Iron-zinc bimetallic organic framework electro-fenton catalyst and preparation method and application thereof

Abstract

The application discloses an iron-zinc bimetallic organic framework electro-Fenton catalyst and a preparation method and application thereof, a certain proportion of bimetallic clusters is prepared, the bimetallic clusters are used as bimetallic nodes, and the Fe / Zn bimetallic organic framework electro-Fenton catalyst can be synthesized by simply stirring at room temperature with competitive organic ligands, and the application of the iron-zinc bimetallic organic framework electro-Fenton catalyst in removal of refractory organic pollutants in water is simultaneously involved. The bimetallic proportion is accurately regulated by pre-synthesizing the bimetallic clusters, the catalyst effectively solves the problems of poor catalytic activity and narrow pH application range of existing electro-catalysts, can be better applied to removal of refractory organic pollutants in water by the electro-Fenton method, and has the advantages of simple preparation process, no need of high temperature and high pressure and the like, and is beneficial to industrial amplification.

Description

Technical Field

[0001] This invention relates to an iron-zinc bimetallic organic framework electro-Fenton catalyst, its preparation method, and its application in the electro-Fenton reaction, belonging to the field of water treatment technology. Background Technology

[0002] Currently, antibiotics (such as tetracycline) are widely used in human treatment, animal disease control, and agricultural feed additives. However, over 75% of antibiotics enter the natural environment through human and animal urine and feces, posing a serious threat to public health and ecosystems. Therefore, there is an urgent need to find a suitable and effective method to safely remove antibiotics and other organic pollutants from aquatic environments.

[0003] For wastewater, common treatment methods include adsorption, biodegradation, and advanced oxidation technologies, and the same applies to antibiotic wastewater. The Fenton process, which generates highly oxidizing free radicals—hydroxyl radicals—to oxidize and degrade organic pollutants, is considered a highly effective method for degrading antibiotics in the aquatic environment due to its advantages such as in-situ hydrogen peroxide generation and simple operation. However, traditional homogeneous electro-Fenton processes require maintaining the solution pH at a strongly acidic level (pH=3), and the addition of ferrous ions can lead to the formation of large amounts of iron sludge, causing secondary pollution. Heterogeneous electro-Fenton catalysts can reduce the formation of iron sludge, and their recyclability makes them a promising replacement for traditional homogeneous electro-Fenton catalysts in the future. Commonly used heterogeneous catalysts are mainly iron oxides and other transition metal oxides; however, these catalysts still suffer from poor catalytic performance and poor recyclability, which greatly limits their widespread application.

[0004] Metal-organic frameworks (MOFs), as hybrid porous materials with well-developed pore structures and large specific surface areas, possess uniformly distributed active sites both internally and on their surface, which is beneficial for catalytic reactions. Iron-based MOF catalysts, as heterogeneous electro-Fenton catalysts, exhibit slightly lower activity compared to homogeneous Fenton catalysts when treating antibiotic wastewater. Researchers have proposed a method to enhance electron transfer rates and thus catalytic activity through the synergistic effect of multiple metals, by adjusting different bimetallic combinations or different metal doping ratios. Therefore, there is an urgent need to obtain a heterogeneous electro-Fenton catalyst with good catalytic activity, a simple preparation process, easy industrial scale-up, and environmental friendliness. This is of great significance for the effective removal of antibiotics from water using electro-Fenton technology. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention aims to provide a method for preparing and applying an iron-zinc bimetallic organic framework electro-Fenton catalyst. By preparing a certain proportion of bimetallic clusters as bimetallic nodes, and then simply stirring with a competing organic ligand at room temperature, an Fe / Zn bimetallic organic framework electro-Fenton catalyst can be synthesized. Applying this catalyst to an electrolyzer solves the problems of narrow applicable pH range, poor activity, and difficulty in industrial scale-up of Fenton catalysis, enabling its better application in the electro-Fenton method for removing high concentrations of antibiotics from water.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] In a first aspect, the present invention provides an iron-zinc bimetallic organic framework electro-Fenton catalyst, wherein the iron-zinc bimetallic organic framework electro-Fenton catalyst is prepared according to the following method:

[0008] S1: CH3COONa·3H2O is dissolved in a solvent, and Fe(NO3)3·9H2O and Zn(NO3)2·6H2O are added. The mixture is stirred at room temperature for 10-30 h. The resulting reaction slurry is centrifuged, and the precipitate is washed with ethanol and dried (drying at 60-100℃ for 10-24 h) to obtain Fe / Zn bimetallic clusters. The molar ratio of Fe(NO3)3·9H2O, CH3COONa·3H2O and Zn(NO3)2·6H2O is 1:1-20:1-30 (preferably 1:10-20:1-10, particularly preferred 1:15:5).

