Iron-based coordination assembly, preparation method and application thereof

Abstract

The application relates to the technical field of water treatment, and discloses an iron-based coordination assembly as well as a preparation method and application thereof. The iron-based coordination assembly comprises ferrous ions as central ions, and perfluoroalkyl sulfonic acid and / or perfluoroalkyl carboxylic acid with a perfluorinated carbon chain having 7 or 8 carbon atoms as ligand compounds; and the iron-based coordination assembly forms an active catalytic system in an aqueous solution with a pH value of 4.0-5.0. The iron-based coordination assembly provided by the application retains the active 3d electron configuration of Fe 2+ , and effectively breaks the dense hydration layer around Fe 2+ by using the extremely strong hydrophobic effect of the carbon-fluorine chain of the ligand compound, so that a hydrophobic microenvironment rich in NO2 ‑ is constructed at the active site, thereby greatly optimizing the electron transfer path, and successfully solving the key bottleneck of slow reaction rate and low mass transfer efficiency in the traditional Fe 2+ nitrite reduction technology.

Description

Technical Field

[0001] This invention relates to the field of water treatment technology, and in particular to an iron-based coordination assembly, its preparation method, and its application. Background Technology

[0002] Nitrite (NO2) - Nitrite is a typical environmental pollutant in water bodies. Its excessive presence not only leads to eutrophication but can also accumulate in organisms through the food chain, posing a potential threat to human health, such as inducing methemoglobinemia and even increasing the risk of cancer. Therefore, developing efficient, economical, and environmentally friendly nitrite removal technologies is of significant environmental and practical importance. Currently, technologies based on ferrous ions (Fe²⁺) are being developed... 2+ The chemical reduction method of Fe has attracted widespread attention due to its low cost and relatively harmless reaction products (such as the generation of NO or N2). Its basic reaction mechanism is Fe... 2+ As an electron donor, NO2 - It is reduced to gaseous nitrogen compounds, thereby achieving denitrification of water bodies.

[0003] However, in practical applications, traditional Fe 2+ The reduction system faces two significant technical bottlenecks. First, Fe... 2+ In aqueous solution, it is usually represented as [Fe(H₂O)₆] 2+ The octahedral complex exists stably, and its tightly bound hydration layer severely hinders the reaction of nitrite and Fe. 2+ Direct contact between active sites leads to low mass transfer efficiency, increased electron transfer energy barrier, and slow overall reaction kinetics; secondly, Fe 2+ It is readily oxidized to Fe by dissolved oxygen in water. 3+ This results in the loss of reducing activity, leading to poor system stability and limited continuous processing capacity.

[0004] To address these issues, existing research has attempted to introduce various ligands with Fe. 2+ Coordination is used to modulate the electronic structure of Fe and enhance its stability. Commonly used ligands, such as ethylenediaminetetraacetic acid (EDTA) and citric acid, can protect Fe through strong coordination. 2+ It is not oxidized, but often excessively occupies Fe. 2+ The coordination orbitals lead to its 3D 6 The change in electronic configuration shields the active sites, thus inhibiting its ability to reduce nitrite. On the other hand, while some surfactant ligands possess certain hydrophobic properties, their molecular structures are not specifically designed for Fe... 2+ Optimizing the interfacial properties of water complexes cannot effectively break down the hydration layer or achieve local enrichment of reactants, thus having a limited effect on improving the reaction rate.

[0005] Therefore, existing technologies have not yet been able to achieve Fe 2+ Simultaneous optimization of reducing activity and stability to develop a method that can retain Fe 2+ Active sites can also overcome hydration layer barriers and promote NO2 production through reasonable interface engineering. - The mass transfer and enrichment of nitrite in water through the Fe(II)-based coordination system is of great significance for environmental protection and human health and safety. Summary of the Invention

[0006] The present invention aims to at least solve one of the aforementioned technical problems existing in the prior art. Therefore, one objective of the present invention is to provide an iron-based coordination assembly.

[0007] The second objective of this invention is to provide a method for preparing such iron-based coordination assemblies.

[0008] A third objective of this invention is to provide applications of such iron-based coordination assemblies.

