Preparation method of a cyclic nitrogen-doped iron-cobalt bimetallic organic framework catalyst and application thereof in catalyzing generation of singlet oxygen

Abstract

The application discloses a preparation method of a cyclic nitrogen-doped iron-cobalt bimetallic organic framework catalyst and application of the catalyst in catalytic generation of singlet oxygen. First, an iron-cobalt bimetallic organic framework is prepared through a solvothermal method, then amino grafting modification is carried out by using a polyamine grafting reagent to construct metal-amine sites, finally, under an oxygen-free inert atmosphere and lower temperature heating conditions, Schiff base reaction and cyclization are carried out with a dialdehyde reagent to directionally form cyclic nitrogen active sites mainly in the form of pyrrole nitrogen, thereby obtaining the cyclic nitrogen-doped iron-cobalt bimetallic organic framework catalyst. The catalyst can efficiently activate persulfate oxidants, under the synergistic action of iron-cobalt bimetallic centers and metal-nitrogen active sites, the free radical path is inhibited, the non-free radical path dominated reaction is promoted, high selectivity generation of singlet oxygen is realized, excellent removal effect is achieved on refractory organic pollutants, the water quality interference resistance is high, the applicable pH range is wide, and the catalyst is suitable for selective treatment of complex wastewater.

Description

Technical Field

[0001] This invention belongs to the field of environmental catalysis and water treatment technology, specifically relating to a cyclic nitrogen-doped iron-cobalt bimetallic organic framework catalyst, its preparation method, and its application in catalytically activating oxidants to generate singlet oxygen. Background Technology

[0002] In existing oxidant activation systems, cobalt-based materials are often used as catalytic active components due to their high oxidant activation efficiency. Especially in the field of persulfate activation, Co sites are generally considered important centers for promoting electron transfer and reactive oxygen species (ROS) generation. However, single cobalt-based catalysts still suffer from problems in practical applications, such as metal ion dissolution, insufficient cycle stability, and a reaction pathway biased towards radical mechanisms, making it difficult to balance catalytic efficiency, selectivity, and environmental friendliness. To improve these shortcomings, researchers have attempted to construct bimetallic synergistic systems by introducing a second metal such as Fe to modulate the electronic structure and improve catalytic stability. On the other hand, nitrogen-doped carbon materials or nitrogen-modified metal-based catalysts are considered to effectively regulate the electronic environment on the catalyst surface and promote non-radical pathways, especially singlet oxygen generation. Among various nitrogen species, pyrrole nitrogen and graphitic nitrogen are considered closely related to oxidant activation and singlet oxygen generation. Pyrrole nitrogen sites, due to their strong electronic regulation capabilities and reactivity, play an important role in constructing highly selective singlet oxygen reaction systems.

[0003] However, in existing technologies, the aforementioned nitrogen-active sites, especially pyrrole nitrogen sites closely related to singlet oxygen generation, are typically constructed primarily through high-temperature pyrolysis processes. For example, high-temperature carbonization, pyrolysis, or calcination of metal-organic frameworks, amine precursors, or other nitrogen-containing organic compounds is often used to form nitrogen-doped structures. While these methods can improve catalyst activity to some extent, they generally suffer from high energy consumption and are not environmentally friendly. Furthermore, under high-temperature conditions, nitrogen-containing precursors often undergo complex decomposition, condensation, and rearrangement processes, leading to highly random formation of nitrogen species. This makes it difficult to precisely control the type, proportion, and spatial distribution of different nitrogen species such as pyrrole nitrogen, pyridine nitrogen, and graphitic nitrogen, thus hindering the targeted construction of highly selective active sites dominated by pyrrole nitrogen. In addition, high-temperature treatment can easily cause migration, agglomeration, or even localized sintering of metal active components, and may lead to the collapse of the original metal-organic framework structure, pore destruction, or a decrease in specific surface area, thereby affecting the catalyst's structural stability, the degree of exposure of active sites, and mass transfer performance. Furthermore, the active center structures of catalysts obtained from high-temperature pyrolysis are often complex, the source of activity is not easily identified, and the reaction pathway is difficult to precisely control. This leads to the actual reaction process still being dominated by the free radical oxidation pathway, making it difficult to fully utilize the advantages of non-radical selective oxidation dominated by singlet oxygen. At the same time, some metal-based catalysts obtained from high-temperature pyrolysis also suffer from problems such as metal ion dissolution, insufficient cycle stability, and limited resistance to interference from coexisting components in actual water treatment systems, thus limiting their further application in complex wastewater treatment.

[0004] Therefore, there is an urgent need to develop a catalyst preparation method that does not require high-temperature pyrolysis, can directionally construct specific nitrogen active sites under mild conditions, especially cyclic nitrogen active sites mainly composed of pyrrole nitrogen, and also has a bimetallic synergistic effect, so as to achieve efficient activation of oxidants and highly selective generation of singlet oxygen, thereby improving the selective removal of recalcitrant organic pollutants in complex water bodies. Summary of the Invention

[0005] To address the problems in existing oxidant activation systems, such as reliance on high-temperature pyrolysis to construct nitrogen-active sites, difficulty in precise control of nitrogen species, insufficient selective generation efficiency of singlet oxygen, and weak resistance to interference in complex water bodies, this invention provides a cyclic nitrogen-doped iron-cobalt bimetallic organic framework catalyst, its preparation method, and its application in singlet oxygen generation. By constructing cyclic nitrogen-active sites dominated by pyrrole nitrogen and combining them with the synergistic effect of iron-cobalt bimetals, efficient activation of the oxidant and highly selective generation of singlet oxygen are achieved, thereby improving the removal efficiency of recalcitrant organic pollutants in wastewater, especially antibiotic pollutants, and enhancing the applicability of the system under conditions where multiple organic substances and anions coexist.

