Preparation method of Fe(III)-modified montmorillonite, Fe(III)-modified montmorillonite, polycyclic aromatic hydrocarbon degradation catalyst and application

Abstract

This invention belongs to the field of soil remediation technology, specifically relating to a method for preparing Fe(III)-modified montmorillonite, Fe(III)-modified montmorillonite, a polycyclic aromatic hydrocarbon (PAH) degradation catalyst, and their applications. The method includes: mixing deionized water and montmorillonite until completely hydrated, centrifuging, and adjusting the pH to 6.6-7.0 with acetate buffer to remove impurities; mixing the purified montmorillonite with a ferric chloride solution, and subjecting the mixture to 3-5 cycles of shaking, washing, and freeze-drying to obtain Fe(III)-modified montmorillonite. This invention also provides a PAH degradation catalyst composed of Fe(III)-modified montmorillonite and persulfate at a weight ratio of 1:25. This catalyst achieves a PAH degradation rate of 76.0% within 30 days and a high PAH degradation rate of up to 91.3% for high molecular weight PAHs. This invention reveals for the first time the synergistic effect mechanism of Fe(III)-modified montmorillonite and persulfate, solving technical problems such as rapid decomposition of oxidants and poor catalyst stability in tropical soil remediation.

Description

Technical Field

[0001] This invention belongs to the field of soil remediation technology, specifically relating to a method for preparing Fe(III) modified montmorillonite, Fe(III) modified montmorillonite, a polycyclic aromatic hydrocarbon degradation catalyst and its application. Background Art

[0002] Tropical regions (such as Hainan) experience rapid migration and diffusion of organic pollutants (e.g., PAHs) in soil due to their hot and humid climate. Traditional remediation technologies face unique challenges: the high temperature and humidity accelerate pollutant volatilization while also causing rapid decomposition of chemical oxidants, reducing remediation efficiency; tropical soils are often acidic and have high iron and aluminum oxide content, which may interfere with the performance of traditional iron-based catalysts; although high temperatures promote microbial activity, heavy rainfall can easily lead to the loss of microbial communities, and HMW-PAHs remain difficult to degrade. Therefore, there is an urgent need to develop an efficient, stable, and environmentally friendly degradation technology for soil remediation in tropical regions.

[0003] Among related technologies, persulfate (PS) is widely used for organic matter degradation due to its strong oxidizing power and long half-life; clay minerals, due to their layered structure and cation exchange capacity, are also often used as pollutant adsorbents or catalyst carriers. However, both of these technologies have limitations in pollution remediation:

[0004] Persulfate activation relies on external energy (such as heat or light) or transition metals (such as Fe2+). The Fe2+ / persulfate activation system has limitations in practical applications: 1. Ferrous ions in the soil are easily oxidized and rapidly converted to ferric ions, leading to a sharp drop in persulfate activation efficiency; 2. The activation system is highly sensitive to pH, maintaining efficient reaction only under acidic conditions (pH < 3), but most actual soils are neutral or weakly alkaline; 3. Excessive ferric ions generate ferric hydroxide precipitate, clogging soil pores and passivating active sites. While heterogeneous iron-based catalysts (such as zero-valent iron and iron oxides) can partially alleviate the aforementioned problems, they still suffer from drawbacks such as easy loss of active components and poor recycling performance.

[0005] Montmorillonite, with its layered structure and cation exchange capacity, is a typical clay mineral. Unmodified montmorillonite has limited adsorption capacity for polycyclic aromatic hydrocarbons (PAHs) and cannot activate persulfates. While Fe(III)-modified montmorillonite can promote the electron transfer degradation of PAHs through surface "cation-π" interactions (e.g., Jia HZ, Zhao JC, Li L, et al. Transformation of polycyclic aromatic hydrocarbons (PAHs) on Fe(III)-modified clayminerals: Role of molecular chemistry and clay surface properties[J]. AppliedCatalysis B: Environmental, 2014, 154: 238-245), its degradation rate for PAHs alone is less than 50%, especially for HMW-PAHs.

[0006] Although the individual applications of Fe(III) modified materials and persulfate (PS) have been studied, the synergistic mechanism of their combined system is still unclear: 1. The activation pathway is unclear. There is a lack of experimental verification on whether Fe(III) modified montmorillonite can efficiently activate persulfate and maintain the Fe(III) / Fe(II) cycle; 2. The degradation selectivity is different. Existing technologies show significant differences in the degradation rates of LMW-PAHs and HMW-PAHs, and the toxicity of intermediate products may be increased.

