A soybean protein nanoparticle coagulant for removing perfluorinated compounds from water, its preparation method and uses

Abstract

This invention provides a soybean protein nanoparticle coagulant for removing perfluorinated compounds (PFAS) from water, its preparation method, and its applications. First, N,N-dimethylhexadecylamine and epichlorohydrin are used to prepare a reaction precursor, glycidylhexadecyldimethylammonium chloride. Simultaneously, soybean protein isolate is hydrolyzed using a protease to obtain a hydrolyzed soybean protein solution. Then, the two are reacted, causing the epoxy groups on the glycidylhexadecyldimethylammonium chloride to undergo a ring-opening addition reaction with the amino groups on the hydrolyzed soybean protein, thus grafting them onto the hydrolyzed soybean protein. After the reaction, acetone is added to generate a precipitate. The precipitate is collected, washed, and dried to obtain the soybean protein nanoparticle coagulant for removing PFAS from water. The soybean protein nanoparticle coagulant prepared by this invention utilizes strong electrostatic and hydrophobic interactions, exhibiting a significantly higher removal capacity and selectivity for PFAS than traditional coagulants, demonstrating excellent removal efficiency and significant anti-interference ability.

Description

Technical Field

[0001] This invention belongs to the field of water treatment functional agent research and development, specifically relating to a soybean protein nanoparticle coagulant for removing perfluorinated compounds from water, its preparation method, and its application. Background Technology

[0002] With the development of industrial society, perfluorinated compounds (PFAS), as highly toxic and persistent pollutants that are difficult to degrade, have been widely detected in various water bodies, posing a serious threat to the ecological environment and human health. Coagulation, as a core component of water treatment, plays a crucial role in removing turbidity, color, and microorganisms in drinking water treatment, and is also an important technical means for phosphorus removal, decolorization, and suspended solids removal in wastewater treatment. However, facing the increasingly severe problem of PFAS pollution, traditional coagulants exhibit significant limitations: inorganic coagulants such as aluminum and iron salts mainly rely on charge neutralization and entrapment to remove colloidal substances, with limited effectiveness in removing dissolved PFAS molecules; while synthetic organic polymeric coagulants, although possessing strong charge neutralization capabilities, suffer from problems such as monomeric residual toxicity and difficulty in biodegradation, and their PFAS removal efficiency remains unsatisfactory.

[0003] Currently, research on PFAS removal technologies mainly focuses on adsorption, membrane separation, and advanced oxidation. While adsorption is effective, it suffers from drawbacks such as high cost and regeneration difficulties; membrane separation is energy-intensive and raises issues regarding concentrate disposal; and advanced oxidation technologies may produce more toxic intermediates. In contrast, developing highly efficient coagulants for PFAS would offer significant advantages, including ease of operation, low cost, and applicability in existing water treatment plants.

[0004] Existing coagulants face several major challenges in PFAS removal: First, traditional coagulants cannot effectively target the unique amphiphilic structure of PFAS molecules, namely the hydrophobic fluorinated carbon chain and the hydrophilic charged head group. Second, existing coagulants lack specific recognition capabilities for PFAS, resulting in limited removal efficiency. Furthermore, synthetic organic coagulants are environmentally unfriendly and may cause secondary pollution. Therefore, developing a novel, environmentally friendly coagulant capable of specifically recognizing and efficiently removing PFAS is of great significance.

[0005] Functional modification based on natural biomass offers a new approach for developing green and efficient PFAS removal coagulants. Soy protein, as a widely available and biodegradable natural polymer, contains abundant active groups in its molecular structure, providing a good foundation for functional modification. However, how to achieve efficient targeted removal of PFAS through molecular design while maintaining excellent coagulation properties remains a pressing technical challenge. Summary of the Invention

[0006] The present invention aims to overcome the above-mentioned defects by using inexpensive soybean protein with abundant surface modification sites as a base material to synthesize a novel coagulant for deep purification of PFAS-contaminated water. Its removal capacity and selectivity for PFAS are far higher than those of traditional coagulants, and it has excellent removal efficiency and significant anti-interference ability.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A method for preparing a soybean protein nanoparticle coagulant for removing perfluorinated compounds from water includes the following steps:

[0009] S1 reacts N,N-dimethylhexadecylamine and epichlorohydrin in methanol at room temperature for 8-12 hours at a molar ratio of 1:(1.5-2.5). After the reaction is complete, excess methanol is removed by rotary evaporation, acetone is added for recrystallization, and the product is washed and vacuum dried to obtain the reaction precursor, i.e., epichlorohydrin hexadecyldimethylammonium chloride.