[0006] To achieve the above objectives, the technical solution provided by the present invention is as follows: A method for preparing a cyclic nitrogen-doped iron-cobalt bimetallic organic framework catalyst includes the following steps: Step 1: Preparation of Fe / Co-MOF (Fe-Co bimetallic organic framework) by solvothermal method; Step 2: Using polyamine grafting reagents as organic nitrogen sources, Fe / Co-MOF is modified by solvothermal grafting to uniformly anchor amino groups on the surface and defect sites of the MOF framework, thus obtaining amino-functionalized Fe / Co-MOF. Step 3: Schiff base reaction for bonding and low-temperature cyclization for shaping: The amino-functionalized Fe / Co-MOF is reacted with a dialdehyde reagent under low-temperature heating in an inert atmosphere to undergo a Schiff base condensation reaction. The efficient reaction between the amino and aldehyde groups generates a stable imine bond intermediate. Then, the intermediate is heated and cyclized in a tube furnace under a nitrogen atmosphere to promote the cyclization and dehydrogenation of the chain imine structure, which is directionally transformed into a cyclic nitrogen active site dominated by pyrrole nitrogen. At the same time, a stable Fe / Co-NC coordination structure is formed, resulting in a cyclic nitrogen-doped iron-cobalt bimetallic organic framework material.

[0007] Further, the specific steps of the solvothermal method in step 1 are as follows: Fe source, Co source and terephthalic acid are added to solvent A, ultrasonically dispersed and then transferred to a high-pressure reactor. The high-pressure reactor is sealed and a solvothermal reaction is carried out under heating. After the reaction is completed, the mixture is cooled, washed and dried to obtain the iron-cobalt bimetallic organic framework Fe / Co-MOF. The molar ratio of Fe source to Co source is 2-5:1, and the ratio of the total molar amount of Fe source and Co source to the molar amount of terephthalic acid is 1-4:1.

[0008] Furthermore, the Co source is at least one of cobalt nitrate, cobalt chloride, and cobalt acetate.

[0009] Furthermore, the temperature of the solvothermal reaction is 80-150℃, preferably 100-120℃, and the reaction time is 10-30h, preferably 20-25h; the molar ratio of the Fe source to the Co source is 3-4:1, and the ratio of the total molar amount of the Fe source and the Co source to the molar amount of terephthalic acid is 2-3:1; the solvent A is DMF.

[0010] Further, the polyamine grafting reagent in step 2 is an aliphatic amine compound containing two or more amino groups, preferably selected from at least one of ethylenediamine, 1,3-propanediamine, 1,4-butanediamine, diethylenetriamine, triethylenetetramine, and tetraethylenepentamine; during amino grafting, Fe / Co-MOF needs to be dispersed in toluene solvent, and the volume ratio of toluene solvent to Fe / Co-MOF mass is 20-120 mL: 1 g; the amount ratio of the polyamine grafting reagent to Fe / Co-MOF is 0.5-5 mL: 1 g, preferably 1-4 mL: 1 g; the reaction temperature for grafting modification is 80-120℃, preferably 100-110℃, and the reaction time is 3-10 h, preferably 8-10 h; after the reaction is completed, the Fe / Co-MOF is obtained by centrifugation, washing, and vacuum drying.

[0011] Further, the dialdehyde reagent in step 3 is selected from at least one of glyoxal, glutaraldehyde, o-phthalaldehyde, and terephthalaldehyde; during the Schiff base reaction, the amino-functionalized Fe / Co-MOF needs to be dispersed in anhydrous ethanol, and high-purity nitrogen or argon inert protective gas is introduced; the molar ratio of the dialdehyde reagent in step 3 to the polyamine grafting reagent in step 2 is 1:1-4, preferably 1:2-3; the Schiff base reaction in step 3 is carried out in anhydrous ethanol solvent, and the volume ratio of the anhydrous ethanol solvent to the mass ratio of Fe / Co-MOF in step 2 is 20-120 mL: 1 g; the temperature of the Schiff base reaction is 40-100℃, preferably 60-70℃, and the reaction time is 6-24 hours, preferably 10-15 h; the temperature of the heating cyclization treatment is 60-180℃, and the time is 2-8 hours; after the reaction, the catalyst is obtained by centrifugation, washing, and drying.

[0012] In this application specification, the iron-cobalt bimetallic organic framework Fe / Co-MOF is also simply referred to as MOF(Fe / Co).

[0013] Furthermore, the pyrrole nitrogen in the catalyst of the present invention accounts for more than 50% of the total nitrogen content.

[0014] The application of a cyclic nitrogen-doped iron-cobalt bimetallic organic framework catalyst in the catalytic generation of singlet oxygen includes the following steps: adding the cyclic nitrogen-doped iron-cobalt bimetallic organic framework catalyst and an oxidant to a wastewater system, catalytically activating the oxidant through the catalyst to selectively generate singlet oxygen, thereby treating the wastewater.