[0007] It is particularly noteworthy that existing studies generally agree that Fe(III) is difficult to directly activate persulfate (e.g., Wang ML, Wang YL, Jing XD, et al. Developments of efficient dithionite-zerovalentiron / persulfate systems with accelerated Fe(III) / Fe(II) cycle for PAHsremoval in water and soils[J]. Chemical Engineering Journal, 2023, 463:142325), and Fe(III)-modified montmorillonite, lacking active iron sites, is even less able to participate in persulfate activation.

[0008] Therefore, how to overcome the inertness limitation of Fe(III) through material design and achieve efficient synergy between Fe(III) modified montmorillonite and persulfate is a current technological gap. Summary of the Invention

[0009] This invention unexpectedly discovered that by optimizing the preparation process of Fe(III)-modified montmorillonite, the interlayer Fe(III) significantly enhances the activation efficiency of PS, and the degradation rate of PAHs after combining the two (76.00%) far exceeds the effect of using Fe(III)-modified montmorillonite alone (40.71%) or persulfate (14.00%). Furthermore, the Fe(III)-modified montmorillonite / persulfate system promotes electron transfer between Fe(III) and persulfate (PS) through surface confinement effect, accelerating Fe(II) regeneration. Its adsorption-oxidation synergistic effect with Fe(III)-modified montmorillonite significantly improves the degradation rate of HMW-PAHs (91.27%). GC-MS confirmed that PAHs ultimately decompose into CO2 and H2O, avoiding the accumulation of toxic intermediates.

[0010] This invention reveals for the first time that Fe(III)-modified montmorillonite and persulfate have a significant synergistic effect, providing an efficient and stable solution for soil remediation in hot zones.

[0011] In a first aspect, the present invention provides a method for preparing Fe(III) modified montmorillonite, the specific technical solution of which is as follows:

[0012] A method for preparing Fe(III) modified montmorillonite, the specific steps of which are as follows:

[0013] Montmorillonite purification: Mix montmorillonite with deionized water and stir until the montmorillonite is completely hydrated; centrifuge to separate the hydrated montmorillonite, and adjust the pH of the montmorillonite with acetate buffer solution to remove impurities, so that the pH is maintained at 6.6-7.0, to obtain purified montmorillonite;

[0014] Montmorillonite modification: The purified montmorillonite was thoroughly shaken and mixed with ferric chloride solution. After 3-5 rounds of shaking and mixing, it was washed with deionized water until the surface was free of chlorine. It was then freeze-dried, ground, and sieved to obtain Fe(III) modified montmorillonite.

[0015] This invention innovatively uses an acetic acid buffer solution (pH=4.7) to adjust the pH value of montmorillonite, gently removing carbonate impurities (reaction formula: CaCO3+2CH3COOH→Ca(CH3COO)2+H2O+CO2↑), precisely controlling the pH within the optimal range of 6.8±0.2, avoiding damage to the montmorillonite crystal structure by strong acid. The resulting ferric acetate intermediate is beneficial for improving the removal rate of Fe3+ intercalated carbonates to 98.5%. After modification, the interlayer spacing (d001) of montmorillonite is stabilized at 1.086nm, and the Fe3+ loading is increased to 19.40%, exhibiting excellent stability under tropical climate conditions.

[0016] Furthermore, in the montmorillonite purification step, the mixing ratio of deionized water to montmorillonite is 1:(15-25); preferably 1:(18-22) (w / w). The specific mixing ratio (w / w) of deionized water to montmorillonite can be 1:18, 1:18.5, 1:19, 1:19.5, 1:20, 1:20.5, 1:21, 1:21.5, 1:20, etc.

[0017] When the mixing ratio of montmorillonite to deionized water is too low (<15:1), insufficient water causes montmorillonite to fail to fully expand, resulting in insufficient exposure of interlayer exchange sites, reduced Fe3+ intercalation efficiency, and a decrease in loading of approximately 22%. When the mixing ratio is too high (>25:1), excessive dilution leads to difficulties in subsequent centrifugation, and there is no significant improvement in Fe3+ adsorption efficiency.

