Fe / co-zif@cnf composite material, preparation method and method for degrading ceftiofur sodium in water body

Abstract

The application discloses a Fe / Co-ZIF@CNF composite material, a preparation method and a degradation method of ceftiofur sodium in water, and belongs to the technical field of water treatment catalytic materials. The composite material takes nanometer carbon fiber as a carrier, uniformly loads Fe / Co bimetallic ZIF crystals on the surface, and the crystals are rhombic dodecahedrons with excellent dispersity. The composite material is prepared by using a room-temperature in-situ coordination reaction, and the process is mild, green and easy to scale. The composite material is used for activating peroxymonosulfate during degradation, and active oxygen species are generated, with sulfate radicals as the main active oxygen species and hydroxyl radicals and singlet oxygen as auxiliary active oxygen species. Under optimal reaction conditions at pH 5-8, the degradation rate of ceftiofur sodium reaches 94.0% within 20 min, the apparent rate constant is 0.135min⁻¹, and the TOC removal rate is 43.8%. The composite material solves the defects of easy agglomeration and difficult recycling of powder MOFs, has stable structure and can be recycled, and is suitable for efficient treatment of water bodies containing ceftiofur sodium, such as aquaculture wastewater.

Description

Technical Field

[0001] This invention relates to the field of catalyst technology, specifically to Fe / Co-ZIF@CNF composite materials, their preparation methods, and methods for the degradation of ceftiofur sodium in water. Background Technology

[0002] With the rapid and large-scale development of the pharmaceutical industry, as well as animal husbandry and aquaculture, antibiotics are being produced and used in large quantities. Ceftiofur sodium (CEF), as a broad-spectrum and highly effective cephalosporin antibiotic, is widely used in animal husbandry and aquaculture due to its excellent antibacterial properties. However, ceftiofur sodium is characterized by its poor biodegradability, strong environmental persistence, and bioaccumulation, making it difficult to degrade and eliminate through natural environmental pathways. It is frequently detected in surface water, groundwater, and aquaculture wastewater. Long-term residues can disrupt the balance of aquatic ecosystems, induce the emergence of drug-resistant bacteria, and ultimately threaten human health through the food chain. Therefore, developing efficient, economical, and environmentally friendly ceftiofur sodium degradation technologies has become an urgent need for water environment management.

[0003] Traditional wastewater treatment processes (biodegradation, physical sedimentation, activated carbon adsorption, etc.) have extremely low removal efficiency for ceftiofur sodium, failing to achieve effective degradation and mineralization. Advanced oxidation processes based on persulfate (PMS) (SR-AOPs) have become the core technology for treating recalcitrant organic pollutants due to their advantages such as strong oxidizing power, wide applicability to a wide range of pollutants, mild reaction conditions, and environmental friendliness. The key to this process lies in the development of efficient and stable heterogeneous catalysts to activate PMS and generate highly oxidizing reactive oxygen species (ROS) to achieve pollutant degradation.

[0004] Metal-organic frameworks (MOFs), especially ZIFs, possess characteristics such as ultra-large specific surface area, tunable pore structure, and abundant metal active sites, making them excellent catalysts for activating polymethyl ether (PMS). Among them, Co-based ZIFs exhibit the most outstanding catalytic activity. Introducing Fe into Co-based ZIFs to construct Fe / Co bimetallic ZIFs can utilize the synergistic effect of Fe and Co to accelerate the redox cycle of metal ions, further enhancing catalytic activity and inhibiting metal leaching. However, powdered Fe / Co-ZIFs suffer from drawbacks such as easy agglomeration, insufficient exposure of active sites, difficulty in solid-liquid separation, and low recycling rate, severely limiting their engineering applications in practical water treatment.

[0005] Carbon nanofibers (CNFs) possess high electrical conductivity, excellent chemical stability, abundant surface functional groups, and ease of separation and recovery, making them ideal supports for MOFs and capable of solving the problems of powdered MOF agglomeration and separation. However, current technologies lack efficient and stable composite catalysts for loading Fe / Co bimetallic ZIFs onto the surface of carbon nanofibers, and also lack efficient activation and degradation methods for ceftiofur sodium in water, making it difficult to meet the application requirements of practical wastewater treatment. Summary of the Invention

[0006] The purpose of this section is to outline some aspects of the embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0007] Therefore, the purpose of this invention is to provide Fe / Co-ZIF@CNF composite materials, preparation methods, and methods for the degradation of ceftiofur sodium in water, so as to solve the problems mentioned in the background art.

[0008] To address the aforementioned technical problems, according to one aspect of the present invention, the present invention provides the following technical solution:

[0009] A Fe / Co-ZIF@CNF composite material, comprising: using carbon nanofibers as a carrier, with Fe / Co bimetallic ZIF crystals uniformly loaded on the surface of the carbon nanofibers, wherein the molar ratio of Fe to Co in the Fe / Co bimetallic ZIF is 0.5:1-2:1.

[0010] As a preferred embodiment of the Fe / Co-ZIF@CNF composite material of the present invention, the molar ratio of Fe to Co in the Fe / Co bimetallic ZIF is 1.25:1.

[0011] As a preferred embodiment of the Fe / Co-ZIF@CNF composite material of the present invention, the Fe / Co bimetallic ZIF crystal has a rhombic dodecahedral structure with a crystal diameter of 0.7μm-0.9μm, and the carbon nanofiber has a diameter of 15μm.

[0012] A method for preparing Fe / Co-ZIF@CNF composite material involves coordinating Fe source, Co source and 2-methylimidazole in the presence of carbon nanofibers to grow Fe / Co bimetallic ZIF crystals in situ and load them onto the surface of carbon nanofibers, thereby obtaining the target composite material.