[0010] S2 disperses soy protein isolate in water at a solid-liquid ratio of 40-80 g / L, adjusts the pH to 7.5-8.5, and hydrolyzes it at 50-60℃ using alkaline protease catalysis. The amount of alkaline protease added accounts for 0.1%-2% of the total substrate mass. The hydrolysis reaction continues until the degree of hydrolysis of soy protein is 4-8%. Then, the alkaline protease is inactivated by heating, and the solution is cooled to room temperature to obtain a hydrolyzed soy protein solution.

[0011] S3. Adjust the pH of the above hydrolyzed soybean protein solution to 10-12, centrifuge to remove insoluble matter, and then add glycidyl hexadecyl dimethyl ammonium chloride to the supernatant. The molar ratio of amino groups in the hydrolyzed soybean protein solution to glycidyl hexadecyl dimethyl ammonium chloride is 1: (1-10). After heating, stir the reaction thoroughly to allow the epoxy groups on glycidyl hexadecyl dimethyl ammonium chloride to undergo a ring-opening addition reaction with the amino groups on the hydrolyzed soybean protein, thereby grafting them onto the hydrolyzed soybean protein. After the reaction is complete, adjust the pH to neutral, centrifuge again to remove insoluble matter, and then add sufficient acetone to the supernatant until a large amount of precipitate appears. After standing for a while, centrifuge the precipitate to separate it and collect the product.

[0012] S4 The product was thoroughly washed with acetone and dried under vacuum to obtain the soybean protein nanoparticle coagulant that removes perfluorinated compounds from water.

[0013] Furthermore, the molar ratio of N,N-dimethylhexadecylamine and epichlorohydrin in S1 is 1:2, and the reaction time is 10 hours.

[0014] Furthermore, the pH of S2 was adjusted to 8 using a 0.1 M sodium hydroxide solution.

[0015] Furthermore, in S2, the alkaline protease used is Alcalase, with an Alcalase-to-substrate ratio of 0.5%, a hydrolysis temperature of 55℃, a hydrolysis reaction duration of 15 minutes, a soybean protein hydrolysis degree of 6%, and an amino equivalent of 7.91 × 10⁻⁶. -4 mmol / g; inactivate alkaline protease by water bath at 85°C for 10 minutes.

[0016] Furthermore, in S3, the pH of the hydrolyzed soybean protein solution was adjusted to 11 with 1 M sodium hydroxide solution, and then centrifuged at 5000 g for 2 minutes to remove insoluble matter.

[0017] Furthermore, the molar ratio of amino content of hydrolyzed soybean protein in S3 to glycidyl hexadecyl dimethyl ammonium chloride is 1:5, and the two are stirred and reacted at 50°C for 12 hours.

[0018] Furthermore, after the reaction in S3 is completed, the pH is adjusted to 7 with 0.1 M hydrochloric acid solution, and then the insoluble matter is removed again by centrifugation at 5000 g for 2 minutes. Then, 2 times the volume of acetone is added to the supernatant to form a precipitate. After the precipitate is formed, it is allowed to stand for 30 minutes, and the precipitate is centrifuged at 8000 g for 10 minutes to obtain the product.

[0019] Furthermore, in S4, the product was washed three times with acetone and then dried in a vacuum drying oven at 35°C for 12 hours.

[0020] A second objective of this invention is to provide a soybean protein nanoparticle coagulant prepared by the above-described method for removing perfluorinated compounds from water.

[0021] A third objective of this invention is to provide the use of the above-mentioned soybean protein nanoparticle coagulant in the purification of perfluorinated compound pollution in water bodies.

[0022] The core innovation of this invention lies in the first design and preparation of a nanoparticle coagulant based on renewable soybean protein, possessing a dual-functional synergistic mechanism of "electrostatic capture" and "hydrophobic anchoring." This design precisely matches the unique amphiphilic structure of the PFAS molecule—a "hydrophilic charged head group-hydrophobic fluorocarbon tail chain"—overcoming the bottleneck of traditional coagulants' near-ineffectiveness in PFAS removal. Through an "enzymatic hydrolysis-grafting" modification strategy, small molecule peptides self-assemble into nanoparticles through hydrophobic interactions between grafted long alkyl chains, combining the green advantages of natural biomass with the precision of molecular functionalization design to create a novel PFAS-targeting nanoparticle coagulant.