[0018] Furthermore, in the montmorillonite purification step, the mixing ratio of deionized water to montmorillonite is 1:20 (w / w), and the Fe(III) modified montmorillonite prepared has an Fe3+ dissolution rate of <1.2% within 30 days.

[0019] Furthermore, during the montmorillonite purification process, the stirring speed should be controlled at 300-400 rpm for at least 2 hours, until the montmorillonite is completely dispersed into a homogeneous suspension. Specific stirring speeds can be 300 rpm, 310 rpm, 320 rpm, 330 rpm, 340 rpm, 350 rpm, 360 rpm, 370 rpm, 380 rpm, 390 rpm, 400 rpm, etc.

[0020] Furthermore, in the montmorillonite purification step, when centrifuging to separate hydrated montmorillonite, the centrifugation speed is 600-700 rpm and the centrifugation time is 5-8 min; the specific centrifugation speed can be 600 rpm, 610 rpm, 620 rpm, 630 rpm, 640 rpm, 650 rpm, 660 rpm, 670 rpm, 680 rpm, 690 rpm, 700 rpm, etc., and the centrifugation time can be 5 min, 5.5 min, 6 min, 6.5 min, 7 min, 7.5 min, 8 min, etc.

[0021] Furthermore, in the montmorillonite purification step, when centrifuging to separate hydrated montmorillonite, the centrifugation speed is 650 rpm and the centrifugation time is 5 min.

[0022] Furthermore, in the montmorillonite modification step, the concentration of the ferric chloride solution used is 0.1-0.5 mol / L. A concentration <0.1 mol / L easily leads to insufficient Fe3+ intercalation, resulting in a loading of <10%, causing a decrease in PAH degradation rate of more than 40%; a concentration >0.5 mol / L: excessive Fe3+ induces hydrolysis and precipitation (Fe(OH)3), blocking the interlayer channels of montmorillonite. Specific concentrations of the ferric chloride solution can be 0.1 mol / L, 0.15 mol / L, 0.2 mol / L, 0.25 mol / L, 0.3 mol / L, 0.35 mol / L, 0.4 mol / L, 0.45 mol / L, 0.5 mol / L, etc.

[0023] Furthermore, in the derocking modification step, the mass ratio of purified montmorillonite to ferric chloride is 1:(0.5-1.2), specifically 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:1, 1:1.1, 1:1.2, etc.

[0024] Furthermore, the specific steps of freeze-drying in the montmorillonite modification process are as follows:

[0025] S1. Pre-freezing: Place the washed Fe(III) modified montmorillonite wet sample in a freezer and cool it to -40℃~-50℃ at a rate of 1~2℃ / min, and keep it warm for 4h;

[0026] S2. Primary drying: Transfer to a freeze dryer, set the vacuum degree to 10-20Pa and the heating plate temperature to 25-30℃, and continue heating for 24-36 hours;

[0027] S3. Drying: Heat to 35-40℃ and maintain for 6 hours until the sample mass change is <0.05%, to obtain dried Fe(III) modified montmorillonite.

[0028] Pre-freezing reduces mechanical stress on montmorillonite layers, resulting in a layer spacing (d001) retention rate of >95%. The selection of process parameters during the sublimation drying stage can reduce residual moisture, reduce Fe3+ hydrolysis, and minimize local pH increases.

[0029] Secondly, the present invention provides an Fe(III) modified montmorillonite, which is prepared by the aforementioned Fe(III) modified montmorillonite preparation method.

[0030] Thirdly, the present invention provides a polycyclic aromatic hydrocarbon degradation catalyst, which is composed of persulfate and Fe(III) modified montmorillonite prepared by the aforementioned Fe(III) modified montmorillonite preparation method, wherein the weight ratio of persulfate to Fe(III) modified montmorillonite is 1:25.

[0031] Fourthly, the present invention provides an application of the aforementioned polycyclic aromatic hydrocarbon (PAH) degradation catalyst in the remediation of PAH-contaminated soil.

[0032] Furthermore, the Fe(III)-modified montmorillonite in the polycyclic aromatic hydrocarbon degradation catalyst was added at a ratio of 5 wt% compared to the contaminated soil.

[0033] The present invention has the following beneficial effects:

[0034] 1. This invention optimizes the preparation process of Fe(III) modified montmorillonite, and the Fe(III) modified montmorillonite obtained can significantly improve the activation efficiency of persulfate.