[0013] In a preferred embodiment of the preparation method of the Fe / Co-ZIF@CNF composite material of the present invention, the Fe source is ferric nitrate, the Co source is cobalt nitrate, and the molar ratio of Fe source to Co source is 0.5:1-2:1; the coordination reaction is carried out in an aqueous solution at room temperature.

[0014] In a preferred embodiment of the preparation method of the Fe / Co-ZIF@CNF composite material described in this invention, the nanofibers in the coordination reaction can constrain the growth and aggregation of Fe / Co bimetallic ZIF crystals, thereby improving crystal dispersion.

[0015] A method for degrading ceftiofur sodium in water includes the following steps: adding the Fe / Co-ZIF@CNF composite material and persulfate as described in any one of claims 1-3 to the water containing ceftiofur sodium, thereby activating the persulfate through the composite material to generate reactive oxygen species, thus achieving the degradation of ceftiofur sodium.

[0016] As a preferred embodiment of the method for degrading ceftiofur sodium in water according to the present invention, the molar ratio of Fe to Co in the Fe / Co-ZIF@CNF composite material is 1.25:1, and the dosage of persulfate is 0.2g / L-0.4g / L.

[0017] As a preferred embodiment of the method for degrading ceftiofur sodium in water as described in this invention, the pH value of the water in the degradation reaction is 5-8, and the reaction time is ≥20 min.

[0018] As a preferred embodiment of the method for degrading ceftiofur sodium in water as described in this invention, the reactive oxygen species in the reaction system are mainly sulfate free radicals, supplemented by hydroxyl free radicals and singlet oxygen. The Fe / Co-ZIF@CNF composite material can be recycled for the degradation of ceftiofur sodium.

[0019] Compared with the prior art, the beneficial effects of the present invention are:

[0020] 1. This invention uses carbon nanofibers (CNF) as a carrier to uniformly grow Fe / Co bimetallic ZIF crystals in situ and load them onto the CNF surface. CNF can effectively constrain crystal growth and inhibit agglomeration, resulting in excellent dispersibility and structural stability of the composite material, completely solving the problems of easy agglomeration and insufficient exposure of active sites in powdered MOFs. Fe and Co form a synergistic effect, accelerating Fe²⁺ / Fe³⁺ and Co²⁺ / Co³⁺ redox cycles, significantly improving PMS activation efficiency, while effectively reducing metal ion leaching and enhancing environmental safety.

[0021] 2. The preparation method employs an in-situ aqueous coordination reaction at room temperature, which is simple, mild, and requires no complex equipment. It allows for precise control of the Fe / Co molar ratio and crystal morphology, achieving uniform loading of Fe / Co-ZIF on the CNF surface. The preparation process is green and environmentally friendly, suitable for large-scale industrial production. Furthermore, when the Fe / Co molar ratio is optimized to 1.25:1, the composite material achieves a degradation rate of 94.0% for ceftiofur sodium within 20 minutes, with an apparent rate constant (kobs) of 0.135 min⁻¹ and a TOC removal rate of 43.8%. The catalytic performance is far superior to that of pure ZIF-67 and unloaded Fe / Co-ZIF, enabling rapid and efficient degradation and mineralization of ceftiofur sodium.

[0022] 3. The active oxygen species generated by activated PMS are dominated by sulfate radicals (SO4・⁻), with ・OH and ¹O2 as auxiliary components. The oxidation pathway is clear and the degradation efficiency is stable. The high conductivity of carbon nanofibers can accelerate electron transfer and further improve the catalytic reaction rate. The composite material is a supported solid catalyst, which is easy to separate into solid and liquid and can be recycled for the degradation of ceftiofur sodium, significantly reducing the catalyst cost for water treatment and solving the industry pain point of difficult recycling of powdered catalysts. Attached Figure Description

[0023] To more clearly illustrate the technical solutions of the embodiments of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and detailed embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein:

[0024] Figure 1 The image shows the microstructure of the Fe / Co-ZIF@CNF composite material provided by this invention. Figure 1 (a) is a SEM image of the Fe / Co-ZIF@CNF composite material. Figure 1 (b) is a microscopic morphology diagram of pure CNF;

[0025] Figure 2 XRD diffraction patterns of the Fe / Co-ZIF@CNF composite material and carbon nanofibers provided by this invention;

[0026] Figure 3 The FT-IR spectrum of the Fe / Co-ZIF@CNF composite material provided by this invention;

[0027] Figure 4 The XPS spectra of Fe / Co-ZIF@CNF before and after the reaction provided by this invention are shown below. Figure 4 (a) is the full spectrum. Figure 4 (b) is the high-resolution spectrum of C 1s. Figure 4 (c) is the high-resolution spectrum of Fe 2p. Figure 4 (d) is the high-resolution spectrum of Co 2p;

[0028] Figure 5 Degradation curves and apparent rate constant fitting curves of CEF with different Fe / Co molar ratios Fe / Co-ZIF@CNF provided by the present invention;

[0029] Figure 6 This is a graph showing the effect of different PMS dosages on CEF degradation, provided by the present invention. Figure 6 (a) is a graph showing the effect of PMS dosage on CEF degradation. Figure 6(b) is a graph showing the effect of solution pH on CEF degradation;

[0030] Figure 7 The performance curve of Fe / Co-ZIF@CNF composite material for cyclic degradation of CEF provided by the present invention;

[0031] Figure 8 A comparison chart of CEF degradation rate and TOC mineralization rate of composite materials with different Fe / Co molar ratios provided by this invention;

[0032] Figure 9 The curve showing the effect of the free radical quencher provided by this invention on the degradation of CEF in the Fe / Co-ZIF@CNF / PMS system;

[0033] Figure 10 The high-resolution XPS spectra of Fe / Co-ZIF@CNF before and after the reaction provided by this invention are as follows: Figure 10 (a) is the high-resolution XPS spectrum before the reaction. Figure 10 (b) is the high-resolution XPS spectrum after the reaction. Detailed Implementation