[0023] Compared with the prior art, the technical solution provided by the present invention has the following significant advantages:

[0024] 1. High removal efficiency and strong anti-interference ability: The quaternary ammonium salt cations on the surface of the coagulant of this invention can efficiently capture the negatively charged head groups (such as -COOH) of PFAS through strong electrostatic interaction. Meanwhile, its hydrophobic long chains can tightly anchor the fluorocarbon tail chains of PFAS through hydrophobic interactions. This dual "head-tail synergistic" mechanism makes its removal capacity and selectivity for PFAS far higher than that of traditional coagulants that rely solely on charge neutralization. Even in complex water bodies containing humic acid, inorganic salts, etc., it can still maintain excellent removal efficiency and has significant anti-interference ability.

[0025] 2. Green, environmentally friendly and sustainable: This invention uses renewable natural soybean protein as raw material. The entire preparation process is mild and the final product has good biocompatibility. It conforms to the concepts of green chemistry and sustainable development and solves the problems of environmental residues and secondary pollution risks associated with traditional synthetic coagulants.

[0026] 3. Significant nano-effects and rapid reaction and mass transfer rates: The coagulant of this invention is in nanoparticle form, possessing abundant surface active sites, enabling rapid dispersion and contact with PFAS molecules in water, significantly improving the kinetic rates of adsorption and aggregation. The nanoscale also makes it easier for it to interact with micro- and nano-sized pollutant colloids in water, enhancing capture efficiency.

[0027] 4. Low application cost and good process compatibility: The raw materials of this invention are inexpensive, the preparation process is simple, and it is easy to scale up production. This coagulant can be seamlessly integrated with the coagulation-flocculation-sedimentation process units of existing water treatment plants, without the need to add complex equipment or change the mainstream process, to achieve efficient and deep removal of PFAS, greatly reducing the threshold for technology application and the total cost. Attached Figure Description

[0028] Figure 1 The flowchart for the preparation of soybean protein nanoparticle coagulant provided in Example 1;

[0029] Figure 2 The infrared spectrum of the coagulant in Example 5;

[0030] Figure 3 Here is a scanning electron microscope image of the coagulant in Example 5;

[0031] Figure 4 This is a particle size distribution diagram of the coagulant in Example 5;

[0032] Figure 5 The diagram shows the Zeta potential of the coagulant in Example 5 at different pH values.

[0033] Figure 6 The graph shows the removal effect of nanoparticle coagulant on 7 types of PFAS at different dosages in Example 6.

[0034] Figure 7 The graph shows the removal effect of ferric chloride on seven PFAS at different dosages in Example 6.

[0035] Figure 8 The effect of nanoparticle coagulants on the removal of 7 types of PFAS under different pH conditions in Example 7 is shown. Detailed Implementation

[0036] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to embodiments.

[0037] Example 1

[0038] The flowchart of the preparation method of the soybean protein nanoparticle coagulant for removing perfluorinated compounds from water provided in this embodiment is as follows: Figure 1 As shown, the specific steps are as follows:

[0039] S1. 118 mL of N,N-dimethylhexadecylamine and 225 mL of methanol were added to a round-bottom flask. 55 mL of epichlorohydrin was added dropwise to the round-bottom flask at a rate of approximately 1 mL / min using a constant-pressure dropping funnel (the molar ratio of N,N-dimethylhexadecylamine to epichlorohydrin was 1:2). The mixture was stirred and reacted at room temperature in the dark for 10 hours. After the reaction was completed, excess methanol was removed by rotary evaporation at 35°C and 0.9 MPa. 500 mL of acetone was added to the remaining reaction solution, and a white precipitate was recrystallized. After precipitating for 10 minutes, the supernatant was discarded. The white precipitate was washed three times with acetone and then naturally dried in a fume hood to obtain a white dry solid precursor, namely epichlorohydrin hexadecyl dimethyl ammonium chloride (EPHDAC). EPHDAC was a white dry solid with an epoxy value of 62%.

