A method for preparing 2,4-dichlorophenoxyacetic acid imprinted material using modified UIO-66-NH2 as a support and its adsorption properties.

Abstract

2,4-Dichlorophenoxyacetic acid (2,4-D) is a common water pollutant, frequently detected in surface and groundwater systems, posing significant water pollution and ecological risks. This invention employs a green synthesis method to prepare a high specific surface area metal-organic framework, UIO-66-NH₂. First, UIO-66-NH₂ is modified with itaconic anhydride to obtain UIO-66-F. Then, using UIO-66-F as a molecularly imprinted carrier, with 2,4-D as a template molecule, MAA as a functional monomer, EGDMA as a crosslinking agent, and AIBN as an initiator, a novel surface molecularly imprinted material, UIO-66-F@MIPs, is successfully constructed for the selective removal of pollutant 2,4-D from wastewater. The synthesis process is green and simple, possessing excellent application potential and promotional value in the fields of selective separation of water pollutants, environmental remediation, and chemical separation. This invention can selectively separate and enrich the environmental pollutant 2,4-D, and exhibits good stability and a simple preparation method.

Description

Technical Field

[0001] This invention belongs to the field of environmental protection technology, and in particular relates to a method for preparing surface imprinted materials based on UIO-66-NH2 nanomaterials and its application in selectively separating 2,4-D. Background Technology

[0002] Currently, the main methods for treating 2,4-D include O3 oxidation, Fenton oxidation, photocatalytic degradation, and adsorption. O3 oxidation technology has high operating costs and is difficult to operate; Fenton oxidation technology is not suitable for treating alkaline wastewater and requires treatment of the resulting iron sludge; photocatalytic degradation has high requirements for light conditions and equipment. Adsorption methods have advantages such as high efficiency, simple operation, wide applicability, and low secondary pollution, and are therefore widely used in environmental remediation.

[0003] Molecular imprinting (MIT) is a rapidly developing technique in recent years for preparing materials with the selective binding ability to specific target molecules. Molecularly imprinted polymers (MIPs) have shown great promise in many fields, such as chromatographic stationary phases, solid-phase extraction, biomimetic chemical sensors, enzyme-mimicking catalysis, drug analysis and detection, and membrane separation technology. Traditional molecular imprinting methods involve reversibly binding a template molecule to a polymerizable functional monomer under certain conditions to form a template molecule-functional monomer complex. Then, a polymerization reaction is carried out using a crosslinking agent and the functional monomer to obtain a polymer. The template molecule is then removed from the polymer, leaving a three-dimensional cavity within the polymer that perfectly matches the template molecule in terms of spatial structure and binding sites. This three-dimensional cavity can selectively bind to the template molecule, thus exhibiting specific recognition ability. This imprinting method is also called bulk imprinting or 3D imprinting.

[0004] Traditional bulk imprinting methods for preparing molecularly imprinted materials (MIPs) often suffer from problems such as difficult template removal, low adsorption capacity, irregular morphology, slow mass transfer rate, and poor reproducibility. These shortcomings have become bottlenecks restricting the wider application of molecularly imprinted materials. To address these issues, researchers have conducted extensive work. The main strategies adopted are: first, surface imprinting on various matrices; and second, miniaturization of imprinted materials, primarily the preparation of various nanoscale imprinted materials. Both strategies aim to locate the imprinting sites on or near the surface of the material.

[0005] Metal-organic frameworks (MOFs) are a class of crystalline porous materials with periodic network structures, formed by the self-assembly of inorganic metal centers (metal ions or metal clusters) and bridging organic ligands. MOFs have become a research hotspot due to their advantages such as simple synthesis, easy functionalization, high specific surface area, and tunable pore size. MOFs and their composites are widely used in separation, enrichment, and analytical detection. However, the adsorption selectivity of MOFs for guests mainly depends on the matching between their specific pores and the target molecules. When faced with different target molecules, it is necessary to design pores that match the size of the target molecules to achieve specific adsorption and separation, which is often very difficult in practice. Therefore, combining molecular imprinting technology with MOFs can improve the adsorption selectivity of MOFs for guests.

