A soil remediation agent, a preparation method and application thereof

Abstract

A soil remediation agent and a preparation method and application thereof relate to the field of soil heavy metal pollution remediation technology, and solve the problems of difficult recovery and low reduction efficiency of the existing soil remediation agent. The soil remediation agent is a binary nanohybrid material formed by covalent bonding of a block copolymer of polylactide and poly-N-isopropyl acrylamide with porphyrin as an end group and titanium dioxide. The polylactide polymer containing a porphyrin group at the end is prepared by ring-opening polymerization, and the polylactide containing a bromine atom at the end and a porphyrin group at the end is prepared by acylation reaction of the hydroxyl group. The block copolymer of polylactide-b-poly-N-isopropyl acrylamide containing a porphyrin group at the end is prepared by ATRP method, and finally the binary nanohybrid material is prepared by Williamson ether synthesis reaction. The application can be applied to efficient, green and recyclable treatment of heavy metal contaminated soil and water.

Description

Technical Field

[0001] This invention relates to the field of soil heavy metal pollution remediation technology, specifically to a soil remediation agent, its preparation method, and its application. Background Technology

[0002] With the acceleration of industrialization and urbanization, heavy metal pollution has become one of the most serious environmental problems worldwide. Heavy metals are characterized by their difficulty in degradation, high mobility, strong bioaccumulation, and high toxicity. Once they enter the human body through the food chain, they can cause irreversible damage to organs such as the nervous system, hematopoietic system, and kidneys, seriously threatening human health and ecological security. Currently, remediation methods for heavy metal-contaminated soil mainly fall into three categories: physical remediation, chemical remediation, and bioremediation. Physical remediation methods, such as topsoil replacement and electroremediation, are fast-acting but have drawbacks such as high cost, large engineering workload, and potential damage to soil structure. Bioremediation methods, such as phytoremediation and microbial remediation, are environmentally friendly but have long remediation cycles, low efficiency, and are greatly affected by soil environmental conditions. Chemical remediation is currently the most widely used method, which involves adding chemical remediation agents to the soil to react with heavy metals through oxidation-reduction, precipitation, and complexation reactions, reducing their bioavailability and mobility.

[0003] However, most existing chemical remediation agents have the following technical bottlenecks: (1) heterogeneous reaction system, the remediation agent particles do not come into sufficient contact with heavy metal ions, the reaction rate is slow and the efficiency is low; (2) the remediation agent is difficult to recycle, and a large amount of residue in the soil will cause secondary pollution; (3) photocatalytic remediation agents have a high photogenerated electron-hole pair recombination rate, low catalytic activity, and low utilization rate of visible light.

[0004] Nano-titanium dioxide (TiO2), as a typical wide-bandgap semiconductor photocatalytic material, has advantages such as good chemical stability, non-toxicity, and low cost, showing great application potential in the field of heavy metal pollution remediation. However, pure TiO2 has problems such as a narrow photoresponse range (it can only absorb ultraviolet light), high recombination rate of photogenerated carriers, easy agglomeration of nanoparticles, and difficulty in recycling, which limit its practical application.

[0005] In summary, developing a recyclable homogeneous soil remediation agent with high heavy metal reduction efficiency is of significant scientific importance and practical value for solving the aforementioned problems in existing technologies. Summary of the Invention

[0006] To address the problems of difficult recycling and low reduction efficiency of existing soil remediation agents, this invention proposes a soil remediation agent, its preparation method, and its application.

[0007] The specific technical solution of the present invention is as follows: A soil remediation agent, characterized in that the soil remediation agent is a binary nano-hybrid material formed by covalently linking a block copolymer of polylactide and polyN-isopropylacrylamide (PNIPAM) with porphyrin-terminated groups and titanium dioxide, with the chemical formula Por-PLA. n -b-PNIPAM m -g-TiO2, where 50≤n≤100, 50≤m≤200; The porphyrin-terminated polylactide is prepared by the following steps: 5-(4-hydroxyphenyl)-10,15,20-triphenylporphyrin, lactide, and stannous isooctanoate were dissolved in toluene and stirred under heating conditions. After the reaction was completed, toluene was removed by vacuum distillation. The remaining mixture was poured into n-hexane to precipitate, and the precipitate was collected by filtration. This precipitate is polylactide containing porphyrin end groups, with the chemical formula Por-PLA. n .

[0008] Preferably, the molar ratio of 5-(4-hydroxyphenyl)-10,15,20-triphenylporphyrin and stannous isooctanoate is 1:0.1.

[0009] Preferably, the heating temperature is 80°C to 110°C.

