A carboxylic acid ligand Ca-MOF for the removal of Pb from water 2+ and Cu 2+ Applications and methods

Abstract

This invention relates to a method for reacting Cu 2+ Pb 2+ A metal-organic framework (MOF) material with highly efficient and complete displacement capability, particularly an adsorbent with CaBDC as its core. This material is synthesized via a solvothermal method, using CaBDC as its core. 2+ A CaBDC structure was formed using a metal node and terephthalic acid (BDC) as the organic ligand. Using ZnBDC as a control system, its effect on Cu was investigated. 2+ or Pb 2+ The adsorption performance of Cu. 2+ or Pb 2+ In wastewater, after stirring or shaking for more than 2 hours, and centrifuging to remove solid precipitate, Cu can be obtained. 2+ or Pb 2+ Pollution removal. CaBDC MOF for Cu 2+ and Pb 2+ The removal capacity is high (maximum approximately 310 and 1015 mg / g), the removal rate is fast (both reach adsorption equilibrium within 60 min), and the removal mechanism is ion exchange. Experimental studies and XRD and SEM images before and after adsorption were used to reflect the synthesized materials and phases. Experimental results show that the adsorption mechanism of CaBDC is Ca... 2+ With Cu 2+ Pb 2+ Complete displacement between them to achieve Cu in aqueous solution 2+ Pb 2+ This invention achieves highly efficient, stable, and irreversible removal, solving the problems of low adsorption capacity, slow reaction rate, and poor selectivity of traditional adsorption materials, while causing no secondary pollution to the environment. This invention provides some inspiration for MOF materials in removing heavy metal pollution from water, and also holds promise for developing more highly efficient, non-toxic, harmless, and large-scale synthesizable novel materials for pollutant removal.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment, specifically relating to the heavy metal ion removal performance of metal-organic frameworks (MOFs), and adsorbents based on ZnBDC and CaBDC and their application in Cu-containing wastewater. 2+ and Pb 2+ Applications in wastewater treatment. In particular, CaBDC adsorbent can remove Ca... 2+ Achieving Cu in wastewater through 100% exchange 2+ and Pb 2+ Highly effective removal. Background Technology

[0002] Due to social development and the intensification of various human activities and industrial and agricultural production, heavy metal (such as arsenic, cadmium, chromium, copper, lead, mercury, nickel, and zinc) pollution of water sources has become a global problem that urgently needs to be addressed. Cu and Pb are typical heavy metal pollutants in water bodies. They cannot be naturally degraded and easily accumulate in organisms, bioaccumulating at each level of the food chain, ultimately posing a significant threat to human health. Taking effective measures to reduce the content of heavy metals in aqueous solutions to acceptable levels is of paramount importance.

[0003] Metal-organic frameworks (MOFs) are a class of adsorbent materials that have emerged in the last 30 years. They are composed of secondary structural units (SBUs), i.e., metal ions or metal clusters bound to organic ligands. Traditional methods for removing pollutants from wastewater include precipitation, coagulation and flocculation, ion exchange, catalysis, membrane filtration, and adsorption. Adsorption processes are favored due to their simplicity, efficiency, and ease of scalability. However, traditional adsorption processes are physical adsorption, and their products are still secondary pollutants, thus having limitations. MOFs are highly porous materials with porosities far exceeding those of metal oxides, zeolites, and carbon-based adsorbents. Furthermore, MOFs possess adjustable pore size and structure, high porosity, and the ability to regulate connective tissue, making them suitable for gas storage and molecular separation, heterogeneous catalysis, and water remediation. While MOFs have demonstrated excellent adsorption performance as adsorbents for removing gases and organic compounds, the main challenges in using MOFs as adsorbents for heavy metal adsorption in aqueous media lie in the fact that existing MOF materials mostly rely on surface complexation, electrostatic interactions, or pore adsorption, making it difficult to achieve high-capacity adsorption. Furthermore, they suffer from poor water stability, low selectivity, and slow adsorption rates. MOF materials that adsorb heavy metals are also difficult to desorb, thus becoming a new type of pollutant. Therefore, it is essential to develop functional MOF materials with high adsorption capacity, fast removal rate, and easy post-treatment separation.

