Iron-silver diatomic catalyst based on ligand complexing effect and preparation method and application thereof

Abstract

The application discloses a kind of iron silver diatomic catalyst based on ligand complexation effect construction and its preparation method and application, belong to material science and environmental engineering technical field;The method utilizes the difference between iron, silver atom and o-phenanthroline, ethylenediamine tetraacetic acid disodium ligand complexing rate and capacity, optimizes the adding order of ferric nitrate and silver nitrate, accurately controls the complexation mode of metal atom and ligand oxygen / nitrogen atom;And further with the directional assembly and melting point reduction effect of intermolecular hydrogen bond, successfully prepare the diatomic catalyst that iron silver atomic spacing and coordination configuration can be controlled;The design essentially strengthens the synergistic catalysis of iron silver double site, realizes the cascade activation of peroxymonosulfate internal oxygen atom, and then generates singlet oxygen with high yield and high output;The application provides an efficient new material and feasible new technical scheme for the advanced treatment of typical phenolic and antibiotic wastewater.

Description

Technical Field

[0001] This invention belongs to the field of materials engineering and environmental engineering technology, specifically relating to a highly efficient iron-silver diatomic catalyst constructed based on ligand complexation effect, its preparation method and application. Background Technology

[0002] In recent years, persulfate-based advanced oxidation technology has gradually become an important means of advanced treatment of organic wastewater. However, due to the coexistence of background ions and natural organic matter in the water, the degradation efficiency of reactive oxygen species such as sulfate radicals and hydroxyl radicals is often low. In contrast, singlet oxygen (1O2), as a mild non-radical species, has a relatively long lifetime (t1 / 2 = 10-6–10-5 s) and migration distance, exhibits strong selectivity for electron-rich organic molecules, and shows good stability over a wide pH range of 3.4 to 10.8. Even in solutions with natural organic matter concentrations as high as 50 mg / L, 1O2 maintains excellent adaptability, demonstrating great potential for advanced wastewater treatment.

[0003] Currently, activated persulfate (PMS) is one of the effective pathways to achieve 100% 1O2 production, but its theoretical stoichiometric ratio is limited to 1:2 (PMS:1O2), while the superoxide anion radical (O2•-) pathway has a ratio of 1:1 (PMS:1O2). Therefore, constructing highly efficient active sites to orderly drive the above two types of reactions and effectively suppress side reactions has become the key to balancing high selectivity and high yield of 1O2 production. Single-atom catalysts, with 100% atom utilization efficiency, can maximize the reaction performance of each catalytic site and possess unique electronic structures and coordination environments. However, a single active site often only catalyzes a single reaction with high selectivity, making it difficult to synergistically complete the multi-step coupled PMS activation dual-pathway 1O2 production process.

[0004] Therefore, there is an urgent need to develop a diatomic catalyst capable of achieving efficient cascade reactions. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by providing an iron-silver diatomic catalyst constructed based on ligand complexation effects, its preparation method, and its application.

[0006] The objective of this invention is achieved through the following technical solution: In a first aspect, the present invention provides an iron-silver diatomic catalyst constructed based on ligand complexation effect, the preparation method of which includes the following steps: S1: Dissolve disodium ethylenediaminetetraacetate in deionized water to prepare a disodium ethylenediaminetetraacetate solution, then add ferric nitrate nonahydrate, stir at room temperature until dissolved, then add silver nitrate and continue stirring to obtain the first solution; wherein the molar ratio of disodium ethylenediaminetetraacetate to iron salt and silver salt is 3:1~5:1; S2: Dissolve cyanuric acid in deionized water to prepare a cyanuric acid solution; mix the first solution with the cyanuric acid solution and stir to obtain a second solution; S3: Melamine is dissolved in deionized water to prepare a melamine solution; the second solution is added to the melamine solution, and the mixture is stirred at room temperature to generate a precipitate; the precipitate is obtained by filtration and drying. S4: The first supramolecular solid obtained in step S3 is subjected to gradient heating, heat preservation and cooling to obtain the first iron-silver diatomic catalyst based on ligand complexation effect, denoted as Fe1-Ag1 / CN.

[0007] Furthermore, in step S2, the temperature at which the first solution is mixed and stirred with the cyanuric acid solution is 35~45℃.

[0008] Further, in step S3, the second solution is added to the melamine solution by dripping at a rate of 5-10 mL / min.

[0009] Further, in step S4, the heating rate of the gradient heating is 2~5℃ / min; the heating endpoint is 500~700℃; and the holding time is 2~7 hours.

