MOF-Derived Mg-Co Binary Oxide Catalyst and Its Preparation Method and Application

Abstract

The present invention discloses a MOFs-derived Mg-Co binary oxide catalyst and its preparation method, which includes the following steps: (1) Dissolve a magnesium salt, a cobalt salt and an organic ligand in a solvent to form a mixed solution, keep the mixed solution at 100-150 °C for 10-24 h for reaction, separate out the crystalline product, wash, dry and grind it to obtain a Mg-Co binary oxide precursor; (2) Calcinate the Mg-Co binary oxide precursor at 500-900 °C for 1-5 h to obtain a Mg-Co binary oxide catalyst. The present invention also discloses the application of the Mg-Co binary oxide catalyst in catalytic ozonation of organic pollutants in wastewater. The Mg-Co binary oxide catalyst of the present invention has good catalytic performance for ozone, can stably exist under acidic and alkaline conditions, and has a wide applicable pH range.

Description

Technical Field

[0001] The present invention relates to the technical field of sewage treatment, and particularly relates to an Mg-Co binary oxide catalyst derived from MOFs, a preparation method thereof, and an application thereof. Background Art

[0002] With the development of human modernization, environmental problems have attracted more and more attention in many countries, and many new water pollution problems have emerged. A series of emerging organic pollutants such as food additives, pesticides, drugs, and hormones have appeared in natural water bodies. At present, these organic substances cannot be effectively treated by physical or biochemical methods, and they are harmful to humans, animals, and plants.

[0003] Currently, the advanced ozone oxidation technology can efficiently treat such refractory organic substances and is one of the most promising technologies for treating refractory organic wastewater. MgO has great advantages in heterogeneous catalytic ozone. When catalyzing ozone, it can not only promote the decomposition of ozone to generate a large amount of hydroxyl radicals by increasing the pH of the solution itself, but also there are active sites on its surface that can also promote the generation of hydroxyl radicals from ozone.

[0004] The Chinese patent application with the publication number CN107442095A discloses a preparation method of a nano-magnesium oxide ozone catalyst and a method for the advanced treatment of coal chemical wastewater by catalytic oxidation using the same. The preparation method of the nano-magnesium oxide ozone catalyst includes: First, prepare a MgCl2 solution; Second, add a dispersant; Third, dropwise add a NaOH solution for aging; Fourth, wash; Fifth, dry.

[0005] The Chinese patent application with the publication number CN110773160A discloses an ozone oxidation catalyst, which is prepared by loading at least one metal oxide on magnesium oxide as a carrier.

[0006] However, MgO will react with water to form Mg(OH)2, and the catalytic activity of Mg(OH)2 in catalyzing ozone is lower than that of MgO, and the hydration effect will also reduce the stability of MgO. Therefore, traditional catalysts with magnesium oxide as the active component or carrier have poor stability in water, and usually have disadvantages such as the dissolution of metal ions leading to the loss of active components, poor effect under neutral pH conditions, and a small pH application range.

[0007] It has been found that the catalytic activity of MgO-based catalysts is proportional to the basic strength of themselves, but the basic strength is inversely proportional to their stability. Existing MgO-based catalysts are difficult to balance catalytic activity and stability. Summary of the Invention

[0008] The present invention provides a MOFs-derived Mg-Co binary oxide catalyst and a preparation method thereof. The Mg-Co binary oxide catalyst has good catalytic performance for ozone and good stability.

[0009] The technical solution of the present invention is as follows:

[0010] A preparation method of a MOFs-derived Mg-Co binary oxide catalyst, comprising the following steps:

[0011] (1) Dissolve a magnesium salt, a cobalt salt and an organic ligand in a solvent to form a mixed solution, keep the mixed solution at 100 - 150 °C for heat preservation reaction for 10 - 24 h, separate out the crystalline product, wash, dry and grind to obtain a Mg-Co binary oxide precursor;

[0012] (2) Calcinate the Mg-Co binary oxide precursor at 500 - 900 °C for 1 - 5 h to obtain a Mg-Co binary oxide catalyst.