[0009] The fourth objective of this invention is to provide a method for synergistically treating nitrite-contaminated wastewater and perfluoroalkyl acid-contaminated wastewater.

[0010] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A first aspect of the present invention provides an iron-based coordination assembly comprising a ferrous ion as the central ion and perfluoroalkyl sulfonic acid and / or perfluoroalkyl carboxylic acid with a carbon chain having 7 or 8 carbon atoms as ligand compounds; the iron-based coordination assembly constitutes an active catalytic system in an aqueous solution with a pH of 4.0-5.0.

[0011] In some embodiments of the present invention, the molar ratio of the central ion to the ligand compound is 1:(1-2).

[0012] In some embodiments of the present invention, the ligand compound is selected from at least one of perfluoroheptylsulfonic acid (PFHpS), perfluoroheptanoic acid (PFHpA), perfluorooctanesulfonic acid (PFOS), and perfluorooctanoic acid (PFOA).

[0013] A second aspect of the present invention provides a method for preparing the iron-based coordination assembly described in the first aspect of the present invention, comprising the following steps: S1. Dissolving water-soluble ferrous salts in water forms [Fe(H2O)6]. 2+ Complex solution; S2. The ligand compound is pre-dried and then dispersed in water, and the resulting dispersion is added dropwise to the [Fe(H2O)6] solution. 2+ In the complex solution, the pH of the system was simultaneously adjusted to 4.0-5.0, and the reaction was carried out to obtain the iron-based coordination assembly.

[0014] In some embodiments of the present invention, in step S1, the inert atmosphere includes nitrogen; the inert atmosphere is introduced to make the oxygen content of the system ≤0.5mg / L.

[0015] In some embodiments of the present invention, in step S1, the water-soluble ferrous sulfate includes at least one of ferrous sulfate, ferrous chloride, ferrous nitrate, and ferrous perchlorate.

[0016] In some embodiments of the present invention, in step S1, the process of dissolving the water-soluble ferrous iron in water is aided by stirring at a speed of 400-600 r / min for 5-15 min.

[0017] In some embodiments of the present invention, in step S1, the [Fe(H2O)6] 2+ The concentration of the complex solution is 3-8 mmol / L.

[0018] In some preferred embodiments of the present invention, in step S1, the [Fe(H2O)6] 2+ The concentration of the complex solution is 4-6 mmol / L.

[0019] In some embodiments of the present invention, in step S2, the temperature of the pre-drying treatment is 70-90°C and the time is 15-30 hours.

[0020] In some preferred embodiments of the present invention, in step S2, the temperature of the pre-drying treatment is 75-85°C and the time is 20-30 hours.

[0021] In some embodiments of the present invention, step S2 includes the pre-drying process being carried out under vacuum conditions.

[0022] Specifically, pre-drying removes trace amounts of moisture from the ligand compound, ensuring the exposure of lone pair electrons of the sulfonic acid / carboxyl groups in the ligand molecule, thus guaranteeing its hydrophobicity and Fe... 2+ - The interfacial compatibility of water complexes helps avoid excessive aggregation that could lead to the shielding of active sites.

[0023] In some embodiments of the present invention, in step S2, the concentration of the dispersion is 0.03-0.08 mmol / L.

[0024] In some preferred embodiments of the present invention, in step S2, the concentration of the dispersion is 0.04-0.06 mmol / L.

[0025] In some embodiments of the present invention, in step S2, the dripping rate is 0.4-0.8 mL / min.

[0026] In some preferred embodiments of the present invention, in step S2, the dripping rate is 0.4-0.6 mL / min.

[0027] In some embodiments of the present invention, step S2, adjusting the pH value of the system to 4.0-5.0 includes adding a pH adjuster; the pH adjuster includes 0.15-0.25 mol / L dilute sulfuric acid.

[0028] In some embodiments of the present invention, the reaction time in step S2 is 30-60 min.

[0029] In some preferred embodiments of the present invention, the reaction time in step S2 is 40-50 min.

[0030] In some embodiments of the present invention, in step S2, the process of adding the dispersion, adjusting the pH of the system, and the reaction is accompanied by stirring at a speed of 400-600 r / min.