[0010] The present invention also provides a method for preparing the above-mentioned soil remediation agent, comprising the following steps: S1, Por-PLA n Anhydrous dichloromethane and triethylamine were added to a two-necked flask and stirred under ice-water bath conditions. Then, α-bromoisobutyryl bromide dissolved in anhydrous dichloromethane was added to the mixture through a constant-pressure dropping funnel, and the reaction continued under ice-water bath conditions. After the reaction was complete, the mixture was washed and dried, and then the dichloromethane solvent was removed by vacuum distillation to obtain polylactide with bromine atoms at the ends and porphyrin groups at the terminal groups, with the chemical formula Por-PLA. n -Br; S2. Under nitrogen protection, place cuprous bromide, pentamethyldivinyltriamine, and N,N-dimethylformamide on one side of an H-type reaction tube and stir at room temperature; add N,N-dimethylformamide and Por-PLA. n -Br and N-isopropylacrylamide were placed on the other side of an H-type reaction tube and stirred thoroughly. The mixtures on both sides of the H-type reaction tube were mixed and the reaction continued. After the reaction was completed, the mixture was exposed to air to terminate the reaction. The resulting solution was diluted with THF and the residual copper complex was removed with neutral alumina. The solution was then purified by precipitation in cold n-hexane, and the insoluble matter was collected by filtration and vacuum dried to obtain a poly-L-type lactide-poly-N-isopropylacrylamide block copolymer with porphyrin groups at the end groups, with the chemical formula Por-(PLA).n -b-(PNIPAM) m -Br; S3. Add acetonitrile to a two-necked flask, then add excess anhydrous potassium carbonate and stir at room temperature; add TiO2 and continue stirring, and finally add Por-(PLA). n -b-(PNIPAM) m -Br, continue stirring the reaction, centrifuge to separate the crude product, and then wash with dichloromethane, ethanol and deionized water respectively to obtain the soil remediation agent.

[0011] Preferably, the preparation method is carried out entirely in a glove box to achieve absolute anhydrousness and oxygen-free conditions.

[0012] Preferably, the stirring time in step S1 is 30 min.

[0013] Preferably, the washing and drying operations in step S1 are as follows: After being subjected to 0.1 mol L... -1 The solution was washed with dilute hydrochloric acid, saturated sodium bicarbonate, and saturated NaCl, dried with anhydrous Na2SO4, and filtered to remove the desiccant.

[0014] Preferably, the TiO2 and Por-(PLA) n -b-(PNIPAM) m The mass ratio of -Br is 5:3.

[0015] The present invention also provides an application of the above-mentioned soil remediation agent in the treatment of heavy metal pollution.

[0016] Compared with the prior art, the specific beneficial effects of the present invention are as follows: This invention utilizes a Williamson ether synthesis reaction to form covalent bonds between the block copolymer and TiO2, resulting in strong interfacial bonding and avoiding polymer detachment issues caused by physical adsorption. This significantly improves the material's stability and lifespan. The material exhibits excellent temperature-sensitive properties, with a minimum critical dissolution temperature (LCST) of approximately 32°C. At low temperatures, it dissolves in water to form a homogeneous system, ensuring sufficient contact with heavy metal ions and high reaction efficiency. At high temperatures, phase separation and precipitation occur, with a recovery rate exceeding 90%, effectively preventing secondary pollution.

[0017] The heterojunction formed by porphyrin and TiO2 effectively promotes the separation and transfer of photogenerated electron-hole pairs; the large conjugated π system of porphyrin can absorb visible light, extending the photoresponse range of TiO2 from the ultraviolet region to the visible light region, and significantly improving the utilization rate of solar energy.

[0018] The introduction of PLA in this invention can adjust the hydrophilicity and hydrophobicity of block copolymers, optimize the solubility and temperature-sensitive properties of materials, and it is a completely biodegradable polymer material that can decompose into carbon dioxide and water in the natural environment without causing secondary pollution to the soil.

[0019] This invention uses atom transfer radical polymerization (ATRP) to prepare block copolymers. The reaction conditions are mild, the molecular weight distribution is narrow (Mw / Mn<1.1), and the molecular weight of the polymer can be precisely controlled by controlling the ratio of monomer to initiator. The entire preparation process is simple to operate and suitable for large-scale industrial production. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the structure of the soil remediation agent of the present invention; Figure 2 For Por-(PLA) with different degrees of polymerization 50 -b-(PNIPAM) m SEC curve of -Br; Figure 3 For Por-(PLA) 50 -b-(PNIPAM) 50 FT-IR spectrum of -g-TiO2; Figure 4 For Por-(PLA) 50 -b-(PNIPAM) 50 SEM image of -g-TiO2 and EDS surface scan spectra of each element; Figure 5 For Por-(PLA) 50 -b-(PNIPAM) 50 XPS spectra of -g-TiO2, where (a) is the total spectrum, (b) is the Ti 2p spectrum, and (c) is the C 1s spectrum. Detailed Implementation

[0021] To make the technical solutions of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. It should be noted that the following embodiments are only used to better understand the technical solutions of the present invention and should not be construed as limiting the present invention.

