Nitrided micron zero-valent iron catalyst as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of environmental functional materials and soil remediation, and particularly relates to a micron-sized zero-valent iron nitride catalyst as well as a preparation method and application thereof. The invention provides a nitrided micron zero-valent iron catalyst which is prepared by doping micron-sized iron powder with urea, the nitrogen content of the catalyst is 0.5 wt%-4.5 wt%, and the particle size of the micron-sized iron powder is 10-300 microns. The preparation method comprises the following steps: putting raw materials urea and micron-sized iron powder into a ball milling tank, adding grinding balls, and carrying out ball milling for 2-10 hours at the rotating speed of 450-550rpm in an air atmosphere; and drying the product after ball milling is finished, thereby obtaining the product. The catalyst is not only suitable for efficient deep treatment of high-concentration organic contaminated leacheate, but also can be directly used for chemical oxidation remediation of contaminated soil, and has remarkable engineering application value.

Description

Technical Field

[0001] This invention belongs to the field of environmental functional materials and soil remediation technology, specifically relating to a nitrided micron-sized zero-valent iron catalyst, its preparation method, and its application. Background Technology

[0002] The efficient remediation of organically contaminated soils (such as former chemical plant sites and oil fields) is a global challenge in environmental governance. Among ex-situ remediation technologies, soil leaching is widely used due to its advantages of good treatment effect and short cycle. This method uses the solubilizing effect of leaching agents (such as Tween 80) to transfer recalcitrant hydrophobic organic pollutants (such as polycyclic aromatic hydrocarbons and petroleum hydrocarbons) from the soil to the leaching solution, achieving phase transfer of pollutants. However, the resulting high-concentration, complex organic pollutant leaching solution requires further treatment. Therefore, the subsequent treatment of the leaching solution has become a key constraint on the widespread application of this technology. Meanwhile, based on sulfate free radicals (… Advanced oxidation technologies, due to their strong oxidizing power, wide pH range, and high degradation efficiency for recalcitrant pollutants, have shown great potential in the treatment of organic wastewater and direct remediation of contaminated soil. Persulfate is typically generated through activation. Common persulfate activation methods include heat, alkali, ultraviolet radiation, and transition metal catalysis. Among these, zero-valent iron (ZVI), as a low-cost and environmentally friendly transition metal, can efficiently activate persulfate (PS) through either electron transfer or surface catalysis, generating highly oxidizing free radicals, thus attracting significant attention in the field of environmental remediation.

[0003] In the selection of ZVI materials, nanoscale ZVI (nZVI) has attracted much attention due to its extremely high specific surface area and reactivity. However, nZVI faces serious challenges in practical engineering applications: 1) Agglomeration and deactivation: Its huge surface energy and magnetic attraction make it prone to agglomeration, leading to a sharp reduction in active sites; 2) Poor stability: Its huge specific surface area makes it easily oxidized in air, forming a dense passivation layer that hinders electron transfer and reduces its reactivity; 3) Cost and safety risks: The production cost of nZVI is high, and traditional liquid-phase reduction methods are widely used. Reducing agents pose safety and secondary pollution risks. In comparison, micron-sized ZVI (mZVI), although slightly less reactive, has greater advantages in large-scale environmental remediation projects due to its low price, stable properties, and ease of storage and transportation. However, mZVI also has significant drawbacks in activating persulfate systems: 1) Insufficient active sites: Small specific surface area results in a limited number of effective reactive sites; 2) Weak sustained reaction capability: In the initial stage of the reaction, it can release Fe... 2+Activating persulfate, but the surface is quickly passivated, resulting in rapid activity decay and poor long-term effectiveness; 3) Side reactions and secondary pollution: During the activation process, non-uniform corrosion occurs, leading to uncontrollable release of iron ions and the generation of a large amount of amorphous iron sludge, which not only causes loss of active sites and difficulty in solid-liquid separation, but may also encapsulate pollutants and affect mass transfer.

[0004] To overcome the aforementioned shortcomings, researchers have attempted various mZVI modification strategies, such as acid washing, sulfur modification, and coupling with noble metals. However, these methods have either limited effectiveness, high costs, or complex procedures, and often require inert gas protection during preparation, making large-scale application difficult. In summary, the current bottleneck in this field urgently needs to be overcome: how to develop an mZVI catalyst that is simple to process, low in cost, environmentally friendly, requires no complex atmosphere protection, and is easy to scale up. Summary of the Invention

[0005] In view of this, the present invention provides a micron-sized zero-valent iron nitride catalyst, its preparation method and application. The catalyst can effectively regulate the electronic structure, enhance the adsorption and activation ability of persulfate, and inhibit iron core passivation, thereby greatly improving the stability and long-term effectiveness of the material. Moreover, the preparation method achieves nitrogen doping of mZVI without the need for inert atmosphere protection, which is a green and safe preparation method.

[0006] To address the above technical problems, this invention provides a micron-sized zero-valent iron nitride catalyst, wherein the catalyst is prepared by doping micron-sized iron powder with urea, the nitrogen content of the catalyst is 0.5wt%~4.5wt%, and the particle size of the micron-sized iron powder is 10~300μm.

[0007] This invention obtains a micron-sized zero-valent iron catalyst by doping nitrogen into micron-sized iron powder. The introduction of nitrogen atoms can significantly regulate the electronic structure of the metal material, increase the density of active sites and electronic conductivity. By modifying zero-valent iron with nitrogen, the nitrided layer formed on the surface can not only effectively inhibit ZVI passivation, but also serve as a highly efficient electron channel, enhancing its own stability and ability to activate persulfate.

