Preparation method and application of photo-Fenton catalytic material

Abstract

The invention is applicable to the technical field of photo-Fenton water treatment, and provides a preparation method and application of a photo-Fenton catalytic material, according to the method, ND is innovatively used as a template, and ND is used as a structural framework to support an MIL-100 (Fe) metal organic framework, so that MIL-ND is constructed, and the MIL-ND is used for degrading MB dye wastewater in photo-Fenton reaction. The MIL / ND enables exposed photo-Fenton active sites on the material to be increased, and meanwhile, a built-in electric field formed between the materials effectively hinders recombination of photo-generated carriers. The introduction of ND effectively improves the adsorption capacity of active sites of Fe and H2O2, reduces the H2O2 adsorption energy barrier, accelerates the circulation of Fe < 3 + > / Fe < 2 + >, forms a stable Fe-O-C structure to promote the generation of OH, and effectively solves the technical problems of low reaction efficiency and slow kinetics of MIL-100 (Fe) in traditional photo-Fenton.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of photo-Fenton water treatment, and particularly relates to a preparation method and application of a photo-Fenton catalytic material. BACKGROUND

[0002] As a high-level derivative form of the traditional Fenton reaction, the photo-Fenton technology has become a frontier field of current advanced oxidation process research, due to its excellent degradation efficiency and significantly reduced operating cost in the treatment of refractory organic wastewater. However, the actual application effect of the technology is highly dependent on the performance of the photo-Fenton catalytic material.

[0003] At present, most of the catalysts have key defects such as insufficient stability and low recycling efficiency, which directly leads to the engineering technical bottlenecks of the photo-Fenton reaction system, such as slow reaction kinetics and limited treatment efficiency. Among the many candidate materials, iron-based metal-organic framework materials (Fe-MOFs) have attracted much attention due to their unique porous crystal structure formed by the coordination self-assembly of metal nodes and organic ligands. Among them, MIL-100(Fe) has a regular pore structure and excellent H2O2 activation characteristics, but there are still two core technical challenges in the actual photo-Fenton application: first, under photoexcitation conditions, the recombination rate of the photo-generated carriers in the Fe-O cluster of the material is too high, which leads to low electron-hole pair separation efficiency, and further seriously restricts the recycling kinetics of Fe 3+ / Fe 2+ and the generation rate of hydroxyl radicals (·OH); secondly, the number of unsaturated metal active sites in the material itself is insufficient, and the limitation of the reaction interface and the H2O2 activation ability together weakens the overall reaction efficiency of the photo-Fenton system. SUMMARY

[0004] The purpose of the embodiments of the present application is to provide a preparation method and application of a photo-Fenton catalytic material, which aims to solve the problems raised in the above background.

[0005] The embodiments of the present application are implemented in the following way: a preparation method of a photo-Fenton catalytic material, comprising the following steps: Step 1: according to the molar ratio of 1:1, six hydrated ferric chloride (FeCl3·6H2O) and 1,3,5-benzene tricarboxylic acid (H3BTC) are weighed and added to a beaker containing deionized water, and stirred to form a uniform mixed solution; Step 2: prepare a catalytic material with ND (size 5-30 nm) as a template, first calculate the required mass of ND according to the mass of Fe and the mass ratio of ND:MIL-100(Fe) = 1:160, then add the required ND to the above mixed solution, and continue to stir to ensure that the ND is uniformly dispersed in the MIL-100(Fe) precursor solution; Step 3: The orange-yellow mixed solution (product of step 2) is transferred to a high-pressure reaction kettle and placed in an oven for heating, so that the MIL-100(Fe) is grown in situ on the surface of the ND; after the reaction is completed, it is cooled to room temperature, then the product is poured into a beaker and washed with a mixed solution of water and ethanol in a volume ratio of 1:1 for multiple times, and precipitated by standing; Step 4: Finally, the washed precipitate is placed in an oven for drying, and the obtained orange-yellow solid powder is the ND framework supported MIL-100(Fe) material.

[0006] In a further technical solution, in the step 1, 0.378 g of FeCl3·6H2O and 0.272 g of H3BTC are accurately weighed and added to a beaker containing 10 mL of deionized water, and stirred with a magnetic stirrer for 30 minutes to form a uniform mixed solution.

[0007] In a further technical solution, in the step 2, the mass of Fe is 78.26 mg, and the mass of the required ND is 0.49 mg.

[0008] In a further technical solution, in the step 2, the ND of a certain size is added to the mixed solution of step 1, and the stirring time is 20 minutes.

[0009] In a further technical solution, in the step 3, the product of step 2 is transferred to a high-pressure reaction kettle and placed in an oven, and the temperature of the oven is set to 130 DEG C, the reaction time is 72 hours, then the product is washed with a 1:1 mixed solution of water and ethanol for 3 times; the standing precipitation time is 6 hours.

[0010] In a further technical solution, in the step 4, the drying temperature of the oven is 80 DEG C.

[0011] Another purpose of the embodiment of the application is the application of the photo-Fenton catalytic material, the ND framework supported MIL-100(Fe) material prepared based on the above method is used as a catalytic material in the photo-Fenton technology to treat refractory industrial wastewater.

[0012] In a further technical solution, the ND framework supported MIL-100(Fe) material is applied to the photo-Fenton treatment of MB refractory dye wastewater.

