Magnesium-Manganese Binary Metal-Organic Framework Catalyst and Its Preparation Method and Application

Abstract

The present invention discloses a magnesium-manganese binary metal-organic framework catalyst, a preparation method thereof and an application thereof. The preparation method comprises the following steps: doping Mn element into a metal-organic framework Mg-MOF by an impregnation method, and then calcining at 400-600 °C for 1-3 h in an inert atmosphere to obtain a magnesium-manganese binary metal-organic framework catalyst MgMn-CMOF; when doping the Mn element by the impregnation method, the doping amount of the Mn element is 0.5%-3% of the mass of the metal-organic framework Mg-MOF. The magnesium-manganese binary metal-organic framework catalyst of the present invention has excellent catalytic ozone oxidation ability.

Description

Technical Field

[0001] The present invention relates to the field of preparation of doped catalysts, and particularly to a magnesium-manganese bimetallic organic framework catalyst, a preparation method thereof, and an application thereof. Background Art

[0002] Ozone, as an effective oxidant, is widely used in drinking water and wastewater treatment. The direct reaction of ozone with organic compounds sometimes produces some by-products that are inactive to ozone, such as acetic acid, resulting in a reduction in oxidation efficiency. Therefore, advanced ozone oxidation processes (AOP-O3), such as catalytic ozonation, H2O2 / O3, and UV / O3, have emerged. In this process, ozone is effectively converted into hydroxyl radicals. Hydroxyl radicals always react quickly and non-selectively with most organic compounds, thus improving the mineralization rate. Heterogeneous catalytic ozonation is considered a promising method due to its high efficiency, convenient operation, etc. The key to this process is the preparation of an efficient catalyst.

[0003] As a solid base catalyst, magnesium oxide has mainly three reaction mechanisms for catalytic ozonation: (1) Its pH PZC is relatively high, and the pH in the ozone degradation environment can be increased to increase the hydroxyl radicals (·OH) generated on the surface of ozone, thereby improving the ozonation efficiency; (2) In the experiment, the surface properties of nano-MgO were analyzed by Fourier transform spectroscopy and isoelectric point, showing that the basic groups on the surface of MgO can promote ozone to generate ·OH; (3) The lattice defects and surface acidic sites of magnesium oxide decompose ozone to generate oxygen-containing free radicals.

[0004] Chinese patent document with publication number CN110773160A discloses an ozone oxidation catalyst, which is prepared by loading at least one metal oxide on magnesium oxide as a carrier, and the molar ratio of the metal oxide to magnesium oxide is 1:10-100; the invention also discloses a preparation method of the above ozone oxidation catalyst, including the steps of coprecipitation, aging, washing, drying, and calcination in sequence; the invention also discloses the application of the above ozone oxidation catalyst for removing organic substances in wastewater.

[0005] Chinese patent document with publication number CN104437546B discloses a heterogeneous ozone catalyst, which includes 36.4%-52.4% of water slag micropowder, 9.1%-14.3% of magnesium oxide (MgO), 18.2%-23.8% of magnesium chloride hexahydrate (MgCl2·6H2O), 4.8%-9% of a foaming agent, and 9.1%-19% of a catalytic active mixture.

[0006] Metal-organic framework materials are a new type of porous materials, which are mainly composed of multi-dentate organic ligands of aromatic acids or bases containing elements such as oxygen and nitrogen and inorganic metal ions to form a three-dimensional periodic network skeleton structure through coordination bond interactions. Compared with transition metal elements, Mg 2+ and Fe 2+ , Co 2+ , Ni 2+ , Zn 2+ have similar radii and hydration energies, and all adopt 6-coordination to form an octahedral configuration. Porous metal-organic framework materials based on magnesium (Mg-MOFs) have potential application values in gas storage and separation, drug slow release, etc., and the research on Mg-MOFs has gradually entered the queue of the water treatment field. Summary of the Invention

[0007] The present invention provides a magnesium-manganese binary metal-organic framework catalyst and a preparation method thereof, which have excellent catalytic ozone oxidation ability.

[0008] The technical solution of the present invention is as follows:

[0009] A preparation method of a magnesium-manganese binary metal-organic framework catalyst includes the following steps:

[0010] Dope Mn element into the metal-organic framework Mg-MOF by the impregnation method, and then calcine at 400-600 °C for 1-3 h in an inert atmosphere to obtain the magnesium-manganese binary metal-organic framework catalyst MgMn-CMOF; when doping Mn element by the impregnation method, the doping amount of Mn element is 0.5%-3% of the mass of the metal-organic framework Mg-MOF.