[0013] The Mg-Co binary oxide catalyst prepared by the MOFs-derived method in the present invention has a porous structure unique to MOFs, a relatively large specific surface area, and oxygen vacancies with catalytic ozone existing on the catalyst surface. This preparation method can provide new active sites for MgO and improve its catalytic activity. In addition, introducing the metal element Co can reduce the basicity intensity of MgO, while increasing new catalytic active sites, improving the catalytic activity and stability of the catalyst. The low-valent metal introduced into its lattice can transform into a high-valent state and undergo electron transfer, thereby interacting with ozone to generate oxygen-containing free radicals.

[0014] The Mg-Co binary oxide catalyst prepared by the MOFs-derived method in the present invention not only overcomes the contradiction between the basicity intensity and stability of MgO itself, but also improves the dispersion of MgO in the catalyst, increases the specific surface area, and adds new catalytic active sites.

[0015] Preferably, the molar ratio of the magnesium salt, the cobalt salt and the organic ligand is 0.5 - 4:0.5 - 3:1.

[0016] The higher the content of the magnesium salt, the higher the catalytic activity of the prepared catalyst, but the stability of the catalyst will decrease. Adding a certain amount of cobalt salt can improve the stability of the catalyst and increase the catalytic activity sites of the acidic sites. However, too much cobalt salt will reduce the catalytic activity of the basic sites of the catalyst. Therefore, the magnesium salt and the cobalt salt need to be added in a suitable ratio. When the molar ratio of the magnesium salt, the cobalt salt and the organic ligand is 0.5 - 4:0.5 - 3:1, the catalytic activity and stability of the catalyst are both good.

[0017] More preferably, the molar ratio of the magnesium salt and the cobalt salt is 0.5 - 3:1.

[0018] The organic ligand described above is 2-aminoterephthalic acid.

[0019] The solvent described above is a mixed solvent of ethanol and DMF; in the mixed solvent, the volume ratio of ethanol to DMF is 1:1.5 - 12.

[0020] Preferably, in step (2), the calcination temperature of the Mg-Co binary oxide precursor is 600 - 900 °C; most preferably, it is 800 °C.

[0021] The present invention also provides an Mg-Co binary oxide catalyst prepared by the above preparation method.

[0022] The Mg-Co binary oxide catalyst described above has strong catalytic activity for ozone, and has good stability in water, and has a wide applicable pH value range.

[0023] The present invention also provides the application of the Mg-Co binary oxide catalyst described above in catalytic ozonation of organic pollutants in wastewater.

[0024] Preferably, the application includes: adding the Mg-Co binary oxide catalyst to the wastewater to be treated, and then introducing ozone for oxidation treatment.

[0025] Preferably, based on the volume of the wastewater to be treated, the dosage of the Mg-Co binary oxide catalyst is 0.1 - 1 g / L; the ozone dosage is 10 - 50 mg / (L·min).

[0026] Preferably, the pH of the wastewater to be treated is 3 - 9.

[0027] Preferably, in the wastewater to be treated, the organic pollutant is a small molecule acid; the concentration of the small molecule acid is 10 - 100 mg / L.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] (1) The Mg-Co binary oxide catalyst of the present invention has the unique porous structure of MOFs, which not only improves the dispersion of MgO by using the porous structure but also increases the specific surface area, and also increases the oxygen vacancies with catalytic ozone on the catalyst surface, thereby improving the catalytic activity;

[0030] (2) The introduction of Co element reduces the basic strength of MgO, improves the stability of the catalyst itself, and provides a new catalytic active site for variable valence metal electron transfer to catalyze ozone;

[0031] (3) The Mg-Co binary oxide catalyst can stably exist under both acidic and basic conditions, can treat wastewater at different pH values, and has a wide applicable pH range. Description of the Drawings