[0010] A method for preparing an iron-silver diatomic catalyst based on ligand complexation effect, characterized by comprising the following steps: S1: Add ferric nitrate nonahydrate and silver nitrate to two portions of o-phenanthroline solution respectively, stir to dissolve and obtain o-phenanthroline iron solution and o-phenanthroline silver solution; wherein the molar ratio of o-phenanthroline to ferric nitrate nonahydrate and o-phenanthroline to silver nitrate are 2:1~6:1; S2: Dissolve cyanuric acid in deionized water to prepare a cyanuric acid solution; simultaneously add the o-phenanthroline iron solution and o-phenanthroline silver solution to the cyanuric acid solution and stir to obtain a third solution; S3: Prepare a melamine solution; add the third solution to the melamine solution and stir to generate a precipitate; filter and dry to obtain a second supramolecular solid; S4: The second supramolecular solid obtained in step S3 is subjected to gradient heating, holding and cooling to obtain the second iron-silver diatomic catalyst based on the ligand complexation effect, denoted as Fe1+Ag1 / CN.

[0011] An iron-silver diatomic catalyst obtained according to any of the above methods.

[0012] Furthermore, in the catalyst, Fe and Ag are both dispersed in the carbon nitride support in the form of single atoms; the coordination structure of Fe sites is Fe-N4 or Fe-Ag, and the Ag sites are Ag-Fe, Ag-N3-O1 or Ag-N2-C2.

[0013] Application of an iron-silver diatomic catalyst prepared according to any of the above methods in the treatment of phenolic pollutants and antibiotics in organic wastewater.

[0014] Furthermore, the application is as follows: the reaction system does not require an external light source, and achieves efficient oxidation degradation in synergy with PMS only under normal temperature and light-protected conditions; the specific process is as follows: the iron-silver diatomic catalyst and PMS are added together to the phenolic or antibiotic wastewater system, and the reaction is stirred at 15~25℃ for 60~180 minutes, which can effectively remove phenols and antibiotics from the wastewater.

[0015] Furthermore, the concentration of the iron-silver diatomic catalyst is 0.3~0.7 g / L, and the concentration of the PMS is 1800~2200 mmol / L.

[0016] Compared with the prior art, the beneficial effects of the present invention are: 1) By controlling the order of addition and mixing ratio of iron source (ferric nitrate nonahydrate), silver source (silver nitrate), o-phenanthroline, and disodium ethylenediaminetetraacetate, this invention successfully prepared iron-silver diatomic catalysts Fe1-Ag1 / CN and Fe1+Ag1 / CN with controllable coordination configuration. 2) By constructing iron-nitrogen, silver-nitrogen-carbon, and iron-silver coordination configurations, the activation efficiency of Fe1-Ag1 / CN for PMS was significantly improved, and the activation efficiency of PMS via SO5 was effectively regulated. •- → 1 O2 and O2 •- → 1 O2 dual-path generation 1 The O2 ratio achieved a utilization efficiency of up to 90% and a concentration of 0.16 mM. 1 O2; 3) The Fe1-Ag1 / CN membrane was prepared and embedded in a continuous flow reactor, which can efficiently remove pollutants such as p-chlorophenol and sulfadiazine from actual wastewater in chemical industrial parks. At the same time, it exhibits low iron and silver ion dissolution rate and excellent cycle stability. This invention fundamentally improves the accessibility of cascade reactions at active sites and provides efficient new materials and feasible new technology solutions for the deep treatment of typical phenolic and antibiotic wastewater. Attached Figure Description