[0011] Preferably, the metal-organic framework Mg-MOF is prepared by the solvothermal method.

[0012] Preparing the metal-organic framework Mg-MOF by the solvothermal method includes:

[0013] Dissolve magnesium salt and 2,5-dihydroxyterephthalic acid in organic solvents respectively, then mix them, heat and react in a high-pressure reaction kettle, cool and separate the precipitate after the reaction is complete, wash and dry to obtain the metal-organic framework Mg-MOF.

[0014] The Mn element can be doped into the metal-organic framework Mg-MOF by the equal-volume impregnation method.

[0015] When doping Mn element by the impregnation method, the calculation formula for the doping amount of Mn element is: doping amount of Mn element = (mass of doped Mn element / mass of Mg-MOF) × 100%.

[0016] Compared with calcination in an air atmosphere, calcination under the protection of an inert gas has a great effect on the support of the microstructure of the material by the remaining carbon in the organic ligand. After calcination under the protection of an inert gas, the original layered structure of the MOFs becomes loose and porous and still maintains the basic framework structure, which greatly increases the specific surface area of the catalyst, thereby increasing the active sites of the catalyst and increasing the contact opportunity between ozone and the active sites of the catalyst, thus greatly improving the catalytic performance of the catalyst for ozone oxidation.

[0017] The inert atmosphere described is a nitrogen atmosphere.

[0018] The present invention also provides a magnesium-manganese bimetallic organic framework catalyst prepared by the above preparation method.

[0019] With the assistance of basic sites (basic sites refer to protonated hydroxyl groups), the electron transfer of multivalent manganese ions in the acidic site lattice of the magnesium-manganese bimetallic organic framework catalyst of the present invention promotes the decomposition of ozone. During the calcination process, manganese forms a new crystal structure with magnesium-containing oxides, forming a small amount of Mg-O-Mn in the original structure of only Mg-O-Mg, forming a magnesium-manganese bimetallic oxide. The basic strength of lattice oxygen in Mg-O-Mn is weaker than that of lattice oxygen in Mg-O-Mg, reducing the dissolution of Mg 2+ and making the catalyst exhibit excellent stability.

[0020] The present invention also provides an application of the above magnesium-manganese bimetallic organic framework catalyst in catalytic ozone degradation of wastewater.

[0021] The application described includes: adding the magnesium-manganese bimetallic organic framework catalyst to the wastewater to be treated, and then introducing ozone for oxidation treatment.

[0022] Preferably, the dosage of the magnesium-manganese bimetallic organic framework catalyst is 0.1-0.5 g / L; the pH of the wastewater to be treated is 3-9.

[0023] Preferably, the main pollutant of the wastewater to be treated is a small molecule acid; in the magnesium-manganese bimetallic organic framework catalyst, the doping amount of Mn element is 0.5-1%.

[0024] The small molecule acid is acetic acid.

[0025] Preferably, the main pollutant of the wastewater to be treated is a chloroaromatic compound; in the magnesium-manganese bimetallic organic framework catalyst, the doping amount of Mn element is 1-3%.

[0026] The chloroaromatic compound is p-chlorobenzoic acid.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] (1) In the magnesium-manganese bimetallic organic framework catalyst of the present invention, the adsorption of carbon on organic matter can enrich organic pollutants in water during the catalytic process, enhancing the utilization rate of oxygen active particles generated by MgMn x -CMOF, such as ·OH, O2 - etc., thereby improving the oxidation efficiency;

[0029] (2) The magnesium-manganese bimetallic organic framework catalyst of the present invention has excellent stability, improving the reusable rate of the magnesium-manganese bimetallic organic framework catalyst in water;

[0030] (3) According to needs, the content of manganese in the catalyst can be adjusted accordingly to always achieve the best treatment effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 SEM diagrams of the products of each step in Example 2; among them, (a) is the Mg-MOF precursor obtained in step 5, (b) is the MgMn1-MOF obtained in step 6, (c) is the MgMn1-CMOF obtained in step 7, and (d) is MgMnO prepared by the coprecipitation method;

[0032] Figure 2 EDS diagram of the MgMn1-CMOF prepared in Example 2;

