Iron-based metal-organic complex catalyst, preparation method and method for removing ofloxacin in water body

Abstract

The invention belongs to the technical field of sewage treatment and new materials, and discloses an iron-based metal-organic complex catalyst, a preparation method and a method for removing ofloxacin in a water body, and the catalyst is prepared by taking ellagic acid EA with an electron-rich structure as a ligand and iron atoms as coordination metal through a hydrothermal method. The invention relates to an iron-based metal-organic complex FeMOCs material which is an iron-based metal-organic complex FeMOCs material and is used for preparing six-coordination black powder with an amorphous nano-scale sheet structure and micron-scale cluster aggregation, the surface pore size distribution is mainly mesopores, and an efficient catalytic interface and a sufficient microscopic space are provided for a rapid and powerful reaction of an oxidizing agent persulfate and ofloxacin in a water body. The catalyst has an adsorption-degradation synergistic effect, and is named as an EFE-150 catalyst. The catalyst is synthesized by adopting a solvothermal method, is applied to catalyzing PDS to efficiently remove ofloxacin in a water body, has the characteristics of quick response, self-sustaining, low cost and the like, and can meet the requirements of large-scale popularization and application.

Description

Technical Field

[0001] The present invention belongs to the technical fields of sewage treatment and new materials, and particularly relates to an iron-based metal-organic complex catalyst, a preparation method thereof, and a method for removing ofloxacin in water bodies. Background Art

[0002] Ofloxacin (OFL) belongs to fluoroquinolone (FQs) antibiotics, which is a broad-spectrum antibiotic and is widely used in the prevention and treatment of related diseases of humans and animals due to its low price and strong applicability. Due to the high electronegativity, chemical stability and anti-microbial degradation ability of the fluorine atoms in its structure, it is easy to bioaccumulate and magnify in the environment through the food chain, resulting in disorders in the structure and function of the ecosystem; the continuous accumulation of OFL and its resistance genes in the human body will also cause diseases such as tendonitis, central nervous system and gastrointestinal dysfunction and have a long-term impact on the immune system. Therefore, ofloxacin (OFL) in water bodies, as a typical fluoroquinolone antibiotic, has a high ecological risk, and its residue may lead to the spread of microbial drug resistance and ecological toxicity. Based on the fact that OFL poses a serious threat to both the ecological environment and human health, it is of great significance to seek economic, efficient, low-cost and sustainable OFL treatment methods and technologies.

[0003] In recent years, methods for removing OFL have been widely studied, including physical methods, chemical methods and biological methods. Among them, the physical method uses the surface activity or porous structure of the adsorbent to capture OFL through physical adsorption, chemical adsorption or ion exchange. However, when the adsorption is saturated, it can no longer play a role, and a large amount of adsorbent needs to be continuously input, such as magnetic Fe3O4@C nanocomposites, etc., with slow treatment efficiency and high cost. Chemical methods have the advantages of fast removal speed, thorough removal effect and complete decomposition of pollutants compared with physical and biological methods. Among them, advanced oxidation technologies (AOPs) usually use ultraviolet radiation or semiconductor / metal / carbonaceous catalysts to catalyze oxidants such as hydrogen peroxide and persulfate to generate reactive oxygen species (ROS) with strong oxidation ability, such as hydroxyl radicals (HO•), sulfate radicals (SO4 - •), superoxide radicals (O2 - •), etc. to degrade pollutants. In recent years, sulfate radical-based advanced oxidation processes (SR-AOP) have become one of the research hotspots in the environmental field. SR-AOP mainly generates SO4 - • and other ROS with strong oxidizing ability by activating persulfates (PS) including peroxymonosulfate (PMS) and peroxydisulfate (PDS), and further mineralize pollutants into H2O and CO2. SO4 -• Similar to HO•, it has a high standard oxidation potential (E0 = 2.5 V - 3.1 V) and a relatively long half-life (30 - 40 μs), and has extremely mild requirements for the pH of the system. Therefore, it can oxidize and degrade pollutants under relatively broad pH conditions.

[0004] However, the catalytic effect of PS is usually affected by various factors such as the catalytic method. Its catalytic effect is unstable, the degradation rate is slow, and continuous input of catalysts and oxidants is required to keep the degradation reaction going. The dosage required is large, and the applicable pH range is narrow (usually 2 - 4). Among them, when using catalytic materials such as metal oxides for catalysis, due to defects such as material agglomeration, metal ion spillover, and poor structural stability; when using carbon-based materials, singlet oxygen ( 1 1O2) can be mediated, but compared with metal oxide catalytic materials, the catalytic sites are limited, and it is difficult to accelerate the PS catalytic rate through electron transfer; when using methods such as thermal activation and ultraviolet activation, continuous external energy input is required, and the generation of ROS is single, which limits the degradation effect of pollutants. The use of other multi-metal materials and complex carbon-based materials can improve the catalytic ability of PDS, but their preparation processes are cumbersome, the raw material costs are high, and they often have poor biocompatibility, and it is difficult for the reaction system to be self-supported and environmentally friendly. Traditional FeMOCs are porous crystal materials formed by coordinating metal ions (Fe 2+ 2+ / Fe 3+ 3+) as metal nodes through organic ligands (such as carboxylic acids, imidazoles, etc.). They have a high specific surface area (500 - 3000 m² / g), adjustable pore structures, and catalytic activities of metal sites, and are widely used in the fields of catalysis, adsorption, energy, etc. However, there are also problems such as high costs, difficulties in engineering, and poor environmental compatibility.

[0005] For example, a method for efficiently catalytically activating persulfate or peroxymonosulfate to treat organic wastewater using metal-organic frameworks disclosed in CN105923738A uses metal-organic framework materials as catalysts. Utilizing the characteristics of high active sites and strong catalytic activity of metal-organic frameworks, persulfate or peroxymonosulfate is catalytically activated at room temperature to generate sulfate radicals to degrade organic pollutants in organic wastewater. The key is to use metal-organic framework material MIL-88A with a hexagonal rod shape and a specific surface area of 10 - 30 m 2 2 / g to achieve short catalytic time, good persistence, and high degradation effect on organic pollutants within a relatively wide pH range. According to the experimental data recorded in its examples, its degradation onset speed is slow, the addition amount of the activated material (oxidant) is large, the reaction system cannot be self-supported, the removal rate within 30 minutes is at most no more than 30%, there is no selectivity for organic pollutants, and it cannot specifically improve the removal efficiency and effect of OFL in water, and secondary pollution is likely to occur.