[0008] Preferably, the catalyst is micron-sized iron powder with a nitrogen content of 1wt% to 3wt%.

[0009] Preferably, the persulfate can be sodium persulfate, potassium persulfate, or other persulfates with oxidizing properties.

[0010] A second aspect of this invention provides a method for preparing the above-mentioned micron-sized zero-valent iron nitride catalyst, comprising the following steps: The raw material urea and micron-sized iron powder are placed in a ball mill jar, grinding balls are added, and the mixture is ball-milled in air at a speed of 450~550 rpm for 2~10 hours. After ball milling, the product is dried to obtain the nitrided micron-sized zero-valent iron catalyst.

[0011] The nitrided micron-sized zero-valent iron catalyst provided by this invention uses urea as a specific nitrogen source. After mixing with micron-sized iron powder, it is ground at a specific speed for a certain period of time in an air atmosphere to obtain a catalyst with high degradation performance. There is no need to grind under a protective atmosphere, which solves the problems of cumbersome process flow and poor controllability in the existing process.

[0012] In conjunction with the second aspect, the micron-sized iron powder is selected from reduced iron powder, industrial by-product iron powder, and iron powder obtained by gas-phase reduction.

[0013] In conjunction with the second aspect, the molar ratio of nitrogen atoms in the urea to iron atoms in the micron-sized iron powder is 0.02~0.2:1.

[0014] In conjunction with the second aspect, the mass ratio of the grinding ball to the raw materials urea and micron-sized iron powder is 1:18~22.

[0015] A third aspect of this invention provides the application of the above-described micron-sized zero-valent iron nitride catalyst or the micron-sized zero-valent iron nitride catalyst prepared according to the above preparation method in activating persulfate to degrade organic pollutants in water, the steps of which include: Micron-sized zero-valent iron nitride catalyst and persulfate were added to the water body, and the reaction was stirred at room temperature for 30-120 minutes. After the reaction was completed, the solid and liquid were separated.

[0016] In conjunction with the third aspect, the water body includes polluted natural water bodies and leachate from polluted soil; the pH of the water body is 3 to 7.

[0017] In conjunction with the third aspect, the dosage of the nitrided micron-sized zero-valent iron catalyst is 0.25~1.0 g / L, and the dosage of the persulfate is 0.5~2.0 mM.

[0018] In conjunction with the third aspect, the organic pollutants include benzo(a)pyrene, polychlorinated biphenyls, etc.

[0019] A fourth aspect of the present invention provides the application of the above-described micron-sized zero-valent iron nitride catalyst or the micron-sized zero-valent iron nitride catalyst prepared according to the above preparation method in activating persulfate to degrade soil organic pollutants, the steps of which include: Nitrogen-encapsulated micron-sized zero-valent iron catalyst and persulfate were added to the soil, and water was added to make the liquid-solid ratio 1:0.2~5. After stirring evenly, the mixture was reacted at room temperature for 1~7 days.

[0020] In conjunction with the fourth aspect, the dosage of the nitrided micron zero-valent iron catalyst is 0.5% to 3%, and the dosage of the persulfate is 0.5% to 2% of the dry soil mass.

[0021] In conjunction with the fourth aspect, the organic pollutants are highly hydrophobic organic pollutants, including benzo(a)pyrene, polychlorinated biphenyls, etc.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) Green and efficient preparation process: The present invention uses mechanical ball milling to achieve nitrogen doping of mZVI without the need for inert atmosphere protection, which completely avoids the use of traditional liquid phase reduction method. It avoids the secondary pollution problems caused by toxic reducing agents, and at the same time avoids the traditional ball milling method which is carried out in a protective gas atmosphere such as nitrogen throughout the process, making it a green and safe synthesis process.

[0023] (2) Significant optimization of material structure: Nitrogen doping constructs stable Fe-N active sites and conductive nitride layer on the mZVI surface, effectively regulating the electronic structure, enhancing the adsorption and activation ability of persulfate, while inhibiting iron core passivation, and improving the stability and long-term effectiveness of the material.

[0024] (3) Excellent catalytic performance: The N@mZVI prepared in this invention shows far superior catalytic efficiency to the original mZVI and other element-doped catalysts in activating persulfate to degrade organic pollutants. At the same time, the use of micron-scale materials instead of nanomaterials avoids the problems of easy agglomeration and deactivation of nanomaterials.

[0025] (4) Strong compatibility: The catalyst prepared by the present invention is not only suitable for the efficient deep treatment of high-concentration organic pollutant leaching solution, but can also be directly used for the chemical oxidation remediation of polluted soil, and has significant engineering application value.

[0026] (5) Extremely low cost and environmentally friendly: The micron-sized iron powder raw material used in this invention is inexpensive and readily available, the preparation process is simple, the energy consumption is low, no toxic chemicals are added throughout the process, the catalyst itself is non-biologically toxic, has good environmental compatibility, and the doped nitrogen element can also be used as a nutrient element, which is conducive to soil ecological restoration and conforms to the concept of green and sustainable development. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the mechanical ball milling preparation process of the N@mZVI catalyst in Example 1 of the present invention. Figure 2 The X-ray photoelectron spectroscopy (XPS) spectrum of N@mZVI in Example 1 of the present invention is shown in Figure a), where Figure a) is the full spectrum and Figure b) is the high-resolution N1s spectrum.