[0009] S2: The Fe / Zn bimetallic clusters described in step S1 are uniformly dispersed in an organic solvent, and a terephthalic acid solution is added. After the first stirring for 2-20 min, a 2-methylimidazole solution is added, and the reaction is stirred for 10-60 min. The resulting reaction mixture is centrifuged, washed, and dried (drying at 60-100℃ for 10-24 h) to obtain the iron-zinc bimetallic organic framework electro-Fenton catalyst. The mass ratio of terephthalic acid to the Fe / Zn bimetallic clusters in the terephthalic acid solution is 1:1-5 (preferably 1:3); the molar ratio of terephthalic acid to 2-methylimidazole in the 2-methylimidazole solution is 1:1-10 (preferably 1:1).

[0010] Furthermore, the solvent mentioned in step S1 is one or more of deionized water, N,N-dimethylformamide, N-methylpyrrolidone, methanol, and ethanol, and in one embodiment of the present invention, it is deionized water.

[0011] Furthermore, the volume of the solvent in step S1, based on the mass of CH3COONa·3H2O, is 2-10 mL / g, and in one embodiment of the present invention, it is 33 mL / g.

[0012] Furthermore, the washing described in step S2 is performed sequentially with N,N-dimethylformamide, methanol, and ethanol.

[0013] The stirring reaction in S2 can be carried out at room temperature.

[0014] Furthermore, the organic solvent in step S2 is one or both of N,N-dimethylformamide and N-methylpyrrolidone, and in one embodiment of the present invention, it is N,N-dimethylformamide. Even further, the volume of the organic solvent, based on the mass of the Fe / Zn bimetallic cluster, is 5–30 mL / g, preferably 16 mL / g.

[0015] In embodiments of the present invention, the solvent for the terephthalic acid solution in step S2 is one or both of N,N-dimethylformamide and N-methylpyrrolidone, and in one embodiment of the present invention, it is N,N-dimethylformamide. Furthermore, the concentration of the terephthalic acid solution is 0.05–0.50 mmol / mL (preferably 0.125 mmol / mL).

[0016] In embodiments of the present invention, the solvent for the 2-methylimidazole solution in step S2 is one or more of methanol, ethanol, and tert-butanol, and in one embodiment of the present invention, it is methanol. Furthermore, the concentration of the 2-methylimidazole solution is 0.05–0.50 mmol / mL (preferably 0.125 mmol / mL).

[0017] 2-Methylimidazole, as a second ligand, provides the function of accelerating the deprotonation of the main ligand, thereby increasing the reaction rate and altering the catalyst morphology.

[0018] Secondly, the present invention provides the application of the above-mentioned iron-zinc bimetallic organic framework electro-Fenton catalyst in the degradation of organic pollutants.

[0019] Furthermore, the organic pollutant is one or a mixture of two or more of methylene blue, ciprofloxacin, tetracycline, and phenol, and in one embodiment of the present invention, it is tetracycline wastewater.

[0020] Specifically, the application is as follows: using an aqueous solution containing 0.05-0.1M sodium sulfate (preferably 0.05M), organic pollutants, and 0.06-0.16 g / L (preferably 0.1 g / L) of the iron-zinc bimetallic organic framework electro-Fenton catalyst as the electrolyte, using a ruthenium-yttrium titanium mesh as the anode and a titanium mesh as the cathode, after fully aerating the electrolyte, an electro-Fenton reaction is carried out at 5-200 mA (20 mA in one embodiment of the present invention) for 60-120 min.

[0021] Furthermore, the concentration of the organic pollutants in the electrolyte is 20 to 200 ppm, and in one embodiment of the present invention it is 100 ppm.