[0015] Furthermore, in the application method, the oxidant is at least one of persulfate, perdisulfate, or hydrogen peroxide, preferably persulfate; the final concentration of the oxidant in the wastewater system is 0.1–5 mmol / L, and the final concentration of the catalyst in the wastewater system is 0.05–1 g / L; The pH of the wastewater system is 3 to 11, and the reaction time for treating the wastewater is 2 to 60 minutes, preferably 20 to 40 minutes.

[0016] Furthermore, in the application method, the singlet oxygen is used for the selective degradation of organic pollutants in water. The organic pollutants include at least one of antibiotics, phenolic compounds, dyes, and endocrine disruptors. The antibiotics are one of several classes of antibiotics, including macrolides, tetracyclines, sulfonamides, and fluoroquinolones.

[0017] Furthermore, in the application method, the catalyst catalyzes the activation of the oxidant to generate singlet oxygen, and the contribution rate of singlet oxygen to all active oxygen species is ≥90%; after the catalyst is recycled 5 times, the singlet oxygen generation efficiency is maintained at ≥90%, and the amount of Fe and Co dissolved in the metal ions is ≤0.1 mg / L.

[0018] Furthermore, under mild conditions of room temperature and neutral pH, the oxidant is rapidly activated by utilizing the MNC active sites on the catalyst surface and the synergistic effect of the iron-cobalt bimetallic compound, blocking the free radical reaction pathway. The entire process is dominated by non-free radical reactions, generating singlet oxygen efficiently and selectively, thereby achieving targeted oxidative degradation of electron-rich organic pollutants in water.

[0019] Compared with the prior art, the beneficial effects achieved by the present invention are: 1. Precise and controllable nitrogen species: Abandoning the traditional high-temperature pyrolysis process, a low-temperature cyclization coupled Schiff base reaction is adopted to avoid the collapse of the MOF framework. High-content pyrrole nitrogen cyclic active sites can be prepared in a targeted manner, eliminating the excessive generation of inert nitrogen species and improving the selectivity of singlet oxygen generation from the source. 2. Enhanced catalytic activity and stability: Polyamine reagents serve as a nitrogen source to achieve strong chemical bond anchoring of nitrogen atoms. Combined with the synergistic effect of Fe / Co bimetals, stable MNC coordination sites are formed, resulting in a significant improvement in electron transfer efficiency, excellent catalyst recycling performance, and extremely low metal leaching. 3. High selectivity of singlet oxygen: The entire reaction is dominated by non-radical pathways, with singlet oxygen contributing more than 90%. It is not affected by conventional water quality anions, has strong targeting for the oxidation of electron-rich and recalcitrant organic matter, and has no secondary pollution, making it suitable for the actual complex water body treatment needs. 4. The preparation process is mild and environmentally friendly: The entire process adopts a low-temperature heating process, the reaction conditions are mild and the energy consumption is low. The nitrogen source and reaction reagents are green and readily available, and no toxic by-products are generated. It is both economical and environmentally friendly, and is suitable for large-scale preparation and engineering applications.

[0020] The catalyst of this invention can efficiently activate persulfate oxidants. Through the synergistic effect of the iron-cobalt bimetallic center and the metal-nitrogen active site, it inhibits free radical pathways and promotes reactions dominated by non-free radical pathways, achieving highly selective generation of singlet oxygen. Compared with traditional high-temperature pyrolysis methods, the preparation conditions of this invention are mild, allowing for precise control of nitrogen species configurations. The resulting catalyst exhibits good stability, low metal dissolution, and a singlet oxygen contribution rate exceeding 90%. It demonstrates excellent removal efficiency for recalcitrant organic pollutants, strong resistance to water quality interference, a wide applicable pH range, and suitability for the selective treatment of complex wastewater. Attached Figure Description

[0021] Figure 1 A graph showing the relationship between the degradation effects of different catalysts on levofloxacin; Figure 2 Graphs showing the effects of different concentrations of furfuryl alcohol on the treatment of levofloxacin with the material of this invention; Figure 3 A graph showing the relationship between the contribution rate of singlet oxygen and the removal rate of levofloxacin at different low-temperature heat treatment temperatures. Figure 4 A graph showing the relationship between the contribution rate of singlet oxygen and the removal rate of levofloxacin in cyclic nitrogen-doped iron-cobalt bimetallic organic framework materials prepared with different amine dosages. Figure 5 This is a graph showing the relationship between the degradation effect of levofloxacin after treatment with the material of this invention following competition among several coexisting substances. Figure 6 A graph showing the relationship between the degradation effect of cyclic nitrogen-doped iron-cobalt bimetallic organic framework materials on levofloxacin under different PMS concentrations. Figure 7 The graph shows the relationship between the degradation effect of cyclic nitrogen-doped iron-cobalt bimetallic organic framework materials on levofloxacin under different pH reactions in water. Figure 8 This is a graph showing the relationship between the degradation effects of cyclic nitrogen-doped iron-cobalt bimetallic organic framework materials on different organic pollutants. Figure 9 This image shows the effect of using a cyclic nitrogen-doped iron-cobalt bimetallic organic framework material to degrade levofloxacin and recycle it 5 times.