[0028] Figure 3Figure 1 shows the effect of using the N@mZVI catalyst of Example 1 to activate the degradation of benzo(a)pyrene (BaP) in the liquid phase by persulfate. Figure 1a) shows the degradation effect of different amounts of catalyst and Figure 1b) shows the degradation effect of different amounts of oxidant. Figure 4 The figure shows the effect of using the N@mZVI catalyst of Example 1 to activate the degradation of benzo(a)pyrene (BaP) in soil by persulfate. In the figure, Figure a) shows the removal effect of different catalytic systems on BaP, Figure b) shows the removal effect of different liquid-solid ratios on BaP, Figure c) shows the removal effect of different dosages of catalyst on BaP, and Figure d) shows the removal effect of different dosages of oxidant on BaP. Figure 5 The graph shows the degradation effect of the N@mZVI-PS system on BaP in contaminated soil under low moisture content conditions and different dosages. Figure 6 The graph shows the removal effect of different systems on BaP in soil leachate. Figure 7 The figures show the removal effect of BaP by the catalysts obtained in Examples 1-5 and Comparative Examples 1-2, respectively.

[0029] Figure 8 The images show the removal effect of the catalysts obtained in Example 1 and Comparative Examples 3-5 on BaP in soil. Detailed Implementation To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0030] It will be understood by those skilled in the art that, unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. It should also be understood that terms such as those defined in general dictionaries should be understood to have the meaning consistent with their meaning in the context of the prior art, and should not be interpreted in an idealized or overly formal sense unless specifically defined.

[0031] Doping modification has been proven to be an effective way to improve the catalytic performance of metallic materials. Although there have been studies on incorporating non-metallic atoms into micron-sized zero-valent iron, the methods mostly rely on high-temperature heat treatment, complex wet chemical processes, or require strict oxygen-free / inert atmospheres. The processes are cumbersome and energy-intensive, which seriously hinders the engineering application of high-performance modified ZVI materials.

[0032] To address the following problems in the existing technology: (1) Material performance defects: Existing mZVI materials have problems such as small specific surface area, few active sites, easy surface passivation, and poor long-term reaction ability, resulting in low activation efficiency of persulfate; and a large amount of iron sludge is easily generated during the reaction, causing activity loss and secondary pollution. (2) Modification process bottleneck: Existing synthesis methods for similar materials mainly include wet synthesis, thermal synthesis and mechanical ball milling synthesis. Among them, wet synthesis usually requires the use of reducing chemical reagents, the process is relatively complicated, and waste liquid may be generated, increasing the subsequent treatment cost and environmental burden; thermal synthesis often depends on high temperature conditions, has high energy consumption, and requires continuous introduction of protective gas (such as argon or nitrogen) during the synthesis process, which increases the complexity of the process and equipment requirements; mechanical ball milling, as a solid synthesis method, has the advantages of simple operation and low energy consumption. However, in the traditional mechanical ball milling process, if non-metallic elements (such as sulfur) are doped and modified, it is still usually necessary to carry out under the protection of nitrogen or inert atmosphere to prevent material oxidation or side reactions. Therefore, existing synthesis methods often suffer from drawbacks such as cumbersome processes, high costs, high energy consumption, and poor controllability, making it difficult to achieve large-scale production and engineering applications.

[0033] Therefore, this invention provides a green, simple, and scalable preparation method for nitrogen-doped micron-sized zero-valent iron catalyst (N@mZVI) based on mechanical ball milling, as well as the efficient application technology of this catalyst in activated persulfate for the remediation of organically contaminated soil and the treatment of leachate.

[0034] In view of this, the present invention provides a micron-sized zero-valent iron nitride catalyst, its preparation method, and its application. This preparation method is green, simple, and scalable, and demonstrates satisfactory remediation effects in key application scenarios such as "direct remediation of contaminated soil" and "deep treatment of high-concentration leachate / contaminated water." This invention provides a material basis and methodological support for promoting the engineering practice of soil remediation technologies based on persulfate advanced oxidation.

[0035] Unless otherwise specified, the raw materials, reagents and equipment used in this invention are all conventional commercially available reagents and equipment.

[0036] Example 1 This embodiment provides a micron-sized zero-valent iron nitride catalyst, the flowchart of which is shown below. Figure 1 As shown, the preparation method is as follows: Accurately weigh 5.00 g of micron-sized reduced iron powder (50~300μm) as the iron source and matrix material, and weigh 0.27 g of urea. This mass ratio corresponds to a molar ratio of N / Fe of 0.1:1.

[0037] Mix the reduced iron powder with urea and place it in an agate planetary ball mill jar. Add 100 g of agate grinding balls and control the ball-to-material ratio in the range of 18:1 to 22:1. After sealing the ball mill jar, place it in a planetary ball mill and ball mill at 500 rpm for 10 hours in an air atmosphere.

[0038] After ball milling, the ball mill jar was opened, the product was collected, and after vacuum drying, a gray-black nitrogen-doped micron zero-valent iron catalyst N@mZVI with a nitrogen content of 1.55 wt% was obtained.