[0004] Transition metal-based organic frameworks (cobalt, nickel, zinc, copper) have been extensively studied, particularly those based on main group metals such as Li. + Ca 2+ Mg2+ Or Al 3+ The coordination chemistry of metal-organic frameworks, especially calcium-based metal-organic frameworks, has been rarely explored, and their properties have not been studied in depth.

[0005] This invention proposes Ca in the CaBDC framework 2+ With Cu 2+ / Pb 2+ A complete replacement reaction is used to achieve thorough removal. Summary of the Invention

[0006] This invention provides a MOF CaBDC (BDC stands for terephthalic acid), which demonstrates high-performance adsorption, strong water stability, and environmental friendliness through comparative experiments with three other adsorbents: CrBDC, FeBDC, and ZnBDC. The adsorbent achieves this through a "complete replacement" process, meaning that after reacting with Cu / Pb, the Ca-MOF material is completely converted to CuBDC·3H₂O and a small amount of CuBDC MOF or PbBDC·H₂O MOF. 2+ It is released into the solution, making downstream separation very easy. This enables the separation of Cu in aqueous solution. 2+ Pb 2+ Its efficient, stable, and irreversible removal solves the problems of low adsorption capacity, slow reaction rate, and poor selectivity of traditional adsorption materials.

[0007] The CaBDC MOF material of this invention can be synthesized by a conventional solvothermal method. The method is characterized by: weighing 10 mmol CaCl2 and 10 mmol BDC (terephthalic acid), dissolving them separately in 50 mL DMF (N,N-dimethylformamide) solution and stirring to mix them evenly so that the reagents are fully dissolved or dispersed. After heating at 180°C for 24 h in a polytetrafluoroethylene reactor and then naturally cooling, the precipitated product is centrifuged and washed (washed once with DMF and twice with ethanol). Finally, the washed product is placed in a regular oven and dried overnight at 80°C.

[0008] A method for efficiently removing Cu and Pb from wastewater using anhydrous Ca-MOF, characterized by adding CaBDC powder to a Cu-containing... 2+ or Pb 2+ In wastewater, stirring or shaking for more than 2 hours, followed by centrifugation to remove solid precipitates, can achieve the removal of pollutant Cu. 2+ Pb 2+ The removal of.

[0009] Furthermore, CaBDC materials are particularly suitable for medium to high concentrations of Cu. 2+ or Pb 2+ For wastewater treatment, the dosage range is typically 0.1–1 g / L (Cu). 2+ or Pb2+ When the concentration is low, the amount added can be even smaller.

[0010] Furthermore, CaBDC adsorption removes Cu from wastewater. 2+ The maximum capacity is approximately 311 mg / g, and it can reach adsorption equilibrium within 30 minutes. The removal mechanism is ion exchange.

[0011] Furthermore, CaBDC adsorption removes Pb from wastewater. 2+ The maximum capacity is approximately 1015 mg / g, and it can reach adsorption equilibrium within 60 minutes. The removal mechanism is ion exchange.

[0012] CaBDC materials and high concentration Cu 2+ or Pb 2+ After the reaction, it is completely converted into CuBDC·3H2O and a small amount of CuBDC or PbBDC·H2O, Ca 2+ Released into the solution, the main precipitate separated by centrifugation is CuBDC·3H2O or PbBDC·H2OMOF.

[0013] Compared with existing technologies, the advantages of this invention include: the CaBDC material preparation method is simple and the preparation cost is low; CaBDC can quickly and efficiently remove Cu from wastewater. 2+ or Pb 2+ The removal mechanism is Cu 2+ or Pb 2+ Ca replacement in Ca-MOF 2+ After the reaction, Ca 2+ Released into the solution, while Cu 2+ or Pb 2+ It mainly transforms into CuBDC·3H2O or PbBDC·H2O precipitate, and the back-end separation is simple and there is no problem of secondary pollution from adsorbent.

