UiO-66 Metal-Organic Framework Materials, Their Preparation Methods and Applications

Abstract

This invention discloses a UiO-66 metal-organic framework material, its preparation method, and its applications, belonging to the technical field of metal-organic framework materials. This invention synthesizes water-induced defective UiO-66 by introducing water into the UiO-66 precursor through a simple solvothermal reaction; and induces ligand loss through vacuum heat treatment, endowing UiO-66 with visible light photocatalytic activity, thereby simultaneously improving the pore structure and electronic structure of UiO-66 and promoting the adsorption-photocatalytic removal of norfloxacin.

Description

Technical Field

[0001] This invention relates to the field of metal-organic framework materials technology, and in particular to a UiO-66 metal-organic framework material and its preparation method. Background Technology

[0002] Environmental pollution and health hazards from drugs and personal care products, particularly antibiotics and nonsteroidal anti-inflammatory drugs (NSAIDs), have become a global concern. Although these pollutants are emitted at extremely low concentrations (ng / L ~ μg / L), their long-term continuous discharge, pseudo-persistence (resistance to photodegradation, chemical degradation, and biodegradation), and even at low concentrations, their direct biotoxicity (such as harm to the reproductive system, inducing malignant tumors, and causing neurotoxicity) and the potential for secondary environmental hazards such as bacterial resistance and the generation and spread of resistance genes are all significant concerns. These substances can penetrate conventional wastewater treatment processes (such as filtration, chlorination, and ozone oxidation) and enter the aquatic environment; therefore, conventional quantitative standards (total phosphorus, total nitrogen, COD, etc.) are no longer sufficient to meet high water quality requirements.

[0003] Photocatalysis is a completely clean energy technology that avoids the introduction of highly toxic or corrosive oxidants found in Fenton or Fenton-like systems. Traditional photocatalytic reactions are inefficient due to severe electron-hole recombination in semiconductor catalysts, and the development of novel photocatalysts presents a challenge in terms of synthesis costs. Combining adsorption technology with photocatalytic reactions can improve photocatalytic performance by shortening the distance between the pollutant and the catalyst interface. However, traditional semiconductor materials with photocatalytic properties exhibit extremely low adsorption capacity for most organic pollutants due to their low specific surface area and limited functional group sites.

[0004] Metal-organic frameworks (MOFs) are porous materials with high porosity and customized pore structures, showing great promise for applications in gas adsorption and the adsorption of organic pollutants in water. MOFs consist of alternating coordination between metal clusters and organic ligands, thus exhibiting dual properties of both organic and inorganic materials. Specifically, MOFs can achieve hierarchical pore synthesis through customized organic ligands, thereby promoting mass transfer in adsorption or catalysis; aromatic organic ligands possess a variety of functional groups, further enhancing adsorption reactions; and metal cluster sites can synergistically absorb and transfer electrons with organic ligands, forming electron transfer from organic ligands to metal cluster sites or vice versa, thereby suppressing recombination of photogenerated carriers. However, the synthesis of MOFs is often limited by strict reaction regulation and low yields.

[0005] Taking UiO-66 as an example, it typically requires synthesis under high temperature and pressure conditions in a reactor. Furthermore, to obtain more perfect crystals, adding strong inorganic acids such as hydrofluoric acid and hydrochloric acid to the reaction precursor can slow down the protonation of ligands, thereby slowing down crystal nucleation. Adding monobasic strong organic acids, such as acetic acid or trifluoroacetic acid, can slow down crystal nucleation through competitive coordination and even regulate the hierarchical porous structure. However, strong organic or inorganic acids usually have extremely strong corrosive properties and a strong pungent odor, which poses difficulties for large-scale reaction design. Traditional UiO-66 has a band gap of approximately 3.9 eV and can only be excited by ultraviolet light. This patent, by using virtually cost-free water as a precursor additive and combining it with a high-temperature thermal activation process, simultaneously achieves improved crystal synthesis, visible light excitation, and adsorption performance of UiO-66. Summary of the Invention

[0006] This invention provides a UiO-66 metal-organic framework material, its preparation method and application, by changing the precursor additives to enable UiO-66 to be excited by visible light.

[0007] In a first aspect, the present invention provides a method for preparing a UiO-66 metal-organic framework material, comprising the following steps:

[0008] S1. Dissolve the zirconium salt in a mixed solution of N,N-dimethylformamide and water, and sonicate until fully dissolved;

[0009] S2. After complete dissolution, add terephthalic acid and dissolve again by sonication.