[0033] Figure 3 XRD diagrams of the MgMn1-CMOF prepared in Example 2 and MgMnO prepared by the coprecipitation method;

[0034] Figure 4 Anodic polarization curves of glassy carbon electrodes (the electrolyte is sodium sulfate solution); among them, (a) is the glassy carbon electrode loaded with MgMn1-CMOF, and (b) is the glassy carbon electrode loaded with MnO2;

[0035] Figure 5 Schematic diagram of the catalytic mechanism of MgMn x -CMOF of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0036] Examples 1-3

[0037] 1. Take 15 mL of anhydrous ethanol and 25 mL of N,N-dimethylformamide in a beaker and mix them evenly for use as an organic solvent;

[0038] 2. Weigh 8 mmol of Mg(NO3)2·6H2O and dissolve it in the previously prepared organic solvent and stir evenly to obtain Solution A;

[0039] 3. Weigh 4 mmol of 2,5-dihydroxyterephthalic acid and dissolve it in the previously prepared organic solvent and stir well to form Solution B.

[0040] 4. Slowly pour Solution B into Solution A, continue to stir and mix the solution evenly, then transfer the obtained mixed solution to a polytetrafluoroethylene high-pressure reactor, heat and react in an oven for 12 h, and take it out after it naturally cools to room temperature.

[0041] 5. Collect the precipitate in the hydrothermal kettle by centrifugation, then wash it 3 times with ethanol until the supernatant is clear, and finally dry the precipitate in an oven for 12 h to obtain the Mg-MOF precursor.

[0042] 6. Weigh 1 g of the Mg-MOF precursor and dope different proportions of manganese elements by the equal-volume impregnation method to obtain MgMn x -MOF.

[0043] 7. After thoroughly grinding MgMn x -MOF, place it in a tubular furnace, introduce nitrogen, and calcine it at 500 °C for 2 h to obtain MgMn x -CMOF doped with different manganese contents.

[0044] In step 6, through preliminary experiments, the saturated impregnation amount of this Mg-MOF precursor is measured to be 0.8 ml / g; prepare manganese-containing solutions with different contents by dissolving appropriate amounts of manganese chloride in 0.8 ml of deionized water for impregnation. Adjust the doping amount of manganese in MgMn x -CMOF by adjusting the concentration of the manganese-containing solution.

[0045] For MgMn x -CMOF in Examples 1-3, x is 0.5, 1, and 3 respectively.

[0046] In MgMn x -MOF, when doping manganese elements by the equal-volume impregnation method, x% = mass ratio of impregnated Mn element to Mg-MOF; for example, when x = 3, it means the mass ratio of impregnated Mn element to Mg-MOF is 3 / 100. In actual operation, take 1 g of the Mg-MOF precursor and mix it with 0.8 mL of a solution containing 0.0686 g of MnCl2.

[0047] Regarding the process of preparing MgMn1-CMOF in Example 2, the SEM image of the Mg-MOF precursor obtained in step 5 is as shown in Figure 1 (a), the SEM image of MgMn1-MOF obtained after impregnating with the manganese-containing solution in step 6 is as shown in Figure 1 (b), and the SEM image of MgMn x -CMOF obtained after calcination in step 7 is as shown in Figure 1As shown in (c), the SEM image of MgMnO prepared by the co-precipitation method is as Figure 1 shown in (d) in

[0048] As can be seen from Figure 1 , the Mg-MOF precursor exhibits an obvious layered structure; after impregnation, the MgMn1-MOF has many layered structures and is very smooth, showing a terraced structure, with fine grains appearing between and on the layers; after nitrogen calcination, the original MOF layered structure of MgMn1-MOF becomes porous, forming MgMn1-CMOF that still maintains a basic framework and has a large number of crystalline particles interspersed and attached therein. Figure 1 In (d), the MgMnO material prepared by the co-precipitation method is in the form of nanoscale microspheres, and the particles are stacked relatively tightly, prone to agglomeration during the ozone degradation process, and the powder is not easy to recover, with poor reuse rate. Combining with the specific surface area data can also show that the number of basic sites is small, resulting in its degradation efficiency being inferior to that of the MgMnx-CMOF prepared by the present invention.