[0022] Example 1. In this embodiment, 5-(4-hydroxyphenyl)-10,15,20-triphenylporphyrin (Por-OH) was synthesized using the Adler method. 2.20 g (18 mmol) of p-hydroxybenzaldehyde and 4.75 mL (54 mmol) of benzaldehyde were added to a 100 mL two-necked flask containing 30 mL of propionic acid and stirred until dissolved. The reaction mixture was heated to reflux (approximately 140 °C), and pyrrole (5 mL, 72 mmol) dissolved in 20 mL of propionic acid was slowly added dropwise through a constant-pressure dropping funnel over approximately 30 min. After the addition was complete, the mixture was refluxed and stirred for 2 h. After the reaction was complete, the reaction mixture was cooled to 60 °C, 60 mL of ethanol was added, and the mixture was stirred for 15 min, then allowed to stand for 12 h. The mixture was filtered under reduced pressure, and the filter cake was washed with ethanol until the filtrate was colorless. The filter cake was collected and dried overnight at 60 °C in a vacuum drying oven. The dried solid was purified by silica gel column chromatography. Using dichloromethane as the eluent, the second band of product was collected, and the solvent was removed by vacuum distillation to obtain 0.730 g of a bright purple solid powder, with a yield of 7%.

[0023] Example 2. This embodiment prepared a polylactide containing porphyrin end groups: In a dry 100 mL single-necked round-bottom flask, Por-OH (0.17 g, 0.27 mmol) and lactide (1.945 g, 13.5 mmol) prepared in Example 1 were added. The mixture was deoxygenated under vacuum-nitrogen circulation three times. Stannous isooctanoate (≈2 mg, ≈5 μmol) was added using a microsyringe, and the mixture was stirred in an oil bath at 100 °C for 2.5 h. After the reaction was complete, the mixture was cooled to room temperature, dissolved in 20 mL of dichloromethane, and filtered through a small piece of diatomaceous earth to remove the catalyst and insoluble matter. The filtrate was slowly poured into 200 mL of cold methanol, stirred to settle, filtered to collect the white solid, and dried under vacuum at 40 °C for 24 h to obtain Por-PLA. 50 1.27g, yield 60%.

[0024] Example 3. This embodiment prepared a terminal porphyrin-terminated polylactide: The Por-PLA obtained in Example 2 50 100 mg (0.02 mmol), 30 mL of anhydrous dichloromethane, and triethylamine (2 mg, 0.02 mmol) were added to a 100 mL two-necked flask, and the mixture was stirred for 30 min in an ice-water bath at 0 °C. α-Bromoisobutyryl bromide (4.6 mg, 0.02 mmol) dissolved in 10 mL of anhydrous dichloromethane was slowly added dropwise through a constant-pressure dropping funnel over approximately 15 min. After the addition was complete, the reaction was continued at 0 °C for 12 h. After the reaction was complete, the reaction solution was successively dilute with 0.1 mol / L... L -1The sample was washed three times each with dilute hydrochloric acid solution, saturated sodium bicarbonate solution, and saturated NaCl solution, 20 mL each time. The organic phase was separated, and dried overnight with anhydrous Na₂SO₄. The drying agent was removed by filtration, and the dichloromethane solvent was removed by vacuum distillation to obtain a pink solid powder, Por-PLA. 50 -Br 88.8 mg, yield 86%.

[0025] Example 4. This embodiment prepared a porphyrin-terminated polylactide-b-polyN-isopropylacrylamide block copolymer, Por-(PLA). 50 -b-(PNIPAM) 50 -Br: In a nitrogen-protected glove box, place cuprous bromide (1.4 mg, 0.01 mmol), PMEDTA (20 μL, 0.01 mmol), and 1 mL DMF on one side of an H-type reaction tube and stir for 10 min at room temperature. Add 1 mL DMF and Por-PLA... 50 -Br (10 mg, 2 μmol) and N-isopropylacrylamide (1.13 g, 10 mmol) were placed on the other side of an H-type reaction tube and stirred thoroughly to dissolve. The H-type reaction tube was sealed and the glove box removed. The mixtures from both sides were combined, and the reaction continued at room temperature for 12 h. After the reaction was complete, the mixture was exposed to air to terminate the reaction. The reaction solution was diluted with 10 mL of THF and the residual copper complex was removed by passing it through a neutral alumina column. The eluent was slowly poured into 200 mL of cold n-hexane, stirred to settle, filtered to collect the insoluble matter, and dried under vacuum at 40 °C for 24 h to obtain a white solid, Por-(PLA). 50 -b-(PNIPAM) 50 -Br 0.54g, yield 47.78%.

