Heat-sensitive ferromagnetic material, preparation method and application thereof, and soil remediation method

Abstract

The invention belongs to the technical field of environmental remediation, and particularly relates to a heat-sensitive ferromagnetic material, a preparation method and application thereof and a soil remediation method. The heat-sensitive ferromagnetic material provided by the invention comprises nano zero-valent iron and poly (N-isopropylacrylamide) connected to the nano zero-valent iron. According to the invention, nano zero-valent iron (nZVI) is modified by a thermosensitive polymer poly (N-isopropylacrylamide) (PNIPAM), so that the oxidation resistance of the thermosensitive ferromagnetic material is enhanced, and the magnetic-thermal active component Fe0 is retained to the greatest extent; the structure and surface characteristics of the PNIPAM are adjusted through a magnetothermal effect, so that the temperature rise kinetics of the heat-sensitive ferromagnetic material is improved; the migration-retention kinetics of the heat-sensitive ferromagnetic material is actively adjusted through the operation parameters of the electromagnetic field, so that the remediation strategy can be adjusted in real time, targeted particle conveying in a polluted area can be achieved on the microcosmic scale and the macroscopic scale, the heat energy utilization efficiency is remarkably improved, and accurate and efficient environment remediation is ensured.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of environmental remediation, and particularly relates to a thermosensitive ferromagnetic material, a preparation method and application thereof, and a soil remediation method. BACKGROUND

[0002] Thermal desorption technology has become one of the mainstream remediation technologies for organic contaminated soil due to its short remediation cycle, high treatment efficiency and less secondary pollution. Traditional thermal desorption technologies mainly include steam extraction technology (SEE), resistance heating technology (ERH) and thermal conduction heating technology (TCH). Traditional thermal desorption technologies rely on direct thermal conduction mechanism, which is easily affected by soil heterogeneity, resulting in uneven soil heating and waste of input energy. In contrast, the application of electromagnetic fields (EMF), such as radio frequency (300 kHz-300 GHz) and microwave (300 MHz-300 GHz), can achieve spatially uniform heating and higher energy efficiency. Nano zero-valent iron (nZVI) can generate heat through eddy current loss, hysteresis loss and relaxation loss in low-frequency alternating electromagnetic fields (AC EMF). Unlike high-frequency technologies that rely on electromagnetic field penetration characteristics to achieve overall soil heating, this technology selectively activates nZVI particles through electromagnetic penetration characteristics to form distributed heat sources, thereby achieving superior desorption efficiency. However, the rapid aggregation and easy oxidation of nZVI make it difficult to be effectively transported to the contaminated area in practical applications. These problems greatly limit the application of nZVI in in-situ thermal desorption. SUMMARY

[0003] Therefore, the present application aims to provide a thermosensitive ferromagnetic material, a preparation method and application thereof, and a soil remediation method. The thermosensitive ferromagnetic material of the present application can actively regulate the transport and retention behavior in different soil environments, achieve targeted particle delivery in the contaminated area at micro and macro scales, significantly improve the efficiency of heat energy utilization, and ensure accurate and efficient environmental remediation.

[0004] To achieve the above-mentioned application purposes, the present application provides the following technical solutions: The present application provides a thermosensitive ferromagnetic material, comprising nano zero-valent iron and poly-N-isopropyl acrylamide connected to the nano zero-valent iron.

[0005] The present application also provides a preparation method of the thermosensitive ferromagnetic material described in the above technical solutions, comprising the following steps: dissolving N-isopropyl acrylamide (NIPAM), a crosslinking agent and an initiator in water to perform a polymerization reaction, thereby obtaining a poly-N-isopropyl acrylamide solution; mixing the poly-N-isopropyl acrylamide solution and ferrous ions, adding a reducing agent to perform a reduction reaction, thereby obtaining the thermosensitive ferromagnetic material.

[0006] Preferably, the crosslinking agent comprises N,N-methylenebisacrylamide (MBA); The initiator comprises potassium persulfate (KPS); The mass ratio of the N-isopropyl acrylamide and the crosslinking agent is 3:0.1; The mass ratio of the N-isopropyl acrylamide and the initiator is 3:0.2.

[0007] Preferably, the temperature of the polymerization reaction is 70-90℃, and the holding time is 0.5h.

[0008] Preferably, the reducing agent comprises sodium borohydride and / or potassium borohydride, and the reducing agent is added in the form of a reducing agent solution; the reducing agent solution is added dropwise.

[0009] Preferably, the molar ratio of the ferrous ions and the reducing agent is 1:2-5; the mass ratio of the poly-N-isopropyl acrylamide and the ferrous ions in the poly-N-isopropyl acrylamide solution, calculated based on the N-isopropyl acrylamide, is 1:0.3-1. The time of the reduction reaction is 10-30min.

[0010] The application further provides the application of the heat-sensitive ferromagnetic material in soil remediation.

[0011] The application further provides a soil remediation method, comprising the following steps: Mixing the soil and the remediation agent, and performing remediation under the condition of applying an electromagnetic field; The remediation agent is the heat-sensitive ferromagnetic material or the heat-sensitive ferromagnetic material prepared by the preparation method.

[0012] Preferably, the mass ratio of the soil and the remediation agent is 5-15:1. The frequency of the electromagnetic field is 30-100kHz.

[0013] Preferably, after the remediation, the remediation agent and the soil are separated by magnetic attraction.

[0014] The application provides a heat-sensitive ferromagnetic material.

