A lattice sulfur controllable doped zero-valent iron, a preparation method thereof and application thereof in groundwater perfluorinated compound removal

Abstract

This invention provides a lattice sulfur-controlled doping of zero-valent iron, its preparation method, and its application in the removal of perfluorinated compounds from groundwater. The preparation method involves adding a sulfur source and a reducing agent to a solution containing Fe. 3+ In a salt solution under a protective atmosphere, lattice sulfur-controlled doped zero-valent iron is obtained through a reaction. This invention prepares sulfur-doped modified sulfide nano-zero-valent iron via a simple liquid-phase reduction method, which can further suppress the hydrogen evolution side reaction of zero-valent iron, regulate interfacial electron transfer and solution redox potential, and improve the yield and lifetime of hydrated electrons of key reducing species, thereby further enhancing the defluorination effect on perfluorinated compounds.

Description

Technical Field

[0001] This invention relates to the fields of environmental engineering and materials engineering, and in particular to a lattice sulfur-controlled doping of zero-valent iron, its preparation method, and its application in the removal of perfluorinated compounds from groundwater. Background Technology

[0002] Groundwater is a vital source of freshwater globally; however, the increasing pollution from perfluorinated and polyfluoroalkyl substances (PFAS) poses a significant threat to groundwater safety. Due to the extremely strong carbon-fluorine bonds in their molecular structure, PFAS exhibit high environmental persistence and bioaccumulation. Among them, perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) have the highest detection rates and are subject to the most stringent regulations. In actual groundwater, PFAS are typically present at trace concentrations (ng / L to μg / L) and in large volumes, leading to limitations in mass transfer kinetics. Currently, adsorption is the mainstream process for treating PFAS in groundwater. However, conventional adsorption only achieves phase transfer of pollutants; the waste adsorbent enriched with PFAS still requires energy-intensive subsequent disposal to prevent secondary pollution release.

[0003] UV-activated sulfite reduction techniques, based on hydrated electrons, can directly break the CF bonds in PFAS, showing promising application potential. However, existing technologies combining adsorption with hydrated electron reduction inherently present a "concentration-defluorination" contradiction: conventional adsorbents (such as activated carbon), while having large adsorption capacities, readily quench hydrated electrons due to their high specific surface area, abundant micropores, and oxygen-containing functional groups; suspended carbon particles severely attenuate UV light; and PFAS tend to become deeply embedded within the material's pores, making effective contact with diffusion-limited hydrated electrons difficult, resulting in low defluorination efficiency. In contrast, nano-zero-valent iron (nFe)... 0 The intrinsically electron-rich surface and reducing microenvironment of nFe can theoretically maximize the activity of hydrated electrons. However, conventional nFe... 0 The application of PFAS removal in groundwater has significant drawbacks: its strong surface hydrophilicity leads to poor PFAS adsorption selectivity; it is prone to hydrogen evolution side reactions that consume electrons; and its surface is easily oxidized and passivated, resulting in deactivation. Therefore, there is an urgent need in this field to develop a novel water treatment material and method to synergistically solve the problem of efficient enrichment and in-situ defluorination of trace amounts of PFAS in groundwater. Summary of the Invention

[0004] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a lattice sulfur-controlled doped zero-valent iron, its preparation method, and its application in the removal of perfluorinated compounds in groundwater. This invention aims to solve the technical problems of existing nano-zero-valent iron in the removal of PFAS from groundwater, such as poor adsorption selectivity due to surface hydrophilicity, easy occurrence of hydrogen evolution side reactions that consume electrons, and easy deactivation due to surface oxidation passivation. This invention also breaks through the bottleneck of the difficulty in achieving synergistic "concentration-defluorination" in conventional adsorption materials, and realizes the efficient enrichment and deep defluorination degradation of trace PFAS in groundwater.