[0035] 2. The degradation rate of PAHs by Fe(III) modified montmorillonite combined with persulfate in this invention (76.00%) far exceeds that of Fe(III) modified montmorillonite alone (40.71%) or persulfate alone (14.00%), significantly improving the degradation rate of HMW-PAHs (91.27%), and ultimately decomposing into CO2 and H2O, avoiding the accumulation of toxic intermediates.

[0036] 3. This invention reveals for the first time that Fe(III) modified montmorillonite and persulfate have a significant synergistic effect, providing an efficient and stable solution for soil remediation in hot zones. Attached Figure Description

[0037] Figure 1 Scanning electron microscope (SEM) images of modified / unmodified montmorillonite;

[0038] Figure 2 EDS energy dispersive spectroscopy results for modified / unmodified montmorillonite;

[0039] Figure 3 XRD spectra of modified / unmodified montmorillonite;

[0040] Figure 4 FTIR Fourier transform infrared spectra of modified / unmodified montmorillonite;

[0041] Figure 5 Figure 1 shows the experimental results of the effect of different treatment groups on the degradation rate of PAHs.

[0042] Figure 6 Figure 1 shows the experimental results of the effect of different treatment groups on the degradation rate of LMW-PAHs and HMW-PAHs.

[0043] Figure 7 Electron spin resonance (EPR) spectra for different treatment groups;

[0044] Figure 8 The image shows the results of the quenching experiment.

[0045] Figure 9 Figure 1 shows the experimental results of the effect of different treatment groups on the Fe(II) content in the soil.

[0046] Figure 10 This is a diagram of the ANT degradation pathway.

[0047] Figure 11 This is a mass spectrum of ANT degradation. Detailed Implementation

[0048] To enable those skilled in the art to better understand the technical solutions of this invention, the present application will be further described in detail below with reference to embodiments.

[0049] [Preparation of Fe(III) modified montmorillonite]

[0050] P1. Montmorillonite purification:

[0051] Mix 100g of montmorillonite with 2000mL of deionized water (1:20, w / w), stir at 350rpm for 2h until fully hydrated, centrifuge at 650rpm for 5min, and discard the supernatant; add 500mL of acetate buffer (pH=4.76) to adjust the pH of the system to 6.8±0.2, stir for 30min to remove carbonate, and centrifuge again to separate and purify montmorillonite.

[0052] In other embodiments, the mixing ratio of montmorillonite to deionized water can be selected in the range of 1:(15-25)(w / w), preferably 1:(18-22)(w / w), and more preferably 1:20(w / w); the centrifugation rate is between 600-700 rpm and the centrifugation time is between 5-8 min, which can meet the preparation requirements.

[0053] P2, Iron Modification:

[0054] The purified montmorillonite was mixed with 0.3 mol / L ferric chloride solution at a mass ratio of 1:1 (calculated as montmorillonite:FeCl3), and the mixture was shaken and mixed 4 times for 10 min each time; the mixture was then washed with deionized water until no chloride ions were detected by AgNO3.

[0055] In other embodiments, a ferric chloride solution with a concentration of 0.1-0.5 mol / L can be used, and the mass ratio of the mixed montmorillonite to ferric chloride is 1:(0.5-1.2). Too low / too high concentrations or mixing ratios may lead to insufficient Fe3+ intercalation, or excessive Fe3+ may induce hydrolysis and precipitation (Fe(OH)3) which blocks the interlayer channels of montmorillonite, potentially causing a decrease in the degradation rate of PAHs.

[0056] P3, freeze-drying:

[0057] The washed Fe(III) modified montmorillonite was placed in a freezer and cooled to -45℃ at a rate of 1.5℃ / min, and kept at that temperature for 4 hours for pre-freezing. Then, the Fe(III) modified montmorillonite was transferred to a freeze desiccant, and the vacuum degree was set to 15Pa and the heating plate temperature to 28℃. The mixture was heated for 28 hours. The temperature was then raised to 38℃ and held for 6 hours until the mass change was <0.05% / h, thus obtaining dried Fe(III) modified montmorillonite.