[0039] The obtained catalyst was subjected to X-ray photoelectron spectroscopy, and the results are as follows: Figure 2 As shown in a) and b) : a) Full spectrum: clearly shows the characteristic peaks of O1s, Fe2p, N1s, and C1s, with the presence of the N1s peak directly proving that nitrogen was successfully doped into the mZVI matrix material. b) High-resolution N1s spectrum: after peak fitting, three characteristic peaks were identified, corresponding to pyridine nitrogen (binding energy 398.5 eV), pyrrole nitrogen (binding energy 399.5 eV), and graphitic nitrogen (binding energy 401.2 eV), with relative contents of 14%, 75%, and 11%, respectively. This result confirms the success of nitrogen doping, reveals the specific chemical morphology and distribution of nitrogen species, and provides key structural evidence for elucidating its high catalytic activity. Among them, pyrrole nitrogen, which has the highest content, may help improve the electron supply capacity of the catalyst, greatly enhancing the electron supply and transport capabilities of the material; while pyridine nitrogen, as a key coordination site, forms an MN structure (such as Fe-Nx) with the iron center, which is crucial for the formation of Fe-Nx catalytic active sites. This structure can regulate the electron cloud density of the iron center, making it positively charged, which is more conducive to the adsorption and activation of persulfate anions (such as S2O8). 2- or HSO5 - This structure significantly enhances the electron supply and conduction capabilities of the material; simultaneously, it effectively stabilizes the valence state of iron, inhibiting the dissolution and passivation of ZVI. The synergistic effect of pyridine nitrogen and pyrrole nitrogen is the fundamental reason for the high activity and high stability of the catalyst of this invention.

[0040] Example 2 This embodiment provides a micron-sized zero-valent iron nitride catalyst, the preparation method of which is as follows: Accurately weigh 5.00 g of micron-sized reduced iron powder (50~300μm) as the iron source and matrix material, and weigh 0.27 g of urea. This mass ratio corresponds to a molar ratio of N / Fe of 0.1:1.

[0041] Mix the reduced iron powder with urea and place it in an agate planetary ball mill jar. Add 100 g of agate grinding balls and control the ball-to-material ratio in the range of 18:1 to 22:1. After sealing the ball mill jar, place it in a planetary ball mill and mill it at 450 rpm for 5 hours in an air atmosphere.

[0042] After ball milling, the ball mill jar was opened, the product was collected, and after vacuum drying, a gray-black nitrogen-doped micron zero-valent iron catalyst N@mZVI with a nitrogen content of 1.32 wt% was obtained.

[0043] Example 3 This embodiment provides a micron-sized zero-valent iron nitride catalyst, the preparation method of which is as follows: Accurately weigh 5.00 g of micron-sized reduced iron powder (50~300μm) as the iron source and matrix material, and weigh 0.27 g of urea. This mass ratio corresponds to a molar ratio of N / Fe of 0.1:1.

[0044] Mix the reduced iron powder with urea and place it in an agate planetary ball mill jar. Add 100 g of agate grinding balls and control the ball-to-material ratio in the range of 18:1 to 22:1. After sealing the ball mill jar, place it in a planetary ball mill and mill it at 550 rpm for 2 hours in an air atmosphere.

[0045] After ball milling, the ball mill jar was opened, the product was collected, and after vacuum drying, a gray-black nitrogen-doped micron zero-valent iron catalyst N@mZVI was obtained with a nitrogen content of 1.09 wt%.

[0046] Example 4 This embodiment provides a micron-sized zero-valent iron nitride catalyst, the preparation method of which is as follows: Accurately weigh 5.00 g of micron-sized reduced iron powder (50~300μm) as the iron source and matrix material, and weigh 0.135 g of urea. This mass ratio corresponds to a molar ratio of N / Fe of 0.05:1.

[0047] Mix the reduced iron powder with urea and place it in an agate planetary ball mill jar. Add 100 g of agate grinding balls and control the ball-to-material ratio in the range of 18:1 to 22:1. After sealing the ball mill jar, place it in a planetary ball mill and mill it at 450 rpm for 10 hours in an air atmosphere.

[0048] After ball milling, the ball mill jar was opened, the product was collected, and after vacuum drying, a gray-black nitrogen-doped micron zero-valent iron catalyst N@mZVI with a nitrogen content of 0.8 wt% was obtained.

[0049] Example 5 This embodiment provides a micron-sized zero-valent iron nitride catalyst, the preparation method of which is as follows: Accurately weigh 5.00 g of micron-sized reduced iron powder (50~300μm) as the iron source and matrix material, and weigh 0.54 g of urea. This mass ratio corresponds to a molar ratio of N / Fe of 0.2:1.

[0050] Mix the reduced iron powder with urea and place it in an agate planetary ball mill jar. Add 100 g of agate grinding balls and control the ball-to-material ratio in the range of 18:1 to 22:1. After sealing the ball mill jar, place it in a planetary ball mill and ball mill at 550 rpm for 10 hours in an air atmosphere.

[0051] After ball milling, the ball mill jar was opened, the product was collected, and after vacuum drying, a gray-black nitrogen-doped micron zero-valent iron catalyst N@mZVI was obtained with a nitrogen content of 2.96 wt%.

