Fe (III) modified montmorillonite preparation method, Fe (III) modified montmorillonite, polycyclic aromatic hydrocarbon degradation catalyst and application

Abstract

The invention belongs to the technical field of soil remediation, and particularly relates to a Fe (III) modified montmorillonite preparation method, Fe (III) modified montmorillonite, a polycyclic aromatic hydrocarbon degradation catalyst and application. The method comprises the following steps: mixing and stirring deionized water and montmorillonite until the mixture is completely hydrated, centrifuging, adjusting the pH value to 6.6-7.0 by using an acetic acid buffer solution, and removing impurities; and mixing the purified montmorillonite with a ferric chloride solution, oscillating for 3-5 rounds, washing, and freeze-drying to obtain the Fe (III) modified montmorillonite. The invention also provides a polycyclic aromatic hydrocarbon degradation catalyst, which is composed of Fe (III) modified montmorillonite and persulfate according to a weight ratio of 1: 25. The degradation rate of the catalyst to PAHs within 30 days reaches 76.0%, and the degradation rate of the catalyst to high molecular weight PAHs reaches 91.3%. The invention discloses a synergistic interaction mechanism of Fe (III) modified montmorillonite persulfate for the first time, and solves the technical problems of quick decomposition of an oxidizing agent, poor stability of a catalyst and the like in soil remediation in tropical regions.

Description

Technical Field

[0001] The present invention belongs to the technical field of soil remediation, and in particular relates to a method for preparing Fe(III)-modified montmorillonite, Fe(III)-modified montmorillonite, a polycyclic aromatic hydrocarbon degradation catalyst and applications. Background Art

[0002] Due to the hot and rainy climate in tropical areas (such as Hainan), the migration and diffusion of organic pollutants (such as PAHs) in the soil are relatively fast, and traditional remediation technologies face special challenges: high temperature and high humidity accelerate the volatilization of pollutants, while also leading to the rapid decomposition of chemical oxidants, reducing remediation efficiency; tropical soils are mostly 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 cause bacterial loss, and HMW-PAHs are still difficult to degrade. Therefore, it is urgent to develop an efficient, stable and environmentally friendly degradation technology for soil remediation in hot areas.

[0003] Among the related technologies, persulfate (PS) is widely used in organic matter reduction due to its strong oxidizing property and long half-life; clay minerals are also often used as pollutant adsorbents or catalyst carriers due to their layered structure and cation exchange capacity. However, both of these technical means have application limitations in pollution remediation: Persulfate activation relies on external energy (such as heat, 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 quickly converted into ferric ions, resulting in a sharp drop in the efficiency of persulfate activation; 2. The activation system is highly sensitive to pH and can only maintain efficient reactions under acidic conditions (pH <3), but actual soils are mostly neutral or weakly alkaline; 3. Excessive iron ions generate iron hydroxide precipitates, which block soil pores and passivate active sites. Although heterogeneous iron-based catalysts (such as zero-valent iron and iron oxides) can partially alleviate the above problems, they still have shortcomings such as easy loss of active components and poor cycle performance.

[0004] Montmorillonite is a typical clay mineral with a layered structure and cation exchange capacity. Unmodified montmorillonite has limited adsorption capacity for PAHs and cannot activate persulfate. Although Fe(III)-modified montmorillonite can promote the electron transfer degradation of PAHs through the surface "cation-π" effect (such as Jia HZ, Zhao JC, Li L, et al. Transformationof 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 single action on PAHs degradation rate is less than 50%, especially for HMW-PAHs.

[0005] Although the separate applications of Fe(III)-modified materials and persulfate (PS) have been studied, the synergistic mechanism of their combined system has not yet been clarified: 1. The activation pathway is unclear, and there is a lack of experimental verification as to whether Fe(III)-modified montmorillonite can efficiently activate persulfate and maintain the Fe(III) / Fe(II) cycle; 2. The degradation selectivity is different. The existing technologies have significant differences in the degradation rates of LMW-PAHs and HMW-PAHs, and the toxicity of the intermediates may increase.