[0032] Figure 1 It is a graph of the measurement results of the pH (pH PZC ) at the point of zero charge on the surface of the Mg-Co binary oxide catalyst and MgO;

[0033] Figure 2 It is a graph of the stability experiment results of the Mg-Co binary oxide catalyst and MgO. Detailed Description of the Invention

[0034] Example 1

[0035] (1) Weigh 2.04 g of solid Mg(NO3)2·6H2O, 1.16 g of solid Co(NO3)2·6H2O and 1.09 g of 2-aminoterephthalic acid and dissolve them in a mixed solution of 20 ml of ethanol and 80 ml of DMF (the amounts of substances of Mg and Co are 8 mmol and 4 mmol respectively);

[0036] (2) After dissolving the above solids in the solvent, put them into a 100 ml hydrothermal reactor and keep them at 120 °C in a vacuum oven for 12 h;

[0037] (3) Centrifuge the product obtained in step (2) and retain the solid product. Then wash the solid product 2-3 times with DMF and ethanol respectively, and then centrifuge to retain the lower-layer solid product;

[0038] (4) Put the solid product collected in step (3) in a vacuum drying oven and dry it at 80 °C for 6 h;

[0039] (5) Grind the substance obtained in step (4) into powder, place it in a tubular furnace, pass N2, and calcine it at 800 °C for 2 h to obtain MOFs-derived Mg-Co binary metal oxide.

[0040] Application Example 1

[0041] Prepare 250 mL of acetic acid solution containing 20 mg / L, adjust the pH to 3, then add the MOFs-derived Mg-Co binary metal oxide catalyst with a dosage of 0.05 g, and then add it to a column reactor. A mixed gas of ozone and oxygen is introduced at the bottom of the reactor. Ozone oxidation alone without adding the catalyst and MgO + O3 are used as comparisons.

[0042] In the mixed gas of ozone and oxygen, the ozone concentration is 40 mg / L, and the gas flow rate of ozone and oxygen is 0.5 L / min. At the beginning of the experiment, samples were taken at 0 min, 3 min, 6 min, and 9 min for detection, and the acetic acid concentration in the water sample was detected by ThermoFisher Dionex Ultimate 3000 high performance liquid chromatography. The results are shown in Table 1.

[0043] Table 1

[0044]

[0045] Application Example 2

[0046] Prepare 250 mL of acetic acid solution containing 20 mg / L, adjust the pH to 5, then add MOFs-derived Mg-Co binary metal oxide catalyst with a dosage of 0.05 g, and then add it to a column reactor. A mixed gas of ozone and oxygen is introduced at the bottom of the reactor. Ozone oxidation alone without adding catalyst and MgO + O3 are used as comparisons.

[0047] In the mixed gas of ozone and oxygen, the ozone concentration is 40 mg / L, and the gas flow rate of ozone and oxygen is 0.5 L / min. At the beginning of the experiment, samples were taken at 0 min, 3 min, 6 min, and 9 min for detection, and the acetic acid concentration in the water sample was detected by ThermoFisher Dionex Ultimate 3000 high performance liquid chromatography. The results are shown in Table 2.

[0048] Table 2

[0049]

[0050] Application Example 3

[0051] Prepare 250 mL of acetic acid solution containing 20 mg / L, adjust the pH to 7, then add MOFs-derived Mg-Co binary metal oxide catalyst with a dosage of 0.05 g, and then add it to a column reactor. A mixed gas of ozone and oxygen is introduced at the bottom of the reactor. Ozone oxidation alone without adding catalyst and MgO + O3 are used as comparisons.

[0052] In the mixed gas of ozone and oxygen, the ozone concentration is 40 mg / L, and the gas flow rate of ozone and oxygen is 0.5 L / min. At the beginning of the experiment, samples were taken at 0 min, 3 min, 6 min, and 9 min for detection, and the acetic acid concentration in the water sample was detected by ThermoFisher Dionex Ultimate 3000 high performance liquid chromatography. The results are shown in Table 3.