[0052] Example 6 This embodiment uses the catalyst obtained in Example 1 to activate persulfate for the degradation of benzo(a)pyrene (BaP) in the liquid phase. The aim is to simplify the verification of the catalytic activity of N@mZVI in the liquid phase system, eliminate interference from the complex matrix in the soil, and optimize the reaction parameters. Specific experimental studies are as follows: Experimental methods: (1) Prepare simulated wastewater: Weigh a certain amount of BaP and dissolve it in acetonitrile as the mother liquor. Take an appropriate amount and add it to ultrapure water. After ultrasonic dispersion, prepare a BaP solution with an initial concentration of 20 mg / L as simulated wastewater with a pH of 6.75.

[0053] (2) Conduct batch experiments: Take a certain volume of simulated wastewater, add a predetermined amount of catalyst N@mZVI and sodium persulfate in sequence, place it in a constant temperature shaker, and react at room temperature and 170 rpm; take samples at different times, add excess methanol immediately to quench the reaction, filter through a 0.22 μm filter membrane, and use high performance liquid chromatography to determine the residual concentration of BaP in the solution.

[0054] Parameter optimization process and results: Effect of catalyst dosage: With a fixed PS concentration of 1 mM and an initial BaP concentration of 20 mg / L, the effect of N@mZVI dosage (0.25, 0.5, 1.0 g / L) was investigated. Figure 3 a) It can be seen that when the N@mZVI dosage is 0.25, 0.5, and 1.0 g / L, the final degradation rate of BaP exceeds 84% ​​(up to 95%), and the initial reaction rate constants are 0.048, 0.104, and 0.095 min, respectively. -1 When the dosage increased from 0.25 g / L to 1.0 g / L, the removal rate decreased from 95.1% to 84.3%, indicating that the excess catalyst dissolved more Fe. 2+ And resulting in The reaction was quenched, and the reaction system performed optimally when the catalyst dosage was 0.5 g / L, removing 95.1% of BaP within 60 minutes, with an initial reaction rate constant of 0.104 min. -1 This indicates that a catalyst dosage of 0.5 g / L is the optimal dosage for this liquid phase system.

[0055] Effect of PS concentration: With a fixed N@mZVI dosage of 0.5 g / L, the effect of PS concentrations (0.5, 1.0, 2.0 mM) was investigated. Figure 3 (b) It can be seen that when the N@mZVI dosage is 0.5 g / L, as the PS concentration increases from 0.5 mM to 2.0 mM, the BaP removal rate significantly increases from 54.2% to 96.5% after 60 minutes, and the initial reaction rate constant increases from 0.044 min. -1 Increased to 0.163 min -1 (A 2.7-fold increase), indicating that the concentration of the oxidant PS is a key factor controlling the reaction rate. However, when the PS concentration exceeds 2.0 mM, the increase in removal rate tends to level off, indicating that the reaction is gradually limited by the number of active sites on the catalyst.

[0056] As can be seen from the above, the catalyst provided by this invention can efficiently and rapidly degrade BaP in the liquid phase system, and the optimal operating parameters for this system are 0.5 g / L N@mZVI dosage and 2.0 mM PS concentration. At the same time, the reaction kinetics are revealed, providing a basis for subsequent practical applications.

[0057] Example 7 This embodiment uses the catalyst obtained in Example 1 to activate persulfate for direct remediation of BaP-contaminated soil. The aim is to verify the actual effectiveness of the catalyst in directly remediating soil contaminated with organic pollutants of high octyl alcohol-water partition coefficients (represented by BaP), evaluate its applicability under near-real-world engineering conditions (low moisture content), and explore the influence of key process parameters. Specific experimental studies are as follows: Experimental methods: Preparation of contaminated soil: Simulated contaminated soil with an initial BaP concentration of 20 mg / kg was collected and prepared, and aged for 2 months to ensure uniform distribution of pollutants and a pH of 5.61.

[0058] Benchmark performance comparison experiment: To eliminate mass transfer limitations and fully evaluate the catalyst activity, the experiment was first conducted under a liquid / solid ratio (L / S) of 1:1, with the following control groups set up: Control group 1: PS equivalent to 2% of the dry weight of soil was added.

[0059] Control group 2: Added PS equivalent to 2% of the dry weight of soil and 4% of mZVI.

[0060] Experimental group: 2% PS and 4% N@mZVI catalyst prepared in Example 1 were added, equivalent to 2% of the dry weight of soil.

[0061] Add deionized water to each group to adjust the L / S ratio to 1:1, stir evenly, and react at room temperature for 24 hours.

[0062] Experiment on the Influence of Process Parameters: In the N@mZVI-PS system, the effects of the following parameters were systematically studied: Effect of L / S ratio: With fixed PS and N@mZVI dosages of 2% and 4%, respectively, the removal effect was examined when the L / S ratio changed from 1:1 to 5:1.

[0063] Effects of catalyst and oxidant dosage: Under an L / S ratio of 1:1, the effects of different PS dosages (0.5-2%) and N@mZVI dosages (1-4%) were investigated.

[0064] Simulated field conditions verification experiment: Actual soil remediation is usually carried out under field water holding capacity conditions (moisture content 20-30%, corresponding to an L / S ratio of approximately 1:5 to 1:3.3), and the dosage of oxidant and catalyst is usually controlled within 2% and 5%, respectively, to balance cost and effectiveness. This study verified the 1-day removal effect of different combinations of PS (0.5%-2%) and N@mZVI (0.5%-2%) dosages on BaP under an L / S ratio of 1:5.