[0015] Compared with the traditional thermal desorption remediation technology, the application has the following advantages: (1) Traditional thermal desorption technology mainly relies on heat conduction to achieve overall soil heating, but due to the natural heterogeneity of soil, it often leads to low energy efficiency and limited desorption efficiency. This invention utilizes mobile nano-zero valent iron (nZVI) particles as a deployable magnetothermal source and combines it with the penetrating ability of electromagnetic field (EMF) to provide a promising solution to this challenge.

[0016] (2) Thermosensitive ferromagnetic materials are prepared by introducing the thermosensitive polymer PNIPAM for modification. This method enhances the oxidation resistance and retains the magnetocaloric active component Fe to the greatest extent. 0 This achieves sustained heating performance and improves pollutant removal efficiency.

[0017] (3) The magnetocaloric effect can modulate the properties of thermosensitive polymers (e.g., phase transition, particle size, surface charge, and amphiphilicity). Increased system temperature triggers a low critical solution temperature transition, which in turn modulates the conformational changes of PNIPAM, resulting in a decrease in the particle size of the thermosensitive ferromagnetic material, a reduction in the surface negative charge, and an increase in surface hydrophobicity. These changes subsequently affect the heating efficiency and the behavior of the thermosensitive ferromagnetic material below / above the low critical solution temperature, ultimately affecting the heating kinetics of the system.

[0018] (4) The migration-retention dynamics of thermosensitive ferromagnetic materials can be actively adjusted by controlling the electromagnetic field parameters, thereby enabling real-time adjustment of the remediation strategy. Targeted particle delivery to contaminated areas can be achieved at both the micro and macro scales, significantly improving thermal energy utilization efficiency. Attached Figure Description

[0019] Figure 1 XRD patterns of PNIPAM-modified nZVI (P-nZVI) and nZVI materials; Figure 2 FTIR spectra of PNIPAM-modified nZVI (P-nZVI) and nZVI materials; Figure 3 Hydrodynamic diameter diagrams for PNIPAM-modified nZVI (P-nZVI) and nZVI materials; Figure 4 VSM plots of P-nZVI and nZVI; Figure 5 The graph shows the change in UV transmittance of P-nZVI with temperature. Figure 6 The graph shows the zeta potential of P-nZVI and nZVI as a function of temperature. Figure 7 The graph shows the contact angle of P-nZVI as a function of temperature. Figure 8 The hydrodynamic diameters of P-nZVI and nZVI vary with temperature. Figure 9 To investigate the effects of different P-nZVI dosages and the overall temperature-raising capacity of nZVI on the system during soil thermal desorption experiments; Figure 10 The concentration of Nap remaining under different P-nZVI dosages and nZVI levels in soil thermal desorption experiments; Figure 11 The XRD patterns of P-nZVI and nZVI isolated from the experimental soil before and after the application of electromagnetic fields in Examples 6, 8, 10, and 12 are shown. Figure 12 P-nZVI content of magnetic and non-magnetic separable components in experimental soil and soil after organic matter removal before and after applying an electromagnetic field; Figure 13 The nZVI content of magnetic and non-magnetic separable components in the experimental soil and the soil after organic matter removal were shown before and after the application of an electromagnetic field. Figure 14 The effective mobility of P-nZVI under different soil columns and electromagnetic field settings in migration and heating experiments; Figure 15 The temperature increment of P-nZVI under different soil columns and electromagnetic field settings during migration and heating experiments; Figure 16 The Nap removal rate of P-nZVI under different soil columns and electromagnetic field settings in migration and heating experiments. Detailed Implementation

[0020] The present invention provides a thermosensitive ferromagnetic material comprising nano-zero valent iron and polyN-isopropylacrylamide attached to the nano-zero valent iron.

[0021] The thermosensitive ferromagnetic material provided by this invention includes nano-zero valent iron. This invention utilizes migratory nano-zero valent iron (nZVI) particles as a deployable magnetothermal source, and combines this with the penetrating ability of electromagnetic fields (EMF) to solve the problems of low energy efficiency and limited desorption efficiency in traditional thermal desorption technologies.

[0022] The thermosensitive ferromagnetic material provided by this invention comprises poly(N-isopropylacrylamide) bonded to nano-zero-valent iron. This invention modifies nano-zero-valent iron (nZVI) with the thermosensitive polymer poly(N-isopropylacrylamide) (PNIPAM), enhancing the oxidation resistance of the thermosensitive ferromagnetic material and maximizing the retention of the magnetocaloric active component Fe. 0By adjusting the structure and surface properties of PNIPAM through the magnetocaloric effect, the heating kinetics of the thermosensitive ferromagnetic material can be improved. By actively adjusting the migration-retention kinetics of the thermosensitive ferromagnetic material through electromagnetic field operation parameters, the remediation strategy can be adjusted in real time. Targeted particle delivery to the contaminated area can be achieved at both the micro and macro scales, significantly improving thermal energy utilization efficiency and ensuring precise and efficient environmental remediation.

[0023] In this invention, the iron content in the thermosensitive ferromagnetic material is preferably 40-50%, specifically preferably 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49% or 50%.

[0024] The present invention utilizes a thermosensitive ferromagnetic material (P-nZVI) modified with thermosensitive poly(N-isopropylacrylamide) (PNIPAM) to modulate the surface properties of nZVI, thereby enabling its migration and retention in soils with varying soil characteristics. The localized heating of the nano-zero-valent iron under an electromagnetic field not only facilitates pollutant desorption but also allows for on-demand control of the phase transition triggered by the PNIPAM shell, thus regulating the particle size and surface properties of the nano-zero-valent iron. This adaptability enables P-nZVI to actively regulate its transport and retention behavior in different soil environments, ensuring precise and efficient environmental remediation.