[0058] In other embodiments, the freeze-drying process parameters can be adjusted within a small range, such as pre-freezing at -40℃ to -50℃, vacuum degree at 10-20Pa, heating plate temperature at 25-30℃, continuous heating for 24-36 hours, and desorption drying temperature at 35-40℃, all of which can meet the preparation requirements.

[0059] To verify the success of the modification, the microstructure and chemical composition of Fe(III) modified montmorillonite were comprehensively characterized by SEM, XRD and FTIR and compared with unmodified montmorillonite (Na@M).

[0060] Figure 1 Images a through c are SEM images of unmodified montmorillonite (Na@M), and images d through f are SEM images of Fe(III)-modified montmorillonite (Fe@M). Figure 1 As shown, unmodified montmorillonite (Na@M) exhibits a clear flaky stacked structure with a smooth surface, while Fe(III)-modified montmorillonite (Fe@M) shows curling and localized layering characteristics due to the larger hydration radius of Fe(III).

[0061] like Figure 2 As shown, the Fe and O content in Fe(III)-modified montmorillonite (Fe@M) is significantly increased. Compared to Fe(III)-modified montmorillonite (Fe@M), the EDS signal of unmodified montmorillonite (Na@M) shows almost no iron, while the iron content of Fe(III)-modified montmorillonite (Fe@M) increases to 19.40%. The increase in Fe and O content confirms the presence of Fe(III) and iron (hydroxide) oxides.

[0062] The interlayer distance between clay flakes determines the material's adsorption capacity, an indicator that can be accurately measured by the d001 spacing characterized by XRD. (Refer to...) Figure 3 The d001 spacing of unmodified montmorillonite (Na@M) is 0.978 nm. After Fe(III) saturation, the d001 spacing increases to 1.086 nm. Due to the cation exchange reaction between Fe(III) ions and Na(I) ions, Fe(III) ions with larger hydration radii intercalate into the interlayer of unmodified montmorillonite (Na@M), increasing the d001 spacing.

[0063] Reference Figure 4FTIR results showed that the bending vibrations of Si-O-Al and Al2OH were fully preserved at 520 cm⁻¹ and 920 cm⁻¹, respectively. Due to the overlap between the characteristic peaks of iron (hydride) oxides and the iron species inherent in the crystal structure of unmodified montmorillonite (Na@M), the Fe-OH peak area at 1000 cm⁻¹ in Fe(III)-modified montmorillonite (Fe@M) was larger than that in unmodified montmorillonite (Na@M).

[0064] [PAH-contaminated soil remediation]

[0065] 5% (by weight) Fe(III)-modified montmorillonite (Fe@M) or unmodified montmorillonite (Na@M) was mixed with 300g of contaminated soil from a coking plant in a flask, and an appropriate amount of sodium persulfate (PS) was added. Specific dosages are shown in Table 1. The mixture was stirred thoroughly with a glass rod, and an appropriate amount of distilled water was added to maintain a water-to-soil ratio of 1:1. Each treatment was repeated three times. Soil samples were collected on days 0, 3, 5, 7, 11, 15, 22, and 30 for PAH determination and other analyses.

[0066] Table 1 - Experimental setup for the Fe@M / PS degradation system

[0067]

[0068] like Figure 5 As shown, at day 30, the degradation rate of PAHs in soil treated with Fe(III)-modified montmorillonite (Fe@M) reached 40.71%, which was 30.0% higher than that of unmodified montmorillonite (Na@M). Furthermore, the degradation rate of PAHs in soil treated with Fe@M+PS was 76.00%, significantly higher than that of Fe@M and PS by 36.67% and 62.00%, respectively. That is, the introduction of Fe@M and Fe@M+PS significantly improved the degradation effect of PAHs in contaminated soil.

[0069] Reference Figure 6 On day 30, Fe@M+PS achieved a degradation rate of 53.62% for LMW-PAHs in soil, which was 19.70% and 33.45% higher than that of Fe@M and PS treatments, respectively. Fe@M+PS achieved a degradation rate of 91.27% for HMW-PAHs in soil, which was 46.49% and 81.88% higher than that of Fe@M and PS treatments, respectively. Fe@M achieved a degradation rate of 44.78% for HMW-PAHs in soil, which was 35.08% higher than that of Na@M. Therefore, Fe@M and Fe@M+PS significantly improved the degradation of HMW-PAHs in contaminated soil within the coking plant.