[0005] To achieve the above and other related objectives, the present invention provides a method for preparing zero-valent iron with controllable sulfur doping in a lattice, characterized in that a sulfur source and a reducing agent are added to a solution containing Fe. 3+ In a salt solution, under a protective atmosphere, a reaction is carried out to obtain lattice sulfur-controlled doped zero-valent iron.

[0006] This application utilizes a simple liquid-phase reduction method to prepare sulfur-doped modified sulfide nano-zero-valent iron, enabling control over interfacial electron transfer and solution redox potential. This facilitates improved hydrated electron yield and extended lifetime of key active species in subsequent defluorination. The preparation of sulfide nano-zero-valent iron with controllable sulfur content and form allows for the construction of an ideal material interface for perfluorinated compound enrichment and efficient defluorination, which is crucial for the remediation of perfluorinated groundwater.

[0007] Preferably, the sulfur source and Fe 3+ The sulfur-iron molar ratio is (0.004~0.051):1.

[0008] Preferably, the sulfur source is sodium dithionite.

[0009] Preferably, the protective atmosphere is a nitrogen atmosphere.

[0010] Preferably, the reaction process further includes solid-liquid separation and vacuum drying.

[0011] Preferably, solid-liquid separation is performed using a separation method.

[0012] Preferably, the vacuum drying temperature is 55~70℃, more preferably 60℃, and the time is 6~8h.

[0013] The present invention also provides a lattice sulfur-controlled doped zero-valent iron prepared by the above preparation method.

[0014] Preferably, the lattice sulfur-controlled doped zero-valent iron has slit-like pores with a pore size of 0.1~10 nm.

[0015] The present invention also provides an application of the above-mentioned lattice sulfur-controlled doping of zero-valent iron in the removal of perfluorinated compounds from groundwater.

[0016] Preferably, the concentration of perfluorinated compounds in the groundwater is 50 μg / L. -1 .

[0017] Preferably, the lattice sulfur-controlled doped zero-valent iron is used to adsorb perfluorinated compounds in groundwater in situ, and then the compounds are recovered by magnetic separation. The recovered lattice sulfur-controlled doped zero-valent iron is added to a solution containing sodium sulfite, and the adsorbed perfluorinated compounds are defluorinated under ultraviolet light irradiation.

[0018] Preferably, lattice sulfur-controlled doped zero-valent iron is mixed with PFAS-containing groundwater to enrich PFAS in situ on the material surface; after enrichment, the material is recovered by magnetic separation; subsequently, sodium sulfite solution is added, and under UV irradiation, the generated strongly reducing species adsorb and degrade the enriched PFAS. This application designs an "enrichment-degradation" strategy, firstly using sulfide nano-zero-valent iron as a groundwater remediation material to enrich perfluorinated compounds in groundwater in situ, then recovering the material through magnetic separation, and ex-situ binding with hydrated electrons of strongly reducing species generated by UV activation of sulfite, thereby achieving efficient defluorination of the perfluorinated compounds enriched on the material.

[0019] As described above, the present invention has the following beneficial effects:

[0020] (1) By controlling the sulfur in the lattice, the hydrophobicity and electron transport capacity of the material interface can be enhanced, a reducing microenvironment conducive to the generation and survival of hydrated electrons can be constructed, the hydrogen evolution side reaction can be reduced, and the defluorination efficiency of PFAS can be improved.

[0021] (2) The slit-like shallow pores on the material surface can achieve efficient enrichment of PFAS and keep it exposed to the reaction interface, reducing mass transfer limitations.

[0022] (3) The process of “in-situ enrichment-magnetic separation and recovery-ex-situ light irradiation defluorination” can take into account both pollutant removal and material recycling, reduce the risk of secondary pollution, and is suitable for the remediation of trace PFAS pollution in groundwater. Attached Figure Description

[0023] Figure 1 The diagram shows a schematic of the preparation of sulfide nano-zero-valent iron by liquid-phase reduction.

[0024] Figure 2 The TEM and elemental distribution diagrams of lattice sulfur-controlled doped zero-valent iron in Examples 1-5 (b-f) and nano-zero-valent iron in Comparative Example 1 (a) are shown.