[0006] It is particularly worth noting that existing studies generally believe that Fe(III) is difficult to directly activate persulfate (such as 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 cannot participate in persulfate activation due to the lack of active iron sites.

[0007] Therefore, how to break through 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

[0008] The present invention unexpectedly discovered that by optimizing the preparation process of Fe(III)-modified montmorillonite, its interlayer Fe(III) can significantly improve the activation efficiency of PS, and the degradation rate of PAHs after the two are compounded (76.00%) is far higher than the effect of using Fe(III)-modified montmorillonite (40.71%) or persulfate (14.00%) alone. Furthermore, the Fe(III)-modified montmorillonite / persulfate system promotes the electron transfer between Fe(III) and persulfate (PS) through the surface confinement effect, accelerates the regeneration of Fe(II), and its adsorption-oxidation synergy with Fe(III)-modified montmorillonite significantly improves the degradation rate of HMW-PAHs (91.27%); GC-MS confirmed that PAHs are finally decomposed into CO2 and H2O, avoiding the accumulation of toxic intermediates.

[0009] The present 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 areas.

[0010] In the first aspect, the present invention provides a method for preparing Fe(III) modified montmorillonite, and the specific technical scheme provided is as follows: A method for preparing Fe(III) modified montmorillonite, the specific steps are as follows: Purification of montmorillonite: Mix ionized water and montmorillonite and stir until the montmorillonite is completely hydrated; centrifuge and separate the hydrated montmorillonite, and use acetic acid buffer solution to adjust the pH value of the montmorillonite to remove impurities and keep the pH at 6.6-7.0 to obtain purified montmorillonite; Montmorillonite modification: The purified montmorillonite and the ferric chloride solution are fully shaken and mixed. After 3-5 rounds of shaking and mixing, the mixture is washed with deionized water until the surface is free of chlorine, freeze-dried, ground, and sieved to obtain Fe(III)-modified montmorillonite.

[0011] The present invention innovatively uses an acetic acid buffer solution (pH=4.7) to adjust the pH value of montmorillonite and gently remove carbonate impurities (reaction formula: CaCO 3 +2CH 3 COOH→Ca(CH 3 COO 2 +H 2 O+CO 2 ↑), the pH is precisely controlled in the optimal range of 6.8±0.2 to avoid the destruction of the montmorillonite crystal structure by strong acid. The formed ferric acetate intermediate is conducive to the subsequent Fe3+ intercalation carbonate removal rate to 98.5%. The interlayer spacing (d001) of the modified montmorillonite is stabilized at 1.086nm, and the Fe3+ loading capacity is increased to 19.40%, with good stability under tropical climate conditions.

[0012] Furthermore, in the montmorillonite purification step, the mixing ratio of deionized water to montmorillonite is 1:(15-25); preferably 1:(18-22) (w / w), and the mixing ratio of deionized water to montmorillonite (w / w) can specifically be 1:18, 1:18.5, 1:19, 1:19.5, 1:20, 1:20.5, 1:21, 1:21.5, 1:20, etc.

[0013] When the mixing ratio of montmorillonite and deionized water is too low (<15:1), insufficient water causes the montmorillonite to fail to fully expand, the interlayer exchange sites are not fully exposed, the Fe3+ intercalation efficiency is reduced, and the loading capacity decreases by about 22%; when the mixing ratio is too high (>25:1), excessive dilution leads to difficulties in subsequent centrifugal separation, and the Fe3+ adsorption efficiency is not significantly improved.

[0014] Furthermore, in the montmorillonite purification step, the mixing ratio of deionized water to montmorillonite was 1:20 (w / w), and the Fe3+ dissolution rate of the prepared Fe(III) modified montmorillonite was <1.2% within 30 days.