[0017] Figure 1 Schematic diagram of site coordination configuration design for iron-silver diatomic catalysts; Figure 2 This is the liquid phase mass spectrum of the complexation reaction of disodium ethylenediaminetetraacetate with ferric nitrate nonahydrate and silver nitrate; Figure 3 The ultraviolet spectrophotometer shows the complexation reaction of disodium ethylenediaminetetraacetate with ferric nitrate nonahydrate and silver nitrate. Figure 4 A comparison chart of the metal loading of the catalysts prepared in Examples 1-4; Figure 5 The X-ray diffraction patterns of the catalysts prepared in Examples 1-4 are shown below. Figure 6 The images shown are aberration-corrected electron micrographs and elemental distribution spectra of Fe, Ag, C, and N for the iron-silver diatomic catalysts prepared in Examples 1-2. Figure 6 In this image, 'a' represents an aberration-corrected electron microscope image and elemental distribution spectra of Fe, Ag, C, and N for the iron-silver diatomic catalyst prepared in Example 1. Figure 6 In the image, b represents the aberration-corrected electron microscope image and elemental distribution spectra of Fe, Ag, C, and N of the iron-silver diatomic catalyst prepared in Example 2. Figure 7 The images show the Fourier transform R-space X-ray extended edge absorption fine structure spectra of the Fe K-side of the catalysts prepared in Examples 1-4, where... Figure 7 In the figure, 'a' represents the Fourier transform (FK-side) R-space X-ray extended edge absorption fine structure spectra of the catalyst, iron oxide, ferric oxide, and iron foil prepared in Examples 1, 2, and 3. Figure 7 In Figure 'b', the extended X-ray absorption fine structure diagrams of the catalysts and iron foils prepared in Examples 1, 2, and 3 are shown. Figure 7 In the figure, 'c' represents the Fourier transform (FK-side) R-space X-ray extended edge absorption fine structure spectra of the catalysts, silver oxide, and silver foil prepared in Examples 1, 2, and 4. Figure 7 In the diagram, d represents the extended X-ray absorption fine structure analysis of the catalyst, silver oxide, and silver foil prepared in Examples 1, 2, and 4. Figure 8 This is a comparison chart of the performance of the catalysts prepared in Examples 1-4 in degrading p-chlorophenol in the PMS system. Figure 8 In Figure 'a', the graph shows a comparison of the degradation effects of the catalysts prepared in Examples 1-4 on PMS for the degradation of chlorophenol. Figure 8 In Figure b, the degradation rate of p-chlorophenol by PMS activated by the catalysts prepared in Examples 1-4 is compared. Figure 9 This is a comparative diagram showing the quencher capture experiment of PMS activated by the catalysts prepared in Examples 1-4 for the degradation of p-chlorophenol. Figure 9 In Figure 'a', the diagram shows a comparison of the quencher capture experiments of PMS degradation of p-chlorophenol activated by the iron-silver diatomic catalyst prepared in Example 1. Figure 9In Figure 'b', the diagram shows a comparison of the quencher capture experiments of PMS activated by the iron-silver diatomic catalyst prepared in Example 2 for the degradation of p-chlorophenol. Figure 9 In the figure, c represents a comparison of the quencher capture experiments of PMS activated by the iron single-atom catalyst prepared in Example 3 for the degradation of p-chlorophenol. Figure 9 In the figure, d represents a comparison of the quencher capture experiments of the silver single-atom catalyst prepared in Example 4 for the activation of PMS to degrade p-chlorophenol; Figure 10 The catalyst prepared in Examples 1-4 was used to activate PMS to generate 1 The performance comparison chart for O2 shows that... Figure 10 In this context, 'a' refers to the catalyst prepared in Examples 1-4 that activates PMS to produce... 1 Comparison chart of O2 accumulation. Figure 10 In this context, 'b' represents the PMS generated by activating the catalyst prepared in Examples 1-4. 1 Comparison of steady-state O2 concentrations Figure 10 In this context, 'c' refers to the catalyst prepared in Examples 1-4 that activates PMS to generate... 1 O2 yield comparison chart; Figure 11 To activate PMS and generate O2 using the catalysts prepared in Examples 1-4 •- Production comparison chart; Figure 12 This is a comparison chart of PMS consumption during the activation of PMS by the catalysts prepared in Examples 1-4; Figure 13 The catalyst prepared in Examples 1-4 was used to activate PMS to generate 1 A comparison chart of O2 sources, in which... Figure 13 In this context, 'a' refers to the product generated by activating PMS with the iron-silver diatomic catalyst prepared in Example 1. 1 A comparison chart of O2 sources. Figure 13 In this context, 'b' represents the product generated by activating PMS with the iron-silver diatomic catalyst prepared in Example 2. 1 A comparison chart of O2 sources. Figure 13 In this context, 'c' represents the PMS generated by activating the iron single-atom catalyst prepared in Example 3. 1 A comparison chart of O2 sources. Figure 13 In this context, d represents the product generated by activating PMS with the silver single-atom catalyst prepared in Example 4. 1 O2 source comparison chart; Figure 14 The catalyst prepared in Examples 1-4 was used to activate PMS to generate 1 A comparison of the contributions of O2 along different pathways, among which, Figure 14 In this context, 'a' refers to the product generated by activating PMS with the iron-silver diatomic catalyst prepared in Example 1. 1 O2 production outputs along each generation path Figure 14 In this context, 'b' represents the product generated by activating PMS with the iron-silver diatomic catalyst prepared in Example 2.1 O2 production outputs along each generation path Figure 14 In this context, 'c' represents the PMS generated by activating the iron single-atom catalyst prepared in Example 3. 1 O2 production outputs along each generation path Figure 14 In this context, d represents the product generated by activating PMS with the silver single-atom catalyst prepared in Example 4. 1 O2 production outputs along each generation path Figure 14 In this context, 'e' represents the product generated by activating PMS with the catalyst prepared in Examples 1-4. 1 Comparison chart of O2 generation path contribution changes; Figure 15 This is a comparison chart showing the efficiency of the iron-silver diatom catalyst prepared in Example 1 in activating PMS to degrade antibiotic pollutants. Figure 15 In the figure, 'a' represents a comparison of the efficiency of PMS degradation of sulfadiazine activated by the iron-silver diatom catalyst prepared in Example 1. Figure 15 In Figure 'b', the graph shows a comparison of the efficiency of PMS degradation of sulfamethoxazole activated by the iron-silver diatom catalyst prepared in Example 2. Figure 15 In the figure, c represents a comparison of the efficiency of PMS degradation of tetracycline by the iron single-atom catalyst prepared in Example 3. Figure 15 In the figure, d represents a comparison of the efficiency of PMS degradation of ciprofloxacin activated by the silver single-atom catalyst prepared in Example 4. Figure 15 In the figure, 'e' represents a comparison of the efficiency of PMS degradation of enrofloxacin by the catalysts prepared in Examples 1-4. Figure 16 This is a comparison chart showing the efficiency of the iron-silver diatom catalyst prepared in Example 1 in activating PMS for the degradation of phenolic pollutants. Figure 16 In the figure, 'a' represents a comparison of the efficiency of PMS degradation of phenol activated by the iron-silver diatom catalyst prepared in Example 1. Figure 16 In Figure 'b', the graph shows a comparison of the efficiency of PMS degradation of 2,4-dichlorophenol activated by the iron-silver diatom catalyst prepared in Example 2. Figure 16 In the figure, c represents a comparison of the efficiency of PMS degradation of 2,6-dichlorophenol activated by the iron single-atom catalyst prepared in Example 3. Figure 16 In the figure, d represents a comparison of the efficiency of PMS degradation of 3,5-dichlorophenol activated by the silver single-atom catalyst prepared in Example 4. Figure 16 In the figure, 'e' represents a comparison of the efficiency of the catalysts prepared in Examples 1-4 in activating PMS to degrade 2,3,5-trichlorophenol. Figure 17 This is a comparison chart showing the efficiency of PMS activation using the iron-silver diatom catalyst prepared in Example 1 for removing actual organic wastewater. Figure 17 In Figure 'a', the graph shows a comparison of the efficiency of PMS activation in degrading dyeing and printing wastewater using the iron-silver diatomic catalyst prepared in Example 1. Figure 17 In Figure 'b', the graph shows a comparison of the efficiency of PMS activation in degrading electroplating wastewater using the iron-silver diatom catalyst prepared in Example 2. Figure 17In the figure, c represents a comparison of the effluent effluent efficiency of PMS degradation in the secondary sedimentation tank activated by the iron single-atom catalyst prepared in Example 3. Figure 17 In the figure, d represents a comparison of the efficiency of PMS activation for the degradation of industrial wastewater A by the silver single-atom catalyst prepared in Example 4. Figure 17 In the figure, 'e' represents a comparison of the efficiency of PMS activation in degrading industrial wastewater B by the catalysts prepared in Examples 1-4. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0019] Unless otherwise specified, the experimental methods described in the following examples are conventional methods; unless otherwise specified, the reagents and materials are commercially available.