[0025] Figure 3 The graph shows the linear relationship between the theoretical S / Fe molar ratio and the actual S / Fe molar ratio. The strong linear correlation indicates that the controllable preparation of SNZVI can be achieved.

[0026] Figure 4 The zero-valent iron content is shown as SNZVI for different S / Fe molar ratios.

[0027] Figure 5 The XRD patterns of lattice sulfur-controlled doped zero-valent iron in Examples 1-5 and nano-zero-valent iron in Comparative Example 1 are shown.

[0028] Figure 6 The water contact angles are shown for lattice sulfur-controlled doped zero-valent iron in Examples 1-5 and nano-zero-valent iron in Comparative Example 1.

[0029] Figure 7 The specific surface area (a), pore size (b), and total pore volume (c) of sulfided nano-zero valent iron with different S / Fe molar ratios are shown.

[0030] Figure 8 The N2 adsorption-desorption isotherms are shown for lattice sulfur-controlled doped zero-valent iron in Examples 1-5 (b-f) and nano-zero-valent iron in Comparative Example 1 (a).

[0031] Figure 9 The images show the Fe K-edge extended X-ray absorption fine structure (EXAFS) spectra and wavelet transform images of zero-valent iron nanoparticles with different S / Fe molar ratios.

[0032] Figure 10 The figures show the electrochemical impedance and solution redox potential of sulfide nano-zero ferric iron with different S / Fe molar ratios. Figure a shows the electrochemical impedance of sulfide nano-zero ferric iron with different S / Fe molar ratios. The results indicate that the material resistance decreases with increasing sulfur-iron molar ratio, suggesting enhanced interfacial electron transfer capability. Figure b shows the solution redox potential of sulfide nano-zero ferric iron with different S / Fe molar ratios. With increasing sulfur content, the redox potential shifts significantly negatively, indicating the formation of a stronger reducing microenvironment.

[0033] Figure 11 The diagram shows the accumulation of sulfide nano-zero-valent iron from groundwater contaminated with perfluorinated compounds.

[0034] Figure 12 The diagram shows the defluorination of nano-zero-valent iron particles enriched with perfluorinated compounds in UV / sulfite.

[0035] Figure 13 The diagram shows the breakthrough curves of perfluorooctanoic acid (PFOA) and PFOA in the adsorption columns of three materials with different sulfur-iron molar ratios in Comparative Example 1, Example 2, and Example 5.

[0036] Figure 14 The figure shows the 10% breakthrough bed volume of perfluorooctanoic acid and perfluorooctane sulfonic acid in adsorption columns of three different sulfur-iron molar ratio materials.

[0037] Figure 15The adsorption kinetics curves of perfluorooctanoic acid and perfluorooctane sulfonic acid in lattice sulfur-controlled doped zero-valent iron in Examples 1-5 and nano-zero-valent iron in Comparative Example 1 are shown: a represents the adsorption kinetics curve of perfluorooctanoic acid, and b represents the adsorption kinetics curve of perfluorooctane sulfonic acid.

[0038] Figure 16 The following are the defluorination kinetic curves of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) in six different sulfur-iron molar ratio material-UV / sulfite systems: a represents the defluorination kinetic curve of PFOA over time, and b represents the defluorination kinetic curve of PFOS over time.

[0039] Figure 17 The figures show the removal and defluorination rates of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) in six different sulfur-iron molar ratio material-UV / sulfite systems. a represents the removal and defluorination rates of PFOA, and b represents the removal and defluorination rates of PFOS.

[0040] Figure 18 The figures show the fluorine balance of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) in six different sulfur-iron molar ratio material-UV / sulfite systems: a) shows the fluorine balance of PFOA over different time periods, and b) shows the fluorine balance of PFOS over different time periods.

[0041] Figure 19 The image shows the identification of hydrated electrons using electron paramagnetic resonance.

[0042] Figure 20 This demonstrates the universality of the sulfide nano-zero-valent iron-UV / sulfite system in different groundwater matrices.