[0034] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0035] This invention provides an Fe / Co-ZIF@CNF composite material, using carbon nanofibers as a carrier, with Fe / Co bimetallic ZIF crystals uniformly loaded on the surface of the carbon nanofibers. The molar ratio of Fe to Co in the Fe / Co bimetallic ZIF is 0.5:1-2:1, preferably 1.25:1. The Fe / Co bimetallic ZIF crystals have a rhombic dodecahedral structure with a crystal diameter of 0.7 μm-0.9 μm. The diameter of the carbon nanofibers is 15 μm. The preparation method of the e / Co-ZIF@CNF composite material is as follows: Fe source, Co source and 2-methylimidazole are subjected to a coordination reaction in the presence of carbon nanofibers to allow Fe / Co bimetallic ZIF crystals to grow in situ and be loaded onto the surface of carbon nanofibers to obtain the target composite material. The Fe source is ferric nitrate, the Co source is cobalt nitrate, and the molar ratio of Fe source to Co source is 0.5:1-2:1. The coordination reaction is carried out in an aqueous solution at room temperature. In the coordination reaction, the carbon nanofibers can constrain the growth and aggregation of Fe / Co bimetallic ZIF crystals and improve the crystal dispersion.

[0036] This invention also provides a method for degrading ceftiofur sodium in water, specifically: adding Fe / Co-ZIF@CNF composite material and persulfate to water containing ceftiofur sodium; the composite material activates the persulfate to generate reactive oxygen species, thereby achieving the degradation of ceftiofur sodium; the molar ratio of Fe to Co in the Fe / Co-ZIF@CNF composite material is 1.25:1; the dosage of persulfate is 0.2 g / L-0.4 g / L; the pH of the water in the degradation reaction is 5-8; the reaction time is ≥20 min; the reactive oxygen species in the reaction system are mainly sulfate radicals, supplemented by hydroxyl radicals and singlet oxygen; the Fe / Co-ZIF@CNF composite material can be recycled for the degradation of ceftiofur sodium.

[0037] To verify the technical effectiveness of the Fe / Co-ZIF@CNF composite material of this invention and its effectiveness in degrading ceftiofur sodium in water, the following experiments were conducted:

[0038] The microstructure of the Fe / Co-ZIF@CNF composite material was observed and analyzed using scanning electron microscopy. The microstructure of the Fe / Co-ZIF@CNF composite material is as follows: Figure 1 As shown, Figure 1 (a) shows a SEM image of the Fe / Co-ZIF@CNF composite material. The Fe / Co bimetallic ZIF constructed on carbon fibers still exhibits a rhombic dodecahedral morphology similar to ZIF-67. It is clearly visible that after loading onto the carbon nanofibers, the Fe / Co-ZIF crystals are uniformly distributed on the surface of the carbon nanofibers. Compared to Fe / Co-ZIF material, the Fe / Co bimetallic ZIF on the Fe / Co-ZIF@CNF composite material shows better dispersion and a more uniform distribution. Figure 1 As shown in (b), pure CNF consists of fine carbon fibers with a diameter of approximately 15 μm. During the preparation of Fe / Co-ZIF materials, the crystal size of ZIF-67 increases significantly with the increase of the Fe / Co ratio. When the Fe / Co doping ratio is 1:1, the diameter of Fe / Co-ZIF is approximately 0.9 μm, larger than that of ZIF-67 (approximately 0.4 μm). However, when Fe / Co-ZIF is constructed on carbon fibers, the carbon nanofibers seem to restrict the growth and aggregation of MOF crystallites. The diameter of bimetallic ZIF-67 in Fe / Co-ZIF@CNF decreases to approximately 0.7 μm, indicating that the carbon matrix has a significant impact on the size and distribution of MOFs.

[0039] To test the phase composition and differences between the Fe / Co bimetallic ZIF composite material constructed on carbon nanofibers and previous samples, XRD diffraction patterns were analyzed on two Fe / Co-ZIF@CNF composite materials with Fe / Co molar ratios of 1:1 and 2:1, as well as on carbon nanofibers. Figure 2 As shown, Fe / Co-ZIF@CNF composites with different Fe doping ratios all exhibited good crystallinity. For pure CNF materials measured without the addition of any other substances, the XRD pattern showed two broad peaks centered at approximately 2θ = 26 ° and 43 °, corresponding to the (002) and (101) crystal planes of carbon, respectively, indicating the presence of a highly crystalline graphite structure in the material. Independent ZIF-67 synthesized without CNF or Fe showed its main characteristic crystalline peaks near 6 °, 11 °, 16 °, and 18 ° at 2θ, along with several other smaller peaks, consistent with previous findings. The characteristic peaks of ZIF-67 remained well-preserved after being doped with iron and constructed on CNF, suggesting that the carbon nanofibers did not hinder the formation of the link between Co(NO3)2·6H2O and 2-methylimidazole. In contrast, the characteristic peaks of ZIF-67 derived materials, including Fe / Co-ZIF to Fe / Co-ZIF@CNF, all showed a slight shift to lower angles in their X-ray diffraction patterns after preparation. This represents the effect of incorporating larger, longer-coordinated Fe3+ ions replacing Co2+ ions into ZIF-67 on the lattice constant of the composite material. Furthermore, after the successful preparation of Fe / Co bimetallic ZIF-67 on a carbon nanofiber matrix, the presence of very distinct broad peaks representing CNF in the characteristic peaks of Fe / Co-ZIF@CNF, combined with previous SEM images, confirms that uniform Fe / Co-ZIF nanoparticles were successfully loaded onto the CNF support.

