A metal-organic framework-based heterogeneous Fenton catalyst, its preparation method and application

Abstract

This invention provides a metal-organic framework-based heterogeneous Fenton catalyst, its preparation method, and its application. The method includes: adding a tannic acid solution dropwise to a MIL-88A solution, stirring at room temperature, centrifuging, and drying to obtain MIL-88A@TA; and calcining the MIL-88A@TA. The catalyst preparation method provided by this invention uses the environmentally friendly iron-based MOF material MIL-88A as a substrate, and synthesizes a porous metal-organic framework-based heterogeneous Fenton catalyst through tannic acid modification combined with heat treatment. The porous structure and abundant defects of this catalyst enhance the mass transfer between the material and the target analyte and strengthen the interaction between the active sites in the material and H2O2, thereby accelerating the activation rate of H2O2.

Description

Technical Field

[0001] This invention relates to the field of catalyst technology, and in particular to a metal-organic framework-based heterogeneous Fenton catalyst, its preparation method, and its application. Background Technology

[0002] Water is a vital environmental carrier, playing a crucial role in the stability of the entire ecosystem. However, increasingly serious water pollution problems have severely threatened human health and the safety of ecosystems, especially persistent organic pollutants, which have even affected the safety of drinking water. Therefore, developing new, green, and efficient water purification technologies has become an urgent priority.

[0003] Fenton catalysis is considered a promising water treatment strategy due to its high reaction rate and ease of operation. Its essence lies in the activation of H₂O₂ by Fe ions to generate a large number of reactive oxygen species (ROS). These highly active ROS can rapidly decompose or even completely mineralize organic pollutants in water into inorganic small molecules (CO₂, H₂O, etc.). However, some drawbacks limit its further application, such as the need for large amounts of H₂O₂ and iron salts, the generation of iron sludge, and a narrow pH adaptability range. In recent years, novel heterogeneous Fenton technology based on nanomaterials has received widespread attention in the water treatment field. Compared to traditional homogeneous Fenton catalysis, heterogeneous Fenton technology using nanocatalysts has a wider pH adaptability, and the nanocatalysts are easy to separate and recycle, eliminating the need for frequent Fe ion replenishment and avoiding secondary pollution and iron sludge generation.

[0004] However, the widespread application of heterogeneous Fenton catalysts is still limited by problems such as high manufacturing costs (some catalysts require precious metals for preparation), narrow pH adaptability, and high H2O2 usage. For example, a functionalized multi-walled carbon nanotube, improved from existing technology, can remove more than 90% of the herbicide atrazine in water within 30 minutes. However, the molar concentration of H2O2 added to this heterogeneous Fenton system based on FCNT-H material is 500 times that of atrazine, resulting in significant waste due to this high oxidant dosage. Therefore, there is an urgent need to develop novel heterogeneous Fenton catalysts with low cost and high H2O2 utilization efficiency. Summary of the Invention

[0005] This invention aims to at least partially solve one of the technical problems in the prior art. Therefore, one object of this invention is to provide a metal-organic framework-based heterogeneous Fenton catalyst, its preparation method, and its applications.

[0006] In a first aspect, the present invention provides a method for preparing a metal-organic framework-based heterogeneous Fenton catalyst, comprising:

[0007] Tannic acid solution was added dropwise to MIL-88A solution, stirred at room temperature, centrifuged and dried to obtain MIL-88A@TA;

[0008] The MIL-88A@TA was heated and calcined.

[0009] According to the catalyst preparation method provided by the present invention, a porous metal-organic framework-based heterogeneous Fenton catalyst is synthesized using the environmentally friendly iron-based MOF material MIL-88A(Fe) as a substrate through tannic acid modification combined with heat treatment. The porous structure of this catalyst enhances mass transfer between the material and the target analyte, thereby accelerating the activation rate of H2O2 and improving the degradation rate of pollutants. Simultaneously, the catalyst possesses abundant defects, which strengthen the interaction between the active sites in the material and H2O2, thus enhancing the activation efficiency of H2O2. Furthermore, the raw materials used in the entire catalyst preparation process are low-cost, green, and non-toxic. Compared with other materials, the entire process avoids the use of toxic organic reagents and high-cost precious metals, significantly reducing production costs.

[0010] In some embodiments of the present invention, the mass ratio of tannic acid in the tannic acid solution to MIL-88A in the MIL-88A solution is (0.5-2):1. For example, mass ratios of 0.5:1, 1:1, 1.5:1, 2:1, or any range between these values. The inventors have discovered that by controlling the mass ratio of tannic acid in the tannic acid solution to MIL-88A in the MIL-88A solution within the above range, the thickness of the tannic acid shell layer on the surface of MIL-88A@TA can be adjusted, with an optimal mass ratio of 1:1 for MIL-88A and tannic acid.