[0065] Sample analysis: After the reaction, the soil sample was freeze-dried and the residual BaP was extracted by ultrasonic extraction (acetonitrile and methanol mixture as solvent). After the extract was concentrated and purified, the concentration was determined by high performance liquid chromatography and the removal rate was calculated (removal rate (%) = (original concentration - residual concentration) / original concentration × 100%).

[0066] Results and Discussion: The activity advantages of the catalyst of this invention are as follows: Figure 4 As shown in a), after one day of reaction under L / S=1:1 conditions, the removal rate of BaP by the PS system alone (control group 1) was only 11.5%, while the removal rate of the mZVI-PS system (control group 2) increased to 18.0%; the removal rate of the N@mZVI-PS system (experimental group) reached 49.4%, which was significantly better than the mZVI-PS system, increasing by about 1.74 times. This indicates that the nitrogen-doped modified catalyst provided in this application greatly enhances the ability of mZVI to activate PS to generate free radicals, thereby more effectively removing BaP from contaminated soil, proving the decisive role of nitrogen doping in improving catalytic activity.

[0067] The influence of operating parameters: The influence of L / S ratio: such asFigure 4 As shown in b), with a fixed PS content of 2% and an N@mZVI dosage of 4%, the removal rate of BaP increased with increasing L / S ratio (up to 3:1), which is beneficial for the dispersion of oxidant and catalyst and the mass transfer of pollutants. However, when the L / S ratio increased to 5:1, the removal rate decreased slightly, which may be related to the excessive dilution of free radicals.

[0068] Effect of catalyst dosage: such as Figure 4 As shown in c), with a fixed PS dosage of 2% and an L / S ratio of 1:1, the BaP removal rate decreased from 65.1% to 49.4% when the N@mZVI dosage increased from 1% to 4%. This is attributed to the free radical quenching effect caused by excess catalyst, proving the existence of an optimal dosage.

[0069] Oxidant dosage: such as Figure 4 As shown in d), with a fixed N@mZVI dosage of 2% and an L / S ratio of 1:1, the BaP removal rate increased from less than 30% to about 50% as the PS dosage increased (from 0.5% to 2%), indicating that sufficient oxidant is a prerequisite for generating enough free radicals.

[0070] Verification of effectiveness under low moisture content conditions: Under conditions of a low L / S ratio (1:5), which is closer to engineering practice, the N@mZVI-PS system still showed a clear repair effect within 1 day. Figure 5 As shown, under low humidity and limited mass transfer conditions, the BaP removal rate increased with increasing PS and N@mZVI dosages, reaching a maximum removal rate of 34.3% when both PS and N@mZVI dosages were 2%. This result confirms that even in actual soil environments with limited moisture and more demanding mass transfer conditions, the N@mZVI catalyst of this invention can still effectively activate PS, demonstrating good potential for field application.

[0071] As can be seen from the above, this embodiment fully demonstrates that the N@mZVI catalyst prepared by the present invention can be directly used for the remediation of highly hydrophobic organic polluted soil. It not only has significantly better activity than the unmodified matrix material, but also shows a clear response law to key parameters such as liquid-solid ratio, catalyst and oxidant dosage. It remains effective under low humidity conditions in simulated field, providing a reliable technical solution for solving the problems of low catalyst efficiency and poor adaptability in soil remediation.

[0072] Example 8 This embodiment uses the catalyst obtained in Example 1 to activate persulfate to treat simulated soil leachate, aiming to establish a baseline control in the simulated leachate system and quantitatively evaluate the performance improvement of N@mZVI compared to the original mZVI and PS alone. Specific experimental studies are as follows: Experimental methods: Preparation of simulated eluent: An aqueous solution containing 10 g / L Tween 80 (a commonly used eluent) and 20 mg / L BaP was prepared, with an initial pH of 5.82. The experiment was conducted in 250 mL Erlenmeyer flasks, with three control groups set up. Individual PS group: Only 0.5 mM of PS is added.

[0073] mZVI-PS group: 0.5 g / L mZVI and 0.5 mM PS were added.

[0074] N@mZVI-PS group: 0.5 g / L of the catalyst N@mZVI prepared in Example 1 and 0.5 mM of PS were added.

[0075] Each group of conical flasks was placed in a constant-temperature shaker and stirred at 170 rpm for 60 minutes at room temperature. Samples were taken at the reaction endpoint, and excess methanol was immediately added to quench the reaction. After filtration through a 0.22 μm filter membrane, the BaP concentration was determined by high-performance liquid chromatography (HPLC), and the removal rate was calculated.

[0076] The results are as follows Figure 6 As shown, after 60 minutes of reaction, the removal rates of BaP in the three groups of experiments showed a stark contrast: PS alone: ​​the removal rate was only 24.9%, confirming that in the micelle solubilization system, PS itself is unable to effectively attack BaP molecules encapsulated within the micelles, and its oxidation capacity is severely limited by mass transfer; mZVI-PS group: the removal rate was 83.9%, indicating that mZVI activated PS, and the generated sulfate radicals and other active species could penetrate or destroy the micelles, effectively degrading BaP; N@mZVI-PS group: the removal rate reached 92.1%, compared with unmodified mZVI, N@mZVI increased the absolute value of the removal efficiency by 8.2 percentage points, indicating that nitrogen doping not only enhances the activation ability of iron materials but also greatly improves the removal efficiency of organic pollutants.