[0031] In some embodiments of the present invention, step S2, after the reaction is completed, further includes filtering and nitrogen purging to remove residual dissolved oxygen.

[0032] In some embodiments of the present invention, in step S2, the filtration includes using an organic phase filter membrane with a pore size of 0.20-0.25 μm.

[0033] In some embodiments of the present invention, in step S2, the nitrogen purging flow rate is 5-15 mL / min and the time is 20-40 min.

[0034] In some preferred embodiments of the present invention, in step S2, the nitrogen purging flow rate is 8-12 mL / min and the time is 25-35 min.

[0035] A third aspect of the present invention provides the application of the iron-based coordination assembly described in the first aspect of the present invention in the treatment of nitrite-contaminated wastewater.

[0036] In some embodiments of the present invention, the application includes mixing the iron-based coordination assembly with nitrite-contaminated wastewater, catalytically reducing the nitrite, and then removing the residual iron-based coordination assembly ligand compound molecules in the water by adsorption with an adsorbent.

[0037] In some embodiments of the present invention, the nitrite content (calculated as nitrite nitrogen) in the nitrite-polluted wastewater is 0.2-5 mmol / L; and the amount of the iron-based coordination assembly is 0.4-0.6 mmol.

[0038] In some embodiments of the present invention, the adsorbent includes activated carbon.

[0039] A fourth aspect of the present invention provides a method for synergistically treating nitrite-contaminated wastewater and perfluoroalkyl acid-contaminated wastewater, wherein the main pollutants in the perfluoroalkyl acid-contaminated wastewater are perfluoroalkyl sulfonic acids and / or perfluoroalkyl carboxylic acids with a perfluorinated carbon chain having 7 or 8 carbon atoms; the method includes the following steps: 1) Mix the nitrite-contaminated wastewater with the perfluoroalkyl acid-contaminated wastewater and adjust the pH of the mixed wastewater to 4.0-5.0; 2) Add water-soluble ferrous salt to the mixed wastewater to form an active catalytic system as described in the first aspect of the present invention, thereby reducing and removing nitrite; 3) Add an adsorbent to the mixed wastewater to adsorb and remove perfluoroalkyl acid pollutants.

[0040] In some embodiments of the present invention, the nitrite content (calculated as nitrite nitrogen) in the nitrite-contaminated wastewater is 0.2-0.5 mmol / L.

[0041] In some embodiments of the present invention, the content of perfluoroalkyl acid pollutants in the perfluoroalkyl acid-contaminated wastewater is 0.05-0.01 mmol / L.

[0042] In some embodiments of the present invention, the main pollutants in the perfluoroalkyl acid polluted wastewater are selected from at least one of perfluoroheptylsulfonic acid, perfluoroheptanoic acid, perfluorooctanesulfonic acid, and perfluorooctanoic acid.

[0043] In some embodiments of the present invention, the amount of water-soluble ferrous salt added must satisfy the molar ratio of ferrous ions to perfluoroalkyl sulfonic acid and / or perfluoroalkyl carboxylic acid with 7 or 8 carbon atoms in the perfluorocarbon chain as 1:(1-2).

[0044] The basic principles of this invention are explained as follows: Fe 2+ In aqueous solution, it is usually represented as [Fe(H₂O)₆] 2+ The complex exists stably, with six water molecules tightly surrounding Fe through strong coordination bonds. 2+ At the center, the first coordination layer is formed, which physically blocks the reactant NO2. - Direct contact with Fe 2+ The 3d active orbitals; this invention uses perfluoroalkyl sulfonic acids and / or perfluoroalkyl carboxylic acids with 7 or 8 carbon atoms in the perfluorocarbon chain as ligand compounds, which contain hydrophilic head groups (sulfonic acid groups or carboxyl groups) and superhydrophobic fluorocarbon chains: The sulfonic acid group or carboxyl group at one end of the ligand compound reacts with [Fe(H2O)6] under slightly acidic conditions of pH 4.0-5.0. 2+ Fe 2+The outer empty orbitals form weak coordination bonds (4s / 4p), enabling the ligands to achieve coordination in Fe. 2+ The center is oriented and anchored, thus partially stabilizing Fe. 2 + This slows down the rate of its oxidation, and because this weak coordination does not strongly occupy Fe... 2+ The key 3D orbitals used for electron transfer are thus preserved to the greatest extent possible; The superhydrophobic fluorocarbon chain at the other end of the ligand compound strongly repels surrounding water molecules. This powerful hydrophobic driving force effectively perturbs the originally tightly ordered [Fe(H2O)6] structure. 2+ The hydration shell displaced some of the coordinated water molecules in the Fe... 2+ A localized, low-polarity hydrophobic microenvironment is created around the active site; The formation of a hydrophobic microenvironment greatly reduces NO2. - Approaching Fe 2+ Space resistance and energy barrier, NO2 - It can more easily penetrate the thinned and loosened hydration layer to reach the reaction center. This hydrophobic microenvironment is conducive to the reaction of NO2, which has a certain degree of polarity. - It also produced a certain local enrichment effect, which further increased the local concentration of reactants near the active site, thereby improving the removal effect of nitrite.