[0013] The embodiment of the present application provides a preparation method and application of a photo-Fenton catalytic material, the method innovatively uses ND as a template, uses the ND as a structural framework to support MIL-100(Fe) metal organic framework, thereby constructing a high-performance MIL / ND framework supported catalytic material, and the high-performance MIL / ND framework supported catalytic material is used for degrading MB dye wastewater in a photo-Fenton reaction. The MIL / ND increases the exposed photo-Fenton active sites on the material, and meanwhile, the built-in electric field formed between the materials effectively hinders the recombination of photo-generated carriers. Moreover, the introduction of the ND effectively improves the adsorption capacity of the Fe active site and H2O2, reduces the adsorption H2O2 energy barrier, accelerates the Fe 3+ / Fe 2+ cycle, and meanwhile, forms a stable Fe-O-C structure to promote the generation of •OH. In the photo-Fenton technology, the MIL / ND not only improves the separation efficiency of photo-generated carriers and inhibits the recombination of e - / h + , but also enhances the exposure of the Fe active site and the generation of •OH, and solves the technical problems of low reaction efficiency and slow kinetics of MIL-100(Fe) in the traditional photo-Fenton. The prepared catalytic material not only has high MB degradation efficiency, but also has low material price, and is easier to realize commercialization. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 A degradation mechanism of the MIL / ND material in the removal of MB; Figure 2 A preparation process of the MIL / ND; Figure 3 Construction of a photo-Fenton degradation MB reaction system under simulated sunlight; Figure 4 An electrolyte prepared in an electrochemical test; Figure 5 A three-electrode system assembled in an electrochemical test; Figure 6 Microscopic images of MIL-100(Fe) and MIL / ND (wherein, a is a TEM image of MIL-100(Fe), b is a TEM image of MIL / ND, and c is an element mapping image of MIL / ND); Figure 7 Nitrogen adsorption / desorption isotherms and pore size distribution curves of three samples (wherein, a is a nitrogen adsorption / desorption isotherm, and b is a pore size distribution curve); Figure 8 Raman spectra of MIL / ND and pure MIL-100(Fe) in different proportions (wherein, a is a Raman spectrum of 0.49 MIL / ND and pure MIL-100(Fe), and b is a Raman spectrum of 7.83 MIL / ND, 0.98 MIL / ND and 1.96 MIL / ND); Figure 9 are the infrared spectra and XRD spectra of ND, MIL-100(Fe) and MIL / ND (wherein a is the infrared spectrum, b is the XRD spectrum); Figure 10 are the full scan XPS spectrum of MIL / ND and the high resolution XPS spectra of Fe, O and C elements in MIL / ND (wherein a is the full scan XPS spectrum of MIL / ND, b, c and d are the high resolution XPS spectra of Fe, C and O elements in MIL / ND, respectively); Figure 11 are the unit cell diagrams of MIL / ND and MIL-100(Fe) and the HOMO and LUMO diagrams of MIL / ND (wherein a is the unit cell diagram of MIL / ND and MIL-100(Fe), b is the HOMO and LUMO diagram of MIL / ND); Figure 12 are the impedance and transient photocurrent diagrams of ND, MIL-100(Fe) and MIL / ND (wherein a is the impedance diagram, b is the transient photocurrent diagram); Figure 13 are the CV and LSV curves of ND, MIL-100(Fe) and MIL / ND (wherein a is the CV curve, b is the LSV curve); Figure 14 are the UV-Vis spectra and corresponding Tauc curves of different catalysts and the Mott-Schottky curves in 1M KOH solution (wherein a is the UV-Vis spectrum, b is the corresponding Tauc curve, c is the Mott-Schottky curve in 1M KOH solution); Figure 15 are the active sites of MIL-100(Fe), ND and MIL / ND at different scan rates and the Cdl of each sample (wherein a is the active site of MIL-100(Fe) at different scan rates, b is the active site of ND at different scan rates, c is the active site of MIL / ND at different scan rates, d is the Cdl of each sample); Figure 16 are the degradation of MB by different ratios of MIL / ND and the degradation of MB by different catalysts (wherein a is the different ratios of MIL / ND, b is the different catalysts); Figure 17 are the fluorescence intensity of •OH generated by MIL / ND under 2-hydroxyterephthalic acid and the transfer of photo-generated electrons by MIL / ND under the action of built-in electric field (wherein a is the fluorescence intensity of •OH generated by MIL / ND under 2-hydroxyterephthalic acid, b is the transfer of photo-generated electrons by MIL / ND under the action of built-in electric field); Figure 18Effect of different catalysts on MB photo-Fenton degradation under dark condition and without H2O2 (wherein a is dark condition, b is without H2O2 condition); Figure 19 Effect of different dosage of MIL / ND on MB degradation; Figure 20 Effect of MIL / ND on photo-Fenton degradation of MB with different initial concentration; Figure 21 Effect of different pH value on photo-Fenton degradation of MB solution; Figure 22 Effect of different dosage of H2O2 on MB photo-Fenton degradation; Figure 23 TOC variation curve of MIL / ND degrading MB, and recycling experiment of MIL / ND photo-Fenton degrading MB (wherein a is TOC variation curve of MIL / ND degrading MB, b is recycling experiment of MIL / ND photo-Fenton degrading MB); Figure 24 Effect of MIL / ND on photo-Fenton degradation of MB in the presence of Cl - , SO4 2- and HCO3 - (wherein a is in the presence of Cl - , b is in the presence of SO4 2- , c is in the presence of HCO3 - ); Figure 25 Radical capture experiment of MIL / ND in the presence of ethylenediaminetetraacetic acid (h + ), tert-butyl alcohol (•OH), ethanol (•OH and SO4 2- ) and benzoquinone (•O2 - ) (wherein a is in the presence of ethylenediaminetetraacetic acid, b is in the presence of tert-butyl alcohol, c is in the presence of ethanol, d is in the presence of benzoquinone); Figure 26 PDOS of Fe 3d orbital in MIL / ND (wherein a is d xy , d yz and d xz , b is and ); Figure 27 COHP of C-O bond and C-Fe bond in MIL / ND (wherein a is C-O bond, b is C-Fe bond); Figure 28 Gibbs free energy of MIL-100(Fe) and MIL / ND generating •OH and d band center (wherein a is Gibbs free energy of MIL-100(Fe) and MIL / ND generating •OH, b is d band center); Figure 29 MIL / ND and MIL-100(Fe) to generate ·OH (wherein a is the process of MIL / ND to generate ·OH, b is the process of MIL-100(Fe) to generate ·OH); Figure 30 The mechanism of the MIL / ND framework supported material to strengthen the degradation of MB by the photo-Fenton process. DETAILED DESCRIPTION

[0015] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application is further described in detail below in combination with the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and do not limit the present application.

[0016] The specific implementation of the present application is described in detail below in combination with specific examples.

[0017] As shown in the preparation method of a photo-Fenton catalytic material provided by an embodiment of the present application, the material is synthesized by a one-step method, which specifically includes the following steps: Figure 2 Step 1: 0.378 g of FeCl3·6H2O and 0.272 g of 1,3,5-benzenetricarboxylic acid (H3BTC, trimesic acid) are accurately weighed and added to a beaker containing 10 mL of deionized water, and stirred with a magnetic stirrer for 30 minutes to form a uniform mixture. Step 2: The catalytic material with nanodiamond (ND) with a size of 20 nm as a template is prepared. First, according to the mass of Fe (78.26 mg) and the mass ratio of ND:MIL-100(Fe) = 1:160, the mass of ND required is calculated to be 0.49 mg. Then, 0.49 mg of ND is added to the above mixture, and stirring is continued for 20 minutes to ensure that the ND is uniformly dispersed in the MIL-100(Fe) precursor solution.

[0018] Step 3: The orange-yellow mixture (product of step 2) is transferred to a high-pressure reaction kettle and placed in an oven, and reacted at 130°C for 72 hours to allow the MIL-100(Fe) to grow in situ on the surface of the ND. After the reaction is completed, it is cooled to room temperature, then the product is poured into a beaker and washed with 40 mL of water and 40 mL of alcohol for 3 times, and left to settle for 6 hours.

[0019] Step 4: Finally, the washed precipitate is placed in an oven at 80°C for drying, and the obtained orange-yellow solid powder is the ND framework supported MIL-100(Fe) material, which is named as 0.49 MIL-100(Fe) / ND (abbreviated as 0.49 MIL / ND).

[0020] ​

[0021] In the embodiments of the present application, the method is strictly controlled according to the 1:1 molar ratio (0.378 g FeCl3·6H2O and 0.272 g H3BTC) to accurately control the proportioning, which is more conducive to the formation of high-purity MIL-100(Fe). The reaction is carried out at 130°C for 72 hours (mild conditions, long-time crystallization). The low-temperature and long-time reaction can be more conducive to the slow growth of crystals and reduce defects. The material takes ND as a template and a structural framework, and MIL-100(Fe) is in-situ grown on the surface of the material and supported by the material, forming a stable framework-supported structure. The material is applied as a catalytic material in the light Fenton technology to treat refractory industrial wastewater (such as dye wastewater, antibiotic wastewater), and is used for advanced purification of wastewater after biochemical treatment to reach the discharge or recycling standard. The core advantages are mainly that the material becomes a high-performance material for efficient treatment of refractory dye wastewater with extremely high degradation rate (degradation of 99.9% in 20 minutes), extremely high stability (92.4% of the performance after 8 cycles) and lower cost.

[0022] The degradation mechanism of the material for treating MB refractory dye wastewater by light Fenton is as shown in Figure 1 .

[0023] As shown in Figure 3 , as a preferred embodiment of the present application, the standard reaction system construction and catalytic performance evaluation are as follows: The light Fenton performance of ND, MIL-100(Fe) and different proportioning MIL / ND catalysts is investigated with MB as the target pollutant. A 500w xenon lamp is used as a visible light source in the experiment. In the light Fenton degradation experiment, 10 mg of MB is dissolved in 1 L of water to prepare a 10 mg / L MB solution. Then 10 mg of catalyst is added to 80 mL of 10 mg / L MB solution, 100 μL of 30% H2O2 is added, and the solution is placed under the xenon lamp for light Fenton degradation reaction. The solution is constantly stirred under the condition of maintaining the uniformity of the solution and controlling the reaction temperature. After the reaction starts, samples are collected every 5 minutes, and centrifuged at 4000 rpm for 7 minutes. The absorbance of the supernatant is measured at λ max =664 nm by a UV-visible spectrophotometer. The MB concentration is determined, and the degradation efficiency is calculated. All experiments are carried out in triplicate to minimize potential errors. In the experiment of studying the light Fenton degradation effect of MB under dark conditions, the other experimental conditions in the standard reaction system remain unchanged, only the xenon lamp is turned off, and the reaction platform is covered with an opaque black cloth to avoid external light sources.