[0015] Furthermore, during the mixing and stirring in the montmorillonite purification step, the stirring speed is controlled at 300-400 rpm for ≥ 2 hours until the montmorillonite is completely dispersed into a uniform suspension. The stirring speed can be specifically 300 rpm, 310 rpm, 320 rpm, 330 rpm, 340 rpm, 350 rpm, 360 rpm, 370 rpm, 380 rpm, 390 rpm, 400 rpm, etc.

[0016] Furthermore, in the montmorillonite purification step, when centrifuging the hydrated montmorillonite, the centrifugal speed is 600-700rpm and the centrifugal time is 5-8min; the centrifugal speed can specifically be 600rpm, 610rpm, 620rpm, 630rpm, 640rpm, 650rpm, 660rpm, 670rpm, 680rpm, 690rpm, 700rpm, etc., and the centrifugal time can be 5min, 5.5min, 6min, 6.5min, 7min, 7.5min, 8min, etc.

[0017] Furthermore, in the montmorillonite purification step, when centrifuging the hydrated montmorillonite, the centrifugal speed is 650 rpm and the centrifugal time is 5 min.

[0018] Furthermore, in the montmorillonite modification step, the concentration of the ferric chloride solution used is 0.1-0.5 mol / L. Concentration <0.1 mol / L can easily lead to insufficient Fe3+ intercalation, and the loading amount <10%, resulting in a more than 40% decrease in the PAHs degradation rate; concentration >0.5 mol / L: excessive Fe3+ induces hydrolysis precipitation (Fe(OH) 3), blocking the interlayer channels of montmorillonite. The concentration of the ferric chloride solution can be 0.1mol / L, 0.15mol / L, 0.2mol / L, 0.25mol / L, 0.3mol / L, 0.35mol / L, 0.4mol / L, 0.45mol / L, 0.5mol / L, etc.

[0019] Furthermore, in the de-stone modification step, the mass ratio of the 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.

[0020] Furthermore, in the montmorillonite modification step, the specific operation steps of freeze drying are as follows: S1. Pre-freezing: Place the washed Fe(III) modified montmorillonite wet sample in a freezer, cool it to -40℃~-50℃ at a rate of 1~2℃ / min, and keep it warm for 4h; S2, primary drying: transfer to freeze dryer, set vacuum degree 10-20Pa, heating plate temperature 25-30℃, continue heating for 24-36h; S3. Desorption and drying: raise the temperature to 35-40°C and maintain for 6 hours until the sample mass change is less than 0.05%, thereby obtaining dry Fe(III)-modified montmorillonite.

[0021] Pre-freezing reduces the mechanical stress on the montmorillonite flakes, and the interlayer spacing (d001) retention rate is >95%. The selection of process parameters in the sublimation drying stage can reduce residual moisture, Fe3+ hydrolysis and local pH increase.

[0022] In a second aspect, the present invention provides a Fe(III)-modified montmorillonite, which is prepared by the aforementioned Fe(III)-modified montmorillonite preparation method.

[0023] In a third aspect, 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, and the weight ratio of persulfate to Fe(III) modified montmorillonite is 1:25.

[0024] In a fourth aspect, the present invention provides an application of the aforementioned PAH degradation catalyst in the remediation of PAH-contaminated soil.

[0025] Furthermore, the addition ratio of Fe(III) modified montmorillonite in the PAH degradation catalyst to the contaminated soil is 5 wt %.