[0006] Another method for efficiently activating peroxymonosulfate to degrade ofloxacin disclosed in CN118047474A uses an accordion-shaped Mxenes support and a degradation catalyst material containing both Mn active sites and N active sites to activate peroxymonosulfate. By utilizing the synergistic effect jointly catalyzed by the Mn active sites and N active sites, the activation effect of peroxymonosulfate is improved, and the degradation of ofloxacin in water is achieved. According to the experimental data recorded in its examples, the degradation catalyst material Mn-U 2.5 @MXenes 1.0 The adsorption and removal rate of ofloxacin in the peroxymonosulfate system within 10 minutes is 21.45%, and the addition amounts of both the catalyst and the oxidant are relatively large, and its reaction system cannot be self-sustaining.

[0007] In summary, for the removal of OFL in water by existing materials and treatment processes, there are generally problems such as high material cost, long onset time, slow degradation rate, and inability of the reaction system to be self-sustaining. Moreover, the raw materials for preparing the catalyst are expensive, the preparation process is cumbersome, the amount of activated materials such as persulfate to be added is large, and the treatment process is complex. Eventually, the overall system solution has deficiencies such as slow onset of treatment, high cost, and low efficiency, and cannot meet the industrial requirements of fast onset, low cost, simple process, high efficiency, and no secondary pollution for the removal of a large amount of ofloxacin wastewater. Summary of the Invention

[0008] Aiming at the deficiencies of the prior art, the object of the present invention is to provide an iron-based metal-organic complex catalyst, a preparation method, and a method for removing ofloxacin in water. By synchronously improving the catalyst components, ratios, and processes, an iron-based metal-organic complex catalyst FeMOCs material EFE-150 with a six-coordinate, nanoscale flake structure is prepared, and it shows micron-scale cluster aggregation. The electron-rich functional groups can provide sufficient electrons to fully activate persulfate PDS. Based on the adsorption-degradation synergistic effect, the onset time is short, the degradation rate is fast, and the reaction system can achieve self-sustainability through electron supply and electron transfer. After adsorption saturation, the catalytic sites can be released by degradation to restore the adsorption ability, making the catalytic degradation system have less material consumption, low cost, high efficiency, and a simple process, without secondary pollution, and can meet the industrial requirements for the efficient removal of a large amount of ofloxacin wastewater.

[0009] The present invention provides the following technical solutions to achieve the above object: An iron-based metal-organic complex catalyst, characterized in that it uses ellagic acid EA with an electron-rich structure as a ligand and iron atoms as coordination metals to prepare a hexacoordinate black powder with an amorphous nanoscale flaky structure and micron-scale cluster aggregation. The surface pore size distribution is mainly mesoporous, and it can catalyze the rapid and efficient reaction of the oxidant persulfate PDS with ofloxacin OFL in water. The iron-based metal-organic complex FeMOCs material with an adsorption-degradation synergistic effect is named the EFE-150 catalyst.

[0010] The EFE-150 catalyst has an amorphous stacked flaky structure at the nanoscale and appears as clusters as a whole. The average thickness of a single sheet is 30 nm, the specific surface area is 35 m 2 / g, the main surface pore size is 4.5 nm, and the C, O, and Fe elements are evenly distributed in the flaky structure without enrichment. The nitrogen adsorption-desorption curve shows the characteristics of a type II adsorption isotherm and has an H3-type hysteresis loop.

[0011] A preparation method of the aforementioned iron-based metal-organic complex catalyst uses ellagic acid EA with an electron-rich structure as a ligand and iron atoms as coordination metals, and is synthesized by a solvothermal method to obtain a hexacoordinate black powder with a nanoscale flaky structure and micron-scale cluster aggregation, that is, the iron-based metal-organic complex catalyst EFE-150.

[0012] A method for removing ofloxacin in water uses the iron-based metal-organic complex catalyst EFE-150 to activate the persulfate PDS oxidant to enhance the degradation of ofloxacin in water. Specifically, an appropriate amount of persulfate PDS oxidant and the pre-prepared EFE-150 catalyst are successively added to the wastewater containing ofloxacin pollutants. EFE-150 provides a sufficient catalytic interface and microscopic space for the rapid and efficient reaction of persulfate PDS and ofloxacin OFL, accelerates the degradation rate, and under the adsorption-degradation synergistic effect, continuously promotes the adsorption-oxidation degradation process of OFL, improves the reaction rate of the system, and reduces the dosage of the catalyst and oxidant in the system.

[0013] Compared with the existing technologies, the present invention has the following advantages and effects: 1. The iron-based metal-organic complex catalyst, preparation method thereof, and application thereof in removing ofloxacin in water provided by the present invention prepare an iron-based metal-organic complex catalyst (FeMOCs material) EFE-150 with a six-coordinate and nanoscale sheet structure through synchronous improvement of components, ratios, and processes, and make it show micron-scale cluster aggregation, having an adsorption-degradation synergistic effect, capable of taking into account the number of high-activity electrons, the iron ion loading capacity, and the high catalytic efficiency, and also capable of taking into account a more appropriate main pore size to improve the targeting. The electron-rich functional groups of the catalyst can provide sufficient electrons to fully activate persulfate, with a short onset time, a fast degradation rate, and a self-supported reaction system. After adsorption saturation, the catalytic sites can be released by degradation to restore the adsorption capacity, making the catalytic degradation system have less material consumption, low cost, high efficiency, and a simple process, without secondary pollution, and can meet the industrial demand for efficient removal of a large amount of ofloxacin wastewater.

[0014] 2. The iron-based metal-organic complex catalyst and preparation method thereof provided by the present invention use the organic ligand EA and the coordination metal Fe, both of which are common materials and have good biocompatibility, and can construct an environmentally friendly catalytic system; the EFE-150 catalyst has a six-coordinate rigid structure and multiple hydroxyl groups (-OH) and lactone rings, and the ligand structure contains a large number of delocalized electrons, significantly enhancing the electron supply and transfer ability, effectively reducing the energy loss during the catalytic PDS process, enhancing the PDS utilization efficiency, and significantly reducing the amounts of the EFE-150 catalyst and PDS in the degradation system. In addition, the catalyst material has excellent structural rigidity, and the catalytic sites are not easily deactivated, so it has good reusability, further saving the economic cost, and is of great significance for the reduction treatment of organic pollutant wastewater. The iron-based metal-organic complex catalyst has low raw material cost, a simple preparation method, a controllable preparation process, and is easy to industrialize.