[0077] In summary, this embodiment clearly and quantitatively demonstrates that the N@mZVI catalyst prepared in this invention exhibits significantly higher catalytic efficiency than the original mZVI material and the single oxidant PS in a complex aqueous system simulating the composition of real soil leachate. Even in the presence of high concentrations of surfactants (which may compete for adsorption or quench free radicals), the performance advantages of the nitrogen-doped modified catalyst N@mZVI of this invention remain very significant, providing direct and strong evidence for the core innovation and indicating that this catalyst is suitable for the efficient and deep treatment of actual soil leachate.

[0078] Comparative Example 1 This comparative example provides a micron-sized zero-valent iron nitride catalyst, which is prepared in a similar manner to Example 1, except that the nitrogen-containing precursor urea in Example 1 is replaced with an equimolar amount (in terms of N) of thiourea. All other steps are the same as in Example 1.

[0079] Comparative Example 2 This comparative example provides a micron-sized zero-valent iron nitride catalyst, which is prepared in a similar manner to Example 1. The only difference is that the nitrogen-containing precursor urea in Example 1 is replaced with an equimolar amount (in terms of N) of melamine. All other steps are the same as in Example 1.

[0080] Comparative Example 3 This comparative example provides a sulfurized micron-sized zero-valent iron catalyst, prepared in a similar manner to Example 1, except that the nitrogen-containing precursor urea in Example 1 is replaced with an equimolar amount (in terms of S) of elemental sulfur. All other steps are the same as in Example 1.

[0081] Comparative Example 4 This comparative example provides a sulfidation micron-sized zero-valent iron catalyst, which is prepared using existing techniques (remediation technology and mechanism study of polycyclic aromatic hydrocarbon pollution in site soil by combining micron-sized sulfidation zero-valent iron).

[0082] Comparative Example 5 This comparative example provides an Fe-Cu bimetallic catalyst prepared using existing techniques (Degradation of PAHs in soil by activated persulfate system with activated carbon supported iron-based bimetal).

[0083] Test Example 1 The effects of the nitride micron-sized zero-valent iron catalysts obtained in Examples 1-5 and Comparative Examples 1-2 on the degradation of BaP were tested respectively: 1.0 g of catalyst was added to an aqueous solution with a BaP concentration of 20 mg / L. After reacting for 60 minutes, the residual BaP concentration was tested, and the removal rate was calculated. The results are as follows: Figure 7 As shown.

[0084] Depend on Figure 7It can be seen that, under the same reaction conditions, the removal rates of BaP by the catalysts obtained in Examples 1-5 modified with urea were 87.7%, 78.6%, 80.4%, 80.6%, and 87.3%, respectively, which are significantly higher than those of the catalysts modified with thiourea (49.0%) and melamine (61.0%). This indicates that the type of precursor used for modification has a significant impact on the catalytic performance of nitrogen-modified mZVI, and not all nitrogen-containing precursors can be used to obtain catalysts with high removal rates.

[0085] Test Example 2 The effects of the catalysts obtained in Example 1 and Comparative Examples 3-5 on the degradation of BaP were tested respectively: (1) Two groups of BaP aqueous solutions with a concentration of 20 ppm were prepared. The catalysts prepared in Example 1 and Comparative Example 3 were added at a dosage of 1 g / L, respectively. PS was added at a concentration of 2.0 mM, respectively. After reacting for 1 h, the residual BaP content in the aqueous solution was measured, and the removal rate was calculated. The results are as follows: Figure 8 As shown.

[0086] It can be seen that the BaP removal rate of zero-valent iron nitriding in Example 1 is as high as 87.7%, while the BaP removal rate of zero-valent iron sulfide in Comparative Example 3 is only 36.9%. This shows that, under the premise that the synthesis method and reaction conditions are all the same, the nitriding modification strategy is significantly better than the traditional sulfide modification strategy in improving the activation performance of micron-sized zero-valent iron in PS.

[0087] (2) BaP-contaminated soils with BaP contents of 20 mg / kg and 30 mg / kg were prepared respectively, with a liquid-to-solid ratio of 3:1. The catalysts prepared in Example 1 (added to the 20 mg / kg contaminated soil) and Comparative Example 4 (added to the 30 mg / kg contaminated soil) were added at a dosage of 2.0% of the soil dry weight, respectively. The catalysts were added at ratios of 2.0% (Example 1) and 7.0% (Comparative Example 4) of the soil dry weight, respectively. After reacting for 1 day, the residual BaP content in the soil was measured, and the removal rate was calculated. The results are as follows: Figure 8 As shown.

[0088] It can be seen that the zero-valent iron nitride catalyst of Example 1 can achieve a removal rate of 57.62% for low concentrations (20 mg / kg) of BaP in soil, while the catalyst of Comparative Example 4 still has a removal rate of less than 30% for high concentrations (30 mg / kg) of BaP. That is, under conditions favorable to pollutant degradation (i.e., higher oxidant dosage and higher BaP concentration), the degradation performance of the catalyst of Comparative Example 4 is still far inferior to the catalyst provided in the embodiments of the present invention, indicating that the catalyst provided in the present invention also has a strong competitive advantage and practicality in the complex environment of actual soil remediation.