[0014] In summary, CaBDC MOF is a method for removing Cu from wastewater. 2+ or Pb 2+ It is an ideal material with broad market value. Attached Figure Description

[0015] Figure 1 The images show the XRD and SEM images of the ZnBDC product prepared by the solvothermal method in Example 1 of this invention.

[0016] Figure 2 The images show the XRD and SEM images of the CaBDC product prepared by the solvothermal method in Example 1 of this invention.

[0017] Figure 3 ZnBDC and CaBDC adsorption for the removal of Cu from water 2+ Performance graph.

[0018] Figure 4 ZnBDC adsorption for the removal of Cu from water 2+ The subsequent XRD and SEM images.

[0019] Figure 5 CaBDC adsorption for the removal of Cu from water 2+ The subsequent XRD and SEM images.

[0020] Figure 6 CaBDC adsorption for the removal of Cu from water 2+ XPS graph.

[0021] Figure 7 ZnBDC and CaBDC adsorption for the removal of Pb from water 2+ Performance graph.

[0022] Figure 8 ZnBDC adsorption for Pb removal in water 2+ The subsequent XRD and SEM images.

[0023] Figure 9 CaBDC adsorption for the removal of Pb from water 2+ The subsequent XRD and SEM images.

[0024] Figure 10 CaBDC adsorption for the removal of Pb from water 2+ XPS graph. Detailed Implementation

[0025] The following examples will help to understand the present invention, but are not intended to limit its scope. It should be noted that, unless otherwise specified, the embodiments and features described in the embodiments of the present invention can be combined with each other.

[0026] Example 1: Preparation of ZnBDC and CaBDC by solvothermal method

[0027] (1) Preparation of ZnBDC

[0028] 3.305 g of zinc nitrate and 0.705 g of BDC were dissolved separately in 40 mL of DMF. The solution was stirred continuously at room temperature to ensure complete dissolution. The two liquids were then mixed thoroughly and added dropwise. The mixture was heated in an oil bath at 135°C for 4 hours. After cooling, the solution was centrifuged and washed three times each with DMF and chloroform. Finally, it was vacuum dried in an oven at 60°C to obtain ZnBDC.

[0029] (2) Preparation of CaBDC

[0030] 1.11 g of anhydrous CaCl2 and 1.678 g of BDC were dissolved separately in 50 mL of DMF. The solutions were stirred on a magnetic oscillator and then thoroughly mixed using a constant pressure funnel (at a rate of approximately 1-2 drops per second). The resulting solutions were placed in a PTFE-lined stainless steel container, aliquoted into 100 mL portions, and heated in an oven at 180°C for 24 h. After cooling to room temperature, the solutions were centrifuged and washed three times consecutively with DMF and ethanol. Finally, the solutions were dried overnight in an oven at 80°C. A white powder, CaBDC, was obtained.

[0031] Depend on Figure 1 It can be seen that the morphology of the obtained product ZnBDC is a regular cubic shape.

[0032] Depend on Figure 2 It can be seen that the morphology of the obtained product CaBDC is an irregular block.

[0033] Example 2: Removal of Cu from Water by ZnBDC 2+ Performance research

[0034] (1) Adsorption capacity determination

[0035] Take 10 mg of ZnBDC powder and place it in 50 mL of Cu with different initial concentrations (25–400 ppm). 2+ The solution was placed in a constant temperature (25℃) air bath shaker and shaken at 200 rpm for 12 h. The supernatant was then drawn off with a syringe and filtered through a 0.22 μm filter. Finally, the residual Cu in the liquid was determined using atomic absorption spectrometry. 2+ The concentration.

[0036] (2) Adsorption kinetics determination

[0037] Take 50 mg of ZnBDC powder and add it to 250 mL of Cu solution with an initial concentration of 200 ppm. 2+ The solution was placed on a stirrer and stirred. Samples were taken at 2, 5, 10, 15, 20, 30, 60, 120, 180, and 360 minutes to determine the residual Cu in the solution. 2+ The concentration is adjusted (using the same method as the previous step), and finally the remaining solution is centrifuged to separate the solid (and dried overnight in an oven at 60°C).