[0024] The calculation formula of MB removal rate is as follows: ; Wherein, is the initial concentration of MB, is the time is the concentration of MB at the time

[0025] As a preferred embodiment of the present application, the preparation of the working electrode in the electrochemical test is as follows: First, cut a piece of carbon cloth 1 cm x 2 cm, then take 0.100 g of catalyst, 0.024 g of polyvinylidene fluoride and 0.024 g of conductive carbon black, the mass ratio of catalyst, polyvinylidene fluoride and conductive carbon black is between 8:2:2 and 8:1:1, take 4-6 mL of N, N-dimethylformamide (liquid) to mix the three materials into a uniformly dispersed solution, take an appropriate amount of mixed solution with a pipette and drop it on the carbon cloth, put the carbon cloth into an oven at 60-80 ℃ for 5-10 min, take out the carbon cloth with the catalyst fixed, roll the carbon cloth with a rolling rod with a force of 20-30 N, so that the catalyst and the carbon cloth are more closely combined, put the rolled carbon cloth into an oven at 60-80 ℃ for 15-20 min until it is dried, the catalyst is completely fixed on the carbon cloth and is closely combined, repeat the above steps three times until all the catalyst and additives are completely fixed on the carbon cloth.

[0026] The preparation of the electrolyte is as follows: Weigh 3.500 g of sodium sulfate pentahydrate with a millionth balance, then dissolve it in a beaker containing 25 mL of deionized water, place the beaker containing the Na2SO4·5H2O solution on a magnetic stirrer and stir for 10-20 min until the solution is clear and free of turbidity, the finally prepared electrolyte is as shown in Figure 4 .

[0027] The assembly of the three-electrode system is as follows: The experiment needs to prepare a three-electrode system (working electrode, auxiliary electrode and reference electrode) and an electrolytic cell system. The prepared carbon cloth coated with the sample is fixed on the working electrode, the load is controlled at about 1 mg / cm 2 , and is placed together with the platinum wire auxiliary electrode and the HgO reference electrode in the 0.5 M Na2SO4·5H2O electrolyte. The assembled three-electrode system is as shown in Figure 5 .

[0028] In the embodiment of the present application, the prepared MIL / ND catalytic material with ND as the template and a high-efficiency stable skeleton support light Fenton catalytic material MIL / ND not only has high degradation efficiency of MB, but also has low material price, and is more likely to realize commercialization. The MIL / ND catalytic material of the MIL-100 (Fe) supported by the ND skeleton as a light Fenton catalyst has enhanced degradation effect of MB and significantly improved degradation efficiency.

[0029] Table 1 Comparison of removal rates of MB by other catalytic materials

[0030] As shown in Table 1, the performance of different catalytic materials for photofenton degradation of MB was compared. The catalytic material MIL / ND prepared in the present patent can achieve a MB removal rate of 99.9% and a TOC mineralization rate of 78.1% in only 20 minutes, and still maintains a high degradation efficiency of 92.4% after 8 cycles. These examples can show that the removal efficiency of MIL / ND for MB is not only much higher than that of other iron-based and metal catalysts, but also the time required in the removal process is much lower than that of other catalytic materials. This not only shows the excellent performance and ultra-high removal rate of MIL / ND for removing MB, but also demonstrates the application potential of MIL / ND in the actual industry.

[0031] The following provides several specific examples to verify the effectiveness of the present method.

[0032] Example 1: Preparation and characterization of catalytic material; (1) Preparation of catalytic material MIL-100(Fe): Accurately weigh 0.378 g of FeCl3·6H2O and 0.272 g of H3BTC, and the molar ratio of the two is 1:1. Add the above two raw materials to a beaker containing 10 mL of deionized water, and use a magnetic stirrer to stir at room temperature for 30 minutes to make them uniformly mixed. After 30 minutes, the orange-yellow mixed solution is transferred to a polytetrafluoroethylene-lined stainless steel high-pressure reaction kettle, which is sealed and placed in an oven. React at 130°C for 72 hours to allow the MIL-100(Fe) crystals to grow fully. After the reaction is completed, the high-pressure kettle is naturally cooled to room temperature, and the product is transferred to a beaker. Add 40 mL of deionized water and 40 mL of anhydrous ethanol and disperse with ultrasonic for 10 minutes, then stand for 6 hours to make the product fully precipitate. Remove the supernatant and repeat the washing for 3 times to remove the unreacted organic ligand and metal ions. The precipitate is placed in an 80°C oven to dry for 12 hours, and then ground into fine powder to obtain orange-yellow MIL-100(Fe) powder.

[0033] (2) Preparation of catalytic material MIL / ND: The material was synthesized by one-step method. First, 0.378 g of FeCl3·6H2O and 0.272 g of H3BTC were accurately weighed and added to a beaker containing 10 mL of deionized water, and stirred with a magnetic stirrer for 30 minutes to form a uniform solution. Then the preparation of the catalytic material with ND as the template was carried out. First, according to the mass of Fe (78.26 mg) and ND:MIL-100(Fe) = 1:160 (mass ratio), the mass of ND required was calculated to be 0.49 mg. Second, 0.49 mg of ND was added to the above mixture, and stirring was continued for 20 minutes to ensure that ND was uniformly dispersed in the MIL-100(Fe) precursor solution. After 20 minutes, the orange-yellow mixture was transferred to a high-pressure reaction kettle and placed in an oven for reaction at 130°C for 72 hours to allow MIL-100(Fe) to grow in situ on the surface of ND. After the reaction was completed, it was cooled to room temperature, then the product was poured into a beaker and washed with 40 mL of water and 40 mL of alcohol for 3 times, and precipitated for 6 hours. Finally, the washed precipitate was placed in an oven at 80°C for drying, and the obtained orange-yellow solid powder was the ND framework supported MIL-100(Fe) material, which was named as 0.49 MIL-100(Fe) / ND (abbreviated as 0.49 MIL / ND).

[0034] To study the effect of ND content on the catalytic performance, 0.24 mg (1:320), 0.98 mg (1:80), 1.96 mg (1:40) and 7.83 mg (1:10) of ND were added respectively to obtain 0.24 MIL-100(Fe) / ND, 0.98 MIL-100(Fe) / ND, 1.96 MIL-100(Fe) / ND and 7.83 MIL-100(Fe) / ND. The preparation steps of all samples were the same, only the amount of ND added was different to ensure the comparability of the experiment. All MIL-100(Fe) / NDs were uniformly abbreviated as MIL / ND.

[0035] (3) Characterization of ND, MIL-100(Fe) and MIL / ND catalytic materials; The morphology and microstructure of MIL-100(Fe) and MIL / ND were systematically characterized by field emission scanning electron microscopy (SEM, MAGELLAN-400). Figure 6It can be seen that MIL-100(Fe) presents good dispersity and irregular flake-like shape. MIL / ND successfully inherits the monodispersity of MIL-100(Fe). In addition, a large number of black ND particles with small size and uniform distribution can be clearly observed adhering to the surface of MIL-100(Fe) particles. This morphological feature strongly confirms that ND successfully acts as a template and plays a role of skeleton support, thereby forming a stable skeleton-supported catalytic material MIL / ND Figure 6 b). The MIL-100(Fe) particles of different sizes in the figure may be because the material is prepared by water system, and part of the particles with large particle size may be due to the agglomeration growth of MOF crystals under high local concentration conditions in the synthesis process. Energy dispersive X-ray (EDX) spectrum further determines the element distribution of MIL / ND, and Fe, O and C elements are uniformly distributed in almost the same position, indicating that a stable and uniform skeleton-supported structure is formed between MIL-100(Fe) and ND Figure 6 c). This synergy not only verifies the effective addition of ND, but also implies that it may have a regulation effect on the electronic structure of MIL-100(Fe), which helps to build an excellent photoelectron transport channel and provides a structural guarantee for the separation of photoelectron-hole pairs in the subsequent photo-Fenton reaction.