[0020] In a first aspect, the present invention provides a method for preparing an iron-silver diatomic catalyst based on ligand complexation effect, wherein the coordination configuration of iron-silver atomic sites is designed by controlling the ligand complexation sequence, as shown in the schematic diagram. Figure 1 As shown, this invention achieves the controllable preparation of iron-silver diatomic catalysts, denoted as Fe1-Ag1 / CN and Fe1+Ag1 / CN, by adjusting the order of addition and mixing ratio of iron source (ferric nitrate nonahydrate), silver source (silver nitrate), o-phenanthroline, and disodium ethylenediaminetetraacetate, as shown in Examples 1 and 2.

[0021] This invention utilizes the differences in complexation sites, complexation rates, and complexation capacities of disodium ethylenediaminetetraacetate (EDTA) for iron and silver ions, employing two strategies: 1) first saturating the complexation of disodium ethylenediaminetetraacetate with ferric nitrate nonahydrate, then complexing it with silver nitrate; 2) preparing two complexation systems: o-phenanthroline-ferric nitrate nonahydrate and o-phenanthroline-silver nitrate. Through pre-anchoring, the coordination configuration of iron and silver atoms is successfully regulated. The complexation principles are as follows: ferric nitrate acts as a hard acid, coordinating with the oxygen site; silver nitrate acts as a soft acid, coordinating with the nitrogen site. o-phenanthroline has a rigid planar heterocyclic structure, with two ortho-nitrogen atoms directionally clamping the metal ions, forming strong, stable six-membered ring chelates with ferric nitrate and silver nitrate respectively, resulting in a highly fixed coordination configuration. Disodium ethylenediaminetetraacetate has a hexadentate chelate structure, comprehensively encapsulating iron and silver metal ions to form ultra-stable cage-like chelates, where the oxygen site is more inclined to complex with iron ions, and the nitrogen site is more inclined to complex with silver ions. Compared to o-phenanthroline, disodium ethylenediaminetetraacetate has both nitrogen and oxygen coordination sites, achieving a differentiated chelation effect.