[0038] Depend on Figure 3 It can be seen that ZnBDC material has a certain effect on Cu in solution. 2+ The maximum adsorption capacity is approximately 250 mg / g, and adsorption equilibrium can be reached within 60 minutes.

[0039] Depend on Figure 4 It can be seen that ZnBDC adsorbs and removes Cu 2+Subsequently, the crystalline phase changes to CuBDC·3H2O, and the original cubic morphology disappears, replaced by irregular blocky particles.

[0040] Example 3: CaBDC Removal of Cu from Water 2+ Performance research

[0041] (1) Adsorption capacity determination

[0042] Take 10 mg of CaBDC powder and place it in 50 mL of Cu with different initial concentrations (25–400 ppm). 2+ The solution was placed in a constant temperature (25℃) air bath shaker and shaken at 200 rpm for 12 h. The supernatant was then drawn off with a syringe and filtered through a 0.22 μm filter. Finally, the residual Cu in the liquid was determined using atomic absorption spectrometry. 2+ The concentration.

[0043] (2) Adsorption kinetics determination

[0044] Take 50 mg of CaBDC powder and add it to 250 mL of Cu solution with an initial concentration of 200 ppm. 2+ The solution was placed on a stirrer and stirred. Samples were taken at 2, 5, 10, 15, 20, 30, 60, 120, 180, and 360 minutes to determine the residual Gu in the solution. 2+ The concentration is adjusted (using the same method as the previous step), and finally the remaining solution is centrifuged to separate the solid (and dried overnight in an oven at 60°C).

[0045] Depend on Figure 3 It can be seen that CaBDC material affects Cu in solution. 2+ The maximum adsorption capacity is approximately 310 mg / g, and adsorption equilibrium can be reached within 60 minutes.

[0046] Depend on Figure 5 It can be seen that CaBDC adsorbs and removes Cu 2+ Subsequently, the main crystalline phase changes to CuBDC·3H2O, with a small amount of CuBDC remaining, forming a smooth, blocky crystal.

[0047] Depend on Figure 6 It can be seen that CaBDC adsorbs and removes Cu 2+ Subsequently, XPS characterization revealed that the signal of Ca disappeared, while the signal of Cu reappeared.

[0048] comprehensive Figure 5 and Figure 6 The results show that CaBDC effectively removes Cu from water. 2+ The mechanism is ion exchange, specifically the exchange of Cu in wastewater. 2 +The Ca in CaBDC was replaced 2+ .

[0049] Example 4: Removal of Pb from water by ZnBDC 2+ Performance research

[0050] (1) Adsorption capacity determination

[0051] Take 10 mg of ZnBDC powder and place it in 50 mL of Pb at different initial concentrations (25–400 ppm). 2+ The solution was placed in a constant temperature (25℃) air bath shaker and shaken at 200 rpm for 24 h. The supernatant was then drawn off with a syringe and filtered through a 0.22 μm filter. Finally, the remaining Pb in the liquid was determined using atomic absorption spectrometry. 2+ The concentration.

[0052] (2) Adsorption kinetics determination

[0053] Take 50 mg of ZnBDC powder and add it to 250 mL of Pb solution with an initial concentration of 200 ppm. 2+ The solution was placed on a stirrer and stirred. Samples were taken at 2, 5, 10, 15, 20, 30, 60, 120, 180, and 360 minutes to determine the remaining Pb in the solution. 2+ The concentration is adjusted (using the same method as the previous step), and finally the remaining solution is centrifuged to separate the solid (and dried overnight in an oven at 60°C).

[0054] Depend on Figure 7 It can be seen that ZnBDC material has a good effect on Pb in solution. 2+ The maximum adsorption capacity is approximately 700 mg / g, and adsorption equilibrium can be reached within 30 minutes.

[0055] Depend on Figure 8 It can be seen that ZnBDC adsorbs and removes Pb 2+ Subsequently, the crystalline phase changes to PbBDC·H2O, and the original cubic morphology disappears, replaced by fine particle aggregates.