[0049] The MgMn x -CMOF prepared by the present invention has the following advantages: 1) It has a high specific surface area and can provide a large number of surface active sites; 2) It has the ability to increase the pH of the solution, which is helpful for the ozone oxidation ability; 3) It generates protonated hydroxyl groups on the catalyst surface. All of these can promote the decomposition of ozone to generate a large number of oxygen-containing free radicals, thereby improving the degradation effect of organic substances.

[0050] The EDS of the MgMn1-CMOF prepared in Example 2 is as Figure 2 shown, in which the mass percentages of carbon, magnesium, and manganese elements in MgMn1-CMOF are 21.34%, 29.10%, and 6.73% of the total mass of MgMn1-CMOF, respectively.

[0051] Comparative Example 1

[0052] 1. Take 15 mL of absolute ethanol and 25 mL of N,N-dimethylformamide in a beaker and mix them evenly for use as an organic solvent.

[0053] 2. Weigh 8 mmol of Mg(NO3)2·6H2O and dissolve it in the previously prepared organic solvent and stir evenly to obtain Solution A.

[0054] 3. Weigh 4 mmol of 2,5-dihydroxyterephthalic acid and dissolve it in the previously prepared organic solvent and stir evenly to obtain Solution B.

[0055] 4. Slowly pour Solution B into Solution A, continue to stir and mix the solution evenly, then transfer the obtained mixture to a polytetrafluoroethylene high-pressure reaction kettle, heat and react in an oven for 12 h, and take it out after it naturally cools to room temperature.

[0056] 5. Collect the precipitate in the hydrothermal reactor by centrifugation, then wash it three times with ethanol until the supernatant is clear, and finally dry the precipitate in an oven for 12 h to obtain the Mg-MOF precursor;

[0057] 6. Place the well-ground Mg-MOF in a tubular furnace, introduce nitrogen, and calcine it at 500 °C for 2 h to obtain Mg-CMOF.

[0058] Comparative Example 2

[0059] 1. Take 15 mL of absolute ethanol and 25 mL of N,N-dimethylformamide and mix them evenly in a beaker as the organic solvent for standby;

[0060] 2. Weigh 8 mmol of Mg(NO3)2·6H2O and dissolve it in the previously prepared organic solvent and stir evenly to obtain Solution A;

[0061] 3. Weigh 4 mmol of 2,5-dihydroxyterephthalic acid and also dissolve it in the previously prepared organic solvent and stir evenly to obtain Solution B;

[0062] 4. Slowly pour Solution B into Solution A, continue to stir and mix the solution evenly, then transfer the obtained mixed solution to a polytetrafluoroethylene high-pressure reactor, heat and react it in an oven for 12 h, and take it out after it naturally cools to room temperature;

[0063] 5. Collect the precipitate in the hydrothermal reactor by centrifugation, then wash it three times with ethanol until the supernatant is clear, and finally dry the precipitate in an oven for 12 h to obtain the Mg-MOF precursor;

[0064] 6. Weigh 1 g of the Mg-MOF precursor and dope 1% of manganese element by the equal-volume impregnation method to obtain MgMn1-MOF;

[0065] 7. Place the well-ground MgMn1-MOF in a tubular furnace, introduce air, and calcine it at 500 °C for 2 h to obtain MgMn1-CMOF(air).

[0066] Comparative Example 3

[0067] Prepare a magnesium-manganese binary oxide powder catalyst by the coprecipitation method. The preparation steps are as follows:

[0068] (1) Dissolve 0.04 mol of Mg(NO3)2·6H2O and 0.04 mol of Mn(NO3)2 solution in 60 mL of secondary distilled water;

[0069] (2) Drop 140 mL of NaOH solution (6 mol / L) into the above solution;

[0070] (3) The solution obtained in step (2) is stirred in an oil bath at 90 °C for 2 h in a temperature-controlled magnetic stirrer;

[0071] (4) The solution obtained in step (3) is centrifuged to obtain the lower-layer precipitate, which is washed with water and then centrifuged again. The washing with water and centrifugation are repeated until the pH of the supernatant after centrifugation is less than 9;

[0072] (5) The precipitate collected in step (4) is dried in a vacuum drying oven at 80 °C for 12 h;

[0073] (6) The substance obtained in step (5) is calcined in a muffle furnace at 500 °C for 2 h while introducing nitrogen gas to obtain magnesium manganese binary oxide, labeled as MgMnO.

[0074] The specific surface areas of the catalysts prepared in Example 2, Comparative Example 2, and Comparative Example 3 were measured, and the results are shown in Table 1.