[0010] S3. After dissolving, place the mixture in an oven to maintain the temperature and allow it to react.

[0011] S4. After the product has been removed and allowed to cool completely, it is first washed with N,N-dimethylformamide, and then washed with methanol.

[0012] S5. After washing, the product is vacuum dried to obtain UiO-66 metal-organic framework material.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention completes the synthesis of water-induced defective UiO-66 by introducing water into the precursor of UiO-66 through a simple solvothermal reaction; and induces the loss of ligands through vacuum heat treatment, endowing UiO-66 with visible light photocatalytic ability, thereby simultaneously improving the pore structure and electronic structure of UiO-66 and promoting the adsorption-photocatalytic removal ability of norfloxacin.

[0014] Furthermore, the S1 zirconium salt is ZrCl4, and the ratio of ZrCl4, N,N-dimethylformamide and water is 160 mg: 40 mL: (0~100) equivalents, wherein 4 equivalents of water is equivalent to 0.05 mL of water.

[0015] Furthermore, the ultrasonic treatment time was 10 minutes for all cases.

[0016] Furthermore, the oven temperature in S3 is 120℃, and the holding time is 24 hours.

[0017] Furthermore, S4 was cleaned with N,N-dimethylformamide for 2 days, with the liquid changed every half day; then it was cleaned with methanol for 2 days, with the liquid changed every half day.

[0018] Furthermore, the vacuum drying activation temperature in S5 is 80℃~200℃, and the drying time is 24h.

[0019] Secondly, the present invention provides a UiO-66 metal-organic framework material obtained by the above method, named UiO-66-xeq-y, where x is the equivalent amount of water added and y is the vacuum activation temperature. If there is no y mark, it means that it has not been activated at high temperature.

[0020] Thirdly, this invention provides an application of the UiO-66 metal-organic framework in the treatment of norfloxacin in water. Attached Figure Description

[0021] Figure 1 The XRD patterns of the products obtained in Examples 5-9 and Comparative Example 2 of this invention are shown below.

[0022] Figure 2 The XRD patterns of the products obtained in Examples 1-4 and Comparative Example 1 of this invention are shown below.

[0023] Figure 3 The attached diagrams show the nitrogen adsorption / desorption spectra of the products obtained in Examples 1-4 and Comparative Example 1 of this invention;

[0024] Figure 4 These are the pore size distribution diagrams of the products obtained in Examples 1-4 and Comparative Example 1 of the present invention;

[0025] Figure 5 Electron paramagnetic resonance spectra of UiO-66 with different equivalent water and different temperatures activated to provide the present invention;

[0026] Figure 6 The UV absorption spectra of the products obtained in Examples 1-3 and Comparative Example 1 of this invention are shown below.

[0027] Figure 7 The images show the adsorption and photocatalytic degradation curves of 0.2 mg / L norfloxacin in Examples 1-3 and Comparative Example 1 of this invention. Detailed Implementation

[0028] To fully understand the purpose, features and effects of the present invention, the present invention will be described in detail through the following specific embodiments, but the present invention is not limited thereto.

[0029] MOF was synthesized using ZrCl4 metal salt, terephthalic acid organic ligand, N,N-dimethylformamide as solvent, and a glass bottle as reactor. Example 1

[0030] 160 mg ZrCl4 was dissolved in 40 mL of DMF (N,N-2-methylformamide) and an equivalent amount of water (70 eq, where eq means equivalent volume, 4 eq = 0.05 mL), and sonicated for 10 min. After complete dissolution, 114.1 mg BDC (terephthalic acid) was added, and the mixture was sonicated for another 10 minutes before being placed in a 120℃ oven for 24 h. After complete cooling, the sample was washed with N,N-2-methylformamide for 2 days, changing the solvent every half day; then washed with methanol for 2 days, changing the solvent every half day. Finally, the sample was vacuum dried at 200℃ for 24 h to obtain the sample named UiO-66-70eq-200. Example 2

[0031] The preparation process was the same as in Example 1, except that the water equivalent was 50 eq, the vacuum drying temperature was 200℃, and the sample name was UiO-66-50eq-200. Example 3

[0032] The preparation process was the same as in Example 1, except that the water equivalent was 20 eq, the vacuum drying temperature was 200℃, and the sample name was UiO-66-20eq-200.