[0026] The present invention has the following beneficial effects: 1. The present invention optimizes the preparation process of Fe(III)-modified montmorillonite, and the obtained Fe(III)-modified montmorillonite can significantly improve the activation efficiency of persulfate; 2. The degradation rate of PAHs (76.00%) after the Fe(III)-modified montmorillonite and persulfate are compounded in the present invention, which is much higher than the effect of using Fe(III)-modified montmorillonite (40.71%) or persulfate (14.00%) alone, and the degradation rate of HMW-PAHs (91.27%) is significantly improved, and finally decomposed into CO2 and H2O, avoiding the accumulation of toxic intermediates. 3. The present invention reveals for the first time that Fe(III)-modified montmorillonite and persulfate have significant synergistic effects, providing an efficient and stable solution for soil remediation in hot areas. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The scanning electron microscope (SEM) images of modified / unmodified montmorillonite; Figure 2 The EDS spectrum analysis results of modified / unmodified montmorillonite are shown; Figure 3 is the XRD spectra of modified / unmodified montmorillonite; Figure 4 FTIR Fourier transform infrared spectra of modified / unmodified montmorillonite; Figure 5 This is the test result diagram of the effect of different treatment groups on the degradation rate of PAHs; Figure 6 This is the test result diagram of the effect of different treatment groups on the degradation rate of LMW-PAHs and HMW-PAHs; Figure 7 Electron spin resonance (EPR) spectra of different treatment groups; Figure 8 This is the result of the quenching experiment; Fig. 9 This is the test result diagram of the effect of different treatment groups on the Fe(II) content in the soil; Fig.10 This is the ANT degradation pathway diagram; Fig.11 This is the mass spectrum of ANT degradation. DETAILED DESCRIPTION

[0028] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the present application will be further described in detail below in conjunction with embodiments.

[0029] [Preparation of Fe(III) modified montmorillonite] P1. Montmorillonite purification: Take 100g of montmorillonite and mix it with 2000mL of deionized water (1:20, w / w), stir at 350rpm for 2h until completely hydrated, centrifuge at 650rpm for 5min, and discard the supernatant; add 500mL of acetate buffer (pH=4.76), adjust the pH of the system to 6.8±0.2, stir for 30min to remove carbonate, and centrifuge again to purify the montmorillonite.

[0030] 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 further preferably 1:20 (w / w); the centrifugal separation rate is 600-700 rpm and the centrifugation time is between 5-8 min, both of which can meet the preparation requirements.

[0031] P2, Iron modification: The purified montmorillonite was mixed with 0.3 mol / L ferric chloride solution in a 1:1 mass ratio (montmorillonite: FeCl 3 Mix with deionized water until AgNO 3 No chloride ions were detected.

[0032] 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 mixed montmorillonite to ferric chloride is 1:(0.5-1.2) based on ferric chloride. Too low / too high a concentration or mixing ratio may easily lead to insufficient Fe3+ intercalation or excessive Fe3+ causing hydrolysis precipitation (Fe(OH) 3 ) block the interlayer channels of montmorillonite, which may lead to a decrease in the degradation rate of PAHs.

[0033] P3. Freeze drying: The washed Fe(III)-modified montmorillonite was placed in a freezer, cooled to -45°C at a rate of 1.5°C / min, and kept warm for 4 hours for pre-freezing; then, the Fe(III)-modified montmorillonite was transferred to a freeze dryer, the vacuum degree was set to 15 Pa, the heating plate temperature was set to 28°C, and heating was continued for 28 hours; then the temperature was raised to 38°C and maintained for 6 hours until the mass change was <0.05% / h, thereby obtaining dry Fe(III)-modified montmorillonite.

[0034] In other embodiments, the freeze-drying process parameters can be adjusted in a small range, including pre-freezing at -40°C to -50°C, vacuum degree at 10-20Pa, heating plate temperature at 25-30°C, continuous heating at 24-36h, and analytical drying temperature at 35-40°C, all of which can meet the preparation requirements.

[0035] To verify the success of the modification, the microstructure and chemical composition of the Fe(III)-modified montmorillonite were comprehensively characterized using SEM, XRD, and FTIR, and compared with the unmodified montmorillonite (Na@M).

[0036] Figure 1 a~c are SEM images of unmodified montmorillonite (Na@M), and d~f are SEM images of Fe(III)-modified montmorillonite (Fe@M). Figure 1 As shown, the unmodified montmorillonite (Na@M) exhibits a clear lamellar stacking structure with a smooth surface, while the Fe(III)-modified montmorillonite (Fe@M) exhibits curling and local stratification characteristics due to the large hydration radius of Fe(III).