[0036] In order to further analyze the specific surface area and pore size distribution of the catalyst, which directly affects the ability of the catalyst to adsorb pollutants and the accessibility of active sites, nitrogen adsorption-desorption test (Micromeritics ASAP 2460) system was used to characterize the specific surface area and pore structure characteristics of the material. The test data were analyzed by BET method and DFT pore model, and the following important findings were obtained: as shown in Figure 7 a, ND presents a typical type II isotherm, while MIL-100(Fe) and MIL / ND present a typical type III isotherm. ND sample shows the highest specific surface area (295.126 m 2 / g), indicating its highly porous characteristics. The specific surface area of MIL-100(Fe) is relatively low, only 54.506 m 2 / g. While the specific surface area of MIL / ND is significantly increased to 221.400 m 2 / g, which is obviously increased compared with pure MIL-100(Fe). This indicates that ND effectively supports the pores in the structure of MIL-100(Fe), which increases its specific surface area, reaction contact area, and thus increases the exposed active sites. Figure 7The pore size distribution curves (b) show that the most likely pore size of MIL / ND is 3.315 nm, significantly smaller than that of MIL-100(Fe) (5.584 nm) and ND (11.106 nm). This pore size reduction can be attributed to the ND framework being supported within and on the surface of MIL-100(Fe), exhibiting a certain degree of embedding and causing partial pore shrinkage. This microstructural modulation helps to form denser photogenerated electron channels and a more efficient space utilization environment, thereby promoting rapid separation of photogenerated electrons and holes, suppressing their recombination behavior, enhancing the utilization efficiency of photogenerated carriers, and thus improving photoFenton catalytic performance.

[0037] To further investigate the interaction mechanism between the ND framework and the MIL-100(Fe) metal-organic framework, Raman spectroscopy was used to systematically characterize three catalysts. The tests were conducted using a 532 nm laser source with power controlled at 5 mW to avoid thermal damage to the samples, and the scanning range was 100–3200 cm⁻¹. -1 The resolution is 2 cm. -1 Characterization results showed that MIL-100(Fe) and MIL / ND at 460 cm⁻¹ -1 The characteristic peak at that location is attributed to the Fe-O-Fe bridging vibration ( Figure 8 a). After the introduction of ND, MIL / ND reached 1350cm. -1 (D peak) and 1580 cm -1 The presence of typical ND-characteristic peaks at the (G peak) confirms successful ND loading and framework support for MIL-100(Fe). These peaks are also attributed to the vibrations of the C=C bonds in the benzene ring of MIL-100(Fe). The I(D) / I(G) ratio is close to 1, indicating a high defect density in ND, which helps accelerate electron migration and optimize photoelectron dynamics. With increasing ND content, the overall intensity of the MIL / ND Raman peaks significantly increases, and the peak shapes change significantly, indicating that the addition of ND alters the molecular structure of MIL-100(Fe). Figure 8 b). The 0.49 MIL / ND sample performed best, indicating that the interface coupling was strongest at this ratio.

[0038] To analyze the chemical structure and crystal composition characteristics of three catalysts—MIL-100(Fe), ND, and MIL / ND—systematic characterization was performed using X-ray diffraction (XRD, 6000 Shimadzu, Kyoto, Japan) and Fourier transform infrared spectroscopy (FT-IR, IFS 66V / S). The results showed that the FT-IR spectrum of MIL-100(Fe) was within the range of 3390 cm⁻¹. -1 and 717 cm -1Two characteristic peaks were observed at 3200 and 3600 cm Figure 9 a respectively, which were caused by the stretching vibration of -OH and C-H groups. Figure 9 a In addition, the absorption bands related to carboxylic groups were observed in the range of 1300 to 1700 cm -1 -1 -1 -1 -1 -1 These characteristic peaks were retained in MIL / ND as a whole, indicating that the skeleton structure was not destroyed. However, the peak intensity was obviously weakened, indicating that the carboxylic ligand in MIL-100(Fe) might have coupled with the C-C bond on the surface of ND. This bonding behavior helps to build an effective photo-induced electron transfer path, promoting the rapid migration and separation of carriers, thereby improving the efficiency of photo-Fenton degradation of MB. Figure 9 b shows the XRD pattern of the prepared catalyst. The sharp, strong diffraction peaks of pure MIL-100(Fe) indicate that the sample is well crystallized, and the characteristic peaks at 10.2°, 11.1°, 18.3°, 20.1°, 24.2°, and 27.7° are consistent with previous reports, indicating that these MIL-100(Fe) materials have been successfully synthesized. In the MIL / ND catalytic material, similar diffraction peak characteristics to MIL-100(Fe) were observed, indicating that the skeleton structure was well preserved. However, the ND diffraction peak was significantly weakened, which was presumably due to the low content of ND. In addition, compared with MIL-100(Fe), the characteristic peaks of MIL / ND were broadened and weakened, indicating that the successful synthesis of MIL / ND could be confirmed by changes and disappearance of the diffraction peaks.

[0039] X-ray photoelectron spectroscopy (XPS) provides key evidence for elucidating the chemical state and interface bonding mechanism of MIL / ND catalytic materials. Therefore, the surface elemental composition and chemical environment of the materials were tested by a Thermo Scientific ESCALAB 250Xi XPS instrument, and the data were analyzed in depth. The full-scan XPS spectrum shows that MIL / ND contains three elements of Fe, C, and O (Fig. Figure 10 a). Among them, the 2p1 / 2(773.6 eV) and 2p3 / 2(760.7 eV) in the high-resolution spectrum of Fe 2p are directed to Fe 3+ oxide state (Fig. Figure 10 b). The satellite peak at 768.2 eV reflects the low-spin characteristics of Fe 3+ , indicating that it has strong redox ability, which is beneficial to the electron transfer process in the photo-Fenton reaction. Figure 10 c shows the high-resolution spectrum of C 1s, which further reveals the various carbon environments in MIL / ND. Among them, 285.0 eV corresponds to the sp 2-C, which exhibits its conjugated pi electron structure, is beneficial as an electron donor. The C-C bond at 285.9 eV is derived from ND, indicating that there are defect states on the surface of ND, which help to improve the e - / h + separation efficiency. The corresponding carboxyl group at 289.4 eV is derived from the -COOH structure on the organic ligand of MIL-100(Fe). These carboxyl structures can enhance the loading capacity and electron transport capacity of ND for MIL-100(Fe), thereby improving the Fenton reaction efficiency. The peak at 532.4 eV in the O 1s spectrum is attributed to the C=O bond or C-O-C bond, which is derived from the MOF skeleton structure of MIL-100(Fe) Figure 10 d). Therefore, the XPS results show that the introduction of the ND skeleton not only stabilizes the existence state of Fe 3+ in MIL-100(Fe), but also promotes the electron transport path and effective separation of photo-generated carriers, thereby improving the light Fenton catalytic ability of MIL / ND.