[0040] S2: 6 g of soy protein isolate was dispersed in 100 mL of water, and the pH was adjusted to 8 with 0.1 M sodium hydroxide solution. 0.33 g of Alcalase enzyme solution (mass ratio of glycerol:water:enzyme = 50:41:9) was added, and the reaction was carried out at 55℃ for 45 minutes. During the reaction, the pH was maintained at approximately 8 with 0.1 M sodium hydroxide solution. The hydrolysis reaction lasted for 15 minutes, and the degree of hydrolysis of soy protein was 6%, with an amino equivalent of 7.91 × 10⁻⁶. -4 mmol / g; after the reaction was completed, the mixture was incubated in a water bath at 85°C for 10 minutes to inactivate the Alcalase enzyme, and then cooled to room temperature to obtain a hydrolyzed soybean protein solution.

[0041] S3 adjusted the pH of the above hydrolyzed soybean protein solution to 11 with 1 M sodium hydroxide solution, centrifuged at 5000 g for 2 minutes to remove a small amount of insoluble matter, and then added 1.71 g of EPHDAC (the molar ratio of amino content of hydrolyzed soybean protein to EPHDAC is 1:1) to the supernatant. The mixture was stirred at 50°C for 12 hours. After the reaction was completed, the pH was adjusted to 7 with 0.1 M hydrochloric acid solution, centrifuged at 5000 g for 2 minutes to remove a small amount of insoluble matter again, and the supernatant was added to 200 mL of acetone. After standing for 10 minutes to precipitate, the precipitate was centrifuged at 8000 g for 10 minutes to obtain the product.

[0042] S4 washed the product three times with acetone and then dried it in a vacuum drying oven at 35°C for 12 hours to obtain a nanoparticle coagulant. The coagulant was a light yellow powder and the product yield was 76%.

[0043] The change in free amino group content of soybean protein before and after the grafting reaction was determined by the o-phthalaldehyde (OPA)-serine method, thereby determining the degree of substitution of amino groups by EPHDAC. The specific test steps are as follows:

[0044] Preparation of OPA reagent: Dissolve 3.810 g of borax and 100 mg of sodium dodecyl sulfate in 75 mL of deionized water and stir until completely dissolved. Dissolve 80 mg of OPA in 2 mL of anhydrous ethanol, then quantitatively transfer the phthalaldehyde solution to the above solution, followed by the addition of 88 mg of dithiothreitol. Make up to 100 mL with deionized water.

[0045] The test procedure is as follows: The sample is diluted with pure water to 0.2 mg / mL. 400 μL of the sample is mixed with 3 mL of OPA reagent and reacted in the dark for 2 min. The absorbance at 340 nm is then measured. The degree of substitution of the amino group by EPHDAC is obtained by dividing the difference in absorbance before and after the reaction by the absorbance before the reaction.

[0046] In this embodiment, the molar ratio of amino content of hydrolyzed soybean protein to EPHDAC is 1:1, and the degree of substitution of amino groups by EPHDAC is 26.8%.

[0047] Example 2

[0048] In this embodiment, the mass of EPHDAC in S3 of Example 1 was increased to 4.28 g (the molar ratio of amino content of hydrolyzed soybean protein to EPHDAC was 1:2.5), and the other steps were the same as in Example 1, to obtain the nanoparticle coagulant. In this embodiment, the degree of substitution of amino groups by EPHDAC was 57.6%.

[0049] Example 3

[0050] In this embodiment, the mass of EPHDAC in S3 of Example 1 was increased to 8.56 g (the molar ratio of amino content of hydrolyzed soybean protein to EPHDAC was 1:5), and the other steps were the same as in Example 1, to obtain the nanoparticle coagulant. In this embodiment, the degree of substitution of amino groups by EPHDAC was 80.6%.

[0051] Example 4

[0052] In this embodiment, the mass of EPHDAC in S3 of Example 1 was increased to 17.1 g (the molar ratio of amino content of hydrolyzed soybean protein to EPHDAC was 1:10), and the other steps were the same as in Example 1, to obtain the nanoparticle coagulant. In this embodiment, the degree of substitution of amino groups by EPHDAC was 82.3%.