[0037] like Figure 2 As shown in the figure, the content of Fe and O in Fe(III) modified montmorillonite (Fe@M) increased significantly. Compared with Fe(III) modified montmorillonite (Fe@M), the EDS signal in unmodified montmorillonite (Na@M) had almost no iron element, while the iron content of Fe(III) modified montmorillonite (Fe@M) increased to 19.40%. The increase in Fe and O content confirmed the presence of Fe(III) and iron (hydroxide) oxides.

[0038] The interlayer distance between clay flakes determines the adsorption capacity of the material, which can be accurately measured by the d001 spacing characterized by XRD. 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) with a larger hydration radius is intercalated into the interlayer of unmodified montmorillonite (Na@M), increasing the d001 spacing.

[0039] Reference Figure 4 , FTIR results show that the bending vibrations of Si-O-Al and Al2OH are completely retained at 520 cm-1 and 920 cm-1, respectively. Due to the overlap between the characteristic peaks of iron (hydr)oxides and the inherent iron species in the crystal structure of unmodified montmorillonite (Na@M), the Fe-OH peak area at 1000 cm-1 of Fe(III)-modified montmorillonite (Fe@M) is larger than that of unmodified montmorillonite (Na@M).

[0040] [PAHs contaminated soil remediation] Mix 5% (weight ratio) of Fe(III) modified montmorillonite (Fe@M) or unmodified montmorillonite (Na@M) with 300g of contaminated soil from the coking plant in a flask, and add an appropriate amount of sodium persulfate (PS). The specific dosage is shown in Table 1. Stir evenly with a glass rod, and add an appropriate amount of distilled water to keep the water-soil ratio at 1:1. Each treatment was repeated 3 times. Soil samples were collected at 0d, 3d, 5d, 7d, 11d, 15d, 22d and 30d for PAHs determination and other analyses.

[0041] Table 1-Experimental setup of Fe@M / PS degradation system

[0042] like Figure 5 As shown. At 30 days, the PAHs degradation rate in the soil treated with Fe(III)-modified montmorillonite (Fe@M) reached 40.71%, which was 30.0% higher than that of unmodified montmorillonite (Na@M). In addition, the PAHs degradation rate in the soil treated with Fe@M+PS was 76.00%, which was 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.

[0043] Reference Figure 6 On the 30th day of treatment, the degradation rate of LMW-PAHs in soil by Fe@M+PS was 53.62%, which was 19.70% and 33.45% higher than those of Fe@M and PS, respectively. The degradation rate of HMW-PAHs in soil by Fe@M+PS was 91.27%, which was 46.49% and 81.88% higher than those of Fe@M and PS, respectively. The degradation rate of HMW-PAHs in soil by Fe@M was 44.78%, which was 35.08% higher than that of Na@M. Therefore, Fe@M and Fe@M+PS significantly improved the degradation effect of HMW-PAHs in contaminated soil in coking plants.

[0044] These results indicate that Fe@M and its composites have excellent performance in degrading HMW-PAHs. In particular, Fe@M+PS also exhibits significant advantages in the treatment of LMW-PAHs.

[0045] [Free radical quenching test] In this experiment, the commonly used 5,5-dimethyl-1-pyrrole-N-oxide (DMPO) was selected as the scavenger of HO· and SO4-· free radicals.

[0046] The steps of Fe@M activating PS to treat PAHs in soil are as follows: Fe@M and PS were reacted in a 50 mL light-proof 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 cavity of the EPR instrument for detection and analysis.

[0047] In this experiment, methanol (MeOH), tert-butyl alcohol (TBA) and potassium iodide (KI) were used as free radical probes to quench the free radicals in the reaction system, thereby achieving the identification effect. In order to explore the main free radicals involved in this experiment, according to the above steps, anthracene (ANT) was used as a representative pollutant, and excess MeOH, TBA and KI were added to the system before the reaction, with a concentration of 100 mM. Compared with the blank group (Untreated) without the addition of quencher, the main free radical types in the Fe@M / PS system were inferred.