[0053] Table 3

[0054]

[0055] As can be seen from Application Example 1 and Application Example 3, the removal rate of acetic acid by Mg-Co binary metal oxide in the reaction solution with pH = 3 (84.04%) is higher than that of MgO + O3 (56.72%) in the reaction solution with pH = 3 and that of Mg-Co binary metal oxide + O3 (77.79%) in the reaction solution with pH = 7. This indicates that the addition of cobalt generates acid active sites on MgO and improves the catalytic performance of the catalyst.

[0056] Application Example 4

[0057] Prepare 250 mL of acetic acid solution containing 20 mg / L, adjust the pH to 9, add the MOFs-derived Mg-Co binary metal oxide catalyst with a dosage of 0.05 g, and then add it to a column reactor. A mixed gas of ozone and oxygen is introduced at the bottom of the reactor. Ozone oxidation alone without adding the catalyst and MgO + O3 are used as comparisons.

[0058] In the mixed gas of ozone and oxygen, the ozone concentration is 40 mg / L, and the gas flow rate of ozone and oxygen is 0.5 L / min. At the beginning of the experiment, samples are taken at 0 min, 3 min, 6 min, and 9 min for detection. The acetic acid concentration in the water sample is detected by the ThermoFisher Dionex Ultimate 3000 high performance liquid chromatography method. The results are shown in Table 4.

[0059] Table 4

[0060]

[0061] Examples 2 and 3

[0062] (1) Weigh 2.04 g of solid Mg(NO3)2·6H2O, 1.16 g of solid Co(NO3)2·6H2O, and 1.09 g of 2-aminoterephthalic acid and dissolve them in a mixed solution of 20 ml of ethanol and 80 ml of DMF (the amounts of substances of Mg and Co are 8 mmol and 4 mmol respectively);

[0063] (2) After dissolving the above solids in the solvent, place them in a 100 ml hydrothermal autoclave and keep them at 120 °C in a vacuum oven for 12 h;

[0064] (3) Centrifuge the product obtained after the reaction in step (2) and retain the solid product. Then wash the solid product 2 - 3 times with DMF and ethanol respectively, and centrifuge again to retain the lower-layer solid product;

[0065] (4) Place the solid product collected in step (3) in a vacuum drying oven and dry it at 80 °C for 6 h;

[0066] (5) Grind the substance obtained in step (4) into powder, place it in a tubular furnace, and calcine it in N₂ at 600 °C and 900 °C for 2 h respectively to obtain MOF-derived Mg-Co binary metal oxide.

[0067] Application Example 5

[0068] Prepare 250 mL of acetic acid solution containing 20 mg / L respectively, adjust the pH to 7, then add the MOF-derived Mg-Co binary metal oxide catalysts prepared in Examples 1-3 respectively, with the dosage of 0.05 g, and then add them to a column reactor. A mixed gas of ozone and oxygen is introduced at the bottom of the reactor.

[0069] In the mixed gas of ozone and oxygen, the ozone concentration is 40 mg / L, and the gas flow rate of ozone and oxygen is 0.5 L / min. At the beginning of the experiment, samples are taken at 0 min, 3 min, 6 min, and 9 min for detection, and the acetic acid concentration in the water sample is detected by ThermoFisher Dionex Ultimate 3000 high performance liquid chromatography. The results are shown in Table 5.

[0070] Table 5

[0071]

[0072] It can be seen from the data in the above table that the catalyst calcined at 800 °C has the best catalytic performance.