[0022] Figure 10 XPS image of nitrogen in the cyclic nitrogen-doped iron-cobalt bimetallic organic framework material of this patent. Detailed Implementation

[0023] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0024] Example 1: A method for preparing a cyclic nitrogen-doped iron-cobalt bimetallic organic framework catalyst, specifically including the following steps: S1. Synthesis of iron-cobalt bimetallic organic framework substrate material: Ferric chloride and cobalt nitrate were added to N,N-dimethylformamide (DMF) solvent at a molar ratio of 75:25, along with terephthalic acid. The total molar amount of ferric chloride and cobalt nitrate was 1 mol, the molar amount of terephthalic acid was 0.5 mol, and the volume of DMF was 30 mL. After ultrasonic dispersion, the mixture was transferred to a polytetrafluoroethylene-lined high-pressure reactor and reacted solvothermically at 110 °C for 20 h. After the reaction was completed, the mixture was allowed to cool naturally, and the solid product was collected by centrifugation. The product was washed three times with DMF and anhydrous ethanol, and then dried under vacuum at 60 °C for 12 h to obtain the iron-cobalt bimetallic organic framework MOF (Fe / Co).

[0025] S2. Amine Grafting Modification: 1 g of the substrate material MOF (Fe / Co) obtained in step S1 was dispersed in toluene (100 mL). Diethylenetriamine was used as the ammonia source, and it was added to the toluene at a ratio of 1 mL:1 g of diethylenetriamine to MOF (Fe / Co). After ultrasonic dispersion, the mixture was reacted at 110 °C for 8 h. After the reaction was completed, the mixture was allowed to cool naturally, and the solid product was collected by centrifugation. The product was washed three times with toluene and anhydrous ethanol, and then dried under vacuum at 60 °C for 12 h to obtain the amine-doped iron-cobalt bimetallic organic framework material DETA-MOF.

[0026] S3. Schiff base reaction for bonding and low-temperature cyclization: Using glyoxal as the aldehyde source, all the material obtained in step S2 was dispersed in anhydrous ethanol (100 mL). Glyoxal was added to the anhydrous ethanol. The molar ratio of the ammonia source used in step S2 to the glyoxal in step S3 was 2:1. After ultrasonic dispersion, high-purity nitrogen gas was introduced, and the reaction was carried out at 60 °C for 12 h in an oxygen-free environment. After the reaction was completed, the mixture was naturally cooled, and the solid product was collected by centrifugation. The product was washed three times with anhydrous ethanol and ultrapure water, and then dried under vacuum at 60 °C for 12 h.

[0027] S4. High-purity nitrogen gas is introduced into a tube furnace, and the material dried in step S3 is reacted at 60°C for 2 hours to obtain a cyclic nitrogen-doped iron-cobalt bimetallic organic framework material (G-DETA-MOF).

[0028] Example 2: The preparation method of the catalyst in Example 2 is the same as that in Example 1, except that in step S2, the ammonia source is replaced with ethylenediamine, and ethylenediamine is added to toluene at a ratio of 1 mL:1 g of ethylenediamine to substrate material. All other conditions remain the same, and an ethylenediamine-doped iron-cobalt bimetallic organic framework material (EDA-MOF) is obtained.

[0029] Example 3: The preparation method of the catalyst in Example 3 is the same as that in Example 1, except that in step S3, the aldehyde source is replaced with glutaraldehyde, and glyoxal is added to anhydrous ethanol. The molar ratio of ammonia source used in step S2 to glutaraldehyde in step S3 is 2:1. Finally, a cyclic nitrogen-doped iron-cobalt bimetallic organic framework material is obtained.

[0030] Example 4: Application of catalyst in catalytic activation of oxidant to generate singlet oxygen, specifically including the following steps: Step 1: Prepare simulated levofloxacin wastewater by adding levofloxacin to the water. The final concentration of levofloxacin added to the wastewater is 10 mg / L, thus obtaining simulated wastewater containing levofloxacin.

[0031] Step 2: Add the cyclic nitrogen-doped iron-cobalt bimetallic organic framework catalyst and persulfate (PMS) oxidant prepared in Example 1 to the simulated wastewater prepared above. The final concentration of the catalyst in the wastewater is 0.2 g / L and the final concentration of PMS in the wastewater is 0.5 mmol / L. Adjust the pH of the wastewater to 8, the reaction time is 40 minutes, and the reaction temperature is room temperature. Allow the reaction to proceed fully so that levofloxacin is oxidized and degraded.

[0032] Example 5: The catalytic application steps in Example 5 are the same as those in Example 4, except that "the oxidant in step 2 is replaced with hydrogen peroxide (H2O2), and the final concentration of H2O2 in the wastewater is 5 mmol / L", with all other conditions remaining unchanged.

[0033] Example 6: The catalytic application steps in Example 6 are the same as those in Example 4, except that "the oxidant in step 2 is replaced with persulfate (PDS), and the final concentration of PDS is 1 mmol / L", while the other conditions remain unchanged.

[0034] Example 7: The catalytic application steps of Example 7 are the same as those of Example 4, except that "furfuryl alcohol of different final concentrations (10mM, 20mM, 30mM, 40mM, 50mM) is added to the wastewater in step 2 as a quencher of singlet oxygen in the system", and the other conditions remain unchanged.

[0035] Example 8: The catalytic application steps of Example 8 are the same as those of Example 4, except that "the catalyst in step 2 is replaced with the iron-cobalt bimetallic organic framework MOF (Fe / Co) of Example 1, and the final concentration of MOF (Fe / Co) in the wastewater is 0.2 g / L", and the other conditions remain unchanged.