[0006] UIO-66-NH2 is a metal-organic framework (MOF) material formed by the coordination of zirconium ions with 2-aminoterephthalic acid. It exhibits high chemical and thermal stability and has wide applications in adsorption separation, catalysis, sensing, and composite materials. In this study, using 2,4-D as a template molecule and UIO-66-NH2 as a molecularly imprinted carrier, UIO-66-NH2 was first modified with itaconic anhydride. After grafting C=C and COOH functional groups onto the surface of UIO-66, functional monomers and crosslinking agents were added, initiating a polymerization reaction to form a molecularly imprinted polymer layer on the surface of UIO-66-NH2. The adsorption performance of the imprinted material was investigated. This study provides a reliable method for preparing MOF-based composite materials with selective adsorption capabilities. Summary of the Invention

[0007] This invention addresses the technical problem of selective adsorption of 2,4-D in domestic sewage by proposing a method for preparing and applying a surface-imprinted polymer that is rationally designed, simple, easy to operate, and capable of selectively separating and enriching 2,4-D from other pesticide pollutants.

[0008] This invention uses UIO-66-NH2 material synthesized by oil bath method as a substrate, and itaconic anhydride (ITA) is added to modify the surface of UIO-66-NH2 in an anhydrous environment. Finally, the imprinted material is obtained by initiating polymerization and eluting template molecules. This invention can selectively separate and enrich environmental pollutant 2,4-D, and has good stability and simple preparation method.

[0009] To achieve the above-mentioned technical objectives, the technical solution adopted by this invention is as follows: (a) Preparation of UIO-66-NH2: This study selected a more economical and environmentally friendly method to synthesize UIO-66-NH2, avoiding the use of environmentally unfriendly organic solvents in this step. Zirconium chloride ZrCl4 and 2-aminoterephthalic acid (H2BDC-NH2, A-PTA) were dissolved in deionized water and acetic acid (3:2), sonicated for 30 min, stirred and refluxed in an oil bath at 100 °C for 24 h, centrifuged to obtain a white solid, washed several times with ethanol, and dried under vacuum at 60 °C to obtain solid UIO-66-NH2. (b) Preparation of UIO-66-NH2 functionalized modified product (UIO-66-F): The UIO-66-NH2 powder obtained in step (1) and itaconic anhydride (ITA) were placed in ultra-dry N,N-dimethylformamide (DMF), sealed to prevent moisture, stirred in an oil bath at 40 °C for 24 h, and centrifuged to obtain the functionalized modified product of UIO-66-NH2, denoted as UIO-66-F. (c) Preparation of UIO-66-NH2 surface imprinted materials (UIO-66-F@MIPs): The UIO-66-F powder obtained in step (2), template molecule 2,4-D, and functional monomer MAA were added to acetonitrile. Under continuous N2 protection, and after thorough stirring, crosslinking agent EGDMA and initiator AIBN were added. The mixture was heated to 60℃ and reacted for 24 h. The precipitate was collected by centrifugation, washed several times with anhydrous ethanol, and dried in a vacuum drying oven at 60℃. It was then extracted in a Soxhlet extractor with a methanol / glacial acetic acid mixture (9:1, V:V) for 48 h. After extraction, the final product was dried at 60℃.

[0010] In the mixture of step (1), the ratio of zirconium chloride ZrCl4, 2-aminoterephthalic acid (BDC-NH2), deionized water and acetic acid is (1.2-1.3)g:(0.9-1.0)g:(30-40)ml:(20-25)ml.

[0011] In step (1), the oil bath reaction temperature is 100℃-120℃, and the hydrothermal reaction time is 12-24 h.

[0012] In the mixture of step (2), the ratio of UIO-66-NH2 powder, itaconic anhydride and ultra-dry DMF is (0.6-0.7) g: (0.3-0.5) g: 60-80 ml.

[0013] In step (3), the ratio of UIO-66-F powder, 2,4-D, MAA and acetonitrile in the mixture is (0.3-0.32) g: 80 mg: 0.14 ml: 120 ml, and the mixture is stirred for 1 h under continuous N2 protection.

[0014] In step (3), after 1 h of prepolymerization, the ratio of crosslinking agent EGDMA to initiator AIBN is 0.8 ml: 0.08 g.

[0015] Meanwhile, following the above method, but without adding the template molecule 2,4-D before polymerization, a non-imprinted polymer of UIO-66-F (UIO-66-F@NIPs) was prepared as a reference for adsorption performance studies.