[0015] 3. The iron-based metal-organic complex material provided by the present invention can efficiently catalyze the degradation of OFL in water by PDS. By adding a small amount of the EFE-150 catalyst, sufficient PDS can be catalyzed, with a short onset time and a fast degradation rate. The degradation rate of OFL can reach more than 85% within 30 minutes, and the removal rate of OFL can reach 91% within one hour. In addition, the removal efficiency remains above 80% under different temperatures, acidic to weakly alkaline environments, and background interferences, and the degradation efficiency for different actual water bodies remains at a high level, and it can be widely applied to different OFL treatment environments.

[0016] 4. The organic ligand ellagic acid (EA) used in the present invention is a natural polyphenolic compound. Its molecular structure consists of a benzene ring, hydroxyl groups (-OH), and a lactone ring. It has strong antioxidant and anti-inflammatory properties and good biocompatibility. The structural characteristics of EA endow it with π-conjugated rigidity and a large number of delocalized electrons, enabling it to have a strong ability to coordinate with metal ions. After being fully chelated with metal iron ions, it can form a metal iron-organic complex with an adjustable pore structure and abundant active sites. Therefore, the EFE-150 catalyst, which combines the transition metal iron with strong catalytic ability and EA with an electron-rich structure, has a mutual enhancement effect. The large number of delocalized electrons contained in EA can significantly improve the catalytic ability of metal iron sites. Especially in the catalytic degradation of organic pollutant OFL by persulfate (PDS), it has strong pertinence, and has the advantages of fast treatment speed, high efficiency, low cost, and simple process in the degradation of OFL in water, making it easy to be popularized and applied on a large scale.

[0017] 5. The method for removing ofloxacin in water provided by the present invention is based on the synergistic effect between the EFE-150 catalyst and the oxidant in the system. The EFE-150 provides a sufficient catalytic interface and microscopic space for the rapid and efficient reaction of persulfate PDS and ofloxacin OFL, accelerating the degradation rate. Under the synergistic effect of adsorption-degradation, it continuously promotes the adsorption-oxidation degradation process of OFL. When the adsorption is saturated, it releases catalytic sites and adsorption sites through degradation, restores the adsorption ability, improves the reaction rate of the system, and reduces the dosage of the catalyst and oxidant in the system. Brief Description of the Drawings

[0018] Figure 1 Schematic diagram of the preparation method of EFE-150 prepared in the embodiment of the present invention; Figure 2 SEM and EDS mapping images of EFE-150 prepared in the embodiment of the present invention. Among them, (a) is the SEM image and EDS mapping image of EFE-150 at the nanoscale, and (b) is the SEM image of EFE-150 at the micron scale; Figure 3 XRD image of EFE-150 prepared in the embodiment of the present invention; Figure 4 FT-IR image of EFE-150 prepared in the embodiment of the present invention; Figure 5 Nitrogen adsorption-desorption curve and BJH pore size distribution image of EFE-150 prepared in the embodiment of the present invention. Among them, (a) is the nitrogen adsorption-desorption curve image of EFE-150, and (b) is the BJH pore size distribution image of EFE-150; Figure 6ESI-MS image of EFE-150 prepared in the embodiments of the present invention; Figure 7 Image for exploring the degradation effect of EFE-150 prepared in the embodiments of the present invention on OFL. Among them, (a) is the comparison image of the degradation effect of different reaction systems on OFL, (b) is the schematic image of the influence of the addition amount of EFE-150 on the degradation effect of OFL, (c) is the schematic image of the influence of the addition amount of PDS on the degradation effect of OFL, (d) is the schematic diagram of the influence of the reaction temperature on the degradation effect of OFL, (e) is the schematic image of the influence of the initial pH value on the degradation effect of OFL, (f) is the schematic image of the influence of different background interferences on the degradation effect of OFL, (g) is the schematic image of the influence of different actual water bodies on the degradation effect of OFL, and (h) is the reuse image of EFE-150 catalyzing PDS to degrade OFL; Figure 8 XPS images of EFE-150 before and after the reaction prepared in the embodiments of the present invention; Figure 9 Electrochemical images of the reaction system participated by EFE-150 in the embodiments of the present invention, where (a) is the OCP image, (b) is the I-t curve image, and (c) is the LSV image. Detailed implementation manners

[0019] In order to make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0020] Basic embodiment A kind of iron-based metal-organic complex catalyst provided in this embodiment is a six-coordinate black powder with an amorphous nanoscale flaky structure and micron-scale cluster aggregation, using ellagic acid EA with an electron-rich structure as a ligand and iron atoms as a coordination metal. The surface pore size distribution is mainly mesoporous, and it can provide an efficient catalytic interface and sufficient microscopic space for the rapid and efficient reaction of the oxidant persulfate PDS and ofloxacin OFL in water. It has an adsorption-degradation synergistic effect and is named EFE-150 catalyst.

[0021] The EFE-150 catalyst has an amorphous stacked flaky structure at the nanoscale and presents as a cluster as a whole. The average thickness of a single sheet is 30 nm, and the specific surface area is 35 m 2 / g, the surface main body pore size is 4.5 nm, the C, O and Fe elements are evenly distributed in the flaky structure without enrichment phenomenon, the nitrogen adsorption and desorption curve presents the characteristics of type II adsorption isotherm, and has an H3-type hysteresis loop.

[0022] The adsorption-degradation synergistic effect of the EFE-150 catalyst is based on its nanoscale flaky FeMOCs structure. Since the EA ligand has a large number of delocalized electrons in the form of π electrons, which are highly delocalized in the polycyclic planar structure of EA, multiple electrostatic potential minima are formed in the polycyclic planar structure. Through π-π interaction and electrostatic interaction, OFL is efficiently adsorbed, reducing the interaction distance with reactive free radicals and increasing the contact frequency with reactive free radicals; multiple hydroxyl groups and lactone rings in the polycyclic planar structure of EA provide sufficient electrons to a large number of iron-based catalytic sites, enabling them to quickly recover their catalytic activity. Combining with carbon-based catalytic sites with delocalized electrons, it efficiently catalyzes PDS to generate a large number of reactive free radicals, and through the synergistic effect of adsorption and oxidation, OFL is rapidly degraded; after OFL is degraded, the originally occupied adsorption sites are re-exposed, and the EFE-150 catalyst restores its adsorption activity, continuously promoting the adsorption-oxidation degradation process of OFL and enhancing the reaction rate of the system.