[0036] Example 9: The catalytic application steps of Example 9 are the same as those of Example 4, except that "the catalyst in step 2 is replaced with the amine-doped iron-cobalt bimetallic organic framework material DETA-MOF of Example 1, and the final concentration of DETA-MOF in the wastewater is 0.2 g / L", and the other conditions remain unchanged.

[0037] Example 10: This example investigates the removal effect of cyclized nitrogen-doped iron-cobalt bimetallic organic framework materials at different temperatures on levofloxacin.

[0038] Example 10 The catalyst preparation method is the same as in Example 1, except that "in step S4, the reaction temperature in the tube furnace is replaced with 60, 100, 150 and 180°C respectively, and the reaction time is kept unchanged for 2 hours". All other conditions remain unchanged, and finally cyclic nitrogen-doped iron-cobalt bimetallic organic framework materials cyclized at different temperatures are obtained.

[0039] The cyclic nitrogen-doped iron-cobalt bimetallic organic framework materials obtained in Example 10 at different temperatures were subjected to levofloxacin degradation experiments according to the steps in Example 4.

[0040] In addition, in Example 10, when the levofloxacin degradation experiment was carried out according to the steps of Example 4, furfuryl alcohol with a final concentration of 10 mM was added to the wastewater as a quencher of singlet oxygen in the system, and the degradation effect was examined under this condition.

[0041] Example 11: This example investigates the removal effect of cyclic nitrogen-doped iron-cobalt bimetallic organic framework materials with different amine dosages on levofloxacin.

[0042] Example 11 Catalyst Preparation Method: The preparation method of the catalyst was repeated in Example 1, except that in step S2, the ratio of the substrate material MOF (Fe / Co) to diethylenetriamine was 1 g:0.5 mL, 1 g:1 mL, 1 g:2 mL, and 1 g:4 mL, respectively. All other conditions remained unchanged, and cyclic nitrogen-doped iron-cobalt bimetallic organic framework materials with different amine dosages were finally obtained, labeled as 0.5DETA, 1DETA, 2DETA, and 4DETA, respectively.

[0043] The cyclic nitrogen-doped iron-cobalt bimetallic organic framework materials with different amine dosages obtained in Example 11 were subjected to levofloxacin degradation experiments according to the steps in Example 4.

[0044] In addition, in Example 11, when the levofloxacin degradation experiment was carried out according to the steps of Example 4, furfuryl alcohol with a final concentration of 10 mM was added to the wastewater as a quencher of singlet oxygen in the system, and the degradation effect was examined under this condition.

[0045] Example 12: The catalytic application steps in Example 12 are the same as in Example 4, except that in Step 1, chloride ions (Cl) are added to the wastewater at a final concentration of 1 mmol / L. - ), and Cl - "The cation that combines is Na ion", with all other conditions remaining unchanged.

[0046] Example 13: The catalytic application steps in Example 13 are the same as in Example 4, except that "in Step 1, a final concentration of 1 mmol / L of bicarbonate ions (HCO3-) is added to the wastewater". - ), with HCO3 - "The cation that combines is Na ion", with all other conditions remaining unchanged.

[0047] Example 14: The catalytic application steps of Example 14 are the same as those of Example 4, except that "humic acid (HA) with a final concentration of 50 mg / L is added to the wastewater in step 1", and the other conditions remain unchanged.

[0048] Example 15: This example investigates the removal effect of the material prepared in Example 1 on levofloxacin at different PMS concentrations.

[0049] Example 15 follows the steps of Example 4, except that the final concentration of PMS in step 2 is adjusted to 0.1, 0.3, 0.5, 1.0, and 2.0 mmol / L, respectively, and levofloxacin degradation experiments are carried out.

[0050] Example 16: This example investigates the removal effect of the material prepared in Example 1 on levofloxacin at different reaction pH levels.

[0051] Example 16 follows the steps of Example 4, except that the pH of the wastewater in step 2 is adjusted to 2, 3, 4, 5, 6, 7, 8, 9, and 10 respectively, and levofloxacin degradation experiments are carried out.

[0052] Example 17: This example explores the removal effect of the material prepared in Example 1 on different organic pollutants.

[0053] Example 17 follows the steps of Example 4, except that the wastewater in step 1 is prepared as sulfamethoxazole wastewater, tetracycline hydrochloride wastewater, or phenol wastewater, with a concentration of 10 mg / L, and degradation experiments are conducted.

[0054] Example 18: This example investigates the effect of cyclic nitrogen-doped iron-cobalt bimetallic organic framework material on the treatment of levofloxacin after 5 cycles. Following the catalytic degradation steps of Example 4, after the degradation reaction, the catalyst was separated from the wastewater and then reused in the next batch of simulated levofloxacin wastewater to repeat the degradation reaction, thereby conducting a catalyst recycling experiment.

[0055] Example 19: This example explores the XPS image of nitrogen element in the cyclic nitrogen-doped iron-cobalt bimetallic organic framework material of Example 1.

[0056] The residual amounts of levofloxacin and other organic pollutants in the wastewater were determined by high-performance liquid chromatography (HPLC). The contribution rate of singlet oxygen was tested by adding 10 mmol / L furfuryl alcohol to the reaction system for singlet oxygen quenching experiments. The pollutant removal rate in the quenching experiment was used as a reflection of the singlet oxygen contribution rate.