[0016] The UIO-66-NH2-based surface-imprinted polymer prepared above was used as an adsorbent material for the selective separation and enrichment of 2,4-D.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: A novel and solvent-saving method for preparing UIO-66-NH2 is provided, reducing production costs. This method is simple, uses inexpensive deionized water and glacial acetic acid, meets environmental protection requirements, and eliminates the need for high-temperature calcination or other treatment steps, resulting in low energy consumption and facilitating mass production. Using itaconic anhydride (ITA) and methacrylic acid (MAA) as functional monomers, the interaction between the functional monomers, carboxyl groups, and 2,4-D is utilized to form imprinted sites in the surface imprinted layer, with carboxyl groups acting as grippers, achieving selective adsorption of 2,4-D. Attached Figure Description

[0018] Figure 1 Infrared spectra of UIO-66-NH2, UIO-66-F, and UIO-66-F@MIPs.

[0019] Figure 2 The simulated XRD spectra of UIO-66, and the XRD patterns of UIO-66-NH2, UIO-66-F, and UIO-66-F@MIPs.

[0020] Figure 3 BET analysis plots for UIO-66-NH2, UIO-66-F, and UIO-66-F@MIPs.

[0021] Figure 4 Thermogravimetric analysis plots for UIO-66-NH2, UIO-66-F, and UIO-66-F@MIPs.

[0022] Figure 5Scanning electron microscope (SEM) images of UIO-66-NH2(a), UIO-66-F(b), UIO-66-F@MIPs(c), UIO-66-F@NIPs(d), UIO-66-NH2@MIPs(e), and UIO-66-NH2@NIPs(f), and UIO-66-F Transmission electron microscopy (TEM) images of (g) and UIO-66-F@MIPs (h). Detailed Implementation

[0023] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be further described below in conjunction with specific embodiments and accompanying drawings. Example

[0024] In this embodiment, UIO-66-NH2 is used as the substrate carrier, and itaconic anhydride is used to chemically modify its surface to prepare a functionalized modified carrier UIO-66-F. Then, functional monomers, template molecules, crosslinking agents and initiators are added to initiate polymerization to obtain a surface imprinted material UIO-66-F@MIPs.

[0025] S1. Accurately weigh 0.7 g of the synthesized UIO-66-NH2 and 3.4 mmol (0.448 g) of itaconic anhydride, and add them together to a reaction vessel containing 50 mL of ultra-dry DMF (moisture content <50 ppm, SafeDry level). Seal the reaction vessel to isolate it from external moisture and air interference, and place the system in a 40 ℃ oil bath under constant temperature magnetic stirring for 24 h. After the reaction is complete, centrifuge to collect the solid product, and after subsequent washing, obtain itaconic anhydride functionalized modified UIO-66-NH2, labeled as UIO-66-F, for use as a carrier raw material for surface molecular imprinting materials.

[0026] S2, 0.3 g UIO-66-F powder, 80 mg template molecule 2,4-D, and 0.14 mL methacrylic acid (MAA) were added sequentially to a 250 mL three-necked flask containing 120 mL acetonitrile solvent; nitrogen atmosphere was continuously introduced into the reaction system to remove oxygen, and the mixture was stirred at room temperature for 1 h to allow the template molecule and functional monomer to fully pre-assemble.

[0027] After pre-assembly, 0.8 mL of ethylene glycol dimethacrylate (EGDMA) crosslinking agent and 0.08 g of azobisisobutyronitrile (AIBN) initiator were added to the system in sequence, and the temperature was slowly raised to 60 °C. The polymerization reaction was carried out under constant temperature and sealed for 24 h.

[0028] After the polymerization reaction, the solid precipitate was collected by high-speed centrifugation at 10,000 r / min. The solid product was then washed repeatedly with anhydrous ethanol to remove unreacted monomers, cross-linking agents, and impurities from the surface. The washed solid was then placed in a Soxhlet extractor and continuously extracted for 48 h with a methanol / glacial acetic acid mixture (9:1 volume ratio) to thoroughly elute and remove the 2,4-D template molecules from the imprinted cavity. After elution, the sample was dried in a 60 ℃ vacuum drying oven, finally yielding the novel surface molecular imprinted material UIO-66-F@MIPs, which can be used for the selective adsorption and removal of 2,4-D pollutants in water.