[0040] Example 2: Because MIL-100(Fe) itself faces two major key limitations, one is that photo-generated carriers are prone to recombination, leading to reduced actual reaction efficiency; the other is that the Fe active site is limited, which limits its efficient use of oxidizing agents and the sustained generation ability of •OH. Therefore, it is difficult to meet the needs of efficient light Fenton catalysis by relying solely on a single MOF framework. Therefore, in order to elucidate the regulation of the electronic structure of ND on MIL-100(Fe) and its role in photoelectron behavior, the crystal cell model of MIL / ND and pure MIL-100(Fe) was constructed using Materials Studio and Vesta Figure 11 a). The Fe 1 and O 2 positions in MIL / ND are consistent with the corresponding atoms in MIL-100(Fe), ensuring the structural comparability of the system. Figure 11 b is the frontier molecular orbital distribution of MIL / ND. The results show that the highest occupied molecular orbital (HOMO) orbital electron cloud is mainly concentrated between the Fe-O bridges of MIL / ND, indicating that this region is the main origin region of photo-generated electrons, with good light response ability. The lowest unoccupied molecular orbital (LUMO) orbital is concentrated in ND and the connecting part, which means that under light conditions, electrons tend to jump from MIL-100(Fe) to the surface of ND, thereby effectively realizing electron-hole separation, inhibiting recombination, improving electron utilization efficiency, and further improving the catalytic activity of the light Fenton reaction.

[0041] Example 3: To prove that MIL / ND catalyst has excellent charge transport performance and catalytic activity in the process of MB degradation, the interface charge transfer resistance (Rct) determined by electrochemical impedance spectroscopy (EIS) was tested by using Shanghai Chenhua CHI660E electrochemical workstation, combined with cyclic voltammetry (CV) to analyze the redox characteristics, photocurrent test to evaluate the carrier separation efficiency and Mott-Schottky curve to analyze the band structure, the interface charge transport characteristics of MIL / ND catalyst were systematically studied. Before testing, the assembled three-electrode system needs to be placed at open circuit potential until the potential is stable, then the frequency range is set to 100-1000 kHz, a small sinusoidal perturbation signal of 10 mV amplitude is used for scanning, and the data quality is ensured by real-time monitoring of Nyquist diagram. After testing, the impedance data obtained is analyzed using Oringe software. The whole testing process needs to be kept in environmental shielding, and repeated three times to ensure data reproducibility, with error controlled within 5%. For cyclic voltammetry and linear sweep voltammetry tests, except for different parameter settings (initially centered at 0 V, set a range, initially set at -2 V, highest point set at 2 V, lowest point set at -2 V, and termination set at 2 V, then click start and adjust the range according to the test curve at any time. CV scan rate is usually 5-100 mV / s; LSV uses single-direction linear scanning, with scan rate generally 1-10 mV / s), other experimental conditions remain the same as EIS testing. Transient photocurrent test requires special light source control, using periodic light (every 20 seconds avoiding light once) to study the photoelectric response characteristics of the material, and recording the current change synchronously during light period to evaluate the photo-generated carrier separation efficiency of the catalyst. All tests need to be carried out under the same electrolyte system and three-electrode configuration to ensure data comparability.

[0042] The impedance characteristics of MIL / ND and MIL-100(Fe) and ND were analyzed by electrochemical impedance spectroscopy Figure 12 a), it was found that the semicircle arc of 0.49 MIL / ND was the smallest, indicating that its charge transfer resistance was the lowest and the electron transport efficiency was the highest, which was beneficial to the separation of photo-generated electron-hole pairs. This is due to the introduction of appropriate amount of ND to enhance the conductivity of the material and introduce moderate surface defects, which is helpful to the exposure of active sites and electron migration. The transient photocurrent response graph Figure 12(b) This further validates the above inference. MIL-100(Fe) exhibits the lowest photocurrent intensity, indicating its weak photocatalytic activity. The addition of ND significantly enhances the photocurrent, especially at 0.49 MIL / ND, demonstrating optimal photogenerated electron-hole separation efficiency and photocatalytic performance. This is because the ND framework supports MIL-100(Fe), providing more active sites and constructing efficient electron transport pathways. Secondly, an appropriate amount of ND can form a good reaction interface with MIL-100(Fe), while a higher ND ratio may cause light shielding or interface blockage, reducing performance.

[0043] To further understand the electrochemical performance of the materials, cyclic voltammetry (CV) and linear sweep voltammetry (LSV) curves of three comparative materials were measured. MIL-100(Fe) exhibited the smallest current response and a large redox potential difference (1.167 V / -0.627 V), reflecting its low electrochemical activity, which may limit its catalytic performance for H2O2. ND alone possessed good electron transport capabilities, with redox peaks at 1.234 V and -0.468 V (1.234 V / -0.468 V), but ND alone showed limited adsorption and catalytic activity for H2O2. In contrast, MIL / ND had the smallest redox potential difference (1.031 V and -0.179 V) and the highest current density. Figure 13 a). This indicates that its reaction polarization is smaller, resulting in higher electrochemical activity and a faster charge transfer rate, which is beneficial for electron transfer from ND to MIL-100(Fe). By comparing the LSV curves of ND, MIL-100(Fe), and MIL / ND, it was found that at the same applied potential, MIL / ND exhibits a significantly enhanced current density response ( Figure 13 (b) This characteristic directly benefits the sustained generation of •OH in the photo-Fenton reaction, thereby improving the degradation efficiency of MB. More importantly, MIL / ND exhibits a lower overpotential in the reduction potential range, indicating that the introduction of ND effectively optimizes the electron transport capability of the material and promotes Fe degradation. 3+ / Fe 2+ The cycle rate is the key mechanism by which the photo-Fenton system maintains high catalytic activity.

[0044] Example 4: In order to study the light absorption properties of the skeleton support material MIL / ND and its mechanism in the process of photo-Fenton degradation of MB, diffuse reflectance spectroscopy (DRS) test was carried out by using Shimadzu U-2600i type ultraviolet-visible spectrometer. First, the dry powder sample was uniformly filled in the sample cell, and BaSO4 was used as the reference standard with 100% reflectivity; the test wavelength range was set to 200-700 nm, covering the ultraviolet to visible light region; the scanning speed was set to low speed, and the slit width was adjusted to 2 nm to ensure the resolution; each sample was tested for 3 times to ensure the reliability of the data. In addition, it can also be observed from the DRS data whether the introduction of ND forms a new energy level structure in the new catalytic material, and these results are mutually verified with the electrochemical test data, which together explain the excellent photocatalytic performance of MIL / ND.

[0045] As Figure 14 a shows the light absorption properties of ND, MIL-100(Fe) and MIL / ND samples under ultraviolet-visible diffuse reflectance spectroscopy. ND itself has a wide band gap, and the absorption is mainly concentrated in the ultraviolet region, with weak absorbance, indicating that its visible light absorption ability is limited. While MIL-100(Fe) has obvious absorption in the ultraviolet and visible light regions, especially in the range of 300-500 nm, indicating that the Fe center has strong light response ability. Compared with ND and MIL-100(Fe), the absorption spectrum of MIL / ND has red shift and the absorption intensity is enhanced. The E2 and B absorption peaks are between 200-300 nm, corresponding to π→π* transition or benzene ring and carboxyl structure on the ligand. The absorption peak near 450 nm is derived from LMCT in Fe-O-C structure. While the ligand field absorption between 500-700 nm may be derived from Fe 3+ d-d transition, reflecting the light response characteristics of the Fe center.

[0046] The band gap energy of the material can be calculated according to the Tauc formula and approximately expressed as: ; In the formula: is the absorption coefficient, is a constant, is the Planck constant, is the light frequency, is the band gap energy of the material.