[0057] Figure 1 These are comparison charts showing the degradation rates of levofloxacin with different catalysts added in Examples 4 and 8-9. Figure 1 The blank group refers to the group without added catalyst, from Figure 1 As can be seen, in the experiment without catalyst, the removal rate of levofloxacin in the wastewater after reaction treatment was 12.88%; in the experiment with the addition of iron-cobalt bimetallic organic framework MOF (Fe / Co) as catalyst, the removal rate of levofloxacin after reaction treatment was 32.77%; in the experiment with the addition of amine-doped iron-cobalt bimetallic organic framework material (DETA-MOF) as catalyst, the removal rate of levofloxacin after reaction treatment was 69.11%; and in the experiment with the addition of cyclic nitrogen-doped iron-cobalt bimetallic organic framework material (G-DETA-MOF) as catalyst, the removal rate of levofloxacin after reaction treatment was 100%. This indicates that the cyclic nitrogen-doped iron-cobalt bimetallic organic framework material of the present invention can significantly improve the ability to activate PMS and achieve a high removal effect of levofloxacin, directly proving that the three-step synergistic process of "DETA grafting-Schiff base reaction-low temperature cyclization" is the core key to improving catalytic activity. Single modification processes or traditional MOF materials cannot achieve the same effect, fully demonstrating the inventiveness of the patented technology.

[0058] Figure 2The image shows the effect of different concentrations of furfuryl alcohol on the treatment of levofloxacin with the material of this invention in Example 7. The results showed that adding 10 mM furfuryl alcohol resulted in a 47.30% removal rate of levofloxacin after the reaction; adding 20 mM furfuryl alcohol resulted in a 41.89% removal rate; adding 30 mM furfuryl alcohol resulted in a 32.11% removal rate; adding 40 mM furfuryl alcohol resulted in a 20.75% removal rate; and adding 50 mM furfuryl alcohol resulted in a 9.87% removal rate. In the reaction without furfuryl alcohol, the removal rate of levofloxacin was 100%. After the furfuryl alcohol quenching experiment on singlet oxygen, the removal rate of levofloxacin ranged from 9.87% to 47.30%, indicating that singlet oxygen was the main active species in this series of experiments and played a key role in degradation. As can be seen from the figure, singlet oxygen contributes more than 90% to this system.

[0059] Figure 3 This is a graph showing the relationship between the contribution rate of cyclic nitrogen-doped iron-cobalt bimetallic organic frameworks to singlet oxygen and the removal rate of levofloxacin at different low-temperature heat treatment temperatures in Example 10. Measurements showed that after 40 minutes of reaction, the removal rate of levofloxacin was 100% for materials treated at various low-temperature heat treatment temperatures. After singlet oxygen quenching experiments, the removal rate of levofloxacin ranged from 37.55% to 40.45%, indicating that singlet oxygen was the main active species in these experiments and played a crucial role in degradation. The graph clearly shows that even at the Schiff base reaction temperature (60°C), the material can activate PMS to generate a large amount of singlet oxygen. This highlights the advantage of this invention—a low-temperature green material—directly proving the scientific validity of this invention by abandoning high-temperature pyrolysis and adopting a low-temperature cyclization process, achieving targeted regulation of cyclic nitrogen active sites from the process source.

[0060] Figure 4This is a graph showing the relationship between the contribution rate of cyclic nitrogen-doped iron-cobalt bimetallic organic framework materials to singlet oxygen and the removal rate of levofloxacin, prepared with different amounts of amine (DETA) in Example 11. Measurements showed that after 40 minutes of reaction, the removal rate of levofloxacin was 97.99-100% for the materials prepared with different amounts of amine. After singlet oxygen quenching experiments, the removal rate of levofloxacin was 60.07% for the 0.5 DETA material, 44.01% for the 1.0 DETA material, 39.67% for the 2.0 DETA material, and 39.97% for the 4.0 DETA material. The reaction data for the 0.5 DETA material shows that singlet oxygen is not the main reactive species, while the data for the subsequent materials indicate that singlet oxygen is the main reactive species in this series of reactions, playing a key role in degradation. This indicates that if the DETA dosage is too low, the amino grafting is insufficient, failing to provide enough active sites for the subsequent Schiff base reaction, resulting in a weak catalytic effect. With increasing DETA dosage, the amino loading in the material increases, and the number of cyclic nitrogen sites obtained after subsequent steps also increases. After considering the above data, the optimal dosage ratio for diethylenetriamine was selected.

[0061] Figure 5 This is a bar chart showing the degradation effect of levofloxacin after treatment with the material of this invention following competition from several common coexisting substances in Examples 12-14. Measurements showed that for chloride ions (Cl... - In contrast to the competition from other treatments, the removal rate of levofloxacin in water treated by this invention was 95.89%; for bicarbonate (HCO3)... - In the face of competition from other ions, the removal rate of levofloxacin in water treated by this invention was 95.89%; in the face of competition from humic acid (HA), the removal rate of levofloxacin in water treated by this invention was 96.43%. Under conditions where common water-related interfering ions such as chloride ions, bicarbonate ions, and humic acid are present, the catalyst degradation efficiency fluctuated by less than 5%, indicating that compared to free radical oxidation systems, the singlet oxygen non-radical pathway is not affected by conventional anion quenching and has extremely strong anti-interference ability, highlighting the advantages of this invention—it can be directly applied to the selective remediation treatment of complex water bodies and wastewater, and its application scenarios are wider.