[0025] This invention also provides a method for preparing the thermosensitive ferromagnetic material described in the above technical solution, comprising the following steps: N-Isopropylamide, a crosslinking agent, and an initiator are dissolved in water and polymerized to obtain a poly-N-isopropylamide solution. The poly(N-isopropylacrylamide) solution and ferrous ions were mixed, and a reducing agent was added to carry out a reduction reaction to obtain the thermosensitive ferromagnetic material.

[0026] Unless otherwise specified, the raw materials used in this invention are preferably commercially available products.

[0027] In this invention, N-isopropylolefin amide, a crosslinking agent, and an initiator are dissolved in water to carry out a polymerization reaction, thereby obtaining a poly-N-isopropylolefin amide solution.

[0028] In this invention, the crosslinking agent preferably comprises N,N-methylenebisacrylamide. In this invention, the mass ratio of the N-isopropylacrylamide to the crosslinking agent is preferably 3:0.1.

[0029] In this invention, the initiator preferably comprises potassium persulfate. In this invention, the mass ratio of the N-isopropylenamide to the initiator is preferably 3:0.2.

[0030] In this invention, the water is preferably deoxygenated water. In this invention, the preferred ratio of N-isopropylamide to water is 3g:150mL.

[0031] In this invention, the polymerization reaction temperature is preferably 70~90℃, more preferably 80℃, and the holding time is preferably 0.5h. In this invention, the polymerization reaction is preferably carried out under stirring conditions, and the stirring rate is preferably 500~1000 r / min, specifically preferably 600 r / min.

[0032] After the polymerization reaction, the present invention preferably obtains the poly-N-isopropylamide solution without any post-treatment.

[0033] After obtaining the poly-N-isopropylacrylamide solution, the present invention mixes the poly-N-isopropylacrylamide solution with ferrous ions, adds a reducing agent, and carries out a reduction reaction to obtain the thermosensitive ferromagnetic material.

[0034] In this invention, the ferrous ions are preferably added in the form of ferrous sulfate, and the ferrous sulfate is more preferably ferrous sulfate heptahydrate. In this invention, the molar ratio of the ferrous ions to the reducing agent is preferably 1:2 to 5, specifically preferably 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5, or 1:5; based on N-isopropylacrylamide, the mass ratio of polyN-isopropylacrylamide to ferrous ions in the polyN-isopropylacrylamide solution is preferably 1:0.3 to 1, specifically preferably 1:0.3, 1:0.4, 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, or 1:1.

[0035] In this invention, the mixing of the poly(N-isopropylacrylamide) solution and ferrous ions is preferably carried out in an oxygen-free glove box, wherein the atmosphere of the oxygen-free glove box is preferably an N2-H2 mixed gas, and the volume ratio of N2 to H2 in the N2-H2 mixed gas is 99:1; the mixing time of the poly(N-isopropylacrylamide) solution and ferrous ions is preferably 12 hours. In this invention, the mixing of the poly(N-isopropylacrylamide) solution and ferrous ions is preferably carried out under stirring conditions, wherein the stirring speed is preferably 400-600 r / min, specifically preferably 500 r / min. In this invention, the mixing of the poly(N-isopropylacrylamide) solution and ferrous ions is to ensure sufficient contact between the polymer and the ferrous ions.

[0036] In this invention, the reducing agent preferably includes sodium borohydride and / or potassium borohydride, more preferably sodium borohydride. In this invention, the reducing agent is preferably added in the form of a reducing agent solution; the concentration of the reducing agent solution is specifically preferably 2.23 mol / L; the reducing agent solution is preferably added dropwise, and the dropwise addition rate is preferably 2 mL / min.

[0037] In this invention, it is preferable to stir the system during the addition of the reducing agent.

[0038] In this invention, the temperature of the reduction reaction is preferably room temperature, i.e., neither additional heating nor additional cooling is required; the time of the reduction reaction is preferably 10-30 minutes, more preferably 20 minutes; the timing of the reduction reaction is preferably started after the reducing agent is completely added. In this invention, the reduction reaction is preferably carried out under stirring conditions.

[0039] Following the reduction reaction, the present invention preferably further includes: solid-liquid separation of the obtained reaction solution, washing and drying the obtained solid to obtain the thermosensitive ferromagnetic material. In this invention, the solid-liquid separation is preferably performed by centrifugation, with a preferred centrifugation speed of 8000 r / min and a preferred centrifugation time of 5 min. In this invention, the washing preferably includes sequential alcohol washing and water washing; the alcohol washing reagent is preferably anhydrous ethanol, and the alcohol washing is preferably performed 3 times; the water washing reagent is preferably deoxygenated water, and the water washing is preferably performed 3 times. In this invention, the drying method is preferably vacuum drying, with a preferred vacuum drying temperature of 50°C and a preferred drying time of 12 h.

[0040] The present invention also provides the application of the thermosensitive ferromagnetic material described in the above technical solution or the thermosensitive ferromagnetic material prepared by the preparation method described in the above technical solution in soil remediation.

[0041] The present invention also provides a soil remediation method, comprising the following steps: The soil and remediation agent are mixed and remediated under the condition of applying an electromagnetic field; The repair agent is the thermosensitive ferromagnetic material described in the above technical solution or the thermosensitive ferromagnetic material prepared by the preparation method described in the above technical solution.

[0042] In this invention, the soil preferably has a particle size of less than 10 mesh, a pH of 6.87, and a soil organic matter (SOM) content of 29.1 g / kg. In this invention, the organic matter preferably includes one or more of humic acid and fulvic acid.