[0023] The EFE-150 catalyst has a six-coordinate rigid structure, multiple hydroxyl groups (-OH) and lactone rings, a large amount of loaded iron ions, and a large number of delocalized electrons in the ligand structure, which can significantly enhance the electron supply and transfer ability, effectively reduce the energy loss during the catalytic PDS process, enhance the utilization efficiency of PDS, and significantly reduce the usage amounts of the EFE-150 catalyst and PDS in the degradation system.

[0024] A preparation method of the aforementioned iron-based metal-organic complex catalyst, which uses ellagic acid EA with an electron-rich structure as a ligand and iron atoms as a coordination metal, and is synthesized by a solvothermal method to obtain a six-coordinate black powder with a nanoscale flaky structure and showing micron-scale cluster aggregation, that is, the iron-based metal-organic complex catalyst EFE-150. Specifically, it includes the following steps: S1: Prepare raw materials Prepare FeCl3·6H2O and ellagic acid EA respectively; S2: Deprotonation reaction Add N, N-dimethylformamide DMF to the reaction kettle, and then sequentially add FeCl3·6H2O and EA with a set molar ratio into it, and ultrasonically dissolve and disperse them completely. Subsequently, add formic acid to deprotonate EA to enhance its coordination ability, and obtain a mixed solution; among them, the molar ratio of FeCl3·6H2O to EA is 1:3, and the concentration range of FeCl3·6H2O is 0.5 mmol - 1.5 mmol; S3: Heating reaction Put the above mixed solution into an oven, heat it to 120 - 180 °C and react for 24 - 72 hours, then turn off the oven and let it cool naturally to room temperature; preferably, the reaction temperature is 150 °C and the reaction time is 24 hours.

[0025] S4: Centrifugal drying Centrifuge and collect the product obtained in step S3, and centrifuge and wash it several times with DMF and isopropanol respectively; then place it in a vacuum drying oven and vacuum dry it at 100 °C. After removing the solvent, a black powdery material, namely the iron-based metal-organic complex catalyst EFE-150, is obtained and placed in a dry container for standby.

[0026] A method for removing ofloxacin in water body, which uses the above-mentioned iron-based metal-organic complex catalyst EFE-150 to activate the persulfate PDS oxidant to enhance the degradation of ofloxacin in water body. Specifically, an appropriate amount of persulfate PDS oxidant and the pre-prepared EFE-150 catalyst are sequentially added to the wastewater containing ofloxacin pollutants. EFE-150 provides a sufficient catalytic interface and microscopic space for the rapid and efficient reaction of persulfate PDS and ofloxacin OFL, accelerates the degradation rate, and under the adsorption-degradation synergistic effect, continuously promotes the adsorption-oxidation degradation process of OFL, improves the reaction rate of the system, and reduces the dosage of the catalyst and oxidant in the system. The specific steps are as follows: A-1: Detect the concentration of OFL in the water body; A-2: Calculate the dosages of the EFE-150 catalyst and PDS oxidant required, and add them to an appropriate amount of water to prepare a stock solution; for the treatment of OFL wastewater with a concentration not greater than 25 mg / L, the concentration ranges of the catalyst and oxidant are both 0.125 - 0.5 g / L; the specific concentration and dosage can be adjusted according to actual needs; A-3: Add the above stock solution to the wastewater and stir. The EFE-150 catalyst and PDS oxidant, through the adsorption-degradation synergistic effect, continuously promote the rapid degradation of OFL in the water body. At this time, the EFE-150 catalyst rapidly catalyzes PDS to generate a variety of reactive oxygen species ROS, and combined with the electron transfer ability of the catalyst itself, a large number of free radicals and non-free radicals are generated to efficiently remove OFL in the water body; A-4: Sample and detect the water body at certain time intervals until the set removal rate or reaction end point is reached.

[0027] After testing, the EFE-150 catalyst and PDS oxidant, through the adsorption-degradation synergistic effect, can achieve a degradation rate of more than 85% for OFL within 30 minutes and more than 90% for OFL within 60 minutes, and exhibit good reuse efficiency. The removal method and catalytic material provided by the embodiments of the present invention have the characteristics of environmental friendliness, high degradation efficiency, and low cost, can meet the needs of large-scale popularization and application, and can quickly obtain a degradation effect of more than 90%.

[0028] For the catalyst and removal method provided in this embodiment, through comprehensive selection of relevant synthesis parameters of the iron-based metal-organic complex, and then selecting to synthesize a target substance with a six-coordination structure; in order to obtain a higher iron ion loading and enable the material to have delocalized electrons that can greatly supplement the catalytic activity of iron ions, ellagic acid EA containing multiple electron-rich groups and capable of inhibiting the metal agglomeration phenomenon during the synthesis process is specifically selected as the ligand. Only through the synergistic effect between the microstructure, components, and distribution positions of the material can better material synthesis and stronger electron transfer effects be obtained. This embodiment selects DMF to form the organic solvent environment for the reaction, sets the reaction temperature at 150 °C to reduce hydration interference; based on the six-coordination characteristics of transition metal Fe and considering the hydration situation, designs the molar ratio of its Fe center to EA ligand to be 1:3, adds formic acid to adjust the pH of the system to a weak acid environment to deprotonate some phenolic hydroxyl groups, promotes the occurrence of the coordination process, and increases the output. The synthesis process designed in this embodiment aims to form a specific microstructure of the catalyst by controlling the component concentration and process parameters, enabling the EA ligand with a large number of delocalized electrons to fully coordinate with iron ions, thereby transferring electrons to iron ions to maintain its high catalytic activity. The EA ligand itself can also provide a large number of carbon-based catalytic sites through delocalized π electrons and enhance the adsorption of OFL through π-π interactions. Its non-planar six-coordination structure can form a partial larger mesopore size distribution, which can effectively promote the full contact between OFL in the water body and the oxidative free radicals in the system, thereby improving the onset time and degradation efficiency of degrading OFL.