[0040] The composite material was characterized using FT-IR spectroscopy, with a wavelength ranging from 500 to 4000 cm⁻¹. -1 FTIR spectra were acquired from the samples to confirm the linkages of Co and Fe with organic ligands and the presence of functional groups in MOFs. Figure 3 As shown, the infrared spectral characteristic peaks of Fe / Co-ZIF@CNF are almost identical to those of ZIF-67 and Fe / Co-ZIF, strongly supporting the successful bonding of Fe / Co-ZIF with carbon fibers. For Fe / Co-ZIF@CNF, the characteristic peaks in the 650-1300 cm⁻¹ range are... -1 and 1300-1550 cm -1 Symmetrical and asymmetric stretching of the imidazole ring were observed at 1409 cm⁻¹, respectively, and the spectrum revealed a stretching at 1409 cm⁻¹. -1 and 1307 cm -1 The peak at 929 cm⁻¹ corresponds to the planar vibrational peak of the imidazole ring. -1The aliphatic CH stretching strips indicate that 2-methylimidazole is the major ligand of ZIF-67. This result demonstrates that the 2-methylimidazole linker remains unchanged after ZIF-67 is incorporated into carbon fibers. Referring to existing research, a difference can be observed at 3430 cm⁻¹ compared to unsynthesized CNF. -1 Some peaks at 1730 cm⁻¹ resemble those of unsynthesized CNF, corresponding to OH stretching vibrations. However, at 1730 cm⁻¹... -1 The peak appearing at 1500 cm⁻¹ is attributed to the C=O stretching vibration spectrum, which is clearly absent in the unmodified CNF. -1 and 2942 cm -1 The peak at this point is mainly due to the C=C stretching vibration in the benzene ring and the CN stretching vibration in the 2-methylimidazolium ring. Some studies also speculate that the CH bond formed during the ZIF-67 synthesis process due to the disruption of the CN bond by Co is also located here. At 750 cm⁻¹ -1 The nearby spikes correspond to the CH bending vibration of benzene. These results indicate that the metal ions successfully coordinate with organic ligands to form MOFs and load them onto CNFs.

[0041] To ensure the correct elemental composition of the synthesized Fe / Co-ZIF@CNF composite material and to investigate the changes in the valence and molecular structure of different elements, XPS was used to analyze the prepared samples. The full XPS spectrum of the Fe / Co-ZIF@CNF composite material is shown below. Figure 4 As shown in (a), the elemental composition of the Fe / Co-ZIF@CNF composite material did not change significantly before and after participating in the advanced oxidation reaction. Characteristic peaks representing C1s, N1s, O1s, Fe2p, and Co2p were observed in both cases, indicating that Fe / Co-ZIF@CNF is mainly composed of C, N, O, Fe, and Co elements. Compared to the newly prepared Fe / Co-ZIF@CNF composite material, the N1s characteristic peak decreased slightly after the reaction, which is presumably due to changes in the composite material's skeletal structure during the reaction. The high-resolution C1s spectrum of the Fe / Co-ZIF@CNF composite material is shown below. Figure 4 As shown in (b), three characteristic peaks corresponding to C1s appeared at binding energies of 284.6 eV, 286.0 eV, and 288.5 eV. The main characteristic peak at 284.6 eV corresponds to the C=C and C=C bonds in the imidazole ligand of Fe / Co-ZIF@CNF. The characteristic peaks at 286.0 eV and 288.5 eV correspond to C=N and CN in the composite material, respectively, indicating that the skeleton of the Fe / Co-ZIF@CNF composite material contains a large amount of nitrogen. Figure 4As shown in (c), multiple valence states of Fe coexist in Fe / Co-ZIF@CNF, and the high-resolution image of Fe 2p can be convolved into 8 peaks. Two characteristic fractions located at 710.5 eV and 724.0 eV correspond to Fe... 2+ The characteristic peaks at 712.4 eV and 726.2 eV correspond to Fe. 3+ And Fe 2+ and Fe 3+ The corresponding satellite peaks are located at 714.1 eV, 718.6 eV, 732.1 eV, and 733.8 eV, respectively. The fitting of these characteristic peaks strongly verifies that the main valence states of Fe in the Fe / Co-ZIF@CNF composite material are divalent and trivalent. Figure 4 Figure (d) shows the high-resolution spectrum of Co 2p. The characteristic peaks at 781.3 eV and 785.9 eV mainly correspond to Co 2p 3 / 2 and their corresponding satellite peaks, while the characteristic peaks at 796.8 eV and 802.5 eV are mainly attributed to Co 2p 1 / 2 and their corresponding satellite peaks. This indicates that Co exists in the divalent form in the newly prepared Fe / Co-ZIF@CNF composite material.

[0042] To eliminate the influence of adsorption on the determination of the advanced oxidation performance of the Fe / Co-ZIF@CNF / PMS system during the experiment, a 30-minute pre-adsorption experiment was conducted. During the pre-adsorption experiment, we found that, unlike other studies on ZIF-based materials which exhibit high adsorption performance in treating various pollutants due to their ultra-high specific surface area and unique pore structure, the Fe / Co-ZIF@CNF composite material showed weak adsorption capacity for ceftiofur sodium. After the 30-minute pre-adsorption experiment, the concentration of ceftiofur sodium in the reaction system did not decrease significantly. After the pre-adsorption experiment, PMS reagent was added to activate the PMS by contacting the active sites on the surface of the Fe / Co-ZIF@CNF composite material in solution. Figure 5As shown, when the Fe / Co molar ratio was 0.5:1, the degradation rate of the Fe / Co-ZIF@CNF / PMS system was slow, with only 84.5% of ceftiofur sodium degraded after 20 min. With the gradual increase of the Fe / Co ratio in the composite material, the degradation rate of the reaction system gradually increased. In spectra b and c, when the Fe / Co ratio was 0.75:1 and 1:1, the Fe / Co-ZIF@CNF / PMS system achieved 89.9% and 93.3% CEF degradation within 20 min, respectively. When the Fe / Co molar ratio in the composite material was 1.25:1, the degradation effect of Fe / Co-ZIF@CNF on CEF reached its maximum, with a degradation rate of 94.0%. These experimental data strongly demonstrate that Fe doping promotes the catalytic performance of the Fe / Co-ZIF@CNF composite material. With further increases in the Fe / Co ratio, the advanced oxidation effect of the reaction system decreased. When the Fe doping ratio was 1.5:1 and 2:1, the degradation rate of CEF within 20 min dropped to 85.8% and 87.6%, respectively. Based on previous characterizations and the specific process in the preparation of the composite material, it is speculated that this is because when the amount of Fe doped increases to a certain value, it becomes difficult to stably prepare Fe / Co bimetallic ZIF-67, and the amount of Fe incorporated onto carbon nanofibers decreases. This indicates that although doping a certain amount of Fe into Co-based ZIF-67 can effectively improve the catalytic performance of Fe / Co-ZIF@CNF, the incorporation of Fe is limited.