[0073] Examples 4-6

[0074] (1) Example 4: Weigh 0.513 g of Mg(NO₃)₂·6H₂O solid, 1.16 g of Co(NO₃)₂·6H₂O solid and 1.09 g of 2-aminoterephthalic acid and dissolve them in a mixed solution of 20 ml of ethanol and 80 ml of DMF (the amounts of substances of Mg and Co are 2 mmol and 4 mmol respectively), and the molar ratio of magnesium salt to cobalt salt is 1:2;

[0075] Example 5: Weigh 1.03 g of Mg(NO₃)₂·6H₂O solid, 1.16 g of Co(NO₃)₂·6H₂O solid and 1.09 g of 2-aminoterephthalic acid and dissolve them in a mixed solution of 20 ml of ethanol and 80 ml of DMF (the amounts of substances of Mg and Co are 4 mmol and 4 mmol respectively), and the molar ratio of magnesium salt to cobalt salt is 1:1;

[0076] Example 6: Weigh 3.08 g of solid Mg(NO3)2·6H2O, 1.16 g of solid Co(NO3)2·6H2O and 1.09 g of 2-aminoterephthalic acid and dissolve them in a mixed solution of 20 ml of ethanol and 80 ml of DMF (the amounts of substances of Mg and Co are 12 mmol and 4 mmol respectively), and the molar ratio of magnesium salt to cobalt salt is 3:1;

[0077] (2) After dissolving the above-mentioned solids with different magnesium-cobalt ratios in a solvent respectively, load them into 100-ml hydrothermal reactors and keep them at 120 °C in a vacuum oven for 12 h;

[0078] (3) Centrifuge the products obtained after the reaction in step (2) respectively and retain the solid products, then wash the solid products 2-3 times each with DMF and ethanol, and then centrifuge to retain the lower-layer solid products;

[0079] (4) Place the solid products collected in step (3) in a vacuum drying oven and dry them at 80 °C for 6 h;

[0080] (5) Grind the substances obtained in step (4) into powders respectively, place them in a tubular furnace, calcine them at 800 °C for 2 h under a nitrogen atmosphere to obtain MOF-derived Mg-Co binary metal oxides with different molar ratios.

[0081] Application Example 6

[0082] Prepare 250 mL of acetic acid solution containing 20 mg / L respectively, adjust the pH to 7, then add the MOF-derived Mg-Co binary metal oxide catalysts prepared in Examples 1, 4-6 respectively, with the dosage of 0.05 g, and then add them to a column reactor. A mixed gas of ozone and oxygen is introduced at the bottom of the reactor.

[0083] In the mixed gas of ozone and oxygen, the ozone concentration is 40 mg / L, and the gas flow rates of ozone and oxygen are 0.5 L / min. At the beginning of the experiment, samples are taken at 0 min, 3 min, 6 min, and 9 min for detection, and the acetic acid concentration in the water sample is detected by ThermoFisher Dionex Ultimate 3000 high-performance liquid chromatography. The results are shown in Table 6.

[0084] Table 6

[0085]

[0086] It can be seen from the data in the table that when the molar ratio of magnesium salt to cobalt salt is 2:1, the synthesized and calcined catalyst has the best catalytic performance.

[0087] Test Example

[0088] By the salt addition method, use a pH meter to measure the pH at the zero point of surface charge of the catalyst (pHPZC ) 0.05 g of the catalyst powder was added to 20 mL of sodium nitrate solution (0.1 mol / L) with different initial pH values and placed in a shaker for 24 h. Then, the pH of the solution was measured. When the pH of the solution was equal to the initial pH, this pH was the pH of the catalyst. PZC The pH of the sodium nitrate solution was adjusted with 0.1 mol / L nitric acid and sodium hydroxide solutions.

[0089] The pH at the point of zero charge on the surface of the catalyst prepared in Example 1 and MgO (pH PZC ) The results are as Figure 1 shown, where ΔpH = pH final - pH initial .