[0048] 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 trap to trap the spins. 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 in Figure 2, HO· and SO4-· free radicals were detected in the Fe@M+PS system.

[0049] The results of free radical quenching experiments are as follows: Figure 8 As shown in the figure, the treatment group without any quencher was set as the blank group (Untreated). After adding methanol (MeOH) to the Fe@M+PS system, the degradation rate of ANT decreased from 73.31% to 47.42%. This indicates that HO· radicals and SO4-· radicals exist in the Fe@M+PS system during the reaction. In contrast, in the Fe@M+PS system with the introduction of tert-butyl alcohol (TBA), the degradation rate of ANT only decreased to 61.91%, indicating that TBA has a weaker quenching effect on free radicals compared with MeOH. The presence of HO· radicals in the system was further confirmed by the relatively high rate constant between TBA and HO· radicals. The results of the MeOH and TBA quenching experiments showed that in the presence of Fe@M, HO· radicals and SO4-· radicals exist simultaneously in the process of PS oxidation of ANT. Subsequently, after the addition of potassium iodide (KI), the degradation rate of ANT dropped to 43.22%, further indicating that the degradation process mainly occurs on the surface of the material.

[0050] These results clearly indicate that in the surface reactions, HO· radicals and SO4-· radicals play a crucial role in the degradation of ANT, especially the role of SO4-· radicals is more significant.

[0051] [Formation of Fe(II)] like Fig. 9 As shown in the figure, the Fe(II) content in the control soil (CK) was 1.52 g / kg. At the 30th day of treatment, the concentration of Fe(II) in the contaminated soil in the coking plant after Fe@M treatment was 1.66 g / kg, which was 12.41% higher than that in the soil treated with Na@M. It is worth noting that there was a significant positive correlation between the Fe(II) concentration in the soil treated with Fe@M and the degradation rate of PAHs (r=0.9508, p<0.05).

[0052] From the above results, it can be seen that the Fe(III) ions between the Fe@M layers react with the PAHs in the soil through electron transfer to generate Fe(II) ions, thereby increasing the Fe(II) content in the soil.

[0053] according to Figure 5-6 The results showed that there was no significant difference in the degradation rate of PAHs in the soils treated with PS and Na@M+PS, indicating that Na@M failed to effectively promote the activation of PS. However, the degradation rate of PAHs under Fe@M+PS treatment was significantly increased by 36.70% compared with that under Fe@M treatment, which significantly promoted the degradation process of PAHs. From the above results, it can be seen that PS was effectively activated by Fe@M. In the Fe@M+PS treatment, the concentration of Fe (II) first decreased and then increased. This phenomenon may be due to the electron transfer of Fe@M when adsorbing PAHs in the soil, resulting in the release of Fe (II) ions from the interlayer participating in the activation process of PS. It is worth noting that the Fe (II) concentration in the soil treated with Fe@M+PS was 16.76% lower than that in the soil treated with CK. This difference may be attributed to the consumption of Fe (II) in the soil during the degradation process of PS.

[0054] [Degradation pathway of ANT] Taking anthracene (ANT) as the main pollutant, GC-MS technology was used to identify the intermediates that may be generated during the degradation of ANT. The results showed that anthraquinone, benzophenone and phenol were the main intermediates in the degradation of ANT. Possible degradation pathways include Fig.10 and Fig.11 shown.