[0045] Compared with the prior art, the beneficial effects of the present invention are: 1) The iron-based coordination assembly provided by this invention is assembled in an aqueous solution with a pH of 4.0-5.0 using perfluoroalkyl sulfonic acid and / or perfluoroalkyl carboxylic acid with 7 or 8 carbon atoms in the perfluorocarbon chain as ligand compounds, while retaining Fe... 2+ While utilizing the active 3d electronic configuration, the strong hydrophobic effect of the fluorine-carbon chain of the ligand compound effectively breaks down Fe. 2+ A dense hydration layer surrounds the site, and NO2-enriched areas are formed at the active sites. - The hydrophobic microenvironment significantly optimizes the electron transfer pathway, successfully solving the problem of traditional Fe... 2+ The key bottleneck in nitrite reduction technology is the slow reaction rate and low mass transfer efficiency. 2) The iron-based coordination assembly provided by this invention can be applied to treat nitrite-contaminated wastewater. While achieving efficient nitrite reduction, it fully considers the environmental risks that ligand compounds may pose, and ensures that the effluent quality meets relevant discharge standards through adsorption-enhanced removal; because the ligand compound reacts with Fe... 2+ Through weak coordination assembly, when nitrite is reduced, Fe 2+After being consumed or transformed into other forms, the original weakly coordinated assembly structure is broken. Perfluoroalkyl sulfonic acids and / or perfluoroalkyl carboxylic acids with 7 or 8 carbon atoms in the perfluorocarbon chain that did not participate in the reaction or dissociated from the assembly re-exist in the water as independent molecules or micelles, and the exposed hydrophobic fluorocarbon chains, activated carbon and other adsorbents have huge specific surface areas and highly hydrophobic surfaces, and can remove ligand compound molecules by physically adsorbing hydrophobic fluorocarbon chains, thereby avoiding the introduction of new pollutants into the water; 3) The method for synergistic treatment of nitrite-contaminated wastewater and perfluoroalkyl acid-contaminated wastewater provided by the present invention is based on the principle of iron-based coordination assemblies and combined with adsorbents for deep removal of perfluoroalkyl acid pollutants. It realizes waste-to-waste treatment, and the effluent nitrite and perfluoroalkyl acid pollutant contents meet the emission standards. It has the characteristics of high efficiency, economy and environmental friendliness. Attached Figure Description

[0046] Figure 1 NO2 in the reaction system using the iron-based coordination assembly of Example 1 - Concentration fluctuations; Figure 2 NO2 in the reaction system using the iron-based coordination assembly of Example 2 - Concentration fluctuations; Figure 3 NO2 in the reaction system using the iron-based coordination assembly of Example 3 - Concentration fluctuations; Figure 4 NO2 in the reaction system using the iron-based coordination assembly of Comparative Example 1 - Concentration fluctuations; Figure 5 NO2 in the reaction system using the iron-based coordination assembly of Comparative Example 2 - Concentration fluctuations; Figure 6 NO2 in the reaction system using the iron-based coordination assembly of Comparative Example 3 - Concentration fluctuations; Figure 7 This is a schematic diagram illustrating the principle of how the iron-based coordination assembly of this invention enhances the nitrite reduction rate. Detailed Implementation

[0047] The present invention will be further described in detail below through specific embodiments. Unless otherwise specified, the raw materials, reagents, or apparatus used in the embodiments and comparative examples are all available from conventional commercial sources or can be obtained by existing technical methods. Unless otherwise specified, the test or experimental methods are conventional methods in the art.