[0047] As Figure 14 b is the curve with the change of , and the energy corresponding to the outer dotted line is the band gap energy The band gaps of MIL-100(Fe) and ND are 2.27 eV and 2.42 eV, respectively, while the band gap of the framework support material MIL / ND decreases to 1.92 eV. The narrower band gap of MILND broadens the range of absorbed light, enhances visible light absorption, and accelerates photogenerated electrons. - and h + The ability to separate makes it easier to stimulate more e in VB. - Entering CB, thus benefiting h + The conduction band positions of MIL-100(Fe) and ND were calculated to be -0.49 V (vs. RHE) and -0.4 V (vs. RHE) respectively, based on the Mott-Schottky (MS) curve. Figure 14 c), according to The calculated valence band (VB) potentials are approximately 1.78 V and 2.02 V, respectively. This band matching ensures effective excitation of MIL / ND under light irradiation, and electron transport with Fe. 3+ / Fe 2+ The rapid cycling significantly improves the degradation efficiency of the photo-Fenton reaction.

[0048] Example 5: To test the number of active sites on the material surface, cyclic voltammetry was used to measure the electrochemical responses of three materials at different scan rates. Before testing, the assembled three-electrode system was allowed to stand at an open-circuit potential until the potential stabilized. Then, the scan potential range was set to -1.00 to 1.00 V, and the scan potential range was adjusted according to the data results. After adjustment, tests were conducted at six scan rates: 20, 40, 60, 80, 100, and 120 mV / s, with each rate repeated three times. By analyzing the linear relationship between the redox peak current and the square root of the scan rate, and combining the electrochemical double-layer capacitance (Cdl) calculation, it was found that the introduction of ND in MIL / ND effectively increased the number of electrochemical active sites and improved charge transport performance.

[0049] Experiments revealed that the area under the curve for MIL-100(Fe) was relatively small, indicating that it has fewer active sites, which limits the performance of the photo-Fenton reaction. Figure 15 a). The weak response of the ND curve indicates that the activity of ND alone is not high. Figure 15 b). The CV area of ​​MIL / ND is significantly increased ( Figure 15 c), and showed a good linear relationship with increasing scan rate, indicating that the synergistic effect of MIL-100(Fe) and ND effectively improved the number of active sites and utilization efficiency. Further, the electrochemical active surface area (ECSA) of each sample was measured by electrochemical double-layer capacitance. Figure 15d). The calculated results show that the Cdl value of MIL / ND is significantly greater than that of MIL-100(Fe) and ND, about 12 times of MIL-100(Fe). While higher Cdl indicates an increase in reactive sites, which positively promotes the continuous performance of the photo-Fenton reaction for the degradation of MB.

[0050] Example 6: To evaluate the photo-Fenton degradation performance of MIL / ND, the photo-Fenton degradation experiment of MB was carried out under the standard simulated sunlight condition. In the standard system of 80 mL, the degradation rate of 0.49 MIL / ND was as high as 99.9%, which was significantly better than that of other ratio samples Figure 16 a). This is because the appropriate amount of ND ensures the effective use of Fe sites and the full activation of H2O2, thereby enhancing the ability to generate •OH and accelerating the degradation of MB. While an excessive amount of ND may cover the active sites of MIL-100(Fe), hindering the light absorption capacity, forming an obstacle to electron transfer, and thus being detrimental to the photo-Fenton degradation of MB. The comparative experiment further confirms the synergistic enhancement effect of MIL / ND Figure 16 b). MIL-100(Fe) has a certain degradation capacity, but is limited by the electron transfer rate and the number of Fe active sites. ND has almost no degradation capacity. Compared with MIL-100(Fe), the degradation rate of MIL / ND for MB is increased by 10.9%. This is because MIL / ND combines the Fe active sites in MIL-100(Fe) with the excellent electron transport performance of ND, effectively inhibiting the e 3+ / h - / h + recombination efficiency, thereby improving the decomposition of H2O2 and the generation of •OH, and thus enhancing the degradation efficiency of the photo-Fenton degradation of MB.

[0051] Example 7: To determine the •OH concentration on the surface of the MIL / ND photocatalyst, terephthalic acid (PTA) was used as a probe molecule to track the generation of •OH by detecting the fluorescence intensity of its derivative 2-hydroxyterephthalic acid. A 300 mL solution of sodium terephthalate was prepared, with a NaOH concentration of 0.01 M and a terephthalic acid concentration of 20 ppm. Then 30 mL of the solution was taken and 0.05 g of MIL / ND catalyst was added. After stirring for 30 minutes, the suspension reached adsorption-desorption equilibrium. Then the simulated sunlight was turned on, and 1 mL of sample was taken at 0, 5, 10, 15, and 20 minutes, and each sample was filtered once with a syringe filter. Finally, the samples were diluted 5 times and the fluorescence spectra of the samples were collected under λ = 315 nm excitation conditions using a fluorescence spectrophotometer, and the fluorescence intensity of the characteristic emission peak at λ = 426 nm was recorded. The test results are as follows Figure 17As shown in Figure 2a, with the gradual extension of the reaction time to 20 min, the spectral intensity of MIL / ND also gradually increased, indicating that it had the highest •OH production, thus achieving the best effect of MB photo-Fenton degradation at 20 min. The highest MIL / ND photo-Fenton degradation rate was because the ND with high carrier mobility transferred electrons to MIL-100(Fe) under static action, thus constructing a built-in electric field, ultimately achieving charge balance and significantly improving the separation and migration efficiency of photo-generated carriers. Figure 17 b).

[0052] Example 8: In order to systematically study the influence mechanism of MIL / ND on the degradation performance of MB, a series of control variable experiments under standard photo-Fenton reaction conditions were designed, and the efficiency relationship was revealed by precisely regulating the key reaction parameters. For example, Figure 18 a, in order to verify the effect of photo-Fenton reaction, comparative experiments were carried out in the dark. The results showed that the degradation rates of the three photo-Fenton materials in the dark were all lower than 0.62%. But the degradation rate of MIL / ND was still higher than that of pure MIL-100(Fe) and ND. This was mainly because H2O2 acted as a lone pair electron donor, filling the empty d z 2 orbitals of Fe, forming σ coordination of O-Fe. And under the action of Lewis acidic Fe 3+ center, it triggered limited non-photo-Fenton reaction to generate •OH, thus participating in the degradation reaction. Figure 18 b found that even without H2O2, 0.49 MIL / ND could achieve 18.7% MB degradation. This may be due to the generation of trace amounts of H2O2 in the system and its participation in the reaction, showing that MIL / ND has certain catalytic activity in photo-Fenton reaction.

[0053] Figure 19 The effect of different doses of MIL / ND on MB degradation. The results showed that with the increase of the dose of MIL / ND, the degradation rate showed a trend of first increasing and then decreasing. 10 mg of MIL / ND showed the best degradation effect, while 15 mg and 20 mg of MIL / ND slightly reduced the degradation rate. This is because at 5 mg, the active sites of MIL / ND are less, and the generation rate of •OH is low, so the degradation rate is slow. At 10 mg, MIL / ND provides sufficient active sites, and the catalytic efficiency of photo-Fenton reaction reaches the best state. But at 15 mg and 20 mg, it may cause the increase of solution turbidity, leading to the decrease of light transmittance, thus inhibiting light absorption, resulting in the decrease of degradation rate.

[0054] Figure 20The degradation effect of MB at different initial concentrations was demonstrated. At both 5 and 10 mg / L, MIL / ND achieved almost complete degradation (99.9%). Due to the limited number of available photo-Fenton active sites on the MIL / ND surface, lower MB concentrations resulted in a higher proportion of MB dye molecules that could be efficiently oxidized per unit time, thus exhibiting a higher degradation rate. As the MB concentration increased, the generated •OH groups in the system were relatively insufficient, limiting the reaction rate. Considering both degradation effect and experimental operability, the degradation efficiency of MIL / ND was best at an MB concentration of 10 mg / L.