[0075] Table 1. Specific surface areas of magnesium manganese binary metal oxides prepared by different methods

[0076] <![CDATA[BET Surface Area(m 2 / g)]]> <![CDATA[MgMn1-CMOF(N2)]]> 589.11 MgMn-CMOF(air) 319.69 <![CDATA[MgMnO coprecipitation method (N2)]]> 203.75

[0077] As can be seen from Table 1, the surface area of MgMn1-CMOF(N2) is the largest, which is 1.84 times and 2.89 times that of MgMn-CMOF(air) calcined in air and MgMnO co-precipitation method (N2), respectively. It can be judged that the formation of metal-organic frameworks has a great effect on the formation of the specific surface area of magnesium-based oxides. Moreover, compared with MgMn-CMOF(air) formed by calcination in air, under the protection of inert gas N2, the remaining carbon in the organic ligand plays a great role in supporting the microstructure of the material.

[0078] The XRD analysis results of MgMn1-CMOF obtained after calcination in nitrogen gas were compared with the standard card, and the positions and intensities of all main peaks corresponded to each other, as Figure 3 shown. It is proved that the preparation method of the present invention forms a stable double-metal magnesium manganese oxide structure.

[0079] Loading MgMn x -CMOF on the glassy carbon electrode, the anodic polarization curve (the electrolyte is sodium sulfate solution, and 10 mg / ml ozone is introduced into the electrolyte for 3 min; at the same time, a control without ozone introduction is made) is as shown in Figure 4 (a); the anodic polarization curve of the glassy carbon electrode loaded with MnO2 (the electrolyte is sodium sulfate solution containing ozone) is as shown in Figure 4 (b).

[0080] The results of linear voltammetry scanning method ( Figure 4 ) show that MgMn x-CMOF undergoes an electron transfer reaction with ozone (a), while MnO2 does not undergo an electron transfer reaction with ozone (b), indicating that Mn in the lattice formed by Mg-O-Mn 2+ can undergo an electron transfer reaction with ozone with the assistance of protonated hydroxyl groups at the basic sites.

[0081] With the assistance of basic sites, MgMn x - The electron transfer of multivalent manganese ions in the acidic sites of CMOF also promotes the decomposition of ozone; the doping of manganese ions changes the crystal form of the original magnesium-containing oxide, making the basicity of lattice oxygen weaker than that of lattice oxygen in Mg-O-Mg, reducing the 2+ dissolution of Mg, showing excellent stability; its high efficiency and easy operation have reference value for the research and development of the degradation of industrial actual wastewater.

[0082] Example 4

[0083] Prepare 200 mL of acetic acid solution containing 20 mg / L, adjust the pH to 6, and then add the MgMn x -CMOF (x = 0, 0.5, 1, 3) catalysts prepared in Comparative Example 1 and Examples 1-3. The dosage is 0.2 g / L, and then add them to a tubular ozone reactor, and introduce ozone from the bottom. After the experiment starts, sample and detect every 3 minutes. The ozone input amount is 40 mg / L (the ozone concentration in the oxygen and ozone mixture treated by the ozone generator), and the gas flow rate is 0.5 L / min.

[0084] At the start of the experiment, at 0 min, 3 min, 6 min, and 9 min treatment periods, extract 1 mL of the sample, filter it through a 0.22 μm syringe filter into a brown sample bottle for high performance liquid chromatography analysis, and the detection results are shown in Table 2.

[0085] Detection method: Acetic acid is detected by high performance liquid chromatography. Instrument model: ThermoFisher DionexUltimate3000; Chromatographic column: Hypersil GOLD C18 (Themo Fisher, USA), 250 mm × 4.6 mm; Mobile phase: A mixture of methanol and 1 g / L phosphoric acid, with a volume ratio of 1:19, and the pH is adjusted to 3; Flow rate: 0.8 mL / min; Ultraviolet absorption wavelength: 210 nm.

[0086] Table 2. Removal of acetic acid in the single ozone and MgMn x -CMOF / O3 system

[0087]

[0088] Example 5

[0089] Put 0.04 g of MgMn 0.5 -CMOF catalyst into the prepared 200 mL acetic acid solutions containing 2, 10, and 50 mg / L respectively, and adjust the pH to 6. Then add it to the tubular ozone reactor and introduce oxygen from the bottom. After the experiment starts, samples are taken for detection every 3 min. The oxygen input is 40 mg / L and the gas flow rate is 0.5 L / min.