[0033] Comparative Example 1

[0034] The preparation process was the same as in Example 1, except that no water was added, the vacuum drying temperature was 200℃, and the sample name was UiO-66-0eq-200. Example 4

[0035] The preparation process was the same as in Example 1, except that the water equivalent was 100 eq, the vacuum drying temperature was 200℃, and the sample name was UiO-66-100eq-200. Example 5

[0036] The preparation process was the same as in Example 1, except that the water equivalent was 100 eq, the vacuum drying temperature was 80℃, and the sample name was UiO-66-100eq-80. Example 6

[0037] The preparation process was the same as in Example 1, except that the water equivalent was 70 eq, the vacuum drying temperature was 80℃, and the sample name was UiO-66-70eq-80. Example 7

[0038] The preparation process was the same as in Example 1, except that the water equivalent was 50 eq, the vacuum drying temperature was 80℃, and the sample name was UiO-66-50eq-80. Example 8

[0039] The preparation process was the same as in Example 1, except that the water equivalent was 20 eq, the vacuum drying temperature was 80℃, and the sample name was UiO-66-20eq-80. Example 9

[0040] The preparation process was the same as in Example 1, except that the water equivalent was 4 eq, the vacuum drying temperature was 80℃, and the sample name was UiO-66-4eq-80.

[0041] Comparative Example 2

[0042] The preparation process was the same as in Example 1, except that no water was added and the vacuum drying temperature was 80°C, resulting in a sample named UiO-66-0eq-80.

[0043] X-ray diffraction analysis was performed on the samples obtained in Examples 1-9 and Comparative Examples 1-2. The results for the samples with vacuum drying activation temperature of 200°C are as follows: Figure 2 As shown, the results for samples activated by vacuum drying at 80℃ are as follows: Figure 1 As shown. The characteristic diffraction peaks of all samples matched well with the characteristic diffraction spectrum of UiO-66, indicating successful synthesis. Water incorporation promoted crystal nucleation within a certain range, resulting in an increase in the intensity of the main peak in the X-ray diffraction pattern (the peak intensity here refers to a point value, while the other is peak broadening. It increased at 4 eq, and then decreased slightly, but this decrease was acceptable. When the water equivalent exceeded 70 eq, the peak broadened at both 80℃ and 200℃, indicating significant damage to crystallinity, suggesting the sample no longer possessed the characteristics of UiO-66). However, the crystal structure was damaged after the water equivalent exceeded 70 eq. After high-temperature activation, the relative diffraction intensity of all water-added precursors significantly decreased, even transforming into an amorphous structure, which may be a defect caused by ligand shedding under high-temperature conditions.

[0044] Experiments revealed that adding water as a precursor additive promoted DMF decomposition, generating more formic acid ligands. Under high temperature (200℃), the formic acid ligands were removed, the electronic structure of the MOF changed, the color brightened, and the material exhibited photocatalytic activity. At 80℃, the formic acid ligands could not be removed, the color remained unchanged, and the resulting UiO-66 material did not possess photocatalytic activity. However, the high temperature also damaged the crystal structure of the MOF, reducing the specific surface area and increasing the number of defects, thus decreasing the adsorption performance. To highlight the photocatalytic activity, samples under 200℃ conditions (i.e., Examples 1-4 and Comparative Example 1) were subjected to nitrogen adsorption-desorption detection, and the results are as follows: Figure 3 , Figure 4 As shown in Table 1. Figure 3 , Figure 4 Table 1 reveals the pore structure of water-induced defect-type UiO after high-temperature activation. UiO-66-0eq-200 without water exhibits almost no microporous structure. In contrast, with increasing water addition, the specific surface area, micropore volume, and mesopore volume of UiO-66 increase, but the trend of specific surface area change differs from the pore size distribution characteristics. This suggests that water incorporation simultaneously regulates crystal growth and defect formation. At a water addition of 100 eq, the pore structure of UiO-66-100eq-200 is significantly weakened, indicating a substantial reduction in its crystal quality.

[0045] Table 1. Data on pore sizes of different samples

[0046] sample <![CDATA[BET specific surface area (m 2 / g)]]> <![CDATA[Micropore pore volume (cm 3 / g)]]> <![CDATA[Mesoporous pore volume (cm 3 / g)]]> UiO-66-0eq-200 676 0.25 0.03 UiO-66-20eq-200 797 0.27 0.18 UiO-66-50eq-200 740 0.23 1.04 UiO-66-70eq-200 699 0.17 1.16 UiO-66-100eq-200 604 0.11 0.63

[0047] This invention achieves the simultaneous synthesis of UiO-66 crystals, visible light excitation, and improvement of its adsorption performance by using almost cost-free water as a precursor additive and combining it with a high-temperature thermal activation process.