[0029] The following is combined with the attached Figures 1 to 9 , and specific selections are made on the basis of the basic embodiment, and multiple specific embodiments are used for detailed description.

[0030] Example 1 This embodiment provides an iron-based metal-organic complex catalyst, a preparation method thereof, and its application in removing ofloxacin in water (a high-efficiency method for removing ofloxacin in water), and on the basis of the basic embodiment, a nanoscale catalyst EFE-150 black powder is specifically prepared.

[0031] The method for preparing the nanoscale EFE-150 material is shown in Figure 1, which is prepared by using commercially available reagent FeCl3·6H2O and ellagic acid (EA) through a solvothermal method, and the specific steps are as follows: Add FeCl3·6H2O to a 100 mL reaction kettle containing 40 mL of DMF, ultrasonicate until completely dissolved, then add EA, continue ultrasonication until completely dispersed, add an appropriate amount of formic acid to the mixture to deprotonate EA for coordination reaction, then seal the reaction kettle and place it in a forced-air drying oven and heat at 150 °C for 24 h. After heating, take out the reaction kettle, cool it to room temperature, then centrifuge and wash the solid material several times with DMF and isopropanol in sequence and place it in a vacuum drying oven and heat at 100 °C for 12 h; Among them, the molar ratio of FeCl3·6H2O to EA is 1:3; among them, the concentration of FeCl3·6H2O is 0.5 mmol, and the concentration of EA is 1.5 mmol; the volume of the added formic acid solution is 2.5 mL; in other embodiments, the concentration of FeCl3·6H2O can also be selected as 1 mmol or 1.5 mmol, and the concentration of EA is adjusted correspondingly according to the ratio.

[0032] Example 2 In this example, the morphology, element distribution, carbon-based structure, functional groups and coordination characteristics, specific surface area and overall structure, etc. of the EFE-150 catalyst material prepared in Example 1 were studied by means of SEM-EDS, XRD, FT-IR, BET and ESI-MS, etc.

[0033] First, the morphology and element distribution of EFE-150 prepared in Example 1 were studied by SEM-EDS characterization. Refer to Figure 2 Figure (a) in, at the nanoscale, it presents an amorphous flake structure; refer to Figure 2 Figure (b) in, at the microscale, the flake structure of the material shows an obvious tendency to aggregate into clusters, and the overall still remains amorphous. The EDS mapping image shows that C, O and Fe elements are evenly distributed in the EFE-150 structure, and there is no element enrichment phenomenon.

[0034] Refer to Figure 3 , the carbon-based structure of the EFE-150 material was studied by XRD characterization. EFE-150 as a whole presents an amorphous non-crystalline structure, and the obvious diffraction peak at 43.6° can be attributed to the (101) crystal plane of the carbon-based structure. The existence of the diffraction peak proves that there is a certain graphitized structure in the carbon-based structure of the EFE-150 material. However, the diffraction peak is broad and not sharp, confirming that it is still an amorphous non-crystalline structure.

[0035] From the FT-IR image of EFE-150 ( Figure 4)(The different vibration modes of multiple structures of its ligand EA can be observed, including the stretching vibrations of C-C / C=C / C=O structures, the bending vibration of -OH structures; and the existence of coordination bonds, i.e., the stretching vibration of Fe-O. The research results verify the existence of multiple functional groups belonging to EA and the existence of metal coordination bonds in the EFE-150 structure, and the structural characteristics can be preliminarily judged.)

[0036] In addition, through nitrogen adsorption-desorption experiments, the BET surface area and pore size distribution of EFE-150 were measured. The results are shown in Figure 5 Figures (a) and (b) in 2 . The detection results show that the specific surface area and the main pore size of the EFE-150 material are 35 m

[0037] / g and 4.5 nm respectively, indicating that the material is a nanoscale mesoporous material. The nitrogen adsorption-desorption curve shows the characteristics of a type II adsorption isotherm and has an H3-type hysteresis loop, indicating that the EFE-150 material as a whole has a relatively large pore structure.) Figure 6 See the appendix 14 for further confirmation of the structural characteristics of the EFE-150 catalyst, in this example, the EFE-150 material was tested by high-resolution mass spectrometry (ESI-MS). By querying the coordination characteristics of trivalent iron and tannic acid-like organic compounds in the existing literature, it was initially assumed that it has a six-coordination structure with a theoretical molecular weight of 956. Combining the analysis of the mass-to-charge ratio (m / z) and peak intensity in the MS image, its molecular ion peak was located at m / z = 485.28317. Considering that the solvent used for detection is deionized water and the functional group characteristics and pore structure of EFE-150 have the possibility of adsorbing water molecules, its theoretical molecular ion peak should be m / z = 487, which is in good agreement with the molecular peak located in the MS image; secondly, the deprotonated ellagic acid structure (C

[0038] Example 3 In this example, the EFE-150 material prepared in Example 1 was specifically applied to the efficient removal of ofloxacin in water. According to the concentration of OFL in the water, the corresponding proportion of the catalyst EFE-150 material and the oxidant PDS were added. With the morphological structure and physical and chemical properties of this material, it can quickly catalyze PDS to generate a variety of ROS to attack OFL, thereby degrading OFL in the water and completing the efficient removal treatment of OFL in the water to obtain ideal removal efficiency and effect. The specific operation is as follows: A-1: Detect the concentration of OFL in the water; A-2: Calculate the dosages of the required EFE-150 catalyst and PDS oxidant, and add them to an appropriate amount of water to prepare a stock solution with a relatively high concentration. The concentration ranges of the catalyst and the oxidant in the stock solution are usually both 0.125 - 0.5 g / L, and can also be further adjusted according to the actual situation. A-3: Add the said stock solution to the wastewater and stir. The two together rapidly degrade OFL in the water body. The EFE-150 catalyst rapidly catalyzes PDS to generate various ROS, combined with its own electron transfer ability, thereby efficiently removing OFL in the water body through free radical and non-free radical pathways. A-4: Sample and detect the water body at certain time intervals until the set removal rate or the reaction end point of the reaction end point is reached, and then stop stirring.

[0039] In this example, a pre-experiment method was used to evaluate the degradation effect of EFE-150 on OFL. The pre-experiment set up groups of EFE-150 catalyzing PDS, organic ligand EA catalyzing PDS, and Fe 2+ catalyzing PDS to explore the degradation effect of OFL under different systems. In addition, groups of only adding the EFE-150 material and only adding PDS were set as control groups to explore the adsorption performance of the materials and the ability of PDS to directly generate ROS.