[0062] Figure 6This is a graph showing the relationship between the degradation effect of the material of the present invention on levofloxacin under different PMS concentrations in Example 15. The results showed that when the PMS concentration was 0.1 mmol / L, the removal rate of levofloxacin after the reaction was 74.13%; when the PMS concentration was 0.3 mmol / L, the removal rate was 90.73%; and when the PMS concentration was between 0.5 and 2.0 mmol / L, the removal rate was 100%. The data shows that as the PMS concentration increased from 0.1 mmol / L to 0.5 mmol / L, the removal rate of levofloxacin increased from 74% to 100%. Further increases in concentration resulted in a stable removal rate. This indicates that the catalytic system of the present invention has strong adaptability to oxidants, achieving efficient activation without high concentrations of oxidants. The reaction is low-cost and mild, meeting the economic requirements of actual wastewater treatment.

[0063] Figure 7 This is a graph showing the relationship between the degradation effect of the material of the present invention on levofloxacin in water under different pH reactions in Example 16. Measurements showed that, within a wide pH range of 2-10, after the reaction, the material achieved a levofloxacin removal rate of 98.12-100%, with a fluctuation range of less than 2%. No additional acid-base adjustment of the system pH is required, overcoming the shortcomings of traditional catalytic systems that have stringent pH requirements. Furthermore, it can adapt to the complex acid-base environments of various actual wastewaters, significantly improving the practicality and engineering adaptability of the technology.

[0064] Figure 8This is a graph showing the relationship between the degradation effects of the material of the present invention on different organic pollutants in Example 17. Measurements showed that the removal rates of levofloxacin and phenol after the reaction were both 100%, indicating that the removal rate of tetracycline hydrochloride was 98.57% and the removal rate of sulfamethoxazole was 87.03%. The data shows that singlet oxygen, as an electrophilic agent, readily attacks electron-rich groups. Pollutants with electron-rich structures such as levofloxacin (containing numerous phenolic hydroxyl groups, amino groups, and conjugated double bonds, resulting in extremely high electron cloud density), tetracycline hydrochloride (containing numerous phenolic hydroxyl groups, amino groups, and conjugated double bonds, resulting in extremely high electron cloud density), and phenol (with a high electron cloud density in its benzene ring structure) are easily oxidized and broken by singlet oxygen, thus exhibiting excellent degradation effects. However, sulfamethoxazole contains sulfonamide groups and pyrimidine rings, structures with strong electron-withdrawing effects, leading to a lower electron cloud density in the benzene ring. Compared to the aforementioned electron-rich pollutants, its reaction kinetics with singlet oxygen are relatively slower, making oxidation slightly more difficult, resulting in a slightly lower degradation rate. Overall, the data demonstrate excellent performance, validating the broad-spectrum catalytic performance of the material and further confirming the unique advantages of the singlet oxygen oxidation system in the treatment of complex wastewater. It is applicable to various organic pollutants and can achieve relatively economical and effective treatment of simulated and actual wastewater containing antibiotics.

[0065] Figure 9 This is a graph showing the effect of using the material of the present invention to degrade levofloxacin after 5 cycles in Example 18. As can be seen from the graph, the cyclic nitrogen-doped iron-cobalt bimetallic organic framework material maintains a strong removal capacity for levofloxacin throughout the 5 cycles. The removal efficiency for levofloxacin remains above 96.07% in the first 3 cycles, and still around 94.07% and 91.19% in the 4th and 5th cycles, respectively. This indicates that after 5 cycles of repeated use, the catalyst maintains a degradation rate of over 91% for pollutants, while the leaching of Fe and Co metals remains below 0.1 mg / L. This demonstrates that the MNC coordination structure formed by the low-temperature cyclization process is stable, and the active sites are not easily lost, solving the technical pain points of poor cycling performance and easy metal leaching in existing MOF-based catalysts, and possessing long-term engineering application potential.

[0066] Figure 10 This is the XPS plot of nitrogen in the cyclic nitrogen-doped iron-cobalt bimetallic organic framework material of the present invention in Example 19. This plot shows the qualitative characterization results of nitrogen species in the material of the present invention. Peak fitting yielded two characteristic peaks: 400.5 eV corresponding to pyrrole nitrogen (61%), and 399.2 eV corresponding to Fe / Co-MN. xMetal-nitrogen coordination structure (39%). The results show that this invention, through a polyamine grafting-Schiff base reaction-low-temperature cyclization process, can directionally construct high-content cyclic nitrogen active sites dominated by pyrrole nitrogen, while simultaneously forming a stable bimetallic-nitrogen coordination structure. This provides core structural support for the catalyst's efficient activation of oxidants and highly selective generation of singlet oxygen, verifying the effectiveness and inventiveness of the process.

[0067] In summary, this invention quantitatively verifies the technical effects from all dimensions, including process optimization, activity comparison, stability, and anti-interference: the data clearly shows the optimal preparation process parameters of this invention, confirming that the metal ion exchange-polyamine grafting-Schiff base reaction + anaerobic low-temperature cyclization process can directionally construct high-content pyrrole nitrogen sites, with a prominent bimetallic synergistic effect; the catalyst's singlet oxygen contribution rate exceeds 90%, and its degradation efficiency for target pollutants far exceeds that of existing comparative samples. It also exhibits excellent cycle stability, strong resistance to water quality interference, and a wide applicable pH range, comprehensively solving the pain points of uncontrollable nitrogen species, poor selectivity, and weak stability in existing technologies, fully demonstrating the outstanding inventiveness and practical application value of this invention.