[0043] Figure 21 This demonstrates the universality of the sulfide nano-zero-valent iron-UV / sulfite system for the removal of 25 perfluorinated compounds.

[0044] Figure 22 The diagram shows a process where sulfide nano-zero-valent iron is first used to enrich PFAS in in-situ from groundwater, then recovered through magnetic separation, and finally defluorinated by hydrated electron-reducing species on adsorbed PFAS. Detailed Implementation

[0045] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0046] It should be noted that the process equipment or apparatus not specifically mentioned in the following embodiments are all conventional equipment or apparatus in the art.

[0047] Furthermore, it should be understood that the existence of other method steps before or after the combined steps, or the insertion of other method steps between these explicitly mentioned steps, does not preclude the existence of other method steps before or after the combined steps, or the insertion of other method steps between these explicitly mentioned steps, unless otherwise stated. It should also be understood that the combined connection relationship between one or more devices / apparatus mentioned in this invention does not preclude the existence of other devices / apparatus before or after the combined devices / apparatus, or the insertion of other devices / apparatus between these explicitly mentioned devices / apparatus, unless otherwise stated. Moreover, unless otherwise stated, the numbering of each method step is merely a convenient tool for identifying each method step, and not for limiting the order of the method steps or limiting the scope of the invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the invention.

[0048] Example 1

[0049] This embodiment provides a method for preparing zero-valent iron with controllable sulfur doping in the crystal lattice, including the following steps:

[0050] First, weigh 5.8 g of anhydrous ferric chloride and dissolve it in 200 mL of deionized water to obtain 29 g·L⁻¹. -1 The ferric chloride solution was prepared by placing it in a 1 L three-necked flask and stirring continuously at 350 rpm under nitrogen purging; 200 ml of 34 g·L⁻¹ ferric chloride solution was then added. -1 Sodium borohydride and 1.6 g·L -1 The mixed solution of sodium dithionite was passed through a constant pressure funnel at a rate of 10 mL / min. -1 Add dropwise at a rate of 200 ml (29 g·L). -1 Synthesize in ferric chloride solution under nitrogen atmosphere with stirring at 350 rpm (≈10 mL min). -1 The sulfur-iron molar ratio was 0.10:1. Solid-liquid separation was performed using a magnet, and the mixture was washed three times with ultrapure water. The solid was then dried in a vacuum drying oven at 60 °C for 8 hours to obtain a dry solid, which was then ground into powder to prepare lattice sulfur-controlled doped zero-valent iron (SNZVI), denoted as [S / Fe]. 实测 =0.004.

[0051] Examples 2-5

[0052] The difference between Examples 2-5 and Example 1 lies in the amount of sodium dithionite added, with sulfur-iron molar ratios of 0.035:1, 0.05:1, 0.07:1, and 0.14:1, respectively. The resulting lattice-controlled sulfur-doped zero-valent iron is labeled as [S / Fe]. 实测 =0.013, 0.018, 0.025, 0.051.

[0053] Comparative Example 1

[0054] The difference between Comparative Example 1 and Example 1 is that sodium dithionite was not added, thus providing a method for preparing nano-zero valent iron, including the following steps: preparing 200 ml of 29 g L... -1 A ferric chloride solution was placed in a 1 L three-necked flask and stirred continuously at 350 rpm under nitrogen purging. 6.8 g of sodium borohydride (NaBH4) was weighed and placed in a beaker, dissolved in 200 mL of ultrapure water, and then distilled through a constant pressure funnel at 10 mL / min. -1 The solution was added dropwise at a constant rate to a ferric chloride solution. After the reaction was complete, black solid particles were obtained. These particles were separated into solid and liquid phases using a magnet, washed three times with ultrapure water, and then dried in a vacuum drying oven at 60 °C for 8 hours to obtain nano-zero valent iron (NZVI), denoted as [S / Fe]. 实测 =0.