[0048] Example 1 This embodiment prepares an iron-based coordination assembly, and the steps are as follows: S11. Under nitrogen protection (oxygen content ≤ 0.5 mg / L), add 1.39 g FeSO4·7H2O to 1 L of deionized water and place on a thermostatic magnetic stirrer. Stir at 500 r / min for 10 min at 25 °C to form [Fe(H2O)6] with a concentration of 5 mmol / L. 2+ Complex solution; S21. Dry 5.0g of perfluoroheptylsulfonic acid under vacuum at 80℃ for 24h to remove trace moisture, and then cool it for later use. S22. Disperse the pre-dried perfluoroheptylsulfonic acid in deionized water to form a dispersion with a concentration of 0.05 mol / L. Under stirring conditions of S23 and 500 r / min, the dispersion was added dropwise to [Fe(H2O)6] at a rate of 2 mL / min. 2+ In the complex solution, perfluoroheptylsulfonic acid reacts with Fe 2+ The molar ratio was 1.5:1, and 0.2 mol / L dilute sulfuric acid was added simultaneously to adjust the pH of the system to 4.5; S24. After the addition is complete, the reaction is stirred at 25℃ and 500r / min for 45min. After the reaction is complete, the solution is filtered through a 0.22μm organic phase filter membrane and then purged with nitrogen at a flow rate of 10mL / min for 30min to obtain an iron-based coordination assembly with a concentration of 5mmol / L.

[0049] Example 2 This embodiment prepares an iron-based coordination assembly, and the steps are as follows: S11. Under nitrogen protection (oxygen content ≤ 0.5 mg / L), add 0.995 g FeCl2·4H2O to 1 L of deionized water and place on a thermostatic magnetic stirrer. Stir at 500 r / min for 10 min at 25 °C to form [Fe(H2O)6] with a concentration of 5 mmol / L. 2+ Complex solution; S21. Dry 5.0g of perfluoroheptylsulfonic acid under vacuum at 80℃ for 24h to remove trace moisture, and then cool it for later use. S22. Disperse the pre-dried perfluoroheptylsulfonic acid in deionized water to form a dispersion with a concentration of 0.05 mol / L. Under stirring conditions of S23 and 500 r / min, the dispersion was added dropwise to [Fe(H2O)6] at a rate of 2 mL / min. 2+ In the complex solution, perfluoroheptylsulfonic acid reacts with Fe 2+ The molar ratio was 1.5:1, and 0.2 mol / L dilute sulfuric acid was added simultaneously to adjust the pH of the system to 4.5; S24. After the addition is complete, the reaction is stirred at 25℃ and 500r / min for 45min. After the reaction is complete, the solution is filtered through a 0.22μm organic phase filter membrane and then purged with nitrogen at a flow rate of 10mL / min for 30min to obtain an iron-based coordination assembly with a concentration of 5mmol / L.

[0050] Example 3 This embodiment prepares an iron-based coordination assembly, and the steps are as follows: S11. Under nitrogen protection (oxygen content ≤ 0.5 mg / L), add 1.39 g FeSO4·7H2O to 1 L of deionized water and place on a thermostatic magnetic stirrer. Stir at 500 r / min for 10 min at 25 °C to form [Fe(H2O)6] with a concentration of 5 mmol / L. 2+ Complex solution; S21. Dry 5.0g of perfluorooctanoic acid under vacuum at 80℃ for 24h to remove trace moisture, and then cool it for later use. S22. Disperse the pre-dried perfluorooctanoic acid in deionized water to form a dispersion with a concentration of 0.05 mol / L; Under stirring conditions of S23 and 500 r / min, the dispersion was added dropwise to [Fe(H2O)6] at a rate of 2 mL / min. 2+ In the complex solution, perfluorooctanoic acid reacts with Fe... 2+ The molar ratio was 1.5:1, and 0.2 mol / L dilute sulfuric acid was added simultaneously to adjust the pH of the system to 4.5; S24. After the addition is complete, the reaction is stirred at 25℃ and 500r / min for 45min. After the reaction is complete, the solution is filtered through a 0.22μm organic phase filter membrane and then purged with nitrogen at a flow rate of 10mL / min for 30min to obtain an iron-based coordination assembly with a concentration of 5mmol / L.