[0011] In some embodiments of the present invention, the concentration of tannic acid in the tannic acid solution is 5-20 mg / mL.

[0012] In some embodiments of the present invention, the concentration of MIL-88A in the MIL-88A solution is 5-20 mg / mL.

[0013] In some embodiments of the present invention, the stirring time at room temperature is 6h-10h.

[0014] In some embodiments of the present invention, the centrifugation speed is 8000-10000 rpm.

[0015] In some embodiments of the present invention, the drying temperature is 50-70°C.

[0016] In some embodiments of the present invention, the calcination temperature is 150~450℃, preferably 200℃-300℃, and the calcination time is 3h-5h. For example, the calcination temperature is 150℃, 200℃, 250℃, 300℃, 350℃, 450℃, etc., or any range between any two of the above values; the time is 3h, 4h, 5h, etc., or any range between any two of the above values. The inventors have found that by controlling the calcination temperature and time within the above ranges, the specific surface area and defect degree of the prepared material can be controlled.

[0017] In some embodiments of the present invention, the rate of heating to the calcination temperature is 1-5°C / min.

[0018] In some embodiments of the present invention, the catalyst preparation method further includes: washing the calcined product with deionized water to remove impurities and then drying it. Further, the drying temperature is 50-70°C.

[0019] In a second aspect, the present invention provides a metal-organic framework-based heterogeneous Fenton catalyst, which is prepared by the above method.

[0020] In some embodiments of the present invention, the specific surface area of ​​the catalyst is 40-50 m². 2 / g. This catalyst has a large specific surface area, and therefore exhibits excellent catalytic activity.

[0021] In a third aspect, the present invention proposes the application of the above-mentioned metal-organic framework-based heterogeneous Fenton catalyst in the degradation of atrazine in water.

[0022] In some embodiments of the present invention, the molar ratio of H2O2 and atrazine added to the water is (30-40):1.

[0023] The present invention has at least the following beneficial effects:

[0024] (1) The raw materials used in the entire preparation process of the catalyst of the present invention are all low-cost, green and non-toxic raw materials. Compared with other materials, the entire process avoids the use of toxic organic reagents and high-cost precious metals.

[0025] (2) The catalyst prepared by this invention has a porous structure, which enhances the mass transfer between the material and the target, thereby accelerating the activation rate of H2O2 and thus improving the degradation rate of pollutants. At the same time, the catalyst has abundant defects, which strengthen the interaction between the active sites in the material and H2O2, thereby enhancing the activation efficiency of H2O2.

[0026] (3) The catalyst of the present invention can still degrade more than 99% of atrazine (2-[4-chloro-6-(ethoxymethoxy)-1,3,5-triazine-2-yl]amino-4-(methoxycarbonyl)-3-hydroxy-5-isooxazolidine) within 30 minutes even with low H2O2 dosage. The heterogeneous Fenton catalyst of the present invention has extremely excellent H2O2 utilization efficiency.

[0027] (4) The catalyst of the present invention can be recycled and reused many times after use, and its catalytic activity is almost reduced. It can still degrade more than 99% of atrazine in 30 minutes. The catalyst of the present invention has excellent stability. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0029] Figure 1 This is a SEM image of MIL-88A provided in Embodiment 1 of the present invention;

[0030] Figure 2 This is a SEM image of MIL-88A@TA provided in Embodiment 1 of the present invention;

[0031] Figure 3 This is a SEM image of MIL-88A@TA-2 provided in Embodiment 1 of the present invention;

[0032] Figure 4 These are nitrogen adsorption-desorption isotherm spectra of MIL-88A, MIL-88A@TA, and MIL-88A@TA-2 provided in Example 1 of this invention;

[0033] Figure 5 The graph shows the ATZ degradation activity test results of the catalysts in the embodiments and comparative examples of this invention.

[0034] Figure 6 This is a graph showing the stability test results of the catalyst prepared in Example 1 of this invention. Detailed Implementation

[0035] Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this invention. The invention will now be described with reference to specific embodiments. It should be noted that these embodiments are merely descriptive and do not limit the invention in any way.

[0036] Example 1

[0037] This embodiment provides a metal-organic framework-based heterogeneous Fenton catalyst, the specific preparation process of which is as follows:

[0038] (1) Preparation of MIL-88A(Fe)

[0039] Fumaric acid (C4H4O4, 5 mM, 580 mg) and ferric chloride hexahydrate FeCl3⋅6H2O (5 mM, 1.3520 g) were dispersed in 30 mL of ultrapure water and stirred for 30 minutes. The suspension was transferred to a reaction vessel and then placed in a 65°C oven for 12 h. The resulting solution was then centrifuged, and the precipitate was washed three times with deionized water and three times with ethanol, and dried overnight in a 60°C vacuum drying oven to obtain the MIL-88A(Fe) catalyst.

