Thiourea-bithiophene bifunctional zirconium-based MOF adsorbent as well as preparation method and application thereof

Abstract

The invention relates to a thiourea-bithiophene bifunctional zirconium-based MOF adsorbent as well as a preparation method and application thereof, and belongs to the technical field of environmental functional materials and water pollution treatment. According to the preparation method, 4-carboxyl phenyl thiourea and [2, 2-bithiophene]-5, 5-dicarboxaldehyde are taken as ligand raw materials, the ligand raw materials and zirconium tetrachloride are synthesized into the Zr-MOF adsorbent with thiourea-bithiophene bifunctional sites through a solvothermal method, the Zr-MOF adsorbent is recorded as Zr-THBD, and the structural formula of the Zr-THBD is shown in the specification. The thiourea-bithiophene bifunctional zirconium-based MOF adsorbent can be used for efficiently and selectively recovering gold ions (Au (III)) from acidic complex wastewater, and the adsorbent has excellent adsorption capacity and high cyclic regeneration capacity.

Description

Technical Field

[0001] This invention relates to a thiourea-bithiophene bifunctionalized zirconium-based MOF adsorbent, its preparation method and application, belonging to the field of environmental functional materials and water pollution control technology. Background Technology

[0002] Currently, the main methods for recovering Au(III) from wastewater include chemical precipitation, solvent extraction, electrolysis, membrane separation, and adsorption. Among these, adsorption is the most promising method due to its flexibility, low energy consumption, ease of achieving high selectivity, and resistance to interference. However, traditional adsorption materials (activated carbon, molecular sieves, functionalized resins, etc.) have many shortcomings. Metal-organic frameworks (MOFs), with their well-defined crystal structures, high specific surface areas, precisely controllable pore sizes, and customizable surface chemistry, have become ideal platforms for constructing high-performance adsorption sites. Specific recognition and capture of target metal ions can be achieved through "pore structure engineering" and "site engineering." However, existing MOF-based adsorbents still have key problems: ① The functional site design is singular, making it difficult to simultaneously achieve high adsorption capacity and excellent selectivity, especially in complex water bodies containing a large number of competing ions for AuCl4. - ① Insufficient selectivity; ② Most MOFs lack chemical stability in real wastewater environments such as strong acid and high salt, and are prone to structural degradation, which seriously limits their industrial applications. Summary of the Invention

[0003] To address the problems of low adsorption capacity, poor selectivity, insufficient stability, and poor cycling performance of existing Au(III) adsorbents, as well as the shortcomings of existing MOF-based adsorbents with single functional site design and easy degradation under strong acid conditions, this invention proposes a thiourea-bithiophene bifunctionalized zirconium-based MOF adsorbent, its preparation method, and its application. This is achieved through the rational design of ligands integrating the thiourea-bithiophene bifunctional units with Zr... 4+ A highly stable Zr-MOF adsorbent (Zr-THBD) was constructed to achieve efficient and selective adsorption of Au(III) in acidic wastewater. The thiourea group (-NH-CS-NH-) is a strong Lewis basic bidentate ligand, whose S and N atoms exhibit specific strong coordination and reducing abilities towards gold and its complexes. The bithiophene unit, as an electron-rich aromatic system, enhances ligand conjugation and chemical stability, and assists in gold species enrichment through sulfur-π interactions. Integrating these two elements into a bifunctional ligand, combined with highly stable Zr... 4+ Constructing MOF materials using cluster metal nodes can achieve site-synergistic enhancement effects while ensuring the structural integrity of the material in extreme chemical environments, providing a new approach to overcome the technical bottlenecks of existing MOF-based adsorbents.

[0004] A thiourea-bithiophene bifunctionalized zirconium-based MOF adsorbent, denoted as ZR-THBD, is a Zr-MOF adsorbent with thiourea-bithiophene bifunctional sites synthesized by a solvothermal method with 4-carboxyphenylthiourea and [2,2-bithiophene]-5,5-dicarboxaldehyde as ligands and zirconium tetrachloride. Its structural formula is as follows: .