[0090] Detect the adsorption amount of MgMn 0.5 -CMOF catalyst for acetic acid, and the results are shown in Table 3. The sampling and liquid chromatography detection methods are the same as in Example 1.

[0091] Table 3. Adsorption of MgMn 0.5 -CMOF on acetic acid solutions with different concentrations

[0092] AcOH adsorption rate 2mg / L 10mg / L 20mg / L 3min 10.2％ 1.3％ 0.4％ 6min 12.5％ 1.5％ 0.4％ 9min 12.9％ 1.5％ 0.5％

[0093] Example 6

[0094] Prepare 200 mL of a solution containing 50 mg / L of p-chlorobenzoic acid (p-CBA), adjust the pH to 6, and then add the MgMn x -CMOF (x = 0, 0.5, 1, 3) catalysts prepared in Comparative Example 1 and Examples 1-3. The dosage is 0.2 g / L, and then add it to the stirred ozone reactor and insert a gas pipe to introduce ozone from the bottom. The ozone dosage is 10 mg / L. After the experiment starts, samples are taken for detection every 3 min. The ozone input is 20 mg / L (the ozone concentration in the oxygen and ozone mixture treated by the ozone generator), and the gas flow rate is 0.5 L / min.

[0095] At the start of the experiment, at the 0 min, 3 min, 6 min, and 9 min treatment periods, 1 mL of the sample is taken, filtered through a 0.22 μm syringe filter into a brown sample bottle for high-performance liquid chromatography analysis, and the detection results are shown in Table 4.

[0096] Detection method: p-CBA is detected by high-performance liquid chromatography. Instrument model: ThermoFisher DionexUltimate3000; chromatographic column: Hypersil GOLD C18 (Themo Fisher, USA), 250 mm × 4.6 mm; mobile phase: a mixture of methanol and 1 g / L phosphoric acid, with a volume ratio of 1:1; flow rate: 1.0 mL / min; ultraviolet absorption wavelength: 255 nm.

[0097] Table 4. Removal of p-chlorobenzoic acid in the single ozone and MgMn x -CMOF / O3 system

[0098]

[0099] Example 7

[0100] Put 0.04 g of MgMn 0.5 -CMOF catalyst into the prepared 200 mL of p-chlorobenzoic acid (p-CBA) solutions containing 2, 10, and 50 mg / L respectively, and adjust the pH to 6. Then add it to the tubular ozone reactor, and introduce oxygen from the bottom. After the experiment starts, samples are taken for detection every 3 min. The oxygen input amount is 20 mg / L, and the gas flow rate is 0.5 L / min.

[0101] Detect the adsorption amount of MgMn 0.5 -CMOF catalyst for p-chlorobenzoic acid. The results are shown in Table 5. The sampling and liquid chromatography detection methods are the same as in Example 3.

[0102] Table 5. Adsorption of p-chlorobenzoic acid with different concentrations by MgMn 0.5 -CMOF

[0103] p-CBA adsorption rate 2mg / L 10mg / L 50mg / L 3min 65.6％ 16.4％ 2.9％ 6min 75.5％ 27.8％ 1.7％ 9min 75.3％ 28.9％ 1.7％

[0104] Example 8

[0105] Prepare 200 mL of p-chlorobenzoic acid (p-CBA) solution containing 50 mg / L, adjust the pH to 6, and then add the MgMn x -CMOF (x = 0, 0.5, 1, 3) catalysts prepared in Comparative Example 1 and Example 3. The dosage is 0.2 g / L, and then add it to the stirred ozone reactor, and introduce ozone from the bottom through the gas pipe. After the experiment starts, samples are taken for detection every 3 min. The ozone input amount is 20 mg / L (the ozone concentration in the oxygen and ozone mixture treated by the ozone generator), and the gas flow rate is 0.5 L / min. At 9 min after the experiment starts, 1 mL of the sample is taken, filtered through a 0.22 μm syringe filter into a brown sample bottle for high performance liquid chromatography analysis.

[0106] After the experiment, recover MgMn x -CMOF and repeat the above catalytic process.

[0107] The detection results of the first catalytic process and the fourth catalytic process are shown in Table 6.