[0055] from Figure 21 The degradation of MB initially increased and then decreased with increasing pH. MB degradation was most efficient under acidic and neutral conditions, especially at pH 7, where the degradation rate reached its highest. This is likely because the photo-Fenton reaction achieves an optimal balance between the formation rate and stability of •OH under neutral conditions, promoting efficient MB degradation. While an acidic environment may facilitate Fe degradation... 3+ Reduction, but too low a pH will inhibit the formation of •OH and induce Fe. 3+ Precipitation limits the reaction. The oxidizing power of •OH is weakened under alkaline conditions, which also hinders the reaction. This indicates that MIL / ND is suitable for a wider pH range and has greater application potential in neutral environments, superior to traditional materials such as 8% Ag / AgBr / ferric hydroxide.

[0056] Based on the results of different H2O2 dosages, it was found that as the H2O2 dosage increased, the MB degradation rate first increased and then tended to stabilize. Figure 22 When the H2O2 addition reached 100 μL, further increasing it to 120 μL had limited effect on improving the degradation rate, indicating that the system was approaching saturation. An appropriate amount of H2O2 can provide sufficient ·OH, improving the efficiency of the photo-Fenton reaction. However, excessive H2O2 may undergo side reactions with ·OH, thus consuming the effective oxidant and weakening the oxidizing activity. Considering both reaction efficiency and resource utilization, 100 μL was determined to be the optimal addition amount.

[0057] Example 9: To accurately evaluate the mineralization capacity of MIL / ND in the degradation of MB, a total organic carbon analyzer (TOC-L CPH, Shimadzu) was used for systematic testing. The specific method is as follows: Under standard photo-Fenton reaction conditions (10 mg catalyst, 80 mL of 10 mg / L MB solution, 100 μL of 30% H2O2), 5 mL samples were taken every 5 minutes, filtered through a 0.22 μm filter membrane, and the TOC value of the solution was measured. The results showed that the mineralization degree of MB by MIL / ND was 78.0%, while the mineralization degree of MB by MIL-100(Fe) was 55.0% (…). Figure 23a). MIL / ND showed significantly better mineralization effect on MB than MIL-100(Fe), which indicated that most of the degradation products of MB were water and carbon dioxide, and only a small amount of organic carbon existed. This conclusion fully embodied the deep oxidation ability of MIL / ND under simulated sunlight conditions and the potential for practical application. In order to systematically evaluate the stability and recycling performance of MIL / ND in practical application, a recycling degradation experiment was carried out. Each experiment was irradiated for 20 minutes under standard photo-Fenton reaction conditions. After the reaction was completed, the remaining material was recovered by centrifugation. The recovered material was repeatedly washed with deionized water for 2-3 times, and then collected after drying at 60°C for 12 hours, and then the photo-Fenton degradation treatment was continued on the recovered material. After 8 times of photo-Fenton degradation experiment, it was found that the degradation efficiency of MIL / ND on MB still remained at 92.4% (MB=10 mg / L, H2O2= 0.5 mL / L, MIL / ND= 0.1 g / L, pH= 7, t= 20 min, λ= 300 W, 300 W xenon lamp, 20 min) Figure 23 b). The results showed that MIL / ND exhibited extremely high chemical stability and could be repeatedly used for the degradation of MB.

[0058] Example 10: In order to systematically evaluate the anti-interference ability of MIL / ND in the actual wastewater environment, three common water inorganic anions were selected: chloride ion (Cl - ), sulfate ion (SO4 2- ) and bicarbonate ion (HCO3 - ). In the experiment, different concentrations of sodium chloride, sodium sulfate and sodium bicarbonate were added respectively in the solution with constant initial conditions and pH value of 7. The solution was placed under xenon lamp for photo-Fenton degradation reaction for 20 minutes, and the concentration of MB was detected every 5 minutes. Figure 24 a shows the effect of Cl - on the degradation efficiency of MB. By comparing the conditions without Cl - and different concentrations of Cl - , it was found that Cl - had little effect on photo-Fenton degradation. Figure 24 b found that the degradation curves almost overlapped under the conditions without SO4 2- and different concentrations of SO4 2- , which indicated that SO4 2- presented good inertness in the system and did not significantly interfere with the photo-Fenton reaction process. This may be due to the fact that MIL / ND as a photo-Fenton catalyst can exhibit high stability and selectivity under certain conditions. Figure 24 c results show that the addition of HCO3 - has obvious inhibition effect on the degradation of MB. This may be because after the addition of bicarbonate, the pH value of the solution changes from acidic to alkaline, resulting in the decrease of the oxidation ability of ·OH.

[0059] Example 11: To investigate the main active species in the reaction system, radical quenching experiments were carried out. In the experiment, ethylenediaminetetraacetic acid, tert-butyl alcohol and benzoquinone were used as quenchers of h + , ·OH and ·O2 - , respectively, while ethanol was used to quench ·OH and ·O2 - at the same time. Under standard photo-Fenton reaction conditions, the four quenchers were added to the system separately, and after 20 minutes of continuous operation, samples were taken every 5 minutes to determine the degradation efficiency of MB, and finally the main active species involved in the degradation process was determined. The results are shown in Figure 25 a h + quenching experiment, it was found that with the increase of ethylenediaminetetraacetic acid concentration, the degradation rate of MB decreased rapidly, especially at high concentration, which significantly inhibited the reaction. This is due to the equilibrium between H + and ·OH, followed by the equation shown: ; Figure 25 b and 25c respectively investigated the influence of ·OH quencher tert-butyl alcohol and multifunctional radical quencher ethanol. The increase of tert-butyl alcohol concentration significantly reduced the degradation rate of MB, indicating that ·OH is the main active species in the MIL / ND system. Although the increase of ethanol concentration also reduced the degradation rate of MB, the inhibition effect was weaker than that of tert-butyl alcohol. This indicates that in addition to quenching ·OH radicals, there are also SO4 2- radicals. Figure 25 d further used benzoquinone as a ·O2 - quencher. The results showed that the addition of benzoquinone also slightly inhibited the degradation of MB. This shows that ·O2 - is also involved in the photo-Fenton process in the MIL / ND system, but its contribution is lower than that of ·OH. Based on the analysis of various active species, by comparing the quenching effect of tert-butyl alcohol and ethanol, it can be known that ·OH is the main active species in the MIL / ND system for degrading MB, and ·O2 - acts as an auxiliary species to enhance the oxidation ability of the system.

[0060] Example 12: In order to more clearly illustrate the essence of the mechanism of the high-efficiency MB degradation of MIL / ND in the photo-Fenton system, density functional theory was used to systematically analyze its electronic structure and interface bonding characteristics. Figure 26 a- Figure 26 b It was found that the spin-up and spin-down in the Fe 3d orbital were basically symmetrical, and the d orbital splitting was small, indicating that Fe was in a low-spin state. Low-spin Fe usually has a higher crystal field stabilization energy (CSE) and stronger electron binding ability, which helps to improve the regulation ability of Fe center in the electron transfer process, thereby accelerating the Fe 3+ / Fe 2+The cycle rate between them. In the photo-Fenton reaction, this low-spin characteristic can more efficiently activate H2O2 to produce ·OH, thereby accelerating the degradation rate of MB.

[0061] Further chemical bonding orbital analysis (COHP) revealed the key bonding behavior at the MIL / ND interface. COHP results showed a high number of bonding orbitals with low energy distribution, thus forming stable and strong σ bonds, which facilitated the separation of photogenerated carriers. Figure 27 a). C-Fe bonds exhibit higher-energy bonding characteristics. Although some antibonding states are close to the Fermi level, bonding orbitals still dominate overall. Figure 27 (b) This indicates that the C-Fe bond forms a structure dominated by π-type electronic coupling, which facilitates rapid electron transfer at the interface. Furthermore, from the perspective of orbital interactions, electrons mainly move from the C 2p orbital to the Fe t orbital. 2g Orbital transitions further lead to σ-π conjugation. This not only endows Fe with structural stability but also makes it a highly efficient electron acceptor center, significantly enhancing the charge migration capability at the MIL / ND interface. PDOS and COHP results demonstrate that low-spin Fe in the MIL / ND interface effectively improves the utilization efficiency of photogenerated electrons by enhancing electron binding and transport capabilities. Meanwhile, the stable CO and C-Fe bonding structure provides a solid guarantee for carrier separation and migration, further promoting the efficient generation of ·OH radicals and significantly enhancing the photo-Fenton reaction performance.