[0022] This invention obtains a fixed proportion of bimetallic clusters through a simple and rapid stirring method, and also obtains an iron-zinc bimetallic organic framework electro-Fenton catalyst through simple stirring. The catalyst is dispersed in wastewater without the need to add exogenous iron ions and hydrogen peroxide. It generates ·OH radicals by self-catalyzing the reduction of oxygen to hydrogen peroxide at the cathode.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] (1) The catalyst has a simple synthesis route and does not require high temperature and high pressure conditions;

[0025] (2) Bimetallic clusters obtained by metal isomorphic substitution can be used as metal nodes, which can control the proportion more precisely;

[0026] (3) No hydrogen peroxide needs to be added during the electro-Fenton reaction, reducing processing costs;

[0027] (4) The electro-Fenton catalyst is dispersed in the wastewater and can be recovered by simple sedimentation after the reaction is completed. Attached Figure Description

[0028] Figure 1 Scanning electron microscope and transmission electron microscope for the catalyst prepared in Example 1;

[0029] Figure 2 A schematic diagram of the application device in the re-electro-Fenton process of the electro-Fenton catalyst;

[0030] Figure 3 The effect of different iron to zinc metal ratios on the removal efficiency of tetracycline (100 ppm) by electro-Fenton catalysts during the electro-Fenton process is shown in the figure.

[0031] Figure 4 SEM images of the catalyst before and after ligand competition;

[0032] Figure 5 Effect of different ligands competing to synthesize electro-Fenton catalysts on the removal efficiency of tetracycline (100 ppm) during the electro-Fenton process.

[0033] Figure 6 The effect of electro-Fenton catalyst on tetracycline (100 ppm) removal during the electro-Fenton process at different pH values;

[0034] Figure 7 The effect of different types of metal-doped FeN (N = Co, Cu, Ni) bimetallic electro-Fenton catalysts on tetracycline (100 ppm) removal during the electro-Fenton process; Detailed Implementation

[0035] The present invention will be described in detail below with reference to specific embodiments. However, the present invention is not limited to the following embodiments. Any variations or implementations that do not depart from the content and scope of the present invention should be included within the technical scope of the present invention.

[0036] Example 1:

[0037] 1. Weigh 4.2 g (30.88 mmol) sodium acetate trihydrate and dissolve it in 14 mL of deionized water. Then weigh 0.80 g (1.99 mmol) ferric nitrate nonahydrate and 2.82 g (9.5 mmol) zinc nitrate hexahydrate and add them separately. Stir magnetically for 20 h to obtain a reaction slurry. The slurry is centrifuged, washed with ethanol, and dried at 80 °C for 10 h to obtain bimetallic clusters.

[0038] 2. Weigh 0.50 g of the obtained bimetallic cluster, 0.166 g (1 mmol) of terephthalic acid, and 0.082 g (1 mmol) of 2-methylimidazole into conical flasks and dissolve them by sonication with 8 ml of N,N-dimethylformamide, 8 ml of N,N-dimethylformamide, and 16 ml of methanol, respectively. Add the evenly dispersed ligand solutions sequentially to the bimetallic cluster solution. First, add the terephthalic acid solution and stir for 15 min, then add the 2-methylimidazole solution and stir for a competitive reaction for 10 min. The resulting precipitate is centrifuged, washed sequentially with N,N-dimethylformamide / methanol / ethanol, and then dried under vacuum at 80 °C for 24 h. This yields a bimetallic organic framework electro-Fenton catalyst.

[0039] Example 2:

[0040] A tetracycline aqueous solution containing 100 ppm was prepared at room temperature with an initial pH of 6.8. 100 mL of the prepared pollutant aqueous solution (tetracycline aqueous solution) was taken into an electro-Fenton reactor consisting of an electrolytic cell. 0.05 M sodium sulfate was added to increase the conductivity. Anode and cathode were inserted, wherein the anode was a ruthenium-yttrium titanium mesh plate and the cathode was a titanium mesh plate. After aeration with an air pump at an air flow rate of 30 mL / min for 10 min, 0.01 g of the bimetallic organic framework electro-Fenton catalyst prepared according to Example 1 was added. A constant current of 20 mA was applied to carry out the electro-Fenton catalytic reaction for the treatment of tetracycline wastewater.