[0043] In this invention, the mass ratio of soil to remediation agent is preferably 5 to 15:1, and more preferably 5:1, 10:1, 12.5:1 or 15:1.

[0044] In this invention, the frequency of the electromagnetic field is preferably 30~100kHz, and more specifically 30kHz, 40kHz, 50kHz, 60kHz, 70kHz, 80kHz, 90kHz, or 100kHz. This invention does not impose a specific limitation on the repair time; it can be set according to the actual situation.

[0045] After the repair, the present invention preferably uses magnetic attraction to separate the repair agent from the soil.

[0046] The following detailed description, in conjunction with embodiments, illustrates the thermosensitive ferromagnetic materials, their preparation methods, applications, and soil remediation methods provided by this invention. However, these descriptions should not be construed as limiting the scope of protection of this invention.

[0047] Example 1 3.0 g NIPAM, 0.1 g MBA, and 0.2 g KPS were dissolved in 150 mL of oxygen-free water in an Erlenmeyer flask. The mixture was stirred continuously at 600 rpm for 30 min at 80 °C. After cooling to room temperature, 50 mL of the cooled PNIPAM solution was placed in a vacuum glove box containing high-purity N2 / H2 (99% / 1%), and 4.964 g FeSO4·7H2O was added. The mixture was stirred continuously at 500 rpm for 12 h to allow PNIPAM to react with Fe. 2+ After thorough mixing and homogenization, remove the stir bar and place the solution on a mechanical stirrer. Add 20 mL of 2.23 mol / L NaBH4 solution dropwise at a rate of 2 mL / min. After the addition is complete, continue stirring for 20 min. Then, place the suspension in a centrifuge and centrifuge at 8000 r / min for 5 min. Discard the supernatant and wash three times with anhydrous ethanol and deoxygenated water, respectively. Place the collected material in a vacuum environment at 50 °C and dry for 12 h. The PNIPAM-modified nZVI (P-nZVI) solid particles obtained after drying are used for solid characterization and desorption experiments.

[0048] Conventional nano-zero valent iron (nZVI) was prepared by adding 2.23 mol / L NaBH4 solution to 50 mL of FeSO4 solution containing 0.36 mol / L.

[0049] Example 2 Naphthalene (Nap) was used as the target pollutant, and Naap-free environmental soil samples were used as experimental soil. 0.5 g of naphthalene was dissolved in 700–800 mL of methanol. After complete dissolution, 1 kg of the experimental soil sample was added to the naphthalene-methanol solution and stirred thoroughly. The mixture was then equilibrated in a sealed container for 72 hours. The soil sample was then left to stand in a cool, ventilated place for one week to allow the methanol solvent to completely evaporate. Afterward, the sample was sealed in a glass bottle and aged in a cool place for one month to obtain the prepared naphthalene-contaminated soil sample. The Naap concentration in the contaminated soil sample was measured to be 251.25 mg / kg. The Nap-contaminated soil was used for static desorption experiments and dynamic targeted desorption experiments.

[0050] An AC electromagnetic field generator was used to generate a low-frequency electromagnetic field with a frequency of 30-100 kHz. Equipped with a 3-turn spiral copper induction coil with an inner diameter of approximately 10 cm, it was used for soil thermal desorption experiments. 50 g of test soil containing naphthalene (Nap) was mixed with 5 g of P-nZVI as described in Example 1 in a sealed container for 24 h. Upon starting the electromagnetic field generator, the container was immediately placed inside the coil and the seal was lifted. Temperature changes were monitored at given time intervals, and the residual concentration of Nap was determined using gas chromatography equipped with a flame ionization detector. After 2 h of reaction, the system temperature rose to 41.5 °C, and the Nap removal reached ~121 mg / kg.

[0051] Example 3 50g of the naphthalene (Nap)-containing test soil from Example 2 was mixed with 4g of P-nZVI from Example 1 in a sealed container for 24 hours. Under the electromagnetic field conditions described in Example 2, the electromagnetic field generator was activated, the container was immediately placed inside the coil, and the container was unsealed. Temperature changes were monitored at given time intervals, and the residual concentration of Nap was determined using gas chromatography equipped with a flame ionization detector. After 2 hours of reaction, the system temperature rose to 38°C, and the Nap removal reached ~111 mg / kg.

[0052] Example 4 50g of the naphthalene (Nap)-containing test soil from Example 2 was mixed with 5g of nZVI from Example 1 in a sealed container for 24 hours. Under the electromagnetic field conditions described in Example 2, the electromagnetic field generator was activated, the container was immediately placed inside the coil, and the container was then unsealed. Temperature changes were monitored at given time intervals, and the residual concentration of Nap was determined using gas chromatography equipped with a flame ionization detector. After 2 hours of reaction, the system temperature rose to 36.4°C, and the Nap removal reached ~96 mg / kg.

[0053] Example 5 Under the electromagnetic field conditions described in Example 2, the electromagnetic field generator was activated, and a sealed container containing 50g of the naphthalene (Nap)-containing test soil described in Example 2 was placed inside the coil and then the container was unsealed. Temperature changes were monitored at given time intervals, and the residual Nap concentration was determined using gas chromatography equipped with a flame ionization detector. After 2 hours of reaction, the system temperature did not exceed 26°C, and the Nap removal amount was only ~5mg / kg.