[0040] (2) Preparation of MIL-88A@TA

[0041] Add 800 mg of MIL-88A prepared in step (1) to 80 mL of ultrapure water and sonicate for 30 minutes. The resulting suspension is denoted as solution A. Then, add 800 mg of tannic acid to 80 mL of ultrapure water and stir continuously until completely dissolved. The resulting reaction solution is denoted as solution B. Subsequently, slowly add solution B to solution A and stir at room temperature for 8 h. Then, centrifuge the resulting solution at 10,000 rpm and wash the precipitate three times with deionized water and ethanol, respectively. Finally, place the washed material in a vacuum drying oven at 60 °C and dry overnight. Then, grind the resulting product into powder to obtain MIL-88A@TA.

[0042] (3) Preparation of metal-organic framework-based heterogeneous Fenton catalysts

[0043] 200 mg of MIL-88A@TA was poured into a covered alumina crucible and transferred to a tube furnace. The mixture was calcined for 240 minutes at a preset temperature of 200 °C and a heating rate of 2 °C / min, with nitrogen gas continuously purging throughout the calcination process. After the reaction, the material was washed three times with deionized water to remove surface impurities. Finally, the washed product was vacuum-dried overnight at 60 °C to obtain the metal-organic framework-based heterogeneous Fenton catalyst (denoted as MIL-88A@TA-2).

[0044] The material morphology of MIL-88A, MIL-88A@TA, and MIL-88A@TA-2 prepared in Example 1 was characterized by scanning electron microscopy (SEM), as detailed in the figure below. Figures 1-3 . Figure 1The image shows a SEM image of MIL-88A, which has a smooth surface and is a bipyramidal tetragonal prism shape, about 300 nm wide and 1.5 μm long. Figure 2 The image shows a SEM image of MIL-88A@TA. The overall morphology is similar to that of MIL-88A, but the surface becomes slightly rougher, indicating that the modification of tannic acid affects its surface structure. Figure 3 The image shows a SEM image of MIL-88A@TA-2, where the surface becomes spongy, indicating the presence of a rich porous structure.

[0045] Figure 4 The nitrogen adsorption-desorption isotherms of MIL-88A, MIL-88A@TA, and MIL-88A@TA-2 show that the specific surface area of ​​MIL-88A@TA-2 is 44 m². 2 / g) and MIL-88A (13 m 2 / g) and MIL-88A@TA (23 m 2 The significant increase in g compared to the previous year further demonstrates that MIL-88A@TA-2 has a porous structure.

[0046] Example 2

[0047] The only difference between Example 2 and Example 1 in the catalyst preparation process is that the preset temperature of the tube furnace in step (3) of Example 3 is 300℃. The obtained catalyst is denoted as MIL-88A@TA-3.

[0048] Example 3

[0049] The only difference between Example 3 and Example 1 in the catalyst preparation process is that the preset temperature of the tube furnace in step (3) of Example 3 is 400℃. The obtained catalyst is denoted as MIL-88A@TA-4.

[0050] Comparative Example 1

[0051] This comparative example provides a catalyst, the specific preparation process of which is as follows:

[0052] (1) Preparation of MIL-88A(Fe) The specific preparation process is the same as in Example 1.

[0053] (2) Preparation of catalyst

[0054] 200 mg of MIL-88A was poured into a covered alumina crucible and transferred to a tube furnace. The crucible was calcined for 240 minutes at a preset temperature of 200 °C and a heating rate of 2 °C / min, with nitrogen gas continuously purging throughout the calcination process. After the reaction, the material was washed three times with deionized water to remove surface impurities. Finally, the washed product was vacuum-dried overnight at 60 °C to obtain the metal-organic framework-based heterogeneous Fenton catalyst (denoted as MIL-88A-2).

[0055] Comparative Example 2

[0056] The only difference between the preparation process of the catalyst in Comparative Example 2 and Comparative Example 1 is that the preset temperature of the tube furnace in step (2) of Comparative Example 2 is 300℃, and the catalyst is designated as MIL-88A-3.

[0057] Comparative Example 3

[0058] The only difference between the preparation process of the catalyst in Comparative Example 3 and Comparative Example 1 is that the preset temperature of the tube furnace in step (2) of Comparative Example 3 is 400℃, and the catalyst is denoted as MIL-88A-4.

[0059] 1) The photo-Fenton degradation activity of the catalysts in the examples and comparative examples, as well as MIL-88A and MIL-88A@TA, on the pesticide atrazine (ATZ) in water was determined.