[0041] During the electro-Fenton reaction, 3-4 mL of the reaction solution was taken at regular intervals and filtered through a 0.45 μm aqueous filter. The tetracycline removal rate was determined by ultraviolet spectrophotometry at an absorption wavelength of 357 nm. The removal rate of tetracycline wastewater was 81.2% after 60 min.

[0042] Example 3:

[0043] Except for the following operations, all procedures were the same as in Example 1: In step one, the amounts of ferric nitrate nonahydrate and zinc nitrate hexahydrate were 0.80 g (1.99 mmol): 1.41 g (4.8 mmol), 0.80 g (1.99 mmol): 0 g (0 mmol), and 0.80 g (1.99 mmol): 5.64 g (19.0 mmol), respectively; the obtained FeZn bimetallic organic framework electro-Fenton catalyst was used to treat tetracycline wastewater according to the procedure in Example 2, and the treatment results are as follows... Figure 3 As shown, the removal rates of tetracycline within 60 min were 75.1%, 60.2%, and 52.5%, respectively. The electro-Fenton catalytic effect on tetracycline showed a trend of first increasing and then decreasing with the increasing proportion of zinc ions in the bimetallic catalyst. There exists an optimal zinc ion doping ratio, namely, the ratio of ferric nitrate nonahydrate to zinc nitrate hexahydrate of 0.80 g (1.99 mmol): 2.82 g (9.5 mmol).

[0044] Example 4:

[0045] Except for the following operations, all procedures were the same as in Example 1: in step two, 2-methylimidazole was replaced with imidazole (1 mmol, 0.068 g) or benzimidazole (1 mmol, 0.118 g), or no competing ligand was added; the resulting iron-zinc bimetallic organic framework electro-Fenton catalyst was used to treat tetracycline wastewater according to the procedure in Example 2, and the results were as follows. Figure 5 As shown, the removal rates of tetracycline within 60 min were 58.5%, 60.2%, and 43.5%, respectively.

[0046] Field emission scanning electron microscopy (SU8010, Hitachi, Japan) was used. Operating conditions: gold sputtering, scanning observation at 10 kV. The morphology of MOF materials generated without ligand competition and those generated after ligand competition showed significant changes; the former were spherical, while the latter had numerous pores within a spherical structure. Figure 4 As shown in the results, changes in material morphology also significantly affect the electro-Fenton catalytic performance.

[0047] Example 5:

[0048] Except for the following operations, all procedures were the same as in Example 2: the pH of the prepared tetracycline aqueous solution was adjusted to 3.02, 5.03, 6.80, and 9.02 using sodium hydroxide / dilute sulfuric acid.

[0049] Experimental results are as follows Figure 6 As shown, the removal rates of tetracycline within 60 min were 82.5%, 79.5%, 81.3%, and 79.9%, respectively. The catalyst maintained good catalytic performance within the pH range of 3-10, indicating that it can effectively broaden the pH range for electro-Fenton applications.

[0050] Example 6:

[0051] Except for the following operations, all procedures were the same as in Example 1: Zinc nitrate hexahydrate in step one was replaced with cobalt nitrate hexahydrate, copper nitrate hexahydrate, and nickel nitrate hexahydrate, with addition amounts of 2.82 g (9.5 mmol), 1.89 g (9.5 mmol), and 2.76 g (9.5 mmol), respectively. The obtained FeN (N = Co, Cu, Ni) bimetallic organic framework electro-Fenton catalyst was used to treat tetracycline wastewater according to the procedure in Example 2. The treatment results are as follows: Figure 7 As shown, the removal rates of tetracycline within 60 min were 60.2%, 40.3%, and 38.5%, respectively.

[0052] Comparative Example 1:

[0053] Anodizing: Same as Example 2 except for the following operations: no catalyst was added during the electro-Fenton treatment, other conditions remained unchanged, and the results are as follows. Figure 3 As shown, the removal rate of tetracycline within 60 minutes was 17.1%.