[0051] Comparative Example 1 In this comparative example, an iron-based coordination assembly was prepared using the following steps: Under nitrogen protection (oxygen content ≤ 0.5 mg / L), 1.39 g of FeSO4·7H2O was added to 1 L of deionized water and placed on a thermostatic magnetic stirrer. The mixture was stirred at 500 rpm for 10 min at 25 °C. Then, 0.2 mol / L dilute sulfuric acid was added to adjust the pH to 4.5. The mixture was then stirred at 500 rpm for another 45 min at 25 °C. Afterward, the solution was filtered through a 0.22 μm organic phase filter membrane, purged with nitrogen at a flow rate of 10 mL / min for 30 min, and diluted with oxygen-free water to obtain a 5 mmol / L [Fe(H2O)6] solution. 2+ Complex solution.

[0052] Comparative Example 2 In this comparative example, an iron-based coordination assembly was prepared using the following steps: S11. Under nitrogen protection (oxygen content ≤ 0.5 mg / L), add 1.39 g FeSO4·7H2O to 1 L of deionized water and place on a thermostatic magnetic stirrer. Stir at 500 r / min for 10 min at 25 °C to form [Fe(H2O)6] with a concentration of 5 mmol / L. 2+ Complex solution; S21. Dry 5.0g of EDTA under vacuum at 80℃ for 24h to remove trace moisture, and then cool it for later use. S22. Dissolve the pre-dried EDTA in deionized water to form a ligand solution with a concentration of 0.05 mol / L; Under stirring conditions of S23 and 500 r / min, the ligand solution was added dropwise to [Fe(H2O)6] at a rate of 2 mL / min. 2+ In the complex solution, EDTA reacts with Fe 2+ The molar ratio was 1.5:1, and 0.2 mol / L dilute sulfuric acid was added simultaneously to adjust the pH of the system to 4.5; S24. After the addition is complete, the reaction is stirred at 25℃ and 500r / min for 45min. After the reaction is complete, the solution is filtered through a 0.22μm organic phase filter membrane and then purged with nitrogen at a flow rate of 10mL / min for 30min to obtain an iron-based coordination assembly with a concentration of 5mmol / L.

[0053] Comparative Example 3 In this comparative example, an iron-based coordination assembly was prepared using the following steps: S11. Under nitrogen protection (oxygen content ≤ 0.5 mg / L), add 1.39 g FeSO4·7H2O to 1 L of deionized water and place on a thermostatic magnetic stirrer. Stir at 500 r / min for 10 min at 25 °C to form [Fe(H2O)6] with a concentration of 5 mmol / L. 2+ Complex solution; S21. Dry 5.0g of citric acid under vacuum at 80℃ for 24h to remove trace moisture, and then cool for later use. S22. Dissolve pre-dried citric acid in deionized water to form a ligand solution with a concentration of 0.05 mol / L; Under stirring conditions of S23 and 500 r / min, the ligand solution was added dropwise to [Fe(H2O)6] at a rate of 2 mL / min. 2+ In the complex solution, citric acid reacts with Fe 2+The molar ratio was 1.5:1, and 0.2 mol / L dilute sulfuric acid was added simultaneously to adjust the pH of the system to 4.5; S24. After the addition is complete, the reaction is stirred at 25℃ and 500r / min for 45min. After the reaction is complete, the solution is filtered through a 0.22μm organic phase filter membrane and then purged with nitrogen at a flow rate of 10mL / min for 30min to obtain an iron-based coordination assembly with a concentration of 5mmol / L.