[0055] Before transferring the material into the anaerobic glove box, it was slowly filled with air in a vacuum for 2 hours to allow for partial oxidation and stabilization. The dried granules were ground into powder using a pestle in a mortar and stored in sealed vials in the anaerobic glove box. See details [link to anaerobic glove box]. Figure 1 .

[0056] The specific chemical reaction formula is as follows:

[0057] .

[0058] TEM characterization and elemental mapping of the lattice sulfur-controlled doped zero-valent iron (SNZVI) in Examples 1-5 and the comparative nano-zero-valent iron (NZVI) revealed that... Figure 2 Part a shows that unmodified sulfur-containing zero-valent iron nanoparticles exhibit a characteristic chain-like structure with an oxide shell. Figure 2 The b~f portion indicates that sulfur is uniformly incorporated into the body-centered cubic lattice of nano-zero valent iron, resulting in a significant increase in particle size. This sulfur impregnation alters the local environment of the Fe crystals.

[0059] The zero-valent iron content of NZVI and several different sulfur-iron ratios (0.01, 0.035, 0.05, 0.07, 0.14) was determined and analyzed. Figure 3 As shown in the figure. The results show a linear negative correlation between the zero-valent iron content and the actual sulfur-iron ratio. The actual sulfur content of nano-zero-valent iron and several different sulfur-iron ratios (0.01, 0.035, 0.05, 0.07, 0.14) was determined and analyzed, as shown in the figure. Figure 4 As shown in the figure. The results show that there is a linear positive correlation between the actual S / Fe ratio and the S / Fe dosage ratio, with the actual measured ratio being approximately 38% of the dosage.

[0060] like Figure 5 As shown, the peak shifts of the characteristic peaks of the zero-valent iron Fe(110) crystal plane in the XRD diffraction pattern indicate that sulfur impregnation has altered the body-centered cubic structure of zero-valent iron, demonstrating the lattice expansion after incorporation of different sulfur contents.

[0061] The contact angles between water and the lattice-controlled sulfur-doped zero-valent iron (SNZVI) of Examples 1-5 and the comparative example nano-zero-valent iron (NZVI) were measured respectively to analyze the effect of sulfidation on the hydrophobicity of the nanomaterials. The results are as follows: Figure 6 As shown, the water contact angle of nano-zero-valent iron is approximately 16.3°, indicating hydrophilicity. In contrast, the water contact angle of high-sulfur content is measured at 94°, showing relative hydrophobicity. This suggests that the sulfidated nanomaterials are more hydrophobic and have a stronger adsorption capacity for hydrophobic pollutants / groups such as perfluorinated compounds.

[0062] The specific surface area, total pore volume, and average pore size of lattice sulfur-controlled doped zero-valent iron (SNZVI) from Examples 1-5 and the comparative example nano-zero-valent iron (NZVI) were measured respectively, and the results are as follows: Figure 7 As shown, with the increase of S content, the specific surface area and total pore volume gradually decrease. Figure 8 The sulfide nano-zero-valent iron exhibits similar type IV N2 adsorption-desorption isotherms and type H3 hysteresis loops, indicating that the sulfide nano-zero-valent iron belongs to mesoporous materials with slit-like pores. The pore sizes of several nanomaterials are mainly distributed between 0 and 10 nm.

[0063] By combining wavelet transform images, materials with measured ratios of zero-valent iron and sulfur-iron of 0.013 and 0.051 were selected and characterized using FeK edge-extended X-ray absorption fine structure (EXAFS) spectroscopy to represent the speciation of sulfur and the local iron coordination environment. The results are as follows: Figure 9 As shown, the Fe K-edge EXAFS fitting was significantly improved by using the Fe-S scattering paths corresponding to FeS and FeS2, confirming that the main sulfides in the materials with sulfur-to-iron ratios of 0.013 and 0.051 are FeS and FeS2, respectively. The fitting results further revealed changes in the surface iron coordination number and Fe–Fe bond length, indicating that sulfur incorporation mainly induced lattice reconstruction rather than simple surface passivation. The sulfur content and morphology of the sulfur in the prepared sulfide nano-zero valent iron obtained in the above examples differ from those in the controllable morphology of the sulfur, demonstrating that the sulfur morphology of sulfide nano-zero valent iron can be controlled by adjusting the type of sulfur reagent.