[0043] To investigate the optimal Fe / Co molar ratio in Fe / Co-ZIF@CNF composites, in Figure 5 The graph shows a plot with the Fe / Co ratio on the horizontal axis and the apparent rate constant k on the horizontal axis. obs The graph shows the reaction kinetics fitting curves with the vertical axis as the ordinate. It is clear from the graph that when the Fe doping ratio in the Fe / Co-ZIF@CNF material is 0.5 and 1.5, the k-values ​​of the Fe / Co-ZIF@CNF / PMS reaction system are... obs Only 0.098 min -1 The degradation effect was poor. When the Fe doping ratio was between 1.1 and 1.3, the reaction system exhibited the largest apparent rate constant, reaching 0.135 min⁻¹. -1 Therefore, after comprehensive consideration, the composite material with the best degradation effect, an Fe / Co ratio of 1.25:1, was selected for further testing of its catalytic performance in subsequent experiments.

[0044] The amount of PMS used has a significant impact on the catalytic performance of the catalyst. Figure 6 Table 1 shows the effect of different PMS dosages on CEF degradation. Figure 6The apparent rate constants of the reaction under different PMS conditions are plotted as follows: Figure 6 As shown in (a), the performance of the Fe / Co-ZIF@CNF composite material in catalyzing the degradation of ceftiofur sodium by activating PMS was investigated when the dosage of Fe / Co-ZIF@CNF was fixed at 0.1 g / L. During the experiment, it was found that ceftiofur sodium was hardly degraded when PMS was used alone, indicating that the catalytic ability of PMS alone is weak, and Fe / Co-ZIF@CNF material is needed as a catalyst to activate the active sites on the surface of the composite material. Subsequently, the effect of different PMS dosages on the catalytic efficiency of CEF was studied under the same Fe / Co-ZIF@CNF dosage. It was observed that as the PMS dosage increased from 10 mg to 20 mg, the degradation rate of CEF in the reaction system increased from 91.6% to 93.9%, and the corresponding k obs The value ranges from 0.093 min. -1 Increased to 0.101 min -1 This phenomenon can be attributed to the fact that as the amount of PMS added increases, the contact effect between PMS and the surface of the composite material improves, and more active sites on the material surface are utilized, thereby enabling the Fe / Co-ZIF@CNF / PMS system to generate more ROS during the reaction process, which accelerates the oxidative degradation of CEF.

[0045] When the PMS dosage was 25 mg, the CEF degradation rate of the Fe / Co-ZIF@CNF / PMS reaction system was 94.0%, corresponding to kJ / g. obs The value is 0.116 min -1 With the PMS dosage further increased to 30 mg, the degradation efficiency of CEF was further improved to 94.4%, and k obs The value reached 0.121 min. -1 However, when the PMS dosage was further increased to 40 mg and 50 mg, the degradation efficiency of the reaction system actually decreased, with corresponding degradation rates of 92.5% and 75.1% within 20 min, respectively. obs The values ​​decreased to 0.108 min. -1 and 0.053 min -1 The cause was found to be excessive SO4. •- •OH may be consumed by itself, undergoing a self-quenching reaction of PMS (Equations 1-3), weakening the degradation effect of the Fe / Co-ZIF@CNF / PMS system on CEF. Some substances with low oxidizing activity can also be degraded by SO4. •- Or •OH with excess PMS (HSO5) -The reaction produces (Equations 4-6). Furthermore, with increasing PMS dosage, the insufficient active sites on the Fe / Co-ZIF@CNF material also lead to a decrease in catalytic activity. It is worth mentioning that, based on previous work, it can be inferred that carbon nanofibers, as the matrix structure, can induce rapid electron transfer and promote PMS activation. Considering both pollutant degradation rate and catalytic reaction cost, a PMS reagent dosage of 0.3 g / L was selected as the appropriate concentration.

[0046] SO4 •- + SO4 •- → S2O8 2- or 2SO4 2- (1)

[0047] •OH + •OH → H2O2(2)

[0048] SO4 •- + •OH → HSO5 - (3)

[0049] HSO5 - + SO4 •- → SO4 2- + SO5 •- + H + (4)

[0050] HSO5 - + •OH → SO5 •- + H2O(5)

[0051] HSO5 - + •OH → HSO4 - + •HO2(6)

[0052] Solution pH affects the form in which PMS exists, the surface properties of the composite material, and the generation of active free radicals. The pK value of the PMS reagent... a The value is 9.4. When pH < 9.4, PMS activation mainly produces HSO5, which has strong catalytic activity. - However, when pH > 9.4, SO5 with lower catalytic activity is produced. 2- With SO5 2- In comparison, HSO5 - It has higher oxidizing power and is effective in generating SO4. •- In this respect, they have an advantage. For example... Figure 6As shown in (b), when the pH range was between 5 and 8, the degradation rate of CEF in the reaction system exceeded 93% within 20 min. However, in the solution at pH 3, the degradation rate of CEF decreased to 83.1%. This is because of the excess H₂. + It will capture •OH and SO4 •- Free radicals inhibit the degradation of CEF. [122,123] Furthermore, at lower pH values, PMS mainly exists in the form of H2SO5, which has low catalytic activity, thus hindering the reaction of SO42-. •- The formation of [the material / component] is also possible. Furthermore, although it can still be activated for oxidation during the reaction, the Fe / Co-ZIF@CNF composite material may simultaneously suffer severe metal leaching and structural damage.