[0054] Example 6 50g of the test soil described in Example 2 and 5g of P-nZVI described in Example 1 were mixed in a sealed container for 24h. Five equal amounts (5.5g each) of soil were randomly selected from the soil mixture. Each sample was mixed with 50mL of deionized water in a 100mL centrifuge tube and shaken at 180rpm for 10min. Then, a square neodymium iron boron magnet was attached to the outside of the tube to separate the ferromagnetic component from the mixture. This magnetic separation process was repeated twice. Subsequently, the collected magnetic fraction was dispersed again in water and sonicated for 5min to remove attached nonmagnetic particles. These suspensions were then subjected to two more magnetic separation processes to further purify the ferromagnetic material. The nonmagnetic fraction was carefully decanted and collected. For the mixture after electromagnetic field irradiation, the water used to disperse the sample was preheated to the appropriate mixture temperature. The obtained ferromagnetic and nonmagnetic samples were vacuum dried at 25°C for 24h for XRD characterization, and the iron content in the magnetic and nonmagnetic fractions was determined by atomic absorption spectrometry. The results showed that iron accounted for 52% of the magnetic components and 48% of the non-magnetic components.

[0055] Example 7 Soil with removed organic matter was prepared by adding 6% sodium hypochlorite (solid-liquid ratio 1:50) to the test soil and treating it continuously for 6 hours. After centrifugation and removal of the supernatant, the resulting solid was washed with water to remove residual sodium hypochlorite. The treated soil was adjusted to pH 6.87±0.05 with hydrochloric acid / sodium hydroxide solution, air-dried, and stored for experimental use.

[0056] 50g of organic-free soil was mixed with 5g of P-nZVI as described in Example 1 in a sealed container for 24 hours. The magnetic and non-magnetic components were separated using the same procedure as in Example 6, and the iron content in the magnetic and non-magnetic fractions was determined by atomic absorption spectrometry. The results showed that iron accounted for 46% of the magnetic component and 54% of the non-magnetic component.

[0057] Example 8 All steps in this embodiment are the same as in Embodiment 6, except that a low-frequency alternating electromagnetic field was applied to the system for 2 hours after mixing. The results show that iron accounts for 17% of the magnetic component and 83% of the non-magnetic component.

[0058] Example 9 All steps in this embodiment are the same as in Embodiment 7, except that a low-frequency AC electromagnetic field was applied to the system for 2 hours after mixing. The results show that iron accounts for 62% of the magnetic component and 38% of the non-magnetic component.

[0059] Example 10 All steps in this embodiment are the same as in Embodiment 6, except that 5g of nZVI described in Embodiment 1 is used instead of P-nZVI. The results show that iron accounts for 97% of the magnetic component and 3% of the non-magnetic component.

[0060] Example 11 All steps in this embodiment are the same as in Embodiment 7, except that 5g of nZVI described in Embodiment 1 is used instead of P-nZVI. The results show that iron accounts for 98% of the magnetic component and 2% of the non-magnetic component.

[0061] Example 12 All steps in this embodiment are the same as in Embodiment 8, except that 5g of nZVI described in Embodiment 1 is used instead of P-nZVI. The results show that iron accounts for 96% of the magnetic component and 4% of the non-magnetic component.

[0062] Example 13 All steps in this embodiment are the same as in Embodiment 9, except that 5g of nZVI described in Embodiment 1 is used instead of P-nZVI. The results show that iron accounts for 93% of the magnetic component and 7% of the non-magnetic component.

[0063] Example 14 An AC electromagnetic field generator was used to generate a low-frequency electromagnetic field with a frequency of 30~100kHz. A 10-turn spiral copper induction coil with an inner diameter of approximately 3cm was used for the migration experiment of P-nZVI in a sand column. The experimental sand column was 12cm long and 1cm in inner diameter. Coarse sand (particle size 0.55~1mm, contact angle 5.45°, zeta potential -35.84mV) was used as the filling medium for the soil column. Nap-contaminated sand (initial Nap concentration in the contaminated sand was 22.08mg / kg) was mixed in at a mass ratio of 2:5 in the downstream zone. Before injection, the P-nZVI suspension described in Example 1, containing 2g / L Fe, was stirred thoroughly and then injected via a peristaltic pump at a rate of 6mL / min in upflow mode. During the P-nZVI injection phase, no electromagnetic field was applied throughout, and the injection time was 4.5min. After the injection phase, a low-frequency electromagnetic field was applied only to the Nap-containing downstream zone for 1h to induce thermal desorption. After the heating experiment, the residual concentration of Nap was determined by gas chromatography equipped with a flame ionization detector. The fractionated samples from the sand column were then acid-digested, and the amount of iron retained in each fraction was analyzed by atomic absorption spectrometry. The effective mobility (target region retention / total Fe flux) of the system was 35.2%, and the Nap removal rate was 33.2% with a temperature increase of 11.6℃.

[0064] Example 15 All steps in this embodiment are the same as in Example 14, except that the packing medium used in the sand column is organic sand (particle size 0.55~1mm, contact angle 76.4°, zeta potential -32.96mV). The effective migration rate of this system is 21.1%, and the Nap removal rate is 19.8% with an increase in system temperature of 8.1℃.

[0065] Example 16 All steps in this embodiment are the same as in Example 14, except that the filling medium used in the sand column is positively charged sand (particle size 0.55~1mm, contact angle 10.11°, zeta potential +23.04mV). The effective mobility of this system is 20.1%, and the Nap removal rate is 19.3% with an increase in system temperature of 8.3℃.

[0066] Example 17 All steps in this embodiment are the same as in Embodiment 14, except that a magnetic field is applied throughout the injection stage. The effective migration rate of this system is 9.6%, the system temperature increases by 4.6℃, and the Nap removal rate is 7.8%.

[0067] Example 18 All steps in this embodiment are the same as in Embodiment 15, except that a magnetic field is applied throughout the injection stage. The effective migration rate of this system is 35.6%, the system temperature increases by 10.6℃, and the Nap removal rate is 26.4%.