[0026] GPC characterization result: Mn(GPC) = 0.98 × 10 4 g mol -1 Mn(MALS) = 1.02 × 10 4 g mol -1 Mw / Mn=1.07.

[0027] Example 5. This embodiment prepared a porphyrin-terminated polylactide-b-polyN-isopropylacrylamide block copolymer, Por-(PLA). 50 -b-(PNIPAM) 100 -Br: Following the method in Example 4, the amount of N-isopropylacrylamide was changed to 2.26 g (20 mmol), while other conditions remained unchanged, to obtain Por-(PLA). 50 -b-(PNIPAM) 100 -Br.

[0028] GPC characterization result: Mn(GPC) = 1.54 × 10 4 g mol - ¹, Mn(MALS) = 1.62 × 10 4 g mol -1 Mw / Mn=1.02.

[0029] Example 6. Porphyrin-terminated polylactide-b-poly(N-isopropylacrylamide) block copolymer (Por-(PLA)) 50 -b-(PNIPAM) 200 -Br: Following the method in Example 4, the amount of N-isopropylacrylamide was changed to 4.52 g (40 mmol), while other conditions remained unchanged, to obtain Por-(PLA). 50 -b-(PNIPAM) 200 -Br.

[0030] GPC characterization result: Mn(GPC) = 1.93 × 10 4 g mol -1 Mn(MALS) = 2.04 × 10 4 g mol -1 Mw / Mn=1.03.

[0031] Example 7. Binary nanohybrid material Por-(PLA) 50 -b-(PNIPAM) 50 Preparation of -g-TiO2 Add 10 mL of acetonitrile to a 50 mL two-necked flask, add excess anhydrous potassium carbonate (0.5 g), and stir at room temperature for 30 min. Add TiO2 (5 mg, particle size approximately 20 nm), and continue stirring for 30 min. Finally, add Por-(PLA) prepared in Example 4. 50 -b-(PNIPAM) 50-Br (3 mg) was stirred in an oil bath at 80 °C for 24 h. After the reaction, the crude product was separated by centrifugation (8000 rpm, 10 min) and washed three times each with dichloromethane, ethanol, and deionized water (10 mL each time). The product was then dried under vacuum at 40 °C for 24 h to obtain a pale purple solid powder, Por-(PLA). 50 -b-(PNIPAM) 50 -g-TiO2.

[0032] Example 8. Binary nanohybrid material Por-(PLA) 50 -b-(PNIPAM) 50 Preparation of -g-TiO2 Add 10 mL of acetonitrile to a 50 mL two-necked flask, add excess anhydrous potassium carbonate (0.5 g), and stir at room temperature for 30 min. Add TiO2 (5 mg, particle size approximately 20 nm), and continue stirring for 30 min. Finally, add Por-(PLA) prepared in Example 5. 50 -b-(PNIPAM) 100 -Br (3 mg) was stirred in an oil bath at 80 °C for 24 h. After the reaction, the crude product was separated by centrifugation (8000 rpm, 10 min) and washed three times each with dichloromethane, ethanol, and deionized water (10 mL each time). The product was then dried under vacuum at 40 °C for 24 h to obtain a pale purple solid powder, Por-(PLA). 50 -b-(PNIPAM) 100 -g-TiO2.

[0033] Example 9. Binary nanohybrid material Por-(PLA) 50 -b-(PNIPAM) 50 Preparation of -g-TiO2 Add 10 mL of acetonitrile to a 50 mL two-necked flask, add excess anhydrous potassium carbonate (0.5 g), and stir at room temperature for 30 min. Add TiO2 (5 mg, particle size approximately 20 nm), and continue stirring for 30 min. Finally, add Por-(PLA) prepared in Example 6. 50 -b-(PNIPAM) 200 -Br (3 mg) was stirred in an oil bath at 80 °C for 24 h. After the reaction, the crude product was separated by centrifugation (8000 rpm, 10 min) and washed three times each with dichloromethane, ethanol, and deionized water (10 mL each time). The product was then dried under vacuum at 40 °C for 24 h to obtain a pale purple solid powder, Por-(PLA). 50 -b-(PNIPAM) 200 -g-TiO2.