[124] Some studies suggest that the H atoms attached to the OO groups of PMS... + It will also increase the interfacial repulsion between PMS and the catalyst, thus affecting the catalytic reaction effect.

[125] Hydrolysis products formed under acidic conditions (CoOH) + This will also limit the Co content in the system. 3+ To Co 2+ The conversion of Fe / Co-ZIF@CNF / PMS inhibits subsequent reactions. Therefore, the overall efficiency of catalytic oxidation of Fe / Co-ZIF@CNF / PMS system is significantly reduced when the pH environment is low.

[0053] However, when the pH of the reaction system gradually increased to 10 and 11, the degradation efficiency of the reaction system decreased to 50.3% and 59.2%, respectively. This phenomenon may be because, under a strongly alkaline environment, •OH in the Fe / Co-ZIF@CNF / PMS reaction system is less reactive than SO42-. •- The changes in the reactive free radicals that dominate the oxidation reaction led to changes in the degradation efficiency of the system. PMS is unstable under alkaline conditions and can self-quench through non-radical pathways, reducing the removal rate of the reaction system (Equation 7). A large amount of OH... - The formation of polyhydroxy surface complexes during the reaction, which adhere to the material surface and hinder the contact between the catalyst and PMS, may be one of the reasons for the reduced degradation efficiency of the Fe / Co-ZIF@CNF / PMS system.

[0054] HSO 5- + OH - → SO4 2- + 1 / 2O2 + H2O (7)

[0055] Table 1 Catalytic performance of materials with different Fe / Co molar ratios

[0056] Material Degradation rate <![CDATA[k obs (min -1 )]]> <![CDATA[Fe / Co-ZIF 0.5 @CNF]]> 84.5 % 0.098 <![CDATA[Fe / Co-ZIF 0.75 @CNF]]> 89.9 % 0.116 <![CDATA[Fe / Co-ZIF 1.0 @CNF]]> 93.3 % 0.126 <![CDATA[Fe / Co-ZIF 1.25 @CNF]]> 94.0 % 0.135 <![CDATA[Fe / Co-ZIF 1.5 @CNF]]> 85.8 % 0.098 <![CDATA[Fe / Co-ZIF2@CNF]]> 87.6 % 0.101

[0057] Although Fe / Co-ZIF@CNF demonstrated high catalytic performance and application potential in the above experiments, its reusability is of great significance in practical wastewater treatment. Therefore, continuous degradation experiments of ceftiofur sodium by Fe / Co-ZIF@CNF were conducted in batches, and degradation efficiency data of the material in multiple cycles were collected. Figure 7 As shown, in the second cycle experiment, the degradation rate of CEF by the reaction system decreased from 97.0% to 93.8% within 20 min. In the third cycle experiment, the degradation rate of CEF by Fe / Co-ZIF@CNF decreased significantly to 83.3%, and further to 74.0% in the fourth cycle. The deactivation of the Fe / Co-ZIF@CNF composite material may be due to the adsorption of CEF or related intermediates on the catalyst surface during the reaction, leading to a reduction in the number of activation sites that can participate in the reaction, thus affecting the reaction process. Furthermore, the insufficient bonding between Fe / Co-ZIF and carbon nanofibers during preparation, resulting in partial detachment of Fe / Co-ZIF during the reaction and regeneration processes, may also contribute to the reduced catalytic performance of Fe / Co-ZIF@CNF.

[0058] In actual wastewater treatment, ceftiofur sodium may be removed through multiple pathways such as adsorption or degradation. It is necessary to measure the mineralization rate of the reaction to determine the amount of CEF that has been completely degraded. For example... Figure 8 As shown, by measuring the residual organic carbon content in the reaction solution, it can be observed that when the Fe / Co ratio of the Fe / Co composite material is 0.5:1 and 0.75:1, the TOC removal efficiency of the Fe / Co-ZIF@CNF / PMS reaction system for CEF is 40.1% and 41.9%, respectively. However, when using Fe / Co composite materials with better catalytic performance at Fe / Co molar ratios of 1:1 and 1.25:1, the TOC removal efficiency of the Fe / Co-ZIF@CNF / PMS system for CEF increases to 43.2% and 43.8%, respectively. This indicates that with an appropriate amount of Fe introduced, more than 43% of CEF is completely removed. Furthermore, compared with the TOC removal rate of Fe / Co-ZIF material, the TOC removal rate of Fe / Co-ZIF material loaded with carbon nanofibers is significantly higher. 1.0 @CNF、Fe / Co-ZIF 1.25The @CNF composite material improved the TOC removal rate of CEF by more than 5%. However, when the Fe / Co molar ratio was increased to 1.5:1 and 2:1, the TOC removal rates of the Fe / Co-ZIF@CNF / PMS reaction system were 43.4% and 41.1%, respectively. This indicates that more Fe is not necessarily better, and selecting an appropriate amount of Fe is crucial for improving the catalytic performance of Fe / Co-ZIF.