[0070] These results demonstrate the superior performance of Fe@M and its complexes in degrading HMW-PAHs. In particular, Fe@M+PS also exhibits significant advantages in the treatment of LMW-PAHs.

[0071] [Free radical quenching experiment]

[0072] In this experiment, the commonly used 5,5-dimethyl-1-pyrrole-N-oxide (DMPO) was selected as a scavenger for HO· and SO4-· free radicals.

[0073] The steps for Fe@M activating PS to treat PAHs in soil are as follows:

[0074] Fe@M and PS reacted in a 50 mL opaque plastic tube. After 5 min of reaction, 1 mL of the filtered reaction solution (0.22 μm) was added to a 1.5 mL centrifuge tube containing 250 μL DMPO. After rapid and thorough mixing, a certain amount of the mixture was transferred to a paramagnetic tube using a capillary quartz tube and placed in the resonance chamber of the EPR instrument for detection and analysis.

[0075] This experiment used methanol (MeOH), tert-butanol (TBA), and potassium iodide (KI) as free radical probes to quench free radicals in the reaction system, thereby achieving identification. To investigate the main free radicals involved in this experiment, following the aforementioned steps, anthracene (ANT) was used as a representative pollutant. Excess MeOH, TBA, and KI were added to the system before the reaction, each at a concentration of 100 mM. The results were compared with the untreated control group to deduce the main free radical types in the Fe@M / PS system.

[0076] The formation of unpaired electrons in the Fe@M+PS and Na@M+PS systems was determined by electron spin resonance spectroscopy (EPR). After the Fe@M+PS and Na@M+PS systems reacted for 5 min, DMPO was used as a standard spin trapping agent for trapping. The characteristic peak signals of DMPO-HO·(1:2:2:1) and DMPO-SO4-·(1:1:1:1:1:1:1) were measured as follows: Figure 7 As shown, HO· and SO4-· free radicals were detected in the Fe@M+PS system.

[0077] The relevant results of the free radical quenching experiment are as follows Figure 8As shown, the treatment group without any quencher was designated as the untreated group. After adding methanol (MeOH) to the Fe@M+PS system, the degradation rate of ANT decreased from 73.31% to 47.42%. This indicates the presence of HO· and SO4-· radicals in the Fe@M+PS system during the reaction. Conversely, in the Fe@M+PS system with the introduction of tert-butanol (TBA), the degradation rate of ANT only decreased to 61.91%, indicating that TBA has a weaker quenching effect on free radicals compared to MeOH. The relatively high rate constant between TBA and HO· radicals further confirmed the presence of HO· radicals in the system. The results of the MeOH and TBA quenching experiments show that, in the presence of Fe@M, PS simultaneously contains HO· and SO4-· radicals during the oxidation of ANT. Subsequently, the addition of potassium iodide (KI) reduced the degradation rate of ANT to 43.22%, further indicating that the degradation process mainly occurs on the material surface.

[0078] These results clearly indicate that HO· radicals and SO4-· radicals play a crucial role in the degradation of ANT during surface reactions, especially the role of SO4-· radicals.

[0079] [Formation of Fe(II)]

[0080] like Figure 9 As shown, the Fe(II) content (CK) in the control soil was 1.52 g / kg. By day 30, the Fe(II) concentration in the contaminated soil of the coking plant treated with Fe@M was 1.66 g / kg, an increase of 12.41% compared to the Fe(II) concentration in the Na@M treated soil. Notably, there was a significant positive correlation between the Fe(II) concentration in the Fe@M treated soil and the degradation rate of PAHs (r = 0.9508, p < 0.05).

[0081] The results above show that Fe(III) ions in the Fe@M layer react with PAHs in the soil through electron transfer, thereby generating Fe(II) ions and increasing the Fe(II) content in the soil.

[0082] according to Figure 5-6The results showed no significant difference in PAH degradation rates between the PS and Na@M+PS treatments, indicating that Na@M failed to effectively promote PS activation. However, the PAH degradation rate under the Fe@M+PS treatment was significantly higher than that under the Fe@M treatment by 36.70%, clearly promoting the PAH degradation process. These results indicate that PS was effectively activated by Fe@M. In the Fe@M+PS treatment, the Fe(II) concentration first decreased and then increased. This phenomenon may be due to electron transfer during Fe@M adsorption of PAHs in the soil, leading to the release of Fe(II) ions from the interlayer participating in the PS activation process. Notably, the Fe(II) concentration in the Fe@M+PS treated soil was 16.76% lower than that in the CK treated soil. This difference may be attributed to the consumption of Fe(II) in the soil during the PS degradation process.