[0056] Example 5: CaBDC Removal of Pb from Water 2+ Performance research

[0057] (1) Adsorption capacity determination

[0058] Take 50 mg of CaBDC powder and add it to 250 mL of Pb solution with an initial concentration of 200 ppm. 2+ The solution was placed on a stirrer and stirred. Samples were taken at 2, 5, 10, 15, 20, 30, 60, 120, 180, and 360 minutes to determine the remaining Pb in the solution. 2+The concentration is adjusted (using the same method as the previous step), and finally the remaining solution is centrifuged to separate the solid (and dried overnight in an oven at 60°C).

[0059] (2) Adsorption kinetics determination

[0060] Take 50 mg of CaBDC powder and add it to 250 mL of Pb solution with an initial concentration of 200 ppm. 2+ The solution was placed on a stirrer and stirred. Samples were taken at 2, 5, 10, 15, 20, 30, 60, 120, 180, and 360 minutes to determine the remaining Pb in the solution. 2+ The concentration is adjusted (using the same method as the previous step), and finally the remaining solution is centrifuged to separate the solid (and dried overnight in an oven at 60°C).

[0061] Depend on Figure 6 It can be seen that CaBDC material has a certain effect on Pb in solution. 2+ The maximum adsorption capacity is approximately 1015 mg / g, and adsorption equilibrium can be reached within 60 minutes.

[0062] Depend on Figure 9 It can be seen that CaBDC adsorbs and removes Pb 2+ Subsequently, the crystalline phase changes to PbBDC·H2O, and the original irregular morphology disappears, replaced by a dense aggregate of blocky particles.

[0063] Combined with CaBDC to remove Cu from water 2+ Mechanism analysis shows that it adsorbs and removes Pb from water. 2+ The mechanism is also ion exchange.

Claims

1. A carboxylic acid ligand Ca-MOF displacement method for removing Pb from water. 2+ and Cu 2+ The application and method are characterized by, The Ca-MOF has the molecular formula CaBDC and does not contain water of crystallization or other solvent molecules. Here, BDC stands for terephthalic acid.

2. The application and method according to claim 1, characterized in that: (1) CaBDC removes Cu from wastewater 2+ The maximum adsorption capacity is about 311 mg / g, and it can reach adsorption equilibrium within 30 min. The removal mechanism is ion exchange and the degree is 100%. (2) CaBDC removes Pb from wastewater 2+ The maximum adsorption capacity is about 1015 mg / g, and it can reach adsorption equilibrium within 60 min. The removal mechanism is ion exchange and the degree is 100%. (3) CaBDC can be synthesized by conventional solvothermal methods, using soluble calcium salts and BDC as raw materials, and N,N-dimethylformamide as an organic solvent. The key point is that the synthesis temperature must be above 150℃ to ensure that the product does not contain water of crystallization or other solvent molecules. (4) CaBDC can also be prepared by first mechanically ball milling Ca(BDC)(H2O)3 and then drying it at 150°C or above.

3. A carboxylic acid ligand Ca-MOF displacement method for removing Pb from water. 2+ and Cu 2+ The application and method thereof are characterized by: Add CaBDC powder to Cu-containing 2+ or Pb 2+ In wastewater, stir or shake for at least 60 minutes, then centrifuge to remove solid precipitate to achieve Cu 2+ or Pb 2+ Pollution removal; the same removal effect can be achieved without stirring or shaking, but it takes more than 120 minutes; or the Ca-MOF can be mixed into a sand-like matrix to construct a filter bed in a column reactor, and then Cu-containing materials can be introduced from the top. 2+ or Pb 2+ The wastewater is purified in the form of wastewater.

4. The method according to claim 3, characterized in that, CaBDC materials are particularly suitable for medium to high concentrations of Cu. 2+ or Pb 2+ For wastewater treatment, the dosage range is usually 0.1 to 1 g / L, and the decontamination efficiency will decrease as the dosage increases.

5. The method according to claim 3, characterized in that, The precipitate collected after the reaction is CuBDC·3H2O (which contains 5% to 10% CuBDC) or pure phase PbBDC·H2O.

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