[0060] Simulated pesticide wastewater with a concentration of 10 mg / L was prepared using ATZ standard reagent (Shanghai Maclean Biochemical Reagent Co., Ltd.) and deionized water. The experiment was conducted in a 100 mL nested beaker equipped with a circulating condenser under magnetic stirring at a temperature maintained at 25 °C. Before the degradation experiment, 50 mL of ATZ solution (10 mg / L) was added to the nested beaker, followed by 20 mg of catalyst (MIL-88A, MIL-88A@TA, MIL-88A-2, MIL-88A-3, MIL-88A-4, MIL-88A@TA-2, MIL-88A@TA-3, MIL-88A@TA-4, 8 parallel experiments). The mixture was stirred in the dark for 60 minutes to reach adsorption-desorption equilibrium. Subsequently, 100 μL of H₂O₂ (Shanghai Maclean Biochemical Reagent Co., Ltd., 3wt% concentration) was added to the mixed solution containing the catalyst and ATZ to initiate the reaction, while irradiation was performed using a 50 W xenon lamp (Beijing Baofeilai Technology Co., Ltd., equipped with a filter with λ>420 nm to remove ultraviolet light). During the reaction, aliquots were periodically collected and immediately quenched with excess Na₂S₂O₃ (Shanghai Maclean Biochemical Reagent Co., Ltd.), then filtered through a 0.22 μm membrane to remove the solid catalyst and stored in amber vials for analysis. Finally, the concentration of ATZ in the samples was determined using high-performance liquid chromatography (HPLC).

[0061] The results of the ATZ degradation activity test are shown below. Figure 5 Among all the catalysts, MIL-88A@TA-2 exhibited the best catalytic activity. Furthermore, the catalytic activities of MIL-88A, MIL-88A-2, MIL-88A-3, and MIL-88A-4 (without tannic acid modification) after heat treatment at different temperatures were all inferior to MIL-88A@TA-2. This indicates that tannic acid modification and the 200℃ heat treatment process are crucial for improving the catalytic activity of the materials. In addition, the molar ratio of H2O2 to ATZ in the MIL-88A@TA-2 photo-Fenton system in this example was 38:1, far lower than the ratio reported in other materials in the literature (500:1). This demonstrates that even with low H2O2 content, the catalyst of this invention can still degrade more than 99% of ATZ within 30 minutes, indicating that the heterogeneous Fenton catalyst synthesized in this invention has extremely excellent H2O2 utilization efficiency.

[0062] 2) To investigate the stability of the catalyst provided by this invention, five recycling and reuse experiments were conducted using the catalyst MIL-88A@TA-2 prepared in Example 1 as the subject. The test procedure is as follows: First, the first ATZ degradation experiment was conducted according to the activity test method in 1). During the experiment, all solid materials were recovered, and the recovered materials were washed with deionized water to remove the residual degradation products from the previous experiment. Then, the recovered materials were tested again according to the steps in 1), and so on, for a total of five reaction experiments.

[0063] The stability test results of the catalyst are as follows: Figure 6 As shown, the MIL-88A@TA-2 Fenton catalyst exhibited almost no decrease in catalytic activity after five recycling cycles, and could still degrade over 99% of ATZ within 30 minutes. This demonstrates the excellent stability of the catalyst synthesized in this invention.

[0064] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a metal-organic framework-based heterogeneous photo-Fenton catalyst, characterized in that, include: Tannic acid solution was added dropwise to MIL-88A solution, stirred at room temperature, centrifuged and dried to obtain MIL-88A@TA; The mass ratio of tannic acid in the tannic acid solution to MIL-88A in the MIL-88A solution is (0.5-2):1; The MIL-88A@TA is heated and calcined at a temperature of 200-300℃ for 3-5 hours.

2. The method according to claim 1, characterized in that, The concentration of tannic acid in the tannic acid solution is 5-20 mg / mL; And / or, the concentration of MIL-88A in the MIL-88A solution is 5-20 mg / mL.

3. The method according to claim 1, characterized in that, The stirring time at room temperature is 6-10 hours. And / or, the centrifugation speed is 8000-10000 rpm; And / or, the drying temperature is 50-70°C.

4. The method according to any one of claims 1-3, characterized in that, The rate at which the temperature is increased to the calcination temperature is 1-5℃ / min.

5. The method according to any one of claims 1-3, characterized in that, Also includes: The product obtained after calcination was washed with deionized water to remove impurities and then dried.

6. A metal-organic framework-based heterogeneous photo-Fenton catalyst, characterized in that, It is prepared by any one of the methods described in claims 1-5.

7. The catalyst according to claim 6, characterized in that, The catalyst has a specific surface area of ​​40-50 m². 2 / g.

8. The application of the metal-organic framework-based heterogeneous photo-Fenton catalyst according to claim 6 or 7 in the degradation of atrazine in water.

9. The application according to claim 8, characterized in that, The molar ratio of H2O2 and atrazine added to the water is (30-40):1.

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