[0090] From Figure 1 it can be obtained that the pH of the Mg-Co binary oxide is PZC = 9.89, and the pH of MgO is PZC = 10.69. Among them, the pH of the Mg-Co binary oxide is PZC less than 10, and the pH of MgO is PZC greater than 10. This is because the addition of cobalt forms Mg-O-Co bonds in magnesium oxide. The basicity of the lattice oxygen in the Mg-O-Co bond is weaker than that of the lattice oxygen in the Mg-O-Mg bond, which weakens the hydration of the Mg-Co binary metal oxide and reduces the dissolution of Mg 2+ , making the Mg-Co binary oxide exhibit excellent stability.

[0091] The results of the repeatability experiment of the Mg-Co binary oxide catalyst prepared in Example 1 and MgO with acetic acid as the degradation target are as Figure 2 shown.

[0092] From Figure 2 it can be seen that the removal rate of acetic acid in the first degradation by the Mg-Co binary oxide is 81.34%, and the removal rate of acetic acid in the fifth degradation is 78.65%, with the acetic acid removal rate decreasing by 2.65%. While the removal rate of acetic acid in the first degradation by MgO is 68.41%, and the acetic acid removal rate in the fifth degradation is 59.12%, with the acetic acid removal rate decreasing by 9.29%. This shows that the addition of cobalt not only improves the stability of the catalyst but also enhances its catalytic performance.

[0093] The BET data of the Mg-Co binary oxide catalyst prepared in Example 1 and MgO are shown in Table 7.

[0094] Table 7

[0095] MgO Mg-Co binary oxide <![CDATA[m 2 / g]]> 84.6218 177.3244

[0096] From the data in Table 7, it can be known that the specific surface area of the Mg-Co binary oxide is 93.3026 m 2 / g higher than that of MgO. The specific surface area of the Mg-Co binary oxide is 2.1 times that of MgO. Thus, it can be seen that the specific surface area of the Mg-Co binary oxide has been greatly improved compared to that of MgO.

[0097] The above-described embodiments have detailed the technical solutions and beneficial effects of the present invention. 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 should be included within the protection scope of the present invention.

Claims

1. Preparation method of MOFs-derived Mg-Co binary oxide catalyst, characterized in that, It includes the following steps: (1) Dissolve a magnesium salt, a cobalt salt and an organic ligand in a solvent to form a mixed solution, keep the mixed solution at 100 - 150 °C for heat preservation reaction for 10 - 24 h, separate out the crystalline product and wash, dry and grind it to obtain a Mg-Co binary oxide precursor; the molar ratio of the magnesium salt, the cobalt salt and the organic ligand is 0.5 - 4:0.5 - 3:1; (2) Calcinate the Mg-Co binary oxide precursor in an inert atmosphere at 600 - 900 °C for 1 - 5 h to obtain a Mg-Co binary oxide catalyst.

2. The preparation method of the MOFs-derived Mg-Co binary oxide catalyst according to claim 1, characterized in that, The organic ligand is 2-aminoterephthalic acid.

3. The preparation method of the MOFs-derived Mg-Co binary oxide catalyst according to claim 1, characterized in that, The solvent is a mixed solvent of ethanol and DMF; in the mixed solvent, the volume ratio of ethanol to DMF is 1:1.5 - 12.

4. A Mg-Co binary oxide catalyst, characterized in that, It is prepared by using the preparation method described in any one of claims 1 - 3.

5. Use of the Mg-Co binary oxide catalyst as described in claim 4 in catalytic ozonation of organic pollutants in wastewater, comprising: Add the Mg-Co binary oxide catalyst to the wastewater to be treated, and then introduce ozone for oxidation treatment.

6. The application according to claim 5, characterized in that, Based on the volume of the wastewater to be treated, the dosage of the Mg-Co binary oxide catalyst is 0.1 - 1 g / L; the ozone dosage is 10 - 50 mg / (L•min).

7. The application according to claim 5, wherein The pH of the wastewater to be treated is 3 - 9.

8. The application according to claim 5, characterized in that, In the wastewater to be treated, the organic pollutant is a small molecule acid; the concentration of the small molecule acid is 10 - 100 mg / L.

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