[0064] Figure 10 The electrochemical impedance and solution redox potential of sulfide nano-zero valent iron with different S / Fe molar ratios are shown. Figure 10Part a in the figure represents the electrochemical impedance of sulfide nano-zero valent iron with different S / Fe molar ratios. The electrochemical impedance results show that as the sulfur-iron molar ratio increases, the material resistance decreases, indicating that the interfacial electron transfer capability is enhanced. Figure 10 Part b in the figure represents the solution redox potential of zero-valent iron nanoparticles with different S / Fe molar ratios. With increasing sulfur content, the redox potential shifts significantly negatively, forming a stronger reducing microenvironment. This result indicates that lattice sulfur doping can promote electron migration and maintain the activity of hydrated electrons, which is beneficial for the efficient defluorination of PFAS in the subsequent process.

[0065] Adsorption experiment

[0066] Dynamic breakthrough experiment of adsorption column: A dynamic concentration column for perfluorinated compounds was constructed in an plexiglass column (15.0 cm long, 2.48 cm inner diameter). The column was filled with quartz sand doped with 2% nano-zero ferric sulfide. The corresponding experimental setup is as follows: Figure 11 As shown. As a common matrix material, quartz sand has limited adsorption capacity for perfluoroalkyl compounds, and its effect can be ignored. Perfluoro compounds (concentration 50 μg / L) were added. -1 ) water at 3.0 mL·min -1 The solution was pumped into the column at a flow rate of 1000 m / s and 1.0 mL of filtrate was collected at predetermined time intervals and stored at 4 °C for HPLC-MS / MS analysis.

[0067] Adsorption kinetics: A 100 mL solution of perfluorooctanoic acid (PFOA) / perfluorooctane sulfonic acid (PFOS) with an initial concentration of 10 ppm was prepared and placed in a 200 mL serum bottle. Nitrogen gas was continuously purged for 30 min. 0.1 g of nano-zero ferric iron or sulfide nano-zero ferric iron was dispensed from a glove box and quickly weighed into the serum bottle. The bottle was sealed and placed on a rotary shaker (30 rpm) for reaction. At specific reaction time points, 2 mL of sample was taken, filtered through a 0.22 μm polyether sulfone (PES) membrane, and the PFOA / PFOS concentration and fluoride ion concentration were determined.

[0068] Defluorination experiment

[0069] Photoreactor: Degradation experiments were conducted in a cylindrical glass container with a diameter of 60 mm and a width of 230 mm. A UV lamp (TUV PL-S 10 W, 254 nm, Philips) was placed in the center of the glass container and fitted with a quartz sleeve to prevent contact with the solution. A 170 mm long, 10 mm diameter perforated tube was used to introduce nitrogen gas into the reactor through the sampling port to agitate the material and reduce mass transfer limitation. For safety, the reactor was wrapped with aluminum foil. The reactor was placed in an ice-water bath to maintain the temperature at 20 °C.

[0070] Specific procedures: Prepare 300 mL of a 20 mM sodium sulfite solution in a 500 mL beaker. Adjust the pH to 12 with hydrochloric acid and sodium hydroxide, and purge with nitrogen for at least 30 min. After the nanomaterials in the system have fully adsorbed and reached equilibrium with perfluorooctanoic acid / perfluorooctane sulfonic acid, recover the perfluorooctanoic acid / perfluorooctane sulfonic acid using a powerful magnet through magnetic separation. Add the recovered perfluorooctanoic acid to the pre-prepared sodium sulfite solution and transfer it to the photoreactor. Continuously purge with nitrogen during the reaction process and seal the sampling port with a sealing film. At specific time points in the reaction, take 5 mL of sample, filter it through a 0.22 μm PES membrane, and store it at 4°C. Within 24 h, determine the F in the sample using ion chromatography (IC) and an ionization electrode (ISE). - The concentration. A flowchart is shown below. Figure 12 As shown.