[0022] Secondly, the present invention provides an iron-silver diatomic catalyst prepared by a method for preparing an iron-silver diatomic catalyst based on the ligand complexation effect.

[0023] Thirdly, the present invention provides an application of an iron-silver diatomic catalyst prepared by a method for constructing an iron-silver diatomic catalyst based on ligand complexation effect in the treatment of phenols and antibiotics in organic wastewater.

[0024] Example 1: A biatom-metallic catalyst (Fe1-Ag1 / CN) was prepared by the following steps: S1: Dissolve 4.8 mmol of disodium ethylenediaminetetraacetate in 75.0 mL of deionized water, then add 1.2 mmol of ferric nitrate nonahydrate. Stir at room temperature until completely dissolved, then add 1.2 mmol of silver nitrate and continue stirring at room temperature until dissolved to obtain the first solution. S2: Dissolve 14.4 mmol of cyanuric acid in 300 mL of deionized water at 85 °C to obtain a cyanuric acid solution; pour the first solution into the cyanuric acid solution and stir continuously for 15 minutes to obtain a second solution; S3: Dissolve 24.0 mmol of melamine in 300 mL of deionized water at 85 °C to obtain a melamine solution; pour the second solution into the melamine solution and stir at room temperature to obtain a yellow-green precipitate. After stirring for 4 hours, filter and dry to obtain a yellow-green supramolecular solid. S4: Place 6 grams of supramolecular solid obtained in step S3 in a ceramic crucible, wrap it with aluminum foil, and heat it to 600°C at a heating rate of 5.5°C / min under a high-purity argon atmosphere. Hold the temperature for 4 hours and then cool it to room temperature to obtain the iron-silver diatomic catalyst (Fe1-Ag1 / CN).

[0025] The iron-silver diatomic catalyst prepared in Example 1 contains Fe-Ag bonds and is therefore denoted as Fe1-Ag1 / CN.

[0026] Example 2: A biatomic iron-silver catalyst (Fe1+Ag1 / CN) was prepared by the following steps: S1: Dissolve 2.4 mmol of o-phenanthroline in 37.5 mL of deionized water to prepare two parallel solutions. Then add 1.2 mmol of ferric nitrate nonahydrate and 1.2 mmol of silver nitrate respectively. Stir at room temperature until completely dissolved to obtain o-phenanthroline iron solution and o-phenanthroline silver solution. S2: Dissolve 14.4 mmol of cyanuric acid in 300 mL of deionized water at 85 °C to obtain a cyanuric acid solution; pour o-phenanthroline iron solution and o-phenanthroline silver solution into the cyanuric acid solution and stir continuously for 15 minutes to obtain a third solution; S3: Dissolve 24.0 mmol of melamine in 300 mL of deionized water at 85 °C to obtain a melamine solution; pour the third solution into the melamine solution and stir at room temperature to obtain a yellow-green precipitate; continue stirring for 4 hours, then filter and dry to obtain a yellow-green supramolecular solid; S4: Place 6 grams of supramolecular solid obtained in step S3 in a ceramic crucible, wrap it with aluminum foil, and heat it to 600°C at a heating rate of 5.5°C / min under a high-purity argon atmosphere. Hold the temperature for 4 hours and then cool it to room temperature to obtain the iron-silver diatomic catalyst (Fe1+Ag1 / CN).

[0027] In Example 2, the Fe and Ag atoms in the iron-silver diatomic catalyst were not bonded, so it was denoted as Fe1+Ag1 / CN.

[0028] Example 3: An iron single-atom catalyst (Fe1 / CN) is prepared by the following steps: S1: Dissolve 4.8 mmol of o-phenanthroline in 75.0 mL of deionized water, then add 1.2 mmol of ferric nitrate nonahydrate, and stir at room temperature until completely dissolved to obtain an o-phenanthroline ferric solution. S2: Dissolve 19.2 mmol of cyanuric acid in 300 mL of deionized water at 85 °C to obtain a cyanuric acid solution; pour the o-phenanthroline iron solution into the cyanuric acid solution and stir continuously for 15 minutes to obtain a fourth solution; S3: Dissolve 24.0 mmol of melamine in 300 mL of deionized water at 85 °C to obtain a melamine solution; pour the fourth solution into the melamine solution and stir to obtain a yellow-green precipitate; continue stirring for 4 hours, then filter and dry to obtain a yellow-green supramolecular solid; S4: Place 6 grams of supramolecular solid obtained in step S3 in a ceramic crucible, wrap it with aluminum foil, and heat it to 600°C at a heating rate of 5.5°C / min under a high-purity argon atmosphere. Hold the temperature for 4 hours and then cool it to room temperature to obtain an iron single-atom catalyst (Fe1 / CN).

