adsorption capacity of the multi-site COF-COF adsorbent for Ga(III) was 49.58 mg / g, with an adsorption efficiency of 96.40%. The adsorbent was eluted with a desorption solution (40 mL) composed of 1% concentrated hydrochloric acid and 10% thiourea for 24 h. After centrifugation, the adsorbent was washed with distilled water until the solution was neutral to complete the regeneration of the adsorbent DPDA. After 5 repeatable experiments, the adsorption rate of Ga(III) in the fifth adsorption was 71.59%.

[0019] Example 2: A method for preparing a multi-site COF-COF adsorbent, the specific steps of which are as follows: (1) Add pyrogallol and diaminomaleitrile to ethanol, stir to dissolve and obtain solution A. Refrigerate solution A at 65°C for 75 h, cool to room temperature, separate solid and liquid, wash the solid with ethanol and dry under vacuum to obtain the primary COF framework, denoted as PDA (see Figure 1 The molar ratio of pyrogallol to diaminomaleitrile is 2:3.5, and the concentration of pyrogallol in solution A is 0.15 mol / L. (2) The primary COF framework and 2,5-dithiourea were added to ethanol and stirred until homogeneous to obtain mixture B. Mixture B was refluxed at 55°C for 2 hours, and then SnCl4 was added and refluxed for another 4 hours. After cooling to room temperature, the solid and liquid were separated. The solid was washed with ethanol and deionized water and dried under vacuum to obtain a multi-site COF-COF adsorbent, denoted as DPDA. In step (2), the molar ratio of 2,5-dithiourea to the primary COF framework was 1:2.5, the concentration of 2,5-dithiourea in mixture B was 0.25 mol / L, and the amount of SnCl4 added was 0.04 mol / L. The selective adsorption performance of the multi-site COF-COF adsorbent DPDA for Ga(III) in this embodiment was determined: At room temperature, DPDA (40 mg) and the adsorption solution (pH = 9, 40 mL) were added to a 50 mL centrifuge tube. The adsorption solution contained Ga(III) 70.82 mg / L, As(V) 74.22 mg / L, Ca(II) 51.18 mg / L, V(V) 61.89 mg / L, and Ge(IV) 59.63 mg / L. The tube was shaken at 230 rpm for 24 h. The adsorbent was separated by centrifugation, and the supernatant was obtained. The residual concentration of the remaining metal ions in the supernatant was determined by ICP-OES. The effect of coexisting ions on the adsorption of gallium ions by the multi-site COF-COF adsorbent prepared in this embodiment: The calculated adsorption rates were 82.32% for Ga(III), 5.26% for As(V), 9.68% for Ca(II), 12.89% for V(V), and 11.76% for Ge(IV); This shows that the multi-site COF-COF adsorbent DPDA produced in this embodiment has strong selectivity for Ga(III). This embodiment measures the adsorption performance of the multi-site COF-COF adsorbent DPDA on Ga(III) alone: At room temperature, DPDA (10 mg) and Ga(III) solution (pH = 9, 10 mL, 60.21 mg / L) were added to a 15 mL centrifuge tube and shaken at 230 rpm for 24 h; the adsorbent was separated by centrifugation and the supernatant was obtained. The residual gallium ion concentration in the supernatant was determined to be 3.61 mg / L by ICP-OES. The adsorption capacity of the multi-site COF-COF adsorbent for Ga(III) was 54.60 mg / g, with an adsorption efficiency of 94.00%. The adsorbent was eluted with a desorption solution (40 mL) composed of 1% concentrated hydrochloric acid and 10% thiourea for 24 h. After centrifugation, the adsorbent was washed with distilled water until the solution was neutral to complete the regeneration of the adsorbent DPDA. After 5 repeatability experiments, the adsorption rate of Ga(III) in the fifth adsorption was 73.85%.