[0054] Performance testing The nitrite reduction performance of the iron-based coordination assemblies prepared in Examples 1-3 and Comparative Examples 1-3 was verified as follows: Take 100 mL of the iron-based coordination assembly solutions prepared in Examples 1-3 and Comparative Examples 1-3 respectively and place them in sealed reaction flasks. Purge with nitrogen for 30 min to remove dissolved oxygen, and add NaNO2 reagent to make the NO2 in each system... - The initial concentration was 2.0 mmol / L. The reaction was then carried out at 25℃ and 250 rpm on a shaker. NO2 was measured at regular intervals on the first and second days of the reaction. - Concentration (nitrite colorimetric reagent, colorimetric method measurement): Three parallel experiments were set up for each group, and the values ​​were taken as the average value.

[0055] Table 1. Test results of nitrite reduction performance of iron-based coordination assemblies in Examples 1-3 and Comparative Examples 1-3

[0056] Table 1 shows the nitrite reduction performance test results of the iron-based coordination assemblies in Examples 1-3 and Comparative Examples 1-3. Figure 1 NO2 in the reaction system using the iron-based coordination assembly of Example 1 - Concentration fluctuations, Figure 2 NO2 in the reaction system using the iron-based coordination assembly of Example 2 - Concentration fluctuations, Figure 3 NO2 in the reaction system using the iron-based coordination assembly of Example 3 - Concentration fluctuations, Figure 4 NO2 in the reaction system using the iron-based coordination assembly of Comparative Example 1 - Concentration fluctuations, Figure 5 NO2 in the reaction system using the iron-based coordination assembly of Comparative Example 2 - Concentration fluctuations, Figure 6 NO2 in the reaction system using the iron-based coordination assembly of Comparative Example 3 - The concentration fluctuations are shown in Table 1 and Figures 1-6 It can be seen that in the reaction system using the iron-based coordination assemblies prepared in Examples 1-3, NO2 levels decreased by 2 days.- The total consumption was 1.74 mmol / L, 1.61 mmol / L, and 1.43 mmol / L, respectively, which was significantly higher than that of Comparative Example 2 (1.22 mmol / L) and Comparative Example 3 (1.18 mmol / L) using traditional iron-based complexes, and even better than that using only [Fe(H2O)6]. 2+ Comparative Example 1 (0.93 mmol / L) of the complex shows that the iron-based coordination assembly provided by the present invention has better catalytic reduction performance of nitrite than iron-based complexes in the prior art.

[0057] Figure 7 This is a schematic diagram illustrating the principle of how the iron-based coordination assembly of the present invention enhances the nitrite reduction rate. Figure 7 (a) in the text represents the absence of ligand modification. Figure 7 (b) in the text indicates ligand modification, by Figure 7 It can be seen that, without ligand modification, nitrite needs to collide with Fe to dissolve Fe. 2+ Coordinated water molecules lead to reactions with low mass transfer efficiency, high electron transfer energy barriers, and slow overall reaction kinetics. This invention, however, utilizes perfluoroalkyl sulfonic acids and / or perfluoroalkyl carboxylic acids with 7 or 8 carbon atoms in the perfluorocarbon chain as ligands. Through a synergistic mechanism of weak coordination and superhydrophobicity, it achieves a reaction while retaining Fe... 2+ While enhancing activity, it also breaks down mass transfer barriers, effectively improving the nitrite reduction performance of iron-based coordination assemblies, thus achieving superior performance compared to [Fe(H2O)6]. 2+ The nitrite reduction effect of complexes or traditional iron-based complexes.

[0058] Application Example 1 This application example provides a method for the synergistic treatment of nitrite-contaminated wastewater and perfluoroalkyl acid-contaminated wastewater, as detailed below: 1000 mL of nitrogen-containing wastewater from the factory (nitrite content 0.3 mmol / L) and 1000 mL of fluoride industrial wastewater (total concentration of perfluoroalkyl acid pollutants 0.007 mmol / L) with perfluorooctane sulfonic acid and perfluorooctanoic acid as the main pollutants were collected respectively. The above-mentioned nitrite-contaminated wastewater was mixed with perfluoroalkyl acid-contaminated wastewater, and dissolved oxygen was removed by aeration. The pH of the mixed wastewater was adjusted to about 4.5. Then, FeSO4·7H2O was added to the mixed wastewater, and the amount added was such that the molar ratio of ferrous ions to perfluorooctane sulfonic acid and perfluorooctanoic acid was 1:1.5. After shaking at 220 r / min for 20 days, the nitrite concentration (calculated as nitrite nitrogen) was measured. Then, 20 g of coconut shell activated carbon was added, and after shaking at 220 r / min for 5 days, the total concentration of perfluoroalkyl acid pollutants was measured.