[0068] The contents described in this specification are merely an enumeration of the implementation forms of the inventive concept, and the scope of protection of this invention should not be regarded as limited to the specific forms described in the embodiments.

Claims

1. A method for preparing a cyclic nitrogen-doped iron-cobalt bimetallic organic framework catalyst, characterized in that, Includes the following steps: Step 1: Preparation of Fe / Co-MOF (Fe-Co bimetallic organic framework) by solvothermal method; Step 2: The Fe / Co-MOF described in Step 1 is grafted and modified using a polyamine grafting agent to obtain amino-functionalized Fe / Co-MOF; Step 3: Under an inert atmosphere, the amino-functionalized Fe / Co-MOF obtained in Step 2 is reacted with a dialdehyde reagent to form an imine intermediate; then, under a nitrogen atmosphere, it is heated and cyclized in a tube furnace to directionally construct cyclic nitrogen active sites mainly composed of pyrrole nitrogen, thus obtaining a cyclic nitrogen-doped iron-cobalt bimetallic organic framework catalyst. The polyamine grafting reagent mentioned in step 2 is an aliphatic amine compound containing two or more amino groups, selected from at least one of ethylenediamine, 1,3-propanediamine, 1,4-butanediamine, diethylenetriamine, triethylenetetramine, and tetraethylenepentamine; The dialdehyde reagent mentioned in step 3 is selected from at least one of glyoxal, glutaraldehyde, o-phthalaldehyde, and terephthalaldehyde; the temperature of the heating cyclization treatment is 60-180℃, and the time is 2-8 hours.

2. The preparation method according to claim 1, characterized in that, The specific steps of the solvothermal method in step 1 are as follows: Fe source, Co source and terephthalic acid are added to solvent A, ultrasonically dispersed and then transferred to a high-pressure reactor. After the high-pressure reactor is sealed, a solvothermal reaction is carried out under heating. After the reaction is completed, the mixture is cooled, washed and dried to obtain the iron-cobalt bimetallic organic framework Fe / Co-MOF. The molar ratio of Fe source to Co source is 2-5:1, and the ratio of the total molar amount of Fe source and Co source to the molar amount of terephthalic acid is 1-4:

1.

3. The preparation method according to claim 2, characterized in that, The temperature of the solvothermal reaction is 80-150℃, and the reaction time is 10-30h; the molar ratio of Fe source to Co source is 3-4:1, and the ratio of the total molar amount of Fe source and Co source to the molar amount of terephthalic acid is 2-3:1; the solvent A is DMF.

4. The preparation method according to claim 1, characterized in that, In step 2, the ratio of the polyamine grafting reagent to Fe / Co-MOF is 0.5–5 mL: 1 g; Step 2, grafting modification, was carried out in toluene solvent, with the volume ratio of toluene solvent to Fe / Co-MOF mass being 20-120 mL: 1 g; the reaction temperature for grafting modification was 80-120 °C, and the reaction time was 3-10 h; after the reaction was completed, the amino-functionalized Fe / Co-MOF was obtained by centrifugation, washing, and vacuum drying.

5. The preparation method according to claim 1, characterized in that, The molar ratio of the dialdehyde reagent in step 3 to the polyamine grafting reagent in step 2 is 1:1-4; the inert atmosphere is nitrogen or argon. Step 3, the Schiff base reaction, is carried out in anhydrous ethanol solvent, with the volume ratio of anhydrous ethanol solvent to the mass ratio of Fe / Co-MOF in step 2 being 20-120 mL: 1 g; the Schiff base reaction temperature is 40-100℃, and the reaction time is 6-24 hours; after the reaction is completed, the catalyst is obtained by centrifugation, washing, and drying.

6. A cyclic nitrogen-doped iron-cobalt bimetallic organic framework catalyst prepared by any one of claims 1-5, wherein pyrrole nitrogen accounts for more than 50% of the total nitrogen content in the catalyst.

7. The application of the cyclic nitrogen-doped iron-cobalt bimetallic organic framework catalyst according to claim 6 in the catalytic generation of singlet oxygen, characterized in that, The cyclic nitrogen-doped iron-cobalt bimetallic organic framework catalyst and oxidant are added to the wastewater system. The oxidant is activated by the catalyst to generate singlet oxygen with high selectivity, thereby treating the wastewater.

8. The application according to claim 7, characterized in that, The oxidant is at least one of persulfate, perdisulfate, or hydrogen peroxide; the final concentration of the oxidant in the wastewater system is 0.1–5 mmol / L, and the final concentration of the catalyst in the wastewater system is 0.05–1 g / L. The pH of the wastewater system is 3–11, and the reaction time for wastewater treatment is 2–60 min.

9. The application as described in claim 7, characterized in that, The singlet oxygen is used for the selective degradation of organic pollutants in water, including at least one of antibiotics, phenolic compounds, dyes, and endocrine disruptors, wherein the antibiotics are at least one of macrolides, tetracyclines, sulfonamides, and fluoroquinolones.

10. The application according to claim 7, characterized in that, The catalyst catalyzes the activation of the oxidant to generate singlet oxygen, and the contribution rate of singlet oxygen to all active oxygen species is ≥90%. After the catalyst is recycled 5 times, the singlet oxygen generation efficiency is maintained at ≥90%, and the amount of Fe and Co dissolved in the metal ions is ≤0.1 mg / L.

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