[0034] Comparative Example 1. Pure TiO2 nanoparticles: Commercially available anatase TiO2 nanoparticles (approximately 20 nm in diameter) were used as a comparative example.

[0035] Characterization Example 1. The molecular weight and molecular weight distribution of the block copolymers prepared in Examples 4-6 were determined using gel permeation chromatography (GPC) with an RI detector, using THF as the mobile phase at a flow rate of 1.0 mL. min -1 The column temperature was 30℃, and PMMA was used as the standard. The absolute molecular weight was determined using a multi-angle laser scattering (MALS) spectrometer. The test results are shown in Table 1 and... Figure 2 As shown.

[0036] Table 1

[0037] from Figure 2 It can be seen that the SEC curves of the three block copolymers all exhibit a single-peak distribution with narrow peaks. As the degree of polymerization of PNIPAM increases, the elution time gradually decreases, and the curve shifts to the left, indicating that the molecular weight of the polymer can be precisely controlled by adjusting the ratio of monomer to initiator. Table 1 shows that the molecular weights measured by GPC and MALS are basically consistent with the theoretical values, and the molecular weight distribution index (Mw / Mn) is less than 1.1, indicating that the ATRP polymerization process has good activity controllability, and block copolymers with uniform molecular weight distribution were successfully prepared.

[0038] Characterization Example 2. The Por-(PLA) prepared in Example 7 was analyzed using Fourier transform infrared spectroscopy (FT-IR). 50 -b-(PNIPAM) 50 The structure of -g-TiO2 was characterized by KBr pellet method, with a scanning range of 4000-4000 cm⁻¹. -1 The test results are as follows: Figure 3 As shown.

[0039] from Figure 3 It can be seen that 3347cm -1 The characteristic peak at 2922 cm⁻¹ belongs to the stretching vibration peak of NH in the PNIPAM block; -1 and 2850cm -1 The characteristic peak at 1750 cm⁻¹ is attributed to the stretching vibration peak of the methylene group on the PNIPAM backbone; -1 The strong absorption peak at 1640 cm⁻¹ is attributed to the stretching vibration of the ester carbonyl group in the PLA block; - ¹ and 1540cm -The characteristic peaks at ¹ represent the amide I band (C=O stretching vibration) and amide II band (coupling of NH bending vibration and CN stretching vibration) of PNIPAM, respectively; 800 cm⁻¹ -1 The characteristic peak at 702 cm⁻¹ is attributed to the vibrational peaks of the porphyrin skeleton; -1 The characteristic peak at 1245 cm⁻¹ belongs to the stretching vibration peak of Ti-O-Ti in TiO₂. Furthermore, the peak at 1245 cm⁻¹... -1 and 1040cm -1 A distinct stretching vibration peak of the ether bond (COC) was observed, indicating that Por-(PLA) 50 -b-(PNIPAM) 50 -Br and TiO2 successfully formed a covalent bond through the Williamson ether synthesis reaction, proving the successful preparation of binary nano-hybrid materials.

[0040] Characterization example 3. The Por-(PLA) prepared in Example 7 was examined using a scanning electron microscope. 50 -b-(PNIPAM) 50 The morphology of -g-TiO2 was observed, and its elemental distribution was analyzed using energy dispersive spectroscopy. The test results are as follows: Figure 4 As shown.

[0041] The SEM images show that Por-(PLA) 50 -b-(PNIPAM) 50 -g-TiO2 exhibits a uniform spherical structure with a particle size of approximately 50–100 nm and a relatively rough surface, which is due to polymer grafting onto the TiO2 surface. EDS (Energy Distributed Spectroscopy) images show that C, N, Ti, and O elements are uniformly distributed in the sample. The distribution of Ti elements coincides with the location of TiO2, while the distribution of C and N elements indicates Por-(PLA) 50 -b-(PNIPAM) 50 The groups were uniformly loaded on the TiO2 surface, further confirming the successful preparation of binary nano-hybrid materials.

[0042] Characterization example 4. X-ray photoelectron spectroscopy was used to analyze the Por-(PLA) prepared in Example 7. 50 -b-(PNIPAM) 50 The surface elemental composition and valence state of -g-TiO2 were analyzed, with C 1s (284.6 eV) as the binding energy reference. The test results are as follows: Figure 5 As shown.