[0059] Table 2. Synergistic treatment effect of nitrite-contaminated wastewater and perfluoroalkyl acid-contaminated wastewater

[0060] Table 2 shows the synergistic treatment effect of nitrite-contaminated wastewater and perfluoroalkyl acid-contaminated wastewater. As can be seen from Table 2, this method effectively reduces the concentration of nitrite in nitrite-contaminated wastewater and the concentration of perfluoroalkyl acid pollutants, mainly perfluorooctane sulfonic acid and perfluorooctanoic acid, in perfluoroalkyl acid-contaminated wastewater. This indicates that the coordination mechanism provided by this invention, with ferrous ions as the central ion and perfluoroalkyl sulfonic acids and / or perfluoroalkyl carboxylic acids with 7 or 8 carbon atoms in the perfluorinated carbon chain as ligands, combined with the adsorption-enhanced removal of perfluoroalkyl acid pollutants, can achieve waste-to-waste treatment.

Claims

1. A iron-based coordination assembly, characterized in that, It includes compounds with ferrous ions as the central ion and perfluoroalkyl sulfonic acids and / or perfluoroalkyl carboxylic acids having 7 or 8 carbon atoms in the perfluorocarbon chain as ligands; the iron-based coordination assemblies constitute an active catalytic system in an aqueous solution with a pH of 4.0-5.

0.

2. The iron-based coordination assembly according to claim 1, characterized in that, The molar ratio of the central ion to the ligand compound is 1:(1-2).

3. The iron-based coordination assembly according to claim 2, characterized in that, The ligand compound is selected from at least one of perfluoroheptylsulfonic acid, perfluoroheptanoic acid, perfluorooctanesulfonic acid, and perfluorooctanoic acid.

4. The method for preparing the iron-based coordination assembly according to any one of claims 1-3, characterized in that, Includes the following steps: S1. Under an inert atmosphere, water-soluble ferrous salts are dissolved in water to form [Fe(H2O)6]. 2+ Complex solution; S2. The ligand compound is pre-dried and then dispersed in water, and the resulting dispersion is added dropwise to the [Fe(H2O)6] solution. 2+ In the complex solution, the pH of the system was simultaneously adjusted to 4.0-5.0, and the reaction was carried out to obtain the iron-based coordination assembly.

5. The preparation method according to claim 4, characterized in that, In step S2, the pre-drying treatment is carried out at a temperature of 70-90°C for 15-30 hours.

6. The preparation method according to claim 4, characterized in that, In step S2, the dripping rate is 0.4-0.8 mL / min.

7. The preparation method according to claim 4, characterized in that, In step S2, the reaction time is 30-60 minutes.

8. The application of the iron-based coordination assembly according to any one of claims 1-3 in the treatment of nitrite-contaminated wastewater.

9. The application according to claim 8, characterized in that, The application involves mixing iron-based coordination assemblies with nitrite-contaminated wastewater, catalytically reducing the nitrite, and then removing residual iron-based coordination assemblies ligand compound molecules from the water by adsorption with an adsorbent.

10. A method for synergistic treatment of nitrite-contaminated wastewater and perfluoroalkyl acid-contaminated wastewater, characterized in that, The main pollutants in the perfluoroalkyl acid-contaminated wastewater are perfluoroalkyl sulfonic acids and / or perfluoroalkyl carboxylic acids with 7 or 8 carbon atoms in the perfluorocarbon chain; the method includes the following steps: 1) Mix the nitrite-contaminated wastewater with the perfluoroalkyl acid-contaminated wastewater and adjust the pH of the mixed wastewater to 4.0-5.0; 2) Add water-soluble ferrous salt to the mixed wastewater to form the active catalytic system as described in claim 1, thereby reducing and removing nitrite; 3) Add an adsorbent to the mixed wastewater to adsorb and remove perfluoroalkyl acid pollutants.

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