[0071] Different sulfur ratios ([S / Fe]) were used. 实测 The adsorption capacities of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) were evaluated using adsorption columns of sulfide nano-zero-valent iron materials (α = 0, 0.013, and 0.051). The results are as follows: Figure 13 As shown. Under low sulfur content conditions ([S / Fe]), 实测 = 0.013), both perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) exhibited earlier breakthrough behavior, indicating that the iron sulfide formed by moderate sulfidation slightly weakens the adsorption affinity of the material for perfluorinated compounds; even so, PFOS still showed significantly stronger adsorption affinity on iron-based surfaces than PFOA. When the sulfur content was further increased to [S / Fe] = 0.051 (measured), the adsorption column exhibited the latest breakthrough characteristic. This phenomenon can be attributed to the synergistic regulatory effect of the decrease in specific surface area and the enhancement of surface hydrophobicity caused by the increase in sulfur content (S / Fe = 0.013). Figure 6 and Figure 7 ).like Figure 14 and 15 As shown, both the 10% breakthrough bed volume and batch adsorption kinetics results consistently confirm the above pattern. Figure 15 Part a in the figure represents the adsorption kinetics curve of perfluorooctanoic acid (PFOA), and part b represents the adsorption kinetics curve of perfluorooctane sulfonic acid (PFOS), indicating that the zero-valent iron material has a much higher adsorption capacity for PFOS than for PFOA.

[0072] The defluorination performance of perfluorinated nanomaterials with different sulfur contents was evaluated in a UV / sulfite system. The results showed that, within the investigated sulfur content range, both perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) adsorbed on the surface of each material could be completely removed within 5 h. Meanwhile, the defluorination efficiency exhibited a typical volcano-dependent relationship with sulfur content: the defluorination rate first increased and then decreased with increasing sulfur content, reaching its maximum at a moderate sulfur doping level ([S / Fe] = 0.013), corresponding to defluorination efficiencies of 75% for PFOA and 68% for PFOS. Specific results are shown below. Figure 16 and Figure 17 As shown.

[0073] Figure 16 Part a in the figure represents the defluorination kinetics curve of perfluorooctanoic acid (PFOA) over time, and part b represents the defluorination kinetics curve of perfluorooctane sulfonic acid (PFOS) over time. This shows that by adjusting the sulfur content, the system can achieve a defluorination rate of 68-75% for both PFAS. This indicates that sulfur doping has a significant promoting effect on improving the defluorination performance of the material, and that there is an optimal range for the sulfur-iron molar ratio, which determines the defluorination efficiency.

[0074] Figure 17 The figures show the removal rate and defluorination rate of perfluorooctanoic acid and perfluorooctane sulfonic acid in six different sulfur-iron molar ratio material-UV / sulfite systems. Figure 17 Part a in the figure represents the removal rate and defluorination rate of PFOA, and part b represents the removal rate and defluorination rate of PFOS. After 5 hours, all PFAS adsorbed on the material can be completely removed, and the defluorination rate can be as high as 68-75%.

[0075] Figure 18 Fluorine balance analysis revealed that both perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) rapidly converted to fluoride ions, short-chain fluorides (C5-C8, C2-C4), and unquantified products during the reaction. In the PFOA system, inorganic fluoride ion release was rapid, while fluoride ion formation was relatively delayed in the PFOS system, indicating a difference in their defluorination pathways. As the reaction proceeded, the proportion of small-molecule fluorides decreased, but a high fluorine balance recovery rate was ultimately achieved, demonstrating that the material-UV / sulfite system can efficiently degrade and defluorinate perfluorinated compounds. Figure 18 It can be seen that PFOA and PFOS degrade rapidly. Initially, they undergo a reducing defluorination reaction to generate long-chain (C5–C8) intermediates, followed by chain breakage to form short-chain (C2–C4) products, and finally mineralize into inorganic fluorides.