[0068] Example 19 All steps in this embodiment are the same as in Embodiment 16, except that a magnetic field is applied throughout the injection stage. The effective migration rate of this system is 34.2%, and with a temperature increase of 10.2°C, the Nap removal rate is 24.2%.

[0069] Example 20 All steps in this embodiment are the same as in Embodiment 14, except that the magnetic field is only set in the downstream region. The effective mobility of this system is 45.3%, and with a system temperature increase of 12.6°C, the Nap removal rate is 47.1%.

[0070] Example 21 All steps in this embodiment are the same as in Embodiment 15, except that the magnetic field is only set in the upstream region. The effective mobility of this system is 44.1%, the system temperature increases by 12.1°C, and the Nap removal rate is 39.8%.

[0071] Example 22 All steps in this embodiment are the same as in Embodiment 16, except that the magnetic field is only set in the upstream region. The effective mobility of this system is 41.1%, the system temperature increases by 11.8°C, and the Nap removal rate is 36.8%.

[0072] Example 23 All steps in this embodiment are the same as in Embodiment 14, except that the material used in the injection stage is the nZVI described in Embodiment 1. The effective migration rate of this system is 0.5%, and with a temperature increase of 0.7°C, the Nap removal rate is 4.4%.

[0073] Example 24 All steps in this embodiment are the same as in Embodiment 15, except that the material used in the injection stage is the nZVI described in Embodiment 1. The effective migration rate of this system is 0.3%, and with a temperature increase of 0.7°C, the Nap removal rate is 4.2%.

[0074] Example 25 All steps in this embodiment are the same as in Embodiment 16, except that the material used in the injection stage is the nZVI described in Embodiment 1. The effective migration rate of this system is 0.4%, and with a temperature increase of 0.6°C, the Nap removal rate is 4.6%.

[0075] Example 26 All steps in this embodiment are the same as in Embodiment 17, except that the material used in the injection stage is the nZVI described in Embodiment 1. The effective migration rate of this system is 0.5%, and with a temperature increase of 0.6°C, the Nap removal rate is 4.3%.

[0076] Example 27 All steps in this embodiment are the same as in Embodiment 18, except that the material used in the injection stage is the nZVI described in Embodiment 1. The effective migration rate of this system is 0.4%, and with a temperature increase of 0.7°C, the Nap removal rate is 4.9%.

[0077] Example 28 All steps in this embodiment are the same as in Embodiment 19, except that the material used in the injection stage is the nZVI described in Embodiment 1. The effective migration rate of this system is 0.3%, and with a temperature increase of 0.7°C, the Nap removal rate is 3.8%.

[0078] The following is based on Figures 1-16 The basic properties of the thermosensitive ferromagnetic material P-nZVI prepared in Example 1 of this invention and its targeted remediation effect on soil were analyzed.

[0079] Figure 1 The XRD pattern shows Fe 0 The characteristic peak is at 44.5°. Because the PNIPAM coating disrupts the periodic arrangement of the nZVI lattice, its peak intensity is weaker than that of conventional nZVI. The 30° Fe3O4 peak observed in nZVI is absent in p-nZVI, indicating that PNIPAM effectively protects nZVI from oxidation.

[0080] Figure 2 The FTIR spectrum showed characteristic peaks corresponding to PNIPAM (~3300 cm⁻¹). -1 ~1550cm -1 ~1653cm -1 ~2972cm -1 2930cm -1 and 2873cm -1 These spectral features are not present in nZVI. Notably, no such features were observed at 1620 cm⁻¹ in the p-nZVI spectrum. -1 The C=C stretching vibration peak (a characteristic peak of NIPAM monomer) at the location confirms that the PNIPAM polymer successfully formed a coating on P-nZVI.

[0081] Figure 3 The results show that the hydrodynamic diameter of P-nZVI is around 160 nm, which is significantly smaller than that of nZVI (320 nm).

[0082] Figures 1-3 This demonstrates the successful synthesis of a polymer PNIPAM / nZVI composite material.

[0083] Figure 4The VSM test results for P-nZVI and nZVI are presented. The area under the hysteresis loop (ΔU), calculated from the saturation magnetization (Ms) and coercivity (Hc), reflects the irreversible magnetization and the subsequent conversion of electromagnetic energy into heat under the influence of an electromagnetic field. The power of the magnetic flux density (MIH) is generally proportional to the ΔU value of the material. The ΔU value of P-nZVI (20122.30 emu·Oe / g) is lower than that of nZVI (28596.22 emu·Oe / g). However, the iron content in P-nZVI (43.91 wt%) is lower than that in nZVI (70.59 wt%). Normalized to the mass of iron, the ΔU value of P-nZVI is 453.26 emu·Oe / g Fe, exceeding that of nZVI (405.10 emu·Oe / g Fe). This enhancement can be attributed to the interfacial effect induced by the polymer coating, which promotes the aggregation and ordered arrangement of magnetic moments in the nanoparticles. These results indicate that this polymer coating not only improves the dispersion of P-nZVI, but also enhances the magnetic responsiveness of iron per unit mass.