[0089] (3) BaP-contaminated soils with BaP contents of 20 mg / kg and 97.8 mg / kg were prepared, with a liquid-to-solid ratio of 1:1. The catalyst and PS from Example 1 were added to the 20 mg / kg contaminated soil at dosages of 1.0% and 2% of the soil dry weight, respectively. The catalyst and PS from Comparative Example 5 were added to the 97.8 mg / kg contaminated soil at dosages of 1.0% and 2.7% of the soil dry weight, respectively. After reacting for 1 day, the residual BaP content in the soil was measured, and the removal rate was calculated. The results are as follows: Figure 8 As shown.

[0090] It can be seen that the conditions in Example 1 (lower pollutant concentration and relatively higher oxidant dosage) seem "more lenient," but in reality, the calculation of the removal rate is more stringent than that in Comparative Example 5 (because it is more difficult to achieve a high percentage removal of low-concentration pollutants). Under these conditions, the removal rate of zero-valent iron nitride in Example 1 still reaches 65.1%, far exceeding the 29.2% removal rate of high-concentration pollutants by the iron-copper bimetallic catalyst in Comparative Example 5. This demonstrates that the catalytic efficiency of the zero-valent iron nitride material provided by this invention is far higher than that of the bimetallic catalyst system. Moreover, the catalyst provided by this invention achieves better treatment results while reducing metal dosage and oxidant consumption, combining high efficiency and economy.

[0091] Through comparative examples 3-5, the advantages of the nitrided micron-sized zero-valent iron of this invention were systematically demonstrated: 1) It is superior to traditional sulfide modification (ball milling preparation method) in intrinsic catalytic activity, and its preparation process is simpler and safer (no inert gas is needed to maintain an oxygen-free / anaerobic environment during ball milling, and the nitrogen source (such as urea) used is safer than the sulfur source (such as elemental sulfur). 2) It is superior to sulfide zero-valent iron materials reported in existing literature in soil remediation, and is more environmentally friendly (the introduced nitrogen element is a nutrient element, which is beneficial to soil ecological restoration). 3) Compared with Fe-Cu bimetallic materials, the preparation process of the material of this invention is simple and the conditions are mild, avoiding the cumbersome liquid-phase synthesis and reducing agent use of complex bimetallic materials.

[0092] In summary, the nitrided micron-sized zero-valent iron catalyst provided by this invention not only outperforms materials such as sulfide zero-valent iron and iron-copper bimetals in pollutant degradation performance, but also has significant advantages in terms of ease of material preparation, safety, environmental friendliness, and potential for engineering applications.

[0093] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A micron-sized zero-valent iron catalyst that is nitrided, characterized in that, The catalyst is prepared by doping micrometer-sized iron powder with urea, the nitrogen content of the catalyst is 0.5wt%-4.5wt%, and the particle size of the micrometer-sized iron powder is 10-300μm.

2. The method of claim 1, wherein the step of The application relates to a nitrogenated micrometer-sized zero-valent iron catalyst and a preparation method thereof and application thereof in water and soil remediation. The raw materials, urea and micrometer-sized iron powder, are placed in a ball mill tank, grinding balls are added, and the ball milling is carried out at a rotating speed of 450-550rpm in an air atmosphere for 2-10h; After the ball milling, the product is dried to obtain the nitrogenated micrometer-sized zero-valent iron catalyst.

3. The method for preparing the micron-sized zero-valent iron nitride catalyst as described in claim 2, characterized in that, The micrometer-sized iron powder is selected from reduced iron powder, industrial by-product iron powder and iron powder prepared by a gas phase reduction method.

4. The method for preparing the micron-sized zero-valent iron nitride catalyst as described in claim 2, characterized in that, The molar ratio of nitrogen atoms in the urea to iron atoms in the micrometer-sized iron powder is 0.02-0.2:

1.

5. The method for preparing the micron-sized zero-valent iron nitride catalyst as described in claim 2, characterized in that, The mass ratio of the grinding balls to the raw materials, urea and micrometer-sized iron powder, is 1:18-22.

6. Use of the nitrogenated micron zero-valent iron catalyst of claim 1 or the nitrogenated micron zero-valent iron catalyst prepared according to the preparation method of any one of claims 2-5 in activating persulfate to degrade organic pollutants in water, characterized in that the step of The application relates to a nitrogenated micrometer-sized zero-valent iron catalyst and a preparation method thereof and application thereof in water and soil remediation. The water body includes a contaminated natural water body and a leaching solution of contaminated soil; and the pH of the water body is 3-7.

7. Use according to claim 6, wherein The adding amount of the nitrogenated micrometer-sized zero-valent iron catalyst is 0.25-1.0g / L, and the adding amount of the persulfate is 0.5-2.0mM.

8. Use according to claim 6, wherein The application relates to a nitrogenated micrometer-sized zero-valent iron catalyst and a preparation method thereof and application thereof in water and soil remediation.

9. Use of the nitrogenated micron zero-valent iron catalyst of claim 1 or the nitrogenated micron zero-valent iron catalyst prepared according to the method of any one of claims 2-5 to activate persulfate salts to degrade soil organic pollutants, characterized in that the steps of The nitrogenated micrometer-sized zero-valent iron catalyst and the persulfate are added into the soil, water is added to a liquid-solid ratio of 1:0.2-5, and then uniform stirring is carried out, and the reaction is carried out at normal temperature for 1-7 days. The adding amount of the nitrogenated micrometer-sized zero-valent iron catalyst is 0.5%-3%, and the adding amount of the persulfate is 0.5%-2% of the dry soil mass.

10. Use according to claim 9, wherein ​

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