[0108] Table 6. Removal rates of p-chlorobenzoic acid in ozone catalyzed by MgMn x -CMOF for the first and fourth times

[0109]

[0110] As can be seen from Table 6, the MgMn prepared by the present invention x- The MgMn-CMOF catalyst can be reused, and the catalytic efficiency shows little change during the fourth reuse, indicating that the MgMn x -CMOF catalyst prepared in this invention is relatively stable and has a long service life.

[0111] MgMn x - The catalytic mechanism of CMOF is as Figure 5 shown. Since the pH value of MgMn x -CMOF is relatively high, adding it to wastewater can increase the pH value of the solution. H2O molecules will be adsorbed on its surface, and the adsorbed H2O will then decompose into HO PZC and H - , and then form surface hydroxyl groups. Protonated hydroxyl groups can enrich ozone molecules on the surface. The redox reaction between the adsorbed ozone and multivalent manganese ions promotes the electron transfer process. And the protonated catalyst surface is positively charged, so a layer of charged hydroxide ion layer is formed nearby. At the same time, dissolved ozone in water is adsorbed on the catalyst surface and interacts with the hydroxyl groups of MgMn + -CMOF to form ·OH. These combined effects lead to the generation of a large amount of hydroxyl radicals in the MgMn x -CMOF / O3 system. Then the pollutants are oxidized in-situ, thus promoting the degradation of organic matter. X -CMOF / O3 system generates a large number of hydroxyl radicals. Then the pollutants are oxidized in-situ, thereby promoting the degradation of organic matter.

[0112] As can be seen from the above embodiments, when treating acetic acid with a pH of 6, the MgMn 0.5 -CMOF / O3 system has a better catalytic effect. When treating p-CBA with a pH of 6, the MgMn3-CMOF / O3 system has a better effect. In addition, when degrading 20 mg / L acetic acid and 50 mg / L p-chlorobenzoic acid, the physical adsorption of MgMn x -CMOF on organic matter has less influence compared to the catalytic degradation effect. The removal effect of organic matter is mainly reflected in the non-selective degradation of oxygen active particles generated by the catalyst catalyzing ozone.

[0113] The content of manganese in the catalyst can be adjusted accordingly according to the water quality situation (the main components in the wastewater) to always achieve the best treatment effect, which has flexibility.

[0114] The above embodiments have described the technical solutions and beneficial effects of the present invention in detail. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the present invention. Any modifications, supplements, equivalent replacements, etc. made within the scope of the principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. Application of a magnesium-manganese bimetallic organic framework catalyst in catalytic ozonation degradation of wastewater, characterized in that Including: Adding the described magnesium-manganese bimetallic metal-organic framework catalyst into the wastewater to be treated, and then introducing ozone for oxidation treatment; The preparation method of the described magnesium-manganese bimetallic metal-organic framework catalyst includes the following steps: Doping the metal-organic framework Mg-MOF with Mn element by the impregnation method, and then calcining at 400-600 °C for 1-3 h in an inert atmosphere to obtain the magnesium-manganese bimetallic metal-organic framework catalyst MgMn-CMOF; when doping with Mn element by the impregnation method, the doping amount of Mn element is 0.5%-3% of the mass of the metal-organic framework Mg-MOF.

2. The application according to claim 1, characterized in that, Preparing the metal-organic framework Mg-MOF by the solvothermal method.

3. The application according to claim 2, characterized in that, Preparing the metal-organic framework Mg-MOF by the solvothermal method, including: Dissolving magnesium salt and 2,5-dihydroxyterephthalic acid in organic solvents respectively, then mixing them, heating and reacting in a high-pressure reaction kettle, cooling and separating the precipitate after the reaction is complete, washing and drying to obtain the metal-organic framework Mg-MOF.

4. The application according to claim 1, characterized in that The dosage of the described magnesium-manganese bimetallic metal-organic framework catalyst is 0.1-0.5 g / L; the pH of the wastewater to be treated is 3-9.

5. The application according to claim 1, characterized in that, The main pollutant of the described wastewater to be treated is small molecule acid; in the described magnesium-manganese bimetallic metal-organic framework catalyst, the doping amount of Mn element is 0.5-1%.

6. The application according to claim 1, characterized in that, The main pollutant of the described wastewater to be treated is chlorinated aromatic compounds; in the described magnesium-manganese bimetallic metal-organic framework catalyst, the doping amount of Mn element is 1-3%.

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