[0029] The iron single-atom catalyst prepared in Example 3 contains only one type of iron atom, and is therefore denoted as Fe1 / CN.

[0030] Example 4: A silver single-atom catalyst (Ag1 / CN) was prepared by the following steps: S1: Dissolve 2.4 mmol of o-phenanthroline in 75.0 mL of deionized water, then add 1.2 mmol of silver nitrate and stir at room temperature until completely dissolved to obtain an o-phenanthroline silver solution. S2: Dissolve 19.2 mmol of cyanuric acid in 305 mL of deionized water at 85 °C to obtain a cyanuric acid solution; pour the o-phenanthroline silver solution into the cyanuric acid solution and stir continuously for 15 minutes to obtain the fifth solution; S3: Dissolve 24.0 mmol of melamine in 300 mL of deionized water at 85 °C to obtain a melamine solution; pour the fifth solution into the melamine solution and stir to obtain a yellow-green precipitate; continue stirring for 4 hours, then filter and dry to obtain a yellow-green supramolecular solid; S4: The supramolecular solid obtained in step S4 is placed in a ceramic crucible, wrapped with aluminum foil, and heated to 600°C at a heating rate of 5.5°C / min under a high-purity argon atmosphere. The temperature is held for 4 hours and then cooled to room temperature to obtain the silver single-atom catalyst (Ag1 / CN).

[0031] Example 4 prepared a thin-layer iron single-atom catalyst containing only one type of silver atom, and therefore it is denoted as Ag1 / CN.

[0032] The catalysts prepared in Examples 1, 2, 3 and 4 were used to design the coordination configuration of iron and silver atomic sites by controlling the ligand complexation sequence.

[0033] Figure 2 The liquid chromatography-mass spectrum of the complexation reaction of disodium ethylenediaminetetraacetate with ferric nitrate nonahydrate and silver nitrate is shown, revealing characteristic peaks of ethylenediaminetetraacetate-iron, ethylenediaminetetraacetate-silver, and ethylenediaminetetraacetate-iron / silver. Ultraviolet spectrophotometry was used for testing. Figure 3 The results show that when disodium ethylenediaminetetraacetate (EDTA) complexes with ferric nitrate nonahydrate, the position of the maximum absorption peak undergoes a blue shift; while when it complexes with silver nitrate, a red shift occurs, indicating that the former is a complexation reaction and the latter is a displacement reaction. When disodium EDTA complexes with ferric nitrate nonahydrate and silver nitrate successively, its maximum characteristic peak is 230 nm, which is between the characteristic peaks of the two single complexes.

[0034] The above results indicate that a single disodium ethylenediaminetetraacetate can simultaneously complex iron and silver. By changing the coordination complexation sequence and capacity, the coordination configuration of iron and silver atoms can be controlled, thereby facilitating the directional activation of a single oxygen site in PMS.

[0035] Figure 4The comparison of metal loadings showed that the loadings of Fe1-Ag1 / CN, Fe1+Ag1 / CN, Fe1 / CN, and Ag1 / CN were approximately 5.5 wt.% (Fe) and 9.0 wt.% (Ag), respectively. After conversion to atomic ratios, the molar ratios of Fe to Ag in Fe1-Ag1 / CN and Fe1+Ag1 / CN were close to stoichiometric ratios. This design helps to eliminate the influence of differences in atomic ratios on performance, indicating that coordination configuration is the main factor affecting catalytic performance.

[0036] Figure 5 The results showed that all four catalysts exhibited (100) and (002) diffraction peaks on the graphite-phase carbon nitride support, and no diffraction signal from any metal particles was detected.

[0037] Figure 6 Further analysis revealed that iron and silver in Fe1-Ag1 / CN and Fe1+Ag1 / CN were uniformly distributed in an atomic state within the carbon nitride framework; in Fe1+Ag1 / CN, the two atoms were dispersed, while in Fe1-Ag1 / CN, a certain distance was maintained between the two atoms. X-ray absorption spectroscopy analysis revealed the local coordination environment around the iron and silver atoms. X-ray absorption near-edge structure spectroscopy (…) Figure 7 As shown in (a) and (c), the absorption edges are located between the Fe foil and Fe₂O₃, and between the Ag foil and Ag₂O, respectively, indicating that the valence state of iron is between +2.4 and +2.8, and the valence state of silver is between +0 and +1. Fourier transform Fe K-edge extended edge absorption fine structure spectrum (EXAFS) ( Figure 7 In diagrams b and d), only a Fe–N coordination peak appears at approximately 1.4 Å, with no Fe–Fe scattering path observed, confirming that iron is a single-atom dispersion. Similarly, Ag–C and Ag–N coordination peaks appear at approximately 1.1 Å and 1.8 Å, respectively, with no Ag–Ag scattering path observed, confirming that silver is also a single-atom dispersion. Quantitative least-squares fitting of the EXAFS spectra further determined the precise coordination environments of the Fe and Ag atomic sites (Table 1), where: Fe1-Ag1 / CN: N4-Fe-Ag-N2C2; Fe1+Ag1 / CN: Fe-N4, Ag-N2C2. Furthermore, the R-factors were all less than 0.02, indicating good fitting results and high reliability.