[0062] Example 13: To reveal the essential reason for the enhanced ·OH generation ability of MIL / ND in the photo-Fenton system from a thermodynamic perspective, the Gibbs free energy changes of key reaction steps were calculated using density functional theory. For example... Figure 28 As shown in figure a, the maximum Gibbs free energy for the photo-Fenton catalytic oxidation of ·OH by MIL / ND is 0.57 eV, while that by MIL-100(Fe) is 0.65 eV. This means that MIL / ND can generate ·OH more efficiently, thus enhancing the photo-Fenton activity. This also indicates that ND, acting as a framework support, modulates the electronic structure of the Fe center, lowers the activation barrier, and accelerates the Fe… 3+ / Fe 2+ Cycle. The initial free energies of both MIL / ND and MIL-100(Fe) are 0 eV. Subsequently, H2O2 adsorbs onto *, *H2O2 reacts and loses an ·OH atom to participate in the photo-Fenton reaction, forming *OH. Then, *OH absorbs an etomidium. - and h + *H₂O is formed, and then one H₂O molecule returns to the initial state. The reaction pathway is as follows: Figure 29 As shown in a and 29b, the reaction process is as follows: ; ; ; ; The d-band center of MIL / ND (-0.883 eV) is closer to the Fermi level than that of MIL-100(Fe) (-1.071 eV). Figure 28 b). This indicates that the introduction of ND enhances the electron-attracting ability of Fe, which helps to improve the ability of Fe active sites to capture and transfer reaction electrons, thereby accelerating the reaction. 3+ / Fe 2+ The cycle enhances the efficiency of the photo-Fenton reaction.

[0063] Example 14: MIL / ND exhibits excellent catalytic performance in the photo-Fenton degradation of MB. The mechanism can be analyzed from two aspects: electronic structure regulation and interfacial synergistic effects between the framework support materials of MIL-100(Fe) supported by ND. Firstly, the Fe in MIL-100(Fe)... 3+ In the low-spin state, its d orbitals are significantly split, and electrons preferentially occupy the low-energy t orbitals. 2g The orbital structure reduces the probability of spin transitions and enhances redox activity. Its strong coordination environment further reduces Fe... 3+ Its reduction potential makes it more readily react with H₂O₂ to generate •OH radicals. The introduction of ND provides abundant sp⁻¹. 2 / sp 3 Hybridized electronic states not only enhance Fe 3+ / Fe 2+ The increased electron transfer efficiency between the electrons effectively suppressed the recombination of photogenerated carriers, thus improving the utilization rate of reaction electrons. Theoretical calculations further revealed that the introduction of ND significantly lowered the energy barrier for H2O2 adsorption, enhanced the cycling activity of Fe, and increased the reaction rate. Under illumination, MIL / ND can efficiently absorb photons, exciting electrons to transition from the valence band to the conduction band to form electrons. - / h + Yes. The high conductivity of ND promotes the rapid separation and directional transfer of photogenerated electrons, synergistically accelerating the reduction reaction of H2O2 and Fe. 3+ / Fe 2+ The recycling of •OH effectively increases the yield of •OH and achieves complete mineralization of MB.

[0064] Furthermore, the system's excellent charge separation capability is also attributed to the built-in electric field induced by the Fermi level difference between ND and MIL-100(Fe). For example... Figure 30 As shown, the band arrangement further confirms the influence of the built-in electric field on e. - / h+ Meanwhile, the σ-electronic structure of ND also forms strong hybridization coupling with the d-orbit of Fe center, which expands the charge transfer path and improves the electron utilization efficiency. The frontier molecular orbital analysis shows that ND adjusts the HOMO / LUMO energy level distribution of MIL-100(Fe), reduces the electron transition barrier and accelerates the process of photo-Fenton reaction. From the reaction process, MIL / ND is excited to generate photo-generated electrons and holes under light irradiation, and then the photo-generated electrons jump from the organic ligand to Fe 3+ , which promotes the regeneration of Fe 2+ , and the generated holes also participate in the photo-Fenton reaction to degrade and mineralize MB. Then, the •OH generated by the photo-Fenton reaction continuously attacks MB, and finally degrades and mineralizes it into H2O and CO2. At the same time, the valence bond and acid-base ion theory further points out that the σ-type coordination between Fe 3+ and H2O2 helps to stabilize the generation of intermediates and maintain the sustainability of the photo-Fenton reaction.

[0065] ; ; ; ; .

[0066] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method of preparing a photo-Fenton catalytic material, characterized in that, Comprising the following steps: Step 1: FeCl3·6H2O and H3BTC are respectively weighed in a molar ratio of 1:1, and added to a beaker containing deionized water, and stirred to form a uniform mixture; Step 2: The catalytic material with ND as a template is prepared, the mass of Fe is calculated according to the mass ratio of ND:MIL-100(Fe) = 1:160, and then the required ND is added to the above mixture and stirred to ensure uniform dispersion of the ND in the MIL-100(Fe) precursor solution; Step 3: The product of step 2 is transferred to a high-pressure reaction kettle and placed in an oven for heating, so that the MIL-100(Fe) grows in situ on the surface of the ND; after the reaction is completed, it is cooled to room temperature, and then the product is poured into a beaker and washed with a mixed solution of water and ethanol in a volume ratio of 1:1, and then precipitated; Step 4: Finally, the washed precipitate is placed in an oven for drying, and the obtained orange-yellow solid powder is the ND skeleton supported MIL-100(Fe) material.

2. The method of claim 1, wherein the photo-Fenton catalytic material is prepared by the steps of: In the step 1, 0.378 g of FeCl3·6H2O and 0.272 g of H3BTC are accurately weighed and added to a beaker containing 10 mL of deionized water, and stirred with a magnetic stirrer for 30 minutes to form a uniform mixture.

3. The method of claim 2, wherein the photo-Fenton catalytic material is prepared by the steps of: In the step 2, the mass of Fe is 78.26 mg, and the mass of ND required is 0.49 mg.

4. The method of preparing a photo-Fenton catalytic material according to claim 3, wherein, In the step 2, ND with a size of 5-30 nm is added to the mixture of step 1, and the stirring time is 20 minutes.

5. The method of claim 4, wherein the photo-Fenton catalytic material is prepared by the steps of: In the step 3, the product of step 2 is transferred to a high-pressure reaction kettle and placed in an oven, and the temperature of the oven is set to 130℃, and the reaction time is 72 hours; then the product is washed with a mixed solution of water and ethanol in a volume ratio of 1:1 for 3-5 times; and the precipitation time is 6 hours.

6. The method of preparing a photo-Fenton catalytic material according to claim 5, wherein, In the step 4, the drying temperature of the oven is 80℃.

7. Use of a photo-Fenton catalytic material, the ND framework supported MIL-100(Fe) material prepared on the basis of the preparation method of the photo-Fenton catalytic material according to any one of claims 1 to 6, characterized in that, The ND skeleton supported MIL-100(Fe) material is applied as a catalytic material in the light Fenton technology for treating refractory industrial wastewater.

8. Use of a photo-Fenton catalytic material according to claim 7, characterized in that, The ND skeleton supported MIL-100(Fe) material is applied in the light Fenton treatment of MB refractory dye wastewater.

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