[0059] Meanwhile, to facilitate comparison with ZIF-67 and Fe / Co-ZIF materials, and to explore the improvement in advanced oxidation performance of Fe / Co-ZIF@CNF composites, Table 2 lists the degradation efficiency of CEF for composites with different Fe / Co molar ratios and other materials, along with the apparent rate constant k. obs And the total organic carbon removal rate. Table 2 shows that Fe / Co-ZIF@CNF, prepared by loading Fe / Co-ZIF material onto carbon nanofibers, exhibits a higher CEF degradation rate and reaction rate compared to ordinary ZIF-67 and Fe / Co-ZIF materials, and also a higher TOC removal rate. When the Fe / Co molar ratio is 1.25:1, the catalytic performance of the material is significantly improved. 1.25 Material degradation rate, k obs The removal rates of iodine and total organic matter (TOC) reached 94.0% and 0.135 min, respectively. -1 And 43.8%, which is a significant improvement compared to Fe / Co-ZIF.

[0060] Table 2 Catalytic performance of different materials

[0061] Material Degradation rate <![CDATA[k obs (min -1 )]]> TOC removal rate ZIF-67 81.3 % 0.085 32-34 % <![CDATA[Fe / Co-ZIF 1.0 ]]> 91.4 % 0.101 37.6 % <![CDATA[Fe / Co-ZIF 1.25 ]]> 91.4 % 0.105 38.4 % <![CDATA[Fe / Co-ZIF 1.5 ]]> 88.7 % 0.091 32.9 % <![CDATA[Fe / Co-ZIF 1.0 @CNF]]> 93.3 % 0.126 43.2 % <![CDATA[Fe / Co-ZIF 1.25 @CNF]]> 94.0 % 0.135 43.8 % <![CDATA[Fe / Co-ZIF 1.5 @CNF]]> 85.8 % 0.098 42.2 %

[0062] After introducing Fe, in order to distinguish the dominant role of specific free radicals in the degradation of pollutants in the Fe / Co-ZIF@CNF / PMS system, this application uses 1000 mM methanol (Meth), tert-butanol (TBA), and furfuryl alcohol (FFA) to capture •OH and SO4 that may be generated in the Fe / Co-ZIF@CNF / PMS system during the reaction. •- and 1 O2. In the ZIF-67 / PMS system, cobalt ions in ZIF-67 play a crucial role in activating PMS. Cobalt ions can alter the Co content. 2+ and Co 3+ The state between, and HSO5 - The reaction produces SO4 •- And •OH. SO4 has strong oxidizing power. •-•OH can effectively degrade pollutants into reaction intermediates and further convert them into non-toxic small molecules.

[0063] Methanol (Meth) is a selective free radical scavenger, effective against SO42-. •- The rate constants for the •OH radical and the OH radical are 3.2 × 10⁻⁶. 7 and 9.7 × 10 8 M -1 s -1 .like Figure 9 As shown, the degradation of CEF was significantly inhibited after the addition of methanol. Compared with before the addition of methanol, the degradation rate of CEF in the reaction system decreased from 92.7% to 37.4%. This indicates incomplete quenching during the removal process, and the removal of •OH and SO42- •- It may have participated in the degradation of CEF to some extent. To further determine the ROS in the reaction system, tert-butanol was selected as the •OH scavenger, with a rate constant of 3.2 × 10⁻⁶. 8 M -1 s -1 It is effective against SO4 •- The rate constant is 4 × 10 5 M -1 s -1 The rate constant for α-OH is 1000 times smaller than that for α-OH, therefore it is considered a scavenger of α-OH. After adding 1000 mM tert-butanol, the degradation rate of the Fe / Co-ZIF@CNF / PMS reaction system decreased from 92.7% to 84.3%, showing only a slight inhibitory effect on CEF degradation. This indicates that α-OH is not the main active free radical in the reaction system, and SO42- is not a major reactive free radical during the reaction. •- The Fe / Co-ZIF@CNF / PMS system plays a major role in the degradation of CEF, while •OH plays a supporting role. Furthermore, when tert-butanol is added to a CEF solution containing PMS, the degradation of CEF by the Fe / Co-ZIF@CNF / PMS system is not significantly affected. Conversely, the degradation performance of the reaction system is greatly affected when 1000 mM methanol solution is added. This result may be attributed to the complexity and stability of the CEF structure; compared to the weaker oxidizing agent •OH, SO42- plays a more significant role. •- It exhibited strong oxidizing ability to decompose CEF, thereby achieving the degradation of CEF.

[0064] During the reaction, the PMS reagent may be activated to form... 1 O2 promotes the degradation of CEF, and many studies have shown that O2 can promote the degradation of CEF. 1 O2 is considered a significant reactive oxygen species (ROS) formed during PMS activation. Therefore, 1000 mM furfuryl alcohol was added as a quencher to eliminate any potential ROS generated in the reaction system. 1O2. It can be observed that after adding 1000 mM furfuryl alcohol, the degradation rate of CEF only decreased from 92.7% to 90.3%, indicating that only a small amount of O2 may have been generated in the reaction system. 1 O2. 1 O2 is not the dominant ROS in the reaction system. In summary, it is preliminarily inferred that SO42- •- It is the main active substance in the Fe / Co-ZIF@CNF / PMS reaction system. The contribution order of ROS to CEF degradation is SO4. •- > •OH > 1 O2.