[0029] The surface molecular imprinted material prepared above is used to extract 2,4-D from water, specifically including the following steps: Add 5 ml of 2,4-D standard solution to a centrifuge tube, then add 20 mg of the blot material. Incubate at room temperature for 3 hours with shaking. Filter through a 0.1 μm microporous membrane (PTFE) to remove solid material. Dilute the filtrate to an appropriate concentration and measure the absorbance at 284 nm using a UV-Vis spectrophotometer to calculate the remaining 2,4-D concentration. C e (μmol / L), the adsorption capacity of the material for 2,4-D was calculated by measuring the concentration change before and after adsorption. Q e (μmol / g).

[0030] According to UV-Vis analysis and Langmuir model calculations, the imprinting material has excellent imprinting effect and strong specific recognition ability for 2,4-D, with an adsorption capacity of 72.94 μmol / g for 2,4-D.

[0031] Comparative Example 1 In this comparative example, a non-imprinted material UIO-66-F@NIPs was prepared using modified UIO-66-NH2 (i.e., UIO-66-F) as the substrate carrier without the addition of template molecule 2,4-D.

[0032] S1. Accurately weigh 0.7 g of the synthesized UIO-66-NH2 and 0.448 g of itaconic anhydride, and add them together to a reaction vessel containing 50 mL of ultra-dry DMF (moisture content <50 ppm, SafeDry level). Seal the reaction vessel to isolate it from external moisture and air interference, and place the system in a 40 ℃ oil bath under constant temperature magnetic stirring for 24 h. After the reaction is complete, centrifuge to collect the solid product, and after subsequent washing, obtain itaconic anhydride functionalized modified UIO-66-NH2, labeled as UIO-66-F, for use as a carrier raw material for the preparation of non-imprinted materials.

[0033] S2, 0.3 g UIO-66-F powder and 0.14 mL methacrylic acid (MAA) were added sequentially to a 250 mL three-necked flask containing 120 mL acetonitrile solvent; nitrogen atmosphere was continuously introduced into the reaction system to remove oxygen, and the mixture was stirred at room temperature for 1 h to allow the components to pre-assemble.

[0034] After pre-assembly, 0.8 mL of ethylene glycol dimethacrylate (EGDMA) crosslinking agent and 0.08 g of azobisisobutyronitrile (AIBN) initiator were added to the system in sequence, and the temperature was slowly raised to 60 °C. The polymerization reaction was carried out under constant temperature and sealed for 24 h.

[0035] After the polymerization reaction was completed, the solid precipitate was collected by high-speed centrifugation at 10,000 r / min. The solid product was then washed repeatedly with anhydrous ethanol to remove unreacted monomers, crosslinking agents, and impurities from the surface. The washed solid was then placed in a Soxhlet extractor and extracted continuously for 48 h with a methanol / glacial acetic acid mixture (9:1 volume ratio). After elution, the sample was dried in a vacuum oven at 60 ℃ to obtain the non-imprinted material UIO-66-F@NIPs.

[0036] The non-imprinted material UIO-66-F@NIPs prepared above was used to extract 2,4-D from water. The specific steps and process conditions were exactly the same as in Example 1, and will not be repeated here. The adsorption capacity of UIO-66-F@NIPs for 2,4-D was measured to be 17.64 μmol / g.

[0037] Comparative Example 2 In this comparative example, UIO-66-NH2 was used as the substrate carrier. Without the addition of itaconic anhydride for modification, polymerization was directly initiated to obtain a surface-imprinted material UIO-66-NH2@MIPs.

[0038] S1. Accurately weigh 0.7 g of the synthesized UIO-66-NH2, and add 0.3 g of UIO-66-NH2 powder, 80 mg of template molecule 2,4-D, and 0.14 mL of methacrylic acid (MAA) to a 250 mL three-necked flask containing 120 mL of acetonitrile solvent. Continuously purge the reaction system with nitrogen atmosphere to remove oxygen, and stir at room temperature for 1 h to allow the template molecule and functional monomer to fully pre-assemble.

[0039] After pre-assembly, 0.8 mL of ethylene glycol dimethacrylate (EGDMA) crosslinking agent and 0.08 g of azobisisobutyronitrile (AIBN) initiator were added to the system in sequence, and the temperature was slowly raised to 60 °C. The polymerization reaction was carried out under constant temperature and sealed for 24 h.