[0043] Figure 5(a) is the XPS total spectrum, where the characteristic peaks of C, N, O, and Ti can be clearly observed, with no peaks of other impurity elements, consistent with the EDS analysis results. The peak at the binding energy of 401.35 eV is attributed to the N1s of the porphyrin ring and the PNIPAM block. Figure 5 (b) is the Ti 2p spectrum, where the two peaks at binding energies of 464.9 eV and 459.1 eV correspond to Ti 2p, respectively. 1 / 2 and Ti2p 3 / 2 The binding energy difference between the two is 5.8 eV, indicating that Ti in the sample mainly exists in the +4 valence form. Figure 5 (c) shows the C1s spectrum, which can be fitted to three peaks with binding energies of 284.6 eV, 285.8 eV, and 288.6 eV, corresponding to the CC / CH bond, CN bond, and O=CO bond, respectively, consistent with the structures of porphyrin, PLA, and PNIPAM. Compared with the pure polymer, the binding energies of the C1s peaks are slightly lower. This is because covalent bonds are formed between the polymer and TiO2, resulting in a change in electron cloud density, further confirming the formation of covalent bonds.

[0044] Example of an effect 1. Temperature sensitivity performance test: The binary nano-hybrid materials prepared in Examples 7, 8, and 9, and the pure TiO2 of Comparative Example 1, were respectively prepared into 1 mg... mL -1 The ultrapure aqueous dispersion was ultrasonically dispersed for 30 min until homogeneous. A UV-Vis spectrophotometer was used to measure the dispersion at a wavelength of 500 nm and a heating rate of 1 °C. min -1 The temperature was gradually increased from 20℃ to 45℃, and the changes in transmittance were recorded in real time. The temperature corresponding to a sudden decrease in transmittance of 50% was defined as the lowest critical dissolution temperature (LCST). 25℃ was used to represent a low-temperature environment, and 40℃ was used to represent a high-temperature environment. The dissolution / precipitation state of the material was observed and recorded.

[0045] The test results are shown in Figure 2.

[0046] Table 2

[0047] The LCSTs of Examples 7-9 were 32.1℃, 31.7℃, and 31.3℃, respectively, all falling within the 31.3~32.1℃ range. This is highly consistent with the temperature-sensitive characteristics of pure PNIPAM, indicating that the PNIPAM segments were successfully grafted onto the TiO2 surface and retained their complete temperature-sensitive phase transition capability. At 25℃ (below LCST), the dispersions of Examples 7-9 were completely transparent, without precipitation, and exhibited a homogeneous solution state. At this temperature, the hydrophilic amide groups (-CONH-) in the PNIPAM segments formed numerous hydrogen bonds with water molecules, allowing the segments to fully extend and driving the TiO2 nanoparticles to be uniformly dispersed in water. This completely solved the technical defects of traditional TiO2, such as easy aggregation, uneven dispersion, and low heterogeneous contact efficiency. At 40℃ (above LCST), the dispersions of Examples 7-9 instantly became turbid, and the solid particles completely precipitated. At this point, the increased temperature disrupts the hydrogen bonds between PNIPAM and water molecules, causing the chain segments to transform from an extended state to a hydrophobic coiled state. This strengthens the hydrophobic interactions between molecules, leading to overall phase separation and precipitation of the material. Solid-liquid separation can be achieved solely through temperature control without the need for additional precipitants, making the operation simple and inexpensive. In Comparative Example 1, pure TiO2 remained in a suspended, turbid state at both 25℃ and 40℃, exhibiting no phase transition behavior. This indicates that pure TiO2 lacks temperature-sensitive response capabilities and cannot achieve a dissolution-precipitation cycle through temperature control. Subsequent recovery requires complex processes such as centrifugation and filtration, and is prone to loss and high degradation.

[0048] Example of effect 2. Heavy metal reduction performance test: Using hexavalent chromium (Cr(VI)), a typical toxic heavy metal in soil / water, as a model pollutant, an initial concentration of 10 mg was prepared. L -1 A K₂Cr₂O₇ aqueous solution was prepared, and the pH of the system was adjusted to 3 using dilute sulfuric acid (simulating an acidic soil / water environment, representing the optimal acidity conditions for Cr(VI) reduction). 50 mg of materials from Examples 7, 8, and 9, and pure TiO₂ from Comparative Example 1 were weighed and added to 50 mL of the aforementioned Cr(VI) solution. The mixture was magnetically stirred for 30 min in the dark to allow the materials and Cr(VI) to reach adsorption-desorption equilibrium, eliminating the interference of physical adsorption on the reduction efficiency. Subsequently, a 300W xenon lamp (equipped with a 420 nm cutoff filter) was used as the visible light source to vertically irradiate the reaction system, with continuous magnetic stirring for 120 min. Every 30 min, 5 mL samples were taken, centrifuged at 10000 rpm for 5 min, and the supernatant was collected. The residual Cr(VI) concentration was determined using the diphenylcarbazide spectrophotometric method at a wavelength of 540 nm. The Cr(VI) reduction rate after 120 min of visible light irradiation was calculated as follows: Reduction rate (%) = (Initial concentration - Residual concentration) / Initial concentration × 100%.