[0005] The preparation method of the thiourea-bithiophene bifunctionalized zirconium-based MOF adsorbent includes the following specific steps: (1) 4-Carboxyphenylthiourea and [2,2-Bithiophene]-5,5-dicarboxaldehyde were dissolved in ethanol, and acetic acid was added as a catalyst. The mixture was reacted at a constant temperature of 70~80℃ with stirring for 18~24h to obtain a bifunctional ligand of thiourea-bithiophene. (2) The bifunctional ligand of zirconium tetrachloride and thiourea-bithiophene was dissolved in N,N-dimethylformamide, and commercially available hydrochloric acid was added. The mixture was ultrasonically mixed to obtain a mixed solution. The mixed solution was transferred to a high-pressure reactor and reacted at 130-140℃ with stirring for 10-12 hours. Solid-liquid separation was performed, and the solid was washed alternately with anhydrous ethanol and deionized water until the eluent was colorless. The solid was then vacuum dried and ground to obtain the Zr-MOF adsorbent Zr-THBD. The reaction process is as follows: .

[0006] Preferably, in step (1), the molar ratio of 4-carboxyphenylthiourea to [2,2-bithiophene]-5,5-dicarboxaldehyde is 1~2:1.

[0007] Preferably, the concentration of 4-carboxyphenylthiourea in the mixed solution of step (1) is 0.04~0.08 mol / L.

[0008] Preferably, the amount of acetic acid catalyst added in step (1) is 10~12 mL / L.

[0009] Preferably, the molar ratio of zirconium tetrachloride in step (2) to 4-carboxyphenylthiourea in step (1) is 1~2:2.5.

[0010] Preferably, the concentration of zirconium tetrachloride in the mixed solution in step (2) is 0.05~0.1mol / L, and the amount of commercially available hydrochloric acid added is 1.5~2mL / L.

[0011] Application of the thiourea-bithiophene bifunctionalized zirconium-based MOF adsorbent ZR-THBD in the selective adsorption of Au(III) in acidic complex wastewater.

[0012] The principle of selective adsorption of Au(III) by the thiourea-bithiophene bifunctionalized zirconium-based MOF adsorbent Zr-THBD: The adsorbent Zr-THBD integrates the N / S sites of thiourea and the S sites of bithiophene, providing sufficient cooperative binding sites for Au(III) adsorption; the material carries a positive charge on its surface within the pH range of 1 to 8, and can efficiently attract negatively charged AuCl4 in the solution through electrostatic interaction. - The N and S soft base sites form stable coordination bonds with Au(III) soft acid according to the hard-soft acid-base (HSAB) theory. At the same time, Zr-THBD can reduce some Au(III) to Au(O) and fix it on the material surface. The above electrostatic interaction, coordination interaction and reduction interaction work together to achieve efficient and highly selective adsorption of Au(III).

[0013] The beneficial effects of this invention are: (1) The thiourea-bithiophene bifunctional zirconium-based MOF adsorbent Zr-THBD of the present invention can achieve a saturated adsorption capacity of 800 mg / g for Au(III) under the optimal conditions of pH=1 and 318 K, which is significantly better than most existing adsorbent materials; in actual copper anode mud leaching solution, the adsorption rate of Au(III) can reach 98.6%, and the adsorption performance is not affected by complex coexisting ions; (2) The thiourea-bithiophene bifunctionalized zirconium-based MOF adsorbent Zr-THBD of the present invention is used in Zn-containing... 2+ Ni 2+ Li + K + Mg 2+ In mixed solutions of multiple competing ions, the distribution coefficient for Au(III) is much higher than that for other ions, showing a significant selective adsorption advantage, which can achieve precise capture of gold ions in complex systems. (3) The thiourea-bithiophene bifunctionalized zirconium-based MOF adsorbent Zr-THBD of the present invention uses Zr 4+ The cluster consists of metallic nodes and bifunctional ligands anchored by carboxyl groups. It exhibits no significant structural degradation in strong acid environments of 0.5~2 mol / L HCl and good thermal stability below 190℃, making it suitable for harsh application environments in actual wastewater treatment. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the three-dimensional structure of the Zr-THBD adsorption sites; Figure 2 SEM image of the thiourea-bithiophene bifunctionalized zirconium-based MOF adsorbent in Example 1; Figure 3 EDS diagram of the thiourea-bithiophene bifunctionalized zirconium-based MOF adsorbent in Example 1; Figure 4 The FT-IR spectrum of the thiourea-bithiophene bifunctionalized zirconium-based MOF adsorbent in Example 1 is shown below. Figure 5 The effect of coexisting ions on the adsorption of gold ions by the thiourea-bithiophene bifunctionalized zirconium-based MOF adsorbent prepared in Example 1; Figure 6 This is a SEM image of gold ions adsorbed by the thiourea-bithiophene bifunctionalized zirconium-based MOF adsorbent in Example 2. Figure 7 XPS image of gold ions adsorbed by thiourea-bithiophene bifunctionalized zirconium-based MOF adsorbent in Example 2; Figure 8 Example 3: Reusability test of gold ion adsorption by thiourea-bithiophene bifunctionalized zirconium-based MOF adsorbent. Detailed Implementation

[0015] 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.