[0038] The characterization results above indicate that ligand complexation regulation only alters the coordination configuration of the target iron and silver atoms, without changing catalyst information such as the support and loading.

[0039] Table 1: Fitting data for catalysts prepared in Examples 1-4

[0040] To evaluate the degradation performance of the catalysts prepared in Examples 1-4 on p-chlorophenol, a model phenolic pollutant, the following experiments were conducted: 20 mL of deionized water was placed in a beaker, and 2 mg of catalyst was added. The mixture was then sonicated to ensure thorough dispersion. Subsequently, p-chlorophenol and PMS were added to bring the initial concentrations to 0.1 mM and 0.2 mM, respectively. The reaction was carried out at a constant speed using a magnetic stirrer without adjusting the initial pH. At each set time point, 1.0 mL of the reaction solution was collected and immediately transferred to a 2.0 mL centrifuge tube pre-filled with 5 μL of 0.1 M NaN3 solution. Quantitative analysis was performed using high-performance liquid chromatography (HPLC).

[0041] like Figure 8 As shown, the Fe1-Ag1 / CN activated PMS system exhibited high degradation efficiency of p-chlorophenol, with a degradation rate of 0.97 min. -1 These are 32 times that of Fe1 / CN and 48 times that of Ag1 / CN, respectively.

[0042] Quenching experiment ( Figure 9 The results show that sodium azide (NaN3, 1 O2 quencher) reduced the degradation efficiency of Fe1 / CN, Ag1 / CN, and Fe1+Ag1 / CN systems to 0%, indicating that 1 O2 is its main active species. However, in the Fe1-Ag1 / CN activated PMS system, even with 50 times the amount of NaN3 compared to PMS, the degradation ability was not completely lost, revealing that in this system... 1 O2 is generated relatively quickly.

[0043] The concentrations of each reaction system were measured using both cumulative concentration (DPBF) and steady-state concentration (FFA). 1 O2 production was tested. For example... Figure 10 As shown, Fe1-Ag1 / CN exhibits the highest 1 O2 concentration, corresponding to a generation rate of 374.6 μM min. -1 O2 •- Yield results ( Figure 11 The data shows that, although O2 •- The yield is only in the μM range, but with the addition of O2 •- The quencher significantly inhibits the reaction, indirectly indicating that O2 •- Only intermediates, all converted to 1 O2. PMS consumption results ( Figure 12 This indicates that the PMS consumption trend is consistent with the catalytic activity, ruling out the surface state contribution of unactivated PMS. Notably, Ag1 / CN showed almost no ability to remove p-chlorophenol, yet consumed nearly 0.075 mM of PMS, suggesting that it primarily generated O2. •- .

[0044] To explore 1To investigate the sources of O2 generation, a comparative experimental group was designed that introduced nitrogen (N2) and oxygen (O2). Figure 13 The results showed that N2 or O2 atmospheres had no significant effect on the removal efficiency, indicating that O2 is not the primary air source for removal. 1 The source of O2. Further setting NaNO2 (SO5) •- Quenching agent) and NBT (O2) •- Quenching agent) control experiment ( Figure 14 The results showed that the Fe1-Ag1 / CN activated PMS system significantly promoted the PMS→O2 conversion. •- The process suggests that the electronic structure of Ag was optimized. Combined with... 1 O2 generation analysis, Fe1-Ag1 / CN activated PMS generation 1 During the O2 process, O2 •- → 1 The O2 pathway contributes 90%, while SO5 in the Fe1 / CN system... •- → 1 The O2 pathway accounts for 92%, indicating that the introduction of Ag atoms on top of Fe atoms promotes... 1 O2 generation pathway from SO5 •- Dominant shift to O2 •- Dominated, achieved 1 High yield and high output of O2.