[0049] The test results are shown in Table 3.

[0050] Table 3

[0051] After 120 minutes of visible light irradiation, the reduction rates of Cr(VI) in Examples 7-9 were 92.0%, 94.8%, and 87.5%, respectively, which were much higher than those of pure TiO2 in Comparative Example 1. Pure TiO2 can only respond to ultraviolet light (accounting for less than 5% of sunlight), and its visible light utilization rate is extremely low. Moreover, the recombination rate of photogenerated electron-hole pairs is fast, and only a small number of electrons can participate in the Cr(VI) reduction reaction. However, the material of this invention significantly improves the reduction efficiency in two aspects through the synergistic effect of porphyrin-TiO2 heterojunction: ① Porphyrin has a large conjugated π electron system, which can efficiently absorb visible light (400~700nm), extending the light response range of TiO2 from the ultraviolet region to the visible light region, and increasing the solar energy utilization rate by more than 5 times; ② Porphyrin and TiO2 form a Type-II heterojunction, and photogenerated electrons are rapidly transferred from the LUMO energy level of porphyrin to the conduction band of TiO2, while holes remain in the HOMO energy level of porphyrin, effectively inhibiting electron-hole recombination, prolonging the lifetime of photogenerated electrons, and allowing more electrons to participate in the Cr(VI)→Cr(III) reduction reaction (Cr(III) is non-toxic, easy to precipitate and fix, and its biological toxicity is significantly reduced).

[0052] Examples 7-9 are homogeneous solutions at low temperatures, where the repair agent molecules and Cr(VI) ions are in full contact at the molecular scale, with no mass transfer resistance and a fast reaction kinetic rate. In contrast, pure TiO2 is a heterogeneous suspension system, where the particles only come into contact with Cr(VI) on the surface, resulting in high mass transfer resistance and a slow reaction rate. This further highlights the technical advantages of the homogeneous catalytic repair of this invention.

[0053] Example of an effect 3. Recycling performance test: The mixture after the visible light reduction reaction was heated to 40°C and magnetically stirred for 10 min to allow for complete phase separation and precipitation. The solid material was then collected by centrifugation at 8000 rpm for 5 min. The solid was washed three times (10 mL each time) with ultrapure water to remove residual Cr(III) ions and impurities. It was then vacuum dried at 40°C for 12 h to obtain the recovered remediation agent. 10 mg of the recovered material was added back into the solution. L - In a Cr(VI) solution, the above-described steps of dark adsorption, visible light reduction, temperature precipitation, centrifugation washing, and drying were repeated five times. The Cr(VI) reduction rate was measured in each cycle to evaluate the cycling stability and recovery performance of the material.

[0054] The test results are shown in Table 4.

[0055] Table 4

[0056] After five cycles, the Cr(VI) reduction rates in Examples 7-9 remained at 85.2%, 88.0%, and 81.2%, respectively, with an average reduction rate exceeding 84% across the five cycles, demonstrating excellent stability during recycling. The core reason is that the material uses covalent ether bonds (COC) to connect the block copolymer and TiO2, resulting in extremely strong interfacial bonding. During multiple dissolution-precipitation and centrifugal washing processes, the copolymer segments are not easily detached from the TiO2 surface, maintaining the integrity of the material structure and minimizing the loss of active sites. Therefore, the reduction efficiency decays slowly during cycling.

[0057] In Comparative Example 1, the initial reduction rate of pure TiO2 was only 15.0%, which dropped to 5.8% after 5 cycles, with an average reduction rate of only 10.4%. The reason is that pure TiO2 is made up of nanoparticles, which have no temperature-sensitive precipitation ability. During centrifugation recovery, the particles are easily lost and agglomerated. In addition, there is no organic protective layer. After multiple cycles, particle agglomeration intensifies, active sites are greatly reduced, and catalytic activity decays rapidly, making it unsuitable for practical recycling applications.