[0016] The thiourea-bithiophene bifunctionalized zirconium-based MOF adsorbent of this invention is a Zr-MOF adsorbent with thiourea-bithiophene bifunctional sites synthesized by solvothermal method with 4-carboxyphenylthiourea and [2,2-bithiophene]-5,5-dicarboxaldehyde as ligand raw materials and zirconium tetrachloride. It is denoted as ZR-THBD and has the following structural formula: ; Zr-THBD integrates the thiourea N / S site and the bithiophene S site.

[0017] Example 1: A method for preparing a thiourea-bithiophene bifunctionalized zirconium-based MOF adsorbent, the specific steps of which are as follows: (1) 4-Carboxyphenylthiourea and [2,2-Bithiophene]-5,5-dicarboxaldehyde were dissolved in ethanol, and acetic acid was added as a catalyst. The mixture was reacted at 70°C with stirring for 24 h to obtain a bifunctional ligand of thiourea-bithiophene. The molar ratio of 4-carboxyphenylthiourea to [2,2-bithiophene]-5,5-dicarboxaldehyde was 2:1, the concentration of 4-carboxyphenylthiourea in the mixed solution was 0.08 mol / L, and the amount of acetic acid added as a catalyst was 10 mL / L. (2) The bifunctional ligand of zirconium tetrachloride and thiourea-bithiophene was dissolved in N,N-dimethylformamide, commercially available hydrochloric acid was added, and the mixture was ultrasonically mixed to obtain a mixed solution. The mixed solution was transferred to a high-pressure reactor and reacted at 130°C with stirring for 10 h. The solid and liquid were separated, and the solid was washed alternately with anhydrous ethanol and deionized water until the eluent was colorless. The solid was dried under vacuum and ground to obtain Zr-MOF adsorbent Zr-THBD. The molar ratio of zirconium tetrachloride to 4-carboxyphenylthiourea in step (1) was 1:2.5, the concentration of zirconium tetrachloride in the mixed solution was 0.032 mol / L, and the amount of commercially available hydrochloric acid added was 1.5 mL / L. The SEM, EDS, and FT-IR images of the thiourea-bithiophene-functionalized zirconium-based MOF adsorbent Zr-THBD in this embodiment are shown below. Figures 2-4 As shown in the figure, the thiourea-bithiophene-functionalized zirconium-based MOF adsorbent Zr-THBD is mainly composed of the elements C, N, S, O, and Zr, with weight percentages of 59.7%, 2.9%, 3.5%, 17.4%, and 16.5%, respectively. In the FT-IR spectrum, at 3419.7 cm⁻¹... -1 The absorption peak is attributed to the N–H stretching vibration in the thiourea group (-NH-CS-NH-), at 1603.4 cm⁻¹. -1 The peak corresponds to the Schiff base group (-CH=N-), indicating that an amine-aldehyde condensation reaction occurred, 1182.44 cm⁻¹. -1 The position is the stretching vibration of the C–N bond in thiourea, 1412.97 cm⁻¹. -1 The peak can be attributed to the coordination of the carboxylate form formed after deprotonation of the carboxyl group with the metal center, which is important evidence for the formation of MOF structures; at 1512.81 cm⁻¹ -1 785.69cm -1 and 617.38cm -1 The absorption peaks at these locations correspond to the C=C stretching vibration, CH bending vibration, and CSC bending vibration in the thiophene ring, respectively, indicating that the molecular skeleton of the reactant remains intact. The presence of these groups confirms the successful synthesis of the thiourea-bithiophene-functionalized zirconium-based MOF adsorbent Zr-THBD. Selective adsorption performance of thiourea-bithiophene bifunctionalized zirconium-based MOF adsorbent ZR-THBD for Au(III): At room temperature, 10 mg of thiourea-bithiophene-functionalized zirconium-based MOF adsorbent Zr-THBD and the adsorption solution (pH=1, 10 mL) were added to a 15 mL centrifuge tube. The adsorption solution contained Au(III) 73.25 mg / L, Zn(II) 57 mg / L, Ni(II) 103.2 mg / L, Li(I) 134.2 mg / L, K(I) 124.7 mg / L, and Mg(II) 103.4 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 gold ions by the thiourea-bithiophene-functionalized zirconium-based MOF adsorbent Zr-THBD prepared in this embodiment is shown in the figure. Figure 5 The adsorption rate of Au(III) was calculated to be 93.7%, while the removal rates of Zn(II), Ni(II), Li(I), K(I), Mg(II) and Na(I) were 8.2%, 4.5%, 19.8%, 17.4% and 0.5%, respectively. It can be seen that the thiourea-bithiophene-functionalized zirconium-based MOF adsorbent Zr-THBD in this embodiment has strong selectivity for Au(III).