[0040] After the polymerization reaction, the solid precipitate was collected by high-speed centrifugation at 10,000 r / min. The solid product was then washed repeatedly with anhydrous ethanol to remove unreacted monomers, crosslinking agents, and impurities from the surface. The washed solid was then placed in a Soxhlet extractor and extracted continuously for 48 h with a methanol / glacial acetic acid mixture (9:1 volume ratio) to thoroughly remove the 2,4-D template molecules from the imprinted cavity. After elution, the sample was dried in a vacuum oven at 60 ℃, finally yielding the surface molecularly imprinted material UIO-66-NH2@MIPs.

[0041] The surface molecularly imprinted material prepared above was used to extract 2,4-D from water. The specific steps and process conditions were exactly the same as in Example 1, and will not be repeated here. The adsorption capacity of UIO-66-NH2@MIPs for 2,4-D was measured to be 31.25 μmol / g.

[0042] By comparing Example 1 with Comparative Examples 1 and 2, it can be seen that modifying UIO-66-NH2 with itaconic anhydride before polymerization is the preferred method for preparing highly selective and highly stable surface molecular imprinted materials.

[0043] In summary, the surface molecularly imprinted polymer UIO-66-F@MIPs provided by this invention exhibits high selectivity in the extraction of 2,4-D, and is recyclable, simple, efficient, environmentally friendly, and easy to industrialize, thus showing good prospects for widespread application.

[0044] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a surface-imprinted material based on UIO-66-NH2, comprising the following steps: (1) Preparation of UIO-66-NH2: Zirconium chloride (ZrCl4) and 2-aminoterephthalic acid (BDC-NH2) were dissolved in deionized water and acetic acid (3:2), sonicated for 30 min, and then subjected to an oil bath at 100 °C for 24 h. After centrifugation, a white solid was obtained, washed several times with ethanol, and then dried under vacuum to obtain a stable UIO-66-NH2 powder. (2) Preparation of UIO-66-F: The UIO-66-NH2 powder obtained in step one and itaconic anhydride were reacted fully in ultra-dry N,N-dimethylformamide (DMF) in an oil bath at 40°C to obtain UIO-66-F; (3) Preparation of UIO-66-NH2 surface-imprinted material UIO-66-F@MIPs: The UIO-66-F powder obtained in step two, template molecule 2,4-D, and functional monomer MAA were added to acetonitrile. Under continuous N2 protection, and after thorough stirring, crosslinking agent EGDMA and initiator AIBN were added. The mixture was heated to 60℃ and reacted for 24 h. The precipitate was collected by centrifugation, washed several times with anhydrous ethanol, and dried in a vacuum drying oven at 60℃. It was then extracted in a Soxhlet extractor with a methanol / glacial acetic acid mixture (9:1, V:V) for 96 h. The extracted product was then dried at 60℃ to obtain the final product.

2. The production method according to claim 1, wherein In the mixture of step (1), the ratio of zirconium chloride ZrCl4, 2-aminoterephthalic acid (BDC-NH2), deionized water and acetic acid is (1.2-1.3)g:(0.9-1.0)g:(30-40)ml:(20-25)ml.

3. The production method according to claim 1, wherein In step (1), the oil bath reaction temperature is 100℃-120℃, and the hydrothermal reaction time is 12-24h.

4. The production method according to claim 1, wherein In the mixture of step (2), the ratio of UIO-66-NH2 powder, itaconic anhydride and ultra-dry DMF is (0.6-0.7) g: (0.3-0.5) g: 60-80 ml.

5. The preparation method according to claim 1, characterized in that, In step (3), the ratio of UIO-66-F powder, 2,4-D, MAA and acetonitrile in the mixture is (0.3-0.32) g: 80 mg: 0.14 ml: 120 ml. The mixture is stirred for 1 hour under continuous N2 protection.

6. The preparation method according to claim 1, characterized in that, After the mixture from step (3) has been prepolymerized for 1 hour, the ratio of crosslinking agent EGDMA to initiator AIBN is 0.8 ml: 0.08 g.

7. The surface-imprinted polymer based on UIO-66-NH2 prepared according to any one of claims 1-6 is used as an adsorbent material for the selective separation and enrichment of 2,4-D. The material has a strong specific recognition ability for 2,4-D and an adsorption capacity of 72.94 μmol / g for 2,4-D.

Images