[0020] Example 3: A method for preparing a multi-site COF-COF adsorbent, the specific steps of which are as follows: (1) Add pyrogallol and diaminomaleitrile to ethanol, stir to dissolve and obtain solution A. Refrigerate solution A at 75°C for 70 h, cool to room temperature, separate solid and liquid, wash the solid with ethanol and dry under vacuum to obtain the primary COF framework, denoted as PDA (see Figure 1 The molar ratio of pyrogallol to diaminomaleitrile is 2:2.8, and the concentration of pyrogallol in solution A is 0.25 mol / L. (2) The primary COF framework and 2,5-dithiourea were added to ethanol and stirred until homogeneous to obtain mixture B. Mixture B was refluxed at 65°C for 1.2 h, and then SnCl4 was added and refluxed for another 3.5 h. After cooling to room temperature, the solid and liquid were separated. The solid was washed with ethanol and deionized water and dried under vacuum to obtain a multi-site COF-COF adsorbent, denoted as DPDA. In step (2), the molar ratio of 2,5-dithiourea to the primary COF framework was 1:1.8, the concentration of 2,5-dithiourea in mixture B was 0.35 mol / L, and the amount of SnCl4 added was 0.06 mol / L. The selective adsorption performance of the multi-site COF-COF adsorbent DPDA for Ga(III) in this embodiment was determined: At room temperature, DPDA (40 mg) and the adsorption solution (pH = 9, 40 mL) were added to a 50 mL centrifuge tube. The adsorption solution contained Ga(III) 59.53 mg / L, As(V) 71.05 mg / L, Ca(II) 45.61 mg / L, V(V) 52.89 mg / L, and Ge(IV) 46.91 mg / L. The tube was shaken at 230 rpm for 24 h. The adsorbent was separated by centrifugation, and the supernatant was obtained. The residual concentration of the remaining metal ions in the supernatant was determined by ICP-OES. The effect of coexisting ions on the adsorption of gallium ions by the multi-site COF-COF adsorbent prepared in this embodiment: The calculated adsorption rates were 78.33% for Ga(III), 5.93% for As(V), 12.91% for Ca(II), 16.02% for V(V), and 7.10% for Ge(IV); This shows that the multi-site COF-COF adsorbent DPDA produced in this embodiment has strong selectivity for Ga(III). This embodiment measures the adsorption performance of the multi-site COF-COF adsorbent DPDA on Ga(III) alone: At room temperature, DPDA (10 mg) and Ga(III) solution (pH = 9, 10 mL, 58.63 mg / L) were added to a 15 mL centrifuge tube and shaken at 230 rpm for 24 h; the adsorbent was separated by centrifugation and the supernatant was obtained. The residual gallium ion concentration in the supernatant was determined to be 3.61 mg / L by ICP-OES. The adsorption capacity of the multi-site COF-COF adsorbent for Ga(III) was 55.98 mg / g, with an adsorption efficiency of 95.48%. The adsorbent was eluted with a desorption solution (40 mL) composed of 1% concentrated hydrochloric acid and 10% thiourea for 24 h. After centrifugation, the adsorbent was washed with distilled water until the solution was neutral to complete the regeneration of the adsorbent DPDA. After 5 repeatable experiments, the adsorption rate of Ga(III) in the fifth adsorption was 70.40%.

[0021] 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 multi-site COF-COF adsorbent, characterized in that, A primary COF framework was constructed using pyrogallol and diaminomaleitrile. This primary COF framework was then modified with 2,5-dithiourea to prepare a multi-site COF-COF adsorbent, the structural formula of which is: 。 2. The method for preparing the multi-site COF-COF adsorbent according to claim 1, characterized in that, The specific steps are as follows: (1) Add pyrogallol and diaminomaleitrile to ethanol, stir to dissolve and obtain solution A. Reflux solution A at 60~80℃ for 67~77h, cool to room temperature, separate solid and liquid, wash the solid with ethanol and dry under vacuum to obtain the primary COF framework. (2) The primary COF framework and 2,5-dithiourea were added to ethanol and stirred until homogeneous to obtain mixture B. Mixture B was refluxed at 50~70℃ for 1~3h, and then SnCl4 was added to continue reflux for 2~4h. After cooling to room temperature, solid and liquid were separated. The solid was washed with ethanol and deionized water and dried under vacuum to obtain multi-site COF-COF adsorbent.

3. The method for preparing the multi-site COF-COF adsorbent according to claim 2, characterized in that: Step (1) The molar ratio of pyrogallol to diaminomaleitrile is 2:2~4, and the concentration of pyrogallol in solution A is 0.15~0.25mol / L.

4. The method for preparing the multi-site COF-COF adsorbent according to claim 2, characterized in that: In step (2), the molar ratio of 2,5-dithiourea to the primary COF skeleton is 1:1~3, and the concentration of 2,5-dithiourea in mixture B is 0.2~0.4 mol / L.

5. The method for preparing the multi-site COF-COF adsorbent according to claim 2 or 4, characterized in that: In step (2), the amount of SnCl4 added is 0.03~0.06 mol / L.

6. The application of the multi-site COF-COF adsorbent of claim 1 in the selective capture of gallium ions in solution.

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