[0018] Example 2: A method for preparing a thiourea-bithiophene bifunctionalized zirconium-based MOF adsorbent, the specific steps of which are as follows: (1) 4-Carboxyphenylthiourea and [2,2-Bithiophene]-5,5-dicarboxaldehyde were dissolved in ethanol, and acetic acid was added as a catalyst. The mixture was reacted at 75°C with stirring for 20 h to obtain a bifunctional ligand of thiourea-bithiophene. The molar ratio of 4-carboxyphenylthiourea to [2,2-bithiophene]-5,5-dicarboxaldehyde was 1.5:1, the concentration of 4-carboxyphenylthiourea in the mixed solution was 0.06 mol / L, and the amount of acetic acid added as a catalyst was 11 mL / L. (2) The bifunctional ligand of zirconium tetrachloride and thiourea-bithiophene was dissolved in N,N-dimethylformamide, commercially available hydrochloric acid was added, and the mixture was ultrasonically mixed to obtain a mixed solution. The mixed solution was transferred to a high-pressure reactor and reacted at 135°C with stirring for 11 h. The solid and liquid were separated, and the solid was washed alternately with anhydrous ethanol and deionized water until the eluent was colorless. The solid was dried under vacuum and ground to obtain Zr-MOF adsorbent Zr-THBD. The molar ratio of zirconium tetrachloride to 4-carboxyphenylthiourea in step (1) was 1.5:2.5, the concentration of zirconium tetrachloride in the mixed solution was 0.036 mol / L, and the amount of commercially available hydrochloric acid added was 1.75 mL / L. This embodiment measures the adsorption performance of the thiourea-bithiophene bifunctionalized zirconium-based MOF adsorbent Zr-THBD for Au(III): Zr-THBD (10 mg) and Au(III) solution (pH=1, 10 mL, 100-1200 mg / L) were added to a 15 mL centrifuge tube at room temperature and shaken at 230 rpm for 24 h. The adsorbent was separated by centrifugation and the supernatant was obtained. The supernatant was then subjected to ICP-4. The concentration of residual gold ions in the supernatant was determined by OES. The adsorption capacity of Zr-THBD for Au(III) was 390 mg / g at 298 K. As the temperature rose to 318 K, the adsorption capacity increased to 800 mg / g. This shows that Zr-THBD has excellent adsorption performance for Au(III). This embodiment presents the SEM, EDS, and XPS analyses of the thiourea-bithiophene-functionalized zirconium-based MOF adsorbent Zr-THBD after gold ion adsorption. Figures 6-7 It was found that Au was uniformly distributed on Zr-THBD; the Au(4f) peak appeared in the XPS spectrum after gold ion adsorption by Zr-THBD, confirming that the adsorbent Zr-THBD, which is rich in N and S sites, successfully adsorbed gold ions.