[0040] The steps of the pre-experiment are as follows: Add 10 mL of OFL solution with a concentration of 25 mg / L to a 20 mL sample bottle, and then add 5 mg of the oxidant PDS and 5 mg of the catalyst EFE-150 material to the sample bottle respectively. Place the sample bottle in a constant temperature shaking incubator and react at a rotation speed of 160 rpm and 30 °C for 2 h, and regularly sample to measure the OFL concentration. In addition, the relevant chemical agent dosages corresponding to the EA catalyzing PDS group, the Fe 2+ catalyzing PDS group, the group of only adding the EFE-150 material, and the group of only adding PDS as the control are the same as those in the previous text (converted in terms of the same amount of substance).

[0041] The results of the pre-experiment are as Figure 7 (a) shows that only adding the EFE-150 material exhibits good adsorption and removal effects on OFL. Only adding PDS has a certain OFL removal effect, but the removal process shows certain fluctuations. In different catalytic systems, the EA catalyzing PDS group does not produce an OFL removal effect, indicating that this ligand does not have the ability to catalyze PDS alone to generate ROS for degrading OFL; Fe 2+The catalytic PDS group did not show OFL removal effect in the first 15 minutes, and then the OFL removal was steady, and the OFL removal rate could reach 50% within 2 h; the EFE-150 catalytic PDS group showed excellent OFL removal efficiency, and 80% of the OFL pollutants could be removed within 5 min, and the OFL removal rate could reach 91% within 2 h. Compared with the addition of only EFE-150 material, the catalytic system showed a great improvement in the reaction rate and removal effect.

[0042] Furthermore, taking the pre-experiment reaction parameters as a reference, a single-factor influence study was carried out. The other reaction parameters were fixed, and the effects of different EFE-150 addition amounts, PDS addition amounts, reaction temperatures, initial pH values, background interferences, real water bodies on the degradation effect of OFL by the EFE-150 catalytic PDS system and the reusability of the material were tested.

[0043] First, the effect of the EFE-150 addition amount on the OFL removal effect was investigated. In this factor exploration, the concentration of OFL was 25 mg / L, the PDS addition amount was fixed at 0.5 g / L, and the addition amounts of EFE-150 were set at 0.125, 0.25, 0.375, 0.5 g / L. As Figure 7 shown in (b), the removal efficiencies of different addition amounts within 5 min of the reaction were 68.9%, 86.4%, 83.1% and 73.0% respectively. The overall removal efficiency first increased and then decreased with the increase of the catalyst addition amount. The removal efficiencies within 2 h of the reaction were 85.1%, 80.2%, 73.4% and 69.6% respectively. The overall removal efficiency showed a gradually decreasing trend with the increase of the catalyst addition amount. It can be seen that the catalyst can achieve an ideal OFL removal effect with a relatively small addition amount, and the increase of the catalyst addition amount does not necessarily improve the removal efficiency.

[0044] As Figure 7 shown in (c), in the exploration of the influence of the PDS addition amount, the OFL concentration was 25 mg / L, the EFE-150 addition amount was fixed at 0.125 g / L, and the OFL removal experiments were carried out with PDS addition amounts of 0.125, 0.25, 0.375, 0.5 g / L. The OFL removal rates within 5 min were 61.6%, 67.1%, 71.7% and 78.8% respectively, and the OFL removal rates within 2 h were 81.6%, 86.8%, 88.4% and 90.2% respectively. The overall OFL removal efficiency showed an increasing trend with the increase of the PDS concentration, and the increasing trend gradually slowed down. It can be seen that the EFE-150 material has a high PDS catalytic efficiency and can catalyze PDS several times the amount of the catalyst material added.

[0045] To investigate the removal ability of EFE-150 material for OFL under different environmental conditions, a single-factor experiment on reaction temperature was conducted. The OFL concentration was set at 25 mg / L, the addition amount of catalyst EFE-150 was 0.125 g / L, and the addition amount of PDS was 0.5 g / L. The removal effects of OFL in the reaction system at temperatures of 25 °C, 35 °C, and 45 °C were investigated respectively. As Figure 7 shown in Figure (d) of

[0046] Subsequently, the OFL removal experiments under different initial pH values were carried out. The OFL concentration was set at 25 mg / L, the addition amount of catalyst EFE-150 was 0.125 g / L, and the addition amount of PDS was 0.5 g / L. The removal effects of OFL in the reaction system under the conditions of pH = 3, 5, 7, 9, and 11 were explored. As Figure 7 shown in Figure (e) of

[0047] The interference of background substances during the OFL removal process was further investigated. The OFL concentration was set at 25 mg / L, the addition amount of catalyst EFE-150 was 0.125 g / L, and the addition amount of PDS was 0.5 g / L. The interference of Cl - , H2PO4 - , HPO4 2- , NO3 2- , SO3 2- and humic acid (HA) was investigated. Three concentration gradients were set for each interfering substance. The anion concentrations were set at 0.25 mM, 0.5 mM, and 0.75 mM, and the HA concentration was set at 2.5 mg / L, 5 mg / L, and 7.5 mg / L. As Figure 7 shown in Figure (f) of

[0048] Based on the above pre-experiment results, further experiments on the degradation performance of the EFE-150 catalyzed PDS system for real water systems such as lake water, mineral water, river water, and leachate were carried out. The OFL concentration was set at 25 mg / L, the addition amount of catalyst EFE-150 was 0.125 g / L, the addition amount of PDS was 0.5 g / L, and the degradation system was prepared from real water bodies. As shown in Figure 7 figure (g) in , the OFL removal rates within 5 min were 79.1%, 85.0%, 80.4%, and 72.3% respectively, and the OFL removal rates within 2 h were 90.1%, 90.4%, 87.8%, and 83.8% respectively. It can be seen that the EFE-150 catalyzed PDS system can exhibit relatively excellent OFL removal efficiency in the face of various water environments.

[0049] The reusability of EFE-150 is as shown in Figure 7 figure (h). The OFL concentration was set at 25 mg / L, the addition amount of catalyst EFE-150 was 0.125 g / L, the addition amount of PDS was 0.5 g / L. After the first degradation experiment, it was recovered and could be reused five times. The OFL removal rates of the 5-time reuse experiments of EFE-150 were 86.8%, 86.8%, 83.8%, 80.3%, and 79.4% in turn, proving that this catalytic material has good reusability.