[0048] Electron paramagnetic resonance (EPR) analysis was performed on UiO-66 with different water equivalents and temperatures to induce activation defects. The results are as follows: Figure 5 As shown; the products obtained in Examples 1-3 and Comparative Example 1 were subjected to ultraviolet light adsorption detection, and the results are as follows. Figure 6As shown, electron paramagnetic resonance (EPR) spectra reveal that water-induced defect-type UiO-66 exhibits a significant free electron signal (g = 2.003, A < 10 G) after high-temperature activation, which is generally attributed to the formation of oxygen vacancies caused by the absence of ligands. The sample changed from white to yellow after high-temperature activation. Under high-temperature vacuum conditions, the crystal structure of MOFs may have changed, leading to adjustments in the electronic or band structure, thus affecting the optical properties of the material. With increasing water incorporation, the absorption of UiO-66 in the visible light range gradually increased. This implies that water incorporation can significantly narrow the band gap by introducing missing joint defects in UiO-66. The color change and band gap reduction indicate the formation of missing joint defects. The removal of organic joints in UiO-66 results in fewer bound oxygen states in the metal clusters, thus reducing the band gap.

[0049] The adsorption-photocatalytic performance of norfloxacin was evaluated in the samples obtained in Examples 1-3 and Comparative Example 1. The specific steps were as follows: The concentration of norfloxacin in the wastewater was 200 μg / L. 50 mL of wastewater was taken, and 4 mg of the sample catalyst (converted to a catalyst concentration of 0.08 g / L) was added. A xenon lamp was used to simulate sunlight, with a light power density of 0.077 W / cm². 2 The adsorption process lasted 90 minutes, followed by catalysis for 30 minutes. Adsorption was performed in a dark environment, while catalysis was conducted under light. Norfloxacin concentration was quantitatively analyzed using liquid chromatography-mass spectrometry (LC-MS).

[0050] The results are as follows Figure 7 As shown, compared to UiO-66-0eq-200 without water regulation, other water-induced defective UiO-66 samples activated at 200℃ showed considerable improvement in adsorption and photocatalytic performance. Due to the most favorable pore structure and visible light absorption range of UiO-66-70eq-200, it exhibited excellent norfloxacin removal performance, achieving complete adsorption and photocatalytic removal of 200 ppb of norfloxacin.

[0051] Finally, it should be noted that the above-listed embodiments are merely preferred embodiments of the present invention. Of course, those skilled in the art can make modifications and variations to the present invention. If such modifications and variations fall within the scope of the claims of the present invention and their equivalents, they should be considered as being within the protection scope of the present invention.

Claims

1. The application of UiO-66 metal-organic framework material in the treatment of norfloxacin in water, characterized in that, The preparation method of the UiO-66 metal-organic framework material includes the following steps: S1. Dissolve the zirconium salt in a mixed solution of N,N-dimethylformamide and water, and sonicate until fully dissolved; S2. After complete dissolution, add terephthalic acid and dissolve again by sonication. S3. After dissolving, place the mixture in an oven to maintain the temperature and allow it to react. S4. After the product has been removed and allowed to cool completely, it is first washed with N,N-dimethylformamide, and then washed with methanol. S5. After washing, the product was vacuum dried to obtain UiO-66 metal-organic framework material; the activation temperature for vacuum drying in S5 was 200℃, and the drying time was 24h. S1 zirconium salt is ZrCl4, and the ratio of ZrCl4, N,N-dimethylformamide and water is 160mg:40mL:(20~70) equivalents, where 4 equivalents of water is equivalent to 0.05mL of water.

2. The application of the UiO-66 metal-organic framework material according to claim 1 in the treatment of norfloxacin in water, characterized in that, The ultrasonic treatment time was 10 minutes for all patients.

3. The application of the UiO-66 metal-organic framework material according to claim 1 in the treatment of norfloxacin in water, characterized in that, The oven in S3 maintains a temperature of 120℃ for 24 hours.

4. The application of the UiO-66 metal-organic framework material according to claim 1 in the treatment of norfloxacin in water, characterized in that, S4 was cleaned with N,N-dimethylformamide for 2 days, with the liquid changed every half day; then it was cleaned with methanol for 2 days, with the liquid changed every half day.

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