[0084] The permeability of P-nZVI suspension was monitored at different system temperatures (controlled by a water bath), and the results are as follows: Figure 5 As shown, the transmittance of the P-nZVI suspension decreased significantly at 31°C. This indicates that P-nZVI exhibits temperature-responsive behavior. Below the lowest critical dissolution temperature (LCST), hydrogen bonds between the amide groups in PNIPAM and water molecules maintain the polymer chains in a fully extended state, thus ensuring the dispersion of P-nZVI in water. However, above the LCST, thermal energy is sufficient to break these hydrogen bonds, leading to intermolecular and intramolecular dehydration and shrinkage of the PNIPAM shell. This shrinkage partially obscures the surface charge of the iron core, as evidenced by the change in the zeta potential of P-nZVI from -24 mV to -1 mV as the temperature increases from 25°C to 40°C; in contrast, the zeta potential of nZVI remains constant at -23 mV over the same temperature range. Figure 6 ).like Figure 7 As shown, the contact angle between P-nZVI and water increases significantly near the LCST as the temperature rises from 25℃ to 40℃. Above the LCST, the decrease in electrostatic repulsion and the enhancement of surface hydrophobicity trigger the aggregation of P-nZVI particles, which is confirmed by the increase in the hydrodynamic diameter of P-nZVI to 294 nm at 32℃. Figure 8 In general, when the temperature exceeds the critical phase transition temperature, the PNIPAM coating changes from a hydrophilic, expanding state to a hydrophobic, contracting state, while simultaneously causing P-nZVI to change from a dispersed state to an aggregated form with lower surface charge in water.

[0085] The electromagnetic field-induced thermal desorption effect was evaluated by measuring the residual Nap concentration in mixed soil containing P-nZVI. The results are as follows: Figure 9 and Figure 10 As shown. Figure 9 and Figure 10 As shown, in the control experiment without the addition of P-nZVI (Example 5), the soil temperature change was minimal, and the Nap removal rate was approximately 2%, indicating that the electromagnetic field had almost no thermal effect on the untreated soil. In soil containing 5 g of P-nZVI (Example 2), the soil temperature increased from 25°C to 41.5°C, and the Nap concentration decreased from 251.1 mg / kg to 130.3 mg / kg. However, 5 g of nZVI (Example 4) only increased the soil temperature to 36.4°C and decreased the Nap concentration to 155.0 mg / kg. Furthermore, in the examples containing 4 g of P-nZVI (Example 3) and 5 g of nZVI (Example 4), the two examples showed comparable increases in soil temperature, but P-nZVI exhibited a significantly superior Nap desorption efficiency. These results confirm that even at the same system temperature, P-nZVI is superior to nZVI in pollutant desorption. This enhanced performance stems from the preferential aggregation of P-nZVI in soil organic matter (SOM) with high pollutant concentrations, enabling more efficient heat absorption. This advantage becomes even more pronounced when the system temperature exceeds the LCST, not only due to enhanced surface hydrophobicity but also because of reduced electrostatic repulsion between P-nZVI and SOM—a synergistic mechanism entirely absent in conventional nZVI. This highlights the advantages of electromagnetically coupled thermistoric zero-valent iron, enabling the system to create localized P-nZVI hotspots with superior microscale heat transfer efficiency, thereby improving overall energy utilization.

[0086] This performance improvement stems partly from the PNIPAM coating's ability to protect the iron core from corrosion in soil. This is because the Hall effect hysteresis loss of iron oxide under electromagnetic fields is significantly lower than that of metallic iron (calculated in molar ratio), and Fe... 0 Oxidation reduces the overall hysteresis loop capacity. Before and after electromagnetic field irradiation, P-nZVI and nZVI particles in the soil mixture were separated for XRD analysis (Examples 6, 8, 10, 12), and the results are as follows: Figure 11 As shown. Compared to the original sample, nZVI after applying an electromagnetic field exhibits Fe... 0 The peak intensity decreased, and the peak shape broadened and became irregular, with a Fe2O3 peak appearing at 35°, indicating partial oxidation during electromagnetic field exposure. In contrast, P-nZVI retained Fe well after the application of a magnetic field. 0 The peak showed no detected iron oxide signal, indicating that the PNIPAM coating effectively protected the Fe. 0It is not oxidized.

[0087] On the other hand, in soil, hydrophobic organic matter acts as a stabilizing phase in the region above the LCST. Increased surface hydrophobicity promotes the redistribution of P-nZVI from hydrophilic phases (e.g., soil water and minerals) to organic matter. The influence of soil organic matter on the preferential aggregation of thermally driven P-nZVI was investigated by comparing the content of magnetically separable P-nZVI in experimental and organic-removed soils. The results are as follows: Figures 12-13 As shown, the results indicate that the magnetically separable fraction of conventional zero-valent nano-iron (nZVI) in both the original soil and the soil with reduced organic matter content ranged from 93% to 97% before and after the application of an electromagnetic field (Examples 10-13). In contrast, the magnetic recovery rate of P-nZVI was significantly lower, likely due to the stronger adhesion between its polymer coating and soil components (Examples 6-9). Before the application of an electromagnetic field, the magnetically separable fraction of P-nZVI in the original soil was 52% (Example 6), and in the soil with removed organic matter, it was 46% (Example 7). This suggests that below LCST, P-nZVI tends to interact more with non-organic soil components than with organic matter. After the application of an electromagnetic field, the content of separable P-nZVI in the original soil decreased sharply to 17% (Example 8), while it increased to 62% in the organic-rich soil (Example 9). The increased magnetic recovery rate in the organic-rich soil suggests that increased temperature weakens the interaction between P-nZVI particles and non-organic soil components. Secondly, the significant reduction in the content of separable P-nZVI particles in the original soil indicates that heating actually enhanced the binding of P-nZVI particles with organic matter.