[0053] The results from Examples 1-4 show that when the molar ratio of amino content of hydrolyzed soybean protein to EPHDAC is 1:5, the substitution of amino groups by EPHDAC is basically saturated. Therefore, the preferred molar ratio of amino content of hydrolyzed soybean protein to EPHDAC is 1:5.

[0054] Example 5

[0055] This embodiment mainly examines the surface functional groups, morphology, particle size, and zeta potential of the synthesized hydrolyzed soybean protein nanoparticle coagulant.

[0056] Take approximately 1-2 mg of dried sample (hydrolyzed soybean protein ESPI and the nanoparticle coagulant C16-QSPI prepared in Example 3) and grind it thoroughly in an agate mortar. Add approximately 100-200 mg of dried potassium bromide and continue mixing and grinding until a uniform and fine powder is formed. Place the mixed powder into a special mold and press it into transparent or translucent sheets using a tablet press at approximately 10 MPa. Subsequently, measure the infrared spectrum using a Fourier transform infrared spectrometer (scanning range: 4000-500 cm⁻¹). -1 Resolution: 4 cm -1 (Number of scans: 64). Detection results are as follows: Figure 2 As shown, compared to hydrolyzed soy protein (ESPI), the coagulant (C16-QSPI) at 2850 cm⁻¹... -1 and 2925cm -1 The absorption peak at 1465 cm⁻¹ is significantly enhanced, which can be attributed to the symmetric and asymmetric stretching vibrations of the methylene group (-CH₂-), respectively. This is due to the introduction of a large number of -CH₂- groups by grafting the hydrophobic chain. -1 The presence of stretching vibrations, representing quaternary ammonium groups, demonstrates the successful reaction of hydrolyzed soybean protein with EPHDAC.

[0057] Weigh a small amount of sample, add it to pure water, disperse it ultrasonically, then drop 1 drop onto a silicon wafer, dry it, sputter-coat it with gold, and perform scanning electron microscopy. The measurement results are as follows: Figure 3 As shown in the figure. A small amount of sample was accurately weighed and prepared into a dispersion with a concentration of 0.1 mg / mL using ultrapure water filtered through a 0.22 μm filter membrane. The particle size distribution and Zeta potential of the coagulant were then determined using a dynamic light scattering and Zeta potential analyzer. Each sample was automatically measured three times, and the average value was taken. The results are shown in the figure. Figure 4 and Figure 5 As shown. From Figure 3 and Figure 4 As can be seen from the scanning electron microscopy and dynamic light scattering, the particle size of the coagulant is mainly distributed in the range of 100~300 nm, with an average particle size of 150 nm, and the morphology is particulate. Figure 5 As can be seen, amino-grafted EPHDAC results in a high Zeta potential for the adsorbent, which is above +20 mV at pH values ​​between 3 and 11. These results collectively demonstrate that the hydrolyzed soybean protein nanoparticle coagulant prepared in this invention has the potential to remove PFAS through the synergistic effect of electrostatic adsorption and hydrophobicity.

[0058] Example 6

[0059] This embodiment mainly investigates the removal effect of the synthesized hydrolyzed soybean protein nanoparticle coagulant on seven PFAS in water in the presence of humic acid: perfluorohexanoic acid (PFHxA), perfluoroheptanoic acid (PFHpA), perfluorooctanoic acid (PFOA), and their substitutes perfluoro(2-methyl-3-oxahexanoic acid) ammonium (GenX), perfluorononanoic acid (PFNA), perfluorodecanoic acid (PFDA), and perfluorooctane sulfonic acid (PFOS). The specific steps are as follows:

[0060] The seven PFAS standards were dissolved in methanol to prepare 10 g / L stock solutions, which were stored in polypropylene bottles. 10 g of humic acid was dissolved in 1 liter of ultrapure water with a pH of 11, stirred overnight, and then filtered through a glass fiber membrane with a pore size of 0.45 micrometers to obtain a humic acid stock solution. 500 mL of tap water was placed in a polypropylene beaker, and the seven PFAS standards and 10 mg / L of humic acid were added to obtain the experimental raw water. The coagulation experiment was conducted using a six-stage stirrer. After stirring at 200 rpm for 1 minute, 10, 15, 20, 25, 30, and 35 mg / L of the hydrolyzed soybean protein nanoparticle coagulant prepared in Example 3 were added to the experimental raw water, respectively. An equivalent dose of ferric chloride was used as a control. After adding the coagulant, the mixture was rapidly stirred at 200 rpm for 2 minutes, and then the speed was reduced to 40 rpm for 20 minutes. After stirring, the mixture was allowed to settle for 30 minutes. A 1 mL sample was taken from the supernatant, filtered through a 0.22 μm pore size glass fiber filter, and the change in PFAS concentration was determined by LC-MS / MS. The above experiment was performed in triplicate to ensure accurate results.