[0076] Electron paramagnetic resonance spectroscopy using TEMPO as a spin probe confirmed the generation of hydrated electrons under UV / sulfite irradiation. The intensity of the characteristic peak of TEMPO decreased with illumination, indicating that the presence of hydrated electrons reduced it to TEMP. Furthermore, sulfidation modification was found to be more conducive to the generation of hydrated electrons, thus enhancing the reduction ability of perfluorinated compounds. Figure 19 ).

[0077] Six different groundwater samples differed in ionic strength, competing anions, and dissolved organic matter, but all maintained complete removal efficiency for perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS), consistent with results obtained in deionized water. Figure 20 The defluorination efficiency in groundwater decreased slightly, reflecting the influence of the water matrix on the generation of hydrated electrons, but the defluorination efficiency remained considerable (above 60%). These results indicate that the material-UV / sulfite treatment process is adaptable to actual groundwater conditions. To further evaluate its applicability, we studied the degradation of a mixture of 25 perfluorinated compounds (containing n = 4-13 perfluorocarboxylic acids, n = 4-10 perfluorosulfonic acids, and other novel perfluorinated compounds). All 25 PFAS compounds were nearly completely removed within 36 hours. Figure 21 ). Figure 22 The diagram illustrates the overall process of first enriching PFAS in groundwater using sulfide nano-zero-valent iron, then recovering them through magnetic separation, and finally defluorinating adsorbed PFAS using hydrated electron-reducing species. These results strongly demonstrate the broad application prospects of sulfide nano-zero-valent iron in the remediation of perfluorinated groundwater.

[0078] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any form or substance. It should be noted that those skilled in the art can make various improvements and additions without departing from the method of the present invention, and these improvements and additions should also be considered within the scope of protection of the present invention. Any modifications, alterations, and equivalent changes made by those skilled in the art based on the above-disclosed technical content without departing from the spirit and scope of the present invention are equivalent embodiments of the present invention. Furthermore, any modifications, alterations, and evolutions made to the above embodiments based on the essential technology of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A method for preparing zero-valent iron with controllable sulfur doping in a lattice, characterized in that, Add sulfur source and reducing agent to a solution containing Fe 3+ In a salt solution, under a protective atmosphere, a reaction is carried out to obtain lattice sulfur-controlled doped zero-valent iron.

2. The preparation method according to claim 1, characterized in that: The sulfur source and Fe 3+ The sulfur-iron molar ratio is (0.004~0.051):

1.

3. The preparation method according to claim 1, characterized in that: The sulfur source is sodium dithionite; the reducing agent is sodium borohydride; and the protective atmosphere is nitrogen.

4. The preparation method according to claim 1, characterized in that: The reaction process also includes solid-liquid separation and vacuum drying.

5. The preparation method according to claim 4, characterized in that: Solid-liquid separation is performed using magnetic separation; vacuum drying is carried out at a temperature of 55~70℃ for 6~8 hours.

6. A lattice sulfur-controlled doped zero-valent iron prepared by the preparation method according to any one of claims 1 to 5.

7. The lattice sulfur-controlled doping of zero-valent iron according to claim 6, characterized in that: The lattice sulfur-controlled doped zero-valent iron has slit-like pores with a pore size of 0.1~10 nm.

8. The application of lattice sulfur-controlled doping of zero-valent iron as described in claim 7 in the removal of perfluorinated compounds from groundwater.

9. The application according to claim 8, characterized in that: The lattice sulfur-controlled doped zero-valent iron is used to adsorb perfluorinated compounds in groundwater in situ. The compounds are then recovered by magnetic separation. The recovered lattice sulfur-controlled doped zero-valent iron is added to a solution containing sodium sulfite, and the adsorbed perfluorinated compounds are defluorinated under ultraviolet light irradiation.

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