[0088] Figures 14-16The transport behavior of nZVI and P-nZVI was compared. Under both electromagnetic field-free and electromagnetic field-applied conditions, the effective migration rate, temperature increment, and Nap removal rate (Examples 23-28) of nZVI in the three different sand media remained largely consistent, indicating that effective thermal desorption of the contaminated area was generally not achieved. In the absence of an electromagnetic field, P-nZVI migration was superior to nZVI, with significant differences in effective migration rates across different columns. In the coarse sand column (Example 14), the effective migration rate of ~35% was significantly higher than that in organic sand (Example 15) and positively charged sand (Example 16) (~20.1%). Most notably, under conditions with an electromagnetic field applied throughout, the migration of P-nZVI exhibited sand-related characteristics. The electromagnetic field inhibited the migration of P-nZVI in coarse sand but enhanced its migration in organic and positively charged sand. Specifically, in coarse sand (Example 17), increased P-nZVI aggregation led to pore blockage, thereby reducing the effective mobility by ~9.6%; in organic sand (Example 18), enhanced surface hydrophobicity facilitated particle redistribution to the compatible organic sand surface, thereby enhancing the effective mobility by ~35%; and in positively charged sand (Example 19), the weakened zeta potential reduced electrostatic interactions with the positively charged sand, thereby enhancing the effective mobility by ~34%. The associated temperature increments and Nap desorption rates generally corresponded to the changes in effective mobility, and the transport variations in these examples were consistent with previous characterization data and elucidated mechanisms. Based on these findings, electromagnetic fields can modulate the transport of P-nZVI according to matrix characteristics, enabling targeted remediation of contaminated soils. Implementing optimized electromagnetic field strategies further improved transport performance, with the electromagnetic field acting only on contaminated areas in coarse sand (Example 20), and only on uncontaminated areas in organic and positively charged sand (Examples 21 and 22). In coarse sand, maintaining high migration rates in the uncontaminated portion while slowing migration in the contaminated portion increased the effective migration rate to 45%. For PS sample columns, applying an electromagnetic field to the uncontaminated portion improved transport efficiency, delivering more particles to the contaminated area, achieving effective migration rates of 44% and 41%, respectively. These results clearly demonstrate that when intelligent electromagnetic field applications are tailored to media characteristics, the transport and retention behavior of P-nZVI can be precisely controlled, resulting in superior targeted delivery. As expected, the optimized electromagnetic field application strategy achieved Nap desorption rates of 47% in coarse columns and 40% and 37% in organic sand, respectively, exceeding the performance of systems with electromagnetic fields applied throughout by 1.5 to 5.9 times, while also being 1.4 to 2 times better than systems without electromagnetic fields. It is worth noting that although the optimized electric field migration strategy produced similar final temperatures (around 40°C) in the contaminated portions of coarse sand (Example 20), organic sand (Example 21), and positively charged sand (Example 22), the Nap desorption rates differed (47% vs. 40% and 37%).This difference reflects the previously described microscopic distribution mechanism, namely, that P-nZVI achieves a more favorable distribution on contaminated sand particles in coarse sand columns, resulting in higher thermal energy utilization efficiency in contaminant treatment compared to organic and positively charged sand. These experiments confirm that the electromagnetic field migration modulation strategy using thermosensitive P-nZVI can achieve superior contaminant desorption by transporting a large number of particles to the target area. Furthermore, rapid transport in uncontaminated soil areas minimizes corrosion deactivation caused by environmental factors during injection.

[0089] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A thermosensitive ferromagnetic material, characterized in that, It includes nano-zero valent iron and polyN-isopropylacrylamide attached to the nano-zero valent iron.

2. The method for preparing the thermosensitive ferromagnetic material according to claim 1, characterized in that, Includes the following steps: N-Isopropylamide, a crosslinking agent, and an initiator are dissolved in water and polymerized to obtain a poly-N-isopropylamide solution. The poly(N-isopropylacrylamide) solution and ferrous ions were mixed, and a reducing agent was added to carry out a reduction reaction to obtain the thermosensitive ferromagnetic material.

3. The preparation method according to claim 2, characterized in that, The crosslinking agent includes N,N-methylenebisacrylamide; The initiator includes potassium persulfate; The mass ratio of the N-isopropylene amide to the crosslinking agent is 3:0.1; The mass ratio of the N-isopropylene amide to the initiator is 3:0.

2.

4. The preparation method according to claim 2 or 3, characterized in that, The polymerization reaction is carried out at a temperature of 70~90℃ for 0.5h.

5. The preparation method according to claim 2, characterized in that, The reducing agent includes one or more of sodium borohydride and / or potassium borohydride, and the reducing agent is added in the form of a reducing agent solution; the reducing agent solution is added dropwise.

6. The preparation method according to claim 2 or 5, characterized in that, The molar ratio of ferrous ions to reducing agent is 1:2~5; based on N-isopropylacrylamide, the mass ratio of polyN-isopropylacrylamide to ferrous ions in the polyN-isopropylacrylamide solution is 1:0.3~1; The reduction reaction takes 10 to 30 minutes.

7. The application of the thermosensitive ferromagnetic material according to claim 1 or the thermosensitive ferromagnetic material prepared by the preparation method according to any one of claims 2 to 6 in soil remediation.

8. A soil remediation method, characterized in that, Includes the following steps: The soil and remediation agent are mixed and remediated under the condition of applying an electromagnetic field; The repair agent is the thermosensitive ferromagnetic material according to claim 1 or the thermosensitive ferromagnetic material prepared by the preparation method according to any one of claims 2 to 6.

9. The soil remediation method according to claim 8, characterized in that, The mass ratio of the soil to the remediation agent is 5~15:1; The frequency of the electromagnetic field is 30~100kHz.

10. The soil remediation method according to claim 8, characterized in that, After the repair, the repair agent and soil are separated by magnetic attraction.

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