[0045] Based on the above high yield and high output generation 1 A continuous flow reactor was designed and constructed using an O2-activated Fe1-Ag1 / CN PMS system to react antibiotics (sulfadiazine, sulfamethoxazole, tetracycline, ciprofloxacin, enrofloxacin, etc.). Figure 15 Degradation experiments were conducted on phenolic pollutants (phenol, 2,4-dichlorophenol, 2,6-dichlorophenol, 3,5-dichlorophenol, and 2,3,5-trichlorophenol, etc.). Figure 16 The results showed that the system achieved a degradation efficiency of nearly 100% within both 60 and 120 minutes. Furthermore, for actual wastewater (dyeing and printing wastewater, electroplating wastewater, secondary sedimentation tank effluent, industrial wastewater A, and industrial wastewater B, etc.) Figure 17 This system also exhibits excellent ability to remove contaminants such as p-chlorophenol and sulfadiazine.

[0046] The above results confirm that the iron-silver diatomic catalyst constructed based on the ligand complexation effect of this invention has the ability to efficiently degrade pollutants such as p-chlorophenol and sulfadiazine. Among them, the Fe1-Ag1 / CN prepared in Example 1 has the best performance and shows good application potential in actual wastewater treatment.

[0047] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing an iron-silver diatomic catalyst based on ligand complexation effect, characterized in that, Includes the following steps: S1: Dissolve disodium ethylenediaminetetraacetate in deionized water to prepare a disodium ethylenediaminetetraacetate solution, then add ferric nitrate nonahydrate, stir at room temperature until dissolved, then add silver nitrate and continue stirring to obtain the first solution; wherein the molar ratio of disodium ethylenediaminetetraacetate to iron salt and silver salt is 3:1~5:1; S2: Dissolve cyanuric acid in deionized water to prepare a cyanuric acid solution; mix the first solution with the cyanuric acid solution and stir to obtain a second solution; S3: Melamine is dissolved in deionized water to prepare a melamine solution; the second solution is added to the melamine solution, and the mixture is stirred at room temperature to generate a precipitate; the precipitate is obtained by filtration and drying. S4: The first supramolecular solid obtained in step S3 is subjected to gradient heating, heat preservation and cooling to obtain the first iron-silver diatomic catalyst based on ligand complexation effect, denoted as Fe1-Ag1 / CN.

2. The method according to claim 1, characterized in that, In step S2, the temperature at which the first solution is mixed and stirred with the cyanuric acid solution is 35~45℃.

3. The method according to claim 1, characterized in that, In step S3, the second solution is added to the melamine solution by dripping at a rate of 5-10 mL / min.

4. The method according to claim 1, characterized in that, In step S4, the heating rate of the gradient heating is 2~5℃ / min; the heating endpoint is 500~700℃; and the holding time is 2~7 hours.

5. A method for preparing an iron-silver diatomic catalyst based on ligand complexation effect, characterized in that, Includes the following steps: S1: Add ferric nitrate nonahydrate and silver nitrate to two portions of o-phenanthroline solution respectively, stir to dissolve and obtain o-phenanthroline iron solution and o-phenanthroline silver solution; wherein the molar ratio of o-phenanthroline to ferric nitrate nonahydrate and o-phenanthroline to silver nitrate are 2:1~6:1; S2: Dissolve cyanuric acid in deionized water to prepare a cyanuric acid solution; simultaneously add the o-phenanthroline iron solution and o-phenanthroline silver solution to the cyanuric acid solution and stir to obtain a third solution; S3: Prepare a melamine solution; add the third solution to the melamine solution and stir to generate a precipitate; filter and dry to obtain a second supramolecular solid; S4: The second supramolecular solid obtained in step S3 is subjected to gradient heating, holding and cooling to obtain the second iron-silver diatomic catalyst based on the ligand complexation effect, denoted as Fe1+Ag1 / CN.

6. An iron-silver diatomic catalyst obtained by any one of claims 1 to 5.

7. The iron-silver diatomic catalyst according to claim 6, characterized in that, In the catalyst, Fe and Ag are both dispersed in the form of single atoms on the carbon nitride support; the coordination structure of Fe sites is Fe-N4 or Fe-Ag, and the Ag sites are Ag-Fe, Ag-N3-O1 or Ag-N2-C2.

8. The application of an iron-silver diatomic catalyst prepared according to any one of claims 1 to 5 in the treatment of phenolic pollutants and antibiotics in organic wastewater.

9. The application according to claim 8, characterized in that, The specific application is as follows: the reaction system does not require an external light source, and achieves efficient oxidation degradation in synergy with PMS only under normal temperature and light-protected conditions; the specific process is as follows: the iron-silver diatomic catalyst and PMS are added together to the phenolic or antibiotic wastewater system, and the reaction is stirred at 15~25℃ for 60~180 minutes, which can effectively remove phenols and antibiotics from the wastewater.

10. The application according to claim 9, characterized in that, The concentration of the iron-silver diatomic catalyst is 0.3-0.7 g / L, and the concentration of the PMS is 1800-2200 mmol / L.

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