[0019] Example 3: A method for preparing a thiourea-bithiophene bifunctionalized zirconium-based MOF adsorbent, the specific steps of which are as follows: (1) 4-Carboxyphenylthiourea and [2,2-Bithiophene]-5,5-dicarboxaldehyde were dissolved in ethanol, and acetic acid was added as a catalyst. The mixture was reacted at 80°C with stirring for 18 h to obtain a bifunctional ligand of thiourea-bithiophene. The molar ratio of 4-carboxyphenylthiourea to [2,2-bithiophene]-5,5-dicarboxaldehyde was 1:1, the concentration of 4-carboxyphenylthiourea in the mixed solution was 0.05 mol / L, and the amount of acetic acid added as a catalyst was 12 mL / L. (2) The bifunctional ligand of zirconium tetrachloride and thiourea-bithiophene was dissolved in N,N-dimethylformamide, commercially available hydrochloric acid was added, and the mixture was ultrasonically mixed to obtain a mixed solution. The mixed solution was transferred to a high-pressure reactor and reacted at 140°C with stirring for 12 hours. The solid and liquid were separated, and the solid was washed alternately with anhydrous ethanol and deionized water until the eluent was colorless. The solid was dried under vacuum and ground to obtain Zr-MOF adsorbent Zr-THBD. The molar ratio of zirconium tetrachloride to 4-carboxyphenylthiourea in step (1) was 2:2.5, the concentration of zirconium tetrachloride in the mixed solution was 0.04 mol / L, and the amount of commercially available hydrochloric acid added was 2 mL / L. This example demonstrates the repeatability of Au(III) adsorption by the thiourea-bithiophene bifunctionalized zirconium-based MOF adsorbent ZR-THBD: At room temperature, 40 mg of Zr-THBD was added to 40 mL of a solution containing Au(III) and placed in a 50 mL centrifuge tube. The mixture was shaken at 230 rpm for 24 hours. After solid-liquid separation, a desorption buffer was added. The desorption buffer consisted of 40 mL of a desorption solution composed of concentrated hydrochloric acid and 10% thiourea, and the solution was eluted for 24 hours. After centrifugation, the adsorbent was washed with distilled water until the solution was neutral, thus regenerating the Zr-THBD adsorbent. After five repeatability experiments, the adsorption rate of Au(III) was above 97% in the first three experiments, while the adsorption rate decreased in the latter two experiments (see...). Figure 8 This demonstrates that Zr-THBD exhibits good renewability and practicality across three cycles.

[0020] 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 thiourea-bithiophene bifunctionalized zirconium-based MOF adsorbent, characterized in that, A Zr-MOF adsorbent with a thiourea-bithiophene bifunctional site, synthesized from 4-carboxyphenylthiourea and [2,2-bithiophene]-5,5-dicarboxaldehyde as ligands via a solvothermal method with zirconium tetrachloride, is designated ZR-THBD. Its structural formula is as follows: 。 2. The preparation method of the thiourea-bithiophene bifunctionalized zirconium-based MOF adsorbent according to claim 1, characterized in that, The specific steps are as follows: (1) 4-Carboxyphenylthiourea and [2,2-Bithiophene]-5,5-dicarboxaldehyde were dissolved in ethanol, and acetic acid was added as a catalyst. The mixture was reacted at a constant temperature of 70~80℃ with stirring for 18~24h to obtain a bifunctional ligand of thiourea-bithiophene. (2) The bifunctional ligands of zirconium tetrachloride and thiourea-bithiophene were dissolved in N,N-dimethylformamide, hydrochloric acid was added, and the mixture was ultrasonically mixed to obtain a mixed solution. The mixed solution was transferred to a high-pressure reactor and reacted at 130~140℃ with stirring for 10~12h. The solid and liquid were separated, and the solid was washed alternately with anhydrous ethanol and deionized water until the eluent was colorless. The solid was dried under vacuum and ground to obtain Zr-MOF adsorbent Zr-THBD.

3. The preparation method of the thiourea-bithiophene bifunctionalized zirconium-based MOF adsorbent according to claim 2, characterized in that: In step (1), the molar ratio of 4-carboxyphenylthiourea to [2,2-bithiophene]-5,5-dicarboxaldehyde is 1~2:

1.

4. The preparation method of the thiourea-bithiophene bifunctionalized zirconium-based MOF adsorbent according to claim 3, characterized in that: In step (1), the concentration of 4-carboxyphenylthiourea in the mixed solution is 0.05~0.08 mol / L.

5. The preparation method of the thiourea-bithiophene bifunctionalized zirconium-based MOF adsorbent according to claim 2, characterized in that: In step (1), the amount of acetic acid catalyst added is 10~12 mL / L.

6. The preparation method of the thiourea-bithiophene bifunctionalized zirconium-based MOF adsorbent according to claim 2, characterized in that: The molar ratio of zirconium tetrachloride in step (2) to 4-carboxyphenylthiourea in step (1) is 1~2:2.

5.

7. The preparation method of the thiourea-bithiophene bifunctionalized zirconium-based MOF adsorbent according to claim 2, characterized in that: In step (2), the concentration of zirconium tetrachloride in the mixed solution is 0.05~0.1mol / L, and the amount of hydrochloric acid added is 1.5~2mL / L.

8. The application of the thiourea-bithiophene bifunctionalized zirconium-based MOF adsorbent according to claim 1 in the selective adsorption of Au(III) in acidic wastewater.

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