[0058] The material recovery process of this invention only requires heating for precipitation, centrifugation, and washing with water, without the need for complex equipment or chemical reagents. It is simple to operate and low in cost. Furthermore, its covalent bond structure is stable, and the material recovery rate remains above 90% after 5 cycles, effectively avoiding secondary pollution caused by residual remediation agents in the soil, thus aligning with the concept of green and environmentally friendly remediation. In summary, the material of this invention combines highly efficient visible light reduction capability, excellent cycle stability, and a convenient recovery process, solving the pain points of traditional remediation agents such as low efficiency, difficulty in recovery, and easy secondary pollution. It has extremely high practical application value in the field of heavy metal contaminated soil / water remediation.

[0059] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A soil remediation agent, characterized in that, The soil remediation agent is a binary nano-hybrid material formed by covalently linking porphyrin-terminated polylactide and polyN-isopropylacrylamide with titanium dioxide, with the chemical formula Por-PLA. n -b-PNIPAM m -g-TiO2, where 50≤n≤100, 50≤m≤200; The porphyrin-terminated polylactide is prepared by the following steps: 5-(4-hydroxyphenyl)-10,15,20-triphenylporphyrin, lactide, and stannous isooctanoate were dissolved in toluene and stirred under heating conditions. After the reaction was completed, toluene was removed by vacuum distillation. The remaining mixture was poured into n-hexane to precipitate, and the precipitate was collected by filtration. This precipitate is polylactide containing porphyrin end groups, with the chemical formula Por-PLA. n .

2. The soil remediation agent according to claim 1, characterized in that, The molar ratio of 5-(4-hydroxyphenyl)-10,15,20-triphenylporphyrin and stannous isooctanoate is 1:0.

1.

3. The soil remediation agent according to claim 1, characterized in that, The heating conditions are provided at a temperature of 80°C to 110°C.

4. A method for preparing a soil remediation agent as described in any one of claims 1 to 3, characterized in that, Includes the following steps: S1, Por-PLA n Anhydrous dichloromethane and triethylamine were added to a two-necked flask and stirred under ice-water bath conditions. Then, α-bromoisobutyryl bromide dissolved in anhydrous dichloromethane was added to the mixture through a constant-pressure dropping funnel, and the reaction continued under ice-water bath conditions. After the reaction was complete, the mixture was washed and dried, and then the dichloromethane solvent was removed by vacuum distillation to obtain polylactide with bromine atoms at the ends and porphyrin groups at the terminal groups, with the chemical formula Por-PLA. n -Br; S2. Under nitrogen protection, place cuprous bromide, pentamethyldivinyltriamine, and N,N-dimethylformamide on one side of an H-type reaction tube and stir at room temperature; add N,N-dimethylformamide and Por-PLA. n -Br and N-isopropylacrylamide were placed on the other side of an H-type reaction tube and stirred thoroughly. The mixtures on both sides of the H-type reaction tube were mixed and the reaction continued. After the reaction was completed, the mixture was exposed to air to terminate the reaction. The resulting solution was diluted with THF and the residual copper complex was removed with neutral alumina. The solution was then purified by precipitation in cold n-hexane, and the insoluble matter was collected by filtration and vacuum dried to obtain a poly-L-type lactide-poly-N-isopropylacrylamide block copolymer with porphyrin groups at the end groups, with the chemical formula Por-(PLA). n -b-(PNIPAM) m -Br; S3. Add acetonitrile to a two-necked flask, then add excess anhydrous potassium carbonate and stir at room temperature; add TiO2 and continue stirring, and finally add Por-(PLA). n -b-(PNIPAM) m -Br, continue stirring the reaction, centrifuge to separate the crude product, and then wash with dichloromethane, ethanol and deionized water respectively to obtain the soil remediation agent.

5. The method for preparing the soil remediation agent according to claim 4, characterized in that, The preparation method is carried out entirely in a glove box to achieve absolute anhydrousness and oxygen-free conditions.

6. The method for preparing the soil remediation agent according to claim 4, characterized in that, The stirring time in step S1 is 30 minutes.

7. The method for preparing the soil remediation agent according to claim 4, characterized in that, The specific operations for washing and drying described in step S1 are as follows: After being subjected to 0.1 mol L... -1 The solution was washed with dilute hydrochloric acid, saturated sodium bicarbonate, and saturated NaCl, dried with anhydrous Na2SO4, and filtered to remove the desiccant.

8. The method for preparing the soil remediation agent according to claim 4, characterized in that, The TiO2 and Por-(PLA) n -b-(PNIPAM) m The mass ratio of -Br is 5:

3.

9. The application of a soil remediation agent as described in any one of claims 1 to 3 in the treatment of heavy metal pollution.

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