[0050] Example 4 In this example, on the basis of Example 3, the EFE-150 catalyst materials before and after the reaction were selected for X-ray photoelectron spectroscopy (XPS) detection respectively, and the specific steps are as follows: B1. XPS detection of EFE-150 materials before and after the reaction The EFE-150 materials before and after the reaction were subjected to XPS detection. By comparing the changes in the fine spectral peak splitting and displacement of each element before and after the reaction, the reaction mechanism was judged and the reaction performance was explored. The specific operation was as follows: B1-1: Place the prepared EFE-150 material in a vacuum drying oven and dry it at 100 °C for 12 h, then seal it for standby.

[0051] B1-2: Weigh a sufficient amount of EFE-150 material according to the optimal chemical dosing ratio in Example 3 for the reaction. After the reaction, collect the EFE-150 catalyst material through a suction filtration device, wash it several times with deionized water, place it in a blast drying oven and dry it at 100 °C for 12 h, then seal it for standby.

[0052] In this example, as shown in Figure 8As shown in Figure (a), the XPS detection results of the EFE-150 catalyst before the reaction showed multiple structures of the ligand EA, including C-C / C=C, C-O-C, O-C=O, etc., as well as the metal coordination feature Fe-O of EFE-150, which were consistent with the FT-IR and ESI-MS detection results, further clarifying the structural characteristics of EFE-150. The XPS detection results of EFE-150 after the reaction showed the same structural characteristics as before the reaction, but the binding energies of the peak splitting of each elemental orbital showed obvious shifts. See Figure 8 Figure (b) in, the binding energy of the peak splitting of the C 1s spectrum increased, its electron cloud density decreased, and at the same time, a π-π* shake-up peak was generated, further indicating that the delocalized electrons in the carbonyl structure of EFE-150 participated in the electron transfer process; as Figure 8 As shown in Figure (c), the binding energies of the peak splitting of the O 1s spectrum all showed a decreasing state, indicating that the oxygen-containing structure participated in the PDS catalytic process as an active site; as Figure 8 As shown in Figure (d), the binding energy of the peak splitting of the Fe 2p spectrum decreased extremely significantly compared with other elements, indicating that there were different valence states of the Fe element in the EFE-150 material and it participated in the PDS catalytic process as a core catalytic site. The XPS results showed that the EFE-150 material had multiple catalytic sites, could catalyze PDS to generate ROS, and its carbonyl structure had good electron transfer ability, and then could degrade pollutants through the electron transfer pathway.

[0053] Example 5 In this example, the electron transfer ability in the EFE-150-catalyzed PDS system was further investigated by evaluating the electrochemical characteristics of the reaction system participated by EFE-150. The detection items included open circuit potential (OCP), current-time curve (I-t curve), and linear voltammetry scan curve (LSV). The specific steps were as follows: C. Electrochemical detection of the reaction system participated by the EFE-150 material OCP, I-t curve, and LSV electrochemical detections were carried out on three systems: the EFE-150 material, EFE-150 and PDS, and EFE-150 catalyzing PDS to degrade OFL. The specific operations were as follows: C-1: A three-electrode system was configured on the electrochemical workstation for relevant detections. The working electrode was made of EFE-150, the counter electrode was a platinum sheet, and the reference electrode was a Hg / HgCl electrode. A 0.1 M Na2SO4 solution was used as the electrolyte.

[0054] C-2: The total volume of the OCP test solution was prepared to be 100 mL. Several milligrams of PDS were added at the 200th second in sequence, and several milligrams of OFL powder were added at the 400th second.

[0055] C-3: Prepare a total volume of 100 mL of the I-t curve test solution. Add several milligrams of PDS at the 120th second and several milligrams of OFL powder at the 240th second in sequence.

[0056] C-4: Prepare a total volume of 100 mL of the LSV test solution. A total of three systems are prepared, namely pure electrolyte solution, PDS solution with a certain concentration, and mixed solution of PDS and OFL with a certain concentration. The scanning voltage range is -0.5~1.5 V (relative to the reference electrode), and the scanning rate is 5 mV / s.

[0057] In the embodiments of the present invention, as Figure 9 shown in Figure (a) therein, after adding PDS to the working electrode system modified with EFE-150 material, the OCP surges sharply, and after continuing to add OFL, the OCP drops suddenly and tends to be stable; Figure 9 Figure (b) therein shows that after adding PDS to the working electrode system modified with EFE-150 material, the current in the I-t Curve curve shows a downward trend, while the current rises steeply after continuing to add OFL; The LSV curve shows that after adding PDS to the working electrode system modified with EFE-150 material, it shows the relatively most significant current enhancement characteristics. At the same time, when PDS and OFL exist simultaneously, the degree of current enhancement is slightly inferior to that of the PDS solution, as shown in Figure 9 Figure (c) therein. In the EFE-150 catalyzed PDS degradation OFL system, significant voltage and current changes are observed in the electrochemical test, indicating that the addition of OFL consumes the metastable PDS intermediate adsorbed on the EFE-150 material in the form of electron transfer, confirming the existence of a non-radical degradation path mainly based on electron transfer, and further indicating the high-efficiency removal ability of EFE-150 material to catalyze PDS for OFL.

[0058] The high-efficiency removal treatment method for OFL in water body and the iron-based metal-organic complex provided by the above embodiments of the present invention. The EFE-150 catalyst as a whole has a six-coordinate rigid electron-rich structure. The raw materials required are cheap and easily available. The preparation process is simple, can catalyze PDS to generate a variety of ROS, and combines the electron transfer process to efficiently remove OFL through radical and non-radical pathways. The degradation rate of OFL reaches more than 85% within 30 minutes, and its degradation efficiency can reach more than 90% within 60 minutes, and shows good reuse efficiency; The material has excellent reuse performance. For the material with decreased catalytic activity, only simple deionized water washing is required after recovery to restore the catalytic activity. It has the characteristics of environmental friendliness, high degradation efficiency, low cost, etc., no secondary pollution, and can meet the needs of large-scale and wide-range promotion and popularization, and has broad application prospects in the field of wastewater treatment.