[0055] First, the single-electron strong oxidant SO4-· radical reacts with ANT at the C9 or C10 position. Since the SO4-· radical is a good leaving group, ANT can undergo a hydroxylation reaction by eliminating the sulfate group and hydrolyzing to generate the intermediate anthracene (A), and then rapidly isomerizes into the thermodynamically favorable anthracene (B). The sulfate anion radical can oxidize anthracene to anthraquinone (D) through oxidation and hydrolysis. At the same time, ANT is adsorbed by Fe@M, accompanied by the surface "cation-π" interaction, which promotes the transfer of electrons from anthracene to Fe (III) on the Fe@M surface, and finally generates the oxidation product anthraquinone). Subsequently, anthraquinone generates the intermediate 2-(2-hydroxybenzoyl)benzaldehyde (2-(2-Hydroxybenzoyl)benzaldehyde) (E) through an addition reaction, and then generates benzophenone (F) through the loss of CO2 and H2O. Benzophenone is oxidized to phenol (G), which is finally decomposed into CO2 and H2O.

[0056] The above are all preferred embodiments of the present application, and the protection scope of the present application is not limited thereto. Therefore, any equivalent changes made according to the structure, shape, and principle of the present application should be included in the protection scope of the present application.

Claims

1. A method for preparing Fe(III) modified montmorillonite, characterized in that: The specific steps are as follows: Purification of montmorillonite: Mix ionized water and montmorillonite and stir until the montmorillonite is completely hydrated; centrifuge and separate the hydrated montmorillonite, and use acetic acid buffer solution to adjust the pH value of the montmorillonite to remove impurities and keep the pH at 6.6-7.0 to obtain purified montmorillonite; Montmorillonite modification: The purified montmorillonite and the ferric chloride solution are fully shaken and mixed. After 3-5 rounds of shaking and mixing, the mixture is washed with deionized water until the surface is free of chlorine, freeze-dried, ground, and sieved to obtain Fe(III)-modified montmorillonite.

2. The method for preparing Fe(III)-modified montmorillonite according to claim 1, characterized in that: In the montmorillonite purification step, the mixing ratio of deionized water to montmorillonite is 1:20 (w / w).

3. The method for preparing Fe(III)-modified montmorillonite according to claim 1, characterized in that: In the montmorillonite purification step, when centrifuging the hydrated montmorillonite, the centrifugal speed is 600-700 rpm and the centrifugal time is 5-8 minutes.

4. The method for preparing Fe(III)-modified montmorillonite according to any one of claims 1 to 3, characterized in that: In the montmorillonite modification step, the concentration of the ferric chloride solution used is 0.1-0.5 mol / L.

5. The method for preparing Fe(III)-modified montmorillonite according to claim 4, characterized in that: In the de-stone modification step, the mass ratio of the purified montmorillonite to ferric chloride is 1:(0.5-1.2).

6. The method for preparing Fe(III)-modified montmorillonite according to claim 4, characterized in that: In the montmorillonite modification step, the specific operation steps of freeze drying are as follows: S1. Pre-freezing: Place the washed Fe(III) modified montmorillonite wet sample in a freezer, cool it to -40℃~-50℃ at a rate of 1~2℃ / min, and keep it warm for 4h; S2, primary drying: transfer to freeze dryer, set vacuum degree 10-20Pa, heating plate temperature 25-30℃, continue heating for 24-36h; S3. Desorption and drying: raise the temperature to 35-40°C and maintain for 6 hours until the sample mass change is less than 0.05%, thereby obtaining dry Fe(III)-modified montmorillonite.

7. An Fe(III)-modified montmorillonite prepared by the method for preparing Fe(III)-modified montmorillonite according to any one of claims 1 to 6.

8. A polycyclic aromatic hydrocarbon degradation catalyst, characterized in that: The invention comprises persulfate and Fe(III)-modified montmorillonite prepared by the method for preparing Fe(III)-modified montmorillonite according to any one of claims 1 to 6, wherein the weight ratio of the persulfate to the Fe(III)-modified montmorillonite is 1:

25.

9. Use of the polycyclic aromatic hydrocarbons degradation catalyst according to claim 8 in the remediation of polycyclic aromatic hydrocarbons contaminated soil.

10. The use according to claim 9, characterized in that: The addition ratio of Fe(III) modified montmorillonite to the contaminated soil in the PAHs degradation catalyst was 5wt%.

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