[0065] Although no significant changes in the elemental composition of the Fe / Co-ZIF@CNF composite material before and after the reaction were observed in the XPS full-spectrum analysis, the elements and valences in the material may change before and after the reaction. Therefore, the changes in the valences of Fe and Co elements in the Fe / Co-ZIF@CNF composite material before and after CEF degradation were analyzed by XPS. Figure 10 As shown, the valence states of Fe and Co elements in the Fe / Co-ZIF@CNF composite material changed to some extent before and after the reaction. The Fe 2p spectrum of the material is shown below. Figure 10 As shown in (a), Fe 2p 3 / 2 can be fitted into two peaks at 710.5 eV and 712.4 eV, corresponding to Fe 2p 3 / 2 and Fe 2p 3 / 2 respectively. 2+ and Fe 3+ Curve integral calculations were performed to determine the Fe content in the freshly prepared Fe / Co-ZIF@CNF composite material. 2+ / Fe 3+ The ratio was 1.90. After the reaction was complete, Fe... 2+ / Fe 3+ The proportion decreased to 1.63, indicating that Fe 2+ It participated in PMS activation during advanced oxidation processes and was partially consumed, transforming into Fe. 3+ Further investigation was conducted into the valence state changes of Co during the reaction process, from... Figure 10 (b) It can be observed that, unlike the XPS spectrum before the reaction, the high-resolution spectrum of Co 2p in the Fe / Co-ZIF@CNF composite after the reaction is convolved into 6 peaks. The characteristic peaks at 781.5 eV and 796.9 eV are attributed to Co at Co 2p 3 / 2 and Co 2p 1 / 2. 2+ Meanwhile, new fitting characteristic peaks appeared at 780.5 eV and 796.0 eV, corresponding to Co 2p 3 / 2 and Co 2p 1 / 2, respectively. 3+The corresponding satellite peaks appear at 786.0 eV and 802.7 eV. This indicates that Co is involved in the reaction process of the Fe / Co-ZIF@CNF / PMS system. 2+ After activation by the PMS reagent, it is converted into Co. 3+ The XPS results above indicate that Fe 2+ / Fe 3+ and Co 2+ / Co 3+ All of these factors participated to some extent in the PMS-activated degradation of CEF. Furthermore, due to the difference in redox potential, Fe... 2+ and Co 3+ Electron capture reactions may also occur.

[0066] In this application, to improve the catalytic performance and recyclability of the material, Fe / Co-ZIF@CNF composite material with good dispersion and stable structure was prepared by successfully loading Fe / Co-ZIF onto CNF. The morphology, elemental composition, and surface functional group changes of the obtained material were comprehensively characterized using SEM, XRD, FT-IR, and XPS. Catalytic performance tests showed that when the Fe / Co molar ratio was 1.25:1, the Fe / Co-ZIF@CNF composite material exhibited good degradation effect on CEF, achieving 94% CEF degradation within 20 min. Systematic physicochemical characterization and free radical quenching experiments indicated that SO42- was the dominant ROS in the reaction system. •- Free radicals, and •OH and 1 O2 plays an auxiliary role in the degradation of CEF. The synergistic effect between Fe and Co, as well as the constraint and dispersion effect of the CNF support on MOFs, are the main reasons for the high catalytic performance of the composite material. Furthermore, the Fe / Co-ZIF@CNF composite material is suitable for a wide pH range and has potential application prospects in practical applications. In summary, this application provides some new ideas for developing MOFs-based composite catalysts with practical application potential and for the effective removal of CEF.

[0067] Although the present invention has been described above with reference to embodiments, various modifications can be made and components can be replaced with equivalents without departing from the scope of the invention. In particular, as long as there is no structural conflict, the features in the disclosed embodiments can be combined with each other in any manner. The lack of an exhaustive description of these combinations in this specification is merely for the sake of brevity and resource conservation. Therefore, the present invention is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A Fe / Co-ZIF@CNF composite material, characterized in that, include: Using carbon nanofibers as a carrier, Fe / Co bimetallic ZIF crystals are uniformly loaded on the surface of the carbon nanofibers, wherein the molar ratio of Fe to Co in the Fe / Co bimetallic ZIF is 0.5:1-2:

1.

2. The Fe / Co-ZIF@CNF composite material according to claim 1, characterized in that, The molar ratio of Fe to Co in the Fe / Co bimetallic ZIF is 1.25:

1.

3. The Fe / Co-ZIF@CNF composite material according to claim 1, characterized in that, The Fe / Co bimetallic ZIF crystal has a rhombic dodecahedral structure with a crystal diameter of 0.7μm-0.9μm, and the carbon nanofiber has a diameter of 15μm.

4. A method for preparing the Fe / Co-ZIF@CNF composite material as described in any one of claims 1-3, characterized in that, Fe source, Co source and 2-methylimidazole were coordinated in the presence of carbon nanofibers to grow Fe / Co bimetallic ZIF crystals in situ and load them on the surface of carbon nanofibers, thus obtaining the target composite material.

5. The method for preparing the Fe / Co-ZIF@CNF composite material according to claim 4, characterized in that, The Fe source is ferric nitrate, the Co source is cobalt nitrate, and the molar ratio of Fe source to Co source is 0.5:1-2:1; the coordination reaction is carried out in an aqueous solution at room temperature.

6. The method for preparing the Fe / Co-ZIF@CNF composite material according to claim 4, characterized in that, In the coordination reaction, carbon nanofibers can constrain the growth and aggregation of Fe / Co bimetallic ZIF crystals, thereby improving crystal dispersion.

7. A method for degrading ceftiofur sodium in water, characterized in that, The steps include: Adding the Fe / Co-ZIF@CNF composite material and persulfate as described in any one of claims 1-3 to water containing ceftiofur sodium, the persulfate is activated by the composite material to generate reactive oxygen species, thereby achieving the degradation of ceftiofur sodium.

8. The method for degrading ceftiofur sodium in water according to claim 7, characterized in that, The Fe / Co-ZIF@CNF composite material has a Fe to Co molar ratio of 1.25:1 and a persulfate dosage of 0.2 g / L to 0.4 g / L.

9. The method for degrading ceftiofur sodium in water according to claim 7, characterized in that, The pH of the water in which the degradation reaction takes place is 5-8, and the reaction time is ≥20 min.

10. The method for degrading ceftiofur sodium in water according to claim 7, characterized in that, The reactive oxygen species in the reaction system are mainly sulfate radicals, with hydroxyl radicals and singlet oxygen as auxiliary species. The Fe / Co-ZIF@CNF composite material can be recycled for the degradation of ceftiofur sodium.

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