[0083] [ANT degradation pathway]

[0084] Using anthracene (ANT) as the main pollutant, GC-MS was used to identify potential intermediates generated during ANT degradation. The results showed that anthraquinones, benzophenones, and phenols were the main intermediates in ANT degradation. Possible degradation pathways include... Figure 10 and Figure 11 As shown.

[0085] First, the single-electron strong oxidizing agent SO4-· radical undergoes an addition reaction with ANT at the C9 or C10 position. Since SO4-· radical is a favorable leaving group, ANT can undergo hydroxylation via the elimination of sulfate groups and hydrolysis to generate the intermediate anthraquinone (A), which then rapidly isomeric to form the thermodynamically favorable anthrone (B). The sulfate anion radical can oxidize, hydrolyze, and then oxidize the anthrone to anthraquinone (D). Simultaneously, ANT is adsorbed by Fe@M, and with the accompanying surface "cation-π" interaction, electrons are transferred from anthraquinone to Fe(III) on the Fe@M surface, ultimately generating the oxidation product anthraquinone. Subsequently, anthraquinone undergoes an addition reaction to generate the intermediate 2-(2-hydroxybenzoyl)benzaldehyde (E), which then generates benzophenone (F) through the loss of CO2 and H2O. Benzophenone is oxidized to phenol (G), which ultimately decomposes into CO2 and H2O.

[0086] The above are all preferred embodiments of the present application, and are not intended to limit the scope of protection of the present application. Therefore, any equivalent changes made based on the structure, shape, and principle of the present application should be included in the scope of protection of the present application.

Claims

1. The application of a polycyclic aromatic hydrocarbon (PAH) degradation catalyst in the remediation of PAH-contaminated soil, characterized in that: The polycyclic aromatic hydrocarbon degradation catalyst is composed of persulfate and Fe(III)-modified montmorillonite in a weight ratio of 1:25; wherein, The specific preparation steps for Fe(III) modified montmorillonite are as follows: Montmorillonite purification: Mix deionized water and montmorillonite at a mass ratio of 1:20 and stir until the montmorillonite is completely hydrated; centrifuge to separate the hydrated montmorillonite, and adjust the pH of the montmorillonite with an acetate buffer solution to remove impurities, so that the pH is maintained at 6.6-7.0, to obtain purified montmorillonite; Montmorillonite modification: The purified montmorillonite was thoroughly shaken and mixed with a ferric chloride solution with a concentration of 0.1-0.5 mol / L. The mass ratio of purified montmorillonite to ferric chloride was 1:(0.5-1.2). After 3-5 rounds of shaking and mixing, the mixture was washed with deionized water until the surface was free of chlorine, freeze-dried, ground, and sieved to obtain Fe(III) modified montmorillonite. The specific steps for freeze-drying are as follows: S1. Pre-freezing: Place the washed Fe(III) modified montmorillonite wet sample in a freezer and cool it to -40℃~-50℃ at a rate of 1~2℃ / min, and keep it warm for 4h; S2. Primary drying: Transfer to a freeze dryer, set the vacuum degree to 10-20Pa and the heating plate temperature to 25-30℃, and continue heating for 24-36 hours; S3. Drying: Heat to 35-40℃ and maintain for 6 hours until the sample mass change is <0.05%, to obtain dried Fe(III) modified montmorillonite.

2. The application of the polycyclic aromatic hydrocarbon degradation catalyst according to claim 1 in the remediation of polycyclic aromatic hydrocarbon contaminated soil, characterized in that: In the montmorillonite purification process, when centrifuging to separate hydrated montmorillonite, the centrifugation speed is 600-700 rpm and the centrifugation time is 5-8 min.

3. The application of the polycyclic aromatic hydrocarbon (PAH) degradation catalyst according to claim 1 or 2 in the remediation of PAH-contaminated soil, characterized in that: The Fe(III)-modified montmorillonite in the polycyclic aromatic hydrocarbon degradation catalyst was added at a ratio of 5 wt% compared to the contaminated soil.

Images