[0061] Test results are as follows Figure 6 and Figure 7 As shown, from Figure 6 As can be seen, due to hydrophobic interactions, the hydrolyzed soybean protein nanoparticle coagulant exhibits high removal rates for long-chain PFAS such as PFNA, PFDA, and PFOS at low dosages. At a dosage of 35 mg / L, the removal rates for PFOA, PFNA, PFDA, and PFOS approach 100%. The removal rates for less hydrophobic short-chain PFAS such as GenX, PFHxA, and PFHpA also gradually increase with increasing dosage, but the removal efficiency is significantly lower than that for long-chain PFAS. Figure 6 and Figure 7 The results show that even at the optimal dosage, ferric chloride's removal rate for each PFAS is significantly lower than that of hydrolyzed soybean protein nanoparticle coagulant. The results indicate that hydrolyzed soybean protein nanoparticle coagulant demonstrates significantly better efficiency and stability than traditional ferric chloride coagulant in PFAS removal.

[0062] Example 7

[0063] This embodiment mainly examines the removal effect of the synthesized nanoparticle coagulant on seven PFAS at different pH levels. The specific steps are as follows:

[0064] The pH of the experimental raw water described in Example 6 was adjusted to 3, 4, 5, 6, 7, 8, 9, 10, and 11 using 0.1 M hydrochloric acid or 0.1 M sodium hydroxide solution, respectively. The mixture was then stirred at 200 rpm for 1 minute using a six-piece stirrer. A hydrolyzed soybean protein nanoparticle coagulant with a final concentration of 30 mg / L was then added. After the coagulant was added, the mixture was rapidly stirred at 200 rpm for 2 minutes, followed by slow stirring at 40 rpm for 20 minutes. After stirring, the mixture was allowed to settle for 30 minutes. A 1 mL sample was taken from the supernatant, filtered through a 0.22 μm pore size glass fiber filter, and the change in PFAS concentration was determined by LC-MS / MS. The above experiment was performed in triplicate to ensure accurate results.

[0065] Figure 8 The study demonstrated the removal efficiency of soybean protein nanoparticle coagulant on PFAS of different chain lengths under different pH conditions: In the pH range of 3-4, the removal rates of short-chain PFAS such as GenX and PFHxA, as well as long-chain PFAS such as PFOA and PFOS, remained at a high level (most components were close to 100%). However, as the pH increased (especially after pH>5), the removal rates of short-chain PFAS such as GenX and PFHxA showed a significant decreasing trend, while the removal rates of long-chain PFAS such as PFOA and PFOS remained at a stable high level. This result can be explained by the charge characteristics of soybean protein: under acidic conditions, the amino groups in the protein molecules are protonated and carry a positive charge, which can bind tightly to the negatively charged groups on the surface of short-chain PFAS through electrostatic interactions, thereby enhancing its removal effect. This result is consistent with the Zeta potential of the coagulant at different pH levels in Example 5 (the Zeta potential is the highest at pH 3). When the pH increases, the degree of protonation of the protein decreases, the number of positive charges decreases, the electrostatic interaction weakens, and the removal rate of short-chain PFAS decreases accordingly. However, long-chain PFAS can maintain a high removal efficiency through hydrophobic interactions. This also reflects the difference in the removal mechanism of the coagulant for PFAS of different chain lengths, and the targeted enhancement effect of the coagulant on short-chain PFAS under acidic conditions.