[0059] It should be particularly noted that within the scope of the components, ratios, and process parameters described in the present invention, other technical solutions obtained through specific selections can all achieve the technical effects of the present invention, so they will not be listed one by one. At the same time, other technical solutions obtained by using components, solvents, and processes similar to those described in the present invention are included within the protection scope of the present invention.

[0060] As described above, it is only a preferred embodiment of the present invention and does not impose any formal restrictions on the present invention. Any person skilled in the art can make many possible changes and modifications to the technical solution of the present invention, or modify it into an equivalent embodiment with equivalent changes, without departing from the scope of the technical solution of the present invention. All equivalent changes made in accordance with the components, ratios, and processes of the present invention shall be covered within the protection scope of the present invention.

Claims

1. An iron-based metal-organic complex catalyst, characterized in that, It uses ellagic acid EA with an electron-rich structure as a ligand and iron atoms as a coordination metal to prepare a hexacoordinate black powder with an amorphous nanoscale flaky structure and showing micron-scale cluster aggregation. The surface pore size distribution is mainly mesoporous, and it has an adsorption-degradation synergistic effect. It is a metal-organic complex FeMOCs material of iron that can catalyze the rapid and efficient reaction of oxidant persulfate PDS with ofloxacin OFL in water, and it is named the EFE-150 catalyst.

2. The iron-based metal-organic complex catalyst according to claim 1, wherein The EFE-150 catalyst is an amorphous stacked flake-like structure at the nanoscale and presents as a cluster as a whole. The average thickness of a single flake is 30 nm, the specific surface area is 35 m 2 / g, the main pore size on the surface is 4.5 nm, and the C, O, and Fe elements are evenly distributed in the flake-like structure without enrichment. The nitrogen adsorption-desorption curve presents the characteristics of a type II adsorption isotherm and has an H3-type hysteresis loop.

3. The iron-based metal-organic complex catalyst according to claim 1, wherein The adsorption-degradation synergistic effect of the EFE-150 catalyst is based on its nanoscale flaky FeMOCs structure. The π electrons in the large number of delocalized electrons of the EA ligand are highly delocalized in the polycyclic planar structure of EA, forming multiple electrostatic potential minima in the polycyclic planar structure. OFL is efficiently adsorbed through π-π interaction and electrostatic interaction; multiple hydroxyl groups and lactone rings in the polycyclic planar structure of EA provide sufficient electrons to a large number of iron-based catalytic sites, enabling them to quickly recover catalytic activity. Combining with carbon-based catalytic sites with delocalized electrons, OFL is rapidly degraded through the synergistic action of adsorption and oxidation; after OFL is degraded, the originally occupied adsorption sites are re-exposed, and the EFE-150 catalyst resumes its adsorption activity.

4. A method for preparing the iron-based metal-organic complex catalyst according to any one of claims 1 to 3, characterized in that, It uses ellagic acid EA with an electron-rich structure as a ligand and iron atoms as a coordination metal, and is synthesized by a solvothermal method to obtain a hexacoordinate black powder with a nanoscale flaky structure and showing micron-scale cluster aggregation, that is, the metal-organic complex catalyst EFE-150 of iron.

5. The preparation method of the iron-based metal-organic complex catalyst according to claim 4, characterized in that, It specifically includes the following steps: S1: Preparation of raw materials Prepare FeCl3·6H2O and ellagic acid EA respectively; S2: Deprotonation reaction Add N, N-dimethylformamide DMF to the reaction kettle, and then sequentially add FeCl3·6H2O and EA in a set molar ratio into it. Ultrasonic to completely dissolve and disperse them, and then add formic acid to deprotonate EA to obtain a mixed solution; S3: Heating reaction Put the above mixed solution into an oven, heat it to 120-180 °C and react for 24-72 hours, then turn off the oven and let it cool naturally to room temperature; S4: Centrifugation and drying Centrifuge to collect the product obtained in step S3, and centrifuge and wash it several times with DMF and isopropanol respectively; then place it in a vacuum drying oven and vacuum dry it at 100 °C. After removing the solvent, a black powdery material, that is, the metal-organic complex catalyst EFE-150 of iron, is obtained and placed in a dry container for standby.

6. The preparation method according to claim 4, wherein In the step S2, the molar ratio of FeCl3·6H2O to EA is 1:3; the concentration range of FeCl3·6H2O is 0.5 mmol-1.5 mmol; The reaction temperature in the step S3 is 150 °C and the reaction time is 24 hours.

7. A method for removing ofloxacin in water bodies, characterized in that, It uses the iron-based metal-organic complex catalyst EFE-150 described in any one of claims 1 to 3 to activate the persulfate PDS oxidant to enhance the degradation of ofloxacin in water. Specifically, the persulfate PDS oxidant and the pre-prepared EFE-150 catalyst are successively added to the wastewater containing ofloxacin pollutants. The EFE-150 catalyzes the rapid and potent reaction of persulfate PDS and ofloxacin OFL, and under the synergistic effect of adsorption-degradation, continuously promotes the adsorption-oxidation degradation process of OFL, improves the reaction rate of the system, and reduces the dosage of the catalyst and oxidant in the system.

8. The method for removing ofloxacin in water according to claim 7, characterized in that, Specifically, it includes the following steps: A-1: Detect the concentration of OFL in the water body; A-2: Calculate the dosages of the EFE-150 catalyst and the PDS oxidant required, and add them to an appropriate amount of water to prepare a stock solution; A-3: Add the stock solution to the wastewater and stir. The EFE-150 catalyst and the PDS oxidant continuously promote the rapid degradation of OFL in the water body through the synergistic effect of adsorption-degradation. At this time, the EFE-150 catalyst rapidly catalyzes PDS to generate various reactive oxygen species ROS, and combined with the electron transfer ability of the catalyst itself, efficiently removes OFL in the water body; A-4: Sample and detect the water body at regular intervals until the set removal rate is reached.

9. The method for removing ofloxacin in water according to claim 8, characterized in that, It includes the following steps: In step A-2, for the treatment of OFL wastewater with a concentration of 25 mg / L, the concentration ranges of both the catalyst and the oxidant are 0.125 - 0.5 g / L.

10. The method for removing ofloxacin in water according to claim 8, characterized in that, It includes the following steps: In step A-3, the degradation rate of the EFE-150 catalyst and the PDS oxidant for OFL reaches more than 85% within 30 min and more than 90% within 60 min.

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