[0054] Comparative Example 2:

[0055] 4.2 g of sodium acetate trihydrate was dissolved in 14 mL of deionized water. Then, 0.80 g (1.985 mmol) of ferric nitrate nonahydrate and 2.82 g (9.5 mmol) of zinc nitrate hexahydrate were added separately and magnetically stirred for 20 h to obtain a reaction slurry. The slurry was centrifuged, washed with ethanol, and dried at 80 °C for 10 h to obtain bimetallic clusters. 0.50 g of bimetallic clusters and 0.082 g (1 mmol) of 2-methylimidazole were dissolved in a volumetric flask by ultrasonication with 8 mL of N,N-dimethylformamide and 16 mL of methanol, respectively. After uniform dispersion, the 2-methylimidazole solution was added to the bimetallic cluster solution, and no precipitate was formed.

Claims

1. A bimetallic organic framework electro-Fenton catalyst, characterized in that... The iron-zinc bimetallic organic framework electro-Fenton catalyst was prepared according to the following method: S1: CH3COONa·3H2O was dissolved in a solvent, and Fe(NO3)3·9H2O and Zn(NO3)2·6H2O were added. The mixture was stirred at room temperature for 10-30 h. The resulting reaction slurry was centrifuged, and the precipitate was washed with ethanol and dried to obtain Fe / Zn bimetallic clusters. The molar ratio of Fe(NO3)3·9H2O, CH3COONa·3H2O and Zn(NO3)2·6H2O was 1:1-20:1-30. S2: The Fe / Zn bimetallic clusters described in step S1 are uniformly dispersed in an organic solvent, terephthalic acid solution is added, and after the first stirring for 2-20 min, 2-methylimidazole solution is added. After the second stirring reaction for 10-60 min, the resulting reaction mixture is centrifuged, washed, and dried to obtain the iron-zinc bimetallic organic framework electro-Fenton catalyst. The mass ratio of terephthalic acid to the Fe / Zn bimetallic cluster in the terephthalic acid solution is 1:1 to 5; the molar ratio of terephthalic acid to 2-methylimidazole in the 2-methylimidazole solution is 1:1 to 10; the solvent of the terephthalic acid solution is one or two of N,N-dimethylformamide and N-methylpyrrolidone; the solvent of the 2-methylimidazole solution is one or more of methanol, ethanol, and tert-butanol.

2. The iron-zinc bimetallic organic framework electro-Fenton catalyst as described in claim 1, characterized in that: The solvent mentioned in step S1 is one or more of deionized water, N,N-dimethylformamide, N-methylpyrrolidone, methanol, and ethanol.

3. The iron-zinc bimetallic organic framework electro-Fenton catalyst as described in claim 1, characterized in that: The volume of the solvent in step S1 is 2-10 mL / g based on the mass of CH3COONa·3H2O.

4. The iron-zinc bimetallic organic framework electro-Fenton catalyst as described in claim 1, characterized in that: The washing described in step S2 involves sequentially washing with N,N-dimethylformamide, methanol, and ethanol.

5. The iron-zinc bimetallic organic framework electro-Fenton catalyst as described in claim 1, characterized in that: The organic solvent in step S2 is one or both of N,N-dimethylformamide and N-methylpyrrolidone; the volume of the organic solvent is 5 to 30 mL / g based on the mass of the Fe / Zn bimetallic cluster.

6. The iron-zinc bimetallic organic framework electro-Fenton catalyst as described in claim 1, characterized in that: The concentration of the terephthalic acid solution in step S2 is 0.05–0.50 mmol / mL.

7. The iron-zinc bimetallic organic framework electro-Fenton catalyst as described in claim 1, characterized in that: The concentration of the 2-methylimidazole solution in step S2 is 0.05–0.50 mmol / mL.

8. The application of the iron-zinc bimetallic organic framework electro-Fenton catalyst as described in any one of claims 1-7 in the degradation of organic pollutants.

9. The application as described in claim 8, characterized in that: The organic pollutant is one or a mixture of two or more of methylene blue, ciprofloxacin, tetracycline, and phenol.

10. The application as described in claim 8, characterized in that... The application is as follows: using an aqueous solution containing 0.05~0.1 M sodium sulfate, organic pollutants and 0.06~0.16 g / L of the iron-zinc bimetallic organic framework electro-Fenton catalyst as the electrolyte, using a ruthenium-yttrium titanium mesh as the anode and a titanium mesh as the cathode, after fully aerating the electrolyte, an electro-Fenton reaction is carried out at 5~200 mA for 60~120 min; The concentration of the organic pollutants in the electrolyte is 20~200 ppm.

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