Claims

1. A method for preparing a soybean protein nanoparticle coagulant for removing perfluorinated compounds from water, characterized in that: Includes the following steps: S1 reacts N,N-dimethylhexadecylamine and epichlorohydrin in methanol at room temperature for 8-12 hours at a molar ratio of 1:(1.5-2.5). After the reaction is complete, excess methanol is removed by rotary evaporation, acetone is added for recrystallization, and the product is washed and vacuum dried to obtain the reaction precursor, i.e., epichlorohydrin hexadecyldimethylammonium chloride. S2 disperses soy protein isolate in water at a solid-liquid ratio of 40-80 g / L, adjusts the pH to 7.5-8.5, and hydrolyzes it at 50-60℃ using alkaline protease (Alcalase) at a concentration of 0.1%-2% of the total substrate mass. The hydrolysis reaction continues until the degree of hydrolysis of soy protein reaches 4-8%. Then, the alkaline protease is inactivated by heating, and the solution is cooled to room temperature to obtain a hydrolyzed soy protein solution. S3. Adjust the pH of the above hydrolyzed soybean protein solution to 10-12, centrifuge to remove insoluble matter, and then add glycidyl hexadecyl dimethyl ammonium chloride to the supernatant. The molar ratio of amino groups in the hydrolyzed soybean protein solution to glycidyl hexadecyl dimethyl ammonium chloride is 1: (1-10). After heating, stir the reaction thoroughly to allow the epoxy groups on glycidyl hexadecyl dimethyl ammonium chloride to undergo a ring-opening addition reaction with the amino groups on the hydrolyzed soybean protein, thereby grafting them onto the hydrolyzed soybean protein. After the reaction is complete, adjust the pH to neutral, centrifuge again to remove insoluble matter, and then add sufficient acetone to the supernatant until a large amount of precipitate appears. After standing for a while, centrifuge the precipitate to separate it and collect the product. S4 The product was thoroughly washed with acetone and dried under vacuum to obtain the soybean protein nanoparticle coagulant that removes perfluorinated compounds from water.

2. The method for preparing soybean protein nanoparticle coagulant for removing perfluorinated compounds from water according to claim 1, characterized in that: In S1, the molar ratio of N,N-dimethylhexadecylamine and epichlorohydrin is 1:2, and the reaction time is 10 hours.

3. The method for preparing the soybean protein nanoparticle coagulant for removing perfluorinated compounds from water according to claim 1, characterized in that: In S2, the pH was adjusted to 8 using 0.1 M sodium hydroxide solution.

4. The method for preparing the soybean protein nanoparticle coagulant for removing perfluorinated compounds from water according to claim 1, characterized in that: In S2, the alkaline protease (Alcalase) to substrate ratio is 0.5%, the hydrolysis temperature is 55℃, the hydrolysis reaction duration is 15 minutes, the degree of hydrolysis of soybean protein is 6%, and the amino equivalent is 7.91 × 10⁻⁶. -4 mmol / g; inactivate alkaline protease by water bath at 85°C for 10 minutes.

5. The method for preparing the soybean protein nanoparticle coagulant for removing perfluorinated compounds from water according to claim 1, characterized in that: In step S3, the pH of the hydrolyzed soybean protein solution was adjusted to 11 with 1M sodium hydroxide solution, and then centrifuged at 5000 g for 2 minutes to remove insoluble matter.

6. The method for preparing the soybean protein nanoparticle coagulant for removing perfluorinated compounds from water according to claim 1, characterized in that: The molar ratio of amino content of hydrolyzed soybean protein in S3 to glycidyl hexadecyl dimethyl ammonium chloride is 1:5, and the two are stirred and reacted at 50°C for 12 hours.

7. The method for preparing soybean protein nanoparticle coagulant for removing perfluorinated compounds from water according to claim 1, characterized in that: After the reaction in S3 is completed, the pH is adjusted to 7 with 0.1 M hydrochloric acid solution, and then the insoluble matter is removed again by centrifugation at 5000 g for 2 minutes. Then, 2 times the volume of acetone is added to the supernatant to form a precipitate. After the precipitate is formed, it is allowed to stand for 30 minutes, and the precipitate is centrifuged at 8000 g for 10 minutes to obtain the product.

8. The method for preparing soybean protein nanoparticle coagulant for removing perfluorinated compounds from water according to claim 1, characterized in that: In S4, the product was washed three times with acetone and then dried in a vacuum drying oven at 35°C for 12 hours.

9. A soybean protein nanoparticle coagulant for removing perfluorinated compounds from water, prepared by any of the preparation methods described in claims 1-8.

10. Use of the soybean protein nanoparticle coagulant of claim 9 in the purification of perfluorinated compound pollution in water bodies.

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